Binder composition for anodes of non-aqueous secondary batteries, slurry for anodes of non-aqueous secondary batteries, anode of non-aqueous secondary batteries, and non-aqueous secondary batteries

Abstract

To provide a binder composition for the negative electrode of a non-aqueous secondary battery that can form a non-aqueous secondary battery with low internal resistance. [Solution] The binder composition for the negative electrode of a non-aqueous secondary battery contains a polymer having a first structural unit derived from a monomer (a1), a composite of poly(3,4-ethylenedioxythiophene) and polystyrene sulfonic acid, and an aqueous medium, wherein the monomer (a1) is a nonionic compound having one ethylenically unsaturated bond.

Description

[Technical Field]

[0001] This disclosure relates to a binder composition for a negative electrode of a non-aqueous secondary battery, a slurry for a negative electrode of a non-aqueous secondary battery, a negative electrode of a non-aqueous secondary battery, and a non-aqueous secondary battery. [Background technology]

[0002] Non-aqueous secondary batteries are widely used as power sources for laptop computers, mobile phones, power tools, and electronic and communication equipment because they can be made smaller and lighter. In recent years, non-aqueous secondary batteries have also been used as power sources for electric vehicles and hybrid vehicles. A typical example of a non-aqueous secondary battery is the lithium-ion secondary battery.

[0003] Non-aqueous secondary batteries include a positive electrode with a metal oxide or the like as the active material, a negative electrode with a carbon material such as graphite as the active material, and an electrolyte. The positive and negative electrodes each comprise a current collector and an electrode active material layer formed on the current collector. The electrode active material layer usually contains a binder that binds the active materials together and between the active materials and the current collector, thereby fixing the electrode active material layer on the current collector. Conventionally, binders used in non-aqueous secondary batteries are known from those described in Patent Documents 1 and 2.

[0004] Patent Document 1 discloses a slurry containing one or more linear polymers, one or more conductive polymers, one or more self-healing polymers, and one or more rubber polymers as a binder. Patent Document 2 discloses a lithium-ion battery comprising, as a component of the active material composition, at least one of the following: a binder of a cellulose-based conductive polymer synthesized using a cellulose-based compound as a template; a mixed conductive polymer binder obtained by mixing the cellulose-based conductive polymer binder with one or more conductive polymers synthesized using other types of compounds as templates; and a binder of a cellulose-based conductive polymer synthesized using a polymer compound having a hydrogen ion concentration (pH) in the range of 2 to 6 in aqueous solution as a template. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Special Publication No. 2023-505592 [Patent Document 2] Special Publication No. 2021-518985 [Overview of the project] [Problems that the invention aims to solve]

[0006] In recent years, there has been a demand for non-aqueous secondary batteries that offer high output and rapid charging capabilities. Therefore, binders used in non-aqueous secondary batteries are required to reduce the internal resistance of the battery.

[0007] This disclosure has been made in view of the above circumstances and aims to provide a binder composition for a non-aqueous secondary battery anode and a slurry for a non-aqueous secondary battery anode that can form a non-aqueous secondary battery with low internal resistance. Furthermore, this disclosure aims to provide a non-aqueous secondary battery negative electrode that can be obtained in a non-aqueous secondary battery with low internal resistance, and a non-aqueous secondary battery equipped with the same. [Means for solving the problem]

[0008] The specific means for achieving the aforementioned objectives are as follows: <1> It contains a polymer having a first structural unit derived from monomer (a1), a composite of poly(3,4-ethylenedioxythiophene) and polystyrene sulfonic acid, and an aqueous medium. A binder composition for a negative electrode of a non-aqueous secondary battery, wherein the monomer (a1) is a nonionic compound having one ethylenically unsaturated bond. <2> The polymer further has a second structural unit derived from monomer (a2), The monomer (a2) is a compound having a carboxyl group and one ethylenically unsaturated bond. <1> A binder composition for the negative electrode of a non-aqueous secondary battery as described above. <3> The polymer further has a third structural unit derived from monomer (a3), The monomer (a3) ​​is a compound having multiple independent ethylenically unsaturated bonds. <1> or <2> A binder composition for the negative electrode of a non-aqueous secondary battery as described above. <4> The monomer (a1) comprises an aromatic compound having an ethylenically unsaturated bond, The content of structural units derived from the aromatic compound having the ethylenically unsaturated bond in the total structural units of the polymer is 41% by mass or more. <1> ~ <3> A binder composition for the negative electrode of a non-aqueous secondary battery as described in any one of the items. <5> The content of the second structural unit in the total structural units of the polymer is 0.10% by mass to 20% by mass. <2> A binder composition for the negative electrode of a non-aqueous secondary battery as described above. <6> The content of the third structural unit in the total structural units of the polymer is 0.010% by mass to 15% by mass. <3> A binder composition for the negative electrode of a non-aqueous secondary battery as described above. <7> The proportion of the composite to the total of the polymer and the composite is 0.10% by mass to 10% by mass. <1> ~ <6> A binder composition for the negative electrode of a non-aqueous secondary battery as described in any one of the items. <8> The polymer and the composite are contained in the form of dispersed particles. The average particle size d50 of the dispersed particles is 0.18 μm to 1.0 μm. <1> ~ <7> A binder composition for the negative electrode of a non-aqueous secondary battery as described in any one of the items. <9> It contains a negative electrode active material, a polymer having a first structural unit derived from monomer (a1), a composite of poly(3,4-ethylenedioxythiophene) and polystyrene sulfonic acid, and an aqueous medium. A slurry for a negative electrode of a non-aqueous secondary battery, wherein the monomer (a1) is a nonionic compound having one ethylenically unsaturated bond. <10> The polymer further has a second structural unit derived from monomer (a2), The slurry for a non-aqueous secondary battery negative electrode according to <9>, wherein the monomer (a2) has a carboxy group and has one ethylenically unsaturated bond. <11> The polymer further has a third structural unit derived from a monomer (a3), The slurry for a non-aqueous secondary battery negative electrode according to <9> or <10>, wherein the monomer (a3) is a compound having a plurality of independent ethylenically unsaturated bonds. <12> The monomer (a1) includes an aromatic compound having an ethylenically unsaturated bond, The slurry for a non-aqueous secondary battery negative electrode according to any one of <9> to <11>, wherein the content of the structural unit derived from the aromatic compound having an ethylenically unsaturated bond in all the structural units of the polymer is 41% by mass or more. <13> The slurry for a non-aqueous secondary battery negative electrode according to <10>, wherein the content of the second structural unit in all the structural units of the polymer is 0.10% by mass to 20% by mass. <14> The slurry for a non-aqueous secondary battery negative electrode according to <11>, wherein the content of the third structural unit in all the structural units of the polymer is 0.010% by mass to 15% by mass. <15> The slurry for a non-aqueous secondary battery negative electrode according to any one of <9> to <14>, wherein the ratio of the composite in the total of the polymer and the composite is 0.10% by mass to 10% by mass. <16> The polymer and the composite are contained in the state of dispersed particles, The slurry for a non-aqueous secondary battery negative electrode according to any one of <9> to <15>, wherein the average particle diameter d50 of the dispersed particles is 0.18 μm to 1.0 μm. <17> A non-aqueous secondary battery negative electrode includes a current collector and a negative electrode active material layer provided on the current collector, The negative electrode active material layer contains a non-volatile component of the slurry for a non-aqueous secondary battery negative electrode according to any one of <9> to <16>. <18> A non-aqueous secondary battery includes the non-aqueous secondary battery negative electrode according to <17>.

Advantages of the Invention

[0009] According to the present disclosure, it is possible to provide a binder composition for a non-aqueous secondary battery negative electrode and a slurry for a non-aqueous secondary battery negative electrode that can form a non-aqueous secondary battery with a low internal resistance. Also, according to the present disclosure, it is possible to provide a non-aqueous secondary battery negative electrode that can obtain a non-aqueous secondary battery with a low internal resistance, and a non-aqueous secondary battery including the same.

Embodiments for Carrying Out the Invention

[0010] Hereinafter, embodiments of the present disclosure will be described in detail. However, the present disclosure is not limited to the following embodiments. In the following embodiments, the components (including element steps, etc.) are not essential unless otherwise specified. The same applies to numerical values and their ranges, which do not limit the present disclosure.

[0011] In the present disclosure, the term "step" includes, in addition to a step independent of other steps, a step that cannot be clearly distinguished from other steps but whose purpose is achieved. In the numerical range indicated by "~" in the present disclosure, the numerical values described before and after "~" are included as the minimum value and the maximum value, respectively. In the numerical ranges described step by step in the present disclosure, the upper limit value or the lower limit value described in one numerical range may be replaced with the upper limit value or the lower limit value of the numerical range described in other step-by-step descriptions. Also, in the numerical ranges described in the present disclosure, the upper limit value or the lower limit value of the numerical range may be replaced with the value shown in the examples. In the present disclosure, each component may include a plurality of corresponding substances. When there are a plurality of substances corresponding to each component in the composition, the content or content rate of each component means the total content or content rate of the plurality of substances present in the composition, unless otherwise specified. In the present disclosure, the particles corresponding to each component may include a plurality of types of particles. When there are a plurality of types of particles corresponding to each component in the composition, the particle diameter of each component means the value for the mixture of the plurality of types of particles present in the composition, unless otherwise specified. In this disclosure, the terms “layer” or “film” include cases where, when the region in which the layer or film exists is observed, it is formed not only over the entire region but also over only a portion of the region. In this disclosure, the term "lamination" refers to stacking layers, and two or more layers may be bonded together or detachable. In this disclosure, the average thickness of a layer or film is given as the arithmetic mean value obtained by measuring the thickness of five points on the layer or film in question. The thickness of a layer or film can be measured using a micrometer or the like. In this disclosure, if the thickness of a layer or film can be measured directly, it is measured using a micrometer. On the other hand, when measuring the thickness of a single layer or the total thickness of multiple layers, the measurement may be performed by observing the cross-section of the object to be measured using an electron microscope. In this disclosure, "non-volatile content" refers to the residue remaining after drying the sample at 1 atmosphere (1013 hPa) and 105°C for 1 hour. The percentage of "non-volatile content" shall be the value determined by the method described below.

[0012] In this disclosure, "(meth)acrylic" is a general term for acrylic and methacrylic. "(meth)acrylate" is a general term for acrylate and methacrylate. "(meth)acrylonitrile" is a general term for acrylonitrile and methacrylonitrile. In this disclosure, "ethylenically unsaturated bond" refers to an ethylenically unsaturated bond that is radically polymerizable, unless otherwise specified.

[0013] In a polymer using a compound having an ethylenically unsaturated bond, the structural unit derived from the compound having the ethylenically unsaturated bond means a structural unit in which the chemical structure of the portion of the compound other than the ethylenically unsaturated bond is the same as the chemical structure of the portion of the structural unit in the polymer other than the portion corresponding to the ethylenically unsaturated bond. The ethylenically unsaturated bond of the compound changes into a single bond when forming a polymer. For example, in a polymer of methyl methacrylate, the structural unit derived from methyl methacrylate is represented by -CH2-C(CH3)(COOCH3)-.

[0014] Furthermore, in the case of polymers of compounds having ionic functional groups and ethylenically unsaturated bonds, for example, as shown in the second structural unit described later, structural units having ionic functional groups such as carboxyl groups are considered to be derived from the same ionic compound, regardless of whether or not some of the functional groups are ion-exchanged. For example, the structural unit represented by -CH2-C(CH3)(COONa)- can also be considered to be a structural unit derived from methacrylic acid.

[0015] Furthermore, for compounds having multiple independent ethylenically unsaturated bonds, one or more ethylenically unsaturated bonds may remain within the structural unit of the polymer of the compound. For example, in the case of a polymer of divinylbenzene, the structural unit derived from divinylbenzene may be a structure without ethylenically unsaturated bonds (a form in which both parts corresponding to the two ethylenically unsaturated bonds of divinylbenzene are incorporated into the polymer chain), or it may be a structure having one ethylenically unsaturated bond (a form in which only the part corresponding to one of the ethylenically unsaturated bonds is incorporated into the polymer chain). Here, multiple independent ethylenically unsaturated bonds mean multiple ethylenically unsaturated bonds that do not form conjugated dienes with each other.

[0016] Furthermore, if, after polymerization, the parts of the polymer other than the chain structure corresponding to the ethylenically unsaturated bond, such as functional groups like carboxyl groups, no longer correspond to the chemical structure of the monomer due to chemical reactions, then the structural units of the polymer shall be considered to be structural units derived from the compound containing the ethylenically unsaturated bond in the polymer. For example, when vinyl acetate is polymerized and then saponified, the structural units of the polymer shall be considered to be derived from vinyl alcohol, rather than from vinyl acetate, based on the chemical structure of the polymer.

[0017] In this disclosure, the term "class" attached to a compound name means a group of compounds that include the compound structure in question, and also includes compounds having substituents.

[0018] <Binder composition for negative electrodes of non-aqueous secondary batteries> The binder composition for a negative electrode of a non-aqueous secondary battery (hereinafter sometimes referred to as the negative electrode binder composition) of this disclosure contains a polymer having a first structural unit derived from a monomer (a1) (hereinafter sometimes referred to as the specific polymer), a composite of poly(3,4-ethylenedioxythiophene) and polystyrene sulfonic acid (hereinafter sometimes referred to as the specific composite or PEDOT:PSS), and an aqueous medium. The specific polymer and specific composite may be contained in the negative electrode binder composition in the form of dispersed particles.

[0019] The negative electrode binder composition disclosed herein makes it possible to form a non-aqueous secondary battery with low internal resistance. The reason for this is not clear, but it is presumed to be as follows. The binder, which is a resin, is generally an insulator, and even if the binder is present between the negative electrode active materials in the negative electrode active material layer, no conductive path is formed. Therefore, increasing the amount of binder used increases the electronic conductivity resistance of the negative electrode active material layer. When the electronic conductivity resistance increases, the DC resistance (DCR) of the non-aqueous secondary battery also increases. On the other hand, if the amount of binder used is reduced to lower the DCR, the negative electrode active material layer may become more prone to peeling off from the current collector. In this disclosure, conductivity is imparted to the binder by using the conductive polymer PEDOT:PSS in combination with a specific polymer. This reduces the electron conduction resistance between the negative electrode active materials and between the negative electrode active materials and the current collector. Therefore, it is presumed that the internal resistance of a non-aqueous secondary battery can be lowered. Furthermore, it is presumed that lowering the internal resistance of a non-aqueous secondary battery will allow for a reduction in the DCR of the non-aqueous secondary battery.

[0020] The following describes the components constituting the negative electrode binder composition of this disclosure. The negative electrode binder composition of this disclosure contains a specific polymer, a specific complex, and an aqueous medium, and may contain other components as needed.

[0021] [Specific polymers] The specific polymer contained in the negative electrode binder composition of this disclosure has at least a first structural unit derived from the monomer (a1) shown below. The specific polymers of this disclosure may include, in addition to the first structural unit, a second structural unit derived from monomer (a2), a third structural unit derived from monomer (a3), and a fourth structural unit derived from other monomers (a4) that do not fall under any of monomers (a1) to monomer (a3).

[0022] [First structural unit] The first structural unit of a particular polymer originates from monomer (a1). Monomer (a1) is a nonionic compound having one ethylenically unsaturated bond. That is, monomer (a1) is a compound that does not have either anionic or cationic functional groups. Monomer (a1) may be a single compound or a combination of two or more compounds.

[0023] It is preferable to use at least one of (meth)acrylic acid esters and aromatic compounds having an ethylenically unsaturated bond as monomer (a1), and it is more preferable to use a combination of both compounds. It is more preferable that the (meth)acrylic acid ester is an alkyl (meth)acrylic acid ester. The number of carbon atoms in the alkyl group of the alkyl (meth)acrylic acid ester is preferably 1 to 20. A monomer (a1) other than alkyl (meth)acrylic acid esters and aromatic compounds having an ethylenically unsaturated bond may also be used in combination as monomer (a1).

[0024] Examples of alkyl (meth)acrylate esters included in the monomer (a1) include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, tert-butyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isobornyl (meth)acrylate, lauryl (meth)acrylate, and stearyl (meth)acrylate. Among these, it is preferable to include 2-ethylhexyl acrylate because it forms a specific polymer that can create a negative electrode active material layer with excellent electrolyte resistance.

[0025] Examples of aromatic compounds having ethylenically unsaturated bonds used in monomer (a1) include styrene, t-butylstyrene, α-methylstyrene, p-methylstyrene, and 1,1-diphenylethylene. When monomer (a1) contains an aromatic vinyl compound, it is more preferable to contain at least one of styrene and α-methylstyrene, as this results in a specific polymer with excellent dispersibility in aqueous media, making the inclusion of styrene even more preferable.

[0026] Examples of monomers (a1) other than alkyl (meth)acrylates and aromatic compounds having an ethylenically unsaturated bond include compounds having an ethylenically unsaturated bond and a polar functional group, aliphatic hydrocarbon compounds having an ethylenically unsaturated bond, and alicyclic hydrocarbon compounds having an ethylenically unsaturated bond.

[0027] In the monomer (a1) and the compound having an ethylenically unsaturated bond and a polar functional group, the polar functional group preferably contains at least one of a hydroxyl group and a cyano group, and more preferably contains a hydroxyl group. Examples of compounds having ethylenically unsaturated bonds and polar functional groups used in monomer (a1) include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and (meth)acrylonitrile. It is preferable to include 2-hydroxyethyl methacrylate because good polymerization stability can be obtained when producing specific polymers.

[0028] [Second structural unit] A specific polymer may have a second structural unit as an arbitrary structural unit. This second structural unit is derived from monomer (a2). Monomer (a2) is a compound having an ethylenically unsaturated bond and a carboxyl group. Preferably, monomer (a2) has one ethylenically unsaturated bond. Monomer (a2) may be a single compound or a combination of two or more compounds. As monomer (a2), a compound having multiple carboxyl groups in one molecule may be used. That is, a specific polymer may contain multiple carboxyl groups in a single structural unit.

[0029] Examples of monomers (a2) having one ethylenically unsaturated bond include unsaturated monocarboxylic acids such as methacrylic acid, acrylic acid, and crotonic acid; and unsaturated dicarboxylic acids such as itaconic acid and fumaric acid. Examples of monomers (a2) having two or more ethylenically unsaturated bonds include sorbic acid, muconic acid, and linoleic acid. Among these, monomer (a2) is preferably at least one of acrylic acid, methacrylic acid, and itaconic acid, as it forms a specific polymer that can create an electrode in which the negative electrode active material layer is less likely to peel off from the current collector. Compounds having a structure that may correspond to either monomer (a2) or monomer (a3) ​​described later will be classified as monomer (a2) in this disclosure.

[0030] At least some of the structural units derived from monomer (a2) may form salts with basic substances. Examples of monomer (a2) that form salts with basic substances include metal salts and ammonium salts of monomer (a2). Examples of metals in metal salts include alkali metals such as lithium, sodium, and potassium.

[0031] Examples of monomers (a2) that form salts with basic substances include lithium (meth)acrylate, lithium itaconate, dilithium itaconate, sodium (meth)acrylate, sodium itaconate, disodium itaconate, ammonium (meth)acrylate, ammonium itaconate, and diammonium itaconate.

[0032] [Third structural unit] A specific polymer may have a third structural unit as an arbitrary structural unit. This third structural unit is derived from monomer (a3). Monomer (a3) ​​is a compound having multiple independent ethylenically unsaturated bonds. "Independent" means that it is not a conjugated double bond like that of 1,3-butadiene. Therefore, monomer (a3) ​​is a compound capable of forming a crosslinked structure in radical polymerization with monomer (a1) and monomer (a2). Monomer (a3) ​​does not correspond to either monomer (a1) or monomer (a2). Monomer (a3) ​​may be a single compound or two or more different compounds.

[0033] Examples of monomers (a3) ​​include compounds having two ethylenically unsaturated bonds, such as divinylbenzene, ethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, and 2-hydroxy-3-acryloyloxypropyl methacrylate, and compounds having three or more ethylenically unsaturated bonds, such as trimethylolpropane tri(meth)acrylate. It is preferable to use at least one of divinylbenzene and trimethylolpropane triacrylate as monomer (a3) ​​because good polymerization stability can be obtained when producing a specific polymer.

[0034] [Fourth structural unit] A specific polymer may have a fourth structural unit as an arbitrary structural unit. This fourth structural unit is derived from another monomer (a4). Other monomers (a4) are monomers that do not fall under monomers (a1), monomers (a2), or monomers (a3). Examples of other monomers (a4) include, but are not limited to, compounds having one ethylenically unsaturated bond and anionic functional groups other than carboxyl groups, such as sulfo groups and phosphate groups; surfactants having an ethylenically unsaturated bond (hereinafter sometimes referred to as "polymerizable surfactants"); and compounds having an ethylenically unsaturated bond and functioning as silane coupling agents. Among these, polymerizable surfactants are preferable as other monomers (a4) because they provide good polymerization stability when producing specific polymers.

[0035] Compounds having one ethylenically unsaturated bond and a sulfo group include aromatic vinyl compounds having a sulfo group and aromatic vinyl compounds having a sulfo group that forms a salt. Among these, it is preferable to use at least one of parastyrene sulfonic acid and parastyrene sulfonate, and more preferable to use parastyrene sulfonate.

[0036] As an example of a polymerizable surfactant, which is another monomer (a4), compounds having an ethylenically unsaturated bond and functioning as a surfactant can be used. Examples of polymerizable surfactants include compounds represented by the following chemical formulas (1) to (4).

[0037] [ka]

[0038] In formula (1), R 1 R is an alkyl group. p is an integer between 1 and 100. 1The C1 is preferably an alkyl group having 10 to 40 carbon atoms, and more preferably a linear, unsubstituted alkyl group having 10 to 40 carbon atoms. Examples of compounds represented by formula (1) include α-[2-(allyloxy)-(alkyloxymethyl)ethyl]-ω-hydroxypolyoxyethylene (trade name: Adekarya Soap ER20, manufactured by ADEKA Corporation).

[0039] [ka]

[0040] In formula (2), R 2 is an alkyl group. q is an integer between 10 and 12. R 2 The C1 is preferably an alkyl group having 10 to 40 carbon atoms, and more preferably a linear unsubstituted alkyl group having 10 to 40 carbon atoms. Examples of compounds represented by formula (2) include polyoxyethylene alkyl ether sulfate ammonium salt (trade name: Aqualon KH-10, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) and α-[2-(allyloxy)-1-(alkyloxymethyl)ethyl]-ω-polyoxyethylene sulfate ammonium salt (trade name: Adekarya Soap SR10, manufactured by ADEKA Corporation).

[0041] [ka]

[0042] In formula (3), R 3 M is an alkyl group. 1 R is either NH4 or Na. 3 It is preferably an alkyl group having 10 to 40 carbon atoms, and more preferably a linear, unsubstituted alkyl group having 10 to 40 carbon atoms.

[0043] [ka]

[0044] In formula (4), R 4is an alkyl group. M 2 is NH4 or Na. R 4 is preferably an alkyl group having 10 to 40 carbon atoms, more preferably a linear unsubstituted alkyl group having 10 to 40 carbon atoms. Examples of the compound represented by the formula (4) include sodium alkyl allyl sulfosuccinate (trade name; Ereminol JS-20, manufactured by Sanyo Chemical Industries, Ltd.).

[0045] Examples of the compound having an ethylenically unsaturated bond and having a function as a silane coupling agent, which is an example of the other monomer (a4), include vinyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, vinyltriethoxysilane, γ-methacryloxypropyltriethoxysilane, and the like.

[0046] [Content ratio of each structural unit in the specific polymer] In the present disclosure, the content ratio of each structural unit in the specific polymer is regarded as the same as the content ratio of each monomer in the total amount of the monomer components used in the production of the specific polymer.

[0047] (Content ratio of the first structural unit in all structural units) The content ratio of the first structural unit in all structural units (in other words, the content ratio of the monomer (a1) in the total amount of the monomer components used in the production of the specific polymer) is preferably 60% by mass or more, more preferably 70% by mass or more, still more preferably 75% by mass or more, and particularly preferably 80% by mass or more. This is because better polymerization stability can be obtained when producing the specific polymer. The content ratio of the first structural unit in all structural units is preferably 97% by mass or less, more preferably 96% by mass or less, and still more preferably 95% by mass or less. This is because it becomes a specific polymer that can form an electrode in which the negative electrode active material layer is more difficult to peel off from the current collector.

[0048] Regarding the composition of monomer (a1), it is preferable to appropriately adjust the type and amount of compound in order to adjust the glass transition temperature of a specific polymer or to adjust the polymerization rate according to the molecular design. Specifically, when monomer (a1) contains an aromatic compound having an ethylenically unsaturated bond, the content of structural units derived from the aromatic compound having an ethylenically unsaturated bond in the total structural units is preferably 41% by mass or more, and more preferably 43% by mass or more. This is because it results in a specific polymer with excellent dispersibility when producing a negative electrode slurry containing the specific polymer. When monomer (a1) contains an aromatic compound having an ethylenically unsaturated bond, the content of structural units derived from the aromatic compound having an ethylenically unsaturated bond in the total structural units is preferably 75% by mass or less, and more preferably 65% ​​by mass or less. This is because it results in a flexible binder. When monomer (a1) contains an aromatic compound having an ethylenically unsaturated bond, the content of structural units derived from the aromatic compound having an ethylenically unsaturated bond in the total structural units is preferably 41% to 75% by mass.

[0049] (Content of the second structural unit in the total structural units) When a specific polymer contains a second structural unit, the content of the second structural unit in the total structural units (in other words, the content of monomer (a2) in the total amount of monomer components used in the production of the specific polymer) is preferably 0.10% by mass or more, more preferably 1.0% by mass or more, even more preferably 3.0% by mass or more, and particularly preferably 4.0% by mass or more. This is because it is possible to form an electrode in which the negative electrode active material layer is less likely to peel off from the current collector. The content of the second structural unit in the total structural units is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less. This is because better polymerization stability can be obtained when producing the specific polymer. The content of the second structural unit in the total structural units is preferably 0.10% to 20% by mass.

[0050] (Content of the third structural unit in all structural units) When a specific polymer contains a third structural unit, the content of the third structural unit in the total structural units (in other words, the content of monomer (a3) ​​in the total amount of monomer components used in the production of the specific polymer) is preferably 0.010% by mass or more, more preferably 0.020% by mass or more, and even more preferably 0.030% by mass or more. This is because the effect of monomer (a3) ​​as an internal crosslinking agent is significantly obtained, the degradation of the specific polymer is suppressed, and a negative electrode binder composition with lower internal resistance for non-aqueous secondary batteries is obtained. The content of the third structural unit in the total structural units is preferably 15% by mass or less, more preferably 5.0% by mass or less, even more preferably 3.0% by mass or less, and particularly preferably 2.0% by mass or less. This is because gelation of the negative electrode binder composition can be suppressed. The content of the third structural unit in the total structural units is preferably 0.010% by mass to 15% by mass.

[0051] (Content of the fourth structural unit in all structural units) When a specific polymer contains a fourth structural unit derived from another monomer (a4), and the other monomer (a4) is a compound having one ethylenically unsaturated bond and a sulfo group, the content of the fourth structural unit in the total structural units (in other words, the content of monomer (a4) in the total amount of monomer components used in the production of the specific polymer) is preferably 0.10% by mass or more, more preferably 0.20% by mass or more, and even more preferably 0.30% by mass or more. This is because good polymerization stability can be obtained when producing the specific polymer. In this case, the content of the fourth structural unit in the total structural units is preferably 6.0% by mass or less, more preferably 5.0% by mass or less, and even more preferably 4.0% by mass or less. This is because the particle size, viscosity, etc. of the specific polymer can be appropriately adjusted. In this case, the content of the fourth structural unit in the total structural units is preferably 0.10% by mass to 6.0% by mass.

[0052] When a specific polymer contains a fourth structural unit derived from another monomer (a4), and the other monomer (a4) is a polymerizable surfactant, the content of the fourth structural unit in the total structural units (in other words, the content of monomer (a4) in the total amount of monomer components used in the production of the specific polymer) is preferably 0.10% by mass or more, more preferably 0.20% by mass or more, and even more preferably 0.30% by mass or more. This is because the effect of including a polymerizable surfactant becomes significant, and good polymerization stability is obtained when producing the specific polymer. In this case, the content of the fourth structural unit in the total structural units is preferably 6.0% by mass or less, more preferably 5.0% by mass or less, and even more preferably 4.0% by mass or less. This is because the particle size, viscosity, etc. of the specific polymer can be appropriately adjusted. In this case, the content of the fourth structural unit in the total structural units is preferably 0.10% by mass to 6.0% by mass.

[0053] [Method for producing specific polymers] The specific polymers in this disclosure can be produced using known polymerization methods, for example, by copolymerizing monomers containing monomer (a1) and, if necessary, monomers (a2), monomer (a3), and other monomers (a4) (polymerization step). Hereinafter, the monomers (components (a1) to (a4)) used to synthesize the specific polymers may be collectively referred to as monomer (a).

[0054] One method for copolymerizing monomer (a) is emulsion polymerization, in which monomer (a) is emulsion polymerized in an aqueous medium (b). When producing a specific polymer by emulsion polymerization, in addition to monomer (a) and aqueous medium (b), components such as a surfactant (c) that does not polymerize, a basic substance (d), a radical polymerization initiator (e), and a chain transfer agent (f) can be used.

[0055] [Aqueous medium (b)] The aqueous medium (b) is selected from the group consisting of water, a hydrophilic solvent, and a mixture containing water and a hydrophilic solvent. Examples of hydrophilic solvents include methanol, ethanol, isopropyl alcohol, and N-methylpyrrolidone. From the viewpoint of polymerization stability, the aqueous medium (b) is preferably water. As long as polymerization stability is not impaired, a mixture of water and a hydrophilic solvent may be used as the aqueous medium (b).

[0056] [Non-polymerizable surfactants (c)] When producing a specific polymer by emulsion polymerization, a non-polymerizable surfactant (c) may be included in the solution containing the aqueous medium (b) and monomer (a) during emulsion polymerization. A non-polymerizable surfactant (c) is a surfactant (c) that does not have polymerizable unsaturated bonds in its chemical structure. Surfactant (c) improves the dispersion stability of the solution during emulsion polymerization and / or the dispersion obtained after polymerization. In particular, if the other monomer (a4) does not contain a polymerizable surfactant containing sodium, good polymerization stability can be obtained when producing the specific polymer, so it is preferable to include a non-polymerizable surfactant (c).

[0057] It is preferable to use at least one of an anionic surfactant and a nonionic surfactant as the surfactant (c).

[0058] Examples of anionic surfactants include alkylbenzene sulfonates, alkyl sulfates, polyoxyethylene alkyl ether sulfates, and fatty acid salts. Examples of nonionic surfactants include polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene polycyclic phenyl ethers, polyoxyalkylene alkyl ethers, sorbitan fatty acid esters, and polyoxyethylene sorbitan fatty acid esters. Among these nonionic surfactants, polyoxyethylene alkyl ethers are preferred because they provide good polymerization stability when producing specific polymers. The surfactant (c) described above may be used alone or in combination of two or more types.

[0059] [Basic substances (d)] When producing a specific polymer by emulsion polymerization, a basic substance (d) may be added to the emulsion polymerization solution containing the aqueous medium (b) and monomer (a), and / or the dispersion after emulsion polymerization. By adding the basic substance (d), the acidic components contained in monomer (a) are neutralized. As a result, the pH of the solution during emulsion polymerization and / or the dispersion after emulsion polymerization becomes within an appropriate range, and the stability of the solution during emulsion polymerization and / or the dispersion after emulsion polymerization is improved.

[0060] Examples of basic substances (d) to be added to the emulsion polymerization solution and / or the dispersion after emulsion polymerization include ammonia, triethylamine, sodium hydroxide, and lithium hydroxide. These basic substances (d) may be used individually or in combination of two or more.

[0061] [Radical polymerization initiator (e)] The radical polymerization initiator (e) used when producing a specific polymer by emulsion polymerization is not particularly limited, and known ones can be used. Examples of radical polymerization initiators (e) include persulfates such as ammonium persulfate and potassium persulfate; hydrogen peroxide; azo compounds; and organic peroxides such as tert-butyl hydroperoxide, tert-butyl peroxybenzoate, and cumene hydroperoxide.

[0062] In this disclosure, when producing a specific polymer by emulsion polymerization, redox polymerization may be performed by using a reducing agent such as sodium bisulfite, rongalit, or ascorbic acid in combination with a radical polymerization initiator (e).

[0063] The amount of radical polymerization initiator (e) added (including the reducing agent if used in combination) is preferably 0.001 parts by mass or more, and more preferably 0.01 parts by mass or more, per 100 parts by mass of monomer (a). This is because it is possible to increase the conversion rate of monomer (a) to the specific polymer when producing the specific polymer by emulsion polymerization. The amount of radical polymerization initiator (e) added is preferably 10 parts by mass or less, and more preferably 5 parts by mass or less, per 100 parts by mass of monomer (a). This is because it is possible to increase the molecular weight of the specific polymer and reduce the swelling rate of the negative electrode containing the specific polymer of this disclosure in the electrolyte.

[0064] [Chain transfer agent (f)] The chain transfer agent (f) used in the production of specific polymers by emulsion polymerization is used to adjust the molecular weight of the specific polymer obtained by emulsion polymerization. Examples of chain transfer agents (f) include n-dodecyl mercaptan, tert-dodecyl mercaptan, n-butyl mercaptan, 2-ethylhexyl thioglycolate, 2-mercaptoethanol, β-mercaptopropionic acid, methyl alcohol, n-propyl alcohol, isopropyl alcohol, t-butyl alcohol, and benzyl alcohol.

[0065] [Emulsion polymerization method] Examples of emulsion polymerization methods used in producing specific polymers include methods in which each component used for emulsion polymerization is continuously supplied into the reaction vessel during emulsion polymerization. The temperature of emulsion polymerization is not particularly limited, but is preferably 30°C to 90°C, preferably 50°C to 85°C, and more preferably 55°C to 80°C. Emulsion polymerization is preferably carried out with stirring. Furthermore, it is preferable to continuously supply monomer (a) and radical polymerization initiator (e) to the solution during emulsion polymerization so that the concentrations of monomer (a) and radical polymerization initiator (e) in the solution during emulsion polymerization become uniform.

[0066] [Specific complex] The specific composite contained in the negative electrode binder composition of this disclosure is a conductive polymer in which poly(3,4-ethylenedioxythiophene) (PEDOT) is doped with polystyrene sulfonic acid (PSS), and can be represented by the following formula, for example. A portion of the specific complex may dissociate and exist in the electrode active material layer in the form of PEDOT and PSS. When a portion of the specific complex is dissociated, the content and amount of the specific complex in the electrode active material layer refer to the content and amount of both the undissociated PEDOT:PSS and the total of the dissociated PEDOT and PSS.

[0067] [ka]

[0068] In the above chemical formula, m represents an integer greater than or equal to 1, and n represents an integer greater than or equal to 1. m can be 25 to 50,000, 50 to 10,000, or 100 to 5,000. n can be between 5 and 200, between 7 and 100, or between 10 and 80. The weight-average molecular weight of PEDOT:PSS as a whole is not particularly limited and may be between 20,000 and 2,000,000, between 50,000 and 400,000, or between 100,000 and 200,000. PEDOT:PSS may be synthesized by known methods or be a commercially available product. PEDOT:PSS may be used in the form of a dispersion in an aqueous medium. Examples of aqueous mediums for dispersing PEDOT:PSS include water.

[0069] The proportion of the specific complex to the total of the specific polymer and the specific complex is preferably 0.10% by mass to 10% by mass. If the proportion of the specific composite is 0.10% by mass or more, it becomes possible to further reduce the internal resistance of non-aqueous secondary batteries. The proportion of the specific composite is preferably 0.50% by mass or more, and more preferably 1.0% by mass or more. If the proportion of the specific composite is 10% by mass or less, an electrode can be formed in which the negative electrode active material layer is less likely to peel off from the current collector. The proportion of the specific composite is preferably 5% by mass or less, and more preferably 3% by mass or less.

[0070] [Aqueous medium (B)] The aqueous medium (B) contained in the negative electrode binder composition of this disclosure is water, a hydrophilic solvent, or a mixture thereof. Examples of hydrophilic solvents include the same hydrophilic solvents exemplified as the aqueous medium (b) used in the synthesis of the specific polymer. The aqueous medium (B) may be the same as or different from the aqueous medium (b) used in the synthesis of the specific polymer.

[0071] If the negative electrode binder composition is obtained by adding a dispersion of a specific complex to a dispersion of a specific polymer produced by emulsion polymerization, then the aqueous medium (B) may be a mixture of the aqueous medium (b) used in the synthesis of the specific polymer and the aqueous medium contained in the dispersion of the specific complex. Alternatively, the aqueous medium (B) may be a mixture of the aqueous medium (b) used in the synthesis of the specific polymer and the aqueous medium contained in the dispersion of the specific complex, to which a new aqueous medium has been added. Alternatively, some or all of the aqueous medium (b) contained in the dispersion of the specific polymer produced by emulsion polymerization may be replaced with a new aqueous solvent before adding the dispersion of the specific composite. Alternatively, a dispersion of a specific polymer produced by emulsion polymerization may be added to a dispersion of a specific complex to form a mixture, and then some or all of the aqueous medium in this mixture may be replaced with a new aqueous solvent. The new aqueous medium used in these cases may have the same composition as the aqueous medium (b) used in the synthesis of the specific polymer, or it may have a different composition.

[0072] The negative electrode binder composition of this disclosure preferably contains a specific polymer and a specific complex dispersed in an aqueous medium (B) in the form of dispersed particles. Examples of dispersed particles of the specific polymer include emulsion particles containing the specific polymer and a non-polymerizable surfactant (c), and particles containing the specific polymer having structural units derived from a polymerizable surfactant. Examples of dispersed particles of the specific complex include particles made of the specific complex, and emulsion particles containing the specific complex and a non-polymerizable surfactant (c).

[0073] The anode binder composition of this disclosure may be a dispersion obtained by adding a dispersion containing a specific complex to a dispersion obtained by producing a specific polymer by emulsion polymerization. That is, the anode binder composition may be a dispersion containing a specific polymer, a specific complex, and an aqueous medium (B). Alternatively, the anode binder composition of this disclosure may be a dispersion obtained by adding a dispersion containing a specific complex to a dispersion obtained by dispersing particles of a specific polymer obtained by a method other than emulsion polymerization in an aqueous medium (B). In this case, a known method can be used to disperse the specific polymer in the aqueous medium (B).

[0074] The negative electrode binder composition of this disclosure may contain other components along with the specific polymer, the specific composite, and the aqueous medium (B). Specifically, the negative electrode binder composition may contain polymers other than the specific polymer, the above-mentioned components used in the synthesis of the specific polymer, etc.

[0075] [Average particle diameter d50] When specific polymers and specific composites are contained in the negative electrode binder composition in the form of dispersed particles, the average particle size d50 of the dispersed particles (i.e., a mixture of dispersed polymer particles and dispersed specific composite particles) is preferably 0.18 μm or larger, and more preferably 0.20 μm or larger. This is because an average particle size d50 of 0.18 μm or larger allows for the formation of an electrode in which the negative electrode active material layer is less likely to peel off from the current collector. The average particle size d50 of the dispersed particles is a value measured by the method described in the examples below.

[0076] When specific polymers and specific composites are contained in the negative electrode binder composition in the form of dispersed particles, the average particle size d50 of the dispersed particles is preferably 1.0 μm or less, more preferably 0.80 μm or less, even more preferably 0.60 μm or less, and particularly preferably 0.50 μm or less. When the average particle size d50 is 1.0 μm or less, suitable pressing conditions can be used when pressing the electrode sheet on which the negative electrode active material layer has been formed on the current collector for the purpose of manufacturing the electrode. As a result, the negative electrode active material can be firmly bound to the current collector. The average particle size d50 of the dispersed particles is preferably 0.18 μm to 1.0 μm.

[0077] The average particle size d50 of the dispersed particles can be adjusted using known methods. For example, this can be adjusted by appropriately selecting the type and amount of monomer (a) and / or nonpolymerizable surfactant (c) used when producing a specific polymer by emulsion polymerization. Furthermore, when producing a specific complex by oxidative polymerization of 3,4-ethylenedioxythiophene in an aqueous medium containing polystyrene sulfonic acid, which is a polyanion, in the presence of an oxidizing agent, the production conditions such as the type and amount of oxidizing agent used, the reaction temperature, the reaction time, and the stirring speed can be adjusted by appropriately selecting these conditions.

[0078] [Non-volatile content concentration] The non-volatile content concentration of the negative electrode binder composition of this disclosure is preferably 30% by mass or more, more preferably 33% by mass or more, and even more preferably 35% by mass or more. This is because it is possible to ensure a sufficient amount of the active ingredient contained in the negative electrode binder composition. The non-volatile content concentration of the negative electrode binder composition can be adjusted by the content of the aqueous medium (B) contained in the negative electrode binder composition. The non-volatile content concentration of the negative electrode binder composition is preferably 70% by mass or less, more preferably 65% ​​by mass or less, and even more preferably 60% by mass or less. This is because it suppresses the increase in viscosity of the negative electrode binder composition, making it easier to prepare the negative electrode slurry. The non-volatile content concentration of the negative electrode binder composition is preferably 30% to 70% by mass.

[0079] The non-volatile components of the negative electrode binder composition are those that remain after weighing 1 g of the negative electrode binder composition, placing it on a 5 cm diameter aluminum dish, and drying it in a dryer at 1 atmosphere (1013 hPa) and 105°C for 1 hour while circulating the air inside the dryer. The non-volatile components of the negative electrode binder composition are those that remain without volatilizing even when heating is performed in the manufacturing method of the non-aqueous secondary battery described later, and are the negative electrode binder contained in the non-aqueous secondary battery.

[0080] The total content of specific polymers and specific complexes in the nonvolatile components of the negative electrode binder composition is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and still more preferably 98% by mass or more. This is because the effects of including specific polymers and specific complexes become significant.

[0081] <Slurry for anodes in non-aqueous secondary batteries> The slurry for a negative electrode of a non-aqueous secondary battery (hereinafter sometimes referred to as "negative electrode slurry") of this disclosure contains a negative electrode active material, a specific polymer, a specific composite, and an aqueous medium. In the negative electrode slurry, the negative electrode active material, specific polymer, and specific composite are preferably dispersed in an aqueous medium. In addition to the above components, the negative electrode slurry may also contain thickeners, conductive additives, components used in the synthesis of the specific polymer or specific composite, etc. Details of the specific polymer or composite constituting the negative electrode slurry are as described above.

[0082] [Content of specific polymers] The content of the specific polymer in the negative electrode slurry is preferably 0.50 parts by mass or more, and more preferably 1.0 part by mass or more, per 100 parts by mass of the negative electrode active material. This is to allow the effects of including the specific polymer to be fully expressed. The content of the specific polymer in the negative electrode slurry is preferably 5.0 parts by mass or less, more preferably 4.0 parts by mass or less, and even more preferably 3.0 parts by mass or less, per 100 parts by mass of the negative electrode active material. This is because it allows for a higher content of the negative electrode active material in the negative electrode slurry. The amount of the specific polymer contained in the negative electrode slurry is preferably 0.50 to 5.0 parts by mass per 100 parts by mass of the negative electrode active material.

[0083] [Percentage of specific complexes] The proportion of the specific composite in the total of the specific polymer and specific composite contained in the negative electrode slurry is preferably 0.10% to 10% by mass. If the proportion of the specific composite is 0.10% by mass or more, it becomes possible to reduce the internal resistance of non-aqueous secondary batteries. The proportion of the specific composite is preferably 0.50% by mass or more, and more preferably 1.0% by mass or more. If the proportion of the specific composite is 10% by mass or less, an electrode can be formed in which the negative electrode active material layer is less likely to peel off from the current collector. The proportion of the specific composite is preferably 5% by mass or less, and more preferably 3% by mass or less.

[0084] [Negative electrode active material] The negative electrode active material contained in the negative electrode slurry is a material that can intercarry and deintercalate charge carrier ions such as lithium ions. The charge carrier ions are preferably alkali metal ions, more preferably lithium ions, sodium ions, and potassium ions, and even more preferably lithium ions.

[0085] The negative electrode active material preferably contains at least one of the following: a carbon material, a silicon-containing material, and a titanium-containing material. Examples of carbon materials used as negative electrode active materials include coke such as petroleum coke, pitch coke, and coal coke, carbonized organic polymers, artificial graphite, and natural graphite. Examples of silicon-containing materials used as negative electrode active materials include elemental silicon and silicon compounds such as silicon oxide. Examples of titanium-containing materials used as negative electrode active materials include lithium titanate. These materials used as negative electrode active materials may be used individually, or they may be used in mixtures or composites.

[0086] The negative electrode active material preferably contains at least one of carbon materials and silicon-containing materials, and more preferably carbon materials. This is because the specific polymer contained in the negative electrode slurry has a significant effect in improving the binding between negative electrode active materials and between the negative electrode active materials and the current collector. In particular, it is preferable that the negative electrode active material contains graphite. The proportion of the negative electrode active material in the non-volatile content of the negative electrode slurry is preferably 90% by mass or more, more preferably 93% by mass or more, and even more preferably 95% by mass or more, from the viewpoint of the energy density of the battery. The proportion of the negative electrode active material in the non-volatile content of the negative electrode slurry may be 98% by mass or less. The proportion of the negative electrode active material in the non-volatile content of the negative electrode slurry is preferably 90% by mass to 98% by mass.

[0087] [Thickening agent] Examples of thickeners that may be included in the negative electrode slurry include celluloses such as carboxymethylcellulose (CMC), hydroxyethylcellulose, and hydroxypropylcellulose, ammonium salts of celluloses, alkali metal salts of celluloses, polyvinyl alcohol, and polyvinylpyrrolidone. It is preferable that the thickener contains at least one of carboxymethylcellulose, ammonium salts of carboxymethylcellulose, and alkali metal salts of carboxymethylcellulose, as this facilitates the dispersion of the negative electrode active material in the negative electrode slurry.

[0088] The amount of thickener contained in the negative electrode slurry is preferably 0.50 parts by mass or more, and more preferably 0.80 parts by mass or more, per 100 parts by mass of negative electrode active material. This is because it improves the bonding between negative electrode active materials contained in the negative electrode prepared using the negative electrode slurry, and between the negative electrode active materials and the current collector. The amount of thickener contained in the negative electrode slurry is preferably 3.0 parts by mass or less, more preferably 2.0 parts by mass or less, and even more preferably 1.5 parts by mass or less, per 100 parts by mass of negative electrode active material. This is because it improves the coating properties of the negative electrode slurry. The amount of thickener contained in the negative electrode slurry is preferably 0.50 to 3.0 parts by mass per 100 parts by mass of the negative electrode active material.

[0089] [Conductive additive] Examples of conductive additives that may be included in the negative electrode slurry of this disclosure include carbon black and carbon fibers. Examples of carbon black include furnace black, acetylene black, Denka Black (registered trademark) (manufactured by Denka Co., Ltd.), and Ketjen Black (registered trademark) (manufactured by Ketjen Black International Co., Ltd.). Examples of carbon fibers include carbon nanotubes and carbon nanofibers. As a carbon nanotube, VGCF (registered trademark, manufactured by Resonac Co., Ltd.), which is a gas-phase carbon fiber, is a preferred example.

[0090] [Method for manufacturing a slurry for negative electrodes] A method for producing the negative electrode slurry according to this disclosure involves mixing, for example, a specific polymer, a specific composite, an aqueous medium, a negative electrode active material, a thickener as needed, a conductive additive as needed, and other components as needed. The mixing order of the components that make up the negative electrode slurry is not particularly limited and can be determined as appropriate. Methods for mixing the components include using a mixing device such as a stirring type, rotary type, or shaking type. The specific polymer and the specific composite may be used in the production of the negative electrode slurry in the form of a dispersion.

[0091] <Non-aqueous secondary battery negative electrode> The negative electrode of a non-aqueous secondary battery (hereinafter sometimes referred to as the negative electrode) of this disclosure comprises a current collector and a negative electrode active material layer provided on the current collector, wherein the negative electrode active material layer includes a negative electrode active material, a polymer having a first structural unit derived from a monomer (a1), and a composite of poly(3,4-ethylenedioxythiophene) and polystyrene sulfonic acid. The negative electrode active material layer may also contain non-volatile components of the negative electrode slurry of this disclosure. The shape of the negative electrode of this disclosure is not particularly limited and includes, for example, a laminate or a wound body. The area in which the negative electrode active material layer is formed on the current collector is not particularly limited; the negative electrode active material layer may be formed on the entire surface of the current collector, or it may be formed on only a portion of the surface of the current collector. If the current collector is in the shape of a plate, foil, etc., the negative electrode active material layer may be formed on both sides of the current collector, or on only one side. Details of the specific polymer or composite constituting the negative electrode are as described above.

[0092] [Current collector] The current collector is preferably a metal sheet with a thickness of 0.001 mm to 0.5 mm. Examples of metals forming the metal sheet include iron, copper, aluminum, nickel, and stainless steel. The current collector is preferably copper foil.

[0093] [Method for manufacturing the negative electrode] The negative electrode of this disclosure can be manufactured, for example, by the following method. First, the negative electrode slurry of this disclosure is applied to a current collector. Next, the negative electrode slurry is dried. This forms a negative electrode active material layer containing non-volatile components of the negative electrode slurry on the current collector, forming a negative electrode sheet. Then, if necessary, the negative electrode sheet is cut to an appropriate size. By performing the above steps, the negative electrode of this disclosure is obtained.

[0094] There are no particular limitations on the method for applying the negative electrode slurry onto the current collector, but examples include the reverse roll method, direct roll method, doctor blade method, knife method, extrusion method, curtain method, gravure method, bar method, dip method, and squeeze method. Among these application methods, considering the various physical properties of the negative electrode slurry, such as viscosity, and its drying properties, it is preferable to use one of the methods selected from the direct roll method, doctor blade method, knife method, or extrusion method. This is because it is possible to obtain a negative electrode active material layer with a smooth surface and small variations in thickness.

[0095] When applying the negative electrode slurry to both sides of the current collector, it may be applied sequentially to one side at a time, or to both sides simultaneously. Furthermore, the negative electrode slurry may be applied continuously or intermittently to the current collector. The amount of negative electrode slurry applied can be appropriately determined according to the battery's design capacity and the composition of the negative electrode slurry.

[0096] The method for drying the negative electrode slurry applied to the current collector is not particularly limited, but for example, methods selected from hot air, reduced pressure or vacuum environment, (far) infrared radiation and low-temperature air can be used individually or in combination. The drying temperature and drying time for the negative electrode slurry can be appropriately adjusted depending on the concentration of non-volatile components in the negative electrode slurry, the amount applied to the current collector, etc. The drying temperature is preferably 40°C to 350°C, and more preferably 60°C to 100°C from the viewpoint of productivity. The drying time is preferably 1 minute to 30 minutes.

[0097] The negative electrode sheet, on which a negative electrode active material layer is formed on a current collector, may be cut to a size and shape suitable for use as an electrode. The method of cutting the negative electrode sheet is not particularly limited, and for example, slitting, laser cutting, wire cutting, cutting machines, die cutting machines, etc., can be used.

[0098] In this disclosure, the negative electrode sheet may be pressed before or after cutting, if necessary. By pressing the negative electrode sheet, the negative electrode active material can be firmly bonded to the current collector, and the thickness of the negative electrode can be reduced, thereby enabling miniaturization of the non-aqueous secondary battery. A general method can be used for pressing the negative electrode sheet. In particular, it is preferable to use a die press method or a roll press method. When using the die pressing method, the press pressure is not particularly limited, but 0.5 t / cm 2 ~5t / cm 2 The following is preferable. When using the roll press method, the press load is not particularly limited, but it is preferably 0.5 t / cm to 10 t / cm. This is because it is possible to obtain the above-mentioned effects of pressing while suppressing a decrease in the insertion and desorption capacity of charge carriers such as lithium ions into the negative electrode active material.

[0099] <Non-aqueous secondary battery> The non-aqueous secondary battery of this disclosure comprises the non-aqueous secondary battery anode of this disclosure. A lithium-ion secondary battery will be described as a preferred example of a non-aqueous secondary battery according to this disclosure. However, the configuration of the non-aqueous secondary battery according to this disclosure is not limited to the example shown below. The lithium-ion secondary battery of this disclosure comprises a positive electrode, the negative electrode of this disclosure as described above, an electrolyte, and known components such as separators, which may be provided as needed, all housed in an outer casing. The shape of the lithium-ion secondary battery may be any shape, such as coin-shaped, button-shaped, sheet-shaped, cylindrical, prismatic, or flat.

[0100] [Positive electrode] As the positive electrode, a known type comprising a current collector and a positive electrode active material layer formed on the current collector can be used. As the current collector, the same type as that used for the negative electrode described above can be used. As the positive electrode active material layer, one can be used that includes a known binder such as polyvinylidene fluoride and the positive electrode active material.

[0101] As the positive electrode active material, a material with a higher standard electrode potential than the negative electrode active material is used. Specifically, examples of positive electrode active materials include lithium composite oxides containing nickel, such as Ni-Co-Mn lithium composite oxides, Ni-Mn-Al lithium composite oxides, and Ni-Co-Al lithium composite oxides; lithium cobalt oxide (LiCoO2); spinel-type lithium manganate (LiMn2O4); olivine-type lithium iron phosphate; and chalcogen compounds such as TiS2, MnO2, MoO3, and V2O5. These positive electrode active materials may be used individually or in combination of two or more types.

[0102] [Electrolyte] As the electrolyte, a non-aqueous liquid with ionic conductivity is used. Examples of electrolytes include solutions in which the electrolyte is dissolved in an organic solvent, and ionic liquids, with the former being preferred. This is because it allows for the production of lithium-ion secondary batteries with low manufacturing costs and low internal resistance.

[0103] Alkali metal salts can be used as electrolytes and can be appropriately selected depending on the type of electrode active material, etc. Examples of electrolytes include LiClO4, LiBF6, LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, and LiB 10 Cl 10 Examples include LiAlCl4, LiCl, LiBr, LiB(C2H5)4, CF3SO3Li, CH3SO3Li, LiC4F9SO3, Li(CF3SO2)2N, and lithium aliphatic carboxylates. Other alkali metal salts can also be used as electrolytes.

[0104] The organic solvent used to dissolve the electrolyte is not particularly limited, but examples include carbonate ester compounds such as ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), fluoroethylene carbonate (FEC), and vinylene carbonate (VC); nitrile compounds such as acetonitrile; and carboxylic acid esters such as ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and propyl propionate. These organic solvents may be used individually or in combination of two or more. Among these, it is preferable to use a combination of linear carbonate solvents such as ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) as the organic solvent.

[0105] [Exterior] As for the exterior, for example, a material made of aluminum laminate consisting of aluminum foil and resin film can be used as appropriate, but is not limited to this. [Examples]

[0106] The present disclosure will be described in detail below with reference to examples and comparative examples. The following examples are provided to facilitate understanding of the contents of this disclosure. This disclosure is not limited to these examples. In the following embodiments, a lithium-ion secondary battery anode was fabricated as an example of a non-aqueous secondary battery anode according to the present disclosure, and a lithium-ion secondary battery was fabricated as an example of a non-aqueous secondary battery. The effects of the present disclosure were confirmed by comparing it with the lithium-ion secondary battery anode and lithium-ion secondary battery according to the comparative example. Furthermore, unless otherwise specified, the water used in the following examples and comparative examples is deionized water.

[0107] <Manufacturing of binder compositions for anodes in non-aqueous secondary batteries> A monomer emulsion was prepared by mixing the monomer (a) shown in Table 1 with 200 parts by mass of water as an aqueous medium (b) and the amount of a nonpolymerizable surfactant (c) shown in Table 1, in the mass ratio shown in Table 1, and emulsifying the mixture. Next, aqueous solutions were prepared by dissolving the radical polymerization initiator (e) shown in Table 1 in the amounts shown in Table 1 in 40 parts by mass of water.

[0108] A separable flask equipped with a condenser, thermometer, stirrer, and dropping funnel was filled with 100 parts by mass of water and heated to 80°C. The monomer emulsion and the aqueous solution in which the radical polymerization initiator (e) was dissolved were continuously supplied to this separable flask over 3 hours while stirring at 80°C to obtain an emulsion polymerization reaction solution. The resulting reaction solution was cooled to room temperature. Then, the amount of 25% by mass aqueous ammonia (17 parts by mass of ammonia, 51 parts by mass of water) shown in Table 1 was added to the reaction solution. Next, the PEDOT:PSS solution was added to the reaction solution and stirred so that the non-volatile content of PEDOT:PSS was in the amount shown in Table 1, thereby obtaining the negative electrode binder compositions of Examples 1 to 4, which consist of dispersions in which polymer dispersion particles and PEDOT:PSS dispersion particles are dispersed in an aqueous medium. Furthermore, comparative examples 1 and 2 of the negative electrode binder compositions were obtained in the same manner as in Examples 1 and 3, except that 135 parts by mass of water were added instead of using the PEDOT:PSS solution.

[0109] On the other hand, the binder composition of Example 5 was obtained by adding a PEDOT:PSS solution to commercially available styrene-butadiene rubber latex (non-volatile content concentration 40% by mass) and stirring. In Comparative Example 3, commercially available styrene-butadiene rubber latex was used as is for the binder composition.

[0110] [Table 1]

[0111] The amount of water as the aqueous medium (b) shown in Table 1 represents the total amount of water (parts by mass) contained in the negative electrode binder composition. The amount of ammonia as a basic substance (d) shown in Table 1 represents the amount of ammonia contained in aqueous ammonia (parts by mass).

[0112] The monomer (a4) shown in Table 1 is as follows: Ether sulfate-type ammonium salt (compound name: α-[2-(allyloxy)-1-(alkyloxymethyl)ethyl]-ω-polyoxyethylene sulfate ammonium salt, trade name: Adekarya Soap SR10, manufactured by ADEKA Corporation) is a polymerizable surfactant consisting of the compound represented by the above chemical formula (2).

[0113] The nonpolymerizable surfactant (c) is the polyoxyethylene alkyl ether Emulgen 1150S-60 manufactured by Kao Corporation. The PEDOT:PSS solution is PEDOT:PSS manufactured by Sigma-Aldrich, and contains water as a solvent.

[0114] <Evaluation of binder compositions for negative electrodes> The particle size (d50) and non-volatile content concentration of the dispersed particles were evaluated for the negative electrode binder compositions of Examples 1 to 5 and Comparative Examples 1 to 3 using the following method. The results are shown in Table 1.

[0115] [Particle size of dispersed particles (d50)] For the negative electrode binder compositions of Examples 1 to 5, the particle size (d50) was measured at room temperature (25°C) using dynamic light scattering (DLS) with a NANOTORAC WAVE II (manufactured by Microtrac-Bell Co., Ltd.) as the volume-based median diameter of the dispersed particles (a mixture of dispersed polymer particles and dispersed PEDOT:PSS particles). For the negative electrode binder compositions of Comparative Examples 1 to 3, the particle size (d50) was measured as the volume-based median diameter of the dispersed particles (polymer dispersed particles) in the same manner as in the Examples.

[0116] [Non-volatile content concentration] One g of the negative electrode binder composition was weighed and placed on a 5 cm diameter aluminum dish, then placed in a drying oven. The mixture was dried for one hour at 1 atmosphere (1013 hPa) and 105°C while circulating the air inside the oven, and the mass of the remaining components was measured. The mass ratio (mass%) of the components remaining after drying to the mass (1 g) of the negative electrode binder composition before drying was calculated and expressed as the non-volatile content concentration (mass%).

[0117] <Manufacturing of non-aqueous secondary batteries> Using the negative electrode binder compositions of Examples 1 to 5 and Comparative Examples 1 to 3, negative electrodes were prepared by the methods described below, and lithium-ion secondary batteries, which are non-aqueous secondary batteries of Examples 1 to 5 and Comparative Examples 1 to 3, were then prepared using these negative electrodes.

[0118] [Fabrication of the positive electrode] LiNi as a positive electrode active material 0.6 Mn 0.2 Co 0.2 A mixture was obtained by mixing 4 parts by mass of O294, 3 parts by mass of acetylene black as a conductive additive, and 3 parts by mass of polyvinylidene fluoride as a binder. 50 parts by mass of N-methylpyrrolidone were added to the mixture and further mixed to obtain a positive electrode slurry.

[0119] A 15 μm thick aluminum foil was prepared as the positive electrode current collector. The positive electrode slurry was applied to both sides of the positive electrode current collector using the direct roll method. The amount of positive electrode slurry applied to the positive electrode current collector was adjusted so that the thickness after the roll press treatment described later was 125 μm per side. The positive electrode slurry applied to the positive electrode current collector was dried at 120°C for 5 minutes, and then pressed using a roll press (manufactured by Sankmetal Co., Ltd., press load 5 t / cm, roll width 7 cm) by the roll press method to obtain a positive electrode sheet having positive electrode active material layers on both sides of the positive electrode current collector. The obtained positive electrode sheet was cut into a rectangle measuring 50 mm in length and 40 mm in width, and conductive tabs were attached to form the positive electrode.

[0120] [Fabrication of the negative electrode] 96.9 parts by mass of artificial graphite (G49, manufactured by Jiangxi Zichen Technology Co., Ltd.) as the negative electrode active material, 3.6 parts by mass (1.4 parts by mass of non-volatile content) of any negative electrode binder composition prepared in Examples 1 to 5 or Comparative Examples 1 to 3, and 60 parts by mass of a 2% by mass aqueous solution of CMC (carboxymethylcellulose-sodium salt) were mixed, and 16 parts by mass of water was added. The mixture was then mixed using a rotation-orbit mixer (ARE-310, manufactured by Thinky Co., Ltd.) to obtain a negative electrode slurry.

[0121] A 10 μm thick copper foil was prepared as the negative electrode current collector. The negative electrode slurry was applied to both sides of the negative electrode current collector using the direct roll method. The amount of negative electrode slurry applied to the negative electrode current collector was adjusted so that the thickness of the negative electrode active material layer after the roll press treatment described later was 170 μm per side. The negative electrode slurry applied to the negative electrode current collector was dried at 90°C for 10 minutes, and then pressed using a roll press (manufactured by Sankmetal Co., Ltd., press load 8 t / cm, roll width 7 cm) by the roll press method. This resulted in obtaining a negative electrode sheet having negative electrode active material layers on both sides of the negative electrode current collector. The obtained negative electrode sheet was cut into a rectangle measuring 52 mm in length and 42 mm in width, and conductive tabs were attached to form the negative electrode.

[0122] [Fabrication of non-aqueous secondary batteries] A separator made of a porous polyolefin film (polyethylene, 25 μm thick) was interposed between the positive and negative electrodes, and the positive electrode active material layer and the negative electrode active material layer were laminated so that they faced each other. These were then housed in an outer casing (battery pack) made of aluminum laminate material. Subsequently, an electrolyte solution was injected into the outer casing, vacuum impregnation was performed, and the battery was packed using a vacuum heat sealer to obtain a lithium-ion secondary battery.

[0123] As the electrolyte, a mixture was used consisting of 99 parts by mass of a solution in which LiPF6 was dissolved at a concentration of 1.0 mol / L in a mixed solvent containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of EC:EMC:DEC = 30:50:20, and 1 part by mass of vinylene carbonate (VC).

[0124] <Evaluation of non-aqueous secondary batteries> The internal resistance and electrode interface resistivity of the lithium-ion secondary batteries of Examples 1 to 5 and Comparative Examples 1 to 3 were evaluated using the methods described below. The results are shown in Table 1.

[0125] [Internal resistance (DCR)] Under conditions of 25°C, the internal resistance (DCR(mΩ)) of a lithium-ion secondary battery was measured using the following procedure. Specifically, the battery was charged at a constant current of 0.2C from rest potential until the voltage reached 3.6V, bringing the charge state to 50% of the initial capacity (SOC50%). Subsequently, discharge was performed for 60 seconds at current values ​​of 0.2C, 0.5C, 1C, and 2C. The internal resistance DCR(mΩ) at SOC50% was determined from the relationship between these four current values ​​(values ​​per second) and voltage.

[0126] [Electrode interface resistivity] For the negative electrode, the electrode interface resistivity was measured at room temperature (23°C) using an XF057 (manufactured by HIOKI E.E. CORPORATION) under the following conditions: measurement current: 50mA, voltage range: 0.1V, and measurement speed: Normal.

[0127] <Evaluation Results> The following can be seen from the evaluation results in Table 1. The lithium-ion secondary batteries of Examples 1 to 5, which have a negative electrode active material layer containing PEDOT:PSS, have a lower internal resistance (DCR) compared to the lithium-ion secondary batteries of Comparative Examples 1 to 3, which have a negative electrode active material layer without PEDOT:PSS, indicating that they are non-aqueous secondary batteries with low internal resistance. Furthermore, a comparison of Example 1 and Example 2 shows that the higher the PEDOT:PSS content in the negative electrode active material layer, the lower the internal resistance (DCR) of the lithium-ion secondary battery tends to be. Furthermore, the evaluation results from Examples 1, 3, and 5 show that, regardless of the type of structural units constituting the polymer, the combination of the polymer and PEDOT:PSS tends to reduce the internal resistance (DCR) of the lithium-ion secondary battery.

Claims

1. It contains a polymer having a first structural unit derived from monomer (a1), a composite of poly(3,4-ethylenedioxythiophene) and polystyrene sulfonic acid, and an aqueous medium. A binder composition for a negative electrode of a non-aqueous secondary battery, wherein the monomer (a1) is a nonionic compound having one ethylenically unsaturated bond.

2. The polymer further has a second structural unit derived from monomer (a2), The binder composition for a negative electrode of a non-aqueous secondary battery according to claim 1, wherein the monomer (a2) is a compound having a carboxyl group and one ethylenically unsaturated bond.

3. The polymer further has a third structural unit derived from monomer (a3), The binder composition for a negative electrode of a non-aqueous secondary battery according to claim 1, wherein the monomer (a3) ​​is a compound having a plurality of independent ethylenically unsaturated bonds.

4. The monomer (a1) contains an aromatic compound having an ethylenically unsaturated bond, The binder composition for a negative electrode of a non-aqueous secondary battery according to claim 1, wherein the content of structural units derived from the aromatic compound having the ethylenically unsaturated bond in the total structural units of the polymer is 41% by mass or more.

5. The binder composition for a negative electrode of a non-aqueous secondary battery according to claim 2, wherein the content of the second structural unit in the total structural units of the polymer is 0.10% by mass to 20% by mass.

6. The binder composition for a negative electrode of a non-aqueous secondary battery according to claim 3, wherein the content of the third structural unit in the total structural units of the polymer is 0.010% by mass to 15% by mass.

7. The binder composition for a negative electrode of a non-aqueous secondary battery according to claim 1, wherein the proportion of the composite to the total of the polymer and the composite is 0.10% by mass to 10% by mass.

8. The polymer and the composite are contained in the form of dispersed particles. The binder composition for a negative electrode of a non-aqueous secondary battery according to claim 1, wherein the average particle size d50 of the dispersed particles is 0.18 μm to 1.0 μm.

9. It contains a negative electrode active material, a polymer having a first structural unit derived from monomer (a1), a composite of poly(3,4-ethylenedioxythiophene) and polystyrene sulfonic acid, and an aqueous medium. A slurry for a negative electrode of a non-aqueous secondary battery, wherein the monomer (a1) is a nonionic compound having one ethylenically unsaturated bond.

10. The polymer further has a second structural unit derived from monomer (a2), The slurry for a negative electrode of a non-aqueous secondary battery according to claim 9, wherein the monomer (a2) is a compound having a carboxyl group and one ethylenically unsaturated bond.

11. The polymer further has a third structural unit derived from monomer (a3), The slurry for a negative electrode of a non-aqueous secondary battery according to claim 9, wherein the monomer (a3) ​​is a compound having a plurality of independent ethylenically unsaturated bonds.

12. The monomer (a1) contains an aromatic compound having an ethylenically unsaturated bond, The slurry for a negative electrode of a non-aqueous secondary battery according to claim 9, wherein the content of structural units derived from the aromatic compound having the ethylenically unsaturated bond in the total structural units of the polymer is 41% by mass or more.

13. The slurry for a negative electrode of a non-aqueous secondary battery according to claim 10, wherein the content of the second structural unit in the total structural units of the polymer is 0.10% by mass to 20% by mass.

14. The slurry for a negative electrode of a non-aqueous secondary battery according to claim 11, wherein the content of the third structural unit in the total structural units of the polymer is 0.010% by mass to 15% by mass.

15. The slurry for a negative electrode of a non-aqueous secondary battery according to claim 9, wherein the proportion of the composite to the total of the polymer and the composite is 0.10% by mass to 10% by mass.

16. The polymer and the composite are contained in the form of dispersed particles. The slurry for a negative electrode of a non-aqueous secondary battery according to claim 9, wherein the average particle size d50 of the dispersed particles is 0.18 μm to 1.0 μm.

17. The device comprises a current collector and a negative electrode active material layer provided on the current collector. The negative electrode active material layer comprises the non-volatile components of the non-aqueous secondary battery negative electrode slurry described in any one of claims 9 to 16.

18. A non-aqueous secondary battery comprising the aqueduct of a non-aqueous secondary battery according to claim 17.

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