Electrode binder composition, electrode slurry, electrode, secondary battery, method for manufacturing electrode, and method for manufacturing electrode slurry

Abstract

The electrode binder composition comprises an electrode binder polymer and an aqueous medium. The electrode binder polymer has a first functional group and a second functional group. The first functional group is at least one selected from carboxyl groups and carboxyl groups that have formed salts. The second functional group is at least one selected from isocyanate groups and blocked isocyanate groups. The electrode binder composition is subjected to atmospheric pressure, 23°C, and an absolute humidity of 10 g / m³. 3 After drying for 5 days, the film was then dried at 60°C for 12 hours at a pressure below 0.01 MPa, resulting in a tensile strength S(St) of over 4.00 MPa.

Description

Technical Field

[0001] This disclosure relates to electrode binder compositions, electrode slurries, electrodes, secondary batteries, methods for manufacturing electrodes, and methods for manufacturing electrode slurries. Background Technology

[0002] Rechargeable batteries can be miniaturized and made lighter, making them widely used as power sources for laptops, mobile phones, power tools, and electronic communication devices. In recent years, they have also been used in electric vehicles and hybrid vehicles. Lithium-ion batteries are a representative example of rechargeable batteries.

[0003] A secondary battery comprises a positive electrode with an active material such as a metal oxide, a negative electrode with an active material such as graphite, and an electrolyte. Both the positive and negative electrodes have current collectors and electrode active material layers formed on the current collectors. The electrode active material layers typically contain a binder, which bonds the active materials to each other and to the current collector. Examples of binders used in secondary batteries include those described in Patent Documents 1 and 2.

[0004] Patent Document 1 describes a secondary battery electrode comprising an electrode layer containing: 100 parts by mass of at least one polymer selected from styrene-butadiene copolymers and copolymers obtained from (meth)acrylates and vinyl monomers having acid components; and 1 to 20 parts by mass of at least one nonionic surfactant selected from polyoxyethylene alkyl ether derivatives, polyoxyethylene-polyoxypropylene condensates and polyoxyethylene-polyoxypropylene alkyl ether derivatives, having a cloud point of 70°C or below.

[0005] Patent Document 2 describes a binder for lithium-ion secondary battery electrodes with a glass transition temperature of 30°C or less. It is obtained by emulsion polymerization of an olefinic unsaturated monomer containing 15-70% by mass of styrene, olefinic unsaturated carboxyl esters and olefinic unsaturated carboxylic acids, and an internal crosslinking agent as essential components relative to all olefinic unsaturated monomers, in the presence of a surfactant.

[0006] In addition, Patent Document 3 describes an electrode binder comprising a polymer having structural units derived from (meth)acrylate alkyl ester monomers, structural units derived from specific structural monomers having aromatic groups, and structural units derived from monomers having at least one selected from epoxy groups, (blocked) isocyanate groups, and urethane groups.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent Application Publication No. 2014-239070

[0010] Patent Document 2: Japanese Patent Application Publication No. 2011-243464

[0011] Patent Document 3: International Publication No. 2023 / 053863 Summary of the Invention

[0012] The problem that the invention aims to solve

[0013] In recent years, secondary batteries have been required to maintain their performance even when exposed to high temperatures for extended periods, i.e., excellent high-temperature storage properties.

[0014] Therefore, the purpose of this disclosure is to provide an electrode binder composition, an electrode slurry, an electrode, a secondary battery, a method for manufacturing the electrode, and a method for manufacturing the electrode slurry, which can produce a secondary battery with excellent high-temperature preservation properties.

[0015] Methods for solving problems

[0016] This disclosure includes the following methods.

[0017] <1> An electrode binder composition comprising an electrode binder polymer and an aqueous medium, said electrode binder polymer having a first functional group and a second functional group, wherein the first functional group is at least one selected from carboxyl groups and carboxyl groups that have formed salts, and the second functional group is at least one selected from isocyanate groups and blocked isocyanate groups.

[0018] The above electrode adhesive composition was subjected to atmospheric pressure, 23°C, and an absolute humidity of 10 g / m². 3 After drying for 5 days, the film was then dried at 60°C for 12 hours at a pressure below 0.01 MPa, resulting in a tensile strength S(St) of over 4.00 MPa.

[0019] <2> According to the electrode adhesive composition described in <1>, the above-mentioned coating is further subjected to atmospheric pressure, 110°C, and absolute humidity of 10 g / m³. 3 The fracture strength S(110) after 1 hour of storage is above 6.00 MPa.

[0020] <3> According to the electrode adhesive composition described in <1> or <2>, wherein the above-mentioned tensile strength S(St) is the same as that obtained by subjecting the above-mentioned coating to atmospheric pressure, 110°C, and 10 g / m² absolute humidity. 3 The ratio of the fracture strength S(110) to the fracture strength S(St) after 1 hour of storage is greater than 1.00.

[0021] <4> The electrode binder composition according to any one of <1> to <3>, wherein the content of the electrode binder polymer in the non-volatile component is 80% by mass or more.

[0022] <5> An electrode binder composition according to any one of <1> to <4>, wherein the electrode binder polymer is dispersed in the aqueous medium.

[0023] <6> An electrode paste comprising an electrode binder composition and an electrode active substance as described in any one of <1> to <5>, or comprising a non-volatile component of an electrode binder composition as described in any one of <1> to <5>, an electrode active substance, and a liquid medium, wherein the non-volatile component comprises the electrode binder polymer described above.

[0024] <7> An electrode having a current collector and an electrode active material layer formed on the current collector, the electrode active material layer comprising a non-volatile component of the electrode binder composition described in any one of <1> to <5> and the electrode active material, the non-volatile component comprising the electrode binder polymer.

[0025] <8> A secondary battery having the electrodes described in <7>.

[0026] <9> A method for manufacturing an electrode, comprising: a coating step of coating an electrode paste as described in <6> onto a current collector; and a drying step of drying the electrode paste coated on the current collector.

[0027] <10> A method for manufacturing an electrode paste, wherein the electrode binder composition described in any one of <1> to <5> is mixed with an electrode active material.

[0028] <11> A method for manufacturing an electrode paste, comprising:

[0029] The process of preparing the non-volatile component of the electrode binder composition described in any one of <1> to <5>; and

[0030] The process of mixing the above-mentioned non-volatile components, electrode active materials and liquid medium

[0031] The aforementioned non-volatile components include the aforementioned electrode binder polymer.

[0032] Invention Effects

[0033] According to this disclosure, it is possible to provide an electrode binder composition, an electrode slurry, an electrode, a secondary battery, a method for manufacturing the electrode, and a method for manufacturing the electrode slurry, which can produce a secondary battery with excellent high-temperature preservation properties. Detailed Implementation

[0034] The embodiments will now be described in detail. However, this disclosure is not limited to the embodiments described below. In the embodiments described below, unless otherwise specified, the constituent elements (including element steps, etc.) are not essential. Similarly, numerical values ​​and their ranges are not limiting to this disclosure.

[0035] In this disclosure, within a numerical range represented by "~", the values ​​before and after "~" are respectively the minimum and maximum values. "Above A" in a numerical range refers to A and a range exceeding A. "Below A" in a numerical range refers to A and a range less than A. Within the numerical ranges described in this disclosure, the upper or lower limit of one numerical range can be replaced by the upper or lower limit of another numerical range described in another stage. Furthermore, within the numerical ranges described in this disclosure, the upper or lower limit can be replaced by the values ​​shown in the embodiments.

[0036] In this disclosure, unless otherwise specified, each component may contain multiple corresponding substances. When multiple substances corresponding to each component are present in the composition, etc., unless otherwise specified, the content or percentage of each component refers to the total content or percentage of the multiple substances present in the composition, etc.

[0037] In this disclosure, the term "layer" includes not only the case where it is formed in the entire region when the region in which the layer exists, but also the case where it is formed only in a part of the region.

[0038] In this disclosure, "(meth)acrylic acid" is a general term for acrylic acid and methacrylic acid. "(meth)acrylate" is a general term for acrylate and methacrylate.

[0039] In this disclosure, unless otherwise specified, "olefin unsaturated bond" refers to an olefin unsaturated bond that is capable of free radical polymerization.

[0040] The "non-volatile component" in the composition is the component that remains as a solid or liquid after drying the composition at 105°C for 1 hour in a desiccator with air circulation at 1 atmosphere (1013 hPa). The composition may be in the form of a solution, dispersion, or slurry, but is not limited to these.

[0041] The "concentration of non-volatile components" in the composition is the mass ratio (mass %) of the component remaining as a solid or liquid after 1 g of the composition is weighed in an aluminum pan with a diameter of 5 cm, dried at 105 °C for 1 hour in a desiccator with air circulation at 1 atmosphere (1013 hPa), relative to the mass of the composition (1 g) before drying.

[0042] Unless otherwise specified, "the coating obtained from the composition" refers to the film obtained by subjecting the composition to atmospheric pressure, 23°C, and 10 g / m² absolute humidity. 3 The coating is obtained by drying for 5 days at a pressure below 0.01 MPa, at 60°C, and for 12 hours. The thickness of the coating is 0.3 mm to 0.6 mm.

[0043] <Electrode binder composition>

[0044] The electrode binder composition disclosed herein comprises an electrode binder polymer and an aqueous medium. The electrode binder polymer has a first functional group and a second functional group. The first functional group is at least one selected from carboxyl groups and carboxyl groups that have formed salts. The second functional group is at least one selected from isocyanate groups and blocked isocyanate groups. The electrode binder composition is subjected to atmospheric pressure, 23°C, and an absolute humidity of 10 g / m³. 3 After drying for 5 days, the film was then dried at 60°C for 12 hours at a pressure below 0.01 MPa, resulting in a tensile strength S(St) of over 4.00 MPa.

[0045] The electrode binder composition may comprise an electrode binder polymer, an aqueous medium, and other components. Specifically, the electrode binder composition may include components used to synthesize the electrode binder polymer, etc.

[0046] The electrode binder composition disclosed herein is preferably used in the manufacture of electrodes for non-aqueous secondary batteries, more preferably in the manufacture of electrodes for lithium-ion secondary batteries, and even more preferably in the manufacture of negative electrodes for lithium-ion secondary batteries.

[0047] In the electrode binder compositions disclosed herein, the electrode binder polymer is preferably dispersed in an aqueous medium. In this disclosure, "electrode binder polymer dispersed in an aqueous medium" means that the electrode binder polymer exists in water without agglomeration or sedimentation, which can be confirmed, for example, by visual confirmation of sedimentation, determination of the concentration gradient in the height direction within the container, and determination of particle size based on dynamic light scattering (DLS).

[0048] The electrode binder composition is more preferably an emulsion formed by dispersing particles containing an electrode binder polymer in an aqueous medium. Examples of particles containing the electrode binder polymer include particles containing the electrode binder polymer, particles containing both the electrode binder polymer and a surfactant, and particles containing other components. Furthermore, particles containing and not containing the electrode binder polymer can coexist in the electrode binder composition.

[0049] The electrode binder composition disclosed herein can be a dispersion obtained by emulsion polymerization of the olefinic unsaturated compounds described later. Alternatively, the electrode binder composition disclosed herein can also be a dispersion obtained by dispersing an electrode binder polymer obtained by methods other than emulsion polymerization in an aqueous medium.

[0050] In this disclosure, the tensile strength of the film obtained from the electrode binder composition is defined as S(St).

[0051] S(St) is 4.00 MPa or more, preferably 6.00 MPa or more, more preferably 8.00 MPa or more, and even more preferably 9.00 MPa or more. This is because, within the above range, not only can the decrease in the charge-discharge capacity maintenance characteristics of the electrode after storage at high temperature be suppressed, but the increase in electrode resistance after storage at high temperature can also be suppressed.

[0052] There is no particular limit to the upper limit of S (St), and the higher the value, the better.

[0053] In this disclosure, the film obtained from the electrode binder composition is subjected to atmospheric pressure, 110°C, and 10 g / m² absolute humidity. 3 The fracture strength after 1 hour of storage is set as S(110).

[0054] S(110) is preferably 6.00 MPa or more, more preferably 8.00 MPa or more, even more preferably 10.0 MPa or more, and particularly preferably 11.0 MPa or more. This is because, within the above range, not only can the decrease in the charge-discharge capacity maintenance characteristics of the electrode after storage at high temperature be further suppressed, but the increase in electrode resistance after storage at high temperature can also be further suppressed.

[0055] There is no particular limit to the upper limit of S(110), and the higher the value, the better.

[0056] The ratio of S(110) to S(St), i.e., S(110) / S(St), is preferably 1.00 or more, more preferably 1.10 or more, even more preferably 1.20 or more, and particularly preferably 1.30 or more. This is because, within the above range, not only can the decrease in the charge-discharge capacity maintenance characteristics of the electrode after storage at high temperature be further suppressed, but the increase in electrode resistance after storage at high temperature can also be further suppressed.

[0057] The ratio of S(110) to S(St), i.e., S(110) / S(St), is preferably 3.00 or less, more preferably 2.00 or less, and even more preferably 1.50 or less. This is because, within the above range, electrode deterioration under high-temperature conditions can be suppressed.

[0058] The value of S(110) / S(St) can be 1.00~3.00, 1.10~2.00, 1.20~1.50, or 1.30~1.50.

[0059] From the viewpoint of increasing the amount of active ingredients contained in the electrode binder composition, the concentration of non-volatile components in the binder composition of this disclosure is preferably 20% by mass or more, more preferably 25% by mass or more, and even more preferably 30% by mass or more. The concentration of non-volatile components in the electrode binder composition can be adjusted by the content of the aqueous medium contained in the electrode binder composition.

[0060] From the viewpoint of suppressing the increase in viscosity of the electrode binder composition and facilitating the preparation of the electrode slurry described later, the concentration of non-volatile components in the electrode binder composition is preferably 80% by mass or less, more preferably 70% by mass or less, and even more preferably 60% by mass or less.

[0061] The content of the electrode binder polymer in the non-volatile component of the 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 particularly preferably 98% by mass or more. This is because, within the above range, the high-temperature storage performance of the secondary battery manufactured using the electrode binder composition is further improved.

[0062] The percentage of electrode binder polymer in the non-volatile components of the electrode binder composition is calculated by assuming that all monomers, surfactants, and polymerization initiators used in the manufacture of the electrode binder polymer have reacted as part of the electrode binder polymer.

[0063] [Electrode binder polymer]

[0064] The electrode binder polymer has a first functional group and a second functional group, wherein the first functional group is selected from at least one of carboxyl groups and carboxyl groups that have formed salts, and the second functional group is selected from at least one of isocyanate groups and blocked isocyanate groups.

[0065] It should be noted that in electrode binder compositions, the functional groups and other components contained in the electrode binder polymer sometimes react with other components, causing a partial change in the structure of the electrode binder polymer. In this case, the structure of the electrode binder polymer after the reaction is also considered as the electrode binder polymer. That is, in electrode binder compositions, the electrode binder polymer also includes the corresponding polymer and the structure of that polymer after reaction with other components.

[0066] In the case of isocyanate groups present as the second functional group in the electrode binder polymer, or when isocyanate groups are blocked, it is believed that isocyanate groups generated by heating, applying voltage, chemical reactions, etc., produce active species through redox reactions during charging and discharging in the electrode. It is believed that these active species react with at least one of the electrolyte and the solid electrolyte interphase (SEI) formed on the surface of the electrode active material through redox reactions of the electrolyte, thereby the electrode binder polymer firmly protects the surface of the electrode active material. The surface of the electrode active material firmly protected by the electrode binder polymer exhibits excellent durability at high temperatures such as 60°C. Therefore, it is believed that the decomposition reactions of the electrolyte and electrolytes generated on the surface of the electrode active material during high-temperature storage are suppressed, and the high-temperature storage characteristics are improved.

[0067] The content F1 of the first functional group of the electrode binder polymer is preferably 0.20 mmol / g or more, more preferably 0.50 mmol / g or more, and even more preferably 0.70 mmol / g or more. This is because, within the above range, the peeling of the electrode active material layer from the current collector is further suppressed. Furthermore, this is because, within the above range, the polymerization stability during the manufacture of the electrode binder polymer is improved, enabling the production of a high-quality electrode binder polymer at low cost.

[0068] From the viewpoint of ensuring the polymerization stability during the manufacture of this binder polymer, the content F1 of the first functional group of the electrode binder polymer is preferably 5.0 mmol / g or less, more preferably 3.0 mmol / g or less, even more preferably 1.5 mmol / g or less, and particularly preferably 1.0 mmol / g or less.

[0069] The content of the first functional group F1 of the electrode binder polymer can be 0.20 mmol / g to 5.0 mmol / g, 0.50 mmol / g to 3.0 mmol / g, 0.70 mmol / g to 1.5 mmol / g, or 0.70 mmol / g to 1.0 mmol / g.

[0070] The content of the first functional group, F1 [mmol / g], was determined by the following method.

[0071] The content of the first functional group, F1 [mmol / g] = (content of the first functional group [mmol]) / (total weight [g] of monomers used in the manufacture of the electrode binder polymer)

[0072] The “content of the first functional group [mmol]” in the formula refers to the sum of (the amount of substance of the monomer with the first functional group (mmol)) × (the number of the first functional groups in one of the above monomers with the first functional group) for all monomers with the first functional group contained in the electrode binder polymer.

[0073] The content of the second functional group F2 in the electrode binder polymer is preferably 0.020 mmol / g or more, more preferably 0.050 mmol / g or more, and even more preferably 0.070 mmol / g or more. This is because, within the above range, the high-temperature storage characteristics of the electrode containing the electrode binder polymer are further improved.

[0074] The content of the second functional group F2 in the electrode binder polymer is preferably 2.0 mmol / g or less, more preferably 1.0 mmol / g or less, even more preferably 0.60 mmol / g or less, and particularly preferably 0.10 mmol / g or less. This is because, within the above range, the yield is increased due to the improved polymerization stability during the manufacture of the electrode binder polymer, thereby reducing the manufacturing cost of the electrode binder polymer.

[0075] The content of the second functional group F2 of the electrode binder polymer can be 0.020 mmol / g to 2.0 mmol / g, 0.050 mmol / g to 1.0 mmol / g, 0.070 mmol / g to 0.60 mmol / g, or 0.070 mmol / g to 0.10 mmol / g.

[0076] The content of the second functional group, F2 [mmol / g], was determined by the following method.

[0077] The content of the second functional group F2 [mmol / g] = (content of the second functional group [mmol]) / (total weight [g] of monomers used in the manufacture of the electrode binder polymer)

[0078] The “content of the second functional group [mmol]” in the formula refers to the sum of (the amount of substance of the monomer with the second functional group (mmol)) × (the number of the second functional groups in one of the above monomers with the second functional group) for all monomers with the second functional group contained in the electrode binder polymer.

[0079] In the electrode binder polymer, from the viewpoint of improving the high-temperature storage characteristics of the battery using the electrode containing the electrode binder polymer, the value of F2 / F1, which is the ratio of the content of the second functional group F2 to the content of the first functional group F1, is preferably 0.020 or more, more preferably 0.050 or more, even more preferably 0.070 or more, and particularly preferably 0.082 or more.

[0080] In the electrode binder polymer, from the viewpoint of ensuring the polymerization stability during the manufacture of the electrode binder polymer, the value of F2 / F1, which is the ratio of the content of the second functional group F2 to the content of the first functional group F1, is preferably 2.0 or less, more preferably 1.0 or less, even more preferably 0.60 or less, and particularly preferably 0.10 or less.

[0081] In the electrode binder polymer, the ratio of the content of the second functional group F2 to the content of the first functional group F1, F2 / F1, can be 0.020 to 2.0, 0.050 to 1.0, 0.082 to 0.60, or 0.082 to 0.10.

[0082] In this disclosure, the carboxyl group that has formed a salt refers to the group in which the carboxyl group forms a salt with a basic substance.

[0083] In this disclosure, the blocked isocyanate group refers to a functional group formed by the bonding of an isocyanate group with a blocking agent. Preferably, the blocked isocyanate group is a structure capable of controlling the conversion to an isocyanate group.

[0084] The blocked isocyanate group is preferably a structure that generates the isocyanate group through external stimulation, chemical reaction, etc., and more preferably a structure that generates the isocyanate group through at least one of heating, applying voltage, and chemical reaction. The conversion from blocked isocyanate group to isocyanate group can occur by removing the blocking agent through redox reaction, such as by heating-based reaction, chemical reaction with Lewis acid, Brønsted acid, etc., electrochemical reaction based on applied voltage, etc.

[0085] Examples of blocking agents include methyl salicylate, 3,5-dimethylpyrazole, 2-butanone-oxime (methyl ethyl ketone oxime), ε-caprolactam, and 1-methoxy-2-propanol. From the perspective of ease of removal, it is preferable that the blocking agent contains at least one selected from methyl salicylate, 3,5-dimethylpyrazole, and 2-butanone-oxime.

[0086] The presence of a first functional group in the electrode binder polymer can be confirmed by quantifying the amount of carboxyl groups or carboxylates using methods such as infrared spectroscopy (IR) and nuclear magnetic resonance (NMR).

[0087] Furthermore, the fact that the electrode binder polymer has a second functional group can be confirmed by quantifying the amount of blocking agent bonded to isocyanate groups or blocked isocyanate groups using infrared spectroscopy (IR), nuclear magnetic resonance (NMR), or other methods.

[0088] The glass transition temperature (Tg) of the electrode binder polymer is preferably -3°C or higher, more preferably 0°C or higher, and even more preferably 5°C or higher. This is because, within the above range, the film fracture strength of the electrode binder polymer is improved, and the increase in electrode resistance after the electrode containing the electrode binder polymer is placed in a high-temperature environment is suppressed.

[0089] From the viewpoint of ensuring the electrode peel strength of the electrode containing the electrode binder polymer, the glass transition temperature Tg of the electrode binder polymer is preferably 50°C or less, more preferably 30°C or less, even more preferably 20°C or less, and particularly preferably 10°C or less.

[0090] The glass transition temperature (Tg) of the electrode binder polymer can be -3℃ to 50℃, 0℃ to 30℃, 5℃ to 20℃, or 5℃ to 10℃.

[0091] The glass transition temperature Tg of the electrode binder polymer was measured using a differential scanning calorimetry (DSC) device (e.g., an EXSTAR DSC / SS7020 manufactured by Hitachi High-Tech Science Co., Ltd.) at a heating rate of 10°C / min under a nitrogen atmosphere, and the peak temperature of the graph obtained as the temperature derivative was determined.

[0092] The solubility of the electrode binder polymer in water at 25°C is preferably 1.0 g / 100 g H₂O or less, more preferably 0.50 g / 100 g H₂O or less, and even more preferably 0.30 g / 100 g H₂O or less. Within this range, the viscosity increase of the electrode binder composition can be suppressed. Furthermore, within this range, the electrode binder polymer exists in particle form in the electrode made using the electrode binder composition. As a result, the electrolyte easily penetrates between the particles, tending to reduce the electrode resistance.

[0093] [Structural example of electrode binder polymer]

[0094] The electrode binder polymer disclosed herein only needs to have a first functional group and a second functional group, and its backbone is not particularly limited. For example, the electrode binder polymer may have structural units having a first functional group and structural units having a second functional group. Hereinafter, the structural unit having a first functional group will also be referred to as the first structural unit, and the structural unit having a second functional group will also be referred to as the second structural unit.

[0095] The electrode binder polymer disclosed herein may further comprise one or more structural units that are not part of either the first or second structural unit. Examples of such structural units include a third structural unit derived from an aromatic hydrocarbon monomer, a fourth structural unit derived from a nonionic monomer, and a fifth structural unit derived from a multifunctional monomer.

[0096] Each monomer may possess olefinically unsaturated bonds. In this disclosure, unless otherwise specified, "olefinically unsaturated bond" refers to an olefinically unsaturated bond capable of free radical polymerization. When each monomer possesses olefinically unsaturated bonds, the structural units contained in the polymer are bonded to each other through the polymerization reaction of the olefinically unsaturated bonds possessed by each monomer. In this case, unless otherwise specified, the structural units contained in the polymer are bonded to each other through covalent bonds.

[0097] It should be noted that, taking a polymer having structural unit A derived from compound A with olefinic unsaturated bonds as an example, the chemical structure of the portion of structural unit A in the polymer other than the portion corresponding to the olefinic unsaturated bond in compound A is the same as the chemical structure of the portion other than the olefinic unsaturated bond in compound A before polymerization. For example, structural units derived from styrene have the structure "-CH2CH(C6H5(phenyl))-" in electrode binder polymers.

[0098] When each monomer has an olefinic unsaturated bond, the monomer that becomes the source of a certain structural unit in the polymer refers to a compound whose structure is formed by replacing the bond between the two carbon atoms in the main chain of the polymer with an olefinic unsaturated bond and breaking it from other structural units.

[0099] Furthermore, when the structure of functional groups other than the olefinic unsaturated bonds in the polymer backbone changes due to chemical reactions, the structural units are classified based on the changed chemical structure. For example, in the case of saponification after polymerization of vinyl acetate, the structural unit is not derived from vinyl acetate but is called a structural unit derived from vinyl alcohol. Similarly, in the case of ion exchange after polymerization of monomers with ionic functional groups, the structural units are classified based on the chemical structure after ion exchange. Specifically, for example, in the case of "-CH2CH(COOH)-" after polymerization of sodium acrylate and ion exchange, the structural unit is not derived from sodium acrylate but is called a structural unit derived from acrylic acid.

[0100] [Structural Unit 1]

[0101] The first structural unit has at least one selected from carboxyl groups that are the first functional group and carboxyl groups that have formed salts.

[0102] In the electrode binder polymer, the first structural unit may contain one type or two or more types.

[0103] The first structural unit may have one carboxyl group or two or more carboxyl groups. The first structural unit may have one carboxyl group that has formed a salt or two or more carboxyl groups that have formed a salt. In the first structural unit, the total number of carboxyl groups and carboxyl groups that have formed a salt contained in one structural unit is preferably 1 to 4, more preferably 1 to 2.

[0104] Examples of carboxylic acid monomers that can serve as the source of the first structural unit include unsaturated monocarboxylic acids such as methacrylic acid, acrylic acid, and crotonic acid; and unsaturated dicarboxylic acids such as itaconic acid and fumaric acid. From the viewpoint of inhibiting the stripping of the electrode active material layer from the current collector, the carboxylic acid monomer preferably includes at least one selected from acrylic acid, methacrylic acid, and itaconic acid.

[0105] The proportion of structural units derived from acrylic acid, methacrylic acid and itaconic acid in the first structural unit (or the total proportion of structural units derived from them if two or more are included) is preferably 80 mol% or more, can be 90 mol% or more, or can be 100 mol%.

[0106] Furthermore, from the viewpoint of improving the adhesion between the binder polymer and the active material or current collector, the carboxylic acid monomer can include both unsaturated monocarboxylic acids and unsaturated dicarboxylic acids. When the carboxylic acid monomer includes both unsaturated monocarboxylic acids and unsaturated dicarboxylic acids, the content of the unsaturated dicarboxylic acid relative to the total amount of the unsaturated monocarboxylic acids and unsaturated dicarboxylic acids is preferably 1 mol% or more, more preferably 5 mol% or more, further preferably 10 mol% or more, and particularly preferably 15 mol% or more. Additionally, the content of the unsaturated dicarboxylic acid relative to the total amount of the unsaturated monocarboxylic acids and unsaturated dicarboxylic acids is preferably 70 mol% or less, more preferably 50 mol% or less, further preferably 40 mol% or less, and particularly preferably 30 mol% or less.

[0107] Examples of salts include metal salts and ammonium salts. Examples of metal salts include alkali metal salts such as lithium salts, sodium salts, and potassium salts.

[0108] [Structural Unit 2]

[0109] The second structural unit has at least one selected from isocyanate group and blocked isocyanate group as the second functional group.

[0110] In the electrode binder polymer, the second structural unit may contain one type or two or more types.

[0111] Examples of isocyanate monomers that can serve as the source of the second structural unit include compounds having (meth)acryloyl, vinyl, or allyl groups. From the viewpoint of ease of acquisition and polymerization reactivity, compounds having (meth)acryloyl groups are preferred. The isocyanate monomer is preferably a compound having at least one selected from isocyanate groups and blocked isocyanate groups, and a (meth)acryloyl group; more preferably, it is a (meth)acrylate having at least one selected from isocyanate groups and blocked isocyanate groups.

[0112] The proportion of structural units derived from (meth)acrylates having at least one of isocyanate groups and blocked isocyanate groups in the second structural unit is preferably 80 mol% or more, can be 90 mol% or more, or can be 99 mol% or more.

[0113] In the total amount of isocyanate groups and blocked isocyanate groups in the electrode binder polymer, the proportion of blocked isocyanate groups is preferably 50 mol% or more, and can be 70 mol% or more, 90 mol% or more, or 100 mol%. If the isocyanate groups are blocked, it is easy to suppress the transformation of isocyanate groups into amino groups through hydrolysis.

[0114] It should be noted that the above example illustrates the case where the first functional group and the second functional group are contained in different structural units, but it is also possible to contain both the first functional group and the second functional group in one structural unit.

[0115] [Structural Unit 3]

[0116] The third structural unit is a structural unit derived from an aromatic hydrocarbon monomer. If the electrode binder polymer has a third structural unit, there is a trend towards improved high-temperature storage characteristics in batteries using electrodes containing the electrode binder polymer. The electrode binder polymer may contain one or more third structural units. The electrode binder polymer may also not have a third structural unit.

[0117] The aromatic hydrocarbon monomer preferably has an olefinic unsaturated bond, contains a hydrocarbon, and does not contain atoms such as oxygen atoms. The third structural unit may have one aromatic ring or two or more aromatic rings within one structural unit. In the third structural unit, the number of aromatic rings contained in one structural unit is preferably 1 to 4, more preferably 1. As an aromatic ring, a benzene ring that may have substituents can be cited as an example.

[0118] Examples of aromatic hydrocarbon monomers include styrene, tert-butylstyrene, α-methylstyrene, p-methylstyrene, and 1,1-diphenylethylene.

[0119] [Structural Unit 4]

[0120] The fourth structural unit is a structural unit derived from a nonionic monomer. If the electrode binder polymer has a fourth structural unit, there is a tendency for the electrode containing the electrode binder polymer to exhibit increased flexibility and electrode peel strength. The electrode binder polymer may contain only one type of fourth structural unit or may contain two or more types. The electrode binder polymer may also not have a fourth structural unit.

[0121] The nonionic monomer is preferably a nonionic (meth)acrylate having an olefinic unsaturated bond and lacking either anionic or cationic functional groups. The nonionic monomer preferably comprises a (meth)acrylate, and more preferably a (meth)acrylate alkyl ester.

[0122] The fourth structural unit can have polar functional groups. Examples of polar functional groups include hydroxyl and cyano groups, but are not limited to these. It should be noted that the concept of a polar functional group, hydroxyl, does not include the OH structure contained in ionic functional groups such as carboxyl or sulfonyl (sulfonic acid) groups.

[0123] Examples of nonionic monomers with polar functional groups include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and (meth)acrylonitrile.

[0124] [Structural Unit 5]

[0125] The fifth structural unit is derived from a multifunctional monomer. If the electrode binder polymer possesses a fifth structural unit, it tends to exhibit improved electrolyte resistance. The fifth structural unit in the electrode binder polymer can consist of one or more different types. The electrode binder polymer may or may not possess a fifth structural unit.

[0126] The multifunctional monomer is preferably a compound having multiple independent olefinic unsaturated bonds. Here, multiple independent olefinic unsaturated bonds refer to multiple olefinic unsaturated bonds that do not form conjugated dienes with each other.

[0127] The fifth structural unit may retain more than one olefinic unsaturated bond within the structural unit. For example, in the case of a polymer of divinylbenzene, the structural unit derived from divinylbenzene may be a structure without olefinic unsaturated bonds (a form in which both portions corresponding to the two olefinic unsaturated bonds of divinylbenzene are incorporated into the polymer chain) or a structure with one olefinic unsaturated bond (a form in which only the portion corresponding to one olefinic unsaturated bond is incorporated into the polymer chain).

[0128] [Other structural units]

[0129] The electrode binder polymer may have other structural units that do not belong to any of the structural units 1 to 5.

[0130] Examples of compounds that can serve as sources of other structural units include: compounds having one olefinic unsaturated bond and anionic functional groups other than carboxyl groups such as sulfonyl or phosphate groups, or their salts; surfactants having one olefinic unsaturated bond (hereinafter sometimes referred to as "polymeric surfactants"); and compounds having one olefinic unsaturated bond and functioning as silane coupling agents (hereinafter sometimes referred to as "polymeric silane coupling agents"), but are not limited to these.

[0131] [Content of each structural unit in the electrode binder polymer]

[0132] The glass transition temperature (Tg) and other physical properties of the electrode binder polymer can also be adjusted by adjusting the content of the first to fifth structural units in the electrode binder polymer.

[0133] For example, the total content of the first, second, third, and fourth structural units (hereinafter, "first, second, third, and fourth structural units" are also referred to as "first to fourth structural units") in the electrode binder polymer is preferably 90% by mass or more, more preferably 95% by mass or more, even more preferably 97% by mass or more, and may be 98% by mass or more, or may be 100% by mass. The total content of the first to fourth structural units in the electrode binder polymer may be 99.5% by mass or less.

[0134] There are no particular limitations on the manufacturing method of the electrode binder polymer. For example, it can be synthesized by copolymerization (polymerization step) using a compound having a first functional group and an olefinic unsaturated bond (hereinafter also referred to as "first monomer") and a compound having a second functional group and an olefinic unsaturated bond (hereinafter also referred to as "second monomer"). In addition, copolymerization can be performed using at least one monomer selected from monomers for forming a third structural unit, monomers for forming a fourth structural unit, monomers for forming a fifth structural unit, and monomers for forming other structural units.

[0135] Emulsion polymerization is a method for copolymerizing monomers. A common emulsion polymerization method is the emulsion polymerization of monomers in an aqueous medium. Examples of aqueous media include the following.

[0136] [Aqueous medium]

[0137] The aqueous medium in the electrode binder composition disclosed herein preferably comprises at least one selected from water and a hydrophilic solvent, more preferably composed of at least one selected from water and a hydrophilic solvent. Examples of hydrophilic solvents include methanol, ethanol, isopropanol, and N-methylpyrrolidone. One hydrophilic solvent may be used alone, or two or more may be used in combination. The aqueous medium preferably comprises water, more preferably 50% by mass or more, further preferably 70% by mass or more, and particularly preferably 90% by mass or more.

[0138] The electrode binder composition disclosed herein can be a dispersion obtained by emulsion polymerization of an olefinic unsaturated compound. Alternatively, the electrode binder composition disclosed herein can also be a dispersion obtained by dispersing an electrode binder polymer obtained by methods other than emulsion polymerization in an aqueous medium.

[0139] [Other ingredients]

[0140] Other components that may be included in the electrode binder composition disclosed herein include surfactants, alkaline substances, and other components used in the synthesis of the electrode binder polymer.

[0141] Surfactants in electrode binder compositions improve the dispersion stability of components dispersed in aqueous media. Anionic or nonionic surfactants are preferred as surfactants. A single surfactant or two or more surfactants may be used in combination.

[0142] Examples of anionic surfactants include alkylbenzene sulfonates, alkyl sulfates, polyoxyethylene alkyl ether sulfates, and fatty acid salts.

[0143] Examples of nonionic surfactants include: polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene polycyclic phenyl ethers, polyoxyethylene alkyl ethers, sorbitol fatty acid esters, and polyoxyethylene sorbitol fatty acid esters.

[0144] Alkaline substances can improve the storage stability of electrode binder compositions by maintaining the pH of the composition within an appropriate range. Examples of alkaline substances include ammonia, triethylamine, sodium hydroxide, and lithium hydroxide. Alkaline substances can be used alone or in combination of two or more.

[0145] Other components used in the synthesis of electrode binder polymers include those derived from initiators and those derived from chain transfer agents.

[0146] <Electrode Paste>

[0147] The electrode slurry disclosed herein comprises the electrode binder composition and electrode active material described herein, or comprises a non-volatile component of the electrode binder composition disclosed herein, an electrode active material, and a liquid medium, wherein the non-volatile component comprises the electrode binder polymer described herein.

[0148] Therefore, in one embodiment of the electrode slurry of this disclosure, the components contained in the electrode binder composition (electrode binder polymer and aqueous medium, and surfactants, alkaline substances, other components used in the synthesis of the electrode binder polymer, etc., as needed) may further include an electrode active material. Alternatively, in another embodiment of the electrode slurry of this disclosure, an electrode active material and a liquid medium may be added to the substance (containing the electrode binder polymer) after the volatile components have been removed from the electrode binder composition.

[0149] In addition to the electrode binder polymer, the non-volatile components of the electrode binder composition may also include, for example, surfactants and other components used in the synthesis of the electrode binder polymer.

[0150] The components contained in the electrode binder composition and the non-volatile components can undergo chemical changes during the electrode slurry manufacturing process. That is, the components contained in the electrode binder composition and the non-volatile components here also include components derived from the electrode binder composition and the non-volatile components.

[0151] The content of the electrode binder polymer in the electrode slurry is preferably 0.50 parts by mass or more, more preferably 1.0 parts by mass or more, relative to 100 parts by mass of the electrode active material. If the content of the electrode binder polymer is within the above range, there is a tendency to more fully exhibit the effects obtained by including the electrode binder polymer.

[0152] The content of the electrode binder composition in the 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, relative to 100 parts by mass of the electrode active material. If the amount of electrode binder polymer is within the above range relative to the amount of electrode active material, the content of electrode active material contained in the electrode slurry can be increased, and there is a tendency for excellent charge-discharge characteristics.

[0153] Relative to 100 parts by weight of electrode slurry, the content of electrode active material in the electrode slurry is preferably 80 parts by weight or more, more preferably 90 parts by weight or more. If the content of electrode active material is within the above range, there is a tendency for excellent charge-discharge characteristics.

[0154] The electrode active material is a material in which ions such as lithium ions, which act as charge carriers, can be intercarried and deintercalated. The ions that act as charge carriers are preferably alkali metal ions, more preferably lithium ions, sodium ions, or potassium ions, and even more preferably lithium ions.

[0155] When the electrode manufactured using electrode paste is a negative electrode, the electrode active material is the negative electrode active material. Preferably, the negative electrode active material comprises at least one material selected from carbon materials, silicon-containing materials, and titanium-containing materials. These materials used as negative electrode active materials can be used individually, in combination of two or more, or in a composite manner.

[0156] Examples of carbon materials used as negative electrode active materials include: petroleum coke, pitch coke, coal coke, and other cokes; organic polymer carbides; 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.

[0157] The negative electrode active material preferably comprises at least one material selected from carbon materials and silicon-containing materials. If the negative electrode active material is one of the above materials, there is a tendency for the effect of the electrode binder polymer contained in the electrode paste on improving the adhesion between negative electrode active materials and between the negative electrode active material and the current collector to increase.

[0158] When the electrode manufactured using electrode paste is the positive electrode, the electrode active material is the positive electrode active material. As the positive electrode active material, a substance with a higher standard electrode potential than the negative electrode active material is used. Specifically, examples of positive electrode active materials include: Ni-Co-Mn lithium composite oxides, Ni-Mn-Al lithium composite oxides, Ni-Co-Al lithium composite oxides, lithium cobalt oxide (LiCoO2), spinel-type lithium manganese oxide (LiMn2O4), olivine-type lithium iron phosphate, and chalcogenides such as TiS2, MnO2, MoO3, and V2O5. These substances used as positive electrode active materials can be used individually or in combination of two or more.

[0159] The liquid medium is preferably selected from at least one of water and a hydrophilic solvent. Examples of hydrophilic solvents include methanol, ethanol, isopropanol, and N-methylpyrrolidone. The liquid medium is preferably an aqueous medium described in the electrode binder composition. The liquid medium may be the same as or different from the aqueous medium used in the synthesis of the electrode binder polymer. The liquid medium may be the same as or different from the aqueous medium used in the electrode binder composition. The liquid medium preferably contains water, more preferably 50% by mass or more, further preferably 70% by mass or more, and particularly preferably 90% by mass or more.

[0160] Electrode pastes may also contain conductive additives, thickeners, etc.

[0161] Examples of thickeners include: carboxymethyl cellulose (CMC), hydroxyethyl cellulose, hydroxypropyl cellulose and other cellulose derivatives, ammonium salts of cellulose derivatives, alkali metal salts of cellulose derivatives, polyvinyl alcohol, polyvinylpyrrolidone, poly(meth)acrylate, poly(meth)acrylamide, poly(meth)N-hydroxyalkylacrylamide, etc. From the viewpoint of dispersibility of electrode active substances in electrode slurry, the thickener preferably contains at least one selected from carboxymethyl cellulose, ammonium salts of carboxymethyl cellulose, and alkali metal salts of carboxymethyl cellulose.

[0162] When the electrode slurry contains a thickener, the content of the thickener in the electrode slurry is preferably 0.50 parts by mass or more, more preferably 0.80 parts by mass or more, relative to 100 parts by mass of the electrode active material. If the mixing amount of the thickener is within the above range, there is a tendency for the coating properties of the electrode slurry to become better.

[0163] Furthermore, when the electrode slurry contains a thickener, the content of the thickener in the 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, relative to 100 parts by mass of the electrode active material. If the mixing amount of the thickener is within the above range, there is a tendency for the adhesion between the electrode active materials contained in the electrode active material layer, as well as between the electrode active material and the current collector, to become better.

[0164] Examples of conductive additives include carbon black and carbon fibers. Examples of carbon black include furnace black, acetylene black, DENKABLACK (manufactured by DENKA Corporation), and Ketjen Black (manufactured by Ketjen Black International Corporation). Examples of carbon fibers include carbon nanotubes and carbon nanofibers. An example of carbon nanotubes is VGCF (manufactured by Resonac Corporation), a gas-phase carbon fiber.

[0165] The electrode slurry disclosed herein is preferably used for manufacturing electrodes for non-aqueous secondary batteries, more preferably for manufacturing electrodes for lithium-ion secondary batteries, and even more preferably for manufacturing negative electrodes for lithium-ion secondary batteries.

[0166] <Method for Manufacturing Electrode Paste>

[0167] As an example of a method for manufacturing the electrode paste of this disclosure, a method of mixing the electrode binder composition of this disclosure with an electrode active material can be cited. The electrode binder composition may contain thickeners, conductive additives, other components, etc.

[0168] Furthermore, as another example of the method for manufacturing the electrode paste of this disclosure, a method for preparing the non-volatile component of the electrode binder composition of this disclosure, and mixing the aforementioned non-volatile component, the electrode active material, and the liquid medium can be cited. The non-volatile component of the electrode binder composition includes an electrode binder polymer, and may also contain thickeners, conductive additives, other components, etc.

[0169] Alternatively, thickeners, conductive additives, and other components can be added to the above-mentioned non-volatile components and mixed to prepare electrode slurry.

[0170] [Mixed Process]

[0171] The electrode binder composition, electrode active material, thickener, and conductive additive used in the mixing process are as described above.

[0172] There is no particular limitation on the mixing order of the components; it can be determined appropriately. Methods for mixing the components include using stirring, rotary, or oscillating mixing devices. More specifically, methods using rotating-revolutionary mixers, screw mixers, or ultrasonic mixers can be cited.

[0173] When a liquid medium is added during the mixing process, the liquid medium is preferably selected from at least one of water and a hydrophilic solvent. Examples of hydrophilic solvents include methanol, ethanol, isopropanol, and N-methylpyrrolidone. The liquid medium may have the same composition as the aqueous medium used in the synthesis of the electrode binder polymer, or it may have a different composition. The liquid medium preferably contains water, more preferably contains 50% by mass or more of water, even more preferably contains 70% by mass or more of water, and particularly preferably contains 90% by mass or more of water.

[0174] <Electrode>

[0175] The electrode disclosed herein comprises a current collector and an electrode active material layer formed on the current collector. The electrode active material layer comprises a non-volatile component of the electrode binder composition disclosed herein and the electrode active material. The non-volatile component of the electrode binder composition comprises the electrode binder polymer.

[0176] Examples of electrode shapes include laminated bodies and wound bodies, and there are no particular limitations. The electrode disclosed herein is preferably an electrode of a non-aqueous secondary battery, more preferably an electrode of a lithium-ion secondary battery, and even more preferably a negative electrode of a lithium-ion secondary battery.

[0177] There is no particular limitation on the formation range of the electrode active material layer on the current collector. The electrode active material layer can be formed on the entire surface of the current collector, or it can be formed only on a part of the surface of the current collector. When the current collector is in the shape of a plate or foil, the electrode active material layer can be formed on both sides of the current collector, or it can be formed on only one side.

[0178] The current collector is preferably a metal sheet. Examples of metals that can be used to form the metal sheet include iron, copper, aluminum, nickel, and stainless steel. When the electrode disclosed herein is the negative electrode of a lithium-ion secondary battery, the current collector is preferably copper foil. The thickness of the metal sheet is not particularly limited, but is preferably 0.001 mm to 0.5 mm.

[0179] In the electrode active material layer, the non-volatile components of the electrode binder composition, the electrode active material, and the electrode binder polymer can be referred to respectively as the non-volatile components, electrode active material, and electrode binder polymer of the electrode binder composition described in the electrode binder composition.

[0180] Relative to 100 parts by mass of the electrode active material, the content of the electrode binder polymer in the electrode active material layer is preferably 0.50 parts by mass or more, more preferably 1.0 parts by mass or more. If the content of the electrode binder polymer is within the above range, there is a tendency to more fully exhibit the effects brought about by including the electrode binder polymer.

[0181] When the electrode contains a thickener, the content of the thickener in the electrode is preferably 0.50 parts by mass or more, more preferably 0.80 parts by mass or more, relative to 100 parts by mass of the electrode active material.

[0182] When the electrode contains a thickener, the content of the thickener in the electrode 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, relative to 100 parts by mass of the electrode active material. There is a tendency for the adhesion between the electrode active materials contained in the electrode active material layer, and between the electrode active material and the current collector, to become better.

[0183] <Methods for manufacturing electrodes>

[0184] The electrode manufacturing method disclosed herein includes: a coating step of coating the electrode paste of the present disclosure onto a current collector; and a drying step of drying the electrode paste coated onto the current collector.

[0185] The electrode manufacturing method disclosed herein may include other steps. It should be noted that, in the following description, detailed explanations of the components already described above used in each step are omitted.

[0186] The electrode manufactured by the manufacturing method of this disclosure is preferably an electrode of a non-aqueous secondary battery, more preferably an electrode of a lithium-ion secondary battery, and even more preferably a negative electrode of a lithium-ion secondary battery.

[0187] The electrode paste used can be prepared by the above method or it can be a commercially available product.

[0188] [Coating process]

[0189] In the coating process, the electrode paste of this disclosure is coated onto at least a portion of the surface of the current collector. There are no particular limitations on the method for coating the electrode paste onto the current collector, and examples include reverse roller coating, direct roller coating, doctor blade coating, knife coating, extrusion coating, curtain coating, gravure coating, rod coating, dip coating, and extrusion coating. Among these coating methods, considering the viscosity and drying properties of the electrode paste, it is preferable to use at least one method selected from direct roller coating, doctor blade coating, knife coating, and extrusion coating. When these methods are applied, there is a tendency to obtain an electrode active material layer with a smooth surface and small thickness deviation.

[0190] There is no particular limitation on the area where the electrode paste is applied to the current collector; it can be the entire surface of the current collector or only a portion of it. When the current collector is in the shape of a plate or foil, the electrode paste can be applied to both sides of the current collector or only to one side.

[0191] When coating the electrode paste onto both sides of the current collector, it can be applied sequentially side by side or simultaneously on both sides. Furthermore, the electrode paste can be applied continuously or intermittently on the current collector. The amount of electrode paste applied can be appropriately determined based on the battery's design capacity and the composition of the electrode paste.

[0192] [Drying process]

[0193] In the drying process, there are no particular limitations on the method of drying the electrode paste coated on the current collector. For example, hot air drying, reduced pressure drying, vacuum drying, (far)infrared drying, low temperature air drying, or a combination thereof can be used.

[0194] The drying temperature and drying time for drying the electrode paste can be adjusted appropriately according to the concentration of non-volatile components in the electrode paste and the amount of coating applied to the current collector. The drying temperature is not particularly limited, but is preferably 40°C to 350°C, and more preferably 60°C to 100°C from a productivity perspective. The drying time is not particularly limited, but is preferably 1 minute to 30 minutes.

[0195] Through a drying process, an electrode sheet with an electrode active material layer formed on the current collector can be obtained. The obtained electrode sheet can be used directly as an electrode, or it can be used as an electrode through other processes described below.

[0196] [Other processes]

[0197] Other processes include, for example, cutting and pressing.

[0198] The cutting process, for example, is performed after the drying process, and involves cutting the electrode sheet to form an appropriate size and shape for use as an electrode. There are no particular limitations on the method of cutting the electrode sheet; slit cutting, laser cutting, wire cutting, a cutter, a Thomson scalpel, etc., can be used.

[0199] The pressing process, for example, is performed after the drying process to press the electrode sheet. Through the pressing process, the active material of the electrode can be more firmly bonded to the current collector, and the battery can be miniaturized by reducing the thickness of the electrode. In the electrode manufacturing method, when both a cutting and pressing process are performed, the pressing process can be performed before or after the cutting process.

[0200] As a pressing method, conventional methods can be used. Die pressing or roller pressing is particularly preferred. When using die pressing, the pressing pressure is not particularly limited, but is preferably set to 0.5 t / cm. 2 ~5t / cm 2 .

[0201] When using the rolling method, the pressing load is not particularly limited, but it is preferably set to 0.5 t / cm to 10 t / cm. If the pressing load is set within the above range, the above-mentioned effects brought about by pressing can be easily obtained, which can suppress the insertion and extraction of charge carriers such as lithium ions into the electrode active material and the tendency for capacity reduction.

[0202] Secondary batteries

[0203] The secondary battery disclosed herein includes the electrodes of this disclosure. The secondary battery of this disclosure is preferably a non-aqueous secondary battery, and more preferably a lithium-ion secondary battery. Hereinafter, a preferred example of the secondary battery of this disclosure will be described, specifically a lithium-ion secondary battery. It should be noted that the configuration of the secondary battery of this disclosure is not limited to the example shown below.

[0204] As an example of a lithium-ion secondary battery, it has a configuration that houses the positive electrode, negative electrode, and electrolyte within an external casing. In addition to the above configuration, a lithium-ion secondary battery may also include a separator between the positive and negative electrodes, or other components. The shape of a lithium-ion secondary battery can be any shape, such as coin-shaped, button-shaped, sheet-shaped, cylindrical, square, or flat.

[0205] One example of the lithium-ion secondary battery disclosed herein is a lithium-ion secondary battery in which one or both of the positive and negative electrodes have the electrode configuration of the present disclosure, preferably the negative electrode has the electrode configuration of the present disclosure.

[0206] In one example of a lithium-ion secondary battery disclosed herein, where only one of the positive electrode active material layer and the negative electrode active material layer has the electrode composition of the present disclosure, it is preferable that the other electrode contains polyvinylidene fluoride or the like as a binder in the electrode active material layer.

[0207] As the electrolyte, a non-aqueous liquid with ion conductivity is preferred. Examples of electrolytes include solutions made by dissolving the electrolyte in an organic solvent and ionic liquids. From the viewpoint of obtaining a lithium-ion secondary battery with low manufacturing cost and low internal resistance, the former is preferred.

[0208] Alkali metal salts can be used as electrolytes, and the appropriate type can be selected based on the type of electrode active material. Examples of suitable electrolytes include LiClO4, LiBF6, LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, and LiB2. 10 Cl 10 Examples of alkali metal salts include LiAlCl4, LiCl, LiBr, LiB(C2H5)4, CF3SO3Li, CH3SO3Li, LiCF3SO3, LiC4F9SO3, Li(CF3SO2)2N, and aliphatic lithium carboxylates. Other alkali metal salts can also be used as electrolytes.

[0209] Organic solvents for dissolving electrolytes are not particularly limited, but can include: carbonate 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); and carboxylic acid esters such as ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and propyl propionate. One organic solvent can be used alone, or two or more can be used in combination. Preferably, two or more straight-chain carbonate solvents are used in combination.

[0210] In addition to the components mentioned above, the electrolyte may also contain additives. Examples of additives include nitrile compounds, sulfur-containing compounds, and boron-containing compounds. Examples of nitrile compounds include succinic anhydride and acetonitrile. Examples of sulfur-containing compounds include methyl ethyl sulfone and 1,3-propane sulfonyl lactone, which have sulfonyl, sulfonate, or sulfonyl lactone structures. Examples of boron-containing compounds include borate esters.

[0211] As an outer casing, an outer casing formed of an aluminum laminate containing aluminum foil and a resin film may be used, but it is not limited to this.

[0212] [Example]

[0213] The following is a detailed description of one embodiment of the present disclosure through examples, but the embodiments are not limited to these examples.

[0214] In the following embodiments, the negative electrode of a lithium-ion secondary battery is used as an example of an electrode of this disclosure, and the lithium-ion secondary battery is used as an example of a battery, for comparison with the negative electrode of a lithium-ion secondary battery and the lithium-ion secondary battery of the comparative examples. Furthermore, unless otherwise specified, the water used in the following embodiments and comparative examples is ion-exchanged water.

[0215] <Preparation of Electrode Binder Polymers and Electrode Binder Compositions>

[0216] In each embodiment and comparative example, the monomers were mixed in the amounts (parts by mass) shown in Table 1 to prepare an emulsion.

[0217] Next, aqueous solutions were prepared by dissolving the polymerization initiator in 50 parts by mass of water in the amounts (parts by mass) shown in Table 1.

[0218] 150 parts by mass of water were added to a separable flask equipped with a condenser, thermometer, stirrer, and dropping funnel, and the temperature was raised to 80°C. Emulsion polymerization was carried out by continuously feeding the above-mentioned monomer emulsion and an aqueous solution containing the above-mentioned polymerization initiator into the separable flask at 80°C for 3 hours while stirring, respectively, to obtain an emulsion containing particles of the electrode binder polymers of Examples 1 to 6 or Comparative Examples 1 to 3 and an aqueous medium.

[0219] The resulting emulsion was cooled to room temperature (25°C). Then, 133 parts by weight of water and 25% by weight of ammonia were added. Thus, electrode binder compositions of Examples 1 to 6 and Comparative Examples 1 to 3 were prepared, which were emulsions containing particles of the electrode binder polymers of Examples 1 to 6 or Comparative Examples 1 to 3 dispersed in an aqueous medium.

[0220] The abbreviations of the monomers in Table 1 are shown below.

[0221] St: Styrene

[0222] 2-EHA: 2-Ethylhexyl acrylate

[0223] BzMA: Benzyl methacrylate

[0224] 2-HEMA: 2-Hydroxyethyl methacrylate

[0225] AA: Acrylic acid

[0226] IA: itaconic acid

[0227] DVB: Divinylbenzene

[0228] p-StSANa: Sodium p-styrenesulfonate

[0229] KH-10: Polyoxyethylene-1-(allyloxymethyl)alkyl ether sulfate ammonium salt (manufactured by Daiichi Kogyo Pharmaceutical Co., Ltd., Aqualon KH-10, polymeric surfactant).

[0230] As monomer 2, a compound having a methacryloxy group and a blocked isocyanate group is used. Specifically, as described below.

[0231] MOI-SM: Methyl 2-[[[[2-[(2-methyl-1-oxo-2-propen-1-yl)oxy]ethyl]amino]carbonyl]oxy]-benzoate (KARENZ MOI-SM (manufactured by Resonac Co., Ltd.))

[0232] MOI-BP: 2-[(3,5-dimethylpyrazolyl)carbonylamino]ethyl methacrylate (KARENZ MOI-BP (manufactured by Resonac Co., Ltd.))

[0233] MOI-BM: 2-[O-(1'-methylpropyleneamino)carboxyamino]ethyl methacrylate (KARENZMOI-BM (manufactured by Resonac Co., Ltd.))

[0234] The polystyrene SFS in the polymerization initiator is the trade name of polystyrene manufactured by Sumitomo Seikan Co., Ltd. The amount of ammonia shown in Table 1, as an alkaline substance, is the amount of ammonia (parts by mass) contained in the ammonia solution. The amount of water shown in Table 1, as an aqueous medium, is the total amount of water (parts by mass) contained in the electrode binder composition.

[0235] The contents of the first functional group F1 and the second functional group F2 in the electrode binder polymer were determined by the above method.

[0236] [Determination of glass transition temperature Tg]

[0237] A film with a thickness of 2 mm containing an adhesive polymer was obtained by coating the electrode adhesive compositions of Examples 1 to 6 or Comparative Examples 1 to 3 onto a release PET (polyethylene terephthalate) film and drying it at 50°C for 5 hours.

[0238] Square test pieces, 2 mm in length and 2 mm in width, were cut from the obtained film. The test pieces were sealed in an aluminum dish, and differential scanning calorimetry (DSC) was performed on the test pieces using a differential scanning calorimeter (EXSTAR DSC / SS7020, manufactured by Hitachi High-Tech Science Co., Ltd.) under a nitrogen atmosphere at a heating rate of 10 °C / min. The temperature range for DSC measurement was set to -40 °C to 200 °C. Then, the peak temperature of the DSC curve obtained as the temperature derivative of the DSC was measured, and this temperature was taken as the glass transition temperature Tg (°C) of the electrode binder polymer.

[0239] [Determination of the concentration of non-volatile components in the electrode binder composition]

[0240] The concentration (mass %) of the non-volatile components of the electrode binder compositions of Examples 1 to 6 or Comparative Examples 1 to 3 was determined using the above method.

[0241] The percentage of electrode binder polymer in the non-volatile components of the electrode binder composition is calculated by assuming that all monomers, surfactants, and polymerization initiators used in the manufacture of the electrode binder polymer have reacted as part of the electrode binder polymer.

[0242] <Evaluation of Electrode Binders>

[0243] [Determination of the tensile strength of the membrane]

[0244] The electrode adhesive compositions prepared in each embodiment and comparative example were coated onto a glass plate covered with a polypropylene sheet and subjected to atmospheric pressure, at 23°C and an absolute humidity of 10 g / m³. 3 Dry at 50% RH for 5 days, then dry under reduced pressure at 60°C or below 0.01 MPa for 12 hours to form a film with a thickness of 0.4 mm. Peel the formed film off the polypropylene sheet to prepare the film as described in (I) or (II) below.

[0245] (I) The coating directly supplied for testing after being peeled from the polypropylene sheet.

[0246] (II) Under atmospheric pressure, at 110℃ and absolute humidity of 10g / m³ 3 The membrane after being placed for 1 hour

[0247] The films obtained in (I) and (II) were cut into test pieces with a length of 60 mm and a width of 10 mm. It should be noted that the atmospheric pressure was set to 1013 hPa.

[0248] For each test piece, a tensile test was performed using an Autograph AG-20kNX precision universal testing machine from Shimadzu Corporation to determine the film breaking strength [MPa]. The tensile direction was along the length of the test piece. The chuck positions were set at two points: 5mm from the center of the length direction (30mm from the two parallel sides in the width direction) and 5mm from both sides. That is, the distance between the chucks was 10mm. The tensile speed, i.e., the test speed, was set to 100mm / min. It should be noted that the tensile test was conducted under atmospheric pressure, at 23°C, and with an absolute humidity of 10g / m³. 3 The experiment was conducted at a relative humidity of 50%RH.

[0249] The maximum load detected in the above tests was divided by the cross-sectional area of ​​the test piece, 10 mm × 0.4 mm, to obtain the film breaking strength S(St) [MPa] of the electrode adhesive after being placed at 23°C and the film breaking strength S(110) [MPa] after being placed at 110°C, as shown in Table 1. In addition, the value of the ratio of S(110) to S(St), i.e., S(110) / S(St), is also shown in Table 1.

[0250] [Table 1]

[0251]

[0252] <Manufacturing of Lithium-ion Secondary Batteries>

[0253] The negative electrodes were fabricated using the electrode binder compositions of Examples 1 to 6 and Comparative Examples 1 to 3, respectively, by the method shown below, and the lithium-ion secondary batteries of Examples 1 to 6 and Comparative Examples 1 to 3 were fabricated using the negative electrodes.

[0254] (The production of the positive electrode)

[0255] 94 parts by mass of LiNi were used as the positive electrode active material. 0.6 Mn 0.2 Co 0.2 O2, 3 parts by mass of acetylene black as a conductive additive, and 3 parts by mass of polyvinylidene fluoride as a binder were mixed to obtain a mixture. 50 parts by mass of N-methylpyrrolidone were added to the obtained mixture and further mixed to obtain a positive electrode slurry.

[0256] Prepare an aluminum foil with a thickness of 15 μm as the positive current collector. Coat both sides of the positive current collector with positive electrode paste using a direct rolling method. Adjust the coating amount of positive electrode paste on the positive current collector so that the thickness after the rolling process described later is 125 μm per side.

[0257] The positive electrode slurry coated on the positive current collector was dried at 120°C for 5 minutes. It was then pressed using a roller press (manufactured by THANK METAL, Inc., with a pressing load of 5 t / cm and a roller width of 7 cm) to obtain a positive electrode sheet with positive active material layers on both sides of the positive current collector. The obtained positive electrode sheet was cut into rectangles 50 mm long and 40 mm wide, and conductive tabs were attached to form the positive electrode.

[0258] (Making the negative electrode)

[0259] 96.9 parts by weight of artificial graphite (G49, manufactured by Jiangxi Zichen Technology Co., Ltd.) as the negative electrode active material, 3.6 parts by weight of any electrode binder composition (1.4 parts by weight of non-volatile component (binder polymer)) prepared in Examples 1 to 6 and Comparative Examples 1 to 3, and 60 parts by weight of a 2% aqueous solution of CMC (carboxymethyl cellulose sodium salt, manufactured by NIPPON PAPER Chemicals Co., Ltd., SUNROSE MAC500LC) were mixed, and 16 parts by weight of water were further added. The mixture was then mixed using a rotary mixer (ARE-310, manufactured by THINKY Co., Ltd.) to obtain a negative electrode slurry (electrode slurry).

[0260] Prepare a 10μm thick copper foil as the negative electrode current collector. Coat both sides of the negative electrode current collector with negative electrode paste using a direct roll coating method. Adjust the coating amount of negative electrode paste on the negative electrode current collector so that the thickness after the roll forming process described later is 170μm per side.

[0261] The negative electrode slurry coated on the negative electrode current collector was dried at 90°C for 10 minutes. Then, it was pressed using a roller press (manufactured by THANK METAL, Ltd., with a pressing load of 8 t / cm and a roller width of 7 cm) to obtain a negative electrode sheet with negative electrode active material layers on both sides of the negative electrode current collector. The obtained negative electrode sheet was cut into rectangles 52 mm long and 42 mm wide, and conductive electrode tabs were installed to form the negative electrode.

[0262] (The manufacture of lithium-ion secondary batteries)

[0263] A separator (made of polyethylene, 25 μm thick) containing a polyolefin-based porous membrane is sandwiched between the positive and negative electrodes. The positive and negative active material layers are stacked with their surfaces facing each other and housed in an outer casing (battery pack) containing an aluminum laminate. Then, electrolyte is injected into the outer casing, vacuum impregnated, and packaged using a vacuum heat sealer, thus obtaining a lithium-ion secondary battery.

[0264] The electrolyte used is a mixture of 99 parts by mass of a solution containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a mixed solvent with a volume ratio of EC:EMC:DEC = 30:50:20, at a concentration of 1.0 mol / L, and 1 part by mass of ethylene carbonate.

[0265] <Evaluation of Non-Aqueous Secondary Batteries>

[0266] For the lithium-ion secondary batteries of Examples 1 to 6 and Comparative Examples 1 to 3, the discharge capacity retention after 500 cycles, the discharge capacity retention after storage at 60°C for 4 weeks, and the rate of increase in internal resistance (DCR) after storage at 60°C for 4 weeks were evaluated using the methods shown below. The results are shown in Table 2.

[0267] [Discharge capacity retention after 500 cycles]

[0268] Under conditions of 45°C, a series of operations (i) to (iv) shown below are performed as one cycle for charging and discharging. The time integral value of the current in operations (i) and (ii) is taken as the charging capacity, and the time integral value of the current in operation (iv) is taken as the discharging capacity. Then, the discharging capacity of the first cycle and the discharging capacity of the 500th cycle are measured, and the discharge capacity retention rate after 500 cycles is calculated by the following formula.

[0269] Discharge capacity retention rate (%) after 500 cycles

[0270] = 100 × (Discharge capacity of the 500th cycle / Discharge capacity of the 1st cycle)

[0271] (i) Charge at a current of 1C until the voltage becomes 4.2V (constant current (CC) charging).

[0272] (ii) Charge at a voltage of 4.2V until the current becomes 0.05C (constant voltage (CV) charging).

[0273] (iii) Let stand for 30 minutes.

[0274] (iv) Discharge at a current of 1C until the voltage becomes 2.75V (constant current (CC) discharge).

[0275] [Discharge capacity retention after storage at 60°C for 4 weeks]

[0276] The battery was charged at 25°C with a current of 1C (CC) until the voltage reached 4.2V, then charged with a current of CV (CV) until the current reached 0.05C. Next, it was discharged at 1C with a current of CC until the voltage reached 2.75V, and the resulting discharge capacity was taken as the discharge capacity before storage. Then, it was charged again with a current of 1C with a current of CC until the voltage reached 4.2V, then charged with a current of CV until the current reached 0.05C, resulting in a fully charged battery. The fully charged battery was then left to stand at 60°C for 4 weeks. Then, it was discharged again at 25°C with a current of 1C with a current of CC until the voltage reached 2.75V, and the resulting discharge capacity was taken as the discharge capacity after storage. The discharge capacity retention rate after 4 weeks of storage at 60°C was calculated using the following formula from the discharge capacity before and after storage.

[0277] Discharge capacity retention rate (%) after storage at 60℃ for 4 weeks

[0278] = 100 × (Discharge capacity after storage / Discharge capacity before storage)

[0279] [Rate of increase in internal resistance (DCR) after storage at 60°C for 4 weeks]

[0280] The internal resistance (DCR (Ω)) of a lithium-ion secondary battery was measured at 25°C according to the following procedure: Constant current charging and discharging was performed at 0.2C until the voltage changed from resting potential to 3.6V, setting the state of charge to 50% of the initial capacity (SOC50%). Then, discharge was performed for 60 seconds at current values ​​of 0.2C, 0.5C, 1C, and 2C. It should be noted that a charge was performed after each discharge to restore the battery to SOC50%. The internal resistance (DCR (Ω) at SOC50) was determined based on the relationship between these four current values ​​(values ​​within 1 second) and voltage.

[0281] The internal resistance (DCR) obtained according to the above steps was measured in the following stages (1) and (2).

[0282] (1) Store for 4 weeks before fully charged and at 60°C.

[0283] (2) After being stored for 4 weeks under conditions of being fully charged and at 60°C

[0284] The internal resistance (DCR) measured in (1) is set as the DCR before storage, and the internal resistance (DCR) measured in (2) is set as the DCR after storage. The rate of increase of internal resistance (DCR) after storage at 60°C for 4 weeks is calculated using the following formula.

[0285] Rate of increase in internal resistance (DCR) (%) after storage at 60°C for 4 weeks

[0286] = 100 × (DCR after saving / DCR before saving)

[0287] [Table 2]

[0288]

[0289] <Evaluation Results>

[0290] The electrode binder compositions obtained in Examples 1 to 6 comprise an electrode binder polymer and an aqueous medium. The electrode binder polymer has a first functional group and a second functional group. The first functional group is at least one selected from carboxyl groups and carboxyl groups that have formed salts, and the second functional group is at least one selected from isocyanate groups and blocked isocyanate groups. Furthermore, the film obtained from the electrode binder compositions synthesized in Examples 1 to 6 exhibits a tensile strength S(St) of 4.00 MPa or higher. Moreover, lithium-ion secondary batteries manufactured using the electrode binder compositions obtained in Examples 1 to 6 all maintain adequate discharge capacity retention even after storage at 60°C for 4 weeks, with minimal increase in discharge capacity reduction (DCR).

[0291] On the other hand, regarding the secondary battery manufactured using the electrode binder composition of Comparative Example 1, which contains an electrode binder polymer that does not have a second functional group, a decrease in discharge capacity retention rate was observed after storage at 60°C for 4 weeks, and a large increase in DCR was also observed.

[0292] Regarding the secondary batteries manufactured using the electrode binder compositions of Comparative Examples 2 and 3, which have low tensile strength S(St) of the film obtained from the electrode binder composition, a decrease in discharge capacity retention rate after storage at 60°C for 4 weeks and a large increase in DCR after storage at 60°C for 4 weeks were observed.

[0293] Therefore, it can be said that when the electrode binder composition comprises an electrode binder polymer and an aqueous medium, and the tensile strength S(St) of the film obtained from the electrode binder composition is 4.00 MPa or higher, a secondary battery with excellent high-temperature storage properties can be obtained. The electrode binder polymer has a first functional group and a second functional group, wherein the first functional group is at least one selected from carboxyl groups and carboxyl groups that have formed salts, and the second functional group is at least one selected from isocyanate groups and blocked isocyanate groups.

[0294] It should be noted that the lithium-ion secondary batteries manufactured using the electrode binder compositions obtained in Examples 1 to 6 maintained sufficient discharge capacity retention even after 500 cycles.

[0295] The disclosures of Japanese Patent Applications Nos. 2023-214286, 2024-188626, and 2024-188627 are incorporated herein by reference in their entirety. All documents, patent applications, and technical standards described herein, and the specific details thereof, which are incorporated herein by reference, are also incorporated herein by reference to the extent that they are specifically described and individually.

Claims

1. An electrode binder composition comprising an electrode binder polymer and an aqueous medium, said electrode binder polymer having a first functional group and a second functional group, said first functional group being at least one selected from carboxyl groups and carboxyl groups that have formed salts, and said second functional group being at least one selected from isocyanate groups and blocked isocyanate groups. The electrode adhesive composition was subjected to atmospheric pressure, 23°C, and an absolute humidity of 10 g / m². 3 After drying for 5 days, the film was then dried at 60°C for 12 hours at a pressure below 0.01 MPa, resulting in a tensile strength S(St) of over 4.00 MPa.

2. The electrode binder composition according to claim 1, wherein, The coating was further subjected to atmospheric pressure, 110°C, and an absolute humidity of 10 g / m³. 3 The fracture strength S(110) after 1 hour of storage is above 6.00 MPa.

3. The electrode binder composition according to claim 1, wherein, The tensile strength S(St) is related to the film being subjected to atmospheric pressure, 110°C, and 10 g / m³ absolute humidity. 3 The ratio of the fracture strength S(110) to the fracture strength S(St) after 1 hour of storage is greater than 1.

00.

4. The electrode binder composition according to claim 1, wherein, The non-volatile component contains at least 80% by mass of the electrode binder polymer.

5. The electrode binder composition according to claim 1, wherein, The electrode binder polymer is dispersed in the aqueous medium.

6. An electrode paste comprising an electrode binder composition according to any one of claims 1 to 5 and an electrode active substance, or comprising a non-volatile component of the electrode binder composition according to any one of claims 1 to 5, an electrode active substance, and a liquid medium, wherein the non-volatile component comprises the electrode binder polymer.

7. An electrode comprising a current collector and an electrode active material layer formed on the current collector, the electrode active material layer comprising a non-volatile component of the electrode binder composition according to any one of claims 1 to 5 and the electrode active material, the non-volatile component comprising the electrode binder polymer.

8. A secondary battery comprising the electrode as described in claim 7.

9. A method for manufacturing an electrode, comprising: a coating step of coating the electrode paste of claim 6 onto a current collector; and a drying step of drying the electrode paste coated on the current collector.

10. A method for manufacturing an electrode paste, wherein, The electrode binder composition according to any one of claims 1 to 5 is mixed with the electrode active material.

11. A method for manufacturing an electrode paste, comprising: The process of preparing the non-volatile component of the electrode binder composition according to any one of claims 1 to 5; as well as The process of mixing the non-volatile components, electrode active materials, and liquid medium. The non-volatile component includes the electrode binder polymer.

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