Binder composition for secondary battery electrode, slurry composition for secondary battery electrode, electrode for secondary battery, and secondary battery

Abstract

The purpose of the present invention is to provide a binder composition for a secondary battery electrode, which is capable of forming an electrode for a secondary battery in which the formation of pits in the surface of the electrode is suppressed, and which is capable of reducing the internal resistance of the secondary battery and exhibiting excellent cycle characteristics. The binder composition for secondary battery electrodes according to the present invention contains a binder material, and has a coating amount of 1.3 g or less after the binder composition for secondary battery electrodes is left to stand at a temperature of 40 DEG C for 2 hours by injecting 10.0 g of a mixed solution obtained by adjusting the binder composition for secondary battery electrodes to a solid content concentration of 30 mass% with water into a polytetrafluoroethylene culture dish having a diameter of 10 cm.

Description

Technical Field

[0001] This invention relates to binder compositions for secondary battery electrodes, slurry compositions for secondary battery electrodes, electrodes for secondary batteries, and secondary batteries. Background Technology

[0002] Secondary batteries, such as those using non-aqueous electrolyte systems with organic solvent electrolytes (hereinafter sometimes simply referred to as "non-aqueous secondary batteries") and all-solid-state secondary batteries that use solid electrolytes instead of organic solvent electrolytes, are characterized by their small size, light weight, high energy density, and ability to be repeatedly charged and discharged, and have been used in a wide range of applications. Therefore, in recent years, research has been conducted on improving battery components such as electrodes with the aim of further improving the performance of secondary batteries.

[0003] Here, the electrode for a secondary battery typically has a current collector and an electrode composite material layer (positive electrode composite material layer or negative electrode composite material layer) formed on the current collector. Moreover, the electrode composite material layer is formed, for example, by dispersing the electrode active material and a secondary battery electrode binder composition (hereinafter, sometimes simply referred to as "binder composition") containing a binder material in a dispersion medium to form a secondary battery electrode slurry composition (hereinafter, sometimes simply referred to as "slurry composition"), applying the slurry composition to the current collector, and drying the applied slurry composition.

[0004] Therefore, in recent years, in order to further improve the performance of secondary batteries, attempts have been made to improve the binder composition used to form the electrode composite layer.

[0005] For example, Patent Document 1 discloses an electrode binder composition with a spherical volume equivalent diameter of 3 μm or more and / or a concentration of 2000 ppm or less. Moreover, according to Patent Document 1, if this binder composition is used, batteries with high capacity retention can be stably manufactured even with high-speed manufacturing processes and extended current collector roll lengths.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent document 1: Japanese Patent Application Publication No. 2011-76917. Summary of the Invention

[0009] The problem the invention aims to solve

[0010] Here, when forming an electrode composite material layer using a slurry composition containing the aforementioned existing binder composition, tiny defects such as circular depressions (hereinafter referred to as "craters") sometimes occur on the electrode surface. Moreover, if an electrode with such craters is used, problems such as increased internal resistance of the secondary battery and reduced cycle characteristics will occur.

[0011] Therefore, the object of the present invention is to provide a secondary battery electrode that can suppress the formation of pits on the electrode surface, a secondary battery electrode binder composition and a secondary battery electrode slurry composition that can reduce the internal resistance of the secondary battery and exhibit excellent cycle characteristics.

[0012] Furthermore, the object of the present invention is to provide an electrode for a secondary battery that suppresses the formation of pits on the electrode surface, reduces the internal resistance of the secondary battery, and exhibits excellent cycle characteristics.

[0013] Moreover, the purpose of this invention is to provide a secondary battery with reduced internal resistance and excellent cycle characteristics.

[0014] Solution for solving the problem

[0015] The inventors conducted in-depth research with the aim of solving the above-mentioned problems. Then, the inventors discovered that if an adhesive composition with a film amount formed when the adhesive composition is left to stand under specified conditions is below a specified value, it is possible to form an electrode with suppressed pit formation and a secondary battery with reduced internal resistance and excellent cycle characteristics, thereby completing the present invention.

[0016] That is, the object of the present invention is to advantageously solve the above-mentioned problems. According to the present invention, the following [1] to [6] binder composition for secondary battery electrode, the following [7] slurry composition for secondary battery electrode, the following [8] electrode for secondary battery and the following [9] secondary battery can be provided.

[0017] [1] A binder composition for a secondary battery electrode, comprising a binder material, wherein 10.0g of a mixture is injected into a polytetrafluoroethylene culture dish with a diameter of 10cm, and the amount of film formed after standing at 40°C for 2 hours is less than 1.3g, wherein the mixture is a mixture in which the binder composition for a secondary battery electrode is adjusted to a solid component concentration of 30% by mass with water.

[0018] An electrode in which the formation of surface pits is suppressed can be fabricated using a binder composition with a film amount below the aforementioned value under specified conditions. Furthermore, the electrode fabricated in this manner reduces the internal resistance of the secondary battery and exhibits excellent cycle characteristics.

[0019] Furthermore, in this invention, the "coating amount" can be measured using the methods described in the embodiments of this specification.

[0020] [2] According to the binder composition for secondary battery electrodes described in [1] above, the binder material comprises a particulate polymer, wherein the particulate polymer comprises a nitrile monomer unit in a proportion of 1% or more and 9% or less by mass, and comprises an olefinic unsaturated carboxylic acid ester monomer unit in a proportion of 1% or more and 9% or less by mass.

[0021] If the binder composition comprises particulate polymers containing nitrile monomer units and olefinic unsaturated carboxylic acid ester monomer units in the above proportions, it can further suppress the formation of pits on the electrode surface, further reduce the internal resistance of the secondary battery, and further improve the cycle characteristics.

[0022] In addition, in this invention, the "monomer unit" of a polymer refers to "the repeating unit from that monomer contained in a polymer obtained using that monomer".

[0023] Furthermore, in this invention, the proportion of monomer units in the polymer can be determined using the methods described in the embodiments of this specification.

[0024] [3] The binder composition for secondary battery electrodes described in [2] above, wherein the particulate polymer is a random copolymer.

[0025] If the particulate polymer contained in the binder composition is a random copolymer, it can further suppress the formation of pits on the electrode surface, further reduce the internal resistance of the secondary battery, and further improve the cycle characteristics.

[0026] [4] According to the binder composition for secondary battery electrodes described in [2] or [3] above, when the average particle size of the particulate polymer measured by dynamic light scattering method is Da (nm) and the volume average particle size of the particulate polymer measured by laser diffraction scattering method is Db (nm), the ratio of Da to Db (Da / Db) is 1.1 or more and 2.0 or less.

[0027] If Da / Db is within the above range, it is possible to further suppress the formation of pits on the electrode surface, further reduce the internal resistance of the secondary battery, and further improve the cycle characteristics. In addition, it is possible to improve the peel strength of the electrode.

[0028] Furthermore, in this invention, the "average particle size Da" of the particulate polymer refers to "the particle size (D50) at which the cumulative frequency of light scattering intensity, calculated from the smallest particle size side, in the particle size distribution determined using the dynamic light scattering method is 50%", and can be measured using the method described in the examples of this specification.

[0029] Furthermore, in this invention, the "volume average particle size Db" of the particulate polymer refers to "the particle size (D50) at which the cumulative volume, calculated from the smallest particle size side, becomes 50% in the particle size distribution (volume basis) determined using laser diffraction scattering method," and can be determined using the method described in the examples of this specification.

[0030] [5] The binder composition for secondary battery electrodes described in any one of [1] to [4] above, wherein the viscosity of the binder composition for secondary battery electrodes is 60 mPa·s or more and 3000 mPa·s or less under the condition that the solid component concentration is 30% by mass.

[0031] According to the binder composition having a viscosity of 60 mPa·s or more and 3000 mPa·s or less under the condition of a solid component concentration of 30% by mass, it is possible to further suppress the formation of pits on the electrode surface, further reduce the internal resistance of the secondary battery, and further improve the cycle characteristics. In addition, it is possible to improve the peel strength of the electrode.

[0032] Furthermore, in this invention, the "viscosity" of the binder composition under the condition of a solid component concentration of 30% by mass can be measured using the method described in the examples of this specification.

[0033] [6] The adhesive composition for secondary battery electrodes described in any one of [1] to [5] above, wherein the adhesive composition for secondary battery electrodes further comprises water and has a pH of 6 or more and 10 or less.

[0034] If the pH of the binder composition is within the above-mentioned range, it can further suppress the formation of pits on the electrode surface, further reduce the internal resistance of the secondary battery, and further improve cycle characteristics. Furthermore, it can improve the peel strength of the electrode.

[0035] In addition, in this invention, the “pH” of the adhesive composition refers to the pH measured at a temperature of 25°C.

[0036] [7] A slurry composition for a secondary battery electrode, comprising an electrode active material and a binder composition for a secondary battery electrode as described in any one of [1] to [6] above.

[0037] An electrode in which the formation of surface pits is suppressed can be fabricated using a slurry composition comprising an electrode active material and any of the aforementioned binder compositions. Furthermore, an electrode fabricated in this manner can reduce the internal resistance of the secondary battery and exhibit excellent cycle characteristics.

[0038] [8] An electrode for a secondary battery having an electrode composite material layer formed using the slurry composition for a secondary battery electrode described above [7].

[0039] The formation of pits on the electrode surface is suppressed in electrodes having an electrode composite material layer obtained using a slurry composition comprising an electrode active material and any of the aforementioned binder compositions. Furthermore, according to this electrode, the internal resistance of the secondary battery can be reduced and excellent cycle characteristics can be achieved.

[0040] [9] A secondary battery having the secondary battery electrode described in [8] above.

[0041] If the electrodes for secondary batteries described above are used, it is possible to manufacture secondary batteries with reduced internal resistance and excellent cycle characteristics.

[0042] Invention Effects

[0043] According to the present invention, it is possible to provide a secondary battery electrode that can suppress the formation of pits on the electrode surface, a secondary battery electrode binder composition that can reduce the internal resistance of the secondary battery and exhibit excellent cycle characteristics, and a secondary battery electrode slurry composition.

[0044] Furthermore, according to the present invention, an electrode for a secondary battery can be provided in which the formation of pits on the electrode surface is suppressed, the internal resistance of the secondary battery is reduced, and excellent cycle characteristics are achieved.

[0045] Moreover, according to the present invention, a secondary battery with reduced internal resistance and excellent cycle characteristics can be provided. Detailed Implementation

[0046] The embodiments of the present invention will now be described in detail.

[0047] Here, the binder composition of the present invention can be used to prepare the slurry composition of the present invention. Furthermore, the slurry composition of the present invention can be used to form electrodes (electrodes for secondary batteries) for secondary batteries such as non-aqueous secondary batteries and all-solid-state secondary batteries. Moreover, the electrode of the present invention is characterized by having an electrode composite material layer formed from the slurry composition of the present invention. In addition, the secondary battery of the present invention is characterized by having an electrode made using the slurry composition of the present invention.

[0048] (Adhesive composition for secondary battery electrodes)

[0049] The adhesive composition of the present invention comprises an adhesive material and may optionally contain a solvent. Furthermore, the adhesive composition of the present invention may further contain components other than the adhesive material and the solvent (other components).

[0050] Here, the adhesive composition of the present invention is characterized in that 10.0g of water is used to adjust the concentration of the solid components of the adhesive composition to 30% by mass, and the mixture is injected into a polytetrafluoroethylene culture dish with a diameter of 10cm. After standing under specified conditions, the amount of film formed is less than 1.3g.

[0051] Furthermore, since the film-coating amount of the binder composition of the present invention is less than or equal to the aforementioned value, using this binder composition can suppress the formation of pits on the electrode surface, reduce the internal resistance of the secondary battery, and exhibit excellent cycle characteristics. The reasons why the above-mentioned effects can be obtained by using the binder composition of the present invention are not yet certain, but are speculated as follows.

[0052] First, the binder composition is affected by air oxidation and spoilage during storage, sometimes resulting in a decrease in pH. Our research shows that this pH decrease weakens the electrostatic repulsion between the solid components (binder materials, etc.) in the binder composition, allowing these solid components to aggregate through hydrophobic interactions and form a film. Furthermore, it is believed that such a film swells and becomes flexible in the solvent of the binder composition and / or slurry composition. When preparing the slurry composition or forming the electrode composite layer, it passes through a filter used to remove foreign matter, causing pitting on the electrode surface and adversely affecting the internal resistance and cycle characteristics of the secondary battery.

[0053] In contrast, the binder composition of the present invention, by producing a film amount of 1.3g or less under specified conditions, can suppress the formation of such a film during storage. Therefore, it is believed that if the binder composition of the present invention is used, it is possible to suppress the formation of pits on the electrode surface, reduce the internal resistance of the secondary battery, and exhibit excellent cycle characteristics.

[0054] <Adhesive Materials>

[0055] In an electrode composite material layer formed using a slurry composition containing a binder composition, the adhesive material prevents components such as electrode active substances from detaching from the electrode composite material layer. There are no particular limitations on the adhesive material, as long as it can be used in a secondary battery. For example, a polymer obtained by polymerizing a monomer composition containing monomers capable of exhibiting adhesive properties can be used as the adhesive material. Furthermore, an adhesive material can be used alone or in combination of two or more in any ratio. Hereinafter, particulate polymers preferred as adhesive materials will be described in detail.

[0056] <<Particulate Polymers>>

[0057] The particulate polymer is a non-water-soluble particle composed of a specified polymer. Furthermore, in this invention, "non-water-soluble" means that when 0.5g of the polymer is dissolved in 100g of water at 25°C, the insoluble component is 90% by mass or more.

[0058] Here, the particulate polymer is not particularly limited as long as it is non-water-soluble and can be dispersed in solvents such as water. However, from the viewpoint of further suppressing the formation of pits on the electrode surface, further reducing the internal resistance of the secondary battery, and further improving the cycle characteristics, the particulate polymer preferably contains at least one of a nitrile-containing monomer unit and an olefinically unsaturated carboxylic acid ester monomer unit, and more preferably contains both a nitrile-containing monomer unit and an olefinically unsaturated carboxylic acid ester monomer unit. In addition, the particulate polymer may optionally further contain monomer units other than the nitrile-containing monomer unit and the olefinically unsaturated carboxylic acid ester monomer unit (hereinafter sometimes referred to as "other monomer units").

[0059] [Contains nitrile-based monomer units]

[0060] Examples of nitrile-containing monomers capable of forming nitrile-containing monomer units include α,β-ene unsaturated nitrile monomers. Specifically, there is no particular limitation on α,β-ene unsaturated nitrile monomers, as long as they are α,β-ene unsaturated compounds having a nitrile group; examples include acrylonitrile; α-haloacrylonitrile such as α-chloroacrylonitrile and α-bromoacrylonitrile; and α-alkylacrylonitrile such as methacrylonitrile and α-ethylacrylonitrile. Among these, acrylonitrile and methacrylonitrile are preferred from the viewpoint of further suppressing the formation of pits on the electrode surface, further reducing the internal resistance of the secondary battery, and further improving cycle characteristics. Furthermore, acrylonitrile-containing monomers can be used alone or in combination of two or more in any ratio.

[0061] When the total amount of monomer units in the particulate polymer is 100% by mass, the content of nitrile-containing monomer units in the particulate polymer is preferably 1% by mass or more, more preferably 1.5% by mass or more, even more preferably 2% by mass or more, preferably 9% by mass or less, more preferably 5% by mass or less, and even more preferably 3.5% by mass or less. If the content of nitrile-containing monomer units in the particulate polymer is at or above the aforementioned lower limit, film formation caused by the aggregation of the particulate polymer can be suppressed. Therefore, the formation of pits on the electrode surface can be further suppressed, while the internal resistance of the secondary battery can be further reduced, and the cycle characteristics can be further improved. On the other hand, if the content of nitrile-containing monomer units in the particulate polymer is at or below the aforementioned upper limit, film formation can be suppressed by suppressing excessive increase in the viscosity of the slurry composition. Therefore, the formation of pits on the electrode surface can be further suppressed, while the internal resistance of the secondary battery can be further reduced, and the cycle characteristics can be further improved.

[0062] [Alkene unsaturated carboxylic acid ester monomer unit]

[0063] As the olefin unsaturated carboxylic acid ester monomer capable of forming olefin unsaturated carboxylic acid ester monomer units, monomers such as those composed of esters of olefin unsaturated monocarboxylic acids or diesters of olefin unsaturated dicarboxylic acids can be used.

[0064] Here, examples of monomers composed of esters of olefinically unsaturated monocarboxylic acids include (meth)acrylate monomers. Furthermore, in this invention, "(meth)acrylate" refers to acrylic acid and / or methacrylic acid.

[0065] Furthermore, examples of (meth)acrylate monomers include: methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, tert-butyl acrylate, isobutyl acrylate, n-pentyl acrylate, isopentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, lauryl acrylate, n-tetradecyl acrylate, stearyl acrylate, and other alkyl acrylates; methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, tert-butyl methacrylate, isobutyl methacrylate, n-pentyl methacrylate, isopentyl methacrylate, hexyl methacrylate, heptyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, decyl methacrylate, lauryl methacrylate, n-tetradecyl methacrylate, stearyl methacrylate, glycidyl methacrylate, and other alkyl methacrylates.

[0066] In addition, examples of monomers formed from diesters of olefinically unsaturated dicarboxylic acids include: dialkyl maleate, dibutyl maleate, and other dialkyl maleate esters; dialkyl fumarate, dibutyl fumarate, and other dialkyl fumarate esters; dialkyl itaconic acid esters, diethyl itaconic acid esters, dibutyl itaconic acid esters, and other dialkyl itaconic acid esters.

[0067] Among these, from the viewpoint of further suppressing the formation of pits on the electrode surface, further reducing the internal resistance of the secondary battery, and further improving cycle characteristics, (meth)acrylate monomers are preferred, and methyl methacrylate is more preferred. Furthermore, olefinic unsaturated carboxylic acid ester monomers can be used alone, or two or more can be used in any ratio.

[0068] When the total amount of monomer units in the particulate polymer is 100% by mass, the content of olefinic unsaturated carboxylic acid ester monomer units in the particulate polymer is preferably 1% by mass or more, more preferably 1.5% by mass or more, even more preferably 2% by mass or more, preferably 9% by mass or less, more preferably 5% by mass or less, and even more preferably 3.5% by mass or less. If the content of olefinic unsaturated carboxylic acid ester monomer units in the particulate polymer is at or above the aforementioned lower limit, film formation caused by the aggregation of the particulate polymer can be suppressed. Therefore, it is possible to further suppress the formation of pits on the electrode surface, further reduce the internal resistance of the secondary battery, and further improve the cycle characteristics. On the other hand, if the content of olefinic unsaturated carboxylic acid ester monomer units in the particulate polymer is at or below the aforementioned upper limit, film formation can be suppressed by suppressing excessive increase in the viscosity of the slurry composition. Therefore, it is possible to further suppress the formation of pits on the electrode surface, further reduce the internal resistance of the secondary battery, and further improve the cycle characteristics.

[0069] [Other single-unit modules]

[0070] The other monomer units contained in the particulate polymer are not particularly limited. Examples of other monomer units include, for instance, aromatic vinyl monomer units, aliphatic conjugated diene monomer units, and monomer units containing acidic groups. Preferably, the particulate polymer contains aliphatic conjugated diene monomer units as other monomer units, and more preferably, it contains both aromatic vinyl monomer units and aliphatic conjugated diene monomer units as other monomer units.

[0071] —Aromatic vinyl monomer unit—

[0072] Examples of aromatic vinyl monomers capable of forming aromatic vinyl monomer units include styrene, α-methylstyrene, p-tert-butylstyrene, butoxystyrene, vinyltoluene, chlorostyrene, and vinylnaphthalene, among other aromatic monovinyl compounds. Styrene is preferred. These can be used alone or in combination of two or more, but using one alone is preferred.

[0073] When the total amount of monomer units in the particulate polymer is 100% by mass, the content of aromatic vinyl monomer units in the particulate polymer is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 20% by mass or more, preferably 65% ​​by mass or less, more preferably 55% by mass or less, even more preferably 47% by mass or less, and particularly preferably 23% by mass or less. If the content of aromatic vinyl monomer units in the particulate polymer is at or above the aforementioned lower limit, the stability of the slurry composition can be improved. On the other hand, if the content of aromatic vinyl monomer units in the particulate polymer is at or below the aforementioned upper limit, the peel strength of the electrode can be improved.

[0074] —Aliphatic conjugated diene monomer unit—

[0075] Examples of aliphatic conjugated diene monomers capable of forming aliphatic conjugated diene monomer units include conjugated diene compounds with 4 or more carbon atoms, such as 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, and 1,3-pentadiene. Among these, 1,3-butadiene and isoprene are preferred, and 1,3-butadiene is more preferred. They can be used alone or in combination of two or more.

[0076] When the total amount of all monomer units in the particulate polymer is 100% by mass, the content of aliphatic conjugated diene monomer units in the particulate polymer is preferably 30% by mass or more, more preferably 40% by mass or more, even more preferably 50% by mass or more, particularly preferably 67% by mass or more, preferably 90% by mass or less, more preferably 85% by mass or less, even more preferably 77% by mass or less, and particularly preferably 72% by mass or less. If the content of aliphatic conjugated diene monomer units in the particulate polymer is at or above the aforementioned lower limit, the peel strength of the electrode can be improved. On the other hand, if the content of aliphatic conjugated diene monomer units in the particulate polymer is at or below the aforementioned upper limit, the stability of the slurry composition can be improved.

[0077] —Monomer units containing acidic groups—

[0078] Examples of monomers capable of forming monomer units containing acidic groups include, for example, monomers containing carboxylic acid groups, monomers containing sulfonic acid groups, and monomers containing phosphate groups. Furthermore, the acidic groups in the monomer units can form salts with alkali metals, ammonia, etc.

[0079] Here, examples of carboxylic acid monomers capable of forming carboxylic acid monomer units include monocarboxylic acids and their derivatives, dicarboxylic acids and their anhydrides, and their derivatives.

[0080] Examples of monocarboxylic acids include acrylic acid, methacrylic acid, and crotonic acid.

[0081] Examples of monocarboxylic acid derivatives include 2-ethylacrylic acid, isocrotonic acid, α-acetoxyacrylic acid, β-trans-aryloxyacrylic acid, and α-chloro-β-E-methoxyacrylic acid.

[0082] Examples of dicarboxylic acids include maleic acid, fumaric acid, and itaconic acid.

[0083] Examples of dicarboxylic acid derivatives include: methylmaleic acid, dimethylmaleic acid, phenylmaleic acid, chloromaleic acid, dichloromaleic acid, fluoromaleic acid; nonyl maleate, decyl maleate, dodecyl maleate, octadecyl maleate, fluoroalkyl maleate, and other maleic acid monoesters.

[0084] Examples of anhydrides that are dicarboxylic acids include maleic anhydride, acrylic anhydride, methylmaleic anhydride, and dimethylmaleic anhydride.

[0085] In addition, as a monomer containing a carboxylic acid group, anhydrides that generate a carboxylic acid group through hydrolysis can also be used.

[0086] In addition, examples of sulfonic acid monomers capable of forming sulfonic acid monomer units include: vinyl sulfonic acid, methyl vinyl sulfonic acid, (methyl)allyl sulfonic acid, styrene sulfonic acid, ethyl (meth)acrylate-2-sulfonate, 2-acrylamido-2-methylpropanesulfonic acid, and 3-allyloxy-2-hydroxypropanesulfonic acid.

[0087] In addition, in this invention, "(methyl)allyl" refers to allyl and / or methylallyl.

[0088] Furthermore, examples of phosphate-containing monomers capable of forming phosphate-containing monomer units include 2-(meth)acryloyloxyethyl phosphate, methyl-2-(meth)acryloyloxyethyl phosphate, and ethyl-(meth)acryloyloxyethyl phosphate.

[0089] In addition, in this invention, "(meth)acrylamide" refers to acrylamide and / or methacrylamide.

[0090] Here, the aforementioned acid-containing monomers can be used alone or in combination of two or more. Moreover, from the viewpoint of improving the stability of the slurry composition and the peel strength of the electrode, acid-containing monomers capable of forming acid-containing monomer units are preferred, carboxylic acid monomers are more preferred, monocarboxylic acid and dicarboxylic acid are more preferred, acrylic acid, methacrylic acid and itaconic acid are even more preferred, methacrylic acid and itaconic acid are even more preferred, and methacrylic acid is particularly preferred.

[0091] When the total amount of all monomer units in the particulate polymer is 100% by mass, the content of acid-containing monomer units in the particulate polymer is preferably 2% by mass or more, more preferably 2.5% by mass or more, preferably 9% by mass or less, more preferably 5% by mass or less, and even more preferably 4% by mass or less. If the content of acid-containing monomer units in the particulate polymer is at or above the aforementioned lower limit, film formation caused by the aggregation of the particulate polymer can be suppressed. Therefore, it is possible to further suppress the formation of pits on the electrode surface, further reduce the internal resistance of the secondary battery, and further improve the cycle characteristics. On the other hand, if the content of acid-containing monomer units in the particulate polymer is at or below the aforementioned upper limit, film formation can be suppressed by suppressing excessive increase in the viscosity of the binder composition. Therefore, it is possible to further suppress the formation of pits on the electrode surface, further reduce the internal resistance of the secondary battery, and further improve the cycle characteristics.

[0092] [Structure of particulate polymers]

[0093] The particulate polymer can be any of, for example, random copolymers, block copolymers, alternating copolymers, etc. Moreover, from the viewpoint of further suppressing the formation of pits on the electrode surface, further reducing the internal resistance of the secondary battery, and further improving the cycle characteristics, the particulate polymer is preferably a random copolymer.

[0094] Furthermore, the particulate polymer can be a particulate polymer with a uniform monomer unit composition (type and proportion of monomer units) or a particulate polymer with a non-uniform monomer unit composition. Examples of particulate polymers with a non-uniform monomer unit composition include, for example, particulate polymers with a core-shell structure or particulate polymers with different monomer unit compositions only in the core portion. The core-shell structure has a core portion and a shell portion covering at least a portion of the outer surface of the core portion, and the monomer unit compositions of the core portion and the shell portion are different.

[0095] Furthermore, from the viewpoint of further suppressing the formation of pits on the electrode surface, further reducing the internal resistance of the secondary battery, and further improving cycle characteristics, the particulate polymer preferably has a core-shell structure. This core-shell structure has a core and a shell. The core is composed of a copolymer containing aromatic vinyl monomer units and aliphatic conjugated diene monomer units, and the shell is composed of a polymer containing monomer units with acidic groups. Additionally, the core-shell structure of the particulate polymer may further include constituent elements other than the core and shell, but it is preferable to consist only of the core and shell.

[0096] The copolymer constituting the core-shell structure of the particulate polymer may contain monomer units other than aromatic vinyl monomer units and aliphatic conjugated diene monomer units, or it may contain only aromatic vinyl monomer units and aliphatic conjugated diene monomer units. Examples of monomer units other than aromatic vinyl monomer units and aliphatic conjugated diene monomer units included in the copolymer constituting the core include, for example, monomer units containing acidic groups.

[0097] Furthermore, the shell portion of the core-shell structure of the particulate polymer can be composed of, for example, a copolymer containing monomer units other than those containing acidic groups, or a homopolymer containing only monomer units containing acidic groups. From the viewpoint of further suppressing the formation of pits on the electrode surface, further reducing the internal resistance of the secondary battery, and further improving cycle characteristics, the shell portion of the core-shell structure of the particulate polymer is preferably composed of a copolymer containing at least one of an acidic monomer unit, a nitrile monomer unit, and an olefinically unsaturated carboxylic acid ester monomer unit, and more preferably a copolymer containing an acidic monomer unit, a nitrile monomer unit, and an olefinically unsaturated carboxylic acid ester monomer unit. Additionally, aromatic vinyl monomer units such as styrene units may also be included in the copolymer constituting the shell portion.

[0098] When the particulate polymer has a core-shell structure, with the total mass of the particulate polymer being 100% by mass, the proportion of the core portion in the particulate polymer is preferably 80% by mass or more, more preferably 85% by mass or more, even more preferably 90% by mass or more, preferably 98% by mass or less, and more preferably 97.5% by mass or less. If the proportion of the core portion in the particulate polymer is at or above the aforementioned lower limit, it is possible to further suppress the formation of pits on the electrode surface, further reduce the internal resistance of the secondary battery, and further improve the cycle characteristics. On the other hand, if the proportion of the core portion in the particulate polymer is at or below the aforementioned upper limit, it is possible to improve the peel strength of the electrode.

[0099] When the particulate polymer has a core-shell structure, and the total mass of the particulate polymer is 100% by mass, the proportion of the shell portion in the particulate polymer is preferably 2% by mass or more, more preferably 2.5% by mass or more, preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less. If the proportion of the shell portion in the particulate polymer is at or above the aforementioned lower limit, the peel strength of the electrode formed using the binder composition can be improved. On the other hand, if the proportion of the shell portion in the particulate polymer is at or below the aforementioned upper limit, the formation of pits on the electrode surface can be further suppressed, while the internal resistance of the secondary battery can be further reduced, and the cycle characteristics can be further improved.

[0100] [Properties of particulate polymers]

[0101] —Average particle size Da determined by dynamic light scattering method—

[0102] The average particle size Da of the particulate polymer is preferably 100 nm or more, more preferably 130 nm or more, even more preferably 150 nm or more, preferably 340 nm or less, more preferably 300 nm or less, even more preferably 260 nm or less, and particularly preferably 240 nm or less.

[0103] Furthermore, the average particle size Da, measured by dynamic light scattering, strongly reflects the spatial expansion of molecular chains in the surface portion of the particulate polymer. That is, it is hypothesized that when the particulate polymer has, for example, the core-shell structure described above, the average particle size Da depends on the overall particle size of the core-shell structure. Therefore, the average particle size Da of the particulate polymer can be adjusted, for example, by changing the type and amount of monomers used to form the particulate polymer, as well as the polymerization method and conditions.

[0104] —Volume average particle size Db determined by laser diffraction scattering method—

[0105] The volume average particle size Db of the particulate polymer is preferably 100 nm or more, more preferably 110 nm or more, even more preferably 120 nm or more, preferably 170 nm or less, more preferably 160 nm or less, and even more preferably 150 nm or less. If the volume average particle size Db of the particulate polymer is within the above range, the peel strength of the electrode can be improved. Furthermore, if the volume average particle size Db of the particulate polymer is above the lower limit mentioned above, the internal resistance of the secondary battery can be further reduced while improving the electrolyte injection performance.

[0106] Furthermore, the volume average particle size Db, measured by laser diffraction scattering, is not significantly affected by the spatial expansion of molecular chains in the surface portion of the particulate polymer. That is, it is speculated that when the particulate polymer has, for example, the core-shell structure described above, the value of the volume average particle size Db is somewhat influenced by the shell portion, but largely depends on the particle size of the core portion. Therefore, the value of the volume average particle size Db of the particulate polymer can be adjusted, for example, by changing the type and amount of monomers used to form the core portion of the particulate polymer, as well as the polymerization method and conditions.

[0107] ―Da / Db―

[0108] Here, the ratio of the average particle size Da of the particulate polymer to the volume average particle size Db (Da / Db) is preferably 1.1 or more, more preferably 1.15 or more, even more preferably 1.3 or more, preferably 2.0 or less, more preferably 1.9 or less, and even more preferably 1.8 or less. This is presumably because if Da / Db is above the lower limit, when forming the electrode composite layer on the current collector using the slurry composition, the transfer (migration) of the particulate polymer to the surface side of the electrode composite layer (i.e., the side opposite to the current collector side) can be suppressed, allowing the particulate polymer to exist in a well-dispersed state within the electrode composite layer, thereby improving the peel strength of the electrode. Furthermore, if Da / Db is below the upper limit, film formation can be suppressed by inhibiting excessive increase in the viscosity of the binder composition. Therefore, it is possible to further suppress the formation of pits on the electrode surface, further reduce the internal resistance of the secondary battery, and further improve cycle characteristics.

[0109] [Preparation methods for particulate polymers]

[0110] There are no particular limitations on the preparation method of particulate polymers. For example, particulate polymers can be prepared by polymerizing monomers that will become the source of the monomer units contained in the particulate polymer in an emulsion. Examples of such polymerization methods include batch emulsion polymerization, emulsion (Em) feeding, and seed polymerization, with batch emulsion polymerization being preferred.

[0111] Batch emulsion polymerization can be carried out through steps such as the following: First, monomers that will become the source of monomer units contained in the particulate polymer are mixed with water, an emulsifier, and a polymerization initiator. The mixture (emulsion) is heated to carry out the polymerization reaction. The reaction is terminated by cooling at a predetermined polymerization conversion point, resulting in a mixture containing particulate polymers. Unreacted monomers are removed from the mixture to obtain an aqueous dispersion of the particulate polymers.

[0112] Here, when preparing particulate polymers by batch emulsion polymerization, from the viewpoint of easily controlling the film content of the binder composition below a specified value, it is preferable to use two-stage polymerization with monomers added in two stages instead of one-stage polymerization. When preparing particulate polymers by two-stage polymerization, it is possible to obtain particulate polymers with a core-shell structure, wherein the core is composed of monomer units from the monomers added in the first stage polymerization and the shell is composed of monomer units from the monomers added in the second stage polymerization.

[0113] In the first stage of polymerization, the monomer for core formation is mixed with water, emulsifier, chain transfer agent, and polymerization initiator. The mixture is heated to carry out the polymerization reaction until the specified polymerization conversion is reached, forming particulate polymers with a core.

[0114] In the second polymerization stage, a shell-forming monomer, along with any emulsifier and water, is continuously added to the reaction solution following the first polymerization reaction, and polymerization continues. The reaction is terminated by cooling at the point where a predetermined polymerization conversion rate is reached, yielding a mixture containing particulate polymer. Unreacted monomers are removed from the mixture to obtain an aqueous dispersion of the particulate polymer with a core-shell structure.

[0115] Heating during the polymerization reaction can be carried out at, for example, above 40°C, above 45°C, above 50°C, above 55°C, or above 60°C, below 90°C, below 85°C, below 80°C, below 75°C, or below 70°C. Furthermore, unreacted monomers can be removed from the mixture by, for example, heated vacuum distillation or the introduction of steam.

[0116] Examples of emulsifiers used in the preparation of particulate polymers include alkyl diphenyl ether disulfonic acid, dodecylbenzene sulfonic acid, lauryl sulfate, or their salts (e.g., potassium or sodium salts). Among these, alkyl diphenyl ether disulfonic acid salts are preferred.

[0117] Examples of polymerization initiators used for preparing particulate polymers include potassium persulfate, n-butyllithium, and ammonium persulfate. Potassium persulfate is preferred.

[0118] Examples of chain transfer agents used in the preparation of particulate polymers include α-methylstyrene dimer, tert-dodecyl mercaptan, and 3-mercapto-1,2-propanediol. Among these, tert-dodecyl mercaptan is preferred.

[0119] <Solvent>

[0120] The binder composition of the present invention is not particularly limited and generally contains a solvent. For example, the binder composition of the present invention may contain only water as a solvent, or it may contain only an organic solvent (e.g., esters, ketones, alcohols) as a solvent, or the solvent may be a mixture of water and an organic solvent. From the viewpoint of further suppressing the formation of pits on the electrode surface, further reducing the internal resistance of the secondary battery, and further improving cycle characteristics, the binder composition of the present invention preferably contains water as a solvent.

[0121] Here, with the total amount of solvent being 100% by mass, the proportion of water in the solvent of the binder composition of the present invention is preferably 70% by mass or more, more preferably 90% by mass or more, even more preferably 99% by mass or more, and particularly preferably 100% by mass (i.e., the binder composition of the present invention contains only water as a solvent). If the proportion of water in the solvent of the binder composition is at or above the above-mentioned lower limit, it is possible to further suppress the formation of pits on the electrode surface, further reduce the internal resistance of the secondary battery, and further improve the cycle characteristics.

[0122] <Other Ingredients>

[0123] In addition to the aforementioned adhesive materials and solvents, the adhesive composition of the present invention may also contain, for example, an acidic water-soluble polymer, an antioxidant, and a preservative. Furthermore, other components may be used individually or in combination of two or more in any ratio.

[0124] The binder composition of the present invention may contain an acidic water-soluble polymer, for example, generated as a byproduct from the monomers of the raw material that become particulate polymers during the polymerization of particulate polymers.

[0125] The weight-average molecular weight of such acidic water-soluble polymer is preferably 500 or more, more preferably 700 or more, even more preferably 1000 or more, preferably 20000 or less, more preferably 15000 or less, even more preferably 8000 or less, and particularly preferably 3500 or less. If the weight-average molecular weight of the acidic water-soluble polymer is above or below the aforementioned lower limit, the peel strength of the electrode can be improved. Furthermore, if the weight-average molecular weight of the acidic water-soluble polymer is below or below the aforementioned upper limit, the formation of pits on the electrode surface can be further suppressed, while the internal resistance of the secondary battery can be further reduced, and the cycle characteristics can be further improved.

[0126] Furthermore, the acidic water-soluble polymer can be in the form of a salt (a salt of the acidic water-soluble polymer). That is, in this invention, "acidic water-soluble polymer" also includes the salt of the acidic water-soluble polymer.

[0127] Examples of antioxidants include hindered phenolic antioxidants (such as 4-[[4,6-bis(octylthio)-1,3,5-triazin-2-yl]amino]-2,6-di-tert-butylphenol, 2,6-di-tert-butyl-p-cresol, stearate 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, pentaerythritol tetra[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and 2,4,6-tris(3',5'-di-tert-butyl-4'-hydroxybenzyl)trimethylbenzene) and oligomeric phenolic antioxidants (such as WINGSTAY (registered trademark)). L), phosphite antioxidants (e.g., 3,9-bis(octadecoxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane, 3,9-bis(2,6-di-tert-butyl-4-methylphenoxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane, 2,2-methylenebis(4,6-di-tert-butylphenyl)2-ethylhexyl phosphite, tris(2,4-di-tert-butylphenyl) phosphite), sulfur-based antioxidants (e.g., didodecyl-3,3'-thiodipropionate), etc. Among these, oligomeric phenolic antioxidants are preferred.

[0128] The amount of antioxidant added is preferably 0.1 parts by mass or more, more preferably 1 part by mass or more, more preferably 10 parts by mass or less, and more preferably 5 parts by mass or less, relative to 100 parts by mass of particulate polymer.

[0129] Examples of preservatives include isothiazolinoid compounds and 2-bromo-2-nitro-1,3-propanediol. Here, the isothiazolinoid compounds are not particularly limited, and examples include those described in Japanese Patent Application Publication Nos. 2013-211246, 2005-097474, and 2013-206624. Furthermore, a single preservative or a combination of two or more can be used. Preferably, 1,2-benzisothiazolin-3-one, 2-methyl-4-isothiazolin-3-one, 5-chloro-2-methyl-4-isothiazolin-3-one, and 2-bromo-2-nitro-1,3-propanediol are preferred preservatives, with 1,2-benzisothiazolin-3-one being more preferred.

[0130] The amount of preservative contained in the adhesive composition is preferably 0.01 parts by weight or more, preferably 0.5 parts by weight or less, more preferably 0.4 parts by weight or less, and even more preferably 0.3 parts by weight or less, relative to 100 parts by weight of the particulate polymer. If the content of the preservative is 0.01 parts by weight or more relative to 100 parts by weight of the particulate polymer, the formation of agglomerates in the adhesive composition after long-term storage can be further suppressed, and if it is 0.5 parts by weight or less, sufficiently high peel strength of the electrode can be ensured.

[0131] <<Properties of the Adhesive Composition>>

[0132] [Coverage Amount]

[0133] Here, the binder composition of the present invention requires a coating amount of 1.3g or less, preferably 1.0g or less, more preferably 0.8g or less, further preferably 0.7g or less, even more preferably 0.6g or less, particularly preferably 0.5g or less, preferably 0.05g or more, and more preferably 0.1g or more. When the coating amount is greater than 1.3g, the number of pits on the electrode surface increases, the internal resistance of the secondary battery increases, and the cycle characteristics decrease. If the coating amount is 1.0g or less, the formation of pits on the electrode surface can be further suppressed, the internal resistance of the secondary battery can be further reduced, and the cycle characteristics can be further improved. Furthermore, if the coating amount is 0.05g or more, the ease of manufacturing the binder composition can be well ensured.

[0134] Furthermore, the film weight can be adjusted by changing, for example, the type and amount of monomers used to prepare the particulate polymer, or the method of preparing the particulate polymer. Specifically, when preparing particulate polymers by batch emulsion polymerization, the film weight can be reduced by using two-stage polymerization instead of single-stage polymerization. Moreover, when using two-stage polymerization, the film weight can be reduced by adding nitrile-containing monomers and / or olefinically unsaturated carboxylic acid ester monomers during the second-stage polymerization.

[0135] [Viscosity]

[0136] Furthermore, the viscosity of the binder composition of the present invention, when the solid component concentration is 30% by mass, is preferably 60 mPa·s or more, more preferably 150 mPa·s or more, even more preferably 250 mPa·s or more, particularly preferably 350 mPa·s or more, preferably 3000 mPa·s or less, more preferably 2500 mPa·s or less, even more preferably 2000 mPa·s or less, and particularly preferably 1400 mPa·s or less. If the viscosity at a solid component concentration of 30% by mass is at or above the aforementioned lower limit, the peel strength of the electrode can be improved. In addition, if the viscosity at a solid component concentration of 30% by mass is at or below the aforementioned upper limit, the formation of pits on the electrode surface can be further suppressed, while the peel strength of the electrode can be improved.

[0137] Furthermore, the viscosity of the adhesive composition at a solids concentration of 30% by mass can be adjusted by changing, for example, the pH of the adhesive composition. Specifically, the viscosity can be reduced by lowering the pH of the adhesive composition, and the viscosity can be increased by raising the pH of the adhesive composition.

[0138] [pH]

[0139] When the binder composition contains water as a solvent, the pH of the binder composition is preferably 6 or higher, more preferably 7 or higher, preferably 10 or lower, more preferably 9 or lower, and even more preferably 8 or lower. If the pH of the binder composition is above or below the aforementioned lower limit, the peel strength of the electrode can be improved. On the other hand, if the pH of the binder composition is below or below the aforementioned upper limit, film formation can be suppressed by inhibiting excessive increase in the viscosity of the binder composition. Therefore, it is possible to further suppress the formation of pits on the electrode surface, further reduce the internal resistance of the secondary battery, and further improve the cycle characteristics.

[0140] Furthermore, pH adjustment can be achieved, for example, by adding an alkaline substance to the binder composition. Examples of alkaline substances include lithium hydroxide, sodium hydroxide, potassium hydroxide, and ammonia. Ammonia is preferred because it is less likely to cause coagulation due to the impact of adding an alkaline substance during neutralization.

[0141] <Preparation Method of Adhesive Composition>

[0142] Furthermore, the method for preparing the adhesive composition of the present invention is not particularly limited. For example, an aqueous dispersion containing particulate polymer obtained by the method described in the "Method for Preparing Particulate Polymer" section can be used directly as an adhesive composition. Additionally, other components can be added to the aqueous dispersion containing particulate polymer, and the adhesive composition can be prepared by mixing using known methods. Furthermore, when preparing the adhesive composition using an aqueous dispersion containing particulate polymer, the liquid component (e.g., water) contained in the aqueous dispersion can be used directly as a solvent for the adhesive composition. Moreover, the pH of the adhesive composition can be arbitrarily adjusted to the aforementioned preferred pH range, and filtration using a metal mesh or the like can be performed to remove aggregates.

[0143] (Slurry composition for secondary battery electrodes)

[0144] The slurry composition of the present invention is a slurry-like composition used for forming an electrode composite material layer of an electrode, comprising at least the above-described binder composition and an electrode active material. For example, the slurry composition of the present invention contains the electrode active material and the binder material in a solvent such as water, and may further contain, as needed, any components other than the solvent, the electrode active material, and the binder material. Moreover, since the slurry composition of the present invention contains the above-described binder composition, if an electrode is made using this slurry composition, it is possible to suppress the formation of pits on the electrode surface, reduce the internal resistance of the secondary battery, and exhibit excellent cycle characteristics.

[0145] <Adhesive Composition>

[0146] The adhesive composition of the present invention described above is used as the adhesive composition.

[0147] Furthermore, there is no particular limitation on the amount of binder composition in the slurry composition. For example, the amount of binder composition relative to 100 parts by weight of electrode active material can be set to be 0.5 parts by weight or more and 15 parts by weight or less, calculated as solid components.

[0148] <Electrode Active Materials>

[0149] Furthermore, there are no particular limitations on the electrode active material, and known electrode active materials used in secondary batteries can be used. Specifically, for example, as an electrode active material that can be used in the electrode composite material layer of a lithium-ion secondary battery, which is an example of a secondary battery, there are no particular limitations, and the following electrode active materials can be used.

[0150] [Positive electrode active material]

[0151] As the positive electrode active material incorporated in the positive electrode composite layer of the positive electrode in a lithium-ion secondary battery, compounds containing transition metals, such as transition metal oxides, transition metal sulfides, and composite metal oxides of lithium and transition metals, can be used. Other examples of transition metals include Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Mo.

[0152] Specifically, as positive electrode active materials, there are no particular limitations, but examples include lithium cobalt oxide (LiCoO2), lithium manganese oxide (LiMn2O4), lithium nickel oxide (LiNiO2), lithium-containing composite oxides of Co-Ni-Mn, lithium-containing composite oxides of Ni-Mn-Al, lithium-containing composite oxides of Ni-Co-Al, olivine-type lithium iron phosphate (LiFePO4), olivine-type lithium manganese phosphate (LiMnPO4), and Li... 1+x Mn 2-x O4 (0 < X ​​< 2) represents the lithium-excess spinel compound, Li[Ni 0.17 Li 0.2 Co 0.07 Mn 0.56 O2, LiNi 0.5 Mn 1.5 O4, etc.

[0153] In addition, the above-mentioned positive electrode active materials can be used alone or in combination of two or more.

[0154] [Negative Electrode Active Material]

[0155] Examples of negative electrode active materials that are incorporated into the negative electrode composite material layer of the negative electrode in a lithium-ion secondary battery include carbon-based negative electrode active materials, metal-based negative electrode active materials, and negative electrode active materials that combine these materials.

[0156] Here, carbon-based anode active materials refer to active materials with a carbon-based backbone that can insert (also called "doping") lithium. Specifically, examples of carbon-based anode active materials include coke, mesophase carbon microspheres (MCMB), mesophase pitch-based carbon fibers, pyrolysis vapor-grown carbon fibers, phenolic resin sintered bodies, polyacrylonitrile-based carbon fibers, quasi-isotropic carbon, furfuryl alcohol resin sintered bodies (PFA), and hard carbon, as well as graphitic materials such as natural graphite and artificial graphite.

[0157] Furthermore, metal-based anode active materials refer to active materials containing metals, typically those containing elements capable of intercalating lithium, and possessing a theoretical capacity of 500 mAh / g or more when lithium is intercalated. Examples of metal-based active materials include lithium metal, elemental metals capable of forming lithium alloys (e.g., Ag, Al, Ba, Bi, Cu, Ga, Ge, In, Ni, P, Pb, Sb, Si, Sn, Sr, Zn, Ti, etc.), and their oxides, sulfides, nitrides, silicides, carbides, phosphides, etc. Furthermore, oxides such as lithium titanate can be cited.

[0158] In addition, the above-mentioned negative electrode active materials can be used alone or in combination of two or more.

[0159] <Any ingredient>

[0160] Any component that can be incorporated into the slurry composition is not particularly limited, and examples include other components described in the section on "binder compositions for secondary battery electrodes," dispersants, viscosity modifiers (thickeners) such as carboxymethyl cellulose, metal catchers, conductive materials such as carbon black, etc. Furthermore, any component can be used alone, or two or more can be combined in any ratio.

[0161] <Preparation of Slurry Composition>

[0162] There are no particular limitations on the preparation method of the slurry composition.

[0163] For example, a slurry composition can be prepared by mixing a binder composition, an electrode active material, and any other components to be used as needed in the presence of, for example, a solvent from the binder composition.

[0164] In addition, there are no particular restrictions on the mixing method; commonly used mixers and dispersers can be used for mixing.

[0165] (Electrodes for secondary batteries)

[0166] The electrode of the present invention has an electrode composite material layer formed using the slurry composition of the present invention described above. Therefore, the electrode composite material layer is formed from the dried product of the slurry composition and typically contains an electrode active material and a binder material, and may further contain any other components. Furthermore, the components included in the electrode composite material layer are the same as those included in the slurry composition, and the preferred proportions of these components are the same as the preferred proportions of the components in the slurry composition. In addition, while the particulate polymer exists in the slurry composition in a particulate form, in the electrode composite material layer formed using the slurry composition, it may be in a particulate form or any other arbitrary shape.

[0167] Furthermore, the electrode of the present invention uses the above-mentioned slurry composition to form an electrode composite material layer, thereby suppressing the formation of pits on the electrode surface, reducing the internal resistance of the secondary battery, and exhibiting excellent cycle characteristics.

[0168] <Methods for forming electrodes>

[0169] Here, the electrode composite material layer of the electrode of the present invention can be formed using, for example, the following method.

[0170] 1) A method of applying the slurry composition of the present invention to the surface of a current collector and then drying it;

[0171] 2) A method for drying a current collector after impregnating it with the slurry composition of the present invention; and

[0172] 3) A method of applying the slurry composition of the present invention onto a release substrate, drying it to produce an electrode composite material layer, and transferring the obtained electrode composite material layer onto the surface of a current collector.

[0173] Of these, the method described in 1) above is particularly preferred because it allows for easy control of the electrode composite material layer thickness. Specifically, the method described in 1) includes a step of applying a slurry composition to a current collector (coating step) and a step of drying the slurry composition applied to the current collector to form an electrode composite material layer on the current collector (drying step).

[0174] [Coating Process]

[0175] There are no particular limitations on the method for applying the above-mentioned slurry composition to the current collector, and known methods can be used. Specifically, as coating methods, methods such as doctor blade coating, dip coating, reverse roller coating, direct roller coating, gravure printing, extrusion coating, and brush coating can be used. In this case, the slurry composition can be applied to only one side of the current collector or to both sides. The thickness of the slurry film on the current collector before drying can be appropriately set according to the thickness of the electrode composite material layer obtained after drying.

[0176] Here, as the current collector of the coating slurry composition, a material that is both conductive and electrochemically durable can be used. Specifically, as the current collector, current collectors formed of, for example, iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, platinum, etc., can be used. In addition, the above-mentioned materials can be used alone, or two or more can be combined in any ratio.

[0177] [Drying Process]

[0178] The method for drying the slurry composition on the current collector is not particularly limited, and known methods can be used, such as drying methods using warm air, hot air, or low-humidity air; vacuum drying methods; and drying methods using irradiation with infrared rays, electron beams, etc. By drying the slurry composition on the current collector in this way, an electrode composite material layer can be formed on the current collector, resulting in an electrode having a current collector and an electrode composite material layer.

[0179] Alternatively, the electrode composite layer can be pressurized using a metal mold or roll forming process after the drying step. This pressurization process improves the adhesion between the electrode composite layer and the current collector while simultaneously increasing the density of the resulting electrode composite layer. Furthermore, if the electrode composite layer contains a curable polymer, it is preferable to cure the polymer after the electrode composite layer is formed.

[0180] (Secondary battery)

[0181] The secondary battery of the present invention includes a positive electrode, a negative electrode, an electrolyte, and a spacer, and uses the electrode of the present invention described above as at least one of the positive and negative electrodes. Furthermore, since the secondary battery of the present invention is manufactured using the electrode of the present invention described above as at least one of the positive and negative electrodes, it achieves excellent cycle characteristics while reducing internal resistance.

[0182] Furthermore, the following description, as an example, illustrates the case where the secondary battery is a lithium-ion secondary battery, but the present invention is not limited to the following example.

[0183] <Electrode>

[0184] Here, there is no particular limitation on the electrode other than the electrode of the present invention, which can be used in the secondary battery of the present invention, and known electrodes used in the manufacture of secondary batteries can be used. Specifically, as an electrode other than the electrode of the present invention, electrodes formed by forming an electrode composite material layer on a current collector using known manufacturing methods can be used.

[0185] Electrolyte

[0186] As the electrolyte, organic electrolytes containing a supporting electrolyte dissolved in an organic solvent are typically used. For example, lithium salts can be used as the supporting electrolyte for lithium-ion secondary batteries. Examples of lithium salts include LiPF6, LiAsF6, LiBF4, LiSbF6, LiAlCl4, LiClO4, CF3SO3Li, C4F9SO3Li, CF3COOLi, (CF3CO)2NLi, (CF3SO2)2NLi, and (C2F5SO2)NLi. LiPF6, LiClO4, and CF3SO3Li are particularly preferred due to their high degree of dissociation from their easy solubility in solvents. Furthermore, a single electrolyte can be used, or two or more can be combined in any ratio. Generally, there is a tendency for higher lithium-ion conductivity to be achieved with a supporting electrolyte having a higher degree of dissociation; therefore, the lithium-ion conductivity can be adjusted according to the type of supporting electrolyte.

[0187] As for the organic solvent used in the electrolyte, there are no particular limitations as long as it can dissolve the supporting electrolyte. Preferred solvents include: carbonates such as dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butyl carbonate (BC), methyl ethyl carbonate (EMC), and vinylene carbonate (VC); esters such as γ-butyrolactone and methyl formate; ethers such as 1,2-dimethoxyethane and tetrahydrofuran; and sulfur-containing compounds such as sulfolane and dimethyl sulfoxide. Mixtures of these solvents can also be used. Carbonates are preferred because they have a high dielectric constant and a wide stable potential range. Generally, there is a tendency for lower solvent viscosity to result in higher lithium-ion conductivity; therefore, the lithium-ion conductivity can be adjusted by the type of solvent used.

[0188] Furthermore, the concentration of electrolyte in the electrolyte can be appropriately adjusted. Additionally, known additives can be added to the electrolyte.

[0189] <spacer>

[0190] There are no particular limitations on the spacer used; for example, the spacer described in Japanese Patent Application Publication No. 2012-204303 can be used. Among these, a microporous membrane formed of a polyolefin-based resin (polyethylene, polypropylene, polybutene, polyvinyl chloride) is preferred from the perspective of reducing the overall film thickness of the spacer, thereby increasing the ratio of electrode active materials in the secondary battery and increasing the capacity per unit volume.

[0191] Furthermore, the secondary battery of the present invention can be manufactured, for example, by overlapping the positive and negative electrodes with a spacer between them, winding or folding them according to the battery shape as needed and placing them into a battery container, injecting electrolyte into the battery container, and sealing it. Here, in the secondary battery of the present invention, the electrodes described above are used as at least one of the positive and negative electrodes, preferably as the negative electrode. Additionally, in the secondary battery of the present invention, to prevent internal pressure rise and overcharging / discharging, overcurrent protection components such as fuses and PTC elements, porous metal mesh, and conductive plates can be provided as needed. The shape of the secondary battery can be, for example, coin-shaped, button-shaped, sheet-shaped, cylindrical, square, or flat.

[0192] Example

[0193] The present invention will now be described in detail based on embodiments, but the present invention is not limited to these embodiments. Furthermore, in the following description, unless otherwise specified, "%" and "parts" refer to quantities based on mass.

[0194] Furthermore, unless otherwise stated, in polymers manufactured by polymerizing multiple monomers, the proportion of a monomer unit formed by polymerizing a particular monomer in the polymer is generally consistent with the proportion (feed ratio) of that particular monomer in all monomers used in the polymerization of the polymer. Moreover, in the examples and comparative examples, the content ratio of each monomer unit in the particulate polymer, the average particle size Da and volume average particle size Db of the particulate polymer, the viscosity and coating amount of the binder composition, the number of pits on the electrode surface, the peel strength of the electrode, and the internal resistance and cycle characteristics of the secondary battery were evaluated by the following methods.

[0195] <Proportion of each monomer unit>

[0196] pass 1 The intensity ratio of peaks from each monomer unit in the particulate polymer is determined by H-NMR (nuclear magnetic resonance) method, converted into mass ratio, and then the content ratio of each monomer unit in the particulate polymer is determined.

[0197] <Average particle size Da of particulate polymers>

[0198] The average particle size Da of the particulate polymers prepared in the examples and comparative examples was measured using a particle size distribution measuring apparatus (manufactured by Otsuka Electronics Co., Ltd., model "nanoSAQLA") based on the dynamic light scattering method. Specifically, the particle size distribution of the aqueous dispersion of the particulate polymer was measured under the following conditions, and the average particle size Da (nm) of the particulate polymer was obtained by taking the particle size at which the cumulative frequency of light scattering intensity calculated from the smallest particle size side becomes 50%.

[0199] Dispersion medium: ion-exchanged water

[0200] Measurement temperature: 25±1℃

[0201] Concentration measured (solid component concentration): 0.5% by mass

[0202] Scattering angle: 168.8°

[0203] Laser wavelength of light source: 660nm

[0204] <Volume average particle size Db of particulate polymer>

[0205] The volume average particle size Db of the particulate polymers prepared in the examples and comparative examples was measured using a particle size distribution measuring apparatus (manufactured by Shimadzu Corporation, product name "SALD-2300") based on the principle of laser diffraction scattering, according to JIS Z 8825. Specifically, the volume average particle size Db (nm) of the particulate polymer was determined by measuring an aqueous dispersion in which the solid component concentration of the particulate polymer was adjusted to 0.1% by mass in the above apparatus, and the particle size distribution (volume basis) obtained was calculated by taking the particle size (D50) that represents 50% of the cumulative volume from the smallest particle size side as the particulate polymer.

[0206] <Coverage Amount>

[0207] The solids concentration of the adhesive compositions prepared in the Examples and Comparative Examples was adjusted to 30% by mass using water to prepare a mixture. Alternatively, when the solids concentration of the adhesive composition was less than 30% by mass, the solids concentration was increased by removing the solvent through distillation, resulting in a mixture with a solids concentration of 30% by mass. 10.0 g of the obtained mixture was poured into a 10 cm inner diameter polytetrafluoroethylene (PTFE) petri dish and allowed to stand for 2 hours at 40°C and 50% RH. Then, the contents of the petri dish were filtered using a stainless steel plain-woven mesh (mesh: 200, wire diameter: 0.05 mm, mesh size: 0.077 mm). After filtration, the mass (g) of the substance remaining on the mesh was measured and used as the film coating amount.

[0208] <Viscosity>

[0209] After adjusting the solid component concentration of the adhesive compositions prepared in the examples and comparative examples to 30% by mass with water, the viscosity of the adhesive compositions was measured using a Type B viscometer (manufactured by Toki Sangyo Co., Ltd., product name "TVB-10", speed: 60 rpm). The temperature for measuring the viscosity was 25°C. Furthermore, if the viscosity of the adhesive composition is 10 mPa·s or more and 3000 mPa·s or less, it can be said that the adhesive composition has good adhesion.

[0210] <Number of dents>

[0211] The electrodes fabricated in the examples and comparative examples were cut into pieces 30 cm long and 10 cm wide. The surface of the electrode composite layer side of the cut electrodes was observed, and the number of pits with an inner diameter of 1 cm or more was measured. This measurement was performed three times, and the average value was calculated. This average value was taken as the number of pits. In addition, if the average value was not an integer, it was rounded to an integer. Then, the evaluation was carried out according to the following criteria.

[0212] A: The number of pits is 0.

[0213] B: The number of pits is more than 1 and less than 3

[0214] C: The number of pits is 4 or more but less than 6

[0215] D: The number of pits is 7 or more.

[0216] <Peel strength>

[0217] The electrodes prepared in the examples and comparative examples were cut into rectangles 100 mm long and 10 mm wide to serve as test pieces. With the electrode composite layer of the test piece facing down, transparent tape was adhered to the surface of the electrode composite layer. The transparent tape specified in JIS Z1522 was used. Furthermore, the transparent tape was pre-fixed to the test bench. Then, the stress was measured when one end of the current collector was stretched vertically upwards at a tensile speed of 50 mm / min and peeled off. This measurement was performed three times, and the average value was calculated as the peel strength. Then, the results were evaluated according to the following criteria.

[0218] A: Peel strength is above 10 N / m

[0219] B: Peel strength is 7 N / m or higher and less than 10 N / m

[0220] C: Peel strength is above 5N / m and below 7N / m

[0221] D: Peel strength less than 5 N / m

[0222] <Internal Resistance>

[0223] To evaluate the internal resistance of the lithium-ion secondary batteries fabricated in the Examples and Comparative Examples, the IV resistance was measured as follows. A conditioning process was performed as follows: at 25°C, the battery was charged at a rate of 0.1C to a voltage of 4.2V. After a 10-minute pause, it was discharged at a constant current (CC) rate of 0.1C to 3.0V. This process was repeated three times. Then, at -10°C, the battery was charged at 1C (C being the value expressed as rated capacity (mA) / 1 hour (h)) to 3.75V. Around 3.75V, the battery was charged and discharged for 20 seconds at rates of 0.5C, 1.0C, 1.5C, and 2.0C, respectively. For each case, the battery voltage on the charging side after 15 seconds was plotted against the current value, and the slope was calculated as the IV resistance (Ω). The obtained IV resistance value (Ω) was compared with the IV resistance of Comparative Example 1, and evaluated according to the following criteria. In addition, the smaller the value of the IV resistor, the lower the internal resistance of the secondary battery.

[0224] A: The IV resistance is less than 85% compared to Comparative Example 1.

[0225] B: The IV resistance is 85% or more but less than 95% compared to Comparative Example 1.

[0226] C: The IV resistance is above 95% compared to Comparative Example 1.

[0227] <Cyclic Characteristics>

[0228] After electrolyte filling, the lithium-ion secondary batteries prepared in the examples and comparative examples were left to stand at 25°C for 5 hours. Next, they were charged at 0.2C constant current method to a cell voltage of 3.65V at 25°C, and then aged at 60°C for 12 hours. Then, they were discharged at 0.2C constant current method to a cell voltage of 3.00V at 25°C. Then, constant current (CC)-constant voltage (CV) charging was performed at 0.2C constant current method (upper limit cell voltage 4.20V), followed by CC discharge at 0.2C constant current method to 3.00V. This 0.2C charge-discharge cycle was repeated three times.

[0229] Then, at a temperature of 25°C, 100 charge-discharge cycles were performed with a battery cell voltage of 4.20-3.00V and a charge-discharge rate of 1.0C. The discharge capacity of the first cycle was defined as X1, and the discharge capacity of the 100th cycle was defined as X2.

[0230] Using the discharge capacities X1 and X2, calculate the capacity retention rate expressed as ΔC = (X2 / X1) × 100 (%), and evaluate it according to the following criteria. The larger the value of the capacity retention rate ΔC, the better the cycling characteristics.

[0231] A: ΔC is above 93%.

[0232] B: ΔC is above 90% and less than 93%.

[0233] C: ΔC is above 87% and less than 90%.

[0234] D: ΔC is less than 87%

[0235] (Example 1)

[0236] <Preparation of binder composition for negative electrode>

[0237] [First paragraph aggregated and added]

[0238] In a 5MPa pressure vessel A equipped with a stirrer, 22 parts of styrene (St) as an aromatic vinyl monomer, 70 parts of 1,3-butadiene (BD) as an aliphatic conjugated diene monomer, 1 part of methacrylic acid (MAA) as an acidic monomer, 0.6 parts of alkyl diphenyl ether disulfonate as an emulsifier, 143 parts of deionized water, 0.1 parts of tert-dodecyl mercaptan as a chain transfer agent, and 0.3 parts of potassium persulfate as a polymerization initiator were added. After thorough stirring, the mixture was heated to 55°C to initiate polymerization and reacted for 10 hours. Next, the mixture was heated to 65°C and reacted for an additional 6 hours.

[0239] [Second paragraph aggregation added]

[0240] Next, 2 parts of acrylonitrile (AN) as a nitrile-containing monomer, 2 parts of methyl methacrylate (MMA) as an olefinic unsaturated carboxylic acid ester monomer, and 3 parts of methacrylic acid (MAA) as an acidic monomer are added to pressure vessel A. The mixture is heated to 85°C and reacted for another 6 hours. Unreacted monomers are then removed by heated vacuum distillation. Through these operations, an aqueous dispersion of a particulate polymer with a core-shell structure is obtained. This core-shell structure is formed by coating at least a portion of the outer surface of the core formed in the first polymerization stage with a shell formed in the second polymerization stage.

[0241] [pH adjustment, filtration]

[0242] The obtained aqueous dispersion of the particulate polymer was neutralized with ammonia water to adjust the pH to 7. Then, it was cooled, and 1 part (equivalent to the solid content) of Wingstay L dispersion (manufactured by Chukyo Oils & Fats Co., Ltd., catalog number "K-840") as an antioxidant was added. After drying at 40°C for 2 hours on a polytetrafluoroethylene petri dish, it was filtered through a stainless steel plain-woven mesh (mesh: 200, wire diameter: 0.05 mm, mesh size: 0.077 mm) to obtain a binder composition for the negative electrode.

[0243] Using this binder composition, the proportion of each monomer unit in the particulate polymer, the average particle size Da and volume average particle size Db of the particulate polymer, the film coating amount, and the viscosity of the binder composition were determined. The results are shown in Table 1.

[0244] <Preparation of Negative Electrode Slurry Composition>

[0245] In a planetary mixer equipped with a disperser, add 100 parts of artificial graphite (tap density: 0.85 g / cm³) as the negative electrode active material. 3 A mixture was prepared by mixing 1 part of carbon black (TIMCAL Corporation, product name "Super C65") as a conductive material and 1.2 parts of carboxymethyl cellulose (Daicel Corporation, product name "Daicel2200") as a thickener, based on the solid content. The mixture was adjusted to a solid content concentration of 60% with deionized water and then mixed at 25°C for 60 minutes. Next, the solid content concentration was adjusted to 52% with deionized water and further mixed at 25°C for 15 minutes to obtain a liquid mixture. To the obtained liquid mixture, 2.0 parts of the binder composition prepared above and deionized water were added, adjusting the final solid content concentration to 48%. After further mixing for 10 minutes, degassing was performed under reduced pressure to obtain a slurry composition for a negative electrode with good flowability.

[0246] <Formation of the Negative Electrode>

[0247] The obtained negative electrode slurry composition was coated using a corner-shaped roller coating machine at a speed of 3.6 m / min to achieve a dry weight of 10.5 mg / cm³. 2 The coating was applied to a 15 μm thick copper foil, which served as the current collector, and then dried. This drying was performed by transporting the copper foil at a speed of 3.6 m / min in an oven at 140°C for 20 seconds, followed by a second transport at 150°C for 20 seconds. The resulting negative electrode raw material was then calendered using a roll press to obtain a negative electrode composite layer with a density of 1.70 g / cm³. 3 The negative electrode was used. For this negative electrode, the number of pits on the surface and the peel strength were evaluated. The results are shown in Table 1.

[0248] <The Formation of the Positive Electrode>

[0249] 100 parts of LiCoO2 with a median particle size of 12 μm, used as the positive electrode active material, 2 parts of acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd., product name "HS-100"), used as the conductive material, 2 parts of polyvinylidene fluoride (manufactured by Kureha Co., Ltd., product name "#7208"), used as the binder, and N-methylpyrrolidone, used as the solvent, were mixed to obtain a total solids concentration of 70%. These were then mixed using a planetary mixer to obtain a slurry composition for the positive electrode.

[0250] The obtained positive electrode slurry composition was coated using a corner-shaped roller coating machine, and the dried unit area weight was 23 mg / cm³. 2 The coating was applied to a 20 μm thick aluminum foil, which served as the current collector, and then dried. This drying was performed by conveying the aluminum foil at 0.5 m / min in an oven at 60°C for 2 minutes. Then, it was heat-treated at 120°C for 2 minutes to obtain the positive electrode raw material. The positive electrode raw material was then calendered using a roll press to obtain a positive electrode composite layer with a density of 4.0 g / cm³. 3 The positive pole.

[0251] <Preparation of Spacers>

[0252] As a spacer made of spacer substrate, a single-layer polypropylene spacer (manufactured by Celgard, product name "Celgard 2500") is prepared.

[0253] <The Manufacturing of Lithium-ion Secondary Batteries>

[0254] The pressed positive and negative electrodes, fabricated as described above, and a spacer (a 20 μm thick polypropylene microporous membrane) are stacked in a spacer / positive / spacer / negative electrode configuration, with the spacer positioned between the positive and negative electrodes, to obtain a laminate. Next, the laminate of electrodes and spacers is wound around a 20 mm diameter core to obtain a wound body containing a positive electrode, spacer, and negative electrode. Then, the wound body is compressed in one direction at a speed of 10 mm / s to a thickness of 4.5 mm to obtain a flat body. Furthermore, the resulting flat body is elliptical in plan view, with a major axis to minor axis ratio (major axis / minor axis) of 7.7.

[0255] In addition, 2% by volume of vinylene carbonate (VC) was added as an additive to a mixed solvent of 1.0 M LiPF6 solution and solvent: ethylene carbonate (EC) / ethyl methyl carbonate (EMC) = 3 / 7 (mass ratio).

[0256] Next, the aforementioned flat body and the aforementioned non-aqueous electrolyte are housed together in an aluminum laminated casing. Then, after connecting the negative and positive electrode leads to the designated locations, the opening of the laminated casing is sealed using heat, thereby manufacturing a laminated lithium-ion secondary battery as a non-aqueous secondary battery. Furthermore, the resulting secondary battery is a pouch-shaped battery with a width of 35mm × height of 48mm × thickness of 5mm and a nominal capacity of 700mAh.

[0257] Then, the internal resistance and cycle characteristics of the lithium-ion secondary battery were evaluated. The results are shown in Table 1.

[0258] (Example 2)

[0259] In preparing the binder composition, the aqueous dispersion of the particulate polymer was adjusted to pH 6 with ammonia. Otherwise, the process was the same as in Example 1 to prepare or manufacture the binder composition for the negative electrode, the slurry composition for the negative electrode, the negative electrode, the positive electrode, the spacer, and the lithium-ion secondary battery. The evaluation was then conducted in the same manner as in Example 1. The results are shown in Table 1.

[0260] (Example 3)

[0261] In preparing the binder composition for the negative electrode, the amounts of each monomer added in the first and second stage polymerizations were changed as follows, except that the process was the same as in Example 1, to prepare or manufacture the binder composition for the negative electrode, the slurry composition for the negative electrode, the negative electrode, the positive electrode, the spacer, and the lithium-ion secondary battery. Then, the evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.

[0262] First aggregate: St23 copies, BD71 copies, MAA0 copies

[0263] Second-stage aggregation: AN 2 parts, MMA 2 parts, MAA 2 parts

[0264] (Example 4)

[0265] In preparing the binder composition for the negative electrode, the amounts of each monomer added in the first and second stage polymerizations were changed as follows, except that the process was the same as in Example 1, to prepare or manufacture the binder composition for the negative electrode, the slurry composition for the negative electrode, the negative electrode, the positive electrode, the spacer, and the lithium-ion secondary battery. Then, the evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.

[0266] First aggregate: St22 copies, BD72 copies, MAA1 copy

[0267] Second aggregate: AN0 parts, MMA2 parts, MAA3 parts

[0268] (Example 5)

[0269] In preparing the binder composition for the negative electrode, the amounts of each monomer added in the first and second stage polymerizations were changed as follows, except that the process was the same as in Example 1, to prepare or manufacture the binder composition for the negative electrode, the slurry composition for the negative electrode, the negative electrode, the positive electrode, the spacer, and the lithium-ion secondary battery. Then, the evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.

[0270] First aggregate: St22 copies, BD72 copies, MAA1 copy

[0271] Second aggregate: AN 2 parts, MMA 0 parts, MAA 3 parts

[0272] (Example 6)

[0273] In preparing the binder composition for the negative electrode, the amounts of each monomer added in the first and second stage polymerizations were changed as follows, except that the process was the same as in Example 1, to prepare or manufacture the binder composition for the negative electrode, the slurry composition for the negative electrode, the negative electrode, the positive electrode, the spacer, and the lithium-ion secondary battery. Then, the evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.

[0274] First aggregate: St 18 copies, BD 70 copies, MAA 1 copy

[0275] Second aggregate: AN 2 parts, MMA 2 parts, MAA 3 parts, St 4 parts

[0276] (Example 7)

[0277] In preparing the binder composition, the aqueous dispersion of the particulate polymer was adjusted to pH 6 with ammonia. Otherwise, the process was the same as in Example 3 to prepare or manufacture the binder composition for the negative electrode, the slurry composition for the negative electrode, the negative electrode, the positive electrode, the spacer, and the lithium-ion secondary battery. The evaluation was then conducted in the same manner as in Example 1. The results are shown in Table 1.

[0278] (Example 8)

[0279] In preparing the binder composition for the negative electrode, the amounts of each monomer added in the first and second stage polymerizations were changed as follows, except that the process was the same as in Example 1, to prepare or manufacture the binder composition for the negative electrode, the slurry composition for the negative electrode, the negative electrode, the positive electrode, the spacer, and the lithium-ion secondary battery. Then, the evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.

[0280] First aggregate: St19 copies, BD67 copies, MAA1 copy

[0281] Second aggregate: AN 8 parts, MMA 2 parts, MAA 3 parts

[0282] (Example 9)

[0283] In preparing the binder composition for the negative electrode, the amounts of each monomer added in the first and second stage polymerizations were changed as follows, except that the process was the same as in Example 1, to prepare or manufacture the binder composition for the negative electrode, the slurry composition for the negative electrode, the negative electrode, the positive electrode, the spacer, and the lithium-ion secondary battery. Then, the evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.

[0284] First aggregate: St19 copies, BD67 copies, MAA1 copy

[0285] Second aggregate: AN 2 parts, MMA 8 parts, MAA 3 parts

[0286] (Comparative Example 1)

[0287] In preparing the binder composition for the negative electrode, the amounts of each monomer added in the first and second stage polymerizations were changed as follows, except that the process was the same as in Example 1, to prepare or manufacture the binder composition for the negative electrode, the slurry composition for the negative electrode, the negative electrode, the positive electrode, the spacer, and the lithium-ion secondary battery. Then, the evaluation was performed in the same manner as in Example 1. The results are shown in Table 2.

[0288] First aggregate: St24 copies, BD72 copies, MAA1 copy

[0289] Second aggregation: 3 copies of MAA

[0290] (Comparative Example 2)

[0291] In preparing the binder composition, the aqueous dispersion of the particulate polymer was adjusted to pH 4 with ammonia. Otherwise, the process was the same as in Example 1 to prepare or manufacture the binder composition for the negative electrode, the slurry composition for the negative electrode, the negative electrode, the positive electrode, the spacer, and the lithium-ion secondary battery. The evaluation was then conducted in the same manner as in Example 1. The results are shown in Table 2.

[0292] (Comparative Example 3)

[0293] In preparing the binder composition for the negative electrode, the amounts of each monomer added in the first and second stage polymerizations were changed as follows, except that the process was the same as in Example 1, to prepare or manufacture the binder composition for the negative electrode, the slurry composition for the negative electrode, the negative electrode, the positive electrode, the spacer, and the lithium-ion secondary battery. Then, the evaluation was performed in the same manner as in Example 1. The results are shown in Table 2.

[0294] First aggregate: St 16.5 parts, BD 59.5 parts, MAA 1 part

[0295] Second aggregate: AN 10 parts, MMA 10 parts, MAA 3 parts

[0296] (Comparative Example 4)

[0297] In preparing the binder composition, the aqueous dispersion of the particulate polymer was adjusted to pH 10 with ammonia. Otherwise, the process was the same as in Example 1 to prepare or manufacture the binder composition for the negative electrode, the slurry composition for the negative electrode, the negative electrode, the positive electrode, the spacer, and the lithium-ion secondary battery. The evaluation was then conducted in the same manner as in Example 1. The results are shown in Table 2.

[0298] (Comparative Example 5)

[0299] In preparing the binder composition, the amounts of each monomer added in the first and second stage polymerization were varied as follows, and the pH of the aqueous dispersion of the particulate polymer was adjusted to 5 with ammonia. Otherwise, the process was the same as in Example 1 to prepare or manufacture the binder composition for the negative electrode, the slurry composition for the negative electrode, the negative electrode, the positive electrode, the spacer, and the lithium-ion secondary battery. The evaluation was then conducted in the same manner as in Example 1. The results are shown in Table 2.

[0300] First aggregate: St19 copies, BD67 copies, MAA1 copy

[0301] Second aggregate: AN 2 parts, MMA 2 parts, MAA 9 parts

[0302] (Comparative Example 6)

[0303] Using the binder composition for the negative electrode prepared as described below, except as in Example 1, a slurry composition for the negative electrode, a negative electrode, a positive electrode, a spacer, and a lithium-ion secondary battery were prepared or manufactured. Then, the evaluation was performed in the same manner as in Example 1. The results are shown in Table 2.

[0304] <Preparation of binder composition for negative electrode>

[0305] In a 5MPa pressure vessel A equipped with a stirrer, 22 parts of styrene (St) as an aromatic vinyl monomer, 70 parts of 1,3-butadiene (BD) as an aliphatic conjugated diene monomer, 4 parts of methacrylic acid (MAA) as an acidic monomer, 2 parts of acrylonitrile (AN) as a nitrile monomer, 2 parts of methyl methacrylate (MMA) as an olefinic unsaturated carboxylic acid ester monomer, 0.6 parts of alkyl diphenyl ether disulfonate as an emulsifier, 143 parts of deionized water, 0.1 parts of tert-dodecyl mercaptan as a chain transfer agent, and 0.3 parts of potassium persulfate as a polymerization initiator were added. After thorough stirring, the mixture was heated to 55°C to initiate polymerization and reacted for 10 hours. Next, the mixture was heated to 65°C and reacted for an additional 6 hours. Unreacted monomers were then removed by heated vacuum distillation to obtain an aqueous dispersion of particulate polymer. The resulting aqueous dispersion of particulate polymer was neutralized with ammonia water to adjust the pH to 7. Then, after cooling, 1 part (equivalent to the solid component) of Wingstay L dispersion as an antioxidant is added. After drying at 40°C for 2 hours on a polytetrafluoroethylene petri dish, the mixture is filtered through a stainless steel plain-woven mesh (mesh: 200, wire diameter: 0.05 mm, mesh size: 0.077 mm) to obtain a binder composition for the negative electrode.

[0306] (Comparative Example 7)

[0307] In preparing the binder composition for the negative electrode, the amounts of each monomer added in the first and second stage polymerizations were changed as follows, except that the process was the same as in Example 1, to prepare or manufacture the binder composition for the negative electrode, the slurry composition for the negative electrode, the negative electrode, the positive electrode, the spacer, and the lithium-ion secondary battery. Then, the evaluation was performed in the same manner as in Example 1. The results are shown in Table 2.

[0308] First aggregate: St18 copies, BD66 copies, MAA1 copy

[0309] Second aggregate: AN 10 parts, MMA 2 parts, MAA 3 parts

[0310] (Comparative Example 8)

[0311] In preparing the binder composition for the negative electrode, the amounts of each monomer added in the first and second stage polymerizations were changed as follows, except that the process was the same as in Example 1, to prepare or manufacture the binder composition for the negative electrode, the slurry composition for the negative electrode, the negative electrode, the positive electrode, the spacer, and the lithium-ion secondary battery. Then, the evaluation was performed in the same manner as in Example 1. The results are shown in Table 2.

[0312] First aggregate: St18 copies, BD66 copies, MAA1 copy

[0313] Second aggregate: AN 2 parts, MMA 10 parts, MAA 3 parts

[0314] Additionally, in Tables 1 and 2 shown below,

[0315] “St” represents a styrene unit.

[0316] “BD” represents the 1,3-butadiene unit.

[0317] "MAA" represents methacrylic acid unit.

[0318] “AN” represents an acrylonitrile unit.

[0319] “MMA” represents methyl methacrylate unit.

[0320] "Viscosity" refers to the viscosity at a solid content concentration of 30% by mass.

[0321] "Da / Db" represents the ratio of the average particle size Da of the particulate polymer determined by dynamic light scattering to the volume average particle size Db of the particulate polymer determined by laser diffraction scattering.

[0322] In addition, in Tables 1 and 2, “Da / Db” is represented by the value obtained by rounding the second digit of a few points.

[0323] [Table 1]

[0324]

[0325] [Table 2]

[0326]

[0327] As shown in Table 1, in Examples 1 to 9, which used binder compositions with a film amount below a specified value, it was possible to produce electrodes that suppressed the formation of pits and secondary batteries with reduced internal resistance and excellent cycle characteristics.

[0328] On the other hand, as shown in Table 2, in Comparative Examples 1-2 and 4-8, which used binder compositions with a film amount greater than the specified value, the formation of pits on the electrode surface could not be sufficiently suppressed, and the internal resistance of the secondary battery increased and the cycle characteristics decreased.

[0329] Furthermore, as shown in Table 2, in Comparative Example 3, which used an adhesive composition with a film amount greater than the specified value, the formation of pits on the electrode surface could not be sufficiently suppressed, and the cycle characteristics of the secondary battery were reduced.

[0330] Industrial availability

[0331] According to the present invention, it is possible to provide a secondary battery electrode that can suppress the formation of pits on the electrode surface, a secondary battery electrode binder composition that can reduce the internal resistance of the secondary battery and exhibit excellent cycle characteristics, and a secondary battery electrode slurry composition.

[0332] Furthermore, according to the present invention, an electrode for a secondary battery can be provided in which the formation of pits on the electrode surface is suppressed, the internal resistance of the secondary battery is reduced, and excellent cycle characteristics are achieved.

[0333] Moreover, according to the present invention, a secondary battery with reduced internal resistance and excellent cycle characteristics can be provided.

Claims

1. A binder composition for a secondary battery electrode, comprising a binder material, 10.0g of the mixture was injected into a 10cm diameter polytetrafluoroethylene (PTFE) culture dish. After standing at 40℃ for 2 hours, the film thickness was less than 1.3g. The mixture is a mixture in which the binder composition for the secondary battery electrode is adjusted with water to a solid component concentration of 30% by mass.

2. The binder composition for secondary battery electrodes according to claim 1, wherein, The adhesive material comprises a particulate polymer. The particulate polymer contains nitrile monomer units in a proportion of 1% to 9% by mass and contains olefinic unsaturated carboxylic acid ester monomer units in a proportion of 1% to 9% by mass.

3. The binder composition for secondary battery electrodes according to claim 2, wherein, The particulate polymer is a random copolymer.

4. The binder composition for secondary battery electrodes according to claim 2, wherein, When the average particle size of the particulate polymer determined by dynamic light scattering is taken as Da (nm) and the volume average particle size of the particulate polymer determined by laser diffraction scattering is taken as Db (nm), the ratio of Da to Db (Da / Db) is 1.1 or more and 2.0 or less.

5. The binder composition for secondary battery electrodes according to claim 1, wherein, The binder composition for the secondary battery electrode has a viscosity of 60 mPa·s or more and 3000 mPa·s or less when the solid component concentration is 30% by mass.

6. The binder composition for secondary battery electrodes according to claim 1, wherein, The binder composition for the secondary battery electrode also contains water, with a pH of 6 or higher and 10 or lower.

7. A slurry composition for a secondary battery electrode, comprising an electrode active material and a binder composition for a secondary battery electrode according to any one of claims 1 to 6.

8. An electrode for a secondary battery having an electrode composite material layer formed using the slurry composition for a secondary battery electrode according to claim 7.

9. A secondary battery having the electrode for a secondary battery as described in claim 8.

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