Hydrophilic polymer, its manufacturing method, and lithium secondary battery containing the hydrophilic polymer

Abstract

The present invention relates to a hydrophilic polymer and a method for producing the same. The hydrophilic polymer is characterized in that it is a copolymer of a conjugated diolefin, a monoolefin, and a hydrophilic monomer represented by formula I. In formula I, X1, X2, and X3 are each independently selected from a hydrogen atom or a linear or branched alkyl group having 1 to 4 carbon atoms. At least one of R1, R2, and R3 is a hydrophilic group, and the remaining are each independently selected from a hydrogen atom, an alkyl group or an alkoxy group having 1 to 4 carbon atoms. [Formula 1] TIFF2024529491000009.tif48170

Description

[Technical Field]

[0001] The present application relates to the technical field of lithium batteries, and more particularly to a hydrophilic polymer that can be used as a binder, a method for producing the same, and a lithium ion secondary battery containing the hydrophilic polymer. [Background technology]

[0002] With the rapid development of industries such as new energy vehicles, smartphones, and home appliances, market demand for lithium-ion batteries is increasing, which also places higher requirements on the adhesives used in electrode manufacturing.

[0003] Polyvinylidene fluoride (PVDF) has traditionally been widely used as an adhesive material in lithium-ion batteries due to its high dielectric constant and strong electrochemical corrosion resistance. However, PVDF's low adhesive strength and poor electrochemical stability at high temperatures make it difficult to provide stable cycle performance. Furthermore, when using PVDF as an adhesive material, organic dispersants such as N-methylpyrrolidone (NMP) are typically used as dispersants, which have drawbacks such as flammability, explosiveness, volatility, high toxicity, and high recovery costs. Therefore, it is extremely important to develop new water-based adhesives with excellent processability and adhesive properties. Summary of the Invention [Problem to be solved by the invention]

[0004] The present inventors have conducted extensive research to solve the above problems, and as a result have found that by copolymerizing a conjugated diolefin, a monoolefin, and a hydrophilic monomer having the structure shown in formula I below, an adhesive having high adhesive strength and almost no problems of lifting or roller sticking can be obtained, thereby completing the present invention. [Means for solving the problem]

[0005] That is, the present invention relates to a hydrophilic polymer obtained by copolymerizing a conjugated diolefin, a monoolefin, and a hydrophilic monomer having the structure shown in formula I below: [ka] In the formula, X1, X2, and X3 are each independently selected from a hydrogen atom or a linear or branched alkyl group having 1 to 4 carbon atoms, and R1, R2, and R3 are each independently selected from a group consisting of at least one hydrophilic group that may be the same or different, and the rest being hydrogen atoms, linear or branched alkyl groups, or alkoxy groups selected from a group consisting of 1 to 4 carbon atoms. This provides a hydrophilic monomer-modified copolymer that has improved hydrophilicity and adhesive properties, enhanced affinity with materials such as graphite, and improved problems of adhesive lifting and roller sticking.

[0006] In a preferred embodiment of the hydrophilic polymer of the present invention, the hydrophilic polymer is a random copolymer, and the conjugated diolefin is one or more of 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, 2,4-hexadiene, 1,3-cyclohexadiene, and 2-chloro-1,3-butadiene, and / or the monoolefin is an aromatic monovinyl compound, preferably one or more of styrene, α-methylstyrene, pt-butylstyrene, butoxystyrene, vinyltoluene, chlorostyrene, and vinylnaphthalene, thereby further improving the hydrophilicity and adhesiveness of the hydrophilic polymer.

[0007] In a preferred embodiment of the hydrophilic polymer of the present invention, the hydrophilic group is at least one selected from the group consisting of a hydroxyl group, an amino group, and a carboxyl group, and is preferably a hydroxyl group, which can further improve the hydrophilicity and adhesiveness of the hydrophilic polymer.

[0008] In a preferred embodiment of the hydrophilic polymer of the present invention, at least two of R1, R2, and R3 are hydrophilic groups, and the remaining R1, R2, and R3 are each independently selected from a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, thereby further improving the hydrophilicity and adhesiveness of the hydrophilic polymer.

[0009] In a preferred embodiment of the hydrophilic polymer of the present invention, X1 and X2 are hydrogen atoms, and X3 is selected from alkyl groups having 1 to 4 carbon atoms.

[0010] In a preferred embodiment of the hydrophilic polymer of the present invention, its number average molecular weight Mn is 12×10 4 ~17×10 4 is.

[0011] In a preferred embodiment of the hydrophilic polymer of the present invention, the ratio of parts by mass of the conjugated diolefin, the monoolefin, and the hydrophilic monomer in the hydrophilic polymer is 10 to 90:90 to 10:1 to 6. This makes it possible to produce a hydrophilic polymer that has stronger adhesive strength and does not gel.

[0012] The present invention further relates to a method for preparing a hydrophilic polymer, comprising the steps of polymerizing a conjugated diolefin, a monoolefin, and a hydrophilic monomer of formula I to obtain said hydrophilic polymer, [ka] In the formula, X1, X2, and X3 are each independently selected from a hydrogen atom or a linear or branched alkyl group having 1 to 4 carbon atoms, at least one of R1, R2, and R3 is a hydrophilic group, and the rest are each independently selected from a hydrogen atom or an alkyl or alkoxy group having 1 to 4 carbon atoms.

[0013] In a preferred embodiment of the method for producing a hydrophilic polymer of the present invention, the hydrophilic polymer is a random copolymer, and the conjugated diolefin is one or more of 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, 2,4-hexadiene, 1,3-cyclohexadiene, and 2-chloro-1,3-butadiene and / or a monoolefin selected from aromatic monovinyl compounds, preferably one or more of styrene, α-methylstyrene, pt-butylstyrene, butoxystyrene, vinyltoluene, chlorostyrene, and vinylnaphthalene, thereby further improving the hydrophilicity and adhesiveness of the hydrophilic polymer.

[0014] In a preferred embodiment of the hydrophilic polymer of the present invention, the hydrophilic group is at least one selected from the group consisting of a hydroxyl group, an amino group, and a carboxyl group, and is preferably a hydroxyl group, which can further improve the hydrophilicity and adhesiveness of the hydrophilic polymer.

[0015] In a preferred embodiment of the method for producing a hydrophilic polymer of the present invention, at least two of R1, R2, and R3 are hydrophilic groups, and the remaining groups are each independently selected from a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, thereby further improving the hydrophilicity and adhesiveness of the hydrophilic polymer.

[0016] In a preferred embodiment of the hydrophilic polymer of the present invention, X1 and X2 are hydrogen atoms, and X3 is selected from alkyl groups having 1 to 4 carbon atoms.

[0017] In a preferred embodiment of the method for producing a hydrophilic polymer of the present invention, the number average molecular weight Mn is 12×10 4 ~17×10 4 is.

[0018] In a preferred embodiment of the method for producing a hydrophilic polymer of the present invention, the ratio of parts by mass of the conjugated diolefin, monoolefin, and hydrophilic monomer in the hydrophilic polymer is 10 to 90:90 to 10:1 to 6. This makes it possible to produce a hydrophilic polymer that has stronger adhesive strength and does not gel.

[0019] The present invention further relates to an electrode active material slurry, which contains an electrode active material, a dispersion medium, and the above-mentioned hydrophilic polymer as a binder. Optionally, the electrode active material slurry is a negative electrode active material slurry. This prevents the binder from floating, thereby enabling the preparation of an active material layer with reduced roller adhesion problems.

[0020] The present invention also relates to a lithium ion secondary battery, which includes a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte, and the negative electrode sheet includes a negative electrode membrane layer prepared from the electrode active material slurry, thereby providing a lithium ion secondary battery with a longer life.

[0021] The present invention relates to a battery pack including the above-mentioned lithium ion secondary battery, which makes it possible to obtain a battery pack with a longer life.

[0022] The present invention further relates to an electrical device including at least one of the above-mentioned lithium ion secondary batteries and battery packs, which can provide an electrical device with a longer lifespan. [Brief explanation of the drawings]

[0023] [Figure 1] 1 is a schematic diagram of a secondary battery according to an embodiment of the present application; [Figure 2] FIG. 2 is an exploded view of the secondary battery according to the embodiment of the present invention shown in FIG. [Figure 3] 1 is a schematic diagram of a battery pack according to an embodiment of the present application. [Figure 4] FIG. 4 is an exploded view of the battery pack according to the embodiment of the present application shown in FIG. 3. [Figure 5]1 is a schematic diagram of an electrical device that uses a secondary battery as a power source according to an embodiment of the present application. DETAILED DESCRIPTION OF THE INVENTION

[0024] The present application will now be described in detail with appropriate reference to the drawings. However, unnecessary detailed description may be omitted. For example, detailed description of known matters or redundant description of actually identical structures may be omitted. This is to avoid unnecessary redundancy in the following description and to facilitate understanding by those skilled in the art. Note that the drawings and the following description are provided to enable those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0025] The "ranges" disclosed herein are defined in the form of lower and upper limits. A given range is defined by selecting one lower limit and one upper limit, and the selected lower and upper limits define the boundaries of that particular range. Such defined ranges may be inclusive or exclusive, and may be arbitrarily combined; i.e., any lower limit may be combined with any upper limit to form a single range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, it is understood that ranges of 60-110 and 80-120 are also contemplated. Furthermore, if minimum range values ​​1 and 2 and maximum range values ​​3, 4, and 5 are listed, the following ranges are also contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. Unless otherwise specified, the numerical range "ab" herein refers to a shorthand notation for any combination of real numbers from a to b, where both a and b are real numbers. For example, the numerical range "0-5" refers to all real numbers between "0-5" listed herein, and "0-5" is simply a shorthand notation for combinations of these numbers. Also, when a parameter refers to an integer ≧2, it corresponds to the parameter being an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0026] Unless otherwise specified, all embodiments and preferred embodiments in this application can be combined with each other to form new technical solutions.

[0027] Unless otherwise specified, all technical features and preferred technical features of the present application can be combined with each other to form new technical solutions.

[0028] Unless otherwise specified, all steps herein may be performed sequentially or randomly, preferably sequentially. For example, a description of a method including steps (a) and (b) indicates that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, a description of a method mentioned above that may include step (c) indicates that step (c) can be added to the method in any order, e.g., the method may include steps (a), (b), and (c), or may include steps (a), (c), and (b), or may include steps (c), (a), and (b).

[0029] Unless otherwise specified, the terms "comprise" and "include" used in this application may be open-ended or exclusive. For example, the terms "comprise" and "include" may further comprise or include other components not listed, or may comprise or include only the listed components.

[0030] Unless otherwise specified, in this application, the term "or" is inclusive. For example, the words "A or B" indicate "A, B, or both A and B." More specifically, any of the following conditions satisfy the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) but B is true (or exists); or both A and B are true (or exist).

[0031] In the present invention, unless otherwise specified, "%" generally means "% by mass" and "parts" generally means "parts by mass".

[0032] Currently, the mainstream water-based adhesive is a styrene-butadiene copolymer (hereinafter simply referred to as styrene butadiene rubber or SBR) emulsion, which is used together with the thickener carboxymethyl cellulose (CMC) to create a slurry and used to bond negative electrode materials such as graphite in lithium batteries.

[0033] In this slurry system, CMC is adsorbed onto the surface of hydrophobic graphite particles through the main chain that is not modified with hydrophobic carboxyl groups, and the graphite particles with CMC adsorbed through the hydrophilic carboxyl groups are stably suspended in water. The good elasticity of SBR and the good dispersing effect of CMC are utilized to achieve adhesion of the negative electrode material for lithium batteries.

[0034] However, because SBR is water-repellent, it can easily become incompatible with graphite slurries containing dispersed CMC. When using water-based CMC-SBR adhesives, the SBR can easily float up while the slurry is left to stand during the negative electrode sheet manufacturing process. Furthermore, the scattering of visible light by the SBR particles, especially blue light with a short wavelength, can cause the slurry to "float up."

[0035] Furthermore, the electrode sheet, for example, the negative electrode sheet, is heated unevenly from top to bottom during the coating and drying process, which further generates convection and capillary phenomena inside the electrode sheet, making it easier for the SBR to rise to the surface of the electrode sheet as moisture moves. Furthermore, the distribution of the adhesive in the longitudinal direction of the electrode sheet after drying becomes uneven, reducing the adhesive strength between the active materials and between the active materials and the current collector. This causes the surface of the negative electrode, which has been pressed by the roll, to stick to the roll, and in severe cases, causing film detachment, ultimately resulting in reduced battery performance.

[0036] The hydrophilic polymer of the present invention is obtained by radical emulsion copolymerization of a conjugated diolefin, a monoolefin, and a hydrophilic monomer represented by the following formula I: [ka] In the formula, X1, X2, and X3 are each independently selected from a hydrogen atom or a linear or branched alkyl group having 1 to 4 carbon atoms, at least one of R1, R2, and R3 is a hydrophilic group, and the rest are each independently selected from a hydrogen atom or an alkyl or alkoxy group having 1 to 4 carbon atoms.

[0037] In the hydrophilic copolymer, the ratio of parts by mass of the conjugated diolefin, the monoolefin and the hydrophilic monomer is 10-90:90-10:1-6, more preferably 10-30:90-70:3-6.

[0038] Other monomers copolymerizable with the conjugated diolefin, monoolefin, and hydrophilic monomer may be copolymerized within the range that does not affect the effects of the present invention.

[0039] Conjugated Diolefins Examples of conjugated diolefins include conjugated diolefins having 4 or more carbon atoms, such as 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, 2,4-hexadiene, 1,3-cyclohexadiene, and 2-chloro-1,3-butadiene. These conjugated diolefins can be used alone or in combination of two or more. From the viewpoint of increasing the peel strength of the electrode, 1,3-butadiene and isoprene are preferred. From the viewpoint of increasing the thermal stability of the polymer and further increasing the peel strength and moisture resistance of the electrode, 1,3-butadiene is more preferred.

[0040] Furthermore, within the scope of the present invention, the conjugated diolefin monomer may have a substituent commonly used in the art. Examples of such a substituent include linear or branched C 1-6Examples of the halogenated alkyl group include alkyl groups or halogenated alkyl groups, specifically methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, 1-methylbutyl, 2-methylbutyl, 3-methylbutyl, 1,1-dimethylpropyl, 1,2-dimethylpropyl, 2,2-dimethylpropyl, n-pentyl, 1-methylpentyl, 2-methylpentyl, 3-methylpentyl, 4-methylpentyl, 1,1-dimethylbutyl, 1,2-dimethylbutyl, 1,3-dimethylbutyl, 1,4-dimethylbutyl, 2,2-dimethylbutyl, 2,3-dimethylbutyl, 3,3-dimethylbutyl, and n-hexyl. The halogenated alkyl group may also include the above-mentioned linear or branched C 1-6 Examples include groups in which one or more hydrogen atoms in an alkyl group are substituted with fluorine, chlorine, bromine, or iodine.

[0041] Monoolefin Examples of monoolefins include compounds having one unsaturated ethylene bond, such as aromatic monovinyl group compounds, olefins such as ethylene and propylene, acrylic compounds such as (meth)acrylic acid, methyl (meth)acrylate, and butyl (meth)acrylate, halogenated olefins such as fluoroethylene and vinyl chloride, unsaturated fatty acids such as oleic acid, ethylene acetate, and acrylonitrile. Preferred are aromatic monovinyl group compounds.

[0042] Examples of aromatic monovinyl group compounds include vinyl derivatives of monocyclic, polycyclic or condensed ring aromatic compounds such as vinyl derivatives of benzene, biphenyl, naphthalene, anthracene, phenanthrene, chrysene, perylene and benzopyrene. In addition, within the scope of the present invention, the vinyl derivatives of the above aromatic compounds may be C 1-6 Alkyl group, C 1-6The monoolefin may have various substituents such as an alkoxy group or a halogen. Examples of such monoolefins include styrene, α-methylstyrene, pt-butylstyrene, butoxystyrene, vinyltoluene, chlorostyrene, and vinylnaphthalene. Styrene is preferred from the viewpoints of improving the thermal stability of the particulate polymer and improving the peel strength and moisture resistance of the electrode. These monoolefins may be used alone or in combination of two or more, and it is preferred to use one type alone.

[0043] Hydrophilic Monomers The hydrophilic monomer of the present invention is a hydrophilic monomer represented by the following formula I: [ka] In the formula, X1, X2, and X3 are each independently selected from a hydrogen atom or a linear or branched alkyl group having 1 to 4 carbon atoms, at least one of R1, R2, and R3 is a hydrophilic group, and the rest are each independently selected from a hydrogen atom or an alkyl or alkoxy group having 1 to 4 carbon atoms.

[0044] Among the hydrophilic monomers, the hydrophilic group may be a hydrophilic group commonly used in this field that readily forms hydrogen bonds, such as a hydroxyl group, an amino group, a carboxyl group, a sulfonic acid group, or a phosphate group. One or more of these hydrophilic groups may be present. From the viewpoints of improving the viscosity stability of the slurry composition, improving the peel strength of the electrode, and providing resistance to adverse environments such as acid, alkali, high temperature, and high humidity, the hydrophilic group is preferably a hydroxyl group, an amino group, or a carboxyl group, more preferably a hydroxyl group or an amino group, and particularly preferably a hydroxyl group.

[0045] The hydrophilic monomer may have only one group selected from the above hydrophilic groups, or may have two or more groups selected from the above hydrophilic groups. From the viewpoints of improving the viscosity stability of the slurry composition, improving the peel strength of the electrode, and resistance to adverse environments such as acid, alkali, high temperature, and high humidity, it is preferable that the hydrophilic monomer has two hydrophilic groups, and it is more preferable that the two hydrophilic groups are located at the ortho positions of each other on the benzene ring.

[0046] Furthermore, when the total amount of repeating units from the monoolefin and conjugated diolefin is 100 parts by mass, the amount of repeating units of the hydrophilic monomer added is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and preferably 6 parts by mass or less, more preferably 4 parts by mass or less. When the amount of repeating units of the hydrophilic monomer added is within the above range, the stability of the slurry composition is improved, the coating density is increased, and floating of the binder is suppressed. Furthermore, the problem of roller adhesion when the electrode sheet is roll-pressed is suppressed, and the operability of the electrode of the electrode composite material layer can be further improved.

[0047] In the present invention, conjugated diolefin, monoolefin, and hydrophilic monomer are copolymerized to structurally improve the hydrophilicity of the binder, so that the binder has a stronger affinity with the active material, fundamentally avoiding the problems of lifting during drying and roller adhesion during roll pressing.

[0048] Although the mechanism by which a hydrophilic polymer with such a structure improves an adhesive system is unknown, the present inventors have hypothesized that it is due to the action of covalent and non-covalent bonds between the hydrophilic group and aromatic ring in the hydrophilic polymer of the present invention. Specifically, the hydrophilic polymer monomer of the present invention has an aromatic ring structure and at least one hydrophilic substituent, and thus has the following non-covalent bond actions (i), (ii), (iii) and covalent bond action (iv). (i) Hydrogen bonding: Among hydrophilic groups such as hydroxyl, amino, carboxyl, sulfonic acid, and phosphate groups, non-hydrogen elements such as O, N, P, and S have strong polarity themselves, making these hydrophilic groups more likely to form hydrogen bonds with other polar groups. Furthermore, these hydrophilic groups also have lone electron pairs, allowing them to form hydrogen bonds with the hydrogen atoms of other active groups. (ii) Coordination: The non-hydrogen elements present in the hydrophilic group give the hydrophilic group weak acidity / weak basicity and strong reducing properties, and have strong metal coordination ability. 3+ , Cu 2+ , V 3+ These metals readily form chelates with metal ions such as , thereby realizing a phase transition from a fluid to a solid, and further realizing hardening of the adhesive. (iii) π-π stacking effect: The hydrophilic polymer of the present invention has a benzene ring and is aromatic, and the valence electrons thereof are involved in bond formation in the form of SP2 hybrid orbitals, and are prone to form π-π non-covalent bond electronic interactions with other aromatic ring groups, such as aromatic ring groups in monoolefins, and SP2 hybrid electrons in active materials such as graphite. (iv) Covalent bonding: Among the hydrophilic groups R1, R2, and R3, the hydrophilic groups all have high activity, are easily oxidized, contribute to polymerization reactions, and are prone to reactions such as Schiff base reaction and Michael addition with substances containing amino groups or mercapto groups, thereby forming stable covalent bonds and strengthening the adhesive properties of the adhesive.

[0049] The present inventors have presumed that the use of a copolymer of a hydrophilic monomer, a conjugated diolefin, and a monoolefin in the present invention makes it possible to utilize the effects of (i), (ii), (iii), and (iv) above, structurally strengthen the affinity between the binder and the active material, and fundamentally avoid the problems of binder lifting during drying and roller adhesion during roll pressing.

[0050] It is particularly preferred that the hydrophilic groups R1, R2, and R3 are two adjacent hydroxyl groups (-OH), i.e., the hydrophilic monomer has a catechol structure. The phenolic hydroxyl groups have very strong polarity and are therefore prone to hydrogen bond formation, have strong reducing properties, and at the same time, are weakly acidic and have very strong metal coordination ability. In addition, the valence electrons of the oxygen atoms therein are prone to bond formation in the SP2 hybrid orbital, and are prone to π-π non-covalent bond electronic interactions with other aromatic ring groups. The phenolic hydroxyl groups themselves are easily oxidized, producing highly chemically active p-benzoquinone, which contributes to polymerization reactions and is prone to reactions such as Schiff base reaction and Michael addition with substances containing amino groups or mercapto groups, thereby easily forming stable covalent bonds and curing the adhesive, making this particularly preferred.

[0051] During the synthesis process, hydrophilic monomers, conjugated diolefins, and monoolefins are copolymerized to increase the hydrophilicity of the copolymer itself, improving the adhesion between the active material and the current collector, thereby alleviating the problem of the electrode sheet lifting during the drying process.

[0052] Other Monomers The hydrophilic polymer of the present invention may contain other monomers without affecting its properties. The other monomers are not particularly limited as long as they are copolymerizable with the conjugated diolefin, monoolefin, and hydrophilic monomer. The other monomers can be polymerized together with the conjugated diolefin, monoolefin, and hydrophilic monomer to obtain a hydrophilic polymer, and after the conjugated diolefin, monoolefin, and hydrophilic monomer are polymerized into a hydrophilic polymer, they can be further copolymerized or graft-polymerized with the polymer.

[0053] Method for producing hydrophilic polymers Another aspect of the present invention relates to a method for producing a hydrophilic polymer, in which the above-mentioned conjugated diolefin, monoolefin, and hydrophilic monomer are dispersed in a dispersion medium, and then an emulsifier and a molecular weight modifier are added as necessary to form a mixed liquid, and then a copolymerization reaction is carried out in the presence of an initiator to obtain a hydrophilic polymer or a dispersion thereof.

[0054] The method for polymerizing the conjugated diolefin, monoolefin, and hydrophilic monomer is not particularly limited, and examples thereof include radical polymerization, active radical polymerization, cationic polymerization, and anionic polymerization from the viewpoint of the active group during polymerization, and suspension polymerization, emulsion polymerization, and solution polymerization from the viewpoint of the type of polymerization system. From the viewpoint of simplicity of polymerization and post-treatment, radical polymerization is preferred, and radical emulsion polymerization is more preferred.

[0055] dispersion medium The dispersion medium used in the present invention may be any dispersion medium commonly used in copolymerization reactions, such as water, alcohols, esters, ethers, ketones, alkanes, alkyl halides, amides, or mixtures thereof. From the viewpoint of environmental protection, water is preferred.

[0056] Radical Initiators The initiator used in the present invention can be any of various water-soluble or oil-soluble radical initiators commonly used in radical polymerization. Specific examples include azo compounds such as azobisisobutyronitrile, azodiisoheptanitrile, azobisisobutyrophosphate dimethyl initiator, and azodiisobutyrimidine hydrochloride; inorganic peroxides and persulfates such as hydrogen peroxide, ammonium persulfate, sodium persulfate, and potassium persulfate; and peroxides such as benzoyl peroxide, cumene peroxide, t-butyl benzoyl peroxide, and butanone peroxide.

[0057] The amount of the radical initiator added is not particularly limited and can be appropriately added depending on the amount of the hydrophilic polymer, and is preferably 0.1 to 2%, more preferably 0.15 to 1%, when the total amount of monomers constituting the structural units of the hydrophilic polymer is taken as 100% by mass. By appropriately adjusting the amount of initiator used, the molecular weight of the hydrophilic polymer can be controlled.

[0058] In the hydrophilic polymer of the present invention, in order to realize viscosity stability of the slurry composition and improvement of the peel strength of the electrode, taking into consideration the ease of dispersion and application of the slurry composition, the number average molecular weight of the hydrophilic polymer of the present invention is preferably 8 × 10 4 ~30×10 4 and more preferably 12 × 10 4 ~17×10 4 The molecular weight is the molecular weight converted into polystyrene as measured by gel permeation chromatography (GPC).

[0059] emulsifier In the process of producing the hydrophilic polymer of the present invention, an emulsifier or the like may be added as needed.

[0060] The emulsifier used in the present invention may be an emulsifier commonly used in radical emulsion copolymerization, such as an anionic emulsifier, a cationic emulsifier, a nonionic emulsifier, or an amphoteric emulsifier.

[0061] Examples of anionic emulsifiers include carboxylate (soap)-type emulsifiers such as sodium oleate, potassium oleate, sodium stearate, potassium stearate, sodium rosinate, sodium laurate, potassium laurate, sodium naphthenate, and rosin oil soap; sulfonate-type emulsifiers such as alkylbenzenesulfonates, α-olefinsulfonates, alkylsulfonates, α-sulfomonocarboxylic acid esters, fatty acid sulfonyl alkyl esters, succinate ester sulfonates, alkylnaphthalenesulfonates, petroleum sulfonates, lignin sulfonates, and alkylglyceryl ether sulfonates; sulfate ester-type emulsifiers such as lauryl sulfates, alkyl sulfates, and allyl polyoxyethylene ether sulfates; and phosphate ester-type emulsifiers such as alkyl phosphate mono- and diester salts, aliphatic alcohol polyoxyethylene ether phosphate monobisester salts, and alkylphenol polyoxyethylene ether phosphate mono- and diester salts.

[0062] Cationic emulsifiers include alkylamine salts and quaternary ammonium salts such as lauryl ammonium chloride, cetyltrimethylammonium bromide, cetylpyridinium bromide, and the like.

[0063] Examples of nonionic emulsifiers include nonionic emulsifiers having an ether group, an ester group, or an amide group in the molecule, and heterocyclic emulsifiers. Specific examples include diol- or polyol-type nonionic emulsifiers such as ethylene oxide, propylene oxide, block copolymers of ethylene oxide and propylene oxide, and polyvinyl alcohol.

[0064] Examples of amphoteric emulsifiers include various amino acid and betaine type amphoteric emulsifiers.

[0065] The amount of the emulsifier added is not particularly limited and can be appropriately added depending on the amount of the hydrophilic polymer. When the total amount of the monomers of the structural units constituting the hydrophilic polymer is taken as 100% by mass, the amount is preferably 0.2 to 2%, and more preferably 0.2 to 0.5%.

[0066] Molecular Weight Regulator In the process of producing the hydrophilic polymer of the present invention, a molecular weight modifier or the like may be added as needed.

[0067] In the hydrophilic polymer of the present invention, a molecular weight modifier or the like may be added as necessary to adjust the molecular weight of the copolymer. The molecular weight modifier used in the present invention may be an aliphatic thiol, xanthogen acid disulfide, polyhydric phenol, or the like that is commonly used in radical emulsion copolymerization, and specific examples thereof include lauryl mercaptan, lauryl mercaptan acetate, dilauryl mercaptan oxalate ester, diisopropyl xanthogen disulfide ester, phenol, eugenol, and the like.

[0068] The amount of the molecular weight modifier added is not particularly limited and can be appropriately added depending on the target molecular weight of the hydrophilic polymer, and is preferably 0.1 to 1%, more preferably 0.1 to 0.5%, when the total amount of monomers constituting the structural units of the hydrophilic polymer is taken as 100% by mass. By appropriately adjusting the amount of the molecular weight modifier used, the molecular weight of the hydrophilic polymer can be controlled.

[0069] The emulsification method used in copolymerizing the conjugated diolefin, monoolefin, and hydrophilic monomer is not particularly limited, and any emulsification method commonly used in this field can be used. For example, various known emulsifying dispersers can be used as the emulsifying device, and a specific example is the IKA-LTRA-TURRAX. Furthermore, the conditions for the emulsification operation using the emulsifying disperser, such as the processing temperature and processing time, are not particularly limited, and can be selected depending on the type of emulsifier and radical initiator, and can be appropriately selected to achieve the desired dispersion state.

[0070] In the above polymerization and emulsification, the types and amounts of additives such as emulsifiers, initiators, dispersion media, and molecular weight modifiers are shown. However, it should be understood by those skilled in the art that the types and amounts of additives such as emulsifiers, dispersion media, initiators, and molecular weight modifiers used above are commonly used and can be appropriately adjusted depending on the polymerization method, etc.

[0071] In the present invention, the particle size of the hydrophilic polymer particles obtained after copolymerization is 80 to 400 nm, preferably 100 to 200 nm. The smaller the particle size of the hydrophilic polymer particles, the more contact points there are between the adhesive and the active material, thereby increasing the adhesive strength. However, if the particle size is too small, the particles tend to migrate during drying, causing problems with lifting. In turn, if the particle size is too small, the dynamic performance of the lithium-ion secondary battery is affected. By having the hydrophilic polymer particles have the above particle size, lifting can be suppressed and good adhesive strength can be maintained.

[0072] In this specification, the particle size of the hydrophilic polymer particles obtained after copolymerization is a particle size measured by laser diffraction.

[0073] To improve the viscosity stability of the slurry composition and the peel strength of the electrode, and to prevent the slurry from floating due to insufficient polymerization and the resulting adhesive floating, the copolymerization of the present invention is preferably carried out at a low temperature and under pressure at a low rotational speed. For example, copolymerization at a temperature of 20 to 100°C, preferably 70 to 95°C, under a pressure of 0.1 to 2.0 MPa, preferably 0.6 to 1.0 MPa, and at a rotational speed of 100 to 250 rpm, preferably 150 to 200 rpm, can produce hydrophilic polymer particles with a particle size within the above range, which is particularly suitable for preparing a slurry for producing an electrode sheet for a lithium-ion battery.

[0074] The solid content of the dispersion thus obtained is 30 to 70%, preferably 40 to 60%. If the solid content is too low, the production equipment becomes heavy and production efficiency decreases, while if the solid content is too high, stirring may become uneven.

[0075] Furthermore, in order to improve the viscosity stability of the slurry composition and the peel strength of the electrode, and to avoid blue floating of the slurry and the resulting floating of the adhesive due to insufficient polymerization, the pH value of the dispersion in the copolymerization of the present invention is preferably controlled to 6 to 9. The pH value can be controlled by using an acid or alkali commonly used in this field, preferably a weak acid or alkali, such as acetic acid, hydrochloric acid, or sulfuric acid, or an alkali such as aqueous ammonia, sodium hydroxide, potassium hydroxide, or diethanolamine.

[0076] Active material slurry The hydrophilic polymer of the present invention can be dispersed in a dispersion medium together with an electrode active material and other materials added as needed to produce an active material slurry composition.

[0077] The electrode active material is not particularly limited, and various active materials contained in the formed electrode sheet described below can be used.

[0078] Negative electrode sheet The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, the negative electrode film layer including a negative electrode active material.

[0079] For example, the negative electrode current collector has two surfaces opposing each other in the thickness direction thereof, and the negative electrode film layer is provided on either one or both of the two opposing surfaces of the negative electrode current collector.

[0080] In some embodiments, the negative electrode current collector may be a metal foil sheet or a composite current collector. For example, copper foil may be used as the metal foil sheet. The composite current collector may include a polymer substrate layer and a metal layer formed on at least one surface of the polymer substrate layer. The composite current collector may be formed by forming a metal material (such as copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, or silver alloy) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), or polyethylene (PE)).

[0081] In some embodiments, the negative electrode active material may be a negative electrode active material for batteries known in the art. For example, the negative electrode active material may include at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based material may be selected from at least one of silicon elemental, silicon oxide, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of tin elemental, stannate compounds, and tin alloys. However, the present application is not limited to these materials, and other conventional materials usable as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination.

[0082] In some embodiments, the negative electrode membrane layer further comprises a binder, wherein the binder comprises the hydrophilic polymer of the present invention.

[0083] During the polymerization process, a hydrophilic polymer is obtained by copolymerizing a hydrophilic monomer, a conjugated diolefin, and a monoolefin. When this hydrophilic polymer is used as an adhesive, the hydrophilicity of the adhesive is significantly increased, which can reduce the adhesive floating to the surface due to water evaporation during drying. The resulting adhesive has a very strong adhesive force due to its structure, which increases the adhesive strength between the active material and the electrode sheet.

[0084] In some embodiments, the negative electrode film layer preferably further comprises a conductive agent, which may be selected from the group consisting of superconducting carbon, acetylene black, carbon black, cochin black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0085] In some embodiments, the negative electrode membrane layer preferably further comprises other auxiliary agents such as a thickener (eg, carboxymethylcellulose sodium (CMC-Na)).

[0086] In some embodiments, the negative electrode sheet can be manufactured as follows: the components for manufacturing the negative electrode sheet, such as the negative electrode active material, conductive agent, binder, and any other components, are dispersed in a dispersion medium (e.g., deionized water) to form a negative electrode slurry, which is then coated onto a negative electrode current collector, followed by processes such as drying and cold pressing, to obtain a negative electrode sheet.

[0087] Positive electrode sheet

[0088] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector, the positive electrode film layer including a positive electrode active material.

[0089] For example, the positive electrode current collector has two surfaces facing each other in the thickness direction thereof, and the positive electrode film layer is provided on one or both of the two facing surfaces of the positive electrode current collector.

[0090] In some embodiments, the positive electrode current collector may be a metal foil sheet or a composite current collector. For example, aluminum foil may be used as the metal foil sheet. The composite current collector includes a polymer substrate layer and a metal layer formed on at least one surface of the polymer substrate layer. The composite current collector may be formed by forming a metal material (such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, or silver alloy) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), or polyethylene (PE)).

[0091] In some embodiments, the positive electrode active material may be a battery positive electrode active material known in the art. For example, the positive electrode active material may include at least one of an olivine-structured lithium-containing phosphate, a lithium transition metal oxide, and a modified compound thereof. The present application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials in batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include cobalt-lithium oxide (e.g., LiCoO), lithium nickel oxide (e.g., LiNiO), lithium manganese oxide (e.g., LiMnO, LiMnO), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, and lithium nickel cobalt manganese oxide (e.g., LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM 333 (can also be abbreviated as LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM 523 (can also be abbreviated as LiNi 0.5Co 0.25 Mn 0.25 O2(NCM 211 (can also be abbreviated as LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM 622 (can also be abbreviated as LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM 811 ), lithium nickel cobalt aluminum oxide (e.g., LiNi 0.85 Co 0.15 Al 0.05 O2) and modified compounds thereof, etc. Examples of the lithium-containing phosphate having an olivine structure include, but are not limited to, at least one of lithium iron phosphate (e.g., LiFePO4 (which can also be abbreviated as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (e.g., LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and a composite material of lithium manganese iron phosphate and carbon.

[0092] In some embodiments, the positive electrode membrane layer further includes a binder, which may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorinated acrylate resin, and may include the hydrophilic polymer of the present invention.

[0093] In some embodiments, the positive electrode membrane layer further comprises a conductive agent, for example, the conductive agent can include at least one of superconducting carbon, acetylene black, carbon black, cochin black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0094] In some embodiments, the positive electrode sheet can be manufactured as follows: the components for manufacturing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder, and any other components, are dispersed in a dispersion medium to form a positive electrode slurry, and the positive electrode slurry is applied to a positive electrode current collector. After undergoing steps such as drying and cold pressing, the positive electrode sheet can be obtained.

[0095] electrolyte The electrolyte serves to conduct ions between the positive electrode sheet and the negative electrode sheet. The present application is not specifically limited to the type of electrolyte, and it can be selected as needed. For example, the electrolyte can be liquid, gelled, or all solid.

[0096] In some embodiments, the electrolyte may be an electrolytic solution, which includes an electrolyte salt and a solvent.

[0097] In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium difluorosulfonylimide, lithium bistrifluoromethanesulfonylimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium bis(oxalato)borate, lithium difluorodisoxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0098] In some embodiments, the solvent can be chosen from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0099] In some embodiments, the electrolyte solution further includes an additive. For example, the additive may include a negative electrode film-forming additive, a positive electrode film-forming additive, or an additive that can improve certain battery performance, such as an additive that improves the overcharge performance of the battery or an additive that improves the high-temperature or low-temperature performance of the battery.

[0100] Separator In some embodiments, the secondary battery further includes a separator. The present application is not particularly limited to the type of separator, and any known porous separator having good chemical and mechanical stability can be selected.

[0101] In some embodiments, the separator may be made of at least one material selected from the group consisting of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator is not particularly limited and may be a single-layer thin film or a multi-layer composite thin film. When the separator is a multi-layer composite thin film, the materials of each layer are not particularly limited and may be the same or different.

[0102] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be manufactured into an electrode assembly by a winding process or a lamination process.

[0103] In some embodiments, the secondary battery may include a housing, which can be used to seal the electrode assembly and electrolyte.

[0104] In some embodiments, the exterior of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the exterior of the secondary battery may be a soft bag, such as a pouch soft bag. The soft bag may be made of plastic, such as polypropylene, polybutylene terephthalate, or polybutylene succinate.

[0105] The present application is not particularly limited to the shape of the secondary battery, and it may be cylindrical, rectangular, or any other shape. For example, Fig. 1 shows an example of a secondary battery 5 having a rectangular structure.

[0106] In some embodiments, referring to FIG. 2 , the exterior may include a housing 51 and a cover plate 53. The housing 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and side plates may surround the housing 51 to form a storage chamber. The housing 51 may have an opening communicating with the storage chamber, and the cover plate 53 may cover the opening to close the storage chamber. The positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly 52 by a winding process or a lamination process. The electrode assembly 52 is sealed in the storage chamber. An electrolyte is impregnated into the electrode assembly 52. ​​The secondary battery 5 may include one or more electrode assemblies 52, and this can be selected by those skilled in the art according to specific practical needs.

[0107] In some embodiments, one or more secondary batteries 5 may be assembled into a battery module 4, which may then be assembled into the battery pack 1. The number of battery modules 4 included in the battery pack 1 may be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack 1.

[0108] The present application also provides an electric device including at least one of the secondary battery, battery module, or battery pack according to the present application. The secondary battery, battery module, or battery pack can be used as a power source for the electric device and also as an energy storage unit for the electric device. The electric device includes, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), trains, ships, satellites, and energy storage systems.

[0109] The electrical device can be selected from a secondary battery, a battery module, or a battery pack depending on the usage requirements.

[0110] 3 and 4 show an example of the battery pack 1. Referring to Fig. 3 and 4, the battery pack 1 may include a battery box and a plurality of battery modules 4 provided in the battery box.

[0111] The battery box includes an upper body 2 and a lower body 3, and the upper body 2 can be covered by the lower body 3 to form a closed space for accommodating the battery modules 4. A plurality of battery modules 4 can be distributed in any manner within the battery box.

[0112] 5 shows an example of an electric device, such as a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density demands of the secondary battery of the electric device, a battery pack or a battery module can be used.

[0113] Other examples include mobile phones, tablets, laptops, etc. Such devices usually require a thin design and can use secondary batteries as a power source.

[0114] Example

[0115] The present invention will be described in detail below based on examples. However, those skilled in the art should understand that the following examples are merely illustrative examples and that the present invention is not limited to these examples.

[0116] In the examples and comparative examples, the proportion of each monomer unit of the polymer of the present invention, solid content, average particle size, pH value, molecular weight, roller adhesion, peeling force and conductivity are measured and evaluated by the following methods.

[0117] Example 1 <Preparation of Hydrophilic Polymer> A 1000 ml pressure reactor was charged with 0.2 parts by weight of sodium dodecyl sulfonate as an emulsifier, 0.1 parts by weight of potassium persulfate as an initiator, and 150 parts by weight of distilled water as a dispersion medium, and the resulting solution was completely dissolved. Then, 10 parts by weight of 1,3-butadiene as a conjugated diene, 90 parts by weight of styrene as a monoolefin, and 3 parts by weight of 3,4-dihydroxystyrene as a hydrophilic monomer were added. The mixture was stirred and heated at 0.6 MPa until the temperature rose to 80°C, at which point the polymerization reaction was carried out for 6 hours. After the reaction was complete, the mixture was filtered until the temperature dropped to 25°C, yielding a hydrophilic polymer emulsion. The solids content of the resulting hydrophilic polymer emulsion, its average particle size measured using a Malven particle size analyzer, its pH measured using a PHS-3C precision pH analyzer, and its molecular weight (polystyrene equivalent) measured using a GPC method are shown in Table 1. The peel strength and roller adhesion of the electrode sheet are also shown in Table 1.

[0118] Here, it is confirmed by NMR measurement that the proportions of the monomers in the obtained hydrophilic polymer are almost the same as the proportions of the monomers added.

[0119] <Preparation of negative electrode sheet> 96.0 parts by mass of graphite as the negative electrode active material, 0.9 parts by mass of conductive carbon black (SP) as a conductive agent, 1.5 parts by mass of carboxymethyl cellulose (CMC) as a thickener, and 1.6 parts by mass of the hydrophilic polymer prepared as described above are thoroughly mixed with an appropriate amount of deionized water to obtain a negative electrode slurry composition with a solid content of 54%.

[0120] When preparing the slurry composition, a pure hydrophilic polymer extracted from a dispersion may be added, or a dispersion of the hydrophilic polymer may be added. When the hydrophilic polymer is added in the form of a dispersion, the amount added is the mass converted to pure hydrophilic polymer. Finally, an appropriate amount of deionized water is added to adjust the solid content in the negative electrode slurry composition. From the viewpoint of ease of operation, after polymerizing the hydrophilic polymer, the hydrophilic polymer dispersion is used directly or after filtering with a filter to prepare the negative electrode slurry composition.

[0121] Dry coating amount is 282mg / cm 2 The slurry is uniformly applied to the surface of a copper foil negative electrode current collector so that the thickness becomes 100 μm, and then dried in an oven at 90° C. to obtain a negative electrode material in which a negative electrode film sheet is formed on the current collector.

[0122] Next, the negative electrode material was roll-pressed at 25°C to obtain a negative electrode sheet. The peel strength (peeling force) of the negative electrode sheet thus obtained was measured as follows, and the degree of roller adhesion was evaluated. The results are shown in Table 1.

[0123] <Peel strength test> In the peel strength test of the present invention, the negative electrode sheet obtained after the roll pressing was first uniformly cut into five samples each measuring 100.0 mm ± 0.1 mm in length and 20.0 mm ± 0.1 mm in width. One side of the test specimen was attached with double-sided tape, and the test surface was pressed with a press roll at 2 kg to completely bond the double-sided tape to the negative electrode sheet. The other side of the double-sided tape was attached to the surface of a 4 x 15 cm 304 stainless steel plate, and one end of the sample was bent in the opposite direction. One end of the stainless steel plate with the electrode sheet attached was fixed to the lower fixture of an H-type tensile machine, and the bent end of the sample was fixed to the upper fixture. The sample angle was adjusted so that the vertical axis of the peeled portion of the sample coincided with the center line of the upper and lower fixtures, and the sample was then properly clamped. Next, under conditions of a temperature of 25±2°C and a relative humidity of 65±5%, the sample is pulled at a rate of 50 mm / min until the entire sample is peeled off from the substrate, and the displacement and force acting during the process are recorded. The force when the force is balanced is taken as the peel force of the electrode sheet. The average value of the five results is taken as the peel force.

[0124] <Evaluation of roller adhesion level> Ten experts visually observed the degree of roller adhesion during the negative electrode sheet preparation process and evaluated it using the three-level classification method below, with the average of these evaluations being the evaluation value for the degree of roller adhesion. ○: Roller adhesion is not observed or is almost not observed △: Slight roller adhesion, but easy to peel off ×: The roller adhesion was so severe that it was not possible to peel it off.

[0125] <Preparation of positive electrode sheet> 95 parts by mass of lithium iron phosphate as the positive electrode active material, 2.5 parts by mass of commercially available carbon black as a conductive agent, and 2.5 parts by mass of commercially available polyvinylidene fluoride as an adhesive were mixed in a planetary mixer. The organic solvent N-methylpyrrolidone was added and the mixture was stirred at a temperature of 25±0.5°C to obtain a positive electrode slurry composition with a viscosity of 11,000 mPa·s (measured using a DV-2TLV Boehler flight-type viscometer at a temperature of 25±0.5°C, a 64# rotor, and a rotor rotation speed of 12 rpm).

[0126] The coating amount after drying was 326±50mg / cm on a 13μm thick aluminum foil as a current collector. 2 The resulting positive electrode slurry composition is applied so that the positive electrode layer is formed on the current collector. The resulting positive electrode material is dried in an oven at 125°C.

[0127] Next, the positive electrode material is roll-pressed in an environment at a temperature of 25°C to obtain a positive electrode sheet.

[0128] <Preparation of separator> As the separator, a general-purpose polyethylene porous separator is prepared.

[0129] <Lithium-ion battery manufacturing> The negative electrode sheet, positive electrode sheet, and separator were stacked to obtain a core. The core was then attached to a housing, filled with an electrolyte, and sealed to obtain a lithium-ion battery. The battery performance was measured as follows, and the results are shown in Table 1.

[0130] <Room temperature cycle performance test for secondary batteries: Method for measuring battery performance> The lithium-ion secondary batteries prepared in each Example and Comparative Example were initially charged and discharged at a constant current and voltage of 1 C to 3.65 V, allowed to stand for 5 minutes at an off-state current of 0.05 C, and then discharged at a constant current of 1 C to a lower off-state voltage of 2.5 V. The discharge capacity of the first cycle was recorded. The batteries were subjected to 500 charge-discharge cycles according to the above method, and the discharge capacity of the 500th cycle was recorded. The cycle capacity retention of the secondary batteries was calculated. Cycle capacity retention (%) = (discharge capacity at 500th cycle / discharge capacity at first cycle) x 100%

[0131] Examples 2 to 46 A hydrophilic polymer, a negative electrode slurry composition, a negative electrode sheet, a positive electrode sheet, a separator, and a lithium ion battery were prepared in the same manner as in Example 1, except that the ratio of the polymerization monomers was changed as shown in Table 1. Evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

[0132] Comparative Example 1 96.0 parts by weight of graphite as the negative electrode active material, 0.9 parts by weight of conductive carbon black (SP) as the conductive agent, 1.5 parts by weight of carboxymethyl cellulose (CMC) as the thickener, and 1.6 parts by weight of conventional SBR were thoroughly mixed with an appropriate amount of deionized water to obtain a negative electrode slurry composition with a solids content of 54%. Subsequently, a negative electrode sheet, a positive electrode sheet, a separator, and a lithium-ion battery were fabricated using the same steps as in Example 1. Evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

[0133] Comparative Example 2 A negative electrode slurry composition, a negative electrode sheet, a positive electrode sheet, a separator, and a lithium ion battery were prepared in the same manner as in Comparative Example 1, except that the thickener used in Comparative Example 1 was replaced with a thickener prepared by mixing sodium carboxymethyl cellulose and a highly substituted guar gum with a degree of substitution of 1.6 in a mass ratio of 1:3. Evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

[0134] Comparative Example 3: A negative electrode slurry composition, a negative electrode sheet, a positive electrode sheet, a separator, and a lithium ion battery were prepared in the same manner as in Comparative Example 1, except that the hydrophilic polymer of the present invention or conventional SBR was not used and 1.6 parts by mass of an adhesive containing polymethacrylate ester-embedded silica was used. Evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

[0135] [Table 1]

[0136] As can be seen from the results in Table 1 above, by preparing a negative electrode adhesive and a negative electrode slurry using the hydrophilic polymer of the present invention, the problems of floating in the adhesive system and roller adhesion during roll pressing of the negative electrode sheet can be suppressed, and the bonding strength between the active material and the current collector can be improved, resulting in a lithium ion battery with performance equal to or better than that of conventional batteries.

[0137] It should be noted that the present application is not limited to the above-described embodiments. The above-described embodiments are merely examples, and any embodiment that has a similar configuration to the technical idea and exhibits the same effects within the scope of the technical solution of the present application is included within the technical scope of the present application. It should be noted that various modifications that a person skilled in the art can make to the embodiments and other forms constructed by combining some of the components of the embodiments are also included within the scope of the present application, as long as they do not deviate from the spirit of the present application. [Explanation of symbols]

[0138] 1 battery pack 2 Upper box 3 Lower box 4 Battery Module 5 Secondary battery 51 Housing 52 Electrode Assembly 53 Cover plate

Claims

1. A hydrophilic polymer, A copolymer of a conjugated diolefin, a monoolefin, and a hydrophilic monomer of formula I: 【Chemical 1】 In the formula I, X １ and X ２ is a hydrogen atom, and X ３ is selected from alkyl groups having 1 to 4 carbon atoms, The R １ , R ２ and R ３ at least one of the above is a hydrophilic group, and the remaining groups are each independently selected from a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or an alkoxy group.

2. The copolymer is a random copolymer, The conjugated diolefin is a conjugated diolefin having 4 or more carbon atoms and may be selected from one or more of 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, 2,4-hexadiene, 1,3-cyclohexadiene, and 2-chloro-1,3-butadiene; and / or The hydrophilic polymer according to claim 1, wherein the monoolefin is an aromatic monovinyl group compound and can be selected from one or more of styrene, α-methylstyrene, pt-butylstyrene, butoxystyrene, vinyltoluene, chlorostyrene, and vinylnaphthalene.

3. 3. The hydrophilic polymer according to claim 1, wherein the hydrophilic group is at least one selected from the group consisting of a hydroxyl group, an amino group, and a carboxyl group.

4. The R １ , R ２ and R ３ The hydrophilic polymer according to claim 1 or 2, wherein at least two of the groups are hydrophilic groups, and the remaining groups are each independently selected from a hydrogen atom or an alkyl group having 1 to 4 carbon atoms.

5. The number average molecular weight Mn is 12 × 10 ４ ~17 x 10 ４ 3. The hydrophilic polymer according to claim 1, wherein

6. 3. The hydrophilic polymer according to claim 1, wherein the ratio of parts by mass of the conjugated diolefin, the monoolefin, and the hydrophilic monomer is 10-90:90-10:1-6.

7. A method for producing a hydrophilic polymer, comprising: polymerizing a conjugated diolefin, a monoolefin, and a hydrophilic monomer of formula I; 【Chemistry 2】 In the formula I, X １ and X ２ is a hydrogen atom, and X ３ is selected from alkyl groups having 1 to 4 carbon atoms, The R １ , R ２ and R ３ at least one of the groups is a hydrophilic group, and the remaining groups are each independently selected from a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or an alkoxy group.

8. The copolymer is a random copolymer, The conjugated diolefin is a conjugated diolefin having 4 or more carbon atoms and may be selected from one or more of 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, 2,4-hexadiene, 1,3-cyclohexadiene, and 2-chloro-1,3-butadiene; and / or 8. The method for producing a hydrophilic polymer according to claim 7, wherein the monoolefin is an aromatic monovinyl group compound and can be selected from one or more of styrene, α-methylstyrene, pt-butylstyrene, butoxystyrene, vinyltoluene, chlorostyrene, and vinylnaphthalene.

9. 9. The method for producing a hydrophilic polymer according to claim 7, wherein the hydrophilic group is at least one selected from the group consisting of a hydroxyl group, an amino group, and a carboxyl group.

10. The R １ , R ２ and R ３ 9. The method for producing a hydrophilic polymer according to claim 7, wherein at least two of the groups are hydrophilic groups, and the remaining groups are each independently selected from a hydrogen atom or an alkyl group having 1 to 4 carbon atoms.

11. The number average molecular weight Mn is 12 × 10 ４ ~17 x 10 ４ 9. The method for producing a hydrophilic polymer according to claim 7, wherein

12. 9. The method for producing a hydrophilic polymer according to claim 7 or 8, wherein the ratio of parts by mass of the conjugated diolefin, the monoolefin, and the hydrophilic monomer is 10-90:90-10:1-6 in the hydrophilic polymer.

13. An electrode active material slurry, 9. An electrode active material slurry comprising an electrode active material, a dispersion medium, and the hydrophilic polymer according to claim 1 or 2 or a hydrophilic polymer prepared by the manufacturing method according to claim 7 or 8.

14. A lithium ion secondary battery, A lithium ion secondary battery comprising a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte, wherein the negative electrode sheet comprises a negative electrode membrane layer prepared from the electrode active material slurry according to claim 13.

15. A battery pack comprising the lithium ion secondary battery according to claim 14.

16. An electrical device comprising the lithium ion secondary battery according to claim 14.

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