Copolymer particles, binder composition comprising same, slurry, electrode, and secondary battery comprising same

Abstract

The present invention relates to a copolymer particle, a binder composition comprising the same, a slurry, an electrode, and a secondary battery comprising the same, and more particularly, to a copolymer particle, a binder composition comprising the same, a slurry, an electrode, and a secondary battery comprising the same, which have excellent adhesive force between an active material and a metal substrate and / or the active material, excellent flexibility, thereby enabling the production of a thick electrode, and high reliability. The present invention relates to copolymer particles, a binder composition containing the copolymer particles, a slurry, an electrode, and a secondary battery including the electrode, and more particularly, to copolymer particles having excellent stability in an electrolyte and excellent slurry dispersibility, thereby enabling the production of a secondary battery having high initial discharge capacity and excellent charge-discharge cycle characteristics.

Description

Technical Field

[0001] The present invention relates to copolymer particles, a binder composition comprising the copolymer particles, a slurry, an electrode, and a secondary battery comprising the electrode. Background Technology

[0002] With the development and increasing demand for IT technologies such as laptops and mobile phones, and the expansion of the market for electric vehicles and hybrid vehicles as solutions to environmental problems and energy shortages, the demand for lithium-ion rechargeable batteries is also growing. To improve the long lifespan, high power, high capacity, high energy density, and stability of lithium-ion rechargeable batteries, extensive research is being conducted.

[0003] This phenomenon is significantly increased in materials such as silicon and tin, which have high discharge capacity. Although the initial charge and discharge capacity is high, the discharge capacity tends to decrease sharply with the increase of the number of cycles.

[0004] Typical lithium-ion rechargeable batteries use graphite as the negative electrode active material, and in recent years, the use of graphite-silicon based active materials has been increasing. However, with repeated charging and discharging processes, the active material undergoes volume changes of expansion and contraction, causing it to separate from the electrode. As the number of cycles increases, the battery capacity decreases, resulting in a shortened battery life.

[0005] To prevent this phenomenon, research is underway to improve electrode stability and battery performance by reducing the size of active materials to the nanoscale or changing the morphology of active materials, as well as by increasing the adhesive strength of binders and suppressing volume expansion through binders.

[0006] In particular, when using binders, low binder adhesion can lead to electrode detachment and a decrease in the charge-discharge cycle life of the secondary battery. Furthermore, the use of non-conductive binders can result in the binder acting as a resistor within the secondary battery. Additionally, ensuring sufficient battery capacity requires multilayer thin-film electrodes, but this necessitates the extensive use of expensive separators and high-density current collectors, leading to cost and volume issues. Therefore, to extend the charge-discharge cycle life of secondary batteries, reduce internal resistance by decreasing the amount of binder used, and increase the capacity of the active material, it is necessary to develop highly adhesive binders.

[0007] [Existing Technical Documents] [Patent Literature] (Patent Document 1) Korean Patent No. 10-1698745 Summary of the Invention The technical issues to be solved The present invention provides copolymer particles and an adhesive composition comprising the copolymer particles, which are polymerized from a mixture having a content of more than 1.0 parts by weight and less than 4.0 parts by weight of soft monomers relative to 1.0 parts by weight of hard monomers, and having a non-core-shell structure.

[0008] In particular, the present invention aims to provide copolymer particles and a binder composition comprising the copolymer particles, wherein the active material exhibits excellent adhesion to the metal substrate and / or excellent flexibility, thereby enabling the production of thick electrodes, excellent stability in the electrolyte and excellent slurry dispersibility, thereby enabling the production of secondary batteries with high initial discharge capacity and excellent charge-discharge cycle characteristics.

[0009] In addition, the present invention provides a slurry comprising the copolymer particles and an electrode, and a secondary battery comprising the electrode.

[0010] However, the technical problems to be solved by this application are not limited to those mentioned above, and those skilled in the art can clearly understand other technical problems not mentioned from the following description.

[0011] Technical solutions to technical problems According to one aspect of this application, a copolymer particle is provided, which is polymerized from a mixture in which the content of soft monomer is more than 1.0 parts by weight and less than 4.0 parts by weight relative to 1.0 parts by weight of hard monomer, and has a non-core-shell structure.

[0012] According to another aspect of this application, an adhesive composition comprising the copolymer particles is provided.

[0013] According to another aspect of this application, a slurry comprising the copolymer particles and an electrode active material is provided.

[0014] According to another aspect of this application, an electrode is provided, comprising a current collector and an electrode active material layer formed on the current collector and containing the copolymer particles.

[0015] According to another aspect of this application, a secondary battery including the said electrodes is provided.

[0016] Invention Effects The copolymer particles of the present invention and the binder composition comprising them improve the adhesion between the active material and the metal substrate and / or the active material, enabling the formation of a flexible and shatter-resistant back electrode film, improving electrolyte stability and slurry dispersibility, thereby ensuring a secondary battery with high initial discharge capacity and excellent charge-discharge cycle characteristics.

[0017] Furthermore, by using copolymer particles with excellent adhesion and a binder composition containing them, it is possible to use only a small amount of binder composition, thereby reducing the internal resistance of the secondary battery and increasing the capacity of the active material. Attached Figure Description

[0018] Figure 1 (a) is a photograph of a thick electrode prepared using a binder composition comprising copolymer particles from Example 1. Figure 1 (b) A photograph of a thick electrode prepared using a binder composition containing copolymer particles of Comparative Example 1.

[0019] Optimal Implementation Method The effects and functions of the invention will be described in more detail below through specific embodiments. However, these embodiments are merely examples of the invention and are not intended to limit the scope of protection of the invention.

[0020] Prior to this, the terms and words used in this specification and claims should not be interpreted according to their conventional or dictionary meanings, but should be interpreted as meanings and concepts consistent with the technical spirit of the invention, based on the principle that the inventors can appropriately define terms and concepts to better explain their invention.

[0021] Therefore, the embodiments described in this specification are only one of the most preferred embodiments of the present invention and do not represent all the technical concepts of the present invention. Therefore, it should be understood that various equivalents and modifications may exist as of the time of this application.

[0022] In this specification, unless the context clearly specifies otherwise, singular expressions include plural expressions. In this specification, terms such as “comprising,” “having,” or “possessing” are intended to indicate the presence of the implemented features, quantities, steps, constituent elements, or combinations thereof, but it should be understood that these terms do not preclude the possibility of the presence or addition of one or more other features, quantities, steps, constituent elements, or combinations thereof, or additional possibilities.

[0023] In this specification, the "to" and "~" in "a to b" and "a ~ b" which represent numerical ranges are defined as ≥ a and ≤ b.

[0024] The copolymer particles of one aspect of this application can be polymerized from a mixture of 1.0 to 4.0 parts by weight of soft monomer relative to 1.0 parts by weight of hard monomer, and have a non-core-shell structure.

[0025] For example, relative to 1.0 parts by weight of the hard monomer, the content of the soft monomer can be from 1.5 parts by weight to 3.5 parts by weight or from 2.0 parts by weight to 3.0 parts by weight.

[0026] If the weight percentage of the soft monomer exceeds the range of this application relative to 1.0 parts by weight of the hard monomer, the stability and mechanical strength within the electrolyte may decrease; if it is below the range of this application, the dispersibility within the slurry may decrease due to poor wettability.

[0027] In one embodiment of this application, the copolymer particles may be single particles rather than a core-shell structure. That is, the copolymer particles may be prepared without seed polymerization, which refers to a method of forming a shell on a core particle using a core particle as a seed. When the copolymer particles are not core-shell structures prepared by seed polymerization, they can be polymerized into single particles without the need for additional seed synthesis, thereby simplifying the process.

[0028] In one embodiment of this application, the soft monomer may include a monomer with a glass transition temperature below 20°C, and the hard monomer may include a monomer with a glass transition temperature above 20°C.

[0029] In one embodiment of this application, the soft monomer may include one or more monomers selected from the group consisting of conjugated diene monomers and acrylate monomers, and the hard monomer may include one or more monomers selected from the group consisting of styrene monomers, methacrylate monomers, acrylonitrile monomers and (meth)acrylamide monomers.

[0030] The conjugated diene monomer may include, but is not limited to, one or more monomers selected from the group consisting of 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene and 1,3-pentadiene.

[0031] The acrylate monomers may include, but are not limited to, one or more monomers selected from the group consisting of methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, n-hexyl acrylate, 2-hexyl methacrylate, n-pentyl acrylate, isopentyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, and lauryl methacrylate.

[0032] The styrene monomers may include, but are not limited to, one or more monomers selected from the group consisting of α-methylstyrene, β-methylstyrene, p-tert-butylstyrene and divinylbenzene.

[0033] The methacrylate monomers may include, but are not limited to, one or more monomers selected from the group consisting of methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-pentyl methacrylate, isoamyl methacrylate, n-hexyl methacrylate, 2-ethylhexyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, isobornyl acrylate, isovinyl acrylate, and isovinyl methacrylate.

[0034] The acrylonitrile monomers may include acrylonitrile or methacrylonitrile, but are not limited thereto.

[0035] The (meth)acrylamide monomers may include, but are not limited to, one or more monomers selected from acrylamide, methacrylamide, N-hydroxymethylacrylamide and N-butoxymethylacrylamide.

[0036] In one embodiment of this application, the glass transition temperature (Tg) of the copolymer particles can be from -40°C to -15°C.

[0037] For example, the glass transition temperature (Tg) of the copolymer particles can be -40°C to -15°C, -38°C to -15°C, -36°C to -15°C, -36°C to -16°C, -34°C to -16°C, -32°C to -16°C, or -32°C to -17°C.

[0038] The copolymer particles have a low glass transition temperature (Tg) of -40°C to -15°C, which is more hydrophobic than copolymers used as existing battery binders, thus inhibiting migration and accelerating film formation, resulting in high adhesion.

[0039] Furthermore, due to the extensive cross-linking of the copolymer particles, they not only exhibit high elasticity and excellent adhesion, but also demonstrate excellent flexibility due to their low glass transition temperature (Tg). Therefore, the copolymer particles can be used in the production of thick electrodes.

[0040] When the glass transition temperature (Tg) of the copolymer particles exceeds the range of this application, the adhesion between the active material and the metal substrate and / or the active material may decrease; when it is below the range of this application, the stability of the electrode coating may decrease.

[0041] In one embodiment of this application, the average particle size of the copolymer particles can be from 20 nm to 500 nm.

[0042] For example, the average particle size of the copolymer particles can be 20nm to 500nm, 25nm to 400nm, 30nm to 300nm, 35nm to 250nm, 40nm to 200nm, 20nm to 100nm, 100nm to 150nm, 150nm to 200nm, 200nm to 250nm, 250nm to 300nm, 300nm to 350nm, 350nm to 400nm, 400nm to 450nm, or 450nm to 500nm.

[0043] When the average particle size of the copolymer particles exceeds the range of this application, the electrode processability may decrease; when it is below the range of this application, the adhesion between the active material and the metal substrate and / or the active material may decrease.

[0044] In one embodiment of this application, the mixture may contain an emulsifier, and the content of the emulsifier may be 1 to 10 parts by weight relative to 100 parts by weight of the first monomer mixture. Furthermore, a surfactant may be used as the emulsifier, such as anionic surfactants, cationic surfactants, amphoteric surfactants, and nonionic surfactants; preferably, anionic surfactants are used.

[0045] Specific examples of the anionic surfactant include, but are not limited to, alkali metal salts of higher fatty acids, N-acrylamide amino acid salts, alkyl ether carbonates, acylated peptides, alkyl sulfonates, alkylbenzenes, alkyl amino acid salts, alkyl naphthalene sulfonates, sulfosuccinates, sulfated oils, alkyl sulfates, alkyl ether sulfates, alkyl aryl ether sulfates, alkyl amide sulfates, alkyl phosphates, alkyl ethoxy phosphates, and alkyl aryl ether phosphates. Preferably, sodium dodecylbenzene sulfonate may be used.

[0046] In one embodiment of this application, the mixture may contain an initiator. The content of the initiator may be 0.1 to 10 parts by weight relative to 100 parts by weight of the first monomer mixture, preferably 0.2 to 5 parts by weight, but not limited thereto, as long as it can perform the function of initiating polymerization.

[0047] The adhesive composition of one aspect of this application may comprise any of the copolymer particles.

[0048] One aspect of the slurry of this application may contain any of the copolymer particles and an electrode active material.

[0049] In one embodiment of this application, the slurry may include organic solvents such as carboxymethyl cellulose, NMP (N-methylpyrrolidone), DMF (dimethylformamide), acetone, and dimethylacetamide, or water, as a solvent. Preferably, carboxymethyl cellulose may be used. Additionally, the slurry may include more than one solvent.

[0050] In the carboxymethyl cellulose, the degree of substitution of hydroxyl groups (-OH) with carboxymethyl groups (-CH2CO2H) is 0.7 to 1.2, the molecular weight (Mn) can be 500,000 to 900,000, and the pH value can be 6.5 to 8.0.

[0051] In one embodiment of this application, the slurry may contain 0.1% to 10% by weight of the copolymer particles relative to 100% by weight of the total slurry weight. For example, the slurry may contain 0.1% to 8%, 0.1% to 6%, 0.1% to 4%, and 0.1% to 3% by weight of the copolymer particles relative to 100% by weight of the total slurry weight. Additionally, the slurry may contain carboxymethyl cellulose (CMC) and electrode active materials capable of intercalating and deintercalating lithium ions.

[0052] One aspect of the electrode may include a current collector and an electrode active material layer formed on the current collector and comprising the copolymer particles. The electrode may be a positive electrode or a negative electrode.

[0053] In one embodiment of this application, the adhesion strength of the negative electrode using a negative electrode slurry comprising 1.8 parts by weight of the copolymer particles per 100 parts by weight relative to the total weight of the negative electrode slurry can be 20 gf / cm or more. For example, it can be 20 gf / cm or more and 26 gf / cm or less, 21 gf / cm or more and 25 gf / cm or less, or 22 gf / cm or more and 24 gf / cm or less. Furthermore, the adhesion strength of the negative electrode using a negative electrode slurry comprising 1.3 parts by weight of the copolymer particles per 100 parts by weight relative to the total weight of the negative electrode slurry can be 15 gf / cm or more. For example, it can be 15 gf / cm or more and 20 gf / cm or less, 15 gf / cm or more and 19 gf / cm or less, or 15.5 gf / cm or more and 18 gf / cm or less.

[0054] In one embodiment of the present application, the current collector is the part where electrons move during the electrochemical reaction of the active material. Depending on the type of electrode, there are negative current collectors and positive current collectors. The surface of the current collector is formed with fine irregularities, thereby enhancing the binding force of the electrode active material, and various forms such as thin films, sheets, foils, meshes, porous bodies, foams, non-woven fabrics, etc. can be adopted.

[0055] The negative current collector is usually formed to have a thickness of 5 µm to 30 µm. As long as it does not cause chemical changes in the battery and has conductivity, there is no particular limitation on the material selection of such a negative current collector. For example, copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, or a combination thereof can be used.

[0056] The positive current collector is usually formed to have a thickness of 3 µm to 500 µm. As long as it does not cause chemical changes in the battery and has conductivity, there is no particular limitation on the material selection of the positive current collector. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel with surfaces treated with carbon, nickel, titanium, silver, etc., and aluminum cadmium alloy, etc. can be used.

[0057] In one embodiment of the present application, the electrode active material is a substance that can cause an electrochemical reaction, and is used to prepare negative and positive pastes. Depending on the type of electrode, there are negative active materials and positive active materials.

[0058] The negative active material can be selected from one or more of the group consisting of carbon and graphite materials that can intercalate and deintercalate lithium ions, silicon-based materials, metals and compounds that can form alloys with lithium, composites of metals and their compounds with carbon and graphite materials, lithium-containing nitrides, etc.

[0059] As carbon and graphite materials, natural graphite, artificial graphite, expanded graphite, carbon fiber, non-graphitized carbon, carbon black, carbon nanotubes, fullerenes, activated carbon, hard carbon, and soft carbon can be included. As silicon-based materials, Si, SiO x [[ID=I7]] (0 < x < 2), Si-Y alloys (where Y is an alkali metal, alkaline earth metal, Group 13 element, Group 14 element, transition metal, rare earth element, or a combination thereof), Si-C composites, or silicon-based compounds such as their combinations, etc. As metals and elements that can form alloys with lithium, Al, Si, Sn, Ag, Bi, Mg, Zn, In, Ge, Pb, Pd, Pt, Ti, etc. are included. Relative to 100 parts by weight of the negative paste, the negative paste may contain 20 to 80 parts by weight of the negative active material.

[0060] As the positive electrode active material, the lithium transition metal oxide represented by the chemical formula 1 may be used alone, or other positive electrode active materials capable of adsorbing and releasing lithium ions may be used in combination as appropriate.

[0061] For example, as the positive electrode active material, layered compounds such as lithium cobalt oxide (LiCoO2) and lithium nickel oxide (LiNiO2), or compounds substituted with one or more transition metals may be used; lithium manganese oxide, chemical formula Li 1+y Mn 2-y O4 (where y is 0 to 0.33), LiMnO3, LiMn2O3, LiMnO2, etc.; lithium copper oxide (Li2CuO2); vanadium oxides, LiV3O8, LiFe3O4, V2O5, Cu2V2O7, etc.; Ni-site type lithium nickel oxide, represented by the chemical formula LiNi 1-y MyO2 (where M is Co, Mn, Al, Cu, Fe, Mg, B or Ga, y = 0.01 to 0.3); lithium manganese composite oxide, represented by the chemical formula LiMn 2-y MyO2 (where M is Co, Ni, Fe, Cr, Zn or Ta, y = 0.01 to 0.1) or Li2Mn3MO8 (where M is Fe, Co, Ni, Cu or Zn); LiMn2O4 in which a part of Li in the chemical formula is substituted with an alkaline earth metal ion; disulfide compounds; Fe2(MoO4)3, etc., but not limited thereto.

[0062] Preferably, the positive electrode active material may include lithium nickel manganese cobalt oxide represented by the chemical formula 1 of Li a Ni x Mn y Co z O2 (in the formula, 0.8 ≤ a < 1.2, 0.2 ≤ x < 1, 0 < y < 1, 0 < z < 1, x + y + z = 1) and LiCoO2. The lithium transition metal oxide represented by the chemical formula 1 has a relatively high discharge capacity. Preferably, the content may be at least 20% by weight or more of the total weight of the positive electrode active material, and more preferably, the content may be 20% to 90% by weight. Based on the total weight of the positive electrode active material, LiCoO2 is contained in an amount of 20% to 80% by weight.

[0063] The secondary battery according to one aspect of the present application may include the electrode.

[0064] In one embodiment of this application, the internal resistance of the secondary battery comprising a negative electrode using a negative electrode slurry containing 1.3 parts by weight of the copolymer particles relative to 100 parts by weight of the total weight of the negative electrode slurry can be 255 mΩ or less. For example, the internal resistance of the secondary battery can be 253 mΩ or less and 235 mΩ or more, 251 mΩ or less and 238 mΩ or more, or 249 mΩ or less and 240 mΩ or more. That is, the secondary battery prepared using copolymer particles whose glass transition temperature (Tg) meets the range of this application can achieve excellent adhesion between the active material and the metal substrate and / or the active material, even using a small amount of copolymer particles, and has the effect of reducing the battery internal resistance value measured based on DC-IR testing.

[0065] In one embodiment of this application, the capacity retention rate of the secondary battery comprising a negative electrode using a negative electrode slurry containing 1.8 parts by weight of the copolymer particles relative to 100 parts by weight of the total weight of the negative electrode slurry can be 95% or more. For example, the capacity retention rate of the secondary battery can be 95% or more and 99% or less, or 96% or more and 98% or less.

[0066] In one embodiment of this application, the secondary battery may include a separator. The separator is located between the positive and negative electrodes and may be an insulating film with high ion permeability and mechanical strength. The pore diameter of the separator is typically from 0.01 µm to 10 µm, and the thickness is typically from 5 µm to 300 µm. As such a separator, olefin polymers such as chemically resistant and hydrophobic polypropylene may be used; sheets or nonwoven fabrics made of glass fiber or polyethylene may also be used. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also serve as the separator.

[0067] The lithium-containing non-aqueous electrolyte is composed of an electrolyte and a lithium salt. The electrolyte can be a non-aqueous organic solvent, an organic solid electrolyte, an inorganic solid electrolyte, etc.

[0068] As the aforementioned non-aqueous organic solvent, aprotic organic solvents may be used, such as N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triphosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolium ketone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl pyropropionate, and ethyl propionate.

[0069] As the organic solid electrolyte, for example, polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate polymers, polylysine, polyester sulfides, polyvinyl alcohol, polyvinylidene fluoride, and polymerizing agents containing ion-dissociating groups can be used.

[0070] As the inorganic solid electrolyte, nitrides, halides, and sulfates of Li, such as Li3N, LiI, Li5NI2, Li3N-LiI-LiOH, LiSiO4, LiSiO4-LiI-LiOH, Li2SiS3, Li4SiO4, Li4SiO4-LiI-LiOH, and Li3PO4-Li2S-SiS2, can be used.

[0071] The lithium salt is a substance that is readily soluble in the non-aqueous electrolyte, and can be, for example, LiCl, LiBr, LiI, LiClO4, LiBF4, or LiB. 10 Cl 10 LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, (CF3SO2)2NLi, lithium chloroborane, lithium lower aliphatic carboxylic acids, lithium 4-phenylborate, imides, etc.

[0072] In addition, to improve charge / discharge characteristics and flame retardancy, the electrolyte may contain additives such as pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, dimethyl ethylene glycol ether, triammonium hexaphosphate, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidinyl ethers, dialkyl ethylene glycol ethers, ammonium salts, pyrrole, 2-methoxyethanol, and aluminum trichloride. Depending on the application, halogenated solvents such as carbon tetrachloride and trifluoroethylene may be added to impart non-flammability; carbon dioxide gas may be included to improve high-temperature storage performance; and fluoroethylene carbonate (FEC), propene sultone (PRS), fluoropropylene carbonate (FPC), ethylene carbonate (EC), ethyl methyl carbonate, and diethyl carbonate may also be added.

[0073] In one embodiment of this application, the secondary battery can be used not only as a battery cell for powering small devices, but also preferably as a unit battery in a medium-to-large battery module, which includes multiple battery cells for powering medium-to-large devices.

[0074] Preferred examples of the medium to large-sized equipment include: power tools driven by electric motors; electric vehicles, including electric vehicles (EVs), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), etc.; electric two-wheelers, including electric bicycles (E-bikes) and electric scooters (E-scooters); and electric golf carts, etc., but not limited to these. Detailed Implementation

[0075] The present invention will now be described in more detail through embodiments. However, the following embodiments are for more specific illustration and are not intended to limit the scope of the invention.

[0076] Examples and Comparative Examples: Preparation of Copolymer Particles Example 1 Add 60g of 1,3-butadiene as a soft monomer, 10g of 2-hydroxyethyl acrylate, and 30g of styrene as a hard monomer to 200g of distilled water.

[0077] Subsequently, 0.5 g of sodium dodecylbenzenesulfonate was added as a surfactant for emulsification and stirring. Then, 1 g of potassium sulfite was added as a decomposition initiator to carry out the polymerization reaction, thereby preparing copolymer particles.

[0078] Example 2 Except for increasing the amount of hard monomer by 5g, copolymer particles were prepared in the same manner as in Example 1.

[0079] Example 3 Except for increasing the amount of hard monomer by 10g, copolymer particles were prepared in the same manner as in Example 1.

[0080] Comparative Example 1 Except for changing the composition of the monomers and adjusting the weight ratio of soft monomers to hard monomers (soft:hard) to 1:2, copolymer particles were prepared in the same manner as in Example 1.

[0081] Comparative Example 2 Except for changing the composition of the monomers and adjusting the weight ratio of soft monomers to hard monomers (soft:hard) to 1:1, copolymer particles were prepared in the same manner as in Example 1.

[0082] Comparative Example 3 Except for changing the composition of the monomers and adjusting the weight ratio of soft monomers to hard monomers (soft:hard) to 2:3, copolymer particles were prepared in the same manner as in Example 1.

[0083] Comparative Example 4 Except for increasing the amount of soft monomer by 20g, copolymer particles were prepared in the same manner as in Example 1.

[0084] Preparation examples: Preparation of negative electrode slurry, negative electrode, and battery. Preparation Example 1 A negative electrode slurry was prepared by mixing 97 parts by weight of graphite as the negative electrode active material, 1.8 parts by weight of copolymer particles from Examples 1 to 3 and Comparative Examples 1 to 4, 1.2 parts by weight of carboxymethyl cellulose, and distilled water.

[0085] The negative electrode slurry was uniformly coated onto a 10µm thick Cu film using a coating tool, and then dried at 100°C for 30 minutes to prepare the negative electrode.

[0086] The positive electrode is prepared by mixing lithium nickel manganese cobalt oxide (as the positive electrode active material), acetylene black (as the conductive agent), and polyvinylidene fluoride (PVDF) (as the positive electrode binder) in a weight ratio of 92:4:4 and coating the mixture onto an aluminum current collector. The electrolyte is prepared by dissolving LiPF6 in a non-aqueous solvent with a composition of ethylene carbonate (EC): ethyl methyl carbonate (EMC): diethyl carbonate (DEC) = 1:2:1 to a concentration of 1M. A porous polyethylene film is used as the separator to prepare the full cell.

[0087] The types of copolymer particles used are shown in Table 1 below.

[0088] Table 1

[0089] Preparation Example 2 A negative electrode slurry was prepared by mixing 97 parts by weight of graphite as the negative electrode active material, 1.3 parts by weight of copolymer particles from Examples 1 to 3 and Comparative Examples 1 to 4, 1.7 parts by weight of carboxymethyl cellulose, and distilled water.

[0090] In addition, the negative electrode and the battery were prepared using the same methods and conditions as in Preparation Example 1.

[0091] Table 2 below shows the types of copolymer particles used.

[0092] Table 2

[0093] Evaluation example Evaluation Example 1: Determination of the glass transition temperature (Tg) of copolymer particles After drying a small amount of the adhesive composition containing copolymer particles of Examples 1 to 3 and Comparative Examples 1 to 4 in an oven at 120°C to form a film, the glass transition temperature (Tg) was determined using a DSC thermal analyzer.

[0094] The measured glass transition temperatures (Tg) are shown in Table 3 below.

[0095] Table 3

[0096] The measurement results confirm that the glass transition temperatures of the adhesive compositions in Examples 1 to 3 are -32°C, -24°C, and -17°C, respectively, which meet the glass transition temperature range of this application, i.e., -40°C to -15°C. When the glass transition temperature range of this application is met, as described below, even with a relatively thick thickness, an electrode with improved flexibility can be manufactured.

[0097] Conversely, it was confirmed that the glass transition temperatures of the binder compositions of Comparative Examples 1 to 3, which differed from the monomer composition of this application, were 4°C, -3°C, and -8°C, respectively, exceeding the glass transition temperature range of this application. When the glass transition temperature range of this application was exceeded, as described below, cracks appeared when preparing thicker electrodes, and it was confirmed that the electrodes using the binder compositions of Examples 1 to 3 of this application had lower flexibility.

[0098] Furthermore, the adhesive composition of Comparative Example 4, whose soft monomer content exceeded the range of this application, had a glass transition temperature of -49°C, which is lower than the glass transition temperature range of this application. When the glass transition temperature is lower than the glass transition temperature range of this application, as described below, the coated electrode surface is uneven, and the coating stability is lower than that of the electrodes using the adhesive compositions of Examples 1 to 3 of this application. In addition, as described below, the adhesion of the electrode of Comparative Example 4, whose glass transition temperature is too low, also decreased.

[0099] Evaluation Example 2: Determining the flexibility of electrodes Electrodes were fabricated by adjusting the height of the coating bar to achieve a thick coating. Specifically, electrodes coated with a higher loading of 45.8 mg / cm² than conventional electrodes were prepared, and electrode breakage was checked when the two ends of the electrode were bent to a difference of approximately 15°. The results are shown in Table 4 below. When the electrode surface coated with the binder composition was uniform, the coating stability was recorded as 0; when it was non-uniform, the coating stability was recorded as X. Furthermore, visual inspection confirmed that if the electrode broke in two, the breakage was recorded as 0; if it did not break and bent flexibly, the breakage was recorded as X.

[0100] Table 4

[0101] When the electrode was prepared using the binder composition containing the copolymer particles of Comparative Example 4, the electrode surface coated with the binder composition was uneven, exhibiting roughness, streaks, and other irregularities, indicating a decrease in coating stability. Therefore, the flexibility of the electrode prepared using the binder composition containing the copolymer particles of Comparative Example 4, which was considered an incomplete electrode, was not evaluated.

[0102] Figure 1 (a) shows a photograph of a thick electrode prepared using a binder composition comprising copolymer particles from Example 1. Figure 1 (b) shows a photograph of a thick electrode prepared using a binder composition comprising copolymer particles of Comparative Example 1. Figure 1 As shown in (a), no breakage occurred in the thick electrode prepared using the binder composition containing the copolymer particles of Example 1, but breakage occurred in the thick electrode prepared using the binder composition containing the copolymer particles of Comparative Example 1. Figure 1 As shown in (b).

[0103] That is, when thick electrodes were prepared using binder compositions containing copolymer particles from Examples 1 to 3, no electrode breakage occurred, confirming that a flexible electrode was prepared.

[0104] Conversely, when thick electrodes were prepared using binder compositions containing copolymer particles from Comparative Examples 1 to 3, electrode breakage occurred, confirming that the flexibility was reduced compared to electrodes prepared using copolymers from Examples 1 to 3 whose glass transition temperatures met the range of this application.

[0105] Evaluation Example 3: Determination of Electrode Adhesion Force The negative electrodes of Preparation Examples 1 and 2, prepared using copolymer particles from Examples 1 to 3 and Comparative Examples 1 to 4, were cut to a size of 25 mm wide and 100 mm long. Double-sided adhesive tape with a width of 20 mm and a length of 40 mm was adhered to an acrylic plate with an area of ​​40 mm wide and 100 mm long. After attaching the prepared electrode to the double-sided adhesive tape, it was gently pressed 5 times with a hand roller and installed onto a UTM (20 kgf load cell). After peeling approximately 25 mm off one side of the negative electrode, the negative electrode was fixed to the upper clamp of the tensile testing machine, and the adhesive tape adhered to the negative electrode side was fixed to the lower clamp. Peeling was performed at a speed of 100 mm / min, and the force required to peel the electrode in the 180° direction was measured. At least five samples were prepared for each sample, and the average value was calculated. The results are shown in Tables 5 and 6.

[0106] Table 5

[0107] The measurement results confirm, as shown in Table 5, that the negative electrodes of Preparation Examples 1-1 to 1-3, prepared from copolymer particles of Examples 1 to 3 containing 1.8 parts by weight, exhibit high adhesion strength of 20 gf / cm or more. That is, it is confirmed that the negative electrodes of Preparation Examples 1-1 to 1-3, prepared from copolymer particles of Examples 1 to 3 containing 1.8 parts by weight, have higher adhesion strength compared to the negative electrodes of Comparative Preparation Examples 1-1 to 1-4, prepared from copolymer particles of Comparative Examples 1 to 4 containing 1.8 parts by weight.

[0108] In particular, the adhesive strength of the negative electrodes of Comparative Preparation Examples 1-1 to 1-3, which are prepared from copolymer particles of Comparative Examples 1 to 3 with glass transition temperatures exceeding the range of this application, increases as the glass transition temperature decreases. However, the negative electrodes of Comparative Preparation Examples 1-4, which are prepared from copolymer particles of Comparative Example 4 with glass transition temperatures below the range of this application, have the lowest adhesive strength.

[0109] This means that when the glass transition temperature (Tg) meets the range of -40°C to -15°C of this application, a negative electrode with better adhesion between the active material and the metal substrate can be obtained.

[0110] Table 6

[0111] The measurement results confirm, as shown in Table 6, that the negative electrodes of Preparation Examples 2-1 to 2-3, prepared from copolymer particles of Examples 1 to 3 containing 1.8 parts by weight, exhibit high adhesion of 15 gf / cm or more. That is, it can be confirmed that the negative electrodes of Preparation Examples 2-1 to 2-3, prepared from copolymer particles of Comparative Examples 1 to 3 containing 1.3 parts by weight, have higher adhesion than the negative electrodes of Comparative Examples 1 to 3 prepared from copolymer particles of Comparative Examples 1 and 2 containing 1.3 parts by weight, and the negative electrodes of Comparative Examples 3 and 4 prepared from copolymer particles of Comparative Examples 1 to 3 containing 1.8 parts by weight.

[0112] In particular, it can be confirmed that in preparation examples 2-1 to 2-3, even if only about 70% of the copolymer particles used in preparation example 1 to 3 were used, the copolymer particles used in preparation example 1 had high adhesion compared to comparative preparation examples 1-1 to 1-4, which used 1.8 parts by weight of copolymer particles from comparative examples 1 to 4.

[0113] This means that when the glass transition temperature (Tg) meets the range of -40°C to -15°C of this application, a negative electrode with better adhesion between the active material and the metal substrate can be obtained.

[0114] Evaluation Example 4: Determining the battery's capacity retention rate For the batteries prepared in Preparation Examples 1-1 to 1-3 and Comparative Preparation Examples 1-1 to 1-4, two charge-discharge cycles were performed at 25°C, with a charge-discharge current density of 0.1C, a charge cut-off voltage of 4.2V, and a discharge cut-off voltage of 2.8V.

[0115] Then, the charge / discharge current density was set to 1C, the charging cutoff voltage was set to 4.2V, and the discharging cutoff voltage was set to 2.8V, and 100 charge / discharge cycles were performed.

[0116] All discharges were performed under constant current / constant voltage conditions, with the cutoff current for constant voltage discharge set to 0.005C.

[0117] At this point, the capacity retention rate is calculated according to the following mathematical formula 1.

[0118] <Mathematical Formula 1> Capacity retention rate [%] = [Discharge capacity at 100th cycle / Discharge capacity at 1st cycle] × 100 The results of the capacity retention measurements of the batteries prepared in Preparation Examples 1-1 to 1-3 and Comparative Preparation Examples 1-1 to 1-4 are shown in Table 7.

[0119] Table 7

[0120] The measurement results confirm, as shown in Table 7, that the batteries prepared in Preparation Examples 1-1 to 1-3, containing 1.8 parts by weight of the copolymer particles from Examples 1 to 3, exhibit a high capacity retention rate of over 95%. That is, it can be confirmed that the batteries prepared in Preparation Examples 1-1 to 1-3, containing 1.8 parts by weight of the copolymer particles from Examples 1 to 3, have a higher capacity retention rate compared to the batteries prepared in Comparative Preparation Examples 1-1 to 1-4, containing 1.8 parts by weight of the copolymer particles from Comparative Examples 1 to 4.

[0121] In particular, the capacity retention of batteries prepared from copolymer particles of Comparative Examples 1 to 3, which contain glass transition temperatures exceeding the range of this application, increases as the glass transition temperature decreases. However, the capacity retention of batteries prepared from copolymer particles of Comparative Example 4, which contain glass transition temperatures below the range of this application, is the lowest.

[0122] This means that when the glass transition temperature (Tg) meets the range of -40°C to -15°C of this application, a battery with better life characteristics can be obtained.

[0123] Evaluation Example 5: Measuring the internal resistance of a battery For the batteries prepared in Preparation Examples 2-1 to 2-3, Comparative Preparation Examples 2-1, 2-2, and Comparative Preparation Examples 1-3 and 1-4, after initialization, the battery internal resistance was measured by the Direct Current Internal Resistance (DC-IR) method under the following conditions: charging at a voltage equivalent to 50% of the battery's state of charge (SOC) at a rate of 0.3C in constant current / constant voltage (CC / CV) mode, followed by discharging at a rate of 2C at 2.75V. The temperature of the chamber was 25°C at this time.

[0124] The results of the measurement of the internal resistance of the batteries prepared in Preparation Examples 2-1 to 2-3, Comparative Preparation Examples 2-1, 2-2, and Comparative Preparation Examples 1-3 and 1-4 are shown in Table 8.

[0125] Table 8

[0126] The measurement results confirm, as shown in Table 8, that the batteries prepared in Preparation Examples 2-1 to 2-3, containing 1.3 parts by weight of the copolymer particles from Examples 1 to 3, have a low internal resistance of less than 255 mΩ. That is, it can be confirmed that the batteries prepared in Preparation Examples 2-1 to 2-3, containing 1.3 parts by weight of the copolymer particles from Comparative Examples 1 and 2, and the batteries prepared in Comparative Examples 1-3 and 1-4, containing 1.8 parts by weight of the copolymer particles from Comparative Examples 3 and 4, have a lower internal resistance value.

[0127] This means that when the glass transition temperature (Tg) meets the range of -40°C to -15°C of this application, a battery with reduced electrical loss due to internal resistance and excellent performance can be obtained.

[0128] The scope of this invention is determined by the claims described below, rather than by the specific embodiments described, and all modifications or variations derived from the claims and their equivalents shall be construed as being included within the scope of this invention.

[0129] Industrial applications The copolymer particles of the present invention and the binder composition comprising them improve the adhesion between the active material and the metal substrate and / or the active material, enabling the formation of a flexible and shatter-resistant back electrode film, improving electrolyte stability and slurry dispersibility, thereby ensuring a secondary battery with high initial discharge capacity and excellent charge-discharge cycle characteristics.

[0130] Furthermore, when using copolymer particles with excellent adhesion and binder compositions containing them, only a small amount of binder composition can be used, thereby reducing the internal resistance of the secondary battery and increasing the capacity of the active material.

Claims

1. A copolymer particle, characterized in that, It is polymerized from a mixture in which the content of soft monomers is more than 1.5 parts by weight and less than 3.0 parts by weight relative to 1.0 parts by weight of hard monomers, and has a non-core-shell structure.

2. The copolymer particles according to claim 1, wherein, The soft monomers include monomers with a glass transition temperature (Tg) below 20°C. The hard monomers include monomers with a glass transition temperature (Tg) of 20°C or higher.

3. The copolymer particles according to claim 1, wherein, The soft monomer includes one or more monomers selected from the group consisting of conjugated diene monomers and acrylate monomers. The hard monomer includes one or more monomers selected from the group consisting of styrene monomers, methacrylate monomers, acrylonitrile monomers, and (meth)acrylamide monomers.

4. The copolymer particles according to claim 1, wherein, The glass transition temperature is -40℃ to -15℃.

5. The copolymer particles according to claim 1, wherein, The average particle size ranges from 20 nm to 500 nm.

6. An adhesive composition, characterized in that, The copolymer particles comprise any one of claims 1 to 5.

7. A slurry, characterized in that, Include: The copolymer particles according to any one of claims 1 to 5; and Electrode active material.

8. An electrode, characterized in that, include: current collector; as well as An electrode active material layer is formed on the current collector and comprises copolymer particles according to any one of claims 1 to 5.

9. A secondary battery, characterized in that, Includes the electrode as described in claim 8.

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