Insulating layer composition for lithium secondary batteries and lithium secondary batteries containing the same

Abstract

An object of the present invention is to provide an insulating layer composition for a lithium secondary battery which is excellent not only in insulating properties and processability but also in storage stability. The present invention relates to an insulating layer composition for a lithium secondary battery, which does not contain carboxymethylcellulose, and contains a conjugated diene copolymer as a binder polymer, a non-aqueous organic solvent, and an emulsifier, the gel content being 70% by weight or more based on the total weight of the conjugated diene copolymer, and the emulsifier content being 0.3% by weight or more based on the total weight of the conjugated diene copolymer.

Description

Technical Field

[0001] The present invention relates to an insulating layer composition for a lithium secondary battery and a lithium secondary battery including the same.

Background Art

[0002] As the technology development and demand for mobile devices increase, the demand for secondary batteries as an energy source has been rapidly increasing, and accordingly, many studies have been conducted on batteries that can meet various needs.

[0003] One of the main research issues for such secondary batteries is to improve safety. The main cause of battery safety-related accidents is the occurrence of an abnormal high-temperature state due to a short circuit between the positive electrode and the negative electrode. That is, under normal circumstances, a separator is located between the positive electrode and the negative electrode to maintain electrical insulation. However, in abnormal misuse situations such as overcharging or over-discharging of the battery, internal short circuit due to dendritic growth or foreign matter of the electrode material, penetration by sharp objects such as nails or screws, or unreasonable deformation due to external force, the conventional separator alone shows limitations.

[0004] Generally, a separator mainly uses a microporous membrane made of a polyolefin resin, but its heat resistance temperature is about 120 to 160 °C and its heat resistance is insufficient. Therefore, when an internal short circuit occurs, there is a problem that the separator shrinks due to the short-circuit reaction heat and the short-circuit part expands, leading to a thermal runaway state where more and larger reaction heats are generated. Therefore, various methods have been studied to reduce the possibility of cell deformation, external impact, or physical short circuit between the positive electrode and the negative electrode.

[0005] For example, to prevent a short circuit from occurring when the electrode assembly moves after the battery is completed and the electrode tabs come into contact with the upper end of the electrode assembly, one method is to apply insulating tape of a predetermined size to the electrode tabs adjacent to the upper end of the current collector. However, winding up such insulating tape is very cumbersome, and if the insulating tape is wound up to a length that extends slightly downward from the upper end of the current collector, this can cause an increase in the thickness of the electrode assembly. Furthermore, there is a problem that the electrode tabs tend to loosen when bent.

[0006] Another method involves forming an insulating layer on the tab portion of the positive electrode using a non-aqueous binder (such as PVDF) or an aqueous styrene-butadiene copolymer (SBL). However, when using a non-aqueous binder (such as PVDF), the wet adhesion strength decreases, making it impossible to prevent the movement of lithium ions to the electrode overlay region, resulting in a problem of capacity development. In particular, when capacity is developed in the electrode overlay region, lithium ions may precipitate, which can lead to a decrease in the stability of the battery cell. Furthermore, when using an aqueous styrene-butadiene copolymer (SBL) binder, when coating simultaneously with the slurry for the positive electrode mixture layer, a decrease in battery performance occurs due to gelation of the PVDF, which is an organic binder used as the positive electrode binder, penetration of the positive electrode slurry into the insulating liquid boundary, and side reactions due to moisture, making simultaneous coating of the slurry for the positive electrode mixture layer and the slurry for the insulating coating layer impossible. In addition, the aforementioned non-aqueous binders (such as PVDF) and aqueous styrene-butadiene copolymer (SBL) insulating layers have the problem of phase separation occurring during storage, resulting in decreased storage stability.

[0007] Furthermore, carboxymethylcellulose is often used as a thickening agent in insulating layer compositions for lithium secondary batteries. However, because such carboxymethylcellulose is brittle, it causes problems in winding and cutting processes, reducing processability.

[0008] Therefore, there is a strong need to develop an insulating solution that not only has excellent insulating properties, but also allows for simultaneous coating of the cathode mixture layer slurry and the insulating coating layer slurry, is not brittle, has excellent processability, and has excellent storage stability. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Korean Registered Patent Publication No. 10-1586530 [Overview of the Initiative] [Problems that the invention aims to solve]

[0010] The present invention has been made in view of the aforementioned problems, and the object of the present invention is to provide an insulating layer composition for lithium secondary batteries that is excellent not only in insulating properties and processability but also in storage stability.

[0011] Another object of the present invention is to provide a method for manufacturing a positive electrode for a lithium secondary battery using the aforementioned insulating layer composition for lithium secondary batteries.

[0012] Another object of the present invention is to provide a positive electrode for a lithium secondary battery comprising the aforementioned insulating layer composition for lithium secondary batteries.

[0013] Another object of the present invention is to provide a lithium secondary battery including the positive electrode for the lithium secondary battery.

[0014] However, the objects of the present invention are not limited to those mentioned above, and any other objects not mentioned should be clearly understood by a person with ordinary skill in the art to which this disclosure belongs ("ordinary skill" or "person skilled in the art") from the description of the claims. [Means for solving the problem]

[0015] To achieve the aforementioned objectives, according to one embodiment of the present invention, an insulating layer composition for lithium secondary batteries is provided, comprising a conjugated diene copolymer as a binder polymer, a non-aqueous organic solvent, and an emulsifier. The gel content is 70% by weight or more based on the total weight of the conjugated diene copolymer, and the emulsifier content is 0.3% by weight or more based on the total weight of the conjugated diene copolymer.

[0016] The aforementioned insulating layer composition for lithium secondary batteries may not contain carboxymethylcellulose.

[0017] The conjugate diene copolymer may include a polymer of (a) a conjugate diene monomer or conjugate diene polymer, (b) at least one monomer selected from the group consisting of acrylate monomers, vinyl monomers and nitrile monomers, and (c) one or more monomers selected from the group consisting of unsaturated carboxylic acid monomers and hydroxyl group-containing monomers.

[0018] The conjugate diene monomer may be one monomer selected from the group consisting of 1,3-butadiene, isoprene, chloroprene, and piperine, and the conjugate diene polymer may be a polymer of two or more monomers selected from the group consisting of 1,3-butadiene, isoprene, chloroprene, and piperine, a styrene-butadiene copolymer, an acrylonitrile-butadiene copolymer, a styrene-isoprene copolymer, an acrylate-butadiene rubber, an acrylonitrile-butadiene-styrene rubber, an ethylene-propylene-diene polymer, or a polymer in which these polymers are partially epoxidized or brominated (Br), or a mixture thereof.

[0019] The acrylate monomer may be one or more monomers selected from the group consisting of methyl acrylate, methacryloxyethyl ethylene urea, β-carboxyethyl acrylate, aliphatic monoacrylate, dipropylene diacrylate, ditrimethylolpropane tetraacrylate, dipentaerythritol hexaacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, and glycidyl methacrylate.

[0020] The vinyl monomer may be one or more monomers selected from the group consisting of styrene, α-methyl styrene, β-methyl styrene, p-t-butyl styrene, and divinyl benzene.

[0021] The nitrile monomer may be one or more monomers selected from the group consisting of acrylonitrile, methacrylonitrile, and allyl cyanide.

[0022] The unsaturated monocarboxylic acid monomer may be one or more monomers selected from the group consisting of maleic acid, fumaric acid, methacrylic acid, acrylic acid, glutaric acid, itaconic acid, tetrahydrophthalic acid, crotonic acid, isocrotonic acid, and nadic acid.

[0023] The hydroxy group-containing monomer may be one or more monomers selected from the group consisting of hydroxyacrylate, hydroxyethyl acrylate, hydroxybutyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, and hydroxybutyl methacrylate.

[0024] The conjugated diene copolymer may contain a polymer of 25 to 45% by weight of the (a) conjugated diene monomer or conjugated diene polymer, 50 to 70% by weight of one or more monomers selected from the group consisting of the (b) acrylate monomer, vinyl monomer and nitrile monomer, and 1 to 20% by weight of one or more monomers selected from the group consisting of the (c) unsaturated carboxylic acid monomer and hydroxy group-containing monomer, based on the total weight.

[0025] The non-aqueous organic solvent may be one or more selected from the group consisting of N-methyl-pyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), ethylene carbonate (EC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate (PC), dipropyl carbonate (DPC), butylene carbonate (BC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), acetonitrile, dimethoxyethane, tetrahydrofuran (THF), gamma-butyrolactone (γ-butyrolactone), methyl alcohol, ethyl alcohol and isopropyl alcohol.

[0026] The conjugated diene copolymer may be a styrene-butadiene copolymer, and the non-aqueous organic solvent may be N-methyl-pyrrolidone (NMP).

[0027] The insulating layer composition for the lithium secondary battery may have a water content of 10,000 ppm or less.

[0028] Another embodiment of the present invention provides a method for manufacturing a positive electrode for a lithium secondary battery, comprising the steps of: producing a water-dispersible conjugated diene copolymer; adding a non-aqueous organic solvent to the water-dispersible conjugated diene copolymer, heating and reducing the pressure to produce a slurry for an insulating coating layer; applying the slurry for a positive electrode mixture layer, containing a positive electrode active material, a non-aqueous binder, a conductive material, and a non-aqueous organic solvent, to one or both sides of a positive electrode current collector; applying the slurry for an insulating coating layer to cover a portion of the slurry for the positive electrode mixture layer applied to the current collector, starting from a portion of the plain portion of the positive electrode current collector; and drying the slurry for the positive electrode mixture layer and the slurry for the insulating coating layer applied to the positive electrode current collector.

[0029] The aforementioned conjugate diene copolymer may be a conjugate diene latex.

[0030] The conjugate diene latex may be styrene-butadiene latex, and the non-aqueous organic solvent may be N-methyl-pyrrolidone (NMP).

[0031] According to another embodiment of the present invention, a positive electrode for a lithium secondary battery is provided, comprising a positive electrode current collector, a positive electrode tab protruding from the positive electrode current collector, and an insulating layer coated with an insulating material on the positive electrode tab, wherein the insulating material comprises the lithium secondary battery insulating layer composition.

[0032] According to another embodiment of the present invention, a lithium secondary battery including the positive electrode for the lithium secondary battery is provided. [Effects of the Invention]

[0033] An insulating layer composition for lithium secondary batteries according to one embodiment of the present invention does not contain carboxymethylcellulose, and therefore is not brittle, resulting in excellent processability during winding and cutting processes.

[0034] Furthermore, the insulating layer composition for lithium secondary batteries according to one embodiment of the present invention allows for simultaneous coating of the insulating solution with the positive electrode by replacing the water, which is the dispersion solvent for the aqueous conjugate diene copolymer, with a non-aqueous organic solvent (e.g., N-methyl-pyrrolidone), resulting in excellent processability during the manufacturing of the positive electrode for lithium secondary batteries.

[0035] Furthermore, the insulating layer composition for lithium secondary batteries according to one embodiment of the present invention has a high gel content and contains an emulsifier, resulting in excellent storage stability.

[0036] However, the effects of the present invention are not limited to those mentioned above, and other effects not mentioned should be clearly understood by a person skilled in the art from the description of the claims. [Brief explanation of the drawing]

[0037] Embodiments of the present invention will be described with reference to the following accompanying drawings, where similar reference numerals indicate similar elements, but are not limited thereto.

[0038] [Figure 1] This figure shows the results of the moisture effect evaluation experiment according to Experimental Example 3. [Modes for carrying out the invention]

[0039] Hereinafter, embodiments of the present invention will be described clearly and in detail with reference to the attached drawings, so that they can be easily implemented by a person with ordinary skill in the art to which the present invention pertains. However, these are presented as examples only and do not limit the present invention, which is defined only by the scope of the claims described below.

[0040] The terms or words used herein and in the claims shall not be construed to be limited to their ordinary or dictionary meanings, but rather to be construed in a way that is consistent with the technical idea of ​​the present invention, based on the principle that inventors may appropriately define the concepts of terms in order to best describe their invention.

[0041] In this specification, expressions such as "including" should be understood as open-ended terms that may include other embodiments.

[0042] In this specification, “preferred” and “preferred” refer to embodiments of the present invention that can provide a given advantage under a given environment. However, other embodiments may also be preferred under the same or different environments. Furthermore, reference to one or more preferred embodiments does not mean that other embodiments are not useful and does not attempt to exclude other embodiments from the scope of the present invention.

[0043] In the present invention, "insulating coating layer" means an insulating member formed by coating and drying at least a portion of the plain portion of the electrode current collector to at least a portion of the electrode mixture layer.

[0044] In the present invention, "metal test piece" refers to a space on which an insulating coating layer is formed, and can mean a metal current collector used in electrode manufacturing, which may be a metal current collector punched out to have a predetermined width and predetermined length. For example, the metal test piece may be aluminum, copper, or an aluminum alloy.

[0045] 1. Insulating layer composition for lithium secondary batteries

[0046] According to one embodiment of the present invention, an insulating layer composition for a lithium secondary battery is provided, comprising a conjugate diene copolymer as a binder polymer, a non-aqueous organic solvent, and an emulsifier, wherein the gel content is 70% by weight or more based on the total weight (gross weight) of the conjugate diene copolymer, and the emulsifier content is 0.3% by weight or more based on the total weight of the conjugate diene copolymer.

[0047] The following describes in detail each component of the insulating layer composition for lithium secondary batteries.

[0048] An insulating layer composition for lithium secondary batteries according to one embodiment of the present invention comprises a conjugated diene copolymer as a binder polymer.

[0049] The conjugate diene copolymer may include a polymer of (a) a conjugated diene monomer or conjugated diene polymer, (b) one or more monomers selected from the group consisting of acrylate monomers, vinyl monomers and nitrile monomers, and (c) one or more monomers selected from the group consisting of unsaturated carboxylic acid monomers and hydroxyl group-containing monomers.

[0050] The aforementioned conjugated diene monomer may be one monomer selected from the group consisting of 1,3-butadiene, isoprene, chloroprene, and piperylene.

[0051] The conjugated diene polymer may be, for example, a polymer of two or more monomers selected from the group consisting of 1,3-butadiene, isoprene, chloroprene, and piperine; a styrene-butadiene copolymer; an acrylonitrile-butadiene copolymer; a styrene-isoprene copolymer; an acrylate-butadiene rubber; an acrylonitrile-butadiene-styrene rubber; an ethylene-propylene-diene polymer; a polymer in which these polymers are partially epoxidized or brominated; or a mixture thereof.

[0052] The acrylate monomer may be one or more monomers selected from the group consisting of methyl ethylacrylate, methacryloxyethyl ethylene urea, β-carboxyethyl acrylate, aliphatic monoacrylate, dipropylene diacrylate, ditrimethylolpropane tetraacrylate, dipentaerythriol hexaacrylate, pentaerythriol triacrylate, pentaerythriol tetraacrylate, and glycidyl methacrylate.

[0053] The vinyl monomer may be at least one monomer selected from the group consisting of styrene, α-methylstyrene, β-methylstyrene, pt-butylstyrene, and divinylbenzene.

[0054] The nitrile monomer may be at least one monomer selected from the group consisting of acrylonitrile, methacrylonitrile, and allyl cyanide.

[0055] The aforementioned unsaturated carboxylic acid monomer may be at least one monomer selected from the group consisting of maleic acid, fumaric acid, methacrylic acid, acrylic acid, glutaric acid, itaconic acid, tetrahydrophthalic acid, crotonic acid, isocrotonic acid, and nadic acid.

[0056] The hydroxyl group-containing monomer may be one or more monomers selected from the group consisting of hydroxyacrylate, hydroxyethyl acrylate, hydroxybutyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, and hydroxybutyl methacrylate.

[0057] The insulating layer composition for lithium secondary batteries according to the present invention contains conjugated diene copolymer particles having an average particle size of 50 nm to 500 nm as independent phases.

[0058] Preferably, the conjugate diene copolymer may be a styrene-butadiene copolymer, and more preferably a styrene-butadiene latex, but is not limited thereto.

[0059] The method for producing the conjugate diene copolymer particles is not particularly limited and can be carried out by known methods such as suspension polymerization, emulsion polymerization, and seed polymerization.

[0060] A monomer mixture for producing copolymer particles may contain one or more other components, such as polymerization initiators, crosslinking agents, coupling agents, buffer solutions, molecular weight modifiers, and emulsifiers.

[0061] Specifically, the copolymer particles may be produced by emulsion polymerization. In this case, the average particle size of the copolymer particles may be adjusted by the amount of emulsifier. Generally, the particle size tends to decrease as the amount of emulsifier increases, and the particle size tends to increase as the amount of emulsifier decreases. The desired average particle size can be achieved by adjusting the amount of emulsifier used, taking into consideration the desired particle size, reaction time, reaction stability, etc. The polymerization temperature and polymerization time may be appropriately determined depending on the polymerization method, the type of polymerization initiator, etc. For example, the polymerization temperature may be 10°C to 150°C, and the polymerization time may be 1 to 20 hours.

[0062] As the polymerization initiator, inorganic or organic peroxides can be used. For example, water-soluble initiators containing potassium persulfate, sodium persulfate, ammonium persulfate, etc., and oil-soluble initiators containing cumene hydroperoxide, benzoyl peroxide, etc., can be used. Furthermore, an activator may be included together with the polymerization initiator to promote the initiation reaction of the peroxide. The activator may be one or more selected from the group consisting of sodium formaldehyde sulfoxylate, sodium ethylenediamine tetraacetate, ferrous sulfate, and dextrose.

[0063] The aforementioned crosslinking agent is a substance that promotes the crosslinking of the binder, and may include, for example, amines such as diethylene triamine, triethylene tetraamine, diethylamino propylamine, xylene diamine, isophorone diamine, dodecyl succinic anhydride, and phthalic anhydride. Acid anhydrides such as anhydride, polyamide resins, polysulfide resins, phenolic resins, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, 1,3-butanediol dimethacrylate, 1,6-hexanediol dimethacrylate, neopentyl glycol dimethacrylate, trimethylolpropane trimethacrylate, trimethylolmethane triacrylate, and glycidyl methacrylate are used as grafting agents, while aryl methacrylates (AMA), triaryl isocyanurates (TAIC), triarylamines (TAA), and diarylamines (DAA) are used.

[0064] The coupling agent is a substance for increasing the adhesion between an active material and a binder, and is characterized by having two or more functional groups, wherein one functional group reacts with a hydroxyl group or carboxyl group on the surface of a silicon, tin, or graphite-based active material to form a chemical bond, and the other functional groups are not particularly limited as long as they form a chemical bond through reaction with the nanocomposite according to the present invention. For example, silane coupling agents such as triethoxysilylpropyl tetrasulfide, mercaptopropyl triethoxysilane, aminopropyl triethoxysilane, chloropropyl triethoxysilane, vinyltriethoxysilane, methacryloxypropyl triethoxysilane, glycidoxypropyl triethoxysilane, isocyanatopropyl triethoxysilane, and cyanatopropyl triethoxysilane may be used.

[0065] The buffer may be, for example, one selected from the group consisting of NaHCO3, Na2CO3, K2HPO4, KH2PO4, Na2HPO4, NaOH, and NH4OH.

[0066] Examples of molecular weight modifiers include mercaptans or terfins such as terpinolenes, dipentenes, and t-terpienes, as well as halogenated hydrocarbons such as chloroform and carbon tetrachloride.

[0067] The conjugate diene copolymer may comprise, by weight, a polymer of (a) 20 to 45% by weight of a conjugated diene monomer or conjugated diene polymer, (b) 50 to 70% by weight of one or more monomers selected from the group consisting of acrylate monomers, vinyl monomers and nitrile monomers, and (c) 1 to 20% by weight of one or more monomers selected from the group consisting of unsaturated carboxylic acid monomers and hydroxyl group-containing monomers. Other components such as emulsifiers, buffers, and crosslinking agents may optionally be included in an amount ranging from 0.1 to 10% by weight.

[0068] If the content ratios of each monomer constituting the conjugate diene copolymer fall within the range described above, the Tg may be between -10°C and 40°C.

[0069] Furthermore, if the content ratios of each monomer constituting the conjugate diene copolymer fall within the aforementioned range, the flexibility, insulating properties, and electrolyte resistance of the insulating layer can be significantly improved.

[0070] In experimental examples of the present invention, it was confirmed that when the content ratio of each monomer constituting the conjugate diene copolymer falls within the range described above, both initial tackiness and insulating properties are excellent.

[0071] On the other hand, the average particle size of the copolymer may be between 50 nm and 500 nm. If the average particle size of the copolymer is less than 50 nm or greater than 500 nm, it is undesirable because the dispersion stability may decrease.

[0072] An insulating layer composition for lithium secondary batteries according to one embodiment of the present invention contains a non-aqueous organic solvent.

[0073] On the other hand, in the composition according to the present invention, when copolymer particles exist as independent phases, the adhesive strength improvement effect is enhanced, so it is very important to prevent the aforementioned agglomeration between particles. Therefore, the composition of the present invention includes a dispersion solvent for dispersing the copolymer particles. In the present invention, a non-aqueous organic solvent is used as such a dispersion solvent.

[0074] The non-aqueous organic solvent may be one or more selected from the group consisting of N-methyl-pyrrolidone (NMP), dimethylformamide (DMF) and dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), ethylene carbonate (EC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate (PC), dipropyl carbonate (DPC), butylene carbonate (BC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), acetonitrile, dimethoxyethane, tetrahydrofuran (THF), gamma-butyrolactone (γ-butyrolactone), methyl alcohol, ethyl alcohol, and isopropyl alcohol.

[0075] Preferably, the non-aqueous organic solvent may be N-methylpyrrolidone (NMP), but is not limited thereto.

[0076] An insulating layer composition for lithium secondary batteries according to one embodiment of the present invention contains an emulsifier. The inclusion of an emulsifier provides excellent storage stability for the insulating layer composition for lithium secondary batteries.

[0077] The emulsifier is a substance that simultaneously possesses both hydrophilic and hydrophobic groups. One specific example is that it may be at least one selected from the group consisting of anionic emulsifiers and nonionic emulsifiers.

[0078] When nonionic emulsifiers are used in conjunction with anionic emulsifiers, they help control particle size and distribution, providing further colloidal stabilization of polymer particles through van der Waals forces, in addition to the electrostatic stabilization of ionic emulsifiers. Nonionic emulsifiers are not often used alone because they produce particles that are less stable than those produced by anionic emulsifiers.

[0079] Anionic emulsifiers may be selected from the group consisting of phosphate-based, carboxylate-based, sulfate-based, succinate-based, sulfosuccinate-based, sulfonate-based, and disulfonate-based emulsifiers. For example, the emulsifier may be selected from the group consisting of sodium alkyl sulfate, sodium polyoxyethylene sulfate, sodium lauryl ether sulfate, sodium polyoxyethylene lauryl ether sulfate, sodium lauryl sulfate, sodium alkyl sulfonate, sodium alkyl ether sulfonate, sodium alkylbenzene sulfonate, sodium linear alkylbenzene sulfonate, sodium alpha-olefin sulfonate, sodium alcohol polyoxyethylene ether sulfonate, sodium dioctyl sulfosuccinate, sodium perfluorooctanesulfonate, sodium perfluorobutanesulfonate, alkyl diphenyl oxide disulfonate, sodium dioctyl sulfosuccinate (DOSS), sodium alkyl-aryl phosphate, alkyl ether phosphate, and sodium lauryl sarcosinate. However, it is not limited to these, and all known anionic emulsifiers may be included in the scope of the present invention.

[0080] The nonionic emulsifier may be of the ester type, ether type, or ester-ether type. For example, it may be polyoxyethylene glycol, polyoxyethylene glycol methyl ether, polyoxyethylene monoallyl ether, polyoxyethylene bisphenol-A ether, polypropylene glycol, or polyoxyethylene alkenyl ether. However, it is not limited to these, and all known nonionic emulsifiers may be included in the scope of the present invention.

[0081] On the other hand, the emulsifier content is 0.3% by weight or more based on the total weight of the conjugate diene copolymer. Preferably, the emulsifier content is 0.3% by weight or more and 5% by weight or less based on the total weight of the conjugate diene copolymer. If the emulsifier content is less than 0.3% by weight, the storage stability of the insulating layer composition for lithium secondary batteries will decrease, and if the emulsifier content exceeds 5% by weight, the insulating properties of the insulating layer composition for lithium secondary batteries may deteriorate.

[0082] A lithium secondary battery composition according to one embodiment of the present invention has a gel content of 70% by weight or more based on the total weight of the conjugate diene copolymer.

[0083] By including a high gel content of 70% by weight or more, the insulating layer composition for lithium secondary batteries has excellent storage stability, and by appropriately adjusting the initial adhesive strength so that it is not too high, it is possible to prevent electrodes from sticking together during the winding and slitting processes, which would otherwise worsen the processability.

[0084] On the other hand, the moisture content of the insulating layer composition for lithium secondary batteries may be 10,000 ppm or less, preferably 5,000 ppm or less, and more preferably 3,000 ppm or less. When the moisture content of the insulating layer composition for lithium secondary batteries is within the above range, it may be coated separately from the electrode (positive electrode) mixture layer, preventing the slurry for the electrode (positive electrode) mixture layer from penetrating into the slurry for the insulating coating layer, thereby preventing a decrease in the physical properties of the electrode, such as the failure to exhibit an insulating effect.

[0085] On the other hand, the insulating layer composition for lithium secondary batteries according to one embodiment of the present invention may not contain carboxymethylcellulose.

[0086] Although carboxymethylcellulose is sometimes used as a thickening agent in insulating layer compositions, its brittleness causes problems in winding and cutting processes, reducing processability. Therefore, the insulating layer composition for lithium secondary batteries according to the present invention does not contain carboxymethylcellulose, and thus is not brittle, which can improve processability in winding and cutting processes.

[0087] 2. Method for manufacturing a positive electrode for lithium secondary batteries

[0088] Another example of the present invention provides a method for producing a positive electrode for a lithium secondary battery, comprising the steps of: producing a water-dispersible conjugated diene copolymer; adding a non-aqueous organic solvent to the water-dispersible conjugated diene copolymer, heating and reducing pressure to produce a slurry for an insulating coating layer; applying the slurry for a positive electrode mixture layer, containing a positive electrode active material, a conductive material, a non-aqueous binder, and a non-aqueous organic solvent, to one or both sides of a positive electrode current collector; applying the slurry for an insulating coating layer so as to cover a portion of the slurry for the positive electrode mixture layer applied to the current collector from a portion of the plain portion of the positive electrode current collector; and drying the slurry for the positive electrode mixture layer and the slurry for the insulating coating layer applied to the positive electrode current collector, wherein the slurry for the insulating coating layer contains an emulsifier.

[0089] First, a water-dispersible conjugated diene copolymer is prepared. The method for its preparation is as disclosed in Section 1, "Insulating Layer Composition for Lithium Secondary Batteries," so its specific details are omitted here.

[0090] Next, the aqueous-dispersed conjugated diene copolymer is mixed with a non-aqueous organic solvent and then heated and subjected to reduced pressure.

[0091] At this time, the water that is the dispersion solvent for the conjugate diene copolymer particles is replaced with a non-aqueous organic solvent.

[0092] The present invention provides an extremely efficient manufacturing process for a positive electrode for a lithium secondary battery, as it allows the positive electrode to be manufactured by applying a slurry for the positive electrode mixture layer and a slurry for the insulating coating layer to a current collector, and then drying them together.

[0093] Preferably, the conjugate diene copolymer may be, but is not limited to, a conjugate diene latex.

[0094] Preferably, the conjugate diene latex may be, but is not limited to, styrene-butadiene latex.

[0095] Preferably, the non-aqueous organic solvent may be N-methylpyrrolidone (NMP), but is not limited thereto.

[0096] Preferably, after raising the temperature to a setting temperature of 40°C to 100°C during the heating process, the pressure can be reduced to less than 200 torr. This allows for efficient replacement of the water, which is the solvent for the water-dispersed conjugate diene latex, with a non-aqueous organic solvent.

[0097] Even after replacing the water dispersion solvent for conjugate diene latex particles with a non-aqueous organic solvent, the conjugate diene latex particles maintain their particle shape. Whether or not the particle shape is maintained can be confirmed by particle size measurement. Particle size can be determined using, but is not limited to, a DLS particle size analyzer, a laser diffraction particle size analyzer, or an electron transmission microscope.

[0098] Furthermore, the slurry for the insulating coating layer contains an emulsifier. The inclusion of an emulsifier in the slurry for the insulating coating layer results in excellent storage stability of the insulating layer composition for lithium secondary batteries manufactured using it.

[0099] Next, a slurry for the positive electrode mixture layer, containing positive electrode active material, a non-aqueous binder, a conductive material, and a non-aqueous organic solvent, is applied to one or both sides of the positive electrode current collector.

[0100] The positive electrode current collector for the lithium secondary battery according to the present invention can be made of a material that has high conductivity without inducing chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, etc. can be used, and in the case of aluminum or stainless steel, materials that have been surface-treated with carbon, nickel, titanium, silver, etc. can also be used. For example, the current collector may be aluminum.

[0101] In the slurry for the positive electrode mixture layer, all positive electrode active materials commonly used in positive electrodes can be used, and lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium iron oxide, or lithium composite oxides combining these materials may be used, but are not limited to these.

[0102] The non-aqueous binder may contain one or more resins selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, and copolymers thereof. As an example, the binder may contain polyvinylidene fluoride.

[0103] The conductive material is used to improve the electrical conductivity and other properties of the positive electrode, and can be one or more selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, and carbon fiber. For example, the conductive material may contain acetylene black.

[0104] The non-aqueous organic solvent may be one or more selected from the group consisting of N-methyl-pyrrolidone (NMP), dimethylformamide (DMF) and dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), ethylene carbonate (EC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate (PC), dipropyl carbonate (DPC), butylene carbonate (BC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), acetonitrile, dimethoxyethane, tetrahydrofuran (THF), gamma-butyrolactone, methyl alcohol, ethyl alcohol, and isopropyl alcohol, for example, N-methyl-2-pyrrolidone (NMP).

[0105] Simultaneously with or immediately after the step of applying the slurry for the positive electrode mixture layer, the slurry for the insulating coating layer is applied so as to cover a portion of the area of ​​the plain part of the positive electrode current collector with a portion of the slurry for the positive electrode mixture layer applied to the current collector.

[0106] Specifically, in the step of applying the insulating coating layer slurry to the current collector, the insulating layer slurry can be applied while the positive electrode mixture layer slurry is still wet, or the positive electrode mixture layer slurry and the insulating layer slurry can be applied simultaneously.

[0107] Next, the slurry for the positive electrode mixture layer and the slurry for the insulating coating layer applied to the positive electrode current collector are dried.

[0108] The step of drying the slurry for the positive electrode mixture layer and the slurry for the insulating coating layer can be carried out using drying methods commonly known in the art, which can completely dry the slurry for the positive electrode mixture layer and the slurry for the insulating coating layer and remove the solvent.

[0109] In specific examples, drying can be performed using various methods such as hot air, direct heating, or induction heating, at a temperature at which all of the solvent evaporates, and is not limited to these methods. For example, the step of drying the insulating coating liquid can be carried out using the hot air method.

[0110] In this case, the drying temperature may be in the range of 50°C to 300°C, preferably 60 to 200°C, and more preferably 70 to 150°C. On the other hand, if the drying temperature of the insulating coating liquid is less than 50°C, the temperature may be too low and it may be difficult to completely dry the insulating coating liquid, and if the drying temperature exceeds 300°C, the drying temperature may be too high and deformation of the electrodes may occur.

[0111] This allows a positive electrode mixture layer and an insulating coating layer to be formed on the positive electrode current collector, which can then be rolled to manufacture a positive electrode for lithium secondary batteries.

[0112] 3. Positive electrode for lithium secondary batteries

[0113] According to another example of the present invention, a positive electrode for a lithium secondary battery is provided, comprising a positive electrode current collector, a positive electrode tab protruding from the positive electrode current collector, and an insulating layer coated with an insulating material on the positive electrode tab, wherein the insulating material includes the lithium secondary battery insulating layer composition.

[0114] Another embodiment of the present invention provides a positive electrode for a lithium secondary battery that includes an insulating layer containing the lithium secondary battery insulating layer composition on the positive electrode tab. This allows for the simultaneous application of the slurry for the positive electrode mixture layer and the slurry for the insulating coating layer, significantly shortening the battery manufacturing process, ultimately reducing the battery manufacturing cost, and further improving battery safety by widening the insulating area. Moreover, it has the effect of significantly reducing the possibility of detachment when the positive electrode tab is bent for attachment to the relevant area, which can occur when using conventional insulating films or tapes, and does not cause an increase in the thickness of the electrode assembly.

[0115] 4. Lithium-ion batteries

[0116] According to another embodiment of the present invention, a lithium secondary battery including the positive electrode for the lithium secondary battery is provided.

[0117] More specifically, another embodiment of the present invention may include a lithium secondary battery comprising a positive electrode, a negative electrode, a separator membrane, and an electrolyte for the lithium secondary battery.

[0118] Furthermore, the lithium secondary battery may selectively further include a battery container for housing the electrode assembly comprising the positive electrode, negative electrode, and separator membrane, and a sealing member for sealing the battery container.

[0119] The negative electrode may include a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0120] The negative electrode current collector is not particularly limited as long as it has high conductivity without inducing chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloys can be used. The negative electrode current collector can also typically have a thickness of 3 μm to 500 μm, and, similar to the positive electrode current collector, fine irregularities can be formed on the surface of the current collector to strengthen the bonding force of the negative electrode active material. For example, it can be used in a variety of forms such as film, sheet, foil, net, porous material, foam, and nonwoven fabric.

[0121] The negative electrode active material layer may optionally include a binder and a conductive material together with the negative electrode active material.

[0122] As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium can be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon, and metallic compounds that can alloy with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys, and SiO βExamples include metal oxides that can be doped and dedoped with lithium, such as (0<β<2), SnO2, vanadium oxide, and lithium vanadium oxide, and composites containing the metallic compound and carbonaceous material, such as Si-C composites or Sn-C composites. One or more of these can be used as a mixture of two or more. A metallic lithium thin film can also be used as the negative electrode active material. In addition, both low-crystalline carbon and high-crystalline carbon can be used as the carbon material. Typical examples of low-crystalline carbon include soft carbon and hard carbon, while typical examples of high-crystalline carbon include amorphous, plate-like, flaky, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch-derived cokes.

[0123] The aforementioned negative electrode active material is included in an amount of 80 to 99 parts by weight, based on the total weight of the negative electrode active material layer.

[0124] The aforementioned binder is a component that assists in bonding between the conductive material, active material, and current collector, and is usually added in an amount of 0.1 to 10 parts by weight based on the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0125] The conductive material is a component for further improving the conductivity of the negative electrode active material, and is added in an amount of 10 parts by weight or less, preferably 5 parts by weight or less, based on the total weight of the negative electrode active material layer. Such a conductive material is not particularly limited as long as it does not induce a chemical change in the battery and has conductivity, and for example, graphite such as natural graphite or artificial graphite, carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black, conductive fibers such as carbon fibers and metal fibers, metal powders such as carbon fluoride, aluminum, and nickel powder, conductive whiskey such as zinc oxide and potassium titanate, conductive metal oxides such as titanium oxide, and conductive materials such as polyphenylene derivatives can be used.

[0126] The negative electrode active material layer may be manufactured by applying a negative electrode active material layer-forming composition, which is prepared by dissolving or dispersing a negative electrode active material, a binder, and a conductive material in a solvent, onto a negative electrode current collector and drying it, or by casting the negative electrode active material layer-forming composition onto a separate support, peeling it off the support, and then laminating the resulting film onto the negative electrode current collector.

[0127] The separation membrane separates the negative and positive electrodes, providing a pathway for lithium ions to move. Any membrane commonly used as a separation membrane in lithium secondary batteries can be used without special limitations, and those with low resistance to electrolyte ion movement while having excellent electrolyte moisture absorption capacity are particularly preferred. Specifically, porous polymer films, such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminated structures of two or more layers thereof, are used. In addition, ordinary porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, may also be used. Furthermore, to ensure heat resistance or mechanical strength, coated separation membranes containing ceramic components or polymeric substances may be used, and they may be used in single-layer or multi-layer structures as desired.

[0128] The aforementioned electrolytes include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0129] Specifically, the organic liquid electrolyte may include an organic solvent and a lithium salt.

[0130] The organic solvent can be any solvent that can function as a medium through which ions involved in the electrochemical reaction of the battery can move, without any special limitations. Specifically, the organic solvents include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; and dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (propylene Carbonate solvents such as carbonate (PC), alcohol solvents such as ethyl alcohol and isopropyl alcohol, nitriles such as R-CN (where R is a hydrocarbon group with 2 to 20 carbon atoms in a linear, branched, or cyclic structure, and may include double bonds, aromatic rings, or ether bonds), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, or sulfolanes can be used. Among these, carbonate solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant that can improve the charge and discharge performance of the battery, and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) is more preferred. In this case, mixing the cyclic carbonate and linear carbonate in a volume ratio of about 1:1 to about 1:9 may result in superior electrolyte performance.

[0131] The lithium salt can be used without any particular limitations, as long as it is a compound that can provide lithium ions for use in lithium secondary batteries. Specifically, the lithium salt can be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2, etc. The concentration of the lithium salt is preferably in the range of 0.1 to 2.0 M. When the concentration of the lithium salt falls within this range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance and lithium ions can move effectively.

[0132] In addition to the electrolyte components, the electrolyte may also contain one or more additives for the purpose of improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity, such as haloalkylene carbonate compounds like difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, and aluminum trichloride. In this case, the additive may be included in an amount of 0.1 to 5 parts by weight relative to the total weight of the electrolyte.

[0133] The embodiments of the present invention will be described in more detail below through examples. However, the following examples are merely preferred embodiments of the present invention, and the present invention is not limited to the following examples.

[0134] Example 1

[0135] Five parts by weight of 55 nm particle size styrene-butadiene seed latex were placed in a reactor and heated to 80°C. Then, 35 g of 1,3-butadiene, 62 g of styrene, and 3 g of itaconic acid were added to the reactor over a period of 4 hours. These additions included 35 g of 1,3-butadiene as monomer, 62 g of styrene, 3 g of itaconic acid, 0.5 g of NaHCO3 as buffer, 1 g of sodium polyoxyethylene lauryl ether sulfate as emulsifier, 1 g of dodecyl mercaptan as molecular weight modifier, and 1 g of potassium persulfate as polymerization initiator. The reaction was carried out over another 4 hours while maintaining the temperature at 80°C to produce a 50% solids styrene-butadiene copolymer latex. During this time, the pH was adjusted to neutral (7) using sodium hydroxide. After polymerization, the size of the copolymer particles was analyzed using a submicron particle sizer (Nicomp™ 380). The average particle size of the polymerized copolymer particles was 150 nm, and the gel content was 85%.

[0136] 100 g of the manufactured styrene-butadiene copolymer latex was placed in a reactor, 700 g of NMP (N-methylpyrrolidone) was added and mixed, and the temperature was raised to 90°C. Then, the pressure was reduced to 15 torr over 3 hours to replace the water, which was the dispersion solvent for the styrene-butadiene copolymer particles, with NMP, thereby producing a composition containing the styrene-butadiene copolymer dispersed in NMP. At this time, the final water content was 10,000 ppm or less, and after checking the solid content, NMP was added until the final solid content was 7.6%. The water content of the final product was measured using a Karl Fischer moisture meter.

[0137] Example 2

[0138] In Example 1, 30 g of 1,3-butadiene, 60 g of styrene, 5 g of methyl methacrylate, 2 g of acrylonitrile, 1 g of hydroxyacrylate, and 3 g of itaconic acid were used as monomers, and alkyl diphenyl oxide disulfonate was used as an emulsifier instead of sodium polyoxyethylene lauryl ether sulfate. An additional 1 g of alkyl diphenyl oxide was added before NMP substitution, and a composition containing the styrene-butadiene copolymer dispersed in NMP was prepared in the same manner as in Example 1.

[0139] Example 3

[0140] A composition containing a styrene-butadiene copolymer dispersed in NMP was prepared in the same manner as in Example 1, except that dodecyl mercaptan was not used as a molecular weight modifier, 0.4 g of sodium polyoxyethylene lauryl ether sulfate was used as an emulsifier, and 450 g of NMP was used.

[0141] Example 4

[0142] A composition containing a styrene-butadiene copolymer dispersed in NMP was prepared in the same manner as in Example 1, except that 2 g of sodium lauryl sulfate was added as an emulsifier before adding the NMP.

[0143] Example 5

[0144] A composition containing a styrene-butadiene copolymer dispersed in NMP was prepared in the same manner as in Example 1, except that 5 g of sodium lauryl sodium lauryl sulfate was added as an emulsifier before adding the NMP.

[0145] Comparative Example 1

[0146] A composition containing a styrene-butadiene copolymer dispersed in NMP was prepared in the same manner as in Example 1, except that 2.3 g of dodecyl mercaptan was used as a molecular weight modifier and the amount of NMP was increased to 1000 g.

[0147] Comparative Example 2

[0148] A composition containing a styrene-butadiene copolymer dispersed in NMP was prepared in the same manner as in Example 1, except that the amount of sodium polyoxyethylene lauryl ether sulfate used as an emulsifier was reduced to 0.1 g.

[0149] Comparative Example 3

[0150] A composition with 8% solids content was prepared by dissolving PVDF (polyvinylidene fluoride) in NMP.

[0151] Comparative Example 4

[0152] A hydrogenated nitrile rubber with 0% gel content was dissolved in NMP to produce a composition with 8% solid content.

[0153] Comparative Example 5

[0154] A styrene-butadiene synthetic rubber with 0% gel content was dissolved in NMP to produce a composition with 8% solid content.

[0155] Comparative Example 6

[0156] A styrene-butadiene copolymer latex with a solid content of 50% was prepared using the same method as in Example 2.

[0157] 100 g of the manufactured styrene-butadiene copolymer latex was placed in a reactor, 530 g of NMP (N-methyl-pyrrolidone) was added and mixed, and the temperature was raised to 85°C. Then, the pressure was reduced to 180 torr over 1 hour to replace the water, which was the dispersion solvent for the styrene-butadiene copolymer particles, with NMP, thereby producing a composition containing styrene-butadiene copolymer dispersed in NMP. NMP was added until the final solids content was 8%, and the final water content at this time was 50,010 ppm. The water content of the final product was measured using a Karl Fischer moisture meter.

[0158] Comparative Example 7

[0159] A styrene-butadiene copolymer latex with a solid content of 50% was prepared using the same method as in Example 2.

[0160] 100 g of the manufactured styrene-butadiene copolymer latex was placed in a reactor, 530 g of NMP (N-methylpyrrolidone) was added and mixed, and the temperature was raised to 90°C. Then, the pressure was reduced to 100 torr over 7 hours to replace the water, which was the dispersion solvent for the styrene-butadiene copolymer particles, with NMP, thereby producing a composition containing styrene-butadiene copolymer dispersed in NMP. At this time, NMP was added to bring the final solids content to 8%, and the final water content was 12,201 ppm. The water content of the final product was measured using a Karl Fischer moisture meter.

[0161] Comparative Example 8

[0162] To compare with a composition containing styrene-butadiene latex without dispersion solvent substitution, a composition was prepared by mixing the styrene-butadiene latex produced in Example 2 with carboxymethylcellulose in a 9:1 weight ratio without separate solvent substitution. Carboxymethylcellulose is used as a thickener to improve the coating properties of styrene-butadiene latex without separate solvent substitution.

[0163] Experimental Example 1

[0164] The water content, viscosity, gel content, and total emulsifier content of the compositions prepared in Examples 1-5 and Comparative Examples 1-7 were measured according to the methods described in Experimental Examples 1-1, 1-2, 1-3, and 1-4 below, and the results are shown in Table 1 below. The total emulsifier content (%) below is based on the total solid content of the composition.

[0165] [Table 1]

[0166] Experimental Example 1-1: Measurement of Moisture Content

[0167] For the compositions prepared in Examples 1-5 and Comparative Examples 1-7, the moisture content was measured by weighing 0.1-0.4 g of sample using a Metrohm 899 Coulometer connected to an 860 KF Thermoprep (oven), with the oven temperature set to 220°C.

[0168] Experimental Example 1-2: Viscosity Measurement

[0169] The viscosity of the compositions prepared in Examples 1-5 and Comparative Examples 1-7 was measured after rotating them at 12 rpm using the No. 63 spindle of a Brookfield LV viscometer at a temperature of 25°C for 1 minute. If the viscosity fell outside the measurement range, the rpm value was reduced and the measurement was repeated.

[0170] Experimental Example 1-3: Measurement of Gel Content

[0171] The gel content was measured for the compositions prepared in Examples 1-5 and Comparative Examples 1-7. 10 g of the obtained sample was dried at 135°C for 30 minutes, then a thin film was made and cut into strips 2 mm x 2 mm wide. A dish was prepared using a 200-mesh mesh and weighed using a precision balance, with the weight denoted as A. 0.3-0.4 g of the cut film was placed in the dish, and the weight of the film was measured and denoted as B. The dish was placed in a 100 ml glass bottle, 75 ml of tetrahydrofuran was added, and the dish and glass bottle were sealed. After sonication in a water bath ultrasonic device for 3 hours, the dish was removed, washed with 50 ml of tetrahydrofuran, dried in a 135°C oven for 30 minutes, and the weight was measured using a precision balance, with the weight denoted as C. During sonication, the water bath temperature should not exceed 50°C. The final gel content (%) was calculated using the following formula.

[0172] Gel content (%) = (CA) / B * 100

[0173] Experimental Example 1-4: Measurement of Total Emulsifier Amount

[0174] The total amount of emulsifier was measured for the compositions prepared in Examples 1-5 and Comparative Examples 1-7. Acetonitrile / methanol was applied to 0.5 g of the obtained sample to precipitate the polymer components. After stirring for 1 hour, the polymer was precipitated using a centrifuge, and the supernatant was filtered. The amount of emulsifier was then measured using HPLC / PDA / MS. The total amount of emulsifier is shown in Table 1, converted to the ratio of emulsifier content to the total weight of solids.

[0175] Experimental Example 2

[0176] Experiments to evaluate the initial tackiness, storage stability, and insulation properties of the compositions produced in Examples 1-5 and Comparative Examples 1-5 were carried out according to the methods described in Experimental Examples 2-1, 2-2, and 2-3 below, and the results are shown in Table 2 below.

[0177] [Table 2]

[0178] Experimental Example 2-1: Evaluation of Initial Tackiness

[0179] The compositions prepared in Examples 1-5 and Comparative Examples 1-5 were coated onto aluminum metal foil and dried at 130°C to prepare metal samples with an insulating coating layer approximately 10 μm thick. After cutting the metal samples to a size of 2 cm × 12 cm, they were laminated onto a SUS plate, and the 90° adhesion strength was measured. The results are shown in Table 2 below.

[0180] As can be seen from Table 2, all compositions in Examples 1 to 5 were found to have low initial tackiness. Low initial tackiness reduces the likelihood of adhesion to electrodes or current collectors during the winding and slitting processes, thus degrading processability. On the other hand, Comparative Example 1, which had a gel content of less than 70% by weight, and Comparative Examples 4 and 5, which had no gel content, had excessively high initial tackiness, which could cause electrodes to stick together during the winding and slitting processes, degrading processability.

[0181] Experimental Example 2-2: Evaluation of Storage Stability

[0182] The compositions prepared in Examples 1-5 and Comparative Examples 1-5 were each placed in 250 ml glass bottles (200 ml each), sealed, stored in a 100°C oven for 7 days, then removed and stored at room temperature for 1 day. The solid content of the upper layer was measured, and the rate of decrease in solid content relative to the base solid content was measured. The results are shown in Table 2.

[0183] The composition of Comparative Example 1, which has a low gel content, and the composition of Comparative Example 2, which has a low emulsifier content, show a higher rate of solid content reduction compared to the compositions of Examples 1 to 5. Therefore, it is likely that phase separation will occur over time, resulting in a definite decrease in storage stability.

[0184] Experimental Example 2-3: Evaluation of Insulation Characteristics

[0185] LiNi 0.8 Co 0.2Mn 0.2 A slurry for the positive electrode mixture layer was prepared by weighing parts by weight of O296, 2 parts by weight of PVdF as a binder, and 2 parts by weight of carbon black as a conductive material, and mixing them in N-methylpyrrolidone (NMP) solvent. The slurry for the mixture layer was applied to aluminum foil, dried, and then rolled to produce a positive electrode with a positive electrode mixture layer with a thickness of 60 μm.

[0186] Subsequently, the insulating liquid compositions prepared in Examples 1-5 and Comparative Examples 1-5 were applied to the positive electrode mixture layer and then dried to form a positive electrode insulating layer with a thickness of 10 μm.

[0187] Using the aforementioned positive electrode, a lithium foil was used as the negative electrode, and a coin-type half-cell was manufactured using an electrolyte containing 1M LiPF4 in a solvent with an EC:EMC ratio of 3:7. After storing the coin-type half-cell in a 60°C oven for 15 days, the discharge capacity of the half-cell was measured to confirm the insulating effect of the insulating layer. For comparison, a half-cell was manufactured with a positive electrode without an insulating coin layer, and the 0.1C discharge capacity was set to 100. The discharge capacity ratio of the positive electrodes with insulating coating layers formed using the compositions of Examples 1-5 and Comparative Examples 1-5 was calculated, and the results are shown in Table 2 below.

[0188] As can be seen from Table 2, the compositions of Comparative Examples 3 to 5 were found to have a higher 0.1C discharge capacity ratio compared to the compositions of Examples 1 to 5. This is because the insulating layer swell or detached, reducing its insulating performance and allowing some of the positive electrode capacity beneath the insulating layer to be expressed. In Example 5, which had an emulsifier content of 5.39%, slightly higher than that of Examples 1 to 4, it was confirmed that the excess emulsifier slightly reduced the wet adhesion strength in the electrolyte, allowing some of the positive electrode capacity to be expressed.

[0189] Experimental Example 3: Evaluation of the effect of moisture

[0190] LiNi 0.8 Co 0.2 Mn 0.2Parts by weight of O296, 2 parts by weight of PVdF as a binder, and 2 parts by weight of carbon black as a conductive material were weighed out and mixed in N-methylpyrrolidone (NMP) solvent to produce a slurry for the cathode composite layer.

[0191] Then, the slurry for the positive electrode mixture layer and the slurry for the insulating coating layer, which was the composition produced in Example 2 and Comparative Examples 6 to 8, were simultaneously applied to the current collector using a doctor blade so as to be overlaid. The condition immediately after application and 1 minute after application were observed, and these are shown in Figure 1.

[0192] As can be seen in Figure 1, a comparison of the state immediately after application and 1 minute after application showed that the composition of Example 2 maintained its initially coated state without penetration of the overlay portion both immediately after application and 1 minute after application. However, the compositions of Comparative Examples 6 to 8, which had a higher water content than Example 2, were unable to reliably maintain the coating boundary because the electrode slurry penetrated into the insulating layer. In particular, in the case of Comparative Example 8, in which the dispersion solvent was not replaced, the area where the positive electrode slurry and the insulating liquid came into contact was agglomerated by water immediately after application. This confirms that simultaneous coating with the positive electrode slurry is impossible with an aqueous insulating liquid that has not been solvent-substituted.

[0193] This can be interpreted as meaning that if the water content of the slurry for the positive electrode insulating coating layer exceeds 10,000 ppm, when the slurry for the positive electrode mixture layer and the slurry for the insulating layer are coated simultaneously, the slurry for the positive electrode mixture layer may penetrate into the slurry for the positive electrode insulating coating layer, making it difficult to achieve the expected insulating effect.

[0194] Experimental Example 4: Evaluation of the effects of carboxymethylcellulose

[0195] The compositions prepared in Example 2 and Comparative Example 8 were coated onto a substrate to a final thickness of 20 μm, dried at 130°C, and then cut into 2 cm wide strips. Brittleness was then measured. After folding the sample in half at room temperature, pressing it once with a 1 kg roller and then unfolding it, the coating film was visually inspected for cracks or tears, and the results are shown in Figure 2 below. In Example 1, the film did not crack or tear, but in Comparative Example 8, the film did tear. The composition of Comparative Example 8 is a mixture of styrene-butadiene latex prepared in Example 2 with carboxymethylcellulose in a weight ratio of 9:1 without separate solvent replacement. Because this composition exhibits high brittleness even with the addition of a small amount of carboxymethylcellulose, a thickening agent, it affects the coating film. Therefore, even when styrene-butadiene latex is coated separately instead of simultaneously, the insulating layer can be damaged or detached during the winding and slitting process for this reason.

[0196] Although preferred embodiments of the present invention have been described above, the present invention is not limited thereto, and can be implemented in various ways within the scope of the claims, the detailed description of the invention, and the accompanying drawings, and these also naturally fall within the scope of the present invention.

[0197] Therefore, the substantial scope of the present invention should be defined by the appended claims and their equivalents.

Claims

1. Conjugate diene copolymer as a binder polymer, Non-aqueous organic solvents, Contains emulsifiers, The gel content is 70% by weight or more based on the total solids weight. The emulsifier content is 0.3% by weight or more based on the total solids weight. It does not contain carboxymethylcellulose. The moisture content is 10,000 ppm or less. Insulating layer composition for lithium secondary batteries.

2. The conjugate diene copolymer comprises a polymer of (a) a conjugated diene monomer or conjugated diene polymer, (b) at least one monomer selected from the group consisting of acrylate monomers, vinyl monomers and nitrile monomers, and (c) at least one monomer selected from the group consisting of unsaturated carboxylic acid monomers and hydroxyl group-containing monomers. The insulating layer composition for lithium secondary batteries according to claim 1.

3. The aforementioned conjugated diene monomer is one monomer selected from the group consisting of 1,3-butadiene, isoprene, chloroprene, and piperylene. The conjugated diene polymer is a polymer of two or more monomers selected from the group consisting of 1,3-butadiene, isoprene, chloroprene, and piperine; a styrene-butadiene copolymer; an acrylonitrile-butadiene copolymer; a styrene-isoprene copolymer; an acrylate-butadiene rubber; an acrylonitrile-butadiene-styrene rubber; an ethylene-propylene-diene polymer; or a polymer in which these polymers are partially epoxidized or brominated; or a mixture thereof. The insulating layer composition for lithium secondary batteries according to claim 2.

4. The acrylate monomer is at least one monomer selected from the group consisting of methyl ethylacrylate, methacryloxyethyl ethylene urea, β-carboxyethyl acrylate, aliphatic monoacrylate, dipropylene diacrylate, ditrimethylolpropane tetraacrylate, dipentaerythriol hexaacrylate, pentaerythriol triacrylate, pentaerythriol tetraacrylate, and glycidyl methacrylate. The insulating layer composition for lithium secondary batteries according to claim 2.

5. The vinyl monomer is at least one monomer selected from the group consisting of styrene, α-methylstyrene, β-methylstyrene, p-t-butylstyrene, and divinylbenzene. The insulating layer composition for lithium secondary batteries according to claim 2.

6. The nitrile monomer is one or more monomers selected from the group consisting of acrylonitrile, methacrylonitrile, and allyl cyanide. The insulating layer composition for lithium secondary batteries according to claim 2.

7. The aforementioned unsaturated carboxylic acid monomer is at least one monomer selected from the group consisting of maleic acid, fumaric acid, methacrylic acid, acrylic acid, glutaric acid, itaconic acid, tetrahydrophthalic acid, crotonic acid, isocrotonic acid, and nadic acid. The insulating layer composition for lithium secondary batteries according to claim 2.

8. The hydroxyl group-containing monomer is one or more monomers selected from the group consisting of hydroxyacrylate, hydroxyethyl acrylate, hydroxybutyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, and hydroxybutyl methacrylate. The insulating layer composition for lithium secondary batteries according to claim 2.

9. The conjugate diene copolymer comprises, by weight, (a) 20 to 45% by weight of a conjugated diene monomer or conjugated diene polymer, (b) 50 to 70% by weight of at least one monomer selected from the group consisting of acrylate monomers, vinyl monomers and nitrile monomers, and (c) 1 to 20% by weight of one or more monomers selected from the group consisting of unsaturated carboxylic acid monomers and hydroxyl group-containing monomers. The insulating layer composition for lithium secondary batteries according to claim 2.

10. The non-aqueous organic solvent is at least one selected from the group consisting of N-methylpyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), ethylene carbonate (EC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate (PC), dipropyl carbonate (DPC), butylene carbonate (BC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), acetonitrile, dimethoxyethane, tetrahydrofuran (THF), gamma-butyrolactone (γ-butyrolactone), methyl alcohol, ethyl alcohol, and isopropyl alcohol. The insulating layer composition for lithium secondary batteries according to claim 1.

11. The conjugate diene copolymer particles, having an average particle size of 50 nm or more and 500 nm or less, exist as an independent phase. The insulating layer composition for lithium secondary batteries according to claim 1.

12. The conjugate diene copolymer is a styrene-butadiene copolymer, and the non-aqueous organic solvent is N-methylpyrrolidone (NMP). The insulating layer composition for lithium secondary batteries according to claim 1.

13. The conjugate diene copolymer is a styrene-butadiene copolymer latex, and the non-aqueous organic solvent is N-methyl-pyrrolidone (NMP). The insulating layer composition for lithium secondary batteries according to claim 1.

14. A step of producing a water-dispersed conjugate diene copolymer, A step of producing a slurry for an insulating coating layer by mixing a non-aqueous organic solvent with the water-dispersed conjugate diene copolymer, and then heating and reducing the pressure. A step of applying a slurry for a positive electrode mixture layer containing a positive electrode active material, a non-aqueous binder, a conductive material, and a non-aqueous organic solvent to one or both sides of a positive electrode current collector, The steps include: applying the insulating coating layer slurry so as to cover a portion of the slurry for the positive electrode mixture layer applied to the current collector, from a portion of the plain area of ​​the positive electrode current collector to a portion of the slurry for the positive electrode mixture layer applied to the current collector; The process includes a step of drying the slurry for the positive electrode mixture layer and the slurry for the insulating coating layer applied to the positive electrode current collector, The slurry for the insulating coating layer contains an emulsifier. A method for manufacturing a positive electrode for lithium secondary batteries.

15. The step of producing the slurry for the insulating coating layer includes replacing the water, which is the dispersion solvent for the conjugate diene copolymer particles, with a non-aqueous organic solvent. A method for manufacturing a positive electrode for a lithium secondary battery according to claim 14.

16. The conjugate diene copolymer particles maintain their particle shape even after the dispersion solvent is replaced with a non-aqueous organic solvent. A method for manufacturing a positive electrode for a lithium secondary battery according to claim 15.

17. The aforementioned conjugate diene copolymer is a conjugate diene latex. A method for manufacturing a positive electrode for a lithium secondary battery according to any one of claims 14 to 16.

18. The aforementioned conjugate diene copolymer is styrene-butadiene latex, The aforementioned non-aqueous organic solvent is N-methylpyrrolidone (NMP). A method for manufacturing a positive electrode for a lithium secondary battery according to claim 14.

19. Positive electrode current collector and A positive electrode tab protruding from the positive electrode current collector, The positive electrode tab comprises an insulating layer coated with an insulating material, The insulating material includes the composition described in claim 1. Positive electrode for lithium secondary batteries.

20. A positive electrode for a lithium secondary battery as described in claim 19, Lithium-ion rechargeable battery.

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