Slurry composition for positive electrode of lithium secondary battery

Abstract

The present invention relates to a slurry composition for a positive electrode of a lithium secondary battery, and more specifically, is prepared by mixing a positive electrode active material and a one-component carbon nanotube-binder slurry, wherein the one-component carbon nanotube-binder slurry is prepared by adding carbon nanotubes, a binder, and a dispersant to a solvent and mixing them. The slurry composition for a positive electrode of a lithium secondary battery according to the present invention has a higher final solid content compared to conventional positive electrode slurry compositions, and has the effect of having high flowability and stability over time relative to the solid content.

Description

Technology Field

[0001] The present invention relates to a slurry composition for a positive electrode of a lithium secondary battery having a high solid content and improved stability over time. Background Technology

[0002] Rechargeable batteries are a representative example of electrochemical devices that utilize electrochemical energy, and their application areas are increasingly expanding. Recently, with the technological development and growing demand for portable devices such as portable computers, mobile phones, and cameras, the demand for rechargeable batteries as an energy source has been rapidly increasing. Among these rechargeable batteries, much research has been conducted on lithium-ion batteries, which have high energy density and high capacity, and they have also been commercialized and are widely used.

[0003] Generally, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. The positive and negative electrodes generally consist of an electrode current collector and an electrode active material layer formed on the electrode current collector, and the electrode active material layer is manufactured by applying an electrode slurry composition containing an electrode active material, a conductive material, a binder, etc. onto the electrode current collector, drying it, and then rolling it.

[0004] Meanwhile, point-type conductive materials such as carbon black have conventionally been primarily used as conductive materials for secondary batteries; however, these point-type materials have the problem of not providing sufficient improvement in electrical conductivity. To address this issue, research is actively underway on methods to apply linear conductive materials such as carbon nanotubes (CNT) or carbon nanofibers (CNF).

[0005] However, in the case of linear conductive materials such as carbon nanotubes or carbon nanofibers, although electrical conductivity is excellent, the dispersibility within the slurry is poor due to the nature of the material itself, which grows in a bundle or entangle type, resulting in poor flowability and processability of the slurry. In particular, when the solid content of the binder is increased, the viscosity becomes excessively high, causing a problem where flowability is significantly reduced. Even if the viscosity is lowered by reducing the solid content of the binder, the initially good flowability cannot be maintained above a certain level for a long period of time. Prior art literature

[0006] Korean Patent Publication No. 2019-0117387 (October 16, 2019) The problem to be solved

[0007] The present invention was developed to solve the above-mentioned problems and aims to provide a slurry composition for a positive electrode of a lithium secondary battery that can increase the content of the final solid content and has high flowability and stability over time compared to the high solid content.

[0008] The problems that the present invention aims to solve are not limited to the technical problems mentioned above, and other unmentioned technical problems will be clearly understood by those skilled in the art to which the present invention belongs from the description below. means of solving the problem

[0009] The present invention, for solving the above-mentioned problems, relates to a slurry composition for a positive electrode of a lithium secondary battery, and more specifically, is characterized by being prepared by mixing a carbon nanotube-binder composite produced by mixing and stirring a positive electrode active material, a carbon nanotube and a binder, and a dispersant. Effects of the invention

[0010] The slurry composition for a positive electrode of a lithium secondary battery according to the present invention has a higher final solid content compared to conventional slurry compositions for positive electrodes, which allows for a reduction in drying time, thereby increasing the production speed of the battery and enabling the manufacture of high-capacity electrodes, and has the effect of having high flowability and stability over time relative to the solid content. Brief explanation of the drawing

[0011] Figure 1 is a graph showing the results of measuring the adhesion of electrodes according to the content of the dispersant for the examples and comparative examples. Specific details for implementing the invention

[0012] The present invention is capable of various modifications and may have various embodiments; specific embodiments are illustrated in the drawings and described in detail in the detailed description. However, this is not intended to limit the present invention to specific embodiments, and it should be understood that it includes all modifications, equivalents, and substitutions that fall within the spirit and scope of the present invention. In describing the present invention, detailed descriptions of related prior art are omitted if it is determined that such detailed descriptions may obscure the essence of the present invention.

[0013] The terms used in this application are used merely to describe specific embodiments and are not intended to limit the invention. The singular expression includes the plural expression unless the context clearly indicates otherwise. In this application, terms such as "comprising" or "having" are intended to specify the presence of the features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, and should be understood as not precluding the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof.

[0014] Terms such as "first," "second," etc., may be used to describe various components, but said components should not be limited by said terms. These terms are used solely for the purpose of distinguishing one component from another.

[0015] The present invention relates to a slurry composition for a positive electrode of a lithium secondary battery, and more specifically, is prepared by mixing a positive electrode active material and a one-component carbon nanotube-binder slurry, wherein the one-component carbon nanotube-binder slurry is prepared by adding carbon nanotubes, a binder, and a dispersant to a solvent and mixing them. The present invention allows for an increase in the content of the final solid component compared to a conventional cathode slurry prepared by simultaneously mixing a carbon nanotube, a binder, and a dispersant with a solvent, and then mixing the prepared one-component carbon nanotube-binder slurry with an active material for a cathode. Furthermore, it allows for increased convenience for the operator in preparing the cathode slurry composition, and furthermore, as the content of the final solid component increases, the drying time can be shortened, thereby increasing the production speed of the battery and enabling the manufacture of high-capacity electrodes. Additionally, it allows for the improvement of electrochemical characteristics such as output characteristics and lifespan characteristics of the lithium secondary battery.

[0016] However, in order to use the above-mentioned one-component carbon nanotube-binder slurry in the preparation of an anode slurry composition, it is important to ensure the storage stability of the above-mentioned one-component carbon nanotube-binder slurry. To this end, the present invention is characterized by adding a dispersant when mixing carbon nanotubes and a binder in a solvent, wherein an acrylic copolymer or a low molecular weight hydrogenated nitrile butadiene rubber (HNBR) with a molecular weight of 40,000 or less is used as the dispersant.

[0017] In the present invention, the positive electrode active material is a positive electrode active material commonly used in the field of lithium secondary batteries, and may be a lithium oxide containing lithium and one or more metals such as cobalt, manganese, nickel, or aluminum. More specifically, the lithium oxide may be a lithium-manganese-based oxide (e.g., LiMnO2, LiMn2O, etc.), a lithium-cobalt-based oxide (e.g., LiCoO2, etc.), a lithium-nickel-based oxide (e.g., LiNiO2, etc.), or a lithium-nickel-manganese-based oxide (e.g., LiNi 1-Y1 Mn Y1 O2(here, 0 <Y1<1), LiNi Z1 Mn 2-Z1 O4 (where 0 < Z1 < 2), etc.), lithium-nickel-cobalt oxides (e.g., LiNi 1-Y2 Co Y2 O2(here, 0 <Y2<1) 등), 리튬-망간-코발트계 산화물(예를 들면, LiCo 1-Y3 Mn Y3 O2(here, 0 <Y3<1), LiMn 2-Z2 Co Z2 O4 (wherein, 0 < Z2 < 2), etc.), lithium-nickel-cobalt-manganese oxide (hereinafter referred to as 'NCM-based cathode active material', for example, Li(Ni P1 Co Q1 Mn R1 )O2(where, 0<P1<1, 0<Q1<1, 0<R1<1, P1+Q1+R1=1), Li(Ni P2 Co Q2 Mn R2 )O4 (where 0 < P2 < 2, 0 < Q2 < 2, 0 < R2 < 2, P2+Q2+R2=2), etc.), lithium-nickel-cobalt-aluminum-based oxide (hereinafter referred to as 'active material for NCA-based cathode') or lithium-nickel-cobalt-manganese-other metal (M) oxide (e.g., Li(Ni P3 Co Q3 Mn R3 M SExamples include )O2(wherein M is selected from the group consisting of Al, Cu, Fe, V, Cr, Ti, Zr, Zn, Ta, Nb, Mg, B, W, and Mo, and P3, Q3, R3, and S are each atomic fractions of independent elements, such that 0 < P3 < 1, 0 < Q3 < 1, 0 < R3 < 1, 0 < S < 1, P3 + Q3 + R3 + S = 1), etc., and any one or more of these compounds may be included. In terms of energy density, the present invention is preferable to use an anode active material having a nickel content of 70 wt% or more as the anode active material, and more preferably, to use an NCM-based anode active material having a nickel content of 70 wt% or more or an NCA-based anode active material having a nickel content of 70 wt% or more.

[0018] In addition, the content of the active material for the anode in the present invention is not particularly limited, but it is preferably 72 to 79 weight percent relative to the total weight of the anode slurry composition.

[0019] In the present invention, the carbon nanotubes may be single-walled carbon nanotubes or multi-walled carbon nanotubes; however, it is preferable to use multi-walled carbon nanotubes to achieve higher electrical conductivity and dispersibility, and at the same time to further enhance the stability of the cathode active material.

[0020] In addition, while the content of the carbon nanotubes is not particularly limited, it is preferable that it be 2.15 to 3 weight percent relative to the total weight of the one-component carbon nanotube-binder slurry. This is because if the content of the carbon nanotubes is less than 2.15 weight percent relative to the total weight of the one-component carbon nanotube-binder slurry, the solid content of the one-component carbon nanotube-binder slurry is low when preparing the anode slurry, making it difficult to prepare an anode slurry with high solid content, and the electrical conductivity becomes excessively low due to the low content of the conductive material in the composition. Furthermore, if it exceeds 3 weight percent, the solid content of the one-component carbon nanotube-binder slurry becomes high when preparing the anode slurry, resulting in excessively high viscosity and reduced storage stability, and there is a problem where the battery performance actually deteriorates due to entanglement between the carbon nanotubes during the preparation of the anode slurry.

[0021] In the present invention, the binder is added to secure adhesion between active materials for electrodes or between an active material and a current collector, and examples include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these alone or a mixture of two or more may be used.

[0022] The content of the binder is not particularly limited, but in order to secure excellent electrode contact power while minimizing the increase in electrode resistance, it is preferable that it be 7% by weight or less relative to the total weight of the one-component carbon nanotube-binder slurry, and more preferably 4 to 6% by weight relative to the total weight of the one-component carbon nanotube-binder slurry.

[0023] In the present invention, the dispersant serves to ensure that the one-component carbon nanotube-binder slurry of the present invention has storage stability. To minimize the degradation of the electrical properties of the carbon nanotubes, it is preferable to disperse the carbon nanotubes in a solvent using a non-covalent polymer wrapping method. In particular, to ensure not only the dispersibility of the carbon nanotubes but also good flowability characteristics of the anode slurry composition, the present invention is characterized by using a copolymer comprising a monomer unit containing one or more aromatic rings that are substituted or not substituted with the dispersant, and an acrylate-based monomer unit containing a linear or branched aliphatic hydrocarbon having 5 to 22 carbon atoms, or using a low molecular weight hydrogenated nitrile butadiene rubber (HNBR) with a molecular weight of 40,000 or less.

[0024] However, the surface area of ​​the carbon nanotube is 200 m² 2 In the case of / g or greater, based on a total copolymer content of 100 mol%, the value obtained by subtracting the mol% of acrylate-based monomer units containing linear or branched aliphatic hydrocarbons having 5 to 22 carbon atoms of the copolymer from the mol% of monomer units containing one or more substituted or unsubstituted aromatic rings may be greater than 0. Meanwhile, the surface area of ​​the carbon nanotube is 200 m² 2In cases where it is less than / g, based on the total copolymer content of 100 mol%, the value obtained by subtracting the mol% of the acrylate series monomer unit containing a linear or branched aliphatic hydrocarbon having 5 to 22 carbon atoms from the mol% of the monomer unit containing one or more substituted or unsubstituted aromatic rings may be less than or equal to 0.

[0025] Monomer units comprising one or more substituted or unsubstituted aromatic rings of the copolymer contribute to the dispersion of carbon nanotubes through π-π interactions between the copolymer and the carbon nanotubes. Additionally, acrylate-based monomer units comprising linear or branched aliphatic hydrocarbons having 5 to 22 carbon atoms of the copolymer contribute to the dispersion of nanotubes by the copolymer wrapping the carbon nanotubes.

[0026] In particular, the surface area is 200 m² 2 In the case of carbon nanotubes with a g / g or higher, the dispersibility of the carbon nanotubes can be further improved by enhancing the π-π interactions of the copolymer through monomer units containing one or more substituted or unsubstituted aromatic rings, and the surface area is 200 m² 2 In the case of carbon nanotubes with less than 1 / g, the dispersibility of the carbon nanotubes can be further improved by further enhancing the wrapping function of the copolymer through acrylate-based monomer units containing linear or branched aliphatic hydrocarbons having 5 to 22 carbon atoms.

[0027] In the present invention, the monomer unit comprising one or more substituted or unsubstituted aromatic rings may include one or more selected from the group consisting of acrylate-based monomer units comprising one or more substituted or unsubstituted aromatic rings and vinyl-based monomer units comprising one or more substituted or unsubstituted aromatic rings.

[0028] In the present invention, the copolymer is cyano(CN), pyrrolidone (NC4H6O), carboxylic acid (COOH), caprolactam (C5H 10 It may additionally include a polar monomer unit comprising one or more selected from the group consisting of CNO), morpholine (C4H8NO), and oxazolidone (C3H4NO2).

[0029] In the present invention, the copolymer comprises, based on a total copolymer content of 100 mol%, 20 mol% or more and 70 mol% or less of acrylate-based monomer units comprising one or more substituted or unsubstituted aromatic rings and vinyl-based monomer units comprising one or more substituted or unsubstituted aromatic rings, 20 mol% or more and 70 mol% or less of acrylate-based monomer units comprising linear or branched aliphatic hydrocarbons having 5 to 22 carbon atoms, and 10 mol% or more and 60 mol% or less of cyano(CN), pyrrolidone (NC4H6O), carboxylic acid (COOH), and caprolactam (C5H 10 It may include a polar monomer unit comprising one or more selected from the group consisting of CNO), morpholine (C4H8NO), and oxazolidone (C3H4NO2).

[0030] For example, the copolymer can be represented by the following chemical formula 1.

[0031]

[0032] In the above chemical formula 1,

[0033] R1 to R 12 They are the same or different from each other, and each independently is hydrogen, a linear or branched hydrocarbon having 1 to 4 carbon atoms, and

[0034] R'1 is a linear or branched aliphatic hydrocarbon having 5 to 22 carbon atoms, and

[0035] R'2 comprises one or more substituted or unsubstituted aromatic rings, and

[0036] R'3 is cyano(CN), pyrrolidone (NC4H6O), carboxylic acid (COOH), caprolactam (C5H 10 One or more selected from the group consisting of CNO), morpholine (C4H8NO), and oxazolidone (C3H4NO2), and

[0037] R'4 comprises one or more substituted or unsubstituted aromatic rings, and

[0038] 20 mol% ≤ l ≤ 70 mol%, 20 mol% ≤ m+o ≤ 70 mol% and 10 mol% ≤ n ≤ 60 mol% may be possible.

[0039] That is, the monomer unit (1) of the above chemical formula 1 corresponds to an acrylate-series monomer unit comprising a linear or branched aliphatic hydrocarbon having 5 to 22 carbon atoms, the monomer unit (2) of the above chemical formula 1 corresponds to an acrylate-series monomer unit comprising one or more substituted or unsubstituted aromatic rings, and the monomer unit (3) of the above chemical formula 1 corresponds to the cyano(CN), pyrrolidone (NC4H6O), carboxylic acid (COOH), caprolactam (C5H 10 It corresponds to a polar monomer unit comprising one or more selected from the group consisting of CNO), morpholine (C4H8NO) and oxazolidone (C3H4NO2), and the monomer unit (4) of the above formula 1 may each correspond to a vinyl series monomer unit comprising one or more substituted or unsubstituted aromatic rings.

[0040] For example, R'1 of the above chemical formula 1 is n-pentyl, n-hexyl, n-heptyl, n-octyl, 2-ethylhexyl, n-nonyl, n-decyl, n-undecyl, lauryl, n-dodecyl, n-tridecyl, n-tetradecyl, n-pentadecyl, cetyl, n-hexadecyl, n-heptadecyl, stearyl, n-octadecyl, n-nonadecyl, n-icosyl, n-henicosyl, n-docosyl, iso-pentyl, iso-heptyl, iso-octyl, iso-nonyl, iso-decyl, iso-undecyl, iso-dodecyl, iso-tridecyl, iso-tetradecyl, iso-pentadecyl, iso-cetyl, iso-hexadecyl, iso-heptadecyl, iso-stearyl, iso-octadecyl, It may be one or more selected from the group consisting of iso-nonadecil, iso-icocil, iso-henicocil, and iso-docosil.

[0041] That is, as the monomers polymerized into monomer units containing R'1, only one type of monomer including a linear or branched aliphatic hydrocarbon having 5 to 22 carbon atoms may be used, or two or more types of monomers including a linear or branched aliphatic hydrocarbon having 5 to 22 carbon atoms may be used together.

[0042] The monomer polymerized into the above-mentioned acrylate series monomer unit containing a linear or branched aliphatic hydrocarbon having 5 to 22 carbon atoms may be an acrylate and / or methacrylate containing a linear or branched aliphatic hydrocarbon having 5 to 22 carbon atoms, and the acrylate series monomer containing one or more substituted or unsubstituted aromatic rings may be an acrylate and / or methacrylate containing one or more substituted or unsubstituted aromatic rings.

[0043] (Meth)acrylate refers to acrylate or methacrylate.

[0044] For example, monomers polymerized into acrylate-series monomer units comprising the above-mentioned linear or branched aliphatic hydrocarbons having 5 to 22 carbon atoms include n-pentyl (meth)acrylate, n-heptyl (meth)acrylate, n-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-nonyl (meth)acrylate, n-decyl (meth)acrylate, n-undecyl (meth)acrylate, and lauryl (meth)acrylate. n-dodecyl (meth)acrylate, n-tridecyl (meth)acrylate, n-tetradecyl (meth)acrylate, n-pentadecyl (meth)acrylate, cetyl (meth)acrylate, n-hexadecyl (meth)acrylate, n-heptadecyl (meth)acrylate, stearyl (meth)acrylate, n-nonadecyl (meth)acrylate, n-eicosyl (meth)acrylate), n-heneicosyl (meth)acrylate, n-dococyl (meth)acrylate, iso-pentyl (meth)acrylate,iso-heptyl (meth)acrylate, iso-octyl (meth)acrylate, iso-nonyl (meth)acrylate, iso-decyl (meth)acrylate, iso-undecyl (meth)acrylate, iso-dodecyl (meth)acrylate, iso-tridecyl (meth)acrylate, iso-tetradecyl (meth)acrylate, iso-pentadecyl (meth)acrylate iso-cetyl (meth)acrylate, iso-hexadecyl (meth)acrylate, iso-heptadecyl (meth)acrylate, iso-stearyl (meth)acrylate, iso-nonadecyl (meth)acrylate, iso-eicosyl (meth)acrylate, iso-heneicosyl (meth)acrylate, iso-docosyl (meth)acrylate, or a combination thereof, but is not limited thereto.

[0045] The monomer unit containing the linear or branched aliphatic hydrocarbon having 5 to 22 carbon atoms can wrap and disperse carbon nanotubes and serve to lower the viscosity of the carbon nanotube slurry composition.

[0046] If the number of carbon atoms in the above linear or branched aliphatic hydrocarbon is less than 5, it cannot sufficiently encapsulate carbon materials (especially carbon nanotubes), resulting in reduced dispersion power, and if it exceeds 22, there is a problem of significantly reduced compatibility with polar solvents such as NMP.

[0047] In addition, it may be preferable that the monomer unit containing the linear or branched aliphatic hydrocarbon having 5 to 22 carbon atoms be included in an amount of 20 to 70 mol% based on the total content of 100 mol% of the total copolymer. This is because if the content of the monomer unit containing the linear or branched aliphatic hydrocarbon having 5 to 22 carbon atoms is less than 20 mol%, the particle size and viscosity of the slurry composition may increase, and if it exceeds 70 mol%, compatibility with polar solvents decreases, which may lead to phase separation.

[0048] For example, R'2 and R'4 of the above formula 1 may be the same or different from each other and may each include one or more selected from the group consisting of benzyl, phenyl, phenoxy, naphthalene, anthracene, and pyrene, which are independently substituted or unsubstituted. For example, R'2 may include one or more selected from the group consisting of 3-phenoxybenzyl, α-phenylphenoxyethyl, biphenylmethyl, 1-naphthyl, 2-naphthyl, 9-anthracene methyl, and 1-pyrene methyl, and R'4 may include phenyl, but is not limited thereto.

[0049] That is, R'2 and R'4 may be the same or different from each other and each may include one or more aromatic rings that are independently substituted or not substituted.

[0050] Meanwhile, R'2 may be a hydrocarbon containing one or more substituted or unsubstituted aromatic rings.

[0051] In addition, as a monomer polymerized into a monomer unit containing R'2, only one type of monomer containing one or more substituted or unsubstituted aromatic rings may be used, or two or more types of monomers containing one or more substituted or unsubstituted aromatic rings may be used together.

[0052] For example, when the above aromatic ring is substituted, the substituent may be a linear or branched hydrocarbon having 1 to 4 carbon atoms, a substituent connected through oxygen (O) (e.g., a substituted or unsubstituted aromatic ring connected through ether, etc.).

[0053] For example, monomers polymerized with monomer units containing R'2 include benzyl acrylate, 3-phenoxybenzyl acrylate, α-phenylphenoxyethyl acrylate, α-phenylphenoxyethyl methacrylate, (1-pyrene) 2-methyl-2-propenoate, 1-naphthyl acrylate, 1-naphthyl methacrylate, 2-naphthyl acrylate, 2-naphthyl methacrylate, and 9-anthracene methyl It may be one or more selected from the group consisting of acrylate (9-anthracene methyl acrylate) and 9-anthracene methyl methacrylate, and the monomer polymerized into monomer units containing R'4 may be styrene.

[0054] The monomer unit containing one or more substituted or unsubstituted aromatic rings acts as a dispersion through π-π interactions with carbon nanotubes and can be compatible with polar solvents such as NMP.

[0055] It may be preferable that the monomer unit containing one or more substituted or unsubstituted aromatic rings be included in an amount of 20 to 70 mol% based on the total content of 100 mol% of the total copolymer. This is because if the content of the monomer unit containing one or more substituted or unsubstituted aromatic rings exceeds 70 mol%, the content of aliphatic hydrocarbons or polar monomer units decreases, which may increase the viscosity of the carbon nanotube slurry composition and increase the particle size of the dispersed carbon material.

[0056] The above cyano(CN), pyrrolidone (NC4H6O), carboxylic acid (COOH), caprolactam (C5H 10 Polar monomer units comprising one or more selected from the group consisting of CNO, morpholine (C4H8NO), and oxazolidone (C3H4NO2) serve to impart compatibility to polar solvents such as NMP.

[0057] For example, the above cyano(CN), pyrrolidone (NC4H6O), carboxylic acid (COOH), caprolactam (C5H 10 The monomer polymerized into a polar monomer unit comprising one or more selected from the group consisting of CNO), morpholine (C4H8NO), and oxazolidone (C3H4NO2) may be acrylic acid, methacrylic acid, acrylonitrile, N-vinylpyrrolidone, N-vinylcaprolactam, 4-acryloyl morpholine, 3-acryloyl-2-oxazolidinone, or copolymers thereof.

[0058] It may be preferable that the above polar monomer unit be included in an amount of 10 to 60 mol% based on the total content of 100 mol% of the total copolymer. This is because if the above polar monomer unit exceeds 60 mol% of the total copolymer, the compatibility with the polar solvent becomes excessively high, which may cause phase separation after dispersion and increase the particle size of the dispersed carbon material.

[0059] In the present invention, the copolymer may be a random or block copolymer depending on the synthesis process.

[0060] In the present invention, the number average molecular weight of the copolymer may be 8,000 or more and 40,000 or less. This is because if the number average molecular weight of the copolymer is less than 8,000, the fluidity of the dispersant increases, which may reduce the ability to prevent the re-aggregation of carbon materials, and if the number average molecular weight exceeds 40,000, there is a problem that the viscosity is excessively high for use.

[0061] Although the content of the above-mentioned dispersant is not particularly limited, it is preferable that the content be 15 to 30 parts by weight relative to 100 parts by weight of the carbon nanotube, and most preferably 25 parts by weight relative to 100 parts by weight of the carbon nanotube, in order to ensure that the anode slurry composition has low viscosity and good flowability even when the binder content is high, and to ensure stability over time that such flowability can be maintained for a long period. This is because if the content of the above-mentioned dispersant is less than 15 parts by weight relative to 100 parts by weight of the carbon nanotube, there is a problem that the storage stability of the one-component carbon nanotube-binder slurry of the present invention is significantly reduced, and if it exceeds 30 parts by weight relative to 100 parts by weight of the carbon nanotube, there is a problem that the adhesion strength of the electrode falls short of the minimum required standard value (red dotted line in Fig. 1), as shown in Fig. 1.

[0063] In the present invention, the solvent is an organic solvent, and it is preferable to use N-methylpyrrolidone. The content of the solvent is not particularly limited, and the content can be appropriately selected within a range where the anode slurry composition of the present invention has an appropriate viscosity.

[0064] In the anode slurry composition of the present invention, the content of the one-component carbon nanotube-binder slurry is not particularly limited, but it is preferably 21 to 24 weight percent relative to the total weight of the anode slurry composition. This is because if the content of the one-component carbon nanotube-binder slurry is less than 21 weight percent relative to the total weight of the anode slurry composition, there is a problem that the electrical conductivity becomes excessively low due to the low content of the conductive material, and if it exceeds 24 weight percent, there is a problem that the battery performance actually decreases due to the excessively high content of the conductive material and the entanglement of carbon nanotubes.

[0065] The method for manufacturing a slurry composition for a positive electrode of a lithium secondary battery according to the present invention is described as follows.

[0066] First, carbon nanotubes, a binder, a dispersant, and a solvent are mixed and stirred to produce a one-component carbon nanotube-binder slurry. Subsequently, an active material for the cathode is mixed with the one-component carbon nanotube-binder slurry and stirred to finally produce a cathode slurry composition for a lithium secondary battery according to the present invention.

[0067] The slurry composition for a positive electrode of a lithium secondary battery according to the present invention has a higher content of final solids compared to conventional slurry compositions for positive electrodes, and has high flowability and stability over time relative to the solid content.

[0068] In addition, a lithium secondary battery manufactured using the anode slurry composition according to the present invention has superior electrochemical properties compared to a lithium secondary battery manufactured using a conventional anode slurry composition.

[0069] The present invention will be explained below through examples. The following examples are merely illustrative of the present invention and do not limit the scope of the invention.

[0070] <Example>

[0071] 1. [Example 1] Preparation of a one-component carbon nanotube-binder slurry: Use of an acrylate-based copolymer as a dispersant

[0072] Multiwalled carbon nanotubes as a conductive material, PVDF as a binder, and an acrylate-based copolymer (JDC-100, Hansol Chemical) as a dispersant were mixed in N-methylpyrrolidone (27.6 g) as a solvent with the composition shown in Table 1 below, and then a one-component carbon nanotube-binder slurry according to an embodiment of the present invention was prepared using a disperser.

[0073] 2. [Example 2] Preparation of a one-component carbon nanotube-binder slurry: Use of low molecular weight hydrogenated nitrile butadiene rubber (HNBR) as a dispersant

[0074] Multi-walled carbon nanotubes as a conductive material, PVDF as a binder, and low molecular weight hydrogenated nitrile butadiene rubber (V5, Nanomaterial) with a molecular weight of 40,000 or less as a dispersant were mixed in N-methylpyrrolidone (27.6 g) as a solvent with the composition shown in Table 1 below, and then a one-component carbon nanotube-binder slurry according to an embodiment of the present invention was prepared using a disperser.

[0075] Carbon nanotubes (g) Binder (PVDF) (g) Dispersant (Percentage of carbon nanotube weight) Example 1 0.9 1.5 25 (Dispersant: JDC-100) Example 2 0.9 1.5 25 (Dispersant: V5)

[0076] 2. [Comparative Example] Preparation of a one-component carbon nanotube-binder slurry: Use of a conventional dispersant (HNBR with a molecular weight of 140,000 to 200,000)

[0077] Multiwalled carbon nanotubes, PVDF as a binder, and hydrogenated nitrile butadiene rubber (HNBR) with a molecular weight of 140,000 to 200,000 as a conventional dispersant were mixed in N-methylpyrrolidone (27.6 g) as a solvent with the composition shown in Table 2 below, and then a one-component carbon nanotube-binder slurry according to the comparative example was prepared using a disperser.

[0078] Carbon nanotubes (g) Binder (PVDF) (g) Conventional dispersants: HNBR with a molecular weight of 140,000 to 200,000 (Percentage of carbon nanotube weight) Comparative Example 1 0.9 1.5 20 Comparative Example 2 0.9 1.35 20 Comparative Example 3 0.9 1.2 20 Comparative Example 4 0.9 1.05 20

[0079] 3. [Example 3] Preparation of a slurry composition for a positive electrode of a lithium secondary battery

[0080] 973.75 g of the prepared active material NCM811 for the cathode and 300 g of the one-component carbon nanotube-binder slurry of Example 1 prepared above were mixed, and then stirred at 4,000 rpm for 15 minutes using a high shear mixer to finally prepare a cathode slurry composition for a lithium secondary battery according to the present invention (Example 3).

[0081] 4. [Example 4] Preparation of a slurry composition for a positive electrode of a lithium secondary battery

[0082] 973.75 g of the prepared active material NCM811 for the cathode and 300 g of the one-component carbon nanotube-binder slurry of Example 2 prepared above were mixed, and then stirred at 4,000 rpm for 15 minutes using a high shear mixer to finally prepare a cathode slurry composition for a lithium secondary battery according to the present invention (Example 4).

[0083] 5. [Comparative Example 5] Preparation of a slurry composition for a positive electrode of a lithium secondary battery

[0084] According to the conventional method, 974.2 g of NCM811 active material for the cathode, 225 g of a carbon nanotube slurry containing multi-walled carbon nanotubes (N-methylpyrrolidone-based, solid content 4%), 187.5 g of a binder solution containing PVDF (N-methylpyrrolidone-based, solid content 8%), and 1.8 g of an acrylic copolymer dispersant (JDC-100, Hansol Chemical) were mixed, and then stirred for 15 minutes at 4,000 rpm using a high shear mixer to prepare a cathode slurry composition for a lithium secondary battery (Comparative Example 5).

[0085] 6. [Comparative Example 6] Preparation of a slurry composition for a positive electrode of a lithium secondary battery

[0086] According to the conventional method, 974.2 g of NCM811 active material for the cathode, 225 g of a carbon nanotube slurry containing multi-walled carbon nanotubes (N-methylpyrrolidone-based, solid content 4%), 187.5 g of a binder solution containing PVDF (N-methylpyrrolidone-based, solid content 8%), and 1.8 g of a dispersant, a low molecular weight hydrogenated nitrile butadiene rubber (V5, Nanosinsoja) with a molecular weight of 40,000 or less, were mixed, and then stirred for 15 minutes at 4,000 rpm using a high shear mixer to prepare a cathode slurry composition for a lithium secondary battery (Comparative Example 6).

[0087] <Experimental Example>

[0088] Experimental Example 1: Flowability and Time-dependent Stability Test

[0089] The viscosity of each of the one-component carbon nanotube-binder slurry samples of Examples 1 to 2 and Comparative Examples 1 to 4 was measured using a viscometer (Brookfield DV2T Viscometer). The viscosity measurement was performed by placing each sample into a 1000 ml plastic container, stirring it at 600 rpm for 3 minutes using a stirrer, placing the stirred sample into a 60 ml plastic tube, and measuring the viscosity using the viscometer (#64 spindle, 12 rpm). The viscosity measurement results are shown in Table 3 below.

[0090] In addition, based on the above viscosity measurement results, the flowability at the time of the initial viscosity measurement was evaluated by indicating it as 'very good', 'good', 'average', and 'bad'. After one week, the viscosity was measured again using the same method, and the flowability was evaluated by indicating it as 'very good', 'good', 'average', and 'bad'. The results are shown in Table 3 below.

[0091] division Initial measured viscosity (cP) the first Flowability After 1 week of hardening Flowability Example 1 3,000 well well Example 2 2,500 Very good well Comparative Example 1 10,500 Bad Bad Comparative Example 2 8,500 commonly Bad Comparative Example 3 6,500 commonly Bad Comparative Example 4 5,000 well Bad

[0092] As can be seen in Table 3 above, the one-component carbon nanotube-binder slurry of Examples 1 and 2 according to the present invention has a lower viscosity compared to the one-component carbon nanotube-binder slurry of Comparative Example 1, which has the same carbon nanotube and PVDF solid content, and thus has relatively much better flowability.

[0093] In addition, the one-component carbon nanotube-binder slurries of Comparative Examples 1 to 4 generally have a higher viscosity than Examples 1 and 2 of the present invention, even when the solid content of the binder (PVDF) is lowered, and it can be seen that the flowability deteriorates rapidly over time, resulting in poor stability over time. On the other hand, it can be confirmed that the one-component carbon nanotube-binder slurries of Examples 1 and 2 of the present invention show almost no decrease in flowability over time.

[0094] Experimental Example 2: Measurement of Solid Content of Anode Slurry Composition

[0095] Each of the anode slurry composition samples of Examples 3 and 4 and Comparative Examples 5 and 6 was placed in a drying container and dried in an oven at 200°C for 8 hours to measure the solid content, and the results are shown in Table 4 below.

[0096] Solid content (Solid content of slurry, weight%) Example 3 78.37 Example 4 78.37 Comparative Example 5 72.02 Comparative Example 6 72.02

[0097] As can be seen in Table 4 above, it can be seen that the anode slurry compositions of Examples 3 and 4 according to the present invention have a higher solid content than the anode slurry compositions of Comparative Examples 5 and 6. This means that when using the anode slurry composition according to the present invention, the drying time can be shortened, which can increase the production speed of the battery and enable the manufacture of high-capacity electrodes.

[0098] As explained above, those skilled in the art to which the present invention pertains will understand that the present invention may be implemented in other specific forms without altering its technical concept or essential features. The scope of the present invention is defined by the claims set forth below rather than by the detailed description above, and all modifications or variations derived from the meaning and scope of the claims and equivalent concepts thereof should be interpreted as being included within the scope of the present invention.

Claims

Claim 1 A slurry composition for a positive electrode of a lithium secondary battery, wherein the positive electrode active material and a one-component carbon nanotube-binder slurry are mixed, the one-component carbon nanotube-binder slurry is prepared by adding carbon nanotubes, a binder, and a dispersant to a solvent and mixing them before being mixed with the positive electrode active material, and the dispersant is a copolymer comprising a monomer unit containing one or more substituted or unsubstituted aromatic rings and an acrylate-based monomer unit containing a linear or branched aliphatic hydrocarbon having 5 to 22 carbon atoms. Claim 2 A slurry composition for a positive electrode of a lithium secondary battery, characterized in that, in claim 1, the carbon nanotube is a multi-walled carbon nanotube. Claim 3 A slurry composition for a positive electrode of a lithium secondary battery, characterized in that, in claim 1, the content of the carbon nanotube is 2.15 to 3 weight% relative to the total weight of the one-component carbon nanotube-binder slurry. Claim 4 A slurry composition for a positive electrode of a lithium secondary battery according to claim 1, wherein the binder is polyvinylidene fluoride (PVdF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof. Claim 5 A slurry composition for a positive electrode of a lithium secondary battery, characterized in that, in claim 1, the content of the binder is 4 to 6 weight% relative to the total weight of the one-component carbon nanotube-binder slurry. Claim 6 delete Claim 7 A slurry composition for a positive electrode of a lithium secondary battery according to claim 1, characterized in that the monomer unit comprising one or more substituted or unsubstituted aromatic rings comprises one or more selected from the group consisting of an acrylate-based monomer unit comprising one or more substituted or unsubstituted aromatic rings and a vinyl-based monomer unit comprising one or more substituted or unsubstituted aromatic rings. Claim 8 In claim 1, the copolymer is cyano(CN), pyrrolidone (NC4H6O), carboxylic acid (COOH), caprolactam (C5H 10 A slurry composition for a positive electrode of a lithium secondary battery, characterized by further comprising a polar monomer unit comprising one or more selected from the group consisting of CNO, morpholine (C4H8NO), and oxazolidone (C3H4NO2). Claim 9 In claim 1, the copolymer comprises, based on a total copolymer content of 100 mol%, 20 to 70 mol% of acrylate-based monomer units comprising one or more substituted or unsubstituted aromatic rings and vinyl-based monomer units comprising one or more substituted or unsubstituted aromatic rings, 20 to 70 mol% of acrylate-based monomer units comprising linear or branched aliphatic hydrocarbons having 5 to 22 carbon atoms, and 10 to 60 mol% of cyano(CN), pyrrolidone (NC4H6O), carboxylic acid (COOH), caprolactam (C5H 10 A slurry composition for a positive electrode of a lithium secondary battery, characterized by comprising a polar monomer unit comprising one or more selected from the group consisting of CNO, morpholine (C4H8NO), and oxazolidone (C3H4NO2). Claim 10 A slurry composition for a positive electrode of a lithium secondary battery, characterized in that, in claim 1, the number average molecular weight of the copolymer is 8,000 or more and 40,000 or less. Claim 11 delete Claim 12 A slurry composition for a positive electrode of a lithium secondary battery, characterized in that, in claim 1, the content of the dispersant is 15 to 30 parts by weight per 100 parts by weight of the carbon nanotube. Claim 13 A slurry composition for a positive electrode of a lithium secondary battery, characterized in that, in claim 1, the positive electrode active material is a positive electrode active material having a nickel content of 70 weight% or more. Claim 14 A slurry composition for a positive electrode of a lithium secondary battery, characterized in that, in claim 1, the content of the one-component carbon nanotube-binder slurry is 21 to 24 weight% relative to the total weight of the slurry composition for the positive electrode. Claim 15 A slurry composition for a positive electrode of a lithium secondary battery, characterized in that, in claim 1, the solvent is N-methylpyrrolidone. Claim 16 A lithium secondary battery comprising a positive electrode manufactured using a positive electrode slurry composition according to any one of claims 1 to 5, 7 to 10, and 12 to 15.

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