Copolymers, viscosity-reducing agents comprising the copolymers and positive electrode slurry compositions, positive electrodes comprising the positive electrode slurry compositions, and secondary batteries including the positive electrodes

Abstract

This invention relates to a copolymer and a viscosity reducer comprising the copolymer, and more specifically, to a copolymer, a viscosity reducer comprising the copolymer, a positive electrode slurry composition, a positive electrode, and a secondary battery. The copolymer is capable of preparing a positive electrode slurry composition with low viscosity and excellent dispersibility, and is capable of preparing a positive electrode with excellent adhesion between the positive electrode active material and the current collector.

Description

Technical Field

[0001] This invention relates to a copolymer and viscosity reducers, positive electrode slurry compositions, positive electrodes, and secondary batteries utilizing the copolymer. More specifically, it relates to a copolymer, a viscosity reducer comprising the copolymer, a positive electrode slurry composition, a positive electrode, and a secondary battery, wherein the copolymer can be used to prepare a low-viscosity positive electrode slurry composition with the same solid composition. Background Technology

[0002] Lithium-ion batteries have high energy density, so they are widely used in the electrical, electronic, communication and computer industries. Their application has expanded from small lithium-ion batteries for portable electronic devices to high-capacity batteries for hybrid vehicles, electric vehicles and other applications.

[0003] With the expansion of application areas, the development of lithium-ion rechargeable batteries has attracted increasing attention. In particular, the expansion of application areas has led to increased demand, thus necessitating an increase in the production speed of rechargeable batteries.

[0004] A lithium secondary battery typically comprises: a positive electrode, on which a positive active material layer is formed on at least one side of a positive current collector; a negative electrode, on which a negative active material layer is formed on at least one side of a negative current collector; and a separator located between the positive and negative electrodes for electrically insulating the positive and negative electrodes.

[0005] The positive and negative electrodes of a lithium-ion secondary battery are collectively referred to as electrodes. To increase the production speed of these electrodes, the solid content of the electrode slurry can be increased. However, if the solid content of the electrode slurry increases to a certain level, the viscosity of the electrode slurry composition will increase, thereby increasing the load on the equipment and making the process impossible. Therefore, it is necessary to develop an electrode slurry composition with low viscosity, excellent dispersibility, and excellent adhesion between electrode active materials or between electrode active materials and current collectors.

[0006] [Existing Technical Documents] [Patent Literature] (Patent Document 1) Korean Patent Publication No. 2022-0078615 Summary of the Invention The technical issues to be solved The purpose of this invention is to provide a copolymer, a viscosity reducer comprising the copolymer, a positive electrode slurry composition, a positive electrode, and a secondary battery. The copolymer can be used to prepare a positive electrode slurry composition with low viscosity and excellent dispersibility, and can also be used to prepare a positive electrode with excellent adhesion between the positive electrode active material and the current collector.

[0007] However, the problems to be solved in this application are not limited to those mentioned above, and those skilled in the art can clearly understand other unmentioned problems based on the following description.

[0008] Technical solutions to technical problems One aspect of this application provides a copolymer comprising: One or more monomer units selected from the group consisting of acrylate monomer units containing one or more substituted or unsubstituted aromatic or aliphatic rings and vinyl monomer units containing one or more substituted or unsubstituted aromatic or aliphatic rings; Acrylate monomer units selected from straight-chain or branched aliphatic hydrocarbons containing 5 to 22 carbon atoms, and monomer units selected from cyano (CN), pyrrolidone (NC4H6O), carboxylic acid (COOH), amide, alkylamide, dialkylamide, alcohol, epoxy group, caprolactam (C5H) 10 One or more monomer units from the group consisting of one or more polar monomer units from the group consisting of CNO, morpholine (C4H8NO), and oxazolidinone (C3H4NO2); and One or more monomer units are selected from the group consisting of acrylate monomer units and vinyl acetate monomer units comprising straight-chain or branched aliphatic hydrocarbons having 1 to 4 carbon atoms.

[0009] In another aspect of this application, a viscosity reducer comprising the copolymer is provided.

[0010] In another aspect, this application provides a positive electrode slurry composition comprising: the copolymer; and a positive electrode active material.

[0011] Another aspect of this application provides a positive electrode, which includes: Current collector; and The positive electrode active material layer is formed by coating the positive electrode slurry composition onto the current collector.

[0012] In another aspect of this application, a secondary battery is provided, which includes the positive electrode.

[0013] Invention Effects As described above, the cathode slurry composition containing the copolymer of the present invention has a low viscosity even when the slurry solids content is high, thus improving processability and production speed.

[0014] Furthermore, the cathode slurry composition containing the copolymer of the present invention has excellent dispersibility and can produce a cathode with excellent adhesion between the cathode active material and the current collector.

[0015] The best way to implement an invention The terms and words used in this specification and claims should not be interpreted according to their conventional or dictionary meanings, but should be interpreted as meanings and concepts consistent with the technical spirit of the invention, based on the principle that the inventors may appropriately define terms and concepts to better explain their invention.

[0016] Therefore, the embodiments described in this specification are only one of the most preferred embodiments of the present invention and do not represent all the technical concepts of the present invention. Therefore, it should be understood that various equivalents and modifications may exist as of the time of this application.

[0017] In this specification, unless the context clearly specifies otherwise, singular expressions include plural expressions. In this specification, terms such as “comprising,” “having,” or “possessing” are intended to indicate the presence of the implemented features, quantities, steps, constituent elements, or combinations thereof, but it should be understood that these terms do not preclude the possibility of the presence or addition of one or more other features, quantities, steps, constituent elements, or combinations thereof, or additional possibilities.

[0018] In this specification, when various parameters are given as a range, preferred range, or preferred upper and lower limits, it should be understood that, regardless of whether the range is disclosed individually, all ranges consisting of any pair of arbitrary upper or preferred limits and any pair of arbitrary lower or preferred limits are specifically disclosed.

[0019] Where a range of numerical values ​​is mentioned in this specification, unless otherwise stated, the range is intended to include its endpoint and all integers and fractions within that range. The scope of this invention is not intended to be limited to the specific values ​​involved in defining the range.

[0020] In this specification, the "to" and "~" in "a to b" and "a ~ b" which represent numerical ranges are defined as ≥ a and ≤ b.

[0021] According to one aspect of the copolymer of the present invention, it may comprise: one or more monomer units selected from the group consisting of acrylate monomer units comprising one or more substituted or unsubstituted aromatic rings or aliphatic rings and vinyl monomer units comprising one or more substituted or unsubstituted aromatic rings or aliphatic rings; acrylate monomer units selected from the group consisting of straight-chain or branched aliphatic hydrocarbons having 5 to 22 carbon atoms; and monomer units selected from the group consisting of cyano (CN), pyrrolidone (NC4H6O), carboxylic acid (COOH), amide, alkylamide, dialkylamide, alcohol, epoxy group, caprolactam (C5H6O). 10One or more monomer units from the group consisting of one or more polar monomer units selected from the group consisting of one or more of the group consisting of one or more of the group consisting of one or more of the group consisting of acrylate monomer units and vinyl acetate monomer units selected from the group consisting of straight-chain or branched aliphatic hydrocarbons containing 1 to 4 carbon atoms.

[0022] In one embodiment, the monomer unit selected from the group consisting of acrylate monomer units comprising one or more substituted or unsubstituted aromatic or aliphatic rings and vinyl monomer units comprising one or more substituted or unsubstituted aromatic or aliphatic rings may be styrene, cyclopentyl acrylate, cyclohexyl acrylate, benzyl acrylate, 3-phenoxybenzyl acrylate, σ-phenyl phenoxy ethyl acrylate, σ-phenyl phenoxy ethyl methacrylate, (1-pyrene)2-methyl-2-propenoate, 1-naphthyl acrylate, 1-naphthyl methacrylate, 2-naphthyl acrylate. It is a polymer of acrylate, 2-naphthyl methacrylate, 9-anthracene methyl acrylate, 9-anthracene methyl methacrylate, or combinations thereof.

[0023] Preferably, the one or more monomer units selected from the group consisting of acrylate monomer units containing one or more substituted or unsubstituted aromatic or aliphatic rings and vinyl monomer units containing one or more substituted or unsubstituted aromatic or aliphatic rings can be polymerized from styrene.

[0024] In one embodiment, the acrylate monomer unit comprising a straight-chain or branched aliphatic hydrocarbon having 5 to 22 carbon atoms can be composed of n-pentyl(meth)acrylate, n-hexyl(meth)acrylate, n-heptyl(meth)acrylate, n-octyl(meth)acrylate, 2-ethylhexyl(meth)acrylate, n-nonyl(meth)acrylate, etc. eth)acrylate), n-decyl(meth)acrylate, n-undecyl(meth)acrylate, lauryl(meth)acrylate, n-dodecyl(meth)acrylate, n-tridecyl(meth)acrylate, n-tetradecyl(meth)acrylate, n-pentadecanyl(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-neicosyl(meth)acrylate, n-heneicosyl(meth)acrylate, n-dococyl(meth)acrylate, isopentyl(meth)acrylate, isoheptyl(meth)acrylate, isooctyl(meth)acrylate, iso-octyl(meth)acrylate, isononyl(meth)acrylate.Isodeyl(meth)acrylate, isoundecyl(meth)acrylate, isododecyl(meth)acrylate, isotridecyl(meth)acrylate, isotetradecyl(meth)acrylate, isoopentadecyl(meth)acrylate, isocetyl(meth)acrylate, isohexadecyl(meth)acrylate It is a polymerized form of 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 combinations thereof.

[0025] Preferably, the acrylate monomer unit containing a straight-chain or branched aliphatic hydrocarbon with 5 to 22 carbon atoms can be polymerized from stearyl acrylate.

[0026] In one embodiment, the molecule comprises a compound selected from cyano (CN), pyrrolidone (NC4H6O), carboxylic acid (COOH), amide, alkylamide, dialkylamide, alcohol, epoxy group, and caprolactam (C5H4H6O). 10One or more polar monomer units from the group consisting of acrylonitrile (CNO), morpholine (C4H8NO), and oxazolidinone (C3H4NO2) can be polymerized from acrylonitrile, vinyl pyrrolidone, acrylic acid, methacrylic acid, itaconic acid, acrylamide, N-methylacylamide, 2-hydroxyethyl acrylate, 2-hydroxyethylmethacrylate, glycidyl methacrylate, or combinations thereof.

[0027] Preferably, it comprises a group selected from cyano (CN), pyrrolidone (NC4H6O), carboxylic acid (COOH), amide, alkylamide, dialkylamide, alcohol, epoxy group, and caprolactam (C5H). 10 One or more polar monomer units from the group consisting of CNO, morpholine (C4H8NO), and oxazolidinone (C3H4NO2) can be polymerized from acrylic acid.

[0028] In one embodiment, the acrylate monomer unit comprising a straight-chain or branched aliphatic hydrocarbon having 1 to 4 carbon atoms can be polymerized from methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, or combinations thereof, and the vinyl acetate monomer unit can be polymerized from vinyl acetate.

[0029] Preferably, the copolymer may contain monomer units polymerized from methyl acrylate, ethyl acrylate, vinyl acetate, or combinations thereof.

[0030] When the copolymer contains monomer units polymerized from methyl acrylate, ethyl acrylate, vinyl acetate, or combinations thereof, it has the effect of enhancing adhesion.

[0031] The monomer units selected from the group consisting of acrylate monomer units and vinyl acetate monomer units comprising straight-chain or branched aliphatic hydrocarbons having 1 to 4 carbon atoms have the effect of enhancing the adhesion between the positive electrode active material and the current collector. That is, copolymers without the monomer units having the adhesion-enhancing effect may cause assembly difficulties such as peeling of the positive electrode active material layer from the current collector. Copolymers containing the monomer units having the adhesion-enhancing effect not only have low viscosity in the positive electrode slurry composition, but also excellent adhesion between the positive electrode active material and the current collector, thus preventing the positive electrode active material from peeling off from the electrode and enabling the fabrication of secondary batteries with excellent lifespan characteristics.

[0032] In one embodiment, the copolymer may be polymerized from styrene, stearyl acrylate, acrylic acid, and methyl acrylate, or from styrene, stearyl acrylate, acrylic acid, and ethyl acrylate, or from styrene, stearyl acrylate, acrylic acid, and vinyl acetate.

[0033] In one embodiment, based on 100 mol% of the copolymer, the copolymer may comprise: 1 mol% to 60 mol% of one or more monomer units selected from the group consisting of acrylate monomer units comprising one or more substituted or unsubstituted aromatic or aliphatic rings and vinyl monomer units comprising one or more substituted or unsubstituted aromatic or aliphatic rings; 5 mol% to 80 mol% of acrylate monomer units selected from straight-chain or branched aliphatic hydrocarbons comprising 5 to 22 carbon atoms and monomer units selected from cyano (CN), pyrrolidone (NC4H6O), carboxylic acid (COOH), amide, alkylamide, dialkylamide, alcohol, epoxy group, caprolactam (C5H6O), etc. 10 One or more monomer units from the group consisting of one or more polar monomer units from the group consisting of one or more of the group consisting of CNO, morpholine (C4H8NO) and oxazolidinone (C3H4NO2); and one or more monomer units from the group consisting of acrylate monomer units and vinyl acetate monomer units selected from straight-chain or branched aliphatic hydrocarbons containing 1 to 4 carbon atoms, at a rate of 5 mol% and less than 40 mol%.

[0034] For example, based on 100 mol% of the copolymer, the copolymer may contain one or more monomer units selected from the group consisting of acrylate monomer units containing one or more substituted or unsubstituted aromatic rings or aliphatic rings, and vinyl monomer units containing one or more substituted or unsubstituted aromatic rings or aliphatic rings, at a rate of 1 mol% to 60 mol%, 10 mol% to 50 mol%, or 15 mol% to 45 mol%. The content of the acrylate monomer units or the vinyl monomer units may be 0 mol%. If the content of one or more monomer units selected from the group consisting of acrylate monomer units containing one or more substituted or unsubstituted aromatic rings or aliphatic rings and vinyl monomer units containing one or more substituted or unsubstituted aromatic rings or aliphatic rings is lower than the range of this application, the dispersibility is weakened, making it difficult to effectively mix the slurry composition. If the content exceeds the range of this application, the proportion of other monomers decreases, which may lead to increased viscosity or decreased adhesion.

[0035] Additionally, for example, based on 100 mol% of the copolymer, the copolymer may contain 5 mol% or more and 80 mol% or less, 10 mol% or more and 70 mol% or less, 15 mol% or more and 60 mol% or less, or 20 mol% or more and 50 mol% of acrylate monomer units containing straight-chain or branched aliphatic hydrocarbons with 5 to 22 carbon atoms. If the content of the acrylate monomer units containing straight-chain or branched aliphatic hydrocarbons with 5 to 22 carbon atoms is lower than the range of this application, the viscosity may be too high; if it exceeds the range of this application, the nonpolarity increases, which may lead to precipitation from polar solvents.

[0036] Furthermore, for example, based on 100 mol% of the copolymer, the copolymer may contain 0 mol% or more and 60 mol% or less, 0 mol% or more and 50 mol% or less, or 0 mol% or more and 40 mol% of the copolymer containing the following components selected from cyano (CN), pyrrolidone (NC4H6O), carboxylic acid (COOH), amide, alkylamide, dialkylamide, alcohol, epoxy group, caprolactam (C5H4H6O), etc. 10 A polar monomer unit selected from one or more of the group consisting of CNO, morpholine (C4H8NO), and oxazolidinone (C3H4NO2). If the unit comprises cyano (CN), pyrrolidone (NC4H6O), carboxylic acid (COOH), amide, alkylamide, dialkylamide, alcohol, epoxy group, caprolactam (C5H4NO2), etc. 10If the content of one or more polar monomer units in the group consisting of CNO, morpholine (C4H8NO) and oxazolidinone (C3H4NO2) exceeds the scope of this application, the compatibility with polar solvents is too high, resulting in the inability to disperse the active material and potentially causing phase separation of the slurry composition.

[0037] For example, based on 100 mol% of the copolymer, the copolymer may contain 5 mol% to 40 mol% or more, 5 mol% to 30 mol% or more, or 5 mol% to 20 mol% or more of acrylate monomers and vinyl acetate monomers selected from the group consisting of straight-chain or branched aliphatic hydrocarbons containing 1 to 4 carbon atoms. If the content of one or more monomers selected from the group consisting of acrylate monomers and vinyl acetate monomers containing 1 to 4 carbon atoms is lower than the range of this application, the bonding strengthening effect is not obvious, and peeling from the current collector may occur. If it exceeds the range of this application, the viscosity reduction effect of the slurry composition may decrease.

[0038] In one embodiment, the copolymer may be represented by the following chemical formula 1.

[0039] [Chemical Formula 1]

[0040] In the chemical formula 1, R1 to R 18 They may be the same as or different from each other, and each is independently hydrogen, or a straight-chain or branched hydrocarbon having 1 to 4 carbon atoms. R1' is a straight-chain or branched aliphatic hydrocarbon with 5 to 22 carbon atoms. R2' contains one or more substituted or unsubstituted aromatic or aliphatic rings. R3' contains one or more substituted or unsubstituted aromatic or aliphatic rings. R4' is selected from cyano (CN), pyrrolidone (NC4H6O), carboxylic acid (COOH), amide, alkylamide, dialkylamide, alcohol, epoxy group, caprolactam (C5H) 10 One or more of the following groups: CNO, morpholine (C4H8NO), and oxazolidinone (C3H4NO2). R5' and R6' are each independently a straight-chain or branched aliphatic hydrocarbon with 1 to 4 carbon atoms. l + m + n + o + p + q = 1, 0.05 ≤ l + o ≤ 0.80, 0.01 ≤ m + n ≤ 0.60, and 0.05 ≤ p + q ≤ 0.40. Where m or n can be 0, p or q can be 0, and o can be 0.

[0041] In one embodiment, in the chemical formula 1, R1 to R 18 Both can be hydrogen.

[0042] In one embodiment, in the chemical formula 1, R1' may include one or more selected from the group consisting of n-pentyl, n-hexyl, n-heptyl, n-octyl, 2-ethylhexyl, n-nonyl, n-decyl, n-undecyl, lauryl, n-dodecyl, n-tridecyl, n-tetradecyl, n-pentadecanyl, cetyl, n-hexadecyl, n-heptadecyl, stearyl, n-octadecyl, n-nonadecanyl, n-eicosyl, n-docodicanyl, isopentyl, isoheptyl, isooctyl, isononyl, isodecanyl, isoundecyl, isotridecyl, isotetradecyl, isopentadecanyl, isocetyl, isohexadecyl, isoheptadecanyl, isostearyl, isooctadecyl, isononadecanyl, isoeicosyl, and isodocodicanyl.

[0043] In one embodiment, in the chemical formula 1, R2' and R3' may be the same as or different from each other, and each independently comprises one or more of the group consisting of substituted or unsubstituted cyclopentyl, cyclohexyl, benzyl, phenyl, phenoxy, naphthalene, anthracene, and pyrene.

[0044] In one embodiment, in the chemical formula 1, R5' and R6' may be the same as or different from each other, and each independently comprises one or more selected from the group consisting of hydrogen, methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl and sec-butyl.

[0045] In one embodiment, in the chemical formula 1, the monomer containing R1' can be n-pentyl(meth)acrylate, n-hexyl(meth)acrylate, n-heptyl(meth)acrylate, n-octyl(meth)acrylate, 2-ethylhexyl(meth)acrylate, or n-nonyl(meth)acrylate. te), n-decyl(meth)acrylate, n-undecyl(meth)acrylate, lauryl(meth)acrylate, n-dodecyl(meth)acrylate, n-tridecyl(meth)acrylate, n-tetradecyl(meth)acrylate, n-pentadecanyl(meth)acrylate The following acrylates are listed: n-pentadecyl(meth)acrylate, cetyl(meth)acrylate, n-hexadecyl(meth)acrylate, n-heptadecyl(meth)acrylate, stearyl(meth)acrylate, n-nonadecyl(meth)acrylate, n-neicosyl(meth)acrylate, n-heneicosyl(meth)acrylate, n-dococyl(meth)acrylate, isopentyl(meth)acrylate, isoheptyl(meth)acrylate, isooctyl(meth)acrylate, and isononyl(meth)acrylate.Isodeyl(meth)acrylate, isoundecyl(meth)acrylate, isododecyl(meth)acrylate, isotridecyl(meth)acrylate, isotetradecyl(meth)acrylate, isopentadecyl(meth)acrylate, isocetyl(meth)acrylate, isohexadecyl(meth)acrylate The acrylates (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 copolymers thereof, but not limited thereto.

[0046] In one embodiment, in the chemical formula 1, the monomer containing R2' can be selected from cyclopentyl acrylate, cyclohexyl acrylate, benzyl acrylate, 3-phenoxybenzyl acrylate, σ-phenyl phenoxy ethyl acrylate, σ-phenyl phenoxy ethyl methacrylate, (1-pyrene)2-methyl-2-propenoate, 1-naphthyl acrylate, 1-naphthyl methacrylate, 2-naphthyl acrylate, 2-naphthyl methacrylate, 9-anthracene methyl methacrylate. One or more of the group consisting of acrylate and 9-anthracene methyl methacrylate, wherein the monomer containing said R3' may be styrene.

[0047] In one embodiment, in the chemical formula 1, the monomer containing R4' can be one or more selected from the group consisting of acrylonitrile, vinyl pyrrolidone, acrylic acid, methacrylic acid, itaconic acid, acrylamide, N-methylacylamide, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, and glycidylmethacrylate.

[0048] In one embodiment, in the chemical formula 1, the monomer containing R5' can be one or more selected from the group consisting of methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, and butyl methacrylate, and the monomer containing R6' can be vinyl acetate.

[0049] In one embodiment, the copolymer may be a random copolymer or a block copolymer, depending on the synthesis process.

[0050] In one embodiment, the number-average molecular weight of the copolymer may be above 8,000 and below 40,000.

[0051] For example, the number average molecular weight of the copolymer can be 8,000 or more and 35,000 or less, 8,000 or more and 30,000 or less, 8,000 or more and 25,000 or less, 8,000 or more and 20,000 or less, or 9,000 or more and 20,000 or less.

[0052] If the number average molecular weight of the copolymer is lower than the range of this application, electrochemical stability cannot be ensured; if it exceeds the range of this application, the viscosity of the slurry composition may not decrease when added to the electrode slurry composition as the molecular weight increases.

[0053] According to another aspect of the invention, the viscosity reducer may contain the copolymer.

[0054] According to another aspect of the present invention, the positive electrode slurry composition may comprise the copolymer and the positive electrode active material.

[0055] In one embodiment, the positive electrode active material can be any positive electrode active material available in the art. Specific examples of such positive electrode active materials include: lithium metal; lithium cobalt oxides, such as LiCoO2; lithium manganese oxides, such as Li... 1+ x Mn 2-x O4 (where x is 0 to 0.33), LiMnO3, LiMn2O3, LiMnO2, etc.; lithium copper oxides, Li2CuO2, etc.; vanadium oxides, LiV3O8, V2O5, Cu2V2O7, etc.; lithium nickel oxides, such as LiNi 1-x M xO2 (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, and x = 0.01 to 0.3); lithium manganese composite oxide, composed of LiMn 2-x M x O2 (where M = Co, Ni, Fe, Cr, Zn or Ta, and x = 0.01 to 0.1) or Li2Mn3MO8 (where M = Fe, Co, Ni, Cu or Zn); lithium-nickel-manganese-cobalt oxide, represented by Li(Ni a Co b Mn[[ID==9]] c )O2 (where 0 < a < 1, 0 < b < 1, 0 < c < 1, and a + b + c = 1); sulfur or disulfide; phosphate, such as LiFePO4, LiMnPO4, LiCoPO4, LiNiPO4, etc.; Fe2(MoO4)3, etc., but not limited thereto.

[0056] Preferably, the positive electrode active material may be a lithium iron phosphate oxide represented by Li 1+a Fe 1-x M x PO 4-b A b (where M = Mn, Ni, Co, Cu, Sc, Ti, Cr, V or Zn, A = S, Se, F, Cl or I, and -0.5 < a < 0.5, 0 ≤ x < 0.5, 0 ≤ b ≤ 0.1).

[0057] For example, the positive electrode active material may be LiFePO4. Further, in order to improve the conductivity, the positive electrode active material may be doped with other metal elements on the particle surface or coated with a carbon-based material.

[0058] Based on the solid components, the content of the positive electrode active material may be 90 to 99% by weight. If the content of the active material is low, the high capacity of the battery cannot be achieved. If the content of the active material is too high, the contents of the binder, conductive material, etc. will be relatively reduced, and thus the electrode adhesion, conductivity, etc. may decrease.

[0059] In one embodiment, the positive electrode paste composition may further contain a conductive material.

[0060] There is no particular limitation on the conductive material, and it can be appropriately selected according to the types of batteries and storage batteries. For example, for lithium-ion secondary batteries, carbon such as graphite, activated carbon, carbon nanotubes, etc. can be used. For nickel-metal hydride secondary batteries, cobalt oxide can be used. For the negative electrode, nickel powder, cobalt oxide, titanium oxide, carbon, etc. can be used As the carbon, acetylene black, furnace black, graphite, carbon fiber, fullerene can be cited.

[0061] Based on 100% by weight of electrode active material, the amount of conductive material used is typically 0.1 to 10% by weight, preferably 0.1 to 5% by weight.

[0062] Reducing the amount of conductive material and increasing the amount of positive electrode active material can improve the energy density of secondary batteries. Therefore, even when using the same amount of conductive material, it is important to make it perform efficiently.

[0063] For conductive materials used in electrode slurries for secondary batteries, the finer and more uniformly dispersed the particles, the higher the conductivity, which reduces the battery's internal resistance and exhibits improved output characteristics, as well as extended battery life. If the particles are large and unevenly dispersed, even using the same amount, their adhesion and conductivity will decrease, thus adversely affecting the battery's life and output characteristics.

[0064] In one embodiment, the positive electrode slurry composition may further include a binder.

[0065] As the adhesive, one or more of the following can be selected, but are not limited to: poly(meth)acrylic acid, poly(meth)acrylamide, carboxymethyl cellulose, polyvinylidene fluoride, polyhexafluoropropylene-polyvinylidene fluoride copolymer (P(VdF / HFP)), polyvinyl acetate, polyvinyl alcohol, polyethylene oxide, polyvinylpyrrolidone, alkylated polyethylene oxide, polyethylene ether, poly(methyl methacrylate), poly(ethyl acrylate), polytetrafluoroethylene, polyvinyl chloride, polyacrylonitrile, polyvinylpyridine, styrene-butadiene rubber, acrylonitrile-butadiene rubber, and copolymers thereof.

[0066] Based on solid content, the binder content in the positive electrode slurry composition may be 0.3% by weight or more and 10% by weight or less. Preferably, the binder content in the positive electrode slurry composition may be 0.7% by weight or more and 8% by weight or less.

[0067] If the content of the binder is lower than the range of this application, it is difficult to expect sufficient adhesion between the current collector and the positive electrode active material or between the positive electrode active materials. If the content of the binder exceeds the range of this application, it may lead to a decrease in battery capacity.

[0068] In one embodiment, the copolymer may be included at a rate of 0.05% to 2.0% by weight, based on 100% by weight of the total weight of the positive electrode slurry composition.

[0069] If the content of the copolymer is lower than the range of this application, the viscosity reduction effect of the slurry composition will decrease. If the content of the copolymer exceeds the range of this application, the viscosity will decrease with the increase of the viscosity reducer content, but the content of the active substance will decrease relatively, which may lead to a decrease in energy density.

[0070] In one embodiment, the viscosity of the positive electrode slurry composition prepared as described in Evaluation Example 2 below can be less than 3500 cps at a shear rate of 10 / s.

[0071] That is, the viscosity of the cathode slurry composition containing the copolymer of this application is less than 3500 cps, which is lower than that of slurry without viscosity reducer, thereby improving processability and production speed.

[0072] According to another aspect of this application, the positive electrode may include: a current collector; and a positive electrode active material layer, formed by coating the positive electrode slurry composition.

[0073] The positive electrode can be prepared by (a) preparing a positive electrode slurry composition comprising a positive electrode active material and a copolymer of the present application and (b) coating the positive electrode slurry composition onto a positive electrode current collector and then drying it.

[0074] The positive electrode slurry composition can be mixed using conventional mixing equipment such as high-speed shear mixers, homogenizers, and P / D mixers in a conventional manner.

[0075] Step (b) is a step of preparing a positive electrode for a lithium secondary battery by coating the positive electrode slurry composition prepared in step (a) onto the positive electrode current collector and then drying it.

[0076] At this time, there is no limitation on the method of coating the positive electrode slurry composition. For example, it can be prepared by doctorblade coating, dip coating, gravure coating, slit diecoating, spin coating, comma coating, bar coating, reverse roll coating, screen coating, cap coating, etc.

[0077] After coating the positive electrode slurry composition, it is dried to finally prepare a positive electrode for secondary batteries with a positive electrode active material layer formed.

[0078] The current collector can be any conductive material that does not chemically react with the electrode forming slurry. Typical current collectors include aluminum foil, copper foil, etc. Current collectors with a thickness between 3 and 50 micrometers can be selected.

[0079] In one embodiment, the adhesion force between the current collector of the positive electrode and the positive electrode active material layer can be 4 gf / mm or higher.

[0080] That is, the positive electrode active material layer formed by coating the positive electrode slurry composition containing the copolymer of this application has an adhesion force of 4 gf / mm or more to the current collector, which has excellent adhesion and can prevent electrode peeling, thereby improving the life of the secondary battery with excellent life characteristics.

[0081] Another aspect of this application's secondary battery may include the positive electrode.

[0082] In one embodiment, the secondary battery may further include a separator.

[0083] The separator should be an insulator capable of separating the negative and positive electrodes, and should also provide channels that allow only lithium ions to pass through. For this purpose, good electrolyte wettability is required, and porous polymer films such as PE / PP or porous nonwoven fabrics are used. To prevent battery short circuits, a ceramic-coated separator can be used to improve heat resistance and mechanical strength; the coating can be single-layer or multi-layered.

[0084] The diaphragm can be made of a porous substrate, as long as the porous substrate is a type of porous substrate commonly used in electrochemical devices, such as polyolefin porous films or nonwoven fabrics, but is not limited thereto.

[0085] The diaphragm may be a porous substrate composed of any one or a mixture of two or more of the following materials: polyethylene, polypropylene, polybutene, polypentene, polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene ether, polyphenylene sulfide, and polyethylene naphthalate.

[0086] The electrolyte of the lithium secondary battery is a non-aqueous electrolyte containing lithium salt, which is composed of lithium salt and solvent. The solvent can be a non-aqueous organic solvent, an organic solid electrolyte, an inorganic solid electrolyte, etc.

[0087] The lithium salt is a substance that is readily soluble in the non-aqueous electrolyte; for example, LiCl, LiBr, LiI, LiClO4, LiBF4, and LiB can be used. 10 Cl 10 LiPF6, LiAsF6, LiSbF6, LiAlCl4, LiSCN, LiC4BO8, LiCF3CO2, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiN(SO2F)2, LiN(SO2C2F5)2, LiC4F9SO3, LiC(CF3SO2)3, (CF3SO2)·2NLi, lithium chloroborane, lower aliphatic carboxylic acids, lithium imine tetraphenylborate, etc.

[0088] As non-aqueous organic solvents, aprotic organic solvents such as N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butenyl carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, 4-methyl-1,3-dioxolane, diethyl ether, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triphosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolium ketone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate can be used.

[0089] As the organic solid electrolyte, for example, polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate polymers, polylysine, polyester sulfides, polyvinyl alcohol, polyvinylidene fluoride, polymers containing secondary dissociation groups, etc., can be used.

[0090] As the inorganic solid electrolyte, nitrides, halides, sulfates of Li such as Li3N, LiI, Li5NI2, Li3N-LiI-LiOH, LiSiO4, LiSiO4-LiI-LiOH, Li2SiS3, Li4SiO4, Li4SiO4-LiI-LiOH, Li3PO4-Li2S-SiS2, etc., can be used.

[0091] In addition, other additives can be added to the non-aqueous electrolyte to improve charge-discharge characteristics, flame retardancy, etc. Examples of such additives include pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-ethylene glycol dimethyl ether (glyme), triammonium hexaphosphate, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolides, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, aluminum trichloride, fluoroethylene carbonate (FEC), propylene sulfonate lactone (PRS), vinylene carbonate (VC), etc.

[0092] In addition to the conventional winding process, the lithium secondary battery of this invention also employs lamination stacking and folding processes for the separator and electrodes. Furthermore, the battery casing can be cylindrical, square, pouch-type, or coin-type, etc. Moreover, this lithium secondary battery can be used in small to medium-sized devices such as automobiles and electronic equipment. Detailed Implementation

[0093] The present invention will now be described in more detail through embodiments. However, the embodiments described below are merely for illustrating the present invention more specifically, and the scope of the present invention is not limited to the embodiments described below.

[0094] Examples and Comparative Examples: Preparation of Copolymers [Example 1] 70 g of N-methylpyrrolidone (NMP) as a solvent was added to a 5-necked flask reactor. Based on a total monomer molar percentage of 100 mol%, 36 mol% styrene (ST), 36 mol% stearyl acrylate (SA), 18 mol% acrylic acid (AA), and 10 mol% methyl acrylate (MA) were added. A reflux cooler and thermometer were installed, and the mixture was purged with nitrogen and heated to 75 °C to prepare a solution.

[0095] Then, 0.15 g of 2,2'-azobis-2,4-dimethylvaleronitrile was dissolved in 20 g of N-methylpyrrolidone and added dropwise to the solution over 30 minutes. After the addition was complete, the temperature was maintained at 75°C for 7 hours to prepare the copolymer.

[0096] [Example 2] The copolymer was prepared in the same way as in Example 1, except that 10 mol% vinyl acetate (VAc) was used instead of 10 mol% methyl acrylate (MA).

[0097] [Example 3] The copolymer was prepared in the same way as in Example 1, except that 10 mol% of ethyl acrylate (EA) was used instead of 10 mol% of methyl acrylate (MA).

[0098] [Comparative Example 1] The copolymer was prepared in the same way as in Example 1, except that methyl acrylate (MA) was not used, and 40 mol% (instead of 36 mol%) of styrene (ST), 40 mol% (instead of 36 mol%) of stearyl acrylate (SA) and 20 mol% (instead of 18 mol%) of acrylic acid (AA) were used.

[0099] [Comparative Example 2] The copolymer was prepared in the same way as in Example 1, except that 100 mol% methyl acrylate (MA) was used, and styrene (ST), stearyl acrylate (SA), and acrylic acid (AA) were not used.

[0100] [Comparative Example 3] The copolymer was prepared in the same way as in Example 1, except that 100 mol% vinyl acetate (VAc) was used, and styrene (ST), stearyl acrylate (SA), acrylic acid (AA) and methyl acrylate (MA) were not used.

[0101] [Comparative Example 4] The copolymer was prepared in the same way as in Example 1, except that 100 mol% ethyl acrylate (EA) was used, and styrene (ST), stearyl acrylate (SA), acrylic acid (AA) and methyl acrylate (MA) were not used.

[0102] Table 1 below shows the content (mol%) of monomers used in the preparation of copolymers in Examples 1 to 3 and Comparative Examples 1 to 4.

[0103] [Table 1]

[0104] In Table 1, ST represents styrene, SA represents stearyl acrylate, AA represents acrylic acid, MA represents methyl acrylate, VAc represents vinyl acetate, and EA represents ethyl acrylate.

[0105] [Evaluation Example] Evaluation Example 1: Determination of the number-average molecular weight (Mn) of the copolymer The number-average molecular weight (Mn) of the copolymers prepared in Examples 1 to 3 and Comparative Examples 1 to 4 was determined by gel permeation chromatography (GPC) using tetrahydrofuran (THF) as a solvent.

[0106] The number-average molecular weights of the copolymers are shown in Table 2 below.

[0107] [Table 2]

[0108] Typically, even polymers with the same composition can have different physical properties depending on their molecular weight. Therefore, viscosity reducers containing copolymers with similar number-average molecular weights have been synthesized.

[0109] Evaluation Example 2: Viscosity determination of positive electrode slurry composition The positive electrode slurry composition of Manufacturing Example 1-1 was prepared by mixing 0.2 g of a viscosity reducer containing the copolymer of Example 1, 40 g of a lithium iron phosphate compound as the positive electrode active material, 14.5 g of polyvinylidene fluoride (PVdF) dissolved in N-methylpyrrolidone at 8% by weight, 4.8 g of a multi-walled carbon nanotube (MWCNT) dispersion, and 5 g of N-methylpyrrolidone. At this time, the solid content of the slurry was 60% by weight.

[0110] By varying the type of viscosity reducer, positive electrode slurry compositions of Manufacturing Examples 1-2, 1-3, and Comparative Manufacturing Examples 1-1 to 1-4 were prepared. Additionally, positive electrode slurry compositions of Comparative Manufacturing Examples 1-5 were prepared without adding a viscosity reducer. Table 3 below shows the types of copolymers contained in the viscosity reducers used in the positive electrode slurry compositions of Manufacturing Examples 1-2, 1-3, and Comparative Manufacturing Examples 1-1 to 1-4.

[0111] [Table 3]

[0112] The viscosity of the positive electrode slurry compositions of Manufacturing Examples 1-1 to 1-3 and Comparative Manufacturing Examples 1-1 to 1-5 was determined using a Haake mars rheometer at shear rates of 1 / s and 10 / s.

[0113] The viscosity of the measured positive electrode slurry composition is shown in Table 4 below.

[0114] [Table 4]

[0115] It can be confirmed that, at shear rates of 1 / s and 10 / s, the cathode slurry compositions of Comparative Manufacturing Examples 1-2, 1-3, and 1-4, which contain viscosity reducers comprising copolymers of Comparative Examples 2, 3, or 4, all exhibit significantly higher viscosity compared to the cathode slurry compositions of Comparative Manufacturing Examples 1-5 that do not contain viscosity reducers.

[0116] In other words, it can be confirmed that polymers prepared by using monomers such as methyl acrylate, vinyl acetate, and ethyl acrylate to increase electrode adhesion alone do not have the effect of reducing the viscosity of the positive electrode slurry composition; on the contrary, they significantly increase the viscosity.

[0117] Evaluation Example 3: Determination of the Adhesion Force of the Positive Electrode A scraper was used to coat any of the positive electrode slurry compositions from Manufacturing Examples 1-1 to 1-3 and Comparative Manufacturing Examples 1-1 to 1-4 onto an aluminum foil with a thickness of 20 µm.

[0118] The electrode coated with the positive electrode slurry composition was dried in an oven at 130°C for more than 12 hours, then calendered and prepared to a density of 2.2 g / cc. It was then vacuum dried at 110°C to prepare the positive electrodes of Manufacturing Examples 2-1 to 2-3 and Comparative Manufacturing Examples 2-1 to 2-4.

[0119] The width of the prepared positive electrode was set to 25 mm, and the adhesion between the aluminum foil and the coating, i.e. the current collector and the coating of the positive electrode slurry composition, was measured using a universal testing machine (UTM).

[0120] The adhesion forces of the positive electrodes of manufacturing examples 2-1 to 2-3 and comparative manufacturing examples 2-1 to 2-4 are shown in Table 5 below.

[0121] [Table 5]

[0122] It can be confirmed that the adhesion between the current collector and the coating of the positive electrode of Comparative Manufacturing Example 2-1, which was prepared using the positive electrode slurry composition of Comparative Manufacturing Example 1-1 with the lowest viscosity, is very low.

[0123] As can be confirmed from Evaluation Examples 2 and 3, only copolymers containing monomer compositions and contents that meet the requirements of this application can simultaneously meet the required levels of viscosity and adhesion of the cathode slurry composition.

[0124] That is, the viscosity of the positive electrode slurry composition will only decrease when it contains copolymers that meet the monomer composition and content requirements of this application, thereby increasing the slurry solids content to improve the electrode production speed. At the same time, the adhesion between the current collector and the coating of the positive electrode slurry composition is high, which can prevent the battery life from being reduced due to electrode peeling.

[0125] The scope of this invention is determined by the claims described below, rather than by the specific embodiments described. All modifications or variations derived from the meaning, scope and equivalents of the claims shall be construed as being included within the scope of this invention.

[0126] Industrial availability As described above, the cathode slurry composition containing the copolymer of the present invention has a low viscosity even when the content of slurry solids is high, thereby improving processability and production speed.

[0127] In addition, the cathode slurry composition containing the copolymer of the present invention has excellent dispersibility and can produce a cathode with excellent adhesion between the cathode active material and the current collector.

Claims

1. A copolymer, characterized in that, Include: One or more monomer units selected from the group consisting of acrylate monomer units containing one or more substituted or unsubstituted aromatic or aliphatic rings and vinyl monomer units containing one or more substituted or unsubstituted aromatic or aliphatic rings; Acrylate monomer units selected from straight-chain or branched aliphatic hydrocarbons containing 5 to 22 carbon atoms, and monomer units selected from cyano (CN), pyrrolidone (NC4H6O), carboxylic acid (COOH), amide, alkylamide, dialkylamide, alcohol, epoxy group, caprolactam (C5H) 10 One or more of the polar monomer units in the group consisting of CNO, morpholine (C4H8NO) and oxazolidinone (C3H4NO2); as well as One or more monomer units are selected from the group consisting of acrylate monomer units and vinyl acetate monomer units comprising straight-chain or branched aliphatic hydrocarbons having 1 to 4 carbon atoms.

2. The copolymer according to claim 1, wherein, The monomer units selected from the group consisting of acrylate monomer units containing one or more substituted or unsubstituted aromatic or aliphatic rings and vinyl monomer units containing one or more substituted or unsubstituted aromatic or aliphatic rings are styrene, cyclopentyl acrylate, cyclohexyl acrylate, benzyl acrylate, 3-phenoxybenzyl acrylate, σ-phenyl phenoxyethyl acrylate, σ-phenyl phenoxyethyl methacrylate, (1-pyrene)2-methyl-2-propenoate, 1-naphthyl acrylate, 1-naphthyl methacrylate, and 2-naphthyl acrylate. It is a polymer of acrylate, 2-naphthylmethacrylate, 9-anthracene methyl acrylate, 9-anthracene methyl methacrylate, or combinations thereof.

3. The copolymer according to claim 1, wherein, The acrylate monomer units comprising straight-chain or branched aliphatic hydrocarbons having 5 to 22 carbon atoms are composed of n-pentyl(meth)acrylate, n-hexyl(meth)acrylate, n-heptyl(meth)acrylate, n-octyl(meth)acrylate, 2-ethylhexyl(meth)acrylate, and n-nonyl(meth)acrylate. ylate), n-decyl(meth)acrylate, n-undecyl(meth)acrylate, lauryl(meth)acrylate, n-dodecyl(meth)acrylate, n-tridecyl(meth)acrylate, n-tetradecyl(meth)acrylate, n-pentadecanyl(meth)acrylate Ester (n-pentadecyl(meth)acrylate), cetyl(meth)acrylate, n-hexadecyl(meth)acrylate, n-heptadecyl(meth)acrylate, stearyl(meth)acrylate, n-nonadecyl(meth)acrylate, n-neicosyl(meth)acrylate, n-heneicosyl(meth)acrylate, n-dococyl(meth)acrylate, isopentyl(meth)acrylate, isoheptyl(meth)acrylate, isooctyl(meth)acrylate, isooctyl(meth)acrylate, isononyl(meth)acrylateIsodeyl(meth)acrylate, isoundecyl(meth)acrylate, isododecyl(meth)acrylate, isotridecyl(meth)acrylate, isotetradecyl(meth)acrylate, isoopentadecyl(meth)acrylate, isocetyl(meth)acrylate, isohexadecyl(meth)acrylate It is a polymerized form of 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 combinations thereof.

4. The copolymer according to claim 1, wherein, The composition includes cyano (CN), pyrrolidone (NC4H6O), carboxylic acid (COOH), amide, alkylamide, dialkylamide, alcohol, epoxy group, caprolactam (C5H) 10 One or more polar monomer units from the group consisting of acrylonitrile (CNO), morpholine (C4H8NO), and oxazolidinone (C3H4NO2) are polymerized from acrylonitrile, vinylpyrrolidone, acrylic acid, methacrylic acid, itaconic acid, acrylamide, N-methylacylamide, 2-hydroxyethyl acrylate, 2-hydroxyethylmethacrylate, glycidyl methacrylate, or combinations thereof.

5. The copolymer according to claim 1, wherein, The monomer units selected from the group consisting of acrylate monomer units containing straight-chain or branched aliphatic hydrocarbons with 1 to 4 carbon atoms and vinyl acetate monomer units are polymerized from vinyl acetate, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, or combinations thereof.

6. The copolymer according to claim 1, wherein, Based on 100 mol% of the copolymer, it comprises: more than 1 mol% and less than 60 mol% of one or more monomer units selected from the group consisting of acrylate monomer units containing one or more substituted or unsubstituted aromatic rings or aliphatic rings and vinyl monomer units containing one or more substituted or unsubstituted aromatic rings or aliphatic rings. The acrylate monomer units selected from straight-chain or branched aliphatic hydrocarbons containing 5 to 22 carbon atoms, comprising 5 mol% or more and 80 mol% or less, are cyanoacrylate monomer units selected from cyano(CN), pyrrolidone (NC4H6O), carboxylic acid (COOH), amide, alkylamide, dialkylamide, alcohol, epoxy group, caprolactam (C5H4H6O). 10 One or more of the polar monomer units in the group consisting of CNO, morpholine (C4H8NO) and oxazolidinone (C3H4NO2); as well as The monomer units selected from the group consisting of acrylate monomer units comprising straight-chain or branched aliphatic hydrocarbons having 1 to 4 carbon atoms and vinyl acetate monomer units, comprising more than 5 mol% and less than 40 mol% of the monomer units.

7. The copolymer according to claim 1, wherein, The copolymer is represented by the following chemical formula 1. [Chemical Formula 1] In the chemical formula 1, R1 to R 18 They may be the same as or different from each other, and each is independently hydrogen, or a straight-chain or branched hydrocarbon having 1 to 4 carbon atoms. R1' is a straight-chain or branched aliphatic hydrocarbon with 5 to 22 carbon atoms. R2' contains one or more substituted or unsubstituted aromatic or aliphatic rings. R3' contains one or more substituted or unsubstituted aromatic or aliphatic rings. R4' is selected from cyano (CN), pyrrolidone (NC4H6O), carboxylic acid (COOH), amide, alkylamide, dialkylamide, alcohol, epoxy group, caprolactam (C5H) 10 One or more of the following groups: CNO, morpholine (C4H8NO), and oxazolidinone (C3H4NO2). R5' and R6' are each independently a straight-chain or branched aliphatic hydrocarbon with 1 to 4 carbon atoms. l + m + n + o + p + q = 1, 0.05 ≤ l + o ≤ 0.80, 0.01 ≤ m + n ≤ 0.60, and 0.05 ≤ p + q ≤ 0.

40. Where m or n can be 0, p or q can be 0, and o can be 0.

8. The copolymer according to claim 7, wherein, R1' includes one or more of the group consisting of n-pentyl, n-hexyl, n-heptyl, n-octyl, 2-ethylhexyl, n-nonyl, n-decyl, n-undecyl, lauryl, n-dodecyl, n-tridecyl, n-tetradecyl, n-pentadecanyl, cetyl, n-hexadecyl, n-heptadecyl, stearyl, n-octadecyl, n-nonadecanyl, n-eicosyl, n-timodecyl, isopentyl, isoheptyl, isooctyl, isononyl, isodecanyl, isoundecyl, isotridecyl, isotetradecyl, isopentadecanyl, isocetyl, isohexyl, isohexadecanyl, isostearyl, isooctadecyl, isononadecanyl, isoeicosyl, and isotimodecyl.

9. The copolymer according to claim 7, wherein, R2' and R3' may be the same as or different from each other, and each independently comprises one or more of the group consisting of substituted or unsubstituted cyclopentyl, cyclohexyl, benzyl, phenyl, phenoxy, naphthalene, anthracene, and pyrene.

10. The copolymer according to claim 7, wherein, R5' and R6' may be the same as or different from each other, and each independently contains one or more of the group consisting of hydrogen, methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl and sec-butyl.

11. The copolymer according to claim 7, wherein, The monomer containing R2' is selected from cyclopentyl acrylate, cyclohexyl acrylate, benzyl acrylate, 3-phenoxybenzyl acrylate, σ-phenyl phenoxy ethyl acrylate, σ-phenyl phenoxy ethyl methacrylate, (1-pyrene)2-methyl-2-propenoate, 1-naphthyl acrylate, 1-naphthyl methacrylate, 2-naphthyl acrylate, 2-naphthyl methacrylate, 9-anthracene methyl acrylate, and 9-anthracene methyl methacrylate. One or more of the group consisting of methacrylate, The monomer containing R3' is styrene.

12. The copolymer according to claim 7, wherein, The monomer containing R4' is selected from one or more of the group consisting of acrylonitrile, vinylpyrrolidone, acrylic acid, methacrylic acid, itaconic acid, acrylamide, N-methylacylamide, 2-hydroxyethyl acrylate, 2-hydroxyethylmethacrylate, and glycidyl methacrylate.

13. The copolymer according to claim 7, wherein, The monomer containing R5' is selected from one or more of the group consisting of methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, and butyl methacrylate. The monomer containing R6' is vinyl acetate.

14. The copolymer according to claim 1, wherein, The copolymer is a random copolymer or a block copolymer.

15. The copolymer according to claim 1, wherein, The copolymer has a number-average molecular weight of 8,000 or more and 40,000 or less.

16. A viscosity reducer, characterized in that, The copolymer comprising any one of claims 1 to 15.

17. A positive electrode slurry composition, characterized in that, Include: The copolymer of any one of claims 1 to 15; and Positive electrode active material.

18. The positive electrode slurry composition according to claim 17, wherein, Based on 100% by weight of the total weight of the positive electrode slurry composition, the copolymer comprises 0.05% by weight and less than 2.0% by weight.

19. A positive electrode, characterized in that, include: current collector; as well as The positive electrode active material layer is formed by coating the current collector with the positive electrode slurry composition of claim 17.

20. The positive electrode according to claim 19, wherein, The adhesion force between the current collector and the positive electrode active material layer is greater than 4 gf / mm.

21. A secondary battery, characterized in that, Includes the positive electrode as described in claim 19.

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