Binder including copolymer, negative electrode for secondary battery including the binder, and secondary battery including the negative electrode

Abstract

To provide a copolymer binder having excellent properties and being usable in dry electrode manufacturing.SOLUTION: A copolymer includes a main chain including a first monomer unit based on styrene, a second monomer unit containing a hydroxy group and having 4 or more and 7 or fewer carbon atoms, and a third monomer unit containing a double bond and having 4 or more and 7 or fewer carbon atoms, wherein the second monomer unit of the main chain includes a grafted polymer chain. In addition, there are proposed a negative electrode slurry, a negative electrode, and a secondary battery, each including the copolymer.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a copolymer that can be used as a binder, and a slurry, an electrode, and a secondary battery containing the copolymer. [Background technology]

[0002] Lithium secondary batteries have a high energy density and are widely used in the electrical, electronic, communication, and computer industries. Following small lithium secondary batteries for portable electronic devices, their application fields are expanding to include high-capacity secondary batteries for hybrid vehicles, electric vehicles, etc.

[0003] As the range of applications expands, lithium secondary batteries are required to have not only higher capacity but also longer life characteristics. One example of a method for increasing the capacity of lithium secondary batteries is to use an active material containing silicon atoms in the negative electrode.

[0004] The application of silicon-containing active materials, which have a higher lithium intercalation / deintercalation rate than conventional carbon-based active materials, can be expected to improve battery capacity. However, silicon-containing active materials undergo large volume changes due to lithium intercalation / deintercalation, resulting in significant expansion and contraction of the negative electrode active material layer during charging and discharging.

[0005] As a result, the conductivity between negative electrode active materials decreases or the conductive path between the negative electrode active material and the current collector is interrupted, resulting in a problem of deterioration in the cycle characteristics of the secondary battery.

[0006] However, the various binders that have been developed so far (PAA, PAA / CMC, Na-PAA, crosslinked PAA, alginate, PVA, etc.) either lack adhesive strength or make the electrodes too brittle and insufficient in durability, making it difficult to expect a solution to the volume expansion problem mentioned above.

[0007] Therefore, there is a demand for a binder that can solve these problems and ensure the capacity maintenance rate of secondary batteries.

[0008] In addition, a wet process is used when manufacturing a secondary battery electrode plate, and the wet process typically involves dispersing and mixing a material in a solution, coating the slurry, and then drying the solvent.

[0009] In this case, the energy, space, and time required for drying the solvent are large, and minimizing the drying process is effective in reducing costs.

[0010] In particular, if there is no recovery system in the process of drying the solvent, it will have an impact on carbon emissions, and the process of recovering and reusing it will require additional costs.

[0011] Meanwhile, during the process of drying the solvent on the electrode, a migration phenomenon occurs in which the binder rises along the upper layer of the electrode, which affects the uneven distribution of the binder within the electrode, causing problems such as reduced adhesion and reduced electrode uniformity.

[0012] Therefore, active research is being conducted into dry electrode fabrication, which involves manufacturing electrodes without using solvents, in view of low cost, environmental friendliness, and uniformity of materials within the electrode.

[0013] Dry electrodes have the advantage that the thickness of the electrode is reduced by rolling after applying a slurry to the side of the cell, which makes it easy for materials to come into contact with each other and reduces the resistance of the electrode.

[0014] Currently, PTFE binder is used as a binder for dry electrodes when manufacturing dry electrodes for positive electrodes, but development of binders for dry electrodes for negative electrodes is at a negligible level. [Prior art documents] [Patent documents]

[0015] [Patent Document 1] Korean Patent Publication No. 10-2023-0064383 Summary of the Invention [Problem to be solved by the invention]

[0016] Therefore, an object of the present invention is to provide a copolymer binder with excellent properties that can be used in dry electrode manufacturing.

[0017] The present invention also seeks to provide a slurry composition with excellent properties using the copolymer.

[0018] Furthermore, the present invention provides an electrode (particularly, a negative electrode) having excellent performance to which the slurry composition is applied, and a secondary battery having excellent characteristics and including the electrode.

[0019] However, the problems to be solved by the present application are not limited to those mentioned above, and other problems not mentioned will be clearly understood by those skilled in the art from the following description. [Means for solving the problem]

[0020] In one aspect of the present application, a styrene-based first monomer unit is provided. a second monomer unit having 4 to 7 carbon atoms and including a hydroxy group; a main chain including a third monomer unit having 4 to 7 carbon atoms and including a double bond, The second monomer unit of the main chain comprises a grafted polymer chain. copolymer, to provide.

[0021] Another aspect of the present application is a polymerizable composition comprising the copolymer and a negative electrode active material; A negative electrode slurry is provided.

[0022] Yet another aspect of the present application is a battery comprising: a current collector; a negative electrode active material layer including the copolymer formed on the current collector, A negative electrode is provided.

[0023] Yet another aspect of the present application is a method for manufacturing a semiconductor device comprising: The negative electrode A secondary battery is provided. [Effects of the Invention]

[0024] The copolymer of the present invention can be used as a binder in dry electrode production, and can improve the performance of electrodes (especially negative electrodes) and secondary batteries.

[0025] In particular, the copolymer of the present invention may also be used to manufacture an all-solid-state electrode or an all-solid-state battery. can. [Brief explanation of the drawings]

[0026] [Figure 1] 1 is a photograph showing the solidification of the slurry for an electrode prepared in Preparation Example 2 using the copolymer binder prepared in Preparation Example 1 of the present invention after re-pulverization. [Figure 2] 1 is a graph showing the results of stress-strain measurements of a copolymer binder prepared according to Preparation Example 1 of the present invention and a styrene-butadiene rubber (SBR) binder. DETAILED DESCRIPTION OF THE INVENTION

[0027] The functions and effects of the invention will be described in more detail below through specific embodiments of the invention, however, these embodiments are presented only as examples of the invention and do not define the scope of the invention.

[0028] Prior to this, the terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted as meanings and concepts that are consistent with the technical idea of ​​the present invention, based on the principle that an inventor can appropriately define the concept of a term in order to explain his or her invention in the best possible way.

[0029] Therefore, it should be understood that the configuration of the embodiment described in this specification is merely one of the most preferred embodiments of the present invention and does not represent the entire technical idea of ​​the present invention, and that there may be various equivalents and modifications that can replace them at the time of this application.

[0030] In this specification, the singular includes the plural unless the context clearly dictates otherwise. In this application, the terms "comprises," "comprises," or "having" are intended to specify the presence of embodied features, numbers, steps, components, or combinations thereof, and should be understood as not precluding the presence or additional possibility of one or more other features, numbers, steps, components, or combinations thereof.

[0031] In this specification, when expressing a numerical range, "a to b" and "a~b", "to" and "to" are defined as ≧a and ≦b.

[0032] The copolymer according to one aspect of the present application may include a main chain including a styrene-based first monomer unit, a second monomer unit having 4 to 7 carbon atoms and including a hydroxy group, and a third monomer unit having 4 to 7 carbon atoms and including a double bond, and may include a polymer chain in which the second monomer unit is grafted to the main chain.

[0033] The third monomer unit may include one or more of the double bonds.

[0034] For example, the second monomer unit may be a hydrocarbon having 4 to 7 carbon atoms and containing a hydroxy group, and the third monomer unit may be a hydrocarbon having 4 to 7 carbon atoms and containing a double bond.

[0035] The copolymer includes the grafted polymer chains, has excellent stretchability, and can be uniformly mixed with active materials, etc., during dry electrode fabrication.

[0036] The copolymer can also be used as a binder in the manufacture of a dry electrode, and can exhibit a sufficient binding effect through fiberization when kneaded with an active material, a conductive agent, etc.

[0037] That is, even in the case of dry electrode manufacturing without using a solvent, the copolymer can exhibit a binding effect through fiberization of the copolymer during the process of mixing with an active material, a conductive agent, etc.

[0038] The grafted polymer chains of the copolymer can contribute to the formation of a network between the copolymers.

[0039] In addition, the copolymer has excellent deformation properties because the main chain and the grafted polymer chain form a single polymer chain and has both hard and soft segments, and chain breakage does not easily occur, allowing it to exhibit effective binding properties.

[0040] In one embodiment, the first monomer unit may be formed by polymerizing a styrene monomer, and the second monomer unit and the third monomer unit may be formed by polymerizing a monomer having a conjugated double bond.

[0041] In one implementation, the monomer having conjugated double bonds may be butadiene, isoprene, or a combination thereof.

[0042] In one embodiment, the copolymer may include a repeating monomer unit represented by the following Formula 1: [ka]

[0043] In Chemical Formula 1, A represents the styrene-based first monomer unit of the main chain, B represents the second monomer unit of the main chain having 4 or more carbon atoms and including the hydroxy group, C represents the third monomer unit of the main chain having 4 to 7 carbon atoms and including the double bond, G represents the grafted polymer chain, and m, n, and l represent the first monomer unit, the second monomer unit, and the molar ratio of the monomer units, respectively.

[0044] m+n+l=1, m may be 0.6 or more and 0.95 or less, and n+l may be 0.05 or more and 0.4 or less.

[0045] For example, m may be 0.7 or more and 0.9 or less, and n+l may be 0.1 or more and 0.3 or less.

[0046] On the other hand, n / (n+l) may be 0.05 or more and 0.3 or less, for example, 0.1 or more and 0.25 or less, or 0.1 or more and 0.2 or less.

[0047] In one embodiment, A in Chemical Formula 1 may include a first monomer repeat unit represented by the following Chemical Formula 2, B in Chemical Formula 1 may include a second monomer repeat unit represented by the following Chemical Formula 3-1, and C in Chemical Formula 1 may include a third monomer repeat unit represented by the following Chemical Formula 3-2. [ka] In the formula 2, m represents the molar ratio of the repeating unit of the monomer of the formula 2.

[0048] [ka] [ka] In the formulas 3-1 and 3-2, R1 represents hydrogen or a linear or branched hydrocarbon having 1 to 4 carbon atoms, n and l represent the molar ratio of the repeating units of the monomers of the formulas 3-1 and 3-2, respectively, and G represents the grafted polymer chain of the formula 1.

[0049] m+n+l=1, m may be 0.6 or more and 0.95 or less, and n+l may be 0.05 or more and 0.4 or less.

[0050] For example, m may be 0.7 or more and 0.9 or less, and n+l may be 0.1 or more and 0.3 or less.

[0051] On the other hand, n / (n+l) may be 0.05 or more and 0.3 or less, for example, 0.1 or more and 0.25 or less, or 0.1 or more and 0.2 or less.

[0052] In one embodiment, the grafted polymer chain can be represented by the following chemical formula 4: [ka] In Chemical Formula 4, * represents a linking part to the main chain, H represents a hydrogen atom, D represents an acrylate-based monomer unit, and p represents the number of the acrylate-based monomer units.

[0053] p may be greater than or equal to 1 and less than or equal to 1,000. For example, p may be greater than or equal to 1 and less than or equal to 100.

[0054] In one embodiment, the acrylate-based monomer unit is methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, or propyl acrylate. acrylate, propyl methacrylate, isopropyl acrylate, isopropyl methacrylate, butyl acrylate, butyl methacrylate, sec-butyl acrylate, sec-butyl methacrylate, tert-butyl acrylate, tert-butyl methacrylate, ethyl hexyl acrylate, ethyl hexyl methacrylate, lauryl acrylate, lauryl methacrylate, stearyl acrylate, stearyl methacrylate, or a combination thereof may be polymerized to form the polymerizable copolymer.

[0055] In one embodiment, D in Formula 4 may include a monomer repeat unit represented by Formula 5 below. [ka] In the above Chemical Formula 5, p represents the number of repeating units of the monomer of the above Chemical Formula 5, and R2 represents a linear or branched hydrocarbon having 1 to 20 carbon atoms.

[0056] In Chemical Formula 5, p may be 1 or more and 1,000 or less. For example, p may be 1 or more and 100 or less.

[0057] In one embodiment, the weight ratio of the first monomer unit to the second monomer unit and the third monomer unit in the main chain (weight of the first monomer unit:weight of the second monomer unit and the third monomer unit) may be 6-9.5:0.5-4.

[0058] If the weight ratio of the first monomer unit to the second monomer unit in the main chain is above or below the range of the present application, it may be difficult to powder the copolymer for application to a dry electrode.

[0059] In one implementation, the backbone of the copolymer may be a random or block copolymer.

[0060] In one embodiment, the weight average molecular weight of the copolymer measured by GPC may be 10,000 g / mol or more and 1,000,000 g / mol or less.

[0061] If the weight average molecular weight of the copolymer is above or below the range of the present application, it may be difficult to powder the copolymer for application to dry electrodes.

[0062] A method for preparing a copolymer according to another aspect of the present application may include a first step of polymerizing a styrene-based monomer and a monomer having a conjugated double bond to form a main chain of the copolymer; a second step of epoxidizing a double bond of the main chain of the copolymer by adding a carboxylic acid to introduce a grafted polymer chain; a third step of adding an acrylic acid-based monomer to react with the epoxidized main chain of the copolymer to introduce a functional group to introduce the grafted polymer chain; and a fourth step of adding an acrylate-based monomer to further polymerize the grafted polymer chain.

[0063] To introduce the grafted polymer chain, the functional group may be an acryl group including vinyl.

[0064] The negative electrode slurry according to another aspect of the present application can include the copolymer and the negative electrode active material.

[0065] That is, the copolymer can be used as a binder for a negative electrode manufactured by a dry process.

[0066] The negative electrode active material may be a compound containing one or more selected from the group consisting of a carbon-based material, silicon, an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, a transition metal, and a rare earth element, and preferably may be silicon or a compound containing silicon.

[0067] Examples of the carbon-based material include, but are not limited to, artificial graphite, natural graphite, hard carbon, soft carbon, etc. The negative electrode active material containing silicon is not particularly limited in its type as long as it is silicon or a compound containing silicon, but preferably, Si, SiO x (0 < x < 2), a Si-Y alloy (where Y is an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, a transition metal, a rare earth element, or a combination thereof and is not Si), and one or more selected from the group consisting of Si-C composites.

[0068] When a negative electrode active material containing silicon and another negative electrode active material are mixed and used as the negative electrode active material, the negative electrode active material containing silicon can be contained at 8% by weight or more of the total weight of the negative electrode active material.

[0069] The negative electrode active material can be contained at 50 to 98% by weight based on the total weight of the negative electrode active material layer.

[0070] If the negative electrode active material is contained less than 50% by weight, the energy density decreases and a high-energy density battery cannot be manufactured. If it is contained more than 98% by weight, the content of the conductive agent and the binder decreases, the electrical conductivity decreases, and the adhesive force between the electrode active material layer and the current collector may decrease.

[0071] Meanwhile, the copolymer composition binder of the present application may be included in an amount of 1 to 35 wt% based on the total weight of the negative electrode slurry. If the copolymer is included in an amount less than 1 wt%, the physical properties of the negative electrode may be deteriorated and the negative electrode active material and conductive agent may be separated out. If the copolymer is included in an amount more than 35 wt%, the ratio of the negative electrode active material to the conductive agent may be relatively reduced, which may result in a decrease in battery capacity and a decrease in the electrical conductivity of the negative electrode.

[0072] In addition to the copolymer composition of the present application, the negative electrode slurry may further include a polymer, such as, but not limited to, polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), polyacrylic acid (PAA), metal polyacrylate (Metal-PAA), polymethacrylic acid (PMA), polymethyl methacrylate (PMMA), polyacrylamide (PAM), polymethacrylamide, polyacrylonitrile (PAN), polymethacrylonitrile, polyimide (PI), chitosan, starch, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, hydroxypropyl cellulose, regenerated cellulose, and various copolymers thereof.

[0073] According to yet another aspect of the present disclosure, a negative electrode may include a current collector and a negative electrode active material layer including the copolymer of the present disclosure formed on the current collector.

[0074] The negative electrode active material layer may further include a conductive agent. The conductive agent is used to further improve the conductivity of the negative electrode active material. The conductive agent may be any conductive agent that does not induce chemical changes in the battery. Examples of the conductive agent include graphite such as natural graphite or artificial graphite; carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; conductive fibers such as carbon fiber and metal fiber; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and polyphenylene derivatives.

[0075] The conductive agent may be included in an amount of 0.05 to 30 wt %, preferably 15 to 25 wt %, based on the total weight of the negative electrode active material layer. If the conductive agent is included in an amount less than 0.05 wt %, the electrical conductivity of the negative electrode is reduced. If the conductive agent is included in an amount greater than 30 wt %, the ratio of the silicon-based negative electrode active material to the binder is relatively reduced, resulting in a reduced battery capacity. Furthermore, since the binder content must be increased to maintain the negative electrode active material layer, the content of the negative electrode active material is reduced, making it difficult to manufacture a high-energy-density battery.

[0076] In the negative electrode of the present invention, the negative electrode active material layer contains the copolymer of the present invention, which can suppress volume expansion of the negative electrode active material that occurs during charge and discharge of the secondary battery, thereby improving the capacity retention rate per cycle.

[0077] The negative electrode may be manufactured by (a) preparing a composition for forming a negative electrode active material layer, including a negative electrode active material and the copolymer composition of the present application, and (b) pressing the composition for forming a negative electrode active material layer onto a negative electrode current collector.

[0078] Meanwhile, the composition for forming the negative electrode active material layer may be prepared in the form of a dry negative electrode slurry without using a solvent.

[0079] The composition for forming the negative electrode active material layer can be mixed by a conventional method using a conventional mixer such as a rate mixer, a high shear mixer, or a homomixer.

[0080] The step (b) is a step of manufacturing a negative electrode for a lithium secondary battery by pressing the composition for forming a negative electrode active material layer manufactured in the step (a) onto a negative electrode current collector.

[0081] The negative electrode current collector may be made of copper, stainless steel, titanium, silver, palladium, nickel, alloys thereof, or combinations thereof. The stainless steel may be surface-treated with carbon, nickel, titanium, or silver, and an aluminum-cadmium alloy may be used as the alloy. Other examples include sintered carbon, a non-conductive polymer surface-treated with a conductive agent, or a conductive polymer.

[0082] The composition for forming a negative electrode active material layer prepared in step (a) is applied onto a negative electrode current collector, and can be coated on the current collector to an appropriate thickness depending on the thickness to be formed, and can preferably be appropriately selected within the range of 10 to 300 μm.

[0083] In this regard, to coat the composition for forming a negative electrode active material layer in the form of a slurry, for example, the composition for forming a negative electrode active material layer may be prepared in a free-standing state and then laminated on an electrode plate, or a powder continuous dry coating method may be used.

[0084] Finally, a negative electrode for a secondary battery (particularly, a lithium secondary battery) having a negative electrode active material layer formed thereon can be manufactured.

[0085] A battery according to yet another aspect of the present disclosure may include a current collector and a negative electrode in which the negative electrode active material layer is formed on the current collector.

[0086] The battery may be a secondary battery (particularly, a lithium secondary battery) including a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte.

[0087] The configurations of the positive electrode, separator, and electrolyte of the lithium secondary battery are not particularly limited in the present invention and may be those known in the art.

[0088] The positive electrode includes a positive electrode active material formed on a positive electrode current collector.

[0089] The positive electrode current collector is not particularly limited as long as it has high conductivity without inducing chemical changes in the battery, and may be, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. In this case, the positive electrode current collector may be in various forms, such as a film, sheet, wheel, net, porous body, foam, or nonwoven fabric, with fine irregularities formed on the surface to enhance adhesion to the positive electrode active material. It is possible.

[0090] The positive electrode active material constituting the positive electrode active material layer 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 LiCoO; Li 1+x Mn 2-x O4 (where x is 0 to 0.33), lithium manganese oxides such as LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxides such as Li2CuO2; vanadium oxides such as LiV3O8, LiFe3O4, V2O5, and Cu2V2O7; LiNi 1-x M x Lithium nickel oxide represented by the formula LiMnO2 (where M=Co, Mn, Al, Cu, Fe, Mg, B, or Ga, and x=0.01 to 0.3); 2-x M xO2 (where M = Co, Ni, Fe, Cr, Zn, or Ta, and x = 0.01 - 0.1) or lithium manganese composite oxide represented by Li2Mn3MO8 (where M = Fe, Co, Ni, Cu, or Zn); Li(Ni a Co b Mn c )O2 (where 0 < a < 1, 0 < b < 1, 0 < c < 1, and a + b + c = 1); sulfur or disulfide compounds; phosphates such as LiFePO4, LiMnPO4, LiCoPO4, LiNiPO4, etc.; Fe2(MoO4)3, etc. can be mentioned, but it is not limited to only these.

[0091] At this time, the positive electrode active material layer can further contain, in addition to the positive electrode active material, a binder, a conductive agent, a filler, and other additives, etc. The conductive agent is the same as the above-mentioned content in the negative electrode for the lithium secondary battery.

[0092] Also, the binder can include polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), polyacrylic acid (PAA), polymethacrylic acid (PMA), polymethyl methacrylate (PMMA), polyacrylamide (PAM), polymethacrylamide, polyacrylonitrile (PAN), polymethacrylonitrile, polyimide (PI), chitosan, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene - propylene - diene polymer (EPDM), sulfonated - EPDM, styrene - butadiene rubber (SBR), fluorine rubber, and various copolymers thereof, etc., but it is not limited thereto.

[0093] The separator can be made of a porous substrate. Usually, any porous substrate that can be used in an electrochemical device can be used. For example, a polyolefin - based porous membrane or a non - woven fabric can be used, but it is not particularly limited thereto.

[0094] The separation membrane may be a porous substrate made of any one selected from the group consisting of polyethylene, polypropylene, polybutylene, polypentene, polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyether ether ketone, polyether sulfone, polyphenylene oxide, polyphenylene sulfide, and polyethylene naphthalate, or a mixture of two or more of these.

[0095] The electrolyte of the lithium secondary battery is a non-aqueous electrolyte containing a lithium salt, and is composed of a lithium salt and a solvent. The solvent may be a non-aqueous organic solvent, an organic solid electrolyte, or an inorganic solid electrolyte.

[0096] The lithium salt is a substance that is easily dissolved in the non-aqueous electrolyte solution, such as LiCl, LiBr, LiI, LiClO4, LiBF4, LiB 10 Cl 10 , LiPF6, L iAsF6, LiSbF6, LiAlCl4, LiSCN, LiC4BO8, LiCF3CO2, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiN(SO2F)2, LiN(SO2C2F5)2, LiC4F9SO3, LiC(CF3SO2)3, (CF3SO2)·2NLi, lithium chloroborane, lithium lower aliphatic carboxylates, lithium 4-phenylborate imide, and the like may be used.

[0097] Examples of non-aqueous organic solvents that can be used include N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydroxyfuran (franc), 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, 4-methyl-1,3-dioxene, diethyl ether, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and aprotic organic solvents such as ethyl propionate.

[0098] Examples of the organic solid electrolyte that can be used include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate ester polymers, polyagitation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, and polymers containing secondary dissociating groups.

[0099] The inorganic solid electrolyte may be, for example, a nitride, halide, or sulfate of Li, such as LiN, LiI, LiNI, LiN-LiI-LiOH, LiSiO, LiSiO-LiI-LiOH, LiSiS, LiSiO, LiSiO-LiI-LiOH, or LiPO-LiS-SiS.

[0100] The non-aqueous electrolyte solution may further contain other additives for the purpose of improving charge / discharge characteristics, flame retardancy, etc. Examples of the additives include pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, aluminum trichloride, fluoroethylene carbonate (FEC), propene sultone (PRS), and vinylene carbonate (VC).

[0101] The lithium secondary battery according to the present invention can be manufactured by laminating and stacking separators and electrodes and folding them in addition to the conventional winding process, and the battery case can be cylindrical, prismatic, pouch-shaped, or coin-shaped.

[0102] The present invention will be described in more detail below using examples, but the present invention is not limited thereto.

[0103] [Production Example 1] Production of copolymer Styrene and isoprene monomer mixture was added dropwise to 2.5 L of dioxane so that the total solid content was 15 wt %. At this time, the weight ratio of styrene to isoprene in the monomer mixture (weight of styrene: weight of isoprene) was 8:2. At the same time, Azo initiator V-65 was dissolved in 0.5 mL of toluene. The mixture was dissolved in 0.5 L at 0.6% by mass and then added to the flask. The mixture was then reacted at 60°C for 12 hours and then cooled.

[0104] Then, for the epoxylation that can introduce acrylic groups into the double bonds of the isoprene of the main chain, 0.25 molar ratio of formic acid and 0.5 molar ratio of H2O2 were added dropwise at 60°C for 12 hours.

[0105] The styrene-isoprene copolymer backbone into which epoxy groups had been introduced through the reaction was purified by precipitation in methanol (MeOH).

[0106] The purified styrene-isoprene copolymer main chain into which epoxy groups had been introduced was dissolved in toluene, and acrylic acid was added dropwise at 80°C in an amount equivalent to twice the molar amount of the copolymer main chain to introduce a vinyl-containing acrylic functional group for the introduction of grafted polymer chains.

[0107] Then, butyl acrylate and V-65 were further reacted to complete the grafted polymer chain.

[0108] The copolymer containing the grafted polymer chains thus prepared was precipitated in methanol and washed to obtain a powder.

[0109] An example of the structure of the copolymer containing the grafted polymer chains thus prepared is shown in Chemical Formula 6 below. [ka] In Chemical Formula 6, m, n, l, and p are as defined in Chemical Formulas 1 and 4.

[0110] [Production Example 2] Production of electrode slurry Based on a total of 100 parts by weight of the slurry solids, 90 parts by weight of graphite as an electrode active material and 10 parts by weight of a binder containing the copolymer prepared in Preparation Example 1 were kneaded in a powder mixer.

[0111] After that, the mixture was re-pulverized and the formation of lumps was confirmed as shown in Figure 1. It was confirmed that the copolymer binder prepared by this method can be used for dry electrode manufacturing without using a solvent.

[0112] [Evaluation example 1] The stress-strain of the copolymer binder prepared in Preparation Example 1 and a styrene-butadiene rubber (SBR) binder (weight ratio of styrene to butadiene (weight of styrene:weight of butadiene=8:2)) was measured.

[0113] The copolymer binder prepared in Preparation Example 1 was dissolved in CHCl3 solvent and poured onto a plate, and the solvent was slowly evaporated to prepare a film.

[0114] The styrene-butadiene rubber (SBR) binder was prepared as a film by pouring the binder in a dispersed form onto a plate and evaporating the water.

[0115] The copolymer binder film and the styrene-butadiene rubber binder film prepared in Preparation Example 1 were cut to the same size, and the stress-strain characteristics were measured using UTM. The results are shown in FIG.

[0116] The copolymer binder prepared in Preparation Example 1 exhibited superior flexibility and strength compared to styrene-butadiene rubber binders, and appeared to be able to effectively protect the active material during kneading for electrode fabrication.

[0117] This is believed to be due to the high strength of the main chain of the copolymer binder prepared in Preparation Example 1 and the flexible grafted polymer chains.

[0118] As a result, it was confirmed that the copolymer containing the grafted polymer chains of the present invention can be used as a binder to manufacture electrodes (especially anodes) in a dry process without using a solvent, and has excellent mechanical properties (flexibility and rigidity).

[0119] Furthermore, it is clear that the copolymer containing the grafted polymer chains of the present invention has properties suitable for use in future all-solid-state batteries.

[0120] The scope of the present invention is represented by the claims set forth below rather than the above detailed description, and all modifications and variations derived from the meaning and scope of the claims and their equivalent concepts should be interpreted as being included in the scope of this application.

Claims

1. a styrene-based first monomer unit; a second monomer unit containing a hydroxy group and having 4 to 7 carbon atoms; a third monomer unit containing a double bond and having 4 to 7 carbon atoms; and a backbone comprising A copolymer comprising a polymer chain to which the second monomer unit of the main chain is grafted.

2. The first monomer unit is formed by polymerizing a styrene monomer, The second monomer unit and the third monomer unit are connected via a conjugated double bond.

2. The copolymer according to claim 1, which is formed by polymerizing a monomer having a double bond.

3. The copolymer according to claim 2, wherein the monomer having a conjugated double bond is butadiene, isoprene, or a combination thereof.

4. The copolymer according to claim 1 , comprising a monomer repeating unit represented by the following Chemical Formula 1: 【Chemistry 1】 A in Formula 1 represents the first styrene-based monomer unit of the main chain; B represents a second monomer unit having 4 or more carbon atoms and containing the hydroxy group in the main chain; C represents a third monomer unit having 4 to 7 carbon atoms including the double bond in the main chain, G represents the grafted polymer chain; m, n, and l represent the molar ratio of the first monomer unit, the second monomer unit, and the third monomer unit, respectively.

5. A in Formula 1 includes a first monomer repeating unit represented by Formula 2 below: B in Formula 1 includes a second monomer repeating unit represented by Formula 3-1 below: The copolymer according to claim 4, wherein C in Formula 1 comprises a third monomer repeating unit represented by Formula 3-2: 【Chemistry 2】 In Formula 2, m represents the molar ratio of the repeating unit of the monomer of Formula 2. 【Transformation 3】 【Chemistry 4】 In the chemical formula 3-1 and the chemical formula 3-2, R １ represents hydrogen or a linear or branched hydrocarbon having 1 to 4 carbon atoms; n and l represent the molar ratio of the repeating units of the monomers of Formula 3-1 and Formula 3-2, respectively; G represents the grafted polymer chain of Formula 1.

6. The copolymer according to claim 1 , wherein the grafted polymer chain is represented by the following chemical formula 4: 【Transformation 5】 * in Chemical Formula 4 represents a linking part to the main chain, H represents a hydrogen atom; D represents an acrylate monomer unit, p represents the number of the acrylate monomer units.

7. The acrylate monomer units include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, isopropyl acrylate, isopropyl methacrylate, butyl acrylate, butyl methacrylate, and sec-butyl acrylate. acrylate), sec-butyl methacrylate, tert-butyl acrylate, tert-butyl methacrylate, ethylhexyl acrylate, ethylhexyl methacrylate 7. The copolymer according to claim 6, which is formed by polymerizing ethyl hexyl methacrylate, lauryl acrylate, lauryl methacrylate, stearyl acrylate, stearyl methacrylate, or a combination thereof.

8. The copolymer according to claim 6 , wherein D in Formula 4 comprises a monomer repeating unit represented by Formula 5: 【Transformation 6】 In Formula 5, p represents the number of repeating units of the monomer of Formula 5, and R ２ represents a linear or branched hydrocarbon having 1 to 20 carbon atoms.

9. 2. The copolymer according to claim 1, wherein a weight ratio of the first monomer unit to the second monomer unit and the third monomer unit in the main chain (weight of the first monomer unit:weight of the second monomer unit and the third monomer unit) is 6 to 9.5:0.5 to 4.

10. The copolymer according to claim 1 , wherein the main chain of the copolymer is a random or block copolymer.

11. 2. The copolymer according to claim 1, wherein the weight average molecular weight of the copolymer is 10,000 g / mol or more and 1,000,000 g / mol or less.

12. The copolymer according to any one of claims 1 to 11, a negative electrode active material; a negative electrode slurry comprising:

13. A current collector; a negative electrode active material layer formed on the current collector, the negative electrode active material layer comprising the copolymer according to any one of claims 1 to 11; a negative electrode comprising:

14. A secondary battery comprising the negative electrode of claim 13.

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