Binder comprising polyamide polymer, cathode for secondary battery comprising binder, and secondary battery comprising cathode

Abstract

The present invention relates to a polyamide polymer, a binder for a cathode comprising same, a cathode slurry, a cathode, and a secondary battery, wherein the polyamide polymer comprises a diamine monomer unit including a sulfone, a diamine monomer unit including carboxylic acid, and a monomer unit including at least one aromatic ring.

Description

A binder comprising a polyamide polymer, a positive electrode for a secondary battery comprising the binder, and a secondary battery comprising the positive electrode

[0001] The present invention relates to a binder for a positive electrode comprising a polyamide polymer, a slurry comprising the same, an electrode, and a secondary battery.

[0002] Lithium secondary batteries have high energy density and are widely used in the electrical, electronic, communications, and computer industries. Their application areas are expanding from small lithium secondary batteries for portable electronic devices to high-capacity secondary batteries for hybrid and electric vehicles.

[0003] In order to provide a lithium secondary battery with high energy density and excellent life characteristics, it is desirable to increase the content of electrode active material and conductive material in the electrode and reduce the content of binder.

[0004] However, as the binder content decreases, the dispersibility and binding strength of the electrode active material and / or conductive material, as well as the flexibility of the electrode active material layer, decrease. Consequently, the electrode active material may detach from the current collector during charge / discharge, resulting in deterioration of cycle performance.

[0005] Therefore, a binder capable of ensuring dispersion of electrode active materials and / or conductive materials, plate adhesion, and plate flexibility within the electrode with a small content is required.

[0006] For example, a fluorine-based binder such as polyvinylidene fluoride (PVDF) without polar groups has less swelling in organic electrolytes, facilitates maintaining the electrode structure during battery operation, and can improve the dispersibility of active materials.

[0007] However, PVDF lacks conductive dispersibility, plate adhesion, and plate flexibility. In particular, long-term exposure to alkaline conditions can lead to the generation of HF gas, which degrades PVDF's stability.

[0008] In addition, non-fluorinated binders such as hydrogenated acrylonitrile-butadiene binders have improved conductive material dispersibility and plate flexibility compared to fluorinated binders, but still have insufficient bonding strength.

[0009] Therefore, a binder is required that can overcome the limitations of these conventional technologies, simultaneously secure improved bonding strength and flexibility, and have excellent stability, thereby improving the lifespan characteristics of lithium secondary batteries.

[0010] [Prior Art Literature]

[0011] [Patent Document]

[0012] (Patent Document 1) Republic of Korea Patent Publication No. 10-2016-0040125

[0013] Accordingly, the purpose of the present invention is to provide a polyamide polymer for a positive electrode binder that can improve the electrochemical characteristics and cycle characteristics of a secondary battery by preventing desorption of the electrode caused by lithium ion movement with improved binding characteristics.

[0014] In addition, the purpose is to provide a cathode binder that improves the stability and lifespan of secondary batteries by not generating harmful gases even when exposed to base for a long period of time.

[0015] The present invention aims to provide a slurry composition that improves the characteristics of a secondary battery by using the polyamide polymer for the positive electrode binder.

[0016] In addition, the present invention aims to provide an electrode (particularly, a positive electrode) having excellent performance to which the slurry composition is applied, and a low-cost and high-performance secondary battery including the same.

[0017] However, the problems that the present invention seeks to solve are not limited to the problems mentioned above, and other problems not mentioned will be clearly understood by those skilled in the art from the description below.

[0018] One aspect of the present invention provides a polyamide polymer comprising a diamine monomer unit comprising a sulfone, a diamine monomer unit comprising a carboxylic acid, and a monomer unit comprising at least one aromatic ring.

[0019] Another aspect of the present invention is a polyamide polymer comprising:

[0020] Provides a binder for positive electrode.

[0021] Another aspect of the present invention is the binder for the positive electrode; and

[0022] Containing a positive electrode active material;

[0023] Provides a cathode slurry.

[0024] Another aspect of the main body is the whole house; and

[0025] A positive electrode active material layer including the positive electrode binder formed on the above-mentioned collector;

[0026] Provides bipolarity.

[0027] Another aspect of our company is,

[0028] including the above positive electrode,

[0029] Provides secondary batteries.

[0030] The positive electrode binder of the present invention exhibits excellent binding properties, thereby improving the electrochemical properties of a secondary battery.

[0031] In addition, the binder for the positive electrode of the present invention does not generate harmful gases (e.g., hydrogen fluoride) even when exposed to a base for a long period of time, thereby improving the stability and lifespan of the secondary battery.

[0032] In addition, the improved binding force of the positive electrode binder of the present invention can reduce the amount of binder used while increasing the amount of active material and conductive agent, thereby providing a lithium secondary battery with high energy density at low cost.

[0033] Figure 1a shows the results of alkali resistance measurement according to Evaluation Example 1 of the polymer for binder of Example 1, and Figure 1b shows the results of alkali resistance measurement according to Evaluation Example 1 of the polymer for binder of Comparative Example 4.

[0034] Hereinafter, the functions and effects of the invention will be described in more detail through specific examples. However, these examples are provided merely as examples of the invention and do not define the scope of the invention.

[0035] Prior to this, the terms or words used in this specification and claims should not be interpreted as limited to their usual or dictionary meanings, and should be interpreted as meanings and concepts that conform to the technical idea of ​​the present invention based on the principle that the inventor can appropriately define the concept of the term to explain his or her own invention in the best way.

[0036] Accordingly, the configuration of the embodiments described in this specification is only one of the most preferred embodiments of the present invention and does not represent all of the technical ideas of the present invention, so it should be understood that various equivalents and modified examples that can replace them may exist at the time of filing this application.

[0037] In this specification, singular expressions include plural expressions unless the context clearly dictates otherwise. In this specification, terms such as "comprise," "include," or "have" should be understood to indicate the presence of a feature, number, step, component, or combination thereof, but not to preclude the possibility of the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0038] In this specification, “a to b” and “a~b” indicating a numerical range are defined as “a to” and “~” as ≥ a and ≤ b.

[0039]

[0040] A polyamide polymer according to one aspect of the present invention may include a diamine monomer unit containing sulfone, a diamine monomer unit containing carboxylic acid, and a monomer unit containing at least one aromatic ring.

[0041] The above polyamide polymer may not contain an aliphatic ring or an aliphatic chain structure in the main chain (it may contain an aliphatic ring or an aliphatic chain structure as a terminal group other than the main chain).

[0042] When a polyamide polymer contains an aliphatic ring or aliphatic chain structure within the main chain, problems such as an electrode expansion suppression effect and precipitation due to reduced solubility occur compared to a polyamide polymer containing a monomer unit containing at least an aromatic ring, and the electrical resistance of the battery may increase, making it difficult to use as a binder.

[0043] The electrode binder containing the above polyamide polymer may exhibit superior electrolyte stability by reducing swelling caused by the electrolyte compared to the electrode binder containing the conventional PVDF polymer. Accordingly, the volume expansion of the cell may also be reduced, thereby improving the stability and lifespan of the battery.

[0044] The above polyamide polymer does not contain fluorine atoms and may not generate hydrogen fluoride during the charging and discharging process of a battery in which the binder is used.

[0045] In comparison, the currently commercialized PVDF binder contains fluorine atoms and has the problem of generating hydrogen fluoride during the charging and discharging process of the battery.

[0046] Meanwhile, the monomer unit containing the sulfone may also contain an aromatic ring. The sulfone and / or aromatic ring of the monomer unit containing the sulfone may be used to form a portion of the main chain of the polyamide polymer. That is, the polyamide polymer may contain a sulfone within the main chain.

[0047] The monomer unit containing the above sulfone can contribute to improving the binding properties of the polyamide polymer. In addition, it can significantly contribute to improving the characteristics of the battery. This is because the improved binding properties of the polyamide polymer prevent detachment of the electrode during charging and discharging of the battery, thereby maintaining the lifespan of the battery, and at the same time, the sulfone group of the polyamide polymer can form a passivation layer (stable protective layer) on the positive electrode surface of the battery, thereby improving the charge and discharge characteristics of the battery.

[0048] In addition, the monomer unit containing the above sulfone can also contribute to improving the initial efficiency of the battery.

[0049] The diamine monomer unit including the above carboxylic acid may include one or more carboxylic acids, and the carboxylic acid may be a substituent of an aromatic ring.

[0050] The diamine monomer unit containing the above carboxylic acid, when used in an appropriate amount, can improve the performance of the battery while enhancing the binding strength of the polyamide polymer.

[0051] The at least one aromatic ring may be used to form a portion of the backbone of the polyamide polymer. That is, the polyamide polymer may include an aromatic ring within the backbone.

[0052] The monomer unit comprising at least one aromatic ring must be capable of polymerizing with a diamine monomer to produce a polyamide polymer, and may include a substituent for this purpose.

[0053] In one embodiment, the monomer forming the monomer unit including the sulfone through polymerization is bis(4-aminophenyl)sulfone, bis(3-aminophenyl)sulfone, 3,3'-diaminodiphenylsulfone, 3,4'-diaminodiphenylsulfone, 4,4'-diaminodiphenylsulfone, 1,3-bis(3-aminophenyl)sulfone, 1,3-bis(4-aminophenyl)sulfone, 1,3-bis(4-aminophenyl)sulfone, 1,4-bis(4-aminophenyl)sulfone, It may be bis〔3-(3-aminophenoxy)phenyl〕sulfone), bis〔3-(4-aminophenoxy)phenyl〕sulfone), bis〔4-(3-aminophenoxy)phenyl〕sulfone), bis〔4-(4-aminophenoxy)phenyl〕sulfone, or a combination thereof.

[0054] In particular, when bis(4-aminophenyl)sulfone is used, the binding properties of the polyamide polymer can be significantly improved. In addition, a positive electrode using bis(4-aminophenyl)sulfone can significantly contribute to improving the characteristics of a battery (e.g., initial efficiency characteristics of the battery).

[0055] In one embodiment, the monomer that forms the diamine monomer unit including the carboxylic acid through polymerization may be 3,5-diaminobenzoic acid (DABA).

[0056] The carboxylic acid of the above 3,5-diaminobenzoic acid can contribute to improving the bonding strength with the aluminum current collector.

[0057] In one embodiment, the monomer that forms the monomer unit including at least one aromatic ring through polymerization may be a terephthaloyl chloride monomer, an isophthaloyl chloride monomer, a phthalic acid monomer, an isophthalic acid monomer, a terephthalic acid monomer, or a combination thereof.

[0058] In one embodiment, the molar ratio of the terephthaloyl chloride and the isophthaloyl chloride used in the polymerization of the polyamide polymer (mol% of the terephthaloyl chloride: mol% of the isophthaloyl chloride) may be 1:9 to 9:1.

[0059] For example, the molar ratio of the terephthaloyl chloride and isophthaloyl chloride may be 8:2 to 2:8 or 3:7 to 7:3.

[0060] That is, terephthaloyl chloride and isophthaloyl chloride can be used together for polymerization of the polyamide polymer of the present invention.

[0061] In one embodiment, the molar ratio of the diamine monomer containing the sulfone and the diamine monomer containing the carboxylic acid used in the polymerization of the polyamide polymer (mol% of the diamine monomer containing the sulfone: mol% of the diamine monomer unit containing the carboxylic acid) may be 9.9:0.1 to 6:4.

[0062] For example, the molar ratio of the diamine monomer containing the sulfone and the diamine monomer containing the carboxylic acid may be 9.5:0.5 to 6:4, 9.5:0.5 to 7:3, 9.5:0.5 to 8:2, 9.0:1.0 to 6:4, 9.0:1.0 to 7:3, or 9.0:1.0 to 8:2.

[0063] If the content of the diamine monomer containing the carboxylic acid exceeds the content of the present invention, the diamine monomer containing the carboxylic acid has a lower molecular weight than the diamine monomer containing the sulfone, so that a decrease in binding force due to a limit on the increase in molecular weight occurs, and the performance of the battery may deteriorate.

[0064] Meanwhile, if the content of the diamine monomer including the carboxylic acid is lower than the content of the present invention, a decrease in binding force may occur and the performance of the battery may deteriorate.

[0065] In one embodiment, the polyamide polymer may include a monomer repeating unit represented by the following chemical formula 1.

[0066]

[0067] [Chemical Formula 1]

[0068]

[0069]

[0070] In the above chemical formula 1,

[0071] X1 comprises at least one aromatic ring substituted with a halogen element, hydrogen, a hydroxyl group, a carboxyl group, a linear or branched hydrocarbon group having 1 to 4 carbon atoms, or a combination thereof,

[0072] X2 is two aromatic rings substituted with a halogen atom, hydrogen, a hydroxyl group, a carboxyl group, a linear or branched hydrocarbon group having 1 to 4 carbon atoms substituted or unsubstituted with a halogen atom, or a combination thereof, which are connected to each other by -SO2-; and

[0073] An aromatic ring having at least one carboxyl group substituted therein;

[0074] n+m=1.

[0075] In the above chemical formula 1, n and m represent mole fractions.

[0076] The halogen element of the above chemical formula 1 may not contain fluorine.

[0077]

[0078] The monomer unit corresponding to X1 in the above chemical formula 1 corresponds to a monomer unit containing at least one aromatic ring.

[0079] For example, the monomer that forms the monomer unit corresponding to X1 of the above chemical formula 1 through polymerization may be a terephthaloyl chloride monomer, an isophthaloyl chloride monomer, a phthalic acid monomer, an isophthalic acid monomer, a terephthalic acid monomer, or a combination thereof.

[0080] In addition, the monomer that forms the monomer unit corresponding to X2 of the above chemical formula 1 through polymerization may be a combination of a diamine monomer that includes sulfone and at least one aromatic ring, and a diamine monomer that includes carboxylic acid.

[0081] For example, a diamine monomer including a sulfone that forms a monomer unit corresponding to X2 of the above chemical formula 1 through polymerization and at least one aromatic ring is bis(4-aminophenyl)sulfone, bis(3-aminophenyl)sulfone, 3,3'-diaminodiphenylsulfone, 3,4'-diaminodiphenylsulfone, 4,4'-diaminodiphenylsulfone, 1,3-bis(3-aminophenylsulfone)benzene, 1,3-bis(4-aminophenylsulfone)benzene, 1,4-bis(4-aminophenyl)sulfone), bis〔3-(3-aminophenoxy)phenyl〕sulfone), bis〔3-(4-aminophenoxy)phenyl〕sulfone), bis〔4-(3-aminophenoxy)phenyl〕sulfone), bis〔4-(4-aminophenoxy)phenyl〕sulfone, or a combination thereof.

[0082] Additionally, the diamine monomer containing a carboxylic acid that forms a monomer unit corresponding to X2 of the above chemical formula 1 through polymerization may be 3,5-diaminobenzoic acid.

[0083] In one embodiment, the weight average molecular weight of the polyamide polymer may be 100,000 or more and 1,000,000 or less.

[0084] Within the range of the weight average molecular weight of the polyamide polymer of the present invention, the higher the weight average molecular weight, the higher the binding force of the polyamide polymer.

[0085] When the weight average molecular weight of the polyamide polymer is less than 100,000, the electrolyte stability of the electrode binder including the polyamide polymer may be reduced. In addition, the stability of the electrode slurry including the binder including the polyamide polymer may be reduced.

[0086] Meanwhile, if the weight average molecular weight of the polyamide polymer exceeds 1,000,000, the viscosity may increase during slurry production, making slurry coating difficult.

[0087] According to another aspect of the present invention, a binder for a cathode may comprise the polyamide polymer.

[0088] According to another aspect of the present invention, the binder solution may include a cathode slurry and a cathode active material for the cathode.

[0089]

[0090] According to another aspect of the present invention, a cathode slurry may include the binder and the cathode active material.

[0091] The positive electrode active material for forming the electrode used in the present invention may be any positive electrode active material available in the relevant technical field. Specific examples of such positive electrode active materials include lithium metal; lithium cobalt oxide such as LiCoO2; Li 1+x Mn 2-x Lithium manganese oxides such as O4 (where x is 0 to 0.33), LiMnO3, LiMn2O3, LiMnO2; lithium copper oxides such as Li2CuO2; vanadium oxides such as LiV3O8, V2O5, Cu2V2O7; LiNi 1-x M xLithium nickel oxide represented by O2 (wherein, M=Co, Mn, Al, Cu, Fe, Mg, B or Ga and x=0.01 to 0.3); LiMn 2-x M x Lithium manganese composite oxide represented by O2 (wherein, M=Co, Ni, Fe, Cr, Zn or Ta and x=0.01 to 0.1) or Li2Mn3MO8 (wherein, M=Fe, Co, Ni, Cu or Zn); Li(Ni a Co b Mn c )O2 (wherein, 0<a<1, 0<b<1, 0<c<1, a+b+c=1); lithium-nickel-manganese-cobalt oxides; sulfur or disulfide compounds; phosphates such as LiFePO4, LiMnPO4, LiCoPO4, and LiNiPO4; Fe2(MoO4)3, but are not limited to these.

[0092] At this time, the positive electrode active material layer may additionally include a dispersant, a conductive agent, a filler, and other additives in addition to the positive electrode active material.

[0093] The above-mentioned positive electrode active material may be included in an amount of 90 to 99 wt% based on the solid content. If the content of the active material is low, the battery cannot produce high capacity, and if the content of the active material is excessively high, the content of binder, conductive agent, etc. will be relatively low, which may reduce electrode adhesion, conductivity, etc.

[0094] The above-mentioned conductive material is not particularly limited and may be appropriately selected depending on the type of battery or capacitor. For example, in the case of lithium-ion secondary batteries, carbon such as graphite or activated carbon may be used, and in the case of nickel-hydrogen secondary batteries, cobalt oxide may be used as the cathode, and nickel powder, cobalt oxide, titanium oxide, carbon, etc. may be used for the anode.

[0095] Examples of the above carbon include acetylene black, furnace black, graphite, carbon fiber, flavonoids, and carbon nanotubes.

[0096] The amount of the above conductive material to be used is usually 1 to 20 parts by weight, preferably 2 to 10 parts by weight, based on 100 parts by weight of the electrode active material.

[0097] Since the energy density of a secondary battery can be improved by reducing the content of the conductive material and increasing the content of the positive electrode active material, it is important to achieve high efficiency even when using the same amount of conductive material.

[0098] The smaller and more uniformly dispersed the conductive material used in secondary battery electrode slurries, the higher the conductivity, resulting in lower internal resistance, improved output characteristics, and improved cycle life. However, if the conductive material is larger and unevenly dispersed, even with the same amount, binding properties and conductivity deteriorate, adversely affecting the cycle life and output characteristics of the battery. Furthermore, lower viscosity of the dispersion can increase the solids content of the slurry, thereby improving electrode production speed.

[0099] As a binder for a secondary battery cathode, in addition to the cathode binder including a polyamide polymer including a monomer unit including an aromatic ring of the present invention, one or more of poly(meth)acrylic acid, poly(meth)acrylamide, carboxymethylcellulose, polyvinylidene fluoride, a copolymer of polyhexafluoropropylene-polyvinylidene fluoride (P(VdF / HFP)), poly(vinylacetate), polyvinyl alcohol, polyethylene oxide, polyvinylpyrrolidone, alkylated polyethylene oxide, polyvinyl ether, poly(methyl methacrylate), poly(ethyl acrylate), polytetrafluoroethylene, polyvinyl chloride, polyacrylonitrile, polyvinylpyridine, styrene-butadiene rubber, acrylonitrile-butadiene rubber, and copolymers thereof may be selected and used together.

[0100] The content of the above binder in the positive electrode slurry composition is preferably 0.3 wt% or more and 10 wt% or less, and more preferably 0.7 wt% or more and 8 wt% or less, based on solid content. If the content is less than 0.3 wt%, it is difficult to expect sufficient binding force in the current collector and electrode composition, and if the content exceeds 10 wt%, the binder ratio in the electrode slurry composition increases, which may reduce the battery capacity.

[0101] According to another aspect of the present invention, a positive electrode may include a current collector; and a positive electrode active material layer including a binder for the positive electrode of the present invention formed on the current collector.

[0102] The above positive electrode can be manufactured through the steps of (a) preparing a composition for forming a positive electrode active material layer including a positive electrode active material and a binder of the present invention, and (b) applying the composition for forming a positive electrode active material layer on a positive electrode current collector and then drying it.

[0103] The composition for forming the above positive electrode active material layer can be mixed by a conventional method using a conventional mixer, such as a high-speed shear mixer or a homomixer.

[0104] The above step (b) is a step of manufacturing a positive electrode for a lithium secondary battery by applying a composition for forming a positive electrode active material layer manufactured in the above step (a) on a positive electrode current collector and then drying it.

[0105] At this time, there is no limitation on the method of applying the composition for forming the positive electrode active material layer in the form of the slurry, and for example, it can be manufactured by performing a method such as doctor blade coating, dip coating, gravure coating, slit die coating, spin coating, comma coating, bar coating, reverse roll coating, screen coating, or cap coating.

[0106] After application, drying is performed to finally form a positive electrode active material layer, thereby manufacturing a positive electrode for a secondary battery (particularly, a lithium secondary battery).

[0107] Any current collector that is conductive and does not chemically react with the electrode-forming slurry may be used. Representative examples include aluminum foil and copper foil. A current collector with a thickness of 3 to 50 micrometers may be selected for use.

[0108] A secondary battery according to another aspect of the present invention may include the positive electrode.

[0109] Meanwhile, a secondary battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte including the positive electrode binder of the present invention can be manufactured.

[0110] The separator must be an insulator that separates the anode and cathode, while also providing a path for lithium ions to flow. To achieve this, it must have good electrolyte wettability, and materials such as porous polymer films (such as PE / PP) or porous nonwoven fabrics can be used. To prevent battery short-circuits, a coated separator with enhanced heat resistance and mechanical strength, such as ceramic, can be used. It can be single- or multi-layered.

[0111] The above separator may be formed of a porous substrate. Any porous substrate commonly used in electrochemical devices may be used as the porous substrate. For example, a polyolefin porous membrane or non-woven fabric may be used, but is not particularly limited thereto.

[0112] The above separation membrane may be a porous substrate made of one selected from the group consisting of polyethylene, polypropylene, polybutylene, polypentene, polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene oxide, polyphenylene sulfide, and polyethylene naphthalate, or a mixture of two or more thereof.

[0113] The electrolyte of the above lithium secondary battery is a non-aqueous electrolyte containing a lithium salt, and is composed of a lithium salt and a solvent. Non-aqueous organic solvents, organic solid electrolytes, and inorganic solid electrolytes are used as the solvent.

[0114] The above lithium salt is a substance that is easy to dissolve in the non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO4, LiBF4, LiB 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, lithium lower aliphatic carboxylic acid, lithium 4-phenylborate imide, etc. can be used.

[0115] Non-aqueous organic solvents include, for example, N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, gamma-butyrolactone, 1,2-dimethoxy ethane, 1,2-diethoxy ethane, tetrahydroxy franc, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, 4-methyl-1,3-dioxene, diethyl ether, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxy methane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, Non-protic organic solvents such as tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate can be used.

[0116] As the organic solid electrolyte, for example, polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate ester polymers, polyagitation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, polymers containing secondary dissociation groups, etc. can be used.

[0117] As the above inorganic solid electrolyte, for example, nitrides, halides, sulfates, etc. 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.

[0118] In addition, the non-aqueous electrolyte may further include other additives for the purpose of improving charge / discharge characteristics, flame retardancy, etc. Examples of the additives include pyridine, triethylphosphite, triethanolamine, cyclic ethers, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine 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), vinylene carbonate (VC), etc.

[0119] The lithium secondary battery according to the present invention can be formed by laminating and stacking a separator and electrodes and folding processes in addition to the conventional winding process. The battery case may be cylindrical, square, pouch-shaped, or coin-shaped.

[0120]

[0121] Hereinafter, the present invention will be described in more detail using examples, but the present invention is not limited thereto.

[0122]

[0123] Manufacturing Example 1. Manufacturing of a polymer for binder

[0124] [Example 1]

[0125] In a 500 ml four-necked flask under a nitrogen atmosphere, N-methyl-2-pyrrolidone (NMP), a monomer forming a monomer unit containing sulfone, bis(4-aminophenyl)sulfone (p-APS), and 3,5-diaminobenzoic acid (DABA), a diamine monomer containing carboxylic acid, were added and stirred.

[0126] The molar ratio of the above bis(4-aminophenyl)sulfone and the above 3,5-diaminobenzoic acid was 9:1.

[0127] Afterwards, the temperature inside the reactor was lowered to 5℃ or less, and isophthaloyl chloride (IPC), a monomer unit containing an aromatic ring, was added and reacted.

[0128] Here, terephthaloyl chloride (TPC), a monomer that forms a monomer unit containing an aromatic aromatic ring, was added and stirred for sufficient time.

[0129] The molar ratio of the above isophthaloyl chloride and the above terephthaloyl chloride was 3:7.

[0130] An olefin neutralizing agent was added to the solution with a certain viscosity increase and stirred to remove HCl generated during the synthesis process.

[0131] Finally, a polyamide copolymer solution for binder with a solid concentration of 15 wt% was prepared.

[0132]

[0133] [Example 2]

[0134] A polyamide copolymer solution for a binder was prepared in the same manner as in Example 1, except that the molar ratio of the bis(4-aminophenyl)sulfone and the 3,5-diaminobenzoic acid was changed to 8:2.

[0135]

[0136] [Comparative Example 1]

[0137] A polyamide copolymer solution for a binder was prepared in the same manner as in Example 1, except that the molar ratio of the bis(4-aminophenyl)sulfone and the 3,5-diaminobenzoic acid was changed to 5:5.

[0138]

[0139] [Comparative Example 2]

[0140] A polyamide copolymer solution for a binder was prepared in the same manner as in Example 1, except that the molar ratio of the bis(4-aminophenyl)sulfone and the 3,5-diaminobenzoic acid was changed to 2:8.

[0141]

[0142] [Comparative Example 3]

[0143] A polyamide copolymer solution for a binder was prepared in the same manner as in Example 1, except that the molar ratio of the bis(4-aminophenyl)sulfone and the 3,5-diaminobenzoic acid was changed to 1:9.

[0144]

[0145] [Comparative Example 4]

[0146] A polyamide copolymer solution for a binder was prepared in the same manner as in Example 1, except that the molar ratio of 3,5-diaminobenzoic acid was not added (the molar ratio of bis(4-aminophenyl)sulfone and the 3,5-diaminobenzoic acid was 10:0).

[0147]

[0148] [Comparative Example 5]

[0149] PVDF polymer powder (weight average molecular weight: 1,000,000, melting point: 150-160 degrees, glass transition temperature: -40 degrees) from SOLVAY was purchased, dissolved in NMP, and used as a polymer solution for binder with a solid content of 6 wt%.

[0150]

[0151] The monomer compositions and molar ratios of p-APS and DABA of Examples 1 and 2 and Comparative Examples 1 to 4 are shown in Table 1 below.

[0152]

[0153] Monomer composition Molar ratio of p-APS and DABA (p-APS:DABA) Example 1 p-APS / DABA / TPC / IPC 9:1 Example 2 p-APS / DABA / TPC / IPC 8:2 Comparative Example 1 p-APS / DABA / TPC / IPC 5:5 Comparative Example 2 p-APS / DABA / TPC / IPC 2:8 Comparative Example 3 p-APS / DABA / TPC / IPC 1:9 Comparative Example 4 p-APS / TPC / IPC 10:0 Comparative Example 5 PVDF (SOLVAY)-

[0154]

[0155] Manufacturing Example 2. Manufacturing of anode slurry and anode

[0156] A slurry composition of a positive electrode active material having a solid content of 70 wt% was prepared by mixing 97.5 wt% of NCM811 as an electrode active material, 2 wt% of the polymer for binder of Examples 1 and 2 and Comparative Examples 1 to 5, 0.5 wt% of a CNT dispersion, and the remainder of NMP.

[0157] Meanwhile, the positive electrode active material slurry composition may include 96 wt% or more and 98 wt% or less of the electrode active material, 1 wt% or more and 3 wt% or less of the binder polymer, and 0.5 wt% or more and 1 wt% or less of the CNT dispersion. In addition, the solid content of the positive electrode active material slurry composition may be 60 wt% or more and 75 wt% or less.

[0158] The manufactured positive electrode slurry composition was coated on an aluminum (Al) foil, which is a positive electrode current collector with a thickness of 20 μm, using an applicator, and dried in a 130°C circulating oven for 1 hour. Then, the dried positive electrode was rolled using a roll press to manufacture a positive electrode.

[0159]

[0160] Manufacturing Example 3. Manufacturing of Cells

[0161] A non-aqueous electrolyte containing 1 wt% of 1M LiPF6 and FEC (Fluoro Ethylene carbonate), 1 wt% of PS (Propylene sulfite), and 1 wt% of LiPO2F2 was used as an electrolyte, and a polyolefin separator was interposed between the positive electrode and the negative electrode using the polymer for binder of Examples 1 and 2 and Comparative Examples 1 to 5 manufactured by Manufacturing Example 2, and a lithium secondary battery was manufactured without distinguishing the shape as a 2032 coin cell type.

[0162]

[0163] Evaluation Example 1. Measurement of alkalinity

[0164] An artificial basic atmosphere was created by adding 0.1 wt% of LiOH relative to the NMP solvent to the PVDF binder polymer of Comparative Example 5 diluted in NMP with the same solid content as the binder polymer of Example 1.

[0165] Afterwards, changes were observed while continuously stirring at room temperature for 5 days.

[0166] As shown in Fig. 1, no particular change was observed in the binder polymer of Example 1 in a basic atmosphere, but it was observed that the PVDF binder polymer of Comparative Example 5 gelled to a blackish brown color.

[0167] This is because LiOH and PVDF form a double bond when they meet, causing a phase change and gelation. PVDF generates HF gas through a dehydrofluorination reaction under basic conditions, and the generated HF gas is known to decompose the CEI layer of the positive electrode and the SEI layer of the negative electrode, thereby reducing the performance of the battery. In addition, the dehydrofluorination reaction is known to be accelerated in high-temperature environments, which aggravates the degradation of high-temperature battery performance.

[0168] That is, it was confirmed that PVDF has the potential to generate HF gas under basic conditions, which may cause battery performance degradation.

[0169] In comparison, it was confirmed that the polyamide polymer for binder of Example 1 had superior alkali resistance compared to the PVDF polymer for binder, and thus was able to maintain stability in the environment within the battery.

[0170] As with the polyamide polymer for binder of Example 1, no special change was observed in the basic atmosphere for the polyamide polymer for binder of Example 2.

[0171]

[0172] Evaluation Example 2. Bonding Strength Measurement

[0173] The positive electrode manufactured by Manufacturing Example 2 was dried at 130°C for 1 hour, and then cut into pieces measuring 15 x 2.5 cm.

[0174] Afterwards, the surface coated with the positive electrode was adhered to an acrylic plate with double-sided tape attached, and a peel-off test sample was prepared by pressing it 3-4 times with a rubber roller for pressing.

[0175] The prepared sample was loaded into a UTM capable of measuring adhesive strength, and a 2.5 cm 180° peel test was performed. The loading value (gf / 25 mm) was measured to calculate the bonding strength of the positive electrode.

[0176] The calculated bonding strength of the anode is shown in Table 2 below.

[0177]

[0178] Polymer anode bonding force for binder (gf / 25mm) Example 120.4 Example 219.2 Comparative Example 117.6 Comparative Example 215.2 Comparative Example 313.1 Comparative Example 418.9 Comparative Example 518.1

[0179]

[0180] As shown in Table 2 above, the binder polymers of Examples 1 and 2 exhibited a bonding strength of 19 gf / 25 mm or more. It was confirmed that the binder polymers of Examples 1 and 2 had improved bonding strength compared to the polyamide binder polymer of Comparative Example 4 or the PVDF binder polymer of Comparative Example 5, which did not use DABA as a monomer.

[0181] In addition, it was confirmed that the anode binding force decreased as the DABA content increased in the molar ratio of p-APS and DABA (mol% of p-APS: mol% of DABA).

[0182] That is, it was confirmed that the binder polymers of Comparative Examples 1 to 3, in which the molar ratio of p-APS and DABA (mol% of p-APS: mol% of DABA) was 5:5 to 1:9, had lower anode binding power than Comparative Example 4, a binder polymer not containing DABA, and Comparative Example 5, a PVDF binder polymer.

[0183]

[0184] Evaluation Example 3. Battery Performance Measurement

[0185] A cell manufactured according to Manufacturing Example 3 using a positive electrode plate using the polymer for binder of Examples 1 and 2 and Comparative Examples 1 to 5 was charged in CC / CV mode at a 0.1 C rate to 4.2 V, discharged at a 0.1 C rate to 2.8 V, then charged at a 0.2 C rate to 4.2 V, discharged at a 0.2 C rate to 2.8 V, then charged at a 0.5 C rate to 4.2 V, and discharged at a 0.5 C rate to 2.8 V (initial formation). At this time, the temperature of the chamber was 25°C. The "C" above represents the discharge rate of the cell, which means a value obtained by dividing the total capacity of the cell by the total discharge time.

[0186] The results of measuring the initial charge capacity, initial discharge capacity, and initial efficiency of the cell manufactured according to Manufacturing Example 3 using the positive electrode plate using the polymer for binder of Examples 1 and 2 and Comparative Examples 1 to 5 are shown in Table 3 below.

[0187] During the initial formation, the charge capacity when charging at a 0.1C rate up to 4.2 V and the discharge capacity when discharging at a 0.1C rate up to 2.8 V were measured as the initial charge capacity and the initial discharge capacity, respectively, and the initial efficiency was calculated using the following mathematical equation 1.

[0188]

[0189] <Mathematical Formula 1>

[0190] Initial efficiency [%] = [Initial discharge capacity / Initial charge capacity] × 100

[0191]

[0192] Initial charge capacity (mAh / g) Initial discharge capacity (mAh / g) Initial Efficiency (%) Example 1 223.05 195.4 287.61 Example 2 222.42 194.68 87.53 Comparative Example 1 221.74 193.01 87.04 Comparative Example 2 222.24 192.54 86.64 Comparative Example 3 219.35 189.08 86.20 Comparative Example 4 2221.78 194.02 87.48 Comparative Example 5 218.75 190.13 86.91

[0193]

[0194] As shown in Table 3 above, the cell manufactured according to Manufacturing Example 3 using the positive electrode plate using the polymer for binder of Examples 1 and 2 exhibited an initial charge capacity of 222 mAh / g or more, an initial discharge capacity of 194 mAh / g or more, and an initial efficiency of 87.5% or more.

[0195] It was confirmed that the cell manufactured according to Manufacturing Example 3 using the positive electrode plate using the polymer for binder of Examples 1 and 2 had improved initial charge capacity, initial discharge capacity, and initial efficiency compared to the cell manufactured according to Manufacturing Example 3 using the positive electrode plate using the polymer for polyamide binder of Comparative Example 4 or the polymer for PVDF binder of Comparative Example 5 that did not use DABA as a monomer.

[0196] In addition, it was confirmed that the initial charge capacity, initial discharge capacity, and initial efficiency decreased as the content of DABA increased in the molar ratio of p-APS and DABA (mol% of p-APS: mol% of DABA).

[0197] That is, it was confirmed that the cell manufactured according to Manufacturing Example 3 using the positive electrode plate using the polymer for binder of Comparative Examples 1 to 3 having a molar ratio of p-APS and DABA (mol% of p-APS: mol% of DABA) of 5:5 to 1:9 had lower initial charge capacity, initial discharge capacity, and initial efficiency compared to the cell manufactured according to Manufacturing Example 3 using the positive electrode plate using the polymer for binder of Examples 1 and 2.

[0198]

[0199] As a result, it was confirmed that the cathode binder of the present invention, which includes a polyamide polymer with an appropriately controlled molar ratio of p-APS and DABA, has excellent bonding properties.

[0200] In addition, it was confirmed that the characteristics of the secondary battery were improved when a positive electrode binder including the polyamide polymer of the present invention was applied.

[0201]

[0202] The scope of the present invention is indicated by the claims described below rather than the detailed description above, and all changes or modifications derived from the meaning and scope of the claims and their equivalent concepts should be interpreted as being included in the scope of the present invention.

[0203] The positive electrode binder of the present invention exhibits excellent binding properties, thereby improving the electrochemical properties of a secondary battery.

[0204] In addition, the binder for the positive electrode of the present invention does not generate harmful gases (e.g., hydrogen fluoride) even when exposed to a base for a long period of time, thereby improving the stability and lifespan of the secondary battery.

[0205] In addition, the improved binding force of the positive electrode binder of the present invention can reduce the amount of binder used while increasing the amount of active material and conductive agent, thereby providing a lithium secondary battery with high energy density at low cost.

Claims

1. A monomer unit comprising a diamine monomer unit containing sulfone, a diamine monomer unit containing carboxylic acid, and a monomer unit containing at least one aromatic ring. Polyamide polymer.

2. In paragraph 1, Monomers formed through polymerization of the monomer unit containing the above sulfone include bis(4-aminophenyl)sulfone, bis(3-aminophenyl)sulfone, 3,3'-diaminodiphenylsulfone, 3,4'-diaminodiphenylsulfone, 4,4'-diaminodiphenylsulfone, 1,3-bis(3-aminophenyl)sulfone, 1,3-bis(4-aminophenyl)sulfone, 1,3-bis(4-aminophenyl)sulfone, 1,4-bis(4-aminophenyl)sulfone, bis〔3-(3-aminophenoxy)phenyl〕sulfone), bis〔3-(4-aminophenoxy)phenyl〕sulfone), bis〔4-(3-aminophenoxy)phenyl〕sulfone), bis〔4-(4-aminophenoxy)phenyl〕sulfone, or a combination thereof, Polyamide polymer.

3. In paragraph 1, The monomer that forms the diamine monomer unit containing the above carboxylic acid through polymerization is 3,5-diaminobenzoic acid (DABA). Polyamide polymer.

4. In paragraph 1, The monomer forming the monomer unit including at least one aromatic ring through polymerization is a terephthaloyl chloride monomer, an isophthaloyl chloride monomer, a phthalic acid monomer, an isophthalic acid monomer, a terephthalic acid monomer or a combination thereof. Polyamide polymer.

5. In paragraph 1, The molar ratio of the diamine monomer containing the sulfone and the diamine monomer containing the carboxylic acid used in the polymerization of the polyamide polymer (mol% of the diamine monomer containing the sulfone: mol% of the diamine monomer unit containing the carboxylic acid) is 9.9:0.1 to 6:

4. Polyamide polymer.

6. In paragraph 1, The above polyamide polymer comprises a monomer repeating unit represented by the following chemical formula 1: [Chemical Formula 1] In the above chemical formula 1, X 1 contains at least one aromatic ring substituted with a halogen element, hydrogen, a hydroxyl group, a carboxyl group, a linear or branched hydrocarbon group having 1 to 4 carbon atoms, or a combination thereof, X 2 is -SO 2 - two aromatic rings substituted with a halogen element, hydrogen, a hydroxyl group, a carboxyl group, a linear or branched hydrocarbon group having 1 to 4 carbon atoms substituted or unsubstituted with a halogen element, or a combination thereof, linked to each other by; and An aromatic ring substituted with at least one carboxyl group; n+m=1.

7. Comprising a polyamide polymer according to any one of claims 1 to 6, Binder for positive electrode.

8. Binder for positive electrode of clause 7; and Containing a positive electrode active material; Bipolar slurry.

9. The entire house; and A cathode active material layer including a cathode binder of claim 7 formed on the entire body of the above-mentioned collector; anode.

10. Including the positive pole of Article 9, Secondary battery.

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