Binder comprising polyamide polymer, positive electrode for secondary battery comprising same, and secondary battery comprising same

Abstract

The present invention relates to a binder, a positive electrode paste containing the binder, a positive electrode, and a secondary battery, in which the binder contains a polyamide polymer having a glass transition temperature of from 100 DEG C to 250 DEG C (inclusive).

Description

Technical Field

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

[0002] Lithium secondary batteries are widely used in the fields of electric, electronic, communication, and computer industries due to their high energy density, and their application fields have expanded from small lithium secondary batteries for portable electronic devices to high-capacity secondary batteries such as hybrid electric vehicles and electric vehicles.

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

[0004] However, if the content of the binder is reduced, the dispersibility, adhesiveness of the electrode active material and / or conductive material, and the flexibility of the electrode active material layer are reduced. Therefore, during charge and discharge, since the electrode active material detaches from the current collector, the cycle characteristics may deteriorate.

[0005] Therefore, there is a need for a binder that can ensure the dispersibility, plate adhesiveness, and plate flexibility of the electrode active material and / or conductive material in the electrode with a smaller content.

[0006] For example, fluorine-based binders such as polyvinylidene fluoride (PVDF) that do not contain polar groups have less swelling in organic electrolytes, are easy to maintain the electrode structure during battery operation, and can improve the dispersibility of the active material.

[0007] However, PVDF lacks dispersibility of conductive materials, plate adhesiveness, and plate flexibility. In particular, when PVDF is exposed to an alkaline condition for a long time, HF gas is generated, which may cause a problem of reduced stability.

[0008] In addition, for example, non-fluorine-based binders such as hydrogenated acrylonitrile-butadiene binders, although they improve the dispersibility of conductive materials and plate flexibility, still have insufficient adhesiveness.

[0009] Therefore, there is an urgent need for a binder that can overcome the limitations of the prior art, can simultaneously ensure improved adhesiveness and flexibility, and has excellent stability, thereby improving the life characteristics of lithium secondary batteries.

[0010] [Prior Art Documents]

[0011] [Patent Documents]

[0012] (Patent Document 1) Korean Patent Publication No. 10-2016-0040125. Summary of the Invention

[0013] Technical problems to be solved by the invention

[0014] In view of this, the object of the present invention is to provide an adhesive for a positive electrode, which can prevent electrode detachment caused by lithium ion movement through improved adhesion characteristics, thereby improving the electrochemical characteristics and cycle characteristics of a secondary battery.

[0015] In addition, the object is to provide an adhesive for a positive electrode that does not generate harmful gases even when exposed to alkalinity for a long time, thereby improving the stability and lifespan of a secondary battery.

[0016] The present invention provides a slurry composition that uses the above-mentioned adhesive for a positive electrode to improve the characteristics of a secondary battery.

[0017] Furthermore, the present invention also aims to provide an electrode (in particular, a positive electrode) with excellent performance using the above-mentioned slurry composition, and a low-cost and high-performance secondary battery including the above-mentioned electrode.

[0018] However, the technical problems to be solved herein are not limited to the above-mentioned problems, and those skilled in the art can clearly understand other unmentioned problems from the following description.

[0019] Means for solving the technical problems

[0020] Provide an adhesive for a positive electrode, comprising: a polyamide polymer having a glass transition temperature of 100 °C or higher and 250 °C or lower.

[0021] On the other hand, the present invention provides a positive electrode slurry, comprising the above-mentioned adhesive for a positive electrode; and

[0022] a positive electrode active material.

[0023] On yet another aspect of the present invention, provide a positive electrode, comprising: a current collector; and

[0024] a positive electrode active material layer comprising the above-mentioned adhesive for a positive electrode formed on the current collector.

[0025] On yet another aspect of the present invention, provide a secondary battery, comprising:

[0026] the positive electrode.

[0027] Effects of the invention

[0028] The adhesive for a positive electrode of the present invention exhibits excellent adhesion characteristics, and can improve the electrochemical characteristics and cycle characteristics of a secondary battery.

[0029] 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 an alkaline environment for a long time, thereby improving the stability and lifespan of the secondary battery.

[0030] Furthermore, the improved adhesive force of the binder for the positive electrode of the present invention can enhance the amount of active material and conductive agent while reducing the usage amount of the binder, thus enabling the provision of a lithium secondary battery with high energy density at low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 A graph showing the cycle capacity retention rate of a battery cell manufactured according to Manufacturing Example 3 using a positive electrode plate with a polymer binder applied in Example 1 and Examples 3 to 5 and Comparative Examples 1 and 2. DETAILED DESCRIPTION OF THE INVENTION

[0032] Hereinafter, the functions and effects of the invention will be further described through specific examples of the invention. However, such examples are only presented as examples of the invention and do not limit the scope of protection of the invention.

[0033] Prior to this, the terms or words used in this specification and claims should not be construed as limited to their general meanings or dictionary meanings. Instead, based on the principle that the inventor can appropriately define the concepts of terms in order to best explain their invention, they should be construed as meanings and concepts that conform to the technical idea of the present invention.

[0034] Therefore, it should be understood that the structure of the embodiments described in this specification is only one of the preferred embodiments of the present invention and does not represent all the technical ideas of the present invention. Thus, in the context of this application, there can be various equivalents and variations that can be substituted.

[0035] Unless the context clearly indicates otherwise, the singular forms used herein include the plural forms. It should be understood that in this specification, terms such as "comprises," "includes," or "has" are intended to specify the presence of implemented features, numbers, steps, components, or combinations thereof, and do not exclude the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0036] In this specification, "to" and "~" in the numerical range "a to b" and "a ~ b" are defined as ≥a and ≤b.

[0037] The binder for the positive electrode according to the first aspect herein may include a polyamide polymer having a glass transition temperature of 100°C or higher and 250°C or lower.

[0038] The glass transition temperature may be, for example, above 150 °C, below 200 °C, above 150 °C, below 180 °C, above 150 °C. Additionally, the glass transition temperature may be below 170 °C.

[0039] When the glass transition temperature of the polyamide polymer is lower than the above range, the high temperature and thermal stability of the secondary battery may decrease.

[0040] Additionally, when the glass transition temperature of the polyamide polymer is higher than the above range, it will exhibit brittle characteristics, thereby reducing the adhesion characteristics and the adhesion force with the current collector (e.g., aluminum current collector).

[0041] In one implementation example, the polyamide polymer may include monomer units including at least one aromatic ring.

[0042] In particular, the aromatic ring may be used to form a part of the backbone of the polyamide polymer. That is, the polyamide polymer may include an aromatic ring within the backbone.

[0043] On the other hand, the polyamide polymer may not include an alicyclic ring or an aliphatic chain structure within the backbone (the end other than the backbone may include an alicyclic ring or an aliphatic chain structure).

[0044] When the polyamide polymer includes an alicyclic ring or an aliphatic chain structure within the backbone, compared with the polyamide polymer including monomer units including at least an aromatic ring, problems such as precipitation caused by the suppression of electrode swelling and the reduction of solubility may occur, and it is difficult to be used as an adhesive by increasing the battery resistance.

[0045] Compared with the electrode adhesive including the existing PVDF-based polymer, the above electrode adhesive including the polyamide polymer reduces the swelling caused by the electrolyte, so the electrolyte stability is excellent, wherein the polyamide polymer includes monomer units including at least one aromatic ring. Thus, the volume expansion of the battery monomer is also reduced, thereby improving the stability and lifespan of the battery.

[0046] In one implementation example, the adhesive does not contain fluorine atoms, and the battery using the adhesive may not generate hydrogen fluoride during the charge and discharge process.

[0047] In contrast, the commonly used PVDF-based adhesive currently contains fluorine atoms, and there is a problem of generating hydrogen fluoride during the charge and discharge process of the battery.

[0048] In one implementation example, the polyamide polymer may further include monomer units including sulfone.

[0049] The sulfone-containing monomer units may together include an aromatic ring. The sulfone and / or the aromatic ring of the sulfone-containing monomer units may be used to form a part of the main chain of the polyamide polymer. That is, the polyamide polymer may include a sulfone within the main chain.

[0050] The sulfone-containing monomer units may contribute to improving the adhesion characteristics of the polyamide polymer. Additionally, it may greatly contribute to improving the characteristics of the battery. This is because the improved adhesion characteristics of the polyamide polymer can prevent the detachment of the electrodes during charging and discharging of the battery, and can play a role in maintaining the battery life. At the same time, the sulfone group of the polyamide polymer forms a Passivation layer (stable protective layer) on the surface of the positive electrode of the battery, which can improve the charging and discharging characteristics of the battery.

[0051] In addition, the sulfone-containing monomer units also contribute to improving the initial efficiency of the battery.

[0052] In one implementation example, at least one aromatic ring of the polyamide polymer may be substituted with a halogen element, hydrogen, a hydroxyl group, a carboxyl group, a linear or branched hydrocarbon group having 1 to 4 carbon atoms with or without halogen substitution, or a combination thereof.

[0053] However, the halogen element does not include fluorine. For example, the halogen element may be Cl or Br.

[0054] On the other hand, at least one aromatic ring of the polyamide polymer may not include any substituents (i.e., may be only substituted with hydrogen).

[0055] In one implementation example, the monomers for polymerizing to form the monomer units including at least one aromatic ring may include one or more selected from the group consisting of diamine monomers including at least one aromatic ring, terephthaloyl chloride monomers, isophthaloyl chloride monomers, phthalic acid monomers, isophthalic acid monomers, terephthalic acid monomers, 4,4'-dibenzoic acid monomers, and 4,4'-dicarboxydiphenyl sulfone monomers.

[0056] In one implementation example, the diamine monomer containing at least one aromatic ring is one or more selected from the group consisting of p-phenylenediamine, m-phenylenediamine, 3,3'-dimethylbenzidine, 2,2'-dimethylbenzidine, tetrachlorobenzidine, 2,4-diaminotoludine, 2,6-diaminotoludine, 3,5-diaminobenzoic acid, Bis(4-aminophenyl)methane, 4,4'-oxydianiline, 3,4'-diaminodiphenyl ether, 2,2-bis(4-aminophenyl)propane, bis(4-aminophenyl)terephthalate, 4,4′-Diaminodipheniyl methane, 4,4′-Methylene-bis(2-methylaniline), 4,4′-diaminobenzophenone, Bis(4-aminophenyl)methane, and 4-(4-aminophenoxy)phenyl)ether).

[0057] In one implementation example, the monomer that forms a monomer unit containing the sulfone through polymerization is one or more selected from the group consisting of bis(4-aminophenyl)sulfone, bis(3-aminophenyl)sulfone, 3,3'-diaminophenylsulfone, 3,4'-diaminophenylsulfone, 4,4'-diaminophenylsulfone, 1,3-bis(3-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, and bis[4-(4-aminophenoxy)phenyl]sulfone.

[0058] In particular, when bis(4-aminophenyl)sulfone is used, the adhesion characteristics of the polyamide polymer can be greatly improved. In addition, it can help improve the characteristics of a battery using a positive electrode using bis(4-aminophenyl)sulfone (for example, battery initial efficiency characteristics, cycle capacity retention characteristics, etc.).

[0059] In one implementation example, the polyamide polymer contained in the present adhesive may include a monomer repeating unit represented by the following Chemical Formula 1.

[0060] [Chemical Formula 1]

[0061]

[0062] In the Chemical Formula 1,

[0063] X 1At least one aromatic ring substituted with hydrogen, a hydroxyl group, a carboxyl group, a linear or branched hydrocarbon group having 1 to 4 carbon atoms, or a combination thereof

[0064] X 2 Two or more aromatic rings substituted with hydrogen, a hydroxyl group, a carboxyl group, a linear or branched hydrocarbon group having 1 to 4 carbon atoms, or a combination thereof

[0065] It is possible that n + m = 1.

[0066] In the chemical formula 1, n and m represent mole fractions.

[0067] The halogen element in the chemical formula 1 may not include fluorine.

[0068] In one implementation example, X in the chemical formula 1 2 can be a single bond, -CH 2 -, -C(CH 3 ) 2 -, -C(=O)-, -S(=O)-, -O- or -SO 2 -connected hydrogen, hydroxyl group, carboxyl group, linear or branched hydrocarbon group having 1 to 4 carbon atoms, or a combination thereof-substituted two aromatic rings; or, hydrogen, hydroxyl group, carboxyl group, linear or branched hydrocarbon group having 1 to 4 carbon atoms, or a combination thereof-substituted naphthalene.

[0069] In one implementation example, the polyamide polymer may include a monomer repeating unit represented by the following chemical formula 2.

[0070] [Chemical formula 2]

[0071]

[0072] In the chemical formula 2,

[0073] X 3 is a single bond, -CH 2 -, -C(CH3) 2 -, -C(=O)-, -S(=O)-, -O- or -SO 2 -,

[0074] R 1 to R 3 are each independently hydrogen, a hydroxyl group, a carboxyl group, a linear or branched hydrocarbon group having 1 to 4 carbon atoms, or a combination thereof,

[0075] It is possible that a + b = 1.

[0076] In the chemical formula 2, a and b represent mole fractions.

[0077] The halogen element in the chemical formula 2 may not include fluorine.

[0078] For example, R in Chemical Formula 2 1 to R 3 hydrocarbons having 1 to 4 carbon atoms may be methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, or tert-butyl.

[0079] On the other hand, the simple bond in Chemical Formulas 1 and 2 may mean a bond in which an aromatic ring and an aromatic ring are directly connected without other atoms.

[0080] The (1) corresponding monomer unit of Chemical Formula 2 corresponds to a monomer unit containing at least one aromatic ring.

[0081] For example, the monomer for forming the (1) corresponding monomer unit of Chemical Formula 2 by polymerization may be any one or more selected from the group consisting of terephthaloyl chloride monomer, isophthaloyl chloride monomer, phthalic acid monomer, isophthalic acid monomer, terephthalic acid monomer, 4,4'-dibenzoic acid monomer, and 4,4'-dicarboxydiphenyl sulfone monomer.

[0082] In addition, the monomer for forming the (2) corresponding monomer unit of Chemical Formula 2 by polymerization may be a diamine monomer that does not contain a sulfone and contains at least one aromatic ring, a diamine monomer that contains a sulfone and contains at least one aromatic ring, or a combination thereof.

[0083] For example, the monomers that form the corresponding monomer units of formula (2) by polymerization are selected from p-phenylenediamine, m-phenylenediamine, 3,3'-dimethylbenzidine, 2,2'-dimethylbenzidine, 2,4-diaminotoludine, 2,6-diaminotoludine, 3,5-diaminobenzoic acid, Bis(4-aminophenyl)methane, 4,4'-oxydianiline, 3,4'-diaminodiphenyl ether, 2,2-bis(4-aminophenyl)propane, bis(4-aminophenyl)terephthalate, 4,4′-Diaminodiphenylmethane, 4,4′-Methylene-bis(2-methylaniline), 4,4′-Diaminobenzophenone, Bis(4-aminophenyl)methane, 4-(4-aminophenoxy)phenyl)ether, bis(4-aminophenyl)sulfone, bis(3-aminophenyl)sulfone, 3,3'-diaminophenylsulfone, 3,4'-diaminophenylsulfone, 4,4'-diaminophenylsulfone, 1,3-bis(3-aminophenyl)sulfone), 1,3-bis(4-aminophenyl)sulfone), 1,4-bis(4-aminophenyl)sulfone))Any one or more selected from the group consisting of 4-bis(4-aminophenyl)sulfone, bis〔3-(3-aminophenoxy)phenyl〕sulfone, bis〔3-(4-aminophenoxy)phenyl〕sulfone, bis〔4-(3-aminophenoxy)phenyl〕sulfone, and bis〔4-(4-aminophenoxy)phenyl〕sulfone.,

[0084] In one implementation example, the weight-average molecular weight of the polyamide polymer may be 100,000 or more and 1,000,000 or less.

[0085] Within the range of the weight-average molecular weight of the polyamide polymer herein, the higher the weight-average molecular weight, the higher the adhesion of the polyamide polymer.

[0086] When the weight-average molecular weight of the polyamide polymer is less than 100,000, the electrolyte stability of the electrode binder contained in the polyamide polymer may decrease. Moreover, the stability of the electrode paste containing the polyamide polymer as the binder may also decrease.

[0087] On the other hand, when the weight-average molecular weight of the polyamide polymer exceeds 1,000,000, it may be inconvenient for paste coating due to the increased viscosity during paste manufacturing.

[0088] In one implementation example, the molar ratio of terephthaloyl chloride to isophthaloyl chloride (mol% of terephthaloyl chloride: mol% of isophthaloyl chloride) used for polymerizing the polyamide polymer may be 2:8 to 8:2.

[0089] For example, the molar ratio of terephthaloyl chloride to isophthaloyl chloride may be 3:7 to 7:3.

[0090] That is, terephthaloyl chloride and isophthaloyl chloride can be used together for the polymerization of the polyamide polymer contained in the positive electrode binder herein.

[0091] According to another aspect herein, the positive electrode paste in the binder solution may contain the positive electrode binder and the positive electrode active material herein.

[0092] According to still another aspect herein, the positive electrode paste may contain the binder and the positive electrode active material.

[0093] All the positive electrode active materials used to form the electrodes in the present invention can be any positive electrode active materials that can be used in the art. Specific examples of such positive electrode active materials include lithium metal; lithium cobalt-based oxides such as LiCoO 2 ; lithium manganese-based oxides such as Li 1 + x Mn 2-x O 4 (where x is from 0 to 0.33), LiMnO 3 , LiMn 2 O 3 , LiMnO 2 ; lithium copper oxides such as Li 2 CuO 2 ; vanadium oxides such as LiV 3 O 8 , V 2 O 5 , Cu 2 V 2 O 7 ; lithium nickel-based oxides represented as LiNi 1-x M x O 2 (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, and x = 0.01 to 0.3); lithium manganese composite oxides represented as LiMn 2-x M x O 2 (where M = Co, Ni, Fe, Cr, Zn or Ta, and x = 0.01 to 0.1) or represented as Li 2 Mn 3 MO 8 (where M = Fe, Co, Ni, Cu or Zn); lithium-nickel-manganese-cobalt-based oxides represented as Li(Ni a Co b Mn c )O 2 (where 0 < a < 1, 0 < b < 1, 0 < c < 1, and a + b + c = 1); sulfides or disulfide compounds; phosphates such as LiFePO 4 , LiMnPO 4 , LiCoPO 4 , LiNiPO 4 ; and Fe 2 (MoO 4 ) 3 etc., but not limited thereto.

[0094] At this time, the positive electrode active material layer may further include, in addition to the positive electrode active material, a conductive material, a filler, and other additives, etc.

[0095] The positive electrode active material may contain 90 to 99% by weight based on the solid content. If the content of the active material is low, the battery may not have a high capacity. If the content of the active material is too high, the contents of the binder, conductive material, etc. will relatively decrease, which may lead to a decrease in electrode adhesion, conductivity, etc.

[0096] The conductive material is not particularly limited and can be appropriately selected according to the types of the battery and the electrical storage device. For example, for a lithium-ion secondary battery, carbon such as graphite and activated carbon can be used. For a nickel-metal hydride secondary battery, cobalt oxide can be used. Nickel powder, cobalt oxide, titanium oxide, carbon, etc. can be used in the negative electrode.

[0097] Examples of the carbon include acetylene black, furnace black, graphite, carbon fiber, fullerene, and carbon nanotube.

[0098] The usage amount of the conductive material is generally 1 to 20 parts by weight, preferably 2 to 10 parts by weight based on 100 parts by weight of the electrode active material.

[0099] The more the content of the conductive material is reduced and the content of the positive electrode active material is increased, the higher the energy density of the secondary battery can be improved. Therefore, it is important to exhibit high efficiency even when using the same amount of the conductive material.

[0100] The smaller and more uniformly dispersed the conductive material for the electrode paste of the secondary battery is, the higher the conductive efficiency can be, thus reducing the internal resistance of the battery, exhibiting better characteristics, and improving the life characteristics. If it is large and unevenly dispersed, even when using the same amount, the adhesion characteristics and conductivity will decrease, which will have an adverse impact on the life characteristics and output characteristics of the battery. In addition, if the viscosity of the dispersion liquid is reduced, the solid content of the paste can be increased to improve the production speed of the electrode.

[0101] As the binder for the positive electrode of the secondary battery, in addition to the binder for the positive electrode containing a polyamide polymer in this article, poly(meth)acrylic acid, poly(meth)acrylamide, carboxymethyl cellulose, polyvinylidene fluoride, copolymer of polyhexafluoropropylene - polyvinylidene fluoride (P(VdF / HFP)), polyvinyl acetate, polyvinyl alcohol, poly(ethylene oxide), polyvinylpyrrolidone, alkylated poly(ethylene oxide), polyvinyl ether, polymethyl methacrylate, polyethyl acrylate, polytetrafluoroethylene, polyvinyl chloride, polyacrylonitrile, polyvinylpyridine, styrene-butadiene rubber, nitrile rubber, and any of their copolymers can be used, or two or more types can be selected and used together. Among them, the polyamide polymer contains monomer units including an aromatic ring.

[0102] The content of the binder in the positive electrode paste composition is preferably 0.3 wt% or more and 10 wt% or less, more preferably 0.7 wt% or more and 8 wt% or less, based on the solid content. When the content is less than 0.3 wt%, it is difficult to expect sufficient adhesion between the current collector and the electrode composition. When the content exceeds 10 wt%, since the ratio of the binder in the electrode paste composition increases, the battery capacity may be reduced.

[0103] According to another aspect of the present invention, the 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.

[0104] The positive electrode can be manufactured by the following steps: (a) manufacturing a composition for forming a positive electrode active material layer, wherein the positive electrode active material layer includes a positive electrode active material and the binder of the present invention; and (b) coating the composition for forming the positive electrode active material layer on a positive electrode current collector and then drying.

[0105] The mixing of the composition for forming the positive electrode active material layer can be carried out by conventional methods using conventional mixers such as a high-speed shear mixer, a high-speed mixer, etc.

[0106] The step (b) is a step of coating the composition for forming the positive electrode active material layer manufactured in the step (a) on a positive electrode current collector and then drying to form a positive electrode for a lithium secondary battery.

[0107] At this time, there is no limitation on the method of coating the composition for forming the paste-like positive electrode active material layer. For example, it can be manufactured by methods such as doctor blade coating, dip coating, gravure coating, slit die coating, spin coating, comma coating, bar coating, reverse roll coating, screen coating, cap coating, etc.

[0108] After coating and drying, a positive electrode for a secondary battery (especially, a lithium secondary battery) having a positive electrode active material layer formed thereon can be finally manufactured.

[0109] For the current collector, as long as it has conductivity and does not chemically react with the paste for forming the electrode, it can be used. Representative examples include an aluminum film, a copper film, etc. A current collector having a thickness between 3 and 50 microns can be selectively used.

[0110] The secondary battery according to another aspect of the present invention may include the positive electrode.

[0111] On the other hand, a secondary battery can be manufactured which is composed of a positive electrode containing the binder for the positive electrode of the present invention, a negative electrode, a separator, and an electrolyte.

[0112] The separator should be an insulator to separate the negative electrode and the positive electrode, and a path through which only lithium ions can move needs to be provided. For this purpose, it is necessary to have good wettability with the electrolyte, and porous polymer films such as PE / PP, porous non-woven fabrics, etc. are used. To prevent battery short circuit, a coated separator coated with ceramics or the like can be used, and it can be coated with a single layer or multiple layers, wherein the ceramics enhance heat resistance and mechanical strength, etc.

[0113] The separator may be composed of a porous substrate, and generally, any porous substrate used for electrochemical devices can be used. For example, a polyolefin porous membrane or non-woven fabric can be used, but it is not particularly limited.

[0114] The separator may be a porous substrate selected from the group consisting of one or a mixture of two or more selected from polyethylene, polypropylene, polybutene, polyisopentene, polyethylene terephthalate, polybutylene terephthalate, polyester fiber, polyacetal, polyamide, polycarbonate, polyimide, polyether ether ketone, polyether sulfone, polyphenylene ether, polyphenylene sulfide, and polyethylene naphthalate.

[0115] 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. As the solvent, non-aqueous organic solvents, organic solid electrolytes, inorganic solid electrolytes, etc. can be used.

[0116] As the lithium salt, a substance suitable for dissolving in the non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO 4 , LiBF 4 , LiB 10 Cl 10 , LiPF 6 , LiAsF 6 , LiSbF 6 , LiAlCl 4 , LiSCN, LiC 4 BO 8 , LiCF 3 CO 2 , LiCH 3 SO 3 , LiCF 3 SO 3 , LiN(SO 2 CF 3 ) 2 , LiN(SO2 F) 2 , LiN(SO 2 C 2 F 5 ) 2 , LiC 4 F 9 SO 3 , LiC(CF 3 SO 2 ) 3 , (CF 3 SO 2 )·2NLi, lithium chloroborane, lithium lower aliphatic carboxylate, 4-phenylborate lithium imide, etc.

[0117] As the non-aqueous organic solvent, aprotic organic solvents can be used, for example, N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran (franc), 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, 4-methyl-1,3-dioxane, diethyl ether, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triphosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, ethyl propionate, etc.

[0118] As the organic solid electrolyte, for example, polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate polymers, polylysine (agitation lysine), polyester sulfides, polyvinyl alcohol, polyvinylidene fluoride, polymers containing secondary dissociation groups, etc. can be used.

[0119] As the inorganic solid electrolyte, for example, Li 3 N, LiI, Li 5 NI 2 , Li 3 N-LiI-LiOH, LiSiO 4 , LiSiO 4 -LiI-LiOH, Li 2 SiS 3 , Li 4 SiO 4 , Li 4 SiO 4 -LiI-LiOH, Li 3 PO 4 -Li 2 S-SiS 2Nitrides, halides, sulfates, etc. of Li and the like.

[0120] In addition, for the purpose of improving charge and discharge characteristics, flame retardancy, etc., the non-aqueous electrolyte may further contain other additives. Examples of the additives are as follows: pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-propyl ether (glyme), hexamethylphosphoric triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazoles, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, aluminum trichloride, vinylene carbonate (VC), propanesultone (PRS), fluoroethylene carbonate (FEC), etc.

[0121] The lithium secondary battery according to the present invention can perform lamination stack and folding processes of the separator and the electrode in addition to the conventional winding process. Moreover, the battery case can be cylindrical, angular, pouch-shaped, coin-shaped, etc.

[0122] Implementation method of the invention

[0123] Hereinafter, the present text will be described more specifically by using examples, but the present text is not limited thereto.

[0124] Production Example 1, Production of Polymer for Adhesive

[0125] [Example 1]

[0126] Bis(4-aminophenyl)sulfone (p-APS) was added to a 500 ml four-necked flask under a nitrogen atmosphere and stirred. Here, the bis(4-aminophenyl)sulfone (p-APS) is a monomer for forming a monomer unit containing N-methyl-2-pyrrolidone (NMP) and sulfone.

[0127] After that, the temperature inside the reactor was lowered to 5°C or below, and isophthaloyl chloride (IPC) was added for reaction. Here, the isophthaloyl chloride (IPC) is a monomer unit containing an aromatic ring.

[0128] After adding terephthaloyl chloride (TPC), sufficient time was given for stirring. Here, the terephthaloyl chloride (TPC) is a monomer used to form a monomer unit containing an aromatic aromatic ring.

[0129] The molar ratio of the isophthaloyl chloride to the terephthaloyl chloride is 5:5.

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

[0131] Finally, a polyamide copolymer solution for adhesives with a solids concentration of 15 wt% (weight average molecular weight of about 226,193 g / mol) was produced.

[0132] [Example 2]

[0133] A polyamide copolymer solution for adhesives was produced in the same manner as in Example 1, except that the solids concentration was changed to 10 wt%.

[0134] [Example 3]

[0135] A polyamide copolymer solution for adhesives was produced in the same manner as in Example 1, except that the solids concentration was changed to 20 wt%.

[0136] [Example 4]

[0137] A polyamide copolymer solution for adhesives was produced in the same manner as in Example 1, except that 1 mol of bis(4-aminophenyl)sulfone (p-APS) was used instead of 1 mol of bis(3-aminophenyl)sulfone (m-APS).

[0138] [Example 5]

[0139] A polyamide copolymer solution for adhesives was produced in the same manner as in Example 1, except that 1 mol of bis(4-aminophenyl)sulfone (p-APS) was used instead of 1 mol of 4,4'-oxydianiline (ODA).

[0140] [Comparative Example 1]

[0141] As the reactor, nitrogen purging was carried out in a 500 mL double jacket equipped with a stirrer, a nitrogen injection device, and a condenser.

[0142] Bis(4-aminophenyl)sulfone and N-Methyl-2-Pyrrolidone (NMP) were added at room temperature and stirred until dissolved. Bis(4-aminophenyl)sulfone is a monomer for forming a monomer unit containing a sulfone.

[0143] After that, 4,4'-Oxydiphthalic anhydride (ODPA), which is a dianhydride monomer, was added and stirred for more than 24 hours. Further, pyridine, which is a dehydration catalyst, was added and reacted to produce a polyimide polymer solution for an adhesive with a solid concentration of 15% by weight.

[0144] [Comparative Example 2]

[0145] A KF7208 PVDF polymer solution manufactured by KUREHA was purchased and used as a polymer solution for an adhesive.

[0146] The polymer solutions for adhesives of Example 1 and 5 and Comparative Examples 1 and 2 were coated on a glass plate to produce a film for cyclic vacuum drying, and the glass transition temperature (Tg) of the polymer for the adhesive measured by DMA analysis (analysis conditions: -50°C to 400°C, 5°C / min) using DMA1 of Mettler is as shown in Table 1 below.

[0147] [Table 1]

[0148] Monomer Composition Tg (°C) Example 1 p-APS / TPC / IPC 161 Example 5 ODA / TPC / IPC 152 Comparative Example 1 p-APS / ODPA 278 Comparative Example 2 PVDF (Kureha) -43

[0149] As shown in Table 1 above, the glass transition temperature of the PVDF polymer for the adhesive in Comparative Example 2 was measured to be -43°C.

[0150] In addition, the polyimide polymer for the adhesive in Comparative Example 1 has an aromatic ring and a rigid imide structure, so the glass transition temperature was measured to be very high, reaching 278°C.

[0151] On the other hand, the polyimide polymers for adhesives in Examples 1 and 5 have an aromatic ring and an amide structure, so the glass transition temperatures were confirmed to be 161°C and 152°C respectively, that is, they have a glass transition temperature of more than 100°C and less than 250°C.

[0152] Production Example 2, Production of Positive Electrode Slurry and Positive Electrode

[0153] 55 to 60% by weight of NCM622 as an electrode active material, 1.5 to 2% by weight of the polymer for the adhesive of Examples 1 to 5 and Comparative Examples 1 and 2, 0.7 to 0.8% by weight of a CNT dispersion liquid, and the remaining NMP were mixed to produce a positive electrode active material slurry composition.

[0154] The prepared positive electrode paste composition is coated on an aluminum (Al) foil, which is a positive electrode current collector with a thickness of 20 μm. After drying in a circulating oven at 130 °C for 1 hour, the dried positive electrode is roll-pressed to manufacture the positive electrode.

[0155] After drying the manufactured positive electrode at 130 °C for 1 hour, it is cut into a size of 15 x 2.5 cm.

[0156] After that, the coated side of the positive electrode is pasted on an acrylic plate with double-sided tape, and pressed 3 - 4 times with a pressing rubber roller to manufacture a sample for the peel-off test.

[0157] The prepared sample is loaded into a UTM capable of measuring the adhesive force for a 2.5 cm, 180° peel test, and the load value (N / mm) is measured to calculate the adhesive force of the positive electrode.

[0158] The calculated adhesive force of the positive electrode is shown in Table 2 below.

[0159] [Table 2]

[0160]

[0161] As shown in Table 2 above, it can be confirmed that the positive electrodes using the polyamide adhesives of Examples 1 to 5 have higher adhesive forces compared to the positive electrode manufactured using the polyimide polymer adhesive of Comparative Example 1.

[0162] In particular, the polyamide polymer adhesives of Examples 1 and 3 containing p-APS as a monomer exhibit higher adhesive forces compared to the PVDF polymer adhesive of Comparative Example 2.

[0163] Moreover, although manufactured with the same composition ratio, comparing the polyamide polymer adhesives of Examples 2 and 3 with different solid content ratios, it can be confirmed that the higher the solid content, the higher the adhesive force.

[0164] Production Example 3, Production of Battery Cell

[0165] A non-aqueous electrolyte containing 1.5 M of LiPF6 and 20 wt% of FEC is used as the electrolyte. After inserting a polyolefin separator membrane between the positive electrode and the negative electrode of the positive electrode plate, a lithium secondary battery is manufactured without distinguishing between 2032 coin cell monomer type or pouch type. The positive electrode plate uses the polymer adhesives of Examples 1 to 5, Comparative Example 1, and Comparative Example 2 manufactured in Manufacturing Example 2 above.

[0166] For the battery cell manufactured according to Manufacturing Example 3 using the positive electrode plate, after charging to 4.2 V at 0.1 C rate in CC / CV mode, discharging to 2.5 V at 0.1 C rate, then charging to 4.2 V at 0.2 C rate and discharging to 2.5 V at 0.2 C rate, and then charging to 4.2 V at 0.5 C rate and discharging to 2.5 V (initial formation), the positive electrode plate used the polymer binders of Example 1, Examples 3 to 5, and Comparative Examples 1 and 2. At this time, the temperature of the chamber was 25 °C. The "C" as the discharge rate of the battery cell means the value obtained by dividing the total capacity of the battery cell by the total discharge hours.

[0167] The initial charge capacity, initial discharge capacity, initial efficiency, and DC-IR measurement results of the battery cell manufactured according to Manufacturing Example 3 using the positive electrode plate are shown in Table 3 below, where the positive electrode plate used the polymer binders of Example 1, Examples 3 to 5, and Comparative Examples 1 and 2.

[0168] In the initial formation, the charge capacity when charging to 4.2 V at 0.1 C rate and the discharge capacity when discharging to 2.5 V at 0.1 C rate were measured as the initial charge capacity and the initial discharge capacity respectively, and the initial efficiency was calculated using the following Mathematical Formula 1.

[0169] <Mathematical Formula 1>

[0170] Initial efficiency [%] = [Initial discharge capacity / Initial charge capacity] × 100

[0171] On the other hand, the DC-IR measurement was carried out under the conditions that after the initial formation of the battery cell manufactured according to Manufacturing Example 3 using the positive electrode plate, charging to the voltage equivalent to 50% of the SOC at 0.3 C rate in CC / CV mode and then discharging to 2.75 V at 2 C rate, where the positive electrode plate used the polymer binders of Example 1, Examples 3 to 5, and Comparative Example 1 and Comparative Example 3. At this time, the temperature of the chamber was 25 °C.

[0172] [Table 3]

[0173]

[0174]

[0175] The measurement results of the initial efficiency, and the battery cells manufactured according to Manufacturing Example 3 using the positive electrode plates with the polymer binders of Example 1 and Examples 3 to 5 all showed an initial efficiency of more than 83%.

[0176] In particular, when applying polyamide adhesives using p-APS monomers (Examples 1 and 3), an initial efficiency of more than 86% is relatively high.

[0177] The DC-IR measurement results for understanding the battery resistance characteristics, and the battery monomers based on the positive electrode plates using the polymer adhesives of Examples 1 and 3 to 5 and manufactured according to Manufacturing Example 3 all show DC-IR measurement values of 0.1120 Ω or less.

[0178] Since this DC-IR measurement is lower than that of the battery monomers applying the polymer adhesives of Comparative Examples 1 and 2, it can be confirmed that the battery monomers applying the polymer adhesives of Examples 1 and 3 to 5 have relatively low resistance characteristics.

[0179] This low resistance characteristic contributes to the active movement of electrons between the positive and negative electrodes in the battery, thus contributing to excellent battery characteristics.

[0180] After the initial formation of the battery monomers based on the positive electrode plates using the polymer adhesives of Examples 1 and 3 to 5 and Comparative Examples 1 and 2 and manufactured according to Manufacturing Example 3, charging was performed to 4.2 V at 1C rate in CC / CV mode, and discharging at 1C rate to 2.5 V was repeated 200 times.

[0181] The discharge capacity during discharge of the first cycle, the discharge capacity during discharge of the 100th cycle, and the discharge capacity during discharge of the 200th cycle were measured, and the 100th cycle capacity retention rate and the 200th cycle capacity retention rate were calculated using the following Mathematical Formula 2 and the following Mathematical Formula 3.

[0182] [Mathematical Formula 2]

[0183] 100th cycle capacity retention rate [%] = [discharge capacity of the 100th cycle / discharge capacity of the first cycle] × 100

[0184] [Mathematical Formula 3]

[0185] 200th cycle capacity retention rate [%] = [discharge capacity of the 200th cycle / discharge capacity of the first cycle] × 100

[0186] The measurement results of the calculated 100th cycle capacity retention rate and 200th cycle capacity retention rate are shown in Table 4 below.

[0187] [Table 4]

[0188]

[0189] The calculated capacity retention rates show a tendency similar to the initial efficiency.

[0190] That is, as Figure 1 shown, the battery cells manufactured according to Manufacturing Example 3 using the positive electrode plates with the polymer binders of Example 1 and Examples 3 to 5 all exhibited a 100th cycle capacity retention rate of more than 88% and a 200th cycle capacity retention rate of more than 86%. Therefore, compared with the battery cells manufactured according to Manufacturing Example 3 using the positive electrode plates with the polymer binders of Comparative Examples 1 and 2, the cycle capacity retention rate characteristics are excellent.

[0191] In particular, when applying polyamide binders (Example 1 and Example 3) using p-APS monomers, relatively high cycle capacity retention rates are exhibited. When applying the polyamide binder of Example 1 with excellent positive electrode adhesion, the highest cycle capacity retention rate is exhibited.

[0192] As a result, it can be confirmed that the positive electrode binder containing polyamide polymer in this article has excellent glass transition temperature characteristics and also has excellent adhesion characteristics technically.

[0193] In addition, it can be confirmed that when applying the positive electrode binder containing the polyamide polymer of this article, the characteristics of the secondary battery are improved.

[0194] The scope of the present invention is represented by the scope of the claims rather than the above detailed description, and should be interpreted to include all changes or variations derived from the meaning and scope of the claims and their equivalent concepts within the scope of the present invention.

[0195] Industrial Applicability

[0196] The positive electrode binder of the present invention exhibits excellent adhesion characteristics and can improve the electrochemical characteristics and cycle characteristics of the secondary battery.

[0197] In addition, the positive electrode binder of the present invention does not generate harmful gases (for example, hydrogen fluoride) even when exposed to alkalinity for a long time, thereby improving the stability and life of the secondary battery.

[0198] Furthermore, the improved adhesion of the positive electrode binder of the present invention can increase the amount of the active material and the conductive agent while reducing the amount of the binder used. Therefore, a lithium secondary battery with high energy density can be provided at low cost.

Claims

1. A binder for a positive electrode, wherein, it comprises: a polyamide polymer having a glass transition temperature of 100 °C or higher and 250 °C or lower.

2. The binder for a positive electrode according to claim 1, wherein, the binder does not contain fluorine atoms, and hydrogen fluoride is not generated during the charge and discharge process of a battery using the binder.

3. The binder for a positive electrode according to claim 1, wherein, the polyamide polymer comprises: a monomer unit containing at least one aromatic ring.

4. The binder for a positive electrode according to claim 3, wherein, the polyamide polymer further comprises: a monomer unit containing sulfone.

5. The binder for a positive electrode according to claim 2, wherein, the at least one aromatic ring is substituted by a halogen element, hydrogen, a hydroxyl group, a carboxyl group, a linear or branched hydrocarbon group having 1 to 4 carbon atoms with the halogen element substituted or unsubstituted, or a combination thereof, wherein the halogen element does not include fluorine.

6. The binder for a positive electrode according to claim 2, wherein, the monomer for forming the monomer unit containing the at least one aromatic ring by polymerization comprises: any one or more selected from the group consisting of a diamine monomer containing at least one aromatic ring, a terephthaloyl chloride monomer, an isophthaloyl chloride monomer, a phthalic acid monomer, an isophthalic acid monomer, a terephthalic acid monomer, a 4,4'-dibenzoic acid monomer, and a 4,4'-dicarboxydiphenyl sulfone monomer.

7. The binder for a positive electrode according to claim 6, wherein, The diamine monomer containing at least one aromatic ring is any one or more selected from the group consisting of p-phenylenediamine, m-phenylenediamine, 3,3'-dimethyl benzidine, 2,2'-dimethylbenzidine, tetrachlorobenzidine, 2,4-diaminotoludine, 2,6-diaminotoludine, 3,5-diaminobenzoic acid, Bis(4-aminophenyl)methane, 4,4'-oxydianiline, 3,4'-diaminodiphenylether, 2,2-bis(4-aminophenyl)propane, bis(4-aminophenyl)terephthalate, 4,4′-Diaminodiphenylmethane, 4,4′-Methylene-bis(2-methylaniline), 4,4′-diaminobenzophenone, Bis(4-aminophenyl)methane, and 4-(4-aminophenoxy)phenyl)ether).

8. The binder for the positive electrode according to claim 4, wherein, The monomers that form monomer units containing the sulfone through polymerization are any one or more selected from the group consisting of bis(4-aminophenyl)sulfone, bis(3-aminophenyl)sulfone, 3,3'-diaminophenylsulfone, 3,4'-diaminophenylsulfone, 4,4'-diaminophenylsulfone, 1,3-bis(3-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, and bis〔4-(4-aminophenoxy)phenyl〕sulfone).

9. The binder for a positive electrode according to claim 1, wherein, the polyamide polymer contains a monomer repeating unit represented by the following Chemical Formula 1, [Chemical Formula 1] in Chemical Formula 1, X 1 Containing a halogen element, hydrogen, hydroxyl group, carboxyl group, a linear or branched hydrocarbon group with 1 to 4 carbon atoms where the halogen element is substituted or unsubstituted, or at least one aromatic ring substituted with a combination thereof X 2 Containing a halogen element, hydrogen, a hydroxyl group, a carboxyl group, a straight-chain or branched hydrocarbon group with 1 to 4 carbon atoms in which the halogen element is substituted or unsubstituted, or a combination thereof, an aromatic ring with 2 or more carbon atoms substituted and, n + m = 1; wherein, the halogen element in Chemical Formula 1 does not include fluorine.

10. The binder for a positive electrode according to claim 9, wherein, X of the chemical formula 1 2 is a simple bond, -CH 2 -, -C(CH 3 ) 2 -, -C(=O)-, -S(=O)-, -O- or -SO 2 - connected to each other by a halogen element, hydrogen, hydroxyl group, carboxyl group, a straight-chain or branched-chain hydrocarbon group having 1 to 4 carbon atoms with or without halogen substitution, or a combination thereof, or two aromatic rings substituted; or a halogen element, hydrogen, a hydroxyl group, a carboxyl group, a linear or branched hydrocarbon group having 1 to 4 carbon atoms in which the halogen element is substituted or unsubstituted, or a naphthalene substituted with a combination thereof.

11. The binder for a positive electrode according to claim 1, wherein, the polyamide polymer contains a monomer repeating unit represented by the following Chemical Formula 2, [Chemical Formula 2] in Chemical Formula 2, X 3 is a simple bond, -CH 2 -, -C(CH 3 ) 2 -, -C(=O)-, -S(=O)-, -O- or -SO 2 (-), R 1 to R 3 are each independently a halogen element, hydrogen, hydroxyl group, carboxyl group, a linear or branched hydrocarbon group having 1 to 4 carbon atoms in which the halogen element is substituted or unsubstituted, or a combination thereof a + b = 1; wherein, the halogen element in Chemical Formula 2 does not include fluorine.

12. The binder for a positive electrode according to claim 1, wherein, the weight-average molecular weight of the polyamide polymer is 100,000 or more and 1,000,000 or less.

13. The binder for a positive electrode according to claim 6, wherein, the molar ratio of terephthaloyl chloride to isophthaloyl chloride for polymerizing the polyamide polymer (mol% of terephthaloyl chloride: mol% of isophthaloyl chloride) is 2:8 to 8:

2.

14. A positive electrode paste, wherein, it comprises: a binder for the positive electrode according to any one of claims 1 to 13; and a positive electrode active material.

15. A positive electrode, wherein, it comprises: a current collector; and a positive electrode active material layer containing the binder for the positive electrode according to any one of claims 1 to 13 formed on the current collector.

16. A secondary battery, wherein, it comprises: a positive electrode according to claim 15.

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