KR20170076298A - Binder composition for secondary battery, and electrode for secondary battery and sodium secondary battery comprising the same - Google Patents

Abstract

The present invention relates to a composition comprising a conjugated dienes binder (A) and an acrylic copolymer binder (B) together, wherein one of the conjugated diene binder (A) and the acrylic copolymer binder (B) Or both of them include two or more different kinds of binders. Since the binder composition for a secondary battery according to the present invention includes three or more different kinds of binders in total, the binder composition exhibits improved adhesion, The adhesion to the electrode collector and the adhesion between the active materials can be improved and the electrode for the secondary battery including the same can exhibit a more stable electrochemical performance. Therefore, the electrode for secondary battery and the sodium secondary battery including the same can be used have.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a binder composition for a secondary battery, and a secondary battery electrode and a sodium secondary battery comprising the binder composition. 2. Description of the Related Art Binder compositions for secondary batteries,

The present invention relates to a binder composition for a secondary battery, and a secondary battery electrode and a sodium secondary battery comprising the binder composition. More particularly, the present invention relates to a binder composition for a secondary battery, which comprises three or more kinds of binders, And an electrode for a secondary battery comprising the same, and a secondary battery including the same.

As technology development and demand for mobile devices have increased, there has been a rapid increase in demand for secondary batteries as energy sources. Among such secondary batteries, lithium secondary batteries, which exhibit high energy density and operating potential, long cycle life, Batteries have been commercialized and widely used.

However, in the case of a lithium secondary battery, there is a problem in that it is not economically feasible to use it as a large-scale power storage secondary battery due to the scarcity of resources of the lithium material.

Therefore, a lot of efforts have been made to prepare an alternative thereto, and there have been many attempts to utilize sodium rich in resources on the earth as a material for a secondary battery. However, sodium secondary batteries using sodium have advantages of low manufacturing cost and low concern about environmental pollution, but sodium is more sensitive to air, ion volume is almost double compared with lithium, It also has the disadvantage that it does not reach the potential.

For example, U.S. Patent Publication No. 20030054255 discloses a sodium sulfur battery in which beta alumina having selective conductivity for sodium ions is used, sodium is used for a cathode, and sulfur is used for a cathode.

The electrode of the sodium secondary battery is prepared by mixing a cathode active material or a negative electrode active material with a binder resin component and dispersing the mixture in a solvent to prepare a slurry and applying the slurry to the electrode collector surface to form a mixture layer after drying.

The binder is used for securing the adhesion or binding force between the active material and the active material, or between the active material and the electrode current collector, but an excessive amount of binder is required to improve the adhesion between the electrode current collector and the active material. However, an excessive amount of the binder has a problem that the capacity and conductivity of the electrode are lowered. On the other hand, insufficient adhesion causes electrode peeling phenomenon in drying process such as electrode drying and pressing process, thereby increasing the defect rate of the electrode. In addition, the electrode having low adhesive force can be peeled off by an external impact, and such peeling of the electrode increases the contact resistance between the electrode material and the current collector, which may cause deterioration of the electrode output performance.

Accordingly, there is provided a binder composition capable of providing a sodium secondary battery having improved performance by solving the problem of deterioration of electrochemical performance due to peeling of the electrode, desorption of the active material from the collector, or change of the contact interface between the active material, There is a continuing need to develop an electrode for a sodium secondary battery manufactured using the same.

US 2003/0054255 A1

A problem to be solved by the present invention is to provide a binder composition for a secondary battery which can further improve the electrochemical performance of a battery by providing an excellent adhesive force.

Another object of the present invention is to provide an electrode for a secondary battery comprising the binder composition for a secondary battery.

Another object of the present invention is to provide a sodium secondary battery including the electrode for a secondary battery.

In order to solve the above problems,

(B) a binder (A) and an acrylic copolymer binder together, wherein the binder (A)

Wherein either one or both of the conjugated diene binder (A) and the acrylic copolymer binder (B) comprises two or more kinds of different binders.

Further, in order to solve the above-mentioned other problems,

And an electrode for a secondary battery comprising the binder composition for the secondary battery.

The present invention also provides a sodium secondary battery including the secondary battery electrode.

Since the binder composition for a secondary battery according to the present invention includes three or more kinds of binders in total, the adhesive force of the electrode material to the collector of the electrode and the adhesive force between the active materials are improved by exhibiting the improved adhesion, And can exhibit a more stable electrochemical performance. Therefore, it can be usefully used for manufacturing an electrode for a secondary battery and a sodium secondary battery including the same.

Hereinafter, the present invention will be described in detail in order to facilitate understanding of the present invention.

The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms and the inventor may appropriately define the concept of the term in order to best describe its invention It should be construed as meaning and concept consistent with the technical idea of the present invention.

The binder composition according to the present invention comprises a conjugated dienes binder (A) and an acrylic copolymer binder (B) together and the conjugated diene binder (A) and the acrylic copolymer binder (B) Or both of them contain two or more kinds of different binders, respectively.

The binder composition according to the present invention comprises the conjugated diene binder (A) and the acrylic copolymer binder (B) together, wherein the conjugated diene binder (A) and the acrylic copolymer binder (B) The above includes two or more different kinds of binders, so that the binder composition according to the present invention includes three or more different kinds of binders.

Since the binder composition includes three or more kinds of different binders, it is possible to exhibit an improved adhesive force. Thus, the adhesion of the electrode material to the collector of the electrode and the adhesive force between the active materials are improved, and the secondary battery has a more stable electrochemical performance And can exhibit improved performance.

The conjugated diene-based binder (A) and the acrylic copolymer-based binder (B) may exist independently of each other, and the conjugated diene-based binder (A) or the acrylic copolymer- When the binder is included, the two or more kinds of binders may exist in independent phases.

The independent phase refers to a state in which each binder is not agglomerated or chemically reacted with other binder and is not deformed.

The conjugated diene-based binder (A) and the acrylic copolymer-based binder (B) may have elasticity like a latex and may be in the form of particles. Accordingly, the binder composition according to an example of the present invention may comprise a conjugated diene-based binder (A) particle and an acrylic copolymer-binder (B) particle.

When the conjugated diene-based binder (A) or the acrylic copolymer-based binder (B) includes two or more different kinds of binders, the two or more different kinds of binders may be in the form of particles, When the conjugated diene-based binder (A) comprises two kinds of binders, that is, the conjugated diene-based binder (A-1) and the conjugated diene-based binder (A-2) (A-1) particle and a conjugated diene binder (A-2), wherein the acrylic copolymer binder (B) is at least one selected from the group consisting of an acrylic copolymer binder (B- (B-1) particles, an acrylic copolymer-based binder (B-2), and an acrylic copolymer-based binder (B- Polymer Binder (B-2 ) Particles and acrylic copolymer binder (B-3) particles.

When the conjugated diene-based binder (A) is in the form of particles, the conjugated diene-based binder (A) particles may have an average particle diameter of 50 nm to 200 nm. When the particles of the conjugated diene-based binder (A) have an average particle diameter of 50 nm to 200 nm, the swelling phenomenon of the electrolytic solution at a high temperature is small and the elasticity exhibits adequate elasticity, If it is out of the above range, the adhesive strength may be lowered.

When the acrylic copolymer binder (B) is in the form of particles, the acrylic copolymer binder (B) particles may have an average particle diameter of 300 nm to 700 nm. When the acrylic copolymer binder (B) particles have an average particle diameter of 300 nm to 700 nm, the adhesion of the binder can be improved. When the acrylic copolymer binder (B) particle size is smaller than the proper range, , And if it is larger than the proper range, the acrylic copolymer binder (B) particles themselves may act as a resistor.

On the other hand, when the conjugated diene-based binder (A) or the acrylic copolymer-based binder (B) includes two or more different kinds of binders and the two or more different kinds of binders are each in the form of particles, Two or more kinds of binders may have different average particle diameters within the average particle diameter range of the conjugated diene-based binder (A) or the acrylic copolymer binder (B).

The binder composition may contain the conjugated diene binder (A) and the acrylic copolymer binder (B) in a weight ratio of 70:30 to 99: 1, and specifically in a weight ratio of 80:20 to 90:10 .

When the acrylic copolymer binder (B) is contained in an amount of 1 part by weight or more based on 99 parts by weight of the conjugated diene binder (A), the adhesive strength of the binder composition can be improved and the acrylic copolymer binder (B) (B) is contained in an amount of 30 parts by weight or less based on 70 parts by weight of the gate diene binder (A), the problem of swelling at high temperature due to affinity with the carbonate-based electrolyte of the acrylic copolymer binder (B) It is possible to prevent the composition from deteriorating the high-temperature characteristics of the battery.

The conjugated diene binder (A) is selected from the group consisting of (A) a conjugated diene monomer or a conjugated diene polymer, (B) an acrylate monomer, a vinyl monomer, a (meth) acrylamide monomer and a nitrile monomer And at least one monomer selected from the group consisting of unsaturated monocarboxylic acid monomers (C).

The conjugated diene binder (A) is obtained by polymerizing 10 to 97.9 parts by weight of the conjugated diene monomer or conjugated diene polymer (a), (b) 1 to 60 parts by weight of at least one monomer selected from the group consisting of monomers having at least one unsaturated monocarboxylic acid group and at least one monomer selected from the group consisting of monomers having at least one unsaturated monocarboxylic acid group, Weight part.

The conjugated diene-based monomer may be 1,3-butadiene, isoprene, chloroprene, or a pyridene.

The conjugated diene polymer may be a polymer of two or more kinds of monomers selected from the group consisting of 1,3-butadiene, isoprene, chloroprene, and pyridene, a styrene-butadiene copolymer, an acrylonitrile-butadiene copolymer, Butadiene rubber, acrylonitrile-butadiene-styrene rubber, ethylene-propylene-diene polymer, and partially hydrogenated, epoxidized, or brominated polymers.

The acrylic copolymer binder (B) is a copolymer obtained by copolymerizing (1) a monomer selected from the group consisting of (meth) acrylate monomers, (b) acrylate monomers, vinyl monomers, (meth) acrylamide monomers and nitrile monomers A monomer of at least one type, and (C) an unsaturated monocarboxylic acid type monomer.

The acrylic copolymer binder (B) may contain 10 to 97.9 parts by weight of the (meth) acrylate monomer based on 100 parts by weight of the total amount of the acrylic copolymer binder (B) 1 to 60 parts by weight of at least one monomer selected from the group consisting of monomers, vinyl monomers, (meth) acrylamide monomers and nitrile monomers, 1 to 20 parts by weight of the unsaturated monocarboxylic acid monomer (c) .

The (meth) acrylic acid ester monomer may be at least one monomer selected from the group consisting of methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, n-amyl acrylate, isoamyl acrylate, n- Ethylhexyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl Methacrylate, n-amyl methacrylate, isoamyl methacrylate, n-hexyl methacrylate, n-ethylhexyl methacrylate, 2-ethylhexyl methacrylate, hydroxyethyl methacrylate, Propyl methacrylate, and the like.

In the conjugated diene-based binder (A) or the acrylic copolymer-based binder (B), the other components are as follows.

 The acrylate monomer may be at least one selected from the group consisting of methacryloxyethyl ethylene urea,? -Carboxyethyl acrylate, aliphatic monoacrylate, dipropylene diacrylate, ditrimethylpropane tetraacrylate, hydroxyethyl acrylate, dipentaerythritol Acrylate, stearyl methacrylate, lauryl methacrylate, cetyl methacrylate, stearyl methacrylate, stearyl methacrylate, stearyl methacrylate, stearyl methacrylate, And the rate may be one or more.

The vinyl-based monomer may be at least one member selected from the group consisting of styrene,? -Methylstyrene,? -Methylstyrene, p-t-butylstyrene and divinylbenzene.

The (meth) acrylamide-based monomer may be at least one selected from the group consisting of acrylamide, n-methylol acrylamide, n-butoxymethylacrylamide, methacrylamide, n-methylol methacrylamide and n-butoxymethylmethacrylamide And the like.

The nitrile monomer may be alkenyl cyanide, and the alkenyl cyanide may be at least one selected from the group consisting of acrylonitrile, methacrylonitrile, and allyl cyanide.

The unsaturated monocarboxylic acid monomer may be at least one member selected from the group consisting of maleic acid, fumaric acid, methacrylic acid, acrylic acid, glutaric acid, itaconic acid, tetrahydrophthalic acid, crotonic acid, isocrotonic acid and nadic acid .

The method for producing the conjugated diene-based binder (A) or the acrylic copolymer-based binder (B) is not particularly limited, but it can be produced by suspension polymerization, emulsion polymerization,

The conjugated diene-based binder (A) or the acrylic copolymer-based binder (B) may contain one or more other components such as a polymerization initiator, a crosslinking agent, a coupling agent, a buffer, a molecular weight modifier and an emulsifier.

For example, in the case where the conjugated diene binder (A) and / or the acrylic copolymer binder (B) are produced by the emulsion polymerization method in the method for producing the binder contained in the binder composition according to an example of the present invention When the conjugated diene-based binder (A) and the acrylic copolymer binder (B), or a binder containing them, are produced by the emulsion polymerization method and the binder has a particle shape, the particle size Specifically, when the amount of the emulsifier is increased, the average particle diameter of the particles can be decreased, and when the amount of the emulsifier is decreased, the average particle diameter of the particles can be increased.

The polymerization temperature and the polymerization time can be appropriately determined according to the kind of the polymerization method polymerization initiator and the like. For example, the polymerization temperature may be from 50 캜 to 300 캜, and the polymerization time may be from 1 to 20 hours, but is not particularly limited.

As the polymerization initiator, an inorganic or organic peroxide may be used. A water-soluble initiator including, for example, potassium persulfate, sodium persulfate, ammonium persulfate and the like, or an oil-soluble initiator including cumene hydroperoxide, benzoyl peroxide, . On the other hand, an activator may be used together with the activator to promote the initiation reaction of the polymerization initiator, and the activator may be selected from the group consisting of sodium formaldehyde sulfoxylate, sodium ethylenediamine tetraacetate, ferrous sulfate and dextrose One or more species can be mentioned.

The crosslinking agent may be used for promoting crosslinking of the binder, and examples thereof include amines such as diethylenetriamine, triethylenetetramine, diethylaminopropylamine, xylenediamine, isophoronediamine, and the like; dodecylsuccinic anhydride dodecyl succinic anhydride and phthalic anhydride, polyamide resins, polysulfide resins, phenol resins, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, 1,3-butanediol dimethacrylate, 1,6-hexanediol dimethacrylate, neopentyl glycol dimethacrylate, trimethylolpropane trimethacrylate, trimethylolmethane triacrylate, glycidyl methacrylate, Acrylate, and the like. On the other hand, grafting agents can be used together, and examples thereof include aryl methacrylate (AMA), triarylisocyanurate (TAIC), triarylamine (TAA), or diarylamine (DAA).

The coupling agent may be used to increase the adhesive force between the active material and the binder, and may be a material having two or more functional groups. For example, triethoxysilylpropyl tetrasulfide, mercaptopropyltriethoxysilane , Aminopropyltriethoxysilane, chloropropyltriethoxysilane, vinyltriethoxysilane, methacryloxypropyltriethoxysilane, methacryloxypropyltriethoxysilane, glycidoxypropyltriethoxysilane, isoshi A silane coupling agent such as isocyanatopropyl triethoxysilane, or cyanatopropyltriethoxysilane may be mentioned.

Examples of the buffer include NaHCO ₃ , NaOH, and NH ₄ OH.

Examples of the molecular weight regulator include mercaptans or terpines such as terpinolene, dipentene and t-terpine, and halogenated hydrocarbons such as chloroform and carbon tetrachloride.

The emulsifier may be an anionic emulsifier, a nonionic emulsifier, or both. When an anionic emulsifier is used in combination with a nonionic emulsifier, in addition to the electrostatic stabilization of the anionic emulsifier, the addition of a colloidal form through the van der Waals force of the polymer particles Stabilization can be provided.

The anionic emulsifier includes, for example, a phosphate-based, carboxylate-based, sulfate-based, succinate-based, sulfosuccinate-based, sulfonate-based or disulfonate-based emulsifier. Sodium lauryl ether sulfate, sodium polyoxyethylene lauryl ether sulfate, sodium lauryl sulfate, sodium alkylsulfonate, sodium alkyl ether sulfonate, sodium alkylbenzenesulfonate, sodium alkyl sulfate, sodium alkyl sulfate, But are not limited to, sodium linear alkylbenzene sulfonate, sodium alpha-olefin sulfonate, sodium alcohol polyoxyethylene ether sulfonate, sodium dioctylsulfosuccinate, sodium perfluorooctanesulfonate, sodium perfluorobutanesulfonate, Disulfonate, sodium dioctyl sulfosuccinate, sodium alum - there may be mentioned aryl phosphates, sodium alkyl ether four-state, or sodium laurate ohril sarcoidosis upon carbonate.

Examples of the nonionic emulsifier include ester type, ether type, and ester-ether type emulsifiers. Specific examples of the nonionic emulsifier include polyoxyethylene glycol, polyoxyethylene glycol methyl ether, polyoxyethylene monoallyl ether, poly Polyoxyethylene stearyl ether, polyoxyethylene decyl ether, polyoxyethylene stearyl ether, polyoxyethylene stearyl ether, polyoxyethylene stearyl ether, polyoxyethylene stearyl ether, polyoxyethylene stearyl ether, polyoxyethylene stearyl ether, , And polyoxyethylene octyl ether.

When the conjugated diene binder (A) and the acrylic copolymer binder (B) contained in the binder composition exist in mutually independent phases, it is necessary to prevent the intergranular agglomeration because they exhibit an effect of improving the adhesive strength. For example, the pH of the conjugate diene binder (A) and the acrylic copolymer binder (B) can be adjusted so that the respective binders in the mixture can maintain independent phases without being agglomerated with each other. Specifically, when the acrylic copolymer binder (B) exhibits an acidic pH, aggregation may occur with the conjugated diene binder (A), so that it can be maintained in an independent phase by titrating it with a base to adjust the pH. Examples of the base include potassium hydroxide, sodium hydroxide, lithium hydroxide and the like, but are not particularly limited.

The binder composition can be used in the production of an electrode for a secondary battery, and thus the present invention also provides an electrode for a secondary battery comprising the binder composition. Specifically, the secondary battery electrode may be an electrode for a sodium secondary battery.

The present invention also provides a sodium secondary battery including the electrode for the secondary battery.

The sodium secondary battery may include a negative electrode, and a separator interposed between the positive electrode and the negative electrode.

The anode may be prepared by a conventional method known in the art. For example, a slurry may be prepared by mixing and stirring a solvent, a binder, a conductive material, and a dispersant in a cathode active material, coating the cathode active material with a current collector of the metallic material, compressing it, .

The current collector of the metal material is a metal having high conductivity and is a metal which can easily adhere to the slurry of the cathode active material and is not particularly limited as long as it has high conductivity without causing chemical change in the battery in the voltage range of the battery But not limited to, stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, or the like. In addition, fine unevenness may be formed on the surface of the current collector to increase the adhesive force of the positive electrode active material. The current collector may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric, and may have a thickness of 3 to 500 μm.

The cathode active material may be selected from the group consisting of sodium cobalt oxide [Na _x CoO ₂ (0.5 <x <1.3)], sodium nickel oxide [Na _x NiO ₂ (0.5 <x <1.3)], sodium chromium oxide [Na _x CrO ₂ < x < 1.3)] or a compound substituted with a further transition metal; Formula _{Na 1 + x Mn 2 - x} O 4 ( where, x is from 0 to _{0.33), NaMnO 3, NaMn 2 O} 3, or _{[Na x MnO 2 (0.5 <} x <1.3)] sodium manganese oxide and the like; Sodium copper oxide (Na ₂ CuO _2); Vanadium oxides such as NaV ₃ O ₈ , NaFe ₃ O ₄ , V ₂ O ₅ , or Cu ₂ V ₂ O ₇ ; A Ni site-type sodium nickel oxide represented by the formula NaNi _{1 - x} M _x O ₂ wherein M = Co, Mn, Al, Cu, Fe, Mg, B or Ga and x = 0.01 to 0.3; Formula NaMn _{2 -x} M _x O ₂ (where, M = Co, Ni, Fe , Cr, and Zn, or Ta, x = 0.01 to 0.1 Im) or Na ₂ Mn ₃ MO ₈ (where, M = Fe, Co, Ni, Cu or Zn); NaMn ₂ O _{4 in} which the Na part of the formula is substituted with an alkaline earth metal ion; Disulfide compounds; Fe ₂ (MoO ₄ ) ₃ , and the like.

Examples of the solvent for forming the anode include organic solvents such as NMP (N-methylpyrrolidone), DMF (dimethylformamide), acetone, and dimethylacetamide, and water. These solvents may be used alone or in combination of two or more Can be mixed and used. The amount of the solvent used is sufficient to dissolve and disperse the cathode active material, the binder and the conductive material in consideration of the coating thickness of the slurry and the production yield.

The conductive material is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery, and examples thereof include graphite such as natural graphite and artificial graphite; Carbon black such as acetylene black, Ketjen black, channel black, panes black, lamp black, and thermal black; Conductive fibers such as carbon fiber and metal fiber; Conductive tubes such as carbon nanotubes; Metal powders such as fluorocarbon, aluminum and nickel powder; Conductive whiskers such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used. The conductive material may be used in an amount of 1 wt% to 20 wt% based on the total weight of the positive electrode slurry.

The dispersing agent may be an aqueous dispersing agent or an organic dispersing agent such as N-methyl-2-pyrrolidone.

The anode may be prepared by a conventional method known in the art. For example, the negative electrode active material may be prepared by preparing a negative electrode active material slurry by mixing and stirring additives such as a solvent, the above-mentioned binder, and a conductive material, applying the negative electrode active material slurry to an anode current collector,

Examples of the negative electrode active material include amorphous carbon or regular carbon, and specifically carbon such as non-graphitized carbon and graphite carbon; Na _x Fe ₂ O ₃ (0 ≦ _x ≦ 1), Na _x WO ₂ (0 ≦ _x ≦ ₁ ), Sn _x Me _1-x Me _y O _z (Me: Mn, Fe, Pb, , B, P, Si, Group 1, Group 2 and Group 3 elements of the periodic table, Halogen, 0 <x <1> 1 <y> 3, 1 <z <8); Sodium metal; Sodium alloy; Silicon-based alloys; Tin alloy; _{SnO, SnO 2, PbO, PbO} 2, Pb 2 O 3, Pb 3 O 4, Sb 2 O 3, Sb 2 O 4, Sb 2 O 5, GeO, GeO 2, Bi 2 O 3, Bi 2 O 4, And Bi ₂ O ₅ ; Conductive polymers such as polyacetylene; Na-Co-Ni-based materials and the like can be used.

Examples of the solvent for forming the negative electrode include organic solvents such as NMP (N-methylpyrrolidone), DMF (dimethylformamide), acetone, and dimethylacetamide, and water. These solvents may be used alone or in combination of two or more Can be mixed and used. The amount of the solvent to be used is sufficient to dissolve and disperse the negative electrode active material, the binder and the conductive material in consideration of the coating thickness of the slurry and the production yield.

The binder may be contained in an amount of 10 wt% or less, specifically 0.1 wt% to 10 wt%, based on the total weight of the slurry for the negative electrode active material. If the content of the binder is less than 0.1 wt%, the effect of use of the binder is insufficient, which is not preferable. If the content of the binder is more than 10 wt%, the capacity of the active material may decrease due to the decrease in the relative content of the active material. It is not preferable.

The conductive material is not particularly limited as long as it has conductivity without causing chemical changes in the battery, and examples of the conductive material include graphite such as natural graphite and artificial graphite; Carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskers such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; And conductive materials such as polyphenylene derivatives. The conductive material may be used in an amount of 1 wt% to 9 wt% with respect to the total weight of the slurry for the negative electrode active material.

The negative electrode collector used in the negative electrode according to an embodiment of the present invention may have a thickness of 3 to 500 mu m. The negative electrode current collector is not particularly limited as long as it has electrical conductivity without causing a chemical change in the battery. The negative electrode current collector may be formed on the surface of copper, gold, stainless steel, aluminum, nickel, titanium, sintered carbon, Carbon, nickel, titanium, silver or the like, an aluminum-cadmium alloy, or the like can be used. In addition, fine unevenness can be formed on the surface to enhance the bonding force of the negative electrode active material, and it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

The active material slurry may contain a viscosity adjusting agent and / or a filler as necessary.

The viscosity modifier may be carboxymethylcellulose, polyacrylic acid, or the like, and the viscosity of the active material slurry may be adjusted to facilitate the production of the active material slurry and the coating of the electrode current collector by the addition.

The filler is an auxiliary component for suppressing the expansion of the electrode. The filler is not particularly limited as long as it is a fibrous material without causing any chemical change in the battery. Examples of the filler include olefin polymers such as polyethylene and polypropylene, Fibrous material.

On the other hand, as the separator, a conventional porous polymeric film conventionally used as a separator, for example, a polyolefinic polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene-butene copolymer, an ethylene-hexene copolymer and an ethylene-methacrylate copolymer Porous nonwoven fabric such as high melting point glass fiber, polyethylene terephthalate fiber or the like may be used as the nonwoven fabric, but the present invention is not limited thereto.

The sodium salt that can be used as an electrolyte for use in the present invention may be any of those conventionally used in an electrolyte for a sodium secondary battery. Examples of the anion of the sodium salt include F ^- , Cl ^- , Br ^- , I ^- , NO _{3 ^{-, N (CN) 2 -}} , BF 4 -, ClO 4 -, PF 6 -, AsF 6 -, SbF 6 -, AlCl 4 -, (CF 3) 2 PF 4 -, (CF 3) 3 PF 3 - _{, (CF 3) 4 PF 2} -, (CF 3) 5 PF -, (CF 3) 6 P -, CF 3 SO 3 -, CF 3 CF 2 SO 3 -, (CF 3 SO 2) 2 N -, ^{_{(FSO 2) 2 N -,}} CF 3 CF 2 (CF 3) 2 CO -, (CF 3 SO 2) 2 CH -, (SF 5) 3 C -, (CF 3 SO 2) 3 C -, CF 3 (CF ₂ ) ₇ SO ₃ ^- , CF ₃ CO ₂ ^- , CH ₃ CO ₂ ^- , SCN ^- and (CF ₃ CF ₂ SO ₂ ) ₂ N ^- .

Examples of the organic solvent included in the electrolytic solution include propylene carbonate (PC), ethylene carbonate (EC), ethylene carbonate (EC), and the like. ), Diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl propyl carbonate, dipropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane , Vinylene carbonate, sulfolane, gamma-butyrolactone, propylene sulfite, and tetrahydrofuran, or a mixture of two or more thereof. Specifically, ethylene carbonate and propylene carbonate, which are cyclic carbonates in the carbonate-based organic solvent, can be preferably used because they have high permittivity as a high viscosity organic solvent and dissociate the lithium salt in the electrolyte well. The cyclic carbonates include dimethyl carbonate and di Low-dielectric-constant linear carbonates such as ethyl carbonate can be mixed in an appropriate ratio to form an electrolytic solution having a high electrical conductivity.

Alternatively, the electrolytic solution stored in accordance with the present invention may further include an additive such as an overcharge inhibitor or the like contained in an ordinary electrolytic solution.

The external shape of the sodium secondary battery of the present invention is not particularly limited, but may be a cylindrical shape, a square shape, a pouch shape, a coin shape, or the like using a can.

The sodium secondary battery according to the present invention can be used not only in a battery cell used as a power source of a small device but also as a unit cell in a middle- or large-sized battery module including a plurality of battery cells.

Example

Hereinafter, the present invention will be described in more detail with reference to Examples and Experimental Examples, but the present invention is not limited by these Examples and Experimental Examples. The embodiments according to the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The embodiments of the present invention are provided to enable those skilled in the art to more fully understand the present invention.

Manufacturing example  : Manufacture of binders

&Lt; Preparation of conjugated diene binder (A1) >

45 g of 1,3-butadiene, 50 g of styrene, 3 g of acrylic acid, 2 g of hydroxyethyl acrylate, 0.4 g of NaHCO ₃ as a buffer, 0.4 g of sodium laurel sulfate and 0.5 g of dodecyl mercaptan as a molecular weight regulator After the mixture was heated to 80 ° C, potassium persulfate was added as a polymerization initiator to initiate the reaction. The reaction was carried out at 80 ° C for 6 hours to obtain butadiene latex particles (A1). The pH of the polymerized butadiene latex particles (A1) was 4.5, which was adjusted to pH 7 using sodium hydroxide. The average particle size of the particles was 150 nm.

&Lt; Preparation of conjugated diene binder (A2) >

49 g of 1,3-butadiene, 40.5 g of styrene, 5 g of methyl methacrylate, 5 g of a mixture of acrylic acid and itaconic acid in a weight ratio of 50:50, 0.5 g of ethylene glycol dimethacrylate as a crosslinking agent, 0.4 g of sodium royl sulfate as an emulsifier And the temperature was raised to 75 캜. Then, potassium persulfate was added as a polymerization initiator to initiate the reaction, and the reaction was carried out at 75 캜 for 7 hours to obtain butadiene latex particles (A2). This was adjusted to pH 7 using sodium hydroxide and the average particle size of the particles was 150 nm.

&Lt; Preparation of Acrylic Copolymer Binder (B1) >

70 g of butyl acrylate, 20 g of styrene, 5 g of acrylic acid, 5 g of hydroxybutyl acrylate, 0.4 g of NaHCO ₃ as a buffer, and 0.4 g of sodium roryl sulfate as an emulsifier were mixed and heated to 75 캜. Polysulfate was added to initiate polymerization. The reaction was carried out at a temperature of 75 캜 for about 6 hours to prepare acrylic copolymer latex particles (B1). The pH of the latex particles was 3.5, which was adjusted to pH 7 using sodium hydroxide. The average particle size of the particles was 460 nm.

&Lt; Preparation of Acrylic Copolymer Binder (B2)

55.5 g of butyl acrylate, 35 g of styrene, 7.5 g of a 50:50 weight ratio mixture of acrylic acid and itaconic acid, 2 g of glycidyl methacrylate as a crosslinking agent, 50 g of sodium lauryl sulfate as an emulsifier, and 50 g of a polyoxyethylene lauryl ether : 50 weight ratio, and 0.4 g of NaHCO ₃ as a buffer were mixed and heated to 75 캜. Then, ammonium persulfate was added as a polymerization initiator to initiate polymerization. And the mixture was reacted for about 5 hours while maintaining the temperature at 75 캜 to prepare acrylic copolymer latex particles (B2). This was adjusted to pH 7 using sodium hydroxide and the average particle diameter of the particles was 460 nm.

Example 1: Binder composition

The binder composition was prepared by mixing the butadiene latex particles (A1), the acrylic copolymer latex particles (B1) and the acrylic copolymer latex particles (B2) prepared in the above Production Example at 80:10:10 (weight ratio).

Example 2: Binder composition

The binder composition was prepared by mixing butadiene latex particles (A1), butadiene latex particles (A2) and acrylic copolymer latex particles (B1) prepared in the above Preparation Example at a weight ratio of 40:40:20.

Example 3: Binder composition

The butadiene latex particles (A1), the butadiene latex particles (A2), the acrylic copolymer latex particles (B1) and the acrylic copolymer latex particles (B2) prepared in the above Production Examples were mixed at a weight ratio of 70:10:10:10 Were mixed to prepare a binder composition.

Example 4: Binder composition

The butadiene latex particles (A1), the butadiene latex particles (A2), the acrylic copolymer latex particles (B1) and the acrylic copolymer latex particles (B2) prepared in the above production examples were mixed at a weight ratio of 40:40:10:10 Were mixed to prepare a binder composition.

Example 5: Binder composition

The butadiene latex particles (A1), the butadiene latex particles (A2), the acrylic copolymer latex particles (B1) and the acrylic copolymer latex particles (B2) prepared in the above Production Examples were mixed at a weight ratio of 50: 40: 5: Were mixed to prepare a binder composition.

Agglomeration phenomenon did not occur in the binder compositions prepared in Examples 1 to 5 by analyzing the sizes of the latex particles using a submicron particle sizer (nicomp TM 380) Respectively.

Example 6: Preparation of negative electrode

The negative electrode was prepared by mixing 96.0 g of natural graphite (particle diameter 20 탆, hardness 7 kg / mm ² ), 0.5 g of conductive material, 2.5 g of the binder composition for a sodium secondary battery prepared in Example 1 and 2.5 g of carboxymethylcellulose And a total solids content of 50% by weight to prepare a slurry for a negative electrode. The slurry was coated on one surface of a copper foil with a thickness of 120 탆 to form an active material layer, followed by drying, and then the density of the active material layer 1.85 g / cc to prepare a negative electrode.

Examples 7 to 10: Preparation of negative electrode

Except that the binder composition for the sodium secondary battery prepared in Example 1 was replaced by 2.5 g of the binder composition for the sodium secondary battery prepared in Examples 2 to 5, respectively, to prepare the negative electrode Respectively.

Example 11: Preparation of sodium secondary battery

&Lt; Preparation of positive electrode &

96 g of NaCoO ₂ as a positive electrode active material, ₂ g of a conductive carbon black and 2 g of polyvinylidene fluoride (PVdF) as a binder were added to a solvent N-methyl-2-pyrrolidone (NMP) After the slurry for the anode mixture was prepared, the slurry of the anode mixture was coated on the aluminum (Al) thin film and dried to prepare a positive electrode, followed by a roll press to prepare a positive electrode.

&Lt; Production of lithium secondary battery >

The anode prepared in Example 6 was punched to have a surface area of 13.33 cm &lt; ^{2 &} gt ;, and the anode produced in the production of the anode was punched to have a surface area of 12.60 cm &lt; ² &gt; A tap was attached to the upper part of the positive electrode and the negative electrode, and the resultant was placed on the aluminum pouch with a separator made of a polyolefin microporous membrane between the negative electrode and the positive electrode. Then, 500 mg of the electrolytic solution was injected into the pouch. The electrolytic solution was prepared by dissolving NaPF ₆ electrolyte at a concentration of 1 M by using a mixed solvent of EC (ethylene carbonate): DEC (diethyl carbonate): EMC (ethyl methyl carbonate) = 4: 3: 3 (volume ratio)

Thereafter, the pouches were sealed using a vacuum packing machine, kept at room temperature for 12 hours, charged at a constant current of about 0.05 C, and maintained in a voltage of about 1/6 of the current . At this time, since the gas is generated inside the cell, degassing and resealing are performed to complete the sodium secondary battery.

Examples 12 to 15: Preparation of sodium secondary battery

A sodium secondary battery was completed in the same manner as in Example 11, except that the cathodes prepared in Example 6 were replaced with the cathodes prepared in Examples 7 to 10, respectively.

Comparative Example 1: Preparation of a binder composition

The binder composition was prepared by mixing butadiene latex particles (A1) and acrylic copolymer latex particles (B1) prepared in the above Preparation Example at a ratio of 50:50 (weight ratio).

Comparative Example 2: Preparation of a binder composition

The binder composition was prepared by mixing butadiene latex particles (A1) and acrylic copolymer latex particles (B1) prepared in the above Production Example at 70:30 (weight ratio).

Comparative Example 3: Preparation of a binder composition

The binder composition was prepared by mixing butadiene latex particles (A1) and acrylic copolymer latex particles (B2) prepared in the above Production Example at a ratio of 30:70 (weight ratio).

Comparative Example 4: Preparation of a binder composition

The binder composition was prepared by mixing butadiene latex particles (A2) and acrylic copolymer latex particles (B1) prepared in the above Production Example at a ratio of 90:10 (weight ratio).

Comparative Example 5: Preparation of a binder composition

The binder composition was prepared by mixing the butadiene latex particles (A2) and the acrylic copolymer latex particles (B2) prepared in the above Production Example at a ratio of 10:90 (weight ratio).

Comparative Example 6: Preparation of a binder composition

Only the butadiene latex particles (A2) prepared in the above Production Example were used.

Comparative Example  7: Preparation of the binder composition

Only the acrylic copolymer latex particles (B1) prepared in the above Production Example were used.

Comparative Examples 8 to 14: Preparation of negative electrode

Except that 2.5 g of the binder composition for each of the sodium secondary batteries prepared in Comparative Examples 1 to 7 was used in place of the binder composition for the sodium secondary battery prepared in Example 1, .

Comparative Examples 15 to 21: Preparation of sodium secondary battery

A sodium secondary battery was completed in the same manner as in Example 11, except that the cathodes prepared in Example 6 were replaced with the cathodes prepared in Comparative Examples 8 to 14, respectively.

Experimental Example 1: Measurement of adhesion force

The negative electrodes prepared in Examples 6 to 10 and Comparative Examples 8 to 14 were cut to a predetermined size and fixed to a slide glass. The current collector was peeled off and the 180 ° peel strength was measured. The results are shown in Table 1 below. The evaluation was made by measuring the peel strengths of 5 or more and calculating the average value.

Adhesion (gf / cm) Example 6 102.2 Example 7 105.5 Example 8 103.0 Example 9 106.9 Example 10 112.1 Comparative Example 8 65.9 Comparative Example 9 87.2 Comparative Example 10 60.3 Comparative Example 11 90.5 Comparative Example 12 57.0 Comparative Example 13 90.8 Comparative Example 14 57.2

As can be seen from the above Table 1, the negative electrode prepared in Examples 6 to 10 contains the conjugated diene binder (A) and the acrylic copolymer binder (B) together, and at least one of the binders It was confirmed that a total of three or more kinds of binders were included and exhibited remarkably excellent adhesion.

Experimental Example 2: Electrochemical Experiment

Discharge tests were carried out twice at a charging / discharging current density of 0.2 C, a charging end voltage of 4.5 V and a discharge end voltage of 2.5 V at the charge / discharge current density of the sodium secondary batteries manufactured in Examples 11 to 15 and Comparative Examples 15 to 21 . Subsequently, charge and discharge tests were performed 48 times at a charging / discharging current density of 1 C, a charging end voltage of 4.5 V, and a discharge end voltage of 2.5 V. All charging was performed at a constant current / constant voltage, and the end current of the constant voltage charging was 0.05 C. After completing a total of 50 cycles, the charge / discharge efficiency (initial efficiency and 50 cycle capacity retention rate) of the first cycle was obtained. The capacity retention rate (50 times / once) was calculated by dividing the charge capacity of 50 cycles by the charge capacity of the first cycle. The results are shown in Table 2 below.

Initial efficiency (%) 50 cycle capacity retention rate (%) Example 11 99.8 97.2 Example 12 99.7 97.5 Example 13 99.9 98.0 Example 14 99.8 97.3 Example 15 99.8 98.2 Comparative Example 15 99.7 93.0 Comparative Example 16 99.2 96.8 Comparative Example 17 99.7 92.7 Comparative Example 18 99.8 95.5 Comparative Example 19 99.6 91.5 Comparative Example 20 99.3 94.9 Comparative Example 21 99.8 90.1

As can be seen from the above Table 2, the sodium secondary batteries according to Examples 11 to 15 exhibited excellent capacity retention ratios as compared with the sodium secondary batteries of Comparative Examples 15 to 21, thereby improving the adhesion between the active material and the electrode (A) and the acrylic copolymer binder (B) according to the present invention, while at least one of the binders includes two or more kinds of binders It was confirmed that the electrode for a secondary battery comprising the binder composition for a secondary battery exhibits excellent capacity retention.

Experimental Example 3: Measurement of thickness change rate

After measuring the thickness of the sodium secondary batteries manufactured in Examples 11 to 15 and Comparative Examples 15 to 21, the charge and discharge current density was set to 0.2 C, the charging end voltage was set to 4.5 V, the discharge end voltage was set to 2.5 V, The test was performed twice. Subsequently, a charge / discharge test was performed 298 times at a charging / discharging current density of 1 C, a charging end voltage of 4.5 V, and a discharge end voltage of 2.5 V.

All charging was performed at a constant current / constant voltage, and the end current of the constant voltage charging was 0.05 C. After a total of 300 cycles were tested, the cell thickness was measured to calculate the rate of cell thickness change. The results are shown in Table 3 below.

Experimental thickness (㎛) The thickness after the experiment (탆) Thickness increase (%) Example 11 80.5 90.2 12.0 Example 12 81.7 91.0 11.4 Example 13 80.9 89.9 11.1 Example 14 81.1 92.1 13.6 Example 15 80.8 90.2 11.6 Comparative Example 15 80.4 100.7 25.2 Comparative Example 16 81.2 95.2 17.2 Comparative Example 17 79.9 94.2 17.9 Comparative Example 18 80.4 92.1 14.5 Comparative Example 19 80.6 110.8 37.5 Comparative Example 20 80.3 92.2 14.8 Comparative Example 21 80.8 118.2 46.3

As can be seen from the above Table 3, the sodium secondary batteries according to Examples 11 to 15 exhibited a lower rate of change in thickness than the sodium secondary batteries of Comparative Examples 16 to 21, whereby the sodium secondary battery according to Examples 11 to 15 Since the secondary battery electrode included in the battery contains the binder composition according to each of Examples 1 to 5, it is confirmed that the change in thickness of the secondary battery can be suppressed by improving the adhesion between the active material and the electrode, I could.

Claims (18)

(B) a binder (A) and an acrylic copolymer binder together, wherein the binder (A)
Wherein one or both of the conjugated diene binder (A) and the acrylic copolymer binder (B) comprises two or more different kinds of binders.
The method according to claim 1,
Wherein the conjugated diene binder (A) and the acrylic copolymer binder (B) are present in independent phases.
The method according to claim 1,
Wherein the two or more kinds of binders are present in independent phases, Binder composition for secondary battery.
The method according to claim 1,
Wherein the binder composition for a secondary battery comprises 1 to 30 parts by weight of the acrylic copolymer binder (B) based on 100 parts by weight of the total solid content of the binder composition for a secondary battery.
The method according to claim 1,
The conjugated diene binder (A) is selected from the group consisting of (A) a conjugated diene monomer or a conjugated diene polymer, (B) an acrylate monomer, a vinyl monomer, a (meth) acrylamide monomer and a nitrile monomer And at least one monomer selected from the group consisting of unsaturated monocarboxylic acid monomers (C).
6. The method of claim 5,
The conjugated diene binder (A) preferably comprises 10 to 97.9 parts by weight of the component (A), 1 to 60 parts by weight of the component (B), and 1 to 60 parts by weight of the component (A) based on 100 parts by weight of the total weight of the conjugated diene binder ) Is contained in an amount of 1 to 20 parts by weight.
6. The method of claim 5,
Wherein the conjugated diene-based monomer is 1,3-butadiene, isoprene, chloroprene,
The conjugated diene polymer may be a polymer of two or more kinds of monomers selected from the group consisting of 1,3-butadiene, isoprene, chloroprene, and pyridene, a styrene-butadiene copolymer, an acrylonitrile-butadiene copolymer, Which is at least one member selected from the group consisting of a copolymer, an acrylate-butadiene rubber, an acrylonitrile-butadiene-styrene rubber, an ethylene-propylene-diene polymer and a partially hydrogenated, epoxidized or brominated polymer. Binder composition.
The method according to claim 1,
The acrylic copolymer binder (B) is a copolymer obtained by copolymerizing (1) a monomer selected from the group consisting of (meth) acrylate monomers, (b) acrylate monomers, vinyl monomers, (meth) acrylamide monomers and nitrile monomers A monomer of at least one kind selected from the group consisting of (meth) acrylic acid monomers, and (C) unsaturated monocarboxylic acid monomers.
9. The method of claim 8,
Wherein the acrylic copolymer binder (B) is used in an amount of 10 to 97.9 parts by weight based on 100 parts by weight of the total amount of the acrylic copolymer binder (B), 1 to 60 parts by weight of the copolymer (B) ) Is contained in an amount of 1 to 20 parts by weight.
9. The method of claim 8,
The (meth) acrylic acid ester monomer may be at least one monomer selected from the group consisting of methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, n-amyl acrylate, isoamyl acrylate, n- Ethylhexyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl Methacrylate, n-amyl methacrylate, isoamyl methacrylate, n-hexyl methacrylate, n-ethylhexyl methacrylate, 2-ethylhexyl methacrylate, hydroxyethyl methacrylate, Propyl methacrylate, and the like.
9. The method according to claim 5 or 8,
The acrylate monomer may be at least one selected from the group consisting of methacryloxyethyl ethylene urea,? -Carboxyethyl acrylate, aliphatic monoacrylate, dipropylene diacrylate, ditrimethylpropane tetraacrylate, hydroxyethyl acrylate, dipentaerythritol Acrylate, stearyl methacrylate, lauryl methacrylate, cetyl methacrylate, stearyl methacrylate, stearyl methacrylate, stearyl methacrylate, stearyl methacrylate, Wherein the binder resin is at least one selected from the group consisting of polyvinyl alcohol and polyvinyl alcohol.
9. The method according to claim 5 or 8,
Wherein the vinyl-based monomer is at least one selected from the group consisting of styrene,? -Methylstyrene,? -Methylstyrene, pt-butylstyrene, and divinylbenzene.
9. The method according to claim 5 or 8,
The (meth) acrylamide-based monomer may be at least one selected from the group consisting of acrylamide, n-methylol acrylamide, n-butoxymethylacrylamide, methacrylamide, n-methylol methacrylamide and n-butoxymethylmethacrylamide Wherein the binder resin is at least one selected from the group consisting of a binder resin and a binder resin.
9. The method according to claim 5 or 8,
Wherein the nitrile monomer is an alkenyl cyanide.
15. The method of claim 14,
Wherein the alkenyl cyanide is at least one selected from the group consisting of acrylonitrile, methacrylonitrile, and allyl cyanide.
9. The method according to claim 5 or 8,
Wherein the unsaturated monocarboxylic acid monomer is at least one member selected from the group consisting of maleic acid, fumaric acid, methacrylic acid, acrylic acid, glutaric acid, itaconic acid, tetrahydrophthalic acid, chorotonic acid, isocrotonic acid and nadic acid A binder composition for a battery.
An electrode for a secondary battery comprising the binder composition for a secondary battery according to claim 1.
A sodium secondary battery comprising the electrode for a secondary battery according to claim 17.