KR20180085512A - Binder - Google Patents

Abstract

The present invention relates to a binder and a use thereof. More specifically, provided are a binder and a user thereof. To this end, uniform dispersion of a conductive material and formation of a secondary structure are induced at the time of forming an electrode for secondary batteries, particularly lithium-sulfur secondary batteries. In addition, the binder shows low solubility for electrolytes and high adsorption to active materials, and also suppresses elution of the active materials, thereby improving cycle properties of the secondary batteries. In addition, it is also possible to prevent reduction in capacity due to sublimation of the active material such as sulfur while improving processability by lowering a drying temperature of the electrode during a manufacturing process.

Description

Binder {BINDER}

The present application relates to a binder, particularly a binder for a positive electrode active material of a lithium-sulfur secondary battery, a production method thereof, an active material including the above, an electrode, and a secondary battery.

As the application area of a secondary battery typified by a lithium ion secondary battery extends to a vehicle such as an electric vehicle or an energy storage device, it is further demanded to realize an energy storage density with respect to a relatively low weight. A lithium-sulfur secondary battery is known as a next-generation secondary battery technology capable of realizing a high energy density, and is attracting attention due to its high commercialization potential.

The lithium-sulfur secondary battery is a battery system using sulfur as a cathode active material and lithium metal as a cathode active material. During the discharge of the secondary battery, sulfur in the anode is reduced by receiving electrons, and lithium in the cathode is ionized while being oxidized. During the reduction reaction of sulfur, a sulfur-sulfur bond (S-S) accepts electrons and is converted into a sulfur anion form. In the oxidation reaction of lithium, lithium metal is changed into lithium ion while releasing electrons, and lithium ion is transferred to the anode through the electrolyte to form a salt with sulfur anion. The sulfur before discharge has a cyclic S8 structure and is converted to lithium polysulfide by a reduction reaction. When the lithium polysulfide is completely reduced, lithium sulfide (Li 2 S) is produced. The theoretical energy density due to the electrochemical reaction is about 2500 Wh / Kg, which is significantly higher than that of conventional secondary batteries. The structure and manufacturing process of the battery are similar to those of existing secondary batteries, There are advantages.

However, there is also a problem to be solved such as stabilization of lithium metal used as a cathode, low conductivity of an anode, and sublimation of sulfur at the time of electrode production. In particular, the degradation of the cycle characteristics due to the loss of active sulfur generated by the reduction and migration of lithium polysulfide produced in the zeolite to the surface of the lithium metal upon charging is necessarily overcome for the commercialization of the lithium-sulfur secondary battery It's a problem.

INDUSTRIAL APPLICABILITY The present application aims at providing a secondary battery, particularly a lithium-sulfur secondary battery, which induces uniform dispersion of a conductive material and formation of a secondary structure at the time of forming an electrode, exhibits high adsorption power for an active material and low solubility for an electrolyte, The present invention provides a binder capable of improving the cycle characteristics of a secondary battery by suppressing elution and capable of preventing a decrease in capacity due to sublimation of active materials such as sulfur while improving the processability by lowering the drying temperature of the electrode during the manufacturing process, .

The present application relates to a binder, particularly a binder for an electrode active material of a secondary battery. The secondary battery is exemplified by a lithium-sulfur secondary battery, and the binder may be a binder for the cathode active material of the secondary battery.

The binder may comprise an acrylic polymer. The term acrylic polymer in the present application means a polymer containing at least 30% by weight of polymerized units of an acrylic monomer. The polymerization unit of the acrylic monomer may include at least 35% by weight, at least 40% by weight, or at least 45% by weight based on the weight of the acrylic polymer. In another embodiment, the proportion of polymerized units of the acrylic monomers may range from about 100 percent by weight to about 95 percent by weight, from about 90 percent by weight to about 85 percent by weight, from about 80 percent by weight to about 75 percent by weight, from about 70 percent by weight to about 65 percent by weight, % ≪ / RTI >

In this specification, the term "polymerization unit of the monomer" means a state in which the monomer undergoes a polymerization reaction to form a skeleton such as a main chain or side chain of the polymer.

The term acrylic monomer in the present application refers to acrylic acid, methacrylic acid or a derivative thereof, and examples of the derivatives of acrylic acid or methacrylic acid include various methacrylates or acrylate compounds, but the present invention is not limited thereto .

In the present application, the acrylic polymer exhibits high solubility in water and low solubility in an electrolytic solution, particularly an ether-based electrolytic solution. The solubility of B in A refers to the maximum amount (in g) of solute that can be dissolved in 100 g of solvent. For example, the solubility of B in A is the maximum amount of B that can be dissolved in A 100 g g). Unless specifically stated otherwise herein, physical properties such as solubility, which are affected by temperature, are values at room temperature. The term ambient temperature means a natural, unheated or non-warmed temperature, for example, any temperature within the range of about 10 ° C to 30 ° C, about 25 ° C or about 23 ° C.

In one example, the acrylic polymer may have a room temperature solubility in water of 20 or more. In another example, the solubility may be less than about 100, less than about 90, less than about 80, less than about 70, less than about 60, less than about 50, less than about 45, less than about 40, less than about 35, The acrylic polymer may have a room temperature solubility of about 1 or less in a mixed solution of ether-based electrolytic solution, for example, 1: 1 by volume of 1,3-dioxolane and dimethoxyethane. The solubility in the electrolytic solution may be, for example, about 0.9 or less, about 0.8 or less, or about 0.75 or less. The lower limit of the solubility in the electrolytic solution is not particularly limited, and may be, for example, about 0.1 or more, about 0.2 or more, or about 0.25 or more.

When the solubility described above is shown, the productivity of the battery can be improved by keeping the electrode drying temperature low while maintaining high capacity characteristics while suppressing the elution of the active material into the electrolytic solution when applied to a battery.

In order to exhibit such solubility characteristics, the acrylic polymer may include polymerized units of a hydrophilic monomer. The term hydrophilic monomer as used herein means a compound which can be applied to the polymerization reaction and which has a room temperature solubility in water of 20 or more. In another example, the solubility may be less than about 100, less than about 90, less than about 80, less than about 70, less than about 60, less than about 50, less than about 45, less than about 40, less than about 35,

In order to ensure proper properties, the polymerized units of the hydrophilic monomers may be contained in the acrylic polymer in an amount of 30% or more by weight. The polymerization unit of the hydrophilic monomer may be contained in the acrylic polymer in an amount of 35 wt% or more, 40 wt% or more, or 45 wt% or more based on the weight of the acrylic polymer. In another embodiment, the ratio of the polymerized units of the hydrophilic monomers may range from about 100% by weight to about 95% by weight, from about 90% by weight to about 85% by weight, from about 80% by weight to about 75% by weight, % ≪ / RTI >

Hereinafter, the hydrophilic monomer may be referred to as a first monomer. As the first monomer, various kinds of polar monomers may be used.

In one example, as the first monomer, a monomer having an alkylene oxide chain represented by the following general formula (1) may be exemplified.

[Chemical Formula 1]

In Formula (1), Q is hydrogen or an alkyl group, U is an alkylene group, Z is hydrogen, an alkyl group or an aryl group, and m is an arbitrary number, for example,

When two or more [-U-O-] units are present in the formula (1), the number of carbon atoms of the U in the unit may be the same or different.

M in formula (1) may be, for example, 3 or more, 4 or more, 5 or more, 6 or more, 7 or more, 8 or more or 8.5 or more. M is not more than 120, less than 115, less than 110, less than 105, less than 100, less than 95, less than 90, less than 85, less than 80, less than 75, less than 70, less than 65, less than 60, less than 55, less than 50, 45 or less, 40 or less, 35 or less, 30 or less, 25 or less, 20 or less, 15 or less, or 10 or less. Within this range, the polymerization efficiency and the crystallinity of the polymer can be maintained in an appropriate range during the production of the polymer, so that the polymer exhibits the desired solubility characteristics.

As used herein, the term alkyl group may mean an alkyl group having 1 to 20 carbon atoms, 1 to 16 carbon atoms, 1 to 12 carbon atoms, 1 to 8 carbon atoms or 1 to 4 carbon atoms, unless otherwise specified. The alkyl group may be straight-chain, branched or cyclic. The alkyl group may be substituted by one or more substituents, or may be unsubstituted.

As used herein, unless otherwise specified, the term "alkylene group" or "alkylidene group" means an alkylene group or an alkylidene group having 1 to 20 carbon atoms, 1 to 16 carbon atoms, 1 to 12 carbon atoms, 1 to 8 carbon atoms, have. The alkylene group or alkylidene group may be linear, branched or cyclic. The alkylene or alkylidene group may be optionally substituted by one or more substituents.

In another embodiment, Q in formula (1) may be an alkyl group, for example, an alkyl group having 1 to 8 carbon atoms or 1 to 4 carbon atoms. When Q is an alkyl group, for example, it may be advantageous that the protective film is easily removed without residue or unevenness on the adherend when the pressure-sensitive adhesive composition is applied to a protective film or the like.

As used herein, the term aryl group, unless otherwise specified, includes a benzene ring, or two or more benzene rings may be connected, or two or more benzene rings may share one or more carbon atoms, May refer to a monovalent residue derived from a compound or a derivative thereof having a structure represented by the following formula: The aryl group may be, for example, an aryl group having 6 to 25 carbon atoms, 6 to 22 carbon atoms, 6 to 16 carbon atoms, or 6 to 13 carbon atoms. Examples of the aryl group include a phenyl group, a phenylethyl group, a phenylpropyl group, a benzyl group, a tolyl group, a xylyl group and a naphthyl group.

Examples of the substituent which may be substituted in the specific functional group, for example, the alkyl group, the alkylidene group or the alkylene group in the present specification include an alkyl group, an alkoxy group, an alkenyl group, an epoxy group, a cyano group, a carboxyl group, An acryloyloxy group, a methacryloyloxy group or an aryl group, but the present invention is not limited thereto.

Examples of the compound represented by the formula (1) include alkoxy dialkylene glycol (meth) acrylic acid ester, alkoxy trialkylene glycol (meth) acrylic acid ester, alkoxy tetraalkylene glycol (meth) acrylic acid ester, aryloxy dialkylene glycol (Meth) acrylic acid esters, aryloxytetraalkylene glycol (meth) acrylic acid esters, and polyalkylene glycol monoalkyl ether (meth) acrylic acid esters. But is not limited to.

Examples of the alkoxy include alkoxy having 1 to 20 carbon atoms, 1 to 16 carbon atoms, 1 to 12 carbon atoms and 1 to 4 carbon atoms, and specifically, a methoxy group or an ethoxy group can be exemplified .

Examples of the alkylene glycol include alkylene glycols having 1 to 20 carbon atoms, 1 to 16 carbon atoms, 1 to 12 carbon atoms and 1 to 4 carbon atoms, and examples thereof include ethylene glycol and propylene glycol In the above, aryloxy is exemplified by aryloxy having 6 to 24 carbon atoms or 6 to 12 carbon atoms such as phenoxy.

The polymerization unit of the monomer of Formula 1 may be contained in the acrylic polymer in an amount of 30% or more by weight. The polymerization unit of the hydrophilic monomer may be contained in the acrylic polymer in an amount of 35 wt% or more, 40 wt% or more, or 45 wt% or more based on the weight of the acrylic polymer. In another embodiment, the ratio of the polymerized units of the hydrophilic monomers may range from about 100% by weight to about 95% by weight, from about 90% by weight to about 85% by weight, from about 80% by weight to about 75% by weight, % ≪ / RTI >

As the hydrophilic monomer, various types other than the monomer of the above formula (1) may be applied.

Examples of hydrophilic monomers that can be applied include, for example, nitrogen-containing monomers, hydroxyl group-containing monomers or carboxyl group-containing monomers.

As the nitrogen-containing monomer, amide group-containing monomers, amino group-containing monomers, imide group-containing monomers or cyano group-containing monomers and the like can be used. Examples of the amide-containing monomer include amides such as (meth) acrylamide or N, N-dimethyl (meth) acrylamide, N, N-diethyl (meth) acrylamide, N- (Meth) acrylamide, N, N'-methylenebis (meth) acrylamide, N, N-dimethylaminopropyl (meth) acrylamide, N-vinylpyrrolidone, N-vinylcaprolactam or (meth) acryloylmorpholine. Examples of the amino group-containing monomer include 2-aminoethyl (meth) acrylate (Meth) acrylate, N, N-dimethylaminoethyl (meth) acrylate or N, N-dimethylaminopropyl (meth) acrylate, As the -containing monomer, N-isopropyl maleate Imide, N-cyclohexylmaleimide or itaconimide, and examples of the cyano group-containing monomer include acrylonitrile and methacrylonitrile, but are not limited thereto no.

Examples of the hydroxyl group-containing monomer include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 6-hydroxyhexyl (Meth) acrylate, 2-hydroxyethyl (meth) acrylate or 2-hydroxypropyleneglycol (meth) acrylate, and hydroxypolyethylene glycol (meth) Hydroxyalkyl (meth) acrylate or hydroxypolyalkylene glycol (meth) acrylate such as hydroxypolypropylene glycol (meth) acrylate and the like, and examples of the carboxyl group-containing monomer include (meth) acrylic acid, 2 (Meth) acryloyloxyacetic acid, 3- (meth) acryloyloxypropyl acid, 4- (meth) acryloyloxybutyric acid, acrylic acid doublet, itaconic acid, maleic acid and maleic anhydride This may be illustrated, but is not limited to this.

The polymerization unit of the hydrophilic monomer other than the monomer of the formula (1) may be, for example, 60 parts by weight or less, 50 parts by weight or less, 40 parts by weight or 35 parts by weight or less based on 100 parts by weight of the monomer unit , And the weight ratio may be 0 parts by weight or more, 0 parts by weight or more, 5 parts by weight or more, 10 parts by weight or more, or 15 parts by weight or more.

The acrylic polymer may further include a polymerization unit of a hydrophobic monomer when necessary for the above-mentioned solubility adjustment. The hydrophobic monomer is a monomer having a solubility at room temperature in water of 15 or less. The solubility may be about 14 or less, about 13 or less, about 12 or less, or about 11.5 or less in another example. The lower limit of the solubility is not particularly limited and may be, for example, zero, more than 0, about 5 or more, or about 7 or more.

Examples of such hydrophobic monomers include monomers such as methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, (meth) acrylate, isobutyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, 2-ethylbutyl (Meth) acrylate, dodecyl (meth) acrylate, n-octyl (meth) acrylate, isooctyl (meth) acrylate, isononyl (Meth) acrylate having an alkyl group having 1 to 20 carbon atoms such as octyl (meth) acrylate, decyl (meth) acrylate, tetradecyl (meth) acrylate, octadecyl (meth) And the like, but the present invention is not limited thereto.

The polymerization unit of the second monomer may be present in the acrylic polymer in an amount of up to about 100 parts by weight, up to about 90 parts by weight, up to about 80 parts by weight, up to about 70 parts by weight, up to about 60 parts by weight, 50 parts by weight or less, about 40 parts by weight or less, about 30 parts by weight or less, or about 25 parts by weight or less. The lower limit of the proportion of the polymerized units of the second monomer is not particularly limited, and the polymerized units may be, for example, at least 0 part by weight, at least 5 parts by weight, at least 10 parts by weight, or at least about 15 parts by weight .

The acrylic polymer may also contain, as polymerized units of the third monomer, at least one monomer selected from the group consisting of (meth) acrylamide, N-alkyl (meth) acrylamide, N, N-dialkyl (meth) acrylamide, Includes polymerized units of one or more monomers selected from the group consisting of vinylpyrrolidone, N-alkenylcaprolactone, N-alkenylcaprolactone, styrene, 2-alkenylpyridine, 4-alkenylpyridine and alkenyl acetate .

It is possible to increase the degree of freedom in adjusting the ratio of the hydrophilic monomer or the hydrophilic monomer to the hydrophobic monomer in the acrylic polymer through the polymerization unit of the third monomer and improve the interaction with the water and the active material, The elution of the active material can be suppressed.

Examples of the alkyl group in the kind of the third monomer include alkyl groups having 1 to 20 carbon atoms, 1 to 16 carbon atoms, 1 to 12 carbon atoms, 1 to 8 carbon atoms and 1 to 4 carbon atoms, , Branched or cyclic, substituted by one or more substituents, or may be unsubstituted. As the alkyl group, a methyl group can be exemplified.

Examples of the alkenyl group of the third monomer include an alkenyl group having 2 to 20 carbon atoms, 2 to 16 carbon atoms, 2 to 12 carbon atoms, 2 to 8 carbon atoms, or 2 to 4 carbon atoms, , Straight-chain, branched or cyclic, substituted by one or more substituents, or unsubstituted. As such an alkenyl group, a vinyl group can be exemplified.

The polymerization unit of the third monomer may be contained in the acrylic polymer in a ratio of about 1 to 300 parts by weight based on 100 parts by weight of the first monomer. In another example, the ratio may be about 290 parts by weight or less, about 280 parts by weight or less, about 270 parts by weight or less, about 260 parts by weight or less, about 250 parts by weight or less, about 240 parts by weight or less, about 230 parts by weight or less, Up to about 220 parts by weight, up to about 210 parts by weight, up to about 200 parts by weight, up to about 190 parts by weight, up to about 180 parts by weight, up to about 170 parts by weight, up to about 160 parts by weight, up to about 150 parts by weight, About 130 parts by weight or less, about 120 parts by weight or less, or about 110 parts by weight or less. In another example, the ratio may be at least about 5 parts by weight, at least about 10 parts by weight, at least about 20 parts by weight, at least about 30 parts by weight, at least about 40 parts by weight, or at least about 50 parts by weight.

The acrylic polymer may contain polymerized units of known monomers, if necessary, in addition to the respective monomers mentioned above.

The acrylic polymer may have a glass transition temperature in the range of -80 占 폚 to 50 占 폚 or -80 占 폚 to 20 占 폚. In the present application, the glass transition temperature is a theoretical value obtained from the monomer composition of the polymer through the so-called Fox equation. Adequate adhesion with the current collector can be ensured in the range of the glass transition temperature, and the electrode physical adsorption ability and resistance to electrolyte can be advantageously secured.

The polymer may have a weight average molecular weight (Mw) in the range of 5,000 to 3,000,000. The weight average molecular weight in the present application may be, for example, a conversion value relative to standard polystyrene measured using GPC (Gel Permeation Chromatograph), and unless otherwise specified, the term molecular weight may refer to a weight average molecular weight have. The molecular weight (Mw) as described above may be useful, for example, when the polymer is applied as a binder.

The polymer may be obtained by selecting a desired monomer among the above-described monomers and then subjecting the mixture of the monomers having the desired proportions of the selected monomers to a solution polymerization, a photo polymerization, a bulk polymerization, suspension polymerization, or emulsion polymerization, for example.

In one example, the polymer can be prepared by a solution polymerization method in consideration of the advantage of securing the desired performance.

That is, the present application also relates to a method for producing a polymer, for example, a method for producing the polymer through a so-called solution polymerization method.

The production method of the present application may include a step of solution polymerization of a monomer mixture containing at least the first monomer and optionally a second and / or third monomer in a solvent.

The specific types of the first to third monomers contained in the monomer mixture are as described above, and the ratio of each monomer can also be adjusted so that the ratio between the above-mentioned polymerized units can be satisfied. The polymerization of such monomers can be carried out in the presence of an appropriate radical initiator, and the kind of the specific initiator used at this time is not particularly limited. However, since the above method corresponds to a solution polymerization method, a surfactant is not applicable. Further, unlike the so-called emulsion polymerization or dispersion polymerization in which a surfactant is applied, the polymer produced by the solution polymerization method is not formed in the form of particles, and thus the particle diameter of the polymer is about 10 nm or less.

The solution polymerization can be carried out using a suitable solvent, suitably using a solvent having a boiling point of 110 ° C or lower. The boiling point of the solvent is the boiling point at atmospheric pressure, i.e., about 1 atm. In another example, the boiling point may be at least about 50 ° C, at least about 60 ° C, at least about 70 ° C, at least about 80 ° C, or at least about 90 ° C. As such a solvent, acetone, methanol, ethanol, acetonitrile, isopropanol, methyl ethyl ketone or water may be exemplified, and water may be suitably applied.

The above production method can be carried out according to the above-mentioned matter, for example, a conventional solution polymerization method other than the use of the monomer mixture and the solvent described above.

The present application also relates to a secondary battery active layer composition comprising the binder, for example, a lithium-sulfur secondary battery active layer composition.

The composition can be prepared by mixing the components of the active layer composition, for example, an active material, a conductive material and the like together with the binder. The proportion of the binder that is the acrylic polymer in the active layer composition may be controlled according to the purpose, for example, it may be included in the composition in an amount of about 20% by weight or less. In another example, the ratio may be at least about 1 wt%, at least about 2 wt%, at least about 3 wt%, or at least about 4 wt%. In addition, the ratio may be about 15% by weight or less, or about 10% by weight or less in another example.

In the present specification, the proportion of each component in the active layer composition is based on the solid content of the composition. The term solid content refers to a state in which the active layer composition does not substantially contain a solvent, for example, the ratio of the solvent in the active layer composition is about 5 wt% or less, 4 wt% or less, 3 wt% or less, 1% by weight or less, or 0.5% by weight or less.

As the active material, known components can be applied without any particular limitation, and the singer composition can include sulfur, for example, as a positive electrode active material of a lithium-sulfur secondary battery. The sulfur may be contained as a single element or in the form of a sulfur compound, i.e., in the form of a sulfur-containing compound containing the sulfur. The kind of the specific active material that can be applied is not particularly limited, and the lithium-sulfur secondary battery used as the positive electrode active material may be applied without limitation. The active material may be contained in the composition in a proportion of about 30 to 95% by weight.

The kind of the conductive material contained in the active layer composition is also not particularly limited and known components can be used. For example, graphite such as natural graphite or artificial graphite, carbon black, acetylene black, ketjen black, channel black, , Carbon black such as lamp black and summer black, conductive fibers such as carbon fiber and metal fiber, metal powder such as carbon fluoride, aluminum and nickel powder, conductive whiskey such as zinc oxide and potassium titanate, conductive metal oxides such as titanium oxide Or a conductive material such as a polyphenylene derivative, but the present invention is not limited thereto. The conductive material may be contained in the composition in a proportion of about 2 to 70% by weight, but the ratio can be adjusted in consideration of the performance of the desired battery.

The active layer composition may further contain, in addition to the above components, a crosslinking agent, a conductive material dispersant, and other components such as a binder other than the acrylic polymer.

For example, a cross-linking agent can be applied to realize the crosslinked structure of the binder such as the acrylic polymer. Examples of the crosslinking agent that can be applied include an isocyanate crosslinking agent, an epoxy crosslinking agent, an aziridine crosslinking agent or a metal chelate crosslinking agent, But is not limited thereto. The cross-linking agent may be included in the active layer composition at a ratio of about 1% by weight or less, but is not limited thereto.

As the conductive material dispersion agent, for example, cellulose-based compounds such as carboxymethylcellulose, starch, hydroxypropylcellulose or regenerated cellulose may be applied. Such a dispersant is used to assist in dispersing and pasteting a non-polar carbon- can do. The dispersant may be contained in the active layer composition in a proportion of, for example, 20% by weight or less, but is not limited thereto.

As the binder other than the acrylic polymer that can be included in the active layer composition, a known binder may be used. For example, fluorine such as polyvinylidene fluoride (PVDF) or polytetrafluoroethylene A rubber binder such as a resin binder, a styrene-butadiene rubber, an acrylonitrile-butadiene rubber and a styrene-isoprene rubber, a polyalcohol binder, a polyolefin binder such as polyethylene or polypropylene, a polyimide binder, a polyester binder, Or a silane-based binder may be used. The binder other than the acrylic polymer may be contained in the active layer composition in a proportion of, for example, 20% by weight or less, but is not limited thereto.

The active layer composition may include a solvent. Examples of the solvent include N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, Methyltetrahydrofuran, dimethylsulfoxide, formamide, dimethylformamide, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, sulfolane, methylsulfolane, 1,3-dimethyl Imidazolidinone, a propylene carbonate derivative, a tetrahydrofuran derivative, an organic solvent such as methyl propionate or ethyl propionate, or water may be applied, and water may be suitably applied.

The present application is directed to an electrode, for example, a positive electrode for a lithium-sulfur secondary battery.

The electrode includes a current collector and an active layer formed on the current collector, and the active layer may include the above-mentioned acrylic polymer as a binder.

The active layer may be formed using the active layer composition described above. Therefore, the respective components included in the active layer and their ratios can be determined according to the contents described in the active layer composition. The method of forming the active layer on the current collector is not particularly limited and the above-mentioned composition may be applied by a known coating method such as bar coating, screen coating, doctor blade coating, dip coating, reverse roll coating, direct roll Coating, gravure coating, extrusion, or the like.

The active layer may be formed on the collector in the same manner as described above, and then, if necessary, may be formed through a known process such as drying or rolling.

Such an electrode may be, for example, in the form of a plate or a sheet.

The kind of the current collector included in the electrode is not particularly limited. For example, a general kind used for manufacturing an electrode of a battery such as a secondary battery can be applied.

As the current collector, for example, stainless steel, aluminum, nickel, titanium, sintered carbon or copper may be used. In some cases, the surface of the stainless steel or the like may be subjected to surface treatment using carbon, nickel, titanium or silver.

The surface of the current collector may have fine irregularities formed thereon. Such unevenness can help improve the adhesion with the active layer. The method of roughening the surface of the current collector of the present application is not particularly limited, and for example, a known method such as mechanical polishing, electrolytic polishing or chemical polishing may be applied.

The current collector may have various forms such as, for example, films, sheets, foils, nets, porous bodies, foams or nonwoven fabrics.

The thickness of the current collector is not particularly limited and may be set in an appropriate range in consideration of mechanical strength, productivity, capacity of the battery, and the like. In general, the current collector may have a thickness within a range of 3 占 퐉 to 500 占 퐉, 10 占 퐉 to 400 占 퐉, or 50 占 퐉 to 300 占 퐉, but is not limited thereto.

In addition, the thickness of the active layer in the electrode is not particularly limited, and can be adjusted to an appropriate range in consideration of the desired performance.

The present application also relates to a battery comprising such an electrode. The battery may be, for example, a secondary battery, specifically, a lithium-sulfur secondary battery. The specific structure of the battery and other structures other than the electrode are not particularly limited and may be selected and used variously without departing from the scope of the present invention.

For example, as the electrolyte, a non-aqueous solvent serving as a medium through which ions involved in an electrochemical reaction of a battery can move can be used. Examples of the non-aqueous solvent include carbonate, ester, ether, Ketone-based, alcohol-based, or non-magnetic solvents. Examples of the carbonate-based solvent include dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, methyl ethyl carbonate, ethylene carbonate, propylene carbonate or butylene carbonate. Include methyl acetate, ethyl acetate, n-propyl acetate, 1,1-dimethyl ethyl acetate, methyl propionate, ethyl propionate, gamma-butyrolactone, decanolide, valerolactone, Examples of the ether solvent include diethyl ether, dipropyl ether, dibutyl ether, dimethoxy methane, trimethoxy methane, dimethoxy ethane, diethoxy ethane, , Diglyme, triglyme, tetraglyme, tetrahydrofuran, 2-methyltetrahydrofuran or polyethyl And glycol dimethyl ether. As the ketone solvent, cyclohexanone and the like can be mentioned. As the alcohol solvent, ethyl alcohol, isopropyl alcohol and the like can be exemplified. As the non-magnetic solvent, , Nitriles such as acetonitrile, amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, and sulfolane. The electrolytic solution may be used alone or in combination of two or more ozone. For example, a 1: 1 (volume ratio) mixture of 1.3-dioxolane and dimethoxyethane may be used.

The present application discloses a method for producing a secondary battery, particularly a lithium-sulfur secondary battery, which induces uniform dispersion of a conductive material and formation of a secondary structure at the time of forming an electrode, exhibits high adsorption power for an active material and low solubility for an electrolyte, The present invention provides a binder capable of improving the cycle characteristics of a secondary battery by suppressing elution and capable of preventing a decrease in capacity due to sublimation of an active material such as sulfur while improving the processability by lowering the drying temperature of the electrode during the manufacturing process .

Hereinafter, the polarizing plate and the like will be described in detail by way of examples according to the present application and comparative examples that do not comply with the present application, but the scope of the present application is not limited to the following.

1. Evaluation of solubility

The solubility in the hydrophilic monomer (first monomer) was measured by mixing the monomer with water in a weight ratio of 2: 8 (hydrophilic monomer: water), stirring for 1 minute and then leaving for 5 minutes in this state, Therefore, it was evaluated. When no phase separation was observed, it was judged that the solubility of the corresponding monomer in water was 20 or more since all of the monomers were dissolved in water. All of the above procedures were carried out at room temperature (25 캜). If the presence of phase separation is judged as to whether the interface between the two substances in the solution, that is, the solute and the solvent, is visible, the phase separation is recognized when the interface is recognized, and if the interface is not recognized, there is no phase separation .

The solubility in the hydrophobic monomer (second monomer) was measured by mixing the monomer with water in a weight ratio of 1: 9 (hydrophobic monomer: water), stirring for 1 minute and then leaving for 5 minutes in that state, Respectively. When phase separation was observed, the monomer was not completely dissolved in water, and the solubility of the monomer in water was evaluated to be less than 15. The above procedure was carried out at room temperature (25 캜), and the criteria for the presence or absence of phase separation were as described above.

The solubility of the binder in water and the solubility of the binder in the electrolyte were also evaluated in a manner similar to the above. A mixture of 1,3-dioxolane and dimethoxyethane in a volume ratio of 1: 1 was applied as an electrolytic solution in the same manner as described above.

2. Measurement of conversion rate

The conversion of the resin was measured by gas chromatography after diluting the reaction product with a concentration of 20 mg / mL in a solvent and adding 5 mg / mL of toluene as a standard substance. The measurement conditions of the gas chromatography are as follows. The change in the ratio of the monomer peak size to the toluene peak area was calculated as the conversion rate.

≪ Gas Chromatographic Measurement Condition >

Analytical instrument

Gas Chromatography (PerkinElmer)

Analysis condition

Solvent: tetrahydrofuran

Initial temperature: 3 minutes at 50 ° C

Ramp: 30 ° C / min at 200 ° C

Injection volume: 0.5 μL

<Calculation of conversion rate>

Conversion rate (%) = 100 x (Aini? Afin) / Aini

Aini: relative to the peak area of the toluene peak of the monomer peak at the start of the reaction

Afin: Contrast ratio of monomer peak to toluene peak area at the end of reaction

3. Evaluation of molecular weight

The weight average molecular weight (Mw) and the molecular weight distribution (PDI) were measured by GPC (Gel Permeation Chromatography) under the following conditions, and standard polystyrene of the Agilent System was used to prepare the calibration curve.

<Measurement Conditions>

Measuring instrument: Agilent GPC (Agilent 1200 series, U.S.A.)

Column: PLGel-M, PLGel-L Serial connection

Column temperature: 40 ° C

Eluent: N, N-dimethylformaldehyde

Flow rate: 1.0 mL / min

Concentration: ~ 1 mg / mL (100 μL injection)

&Lt; Formation of positive electrode active layer &

A mixture of carbon powder and sulfur in a weight ratio of 1: 9 (carbon powder: sulfur) was wet ball milled to form a carbon-sulfur complex. The composite, conductive material (Super P) and binder were mixed in a weight ratio of 75: 20: 5 (composite: conductive material: binder) and appropriately diluted with water to prepare a positive electrode slurry. The positive electrode slurry was coated on the aluminum current collector to a thickness of about 20 탆 and dried at 80 캜 for about 12 hours to prepare a positive electrode having a loading amount of 2.0 mAh / cm 2. When N-methylpyrrolidone was used as a solvent, it was dried at 80 DEG C for 24 hours to prepare a positive electrode having the same loading amount.

Production Example 1. Preparation of acrylic polymer (A)

(Solubility in water: 20 or more) (PEOMA) (added number of moles: 9), N-vinyl-2-pyrrolidone (VP), acryloylmethyl ether methacrylate Nitrile (AN) and 2-hydroxyethyl methacrylate (HEA) (hydrophilic monomer, solubility in water of 20 or more) were charged in a weight ratio of 7.5: 4.5: 1.5: 1.5 (PEOMA: VP: AN: HEA) Water was then added as a solvent at a ratio of 400 parts by weight per 100 parts by weight of the monomer, and the inlet of the flask was sealed. The flask was immersed in an oil bath at about 60 DEG C and 1 part by weight of initiator (VA-057, Wako Chem) was added per 100 parts by weight of the monomer, and then the reaction was initiated. The reaction was conducted for about 24 hours to obtain an acrylic polymer (conversion: 99%, molecular weight (Mw): 320,000).

Production Examples 2 to 7. Acrylic Polymers (Preparation of A2 to A7)

An acrylic polymer was prepared in the same manner as in Preparation Example 1 except that the kind and ratio of the monomers were changed as shown in Table 1 below.

Preparation Example (Acrylic Polymer) One 2 3 4 5 6 7 A1 A2 A3 A4 A5 A6 A7 The first monomer


PEOMA 50 50 50 50 50 50 50 DMAEMA 10 5 HEMA 10 10 5 MAA 5 The second monomer MMA 10 Third monomer

VP 30 35 30 30 40 25 40 AN 10 10 10 10 DMAA 25 Molecular weight (Mw) (x 10 ⁴ ) 32 42 35 35 35 50 40 First monomer:
Second monomer:
Content Unit: Weight ratio
PEOMA: poly (ethylene oxide) methylether methacrylate (ethylene oxide addition mole number: 9)
DMAEMA: 2- (N, N-dimethylamino) ethyl methacrylate
HEMA: 2-hydroxyethyl methacrylate
MAA: methacrylic acid
MMA: methyl methacrylate
VP: N-vinyl-2-pyrrolidone
AN: acrylonitrile
DMAA: N, N-dimethyl acrylamide

Production Example 8. Preparation of acrylic polymer (B1)

(AN), butyl acrylate (BA) and N-methylpyrrolidone (NMP) in a weight ratio of 6: 8: 60 (AN: BA: NMP) to a 250 mL round bottom flask And the inlet of the flask was sealed. The flask was immersed in an oil bath at about 60 DEG C and about 0.02 part by weight of an initiator (azobisisobutyronitrile) was added per 100 parts by weight of the monomer, followed by initiation of the reaction . The reaction was conducted for about 48 hours to obtain an acrylic polymer (conversion: 93%, molecular weight (Mw): 220,000).

Example 1.

A positive electrode was prepared in the manner described above by applying the acrylic polymer (A1) obtained in Preparation Example 1 as a binder. Then, a known negative electrode for a lithium-sulfur secondary battery and an electrolyte (an ether-based electrolyte) were applied to fabricate a battery cell. The remaining capacity in the second cycle and the remaining capacity in the 50th cycle were calculated after driving 100 cycles between 1.5 V and 2.8 V with charging / discharging 0.1 C / 0.1 C for the prepared battery cell, The results are summarized in Table 2 below.

Examples 2-7.

A battery cell was prepared in the same manner as in Example 1 except that the acrylic polymers (A2 to A7) obtained in Production Examples 2 to 7 were used as binders, and the capacity retention rate was evaluated.

Comparative Examples 1 to 3.

(B3) of styrene-butadiene rubber and carboxymethylcellulose (Comparative Example 1), polyvinylidene fluoride (B2) (Comparative Example 2) which is a general electrode binder, the acrylic polymer (B1) (Comparative Example 3) was applied to the battery cell, and the capacity retention rate was evaluated.

Example Comparative Example One 2 3 4 5 6 7 One 2 3 bookbinder A1 A2 A3 A4 A5 A6 A7 B1 B2 B3 Binder solvent water water water water water water water NMP NMP water Solubility of electrolyte 0.7 0.7 0.3 0.4 0.7 0.3 0.4 > 10 0.1 <1 Water solubility > 20 > 20 > 20 > 20 > 20 > 20 > 20 <1 <1 <5 Capacity retention rate (%) 88 86 90 90 85 88 88 60 75 82 Binder solvent: Applicable solvent for the preparation of positive electrode slurry
Solubility of electrolyte: Solubility of binder in electrolyte
Water solubility: Solubility of the binder in water
NMP: N-methylpyrrolidone

As shown in Table 2, the examples showed high capacity retention ratios. This is because the binder of the embodiment is physically and / or chemically bonded to the components in the electrode active layer to form a stable electrode with high resistance to the electrolyte and effectively inhibit the leaching of the sulfur component. In addition, in the case of the embodiment, since water can be applied as a dispersion medium, it is confirmed that the productivity of the electrode can be improved by shortening the drying time of the electrode.

Claims (16)

And a polymerization unit of a hydrophilic monomer having a room temperature solubility in water of 20 or more and having a room temperature solubility in water of 20 or more and an ordinary temperature solubility to an ether based electrolyte of 1 or less. The binder for a secondary battery active layer according to claim 1, wherein the weight ratio of the polymerized units of the hydrophilic monomers in the acrylic polymer is 30% or more. The binder for a secondary battery active layer according to claim 1, wherein the hydrophilic monomer is a monomer represented by the following formula (1)
[Chemical Formula 1]

In Formula (1), Q is hydrogen or an alkyl group, U is an alkylene group, Z is hydrogen, an alkyl group or an aryl group, and m is an arbitrary number, for example, The binder for a secondary battery active layer according to claim 3, wherein the weight ratio of the polymerized units of the monomers of formula (1) in the acrylic polymer is 30% or more. The binder for a secondary battery active layer according to claim 1, wherein the hydrophilic monomer comprises a nitrogen-containing monomer, a hydroxyl group-containing monomer, or a carboxyl group-containing monomer. The binder for a secondary battery active layer according to claim 1, wherein the acrylic polymer further comprises a polymerized unit of a hydrophobic monomer having a room temperature solubility in water of not more than 15 at a ratio of not more than 100 parts by weight based on 100 parts by weight of the hydrophilic monomer. The method of claim 1, wherein the acrylic polymer is selected from the group consisting of (meth) acrylamide, N-alkyl (meth) acrylamide, N, N-dialkyl (meth) acrylamide, (meth) acrylonitrile, Polymerized units of at least one third monomer selected from the group consisting of N, N-alkenylcaprolactam, N-alkenylcaprolactone, styrene, 2-alkenylpyridine, 4-alkenylpyridine and alkenyl acetate, Wherein the binder further comprises 1 to 300 parts by weight based on 100 parts by weight of the polymerized units. And polymerizing the monomer mixture comprising a hydrophilic monomer having a room temperature solubility of 20 or more in water in a solvent having a boiling point of 110 캜 or lower. The method of producing a binder for a secondary battery active layer according to claim 8, wherein the solvent is water. An active layer composition comprising the binder for a secondary battery active layer according to claim 1. 11. The active layer composition according to claim 10, further comprising sulfur as an active material. 11. The active layer composition according to claim 10, further comprising a conductive material. 11. The active layer composition according to claim 10, which comprises water as a solvent. And an active layer formed on one surface of the current collector and the current collector, wherein the active layer comprises the binder according to claim 1. 15. The electrode according to claim 14, wherein the active layer further comprises sulfur as an active material. A lithium-sulfur secondary battery comprising the electrode of claim 14 as a positive electrode.