KR101995374B1 - Binder suspension composition, method for preparing electrode for secondary battery using the same, and electrode for secondary battery prepared thereby - Google Patents

Abstract

The present invention relates to a binder suspension composition having an absolute value of zeta potential of 10 mV or higher, a method for producing an electrode using the same, and an electrode for a secondary battery manufactured by the method.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a binder suspension composition, a method of manufacturing an electrode for a secondary battery using the same, and an electrode for a secondary battery manufactured by the above method. BACKGROUND OF THE INVENTION 1. Field of the Invention [0001]

The present invention relates to a binder suspension composition having excellent dispersibility, a method for producing an electrode for a secondary battery using the same, and an electrode for a secondary battery having an improved adhesive strength produced by the method.

Recently, miniaturization and weight reduction of electronic equipment have been realized and the use of portable electronic devices has become common, so researches on lithium secondary batteries used as power sources thereof have been actively conducted.

Generally, a lithium secondary battery comprises a separator disposed between an anode, a cathode, and both electrodes, and an electrolytic solution, and an electrolyte in which an appropriate amount of a lithium salt is dissolved in an organic solvent is used. The electrode of the lithium secondary battery is fabricated by coating an electrode mixture on a metal foil. The electrode mixture includes an electrode active material for intercalating and deintercalating lithium ions, a conductive material for imparting electrical conductivity, .

On the other hand, in such an electrode mixture, when the particle components of the electrode active material or the like are not uniformly dispersed in the solvent or the dispersion stability is low, aggregation or precipitation occurs.

This disadvantage is that when the electrode mixture is applied on the current collector, it is necessary to pass through a narrow space such as a filter for filtering the aggregate, the aggregate may block the space excessively and the productivity may be lowered have. In addition, when the electrode mixture is coated on the current collector, low uniformity is exhibited, resulting in a decrease in the adhesive force between the electrode mixture layer and the current collector. As a result, the electrode mixture layer may be separated from the current collector due to a change in the volume of the electrode caused by the progress of charging / discharging of the battery, or the internal resistance may be increased to decrease the charge / discharge capacity. .

The agglomeration and sedimentation between these particles are mostly caused when the absolute value of zeta potential of the electrode mixture composition is less than 10 mV, and the particle components can not exert the electrostatic repulsion at all in the electrode mixture.

Recently, a method of controlling the dispersion of particles in the electrode mixture by changing the physical parameters that can be controlled in the mixing process has been proposed. However, there are limitations in preventing precipitation and aggregation due to the density difference and achieving a desired dispersion improvement only by the control by such physical factors. For example, when the time of the mixing process is increased, sedimentation and coagulation phenomenon can be slightly retarded, but the chemical action does not change, so there is a limit to improvement of the fundamental dispersion.

Alternatively, when a dispersant is added or added, there is a disadvantage that the capacity of the battery is decreased because the active material content is reduced by the amount.

Korean Patent Publication No. 10-2013-0103946 Korean Patent Publication No. 10-2006-0112822 Korean Patent Publication No. 10-2008-0042968 Korean Patent Laid-Open Publication No. 10-2015-0067016

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above problems, and it is a first object of the present invention to provide a method for manufacturing an electrode for a secondary battery with improved uniformity and adhesion.

A second object of the present invention is to provide a binder suspension composition which can be used in the electrode production method and can improve the dispersibility among particles in an electrode mixture composition.

A third object of the present invention is to provide an electrode for a secondary battery manufactured by the above method.

It is still another object of the present invention to provide a lithium secondary battery having the secondary battery electrode.

In order to solve the above problems, in one embodiment of the present invention

Preparing a binder suspension composition having an absolute value of zeta potential of 10 mV or higher;

Dispersing the electrode active material, the conductive material and the binder suspension composition in a solvent to prepare an electrode mixture; And

Applying the electrode mixture onto a current collector, and drying the electrode mixture to produce an electrode mixture layer.

The absolute value of the zeta potential of the binder suspension composition may be between 12 and 60 mV.

In an embodiment of the present invention,

As the binder suspension composition used in the electrode production method of the present invention,

Water-soluble copolymer and water,

Wherein the absolute value of the zeta potential is 10 mV or more.

The water-soluble copolymer includes (a) an unsaturated monocarboxylic acid-based monomer; (b) an aromatic vinyl monomer; (c) a mixture of at least two selected from the group consisting of a conjugated diene monomer, a (meth) acrylate monomer, and a nitrile monomer, and may be used in an amount of 0.05 to 0.5 wt% based on the total weight of the binder suspension composition %, Specifically 0.1% by weight.

The binder suspension composition for a secondary battery may further include an acidity adjusting agent.

The present invention also provides an electrode for a secondary battery, comprising an electrode current collector and an electrode mixture coated on the electrode current collector, wherein the electrode mixture is manufactured by the method of the present invention.

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

According to the present invention, by including the binder suspension composition having an absolute value of zeta potential of 10 mV or more at the time of manufacturing an electrode, dispersibility of particles in the electrode mixture can be improved, and agglomeration between particles can be effectively prevented. Accordingly, it is possible not only to secure uniformity of the surface of the electrode by reducing the deviation of the particle distribution and the thickness in the electrode, but also to manufacture an electrode for a secondary battery with reduced resistance of the electrode interface and improved adhesion between the electrode mixture and the current collector. Further, by including it, a secondary battery having improved cycle characteristics can be manufactured.

Hereinafter, the present invention will be described in detail in order to facilitate understanding of the present invention. Herein, terms and words used in the present specification and claims should not be construed to be limited to ordinary or dictionary meanings, and the inventor may appropriately define the concept of the term to describe its own invention in the best way. It should be construed as meaning and concept consistent with the technical idea of the present invention.

There is a disadvantage that it is difficult to form an electrode coating layer which is uniform and has excellent adhesive strength, while causing clumping and precipitation phenomenon between particles in the composition at the time of manufacturing an electrode mixture composition for a secondary battery.

Accordingly, the present invention provides an electrode for a secondary battery having improved uniformity and adhesion by providing a method of manufacturing an electrode using a binder suspension composition for a secondary battery having improved dispersibility.

≪ Binder suspension composition and method for manufacturing electrode for secondary battery using same &

Specifically, in one embodiment of the present invention

Preparing a binder suspension composition having an absolute value of zeta potential of 10 mV or higher;

Dispersing the electrode active material, the conductive material and the binder suspension composition in a solvent to prepare an electrode mixture; And

Applying the electrode mixture onto a current collector, and drying the electrode mixture to produce an electrode mixture layer.

In the method of the present invention, the binder suspension composition having an absolute value of the zeta potential of 10 mV or more may be prepared by mixing a water-soluble copolymer and water.

At this time, the water-soluble copolymer may contain 0.05% by weight to 0.5% by weight, specifically 0.1% by weight, based on the total weight of the binder suspension composition.

In addition, the absolute value of the zeta potential of the binder suspension composition of the present invention is such that the binder suspension composition is prepared so that the solid content concentration of the composition, that is, the content of the water soluble copolymer is 0.05 wt% to 0.5 wt%, specifically 0.1 wt% Lt; / RTI >

The term "Zeta potential" is an index indicating the degree of surface charge of suspended or dispersed colloidal particles in a medium (water and / or organic solvent). When an external electric field is applied to the colloid, (Moving) in the opposite direction to the sign of the surface potential. In this case, the numerical value is calculated in consideration of the strength of the electric field and the hydrodynamic effect (viscosity of the solvent, permittivity) of the particle moving velocity.

That is, the dispersion stability of the colloidal particles suspended in the liquid is determined by the magnitude of the zeta potential absolute value. For example, when the absolute value of the zeta potential of the electrochemical active material particles is increased in the preparation of the electrode material mixture composition, the repulsive force between particles becomes stronger, and the dispersion and the degree of dispersion maintenance become higher. On the other hand, when the zeta potential absolute value approaches zero, the electrostatic attraction between the particles facilitates flocculation and sedimentation, and the suspension of the particles of the aqueous solution or the organic solution becomes unstable. Thus, the particles tend to agglomerate, and consequently have a direct correlation with the densification and porosity of the electrode.

The absolute value of the zeta potential of the binder suspension composition used in the method of the present invention may be at least 10 mV, specifically between 12 and 60 mV.

At this time, when the absolute value of the zeta potential of the binder suspension composition for secondary battery is 10 mV or more, the dispersibility of the particles contained in the electrode mixture can be improved and the aggregation of particles can be effectively prevented. If the absolute value of the zeta potential is less than 10, the amount of the aggregate rapidly increases, so that the stability of the electrode mixture is rapidly deteriorated.

The water-soluble copolymer contained in the binder suspension composition, which is used in the method of the present invention,

(a) an unsaturated monocarboxylic acid-based monomer;

(b) an aromatic vinyl monomer; And

(c) a mixture of at least two members selected from the group consisting of a conjugated diene monomer, a (meth) acrylic acid ester monomer, and a nitrile monomer.

Specifically, examples of the unsaturated monocarboxylic acid monomer (a) include unsaturated monocarboxylic acid monomers such as maleic acid, fumaric acid, methacrylic acid, acrylic acid, glutaconic acid, itaconic acid, tetrahydrophthalic acid, crotonic acid, isocrotonic acid and nadic acid May comprise a single or a mixture of two or more compounds selected from 3 to 10% by weight based on the total weight of the water-soluble polymer.

If the unsaturated monocarboxylic acid monomer (a) is contained in an amount of less than 3% by weight, the stability of the latex is decreased and the possibility of precipitation increases. When the unsaturated monocarboxylic acid monomer is contained in an amount of more than 10% by weight, There is a disadvantage in that the adhesion is reduced.

The aromatic vinyl monomer (b) is a component included for controlling the glass transition temperature of the binder, and examples thereof include styrene,? -Methylstyrene, m-methylstyrene,? -Ethylstyrene, p- tert-butylstyrene, or two or more compounds.

The aromatic vinyl monomer (b) may be contained in an amount of 20 to 70% by weight based on the total weight of the water-soluble polymer. If the content of the aromatic vinyl monomer is less than 20% by weight, the cohesive force of the binder decreases, and the adhesive ability of the binder decreases. When the content exceeds 70% by weight, the glass transition temperature becomes higher than room temperature .

Also, the water-soluble copolymer may include (c) 20 to 70% by weight of a single substance selected from the group consisting of a conjugated diene monomer, a (meth) acrylic acid ester monomer and a nitrile monomer, or a mixture of two or more thereof.

The conjugated diene-based monomer is included in order to control the adhesive strength and the resistance of the battery. Typical examples thereof include a single compound selected from the group consisting of 1,3-butadiene, isoprene, chloroprene, and piperrylene or two or more compounds And may specifically be 1,3-butadiene.

The conjugated diene monomer may be at least one selected from the group consisting of an?,? - unsaturated nitrile compound such as acrylonitrile and methacrylonitrile; an aromatic vinyl compound such as chlorostyrene, vinyltoluene, vinylbenzoic acid, vinylbenzoate, vinylnaphthalene, chloromethylstyrene, Unsaturated carboxylic acids such as acrylic acid and methacrylic acid; olefins such as ethylene and propylene; halogen atom-containing monomers such as vinyl chloride and vinylidene chloride; vinyl acetate, vinyl propionate, vinyl butyrate Vinyl ethers such as methyl vinyl ether, ethyl vinyl ether and butyl vinyl ether, vinyl ethers such as methyl vinyl ketone, ethyl vinyl ketone, butyl vinyl ketone, hexyl vinyl ketone and isopropenyl vinyl ketone; Ketones, and vinyl compounds containing rings such as N-vinylpyrrolidone, vinylpyridine, and vinylimidazole.

The (meth) acrylic acid ester monomer is a component included for controlling the swelling of the electrolyte and the resistance of the electrode. Typical examples thereof include butyl acrylate,? -Carboxyethyl acrylate, aliphatic monoacrylate, dipropylene diacrylate, Ditrimethylolpropane tetraacrylate, ditrimethylolpropane tetraacrylate, hydroxyethyl acrylate, dipentaerythritol hexaacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, lauryl acrylate, seryl acrylate, stearyl acrylate, Lauryl methacrylate, seryl methacrylate, stearyl methacrylate, and methacryloxyethylethylene urea.

The nitrile monomer is a component for adjusting the adhesion and the swelling of the electrolyte, and includes an ethylenically unsaturated nitrile monomer. Representative examples thereof include acrylonitrile, methacrylonitrile, fumaronitrile,? -Chloronitrile and acrylonitrile, and? -cyanoethyl acrylonitrile.

The weight ratio of the conjugated diene monomer: (meth) acrylic acid ester monomer: nitrile monomer in the mixture is in the range of 0 to 100: 0 to 100: 0 to 100, specifically 10 to 70:10 to 70:10 to 70, More specifically in a ratio of 20 to 50:20 to 50:20 to 50.

If the mixture contains only the conjugated diene monomer, if the content of the conjugated diene monomer exceeds 70% by weight, the resistance of the battery increases. On the other hand, when the mixture is composed only of a (meth) acrylate-based monomer or a nitrile-based monomer, if the content of the monomer exceeds 70 wt%, the swelling of the electrode becomes 300% or more, There are disadvantages.

Specifically, the binder suspension composition used in the electrode manufacturing method of the present invention comprises (a) 3 to 10 wt% of acrylic acid, (b) 20 to 70 wt% of styrene, and (c) 1,3-butadiene and butyl acrylate A water-soluble copolymer comprising 20 to 70% by weight of a single substance or a mixture of two or more selected from the group consisting of

The water-soluble polymer may be produced by, for example, a polymerization method such as emulsion polymerization, reversed-phase suspension polymerization, suspension polymerization, solution polymerization, aqueous solution polymerization or bulk polymerization. Among these polymerization methods, The law can be used.

Since the emulsion polymerization proceeds inside the micelle, it is possible to easily polymerize a high molecular weight copolymer at a high concentration, and the viscosity of the polymerization solution is also low.

The emulsion polymerization can be carried out using an emulsifier. Examples of such emulsifiers include, but are not limited to, an anionic surfactant, a nonionic surfactant, a cationic surfactant, a polymer surfactant, and a reactive surfactant having a radical polymerizable unsaturated group in the structure of these surfactants One or more selected ones may be used.

Examples of the solvent which can be used in the solution polymerization include aromatic solvents such as toluene and xylene; ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone; alcohols such as normal butanol, isobutanol and isopropyl alcohol; Esters such as ethyl acetate and n-butyl acetate, etc. These may be used alone or in combination.

In the solution polymerization method, a polymerization initiator may be used.

The polymerization initiator is not particularly limited as long as it generates radical molecules by heat, and examples thereof include persulfates such as potassium persulfate, ammonium persulfate and sodium persulfate; Water-soluble azo compounds such as 2,2'-azobis (2-amidinopropane) -2-hydrochloride and 4,4'-azobis (4-cyanopentanoic acid); Pyrolysis initiators such as hydrogen peroxide; Hydrogen peroxide and ascorbic acid, t-butyl hydroperoxide and rongalite, potassium persulfate and metal salts, redox initiators such as ammonium persulfate and sodium hydrogen sulfite, and the like. These polymerization initiators may be used alone or in combination of two or more.

The polymerization initiator is preferably included in an amount of 0.05 to 2 parts by weight, more preferably 0.1 to 1 part by weight, based on 100 parts by weight of the entire monomer components to be added to the polymerization reaction.

The polymerization can be carried out at a temperature of 40 to 180 ° C, preferably 60 to 150 ° C, for 2 to 8 hours, preferably 3 to 6 hours.

In the present invention, the zeta potential of the binder suspension composition for a secondary battery of the present invention can be appropriately controlled by controlling the type and amount of the emulsifier, monomer, salt and additives used in the polymerization of the monomers.

In addition, the binder suspension composition used in the electrode manufacturing method of the present invention may further include an acidity adjusting agent to adjust the absolute value of zeta potential. That is, when the absolute value of the zeta potential of the binder suspension composition for a secondary battery used in the method of the present invention is less than 10 mV, the absolute value of zeta potential can be increased to 10 mV or more by further adding an acidity control agent.

The acidity controlling agent is a substance that causes chemical changes in the water-soluble copolymer components or the binder suspension composition containing the same, and may be included in such a range as to increase the absolute value of the zeta potential to induce repulsion between particles. If the content of the acidity regulator is too much or too small, the absolute value of the zeta potential may become rather small, so that the aggregation and sedimentation of the particles may occur.

The acid controlling agent may be an acidic or basic substance, and representative examples thereof include potassium aluminum sulfate, oxalic acid, maleic acid, fumaric acid, malic acid, formic acid, an acidic substance such as acetic acid, isopropyl alcohol, phosphoric acid, sulfuric acid, hydrochloric acid or nitric acid, or an amine compound such as triethylamine or trimethylamine, tetramethylammonium hydroxide, ammonia, And a basic substance such as sodium hydroxide solution or potassium hydroxide solution. Among them, a weakly acidic or weakly basic acidity control agent capable of minimizing the chemical action on the electrode material mixture components and the side reaction in the battery while improving the dispersibility is more preferable.

Further, in the electrode manufacturing method of the present invention, the step of preparing the electrode mixture may be performed by mixing an electrode active material, a binder suspension composition, a solvent, and optionally a conductive material.

At this time, when the electrode for a secondary battery of the present invention is a cathode, the electrode active material may be crystalline carbon, amorphous carbon, or both. Examples of the crystalline carbon include graphite such as natural graphite or artificial graphite in the form of amorphous, plate-like, flake, spherical or fiber, and examples of the amorphous carbon include soft carbon (soft carbon) Or hard carbon, mesophase pitch carbide, fired coke, and the like. Preferably, the negative electrode active material is selected from the group consisting of Si, SiO _x (0 <x <2), Sn, SnO ₂ , or a silicon-containing metal alloy and mixtures thereof. At least one of Al, Sn, Ag, Fe, Bi, Mg, Zn, In, Ge, Pb and Ti may be used as the metal for forming the silicon alloy.

If the electrode for a secondary battery of the present invention is a cathode, a compound capable of reversibly intercalating and deintercalating lithium (a lithium intercalation compound) may be used as the electrode active material. Specific examples thereof include lithium-manganese-based oxides (for example, LiMnO ₂ , LiMn ₂ O ₄ And the like), lithium-cobalt oxide (e.g., LiCoO ₂ and the like), lithium-nickel-based oxide (for example, LiNiO ₂ and the like), lithium-nickel-manganese-based oxide (for example, LiNi _{1 -Y} Mn _Y O ₂ (where, 0 <Y <1), LiMn _2-z Ni _z O ₄ (where, 0 <Z <2) and the like), lithium-nickel-cobalt-based oxide (for example, LiNi _{1- Y1} Co _Y1 O ₂ (here, 0 <Y1 <1) and the like), lithium-manganese-cobalt oxide (e. g., LiCo _1-Y2 Mn _Y2 O ₂ (here, 0 <Y2 <1), LiMn _{2 - z1} Co _z1 O ₄ (here, 0 <Z1 <2) and the like), lithium-nickel-manganese-cobalt oxide (e.g., Ni _p Co _q Mn _r1 (Li) O ₂ (here, 0 <p <1, 0 <q <1, 0 <r1 <1, p + q + r1 = 1) , or _{Li (Ni p1 Co q1 Mn r2} ) O 4 ( here, 0 <p1 <2, 0 <q1 <2, 0 <r2 <2 , p1 + q1 + r2 = 2) , etc.), or lithium-nickel-cobalt-transition metal (M) oxide (e.g., Li (Ni _p2 Co _q2 Mn _r3 M _S2) O ₂ , wherein M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg and Mo and p2, q2, 1, 0 <r3 <1, 0 <s2 <1, p2 + q2 + r3 + s2 = 1) and the like can be given as the atomic fraction of the lubrication elements , And any one or two or more of these compounds may be included. The lithium composite metal oxide may be LiCoO ₂ , LiMnO ₂ , LiNiO ₂ , lithium nickel manganese cobalt oxide (for example, Li (Ni _0.6 Mn _0.2 Co _0.2 ) O ₂ , Li (Ni _0.5 Mn _0.3 Co _0.2 ) O ₂ or Li (Ni _0.8 Mn _0.1 Co _0.1 ) O ₂ ) or lithium nickel cobalt aluminum oxide (for example, Li (Ni _0.8 Co _0.15 Al _0.05 ) O ₂ ), Etc., and considering the remarkable improvement effect according to the kind and content ratio of the constituent elements forming the lithium composite metal oxide, the lithium composite metal oxide is Li (Ni _0.6 Mn _0.2 Co _0.2 ) O ₂ , _{Li (Ni 0.5 Mn 0.3 Co 0.2} ) O 2, Li (Ni 0.7 Mn 0.15 Co 0.15) O 2 or _{Li (Ni 0.8 Mn 0.1 Co 0.1} ) O 2 and the like, any one or a mixture of two or more may be used of which have.

The electrode active material may include 80% by weight to 99% by weight based on the total weight of the electrode mixture.

In addition, the binder suspension composition may be contained in an amount of 10% by weight or less, specifically 0.1 to 10% by weight in the electrode mixture. If the amount of the binder suspension composition for secondary battery is less than 0.1% by weight, the adhesive strength may be decreased and battery cycle characteristics may be deteriorated. In addition, when the binder suspension composition for a secondary battery contains more than 10% by weight, the content of the electrode active material may be relatively decreased, and the capacity of the battery may decrease and the resistance may increase.

The solvent may include water or an organic solvent such as N-methyl-2-pyrrolidone (NMP), and may be used in an amount that makes it desirable to contain the negative electrode active material, and optionally, a binder and a conductive material .

Also, the conductive material may be added in an amount of 1 to 10 wt% based on the total weight of the negative electrode material mixture, as a component for further improving the conductivity of the negative electrode active material. Such a conductive material is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery, for example, graphite such as natural graphite or artificial graphite; Carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskey 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.

Further, in the electrode manufacturing method of the present invention, the step of producing the electrode mix layer may be carried out by applying the electrode mixture onto the current collector, and then heating and rolling drying the same at the time of drying.

The electrode compound coating process may be performed by a screen printing method, a spray coating method, a coating method using a doctor blade, a gravure coating method, a dip coating method, a silk screen method, a painting method, and a slot die And the coating method used may be selected.

The current collector is not particularly limited as long as it has electrical conductivity without causing chemical changes in the secondary battery. For example, the collector may be formed of a metal such as carbon, , Nickel, titanium, silver, or the like, aluminum-cadmium alloy, or the like, and is generally made to have a thickness of 3 to 500 μm.

Further, fine unevenness may be formed on the surface to enhance the bonding force of the negative electrode active material, and it may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, or a nonwoven fabric.

&Lt; Preparation of electrodes and secondary batteries containing the same &

In an embodiment of the present invention,

Electrode collector, and

And an electrode mixture coated on the electrode current collector,

The electrode mixture includes an electrode active material, a conductive material, and a binder suspension composition for a secondary battery of the present invention.

The secondary battery electrode of the present invention may be a negative electrode, and may specifically include a negative electrode for a lithium ion battery or a negative electrode for a lithium polymer battery.

The present invention also provides a lithium secondary battery comprising a positive electrode, a negative electrode, a separator interposed between the positive and negative electrodes, and a non-aqueous electrolyte, wherein at least one of the positive electrode and the negative electrode includes the electrode for a secondary battery of the present invention do.

At this time, the separation membrane is interposed between the anode and the cathode, and an insulating thin film having high ion permeability and mechanical strength is used. The pore diameter of the separator is generally 0.01 to 10 mu m, and the thickness is generally 300 mu m in 5 mu m. Such separation membranes include, for example, olefinic polymers such as polypropylene, which are chemically resistant and hydrophobic; A sheet or nonwoven fabric made of glass fiber, polyethylene or the like is used. When a solid electrolyte such as a polymer is used as an electrolyte, the solid electrolyte may also serve as a separation membrane.

In the separation membrane, a specific example of the olefin-based polymer may be polyethylene, polypropylene, polyvinylidene fluoride or a multilayer film of two or more thereof. The separator may be a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three- A multi-layered film such as a polypropylene / polyethylene / polypropylene three-layer separator or the like may be used.

The non-aqueous electrolyte is composed of a non-aqueous organic solvent and a lithium salt. As the non-aqueous electrolyte, a non-aqueous electrolyte, a solid electrolyte, an inorganic solid electrolyte and the like are used.

Examples of the nonaqueous organic solvent include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylenecarbonate, dimethyl carbonate, diethyl carbonate, But are not limited to, butylolactone, 1,2-dimethoxyethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, But are not limited to, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxy methane, dioxolane derivatives, sulfolane, methyl sulfolane, Derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, ethyl propionate and the like can be used.

The lithium salt is a substance which is soluble in the non-aqueous electrolyte, and includes, for example, Li ⁺ as a cation and F ^- , Cl ^- , Br ^- , I ^- , NO ₃ ^- and N (CN) _{^{2 -, BF 4 -, ClO}} 4 -, AlO 4 -, AlCl 4 -, PF 6 -, SbF 6 -, AsF 6 -, BF 2 C 2 O 4 -, BC 4 O 8 -, (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 -, C ₄ F ₉ SO _{3 -, CF 3 CF 2 SO 3} -, (CF 3 SO 2) 2 N -, (F 2 SO 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 ^- may be used.

In addition, the present invention can provide a middle- or large-sized battery pack including a plurality of the lithium secondary batteries electrically connected to each other. The middle- or large-sized battery pack includes a power tool; An electric vehicle including an electric vehicle (EV), a hybrid electric vehicle (HEV), and a plug-in hybrid electric vehicle (PHEV); Electric truck; Electric commercial vehicle; Or a power storage system, as shown in FIG.

Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples. It should be noted, however, that the examples are for illustrative purposes only and are not intended to limit the scope of the invention.

Example

I. Preparation of Binder Suspension Composition for Secondary Battery

Example  One.

5% by weight of acrylic acid, 25% by weight of styrene and 70% by weight of butyl acrylate were polymerized by emulsion polymerization at 80 DEG C for 9 hours to prepare a water-soluble copolymer (pH 3.8).

Then, distilled water was added to the water-soluble copolymer to prepare a binder suspension composition containing 0.1% by weight of solid content, and the zeta potential of the binder suspension composition was measured at room temperature. The results are shown in Table 1 below.

The amount of agglomerates (70 ° C, 1000 rpm, 50 g of latex) from the latex stability test (Maron test) for the water-soluble copolymer is also shown in Table 1 below. The latex stability test was carried out using a Maron tester, and 50 g of the latex sample was placed in the sample frame, and the weight of the agglomerate was measured after shearing stress at 70 rpm at 1000 rpm.

Example  2.

A water-soluble copolymer (pH 3.2) was prepared by polymerizing 10 wt% of acrylic acid, 30 wt% of styrene and 60 wt% of butyl acrylate at 80 ° C for 9 hours by emulsion polymerization.

Then, distilled water was added to the water-soluble copolymer to prepare a binder suspension composition containing 0.1% by weight of solid content, and the zeta potential of the binder suspension composition was measured at room temperature. The results are shown in Table 1 below.

The amount of agglomerates (70 ° C, 1000 rpm, 50 g of latex) from the latex stability test (Maron test) for the water-soluble copolymer is also shown in Table 1 below.

Example  3.

To the aqueous copolymer prepared in Example 2, 35% sodium hydroxide solution as an acidity regulator was added to adjust the pH to 6.5, and then distilled water was further added at room temperature to prepare a binder suspension composition containing 0.1% by weight of solid content Respectively. The zeta potential of the binder suspension composition was measured at room temperature and the results are shown in Table 1 below.

The amount of agglomerates (70 ° C, 1000 rpm, 50 g of latex) from the latex stability test (Maron test) for the water-soluble copolymer is also shown in Table 1 below.

Example  4.

5% by weight of acrylic acid, 60% by weight of styrene and 35% by weight of 1,3-butadiene were polymerized by emulsion polymerization at 80 DEG C for 9 hours to prepare a water-soluble copolymer (pH 3.9).

Next, 35% sodium hydroxide solution as an acidity regulator was added to the water-soluble copolymer to adjust the pH to 6.5, and distilled water was further added at room temperature to prepare a binder suspension composition containing 0.1% by weight of solid content. The zeta potential of the binder composition was measured at room temperature and the results are shown in Table 1 below.

The amount of agglomerates (70 ° C, 1000 rpm, 50 g of latex) from the latex stability test (Maron test) for the water-soluble copolymer is also shown in Table 1 below.

Comparative Example  One.

A water-soluble copolymer (pH 5.0) was prepared by polymerizing 2 wt% of acrylic acid, 23 wt% of styrene, and 75 wt% of 1,3-butadiene at 80 ° C for 9 hours by emulsion polymerization.

Then, distilled water was added to the water-soluble copolymer to prepare a binder suspension composition containing 0.1% by weight of solid content, and the zeta potential of the binder suspension composition was measured at room temperature. The results are shown in Table 1 below.

In addition, the amount of the agglomerate in the Maron test for the water-soluble copolymer is shown in Table 1 below.

Comparative Example  2.

A water-soluble copolymer (pH 4.9) was prepared by polymerizing 2% by weight of acrylic acid, 58% by weight of styrene and 40% by weight of butyl acrylate at 80 ° C for 9 hours by emulsion polymerization.

Then, distilled water was added to the water-soluble copolymer to prepare a binder suspension composition containing 0.1% by weight of solid content, and the zeta potential of the binder suspension composition was measured at room temperature. The results are shown in Table 1 below.

In addition, the amount of the agglomerate in the Maron test for the water-soluble copolymer is shown in Table 1 below.

Water-soluble polymer (weight ratio) pH Zeta potential
(mV) Aggregate weight
(g) Example 1 Acrylic acid: styrene: butyl acrylate =
5: 25: 70 3.8 - 13.2 0.02 Example 2 Acrylic acid: styrene: butyl acrylate = 10: 30: 60 3.2 -18.6 <0.01 Example 3 Acrylic acid: styrene: butyl acrylate = 10: 30: 60 6.5 - 24.0 <0.01 Example 4 Acrylic acid: styrene: 1,3-butadiene
= 5: 60: 35 6.5 -12.4 0.02 Comparative Example 1 Acrylic acid: styrene: 1,3-butadiene
= 2: 23: 75 5.0 -3.8 10.2 Comparative Example 2 Acrylic acid: styrene: butyl acrylate
= 2: 58: 40 4.9 -4.1 7.8

As shown in Table 1, the amount of aggregates produced in the latex safety tests of Comparative Examples 1 and 2, in which the absolute value of the zeta potential of the binder suspension composition was less than 10 mV, increased sharply, indicating that the stability of the binder suspension composition was unstable Able to know.

On the other hand, in the case of the binder suspension compositions of Examples 1 to 4 in which the zeta potential absolute value is 10 mV or more, it can be seen that almost no aggregates are generated. From these results, it can be seen that, even in the case of the binder suspension composition containing a similar water-soluble polymer, the degree of increase of the aggregate is different according to the absolute value of zeta potential.

Therefore, in order to prepare a binder suspension composition having excellent adhesion and improving dispersibility among the particles, the absolute value of the zeta potential must be 10 mV or more. To this end, the respective monomer ratios, pH, and solids concentration of the water- It can be seen that all of them must be combined organically.

II. Secondary battery manufacturing

Example  5.

86% by weight of a cathode active material (LiCoO ₂ ), 8% by weight of Super-P (conductive material) and 6% by weight of acrylonitrile butadiene rubber (binder) were added to water to prepare a cathode mixture electrode mixture. This was coated on one side of an aluminum foil, dried and pressed to prepare a positive electrode.

A mixture of 94.5% by weight of an anode active material (graphite), 2% by weight of Super-P (conductive material) and 2.5% by weight of a binder suspension composition for a secondary battery of Example 1 and 1.5% by weight of CMC (thickener) And the negative electrode was prepared by coating, drying, and pressing on one side of the copper foil.

The electrode assembly was prepared by laminating the positive electrode and the negative electrode using a Celgard TM membrane as a separation membrane, and then 1M LiPF ₆ was contained in a mixed solvent of ethyl carbonate and dimethyl ether solvent (EC / DME = 20: 80, weight ratio) A lithium non-aqueous electrolyte was added to prepare a lithium secondary battery.

Example  6.

A negative electrode and a lithium secondary battery comprising the negative electrode were prepared in the same manner as in Example 5 except that the binder suspension composition of Example 2 was used instead of the binder suspension composition of Example 1 as the binder suspension composition.

Example  7.

Except that the binder suspension composition of Example 3 was used in place of the binder suspension composition of Example 1 as the binder suspension composition, a negative electrode and a lithium secondary battery comprising the negative electrode were prepared.

Example  8.

Except that the binder suspension composition of Example 4 was used in place of the binder suspension composition of Example 1 as the binder suspension composition, a negative electrode and a lithium secondary battery comprising the negative electrode were prepared.

Comparative Example  3.

Except that the binder suspension composition of Comparative Example 1 was used in place of the binder suspension composition of Example 1 as the binder suspension composition, a negative electrode and a lithium secondary battery comprising the negative electrode were prepared.

Comparative Example  4.

A negative electrode and a lithium secondary battery comprising the same were prepared in the same manner as in Example 5 except that the binder suspension composition of Comparative Example 2 was used instead of the binder suspension composition of Example 1 as the binder suspension composition.

Experimental Example

Experimental Example  1: Adhesion test

The adhesive strengths of the negative electrode prepared in Examples 5 to 8 and the negative electrode prepared in Comparative Examples 3 and 4 were measured and the results are shown in Table 2 below. The relative adhesive strength ratios of the negative electrode prepared in Examples 5, 7 and 8 and the negative electrode prepared in Comparative Examples 3 and 4 were calculated on the basis of the negative electrode prepared in Example 6, Respectively. At this time, the measurement of the adhesive strength of the manufactured negative electrode was carried out by a 180-degree peel test in a general adhesive strength measuring method.

Adhesion [gf] The relative adhesive force ratio to the negative electrode of Example 6 The cathode of Example 5 95.7 119 The cathode of Example 6 80.4 100 The cathode of Example 7 91.2 113 The cathode of Example 8 109.6 136 The cathode of Comparative Example 3 78.2 97 The cathode of Comparative Example 4 73.0 91

In Table 2, the relative adhesive strength ratios of the negative electrode prepared in Examples 5, 7 and 8 and the negative electrode prepared in Comparative Examples 3 and 4, which were calculated on the basis of the negative electrode prepared in Example 6, It can be seen that the adhesive strength of the negative electrode of Examples 5 to 8 using the binder suspension composition is improved relative to that of the negative electrodes of Comparative Examples 3 and 4.

Experimental Example  2: Life characteristics experiment

The life span of the lithium secondary batteries prepared in Examples 5 to 8 and Comparative Examples 3 and 4 was measured after charging at 1 C at 45 ° C and after 100 cycles of 2 C discharging, and the results are shown in Table 3 below.

Life characteristics comparison Example 5 98.5 Example 6 98.8 Example 7 98.6 Example 8 98.7 Comparative Example 3 97.5 Comparative Example 4 97.7

As shown in Table 3, it can be seen that the capacity reduction rate of the secondary batteries of Examples 5 to 8 including the binder suspension composition of the present invention is lower than that of the secondary batteries of Comparative Examples 3 and 4.

Claims (20)

Preparing a binder suspension composition comprising a water-soluble copolymer and water, wherein the water-soluble copolymer is contained in an amount of 0.05 to 0.5% by weight and an absolute value of zeta potential is 10 mV or more;
Preparing an electrode mixture by dispersing an electrode active material, a conductive material, and a binder suspension composition having controlled zeta potential in a solvent; And
Applying the electrode mixture onto a current collector, and drying the electrode mixture to produce an electrode mixture layer,
The water-soluble copolymer comprises (a) 3 to 10% by weight of acrylic acid; (b) 20 to 70% by weight of styrene; And (c) 20 to 70% by weight of a single substance selected from the group consisting of 1,3-butadiene and butyl acrylate, or a mixture of two or more thereof.
The method according to claim 1,
Wherein an absolute value of the zeta potential of the binder suspension composition is from 12 mV to 60 mV.
delete delete delete The method according to claim 1,
Wherein the binder suspension composition is contained in the electrode mixture in an amount of 0.1 wt% to 10 wt%.
A binder suspension composition prepared in the step of preparing the binder suspension composition of claim 1,
Soluble copolymer and water, wherein the water soluble copolymer comprises from 0.05% to 0.5% by weight, based on the total weight of the binder suspension composition,
Wherein the absolute value of the zeta potential is at least 10 mV.
delete delete delete delete delete delete delete delete delete The method of claim 7,
Wherein the binder suspension composition further comprises an acidity adjusting agent.
Electrode collector, and
And an electrode mixture coated on the electrode current collector,
Wherein the electrode mixture contains an electrode active material, a binder suspension composition for a secondary battery according to claim 7, a solvent, and a conductive material.
19. The method of claim 18,
Wherein the electrode is a negative electrode.
A negative electrode, a positive electrode, a separator interposed between the negative electrode and the positive electrode, and a nonaqueous electrolyte solution containing a lithium salt,
And the negative electrode comprises the electrode of claim 19.