KR101047243B1 - Binder for Electrode of Lithium Secondary Battery, Electrode with Lithium Secondary Battery - Google Patents

Abstract

The present invention provides a binder for an electrode of a lithium secondary battery that is fixed and connected between the electrode active material particles and the electrode active material particles and the current collector, comprising: (a) a styrene monomer unit, (b) a 1,3-butadiene monomer unit, Provided is a copolymer comprising (c) a butyl acrylate monomer unit and (d) an ethylhexyl acrylate monomer unit.

The binder according to the present invention not only shows good electrochemical stability but also has excellent adhesiveness and flexibility, which is very useful as a binder for electrodes of lithium secondary batteries.

Description

Binder for Lithium Secondary Batteries, Electrodes and Lithium Secondary Batteries {BIN FORM FOR ELECTRODE OF A LITHIUM SECONDARY BATTERY

The present invention relates to a binder for an electrode of a lithium secondary battery for fixing and connecting between the electrode active material particles and the electrode active material particles and the current collector, an electrode having the same and a lithium secondary battery.

A lithium secondary battery typically includes a positive electrode having a positive electrode active material layer formed on at least one surface of a positive electrode current collector, a negative electrode having a negative electrode active material layer formed on at least one surface of a negative electrode current collector, and interposed between the positive electrode and the negative electrode to electrically insulate them. A separator is provided.

In the method of forming the electrode active material layer on the current collector, an electrode active material slurry obtained by dispersing the electrode active material particles and the binder in a solvent is formed by directly applying and drying the electrode active material slurry on the current collector, or by applying and drying the electrode active material slurry on a separate support. Then, the film peeled from this support body is formed by the method of laminating on an electrical power collector.

The binder performs a function of fixing and connecting between the electrode active material particles, as well as between the electrode active material particles and the current collector, thereby greatly affecting the performance of the electrode. That is, the binder should be relatively excellent in adhesion to increase the content of the electrode active material particles, and should be electrochemically stable so that no side reactions occur. In addition, there must be some flexibility so as not to break during the assembly of the battery.

The polyvinylidene fluoride polymer used as a binder of a lithium secondary battery has an advantage of being electrochemically stable. However, this binder is not only insufficient in adhesive strength, but also has an environmental problem in that it is dissolved in an organic solvent such as NMP (N-methyl-2-pyrrolidone) to prepare an electrode active material slurry.

Accordingly, in recent years, a method of forming an electrode by dispersing a synthetic rubber such as rubber (SBR) made of styrene unity-butadiene unit as water as a binder is used. By the way, since the synthetic rubber-based binder exhibits adhesiveness characteristics, the contact area is narrow and the adhesive force is not sufficiently exhibited. Therefore, in the case of a synthetic rubber binder, better adhesion is required.

Korean Patent No. 10-0767966 discloses a synthetic rubber binder further comprising an unsaturated carboxylic acid monomer unit such as acrylic acid or itaconic acid as a binder for an electrode having improved adhesive properties. However, this binder may generate gas due to the remaining acid component.

On the other hand, when a separator having a porous coating layer formed of a mixture of inorganic particles and a binder polymer is applied to a lithium secondary battery, lamination of the porous coating layer and the electrode is not easy. Therefore, it is necessary to develop an electrode with high adhesion to a separator having a porous coating layer.

Accordingly, the problem to be solved by the present invention is to solve the above problems, to provide an electrochemically good stability, to provide an electrode binder of a lithium secondary battery excellent in adhesion and flexibility, and to provide an electrode and a lithium secondary battery having the same. It is.

In order to achieve the above object, according to the present invention, a binder for an electrode of a lithium secondary battery for fixing and connecting between the electrode active material particles and the electrode active material particles and the current collector, (a) a styrene monomer unit, (b) A copolymer comprising a 1,3-butadiene monomer unit, (c) butyl acrylate monomer unit and (d) ethylhexyl acrylate monomer unit is provided.

In the binder of the present invention, the content of (a), (b), (c) and (d) is 5 to 20% by weight, 10 to 30% by weight, 40 to 80% by weight, respectively, based on the total weight of the copolymer % And 5 to 20% by weight.

In the binder of the present invention, the binder is preferably a copolymer further comprising an acrylonitrile monomer unit, the content of which is more preferably 5 to 30% by weight based on the total weight of the copolymer.

The lithium secondary battery electrode of the present invention includes a binder including the copolymer of the present invention described above and electrode active material particles fixed and connected to each other by the binder.

In the electrode according to the present invention, the electrode preferably further comprises a thickener component. Examples of the thickener component include cellulose compounds, and examples thereof include carboxymethyl cellulose and carboxyethyl cellulose, and compounds in which these are substituted with cations such as ammonium ions and monovalent metal ions.

The electrode described above may be used as a positive electrode, a negative electrode, or a positive electrode of a conventional lithium secondary battery including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode.

In the lithium secondary battery of the present invention, any separator can be used as the separator used for the lithium secondary battery. In particular, a porous substrate having a plurality of pores; And a separator coated on at least one surface of the porous substrate and having a porous coating layer formed of a mixture of a plurality of inorganic particles and a binder polymer. The weight ratio of the inorganic particles and the binder polymer constituting the porous coating layer of the separator is preferably 50:50 to 99: 1, the thickness of the porous coating layer is 0.01 to 20 ㎛, pore size and porosity of 0.001 to 10 ㎛, respectively And 10 to 90%.

Copolymers, which are binders according to the present invention, include styrene-based monomer units and are electrochemically stable and have degradability. In addition, flexibility is imparted by including 1,3-butadiene monomer units. In addition, the butyl acrylate monomer unit and the ethylhexyl acrylate monomer unit included in the copolymer improve the adhesion between the electrode active material particles and between the electrode active material particles and the current collector. The ethylhexyl acrylate monomer unit compensates for the problem that the copolymer is degraded with the introduction of butyl acrylate. Therefore, the copolymer of the present invention not only shows good electrochemical stability but also has excellent adhesiveness and flexibility, which is very useful as a binder for electrodes of lithium secondary batteries.

In particular, the lithium secondary battery to which the electrode binder and the separator having the porous coating layer formed of a mixture of the inorganic particles and the binder polymer is simultaneously applied has a problem of poor lamination with the electrode due to the application of the separator having the porous coating layer. Resolved. Accordingly, the inorganic particle content of the porous coating layer can be increased, thereby further improving the stability of the lithium secondary battery.

Hereinafter, the present invention will be described in detail. Prior to this, terms or words used in the specification and claims should not be construed as having a conventional or dictionary meaning, and the inventors should properly explain the concept of terms in order to best explain their own invention. Based on the principle that can be defined, it should be interpreted as meaning and concept corresponding to the technical idea of the present invention. Therefore, the configurations described in the embodiments described herein are only one of the most preferred embodiments of the present invention and do not represent all of the technical ideas of the present invention, and various equivalents may be substituted for them at the time of the present application. It should be understood that there may be variations.

According to the present invention, a binder for an electrode of a lithium secondary battery that fixes and connects between electrode active material particles and between the electrode active material particles and a current collector may include (a) a styrene monomer unit and (b) a 1,3-butadiene monomer unit. and (c) a butyl acrylate monomer unit and (d) an ethylhexyl acrylate monomer unit. In the case of the copolymer including the above-mentioned four-component monomer unit, all copolymers such as random copolymers and block copolymers are included in the copolymer of the present invention.

In the binder according to the present invention, styrene-based monomer units such as styrene, α-styrene, α-methylstyrene, β-methylstyrene, and p - t -butylstyrene are electrochemically stable, and therefore, particularly decomposable to copolymers. Grant. In addition, the 1,3-butadiene monomer unit included in the copolymer imparts flexibility to the copolymer. In addition, the butyl acrylate monomer unit and ethylhexyl acrylate monomer unit included in the copolymer improve the adhesion of the copolymer between the electrode active material particles and between the electrode active material particles and the current collector. In addition, the ethylhexyl acrylate monomer unit compensates for the problem that the copolymer is degraded by introducing butyl acrylate having poor flexibility. Accordingly, the copolymer containing the four components according to the present invention not only shows good electrochemical stability, but also has excellent adhesiveness and flexibility, which is very useful as a binder for electrodes of lithium secondary batteries.

In the binder of the present invention, the content of each of the monomer units constituting the copolymer, that is, the content of (a), (b), (c) and (d) is determined in order to optimally realize the above-described properties. It is preferably 5 to 20% by weight, 10 to 30% by weight, 40 to 80% by weight and 5 to 20% by weight based on the weight, and can adjust the molecular weight of the copolymer to suit the purpose of the present invention, of course. to be.

In the binder of the present invention, the copolymer may further include other monomer units in addition to the above-mentioned four components, as long as the object of the present invention is not impaired. In particular, the binder is preferably a copolymer further comprising an acrylonitrile monomer unit, thereby improving the electrochemical stability to improve the high temperature life characteristics, the content of the acrylonitrile monomer unit is based on the total weight of the copolymer It is preferably 5 to 30% by weight.

As the binder of the present invention, other additives such as a binder component and a crosslinking agent may be used in addition to the copolymer described above.

The copolymer according to the present invention may be prepared according to a conventional polymerization method known in the art, for example, emulsion polymerization method or suspension polymerization method may be used.

The above-mentioned binder for electrodes of a lithium secondary battery is used for electrode formation according to a conventional method as follows.

First, the electrode active material particle | grains and the binder containing the above-mentioned copolymer are added to a solvent or a dispersion medium, and an electrode active material slurry is prepared.

In preparing the electrode active material slurry, the binder component is preferably added to 0.1 to 5.0 wt% based on the total weight of solids.

The electrode active material particles are not particularly limited as long as they can be used as electrode active materials of a lithium secondary battery. For example, the negative electrode active material particles include carbon, petroleum coke, activated carbon, and graphite. ) Or other carbonaceous materials such as carbons, metals such as silicon or tin, or oxides thereof. Non-limiting examples of the positive electrode active material may include lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium iron oxide, lithium composite oxide in combination thereof.

As a solvent or a dispersion medium, it is water; Alcohols such as ethanol, ethanol, propanol and butanol; Ketones such as acetone and kenyl ethyl ketone; Ethers such as methyl ethyl ether, diethyl ether and diisoamyl ether; Lactones such as gamma-butyrolactone; Lactams such as beta-lactam; Cyclic aliphatic compounds such as cyclopentane and cyclohexane; Aromatic hydrocarbons such as benzene and toluene; Ester, such as methyl lactate and ethyl lactate, etc. are mentioned. In particular, water may be used as an environmentally friendly dispersion medium.

A thickener component may be further added as needed in preparing the electrode active material slurry. Examples of the thickener component include cellulose compounds, and examples thereof include carboxymethyl cellulose and carboxyethyl cellulose, and compounds in which these are substituted with cations such as ammonium ions and monovalent metal ions.

Subsequently, the prepared electrode active material slurry is applied onto a substrate, and then dried to form a electrode by removing a solvent or a dispersion medium.

As a coating method of the electrode active material slurry, a conventional coating method known in the art may be used. For example, various methods such as dip coating, die coating, roll coating, comma coating, or a mixture thereof may be used. In addition, the electrode active material slurry is directly applied onto a substrate made of a current collector, such as a metal thin film, a mesh-type expanded metal, a punched metal, and then dried to form an electrode, or the electrode active material slurry may be separately prepared such as a polyethylene terephthalate film. The electrode can be formed by applying and drying the upper substrate of the support, and then laminating the film peeled from the support onto the current collector.

The electrode manufactured as described above may be used as a positive electrode, a negative electrode, or a positive electrode of a conventional lithium secondary battery including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode.

In the lithium secondary battery of the present invention, a separator commonly used in a lithium secondary battery may be used. For example, a porous polymer film, more specifically a porous polymer film made of a polyolefin-based polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer and ethylene / methacrylate copolymer These may be used alone or in combination of these. In addition, a conventional porous nonwoven fabric proposed as a separator of a lithium secondary battery, for example, a non-woven fabric made of high melting point glass fiber, polyethylene terephthalate fiber, or the like may be used, but is not limited thereto.

The lithium secondary battery of the present invention, in particular, a porous substrate having a plurality of pores; And a separator coated on at least one surface of the porous substrate and having a porous coating layer formed of a mixture of a plurality of inorganic particles and a binder polymer. That is, the butyl acrylate monomer unit and ethylhexyl acrylate monomer unit included in the copolymer used as the binder of the electrode according to the present invention improves the adhesion between the electrode active material particles and between the electrode active material particles and the current collector. Of course, it also improves the adhesion with the inorganic particles of the main component of the porous coating layer. Accordingly, the lithium secondary battery to which the electrode to which the electrode binder is applied according to the present invention and the separator having the porous coating layer formed of a mixture of inorganic particles and the binder polymer is simultaneously applied is laminated with the electrode according to the application of the separator having the porous coating layer. The problem of defect is solved. Accordingly, the inorganic particle content of the porous coating layer can be increased, thereby further improving the stability of the lithium secondary battery.

Hereinafter, a method of manufacturing a separator having a porous coating layer will be described in detail.

First, a porous substrate having a plurality of pores is prepared.

The porous substrate may be used as long as the porous substrate is a planar porous substrate commonly used in electrochemical devices such as a porous membrane or a nonwoven fabric formed of various polymers. For example, a polyolefin-based porous membrane or a nonwoven fabric made of polyethylene terephthalate fiber, which is used as an electrochemical device, in particular, a separator of a lithium secondary battery, may be used. For example, the polyolefin-based porous membrane (membrane) is a polyolefin-based polymer such as polyethylene, polypropylene, polybutylene, polypentene, such as high density polyethylene, linear low density polyethylene, low density polyethylene, ultra high molecular weight polyethylene, or a mixture thereof. The polymer may be formed, and the nonwoven fabric may also be made of a fiber using a polyolefin-based polymer or a polymer having higher heat resistance. The thickness of the porous substrate is not particularly limited, but is preferably 1 to 100 μm, more preferably 5 to 50 μm, and the pore size and pore present in the porous substrate are also not particularly limited, but are 0.001 to 50 μm and 10, respectively. It is preferably from 95%.

Subsequently, the slurry in which the inorganic particles are dispersed and the binder polymer is dissolved in the solvent is coated on at least one surface of the porous substrate.

The inorganic particles are not particularly limited as long as they are electrochemically stable. That is, the inorganic particles that can be used in the present invention are not particularly limited as long as the oxidation and / or reduction reactions do not occur in the operating voltage range (for example, 0 to 5 V on the basis of Li / Li ⁺ ) of the applied electrochemical device. In particular, when inorganic particles having a high dielectric constant are used as the inorganic particles, the ionic conductivity of the electrolyte may be improved by contributing to an increase in the dissociation degree of the electrolyte salt, such as lithium salt, in the liquid electrolyte.

For the reasons described above, the inorganic particles preferably include high dielectric constant inorganic particles having a dielectric constant of 5 or more, preferably 10 or more. Non-limiting examples of inorganic particles having a dielectric constant of 5 or more include BaTiO ₃ , Pb (Zr, Ti) O ₃ (PZT), Pb _1-x La _x Zr _1-y Ti _y O ₃ (PLZT, where 0 <x <1, 0 <y <1), Pb (Mg _1/3 Nb _2/3 ) O ₃ -PbTiO ₃ (PMN-PT), Hafnia (HfO ₂ ), SrTiO ₃ , SnO ₂ , CeO ₂ , MgO , NiO, CaO, ZnO, ZrO ₂ , Y ₂ O ₃ , Al ₂ O ₃ , TiO _2, SiC Or mixtures thereof.

In addition, the inorganic particles may be inorganic particles having lithium ion transfer capability, that is, inorganic particles containing lithium elements but having a function of transferring lithium ions without storing lithium. Non-limiting examples of inorganic particles having a lithium ion transfer capacity include lithium phosphate (Li ₃ PO ₄ ), lithium titanium phosphate (Li _x Ti _y (PO ₄ ) ₃ , 0 <x <2, 0 <y <3), Lithium aluminum titanium phosphate (Li _x Al _y Ti _z (PO ₄ ) ₃ , 0 <x <2, 0 <y <1, 0 <z <3), 14Li ₂ O-9Al ₂ O ₃ -38TiO ₂ -39P ₂ (LiAlTiP) _x O _y series glass such as O ₅ (0 <x <4, 0 <y <13), lithium lanthanum titanate (Li _x La _y TiO ₃ , 0 <x <2, 0 <y <3) , Li germanium thiophosphate such as Li _3.25 Ge _0.25 P _0.75 S ₄ (Li _x Ge _y P _z S _w , 0 <x <4, 0 <y <1, 0 <z <1, 0 <w <5 ), Lithium nitride such as Li ₃ N (Li _x N _y , 0 <x <4, 0 <y <2), SiS ₂ based glass such as Li ₃ PO ₄ -Li ₂ S-SiS ₂ (Li _x Si P ₂ S ₅ series glass (Li _x P _y S _z , 0 <x, such as _y S _z , 0 <x <3, 0 <y <2, 0 <z <4), LiI-Li ₂ SP ₂ S _5, etc. <3, 0 <y <3, 0 <z <7) or mixtures thereof.

In addition, the average particle diameter of the inorganic particles is not particularly limited, but for forming a coating layer of uniform thickness and proper porosity, it is preferably in the range of 0.001 to 10 μm. When the thickness is less than 0.001 μm, the dispersibility may be reduced, and when the thickness is more than 10 μm, the thickness of the coating layer formed may be increased.

As the binder polymer, it is preferable to use a polymer having a glass transition temperature (T _g ) of -200 to 200 ° C, because it can improve mechanical properties such as flexibility and elasticity of the finally formed coating layer. .

In addition, the binder polymer does not necessarily have an ion conducting ability, but when a polymer having an ion conducting ability is used, the performance of the electrochemical device may be further improved. Therefore, the binder polymer is preferably as high as possible dielectric constant. In fact, since the dissociation degree of the salt in the electrolyte depends on the dielectric constant of the solvent of the electrolyte, the higher the dielectric constant of the binder polymer, the higher the dissociation of the salt in the electrolyte. The dielectric constant of the binder polymer may be in the range of 1.0 to 100 (measurement frequency = 1 kHz), particularly preferably 10 or more.

In addition to the above-described function, the binder polymer may have a feature that can exhibit a high degree of swelling of the electrolyte by gelling upon impregnation of the liquid electrolyte. Accordingly, it is preferred to use polymers having a solubility index of 15 to 45 MPa ^1/2 , more preferred solubility indices in the range of 15 to 25 MPa ^1/2 and 30 to 45 MPa ^1/2 . Therefore, it is preferable to use hydrophilic polymers having more polar groups than hydrophobic polymers such as polyolefins. This is because when the solubility index is less than 15 MPa ^{1/2 and more} than 45 MPa ^1/2 , it is difficult to be swelled by a conventional battery liquid electrolyte.

Non-limiting examples of such binder polymers include polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, and polymethylmethacrylate. Polymethylmethacrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, ethylene vinyl acetate copolymer (polyethylene-co-vinyl acetate ), Polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylflurane ( cyanoethylpullulan), cyanoethylpoly Carbonyl may be mentioned alcohols (cyanoethylpolyvinylalcohol), cyanoethyl cellulose (cyanoethylcellulose), cyanoethyl sucrose (cyanoethylsucrose), pullulan (pullulan), carboxymethyl cellulose (carboxyl methyl cellulose) and the like.

The weight ratio of the inorganic particles and the binder polymer is preferably in the range of 50:50 to 99: 1, more preferably 70:30 to 95: 5. When the content ratio of the inorganic particles to the binder polymer is less than 50:50, the pore size and porosity of the coating layer formed by increasing the content of the polymer may be reduced. When the content of the inorganic particles exceeds 99 parts by weight, the binder polymer content is reduced, so that the peeling resistance of the coating layer formed may be weakened.

As a solvent of the binder polymer, a solubility index is similar to that of the binder polymer to be used, and a boiling point is preferably low. This is to facilitate uniform mixing and subsequent solvent removal. Non-limiting examples of solvents that can be used include acetone, tetrahydrofuran, methylene chloride, chloroform, dimethylformamide, N-methyl-2-pyrrolidone ( N-methyl-2-pyrrolidone, NMP), cyclohexane, water or a mixture thereof.

The slurry in which the inorganic particles are dispersed and the binder polymer is dissolved in the solvent may be prepared by dissolving the binder polymer in the solvent and then adding the inorganic particles and dispersing the binder polymer. The inorganic particles may be added in a state of being crushed to an appropriate size, but after adding the inorganic particles to the solution of the binder polymer, it is preferable to disperse the inorganic particles while crushing by using a ball mill method.

The loading amount of the slurry coated on the porous substrate is preferably adjusted so that the finally formed coating layer is in the range of 5 to 20 g / m ² in consideration of the function of the coating layer and suitability for high capacity batteries. The coating method of the slurry can be carried out using a known method such as dip coating, slot die coating, slide coating, curtain coating.

Finally, the solvent present in the slurry coated on the porous substrate is dried. As the solvent of the coating layer is dried, the inorganic particles are connected and fixed to each other by the binder polymer, and pores are formed due to the interstitial volume between the inorganic particles.

In addition, a nonaqueous electrolyte solution can be used for the lithium secondary battery of this invention. As the solvent, it is preferable to use a carbonate organic solvent having a high dielectric constant for the long life of the battery. Specific examples of the organic solvent include propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate, dipropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, gamma-butyro Lactone, ethylene sulfite, propylene sulfite, tetrahydrofuran, and the like may be used alone or in combination thereof, but is not limited thereto. Moreover, it is preferable that electrolyte solution contains a lithium salt further. Any lithium salt can be used as long as it is used in a conventional lithium secondary battery. Examples of the lithium salt include lithium perchlorate (LiClO ₄ ), lithium tetrafluoroborate (LiBF ₄ ), lithium hexafluorophosphate (LiPF ₆ ), Lithium hexafluoride (LiAsF ₆ ), lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ), lithium bistrifluoromethanesulfonylamide (LiN (CF ₃ SO ₂ ) ₂ ), etc. may be used alone or in combination thereof. However, the present invention is not limited thereto.

Hereinafter, examples will be described in order to describe the present invention in more detail. However, embodiments according to the present invention can be modified in many different forms, the scope of the present invention should not be construed as limited to the embodiments described below. Embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art.

Example 1

Preparation of the binder

167.4 g of ion-exchanged water was introduced into the reactor and the temperature was raised to 75 ° C. When the temperature of ion-exchange water reached 75 degreeC, 10.4g of butyl acrylates, 3.7g of styrene, and 0.18g of sodium lauryl sulfate were added. Seed (1) was completed by dissolving 0.14 g of potassium persulfate in 9.0 g of ion-exchanged water while maintaining the reactor internal temperature at 75 ° C.

3 hours of the reaction mixture was suspended by mixing 167.4 g of ion-exchanged water, 6.3 g of styrene, 15 g of butyl acrylate, 45.2 g of ethylhexyl acrylate, 20 g of 1,3-butadiene, and 0.27 g of sodium lauryl sulfate. The binder copolymer was synthesize | combined by dissolving 0.38 g of potassium persulfate in 18.0 g of ion-exchange water, and adding for 3 hours similarly.

After adjusting to pH = 7 using potassium hydroxide for the binder copolymer, distilled water was added to the binder copolymer to distill at 90 degrees to remove the unreacted product.

Preparation of Slurry for Electrode

For the negative electrode slurry, water was used as a dispersion medium, and 98.0 wt% of graphite (Hitachi Chemical Co., Ltd.), 1.0 wt% of styrene-butadiene rubber and 1.0 wt% of carboxymethyl cellulose, were used as water based on the total weight of solids. It was added and mixed to prepare a uniform negative electrode active material slurry.

The slurry for the positive electrode, using water as a dispersion medium, 96.3% by weight of LiCoO ₂ having an average particle size of 10㎛ based on the total weight of solids, 2.5% by weight of conductive carbon (Super-P), 0.4% by weight of the binder copolymer, CMC 0.8 Weight percent was added to water and mixed to prepare a uniform negative electrode active material slurry.

Preparation of the electrode

The cathode and anode slurries completed by the method described above were applied to copper foil and aluminum foil at 200 μm thickness, respectively, and dried at 90 ° C. for 10 minutes, at 120 ° C. for 10 minutes, and vacuum at 120 ° C. for 2 hours. Dried. The dried electrode was pressed to have a porosity of 30% to prepare a positive electrode.

Manufacture of separator

PVdF-CTFE (polyvinylidene fluoride-chlorotrifluoroethylene copolymer) and Cyanoethylpullulan (cyanoethyl pullulan) were added to acetone in a weight ratio of 10: 2, respectively, and dissolved at 50 ° C. for at least 12 hours. Was prepared. The slurry was prepared by adding barium titanate (BaTiO ₃ ) powder to the polymer solution thus prepared, such that the polymer mixture / active carbon powder = 10/90, and crushing and dispersing the inorganic particles using a ball mill method for at least 12 hours. It was. The particle diameter of the inorganic particles of the slurry thus prepared was 600 nm on average.

The slurry thus prepared was coated on both sides of a 12 μm thick polyethylene porous membrane (45% porosity) by dip coating and dried. The loading of slurry for each side was adjusted to 12.5 g / m ² .

Manufacture of batteries

After assembling the battery using the positive electrode, the negative electrode and the separator prepared by the method described above, a non-aqueous electrolyte prepared by adding 1M LiPF ₆ to a solvent in which ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 3: 7 was injected. To complete the battery.

Examples 2-4

A battery was manufactured in the same manner as in Example 1, except that the amount of the positive electrode binder changed as shown in Table 1 when the positive electrode slurry was prepared .

Example 5

A battery was manufactured in the same manner as in Example 3, except that 20 g of acrylonitrile was further added to prepare a binder for the cathode.

Comparative Example 1

95% by weight of LiCoO ₂ having an average particle diameter of 10 μm, 2.5% by weight of conductive carbon (Super-P), and 2.5% by weight of PVdF, based on the total weight of solids, were added to NMP, except that a positive electrode active material slurry was prepared. Prepared a battery in the same manner as in Example 1.

Comparative Example 2

The composition of the positive electrode binder was changed to three components except butyl acrylate (15 wt% of styrene, 65 wt% of 1,3-butadiene, and 20 wt% of ethylhexyl acrylate based on the total weight of the binder). A battery was manufactured in the same manner as in Example 2, except that coalescence was used.

Comparative Example 3

The composition of the positive electrode binder was changed to three components excluding ethylhexyl acrylate (15 wt% styrene content, 20 wt% 1,3-butadiene content and 65 wt% butyl acrylate content) based on the total weight of the binder. A battery was manufactured in the same manner as in Example 2, except that coalescence was used.

Comparative Example 4

The air of which the components of the positive electrode binder were changed to three components excluding 1,3-butadiene (styrene content 33.3 weight%, butyl acrylate content 58.5 weight%, ethylhexyl acrylate content 8.2 weight%) based on the total binder weight A battery was manufactured in the same manner as in Example 2, except that coalescence was used.

<Evaluation of Discharge Capacity of Battery>

After charging the battery of the Example and the comparative example to 4.35V, respectively, 0.2C discharge capacity and 1.0C discharge capacity were measured, and it is shown in Table 2.

<Evaluation of the adhesive strength of the binder>

In order to evaluate the adhesive force of the positive electrode binder to the current collector, the following experiment was conducted.

The positive and negative electrodes of Examples and Comparative Examples were cut to a thickness of 1 cm and attached to a glass plate, and then 180 ° peel strength of the positive electrode active material layer with respect to the current collector was measured. Peel strength was measured for each of five samples to obtain an average value, and the results are shown in Table 3 below.

In addition, to evaluate the adhesion between the positive electrode binder and the separator having a porous coating layer, the following experiment was conducted.

After laminating the positive electrode and the separator of Examples and Comparative Examples at 70 degrees, the peel strength of the 180 degrees of the positive electrode with respect to the separator was measured. Peel strength was measured for each of five samples to obtain an average value, and the results are shown in Table 3 below.

<Evaluation of Binder Electrochemical Stability>

In order to evaluate the electrochemical stability of the positive electrode binder, the life characteristics of the battery at high temperature and high voltage were measured as follows. This is because, when the binder is electrochemically unstable, lifespan decreases at high temperature and high voltage conditions.

The batteries of Examples 1 to 5 and conventional Comparative Example 1 were subjected to 4.35V charge and 3.0V discharge at 55 degrees to evaluate their lifetime and are shown in FIG. 1.

1 is a graph evaluating the life of the battery by repeating the 4.35V charge and 3.0V discharge at 55 degrees for the battery according to the Examples and Comparative Examples of the present invention.

Claims (15)

In the binder for the electrode of a lithium secondary battery for fixing and connecting between the electrode active material particles and the electrode active material particles and the current collector, The binder is a copolymer comprising (a) a styrene monomer unit, (b) a 1,3-butadiene monomer unit, (c) a butyl acrylate monomer unit and (d) an ethylhexyl acrylate monomer unit, The content of (a), (b), (c) and (d) is 5 to 20% by weight, 10 to 30% by weight, 40 to 80% by weight and 5 to 20% by weight, respectively, based on the total weight of the copolymer The binder for electrodes of a lithium secondary battery characterized by the above-mentioned. delete The method of claim 1, The styrene monomer unit is a binder for an electrode of a lithium secondary battery, characterized in that at least one monomer unit selected from the group consisting of styrene, α-styrene, α-methylstyrene, β-methylstyrene, and p - t -butylstyrene. .  The method of claim 1, The binder is a binder for a lithium secondary battery electrode, characterized in that the copolymer further comprises an acrylonitrile monomer unit. The method of claim 4, wherein The content of the acrylonitrile monomer unit is a binder for a lithium secondary battery electrode, characterized in that 5 to 30% by weight based on the total weight of the copolymer. A binder according to any one of claims 1 and 3 to 5; And An electrode for a lithium secondary battery comprising electrode active material particles fixed and connected to each other by the binder. The method of claim 6, The electrode is a lithium secondary battery electrode, further comprising a thickener component. The method of claim 7, wherein The thickener component is a lithium secondary battery electrode, characterized in that the cellulose-based compound. In a lithium secondary battery comprising a positive electrode, a negative electrode and a separator interposed between the positive electrode and the negative electrode, The positive electrode, the negative electrode or the positive electrode is a lithium secondary battery, characterized in that the electrode of claim 6. The method of claim 9, The electrode further comprises a thickener component. The method of claim 10, The thickener component is a lithium secondary battery, characterized in that the cellulose-based compound. The method of claim 9, The separator includes a porous substrate having a plurality of pores; And a separator coated on at least one surface of the porous substrate and having a porous coating layer formed of a mixture of a plurality of inorganic particles and a binder polymer. The method of claim 12, Lithium secondary battery, characterized in that the weight ratio of the inorganic particles and the binder polymer is 50:50 to 99: 1. The method of claim 12, The thickness of the porous coating layer is 0.01 to 20 ㎛, pore size and porosity are 0.001 to 10 ㎛ and 10 to 90%, respectively, characterized in that. The method of claim 12, The porous substrate is a lithium secondary battery, characterized in that the porous membrane or nonwoven fabric.

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