KR101326070B1 - Binder for Secondary Battery Exhibiting Excellent Adhesive Force and Tensile Strength - Google Patents

Abstract

The present invention is a binder for an electrode of a secondary battery, comprising three or more monomers and a polymerized reactive emulsifier to polymer particles having an average particle diameter of 0.05 ㎛ to 0.7 ㎛, tensile strain (100) in the film production Provided is a binder for a secondary battery electrode, characterized in that the 500% and the tensile strength (3 MPa or more), the adhesive strength of 15 gf / cm or more. Such a binder provides a secondary battery having excellent cycle characteristics due to physical properties of a combination of specific components as described above.

Description

Binder for Secondary Battery Exhibiting Excellent Adhesive Force and Tensile Strength}

The present invention relates to a binder for an electrode of a secondary battery, and more particularly, polymerized particles having an average particle diameter of 0.05 μm to 0.7 μm by polymerizing three or more types of monomers with a reactive emulsifier, and tensile deformation during film production. It relates to a binder for a secondary battery electrode, wherein the tensile strain is 100 to 500%, the tensile strength is 3 MPa or more, and the adhesive force is 15 gf / cm or more.

Due to the rapid increase in the use of fossil fuels, the demand for the use of alternative energy or clean energy is increasing. As a part of this, the most active field of research is electric power generation and storage.

A representative example of an electrochemical device using such electrochemical energy is a secondary battery, and its use area is gradually increasing.

Recently, as the development and demand for portable devices such as portable computers, portable telephones, cameras, and the like, the demand for secondary batteries is rapidly increasing, and these secondary batteries exhibit high energy density and operating potential, and have a cycle life. Many studies have been conducted on this long, low self-discharge rate lithium battery and are commercially available and widely used.

In addition, as interest in environmental issues grows, researches on electric vehicles and hybrid electric vehicles, which can replace vehicles using fossil fuel, such as gasoline and diesel vehicles, which are one of the main causes of air pollution, are being conducted. . Although nickel-metal hydride secondary batteries are mainly used as power sources for such electric vehicles and hybrid electric vehicles, researches using lithium secondary batteries having high energy density and discharge voltage are being actively carried out, and they are in the commercialization stage.

Conventionally, a typical lithium secondary battery uses graphite as a negative electrode active material, and charging and discharging are performed while repeating a process in which lithium ions of a positive electrode are inserted into and detached from a negative electrode. The theoretical capacity of the battery is different depending on the type of electrode active material, but the charge and discharge capacity decreases as the cycle progresses.

This phenomenon is the biggest cause of the separation of the electrode active material or between the electrode active material and the current collector due to the change of the volume of the electrode caused by the progress of the charging and discharging of the battery, so that the active material fails to function. In addition, during the insertion and desorption process, lithium ions inserted into the negative electrode do not escape properly, thereby reducing the active point of the negative electrode. As a result, the charge and discharge capacity and life characteristics of the battery may decrease as the cycle progresses.

In particular, in order to increase the discharge capacity, when a material such as silicon, tin, a silicon-tin alloy having a large discharge capacity is mixed with natural graphite having a theoretical discharge capacity of 372 mAh / g, the material is charged and discharged. The volume expansion of is significantly increased, resulting in the release of the negative electrode material, resulting in a problem that the capacity of the battery sharply decreases as the repetitive cycle proceeds.

Therefore, it is possible to prevent separation between the electrode active material or between the electrode active material and the current collector with strong adhesive force, and to control the volume expansion of the electrode active material generated during repeated charge and discharge, thereby improving the structural stability of the electrode and the performance of the battery There is an urgent need in the art for a study of possible binder and electrode materials.

Recently, since styrene-butadiene rubber (SBR) is polymerized in water phase to prepare emulsion particles, since the conventional solvent-based binder polyvinylidene fluoride (PVdF) does not satisfy the above requirement, And a method of using it in combination with the agent has been proposed and is currently being used commercially. In the case of such a binder, there is an advantage that it is environmentally friendly and the battery capacity can be increased by reducing the content of the binder, but even in this case, the adhesion sustainability is improved by rubber elasticity, but the adhesive force itself does not show a great effect.

Therefore, there is a high demand for developing a binder having excellent adhesive strength while improving structural stability of the electrode while improving cycle characteristics of the battery.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-described problems of the prior art and the technical problems required from the past.

After extensive research and various experiments, the inventors of the present application improve the cycle characteristics of a secondary battery when a binder for a secondary battery electrode including polymer particles having a specific composition and having specific physical properties as described later is used. It was confirmed that the adhesive force could be improved while contributing to the present invention, and the present invention was completed.

Accordingly, the electrode binder of the secondary battery according to the present invention includes polymer particles having an average particle diameter of 0.05 μm to 0.7 μm by polymerizing three or more types of monomers with a reactive emulsifier, and exhibiting tensile strain during film production. It is composed of 100 to 500% and a tensile strength of 3 MPa or more, and an adhesive force of 15 gf / cm or more.

Balanced tensile strain and tensile strength contribute to the cycle characteristics of the secondary battery by excellent elasticity and strength. Therefore, excellent cycle characteristics can be exhibited when the tensile strain and the tensile strength are each within a predetermined range.

However, in general, as the tensile strength is higher, the internal bonding strength of the binder increases, so that the adhesive strength of the binder to the active material, the current collector, and the like tends to decrease. Low adhesion means that the binder does not function properly in the secondary battery.

On the other hand, according to the present invention, the binder for the electrode of the secondary battery has a tensile strain of 100 to 500% and a tensile strength of 3 MPa or more based on the specific composition as described above and excellent adhesion. Therefore, the binder according to the present invention can exhibit excellent cycle characteristics while sufficiently exhibiting its original function as a binder for electrodes of a secondary battery.

The tensile strain and tensile strength may be generally measured using a tensile pressure applying device after preparing a sample in the shape of a dog bone (5 * 100 mm) film having a thickness of 100 μm. For example, the tensile pressure applying device may use a universal testing machine (UTM). The tensile strain value refers to the ratio of the length in which the sample is elongated without breaking relative to the original length, and the tensile strength means the maximum value of the tensile pressure until the sample is broken.

If the tensile strength is too high, the adhesive force can be reduced, it is preferably 20 MPa or less, more preferably 15 MPa or less.

The adhesive force is a value measured by peeling strength of 180 degrees while peeling off the current collector after manufacturing the electrode using the binder and fixing it to the slide glass. For more specific information about this can be referred to the content of Experimental Example 2 described later.

The binder according to the present invention can exhibit an adhesive force of 15 gf / cm or more, if less than 15 gf / cm may be difficult to exhibit the desired level of cycle characteristics. The upper limit of the adhesive force is not particularly limited, and may be, for example, 40 gf / cm.

Accordingly, the binder for secondary battery electrodes according to the present invention exhibits superior cycle characteristics than any conventional binder by a balanced combination of tensile strain, tensile strength and adhesive force.

In general, emulsifiers refer to materials having both hydrophilic and hydrophobic groups. Therefore, moisture impregnation may occur in the air due to the hydrophilic group. However, in the case of lithium secondary batteries, the presence of moisture causes a big problem in safety. For this reason, efforts have been made to prevent moisture impregnation into the battery for the safety of the battery.

The binder according to the present invention forms a polymer by the reaction of the reactive emulsifier with each other or the reaction between the reactive emulsifier and the monomer by using the reactive emulsifier, thereby providing a binder having low water impregnation in air.

Specifically, emulsifiers tend to separate and move or gather over the film or coating surface when forming or coating the film. In this case, the osmotic pressure by the moisture is increased to increase the moisture impregnation. The binder according to the present invention uses a reactive emulsifier to form a polymer by reaction between the reactive emulsifiers or between the reactive emulsifiers and the monomers, thereby providing a binder having low moisture impregnation in the air since the emulsifiers are not separated separately. .

In one preferred embodiment, the three or more monomers are (a) at least one monomer selected from the group consisting of (meth) acrylic acid ester monomers, (b) acrylate monomers, vinyl monomers and nitrile monomers, And (poly) unsaturated monocarbon-based monomers.

In this configuration, the (A) (meth) acrylic acid ester monomer is contained in 10 to 97.9% by weight based on the total weight of the binder, the (B) group monomer is contained in 1 to 60% by weight, ( C) Unsaturated monocarboxylic acid monomer is contained in 1 to 20% by weight, the reactive emulsifier is preferably included in 0.1 to 10% by weight. More preferably, the (A) (meth) acrylic acid ester monomer is contained in 25 to 80% by weight, the (B) group monomer is contained in 3 to 50% by weight, and the (C) group monomer is 1 to It is included in 20% by weight, 0.1 to 5% by weight of the reactive emulsifier may be included. However, this content range may be appropriately changed according to the properties of the respective monomers and the required binder properties.

The (meth) acrylic acid ester monomer which is the (A) group monomer is, for example, methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, n- Amyl acrylate, isoamyl acrylate, n-ethylhexyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate , N-butyl methacrylate, isobutyl methacrylate, n-amyl methacrylate, isoamyl methacrylate, n-hexyl methacrylate, n-ethylhexyl methacrylate, 2-ethylhexyl methacrylate It may be one or more monomers selected from the group consisting of, hydroxyethyl methacrylate, and hydroxypropyl methacrylate.

Examples of the acrylate monomers belonging to the (b) group monomers include, for example, methacryloxy ethyl urea, β-carboxy ethyl acrylate, aliphatic monoacrylate, dipropylene diacrylate, and ditrimethyllopropane tetraacrylic. Latex, hydroxyethyl acrylate, dipentaerytriol hexaacrylate, pentaerytriol triacrylate, pentaerytriol tetraacrylate, lauryl acrylate, seryl acrylate, stearyl acrylate, lauryl meta It may be at least one selected from the group consisting of acrylate, cetyl methacrylate and stearyl methacrylate.

The vinyl monomers belonging to the (b) group monomer may be one or more selected from the group consisting of styrene, α-methylstyrene, β-methylstyrene, p-t-butylstyrene, divinylbenzene, and mixtures thereof.

The nitrile monomers belonging to the (b) group monomers may be, for example, succinonitrile, sebaconnitrile, fluorinated nitrile, nitrile chloride, acrylonitrile, methacrylonitrile, and the like, more preferably acryl. It may be at least one selected from the group consisting of nitrile, methacrylonitrile or mixtures thereof.

The unsaturated monocarboxylic acid monomers belonging to the (C) group monomers are selected from the group consisting of maleic acid, fumaric acid, methacrylic acid, acrylic acid, glutamic acid, itaconic acid, tetrahydrophthalic acid, corrotonic acid, isocrotonic acid and nadic acid. It may be one or more kinds to select.

The binder of the present invention may further contain a molecular weight modifier and / or a crosslinking agent as a polymerization additive in addition to the monomer.

The molecular weight regulator may be selected from those known in the art, for example, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, 1,3- Butadiene dimethacrylate, neopentyl glycol dimethacrylate, trimethylolpropane trimethacrylate, trimethylolmethane triacrylate, aryl methacrylate (AMA), and the like. , Triallyl isocyanurate (TAIC), triarylamine (TAA), diarylamine (DAA), polyethylene glycol dimethacrylate, polypropylene glycol dimethacrylate, polybutylene glycol diacrylate, Is used.

The binder according to the present invention can be prepared by emulsion polymerization using the monomers and crosslinking agents. The polymerization temperature and the polymerization time may be appropriately determined according to the polymerization method or the kind of the polymerization initiator to be used. For example, the polymerization temperature may be about 50 ° C. to 200 ° C., and the polymerization time may be about 1 to 20 hours. .

In addition, an inorganic or organic peroxide may be used as the polymerization initiator for emulsion polymerization, and for example, a water-soluble initiator including potassium percellate, sodium persulfate, ammonium persulfate, cumene hydroperoxide, benzoyl peroxide, and the like. Oil-soluble initiators, including the like, can be used. In addition, the polymerization initiator may further include an activator to promote the initiation reaction of the peroxide, and such activators include sodium formaldehyde sulfoxylate, sodium ethylenediaminetetraacetate, ferrous sulfate and dextrose. One or more selected from the group consisting of can be used.

In the present invention, the reactive emulsifier preferably includes a reactor having a hydrophilic group and a hydrophobic group and capable of a polymerization reaction at the same time.

In one preferred embodiment, the emulsifier may be one or more selected from the group consisting of ionic emulsifiers and nonionic emulsifiers. The ionic emulsifier may be one or more selected from the group consisting of cationic emulsifiers, anionic emulsifiers and amphoteric emulsifiers.

In the reactive emulsifier according to the present invention, the reactor capable of the polymerization reaction preferably includes at least one carbon-carbon double bond.

In one preferred example, the reactive emulsifier includes a carbon-carbon double bond on one side, and includes one or more selected from the ionic emulsification group and the nonionic emulsification group.

Preferred examples of the anionic emulsification group include fatty acid salts, sulfates, sulfonates, phosphates, sulfosuccinates, and the like. Preferred examples of the nonionic emulsification groups include 1 selected from water-soluble groups such as ethylene oxide and propylene oxide. And one or more types of water-insoluble groups selected from non-aqueous groups such as butyl oxide, phenyl and alkyl groups. These may be included alone or in combination of two or more of the reactive emulsifiers.

Examples of such reactive emulsifiers include sulfate salts of polyoxyethylene allylglycidyl nonylphenyl ether, ammonium sulfate salt, and the like, and nonylphenol used as a raw material of the emulsifier is attracting attention as one of environmental hormones. Therefore, particularly preferably, an environmentally friendly polyoxyalkylene alkenyl ether ammonium sulfate or sodium polyoxyethylene alkyl ether sulfate is used as the anionic reactive emulsifier, and polyoxyalkalen alkenyl ether or the like is used as the nonionic reactive emulsifier. Can be.

In addition, non-reactive emulsifiers may be further added for stability of the reaction. The non-reactive emulsifier may be, for example, at least one selected from the group consisting of fatty acid salts, sulfates, sulfonates, phosphates, and sulfosuccinates, and may be added within 100% of the weight of the reactive emulsifier. Preferably, non-reactive anionic emulsifiers such as sulfate, sulfonate, phosphate and the like may be further added. More specific examples of such non-reactive emulsifiers are known in the art, and a detailed description thereof will be omitted herein.

In some cases, (meth) acrylamide monomers may be further included. In this case, the (meth) acrylamide monomers may be included in an amount of 0.1 to 10 wt% based on the total weight of the binder.

The average particle diameter of the polymer may be 0.05 to 0.7 μm, and the gel content may be 50 to 100%.

The average particle diameter may be controlled by the amount of the emulsifier. In general, as the amount of the emulsifier increases, the particle size decreases, and as the amount of the emulsifier decreases, the particle size tends to increase. In consideration of the desired particle size, reaction time, reaction stability, etc., the amount of the emulsifier used may be adjusted to achieve a desired average particle size.

The gel content is not dissolved when the binder film or dried binder is taken out after immersing in a 3: 2: 5 (weight ratio) mixed solution of ethylene carbonate, propylene carbonate, and diethyl carbonate, which are a mixed solution of an electrolyte solution, at room temperature for 2 days. The weight of is represented by the weight ratio of the initial binder film or the dried binder.

In the present invention, the binder preferably further comprises at least one material selected from the group consisting of a viscosity modifier and a filler. The viscosity modifier and filler will be described in more detail later.

The present invention also provides a mixture for electrodes of a secondary battery comprising the binder and an electrode active material capable of occluding / discharging lithium.

It is preferable that the mixture for electrodes of the said secondary battery further contains a electrically conductive material. The conductive material will be described in more detail later.

Preferred examples of the electrode active material include lithium transition metal oxide powder or carbon powder.

The present invention also provides an electrode for secondary batteries, wherein the electrode mixture is coated on a current collector.

The electrode may be prepared by applying a mixture for electrodes on a current collector, followed by drying and rolling. The secondary battery electrode may be a positive electrode or a negative electrode.

The positive electrode is prepared, for example, by applying a mixture of a positive electrode active material, a conductive material, a binder and the like on the positive electrode current collector, and drying the mixture. The negative electrode is formed by applying a mixture of a negative electrode active material, Followed by drying. In some cases, a conductive material may not be included in the negative electrode.

In the electrode, the electrode active material is a material capable of causing an electrochemical reaction, and a positive electrode active material and a negative electrode active material exist according to the type of electrode.

The positive electrode active material is a lithium transition metal oxide, and includes two or more transition metals, and for example, layered compounds such as lithium cobalt oxide (LiCoO ₂ ) and lithium nickel oxide (LiNiO ₂ ) substituted with one or more transition metals. ; Lithium manganese oxide substituted with one or more transition metals; Formula _{LiNi 1-y M y O 2} ( where, M = Co, Mn, Al , Cu, Fe, Mg, B, Cr, Zn or Ga and Lim, 0.01≤y≤0.7 include one or more elements of the element) A lithium nickel-based oxide represented by the following formula: _{Li 1 + z Ni 1/3 Co 1/3} Mn 1/3 O 2, Li 1 + z Ni 0.4 Mn 0.4 Co 0.2 O 2 , such as _{Li 1 + z Ni b Mn c} Co 1- (b + c + d _{) M d O (2-e} ) A e ( where, -0.5≤z≤0.5, 0.1≤b≤0.8, 0.1≤c≤0.8, 0≤d≤0.2 , 0≤e≤0.2, b + c + d <1, M = Al, Mg, Cr, Ti, Si or Y, and A = F, P or Cl; lithium nickel cobalt manganese composite oxide; And the formula _{Li 1 + x M 1-y} M 'y PO 4-z X z ( wherein, M = a transition metal, preferably Fe, Mn, Co or Ni, M' = Al, Mg or Ti, X = F, S or N, and -0.5? X? +0.5, 0? Y? 0.5, and 0? Z? 0.1), but the present invention is not limited thereto.

Examples of the negative electrode active material include carbon and graphite materials such as natural graphite, artificial graphite, expanded graphite, carbon fiber, non-graphitizable carbon, carbon black, carbon nanotube, fullerene, and activated carbon; Metals such as Al, Si, Sn, Ag, Bi, Mg, Zn, In, Ge, Pb, Pd, Pt and Ti which can be alloyed with lithium and compounds containing these elements; Complexes of metals and their compounds and carbon and graphite materials; Lithium-containing nitrides, and the like. Among them, a carbon-based active material, a silicon-based active material, a tin-based active material, or a silicon-carbon based active material is more preferable, and these may be used singly or in combination of two or more.

The conductive material is a component for further improving the conductivity of the electrode active material, and may be added at 0.01 to 30 wt% based on the total weight of the electrode mixture. 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 carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; Carbon derivatives such as carbon nanotubes and fullerenes, conductive fibers such as carbon fibers and metal fibers; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskeys 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.

In the electrode, the current collector is a portion where electrons move in the electrochemical reaction of the active material, and a positive electrode current collector and a negative electrode current collector exist according to the type of electrode.

The positive electrode current collector is generally made of a thickness of 3 ~ 500 ㎛. Such a positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, the surface of stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel Surface treated with carbon, nickel, titanium, silver or the like can be used.

The negative electrode current collector is generally made to have a thickness of 3 to 500 mu m. Such an anode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery, and may be formed of a material such as copper, stainless steel, aluminum, nickel, titanium, fired carbon, surface of copper or stainless steel A surface treated with carbon, nickel, titanium, silver or the like, an aluminum-cadmium alloy, or the like can be used.

These current collectors may form fine concavities and convexities on the surface thereof to enhance the bonding strength of the electrode active material, and may be used in various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics.

The mixture (electrode mixture) of the electrode active material, the conductive material, and the binder may further include at least one material selected from the group consisting of a viscosity modifier and a filler.

The viscosity adjusting agent may be added up to 30% by weight based on the total weight of the electrode mixture, so as to control the viscosity of the electrode mixture so that the mixing process of the electrode mixture and the coating process on the collector may be easy. Examples of such viscosity modifiers include, but are not limited to, carboxymethyl cellulose, polyacrylic acid, and the like.

The filler is an auxiliary component that suppresses the expansion of the electrode, and is not particularly limited as long as it is a fibrous material without causing chemical changes in the battery. Examples of the filler include olefin polymers such as polyethylene and polypropylene; Fibrous materials such as glass fibers and carbon fibers are used.

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

The lithium secondary battery generally includes a separator and a lithium salt-containing nonaqueous electrolyte in addition to the electrode.

The separator is an insulating thin film interposed between the anode and the cathode and having high ion permeability and mechanical strength. The pore diameter of the separator is generally 0.01 to 10 mu m and the thickness is generally 5 to 300 mu m. As such a separation membrane, for example, a sheet or a nonwoven fabric made of an olefin-based polymer such as polypropylene which is chemically resistant and hydrophobic, 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.

The lithium-containing non-aqueous electrolyte solution consists of a non-aqueous electrolyte solution and a lithium salt.

Examples of the nonaqueous electrolytic solution include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, But are not limited to, lactone, 1,2-dimethoxyethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, Nitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives , Tetrahydrofuran derivatives, ether, methyl pyrophosphate, ethyl propionate and the like can be used.

The lithium salt is a material that is easy to dissolve in the non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF _{6, LiSbF 6, LiAlCl 4,} CH 3 SO 3 Li, (CF 3 SO 2) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, lithium tetraphenyl borate and imide.

In some cases, an organic solid electrolyte, an inorganic solid electrolyte, or the like may be used.

Examples of the organic solid electrolyte include a polymer electrolyte such as a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, an agitation lysine, a polyester sulfide, a polyvinyl alcohol, a polyvinylidene fluoride, Polymers containing ionic dissociation groups, and the like can be used.

Examples of the inorganic solid electrolyte include Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Nitrides, halides and sulfates of Li such as Li ₄ SiO ₄ -LiI-LiOH and Li ₃ PO ₄ -Li ₂ S-SiS ₂ can be used.

In addition, for the purpose of improving charge / discharge characteristics, flame retardancy, etc., the non-aqueous electrolyte solution includes, for example, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, and hexaphosphate triamide. , Nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N, N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxy ethanol, aluminum trichloride, etc. are added May be In some cases, in order to impart nonflammability, a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoride may be further included, and carbon dioxide gas may be further included to improve high temperature storage characteristics, and FEC (Fluoro-Ethylene) may be further included. carbonate), PRS (propene sultone) and the like may be further included.

The secondary battery according to the present invention may not only be used in a battery cell used as a power source for a small device, but also preferably used as a unit battery in a medium and large battery module including a plurality of battery cells used as a power source for a medium and large device. .

Preferred examples of the above medium to large devices include a power tool that is powered by an electric motor and moves; An electric vehicle including an electric vehicle (EV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), and the like; An electric motorcycle including an electric bike (E-bike) and an electric scooter (E-scooter); An electric golf cart; An energy storage system and the like, but are not limited thereto.

As described above, the binder for the electrode of the secondary battery according to the present invention comprises polymer particles having an average particle diameter of 0.05 μm to 0.7 μm by polymerizing three or more types of monomers with a reactive emulsifier, and the tensile strain and the tension during film production While the strength is at least a predetermined range, the adhesion is excellent, contributing to the improvement of the cycle characteristics.

Hereinafter, the present invention will be further described with reference to Examples and the like, but the scope of the present invention is not limited thereto.

Example 1

Butyl acrylate (80 g), styrene (20 g), acrylic acid (5 g) as a monomer, ethylene glycol dimethacrylate (1 g) as a crosslinking agent, and latemul PD104 (KAO), an anionic reactive emulsifier as an emulsifier (0.5) g) and latemul E-118B (0.5 g), an anionic emulsifier, were added to water containing potassium peroxide as an initiator, and these were mixed and polymerized at a temperature of 70 ° C. for about 10 hours. Through the polymerization as described above, a binder for an electrode of a secondary battery including polymer particles having an average particle diameter of 0.4 μm in which monomers and crosslinkers were polymerized was prepared. The average particle diameter is controlled by the amount of the emulsifier. In general, as the amount of the emulsifier increases, the particle size decreases, so that the amount of the emulsifier used is adjusted in consideration of the desired particle size, reaction time, and reaction stability.

 [Example 2]

A secondary battery including polymer particles having an average particle diameter of 0.25 μm was obtained in the same manner as in Example 1, except that anionic reaction type emulsifier latemul PD104 (1 g) and anionic emulsifier latemul E-118B (0.5 g) were used. A binder for electrodes was prepared.

[Example 3]

A secondary battery including polymer particles having an average particle diameter of 0.1 μm was obtained in the same manner as in Example 1 except that anionic reaction type emulsifier latemul PD104 (1 g) and anionic emulsifier latemul E-118B (1 g) were used. A binder for electrodes was prepared.

Comparative Example 1

Polyvinylidene fluoride (PVdF: polyvinylidene fluoride, KF1100, Kureha Chemical, Japan) was prepared as a binder for a secondary battery electrode.

Comparative Example 2

Butadiene was used in place of the butyl acrylate of Example 1, and the same method as in Example 1 was used except that the anionic emulsifier latemul E118B (1 g) was used instead of the latemul PD104 (1 g), an anionic reactive emulsifier. A binder for an electrode of a secondary battery including polymer particles having a particle diameter of 0.1 μm was manufactured.

 [Comparative Example 3]

An electrode of a secondary battery including polymer particles having an average particle diameter of 0.2 μm using the same method as in Example 1, except that anionic emulsifier latemul E118B (1 g) was used instead of latemul PD104 (1 g), an anionic reactive emulsifier. A binder was prepared.

[Comparative Example 4]

Secondary battery including polymer particles having an average particle diameter of 0.8 μm using the same method as Example 1 except for using anionic emulsifier latemul E-118B (0.4 g) instead of anionic reactive emulsifier latemul PD104 (1 g) The binder for electrodes was manufactured.

Experimental Example 1 Tensile Strength and Tensile Strain Test

The binders prepared in Examples 1 to 3 and Comparative Examples 1 to 4 were coated on PET films, and then dried at room temperature for 1 hour and at 60 ° C. for 2 hours to prepare 100 μm thick films. The prepared film was cut into dog bone (5 * 100 mm) shapes, and tensile strength and tensile strain were measured using a universal testing machine (UTM), and the results are shown in Table 1 below. The evaluation measured 5 values and set it as the average value.

[Table 1]

As shown in Table 1, the binders of Examples 1 to 3 have a much higher tensile strain than the PVdF binder of Comparative Example 1, and are more tensile than the binders of Comparative Examples 2 to 4 without using a reactive emulsifier. The strain values are similar but the tensile strength values are excellent.

[Experimental Example 2] Adhesion test

When the binders prepared in Examples 1 to 3 and Comparative Examples 1 to 4 were used as negative electrode binders for lithium secondary batteries, the adhesion between the electrode active material and the current collector was measured.

First, a slurry was prepared by adding the binders according to Examples 1 to 3 and the binders according to Comparative Examples 1 to 4 so that the ratios of the active material, the conductive material, the viscosity regulator, and the binder were 96: 1: 1: 1: 1. Thereafter, the slurry was coated on Cu foil to prepare an electrode.

After cutting the prepared electrode surface was fixed to the slide glass, peeling off the current collector was measured 180 ° peeling strength and the results are shown in Table 2 below. Evaluation was made into the average value by measuring five or more peeling strengths.

[Table 2]

As shown in Table 2, it can be seen that the binders of Examples 1 to 3 using the reactive emulsifier not only have better adhesion than the PVdF binder of Comparative Example 1 but also exhibit at least 15 gf / cm of adhesion. In addition, it is excellent in the dispersibility of the slurry, it can be confirmed that the adhesive strength is larger than the binders of Comparative Examples 2 to 4.

The binders of Comparative Examples 2 to 4 exhibited similar adhesion to the binders of Comparative Example 1, but as described above, the binders of Examples 1 to 3, as can be seen in Experimental Example 3 described later due to the low tensile strength. Its cycle characteristics are not good compared to these.

Experimental Example 3 Cycle Characteristic Test

After the binders of Examples 1 to 3 and the binders according to Comparative Examples 1 to 4 were added in the ratios of the active material, the conductive material, the thickener, and the binder in the ratio of 96: 1: 1: 1, the slurry was prepared. The slurry was coated onto Cu foil to make an electrode. Li metal was used as a counter electrode, and a coin-type battery was manufactured by using an electrolyte solution containing 1 M LiPF ₆ in a solvent having EC: DMC: DEC = 1: 1: 1: 1.

For each of the coin batteries, charge and discharge characteristic changes were tested using a charge and discharge measuring device. The obtained cell obtained the first cycle discharge capacity through 0.1 C charge and 0.1 C discharge, and repeated 50 cycles of charging and discharging to measure the capacity retention rate (%) at 50 cycles relative to the initial capacity. The results are shown in Table 3 below.

[Table 3]

As shown in Table 3, the battery of Examples 1 to 3 using the binder according to the present invention exhibited a capacity retention of at least 94% or more compared to the initial capacity even after 50 cycles. This is much higher than Comparative Example 1, and improved by 2% or more compared with Comparative Examples 2 to 4. This difference is more pronounced in the medium-large secondary battery using an increased number of cycles or a large amount of active material in one battery cell.

Those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims (20)

As a binder for an electrode of a secondary battery, three or more monomers and a reactive emulsifier are polymerized to include polymer particles having an average particle diameter of 0.05 μm to 0.7 μm, and the tensile strain of the film is 100 to 500%. , Tensile strength is 3 MPa or more, adhesive strength is more than 15 gf / cm, the reactive emulsifier includes a carbon-carbon double bond on one side, in the ionic emulsification group and nonionic emulsification group on the other side A binder for a secondary battery electrode, comprising at least one selected. According to claim 1, wherein the three or more monomers are (A) at least one monomer selected from the group consisting of (meth) acrylic acid ester monomers, (b) acrylate monomers, vinyl monomers and nitrile monomers, And (c) a mixture of unsaturated monocarboxylic acid monomers. According to claim 2, wherein the (A) (meth) acrylic acid ester monomer is contained in 10 to 97.9% by weight based on the total weight of the binder, the (B) group monomer is contained in 1 to 60% by weight , (C) unsaturated monocarboxylic acid-based monomer is contained 1 to 20% by weight, the binder for the electrode of the secondary battery, characterized in that the reactive emulsifier is contained in 0.1 to 10% by weight. The method of claim 2, wherein the (meth) acrylic acid ester monomer is methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, n- amyl acrylate, iso Amyl acrylate, n-ethylhexyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, n-butyl Methacrylate, isobutyl methacrylate, n-amyl methacrylate, isoamyl methacrylate, n-hexyl methacrylate, n-ethylhexyl methacrylate, 2-ethylhexyl methacrylate, hydroxyethyl methacrylate Electrode of a secondary battery, characterized in that at least one monomer selected from the group consisting of acrylate and hydroxypropyl methacrylate Binder. The method of claim 2, wherein the acrylate monomer is methacryloxy ethyl ethylene urea, β-carboxy ethyl acrylate, aliphatic monoacrylate, dipropylene diacrylate, ditrimethyllopropane tetraacrylate, hydroxyethyl acrylic Latex, dipentaerythritol hexaacrylate, pentaerytriol triacrylate, pentaerytriol tetraacrylate, lauryl acrylate, ceryl acrylate, stearyl acrylate, lauryl methacrylate, cetyl methacrylate A binder for a secondary battery electrode, characterized in that at least one monomer selected from the group consisting of a rate and stearyl methacrylate. The electrode of a secondary battery according to claim 2, wherein the vinyl monomer is at least one monomer selected from the group consisting of styrene, α-methylstyrene, β-methylstyrene, pt-butylstyrene, and divinylbenzene. Binder. The method of claim 2, wherein the nitrile monomers are secondary, characterized in that at least one monomer selected from the group consisting of succinonitrile, sebaconnitrile, fluoride nitrile, nitrile chloride, acrylonitrile and methacrylonitrile. Binder for electrodes of battery. The method of claim 2, wherein the unsaturated monocarboxylic acid monomer is selected from the group consisting of maleic acid, fumaric acid, methacrylic acid, acrylic acid, glutaric acid, itaconic acid, tetrahydrophthalic acid, corrotonic acid, isocrotonic acid and nadic acid. A binder for secondary electrode electrodes, characterized in that at least one monomer. delete The binder of claim 1, wherein the ionic emulsifying group is at least one selected from the group consisting of a cationic emulsifying group, an anionic emulsifying group, and a positive emulsifying group. The binder of claim 10, wherein the anionic emulsifying group is at least one selected from the group consisting of sulfate, sulfonate, phosphate and sulfosuccinate. 2. The binder for electrodes of secondary batteries according to claim 1, wherein the nonionic emulsifying group includes a water-soluble group and a water-insoluble group. The binder for an electrode of a secondary battery of claim 1, further comprising a non-reactive emulsifier in addition to the reactive emulsifier. The binder of claim 13, wherein the non-reactive emulsifier is contained within 100% of the weight of the reactive emulsifier. 15. An electrode binder for a secondary battery comprising a binder for an electrode of a secondary battery according to any one of claims 1 to 8 and 10 to 14, and an electrode active material capable of occluding / discharging lithium. Mixture. The mixture for secondary battery electrodes according to claim 15, wherein the electrode active material is lithium transition metal oxide powder or carbon powder. A secondary battery electrode, wherein the electrode mixture of the secondary battery according to claim 15 is coated on a current collector. 18. The electrode of claim 17, wherein the electrode current collector has a thickness of 3 to 500 µm and fine irregularities are formed on a surface thereof. A lithium secondary battery comprising the secondary battery electrode according to claim 18. As a binder for an electrode of a secondary battery, three or more monomers and a reactive emulsifier are polymerized to include polymer particles having an average particle diameter of 0.05 μm to 0.7 μm, and the tensile strain of the film is 100 to 500%. A binder for a secondary battery electrode having a tensile strength of 3 MPa or more and an adhesive strength of 15 gf / cm or more and further comprising a non-reactive emulsifier in addition to the reactive emulsifier.