KR20080034218A - Binder composition for secondary battery, and electrode employed with the same, and lithium secondary battery - Google Patents

Abstract

A binder composition for a secondary battery is provided to improve adhesiveness between electrode active materials and between an electrode active material and a current collector and produce a secondary battery having excellent coating characteristics and battery characteristics. A binder composition for a secondary battery has (A) conjugated diene-based latex particles and (B) copolymer latex particles which are present as independent phase. The latex particles(A) have an average particle size of at least 200 nm or larger and are contained in an amount of 30wt% or more, based on the mass of the solids in the composition. The latex particles(B) have an average particle size of 100-260 nm. An electrode material for a secondary battery comprises the binder composition, and an electrode active material.

Description

Binder composition for secondary battery, electrode and lithium secondary battery using same {Binder Composition for Secondary Battery, and Electrode Employed with the Same, and Lithium Secondary Battery}

The present invention is a binder composition for a secondary battery, more specifically, conjugated diene-based latex particles (A) and polymer copolymer latex particles (B) are present in an independent phase, the latex particles (A) is at least 200 nm or more The present invention relates to a composition having an average particle diameter and containing at least 30% by weight based on the mass of solids, and an electrode and a lithium secondary battery using the same.

As technology development and demand for mobile devices increase, the demand for secondary batteries as energy sources is rapidly increasing, and lithium secondary batteries having high energy density and voltage are commercially used in such secondary batteries. Such lithium secondary batteries generally use lithium transition metal oxides as positive electrode active materials and graphite-based materials as negative electrode active materials.

The electrode of a lithium secondary battery is prepared by mixing such an active material and a binder resin component and dispersing it in a solvent to make a slurry, applying it to the surface of the current collector, and drying the mixture to form a mixture layer. However, the charge and discharge cycle proceeds due to the volume change caused by the reaction with lithium during charge and discharge, the negative electrode active material is detached from the current collector during continuous charge and discharge, or the resistance increases due to the change of the contact interface between the negative electrode active materials. As a result, the capacity is drastically lowered, resulting in a shorter cycle life.

The binder gives a binding force between the active material as well as between the active material and the current collector, and has an important effect on battery characteristics by suppressing volume expansion caused by charging and discharging of the battery. However, when an excessive polymer is used as a binder to reduce the volume change during charging and discharging, it is possible to reduce the detachment of the active material from the current collector, but the electrical resistance of the negative electrode increases due to the electrical insulation of the binder, and relatively As the amount decreases, problems such as capacity reduction arise.

Polyvinylidene fluoride (PVdF) has been widely used as such a binder resin, but the adhesion is poor, there is a problem in safety, and by using an organic solvent during slurry production, problems such as environmental pollution are generated. In order to solve the problem of PVdF, a method of polymerizing styrene-butadiene rubber (SBR) in an aqueous phase and using a thickener and the like has been proposed. Such a binder has an advantage of being environmentally friendly and increasing battery capacity by reducing the amount of binder used. However, even in this case, the binding sustainability is improved by the elasticity of the rubber, but the binding force itself does not show a great effect, and the improvement of battery characteristics is also required. Many methods have been proposed to provide excellent binding power and to improve battery characteristics.

In this regard, some prior art has been proposed to solve the problem when using the SBR alone as a binder, which will be described as an example.

Korean Patent Application Publication No. 2003-0033595 discloses a method of mixing a mixture of PVdF and SBR at a predetermined ratio, and Korean Patent Registration No. 0582518 describes an ideal structure in which two or more polymers having different chemical structures form an ideal structure. The present invention relates to a battery binder containing composite polymer particles. Korean Patent Application Publication No. 2004-0078927 discloses a composite polymer particle having a two-phase or more structure containing a polymer which is respectively related to battery characteristics, adhesion and coating characteristics. US Patent No. 6,773,838 claims that high charge and discharge efficiency and stability can be achieved by using modified SBR binders and thickeners in a range of amounts. In addition, US Patent No. 6,881,517 discloses a method of using a polymer binder containing a butadiene structure in a certain ratio, US Patent No. 6,428,929 discloses a method of adding an acrylic acid derivative copolymer to a binder containing a butadiene structure. Is starting.

In addition, mixture binders of various compositions have been proposed in that the properties of the binder can be improved by properly combining the properties of the respective polymers used in the preparation of the binder. U. S. Patent No. 5,380, 606 discloses a composition comprising a polyamic acid, and U. S. Patent No. 6,399, 246 discloses a method of mixing styrene-butadiene copolymer or styrene-acrylate copolymer with polyacrylamide. Is disclosed.

However, in spite of these various technical proposals, binders which still exhibit desired levels of physical properties have not been developed.

On the other hand, as the cathode made of graphite-based material almost reaches its theoretical maximum capacity of 372 mAh / g (844 mAh / cc), it is limiting its ability to play a sufficient role as an energy source for the rapidly changing next generation mobile devices. have. Lithium metal, which has been examined as a negative electrode material, has a very high energy density to realize a high capacity, but has a problem of safety due to dendrite growth and short cycle life during repeated charging and discharging. In addition, attempts have been made to use carbon nanotubes as negative electrode active materials, but problems such as low productivity, high price, and low initial efficiency of 50% or less have been pointed out.

In this regard, many studies have recently been made, with silicon, tin, or alloys thereof known to be capable of reversibly occluding and releasing large amounts of lithium through compound formation reactions with lithium. It's going on. For example, silicon is promising as a high capacity cathode material because the theoretical maximum capacity is about 4020 mAh / g (9800 mAh / cc, specific gravity 2.23), which is much larger than graphite-based materials.

However, since silicon, tin, or alloys thereof have a very large volume change of 200 to 300% due to reaction with lithium during charge and discharge, the negative electrode active material detaches from the current collector or contacts the negative electrode active material during continuous charge and discharge. Due to the increase in resistance due to the large change in the interface, as the charge and discharge cycle proceeds, there is a problem that the capacity is drastically lowered and the cycle life is shortened. Due to these problems, when the conventional binder for graphite negative electrode active material, that is, PVdF, SBR, or the like is used as it is for a silicon-based or tin-based negative electrode active material, a desired effect cannot be obtained.

Therefore, in the conventional graphite-based lithium secondary battery, a silicon or tin-based negative electrode active material with a technology that can improve the capacity of the battery by securing the adhesion between the active material and the current collector and the active materials even when using a small amount of binder, In the lithium secondary battery using the need to develop an excellent binder that can maintain the adhesive force with the current collector while absorbing a large volume change of the negative electrode active material during charge and discharge.

In this regard, the present invention provides a composition containing conjugated diene-based latex particles, which are present in an independent phase and have a predetermined particle diameter, as described below.

On the other hand, the present applicant in the Korean Patent Application Publication No. 2004-078927, a two-phase or more binder in which physical properties are distinguished in relation to adhesive strength and / or coating properties, the polymer comprising a monomer which can control the battery characteristics, and the adhesive force It has been proposed a technique using a 'composite polymer particles' consisting of a polymer containing a monomer capable of controlling the as a binder. The composite polymer particles are particles which are bonded to each other by chemical bonding instead of a single homogeneous phase, and have been described as exhibiting excellent adhesion in the range of 100 to 300 nm in final particle diameter.

The prior art exemplifies a conjugated diene monomer as an example of a monomer capable of controlling battery characteristics, which is a form having two or more phase structures in which different monomers are distinguished from each other by chemical bonding in one latex particle. In this respect, the independent particles composed only of the conjugated diene-based structure are distinguished from the present invention composed of having a range of particle sizes.

In addition, the inventors of the present application continually researched, select the monomers constituting the composite polymer particles as a specific component, and added more than a certain amount of the specific particle size over a predetermined range, these are complete When the composition is configured to form an independent phase, it was confirmed that the application exhibits an unexpected effect.

In the case of the free-phase latex particles according to the present invention, it is assumed that the self-developed latex particles exhibit excellent properties as a rubber in the electrode as compared with the composite polymer particles, thereby greatly contributing to the improvement of binder adhesion. In this regard, according to an experiment conducted by the inventors of the present application, as a result of comparing the adhesive force under the same binder usage conditions as the prior art, it was confirmed that the adhesive force of the present invention is much superior.

On the other hand, some techniques are known to illustrate the possibility of using a variety of polymers as a binder. For example, Korean Patent Application Publication No. 2001-099909 discloses a structural unit derived from a monoethylenically unsaturated carboxylic acid ester monomer, a structural unit derived from a monoethylenically unsaturated carboxylic acid monomer, and a conjugated diene monomer. Disclosed is a binder composition for a lithium ion secondary battery electrode comprising at least one structural unit selected from structural units and dispersed in an organic dispersion medium as composite polymer particles present in the form of particles. However, the above technique has a problem in that since the polymer particles are difficult to dissolve in the electrolyte, a predetermined electrolyte must be used and the gel content range must be limited.

In addition, Korean Patent Publication No. 2005-075635 discloses a mixed binder including an active material material capable of occluding and releasing lithium, a synthetic rubber latex binder, a cellulose binder, and an acrylamide water-soluble polymer. This is superior to the conventional binder, but when used as a binder of the active material having a large volume expansion during charging and discharging, the crack of the electrode increases with repeated charge and discharge, thereby increasing the irreversible portion, ultimately the secondary battery There is a limit to increasing the lifespan.

However, these prior arts merely illustrate various kinds of polymers that can be used as binders, and do not suggest binders consisting of combinations having specific particle diameters and content ranges according to the present invention as described below. This particular combination does not imply or teach a significant synergistic effect of the adhesion and battery properties of the binder.

On the other hand, Japanese Patent Application Laid-Open No. 1998-241693 is a binder for hydrogen storage electrodes, comprising an aromatic vinyl unit, a conjugated unsaturated hydrocarbon unit, a (meth) acrylic acid ester unit and a functional group-containing compound unit which are 10 to 40% by weight of the copolymer. A composition consisting of an aqueous dispersion of a copolymer is disclosed.

However, the above technique is a binder for a hydrogen storage electrode of a nickel hydride secondary battery, and since the hydrogen storage battery has a large difference from the lithium secondary battery in the electrolyte composition, etc., due to the difference in the mechanism of action during charging and discharging, the binder for the hydrogen storage battery is a lithium secondary battery. It is difficult to use it as it is, and it is also different in practical applications.

Accordingly, an object of the present invention is to solve the problems of the prior art as described above and the technical problems that have been requested from the past.

After extensive research and various experiments, the inventors of the present application have conjugated diene-based latex particles and polymer copolymer latex particles as independent phases, and secondary battery binders containing a large amount of latex particles in a predetermined amount or more. The composition was found to exhibit excellent adhesion and coating properties and balanced physical properties of battery characteristics, and came to complete the present invention.

Accordingly, in the binder composition for a secondary battery according to the present invention, the conjugated diene-based latex particles (A) and the polymer copolymer latex particles (B) exist as independent phases, and the latex particles (A) have a particle diameter of at least 200 nm or more. It is comprised by 30 weight% or more based on solid content mass.

Although the basic physical properties of the latex particles (A) and the polymer copolymer latex particles (B) are known, when the large diameter latex particles (A) as in the present invention are contained in a certain amount or more as an independent phase, they are generally It was newly confirmed that a significant effect increase over expected physical properties was obtained, and this fact can be confirmed in later experimental examples.

Therefore, when the binder composition according to the present invention is applied to the electrode mixture and the secondary battery, it is possible to maintain excellent bonding between the active materials and the electrode active material and the current collector, which undergo a volume change during charge and discharge, and improve the coating properties and cycle characteristics. In addition, it can improve battery characteristics by providing high electrical conductivity by activating the movement of electrons and lithium ions by acting as electrically conductive particles.

The latex particles (A) according to the present invention, as defined above, have an average particle diameter of at least 200 nm or more, preferably 250 to 400 nm. In addition, the latex particles (A) is included in the 30 wt% or more based on the solids mass, preferably 50 to 75 wt% based on the solids mass.

According to the experiments performed by the inventors of the present application, when the particle size of the latex particles (A) is less than 200 nm or when the content is included in less than 30% by weight, the adhesion is greatly reduced, on the contrary, the content of the latex particles (A) is Too much swelling of the latex particles causes desorption of the electrode from the current collector, resulting in deterioration of coating and battery characteristics.

The method for producing the large-diameter latex particles (A) is not particularly limited, and for example, agglomeration method for acid-enlarging or freezing small-diameter latex particles to increase particle size, or emulsion polymerization of the latex particles directly without enlargement process, etc. This can be used.

The average particle diameter of the latex particles (B) is not particularly limited, and may be preferably 100 to 260 nm.

However, when the average particle diameter of the latex particle (B) is too large, it causes an increase in internal degradation by disturbing the movement of the electrode active material, and on the contrary, when too small, the flexibility and the bonding strength of the binder become weak, which is not preferable.

The latex particles (A) are, for example, styrene-butadiene copolymer, acrylonitrile-butadiene copolymer, styrene-isoprene copolymer, acrylate-butadiene rubber, acrylonitrile-butadiene-styrene rubber, ethylene-propylene- Diene-based polymers or partially polymerized, hydrogenated, epoxidized, brominated polymers and mixtures thereof may be used, but are not limited thereto, and preferably, 1,3-butadiene, isoprene, chloroprene, and p It may be a polymer of one or more monomers selected from the group consisting of leriden.

The latex particles (B) are not particularly limited and are preferably selected from the group consisting of aromatic vinyl compounds, vinyl cyan compounds, (meth) acrylic acid ester compounds, (meth) acryl amide compounds and unsaturated monocarboxylic acid compounds. It may be a polymer of one or more monomers.

As the aromatic vinyl compound, for example, alpha-methylstyrene, para-methylstyrene, vinyltoluene, etc. may be used in addition to styrene, and the vinyl cyan compound may be, for example, acrylonitrile, methacrylonitrile or eta. Chloronitrile and the like can be used.

The acrylic acid ester compound is, for example, methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, n-hexyl acrylate, 2-ethylhexyl Acrylate, hydroxyethyl acrylate, lauryl acrylate and the like can be used, and the methacrylic acid ester compound is methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, n-butyl meta Acrylate, isobutyl methacrylate, n-hexyl methacrylate, 2-ethylhexyl methacrylate, hydroxyethyl methacrylate, lauryl methacrylate and the like can be used.

The (meth) acryl amide compound is, for example, acrylamide, n-methylol acrylamide, n-butoxy methylacrylamide, methacrylamide, n-methylol methacrylamide, n-butoxy methyl meth Krillamide may be used, and the unsaturated monocarboxylic acid-based compound may be acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, styrene sulfonic acid and the like.

The conjugated diene-based latex particles, which are latex particles (A), may be prepared using, for example, conjugated diene-based monomers, a polymerization initiator, an electrolyte, a molecular weight regulator, an emulsifier, and the like, and the latex particles (B) may be, for example, By adding a polymerization initiator, a crosslinking agent, a molecular weight modifier emulsifier, etc., it may be prepared using a known suspension polymerization method, dispersion polymerization method, two-stage polymerization method of a seed polymerization method and the like, The polymerization time may be adjusted to about 0.5 to 20 hours to prepare the emulsion polymerization method.

The polymerization initiator may be an inorganic or organic peroxide, for example, a water-soluble initiator including potassium persulfate, sodium persulfate, ammonium persulfate, and the like, and an oil-soluble initiator including cumene hydroperoxide, benzoyl peroxide, and the like. Can be used. In addition, the polymerization initiator may further include an activator to promote the initiation reaction of the peroxide, wherein the activator is sodium formaldehyde sulfoxylate, sodium ethylenediamine tetraacetate, ferrous sulfate and dextrose It may be one or more selected from the group consisting of.

The crosslinking agent is, for example, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, 1,3-butanediol dimethacrylate, 1,6-hexanediol dimethacrylate Laterate, neopentyl glycol dimethacrylate, trimethylol propane trimethacrylate, trimethylol methane triacrylate and the like. Grafting agents include aryl methacrylate (AMA), triaryl isocyanurate (TAIC), triaryl amine (TAA), diaryl amine (DAA) and the like.

The emulsifier may be, for example, a fatty acid salt system represented by oleic acid, stearic acid, lauric acid, sodium or potassium salts of mixed fatty acids, general anionic emulsifiers such as rosin acid, and the like, preferably latex. Reactive emulsifiers may be added to improve the stability of the. The said emulsifier can be used individually or in mixture of 2 or more types.

As said molecular weight regulator, mercaptans, terpines, such as terbinolene, dipentene, t-terpyene, halogenated hydrocarbons, such as chloroform and carbon tetrachloride, can be used, for example.

When the latex particles (A) and latex particles (B) are present in independent phases, it is very important that the agglomeration between the particles does not occur since the effect of improving adhesion is improved.

In one preferred embodiment, the acidity (pH) of the prepared latex particles (A) and latex particles (B) can be adjusted to maintain the independent phase without aggregation of the particles (A, B) in the mixture.

When the pH of the latex particles (B) is acidic, aggregation with the latex particles (A) may occur, so that the independent phase may be maintained by adjusting the pH by titrating it with a base. In this case, for example, potassium hydroxide, sodium hydroxide, lithium hydroxide, and the like may be used, but are not limited thereto. Preferably, the base may be lithium hydroxide.

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

The electrode active material is a material that plays an important role in determining the capacity of the battery. Among them, examples of the active material for a positive electrode include a compound substituted with a layered compound such as lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), or one or more transition metals; Lithium manganese oxides such as Li _{1 + x} Mn _2-x O ₄ (where x is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ , LiMnO _2, and the like; Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ , Cu ₂ V ₂ O ₇ and the like; Ni-site type lithium nickel oxide represented by the formula LiNi _1-x M _x O ₂ , wherein M = Co, Mn, Al, Cu, Fe, Mg, B, or Ga, and x = 0.01 to 0.3; Formula LiMn _2-x M _x O ₂ (wherein M = Co, Ni, Fe, Cr, Zn or Ta and x = 0.01 to 0.1) or Li ₂ Mn ₃ MO ₈ (wherein M = Fe, Co, Lithium manganese composite oxide represented by Ni, Cu or Zn); LiMn ₂ O _{4 in} which a part of Li in the formula is substituted with alkaline earth metal ions; Disulfide compounds; Fe ₂ (MoO ₄ ) ₃ and the like.

Examples of the negative electrode active material include natural graphite, artificial graphite, MPCF, MCMB, PIC, phenol resin fired body, PAN-based carbon fiber, petroleum coke, activated carbon, graphite, and the like. Carbonaceous substances, conductive polymers such as polyacene, and lithium-based metals such as lithium metal and lithium alloy.

The form of the graphite is not particularly limited, and may be amorphous, flat, flake, granular or the like. The average particle diameter of graphite is 0.1-100 micrometers, Preferably it is 1-40 micrometers, More preferably, it is 2-30 micrometers. In addition, a silicon-graphite composite active material or a tin-graphite composite active material may be used by mixing, pulverizing and firing silicon or tin with the graphite. At this time, the size of the silicon or tin particles is 0.1 to 5 ㎛, preferably 0.1 to 2 ㎛, more preferably about 0.1 to 1 ㎛.

In addition to the electrode active material and the binder, the electrode mixture according to the present invention may further include other components such as a dispersion medium, a conductive material, a viscosity modifier, a filler, a coupling agent, an adhesion promoter, or a combination of two or more thereof.

The dispersion medium is not particularly limited, and in particular, the binder according to the present invention may be dispersed in water as well as an organic solvent. When the slurry for battery electrodes of this invention is apply | coated and dried to an electrical power collector, it is preferable that it is a liquid at normal temperature and normal pressure which can maintain the shape of a polymer particle. For example, water; Alcohols such as methanol, ethanol, propanol, isopropanol, butanol, isobutanol, s-butanol, t-butanol, pentanol, isopentanol and hexanol; Ketones such as acetone, methyl ethyl ketone, methyl propyl ketone, ethyl propyl ketone, cyclopentanone, cyclohexanone and cycloheptanone; Methyl ethyl ether, diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, diisobutyl ether, din-amyl ether, diisoamyl ether, methylpropyl ether, methyl isopropyl ether, methyl butyl ether, Ethers such as ethyl propyl ether, ethyl isobutyl ether, ethyl n-amyl ether, ethyl isoamyl ether and tetrahydrofuran; Lactones such as gamma-butyrolactone and delta-butyrolactone; Lactams such as beta-lactam; Cyclic aliphatic compounds such as cyclopentane, cyclohexane and cycloheptane; Aromatic hydrocarbons such as benzene, toluene, o-xylene, m-xylene, p-xylene, ethylbenzene, propylbenzene, isopropylbenzene, butylbenzene, isobutylbenzene, n-amylbenzene; Aliphatic hydrocarbons such as heptane, octane, nonane and decane; Linear and cyclic amides such as dimethylformamide and N-methylpyrrolidone; Esters such as methyl lactate, ethyl lactate, propyl lactate, butyl lactate, and methyl benzoate; Although the liquid substance which comprises the solvent of the electrolyte solution mentioned later is mentioned, It is not limited only to these, You may use it, mixing about 2-5 types of said dispersion mediums.

It is preferable in the process of electrode preparation that a boiling point uses a dispersion medium of 80 degreeC or more, Preferably it is 85 degreeC or more as said dispersion medium.

The conductive material is a component for further improving the conductivity of the electrode active material, and may be added in an amount of 1 to 20 wt% based on the total weight of the electrode mixture. Such a conductive material is not particularly limited as long as it has conductivity without causing chemical change in the battery, and examples thereof include graphite such as natural graphite and artificial graphite; Carbon blacks such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fibers and metal fibers; Metal powders such as carbon fluoride powder, aluminum powder 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.

The viscosity modifier is a component that adjusts the viscosity of the electrode mixture so that the mixing process of the electrode mixture and the coating process on the current collector thereof can be easily added, up to 30% by weight based on the total weight of the electrode mixture. Examples of such viscosity modifiers include, but are not limited to, carboxymethyl cellulose, polyvinylidene fluoride, and the like. In some cases, the solvent described above can serve as a viscosity modifier.

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 fiber and carbon fiber, are used.

The coupling agent is an auxiliary component for increasing the adhesion between the electrode active material and the binder, it characterized in that it has two or more functional groups, can be used up to 30% by weight based on the weight of the binder. Such coupling agents include, for example, one functional group reacting with a hydroxyl group or a carboxyl group on the surface of a silicon, tin, or graphite-based active material to form a chemical bond, and the other functional group is chemically bonded through a reaction with a polymer binder. It may be a material forming a. Specific examples of the coupling agent include triethoxysilylpropyl tetrasulfide, mercaptopropyl triethoxysilane, aminopropyl triethoxysilane, and chloropropyl triethoxysilane ( chloropropyl triethoxysilane, vinyl triethoxysilane, methacryloxypropyl triethoxysilane, glycidoxypropyl triethoxysilane, isocyanatopropyl triethoxysilane, cyan Although silane coupling agents, such as atopropyl triethoxysilane, are mentioned, It is not limited only to these.

The adhesion promoter is an auxiliary component added to improve the adhesion of the active material to the current collector, it may be added in less than 10% by weight compared to the binder, for example, oxalic acid (oxalic acid), adipic acid (adipic acid), Formic acid, acrylic acid derivatives, itaconic acid derivatives, and the like.

As the molecular weight modifier, t-dodecyl mercaptan, n-dodecyl mercaptan, n-octyl mercaptan, etc. may be used, and as a crosslinking agent, 1,3-butanediol diacrylate, 1,3-butanediol dimethacrylate, 1,4-butanediol diacrylate, 1,4-butanediol dimethacrylate, aryl acrylate, aryl methacrylate, trimethylolpropane triacrylate, tetraethyleneglycol diacrylate, tetraethyleneglycol dimethacrylate or Divinylbenzene and the like can be used.

The present invention also provides a secondary battery electrode formed by applying the electrode mixture to a current collector.

The secondary battery electrode is manufactured by coating an electrode mixture, in which an electrode active material, a binder, and optionally a conductive material, a filler, and the like are mixed with a current collector. For example, the slurry may be prepared by applying a slurry on a current collector such as a metal foil, followed by drying and pressing.

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

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

The positive electrode current collector is generally made to a thickness of 3 to 500 μm. 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.

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 secondary battery electrode according to the present invention can be used for both the negative electrode and the positive electrode, of which the negative electrode is more preferred. In particular, a silicon-based active material, a tin-based active material, a silicon-carbon-based active material, or the like, which has a high capacity but has a large volume change during charge and discharge, is more preferable.

The silicon or tin-based negative active material is meant to include silicon (Si) particles, tin (Sn) particles, silicon-tin alloys, their respective alloy particles, composites, and the like. Typical examples of the alloy include, but are not limited to, solid solutions such as aluminum (Al), manganese (Mn), iron (Fe), titanium (Ti), intermetallic compounds, eutectic alloys, and the like. . The composite can be used as a preferred example, a silicone / graphite composite according to the applicant's international patent application WO 2005/011030, the contents of which are incorporated by reference in the context of the present invention. Artificial graphite and natural graphite may be used as the graphite, and the shape of the graphite is not particularly limited, and may be amorphous, flat, flake, or granular.

The present invention also provides a lithium secondary battery comprising the electrode. The lithium secondary battery has a structure in which a lithium salt-containing non-aqueous electrolyte is impregnated into an electrode assembly having a separator interposed between a positive electrode and a negative electrode.

When the binder is used only in the positive electrode and the negative electrode, for example, the negative electrode, a general binder known in the art may be used for the positive electrode. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, Polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butylene rubber, fluorine rubber, various copolymers, high polymer polyvinyl alcohol, and the like.

The separator is interposed between the anode and the cathode, an insulating thin film having high ion permeability and mechanical strength is used. The pore diameter of the separator is generally from 0.01 to 10 ㎛ ㎛, thickness is generally 5 ~ 300 ㎛. As such a separator, for example, a sheet, a nonwoven fabric, or the like made of an olefin polymer such as polypropylene having chemical resistance and hydrophobicity, glass fiber or polyethylene, or the like is used. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also serve as a separator.

The lithium salt-containing non-aqueous electrolyte consists of a non-aqueous electrolyte and a lithium salt. As the non-aqueous electrolyte, a liquid solvent, a solid electrolyte, an inorganic solid electrolyte, and the like are used.

As said liquid solvent, for example, N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, fluoro ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butylo lactone, 1, 2-dimethoxy ethane, tetrahydroxy franc, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolon, formamide, dimethylformamide, dioxoron, acetonitrile, nitromethane, Methyl formate, methyl acetate, phosphate triester, trimethoxy methane, dioxoron derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether Aprotic organic solvents such as methyl pyroionate and ethyl propionate can be used.

Examples of the organic solid electrolyte include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate ester polymers, polyedgetion lysine, polyester sulfides, polyvinyl alcohols, polyvinylidene fluorides, Polymers containing ionic dissociating 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, sulfates and the like of Li, such as Li ₄ SiO ₄ -LiI-LiOH, Li ₃ PO ₄ -Li ₂ S-SiS ₂ , and the like, may be used.

The lithium salt is a good material to be dissolved 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 3 Li, (CF 3 SO 2) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, lithium tetraphenyl borate and imide have.

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 derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxy ethanol, aluminum trichloride, etc. It 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, or carbon dioxide gas may be further included to improve high temperature storage characteristics.

In the following Examples, Comparative Examples and Experimental Examples, the content of the present invention will be described in more detail, but the present invention is not limited thereto.

Example 1

1-1. Preparation of Large Diameter Latex Particles (A1)

100 parts by weight of ion-exchanged water, 100 parts by weight of 1,3-butadiene, 2 parts by weight of potassium rosin salt, 2.0 parts by weight of potassium carbonate as electrolyte, and dodecyl mercaptan as molecular weight regulator in a nitrogen-substituted polymerization reactor (autoclave) 0.3 After weight-in-weight administration, and it heated up to 70 degreeC, 0.7 weight part of potassium persulfates were put, and reaction was started. Then, it was reacted for 20 hours while maintaining at 70 ℃ to obtain large diameter butadiene latex particles (A1). The average particle diameter of the polymerized latex particles was 300 nm.

1-2. Preparation of Latex Particles (B)

120 parts by weight of ion-exchanged water, 70 parts by weight of n-butyl acrylate, 30 parts by weight of styrene, and 2 parts by weight of sodium lauryl sulfate were collectively administered to a nitrogen-substituted polymerization reactor (autoclave), and then heated to 70 ° C. 1 part by weight of persulfate was added to initiate the reaction. The average particle diameter of the obtained copolymer latex was 200 nm, and pH was adjusted to 7 using lithium hydroxide.

1-3. Preparation of Binder Composition

A binder composition was prepared by mixing the obtained binder with a large-diameter conjugated diene-based latex particle (A1): polymer copolymer for binder (B) = 50:50 at a solid mass ratio. After mixing, the size of the latex particles was analyzed using a submicron particle sizer (Nicomp ^™ 380) to confirm that agglomeration did not occur.

1-4. Slurry  And preparation of electrodes

The negative electrode was mixed with 96 parts by weight of natural graphite using water as a dispersion medium, 1 part by weight of acetylene black as a conductive material, 1.5 parts by weight of a binder composition, and 1.5 parts by weight of carboxy methyl cellulose as a thickener, so that the total solid content was 45%. To prepare a slurry for the negative electrode, coated on a copper foil with a thickness of 200 μm, vacuum drying and pressing to prepare a negative electrode.

In the case of the positive electrode, a slurry was prepared by using NMP as a dispersion medium, 96 parts by weight of LiCO ₂ , 2 parts by weight of acetylene black as a conductive agent, and 2 parts by weight of PVdF as a binder, so that the total solid content was 45%. After coating with a vacuum dried and pressed to prepare a positive electrode.

1-5. Fabrication of Lithium Secondary Battery

A coin-type battery was manufactured by putting a separator consisting of a polyolefin microporous membrane between the prepared positive electrode and the negative electrode. Then, a battery was prepared by adding an electrolyte solution in which a LiPF ₆ electrolyte was dissolved at a concentration of 1 M using an EC: EMC = 1: 2 mixed solvent.

Example 2

A lithium secondary compound was prepared in the same manner as in Example 1, except that a binder composition was prepared by mixing a large-diameter conjugated diene-based latex particle (A1): polymer copolymer for binder (B) = 75:25 in a solid mass ratio. The battery was prepared.

Example 3

A lithium secondary compound was prepared in the same manner as in Example 1, except that the binder composition was prepared by mixing a large-diameter conjugated diene-based latex particle (A1): polymer copolymer for binder (B) = 30:70 in a solid mass ratio. The battery was prepared.

Example 4

A lithium secondary battery was manufactured in the same manner as in Example 1, except that the average particle diameter of the large-diameter latex particles A1 was adjusted to 200 nm.

Comparative Example 1

A lithium secondary compound was prepared in the same manner as in Example 1, except that a binder composition was prepared by mixing a large-diameter conjugated diene-based latex particle (A1): polymer copolymer for binder (B) = 25: 75 in a solid mass ratio. The battery was prepared.

Comparative Example 2

2-1. Preparation of Small Diameter Latex Particles (A2)

100 parts by weight of ion-exchanged water, 85 parts by weight of 1,3-butadiene, 0.5 parts by weight of potassium rosin salt, 1.5 parts by weight of potassium oleate salt, 0.5 parts by weight of potassium carbonate as electrolyte, molecular weight in a nitrogen-substituted polymerization reactor (autoclave) 0.3 parts by weight of dodecyl mercaptan was collectively administered as a regulator, and the temperature was raised to 55 ° C, and 0.7 parts by weight of potassium persulfate was added to initiate the reaction. After the reaction was maintained at 55 ℃ for 10 hours, 15 parts by weight of 1,3-butadiene, 0.05 parts by weight of dodecyl mercaptan was administered and further reacted for 5 hours to obtain small-diameter latex particles (A2). The average particle diameter of the polymerized latex particles (A2) was 100 nm.

2-2. Fabrication of Lithium Secondary Battery

Small-diameter latex particles (A2) prepared in Example 2-1 and latex particles (B) prepared according to Example 1-2 in terms of solid mass ratio of small-diameter latex particles (A2): latex particles (B) = 50: A lithium secondary battery was manufactured in the same manner as in Example 1, except that the binder composition was prepared by mixing 50.

Comparative Example 3

A lithium secondary battery was manufactured in the same manner as in Comparative Example 2, except that the binder composition was mixed in a solid mass ratio of small-diameter latex particles (A2): latex particles (B) = 25:75.

[Comparative Example 4]

A lithium secondary battery was manufactured in the same manner as in Comparative Example 2, except that the binder composition was mixed in a solid mass ratio of small-diameter latex particles (A2): latex particles (B) = 75:25.

[Comparative Example 5]

A lithium secondary battery was manufactured in the same manner as in Example 1, except that only the large-diameter latex particles (A1) were added to the binder composition alone.

Comparative Example 6

A lithium secondary battery was manufactured in the same manner as in Comparative Example 2, except that only the small-diameter latex particles (A2) were added to the binder composition alone.

Comparative Example 7

A lithium secondary battery was manufactured in the same manner as in Example 1, except that only the latex particles (B) were included in the binder composition alone.

Comparative Example 8

The small-diameter latex particles (A2) prepared according to Comparative Example 2-1 were further administered, and the binder composition was added to the large-diameter mass ratio of the large-diameter latex particles (A1): the small-diameter latex particles (A2): the latex particles (B) A lithium secondary battery was manufactured in the same manner as in Example 1, except that the mixture was mixed at 25:25:50.

Comparative Example 9

As a binder composition, the pH of the binder polymer was maintained at 5, and the latex particles (A) and the latex particles (B) were mixed to cause agglomeration to increase the particle size and widen the particle distribution. Manufactured a lithium secondary battery in the same manner as in Example 1.

Comparative Example 10

120 parts by weight of ion-exchanged water, 50 parts by weight of 1,3-butadiene, 30 parts by weight of n-butyl acrylate, 20 parts by weight of styrene, and 2 parts by weight of sodium lauryl sulfate were administered to a nitrogen-substituted polymerization reactor (autoclave). After heating up to 70 degreeC, 1 weight part of potassium persulfates were put, and reaction was started. The average particle diameter of the obtained copolymer latex was 200 nm, except that it was used alone as a binder, a lithium secondary battery was prepared in the same manner as in Example 1.

Comparative Example 11

A lithium secondary battery was manufactured in the same manner as in Comparative Example 2, except that the average particle diameter of the small-diameter latex particles A2 was adjusted to 150 nm.

Experimental Example 1

Battery characteristics were measured by the following experimental methods using the lithium secondary batteries prepared in Examples 1 and 2 and Comparative Examples 1 to 10, respectively.

1-1. Coating property evaluation

In order to evaluate the coating properties, after the slurry was prepared, the coating state was applied by applying a thickness of 200 μm to the current collector (O: the slurry was completely applied to the current collector and there was no agglomeration phenomenon. Part or slurry clumping).

1-2. Adhesion Evaluation

In order to measure the adhesive force between the electrode active material and the current collector when the composition of the present invention is used as a binder, the prepared electrode surface is cut to a fixed size and fixed to a slide glass, and then the peeling strength of the current collector is peeled off and the peeling strength is 180 degrees. Measured. Evaluation was made as an average value by measuring 5 or more peeling strengths.

1-3. Battery characteristic evaluation

In order to evaluate the performance of the coin-type battery, the batteries were repeatedly charged and discharged with 0.1 C constant current / constant voltage method and 0.5 C constant current / constant voltage method, and their initial capacity and initial efficiency were compared. Evaluation was made into the average value after evaluating five or more coin type batteries about the same binder composition.

TABLE 1

As can be seen from the results of the above experiment, the large diameter latex particles (A1) having an average particle diameter of 300 nm and the polymer copolymer for binders (B) having an average particle diameter of 200 nm are included, and the large diameter latex particles (A1) are 30% by weight or more. (Examples 1 to 3) and a large-diameter latex particle (A1) having an average particle diameter of 200 nm and a polymer copolymer for binder (B) having an average particle diameter of 200 nm; In the case of containing more than% by weight (Example 4), it can be confirmed that the adhesive strength is significantly improved compared to the secondary batteries prepared according to Comparative Examples 1 to 10. On the other hand, in the case of using only the latex particles (A) (Comparative Example 5), the adhesion is greatly improved, but the coating properties, initial capacity and initial efficiency is very poor, only the latex particles (B) (Comparative Example 6) and In the case where these two particles form an agglomerated phase (Comparative Example 9), both adhesion and coating properties were found to be remarkably inferior.

Therefore, in the case of containing 30 wt% or more of the large-diameter latex particles (A) having an average particle diameter of 200 nm or more and including the latex particles (B), not only the adhesion is greatly improved, but also excellent coating properties, initial capacity and initial efficiency, etc. It can be seen that the overall physical properties are very excellent.

While the above has been described above with reference to embodiments according to the present invention, those of ordinary skill in the art to which the present invention pertains can make various applications and modifications within the scope of the present invention. will be.

As described above, the binder composition according to the present invention has excellent bonding strength between the active materials and the current collector despite the excellent battery characteristics, and when applied to an electrode and a lithium secondary battery in an electrode mixture, coating characteristics and batteries A large capacity secondary battery having excellent characteristics can be manufactured.

Claims (12)

As a binder composition for a secondary battery, conjugated diene-based latex particles (A) and polymer copolymer latex particles (B) exist as independent phases, and the latex particles (A) have an average particle diameter of at least 200 nm and have a solid content mass. 30% by weight or more based on the composition, characterized in that. The composition of claim 1, wherein the average particle diameter of the latex particles (A) is 250 to 400 nm. The composition of claim 1, wherein the latex particles (A) are contained in an amount of 50 to 75% by weight based on the mass of solids. The composition of claim 1, wherein the average particle diameter of the latex particles (B) is 100 to 260 nm. The composition of claim 1, wherein the latex particles (A) are polymers of one or more monomers selected from the group consisting of 1,3-butadiene, isoprene, chloroprene and pyreriden. The latex particle (B) is one selected from the group consisting of an aromatic vinyl compound, a vinyl cyan compound, a (meth) acrylic acid ester compound, a (meth) acryl amide compound, and an unsaturated monocarboxylic acid compound. Or a polymer of two or more monomers. The method according to claim 1, wherein the acidity (pH) of each of the latex particles (A) and latex particles (B) produced is adjusted to maintain the independent phase without agglomeration of the particles (A, B) in the mixture. Composition. The electrode mixture for secondary batteries comprised from the binder composition in any one of Claims 1-7, and an electrode active material. A secondary battery electrode formed by applying the electrode mixture according to claim 8 to a current collector. 10. The secondary battery electrode as claimed in claim 9, wherein the electrode is a cathode. The electrode of claim 10, wherein the negative electrode comprises a carbon-based active material, a silicon-based active material, a tin-based active material, or a silicon-carbon-based active material. A lithium secondary battery comprising the electrode according to claim 9.