KR101822638B1 - Binder Composition Having Higher Performance and Lithium Secondary Battery Comprising the Same - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a binder composition for a secondary battery and a lithium secondary battery using the binder composition. More particularly, the present invention relates to a conjugated dienes latex particle (A) and an acrylic copolymer latex particle B), and the sum of the kind of the conjugated diene-based latex particles (A) and the kind of the acrylate-based copolymer latex particles (B) And a lithium secondary battery using the binder composition.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a binder composition having excellent performance and a secondary battery comprising the binder composition.

The present invention relates to a binder composition for a secondary battery and a lithium secondary battery using the same.

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.

At present, a typical example of an electrochemical device utilizing such electrochemical energy is a secondary battery, and the use area thereof is gradually increasing.

Recently, as technology development and demand for portable devices such as portable computers, portable telephones, cameras, and the like have increased, the demand for secondary batteries as energy sources has been rapidly increasing. Among these secondary batteries, they exhibit high energy density and operating potential, Many studies have been made on a lithium secondary battery having a long self discharge rate, and it has been commercialized and widely used.

In addition, as the interest in environmental issues grows, researches on electric vehicles and hybrid electric vehicles that can replace fossil fuel-based vehicles such as gasoline vehicles and diesel vehicles, which are one of the main causes of air pollution, , Lithium secondary batteries are also used as power sources for such electric vehicles and hybrid electric vehicles.

Such a lithium secondary battery generally uses a lithium transition metal oxide as a cathode active material and a graphite based material as an anode active material. The electrode of the lithium secondary battery is produced by mixing such an active material and a binder resin component and dispersing the mixture in a solvent to prepare a slurry and applying the slurry to the collector surface to form a mixture layer after drying.

Generally, in a lithium secondary battery, charging and discharging proceed while repeating the process in which lithium ions in the positive electrode are inserted into the negative electrode and desorbed. Such insertion and desorption of lithium ions repeatedly progresses, so that the bond between the electrode active material or the conductive material is loosened and the contact resistance between the particles is increased. As a result, the ohmic resistance of the electrode rises and the battery characteristics may deteriorate. Therefore, the binder is preferably a polymer having elasticity, since it is required to be capable of buffering against the expansion and contraction of the electrode active material due to insertion and desorption of lithium ions in the electrode.

Further, the binder is required to have an adhesive strength enough to maintain the binding force between the electrode active material and the current collector during the drying process of the electrode plate. Particularly, in order to increase the discharge capacity, when a material such as silicon, tin, silicon-tin alloy having a large discharging capacity is mixed with natural graphite having a theoretical discharge capacity of 372 mAh / g is used, The volume expansion of the negative electrode material significantly increases. As a result, deterioration of the negative electrode material occurs. As a result, the cyclic capacity of the battery decreases sharply and the cycle life can be shortened.

In addition, since the swelling of the electrolyte in the binder affects the volume expansion of the lithium ion battery, a binder having a low electrolyte swelling is required. The lithium ion battery has a phenomenon of swelling due to the gas generated upon decomposition of the electrolyte inside the battery, and this phenomenon is referred to as " electrolytic solution swelling. &Quot; Since decomposition of the electrolyte is promoted at a high temperature, when the battery is left at a high temperature, the phenomenon of swelling is promoted. As the temperature of the battery increases, the electrolyte decomposes or side reactions occur, resulting in gas such as carbon dioxide or carbon monoxide, which increases the thickness of the battery. On the other hand, the increase in thickness in high-temperature storage is an important consideration in a small-sized battery, and the temperature of the battery sharply increases according to the use of a small-sized device, which causes a problem of thickness and safety at high temperatures.

Therefore, it is possible to prevent separation between the electrode active material or between the electrode active material and the current collector during the production of the electrode with strong adhesive force, and to control the volume expansion of the electrode active material generated during repetitive charging and discharging with strong physical properties, There is a great demand in the art for a study on a binder and an electrode material capable of improving the performance of the electrode.

Representative binders currently commercialized include polyvinylidene fluoride (PVdF), styrene-butadiene rubber (SBR), carboxy methyl cellulose (CMC), and the like. In the case of a negative electrode having a large volume expansion, SBR / CMC, which has a smaller amount of use and has a better binding force than PVdF, is used.

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 above-mentioned method has been proposed, and it is currently being used commercially. In the case of such a binder, there is an advantage in that the battery capacity can be increased by reducing the amount of the binder used and environment-friendly. In this case, however, the adhesion persistence is improved by the rubber elasticity,

Therefore, there is a high need for the development of a binder having an excellent adhesive strength while improving the cyclic characteristics of the battery, the structural stability of the electrode, and the like.

As described above, the binder is preferable to have elasticity, and the adhesion and the adhesive holding force are excellent in the secondary battery, so that the capacity is maintained after the charge / discharge cycle, and the increase in the thickness of the electrode is minimized because the electrolyte swelling is low. For example, in the case of SBR latex or thermosetting resins, the swelling of the electrolyte may be affected by the degree of crosslinking.

The inventors of the present application have found that when three or more kinds of conjugated diene-based latex particles and acrylic copolymer latex particles are mixed at a predetermined ratio and applied to a lithium secondary battery, the volume expansion of the battery is reduced at a high temperature, The present invention has been accomplished.

Accordingly, in the binder composition for a secondary battery according to the present invention,

(A) and at least one kind of acrylic copolymer latex particles (B), wherein the conjugated dienes latex particles (A) and the copolymer latex particles (B) And the total of the kinds of the acrylate-based copolymer latex particles (B) are mixed in the composition in total of three or more.

The inventors of the present application have unexpectedly found that when the binder is prepared by mixing three or more kinds of the above-mentioned binder compositions, the performance of the battery is improved as compared with a conventional binder in which two kinds of binder compositions are mixed.

That is, the binder mixed with three or more kinds improves the adhesive force of the electrode compared to the two kinds of binders of the prior art, and the battery using the same reduces the resistance of the electrode and exhibits a good capacity retention rate.

'Different kind of latex particles' means that the monomer composition of the latex particles, which are polymers, is different and does not necessarily require all the monomers to be different.

For example, when the conjugated dienic latex particle (A1) is composed of a butadiene monomer, a styrene monomer, an acrylic acid monomer, and a hydroxyethyl acrylate monomer, and the conjugated dienic latex particle (A2) is a styrene monomer, a butadiene monomer, The conjugated diene-based latex particles (A1) and the conjugated diene-based latex particles (A2) correspond to different kinds of particles even though they are composed of acrylate monomer, acrylate monomer, and itaconic acid monomer.

That is, the conjugated diene-based latex particles (A1, A2) include butadiene monomer, styrene monomer, and acrylic acid monomer, but they are different latex particles because the composition of the remaining monomers is different.

On the other hand, the latex particles mixed by the combination of three or more exist as independent phases, thereby contributing to the improvement of the adhesion.

For example, in the case of the conjugated diene-based latex particles (A1, A2), they exist in independent phases, and they exist independently of the acrylic copolymer latex particles (B).

Specifically, the conjugated diene-based latex particles (A) and the acrylic copolymer latex particles (B) may be contained in a ratio of 50:50 to 99: 1 based on the weight ratio. Specifically 70:30 to 99: 1, more specifically 90:10 to 99: 1.

That is, it is preferable that the content of the conjugated diene-based latex particles (A) in the latex particles is larger than the content of the acrylic copolymer latex particles (B) in mixing three or more latex particles in terms of swelling properties and adhesion.

When the contents of the conjugated diene-based latex particles (A) and the acrylic copolymer latex particles (B) fall within the above-mentioned ranges, the respective latex particles exist in independent phases, and as a binder in the electrode, You can contribute.

With respect to the above-mentioned content ratio, the acrylic copolymer latex particles (B) contain a functional group that provides an adhesive force to the particle surface and have a relatively high swelling degree. Therefore, when the acrylic copolymer latex particles (B) are not contained or the content thereof is extremely small, the resistance of the electrode may be rather increased, and the ion conductivity may be lowered.

However, since the acrylic copolymer latex particles (B) contain a monomer having good affinity with the carbonate electrolyte, when the battery is left at a high temperature, the electrolytic solution swelling phenomenon is promoted and electrolyte decomposes or side reactions occur, And ultimately, desorption of the electrode can be caused.

The inventors of the present application have found that when the content of the acrylic copolymer latex particles (B) exceeds 90% by weight based on the total solids mass of the composition, it swells at a high temperature to increase the thickness of the electrode, The content of the acrylic copolymer latex particles (B) is preferably less than 90% by weight of the total solid mass, more preferably less than the conjugated diene-based latex particles (A).

Thus, the binder composition according to the present invention comprises three or more kinds of latex particles and a predetermined amount of the acrylic copolymer latex particles (B) together with a large amount of the conjugated diene-based latex particles (A) Improves performance.

The binder composition mixed in the above content range is obtained by mixing 3 kinds of the conjugate diene-based latex particles (A) and 3 kinds of the acrylate-based copolymer latex particles (B) Lt; / RTI > Relevant examples are listed below.

- a combination of one kind of conjugated dienic latex particles (A) and two kinds of acrylic copolymer latex particles (B);

- a combination of two kinds of conjugated dienic latex particles (A) and one kind of acrylic copolymer latex particles (B);

A combination of one kind of conjugated dienic latex particles (A) and three kinds of acrylic copolymer latex particles (B);

A combination of two kinds of conjugated dienic latex particles (A) and two types of acrylic copolymer latex particles (B);

A combination of three kinds of conjugated dienic latex particles (A) and one kind of acrylic copolymer latex particles (B).

The average particle diameter of the conjugated diene-based latex particles (A) is preferably 50 nm or more and 700 nm or less.

The conjugated diene-based latex particles (A) have a small electrolyte swelling phenomenon at a high temperature, and as a binder having rubber elasticity, reduce the thickness of the electrode and the gas generation phenomenon. However, when the average particle diameter is less than 50 nm or exceeds 700 nm, the electrode adhesive strength is remarkably lowered and its role as a binder can not be expected, which is not preferable.

For the same reason, the average particle diameter of the conjugated diene-based latex particles (A) may be 60 nm to 300 nm.

The average particle diameter of the acrylic copolymer latex particles (B) is preferably 30 nm or more and 800 nm or less.

The acrylic copolymer latex particles (B) are excellent binders, and prevent separation between the electrode active materials or between the electrode active material and the current collector during electrode production. But. When the average particle diameter is less than 30 nm, the adhesive force may be lowered. When the average particle diameter is more than 800 nm, the swelling becomes so high that a role as a binder can not be expected.

For the same reason, the average particle diameter of the acrylic copolymer latex particles (B) may be 70 nm to 650 nm.

On the other hand, the conjugated diene-based latex particles (A) include, for example, (A) a conjugated diene monomer or a conjugated diene oligomer, (B) an acrylate monomer, (meth) acrylate ester monomers, , (Meth) acrylamide-based monomer and nitrile-based monomer, and (C) a polymer of unsaturated monocarboxylic acid-based monomer.

The latex particles (B) include, for example, a mixture of (A) a (meth) acrylic acid ester monomer and (B) a group consisting of an acrylate monomer, a vinyl monomer, a (meth) acrylamide monomer and a nitrile monomer , And (C) a polymer of an unsaturated monocarboxylic acid-based monomer.

The conjugated diene-based monomer may be a monomer selected from the group consisting of 1,3-butadiene, isoprene, chloroprene, and pyridene.

Examples of the conjugated diene oligomer include a polymer of two or more monomers selected from the group consisting of 1,3-butadiene, isoprene, chloroprene, and pyridene, a styrene-butadiene copolymer, an acrylonitrile-butadiene copolymer , Styrene-isoprene copolymers, acrylate-butadiene rubbers, acrylonitrile-butadiene-styrene rubbers, ethylene-propylene-diene polymers or polymers thereof may be partially hydrogenated, epoxidized, brominated polymers and mixtures thereof .

The (meth) acrylic acid ester monomer may be at least one monomer selected from the group consisting of 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, hydroxyethyl methacrylate, Propyl methacrylate, and the like.

The acrylate monomer may be at least one selected from the group consisting of methacryloxyethyl ethylene urea,? -Carboxyethyl acrylate, aliphatic monoacrylate, dipropylene diacrylate, ditrimethylpropane tetraacrylate, hydroxyethyl acrylate, dipentaerythritol Acrylate, stearyl acrylate, stearyl acrylate, lauryl methacrylate, cetyl methacrylate, stearyl methacrylate, stearyl methacrylate, stearyl methacrylate, Acrylate, and the like.

The vinyl-based monomer may be at least one monomer selected from the group consisting of styrene,? -Methylstyrene,? -Methylstyrene, p-t-butylstyrene and divinylbenzene.

The (meth) acrylamide-based monomer may be at least one selected from the group consisting of acrylamide, n-methylol acrylamide, n-butoxymethylacrylamide, methacrylamide, n-methylol methacrylamide and n-butoxymethylmethacrylamide . ≪ / RTI >

The nitrile monomer may be an alkenyl cyanide and may be, but is not limited to, acrylonitrile, methacrylonitrile, allyl cyanide, and the like.

The unsaturated monocarboxylic acid monomer is at least one monomer selected from the group consisting of maleic acid, fumaric acid, methacrylic acid, acrylic acid, glutaric acid, itaconic acid, tetrahydrophthalic acid, crotonic acid, isocrotonic acid and nadic acid Lt; / RTI >

In one specific example, the conjugated diene-based latex particles (A)

Butadiene monomers, styrene monomers, acrylic acid monomers, hydroxyethyl acrylate monomers, methyl methacrylate monomers, and itaconic acid monomers.

More specifically, the conjugated diene-based latex particles (A) comprise a polymer (A1) as a butadiene monomer, a styrene monomer, an acrylic acid monomer, and a hydroxyethyl acrylate monomer; Or polymers (A2) of styrene monomers, butadiene monomers, methyl methacrylate monomers, acrylic acid monomers, and itaconic acid monomers.

On the other hand, the acrylic copolymer latex particles (B)

A styrene monomer, an acrylic acid monomer, a hydroxybutyl acrylate monomer, and an itaconic acid monomer.

More specifically, the acrylic copolymer latex particles (B) are obtained by polymerizing a polymer (B1) of a butyl acrylate monomer, a styrene monomer, an acrylic acid monomer, and a hydroxybutyl acrylate monomer; Or polymers (B2) of butyl acrylate monomers, styrene monomers, acrylic acid monomers, and itaconic acid monomers.

Each of the latex particles A1, A2, B1 and B2 may contain one or more other components such as a polymerization initiator, a crosslinking agent, a coupling agent, a buffer, a molecular weight modifier, and an emulsifier, This will be described later.

The binder composition according to the present invention contains at least one or more latex particles (A, B) as described above, and the kind of the conjugated diene latex particles (A) and the kind of the latex particles The sum of the types should be 3 or more in total in the composition.

Therefore, in the case of the latex particles (A1, A2, B1, B2), the composition may be formed by combining latex particles (A1, A2, B1), latex particles (A1, B1, B2) The latex particles (A1, A2) and the latex particles (A1, B2).

It goes without saying that even when three kinds of the conjugated dienic latex particles (A) alone or three types of the acrylate based copolymer latex particles (B) are combined, they can be included in the binder composition according to the present invention.

The production method of the latex particles (A) and the latex particles (B) is not particularly limited and can be produced by a known suspension polymerization method, emulsion polymerization method, seed polymerization method and the like.

The latex particles (A) and the latex particles (B) may be prepared by emulsion polymerization. In this case, the latex particles (A) and the latex particles (B) Can be controlled by the amount of the emulsifier. Generally, 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. Accordingly, the desired average particle size can be realized by controlling the amount of the emulsifier used in consideration of the desired particle size, reaction time, and reaction stability.

The polymerization temperature and the polymerization time may be appropriately determined depending on the kind of the polymerization initiator and the like. For example, the polymerization temperature may be from 50 캜 to 300 캜, and the polymerization time may be from 1 to 20 hours.

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, Can be used. The polymerization initiator may further include an activating agent to promote the initiating reaction of the peroxide with the polymerization initiator. Examples of the activating agent include sodium formaldehyde sulfoxylate, sodium ethylenediamine tetraacetate, ferrous sulfate and dextrose One or more selected from the group consisting of

The crosslinking agent may be added in an amount of not more than 50% by weight based on the weight of the binder as a substance promoting crosslinking of the binder. For example, amines such as diethylene triamine, triethylene tetramine, diethylamino propylamine, xylene diamine, isophorone diamine and the like Dodecyl succinic anhydride, and phthalic anhydride, polyamide resins, polysulfide resins, phenol resins, ethylene glycol dimethacrylate, diethylene glycol di Methacrylate, triethylene glycol dimethacrylate, 1,3-butanediol dimethacrylate, 1,6-hexanediol dimethacrylate, neopentyl glycol dimethacrylate, trimethylolpropane trimethacrylate, Trimethylolmethane triacrylate, glycidyl methacrylate and the like are used. As the grafting agent, aryl methacrylate (AMA), triaryl Cyano, may be used, such as leakage rate (TAIC), triarylamine (TAA), diarylamine (DAA).

The coupling agent is a material for increasing the adhesive force between the active material and the binder and has two or more functional groups. The coupling agent may be added in an amount of 30 wt% or less based on the weight of the binder. If one functional group is a material which reacts with a hydroxyl group or a carboxyl group on the surface of a silicon, tin or graphite active material to form a chemical bond and the other functional group forms a compound bond through a reaction with the nanocomposite according to the present invention But is not particularly limited to, for example, triethoxysilylpropyl tetrasulfide, mercaptopropyl triethoxysilane, aminopropyl triethoxysilane, chloropropyltriethoxysilane, But are not limited to, chloropropyl triethoxysilane, vinyltriethoxysilane, methacryloxytpropyl triethoxysilane, methacryloxypropyl triethoxysilane, glycidoxypropyl triethoxysilane, (glycidoxypropyl triethoxysilane), isocyanate Peel triethoxysilane silane-based coupling agent may be used, such as (isocyanatopropyl triethoxysilane), cyan in ato propyl triethoxysilane (cyanatopropyl triethoxysilane).

The buffer can be in the range of up to 30 wt% based on the weight of the binder, and can be, for example, selected from the group consisting of NaHCO ₃ , NaOH, and NH ₄ OH.

Examples of the molecular weight regulator include mercaptans or terpines such as terbinol, dipentene and t-terpine; halogenated hydrocarbons such as chloroform and carbon tetrachloride; and the like.

The emulsifier is a substance having both a hydrophilic group and a hydrophobic group. In a non-limiting example, it may be one or more selected from the group consisting of anionic emulsifiers and nonionic emulsifiers.

The use of nonionic emulsifiers in combination with anionic emulsifiers helps control the particle size and distribution and can provide additional stabilization of the colloidal form through the van der Waals forces of the polymer particles in addition to the electrostatic stabilization of the ionic emulsifier. The use of a nonionic emulsifier alone is not very common because it produces less stable particles than anionic emulsifiers.

The anionic emulsifier may be selected from the group consisting of phosphate, carboxylate, sulfate, succinate, sulfosuccinate, sulfonate, and disulfonate. In a non-limiting example, sodium alkyl sulfate, sodium polyoxyethylene sulfate, sodium lauryl ether sulfate, sodium polyoxyethylene lauryl ether sulfate, sodium lauryl sulfate, sodium alkyl Sodium dioctyl sulfosuccinate, sodium alkyl sulfonate, sodium alkyl sulfonate, sodium alkyl sulfonate, sodium alkyl sulfonate, sodium alkyl sulfonate, sodium alkyl sulfonate, sodium alkyl sulfonate, sodium alkyl sulfonate, , Sodium perfluorooctanesulfonate, sodium perfluorobutanesulfonate, alkyldiphenyloxide disulfonate, sodium dioctyl sulfosuccinate (DOSS), sodium alkyl-aryl phosphate , Sodium alkyl ether May be selected from the group consisting of lactate, sodium laurate ohril sarcoidosis When carbonate or the like. However, the present invention is not limited thereto, and all known anionic emulsifiers may be included in the scope of the present invention.

The nonionic emulsifier may be an ester type, an ether type, an ester type, an ether type, or the like.

In a non-limiting example, polyoxyethylene glycol, polyoxyethylene glycol methyl ether, polyoxyethylene monoallyl ether, polyoxyethylene bisphenol-A ether, polypropylene glycol, polyoxyethylene neopentyl ether, polyoxyethylene cetyl ether , Polyoxyethylene lauryl ether, polyoxyethyl oleyl ether, polyoxyethylene stearyl ether, polyoxyethylene decyl ether, polyoxyethylene octyl ether, and the like. However, the present invention is not limited thereto, and all known nonionic emulsifiers may be included in the scope of the present invention.

In a non-limiting embodiment of the present invention, the (a) conjugated diene-based monomer or conjugated diene-based polymer is contained in an amount of 45 to 97.9% by weight, based on the total weight of the solid content of the conjugated dienic latex particles (A) The monomer (b) may be contained in an amount of 1 to 50 % by weight, and the unsaturated monocarboxylic acid monomer may be contained in an amount of 1 to 20% by weight. Other components such as emulsifiers, buffers, crosslinking agents and the like may optionally be included in the range of 0.1 to 10% by weight.

(Meth) acrylic ester monomer is contained in an amount of 55.5 to 97.9% by weight based on the total weight of the solid content of the acrylic copolymer latex particles (B), and 1 to 35 % by weight of the (b) , And (C) the unsaturated monocarboxylic acid monomer may be contained in an amount of 1 to 20% by weight. Other components such as emulsifiers, buffers, crosslinking agents and the like may optionally be included in the range of 0.1 to 10% by weight.

On the other hand, an antioxidant and an antiseptic may be added during the production of the binder. Particularly, when the conjugated diene polymer is used in the binder, deterioration of physical properties tends to occur due to softening or gelation during the operation of the battery, so that the lifetime of the battery can be shortened. Therefore, Can be used.

When the latex particles (A) and the latex particles (B) are present in independent phases, it is important to prevent agglomeration between the particles because the effect of improving the adhesion is improved.

In one preferred example, the pH of the prepared latex particles (A) and latex particles (B) are adjusted so that the particles (A, B) in the mixture can maintain an independent phase without aggregation.

When the pH of the latex particles (B) is acidic, coagulation with the latex particles (A) may occur. Therefore, it is possible to maintain the independent phase by adjusting the pH by titrating with the base. At this time, the base may be, for example, potassium hydroxide, sodium hydroxide, lithium hydroxide or the like, but not limited thereto, preferably lithium hydroxide.

In the present invention, the binder composition may further include at least one material selected from the group consisting of a viscosity modifier and a filler. These viscosity modifiers and fillers are described in more detail below.

The present invention also provides a binder for an electrode of a secondary battery comprising the binder composition and an electrode active material capable of intercalating / deintercalating lithium. The electrode mixture of the secondary battery may further include a conductive material. The conductive material will be described later in more detail.

Preferable examples of the electrode active material include a lithium transition metal oxide powder or carbon powder. The present invention also provides an electrode for a secondary battery, wherein the electrode mixture is applied to a current collector. The electrode can be manufactured by applying the electrode mixture to the current collector, followed by drying and rolling. The electrode for the secondary battery may be an anode or a cathode.

The positive electrode is prepared, for example, by coating 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 prepared by applying a mixture of the negative electrode active material, Followed by drying. In some cases, the negative electrode may not contain a conductive material.

The positive electrode active material is a lithium transition metal oxide. The lithium-transition metal oxide is a layered compound such as lithium cobalt oxide (LiCoO ₂ ) and lithium nickel oxide (LiNiO ₂ ), which contains two or more transition metals and is substituted with, for example, 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 they 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 in an amount of 0.01 to 30% by weight 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 fibers such as carbon nanotubes and fullerene; conductive fibers such as carbon fibers and metal fibers; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

The current collector in the electrode is a portion where electrons move in the electrochemical reaction of the active material, and the positive electrode collector and the negative electrode collector exist depending on the type of the electrode.

The cathode current collector is generally made to have a thickness of 3 to 500 mu m. Such a positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery, and may be formed of a material such as stainless steel, aluminum, nickel, titanium, sintered carbon, or a surface of aluminum or stainless steel Treated with carbon, nickel, titanium, silver or the like may 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 be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, or the like, by forming fine irregularities on the surface of the current collectors to enhance the binding force of the electrode active material.

The mixture (electrode mixture) of the electrode active material, the conductive material, the binder and the like may further contain at least one substance selected from the group consisting of a viscosity adjusting agent 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 carboxymethylcellulose, polyacrylic acid, and the like, but are not limited thereto.

The filler is an auxiliary component for suppressing the expansion of the electrode. The filler is not particularly limited as long as it is a fibrous material without causing a chemical change in the battery, and examples thereof 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 comprises a separator and a non-aqueous electrolyte containing a lithium salt 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 is composed of a non-aqueous electrolyte 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, tetrahydrofuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, , Methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran Derivatives, ethers, methyl pyrophosphate, ethyl propionate and the like can be used.

The lithium salt is a material which is soluble in the non-aqueous liquid electrolyte and includes, 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, organic solid electrolytes, inorganic solid electrolytes, etc. 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.

For the purpose of improving the charge-discharge characteristics and the flame retardancy, the non-aqueous liquid electrolyte may contain, for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, , Nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxyethanol, . In some cases, halogen-containing solvents such as carbon tetrachloride and ethylene trifluoride may be further added to impart nonflammability. In order to improve the high-temperature storage characteristics, carbon dioxide gas may be further added. FEC (Fluoro-Ethylene Carbonate, PRS (Propenesultone), and the like.

The battery pack according to the present invention can be used as a unit battery. The battery pack can be used not only for a battery cell used as a power source for a small device but also for a plurality of battery cells used as a power source for a medium- And may be suitably used as a unit cell in a middle- or large-sized battery module.

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; And an energy storage system, but the present invention is not limited thereto.

Such devices or devices are well known in the art, so a detailed description thereof will be omitted herein.

As described above, in the binder composition according to the present invention, the sum of the kinds of the conjugated diene-based latex particles (A) and the types of the acrylate-based copolymer latex particles (B) It is possible to provide a secondary battery which can maintain a better bonding force between the electrode materials and between the electrode material and the current collector as compared with the conventional binder composition of the combination of the two types, The increase in thickness and the generation of gas at a high temperature are reduced, so that a battery having improved safety can be provided.

In addition, the binder made of three or more kinds of combinations can be used not only in the case of using a natural graphite active material as a negative electrode active material but also in the case of using an artificial graphite based active material favoring a change in the thickness of a battery, The adhesive strength between the adhesive layer and the adhesive layer is improved.

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

&Lt; Production of conjugated diene-based latex particles (A1)

The monomers were prepared by dissolving NaHCO ₃ (0.4 g), sodium lauryl sulfate (0.5 g), and diisopropylethylamine (2 g) in 1,3-butadiene (45 g), styrene (50 g), acrylic acid (3 g), hydroxyethyl acrylate 0.4 g), and dodecylmercaptan (0.5 g) as a molecular weight regulator.

These were mixed and heated to 80 ° C. Then, potassium persulfate was added as a polymerization initiator to initiate the reaction. Then, the reaction was carried out at 80 ° C for 6 hours to obtain butadiene latex particles (A1) ) Was 4.5.

The average particle size of the polymerized latex particles (A1) was 185 nm. The average particle diameter is controlled by the amount of the emulsifier. Generally, as the amount of the emulsifier increases, the particle size becomes smaller. Therefore, the amount of the emulsifier to be used can be adjusted considering the desired size, reaction time, and reaction stability.

&Lt; Production of conjugated diene-based latex particles (A2)

As the monomer, 40.5 g of styrene, 49 g of 1,3-butadiene, 5 g of methyl methacrylate, 5 g of acrylic acid and itaconic acid, 0.5 g of ethylene glycol dimethacrylate as a crosslinking agent, sodium lauryl sulfate as an emulsifier, The persulfate was added to water, mixed and polymerized at 75 DEG C for about 7 hours.

The polymerized latex particles (A2) had a pH of 4.5 and an average particle size of 90 nm.

&Lt; Preparation of acrylic copolymer latex particles (B1) >

(70 g), styrene (20 g), acrylic acid (5 g), hydroxybutyl acrylate (5 g), NaHCO ₃ (0.4 g) as buffer, sodium lauryl sulfate Were added to water, mixed and heated to 75 캜, and then ammonium persulfate was added as a polymerization initiator to initiate polymerization.

And the mixture was reacted for about 6 hours while maintaining the temperature at 75 캜 to prepare latex particles (B1). The polymerized latex particles (B1) had a pH of 3.5 and an average particle diameter of 470 nm.

&Lt; Preparation of acrylic copolymer latex particles (B2)

55.5 g of butyl acrylate, 35 g of styrene, 7.5 g of acrylic acid and itaconic acid, 2 g of glycidyl methacrylate as a crosslinking agent, 0.7 g of sodium lauryl sulfate and polyoxyethylene lauryl ether as an emulsifier, 0.4 g of NaHCO ₃ as a buffer , Ammonium persulfate as a polymerization initiator was added to water, mixed and polymerized at a temperature of 75 캜 for about 5 hours.

The polymerized latex particles (B2) had a pH of 3.5 and an average particle diameter of 150 nm.

&Lt; Example 1 > (Binder composition mixed in three kinds)

&Lt; Example 1-1 >

The binder thus obtained was mixed with the conjugated diene-based latex particles (A1): acrylic copolymer latex particles (B1): acrylic copolymer latex particles (B2) = 80: 10: 10 in a solid mass ratio to prepare a binder composition. After mixing, the size of the latex particles was analyzed using a submicron particle sizer (Nicomp TM 380) to confirm that agglomeration did not occur.

&Lt; Example 1-2 >

The binder thus obtained was mixed with the conjugated diene latex particles (A1): conjugated diene latex particles (A2): acrylic copolymer latex particles (B1) = 40: 40: 20 in a solid mass ratio to prepare a binder composition. After mixing, the size of the latex particles was analyzed using a submicron particle sizer (Nicomp TM 380) to confirm that agglomeration did not occur.

&Lt; Example 2 > (Binder composition mixed by four kinds)

The binder thus obtained was dispersed in a solid mass ratio of the conjugated diene latex particles (A1): conjugated diene latex particles (A2): acrylic copolymer latex particles (B1): acrylic copolymer latex particles (B2) = 40:40:10 : 10 to prepare a binder composition. After mixing, the size of the latex particles was analyzed using a submicron particle sizer (Nicomp TM 380) to confirm that agglomeration did not occur.

&Lt; Example 3 > (Preparation of electrode slurry and electrode)

&Lt; Example 3-1 >

The negative electrode was prepared by mixing 96.0 g of natural graphite, 0.5 g of a conductive material, 2.5 g of the binder for a lithium secondary battery prepared in Example 1-1, and 1.0 g of carboxymethyl cellulose as a thickener, based on 100 g of a total solid content of 100 g as a dispersion medium And a total solid content of 50% by weight. A negative electrode slurry was prepared, applied to a copper foil, vacuum-dried, and pressed to prepare a negative electrode.

The positive electrode was prepared by mixing 96 g of active material LiCoO ₂ , ₂ g of conductive material, and 2 g of PVDF binder 2 (N-methyl-2-pyrrolidone)

g were mixed to prepare a positive electrode slurry, which was then applied to an aluminum foil and dried

Followed by pressing to prepare a positive electrode.

&Lt; Example 3-2 >

A positive electrode and a negative electrode were prepared in the same manner as in Example 3-1, except that the negative electrode was prepared using the binder prepared in Example 1-2.

<Example 3-3>

A positive electrode and a negative electrode were prepared in the same manner as in Example 3-1, except that the negative electrode was prepared using the binder prepared in Example 2.

Example 4 (Production of lithium secondary battery)

&Lt; Example 4-1 >

The negative electrode plate prepared in Example 3-1 was punched at a surface area of 13.33 cm ² , and the positive electrode plate prepared in Example 3-1 was punched at a surface area of 12.60 cm ² to prepare a single cell (mono-cell). A tap was attached to the upper portion of the positive electrode and the negative electrode, and the resultant was placed on the aluminum pouch between the negative electrode and the positive electrode through a separator made of a polyolefin microporous membrane. Then, 500 mg of the electrolytic solution was injected into the pouch. The electrolyte was prepared by dissolving the LiPF ₆ electrolyte at a concentration of 1M using a mixed solvent of ethyl carbonate (EC): diethyl carbonate (EMC) and ethyl methyl carbonate (EMC) in a volume ratio of 4: 3: 3.

Thereafter, the pouch was sealed using a vacuum packing machine, kept at room temperature for 12 hours, filled with a constant current at a rate of about 0.05 C, and subjected to a tangential pressure charging process in which the voltage was maintained until it was about 1/6 of the current . At this time, since the gas is generated inside the cell, degassing and resealing are performed to complete the lithium secondary battery.

&Lt; Example 4-2 >

A lithium secondary battery was completed in the same manner as in Example 4-1 except that the positive electrode and the negative electrode prepared in Example 3-2 were used.

<Example 4-3>

A lithium secondary battery was completed in the same manner as in Example 4-1 except that the positive electrode and the negative electrode prepared in Example 3-3 were used.

&Lt; Comparative Example 1 &

A lithium secondary battery was produced in the same manner as in Examples 1 to 4 except that the binder composition was prepared by mixing the conjugated diene-based latex particles (A1) and acrylic copolymer latex particles (B1) in a ratio of 50:50 Respectively.

&Lt; Comparative Example 2 &

A lithium secondary battery was prepared in the same manner as in Examples 1 to 4 except that the binder composition was prepared by mixing the conjugated diene-based latex particles (A1) and the acrylic copolymer latex particles (B2) in a ratio of 50:50 Respectively.

&Lt; Comparative Example 3 &

A lithium secondary battery was produced in the same manner as in Examples 1 to 4 except that the binder composition was prepared by mixing the conjugated dienic latex particles (A2) and the acrylic copolymer latex particles (B1) = 50:50. Respectively.

&Lt; Comparative Example 4 &

A lithium secondary battery was produced in the same manner as in Examples 1 to 4 except that the binder composition was prepared by mixing the conjugated diene-based latex particles (A2) and the acrylic copolymer latex particles (B2) in a weight ratio of 50:50 Respectively.

<Experimental Example 1>

&Lt; Adhesion Test &

Experiments were conducted to measure the adhesive force between the negative electrode composition and the current collector when the binder according to Examples 3-1 to 3-3 and Comparative Examples 1 to 4 was used for the negative electrode. The negative electrode plates prepared in Examples 3-1 to 3-3 and Comparative Examples 1 to 4 were cut to a predetermined size and fixed to a slide glass. The collector was peeled off and the 180 ㅀ peel strength was measured. The results are shown in Table 1 Respectively. The evaluation was made by measuring the peel strengths of 5 or more and calculating the average value.

Adhesion (gf / cm) Example 3-1 102.2 Example 3-2 105.5 Example 3-3 106.0 Comparative Example 1 65.9 Comparative Example 2 68.2 Comparative Example 3 78.5 Comparative Example 4 77.0

Referring to Table 1, it can be seen that the adhesive strength of the negative electrode according to the embodiment is far superior to that of the negative electrode according to the comparative example.

That is, when three kinds or four types of latex particles are used, the adhesion between the current collector and the electrode composition is significantly improved as compared with the case where two types of latex particles are used. The adhesive strengths of Examples 3-1 and 3-2 using three kinds of latex particles and Example 3-3 using four types of latex particles are similar to each other.

Meanwhile, although the natural graphite is used as the negative electrode active material in the above embodiment, the binder composition according to the present invention can be suitably used for artificial graphite which requires less adverse change in volume due to charging and discharging, but which requires high adhesion strength in terms of particle structure.

<Experimental Example 2>

<Battery Test>

Charging and discharging tests of the batteries manufactured in Examples 4-1 to 4-3 and Comparative Examples 1 to 4 were carried out. First, charge and discharge tests were carried out twice at a charge / discharge current density of 0.2C, a charge end voltage of 4.2V (Li / Li +) and a discharge end voltage of 2.5V (Li / Li +). Charging and discharging tests were carried out 48 times with charging / discharging current density of 1C, end-of-charge voltage of 4.2V (Li / Li +) and end-of-discharge voltage of 3V (Li / Li +). All charging was performed at constant current / constant voltage, and the end current of constant voltage charging was 0.05C. After completing a total of 50 cycles, the charge / discharge efficiency (initial efficiency and 50 cycle capacity retention rate) of the first cycle was obtained. Then, the capacity ratio (50th / 1st) of dividing the charge capacity of 50 cycles by the charge capacity of the first cycle was calculated and regarded as the capacity retention rate. The results are shown in Table 2 below.

Initial efficiency (%) 50 cycle capacity retention rate (%) Example 4-1 99.8 97.2 Example 4-2 99.7 97.5 Example 4-3 99.9 98.0 Comparative Example 1 99.7 93.2 Comparative Example 2 99.2 92.8 Comparative Example 3 99.8 93.5 Comparative Example 4 99.6 95.5

Referring to Table 2, it can be seen that the initial efficiencies of Examples 4-1 to 4-3 and Comparative Examples 1 to 4 are similar but the 50-cycle capacity retention ratio is better than that of the Comparative Example.

This seems to be due to the fact that the binder composition composed of three or more types of latex particles maintains the bonding force between the constituent components of the electrode even when the volume expands due to repeated charge and discharge. That is, the binder composition according to the present invention has the effect of providing a lithium secondary battery having a life characteristic and safety.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. will be.

Claims (20)

As a binder composition for a secondary battery,
(A) and at least one kind of acrylic copolymer latex particles (B), wherein the conjugated dienes latex particles (A) and the copolymer latex particles (B) And the kind of the acrylic copolymer latex particles (B) is 4 or more in the entire composition,
Is contained in combination of two kinds of conjugated dienic latex particles (A) and two types of acrylic copolymer latex particles (B);
The conjugated diene-based latex particles (A) are a butadiene-styrene-hydroxyethyl acrylate-acrylic acid copolymer and a butadiene-styrene-methyl methacrylate-acrylic acid-itaconic acid copolymer;
The acrylic copolymer latex particles (B) are obtained by reacting a butyl acrylate-styrene-hydroxybutyl acrylate-acrylic acid copolymer,
Styrene-acrylic acid-itaconic acid copolymer, which contains both a nonionic emulsifier and an anionic emulsifier;
Composition. The composition of claim 1, wherein the latex particles mixed in the combination of at least four are present in independent phases. The composition according to claim 1, wherein the conjugated diene-based latex particles (A) and the acrylic copolymer latex particles (B) are contained in a ratio of 50:50 to 99: 1 based on the weight ratio. The composition according to claim 1, wherein the conjugated diene-based latex particles (A) and the acrylic copolymer latex particles (B) are contained in a ratio of 70:30 to 99: 1 based on the weight ratio. delete delete delete delete delete The composition according to claim 1, wherein the average particle diameter of the latex particles (A) is 50 to 700 nm. The composition according to claim 1, wherein the average particle size of the latex particles (B) is from 30 to 800 nm. delete delete delete delete delete delete An electrode assembly for a secondary battery, comprising a composition according to claim 1 and an electrode active material capable of intercalating and deintercalating lithium. An electrode for a secondary battery, characterized in that the electrode mixture according to claim 18 is applied to a current collector. A lithium secondary battery comprising the electrode for a secondary battery according to claim 19.