KR102244954B1 - Positive electrode slurry composition for secondary battery, and positive electrode for secondary battery and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention is a lithium transition metal oxide containing nickel; And (i) a unit derived from a nitrile-based monomer, (ii) a unit derived from an alkylene oxide-based monomer, and (iii) a unit derived from an acrylate-based monomer, wherein the copolymer The binder relates to a positive electrode slurry composition comprising 5% by weight or less of a unit derived from a monomer containing fluorine in a molecule based on the total weight of the copolymer binder, and the positive electrode slurry composition according to the present invention is derived from a specific monomer. Since it contains a binder containing a unit derived from a monomer containing fluorine in the molecule in an amount of 5% by weight or less based on the total weight of the copolymer binder, even if a lithium transition metal oxide containing nickel is included, the binder The gelation does not occur, so it can exhibit improved adhesion and more stable electrochemical performance.

Description

A positive electrode slurry composition for a secondary battery, and a positive electrode and a lithium secondary battery for a secondary battery including the same TECHNICAL FIELD OF THE INVENTION

The present invention relates to a positive electrode slurry composition for a secondary battery, an electrode for a secondary battery including the same, and a lithium secondary battery, and more particularly, in the positive electrode slurry composition containing a lithium transition metal oxide containing nickel, The present invention relates to a positive electrode slurry composition having no problem of increasing the viscosity of the positive electrode slurry, a positive electrode for a secondary battery including the same, and a lithium secondary battery including the same.

As technology development and demand for mobile devices increase, the demand for secondary batteries as an energy source is rapidly increasing, and among such secondary batteries, lithium secondary batteries exhibit high energy density and operating potential, long cycle life, and low self-discharge rate. Batteries have been commercialized and are widely used.

The electrode of a lithium secondary battery is manufactured by mixing a positive electrode active material or a negative electrode active material and a binder resin component and dispersing it in a solvent to form a slurry, which is applied to the surface of an electrode current collector and dried to form a mixture layer.

As the positive electrode active material, a lithium-containing cobalt oxide such as _{LiCoO 2 in a} layered structure, a lithium-containing nickel oxide such as _{LiNiO 2 in a} layered structure, and a lithium-containing manganese oxide such as _{LiMn 2} O _{4 in a spinel crystal structure} Etc. are being used.

LiCoO ₂ is currently widely used because of its excellent physical properties such as excellent cycle characteristics, but it is low in safety, and is expensive due to the resource limitation of cobalt as a raw material, and there is a limitation in mass use as a power source in fields such as electric vehicles. In addition, LiNiO ₂ is relatively inexpensive and exhibits high discharge capacity battery characteristics, but a rapid phase transition of the crystal structure appears according to the volume change accompanying the charge/discharge cycle, and the stability is rapidly deteriorated when exposed to air and moisture. There is this. On the other hand, _{lithium manganese oxides such as LiMnO 2} and LiMn ₂ O ₄ have the advantage of using manganese, which is rich in resources and is environmentally friendly as a raw material, but has disadvantages of low capacity, poor high temperature characteristics, and poor cycle characteristics. have.

In order to solve these problems, many attempts and studies have been conducted to use a lithium transition metal oxide mixed with nickel-cobalt-manganese in a positive electrode active material. A positive electrode active material prepared by mixing nickel, cobalt, and manganese has an advantage in that overall physical properties are improved compared to a battery prepared using each of the transition metals separately.

However, in the case of the lithium transition metal oxide in which nickel-cobalt-manganese is mixed, there is a problem in that stability is deteriorated when exposed to moisture in the air due to the presence of nickel contained therein. Specifically, moisture in the air and nickel in nickel-cobalt-manganese react to generate a hydroxy group, and the resulting hydroxy group reacts with a binder containing fluorine in a commonly used molecule contained in the positive electrode active material slurry. This causes gelation. When the binder is gelled, the viscosity of the positive electrode active material slurry also rapidly increases, and thus the uniformity of the positive electrode active material layer decreases, leading to a decrease in adhesion between the electrode and the electrode, and problems such as non-expression of the cell capacity and reduction in output occur.

Therefore, when using a lithium transition metal oxide containing a ternary transition metal of nickel-cobalt-manganese, it is required to improve resistance to moisture, and for this purpose, a positive electrode active material including a binder that is not affected by the reaction between nickel and moisture. It requires the development of a slurry.

An object to be solved by the present invention is to provide a positive electrode slurry composition capable of improving the electrochemical performance of a battery by suppressing gelation of a binder due to moisture in the air.

Another object of the present invention is to provide a positive electrode for a lithium secondary battery comprising the positive electrode slurry composition.

Another problem to be solved of the present invention is to provide a lithium secondary battery including the positive electrode for the lithium secondary battery.

In order to solve the above problem, the present invention

Lithium transition metal oxide including nickel; And

(i) a unit derived from a nitrile-based monomer, (ii) a unit derived from an alkylene oxide-based monomer, and (iii) a copolymer binder containing a unit derived from an acrylate-based monomer,

The binder provides a positive electrode slurry composition comprising 5% by weight or less of a unit derived from a monomer containing fluorine in a molecule based on the total weight of the copolymer binder.

In addition, the present invention provides a positive electrode for a lithium secondary battery comprising the positive electrode slurry composition in order to solve the other problems.

In addition, the present invention provides a lithium secondary battery including the positive electrode for the lithium secondary battery in order to solve the another problem.

Since the positive electrode slurry composition according to the present invention includes a copolymer binder containing a specific unit, and a binder containing 5% by weight or less of a unit derived from a monomer containing fluorine in the molecule, based on the total weight of the copolymer binder, , Even if a lithium transition metal oxide including nickel is included, gelation of the binder does not occur, thus exhibiting improved adhesion, thereby exhibiting more stable electrochemical performance.

Hereinafter, the present invention will be described in more detail to aid understanding of the present invention.

The terms or words used in the specification and claims should not be construed as being limited to their usual or dictionary meanings, and the inventor may appropriately define the concept of terms in order to describe his own invention in the best way. It should be interpreted as a meaning and concept consistent with the technical idea of the present invention based on the principle that there is.

The positive electrode slurry composition according to the present invention comprises a lithium transition metal oxide including nickel; And (i) a unit derived from a nitrile-based monomer, (ii) a unit derived from an alkylene oxide-based monomer, and (iii) a unit derived from an acrylate-based monomer, wherein the binder is , The unit derived from a monomer containing fluorine in the molecule is included in an amount of 5% by weight or less based on the total weight of the copolymer binder.

The copolymer binder included in the positive electrode slurry composition of the present invention includes (i) a unit derived from a nitrile-based monomer, (ii) a unit derived from an alkylene oxide-based monomer, and (iii) a unit derived from an acrylate-based monomer. As a copolymer comprising, since the unit derived from the monomer containing fluorine in the molecule is contained in an amount of 5% by weight or less based on the total weight of the copolymer binder, the lithium transition metal oxide containing nickel contained in the positive electrode slurry composition Even when the nickel reacts with moisture in the air to form a hydroxyl group and increases the pH of the positive electrode slurry composition, gelation or gelation of the binder does not occur.

The nitrile-based monomer may include, for example, a unit derived from alkenyl cyanide, and specifically may be at least one selected from the group consisting of acrylonitrile, methacrylonitrile, and allyl cyanide. And, more specifically, it may be acrylonitrile.

The alkylene oxide-based monomer may be one or more selected from the group consisting of ethylene oxide, propylene oxide, butylene oxide, styrene oxide, epichlorohydrin, and tetrahydrofuran, and specifically ethylene oxide.

The copolymer binder may include a unit derived from the nitrile-based monomer and a unit derived from the alkylene oxide-based monomer in a weight ratio of 1:1 to 10:1, specifically 3:1 to 8:1 It can be included in a weight ratio.

When the weight ratio of the unit derived from the alkylene oxide-based monomer and the unit derived from the nitrile-based monomer satisfies the above range, the copolymer binder including the same can exhibit appropriate adhesion, and thus a positive electrode slurry composition comprising the same When manufacturing a positive electrode for a lithium secondary battery and a lithium secondary battery by using, more stable electrochemical performance can be exhibited. On the other hand, when the weight ratio of the unit derived from the alkylene oxide monomer and the unit derived from the nitrile-based monomer is out of the above range, it is impossible to manufacture a positive electrode using this due to insufficient adhesion, or the resistance of the prepared positive electrode becomes too large. Problems may occur, and deterioration may be accelerated when cycling at high temperatures, resulting in a decrease in high temperature cycle life.

The acrylate monomers are methyl acrylate, ethyl acrylate, t-butyl acrylate, methyl methacrylate, methacryloxy ethylethylene urea, β-carboxyethyl acrylate, aliphatic monoacrylate, dipropylene diacrylate , Ditrimethyllopropane tetraacrylate, hydroxyethyl acrylate, dipentaerythrolhexaacrylate, pentaerytrioltriacrylate, pentaerytriol tetraacrylate, lauryl acrylate, seryl acrylate, ste It may be one or more selected from the group consisting of aryl acrylate, lauryl methacrylate, cetyl methacrylate, and stearyl methacrylate, specifically methyl acrylate, ethyl acrylate, t-butyl acrylate and methyl meth It may be one or more selected from the group consisting of acrylate, and the acrylate-based oligomer may be a polymerized monomer.

Meanwhile, the unit derived from the alkylene oxide-based monomer and the unit derived from the acrylate-based monomer may be derived from an alkylene oxide-based macromer, but are not limited thereto.

The "macromer" is also referred to as a macromonomer, and refers to a macromolecule having a polymerizable group at one or more ends of a side chain or a polymer chain.

The alkylene oxide-based macromer may specifically be one in which an acrylate-based monomer is bonded to an end of the alkylene oxide-based polymer chain, and the acrylate-based monomer is on one or both sides of the alkylene oxide-based polymer chain. It may be located, and more specifically, the acrylate-based monomer may be located at one end of the alkylene oxide-based polymer chain.

In one example of the present invention, the copolymer binder may be one in which an acrylate-based monomer of the alkylene oxide-based macromer is bonded to a main chain consisting of units derived from the nitrile-based monomer.

In another example of the present invention, in the copolymer binder, the acrylate-based monomer is bonded to a main chain consisting of a unit derived from the nitrile-based monomer, and the acrylate-based monomer is derived from the nitrile-based monomer. It may be that a unit derived from the alkylene oxide-based monomer is bonded to the other end bonded to the chain of the unit.

That is, the copolymer binder The unit derived from the nitrile-based monomer forms a main chain, and the unit derived from the alkylene oxide-based monomer forms a branch, wherein the acrylate-based monomer is a unit derived from the nitrile-based monomer and the alkyl The unit derived from the renoxide-based monomer may be located at a connection site to which a unit is connected, and may serve as a medium for fastening.

The copolymer binder may contain a unit derived from the acrylate-based monomer in an amount of 0.1 to 20 parts by weight, specifically 1 to 10 parts by weight, based on 100 parts by weight of the unit derived from the alkylene oxide monomer. That is, the amount of the unit derived from the acrylate-based monomer may be determined based on the content of the unit derived from the alkylene oxide monomer, and when expressed as a weight ratio, the unit derived from the acrylate-based monomer and the alkylene oxide The unit derived from the monomer may be included in a weight ratio of 0.001:1 to 0.2:1, specifically 0.01 to 0.1.

The unit derived from the acrylate-based monomer is located between the main chain of the unit derived from the nitrile-based monomer and the unit derived from the alkylene oxide monomer, and the main chain formed by the unit derived from the nitrile-based monomer and the alkylene Since the unit derived from the oxide monomer serves as a mediator for the connection between the branches formed, when the unit derived from the acrylate-based monomer is 0.1 parts by weight or more with respect to 100 parts by weight of the unit derived from the alkylene oxide monomer , It may have an appropriate content to serve as a medium for the connection, and if it is less than 20 parts by weight, the amount of the acrylate-based monomer that does not participate as a medium for the connection increases, and the positive electrode and lithium secondary containing the same It is possible to prevent the problem of rapidly deteriorating the electrochemical properties of the battery.

In the copolymer binder, the main chain formed by the unit derived from the nitrile-based monomer may have a weight average molecular weight of 3,000 to 50,000, and specifically may have a weight average molecular weight of 5,000 to 20,000. When the main chain formed by the unit derived from the nitrile-based monomer has a weight average molecular weight of 3,000 or more, the unit derived from the nitrile-based monomer can properly form the main chain of the copolymer binder and have a weight average molecular weight of 50,000 or less. In this case, it is possible to prevent the problem that the weight average molecular weight of the prepared copolymer binder becomes too large.

The branch formed by the unit derived from the alkylene oxide-based monomer may have a weight average molecular weight of 500 to 15,000, and specifically may have a weight average molecular weight of 1,000 to 8,000. When the branch formed by the unit derived from the alkylene oxide-based monomer has a weight average molecular weight of 500 or more, the branch formed by the unit derived from the alkylene oxide-based monomer is appropriately connected to the main chain of the copolymer binder to form a branch. If it has a weight average molecular weight of 15,000 or less, the chain length of the branch formed by the unit derived from the alkylene oxide-based monomer is appropriate, and the physical properties of the prepared copolymer are suitable as a copolymer binder used in the positive electrode slurry. Do. On the other hand, when the branch formed by the unit derived from the alkylene oxide-based monomer has a weight average molecular weight of more than 15,000, the chain length is too long to prepare a positive electrode slurry containing the prepared copolymer, and then use the positive electrode slurry. Thus, when the positive electrode is manufactured, cracks may occur on the surface of the positive electrode.

Meanwhile, a unit derived from a monomer containing fluorine in the molecule refers to a unit derived from a monomer having one or more fluorine substituents in the molecular structure, and a unit derived from a monomer containing fluorine in the molecule is the copolymer It may be included in an amount of 5 wt% or less, specifically 0 wt% to 5 wt% based on the total weight of the binder.

When a unit derived from a monomer containing fluorine in the molecule is included in the copolymer binder, a hydroxyl group produced by reacting moisture in the air with nickel contained in the lithium transition metal oxide reacts with the fluorine, and the copolymer binder Since the gelation of is caused, the unit derived from the monomer containing fluorine in the molecule needs to be controlled to a certain content or less with respect to the total weight of the copolymer binder, and therefore, it needs to be controlled to 5% by weight or less.

Examples of monomers containing fluorine in the molecule include 1,1-difluoroethylene, 1-2-difluoroethylene, fluoroethylene, hexafluoropropylene, and tetrafluoroethylene. One or more selected from the group may be mentioned.

The copolymer binder may have a weight average molecular weight of 100,000 to 2,000,000, specifically 400,000 to 1,500,000, and more specifically 400,000 to 1,400,000.

When the binder has a weight average molecular weight of 100,000 to 2,000,000, there is no problem of decrease in adhesion that may occur when the weight average molecular weight is too small, while the binder in manufacturing a positive electrode slurry that may occur when the weight average molecular weight is too large. Problems such as poor dissolution or decreased phase stability of the positive electrode slurry can be prevented.

The method for preparing the copolymer binder is not particularly limited, but may be prepared according to, for example, a suspension polymerization method, an emulsion polymerization method, or a seed polymerization method.

The copolymer binder includes the nitrile-based monomer, an alkylene oxide-based monomer, and an acrylate-based monomer, and if necessary, a binder containing one or more other components such as a polymerization initiator, a crosslinking agent, a buffer, a molecular weight control agent, and an emulsifier. It may be prepared by polymerizing the composition, alternatively, the nitrile-based monomer and the acrylate-based monomer include an alkylene oxide-based macromer bonded to the terminal, and if necessary, a polymerization initiator, a crosslinking agent, a buffer, a molecular weight control agent, and an emulsifier It may be prepared by polymerizing a binder composition including one or more other components such as.

The polymerization temperature and the polymerization time may be appropriately determined depending on the type of polymerization method polymerization initiator, and the like. For example, the polymerization temperature may be 50 to 300°C, and the polymerization time may be 1 to 20 hours, but are not particularly limited.

The polymerization initiator may be an inorganic or organic peroxide, for example, a water-soluble initiator including potassium persulfate, sodium persulfate, ammonium persulfate, or oil-soluble initiators including cumene hydroperoxide, benzoyl peroxide, etc. I can. Meanwhile, an activator may be used together to accelerate the initiation reaction of the polymerization initiator, and the activator is selected from the group consisting of sodium formaldehyde sulfoxylate, sodium ethylenediamine tetraacetate, ferrous sulfate and dextrose. One or more can be mentioned.

The crosslinking agent may be used to accelerate the crosslinking of the binder, for example, amines such as diethylenetriamine, triethylene tetraamine, diethylamino propylamine, xylene diamine, isophorone diamine, dodecyl succinic anhydride (dodecyl succinic anhydride), acid anhydrides such as phthalic anhydride, polyamide resin, polysulfide resin, phenol resin, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, 1,3-butanediol dimethacrylate, 1,6-hexanediol dimethacrylate, neopentyl glycol dimethacrylate, trimethylol propane trimethacrylate, trimethylol methane triacrylate, glycidyl methacrylate Acrylate, etc. are mentioned. Meanwhile, a grafting agent may be used together, and examples thereof include aryl methacrylate (AMA), triaryl isocyanurate (TAIC), triaryl amine (TAA), or diaryl amine (DAA).

Examples of the buffer include NaHCO ₃ , NaOH, or NH ₄ OH.

Examples of the molecular weight modifier include mercaptans, terbinolene, dipentene, t-terpiene, and other halogenated hydrocarbons such as chloroform and carbon tetrachloride.

The emulsifier may be an anionic emulsifier, a nonionic emulsifier, or both, and when a nonionic emulsifier is used together with an anionic emulsifier, in addition to the electrostatic stabilization of the anionic emulsifier, the addition of a colloidal form through the van der Waals force of the polymer particles It can provide stabilization.

Examples of the anionic emulsifier include phosphate-based, carboxylate-based, sulfate-based, succinate-based, sulfosuccinate-based, sulfonate-based, or disulfonate-based emulsifiers, and are not particularly limited, but specifically Sodium alkyl sulfate, sodium polyoxyethylene sulfate, sodium lauryl ether sulfate, sodium polyoxyethylene lauryl ether sulfate, sodium lauryl sulfate, sodium alkyl sulfonate, sodium alkyl ether sulfonate, sodium alkylbenzene sulfonate, Sodium linear alkylbenzene sulfonate, sodium alpha-olefin sulfonate, sodium alcohol polyoxyethylene ether sulfonate, sodium dioctylsulfosuccinate, sodium perfluorooctanesulfonate, sodium perfluorobutanesulfonate, alkyldiphenyloxide Disulfonate, sodium dioctyl sulfosuccinate, sodium alkyl-aryl phosphate, sodium alkyl ether postate, or sodium lauryl sarcosinate.

Examples of the nonionic emulsifier include ester-type, ether-type, and ester-ether-type emulsifiers, and are not particularly limited, but specifically polyoxyethylene glycol, polyoxyethylene glycol methyl ether, polyoxyethylene monoallyl ether, poly Oxyethylenebisphenol-A ether, polypropylene glycol, polyoxyethylene neopentyl ether, polyoxyethylene cetyl ether, polyoxyethylene lauryl ether, polyoxyethyloleyl ether, polyoxyethylene stearyl ether, polyoxyethylenedecyl Ether and polyoxyethylene octyl ether.

The positive electrode slurry composition may further include an auxiliary binder other than the copolymer binder.

The auxiliary binder is not particularly limited as long as it is typically used for preparing a slurry of the positive electrode active material of a lithium secondary battery, but when the auxiliary binder contains fluorine in the binder molecular structure, the amount of the binder containing fluorine is the entire positive electrode slurry composition. It needs to be adjusted within an appropriate range based on the weight.

For example, the auxiliary binder, of the binder mixture including the copolymer binder and the auxiliary binder, a unit derived from a monomer, oligomer, or macromer containing fluorine in the binder molecular structure is 5 weight based on the total weight of the binder mixture It may be included to satisfy% or less, and specifically, may be included in an amount of 0% to 5% by weight. That is, in the entire binder included in the positive electrode slurry composition, a unit derived from a monomer, oligomer, or macromer containing fluorine may be adjusted within the above content range.

The auxiliary binder is polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidenefluoride, polyacrylonitrile, polymethylmethacrylate, Polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), It may be at least one selected from the group consisting of sulfonated EPDM, styrene butadiene rubber (SBR), fluorine rubber, polyacrylic acid, and polymers in which hydrogen is substituted with Li, Na, or Ca.

The lithium transition metal oxide may be selected from the group consisting of a lithium-nickel-based oxide, a lithium-nickel-manganese-based oxide, a lithium-nickel-cobalt-based oxide, and a lithium-nickel-manganese-cobalt-based oxide, and specifically Li _{1 + x} (Ni _a Co _b Mn _c )O ₂ (0<a<1, 0≤b<1, 0≤c<1, -0.2≤x≤0.2, and x+a+b+c=1), Li(Ni _d Co _e Mn _f )O ₄ (0<d<2, 0<e<2, 0<f<2, d+e+f=2), Li _g NiO ₂ (0.5<g<1.3) , LiNi _{1 - h} M _h O ₂ (M=Co, Mn, Al, Cu, Fe, Mg, B or Ga, 0≤h<1), LiMn _2-y Ni _y O ₄ (0<y<2 ), LiMn _2-z Co _z O ₄ (0<Z<2).

In one example of the present invention, the lithium transition metal oxide may be specifically represented by Formula 1 below.

[Formula 1]

Li _1+x (Ni _a Co _b Mn _c )O ₂

In Formula 1, 0<a<1, 0≤b<1, 0≤c<1, -0.2≤x≤0.2, and x+a+b+c=1.

In addition, in another example of the present invention, in Formula 1, 1/3≤a≤1, 0≤b≤2/3, 0≤c≤2/3, -0.2≤x≤0.2, and x+a It may be +b+c=1.

Further, in another example of the present invention, in Formula 1, 0.6≤a≤1, 0≤b≤0.4, 0≤c≤0.4, -0.2≤x≤0.2, and x+a+b+c= May be 1.

The positive electrode slurry prepared from the positive electrode slurry composition may be prepared by a conventional method known in the art. For example, it may be prepared by mixing and stirring a solvent, a copolymer binder according to the present invention, and optionally a conductive material and/or a dispersant in the lithium transition metal oxide containing nickel as a positive electrode active material.

For example, the positive electrode slurry composition may include 70 to 99% by weight of lithium transition metal oxide, 0.1 to 10% by weight of a binder, and 0.01 to 20% by weight of a conductive material based on the total weight of the positive electrode slurry composition. Specifically, the positive electrode slurry composition may include 85% to 99.7% by weight of lithium transition metal oxide, 0.2% to 5% by weight of a binder, and 0.1% to 10% by weight of a conductive material.

The preparation of the positive electrode slurry composition may be performed in the atmosphere, and the positive electrode slurry composition is the copolymer binder even if the lithium transition metal oxide containing nickel reacts with moisture contained in the atmosphere to form a hydroxyl group and increases the pH. Including, the copolymer binder, since the unit derived from a monomer containing fluorine in the molecule is 5% by weight or less based on the total weight of the copolymer binder, gelation is suppressed, so that an increase in viscosity of the positive electrode slurry composition is also suppressed. I can.

Specifically, the positive electrode slurry composition is a positive electrode slurry after preparing a positive electrode slurry by mixing the lithium transition metal oxide, a copolymer binder, and a conductive material in an environment of 70% relative humidity, and then leaving it for 45 hours in an environment of 100% relative humidity. The viscosity of may increase to 150% or less, specifically 5 to 90%, and more specifically 10% to 90% compared to the viscosity of the positive electrode slurry at the initial stage of mixing. In addition, the viscosity of the positive electrode slurry after being left for 60 hours in an environment of 100% relative humidity may increase to 300% or less compared to the viscosity of the positive electrode slurry at the beginning of mixing, and specifically, may increase by 10% to 195%, and more specifically It can be increased by 20% to 195%.

The positive electrode slurry composition is prepared by mixing each component included in the positive electrode slurry composition in an environment of 70% relative humidity to prepare a positive electrode slurry, and then even when left in an environment of 100% relative humidity, the increase in viscosity of the positive electrode slurry is small. When the anode is configured by using the anode, the anode layer can maintain a more uniform state, and thus, it is possible to suppress the occurrence of problems such as a decrease in anode capacity and a decrease in output.

The environment with a relative humidity of 70% and an environment with a relative humidity of 100% may be an environment with a relative humidity of 70% and an environment with a relative humidity of 100%, respectively, regardless of a specific temperature, as long as the temperature is generally allowed in the positive electrode slurry manufacturing process. In one example of the present invention, the relative humidity may be a relative humidity measured at a temperature in a conventional manufacturing process of the positive electrode slurry, and the temperature may be room temperature, specifically 25°C.

The positive electrode slurry composition may be coated (coated) on a current collector of a metal material, compressed, and dried to prepare a positive electrode for a lithium secondary battery, and the positive electrode may be manufactured by a conventional method known in the art.

Accordingly, the present invention provides a positive electrode for a lithium secondary battery comprising a positive electrode current collector and the positive electrode slurry composition, and wherein the positive electrode slurry composition is coated on one or both surfaces of the positive electrode current collector.

The lithium secondary battery may include a negative electrode and a separator interposed between the positive electrode and the negative electrode.

The current collector of the metallic material is a metal with high conductivity, and is a metal that can be easily adhered to the slurry of the positive electrode active material, and is particularly limited as long as it has high conductivity without causing chemical changes to the battery in the voltage range of the battery. It is not, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, or the like may be used. In addition, it is possible to increase the adhesion of the positive electrode active material by forming fine irregularities on the surface of the current collector. The current collector can be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc., and may have a thickness of 3 to 500 μm.

As a solvent for forming the positive electrode slurry, there are organic solvents such as NMP (N-methyl pyrrolidone), DMF (dimethyl formamide), acetone, dimethyl acetamide, or water, and these solvents may be used alone or in two types. The above can be mixed and used. The amount of the solvent is sufficient as long as it can dissolve and disperse the positive electrode active material, the binder, and the conductive material in consideration of the coating thickness and production yield of the slurry.

The conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery, for example, graphite such as natural graphite or artificial graphite; Carbon blacks such as acetylene black, Ketjen black, channel black, Parnes black, lamp black, and thermal black; Conductive fibers such as carbon fibers and metal fibers; Conductive tubes such as carbon nanotubes; Metal powders such as fluorocarbon, aluminum, and nickel powder; Conductive whiskers such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives may be used. The conductive material may be used in an amount of 1% to 20% by weight based on the total weight of the positive electrode slurry.

The dispersant may be an aqueous dispersant or an organic dispersant such as N-methyl-2-pyrrolidone.

The negative electrode may be manufactured by a conventional method known in the art. For example, the negative electrode active material, the above-described binder, and additives such as a conductive material are mixed and stirred to prepare a negative electrode active material slurry, which is then added to the negative electrode current collector. It can be prepared by applying, drying and compressing.

As a solvent for forming the negative electrode, there are organic solvents such as NMP (N-methyl pyrrolidone), DMF (dimethyl formamide), acetone, dimethyl acetamide, or water, and these solvents may be used alone or in two or more Can be used by mixing. The amount of the solvent is sufficient as long as it can dissolve and disperse the negative electrode active material, the binder, and the conductive material in consideration of the coating thickness and production yield of the slurry.

The binder may be included in an amount of 10% by weight or less with respect to the total weight of the slurry for an anode active material, and specifically in an amount of 0.1% to 10% by weight. If the content of the binder is less than 0.1% by weight, the effect of the use of the binder is not preferable, and if it exceeds 10% by weight, the capacity per volume may decrease due to a decrease in the relative content of the active material due to an increase in the content of the binder. Not desirable.

The conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery, and examples of the conductive material include graphite such as natural graphite or artificial graphite; Carbon blacks such as 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, aluminum, and nickel powder; Conductive whiskers such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Alternatively, conductive materials such as polyphenylene derivatives may be used. The conductive material may be used in an amount of 1% to 9% by weight based on the total weight of the slurry for the negative electrode active material.

The negative electrode current collector used for the negative electrode according to an embodiment of the present invention may have a thickness of 3 μm to 500 μm. The negative electrode current collector is not particularly limited as long as it has conductivity without causing chemical changes to the battery, for example, copper, gold, stainless steel, aluminum, nickel, titanium, calcined carbon, copper, or stainless steel. Surface treatment with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. may be used. In addition, by forming fine irregularities on the surface, the bonding strength of the negative electrode active material may be strengthened, and may be used in various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics.

The active material slurry may include a viscosity modifier and/or a filler, if necessary.

The viscosity modifier may be carboxymethylcellulose, polyacrylic acid, or the like, and the viscosity of the active material slurry may be adjusted to facilitate the preparation of the active material slurry and the application process on the electrode current collector by addition.

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 to the battery. For example, olefin-based polymers such as polyethylene, polypropylene, glass fiber, carbon fiber, etc. It may be a fibrous material.

On the other hand, the separator is a conventional porous polymer film used as a separator in the past, such as polyolefin-based polymers such as ethylene homopolymer, propylene homopolymer, ethylene-butene copolymer, ethylene-hexene copolymer, and ethylene-methacrylate copolymer. The porous polymer film prepared with may be used alone or by stacking them, or a conventional porous nonwoven fabric, such as a nonwoven fabric made of a high melting point glass fiber, polyethylene terephthalate fiber, etc., may be used, but is not limited thereto.

A lithium salt which can be included as an electrolyte used in the present invention can be used without limitation, those which are commonly used in a lithium secondary battery electrolyte, for example the lithium salt of the anion is ^{F -, Cl -, Br -} , I -, NO 3 _{^{-, N (CN) 2 -}} , BF 4 -, ClO 4 -, PF 6 -, (CF 3) 2 PF 4 -, (CF 3) 3 PF 3 -, (CF 3) 4 PF 2 -, (CF ^{_{3) 5 PF -, (CF}} 3) 6 P -, CF 3 SO 3 -, CF 3 CF 2 SO 3 -, (CF 3 SO 2) 2 N -, (FSO 2) 2 N -, CF 3 CF 2 ^{_{(CF 3) 2 CO -,}} (CF 3 SO 2) 2 CH -, (SF 5) 3 C -, (CF 3 SO 2) 3 C -, CF 3 (CF 2) 7 SO 3 -, CF 3 CO ₂ ^- , CH ₃ CO ₂ ^- , SCN ^- and (CF ₃ CF ₂ SO ₂ ) ₂ N ^-It may be any one selected from the group consisting of.

In the electrolytic solution used in the present invention, the organic solvent contained in the electrolytic solution may be used without limitation, typically used in the electrolytic solution for secondary batteries, and typically propylene carbonate (PC), ethylene carbonate (EC). ), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), methylpropyl carbonate, dipropyl carbonate, dimethyl sulfur oxide, acetonitrile, dimethoxyethane, diethoxyethane , Vinylene carbonate, sulfolane, gamma-butyrolactone, any one selected from the group consisting of propylene sulfite and tetrahydrofuran, or a mixture of two or more of them may be typically used. Specifically, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are highly viscous organic solvents and can be preferably used because they dissociate lithium salts in the electrolyte well due to their high dielectric constant. When a low viscosity, low dielectric constant linear carbonate such as ethyl carbonate is mixed and used in an appropriate ratio, an electrolyte solution having a high electrical conductivity can be prepared, and thus it can be more preferably used.

Optionally, the electrolyte stored according to the present invention may further include an additive such as an overcharge preventing agent included in a conventional electrolyte.

The appearance of the lithium secondary battery of the present invention is not particularly limited, but it may be a cylindrical shape using a can, a square shape, a pouch type, or a coin type.

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

Example

Hereinafter, examples and experimental examples will be described in more detail in order to specifically describe the present invention, but the present invention is not limited by these examples and experimental examples. The embodiments according to the present invention may be modified in various different forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The embodiments of the present invention are provided to more completely describe the present invention to those of ordinary skill in the art.

Manufacturing example

100 g of an acrylonitrile monomer and 16 g of an ethylene oxide macromer (weight average molecular weight of 1,600) having an acrylate terminal were prepared and placed in a reactor under an AIBN (azobisisobutyronitrile) polymerization initiator and a DMF solvent, and the reaction was carried out. After the initiation, 65 was maintained and reacted sufficiently for 30 hours to prepare a copolymer binder having a weight average molecular weight of 1,000,000.

Example 1

In an atmosphere of 70% relative humidity, Li(Ni _0.8 Mn _0.1 Co _0.1 )O _{2 as a positive electrode active material} 97 g, 1 g of acetylene black as a conductive material, and 2 g of the copolymer binder prepared in Preparation Example 1 as a binder were added to N-methyl-2-pyrrolidone (NMP) as a solvent to prepare a positive electrode slurry.

Comparative Example 1

In an atmosphere of 70% relative humidity, Li(Ni _0.8 Mn _0.1 Co _0.1 )O _{2 as a positive electrode active material} 97 g, 1 g of acetylene black as a conductive material, and 2 g of polyvinylidene fluoride (PVDF) as a binder were added to N-methyl-2-pyrrolidone (NMP) as a solvent to prepare a positive electrode slurry.

Comparative Example 2

In a dry room with a dew point temperature of -60°C, _{97 g of Li(Ni 0.8} Mn _0.1 Co _0.1 )O ₂ as a positive electrode active material, 1 g of acetylene black as a conductive material, and polyvinylidene fluoride (PVDF) 2 as a binder g was added to N-methyl-2-pyrrolidone (NMP) as a solvent to prepare a positive electrode slurry.

Example 2

After leaving the positive electrode slurry prepared in Example 1 for 12 hours in an environment of 100% relative humidity, it was applied to an aluminum (Al) thin film that is a positive electrode current collector having a thickness of about 20 μm, dried to prepare a positive electrode, and then roll pressed. (roll press) was performed to prepare a positive electrode.

In addition, carbon powder as an anode active material, PVDF as a binder, and carbon black as a conductive material were added in 96% by weight, 3% by weight, and 1% by weight, respectively, to NMP as a solvent to prepare a negative electrode mixture slurry. The negative electrode mixture slurry was coated on a copper (Cu) thin film of a negative electrode current collector having a thickness of 10 μm, dried to prepare a negative electrode, and then roll pressed to prepare a negative electrode.

The positive and negative electrodes thus prepared were prepared with a separator consisting of three layers of polypropylene/polyethylene/polypropylene (PP/PE/PP) and a polymer-type battery was produced by a conventional method, and then EC (ethylene carbonate): DEC (diethyl carbonate). ):EMC (ethyl methyl carbonate) = 4:3:3 (volume ratio) A lithium secondary battery was prepared by injecting a non-aqueous electrolyte prepared by dissolving _{a LiPF 6 electrolyte at a concentration of 1 M using a mixed solvent.}

Comparative Example 3

After leaving the positive electrode slurry prepared in Comparative Example 1 for 12 hours in an environment of 100% relative humidity, an attempt was made to prepare a positive electrode according to the positive electrode manufacturing method described in Example 2, but it was applied to the positive electrode current collector due to the gelation of the positive electrode slurry. Was not made smoothly, and the production of the positive electrode failed.

Comparative Example 4

As the positive electrode slurry in Example 2, the positive electrode slurry prepared in Comparative Example 2 was used in place of the positive electrode slurry prepared in Example 1, but the positive electrode was prepared immediately after preparation of the positive electrode slurry without leaving it in an environment of 100% relative humidity. Except for proceeding, a lithium secondary battery was manufactured in the same manner as in Example 2.

Experimental Example 1: Measurement of viscosity change over time of positive electrode slurry

The viscosity of the positive electrode slurry prepared in Example 1 and Comparative Example 1 was measured at the beginning of the preparation of the positive electrode slurry, after standing for 45 hours in an environment of 100% relative humidity, and after standing for 60 hours in an environment of 100% relative humidity [B Type viscometer (manufactured by Brookfield Corporation), room temperature, 12 rpm] and shown in Table 1 below.

Initial viscosity 45 hours elapsed 60 hours elapsed Example 1 2,000 cP 3,800 cP 5,900 cP Comparative Example 1 5,500 cP 55,000 cP Not measurable

Referring to Table 1 above, since the positive electrode slurry of Example 1 exhibited 3,800 cP after 45 hours and 5,900 cP after 60 hours, it was confirmed that a sudden increase in viscosity or gelation problem did not occur even in a humid environment. Could.

On the other hand, the positive electrode slurry of Comparative Example 1 had a viscosity of 55,000 cP after 45 hours. If the viscosity of the positive electrode slurry is 10,000 cP or more, there is a problem that the uniformity of the prepared positive electrode is deteriorated. Considering that coating of the positive electrode slurry for production was impossible, it was found that the positive electrode slurry of Comparative Example 1 was difficult to be used for manufacturing the positive electrode due to gelation after 45 hours.

Therefore, it was confirmed that the positive electrode slurry of Comparative Example 1 in which PVDF was used as a binder was required to control humidity immediately after preparation, when not used for positive electrode production, and otherwise lost its function as a positive electrode slurry.

Experimental Example 2: Measurement of discharge capacity

For each of the lithium secondary batteries prepared in Example 2 and Comparative Example 4, first, the charge/discharge current density was set to 0.2 C, the charge end voltage was 4.2 V (Li/Li ⁺ ), and the discharge end voltage was 3 V (Li/ The charge/discharge test was performed twice with ^{Li + ).} Subsequently, the discharge capacity was measured with the charging current density as 0.2 C and the discharge current density as 0.4 C, and then the capacity ratio was calculated by dividing by the second discharge capacity, and then regarded as 0.4 C discharge capacity (%). The results are shown in Table 2 below.

Meanwhile, 0.8 C discharge capacity and 1.2 C discharge capacity were obtained as described above, except that the discharge current density was changed to 0.8 C and 1.2 C, respectively, and are shown in Table 2 below.

0.4 C
Discharge capacity (%) 0.8 C
Discharge capacity (%) 1.2 C
Discharge capacity (%) Example 2 100 94 90 Comparative Example 3 Anode manufacturing failure Anode manufacturing failure Anode manufacturing failure Comparative Example 4 100 95 92

In the lithium secondary battery of Example 2, the positive electrode slurry prepared in Example 1 containing the _{Li(Ni 0.8} Mn _0.1 Co _0.1 )O ₂ positive electrode active material prepared in an atmosphere of 70% relative humidity was used in an environment of 100% relative humidity. After being allowed to stand for a period of time, despite including the positive electrode manufactured using this, a degree equivalent to that of the lithium secondary battery of Comparative Example 4 including the positive electrode manufactured using the positive electrode slurry of Comparative Example 2 manufactured in an environment in which moisture was excluded Shows the discharge capacity of.

On the other hand, as in Example 1, when the positive electrode slurry prepared in Comparative Example 1 prepared in an atmosphere of 70% relative humidity was left for 12 hours in an environment of 100% relative humidity as in Example 2, the gelation of the positive electrode slurry was severe. As it occurred, it was impossible to manufacture a positive electrode using this.

As described above, the positive electrode slurry of Example 1 contains a copolymer binder including a unit derived from a nitrile-based monomer, a unit derived from an alkylene oxide-based monomer, and a unit derived from an acrylate-based monomer, and thus contains nickel. _{When preparing a positive electrode slurry containing Li(Ni 0.8} Mn _0.1 Co _0.1 )O ₂ , which is a positive electrode active material, gelation of the positive electrode slurry did not occur despite the presence of moisture, and a positive electrode manufactured using the same was included. It was also confirmed that the electrochemical performance of the lithium secondary battery did not deteriorate.

Claims (15)

Lithium transition metal oxide including nickel; And
(i) a unit derived from a nitrile-based monomer, (ii) a unit derived from an alkylene oxide-based monomer, and (iii) a copolymer binder containing a unit derived from an acrylate-based monomer,
The copolymer binder contains 5% by weight or less of a unit derived from a monomer containing fluorine in the molecule, based on the total weight of the copolymer binder, and is derived from a unit derived from the nitrile-based monomer and the alkylene oxide-based monomer. The positive electrode slurry composition containing the unit in a weight ratio of 1:1 to 10:1.
The method of claim 1,
The nitrile-based monomer is at least one selected from the group consisting of acrylonitrile, methacrylonitrile, and allyl cyanide, the positive electrode slurry composition.
The method of claim 1,
The alkylene oxide-based monomer is at least one selected from the group consisting of ethylene oxide, propylene oxide, butylene oxide, styrene oxide, epichlorohydrin, and tetrahydrofuran, a positive electrode slurry composition.
delete The method of claim 1,
The acrylate monomers are methacryloxy ethylethylene urea, β-carboxyethyl acrylate, aliphatic monoacrylate, dipropylene diacrylate, ditrimethyllopropane tetraacrylate, hydroxyethyl acrylate, dipentaerythrate All hexaacrylate, pentaerytriol triacrylate, pentaerytriol tetraacrylate, lauryl acrylate, seryl acrylate, stearyl acrylate, lauryl methacrylate, cetyl methacrylate and stearyl methacrylic At least one selected from the group consisting of a rate, the positive electrode slurry composition.
The method of claim 1,
The copolymer binder comprises 0.1 to 20 parts by weight of a unit derived from the acrylate-based monomer based on 100 parts by weight of a unit derived from the alkylene oxide monomer.
The method of claim 1,
The binder has a weight average molecular weight of 100,000 to 1,000,000, the positive electrode slurry composition.
The method of claim 1,
The positive electrode slurry composition further comprises an auxiliary binder other than the copolymer binder,
The mixture of the copolymer binder and the auxiliary binder comprises 5% by weight or less of a unit derived from a monomer containing fluorine in a molecule based on the total weight of the binder mixture.
The method of claim 8,
The auxiliary binder is polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidenefluoride, polyacrylonitrile, polymethylmethacrylate, Polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), Sulfonated EPDM, styrene butadiene rubber (SBR), fluorine rubber, polyacrylic acid (poly acrylic acid), and at least one selected from the group consisting of polymers in which hydrogen is substituted with Li, Na or Ca, etc., positive electrode slurry composition.
The method of claim 1,
The lithium transition metal oxide is a compound represented by the following formula (1), a positive electrode slurry composition:
[Formula 1]
Li _{1 + x} (Ni _a Co _b Mn _c )O ₂
In Formula 1, 0<a<1, 0≤b<1, 0≤c<1, -0.2≤x≤0.2, and x+a+b+c=1.
The method of claim 10,
In Formula 1, 1/3≤a≤1, 0≤b≤2/3, 0≤c≤2/3, -0.2≤x≤0.2, and x+a+b+c=1, a positive electrode slurry Composition.
The method of claim 1,
The positive electrode slurry composition further comprises a conductive material,
Based on the total weight of the positive electrode slurry composition, including 85% to 99.7% by weight of the lithium transition metal oxide, 0.2% to 5% by weight of the binder, and 0.1% to 10% by weight of the conductive material , Positive electrode slurry composition.
The method of claim 12,
When the positive electrode slurry composition is prepared by mixing the lithium transition metal oxide, a copolymer binder, and a conductive material included in the positive electrode slurry composition in an environment of 70% relative humidity,
A positive electrode slurry composition in which the viscosity of the positive electrode slurry after standing for 45 hours in an environment of 100% relative humidity increases to 150% or less compared to the viscosity of the positive electrode slurry at the beginning of mixing.
A positive electrode current collector, and a positive electrode slurry composition according to any one of claims 1 to 3 and 5 to 13,
A positive electrode for a lithium secondary battery in which the positive electrode slurry composition is coated on one or both surfaces of the positive electrode current collector.
A lithium secondary battery comprising the positive electrode for a lithium secondary battery according to claim 14.