WO2024106932A1 - Binder comprising copolymer, negative electrode for secondary battery, comprising binder, and secondary battery comprising negative electrode - Google Patents

Abstract

The present invention relates to a copolymer prepared by copolymerizing and hydrolyzing an acrylate-based monomer and a vinyl acetate-based monomer, and a negative electrode slurry, negative electrode, and secondary battery comprising same.

Description

A binder containing a copolymer, a negative electrode for a secondary battery containing the binder, and a secondary battery containing the negative electrode.

The present invention relates to a copolymer that can be used as a binder, a slurry containing the same, an electrode, and a secondary battery.

Lithium secondary batteries have a high energy density, so they are widely used in the electrical, electronics, communications, and computer industries. Following small lithium secondary batteries for portable electronic devices, their application areas are expanding to high-capacity secondary batteries such as hybrid vehicles and electric vehicles. there is.

As the field of application expands, lithium secondary batteries are required to have higher capacity and longer lifespan characteristics. An example of a method for increasing the capacity of lithium secondary batteries is using an active material containing silicon atoms for the negative electrode.

When an active material containing silicon atoms with a large amount of lithium insertion/extraction is applied compared to conventional carbon-based active materials, improvement in battery capacity can be expected. However, since the silicon-containing active material has a large volume change accompanying lithium insertion/extraction, the negative electrode active material layer expands and contracts significantly during charging and discharging.

As a result, there was a problem that the conductivity between the negative electrode active material and the negative electrode active material was lowered, the conductive path between the negative electrode active material and the current collector was blocked, and the cycle characteristics of the secondary battery deteriorated.

Additionally, when a highly basic binder is used when manufacturing a negative electrode slurry using silicon as the negative electrode active material, bubbles and gas may be generated within the slurry.

The generation of these bubbles and gases is because silicon is oxidized when it meets water and hydrogen (H ₂ ) is generated. In particular, the generation of hydrogen can be promoted by a base. Meanwhile, generated bubbles and gases can significantly reduce the stability of the slurry and cause coating defects in the electrode process.

Therefore, there is a need for a binder that can solve these problems and secure secondary batteries with excellent characteristics.

[Prior art literature]

[Patent Document]

(Patent Document 1) Republic of Korea Patent Publication No. 10-2013-0117901

Accordingly, the present invention provides a copolymer with excellent electrical conductivity and high stability and coating properties that improves the stability of the slurry by suppressing the generation of bubbles and gases when producing a slurry (e.g., a negative electrode slurry using a silicon negative electrode active material). There is a purpose to doing so.

In addition, the present invention seeks to provide a slurry composition with excellent electrode swelling inhibition ability using the above copolymer.

In addition, the present invention seeks to provide an electrode (particularly a negative electrode) with excellent performance to which the slurry composition is applied and a secondary battery with excellent life characteristics (capacity retention rate) including the electrode.

However, the problem to be solved by the present application is not limited to the problems mentioned above, and other problems not mentioned will be clearly understood by those skilled in the art from the description below.

However, the problem to be solved by the present application is not limited to the problems mentioned above, and other problems not mentioned will be clearly understood by those skilled in the art from the description below.

One aspect of the present application is a product manufactured by copolymerizing and hydrolyzing an acrylate-based monomer and a vinyl acetate-based monomer.

A copolymer is provided.

Another aspect of the present application is the copolymer; and

Negative active material; containing,

Provide a cathode slurry.

Another aspect of the present application is a current collector; and

A negative electrode active material layer comprising the copolymer of any one of claims 1 to 9 formed on the current collector.

Provides a cathode.

Another aspect of the present application includes the cathode,

Secondary batteries are provided.

The copolymer of the present invention can improve the stability of the slurry by suppressing the generation of bubbles and gases during slurry production. In addition, the lifespan characteristics (capacity maintenance rate) of a lithium secondary battery can be improved by improving the ability to suppress electrode expansion.

Hereinafter, the operation and effects of the invention will be described in more detail through specific examples of the invention. However, these examples are merely presented as examples of the invention, and the scope of the invention is not determined by them.

Prior to this, the terms or words used in this specification and claims should not be construed as limited to their usual or dictionary meanings, and the inventor should appropriately define the concept of terms in order to explain his or her invention in the best way. It must be interpreted as meaning and concept consistent with the technical idea of the present invention based on the principle of definability.

Therefore, the configuration of the embodiments described in this specification is only one of the most preferred embodiments of the present invention and does not represent the entire technical idea of the present invention, so various equivalents and modifications that can replace them at the time of filing the present application It should be understood that examples may exist.

In this specification, singular expressions include plural expressions, unless the context clearly dictates otherwise. In this specification, terms such as “comprise,” “comprise,” or “have” are intended to designate the presence of implemented features, numbers, steps, components, or a combination thereof, and are intended to indicate the presence of one or more other features or It should be understood that this does not exclude in advance the possibility of the presence or addition of numbers, steps, components, or combinations thereof.

In this specification, “a to b” and “a to b” that indicate numerical ranges, “to” and “~” are defined as ≥ a and ≤ b.

The copolymer according to one aspect of the present application may be produced by copolymerizing and hydrolyzing an acrylate-based monomer and a vinyl acetate-based monomer.

The hydrolysis may be alkaline hydrolysis.

In one embodiment, it can be produced by copolymerizing and hydrolyzing 65 mol% or more and 99 mol% or less of the acrylate-based monomer and 1 mol% or more and 35 mol% or less of the vinyl acetate-based monomer.

In one embodiment, the copolymer contains 65 mol% or more and 99 mol% or less of acrylate-based monomer units and acrylic acid-based monomer units and 1 mole, based on 100 mol% of the total copolymer weight. It may contain more than % and less than 35 mol% of vinyl acetate-based monomer units and vinyl alcohol-based monomer units.

Meanwhile, the acrylic acid-based monomer unit and the vinyl alcohol-based monomer unit may exceed 0% by weight.

For example, the copolymer contains 0 mol% or more and 5 mol% or less of acrylate-based monomer units and 0 mol% or more and 5 mol% or less of vinyl acetate-based units, based on 100 mol% of the total copolymer weight. It may contain monomer units.

That is, the acrylate-based monomer and the vinyl acetate-based monomer may be copolymerized to form the acrylate-based monomer unit and the vinyl acetate-based monomer unit, respectively.

In one embodiment, the acrylate-based monomer unit is methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, and propyl acrylate. propyl acrylate, propyl methacrylate, isopropyl acrylate, isopropyl methacrylate, butyl acrylate, butyl methacrylate , sec-butyl acrylate, sec-butyl methacrylate, tert-butyl acrylate, tert-butyl methacrylate , ethyl hexyl acrylate, ethyl hexyl methacrylate, lauryl acrylate, lauryl methacrylate, stearyl acrylate, and It may be formed by polymerizing one or more types selected from the group consisting of steeryl methacrylate.

Additionally, the vinyl acetate series monomer unit may be formed by polymerizing vinyl acetate.

Meanwhile, some of the vinyl acetate-based monomer units may be changed into vinyl alcohol-based monomer units by the hydrolysis.

Additionally, some of the acrylate-based monomer units may be changed into acrylic acid-based monomer units by the hydrolysis.

The degree of hydrolysis can be adjusted to, for example, 70% or more, 75% or more, 80% or more, 85% or more, 90% or more, or 95% or more.

This means, for example, that more than 70%, more than 75%, more than 80%, more than 85%, more than 90%, more than 95% of the monomer units of the vinyl acetate series can be changed to monomer units of the vinyl alcohol series. am.

In addition, for example, it means that at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, at least 95% of the acrylate-based monomer units can be changed to the acrylic acid-based monomer units. am.

If the acrylate-based monomer unit exceeds or falls below the content range of the present application, binding strength may be reduced.

If the acrylic acid-based monomer unit exceeds or falls below the content range of the present application, it may cause polymer aggregation and precipitation or a decrease in adhesion.

If the vinyl acetate monomer unit exceeds or falls below the content range of the present application, it may cause stability problems such as storage stability.

If the vinyl alcohol-based monomer unit exceeds or falls below the content range of the present application, it may cause a decrease in adhesion, an increase in viscosity, and an increase in particle size.

In one embodiment, the acrylic acid-based monomer unit may be combined with an alkali metal.

That is, the carboxylate group of the acrylic acid-based monomer unit can be combined with an alkali metal.

Meanwhile, the weight ratio of the alkali metal and the copolymer (weight of the alkali metal: weight of the copolymer) may be 0.8 to 6.5:100.

If the weight ratio of the alkali metal and the copolymer exceeds or falls below the weight ratio of the present application, the binding characteristics of the binder may be reduced.

The binding force of the binder containing the alkali metal may be determined depending on the strength of cohesion and repulsion between elements, and the adhesion may change due to changes in the superiority or inferiority of cohesion, adhesion, and repulsion depending on the change in content.

The binding power of the binder can improve the lifespan characteristics of secondary batteries.

The copolymer of the present application improves the wettability of the copolymer by combining with an alkali metal and creating an alcohol functional group, and an anchor effect can be induced to maximize adhesion.

In one embodiment, the copolymer may include a monomer repeating unit represented by the following formula (1).

[Formula 1]

In Formula 1,

R ₁ and R ₃ are each independently hydrogen, a linear or branched hydrocarbon having 1 to 4 carbon atoms, or a combination thereof, R ₂ and R ₄ are each independently a linear or branched hydrocarbon having 1 to 3 carbon atoms, R ₅ is -OH, M is an alkali metal, and x+y+m+n=1.

In Formula 1, x, y, m, and n correspond to the mole fraction of each monomer unit, and the sum of the mole fractions of each monomer unit is 1.

In one embodiment, R ₁ and R ₃ of Formula 1 each independently include one or more selected from the group consisting of hydrogen, methyl, and ethyl, and R ₂ and R ₄ of Formula 1 each independently include methyl. and ethyl.

Meanwhile, M in Formula 1 may be Li, Na, or K, but is not limited thereto.

In one embodiment, the copolymer may be a random or block copolymer depending on the synthesis process.

In one embodiment, the number average molecular weight of the copolymer may be 250,000 or more and 350,000 or less.

If the number average molecular weight of the copolymer is above or below the range specified herein, the binding strength and binding strength gradient may be reduced, and thus the binding characteristics may be reduced when used as a binder. Additionally, when applied to a secondary battery, the capacity maintenance rate of the secondary battery may decrease and the electrode expansion rate may increase, which may deteriorate the performance of the secondary battery. In addition, when applied to slurry, the amount of gas generated may increase.

This is because if the number average molecular weight of the copolymer of the present application is outside the range, the coverage of the negative electrode active material (for example, silicon particles) is lowered below an appropriate level or increased beyond an appropriate level.

That is, only within the range of the number average molecular weight of the appropriate copolymer of the present application, the coverage of the negative electrode active material (e.g., silicon particles) is appropriate, and the binding force, binding force gradient, electrode expansion rate, capacity retention rate of the secondary battery, and slurry Appropriate levels can be maintained in all aspects of gas generation.

A negative electrode slurry according to another aspect of the present disclosure may include the above copolymer and a negative electrode active material.

That is, the copolymer can be used as a binder for a negative electrode, and in particular, it can be an aqueous binder.

The cathode slurry of the present invention may have a pressure change of 0.15 atm or less due to gas generation after being left for 72 hours.

The negative electrode active material may be a compound containing one or more types selected from the group consisting of carbon-based materials, silicon, alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, and rare earth elements, preferably silicon. Alternatively, it may be a compound containing silicon.

The carbon-based material includes, for example, artificial graphite, natural graphite, hard carbon, and soft carbon, but is not limited thereto. The type of the negative electrode active material containing silicon is not particularly limited as long as it is silicon or a compound containing silicon, but is preferably Si, SiO _x (0<x<2), Si-Y alloy (Y is an alkali metal , an alkaline earth metal, a Group 13 element, a Group 14 element, a transition metal, a rare earth element, or a combination thereof, but not Si.) and a Si-C composite.

In addition, when using a mixture of a negative electrode active material containing silicon and another negative electrode active material as the negative electrode active material, the negative electrode active material containing silicon may be included in more than 8% by weight of the total weight of the negative electrode active material.

The negative electrode active material may be included in an amount of 50 to 99% by weight, preferably 60 to 80% by weight, based on the total weight of the negative electrode active material layer.

If the negative active material is included in less than 50% by weight, the energy density decreases, making it impossible to manufacture a high energy density battery, and if it is included in more than 99% by weight, the content of the conductive material and binder decreases, resulting in a decrease in electrical conductivity. The adhesion between the electrode active material layer and the current collector may decrease.

Meanwhile, the copolymer of the present application may be included in an amount of 2% by weight or more and 5% by weight or less based on the solid content of the anode slurry. If the copolymer is less than 2% by weight, the physical properties of the negative electrode may deteriorate and the negative electrode active material and the conductive material may fall off, and if the copolymer exceeds 5% by weight, the ratio of the negative electrode active material and the conductive material may be relatively reduced, resulting in a decrease in battery capacity. , the electrical conductivity of the cathode may decrease.

In addition, the negative electrode slurry may include an additional polymer in addition to the copolymer composition of the present application. The polymer specifically includes, for example, polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), polyacrylic acid (PAA), polyacrylic acid metal salt (Metal-PAA), polymethacrylic acid (PMA), and polymethyl methacrylate. Crylate (PMMA), polyacrylamide (PAM), polymethacrylamide, polyacrylonitrile (PAN), polymethacrylonitrile, polyimide (PI), chitosan (Chitosan), starch, polyvinylpyrrolidone, Tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluoroelastomer, hydroxypropylcellulose, regenerated cellulose and various copolymers thereof, etc. Examples include, but are not limited to.

A negative electrode according to another aspect of the present application may include a current collector and a negative electrode active material layer including the copolymer of the present application formed on the current collector.

The binding force and binding force gradient of the cathode of the present invention may be 7.5 to 9.5 gf/cm and 75 to 79%, respectively.

The negative electrode active material layer may additionally include a conductive material. The conductive material is used to further improve the conductivity of the negative electrode active material. These conductive materials are not particularly limited as long as they have conductivity without causing chemical changes in the battery, and examples include 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; Conductive fibers such as carbon fiber and metal fiber; 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; Polyphenylene derivatives, etc. may be used.

The conductive material may be included in an amount of 0.5 to 30% by weight, preferably 15 to 25% by weight, based on the total weight of the negative electrode active material layer. If the conductive material is included in less than 0.5% by weight, the electrical conductivity of the cathode is lowered. If it is contained in excess of 30% by weight, the ratio of the silicon-based negative active material to the binder is relatively reduced, thereby reducing battery capacity. Since the content of the binder must be increased to maintain the negative electrode active material layer, the content of the negative electrode active material is reduced, resulting in high energy density. batteries cannot be manufactured.

In the negative electrode of the present application, the negative electrode active material layer includes the copolymer of the present application, which can suppress the volume expansion of the negative electrode active material that occurs during charging and discharging of the secondary battery, improve initial efficiency and capacity maintenance per cycle, and lower electrical resistance. You can.

The negative electrode includes the steps of (a) preparing a composition for forming a negative electrode active material layer containing a negative electrode active material and the copolymer composition of the present application, and (b) applying the composition for forming a negative electrode active material layer on a negative electrode current collector and then drying it. It can be manufactured through

The composition for forming the negative electrode active material layer is manufactured in a negative electrode slurry state, and the solvent for preparing the slurry state must be easy to dry, and can well dissolve the binder of the copolymer composition of the present application, but does not dissolve the negative electrode active material and is in a dispersed state. It is most desirable to be able to maintain it.

The solvent according to the present application can be water or an organic solvent, and the organic solvent is at least one selected from the group consisting of methylpyrrolidone, dimethylformamide, isopropyl alcohol, acetonitrile, methanol, ethanol, and tetrahydrofuran. Organic solvents containing are applicable.

The composition for forming the negative electrode active material layer can be mixed in a conventional manner using a conventional mixer, such as a rate mixer, a high-speed shear mixer, or a homomixer.

Step (b) is a step of manufacturing a negative electrode for a lithium secondary battery by applying the composition for forming a negative electrode active material layer prepared in step (a) on the negative electrode current collector and drying it.

The negative electrode current collector may be specifically selected from the group consisting of copper, stainless steel, titanium, silver, palladium, nickel, alloys thereof, and combinations thereof. The stainless steel may be surface treated with carbon, nickel, titanium, or silver, and an aluminum-cadmium alloy may be used as the alloy. In addition, calcined carbon, a non-conductive polymer surface-treated with a conductive material, or a conductive polymer may be used.

The composition for forming the negative electrode active material layer prepared in step (a) is applied on the negative electrode current collector, and can be coated on the current collector with an appropriate thickness depending on the thickness to be formed, preferably within the range of 10 to 300 μm. You can choose.

At this time, the method of applying the composition for forming the negative electrode active material layer in the slurry form is not limited, for example, doctor blade coating, dip coating, gravure coating, slit die coating ( Slit die coating, spin coating, comma coating, bar coating, reverse roll coating, screen coating, cap coating method, etc. It can be manufactured by performing.

After application and drying, a negative electrode for a secondary battery (particularly a lithium secondary battery) with a negative electrode active material layer finally formed can be manufactured.

A battery according to another aspect of the present disclosure may include a current collector and a negative electrode in which the negative electrode active material layer is formed on the current collector.

The battery may be a secondary battery (particularly, a lithium secondary battery) including a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte solution.

The initial efficiency of the secondary battery may be 80% or more, and the electrical resistance may be 0.02 Ω or less.

Additionally, when charging and discharging of the secondary battery is repeated for 300 cycles, the capacity retention rate may be 80% or more and the expansion rate of the negative electrode may be 33% or less.

The composition of the positive electrode, separator, and electrolyte of the lithium secondary battery is not particularly limited in the present invention and follows what is known in the field.

The positive electrode includes a positive electrode active material formed on the positive electrode current collector.

The positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or carbon or nickel on the surface of aluminum or stainless steel. , titanium, silver, etc. can be used. At this time, the positive electrode current collector can be used in various forms such as films, sheets, foils, nets, porous materials, foams, and non-woven fabrics with fine irregularities formed on the surface to increase adhesion with the positive electrode active material.

The cathode active material constituting the cathode active material layer can be any cathode active material available in the art. Specific examples of such positive electrode active materials include lithium metal; Lithium cobalt-based oxides such as LiCoO ₂ ; Lithium manganese-based oxides such as Li _1+x Mn _2-x O ₄ (where x is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ , and LiMnO ₂ ; Lithium copper oxide such as Li ₂ CuO ₂ ; Vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ , and Cu ₂ V ₂ O ₇ ; LiNi _1-x M _x O ₂ (where M=Co, Mn, Al, Cu, Fe, Mg, B or Ga, and x=0.01 to 0.3) lithium nickel-based oxide; _{LiMn 2 - x M ​} , Cu or Zn); lithium manganese composite oxide expressed as Lithium-nickel-manganese-cobalt expressed as Li(Ni _a Co _b Mn _c )O2 (where 0<a<1, 0<b<1, 0<c<1, a+b+c=1) based oxide; Sulfur or disulfide compounds; Phosphates such as LiFePO ₄ , LiMnPO ₄ , LiCoPO ₄ , and LiNiPO ₄ ; Fe ₂ (MoO ₄ ) ₃ etc. may be mentioned, but it is not limited to these alone.

At this time, the positive electrode active material layer may further include a binder, a conductive material, a filler, and other additives in addition to the positive electrode active material, and the conductive material is the same as that described above for the negative electrode for a lithium secondary battery.

In addition, the binder is polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), polyacrylic acid (PAA), polymethacrylic acid (PMA), polymethyl methacrylate (PMMA), polyacrylamide (PAM), Polymethacrylamide, polyacrylonitrile (PAN), polymethacrylonitrile, polyimide (PI), chitosan, starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene , polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluorine rubber, and various copolymers thereof, but are not limited thereto.

The separator may be made of a porous substrate. Any porous substrate commonly used in electrochemical devices can be used. For example, a polyolefin-based porous membrane or non-woven fabric may be used, but it is not specifically limited thereto. That is not the case.

The separator is made of polyethylene, polypropylene, polybutylene, polypentene, polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, It may be a porous substrate made of any one selected from the group consisting of polyphenylene oxide, polyphenylene sulfide, and polyethylene naphthalate, or a mixture of two or more of these.

The electrolyte solution of the lithium secondary battery is a non-aqueous electrolyte containing a lithium salt and is composed of a lithium salt and a solvent. The solvent used includes a non-aqueous organic solvent, an organic solid electrolyte, and an inorganic solid electrolyte.

The lithium salt is a material that is easily soluble in the non-aqueous electrolyte solution, for example, LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiAsF ₆ , LiSbF ₆ , LiAlCl ₄ , LiSCN, LiC ₄ BO ₈ , LiCF ₃ CO ₂ , LiCH ₃ SO ₃ , LiCF ₃ SO ₃ , LiN(SO ₂ CF ₃ ) ₂ , LiN(SO ₂ F) ₂ , LiN(SO ₂ C ₂ F ₅ ) ₂ , LiC ₄ F ₉ SO ₃ , LiC(CF ₃ SO ₂ ) ₃ , (CF ₃ SO ₂ )·2NLi, lithium chloroborane, lithium lower aliphatic carboxylate, lithium 4-phenyl borate imide, etc. may be used.

Non-aqueous organic solvents include, for example, N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, gamma-butyrolactone, 1,2 -Dimethoxy ethane, 1,2-diethoxy ethane, tetrahydroxy franc, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, 4-methyl-1,3-dioxene, Diethyl ether, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxy methane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3- Aprotic organic solvents such as dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ether, methyl propionate, and ethyl propionate may be used.

The organic solid electrolyte includes, for example, polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphoric acid ester polymers, poly agitation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, Polymers containing secondary dissociation groups, etc. may 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 , Nitride, halide, sulfate, etc. of Li such as Li ₄ SiO ₄ -LiI-LiOH, Li ₃ PO ₄ -Li ₂ S-SiS ₂ may be used.

Additionally, the non-aqueous electrolyte may further contain other additives for the purpose of improving charge/discharge characteristics, flame retardancy, etc. Examples of the additives include pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dye, N-substituted oxazolyl. Dinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, aluminum trichloride, fluoroethylene carbonate (FEC), propene sultone (PRS), vinylene carbonate ( VC), etc.

The lithium secondary battery according to the present invention is capable of lamination stacking and folding processes of separators and electrodes in addition to the general winding process. And the battery case may be cylindrical, prismatic, pouch-shaped, or coin-shaped.

Hereinafter, the present application will be described in more detail using examples, but the present application is not limited thereto.

[Preparation Example 1] Preparation of copolymer

After adding 1,050 g of distilled water and 10 g of alkyldiphenyloxide disulfonate to the reactor, nitrogen was added and stirring was performed for 1 hour.

Afterwards, potassium persulfate of which the content was adjusted was added to the reactor, the temperature was raised to 60°C, and 110 g of vinyl acetate and 330 g of ethyl acrylate were added in portions over 3 hours, and then heated for 2 hours. The temperature was maintained to obtain a vinyl acetate-ethyl acrylate copolymer with a solid content of 30% by weight.

100 g of the prepared vinyl acetate-ethyl acrylate copolymer with a solid content of 30% by weight, 150 g of ethanol, hydroxide, and organic salt were placed in a reactor and hydrolysis was performed while stirring at 60°C for 4 hours.

After completion of hydrolysis, the precipitated hydrolyzate was dissolved in distilled water, heated to 80°C, stirred and stripped for 8 hours to prepare a copolymer for a negative electrode binder.

[Manufacture Example 2] Manufacture of lithium secondary battery

An anode slurry was prepared by mixing 53.2 g of artificial graphite as an electrode active material, 13.3 g of a Si active material, and the anode binder prepared in Preparation Example 1 with distilled water.

The prepared negative electrode slurry was uniformly applied on a copper current collector, dried at 110°C, rolled, and vacuum dried in a vacuum oven at 110°C for more than 4 hours to prepare a negative electrode.

Afterwards, a non-aqueous electrolyte containing lithium salt was used as an electrolyte, a polyolefin separator was interposed between the positive electrode and the negative electrode, and a lithium secondary battery was manufactured without distinguishing the form into a pouch or coin cell type.

As the non-aqueous electrolyte, 5% by weight FEC and 1% by weight LiPO ₂ F ₂ were added to a solvent in which ethylene carbonate: ethylmethyl carbonate: diethyl carbonate was mixed at a volume ratio of 2:1:7, and LiPF ₆ electrolyte was added at 1.5 M. It was used dissolved at a concentration of .

[Example 1]

Using 2.0 g of potassium persulfate, a copolymer for a negative electrode binder with a number average molecular weight of 340,000 was prepared according to Preparation Example 1, and then a copolymer for a negative electrode binder was prepared according to Preparation Example 2, containing 3.5 g based on solid content. A negative electrode slurry, negative electrode, and lithium secondary battery were prepared.

[Example 2]

Using 2.3 g of potassium persulfate, a copolymer for a negative electrode binder having a number average molecular weight of 280,000 was prepared according to Preparation Example 1, and then, according to Preparation Example 2, a copolymer for a negative electrode binder was prepared in an amount of 3.5 g based on solid content. The included negative electrode slurry, negative electrode, and lithium secondary battery were manufactured.

[Comparative Example 1]

When preparing the negative electrode slurry according to Preparation Example 2, the negative electrode slurry, negative electrode, and lithium secondary battery were prepared in the same manner as Example 1, except that 1.4 g of a copolymer for a negative electrode binder (number average molecular weight: 340,000) was included based on solid content. .

[Comparative Example 2]

When preparing the negative electrode slurry according to Preparation Example 2, the negative electrode slurry, negative electrode, and lithium secondary battery were prepared in the same manner as Example 1, except that 2.45 g of a copolymer for a negative electrode binder (number average molecular weight: 340,000) was included based on solid content. .

[Comparative Example 3]

Using 2.5 g of potassium persulfate, a copolymer for a negative electrode binder with a number average molecular weight of 240,000 was prepared according to Preparation Example 1, and then a copolymer for a negative electrode binder was prepared according to Preparation Example 2, including 3.5 g based on solid content. A negative electrode slurry, negative electrode, and lithium secondary battery were prepared.

[Comparative Example 4]

Using 3.0 g of potassium persulfate, a copolymer for a negative electrode binder with a number average molecular weight of 140,000 was prepared according to Preparation Example 1, and then according to Preparation Example 2, the copolymer for a negative electrode binder was mixed with 3.5 g of solid content. A negative electrode slurry, negative electrode, and lithium secondary battery were prepared.

[Comparative Example 5]

Using 1.5 g of potassium persulfate, a copolymer for a negative electrode binder with a number average molecular weight of 410,000 was prepared according to Preparation Example 1, and then a copolymer for a negative electrode binder was prepared according to Preparation Example 2, containing 3.5 g of solid content. A negative electrode slurry, negative electrode, and lithium secondary battery were prepared.

The number average molecular weight of the copolymers for negative electrode binders of Examples 1 and 2 and Comparative Examples 1 to 5 was measured by gel filtration chromatography (GFC) using water as a solvent.

[Evaluation Example 1] Evaluation of cohesion

In order to measure the binding force of the negative electrodes prepared in Examples 1 and 2 and Comparative Examples 1 to 5, the combined side of the negative electrodes prepared in Examples 1 and 2 and Comparative Examples 1 to 5 were attached to an acrylic plate, and then UTM was used. A 180° peel test was performed to measure the binding force.

[Evaluation Example 2] Evaluation of cohesion gradient (cohesion by layer)

The adhesion gradient of the negative electrodes prepared in Examples 1 and 2 and Comparative Examples 1 to 5 was measured using a surface and interfacial cutting analysis system (SAICAS).

To measure the bond strength gradient, the bond strength was measured at 30% depth and 90% depth from the surface of the cathode (composite layer), and then the gap gap gradient was calculated according to Equation 1 below.

[Equation 1]

Cohesion gradient [%] = (Cohesion strength at 90% depth from the surface of the composite layer/Cohesion strength at 30% depth from the surface of the composite layer) Х100

[Evaluation Example 3] Evaluation of capacity retention rate and anode expansion rate of secondary battery

The lithium secondary batteries prepared in Examples 1 and 2 and Comparative Examples 1 to 5 were charged and discharged three times at 25°C with a charge/discharge current density of 0.1C, a charge end voltage of 4.8V, and a discharge end voltage of 2.7V. did.

Afterwards, charge and discharge were performed 300 times at a charge/discharge current density of 1C, a charge end voltage of 4.8V, and a discharge end voltage of 2.7V, and the capacity retention rate was measured.

All discharges were performed under constant current/constant voltage conditions, and the termination current of the constant voltage discharge was 0.005C.

The capacity retention rate and electrode expansion rate were calculated according to the following equations 2 and 3, respectively.

[Equation 2]

Capacity maintenance rate (%) = (Discharge capacity after 300 cycles / Discharge capacity after the initial 3 cycles) Х 100

[Equation 3]

Electrode expansion rate (%) = [(Cathode thickness after 300 cycles - Initial cathode thickness after vacuum drying) / Initial cathode thickness after vacuum drying] Х 100

[Evaluation Example 4] Gas generation evaluation

100 g of the slurry prepared in Examples 1 and 2 and Comparative Examples 1 to 5 was added to a 0.2L stainless steel container. Pressure sensing and monitoring equipment connected to a stainless steel container is used to measure the change in pressure after it is sealed and left for 72 hours.

In other words, it can be seen that the greater the change in pressure (the higher the pressure), the more gas was generated.

The measured values of binding force, binding force gradient, capacity retention rate, electrode expansion rate, and gas generation evaluated by Evaluation Example 1 and 4 are shown in Table 1 below.

	cohesion (gf/cm)	Cohesion gradient (%)	300 cycle Capacity maintenance rate (%)	300 cycle Electrode expansion rate (%)	Gas generation (△P) 72hr(atm)
Example 1	8.4	77	83	30	0.13
Example 2	8.0	75	81	33	0.12
Comparative Example 1	6.4	66	75	51	0.45
Comparative example 2	7.2	72	80	45	0.26
Comparative example 3	4.2	68	76	49	0.50
Comparative example 4	6.0	73	81	38	0.28
Comparative Example 5	9.8	80	79	35	0.18

As shown in Table 1, the bonding force of the negative electrodes prepared in Examples 1 and 2 was measured to be 8.0 to 8.4 gf/cm, and the bonding force gradient was measured to be 75 to 77%.

In addition, the capacity retention rate of the lithium secondary batteries manufactured in Examples 1 and 2 was measured to be 81 to 83%, and the electrode expansion rate was measured to be 30 to 33%.

Meanwhile, the change in pressure due to gas generation in the cathode slurry prepared in Examples 1 and 2 was measured to be 0.12 to 0.13 atm.

In comparison, the same copolymer for the negative electrode binder as in Example 1 is used, but when producing the negative electrode slurry, the content of the copolymer for the negative electrode binder is lowered compared to Example 1 so as to exceed or fall below the range of the content of the copolymer of the present application. In the case of Comparative Examples 1 and 2, the bonding force and bonding force gradient of the negative electrode were lowered compared to Example 1, resulting in a decrease in bonding characteristics, and the capacity retention rate of the secondary battery decreased and the electrode expansion rate increased, resulting in a decrease in the performance of the secondary battery cell. .

Additionally, as the amount of gas generated increased, the measured pressure value increased significantly.

In other words, it was confirmed that changes in the content of the copolymer for the negative electrode binder during the production of the negative electrode slurry affected the characteristics and performance of the negative electrode slurry, negative electrode, and secondary battery.

On the other hand, in the case of Comparative Examples 3 and 4 using a copolymer for a negative electrode binder with a number average molecular weight lower than that of Examples 1 and 2, which is below the number average molecular weight range of the copolymer of the present application, the The bonding force and the bonding force gradient decreased, resulting in a decrease in bonding characteristics, a decrease in the capacity retention rate of the secondary battery, and an increase in the electrode expansion rate, and a decrease in the performance of the secondary battery cell.

Additionally, as the amount of gas generated increased, the measured pressure value increased significantly.

In the case of Comparative Example 5 using a copolymer for a negative electrode binder with a higher number average molecular weight than Examples 1 and 2, which exceeds the range of the number average molecular weight of the copolymer of the present application, the binding force and binding force gradient of the negative electrode compared to Examples 1 and 2 Although the binding characteristics shown were improved, the capacity retention rate of the secondary battery decreased and the electrode expansion rate increased, and the performance of the secondary battery also deteriorated.

Additionally, as the amount of gas generated increased, the measured pressure value increased.

In other words, it was confirmed that changes in the number average molecular weight of the copolymer for the negative electrode binder affect the characteristics and performance of the negative electrode slurry, negative electrode, and secondary battery.

The scope of the present invention is indicated by the claims described below rather than the detailed description above, and all changes or modified forms derived from the meaning and scope of the claims and their equivalent concepts are interpreted to be included in the scope of the present invention. It has to be.

The copolymer of the present invention can improve the stability of the slurry by suppressing the generation of bubbles and gases during slurry production. Additionally, the lifespan characteristics (capacity maintenance rate) of a lithium secondary battery can be improved by improving the ability to suppress electrode expansion.

Claims (13)

1. Manufactured by copolymerizing and hydrolyzing acrylate-based monomers and vinyl acetate-based monomers.

   copolymer.
2. According to paragraph 1,

   Prepared by copolymerizing and hydrolyzing 65 mol% or more and 99 mol% or less of the acrylate series monomer and 1 mol% or more and 35 mol% or less of the vinyl acetate series monomer,

   copolymer.
3. According to paragraph 1,

   Based on 100 mol% of the total copolymer weight, 65 mol% or more and 99 mol% or less of acrylate-based monomer units and acrylic acid-based monomer units; and

   Containing 1 mol% or more and 35 mol% or less of vinyl acetate-based monomer units and vinyl alcohol-based monomer units,

   copolymer.

   (However, the acrylic acid-based monomer unit and vinyl alcohol-based monomer unit exceed 0% by weight)
4. According to paragraph 3,

   The acrylic acid-based monomer unit is combined with an alkali metal,

   copolymer.
5. According to clause 4,

   The weight ratio of the alkali metal and the copolymer (weight of the alkali metal: weight of the copolymer) is 0.8 to 6.5:100,

   copolymer.
6. According to paragraph 1,

   Containing a monomer repeating unit represented by Formula 1 below,

   copolymer.

   [Formula 1]

   

   In Formula 1,

   R ₁ and R ₃ are each independently hydrogen, a linear or branched hydrocarbon having 1 to 4 carbon atoms, or a combination thereof,

   R ₂ and R ₄ are each independently a linear or branched hydrocarbon having 1 to 3 carbon atoms,

   R ₅ is -OH,

   M is an alkali metal,

   x+y+m+n=1.
7. According to clause 6,

   R ₁ and R ₃ of Formula 1 each independently include one or more selected from the group consisting of hydrogen, methyl, and ethyl,

   R ₂ and R ₄ of Formula 1 each independently include one or more selected from the group consisting of methyl and ethyl,

   copolymer.
8. According to paragraph 1,

   The copolymer is a random or block copolymer,

   copolymer.
9. According to paragraph 1,

   The number average molecular weight of the copolymer is

   A number average molecular weight of 250,000 or more and 350,000 or less,

   copolymer.
10. The copolymer of any one of claims 1 to 9; and

    Negative active material; containing,

    cathode slurry.
11. According to clause 10,

    The copolymer is contained in an amount of 2% by weight or more and 5% by weight or less compared to the solid content of the negative electrode slurry,

    cathode slurry.
12. house collector; and

    A negative electrode active material layer comprising the copolymer of any one of claims 1 to 9 formed on the current collector.

    cathode.
13. Comprising the cathode of claim 12,

    Secondary battery.