KR20230055731A - Binder composition for secondary battery separator, separator for secondary battery and secondary battery having the same - Google Patents

Abstract

The present invention relates to a binder composition for a separator of a secondary battery, a separator for a secondary battery including the same, and a secondary battery, wherein the binder composition for a separator of a secondary battery includes a binder resin including: 5 to 20 wt% of a first structural unit derived from vinyl ester represented by a specific chemical formula; 7.5 to 31.5 wt% of a second structural unit derived from a (meth)acrylic acid ester monomer; 56.5 to 80.5 wt% of a third structural unit derived from an aromatic vinyl monomer; and 0.1 to 5 wt% of a fourth structural unit derived from an unsaturated carboxylic acid monomer.

Description

Binder composition for separators of secondary batteries, separators for secondary batteries including the same, and secondary batteries

The present invention relates to a binder composition for a separator of a secondary battery, a separator for a secondary battery including the same, and a secondary battery, which can improve coating properties of inorganic particles, as well as electrode adhesiveness, air permeability, and low resistance characteristics. It relates to a binder composition for a separator of a secondary battery that can be improved, a separator for a secondary battery including the binder composition, and a secondary battery.

A secondary battery has a positive electrode, a negative electrode, a separator, and an electrolyte as its basic composition, and is an energy storage device with high energy density that can be charged and discharged by using reversible mutual conversion of chemical energy and electrical energy. Widely used.

Recently, as interest in environmental issues has increased, research on electric vehicles and hybrid electric vehicles that can replace vehicles using fossil fuels such as gasoline vehicles and diesel vehicles, which are one of the main causes of air pollution, is being conducted. , Secondary batteries are used as power sources for electric vehicles and hybrid electric vehicles.

In manufacturing and using such a secondary battery, securing the stability of the battery is the most important matter to be considered. In particular, separators commonly used in secondary batteries exhibit extreme heat shrinkage behavior at high temperatures, resulting in stability problems such as internal short circuits.

Therefore, in order to secure the stability of the secondary battery, a separator coated with a mixture of inorganic particles and a binder resin on a porous substrate, a so-called safety reinforced separator (SRS), is disposed between the positive electrode and the negative electrode. However, when the electrode assembly is formed by stacking the separator and the electrode, the interlayer binding force between the separator and the electrode is low, resulting in an electrode short circuit.

Accordingly, Korean Patent Laid-Open Publication No. 10-2006-0116043 attempted to improve the adhesion between the stability enhancing separator and the electrode by using a porous adhesive layer. The porous adhesive layer had low resistance during battery operation, but was swollen after injection during battery manufacturing, resulting in poor bonding strength with the separator, and interlayer mixing closed the pores in the porous adhesive layer, lowering the air permeability of the separator. A problem occurred.

Therefore, it is necessary to develop a new separator having excellent electrode adhesion and air permeability while having low resistance characteristics.

An object of the present invention is to provide a binder composition for preparing a separator having excellent electrode adhesion, air permeability and low resistance characteristics.

Another object of the present invention is to provide a secondary battery separator having low resistance, excellent air permeability and adhesion to an electrode, and a secondary battery including the same, by applying the above-described binder composition.

In order to achieve the above object, the present invention is a first structural unit derived from a vinyl ester represented by the following formula (1) 5 to 20% by weight; 7.5 to 31.5% by weight of a second constituent unit derived from a (meth)acrylic acid ester monomer; 56.5 to 80.5% by weight of a third structural unit derived from an aromatic vinyl monomer; And 0.1 to 5% by weight of a fourth constituent unit derived from an unsaturated carboxylic acid monomer; It provides a binder composition for a separator of a secondary battery, comprising:

[Formula 1]

(In Formula 1 above,

R ₁ is a C ₅ ~ C ₂₀ branched alkyl group;

R ₂ and R ₃ are the same as or different from each other, and each independently represents hydrogen, heavy hydrogen, and a C ₁ to C ₁₂ alkyl group).

According to an example of the present invention, in Formula 1, R ₁ is a C ₅ ~ C ₁₂ branched alkyl group, and both R ₂ and R ₃ may be hydrogen or a methyl group.

According to an example of the present invention, the vinyl ester represented by Chemical Formula 1 may be 2-ethylhexanoic acid vinyl ester.

According to an example of the present invention, the binder resin may have a glass transition temperature (Tg) of 20 to 60 ℃.

In addition, the present invention is a porous substrate; a porous coating layer disposed on at least one surface of the porous substrate and including inorganic particles and a binder resin; and an adhesive layer disposed on a surface of the porous coating layer and a surface of a porous substrate on which the porous coating layer is not disposed, and formed of the above-described binder composition.

According to an example of the present invention, the binder resin may be the same as the copolymer in the binder composition.

According to an example of the present invention, the separator for a secondary battery may have adhesion to an electrode of 70 gf/25 mm or more, air permeability of 140 sec/100 cc or less, and resistance of 1 Ω or less.

In addition, the present invention provides a secondary battery including the above-described secondary battery separator.

The binder composition according to the present invention includes a copolymer containing a structural unit derived from a vinyl ester having a specific structure, thereby improving the adhesion of the separator to the electrode and at the same time increasing the air permeability of the separator and lowering the resistance. there is.

Hereinafter, the present invention will be described in detail.

All terms (including technical and scientific terms) used in this specification, unless otherwise defined, may be used in a meaning commonly understood by those of ordinary skill in the art to which the present invention belongs. In addition, terms defined in commonly used dictionaries are not interpreted ideally or excessively unless explicitly specifically defined.

Throughout this specification, when a certain component is said to "include", it is an open term that implies the possibility of further including other components, not excluding other components, unless otherwise stated ( open-ended terms).

In addition, throughout the specification, "above" or "on" means not only the case of being located above or below the target part, but also the case of another part in the middle thereof, and must be in the direction of gravity. It does not mean that it is located above the reference point.

Also, terms such as "first" and "second" in the present specification do not indicate any order or importance, but are used to distinguish components from each other.

<Binder composition for separator>

A binder composition for a separator of a secondary battery according to the present invention is a polymer solution in which a copolymer is dispersed in a solvent, and the copolymer includes a first structural unit derived from a vinyl ester represented by Formula 1 below; a second structural unit derived from a (meth)acrylic acid ester-based monomer; a third constituent unit derived from an aromatic vinyl monomer; and a copolymer containing a fourth structural unit derived from an unsaturated carboxylic acid-based monomer, wherein the copolymer comprises about 5 to 20% by weight of the first structural unit and about 7.5 to 31.5% by weight of the first structural unit, based on the total amount. The second structural unit, about 56.5 to 80.5% by weight of the third structural unit, and about 0.1 to 5% by weight of the fourth structural unit. This copolymer is a water-based binder resin, which not only improves electrode adhesion, but also improves air permeability and low resistance characteristics by uniformly and thinly coating inorganic particles on a porous substrate in an environmentally friendly manner. Therefore, the binder composition of the present invention can produce a separator having excellent electrode adhesion, air permeability and low resistance characteristics.

The copolymer according to the present invention includes a first constituent unit derived from a vinyl ester monomer represented by Formula 1 below. The copolymer including the first constituent unit can adjust the hydrophilicity of the binder resin itself to increase the electrode adhesion of the separator, and at the same time, facilitate the transfer of lithium ions in the electrolyte solution to lower the battery resistance.

In Formula 1,

R ₁ is a C ₅ ~ C ₂₀ branched alkyl group, and may specifically be a C ₅ ~ C ₁₂ branched alkyl group;

R ₂ and R ₃ are the same as or different from each other, and each independently represent hydrogen, heavy hydrogen, and a C ₁ to C ₁₂ alkyl group, and specifically may be hydrogen or a methyl group.

According to one example, the vinyl ester represented by Chemical Formula 1 may be 2-ethylhexanoic acid vinyl ester.

The content of the above-mentioned first structural unit is in the range of about 5 to 20% by weight based on the total amount of the copolymer. If the content of the first structural unit is less than about 5% by weight, the effect of improving electrode adhesiveness, air permeability and low resistance characteristics may be insufficient, while if the content of the first structural unit exceeds about 20% by weight , the hydrophilicity of the separator may be excessively increased, resulting in deterioration in electrode adhesion.

The copolymer according to the present invention includes a second constituent unit derived from a (meth)acrylic acid ester monomer. The second structural unit is a material that can be copolymerized together with the third structural unit, and the cohesive strength and fluidity (wetability) of the binder can be improved by adjusting the glass transition temperature (Tg) of the final copolymer.

For example, the (meth)acrylic acid ester-based monomer may be a (meth)acrylic acid ester-based monomer containing a C ₁ ~ C ₂₀ alkyl group.

Specifically, non-limiting examples of the (meth)acrylic acid ester monomer include methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, n-amyl acrylate , isoamyl acrylate, n-ethylhexyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, n-Butyl methacrylate, isobutyl methacrylate, n-amyl methacrylate, isoamyl methacrylate, n-hexyl methacrylate, n-ethylhexyl methacrylate, 2-ethylhexyl methacrylate, hydroxy There are oxyethyl methacrylate, hydroxypropyl methacrylate, and the like, and these may be used alone or in combination of two or more.

The content of these second structural units may be in the range of about 7.5 to 31.5% by weight based on the total weight of the copolymer. If the content of the second constituent unit is less than 7.5% by weight, the glass transition temperature of the copolymer is too high, and as a result, the fluidity (wettability) of the binder is low, and electrode adhesiveness may be deteriorated. On the other hand, when the content of the second structural unit exceeds about 31.5% by weight, the glass transition temperature of the copolymer is too low, and as a result, the cohesive force of the binder is low, so the effect of improving electrode adhesion is insufficient, and air permeability and low resistance properties are poor. may be lowered According to one example, the content of the second structural unit may be about 9 to 31% by weight based on the total amount of the copolymer.

The copolymer according to the present invention includes a third constituent unit derived from an aromatic vinyl monomer. The third structural unit is a material that can be copolymerized together with the second structural unit, and can improve the cohesive force and fluidity (wetability) of the binder by adjusting the glass transition temperature (Tg) of the final copolymer.

The aromatic vinyl monomer is an aromatic compound containing a vinyl group, for example, styrene, α-methylstyrene, β-methylstyrene, p-methylstyrene, p-t-butylstyrene, vinyltoluene, and the like, but is not limited thereto.

The content of these third structural units ranges from about 56.5 to 80.5% by weight based on the total amount of the copolymer. If the content of the third structural unit is less than about 56.5% by weight, the glass transition temperature of the copolymer is too low, and as a result, the cohesive force of the binder is low, so electrode adhesion, air permeability, and low resistance characteristics may be deteriorated. there is. On the other hand, when the content of the third structural unit exceeds about 80.5% by weight, the glass transition temperature of the copolymer is too high, and as a result, the fluidity (wettability) of the binder is low, and electrode adhesion may be deteriorated. According to one example, the copolymer includes about 58 to 79% by weight of the third constituent unit based on the total amount.

The copolymer according to the present invention includes a fourth constituent unit derived from an unsaturated carboxylic acid-based monomer. Because of the fourth structural unit, the copolymer of the present invention can maintain a stably dispersed state during polymerization and storage.

Non-limiting examples of the unsaturated carboxylic acid-based monomer include acrylic acid, methacrylic acid, crotonic acid, isocrotonic acid, maleic anhydride, fumaric acid, and itaconic acid, which may be used alone or in combination of two or more. there is.

The content of this fourth structural unit is in the range of about 0.1 to 5% by weight based on the total amount of the copolymer. If the content of the fourth structural unit is less than about 0.1% by weight, emulsion polymerization stability or mechanical stability may be lowered and the heat resistance of the separator may be lowered, while when the content of the fourth structural unit exceeds about 5% by weight , the electrode adhesiveness of the separator may be deteriorated. According to one example, the copolymer includes about 1 to 2.5% by weight of the fourth constituent unit based on the total amount.

As described above, the copolymer according to the present invention may have a glass transition temperature (Tg) of about 20 to 60 °C by containing the first to fourth structural units, but adjusting the content thereof within a specific range. If the copolymer has a glass transition temperature of less than about 20° C., the cohesive force of the binder is low, and electrode adhesion, air permeability, and low resistance characteristics may be deteriorated. On the other hand, when the glass transition temperature of the copolymer exceeds about 60 °C, the fluidity (wettability) of the binder is low, and electrode adhesion may be deteriorated.

In addition, the copolymer according to the present invention may have a weight average molecular weight in the range of about 100,000 to 1000,000 g / mol.

The content of the copolymer according to the present invention is not particularly limited, and may include, for example, about 20 to 50% by weight based on 100% by weight of the binder composition.

The copolymer according to the present invention may be prepared through a conventional polymerization method known in the art (eg, emulsion polymerization method, etc.). For example, additives such as vinyl ester monomer, (meth)acrylic acid ester monomer, aromatic vinyl monomer and unsaturated carboxylic acid monomer of Formula 1, dispersant, pH adjuster, etc. are added to the water containing the emulsifier, if necessary. After stirring, a polymerization initiator was added thereto and polymerization was performed at a temperature of about 30 to 100 °C, specifically about 70 to 80 °C for about 3 to 7 hours to prepare the copolymer of the present invention.

The emulsifier is not particularly limited, and may be, for example, an anionic surfactant or a nonionic surfactant. Examples of specific emulsifiers include alkylbenzene sulfonates, alkyl sulfate ester salts, polyoxyethylene alkyl ether sulfate ester salts, fatty acid salts, polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene polycyclic phenyl ethers, polyoxyethylene Alkylene alkyl ethers, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, and the like, are not limited thereto. These may be used alone or in combination of two or more. The content of this emulsifier is not particularly limited, and may be about 0.01 to 10 parts by weight, specifically about 0.05 to 5 parts by weight, based on 100 parts by weight of the total monomers.

The polymerization initiator is not particularly limited as long as it is a conventional emulsion polymerization initiator known in the art, and examples thereof include ammonium persulfate, potassium persulfate, hydrogen peroxide, and t-butyl hydroperoxide. Such a polymerization initiator may be about 0.01 to 5 parts by weight, specifically about 0.05 to 3 parts by weight based on 100 parts by weight of the total amount of all monomers.

The binder composition for a separator of a secondary battery according to the present invention is an aqueous binder composition, and the solvent may be water or an aqueous solvent compatible with water (eg, ethanol). The content of these solvents is not particularly limited. The remaining amount may be adjusted so that the total amount of the binder composition is 100% by weight.

<Separator for secondary battery>

Meanwhile, the present invention provides a separator for a secondary battery including the above-described binder composition.

The separator for a secondary battery of the present invention is interposed between a negative electrode and a positive electrode to separate them, is impregnated with an electrolyte, and provides a passage for lithium ions to move.

According to one example, the separator for a secondary battery of the present invention includes a porous substrate; a porous coating layer disposed on at least one surface of the porous substrate and including inorganic particles and a binder resin; and an adhesive layer formed of the binder composition disposed on a surface of the porous coating layer and a surface of the porous substrate on which the porous coating layer is not disposed.

The porous substrate is not particularly limited as long as it is a substrate including pores, and may be, for example, a heat-resistant porous substrate having a melting temperature of 200 °C or higher. In this case, the thermal safety of the separation membrane is improved, so that a risk caused by external and/or internal thermal stimulation can be prevented.

Examples of materials for the porous substrate include polyolefins (eg, high-density polyethylene, low-density polyethylene, linear low-density polyethylene, ultra-high molecular weight polyethylene, polypropylene, etc.), polyesters (eg, polyethylene terephthalate, polybutylene terephthalate, etc.), polyacetal, polyamide, polycarbonate, polyimide, polyether ether ketone, polyether sulfone, polyphenylene oxide, polyphenylene sulfide, polyethylene naphthalene, etc., which may be used alone or in combination of two or more. . In addition, other heat-resistant engineering plastics may also be used without limitation.

The thickness of the porous substrate is not particularly limited, and may be, for example, about 1 to 100 μm, specifically about 5 to 50 μm, and more specifically about 10 to 20 μm.

The pore size and porosity of the porous substrate are not particularly limited and may be adjusted within a range common in the art. For example, the separator may have a pore size (diameter) of about 0.01 to 50 μm, specifically about 0.1 to 20 μm, and a porosity of about 5 to 99%, specifically about 9 to 99%.

The porous substrate may be in the form of a fiber or a membrane, and in the case of a fiber, it is a nonwoven fabric forming a porous web, and may be in the form of a spunbond or melt blown composed of long fibers. there is.

In the separator for a secondary battery of the present invention, the porous coating layer includes a plurality of inorganic particles and a binder resin, and the surface of the porous substrate is coated with the inorganic particles to improve heat resistance and mechanical properties of the separator.

In the porous coating layer, inorganic particles not only create an interstitial volume to impart a microporous structure to the porous coating layer, but also serve as a kind of spacer capable of maintaining a physical shape. In addition, since inorganic particles generally have properties that do not change even at a high temperature of about 200 ° C. or higher, the porous coating layer can impart excellent heat resistance to the separator.

These inorganic particles are not particularly limited as long as they are electrochemically stable. In particular, when the inorganic particles have ion transport capability, the performance of the secondary battery can be improved by increasing the ion conductivity. In addition, when the inorganic particles have a high permittivity, the dissociation degree of electrolyte salts (eg, lithium salts) in the liquid electrolyte may be increased, thereby improving ionic conductivity of the electrolyte solution.

Non-limiting examples of the inorganic particles include SiO ₂ , TiO ₂ , Al ₂ O ₃ , ZrO ₂ , SnO ₂ , CeO ₂ , MgO, CaO, ZnO, Y ₂ O ₃ , Pb(Zr,Ti)O ₃ (PZT) ), Pb _1-x La _x Zr _1-y Ti _y O ₃ (PLZT), PB(Mg ₃ Nb _2/3 )O ₃ -PbTiO ₃ (PMN-PT), BaTiO ₃ , hafnia (HfO ₂ ), SrTiO There are ₃ , and these may be used alone or in combination of two or more. Since these inorganic particles (except for SiO ₂ ) exhibit a high permittivity of 5 or more, lithium ions moving in the battery can be easily transferred and battery performance can be improved.

The size (average particle diameter) of the inorganic particles is not particularly limited, but is about 0.001 to 10 μm, specifically about 0.05 to 5 μm, more specifically about 0.01 to 3 μm, in order to form a porous coating layer with a uniform thickness and an appropriate porosity. can be

The binder resin forms a porous coating layer together with inorganic particles, and may be the same as or different from the copolymer of the binder composition described above.

The binder resin usable in the present invention is not particularly limited as long as it is a polymer capable of stably fixing by connecting inorganic particles, and for example, polyvinylidene fluoride-co-hexafluoropropylene , polyvinylidene fluoride-co-trichloroethylene, polymethylmethacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate ( polyvinylacetate, ethylene-co-vinyl acetate, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate ), cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, carboxylmethylcellulose cellulose), acrylonitrile-styrene-butadiene copolymer, polyimide, and styrene butadiene rubber (SBR), which may be used alone or in combination of two or more. .

According to one example, the binder resin of the porous coating layer may be a copolymer in the binder composition.

According to another example, the binder resin of the porous coating layer is a copolymer in the binder composition; and the aforementioned polymers (eg, water-based polymers). In this case, the use ratio (mixing ratio) of the copolymer and the above-mentioned polymer is not particularly limited, for example, 10:90 to 90:10 weight ratio, specifically 20:80 to 60:40 weight ratio, more specifically 30:70 to It may be a 50:50 weight ratio.

In the porous coating layer of the present invention, the use ratio of the inorganic particles and the binder resin is not particularly limited. However, when the content of the binder resin is less than the content of the inorganic particles, the effect of binding the inorganic particles is weak, and a desired shutdown function may not be implemented. On the other hand, when the content of the binder resin is too large compared to the content of the inorganic particles, thermal shrinkage may occur, and the size or porosity of pores formed between the inorganic particles may decrease, resulting in deterioration in thermal stability and performance of the battery itself. Therefore, the ratio between the inorganic particles and the binder resin is preferably adjusted to a volume ratio of 50:50 to 99:1, specifically 70:30 to 95:1.

The thickness of the porous coating layer is not particularly limited, and may be, for example, about 0.01 to 20 μm.

In addition, the pore size and porosity of the porous coating layer are also not particularly limited, and for example, the pore size may be in the range of about 0.001 to 10 μm and the porosity may be in the range of about 10 to 99%. The pore structure of this porous coating layer is filled with an electrolyte solution to be injected later, and the filled electrolyte solution plays a role in ion transfer.

In the separator for a secondary battery of the present invention, the adhesive layer is disposed on the surface of both porous coating layers, or is disposed on the surface of the porous coating layer and the surface of the porous substrate on which the porous coating layer is not disposed, so that the separator and the electrode It is a part that improves the adhesion between the parts, and is formed by applying the above-described binder composition. Since the binder composition has been described above, it is omitted.

The adhesive layer may be formed by applying the binder composition to at least a portion of the surface of the porous substrate and/or the porous coating layer.

In one example, the adhesive layer may cover about 50 to 90% of the entire area of the surface to which the binder composition is applied (eg, the surface of the porous substrate or the surface of the porous coating layer). In this case, the separation membrane of the present invention can secure binding force with the electrode without deterioration in air permeability and ionic conductivity.

In another example, the adhesive layer may be patterned to have a predetermined pattern on the surface of the porous substrate and/or the porous coating layer. Specifically, the adhesive layer may be formed in a pattern of stripes and dots spaced at predetermined intervals on a porous substrate. At this time, the separation distance or width of each pattern may be appropriately determined in consideration of the ionic conductivity of the separator, electrode adhesion, and the like.

Since the above-described separator for secondary batteries of the present invention has high adhesion to electrodes, high air permeability, and low resistance, it is possible to minimize the occurrence of electrode short circuit when applied to secondary batteries, and to improve cycle characteristics and life characteristics of batteries. can improve For example, the separator for a secondary battery of the present invention may have adhesive strength to an electrode of about 70 gf/25 mm or more, air permeability of about 140 sec/100 cc or less, and resistance of about 1 Ω or less.

The separator for a secondary battery of the present invention may be manufactured by various methods.

As an example, the separator for a secondary battery of the present invention includes the steps of (S10) coating an inorganic slurry on at least one surface of a porous substrate and drying it to form a porous coating layer; and (S20) forming an adhesive layer by coating the above-described binder composition on the surface of the porous coating layer and the surface of the porous substrate on which the porous coating layer is not formed.

(a) forming a porous coating layer

An inorganic slurry is coated on one or both sides of the porous substrate and dried to form a porous coating layer (hereinafter, '(S10) step').

The porous substrate is omitted because it is the same as described in the separation membrane section.

The inorganic slurry is an inorganic dispersion, and may include inorganic particles and a binder resin, and may optionally further include a solvent. Here, since the inorganic particles and the binder resin have already been described in the porous coating layer of the separator, they are omitted.

The solvent is not particularly limited as long as it can dissolve the binder resin while uniformly mixing the inorganic particles and the binder resin, and can be easily removed later. For example, acetone, tetrahydrofuran, methylene chloride, chloroform, dimethylformamide, N-methyl-2-pyrrolidone (N-methyl -2-pyrrolidone, NMP), cyclohexane, water, and the like, which may be used alone or in combination of two or more.

The coating method of the inorganic slurry is not particularly limited as long as it is a method commonly known in the art, and for example, dip coating, die coating, roll coating, comma coating, spray ( spray) coating, inkjet printing, laser printing, screen printing, or a combination thereof.

Meanwhile, the binder resin of the porous coating layer may be the same as the copolymer of the aforementioned binder composition. That is, the inorganic slurry may include inorganic particles and the aforementioned binder composition. In this case, when the coated inorganic slurry is dried, phase separation of the inorganic slurry may occur. Due to this phase separation, the copolymer in the binder composition migrates to the surface of the porous coating layer, and an adhesive layer made of the copolymer may be formed on the surface of the porous coating layer. In this case, the process of forming a separate adhesive layer on the surface of the porous coating layer using the binder composition of the present invention [below '(S20) step'] can be omitted, and as described later, optionally the binder composition An adhesive layer may be formed by applying and drying the surface of the porous substrate on which the porous coating layer is not formed. However, when the adhesive strength of both sides of the separator is different, it is preferable to perform an additional adhesive layer forming process.

(b) forming an adhesive layer

The binder composition is coated on the surface of the porous coating layer formed in step (S10) and the surface of the porous substrate on which the porous coating layer is not formed, and dried to form an adhesive layer (hereinafter, '(S20) step').

As described above, the porous coating layer may be formed on only one side of the porous substrate, or may be formed on both sides of the porous substrate. If the porous coating layer is formed on only one surface of the porous substrate, the adhesive layer may be formed by coating the binder composition on the surface of the porous coating layer and the other surface of the porous substrate and drying. Meanwhile, when the porous coating layer is formed on both sides of the porous substrate, an adhesive layer may be formed by coating the binder composition on the surface of both porous coating layers and drying the porous coating layer.

Since the binder composition and the coating method have been described above, they will be omitted. On the other hand, if necessary, the adhesive layer may be formed using a coating composition for forming an adhesive layer further comprising a solvent (eg, water) and/or a dispersant (eg, polyacrylic acid) as well as the binder composition. In this case, the content of the binder composition is not particularly limited, for example, about 10 to 40% by weight, specifically about 15 to 30% by weight, more specifically about 15 to 25% by weight based on the total amount of the coating composition for forming the adhesive layer. can

Solvents and dispersants that can be used in the present invention are not particularly limited as long as they are commonly used in the art when forming an adhesive layer.

The content of the solvent is not particularly limited, and may be the remaining amount adjusted so that the total amount of the coating composition for forming an adhesive layer is 100% by weight.

In addition, the content of the dispersant is not particularly limited, and may be, for example, about 0.01 to 3% by weight, specifically about 0.1 to 1% by weight, based on the total amount of the coating composition for forming an adhesive layer.

<Secondary Battery>

Meanwhile, the present invention provides a secondary battery including the aforementioned separator.

A secondary battery according to the present invention includes a cathode; cathode; The separator interposed between the anode and the cathode; and electrolytes. Such a secondary battery is an electrochemical device that undergoes continuous electrochemical reactions through charging and discharging, and may be, for example, a secondary battery capable of charging and discharging by occluding and releasing lithium, specifically, a lithium metal secondary battery, a lithium ion secondary battery, It may be a lithium polymer secondary battery or a lithium ion polymer secondary battery.

The lithium secondary battery can be manufactured by a conventional method known in the art, for example, (a) preparing an electrode assembly by interposing the above-described separator between a cathode, a cathode, and the cathode and the anode. Then, putting it into the battery case; and (b) injecting an electrolyte into the case.

The electrode to be applied together with the above-described separator is not particularly limited, but the cathode active material is formed of lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, or a combination thereof. A cathode is composed of a lithium intercalation material, such as a composite oxide, as a main component, and is bound to a foil made of a cathode current collector, for example, aluminum, nickel, or a combination thereof.

Anode active materials are mainly composed of lithium metal or lithium alloys and lithium adsorption materials such as carbon, petroleum coke, activated carbon, graphite, or other carbons, which are used for anode current The negative electrode is configured in a form bound to a current collector, for example, a foil made of copper, gold, nickel, or a copper alloy or a combination thereof.

The electrolyte solution includes a non-aqueous electrolyte solution in which an electrolyte salt (eg, lithium salt) is dissolved in an organic solvent.

The electrolyte salt is a salt having the same structure as A ⁺ B ^- , wherein A ⁺ includes an alkali metal cation such as Li ⁺ , Na ⁺ , or K ⁺ or an ion composed of a combination thereof, and B ^- is PF ₆ ^- , BF ₄ ^- , Cl ^- , Br ^- , I ^- , ClO ₄ ^- , AsF ₆ ^- , CH ₃ CO ₂ ^- , CF ₃ SO ₃ ^- , N(CF ₃ SO ₂ ) ₂ ^- , C(CF ₂ SO ₂ ) ₂ ^- It is a salt containing an ion composed of an anion such as or a combination thereof. These can be used individually or in mixture of 2 or more types. According to one example, the electrolyte salt may be a lithium salt.

Specifically, the lithium salt is LiCl, LiBr, LiI, LiBF ₄ , LiClO ₄ , LiAlO 4 , LiAlCl ₄ , LiPF ₆ , LiSbF _{6 , LiAsF 6 ,} LiB ₁₀ Cl ₁₀ , LiBOB (LiB(C ₂ O ₄ ) ₂ ) , LiCF ₃ SO ₃ , LiTFSI (LiN(SO ₂ CF ₃ ) ₂ ), LiFSI (LiN(SO ₂ F) ₂ ), LiCH ₃ SO ₃ , LiCF ₃ CO ₂ , LiCH ₃ CO ₂ , LiBETI (LiN(SO ₂ CF ₂ CF ₃ ) ₂ and the like, and these may be used alone or in combination of two or more.

Examples of the organic solvent include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BE), fluoroethylene carbonate (FEC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate ( DPC), carbonates such as ethylmethyl carbonate (EMC) and methylpropyl carbonate (MPC); ethers such as dibutyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, and 1,2-dimethoxyethane; esters such as n-methyl acetate, n-ethyl acetate, methyl propionate, methyl pivalate, methyl formate, and gamma butyrolactone (GBL); amides such as N,N-dimethylformamide and N,N-dimethylacetamide; sulfur-containing compounds such as sulfolane, dimethylsuloxide, and 1,3-propanesultone; There exist carbamates, such as 3-methyl-2-oxazolidone, etc., but it is not limited to these. These can be used individually or in mixture of 2 or more types.

The external shape of the secondary battery is not particularly limited, and may be, for example, a cylindrical shape of a can, a coin shape, a prismatic shape, or a pouch shape.

The secondary battery described above can be used not only for battery cells used as power sources for small devices, but also for batteries containing a plurality of battery cells used as power sources for medium and large-sized devices requiring high temperature stability, long cycle characteristics, and high rate characteristics. It can also be used as a unit battery for a medium or large-sized device including a pack and the battery pack as a power source.

Examples of the medium-to-large device include a mobile electronic device, a power tool powered by a battery-based motor and moving; electric vehicles, including electric vehicles (EVs), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and the like; electric two-wheeled vehicles including electric bicycles (E-bikes) and electric scooters (E-scooters); electric golf carts; A power storage system may be used, but is not limited thereto.

Hereinafter, the present invention will be described in detail through examples, but the following examples and experimental examples are merely illustrative of one form of the present invention, and the scope of the present invention is not limited to the following examples and experimental examples.

<Example 1> - Preparation of binder composition

19 g of butyl acrylate, 69 g of styrene, 2 g of acrylic acid, and 10 g of 2-ethylhexanoic acid vinyl ester as monomers were added to 150 g of water in which 0.3 g of sodium lauryl sulfate, an emulsifier, was added and mixed. A binder composition for a separator containing a copolymer (average particle diameter: 150 nm, number average molecular weight: 500,000 g/mol) was prepared by adding 0.1 g of potassium persulfate as a polymerization initiator at °C and polymerizing for 5 hours.

<Examples 2 to 5>

According to the composition shown in Table 1 below, except for using butyl acrylate, styrene, acrylic acid and 2-ethylhexanoic acid vinyl ester, the binder composition for separators of Examples 2 to 5 was carried out in the same manner as in Example 1 was manufactured. In Table 1 below, the content unit of each material is in weight%, based on 100% by weight of the total amount of all monomers.

Example 1 Example 2 Example 3 Example 4 Example 5 butyl acrylate 19 23 11 30 9 Styrene 69 70 67 58 79 acrylic acid 2 2 2 2 2 2-EAV 10 5 20 10 10 * 2-EAVE: 2-ethylhexanonic acid vinyl ester

<Comparative Examples 1 to 5>

Binder compositions for separators of Comparative Examples 1 to 5 in the same manner as in Example 1, except for using butyl acrylate, styrene, acrylic acid and 2-ethylhexanoic acid vinyl ester according to the composition shown in Table 2 below. was manufactured. In Table 2 below, the content unit of each material is weight%, based on 100% by weight of the total amount of all monomers.

Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 butyl acrylate 27 23.5 9 32 7 Styrene 71 70 67 56 81 acrylic acid 2 2 2 2 2 2-EAV - 4.5 22 10 10 * 2-EAVE: 2-ethylhexanonic acid vinyl ester

<Experimental Example 1> - Glass transition temperature of copolymer

Glass transition temperatures of the copolymers in the binder compositions of Examples 1 to 5 and Comparative Examples 1 to 5 were measured, and the results are shown in Table 3 below.

After drying the binder composition, 10 mg of the copolymer was placed in an aluminum pan, and then differential scanning calorimetry (DSC) was performed at a heating rate of 10 °C/min between -100 °C and 500 °C with a differential thermal analysis measuring device. was carried out. In the measured DSC curve, the intersection point of the tangent line of the DSC curve at the inflection point first appearing after the base line immediately before the endothermic peak of the DSC curve appeared during the heating process and the endothermic peak was taken as the glass transition temperature (Tg).

Example comparative example One 2 3 4 5 One 2 3 4 5 Tg(℃) 41 41 40 22 59 41 40 40 18 63

<Production Example 1>

(a) forming a porous coating layer

57.5% by weight of water, 40% by weight of inorganic Al ₂ O ₃ , 0.5% by weight of a dispersant (polyacrylic acid), and 2% by weight of a binder resin (SBR-based) were mixed to prepare a coating liquid (inorganic slurry). The coating solution was coated on the cross section of polyethylene (PE) fabric (thickness: 9 ㎛, air permeability: 100 s/100c, porous substrate) in a thickness of 2 ㎛ by bar coating method, and then dried in an oven at 50 ° C. for 30 minutes By doing so, a porous coating layer was formed.

(b) forming an adhesive layer

A coating liquid was prepared by mixing 79.5 wt % of water, 0.5 wt % of a dispersant (polyacrylic acid), and 20 wt % of the binder composition for a separator prepared in Example 1 above. A secondary battery separator was prepared by coating the coating crude solution on the cross section of the porous coating layer in a bar coating method to a thickness of 2 μm, and then drying in an oven at 50 ° C. for 30 minutes to form an adhesive layer.

<Preparation Examples 2 to 5> and <Comparative Preparation Examples 1 to 5>

Except for using the binder compositions of Examples 2 to 5 and Comparative Examples 1 to 5 instead of the binder composition of Example 1, the preparation of Preparation Examples 2 to 5 and Comparative Examples 1 to 5 was performed in the same manner as in Preparation Example 1, except for using the binder compositions of Examples 2 to 5 and Comparative Examples 1 to 5 A separator for a secondary battery was prepared.

<Experimental Example 2> - Evaluation of physical properties of the separator

The physical properties of the separators of Preparation Examples 1 to 5 and Comparative Preparation Examples 1 to 5 were measured as follows, and the results are shown in Table 4.

(1) Electrode adhesion

After the separator was laminated on the negative electrode so that the adhesive layer of the separator is in contact with the negative electrode active material layer of the negative electrode, the separator and the negative electrode were bonded in a chamber at 60 ° C using lamination equipment. Thereafter, the stack of electrodes and cathodes was cut into a certain size (width: 25 mm, length: 50 mm) to prepare a sample, and then, using a tension meter (Stable Micro Systems, TA-XT), the The force required for peeling was measured.

(2) air permeability

According to the ASTM D 726-94 test method, the time (seconds) required for 100 cc of air to pass through the separator (cross-sectional area: 1 inch ² ) was measured using a densometer.

(3) Resistance

After a separator was interposed between the negative electrode and the positive electrode, a non-aqueous electrolyte was injected thereto to manufacture a coin cell. At this time, the negative electrode is prepared by using 95 parts by weight of artificial graphite as an active material, 1.5 parts by weight of acetylene black as a conductive material, 2.0 parts by weight of an SBR binder, and 1.5 parts by weight of carboxymethyl cellulose as a thickener, and the positive electrode is made of Li as an active material It was prepared using 90 parts by weight of _1.03 Ni _0.6 Co _0.6 Mn _0.2 O ₂ , 5 parts by weight of acetylene black as a conductive material, and 5 parts by weight of polyvinylidene fluoride (PVdF) as a binder, and the electrolyte solution was 1 M LiPF ₆ This dissolved carbonate-based complex solution [ethylene carbonate (EC) / propylene carbonate (PC) / diethyl carbonate (PC) (EC / PC / DEC = 30: 30: 40% by weight)]. Thereafter, the prepared coin cell was left at room temperature (about 25 ° C.) for 1 day, and then the resistance of the separator was measured according to an impedance measurement method.

manufacturing example Comparative Manufacturing Example One 2 3 4 5 One 2 3 4 5 electrode adhesion
(gf/25㎜) 81 75 71 73 70 59 67 63 63 61 Air permeability (sec/100cc) 127 135 126 139 121 157 135 123 153 121 Resistance (Ω) 0.83 0.85 0.81 0.87 0.79 1.10 0.59 0.78 1.05 0.78

As can be seen in Table 4, the separators of Preparation Examples 1 to 5 have adhesive strength to the electrode of 70 gf / 25 mm or more, air permeability of 140 sec / 100 cc or less, and resistance of 1 Ω or less, Comparative Preparation Example 1 Unlike the separator of ~5, the adhesion to the electrode was high, the air permeability was excellent, and the resistance was low.

Claims (8)

5 to 20% by weight of a first structural unit derived from a vinyl ester represented by the following formula (1);
7.5 to 31.5% by weight of a second constituent unit derived from a (meth)acrylic acid ester monomer;
56.5 to 80.5% by weight of a third structural unit derived from an aromatic vinyl monomer; and
0.1 to 5% by weight of a fourth structural unit derived from an unsaturated carboxylic acid monomer;
A binder composition for a secondary battery separator comprising a copolymer containing:
[Formula 1]

(In Formula 1,
R ₁ is a C ₅ ~ C ₂₀ branched alkyl group;
R ₂ and R ₃ are the same as or different from each other, and each independently represents hydrogen, heavy hydrogen, and a C ₁ to C ₁₂ alkyl group). According to claim 1,
R ₁ is a C ₅ ~ C ₁₂ branched alkyl group;
Wherein R ₂ and R ₃ are both hydrogen, a binder composition for a separator of a secondary battery. According to claim 1,
The vinyl ester represented by Formula 1 is 2-ethylhexanoic acid vinyl ester, a binder composition for a separator of a secondary battery. According to claim 1,
The copolymer is a binder composition for a secondary battery separator having a glass transition temperature (Tg) of 20 to 60 ° C. porous substrates;
a porous coating layer disposed on at least one surface of the porous substrate and including inorganic particles and a binder resin; and
An adhesive layer formed of the binder composition according to any one of claims 1 to 4, disposed on a surface of the porous coating layer and a surface of a porous substrate on which the porous coating layer is not disposed.
A separator for a secondary battery comprising a. According to claim 5,
The binder resin is the same as the copolymer in the binder composition, a separator for a secondary battery. According to claim 5,
A separator for a secondary battery that satisfies the following conditions (i) to (iii):
(i) adhesion to electrodes of 70 gf/25 mm or more;
(ii) air permeability of 140 sec/100cc or less; and
(iii) Resistance of 1 Ω or less. A secondary battery comprising the separator for secondary batteries according to claim 5.