KR102818546B1 - Separator for secondary battery and secondary battery containing the same - Google Patents

Abstract

A secondary battery separator comprising: a porous polymer substrate having a plurality of pores; and a porous coating layer positioned on at least one surface of the porous polymer substrate and including a plurality of inorganic particles, a binder polymer, and a cross-linked polymer containing a urethane bond, wherein the binder polymer and the cross-linked polymer containing a urethane bond are positioned on part or the entire surface of the inorganic particles to connect and fix the inorganic particles; wherein the urethane bond-containing cross-linked polymer is a cross-linking reaction result of an OH group-containing polyvinylidene fluoride-based cross-linkable polymer and an NCO group-containing acrylate-based cross-linkable polymer, and wherein the content of the cross-linked polymer is 3 to 70 parts by weight relative to 100 parts by weight of the total of the binder polymer and the cross-linked polymer; and a secondary battery including the same are provided.

Description

Separator for secondary battery and secondary battery containing the same {SEPARATOR FOR SECONDARY BATTERY AND SECONDARY BATTERY CONTAINING THE SAME}

The present invention relates to a separator for a secondary battery and a secondary battery including the same, and more particularly, to a separator for a secondary battery having improved heat resistance and improved adhesion to an electrode, and a secondary battery including the same.

Recently, interest in energy storage technology has been increasing. As the application fields are expanding to include energy for mobile phones, camcorders, notebook PCs, and even electric vehicles, efforts to research and develop electrochemical devices are becoming more specific. Electrochemical devices are the most notable field in this regard, and among them, the development of rechargeable secondary batteries is the focus of interest, and recently, in developing such batteries, research and development is being conducted on new electrodes and battery designs to improve capacity density and specific energy.

Among the secondary batteries currently in use, lithium secondary batteries developed in the early 1990s are receiving attention due to their advantages of higher operating voltage and much higher energy density than conventional batteries such as Ni-MH, Ni-Cd, and sulfuric acid-lead batteries that use aqueous electrolytes. However, these lithium-ion batteries have safety issues such as ignition and explosion due to the use of organic electrolytes, and they are difficult to manufacture.

Recent lithium-ion polymer batteries are considered as next-generation batteries by improving the weaknesses of lithium-ion batteries. However, the battery capacity is still relatively low compared to lithium-ion batteries, and in particular, the discharge capacity at low temperatures is insufficient, so improvement in this area is urgently required.

Secondary batteries such as the above are produced by many companies, but their safety characteristics show different aspects. The safety evaluation and safety assurance of such secondary batteries are very important. The most important consideration is that the secondary battery should not cause injury to the user in the event of a malfunction, and for this purpose, safety standards strictly regulate ignition and smoke generation within the secondary battery. In terms of the safety characteristics of secondary batteries, there is a high risk of explosion if the secondary battery overheats and thermal runaway occurs or the separator is penetrated. In particular, the polyolefin porous polymer substrate commonly used as the separator of secondary batteries exhibits extreme heat shrinkage behavior at temperatures above 100℃ due to the material characteristics and manufacturing process characteristics including stretching, causing a short circuit between the cathode and the anode.

In order to solve the safety problem of such secondary batteries, a separator has been proposed in which a mixture of an excessive amount of inorganic particles and a binder polymer is coated on at least one side of a porous polymer substrate having a large number of pores to form a porous organic-inorganic coating layer.

However, the introduction of a porous organic-inorganic coating layer causes problems such as increased resistance of the separator, decreased adhesion between electrodes, and the thermal shrinkage problem of the separator is not sufficiently improved, so a solution to this problem is still required.

Therefore, the problem that the present invention seeks to solve is to provide a secondary battery separator having excellent heat shrinkage characteristics.

Another problem that the present invention seeks to solve is to provide a secondary battery having the above-described separator.

In order to solve the above problem, according to one aspect of the present invention, a secondary battery separator of the following embodiment is provided.

According to the first implementation example,

A porous polymer substrate having a plurality of pores, and

A porous coating layer positioned on at least one surface of the porous polymer substrate, comprising a plurality of inorganic particles, a binder polymer, and a cross-linked polymer containing a urethane bond, wherein the binder polymer and the cross-linked polymer containing a urethane bond are positioned on part or all of the surfaces of the inorganic particles to connect and fix the inorganic particles;

The above urethane bond-containing cross-linked polymer is a cross-linking reaction result of an OH group-containing polyvinylidene fluoride-based cross-linked polymer and an NCO group-containing acrylate-based cross-linked polymer.

A secondary battery separator is provided in which the content of the crosslinked polymer is 3 to 70 parts by weight relative to 100 parts by weight of the total of the binder polymer and the crosslinked polymer.

According to the second embodiment, in the first embodiment,

The above OH group-containing polyvinylidene fluoride cross-linkable polymer,

It is grafted onto a polyvinylidene fluoride-based polymer backbone, and may include 1) a graft copolymer comprising a repeating unit derived from an OH-group-containing acrylate-based monomer; or, 2) a graft copolymer comprising a repeating unit derived from an OH-group-free acrylate-based monomer and a repeating unit derived from an OH-group-containing acrylate-based monomer; or, 3) two or more of these.

According to a third embodiment, in the first embodiment or the second embodiment,

The above NCO group-containing acrylate-based cross-linking polymer,

A homopolymer comprising a repeating unit derived from an acrylate monomer containing an NCO group;

In addition to the repeating unit derived from an acrylate monomer containing an NCO group, a copolymer comprising: 1) a repeating unit derived from an acrylate monomer containing an alkyl group, 2) a repeating unit derived from an acrylate monomer containing a cyano group, an amino group, an amide group, or two or more of these functional groups, or 3) all of these repeating units; or

It may contain two or more of these.

According to the fourth embodiment, in any one of the first to third embodiments,

The weight average molecular weight of the above OH group-containing polyvinylidene fluoride-based cross-linkable polymer may be from 300,000 to 2 million, and the weight average molecular weight of the above NCO group-containing acrylate-based cross-linkable polymer may be from 30,000 to 1.8 million.

According to the fifth embodiment, in any one of the first to fourth embodiments,

The content of the crosslinked polymer may be 10 to 60 parts by weight relative to 100 parts by weight of the total of the binder polymer and the crosslinked polymer.

According to the sixth embodiment, in any one of the first to fifth embodiments,

The heat shrinkage rate of the above separator may be 32% or less.

According to the seventh embodiment, in any one of the first to sixth embodiments,

The above urethane bond-containing cross-linked polymer can be obtained through a urethane reaction of the OH group-containing polyvinylidene fluoride-based cross-linked polymer and the NCO group-containing acrylate-based cross-linked polymer during the activation process of the secondary battery.

According to one aspect of the present invention, a lithium secondary battery of the following embodiment is provided.

According to the 8th implementation example,

A lithium secondary battery is provided, wherein the secondary battery comprises a cathode, an anode, and a separator interposed between the cathode and the anode, wherein the separator is a secondary battery separator according to any one of the first to seventh embodiments.

According to one aspect of the present invention, a method for manufacturing a secondary battery of the following embodiment is provided.

According to the ninth embodiment, a method for manufacturing a secondary battery having a separator according to any one of the first to seventh embodiments,

The above manufacturing method comprises the steps of preparing a slurry including a plurality of inorganic particles, a binder polymer, an OH group-containing polyvinylidene fluoride-based cross-linking polymer, an NCO group-containing acrylate-based cross-linking polymer, and a dispersion medium;

A step of preparing a preliminary separation membrane having a porous coating layer by applying the above slurry onto at least one surface of a porous polymer substrate;

A step of preparing a preliminary separator-electrode composite by laminating an electrode having a current collector and an electrode layer positioned on at least one surface of the current collector on the upper surface of the porous coating layer of the preliminary separator, and allowing the electrode layer to come into contact with the porous coating layer;

A step of preparing a secondary battery having the above-mentioned preliminary membrane-electrode complex; and

Comprising a step of activating the secondary battery,

A method for manufacturing a secondary battery is provided, in which, in the step of activating the secondary battery, an OH group-containing polyvinylidene fluoride-based cross-linkable polymer and an NCO group-containing acrylate-based cross-linkable polymer of the porous coating layer are cross-linked to obtain a urethane bond-containing cross-linked polymer.

According to the 10th embodiment, in the 9th embodiment,

The above OH group-containing polyvinylidene fluoride-based cross-linkable polymer may include a graft copolymer comprising a repeating unit derived from an OH group-containing acrylate monomer, wherein the graft copolymer comprises a repeating unit derived from an acrylate monomer and a repeating unit derived from an OH group-containing acrylate monomer; or all of the above.

According to the eleventh embodiment, in the ninth or tenth embodiment,

The above NCO group-containing acrylate-based cross-linking polymer,

A homopolymer, a copolymer, or both comprising a repeating unit derived from an acrylate monomer containing an isocyanate group,

The above copolymer may include, in addition to a repeating unit derived from an acrylate monomer containing an isocyanate group, a repeating unit derived from an acrylate monomer, a repeating unit derived from an acrylate monomer containing a cyano group, an amino group, an amide group, or two or more functional groups thereof, or all of these repeating units.

According to the 12th embodiment, in any one of the 9th to 11th embodiments,

The above OH group-containing polyvinylidene fluoride-based cross-linking polymer is selected from the group consisting of polyvinylidene fluoride-graft-(methyl acrylate-4-hydroxybutylacrylate), polyvinylidene fluoride-graft-(ethyl acrylate-4-hydroxybutylacrylate), polyvinylidene fluoride-graft-(butylacrylate-4-hydroxybutylacrylate), polyvinylidene fluoride-graft-(methyl methacrylate-4-hydroxybutylacrylate), polyvinylidene fluoride-graft-(butyl methacrylate-4-hydroxybutylacrylate), polyvinylidene fluoride-graft-(methyl acrylate-2-hydroxyethyl acrylate), polyvinylidene fluoride-graft-(ethyl acrylate-2-hydroxyethyl acrylate), Polyvinylidene fluoride-graft-(butylacrylate-2-hydroxyethyl acrylate), polyvinylidene fluoride-graft-(methyl methacrylate-2-hydroxyethyl acrylate), polyvinylidene fluoride-graft-(butyl methacrylate-2-hydroxyethyl acrylate), or two or more of them,

The above NCO group-containing acrylate-based cross-linking polymer may include an ethyl acrylate-acrylonitrile-2-isocyanatoethyl acrylate copolymer, a methyl methacrylate-acrylonitrile-2-isocyanatoethyl acrylate copolymer, an n-butylacrylate-acrylonitrile-2-isocyanatoethyl acrylate copolymer, an ethyl acrylate-acrylonitrile-isocyanatomethyl acrylate copolymer, a methyl methacrylate-acrylonitrile-isocyanatomethyl acrylate copolymer, an n-butylacrylate-acrylonitrile-isocyanatomethyl acrylate copolymer, or two or more thereof.

According to the 13th embodiment, in any one of the 9th to 12th embodiments,

The step of activating the secondary battery may include an initial charging step and a high-temperature aging step.

According to the 14th embodiment, in the 13th embodiment,

The above high temperature aging step can be performed at a temperature of 50° C. or higher.

According to the 15th embodiment, in the 13th embodiment or the 14th embodiment,

A low-temperature aging step performed at 20°C to 40°C may be further included between the initial charging step and the high-temperature aging step.

According to one embodiment of the present invention, before crosslinking occurs, a crosslinkable polymer present in a porous coating layer of a separator easily adheres to an active material layer of an electrode, so that the adhesive strength between the electrode and the separator can be improved.

In addition, according to one embodiment of the present invention, a crosslinkable polymer present in a porous coating layer of a separator is crosslinked during a battery manufacturing process, thereby suppressing polymer swelling in an electrolyte-impregnated state, thereby preventing detachment of inorganic particles and significantly improving thermal shrinkage of the separator.

On the other hand, when a conventional crosslinked polymer is included in the porous coating layer of the separator, the crosslinked polymer has a rigid property and poor adhesiveness compared to the crosslinked polymer according to one embodiment of the present invention, and thus does not sufficiently exhibit adhesive force between the inorganic particles and the porous polymer substrate, and between the active material layer of the electrode.

Since the cross-linked polymer included in the porous coating layer of the above separator is obtained through a cross-linking reaction of one or more cross-linkable polymers included in the porous coating layer during the activation process of the secondary battery, no additional process is required after the cross-linked polymer coating. That is, most of the coating layers including the conventional cross-linked polymer were cross-linked by applying a slurry including a polymer capable of cross-linking (cross-linkable polymer) on at least one surface of a porous polymer substrate, and then performing an additional process (heat treatment, UV, etc.) so that cross-linking of the cross-linkable polymer can proceed. However, in one embodiment of the present invention, cross-linking of the cross-linkable polymer can proceed in the activation process performed during the battery manufacturing process without such an additional process for cross-linking.

In addition, by applying a crosslinkable polymer instead of a monomer, which is mainly used in the past, as a starting material for obtaining a crosslinked polymer, it is possible to prevent the monomers in the porous coating layer from dissolving when crosslinking progresses in the electrolyte during the activation process.

Hereinafter, the present invention will be described in detail. The terms or words used in this specification and claims should not be interpreted as limited to their usual or dictionary meanings, and should be interpreted as meanings and concepts that conform to the technical idea of the present invention based on the principle that the inventor can appropriately define the concept of the term in order to explain his or her own invention in the best way.

A secondary battery separator according to one aspect of the present invention comprises a porous polymer substrate having a plurality of pores, and

A porous coating layer positioned on at least one surface of the porous polymer substrate, comprising a plurality of inorganic particles, a binder polymer, and a cross-linked polymer containing a urethane bond, wherein the binder polymer and the cross-linked polymer containing a urethane bond are positioned on part or all of the surfaces of the inorganic particles to connect and fix the inorganic particles;

The above urethane bond-containing cross-linked polymer is a cross-linking reaction result of an OH group-containing polyvinylidene fluoride-based cross-linked polymer and an NCO group-containing acrylate-based cross-linked polymer.

The content of the crosslinked polymer is 3 to 70 parts by weight relative to 100 parts by weight of the total of the binder polymer and the crosslinked polymer.

In the past, in order to improve the safety of secondary batteries, the heat resistance of the separator was improved by coating an inorganic substance, and at this time, a high heat-resistant binder was applied to additionally improve the heat resistance during the coating. At this time, when a crosslinked polymer was applied as a high heat-resistant binder, an additional crosslinking process was required, which increased the process cost, and since the coating layer formed on the separator after crosslinking became hard, there was a difficulty in that the adhesive strength with the electrode decreased during the subsequent process of forming the electrode assembly.

In order to solve these difficulties, the inventors of the present invention manufactured a separator by including a cross-linkable polymer in the porous coating layer of the separator without including a cross-linkable polymer in advance in the porous coating layer of the separator, and formed an electrode assembly so that the cross-linkable polymer can be completely cross-linked during an activation process (for example, 60° C., 12 hours) after secondary battery assembly. At this time, a cross-linkable polymer having a urethane cross-link that can react under low temperature conditions can be applied so that cross-linking can be completely performed during the activation process, and further, a cross-linkable polymer rather than a cross-linkable monomer can be applied so that the porous coating layer does not dissolve before cross-linking in an electrolyte.

The above porous polymer substrate may specifically be a porous polymer film substrate or a porous polymer nonwoven fabric substrate.

The above porous polymer film substrate may be a porous polymer film made of polyolefin such as polyethylene or polypropylene, and such polyolefin porous polymer film substrate exhibits a shutdown function at a temperature of, for example, 80 to 130°C.

At this time, the polyolefin porous polymer film can be formed of a polymer by using a single or a mixture of two or more types of polyolefin polymers such as polyethylene, polypropylene, polybutylene, polypentene, etc., such as high-density polyethylene, linear low-density polyethylene, low-density polyethylene, and ultra-high molecular weight polyethylene.

In addition, the porous polymer film substrate may be manufactured by forming into a film shape using various polymers such as polyester in addition to polyolefin. In addition, the porous polymer film substrate may be formed as a structure in which two or more film layers are laminated, and each film layer may be formed solely of the aforementioned polymers such as polyolefin, polyester, etc., or a polymer in which two or more types are mixed.

In addition, the porous polymer film substrate and the porous nonwoven fabric substrate may be formed of polymers, either singly or in combination, of polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenyleneoxide, polyphenylenesulfide, polyethylenenaphthalene, etc., in addition to the polyolefins mentioned above.

The thickness of the porous polymer substrate is not particularly limited, but may be 1 to 100 ㎛, or 5 to 50 ㎛, and the pore size and pore content present in the porous polymer substrate are also not particularly limited, but may be 0.01 to 50 ㎛ and 10 to 95%, respectively.

In the separator according to one aspect of the present invention, as the binder polymer used for forming the porous coating layer, a polymer commonly used in the art for forming a porous coating layer can be used. In particular, a polymer having a glass transition temperature (T _g ) of -200 to 200°C can be used, because this can improve the mechanical properties of the porous coating layer finally formed, such as flexibility and elasticity. Such a binder polymer faithfully performs the role of a binder that connects and stably fixes inorganic particles, thereby contributing to preventing deterioration of the mechanical properties of the separator into which the porous coating layer has been introduced.

In this specification, binder polymer means a non-crosslinked polymer, as opposed to a crosslinked polymer.

In addition, the binder polymer does not necessarily have to have ion conducting ability, but if a polymer having ion conducting ability is used, the performance of the electrochemical device can be further improved. Therefore, the binder polymer may have a high dielectric constant as much as possible. In fact, since the degree of salt dissociation in the electrolyte depends on the dielectric constant of the electrolyte solvent, the higher the dielectric constant of the binder polymer, the more the degree of salt dissociation in the electrolyte can be improved. The dielectric constant of the binder polymer can be used in the range of 1.0 to 100 (measurement frequency = 1 kHz), and in particular, can be 10 or more.

In addition to the functions described above, the binder polymer may have a characteristic of exhibiting a high degree of swelling of the electrolyte by being gelled when impregnated with a liquid electrolyte. Accordingly, the solubility index of the binder polymer, i.e., the Hildebrand solubility parameter, is in a range of 15 to 45 MPa ^1/2 or 15 to 25 MPa ^1/2 and 30 to 45 MPa ^1/2 . Accordingly, hydrophilic polymers having many polar groups may be used more than hydrophobic polymers such as polyolefins. This is because when the solubility index is less than 15 MPa ^1/2 and exceeds 45 MPa ^1/2 , swelling may be difficult with a typical liquid electrolyte for a battery.

Non-limiting examples of such binder polymers include polyvinylidene fluoride, polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethylmethacrylate, polybuthylacrylate, polybuthylmethacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate Examples thereof include, but are not limited to, cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, and carboxyl methyl cellulose.

According to one embodiment of the present invention, the binder polymer can be divided into a dispersant binder polymer that also functions as a dispersant and a non-dispersant binder polymer. The dispersant binder polymer is a polymer having at least one dispersion-contributing functional group in the main chain or side chain of the polymer, and the dispersion-contributing functional group may be an OH group, a CN group, or the like. Examples of such dispersant binder polymers may include cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, carboxyl methyl cellulose, and the like. Non-dispersant binder polymers may include examples of the above binder polymers excluding dispersant binder polymers.

In one embodiment of the present invention, the binder polymer may be a dispersant binder polymer and a non-dispersant binder polymer used at the same time, or only one of them may be used. When the binder polymer is a dispersant binder polymer and a non-dispersant binder polymer used at the same time, the weight ratio of the dispersant binder polymer and the non-dispersant binder polymer may be 1:1.5 to 1:20, or 1:2 to 1:15.

When this weight ratio is satisfied, the slurry dispersibility is stable and electrode adhesion after coating can be secured.

The above urethane bond-containing cross-linked polymer is a cross-linking reaction product obtained through a cross-linking reaction between a polyvinylidene fluoride-based cross-linked polymer containing a hydroxyl group (-OH), which is a urethane reactive functional group, and an NCO group-containing acrylate-based cross-linked polymer.

According to one embodiment of the present invention, the OH group-containing polyvinylidene fluoride-based cross-linkable polymer is grafted onto a polyvinylidene fluoride-based polymer backbone, and may include 1) a graft copolymer including a repeating unit derived from an OH group-containing acrylate-based monomer; or, 2) a graft copolymer including a repeating unit derived from an OH group-free acrylate-based monomer and a repeating unit derived from an OH group-containing acrylate-based monomer; or, 3) two or more of them.

Here, the polyvinylidene fluoride-based polymer refers to both polyvinylidene fluoride homopolymer and polyvinylidene fluoride copolymer. The polyvinylidene fluoride copolymer is a resin in which vinylidene fluoride and a comonomer are copolymerized at a weight ratio of, for example, 50:50 to 99:1, and the comonomer may include vinyl fluoride, trifluoroethylene, chlorofluoroethylene, trichloroethylene, 1,2-difluoroethylene, tetrafluoroethylene, hexafluoropropylene, perfluoro(alkylvinyl)ether, perfluoro(1,3-dioxole), perfluoro(2,2-dimethyl-1,3-dioxole), or two or more thereof, and non-limiting examples thereof include polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-trichloroethylene, and polyvinylidene fluoride-trifluoroethylene.

In addition, the above acrylate monomer refers to an acrylate monomer that does not contain an OH group, as opposed to an acrylate monomer that contains an OH group. At this time, examples of acrylate monomers not containing an OH group include, but are not limited to, methyl (meth)acrylate, ethyl (meth)acrylate, hexyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, t-butyl (meth)acrylate, sec-butyl (meth)acrylate, pentyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, 2-ethylbutyl (meth)acrylate, n-octyl (meth)acrylate, isobornyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, and lauryl (meth)acrylate.

The above OH group-containing acrylate monomer has a structure in which at least one hydrogen of the above acrylate monomer is substituted with an OH group, and non-limiting examples thereof may include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 2-hydroxyethylene glycol (meth)acrylate, or 2-hydroxypropylene glycol (meth)acrylate.

Examples of the above OH group-containing polyvinylidene fluoride-based cross-linkable polymer may include, but are not limited to, polyvinylidene fluoride-graft-(ethyl acrylate-4-hydroxybutylacrylate), polyvinylidene fluoride-graft-(methyl methacrylate-4-hydroxybutylacrylate), polyvinylidene fluoride-graft-(butylacrylate-2-hydroxyethyl acrylate), polyvinylidene fluoride-graft-(ethyl acrylate-2-hydroxyethyl acrylate), polyvinylidene fluoride-graft-(methyl methacrylate-2-hydroxyethyl acrylate), polyvinylidene fluoride-graft-(butylacrylate-4-hydroxybutylacrylate), or two or more thereof.

The above NCO group-containing acrylate-based cross-linkable polymer may include a homopolymer including a repeating unit derived from an NCO group-containing acrylate-based monomer; a copolymer including, in addition to a repeating unit derived from an NCO group-containing acrylate-based monomer, 1) a repeating unit derived from an alkyl group-containing acrylate-based monomer, 2) a repeating unit derived from an acrylate-based monomer containing a cyano group, an amino group, an amide group, or two or more of these functional groups, or 3) all of these repeating units; or two or more of these.

The above copolymer may include, in addition to a repeating unit derived from an acrylate monomer containing an isocyanate group, a repeating unit derived from an acrylate monomer, a repeating unit derived from an acrylate monomer containing a cyano group, an amino group, an amide group, or two or more functional groups thereof, or all of these repeating units.

At this time, the acrylate monomer means an acrylate monomer that does not contain a functional group such as an isocyanate group, a cyano group, an amino group, or an amide group, and includes methyl (meth)acrylate, ethyl (meth)acrylate, hexyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, t-butyl (meth)acrylate, sec-butyl (meth)acrylate, pentyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, 2-ethylbutyl (meth)acrylate, n-octyl (meth)acrylate, isobornyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, and Examples include, but are not limited to, lauryl (meth)acrylate.

The acrylate monomer containing the above isocyanate group may include aliphatic isocyanatoalkyl (meth)acrylates such as 2-isocyanatoethyl (meth)acrylate, isocyanatomethyl (meth)acrylate, 2-isocyanatopropyl (meth)acrylate, and 3-isocyanatopropyl (meth)acrylate.

The acrylate monomer containing the above cyano group, amino group, amide group, or two or more functional groups thereof may be exemplified as a cyano group-containing monomer, such as acrylonitrile or methacrylonitrile, and as an amide group-containing monomer, for example, (meth)acrylamide or N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N-isopropyl(meth)acrylamide, N-methylol(meth)acrylamide, diacetone(meth)acrylamide, N-vinylacetamide, N,N'-methylenebis(meth)acrylamide, N,N-dimethylaminopropyl(meth)acrylamide, N,N-dimethylaminopropylmethacrylamide, N-vinylpyrrolidone, N-vinylcaprolactam, or (meth)acryloylmorpholine. Examples of amino group-containing monomers include, but are not limited to, aminoethyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate, or N,N-dimethylaminopropyl (meth)acrylate, and examples of imide group-containing monomers include, but are not limited to, N-isopropylmaleimide, N-cyclohexylmaleimide, or itaconimide.

The above NCO group-containing acrylate-based cross-linking polymer may include an ethyl acrylate-acrylonitrile-2-isocyanatoethyl acrylate copolymer, a methyl methacrylate-acrylonitrile-2-isocyanatoethyl acrylate copolymer, an n-butylacrylate-acrylonitrile-2-isocyanatoethyl acrylate copolymer, an ethyl acrylate-acrylonitrile-isocyanatomethyl acrylate copolymer, a methyl methacrylate-acrylonitrile-isocyanatomethyl acrylate copolymer, an n-butylacrylate-acrylonitrile-isocyanatomethyl acrylate copolymer, or two or more thereof.

The weight average molecular weight of the above OH group-containing polyvinylidene fluoride-based cross-linking polymer may be 300,000 to 2 million, or 500,000 to 1.8 million, and the weight average molecular weight of the above NCO group-containing acrylate-based cross-linking polymer may be 30,000 to 1.8 million, or 50,000 to 1.5 million.

When the weight average molecular weight of the crosslinkable polymer satisfies this range, the problem of the porous coating layer being detached from the porous polymer substrate or the thermal shrinkage rate of the separator being reduced due to the inorganic particles being dissolved by the electrolyte during crosslinking and not being sufficiently connected and fixed can be prevented, and further, short circuiting due to short circuiting can be prevented.

The content of the crosslinked polymer is 3 to 70 parts by weight relative to the total 100 parts by weight of the binder polymer and the crosslinked polymer, and according to one embodiment of the present invention, may be 10 to 60 parts by weight, 10 to 58 parts by weight, or 10 to 23 parts by weight, or 22 to 58 parts by weight.

When the content of the crosslinked polymer is less than 3 parts by weight relative to the total 100 parts by weight of the binder polymer and crosslinked polymer, the crosslinking effect is not exerted and the thermal shrinkage rate of the separator significantly increases. When it exceeds 70 parts by weight, the ventilation time of the porous coating layer becomes excessively long, and there is a problem that the electrode adhesive strength decreases due to excessive crosslinking.

The weight ratio of the above-mentioned inorganic particles to the total sum of the binder polymer and the crosslinked polymer is, for example, 50:50 to 99:1, specifically, 70:30 to 95:5. When the content ratio of the inorganic particles to the total sum of the binder polymer and the crosslinked polymer satisfies the above range, the problem of a decrease in the pore size and porosity of the coating layer formed due to an increase in the content of the binder polymer and the crosslinked polymer can be prevented, and the problem of a weakening of the peeling resistance of the coating layer formed due to a decrease in the content of the binder polymer and the crosslinked polymer can also be resolved.

A separation membrane according to one aspect of the present invention may further include other additives in addition to the inorganic particles and polymers described above as porous coating layer components.

In the present invention, non-limiting examples of inorganic particles include high-dielectric constant inorganic particles having a dielectric constant of 5 or more, specifically 10 or more, inorganic particles having lithium ion transfer capability, or mixtures thereof.

Non-limiting examples of inorganic particles having a dielectric constant of 5 or higher include BaTiO 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), hafnia (HfO ₂ ), SrTiO ₃ , SnO ₂ , CeO ₂ , MgO, NiO, CaO, ZnO, ZrO ₂ , Y ₂ O ₃ , Al _{2 O 3} , TiO _2, SiC, AlO(OH), Al ₂ O ₃ ㅇH ₂ O, Or mixtures of these.

In the present specification, the 'inorganic particle having lithium ion transport capability' refers to an inorganic particle containing a lithium element but not storing lithium and having a function of transporting lithium ions, and non-limiting examples of the inorganic particle having lithium ion transport capability include lithium phosphate (Li ₃ PO ₄ ), lithium titanium phosphate (Li _x Ti _y (PO ₄ ) ₃ , 0<x<2, 0<y<3), lithium aluminum titanium phosphate (Li _x Al _y Ti _z (PO ₄ ) ₃ , 0 <x<2, 0<y<1, 0<z<3), (LiAlTiP) _x O _y series glass (0<x<4, 0<y<13) such as 14Li ₂ O -9Al ₂ O ₃ -38TiO ₂ -39P ₂ O ₅ ), lithium lanthanum titanate (Li _x La _y TiO ₃ , Examples thereof include lithium germanium thiophosphates (Li _x Ge _y P _z S _w , 0<x<4, 0<y<1, 0<z<1, 0<w<5) such as Li _3.25 Ge _0.25 P _0.75 S ₄ , lithium nitrides (Li _x N _y , 0<x<4, 0<y<2) such as Li ₃ PO ₄ -Li ₂ S-SiS ₂ , SiS ₂ series glasses (Li _x Si _y S _z , 0<x<3, 0<y<2, 0<z<4) such as LiI-Li ₂ SP ₂ S ₅ , P ₂ S ₅ series glasses (Li _x P _y S _z , 0< _x <3, 0<y<3, 0<z<7) such as LiI-Li 2 SP 2 S 5 , or mixtures thereof.

The thickness of the porous coating layer is not particularly limited, but may be 1 to 10 ㎛, or 1.5 to 6 ㎛, and the pores of the porous coating layer are also not particularly limited, but may be 35 to 65%.

According to one embodiment of the present invention, the porous coating layer may be an organic coating layer using an organic slurry or an aqueous coating layer using an aqueous slurry, and in the case of an aqueous coating layer, it may be more advantageous in that it is advantageous for thin film coating and reduces the resistance of the separation membrane.

In one embodiment of the present invention, the binder of the porous coating layer can attach the inorganic particles to each other (i.e., the binder connects and fixes the inorganic particles) so that the inorganic particles can maintain a state in which they are bound to each other, and further, the binder can maintain the inorganic particles and the porous polymer substrate in a state in which they are bound to each other. The inorganic particles of the porous coating layer can form an interstitial volume in a state in which they are substantially in contact with each other, and at this time, the interstitial volume means a space defined by the inorganic particles that are substantially in contact in a filling structure (closely packed or densely packed) by the inorganic particles. The interstitial volume between the inorganic particles can become an empty space and form pores of the porous coating layer.

According to one embodiment of the present invention, the thermal shrinkage rate of the separator may be 32% or less, or 1 to 30%, or 6 to 32%, or 6 to 27%.

At this time, the thermal shrinkage rate of the separator before cross-linking and the separator after the activation process (final separator) can be calculated by preparing a sample of the separator with the specifications of 5 cm X 5 cm, storing it at 150℃ for 30 minutes, and calculating it with the formula [(initial length) - (length after heat shrinkage treatment for 150℃/30 minutes)/(initial length)] X 100. The thermal shrinkage rate of the separator after the activation process can be measured by storing the separator before cross-linking under the same activation process conditions of the battery without the assembly process with the electrode, and then obtaining a cross-linked separator, and measuring the thermal shrinkage rate of the final separator thus obtained under the same conditions as above.

A method for manufacturing a secondary battery having a separator according to one aspect of the present invention is as follows:

The above manufacturing method comprises the steps of preparing a slurry including a plurality of inorganic particles, a binder polymer, an OH group-containing polyvinylidene fluoride-based cross-linking polymer, an NCO group-containing acrylate-based cross-linking polymer, and a dispersion medium;

A step of preparing a preliminary separation membrane having a porous coating layer by applying the above slurry onto at least one surface of a porous polymer substrate;

A step of preparing a preliminary separator-electrode composite by laminating an electrode having a current collector and an electrode layer positioned on at least one surface of the current collector on the upper surface of the porous coating layer of the preliminary separator, and allowing the electrode layer to come into contact with the porous coating layer;

A step of preparing a secondary battery having the above-mentioned preliminary membrane-electrode complex; and

Comprising a step of activating the secondary battery,

In the step of activating the secondary battery, the OH group-containing polyvinylidene fluoride-based cross-linkable polymer and the NCO group-containing acrylate-based cross-linkable polymer of the porous coating layer are cross-linked to obtain a urethane bond-containing cross-linked polymer.

A detailed look at each of the above steps is as follows.

First, in order to form a porous coating layer, a binder polymer, an OH group-containing polyvinylidene fluoride-based cross-linking polymer, and an NCO group-containing acrylate-based cross-linking polymer may be dissolved in a solvent, and then inorganic particles may be added and dispersed to prepare a slurry. The inorganic particles may be added in a state in which they have been crushed in advance to have a predetermined average particle size, or the inorganic particles may be added to a solution of the binder polymer, the OH group-containing polyvinylidene fluoride-based cross-linking polymer, and the NCO group-containing acrylate-based cross-linking polymer, and then the inorganic particles may be crushed and dispersed while being controlled to have a predetermined average particle size using a ball mill method or the like.

The method for coating the slurry on the porous polymer substrate is not particularly limited, but a slot coating method or a dip coating method may be used. The slot coating method is a method in which the slurry supplied through a slot die is applied to the entire surface of the substrate, and the thickness of the coating layer can be controlled according to the flow rate supplied from a quantitative pump. In addition, the dip coating method is a method in which the substrate is immersed in a tank containing a composition to coat, and the thickness of the coating layer can be controlled according to the concentration of the slurry and the speed at which the slurry is taken out of the tank. In order to control the coating thickness more accurately, post-measuring can be performed using a Meyer bar or the like after immersion.

By drying the porous polymer substrate coated with the slurry in this way using a dryer such as an oven, a porous coating layer is formed on at least one surface of the porous polymer substrate.

Non-limiting examples of the solvent used at this time may include one compound or a mixture of two or more compounds selected from acetone, tetrahydrofuran, methylene chloride, chloroform, dimethylformamide, N-methyl-2-pyrrolidone, methyl ethyl ketone, cyclohexane, methanol, ethanol, isopropyl alcohol, propanol, and water.

After coating the above slurry on the porous polymer substrate, the solvent can be removed by drying at 90 to 180°C or 100 to 150°C.

A preliminary separation membrane is prepared, which comprises a porous polymer substrate, a binder polymer, an OH group-containing polyvinylidene fluoride-based cross-linking polymer, an NCO group-containing acrylate-based cross-linking polymer, and inorganic particles, and a porous coating layer positioned on at least one surface of the porous polymer substrate.

The above OH group-containing polyvinylidene fluoride-based cross-linkable polymer and the NCO group-containing acrylate-based cross-linkable polymer then undergo a urethane cross-linking reaction to become a urethane bond-containing cross-linked polymer.

The OH group-containing polyvinylidene fluoride-based cross-linkable polymer and the NCO group-containing acrylate-based cross-linkable polymer that can be applied at this time are as described above.

The content of the crosslinking polymer is 3 to 70 parts by weight relative to the total 100 parts by weight of the binder polymer and the crosslinking polymer, and according to one embodiment of the present invention, may be 10 to 60 parts by weight, 10 to 58 parts by weight, or 10 to 23 parts by weight, or 22 to 58 parts by weight.

In addition, the weight ratio of the OH group-containing polyvinylidene fluoride-based cross-linkable polymer and the NCO group-containing acrylate-based cross-linkable polymer may be 90:10 to 10:90, or 30:70 to 70:30. In this case, when the weight ratio satisfies this range, the formation of a urethane cross-linking reaction may be facilitated.

Thereafter, an electrode having a current collector and an electrode layer positioned on at least one surface of the current collector is laminated on the upper surface of the porous coating layer of the preliminary separator, and the electrode layer is brought into contact with the porous coating layer to prepare a preliminary separator-electrode composite.

After placing the above preliminary membrane-electrode complex in a battery container, an electrolyte is injected to prepare a secondary battery.

The preliminary battery, in which a non-aqueous electrolyte is injected into a battery container containing the above-described preliminary separator-electrode complex and sealed, may undergo an activation step of initial charging to activate the electrode active material and form an SEI film on the electrode surface. In addition, an aging step may be further performed before the activation step so that the injected electrolyte can sufficiently penetrate into the electrode and the preliminary separator.

At this time, in the step of activating the secondary battery, the crosslinkable polymer of the porous coating layer undergoes a crosslinking reaction to obtain a crosslinked polymer containing a urethane bond.

The step of activating the secondary battery is a step of performing initial charging to activate the electrode active material and form an SEI film on the electrode surface, and may further undergo an aging step so that the electrolyte injected before the activation step can sufficiently penetrate into the electrode and separator.

The step of activating a secondary battery according to one embodiment of the present invention may include an initial charging step and a high-temperature aging step, or may include an initial charging step, a room-temperature aging step, and a high-temperature aging step.

The above initial charging can be performed in a range where the state of charge (SOC) is 10% or more, or 30% or more, or 50% or more, and the upper limit of the SOC is not particularly limited, but may be 100% or 90%. In addition, the initial charging can have an end voltage of 3.5 V or more, or 3.5 to 4.5 V, or 3.65 to 4.5 V.

The C-rate during the initial charge may be 0.05C to 2C, or 0.1C to 2C.

The above high-temperature aging step serves to provide conditions for the crosslinkable polymer of the porous coating layer to undergo a crosslinking reaction, and may be performed at a temperature of, for example, 50° C. or higher, or 50 to 100° C., or 60 to 100° C., or 60 to 80° C. The above high-temperature aging step may be performed for 0.5 to 2 days, or 0.5 to 1.5 days.

In addition, the room temperature aging step is a step that may be additionally included between the initial charging step and the high temperature aging step, and may be performed at a temperature of 20° C. to 40° C., or 23° C. to 35° C., or 23° C. to 30° C., or 23° C. to 27° C., or 23° C. to 25° C. In this case, the room temperature aging step may be performed for 1 day to 7 days, or 1 day to 5 days.

According to one embodiment of the present invention, the step of activating the secondary battery may be performed by charging it to 3.65 V with an SOC of 30% under 0.1C CC conditions, storing it at room temperature of 25°C for 3 days, and then aging it by storing it at a high temperature of 60°C for 1 day.

An electrochemical device according to one aspect of the present invention comprises a cathode, an anode, and a separator interposed between the cathode and the anode, wherein the separator is a separator according to one embodiment of the present invention described above.

These electrochemical devices include all devices that perform electrochemical reactions, and specific examples thereof include capacitors such as all types of primary and secondary batteries, fuel cells, solar cells, or supercapacitor devices. In particular, among the secondary batteries, a lithium secondary battery including a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery is preferable.

The cathode and anode to be applied together with the separator of the present invention are not particularly limited, and the electrode active material can be manufactured in a form in which it is bound to the electrode current collector according to a conventional method known in the art. Non-limiting examples of the cathode active material among the electrode active materials include conventional cathode active materials that can be used in cathodes of conventional electrochemical devices, and in particular, lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium iron oxide, or a lithium composite oxide combining these are preferably used. Non-limiting examples of the anode active material include conventional anode active materials that can be used in anodes of conventional electrochemical devices, and in particular, lithium metal or lithium alloy, carbon, petroleum coke, activated carbon, graphite, or other carbons, and lithium adsorbents are preferable. Non-limiting examples of cathode current collectors include foils made of aluminum, nickel, or combinations thereof, and non-limiting examples of anode current collectors include foils made of copper, gold, nickel, or copper alloys, or combinations thereof.

An electrolyte that can be used in a secondary battery according to one embodiment of the present invention is a salt having a structure such as A ⁺ B ^- , wherein A ⁺ contains an ion formed by an alkali metal cation such as Li ⁺ , Na ⁺ , K ⁺ or a combination thereof, and B ^- contains an ion formed by an anion such as 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 ) ₃ ^- or a combination thereof, and the salt is selected from the group consisting of propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, Dissolved or dissociated in an organic solvent consisting of, but not limited to, N-methyl-2-pyrrolidone (NMP), ethyl methyl carbonate (EMC), gamma butyrolactone (g-butyrolactone), or a mixture thereof.

The above electrolyte injection can be performed at an appropriate stage during the battery manufacturing process, depending on the manufacturing process and required properties of the final product. That is, it can be applied before battery assembly or at the final stage of battery assembly.

Hereinafter, the present invention will be described in detail by way of examples in order to specifically explain the present invention. However, the examples according to the present invention may be modified in various different forms, and the scope of the present invention should not be construed as being limited to the examples described below. The examples of the present invention are provided in order to more completely explain the present invention to a person having average knowledge in the art.

Manufacturing Example 1-1: Synthesis of crosslinkable polyvinylidene fluoride polymer containing OH groups

In a round-bottom flask, 13 g (36 parts by weight) of 32008 (Solvay, PVdF-CTFE), 20.6 g (57 parts by weight) of ethyl acrylate, 2.54 g (7 parts by weight) of 4-hydroxybuthyl acrylate, and 165 g of acetone were added, and the mixture was stirred at room temperature for 30 minutes under a nitrogen atmosphere. After heating to 55℃, 0.23mg _of CuCl2 and 9.7mg of TPMA(tris(2-pyridylmethyl)amine) were added to the reactor, and 62.4mg of V-65 (2,2'-azobis(2,4-dimethyl valeronitrile)) was added, stirred for 24 hours, and the reaction was terminated, thereby obtaining polyvinylidene fluoride-graft-(ethyl acrylate-4-hydroxybutylacrylate) (PVDF)-graft-(ethyl acrylate-r-4-hydroxybuthylacryate), a polyvinylidene fluoride-based cross-linked polymer containing OH groups. At this time, the weight average molecular weight of the polyvinylidene fluoride-based cross-linked polymer containing OH groups was 820,000.

Manufacturing Example 1-2: Synthesis of crosslinkable polyvinylidene fluoride polymer containing OH groups

In a round-bottom flask, 13 g (34 parts by weight) of 32008 (Solvay, PVdF-CTFE), 21.02 g (56 parts by weight) of ethyl acrylate, 3.70 g (10 parts by weight) of 4-hydroxybuthyl acrylate, and 172.2 g of acetone were added, and the mixture was stirred at room temperature for 30 minutes under a nitrogen atmosphere. After heating to 55℃, 0.23mg _of CuCl2 and 9.7mg of TPMA(tris(2-pyridylmethyl)amine) were added to the reactor, and 62.4mg of V-65 (2,2'-azobis(2,4-dimethyl valeronitrile)) was added, stirred for 24 hours, and the reaction was terminated, thereby obtaining polyvinylidene fluoride-graft-(ethyl acrylate-4-hydroxybutylacrylate)(PVDF)-graft-(ethyl acrylate-r-4-hydroxybuthylacryate), a polyvinylidene fluoride-based cross-linked polymer containing OH groups. At this time, the weight average molecular weight of the polyvinylidene fluoride-based cross-linked polymer containing OH groups was 830,000.

Manufacturing Example 1-3: Synthesis of crosslinkable polyvinylidene fluoride polymer containing OH groups

In a round-bottom flask, 13 g (38 parts by weight) of 32008 (Solvay, PVdF-CTFE), 18.34 g (54 parts by weight) of ethyl acrylate, 2.56 g (8 parts by weight) of 4-hydroxybuthyl acrylate, and 154.8 g of acetone were added, and the mixture was stirred at room temperature for 30 minutes under a nitrogen atmosphere. After heating to 55℃, 0.23mg _of CuCl2 and 9.7mg of TPMA(tris(2-pyridylmethyl)amine) were added to the reactor, and 62.4mg of V-65 (2,2'-azobis(2,4-dimethyl valeronitrile)) was added, stirred for 24 hours, and the reaction was terminated, thereby obtaining polyvinylidene fluoride-graft-(ethyl acrylate-4-hydroxybutylacrylate)(PVDF)-graft-(ethyl acrylate-r-4-hydroxybuthylacryate), a polyvinylidene fluoride-based cross-linked polymer containing OH groups. At this time, the weight average molecular weight of the polyvinylidene fluoride-based cross-linked polymer containing OH groups was 660,000.

Manufacturing Example 1-4: Synthesis of crosslinkable polyvinylidene fluoride polymer containing OH groups

In a round-bottom flask, 13 g (27 parts by weight) of 32008 (Solvay, PVdF-CTFE), 31.31 g (65 parts by weight) of ethyl acrylate, 3.86 g (8 parts by weight) of 4-hydroxybuthyl acrylate, and 219.7 g of acetone were added, and the mixture was stirred at room temperature for 30 minutes under a nitrogen atmosphere. After heating to 55℃, 0.17mg _of CuCl2 and 7.1mg of TPMA(tris(2-pyridylmethyl)amine) were added to the reactor, and 45.8mg of V-65 (2,2'-azobis(2,4-dimethyl valeronitrile)) was added, stirred for 24 hours, and the reaction was terminated, thereby obtaining polyvinylidene fluoride-graft-(ethyl acrylate-4-hydroxybutylacrylate)(PVDF)-graft-(ethyl acrylate-r-4-hydroxybuthylacryate), a polyvinylidene fluoride-based cross-linked polymer containing OH groups. At this time, the weight average molecular weight of the polyvinylidene fluoride-based cross-linked polymer containing OH groups was 1.66 million.

Manufacturing Example 1-5: Synthesis of crosslinkable polyvinylidene fluoride polymer containing OH groups

In a round-bottom flask, 13 g (36 parts by weight) of 32008 (Solvay, PVdF-CTFE), 20.37 g (56 parts by weight) of methyl acrylate, 2.77 g (8 parts by weight) of 4-hydroxybuthyl acrylate, and 165 g of acetone were added, and the mixture was stirred at room temperature for 30 minutes under a nitrogen atmosphere. After heating to 55℃, 0.23mg _of CuCl2 and 9.7mg of TPMA(tris(2-pyridylmethyl)amine) were added to the reactor, and 62.4mg of V-65 (2,2'-azobis(2,4-dimethyl valeronitrile)) was added, stirred for 24 hours, and the reaction was terminated, thereby obtaining polyvinylidene fluoride-graft-(methyl acrylate-4-hydroxybutylacrylate)(PVDF)-graft-(methyl acrylate-r-4-hydroxybuthylacryate), a polyvinylidene fluoride-based cross-linked polymer containing OH groups. At this time, the weight average molecular weight of the polyvinylidene fluoride-based cross-linked polymer containing OH groups was 790,000.

Manufacturing Example 1-6: Synthesis of crosslinkable polyvinylidene fluoride polymer containing OH groups

In a round-bottom flask, 13 g (27 parts by weight) of 32008 (Solvay, PVdF-CTFE), 31.49 g (66 parts by weight) of butyl acrylate, 3.11 g (7 parts by weight) of 4-hydroxyethyl acrylate, and 217.2 g of acetone were added, and the mixture was stirred at room temperature for 30 minutes under a nitrogen atmosphere. After heating to 55℃, 0.23mg _of CuCl2 and 9.7mg of TPMA(tris(2-pyridylmethyl)amine) were added to the reactor, and 62.4mg of V-65 (2,2'-azobis(2,4-dimethyl valeronitrile)) was added, stirred for 24 hours, and the reaction was terminated, thereby obtaining polyvinylidene fluoride-graft-(butylacrylate-2-hydroxyethylacrylate)(PVDF)-graft-(buthyl acrylate-r-2-hydroxyethylacryate), a polyvinylidene fluoride-based cross-linked polymer containing OH groups. At this time, the weight average molecular weight of the polyvinylidene fluoride-based cross-linked polymer containing OH groups was 870,000.

Manufacturing Example 2-1: Synthesis of NCO group-containing acrylate-based crosslinkable polymer

In a round-bottomed flask, 320 g (80 parts by weight) of ethyl acrylate, 40 g (10 parts by weight) of acrylonitrile, 40 g (10 parts by weight) of 2-isocyanatoethyl acrylate (trade name: AOI, TCI), and 600 g of acetone were charged, and the mixture was stirred at room temperature for 30 minutes under a nitrogen atmosphere. After the temperature was increased to 50°C, 2.4 g of V-65 was added, and after stirring for 48 hours, the reaction was terminated to obtain an NCO-containing acrylate crosslinked polymer, an ethyl acrylate-r-acrylonitrile-r-2-isocyanatoethylacrylate copolymer. At this time, the weight average molecular weight of the NCO-containing acrylate crosslinked polymer was 460,000.

Manufacturing Example 2-2: Synthesis of NCO group-containing acrylate-based crosslinkable polymer

In a round-bottomed flask, 308 g (77 parts by weight) of ethyl acrylate, 40 g (10 parts by weight) of acrylonitrile, 52 g (13 parts by weight) of 2-isocyanatoethyl acrylate (trade name: AOI, TCI), and 600 g of acetone were charged, and the mixture was stirred at room temperature for 30 minutes under a nitrogen atmosphere. After the temperature was increased to 50°C, 2.4 g of V-65 was added, and after stirring for 48 hours, the reaction was terminated to obtain an NCO-containing acrylate crosslinked polymer, an ethyl acrylate-r-acrylonitrile-r-2-isocyanatoethylacrylate copolymer. At this time, the weight average molecular weight of the NCO-containing acrylate crosslinked polymer was 460,000.

Manufacturing Example 2-3: Synthesis of NCO group-containing acrylate-based crosslinkable polymer

In a round-bottomed flask, 320 g (80 parts by weight) of ethyl acrylate, 40 g (10 parts by weight) of acrylonitrile, 40 g (10 parts by weight) of 2-isocyanatoethyl acrylate (trade name AOI, TCI), and 600 g of acetone were charged, and the mixture was stirred at room temperature for 30 minutes under a nitrogen atmosphere. After the temperature was increased to 50°C, 6 g of V-65 was added, and after stirring for 48 hours, the reaction was terminated to obtain an NCO-containing acrylate crosslinked polymer, an ethyl acrylate-r-acrylonitrile-r-2-isocyanatoethylacrylate copolymer. At this time, the weight average molecular weight of the NCO-containing acrylate crosslinked polymer was 80,000.

Manufacturing Example 2-4: Synthesis of NCO group-containing acrylate-based crosslinkable polymer

In a round-bottomed flask, 320 g (80 parts by weight) of ethyl acrylate, 40 g (10 parts by weight) of acrylonitrile, 40 g (10 parts by weight) of 2-isocyanatoethyl acrylate (trade name: AOI, TCI), and 600 g of acetone were charged, and the mixture was stirred at room temperature for 30 minutes under a nitrogen atmosphere. After the temperature was increased to 50°C, 1.8 g of V-65 was added, and after stirring for 48 hours, the reaction was terminated to obtain an NCO-containing acrylate crosslinked polymer, an ethyl acrylate-r-acrylonitrile-r-2-isocyanatoethylacrylate copolymer. At this time, the weight average molecular weight of the NCO-containing acrylate crosslinked polymer was 770,000.

Manufacturing Example 2-5: Synthesis of NCO group-containing acrylate-based crosslinkable polymer

In a round-bottomed flask, 320 g (80 parts by weight) of methyl methacrylate, 40 g (10 parts by weight) of acrylonitrile, 40 g (10 parts by weight) of 2-isocyanatoethyl acrylate (trade name: AOI, TCI), and 600 g of acetone were added, and the mixture was stirred at room temperature for 30 minutes under a nitrogen atmosphere. After the temperature was increased to 50°C, 2.4 g of V-65 was added, and after stirring for 48 hours, the reaction was terminated to obtain a methyl methacrylate-r-acrylonitrile-r-2-isocyanatoethylacrylate copolymer, which is an NCO-containing acrylate crosslinking polymer. At this time, the weight average molecular weight of the NCO-containing acrylate crosslinking polymer was 490,000.

Manufacturing Example 2-6: Synthesis of NCO group-containing acrylate-based crosslinkable polymer

In a round-bottomed flask, 316 g (79 parts by weight) of butylacrylate, 40 g (10 parts by weight) of acrylonitrile, 44 g (11 parts by weight) of 2-isocyanatoethyl acrylate (trade name: AOI, TCI), and 600 g of acetone were charged, and the mixture was stirred at room temperature for 30 minutes under a nitrogen atmosphere. After the temperature was increased to 50°C, 2.4 g of V-65 was added, and after stirring for 48 hours, the reaction was terminated to obtain a butylacrylate-r-acrylonitrile-r-2-isocyanatoethylacrylate copolymer, which is an NCO-containing acrylate crosslinked polymer. At this time, the weight average molecular weight of the NCO-containing acrylate crosslinked polymer was 410,000.

Example 1

18 parts by weight of polyvinylidene fluoride (PVDF) as a binder polymer, 1 part by weight of polyvinylidene fluoride-graft-(ethyl acrylate-4-hydroxybutylacrylate) (PVDF)-graft-(ethyl acrylate-r-4-hydroxybuthylacryate) (weight average molecular weight: 820,000) manufactured in Manufacturing Example 1 as a crosslinked polymer, and 1 part by weight of ethyl acrylate-r-acrylonitrile-r-2-isocyanatoethylacrylate copolymer (weight average molecular weight: 460,000) manufactured in Manufacturing Example 2-1 were added to 93 parts by weight of acetone as a solvent, and stirred at 25°C for about 3 hours to prepare a binder polymer solution.

At this time, the weight ratio of the vinylidene fluoride-derived repeating unit, the ethyl acrylate-derived repeating unit, and the 4-hydroxybutylacrylate-derived repeating unit in polyvinylidene fluoride-graft-(ethyl acrylate-4-hydroxybutylacrylate)(PVDF)-graft-(ethyl acrylate-r-4-hydroxybuthylacryate) was 36:57:7.

Additionally, the weight ratio of the ethyl acrylate-derived repeating unit, the acrylonitrile-derived repeating unit, and the 2-isocyanatoethyl acrylate-derived repeating unit in the ethyl acrylate-acrylonitrile-2-isocyanatoethyl acrylate copolymer was 80:10:10.

78 parts by weight of alumina (Al ₂ O ₃ ) particles having an average particle size of 500 nm and 2 parts by weight of cyanoethylflurane (as a binder polymer and a dispersant) were added to 75 parts by weight of acetone and dispersed to obtain a dispersion, and then the dispersion was stirred with a polymer solution to prepare a slurry for a porous coating layer.

The slurry thus manufactured was coated on both sides of a 9 ㎛ thick polyethylene porous membrane (resistance 0.66 ohm, air permeability 142 sec/100 cc) by a dip coating method, and dried in an oven at 100°C to manufacture a preliminary separation membrane having porous coating layers on both sides. At this time, the total thickness of the porous coating layer was 6 ㎛.

A cathode mixture was prepared by mixing 96.7 parts by _weight of Li _{[ Ni0.6Mn0.2Co0.2} ] _O2 functioning as a cathode active material, 1.3 parts by weight of graphite functioning as a conductive agent, and 2.0 parts by weight of polyvinylidene fluoride (PVdF) functioning as a binder. The obtained cathode mixture was dispersed in 1-methyl-2-pyrrolidone functioning as a solvent, thereby preparing a cathode mixture slurry. This slurry was coated, dried, and pressed on both sides of a 20 ㎛ thick aluminum foil, respectively, to manufacture a cathode.

An anode mixture was prepared by mixing 97.6 parts by weight of artificial graphite and natural graphite (weight ratio: 90:10) functioning as an anode active material, 1.2 parts by weight of styrene-butadiene rubber (SBR) functioning as a binder, and 1.2 parts by weight of carboxymethyl cellulose (CMC). An anode mixture slurry was prepared by dispersing this anode mixture in ion-exchange water functioning as a solvent. This slurry was coated on both sides of a 20 ㎛ thick copper foil, dried, and pressed to manufacture an anode.

A non-aqueous electrolyte was prepared by dissolving LiPF ₆ in an organic solvent mixed with ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) in a ratio of 3:3:4 (volume ratio) to a concentration of 1.0 M.

The preliminary separator was interposed between the cathode and anode manufactured as described above, and laminated so that at least one of the active material layers of the cathode and the anode was in contact with the porous coating layer of the preliminary separator, thereby preparing a preliminary separator-electrode composite. After storing the preliminary separator-electrode composite in a pouch, the electrolyte was injected to manufacture a secondary battery.

Afterwards, the secondary battery equipped with the above-mentioned preliminary separator was charged to 3.65 V at 30% SOC under 0.1C CC conditions, stored at room temperature (25°C) for 3 days, and then aged at a high temperature (60°C) for 1 day, thereby undergoing an activation process.

During the above activation process, the isocyanate group and the hydroxyl group of the crosslinkable polymer included in the porous coating layer of the preliminary separation membrane undergo an addition reaction (addition reaction) to form urethane crosslinking, thereby forming a crosslinked polymer containing a urethane bond.

As a result, a secondary battery separator including a cross-linked polymer containing a urethane bond in a porous coating layer and a secondary battery having the same were finally manufactured.

The content ratio of the above cross-linked polymer is shown in Table 1 below.

At this time, the content of the crosslinked polymer was calculated by dissolving the porous coating layer in acetone, separating the inorganic particles and the binder solution layer, and measuring the mass of the undissolved polymer in the binder solution, i.e., the crosslinked polymer.

In addition, the weight average molecular weight of the crosslinked polymer was measured using GPC (Agilent Infinity 1200 system) equipment in THF solvent at 1.0 ml/min and 35°C.

The content ratio and weight average molecular weight of the crosslinked polymers in the following examples and comparative examples were also measured and calculated using the same method as above.

Example 2

16 parts by weight of polyvinylidene fluoride (PVDF) as a binder polymer, 2 parts by weight of polyvinylidene fluoride-graft-(ethyl acrylate-4-hydroxybutylacrylate) (PVDF)-graft-(ethyl acrylate-r-4-hydroxybuthylacryate) (weight average molecular weight: 820,000) manufactured in Manufacturing Example 1-1 as a crosslinked polymer, and 2 parts by weight of ethyl acrylate-r-acrylonitrile-r-2-isocyanatoethylacrylate copolymer (weight average molecular weight: 460,000) were added to 93 parts by weight of acetone as a solvent, and stirred at 60°C for about 3 hours to prepare a binder polymer solution.

At this time, the weight ratio of the vinylidene fluoride-derived repeating unit, the ethyl acrylate-derived repeating unit, and the 4-hydroxybutylacrylate-derived repeating unit in polyvinylidene fluoride-graft-(ethyl acrylate-4-hydroxybutylacrylate)(PVDF)-graft-(ethyl acrylate-r-4-hydroxybuthylacryate) was 36:57:7.

Additionally, the weight ratio of the ethyl acrylate-derived repeating unit, the acrylonitrile-derived repeating unit, and the 2-isocyanatoethyl acrylate-derived repeating unit in the ethyl acrylate-acrylonitrile-2-isocyanatoethyl acrylate copolymer was 80:10:10.

78 parts by weight of alumina (Al ₂ O ₃ ) particles having an average particle size of 500 nm and 2 parts by weight of cyanoethylflurane (which is a binder polymer and a dispersant) were added to 75 parts by weight of acetone and dispersed to obtain a dispersion, which was then stirred with a polymer solution to prepare a slurry for a porous coating layer. Other than that, a secondary battery separator and a secondary battery equipped with the same were finally manufactured in the same manner as in Example 1.

Example 3

12 parts by weight of polyvinylidene fluoride (PVDF) as a binder polymer, 4 parts by weight of polyvinylidene fluoride-graft-(ethyl acrylate-4-hydroxybutylacrylate) (PVDF)-graft-(ethyl acrylate-r-4-hydroxybuthylacryate) (weight average molecular weight: 820,000) manufactured in Manufacturing Example 1-1 as a crosslinked polymer, and 4 parts by weight of ethyl acrylate-r-acrylonitrile-r-2-isocyanatoethylacrylate copolymer (weight average molecular weight: 460,000) were added to 93 parts by weight of acetone as a solvent, and stirred at 60°C for about 3 hours to prepare a binder polymer solution.

At this time, the weight ratio of the vinylidene fluoride-derived repeating unit, the ethyl acrylate-derived repeating unit, and the 4-hydroxybutylacrylate-derived repeating unit in polyvinylidene fluoride-graft-(ethyl acrylate-4-hydroxybutylacrylate)(PVDF)-graft-(ethyl acrylate-r-4-hydroxybuthylacryate) was 36:57:7.

Additionally, the weight ratio of the ethyl acrylate-derived repeating unit, the acrylonitrile-derived repeating unit, and the 2-isocyanatoethyl acrylate-derived repeating unit in the ethyl acrylate-acrylonitrile-2-isocyanatoethyl acrylate copolymer was 80:10:10.

78 parts by weight of alumina (Al ₂ O ₃ ) particles having an average particle size of 500 nm and 2 parts by weight of cyanoethylflurane (which is a binder polymer and a dispersant) were added to 75 parts by weight of acetone and dispersed to obtain a dispersion, which was then stirred with a polymer solution to prepare a slurry for a porous coating layer. Other than that, a secondary battery separator and a secondary battery equipped with the same were finally manufactured in the same manner as in Example 1.

Example 4

16 parts by weight of polyvinylidene fluoride (PVDF) as a binder polymer, 2 parts by weight of polyvinylidene fluoride-graft-(ethyl acrylate-4-hydroxybutylacrylate) (PVDF)-graft-(ethyl acrylate-r-4-hydroxybuthylacryate) (weight average molecular weight: 830,000) prepared in Manufacturing Example 1-2 as a crosslinked polymer, and 2 parts by weight of ethyl acrylate-r-acrylonitrile-r-2-isocyanatoethylacrylate copolymer (weight average molecular weight: 510,000) prepared in Manufacturing Example 2-2 were added to 93 parts by weight of acetone as a solvent, and stirred at 60°C for about 3 hours to prepare a binder polymer solution.

At this time, the weight ratio of the vinylidene fluoride-derived repeating unit, the ethyl acrylate-derived repeating unit, and the 4-hydroxybutylacrylate-derived repeating unit in polyvinylidene fluoride-graft-(ethyl acrylate-4-hydroxybutylacrylate)(PVDF)-graft-(ethyl acrylate-r-4-hydroxybuthylacryate) was 34:56:10.

Additionally, the weight ratio of the ethyl acrylate-derived repeating unit, the acrylonitrile-derived repeating unit, and the 2-isocyanatoethyl acrylate-derived repeating unit in the ethyl acrylate-acrylonitrile-2-isocyanatoethyl acrylate copolymer was 77:10:13.

78 parts by weight of alumina (Al ₂ O ₃ ) particles having an average particle size of 500 nm and 2 parts by weight of cyanoethylflurane (which is a binder polymer and a dispersant) were added to 75 parts by weight of acetone and dispersed to obtain a dispersion, which was then stirred with a polymer solution to prepare a slurry for a porous coating layer. Other than that, a secondary battery separator and a secondary battery equipped with the same were finally manufactured in the same manner as in Example 1.

Example 5

16 parts by weight of polyvinylidene fluoride (PVDF) as a binder polymer, 2 parts by weight of polyvinylidene fluoride-graft-(ethyl acrylate-4-hydroxybutylacrylate) (PVDF)-graft-(ethyl acrylate-r-4-hydroxybuthylacryate) (weight average molecular weight: 660,000) prepared in Manufacturing Example 1-3 as a crosslinked polymer, and 2 parts by weight of ethyl acrylate-r-acrylonitrile-r-2-isocyanatoethylacrylate copolymer (weight average molecular weight: 80,000) prepared in Manufacturing Example 2-3 were added to 93 parts by weight of acetone as a solvent, and stirred at 60°C for about 3 hours to prepare a binder polymer solution.

At this time, the weight ratio of the vinylidene fluoride-derived repeating unit, the ethyl acrylate-derived repeating unit, and the 4-hydroxybutylacrylate-derived repeating unit in polyvinylidene fluoride-graft-(ethyl acrylate-4-hydroxybutylacrylate)(PVDF)-graft-(ethyl acrylate-r-4-hydroxybuthylacryate) was 38:54:8.

Additionally, the weight ratio of the ethyl acrylate-derived repeating unit, the acrylonitrile-derived repeating unit, and the 2-isocyanatoethyl acrylate-derived repeating unit in the ethyl acrylate-acrylonitrile-2-isocyanatoethyl acrylate copolymer was 80:10:10.

78 parts by weight of alumina (Al ₂ O ₃ ) particles having an average particle size of 500 nm and 2 parts by weight of cyanoethylflurane (which is a binder polymer and a dispersant) were added to 75 parts by weight of acetone and dispersed to obtain a dispersion, which was then stirred with a polymer solution to prepare a slurry for a porous coating layer. Other than that, a secondary battery separator and a secondary battery equipped with the same were finally manufactured in the same manner as in Example 1.

Example 6

16 parts by weight of polyvinylidene fluoride (PVDF) as a binder polymer, 2 parts by weight of polyvinylidene fluoride-graft-(ethyl acrylate-4-hydroxybutylacrylate) (PVDF)-graft-(ethyl acrylate-r-4-hydroxybuthylacryate) (weight average molecular weight: 1.66 million) prepared in Manufacturing Example 1-4 as a crosslinking polymer, and 2 parts by weight of ethyl acrylate-r-acrylonitrile-r-2-isocyanatoethylacrylate copolymer (weight average molecular weight: 770,000) prepared in Manufacturing Example 2-4 were added to 93 parts by weight of acetone as a solvent, and stirred at 60°C for about 3 hours to prepare a binder polymer solution.

At this time, the weight ratio of the vinylidene fluoride-derived repeating unit, the ethyl acrylate-derived repeating unit, and the 4-hydroxybutylacrylate-derived repeating unit in polyvinylidene fluoride-graft-(ethyl acrylate-4-hydroxybutylacrylate)(PVDF)-graft-(ethyl acrylate-r-4-hydroxybuthylacryate) was 27:65:8.

Additionally, the weight ratio of the ethyl acrylate-derived repeating unit, the acrylonitrile-derived repeating unit, and the 2-isocyanatoethyl acrylate-derived repeating unit in the ethyl acrylate-acrylonitrile-2-isocyanatoethyl acrylate copolymer was 80:10:10.

78 parts by weight of alumina (Al ₂ O ₃ ) particles having an average particle size of 500 nm and 2 parts by weight of cyanoethylflurane (which is a binder polymer and a dispersant) were added to 75 parts by weight of acetone and dispersed to obtain a dispersion, which was then stirred with a polymer solution to prepare a slurry for a porous coating layer. Other than that, a secondary battery separator and a secondary battery equipped with the same were finally manufactured in the same manner as in Example 1.

Example 7

16 parts by weight of polyvinylidene fluoride (PVDF) as a binder polymer, 2 parts by weight of polyvinylidene fluoride-graft-(methyl methacrylate-4-hydroxybutylacrylate) (PVDF)-graft-(methyl methacrylate-r-4-hydroxybuthylacryate) (weight average molecular weight: 790,000) prepared in Manufacturing Example 1-5 as a crosslinking polymer, and 2 parts by weight of methyl methacrylate-r-acrylonitrile-r-2-isocyanatoethylacrylate copolymer (weight average molecular weight: 490,000) prepared in Manufacturing Example 2-5 were added to 93 parts by weight of acetone as a solvent, and the mixture was stirred at 60°C for about 3 hours to prepare a binder polymer solution.

At this time, the weight ratio of the vinylidene fluoride-derived repeating unit, the methyl acrylate-derived repeating unit, and the 4-hydroxybutylacrylate-derived repeating unit in polyvinylidene fluoride-graft-(methyl acrylate-4-hydroxybutylacrylate)(PVDF)-graft-(methyl acrylate-r-4-hydroxybuthylacryate) was 36:56:8.

Additionally, the weight ratio of the methyl methacrylate-derived repeating unit, the acrylonitrile-derived repeating unit, and the 2-isocyanatoethyl acrylate-derived repeating unit in the methyl methacrylate-acrylonitrile-2-isocyanatoethyl acrylate copolymer was 80:10:10.

78 parts by weight of alumina (Al ₂ O ₃ ) particles having an average particle size of 500 nm and 2 parts by weight of cyanoethylflurane (which is a binder polymer and a dispersant) were added to 75 parts by weight of acetone and dispersed to obtain a dispersion, which was then stirred with a polymer solution to prepare a slurry for a porous coating layer. Other than that, a secondary battery separator and a secondary battery equipped with the same were finally manufactured in the same manner as in Example 1.

Example 8

16 parts by weight of polyvinylidene fluoride (PVDF) as a binder polymer, 2 parts by weight of polyvinylidene fluoride-graft-(butylacrylate-2-hydroxyethyl acrylate) (PVDF)-graft-(buthyl acrylate-r-2-hydroxyetylacryate) (weight average molecular weight: 870,000) prepared in Manufacturing Example 1-6 as a crosslinked polymer, and 2 parts by weight of butylacrylate-r-acrylonitrile-r-2-isocyanatoethylacrylate copolymer (weight average molecular weight: 410,000) prepared in Manufacturing Example 2-6 were added to 93 parts by weight of acetone as a solvent, and the mixture was stirred at 60°C for about 3 hours to prepare a binder polymer solution.

At this time, the weight ratio of the vinylidene fluoride-derived repeating unit, the butylacrylate-derived repeating unit, and the 2-hydroxyethylacrylate-derived repeating unit in polyvinylidene fluoride-graft-(butylacrylate-2-hydroxyethylacrylate)(PVDF)-graft-(buthyl acrylate-r-2-hydroxyethylacryate) was 27:66:7.

Additionally, the weight ratio of the butylacrylate-derived repeating unit, the acrylonitrile-derived repeating unit, and the 2-isocyanatoethyl acrylate-derived repeating unit in the butylacrylate-acrylonitrile-2-isocyanatoethyl acrylate copolymer was 79:10:11.

78 parts by weight of alumina (Al ₂ O ₃ ) particles having an average particle size of 500 nm and 2 parts by weight of cyanoethylflurane (which is a binder polymer and a dispersant) were added to 75 parts by weight of acetone and dispersed to obtain a dispersion, which was then stirred with a polymer solution to prepare a slurry for a porous coating layer. Other than that, a secondary battery separator and a secondary battery equipped with the same were finally manufactured in the same manner as in Example 1.

Comparative Example 1

A secondary battery separator and a secondary battery equipped with the same were finally manufactured in the same manner as in Example 1, except that 20 parts by weight of polyvinylidene fluoride (PVDF) and 2 parts by weight of cyanoethylflurane were used as binder polymers and no crosslinking polymer was used.

Comparative Example 2

16 parts by weight of polyvinylidene fluoride (PVDF) as a binder polymer, 4 parts by weight of polyvinylidene fluoride-graft-(ethyl acrylate-4-hydroxybutylacrylate) (PVDF)-graft-(ethyl acrylate-r-4-hydroxybuthylacryate) (weight average molecular weight: 820,000) as a crosslinking polymer were added to 93 parts by weight of acetone as a solvent, and stirred at 60°C for about 3 hours to prepare a binder polymer solution.

At this time, the weight ratio of the vinylidene fluoride-derived repeating unit, the ethyl acrylate-derived repeating unit, and the 4-hydroxybutylacrylate-derived repeating unit in polyvinylidene fluoride-graft-(ethyl acrylate-4-hydroxybutylacrylate)(PVDF)-graft-(ethyl acrylate-r-4-hydroxybuthylacryate) was 36:57:7.

78 parts by weight of alumina (Al ₂ O ₃ ) particles having an average particle size of 500 nm and 2 parts by weight of cyanoethylflurane (which is a binder polymer and a dispersant) were added to 75 parts by weight of acetone and dispersed to obtain a dispersion, and then the dispersion was stirred with a polymer solution to prepare a slurry for a porous coating layer.

In addition, a secondary battery separator and a secondary battery equipped with the same were finally manufactured in the same manner as Example 1. At this time, since the slurry for the porous coating layer contained only an OH group-containing polyvinylidene fluoride-based cross-linking polymer and did not contain an NCO group-containing acrylate-based cross-linking polymer, no cross-linking reaction occurred and thus no cross-linking polymer was obtained.

Comparative Example 3

16 parts by weight of polyvinylidene fluoride (PVDF) as a binder polymer, 4 parts by weight of ethyl acrylate-r-acrylonitrile-r-2-isocyanatoethylacrylate copolymer (weight average molecular weight: 460,000) as a crosslinking polymer, and 93 parts by weight of acetone as a solvent were added, and stirred at 60°C for about 3 hours to prepare a binder polymer solution.

At this time, the weight ratio of the ethyl acrylate-derived repeating unit, the acrylonitrile-derived repeating unit, and the 2-isocyanatoethyl acrylate-derived repeating unit in the ethyl acrylate-acrylonitrile-2-isocyanatoethyl acrylate copolymer was 80:10:10.

78 parts by weight of alumina (Al ₂ O ₃ ) particles having an average particle size of 500 nm and 2 parts by weight of cyanoethylflurane (which is a binder polymer and a dispersant) were added to 75 parts by weight of acetone and dispersed to obtain a dispersion, and then the dispersion was stirred with a polymer solution to prepare a slurry for a porous coating layer.

In addition, a secondary battery separator and a secondary battery equipped with the same were finally manufactured in the same manner as Example 1. At this time, since the slurry for the porous coating layer contained only a polyvinylidene fluoride-based cross-linking polymer containing an NCO group and did not contain an acrylate-based cross-linking polymer containing an OH group, a cross-linking reaction did not occur, and thus a cross-linking polymer was not obtained.

Comparative Example 4

19 parts by weight of polyvinylidene fluoride (PVDF) as a binder polymer, 0.2 parts by weight of polyvinylidene fluoride-graft-(ethyl acrylate-r-4-hydroxybutylacrylate) (PVDF)-graft-(ethyl acrylate-r-4-hydroxybuthylacryate) (weight average molecular weight: 820,000) as a crosslinking polymer, and 0.2 parts by weight of ethyl acrylate-r-acrylonitrile-r-2-isocyanatoethylacrylate copolymer (weight average molecular weight: 460,000) were added to 93 parts by weight of acetone as a solvent, and stirred at 60°C for about 3 hours to prepare a binder polymer solution.

At this time, the weight ratio of the vinylidene fluoride-derived repeating unit, the ethyl acrylate-derived repeating unit, and the 4-hydroxybutylacrylate-derived repeating unit in polyvinylidene fluoride-graft-(ethyl acrylate-4-hydroxybutylacrylate)(PVDF)-graft-(ethyl acrylate-r-4-hydroxybuthylacryate) was 36:57:7.

Additionally, the weight ratio of the ethyl acrylate-derived repeating unit, the acrylonitrile-derived repeating unit, and the 2-isocyanatoethyl acrylate-derived repeating unit in the ethyl acrylate-acrylonitrile-2-isocyanatoethyl acrylate copolymer was 80:10:10.

78 parts by weight of alumina (Al ₂ O ₃ ) particles having an average particle size of 500 nm and 2 parts by weight of cyanoethylflurane (which is a binder polymer and a dispersant) were added to 75 parts by weight of acetone and dispersed to obtain a dispersion, and then the dispersion was stirred with a polymer solution to prepare a slurry for a porous coating layer.

Other than that, a secondary battery separator and a secondary battery equipped with the same were finally manufactured using the same method as in Example 1.

Evaluation Results

For the separators of Examples 1 to 8 and Comparative Examples 1 to 4, the resistance, ventilation time, electrode-separator adhesion (gf/25 mm), and thermal shrinkage (before crosslinking, after activation process) were evaluated, respectively, and are shown in Table 1 below.

Their specific evaluation methods are as follows.

(1) Resistance of the membrane

The resistance value of the separators manufactured in Examples 1 to 8 and Comparative Examples 1 to 4 when immersed in an electrolyte was measured by an AC method at 25°C using a 1 M LiPF ₆ -ethylene carbonate/ethyl methyl carbonate (weight ratio 3:7) electrolyte.

(2) Ventilation

The air permeability (Gurley) was measured by the ASTM D726-94 method. The Gurley used here, which is the resistance to air flow, was measured by a Gurley densometer. The air permeability values described herein are expressed as the time (in seconds) required for 100 cc of air to pass through the cross-section of 1 in ² of the membranes manufactured in Examples 1 to 8 and Comparative Examples 1 to 4 under a pressure of 12.2 inH ₂ O, i.e., the air permeability time.

(3) Evaluation of electrode-separator adhesion (gf/25mm)

An anode was manufactured by mixing active material [natural graphite and artificial graphite (weight ratio 5:5)], conductive agent [super P], and binder [polyvinylidene fluoride (PVdF)] in a weight ratio of 92:2:6, dispersing the mixture in water, and then coating the mixture on copper foil, and cutting it into a size of 25 mm X 70 mm.

The membranes manufactured in Examples 1 to 8 and Comparative Examples 1 to 4 were cut to a size of 25 mm X 70 mm and prepared.

The prepared separator and anode were overlapped with each other, sandwiched between 100 μm PET films, and then bonded using a flat plate press. At this time, the conditions of the flat plate press were heating at 90°C and 8 MPa of pressure for 1 second.

After mounting the bonded separator and the end of the anode on the UTM equipment (LLOYD Instrument LF Plus), force was applied in both directions at a measurement speed of 300 mm/min to measure the force required to separate the bonded separator.

(4) Evaluation of heat shrinkage rate

The heat shrinkage rate of the above-mentioned pre-crosslinked membrane was calculated by preparing a specimen of each membrane with the specifications of 5 cm X 5 cm, storing it at 150°C for 30 minutes, and calculating it using the formula of (initial length - length after heat shrinkage treatment for 150°C/30 minutes)/(initial length) X 100.

The heat shrinkage rate of the separator after the activation process was measured by storing the separator before crosslinking under the same battery activation process conditions without the assembly process with the electrode, obtaining a crosslinked separator, and preparing a specimen with the specifications of 5 cm X 5 cm for the final separator thus obtained under the same conditions as above, storing it at 150°C for 30 minutes, and calculating the heat shrinkage rate using the formula: [(initial length) - (length after heat shrinkage treatment for 150°C/30 minutes)]/(initial length) X 100.

Content of cross-linked polymer (weight part of the cross-linked polymer relative to 100 weight parts of the total of binder polymer and cross-linked polymer) resistance
(Ω) Ventilation
(Ventilation
hour)
(sec) Electrode-Separator Adhesion
(gf/25mm) Heat shrinkage rate (%)
After the activation process
(after bridge) Example 1 9.1 0.69 398 66 27 Example 2 18.2 0.73 393 70 10 Example 3 36.4 0.84 431 72 7 Example 4 18.2 0.78 404 68 8 Example 5 18.2 0.67 387 67 18 Example 6 18.2 0.92 464 74 9 Example 7 18.2 0.86 512 52 7 Example 8 18.2 0.88 477 67 13 Comparative Example 1 0 0.62 381 64 44 Comparative Example 2 0 0.64 391 66 43 Comparative Example 3 0 0.76 412 71 48 Comparative Example 4 1.9 0.66 388 65 38

Referring to Table 1 above, it was confirmed that the membranes of Examples 1 to 8 were significantly improved in terms of heat shrinkage rate compared to Comparative Examples 1 to 4.

Typically, in order to perform the activation process of a secondary battery, an electrolyte is injected into a membrane-binder assembly. At this time, if a phenomenon in which the polymer binder is swollen by the electrolyte occurs, the binder layer bound to the inorganic particles is detached from the inorganic or pore-containing membrane material, which results in not being able to prevent shrinkage of the membrane due to heat. However, as in the embodiment of the present invention, since the cross-linked polymer included in the porous coating layer can prevent the swelling phenomenon due to the electrolyte, strong binding with the inorganic particles can be maintained even if the electrolyte is injected. Therefore, it is judged that an excellent thermal ripening rate of the separator can be achieved by the binding of the inorganic particles even when stress that causes shrinkage of the separator material due to heat occurs.

As described above, although the present invention has been described by means of limited embodiments, the present invention is not limited thereby, and various modifications and variations are possible by those skilled in the art within the technical spirit of the present invention and the scope of equivalents of the claims to be described below.

Claims (15)

A porous polymer substrate having a plurality of pores, and
A porous coating layer positioned on at least one surface of the porous polymer substrate, comprising a plurality of inorganic particles, a binder polymer, and a cross-linked polymer containing a urethane bond, wherein the binder polymer and the cross-linked polymer containing a urethane bond are positioned on part or all of the surfaces of the inorganic particles to connect and fix the inorganic particles;
The above urethane bond-containing cross-linked polymer is a cross-linking reaction result of an OH group-containing polyvinylidene fluoride-based cross-linked polymer and an NCO group-containing acrylate-based cross-linked polymer.
A secondary battery separator having a content of the crosslinked polymer of 3 to 70 parts by weight relative to 100 parts by weight of the total of the binder polymer and the crosslinked polymer. In the first paragraph,
The above OH group-containing polyvinylidene fluoride cross-linkable polymer,
A secondary battery separator characterized by comprising: 1) a graft copolymer comprising a repeating unit derived from an acrylate monomer containing an OH group, which is grafted onto a polyvinylidene fluoride-based polymer backbone; or, 2) a graft copolymer comprising a repeating unit derived from an acrylate monomer not containing an OH group and a repeating unit derived from an acrylate monomer containing an OH group; or, 3) two or more of them. In the first paragraph,
The above NCO group-containing acrylate-based cross-linking polymer,
A homopolymer comprising a repeating unit derived from an acrylate monomer containing an NCO group;
In addition to the repeating unit derived from an acrylate monomer containing an NCO group, a copolymer comprising: 1) a repeating unit derived from an acrylate monomer containing an alkyl group, 2) a repeating unit derived from an acrylate monomer containing a cyano group, an amino group, an amide group, or two or more of these functional groups, or 3) all of these repeating units; or
Containing two or more of these
A secondary battery separator characterized by: In the first paragraph,
A secondary battery separator, characterized in that the weight average molecular weight of the OH group-containing polyvinylidene fluoride-based cross-linking polymer is 300,000 to 2 million, and the weight average molecular weight of the NCO group-containing acrylate-based cross-linking polymer is 30,000 to 1.8 million. In the first paragraph,
A secondary battery separator, characterized in that the content of the crosslinked polymer is 10 to 60 parts by weight based on 100 parts by weight of the total of the binder polymer and the crosslinked polymer. In the first paragraph,
The heat shrinkage rate of the above separator is 32% or less,
A secondary battery separator, characterized in that the above heat shrinkage rate is calculated by preparing a specimen of the separator with the specifications of 5 cm X 5 cm, storing it at 150°C for 30 minutes, and calculating [(initial length) - (length after heat shrinkage treatment at 150°C/30 minutes)/(initial length)] X 100. In the first paragraph,
A secondary battery separator, characterized in that the urethane bond-containing cross-linked polymer is obtained through a urethane reaction of the OH group-containing polyvinylidene fluoride-based cross-linked polymer and the NCO group-containing acrylate-based cross-linked polymer during the activation process of the secondary battery. A lithium secondary battery comprising a cathode, an anode, and a separator interposed between the cathode and the anode, wherein the separator is a secondary battery separator according to any one of claims 1 to 7. A method for manufacturing a secondary battery having a separator according to claim 1,
The above manufacturing method comprises the steps of preparing a slurry including a plurality of inorganic particles, a binder polymer, an OH group-containing polyvinylidene fluoride-based cross-linking polymer, an NCO group-containing acrylate-based cross-linking polymer, and a dispersion medium;
A step of preparing a preliminary separation membrane having a porous coating layer by applying the above slurry onto at least one surface of a porous polymer substrate;
A step of preparing a preliminary separator-electrode composite by laminating an electrode having a current collector and an electrode layer positioned on at least one surface of the current collector on the upper surface of the porous coating layer of the preliminary separator, and allowing the electrode layer to come into contact with the porous coating layer;
A step of preparing a secondary battery having the above-mentioned preliminary membrane-electrode complex; and
Comprising a step of activating the secondary battery,
A method for manufacturing a secondary battery, wherein, in the step of activating the secondary battery, the OH group-containing polyvinylidene fluoride-based cross-linkable polymer and the NCO group-containing acrylate-based cross-linkable polymer of the porous coating layer are cross-linked to obtain a urethane bond-containing cross-linked polymer. In Article 9,
A method for manufacturing a secondary battery separator, characterized in that the OH group-containing polyvinylidene fluoride-based cross-linkable polymer is grafted onto a polyvinylidene fluoride-based polymer backbone, and comprises a graft copolymer comprising a repeating unit derived from an OH group-containing acrylate monomer; a graft copolymer comprising a repeating unit derived from an acrylate monomer and a repeating unit derived from an OH group-containing acrylate monomer; or all of these. In Article 9,
The above NCO group-containing acrylate-based cross-linking polymer,
A homopolymer, a copolymer, or both comprising a repeating unit derived from an acrylate monomer containing an isocyanate group,
A method for manufacturing a separator for a secondary battery, characterized in that the copolymer comprises, in addition to a repeating unit derived from an acrylate monomer containing an isocyanate group, a repeating unit derived from an acrylate monomer, a repeating unit derived from an acrylate monomer containing a cyano group, an amino group, an amide group, or two or more functional groups thereof, or all of these repeating units. In Article 9,
The above OH group-containing polyvinylidene fluoride-based cross-linking polymer is selected from the group consisting of polyvinylidene fluoride-graft-(methyl acrylate-4-hydroxybutylacrylate), polyvinylidene fluoride-graft-(ethyl acrylate-4-hydroxybutylacrylate), polyvinylidene fluoride-graft-(butylacrylate-4-hydroxybutylacrylate), polyvinylidene fluoride-graft-(methyl methacrylate-4-hydroxybutylacrylate), polyvinylidene fluoride-graft-(butyl methacrylate-4-hydroxybutylacrylate), polyvinylidene fluoride-graft-(methyl acrylate-2-hydroxyethyl acrylate), polyvinylidene fluoride-graft-(ethyl acrylate-2-hydroxyethyl acrylate), Polyvinylidene fluoride-graft-(butylacrylate-2-hydroxyethyl acrylate), polyvinylidene fluoride-graft-(methyl methacrylate-2-hydroxyethyl acrylate), polyvinylidene fluoride-graft-(butyl methacrylate-2-hydroxyethyl acrylate), or two or more of them,
A method for manufacturing a secondary battery separator, characterized in that the NCO group-containing acrylate-based cross-linking polymer comprises an ethyl acrylate-acrylonitrile-2-isocyanatoethyl acrylate copolymer, a methyl methacrylate-acrylonitrile-2-isocyanatoethyl acrylate copolymer, an n-butylacrylate-acrylonitrile-2-isocyanatoethyl acrylate copolymer, an ethyl acrylate-acrylonitrile-isocyanatomethyl acrylate copolymer, a methyl methacrylate-acrylonitrile-isocyanatomethyl acrylate copolymer, an n-butylacrylate-acrylonitrile-isocyanatomethyl acrylate copolymer, or two or more thereof. In Article 9,
A method for manufacturing a secondary battery, characterized in that the step of activating the secondary battery includes an initial charging step and a high-temperature aging step. In Article 13,
A method for manufacturing a secondary battery, characterized in that the high-temperature aging step is performed at a temperature of 50°C or higher. In Article 13,
A method for manufacturing a secondary battery, characterized in that it may further include a low-temperature aging step performed at 20°C to 40°C between the initial charging step and the high-temperature aging step.