KR20210019305A - Separator for secondary battery, preparing method thereof, and secondary battery including the same - Google Patents

Abstract

Provided are a separating film for a secondary battery, a manufacturing method thereof, and the secondary battery including the same. The separating film for a secondary battery has a porous substrate, a porous polyimide disposed on at least one surface of the porous substrate, and a coating film containing inorganic particles. In the coating film, a mixed volume ratio of the porous polyimide and the inorganic particles is 1 : 1.5 to 1 : 8.

Description

Separator for secondary battery, manufacturing method thereof, and secondary battery including the same {Separator for secondary battery, preparing method thereof, and secondary battery including the same}

It relates to a separator for a secondary battery, a method of manufacturing the same, and a secondary battery including the same.

A secondary battery represented by a lithium secondary battery has a high energy density and is widely used as a main power source for portable electronic devices such as mobile phones and notebook computers. These secondary batteries are required to have higher energy density, but securing safety becomes a technical task.

In a secondary battery, when an electrolyte decomposition reaction and thermal runaway occur due to heat generation due to an internal short circuit, overcharging, or overdischarging, the internal pressure of the battery may rise rapidly, causing an explosion of the battery.

The role of a separator is very important for the production of high-capacity batteries along with the recent trend of reducing battery weight and size. In order to achieve high performance, such as high output and high capacity, as well as stability and reliability of the battery, a separator having improved heat resistance and safety is required for thin film coating while securing air permeability characteristics.

One aspect is to provide a separator for secondary batteries with improved heat resistance while securing air permeability characteristics.

Another aspect is to provide a method of manufacturing the above-described separator for a secondary battery.

Another aspect is to provide a secondary battery with improved safety including the above-described separator.

According to one aspect,

It is a separator for a secondary battery having a porous substrate and a coating film containing porous polyimide and inorganic particles disposed on at least one side of the porous substrate,

In the coating film, a mixture weight ratio of the porous polyimide and the inorganic particles is 1:1.5 to 1:8, a separator for a secondary battery is provided.

According to another aspect, it includes the step of forming a coating film by coating and drying a composition for forming a coating film containing a porous polyimide, inorganic particles and a solvent on at least one surface of the porous substrate,

In the coating membrane, a mixing weight ratio of the porous polyimide and the inorganic particles is provided in a method of manufacturing a separator for a secondary battery of 1:1.5 to 1:8.

Anode according to another aspect; cathode; And a secondary battery including the above-described separator interposed between the positive electrode and the negative electrode.

When the separator according to an embodiment is used, air permeability can be ensured within a desired range, and heat resistance and adhesion are improved even when a thin coating film is employed. Using such a separator, it is possible to manufacture a secondary battery with improved safety without increasing cell resistance.

1 is a schematic diagram showing the structure of a lithium secondary battery according to an embodiment.

Hereinafter, a separator according to an embodiment, a method of manufacturing the same, and a secondary battery including the same will be described in more detail.

A separator for secondary batteries having a porous substrate and a coating film containing porous polyimide and inorganic particles disposed on at least one side of the porous substrate, and porous polyimide and inorganic particles in the coating film containing the porous polyimide, inorganic particles and binder. A mixture weight ratio of 1:1.5 to 1:8 is provided for a secondary battery separator.

As the battery separator has high capacity, air permeability is secured, and heat resistance and safety are secured even when coating a thin film.

Accordingly, the present inventors have completed the present invention for a separator for a secondary battery having improved heat resistance while securing air permeability by using a porous polyimide when forming a coating film of the separator.

The porous polyimide has a weight average molecular weight of 300,000 to 500,000, and a porosity of 15 to 50%. Porous polyimide differs in pore formation characteristics when volatilized according to the presence or absence of a solvent compared to non-porous polyimide. If such a porous polyimide is used, desired air permeability properties can be secured, and even when a coating film having a thin film thickness is provided, a separator having excellent adhesion, resistance and heat resistance can be manufactured.

The porous polyimide used in the present invention may be a compound represented by the following formula (1).

[Formula 1]

In Formula 1, X ₁ is selected from the group consisting of oxygen (O), sulfur (S), sulfur monoxide (SO), sulfur dioxide (SO ₂ ), and selenium (Se), and is, for example, oxygen,

Ar ₁ and Ar ₂ are selected from the group represented by the following formula 1-1,

[Formula 1-1]

In Formula 1-1, R ₁ to R ₄ are independently of each other hydrogen, a substituted or unsubstituted C1 to C20 alkyl group, a substituted or unsubstituted C6 to C20 aryl group, a substituted or unsubstituted C3C20 A heteroaryl group, a substituted or unsubstituted C5 to C20 aliphatic ring, a halogen atom, a hydroxy group or a cyano group,

R ₅ is one selected from the group represented by Formula 1-2,

[Formula 1-2]

n is an integer of 10 to 1,000, for example an integer of 15 to 500, for example an integer of 20 to 100.

In Formula 1, X ₁ is oxygen (O), and Ar ₁ and Ar ₂ are groups represented by the following formula.

In the formula, R ₁ to R ₄ are each independently hydrogen, a C1 to C20 alkyl group, a C6 to C20 aryl group, a heteroaryl group, a C5 to C20 aliphatic ring, a halogen atom, a hydroxy group, or a cyano group.

R ₅ is, for example, a group represented by the following formula.

The porous polyimide of the present invention may be, for example, a polymer represented by Formula 2 below.

[Formula 2]

In Formula 2, n is an integer of 10 to 1,000, for example, an integer of 15 to 500, for example, an integer of 20 to 100.

The polymer of Formula 2 has a conjugated structure and has heat resistance, mechanical properties, chemical resistance, and electrical insulation properties due to the strong molecular force of the imide bond.

The polymer of Formula 1 may be prepared according to a general polyimide synthesis method.

The polymer of Formula 2 may be prepared according to a manufacturing process as shown in Scheme 1 below.

[Scheme 1]

The coating film containing the porous polyimide and inorganic particles of the present invention contains inorganic particles, and the content of the porous polyimide in the coating film and the mixing weight ratio of the inorganic particles and the porous polyimide have an important effect on the heat resistance, air permeability and adhesion of the separator. I can.

The content of the porous polyimide in the coating membrane constituting the separator of the present invention is 10 to 40 parts by weight based on the total weight of the porous polyimide and inorganic particles. When the content of the porous polyimide is within the above range, the separator has excellent heat resistance, air permeability, and adhesion.

The content of the inorganic particles in the composition for forming a coating film of the present invention is 10 to 20 parts by weight, for example 10 to 15 parts by weight, based on 100 parts by weight of the composition for forming a coating film. 100 parts by weight of the composition for forming a coating film is equal to 100 parts by weight of the total weight of the separator. When the content of the inorganic particles is within the above range, the uniformity of pores in the separator is excellent, and mechanical strength, air permeability, and thermal stability are excellent.

The average particle diameter of the inorganic particles is 0.1 μm or less.

The mixing volume ratio of the porous polyimide and inorganic particles in the coating film is 1:1.5 to 1:8, for example 1:1.5 to 1:4, for example 1:2 to 1:3.5. For example, 1:2.5 to 1:3. If the content of the porous polyimide for the inorganic particles is greater than the above range, the air permeability of the separator is increased and the adhesion is lowered, making it difficult to secure heat resistance.

In the case where the mixing volume ratio of the porous polyimide and the inorganic particles in the coating film is greater than 1:4 to 1:8, at least one binder selected from polyvinylidene fluoride and an acrylic polymer may be further included. The content of at least one binder selected from polyvinylidene fluoride and acrylic polymer is 50 to 150 parts by weight based on 100 parts by weight of porous polyimide. When the content of the binder is within the above range, the adhesion of the coating film to the porous substrate is excellent.

Examples of the acrylic polymer include polymethyl methacrylate, polyethyl methacrylate, polybutyl methacrylate, and polyisobutymethacrylate.

When preparing the coating film of the separator of the present invention, a general binder may be further used.

The binder is, for example, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene. -Propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluorine rubber, or combinations thereof.

The inorganic particles are boehmite, alumina, aluminum oxyhydroside (AlOOH), zirconia, yttria, ceria, magnesia, titania, silica, aluminum carbide, titanium carbide, tungsten carbide, boron nitride, aluminum nitride. Calcium carbonate, barium sulfate, aluminum hydroxide, magnesium hydroxide, or combinations thereof.

The size of the inorganic particles is 0.1 μm or more, for example 0.1 to 10 μm, for example 1 to 5 μm. And the porosity of the separator is 10 to 95%, for example, 35 to 50%, and the size of the pores is 0.01 to 50㎛. In the present specification, "the size of the inorganic particles" indicates the average diameter when the inorganic particles are spherical and the long axis length when the inorganic particles are non-spherical. The size of the inorganic particles can be measured using a particle size measuring device or an electron scanning microscope. In the present specification, "the size of the pores" indicates the diameter when the pores are spherical, and indicates the length of the major axis when the pores are non-spherical.

The inorganic particles may have a spherical shape or a plate shape.

The porosity of the separator is 10 to 95%, for example 30 to 80%, for example 35 to 50%, and the size of the pores in the separator is 0.01 to 50 μm. The total thickness of the separator is, for example, 10 to 20 µm, for example, 14 to 20 µm. The thickness of the separator is 14 to 20 μm.

The air permeability of the separator according to an embodiment is 170 to 280 sec/100cc, for example 170 to 250 sec/100cc, the shrinkage rate is 20 to 50%, the adhesive strength is 2.5 to 4.0 g/mm, and the resistance is 13 to 20 (Ω·cm ² ).

The air permeability of the separator can be measured according to JIS P 8117. For example, after making 10 specimens cut at 10 different points, a separator with a circular area of 1 inch in diameter permeates 100 cc of air in each of the specimens by using an air permeability measuring device (Asahi Seiko). Measure the air permeability by measuring the average time it takes five times each, and then calculating the average value.

When the air permeability of the separator of the present invention is within the above range, the pores formed in the separator are sufficiently opened, so that ionic conductivity is excellent, and battery output and battery performance can be improved.

By employing the separator of the present invention, it is possible to manufacture a secondary battery with improved safety while securing air permeability and securing thermal properties.

In another aspect, a method of manufacturing a separator according to an embodiment is provided.

First, a coating film is formed by coating and drying a composition for forming a coating film containing a porous polyimide, inorganic particles, and a solvent on at least one surface of a porous substrate.

The composition for forming a coating film may further include one or more binders selected from polyvinylidene fluoride and acrylic polymers. If such a binder is further added to the coating film-forming composition, the adhesion of the coating film to the porous substrate may be further improved.

The drying is carried out, for example, at 25 to 100°C.

The separator having a coating film obtained according to the above manufacturing method has a reduced resistance in the cell and a defect rate compared to a separator in which a porous coating film is formed using non-porous polyimide, non-solvent or non-solvent, and inorganic particles. Decreases.

In the separation membrane of the present invention, the porosity of the coating membrane is 40 to 50%. When the porosity of the coating film is within the above range, the air permeability of the separator is excellent.

According to another aspect, there is provided a secondary battery including a positive electrode, a negative electrode, and the above-described separator interposed between the positive electrode and the negative electrode.

The secondary battery may be, for example, a lithium secondary battery such as a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

The secondary battery can be manufactured using a method commonly used in the technical field of the present invention.

The positive electrode and the negative electrode are prepared by coating and drying a composition for forming a positive electrode active material layer and a composition for forming a negative electrode active material layer on a current collector, respectively.

The composition for forming a positive electrode active material is prepared by mixing a positive electrode active material, a conductive agent, a binder, and a solvent, and the positive electrode active material according to the embodiment is used as the positive electrode active material.

The binder is a component that aids in the binding between the active material and the conductive agent and the bond to the current collector, and non-limiting examples include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, and hydrogen. Roxypropylcellulose, recycled cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluorine rubber, And various copolymers.

The conductive agent is not particularly limited as long as it does not cause chemical change in the battery and has conductivity, and examples thereof include graphite such as natural graphite or artificial graphite; Carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; Conductive fibers such as carbon fibers and metal fibers; Carbon fluoride; Metal powders such as aluminum and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives may be used.

As a non-limiting example of the solvent, N-methyl 2-pyrrolidone and the like are used.

The content of the binder, the conductive agent and the solvent is at a conventional level.

The positive electrode current collector has a thickness of 3 to 500 μm, and is not particularly limited as long as it has high conductivity without causing chemical changes to the battery. For example, stainless steel, aluminum, nickel, titanium, heat-treated carbon, Alternatively, a surface-treated aluminum or stainless steel surface with carbon, nickel, titanium, silver, or the like may be used. The current collector may increase the adhesion of the positive electrode active material by forming fine irregularities on its surface, and various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics are possible.

Separately, a negative active material, a binder, a conductive agent, and a solvent are mixed to prepare a composition for forming a negative active material layer.

As a non-limiting example, the negative active material may be a carbon-based material such as graphite or carbon, a lithium metal, an alloy thereof, or a silicon oxide-based material.

The binder, the conductive agent, and the solvent may be made of the same type of material as in manufacturing the positive electrode.

The negative electrode current collector is generally made to have a thickness of 3 to 500 μm. Such a negative electrode current collector is not particularly limited as long as it has conductivity without causing a chemical change in the battery, for example, copper, stainless steel, aluminum, nickel, titanium, heat-treated carbon, copper or stainless steel. For the surface treatment with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloys, etc. may be used. In addition, like the positive electrode current collector, it is possible to enhance the bonding strength of the negative electrode active material by forming fine irregularities on the surface thereof, and may be used in various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics.

A secondary battery may be manufactured by interposing a separator according to an exemplary embodiment between the positive electrode and the negative electrode manufactured according to the above process.

The secondary battery contains a non-aqueous electrolyte. The non-aqueous electrolyte includes a lithium salt, and at least one selected from a non-aqueous electrolyte, an organic solid electrolyte, and an inorganic solid electrolyte.

Examples of the non-aqueous electrolyte include, but are not limited to, N-methyl 2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2- Dimethoxyethane, 2-methyl tetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, N,N-formamide, N,N-dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate , Methyl acetate, phosphoric acid tryester, trimethoxy methane, dioxolane derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, pyro An aprotic organic solvent such as methyl pionate and ethyl propionate may be used.

Examples of the organic solid electrolyte include, but are not limited to, polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphoric acid ester polymers, polyester sulfides, polyvinyl alcohol, polyvinylidene fluoride, and the like.

The inorganic solid electrolyte may include, but is not limited to, Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Li ₄ SiO ₄ -LiI-LiOH, Li ₃ PO ₄ -Li ₂ S-SiS ₂ or the like may be used.

The lithium salt is a material that is soluble in the non-aqueous electrolyte, and is not limited to, for example, LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO _{2, LiAsF 6, LiSbF 6,} LiAlCl 4, CH 3 SO 3 Li, CF 3 SO 3 Li, (CF 3 SO 2) ₂ NLi, (FSO ₂ ) ₂ NLi, lithium chloroborate, a compound represented by the following formula, a mixture thereof, or a combination thereof may be used.

1 is a cross-sectional view schematically showing a typical structure of a lithium secondary battery, which is one of the secondary batteries according to an embodiment.

Referring to FIG. 1, a lithium secondary battery 100 includes a positive electrode 40, a negative electrode 50, and a separator 10. The electrode assembly 60 obtained by winding or folding the positive electrode 40, the negative electrode 50, and the separator 10 described above is accommodated in the battery case 70. Subsequently, an electrolyte (not shown) is injected into the battery case 25 to complete a lithium secondary battery. The battery case 70 has a rectangular shape in FIG. 1. The lithium secondary battery may be a lithium ion battery. The electrode assembly 60 may be in the form of a jelly roll. A plurality of electrode assemblies may be stacked to form a battery pack, and such a battery pack may be used in all devices requiring high capacity and high output. For example, it can be used for laptop computers, smart phones, electric vehicles, and the like.

In addition, since the lithium secondary battery has excellent storage stability, life characteristics, and high rate characteristics at high temperatures, it can be used in an electric vehicle (EV). For example, it may be used in hybrid vehicles such as plug-in hybrid electric vehicles (PHEVs).

The present invention will be described in more detail through the following examples and comparative examples. However, the examples are for illustrative purposes only and are not intended to limit the scope of the present invention.

Example 1: Preparation of the separator

First, a composition for forming a coating film was prepared by mixing a porous polyimide (BSP-L6 (Unitika, SP-L6U), alumina (Al2O3) having an average diameter of about 60 nm) and a solvent, N-methylpyrrolidone (NMP). The mixing weight ratio of alumina and porous polyimide is 6:4 (3:2), and the content of N-methylpyrrolidone (NMP) as a solvent is 60 parts by weight based on 100 parts by weight of the composition for forming a coating film. The porous polyimide has a weight average molecular weight of about 400,000, a porosity of about 30%, and is represented by the following formula (2).

[Formula 2]

In Formula 2, n is 61.

The coating film-forming composition obtained according to the above process was coated on the top of the polyethylene film, and then dried at 110° C. for 10 minutes to form a coating film to a thickness of about 3 μm to prepare a separator.

Example 2-3: Preparation of separator

A separator was manufactured in the same manner as in Example 1, except that the mixing weight ratio of alumina and porous polyimide was changed to 75:25 (3:1) and 80:20 (4:1).

Example 4: Preparation of the separator

A separator was prepared in the same manner as in Example 1, except that polyvinylidene fluoride was further added when preparing the composition for forming a coating film. Here, the mixing weight ratio of alumina, porous polyimide, and polyvinylidene fluoride in the composition for forming a coating film was 80:10:10.

Comparative example 1: Preparation of the separator

A separator was prepared in the same manner as in Example 1, except that polyimide (Kukdo Chemical Co., Ltd., KDPL-1104) was used instead of porous polyimide when preparing the composition for forming a coating film. The weight average molecular weight of polyimide is about 250,000.

Comparative example 2: Preparation of the separator

A separator was prepared in the same manner as in Example 2, except that polyimide (Kukdo Chemical Co., Ltd., KDPL-1104) was used instead of the porous polyimide when preparing the composition for forming a coating film. The weight average molecular weight of polyimide is about 250,000.

Comparative example 3: Preparation of the separator

To 100 parts by weight of a mixture of 70 parts by weight of acetone and 30 parts by weight of methanol as a solvent, as a polymer binder, 3 parts by weight of polyvinylidene fluoride-hexafluoropropylene (Kynar2751, Arkema) was added. It dissolved at 50 degreeC for about 12 hours or more, and the slurry for separator coating was prepared.

The slurry was coated on a polyethylene porous membrane (C210, Celgard) having a thickness of 16 μm by a dip coating method to prepare a separator. The coating thickness was adjusted to about 4 μm.

Comparative example 4: Preparation of the separator

In the composition for forming a coating film, a separator was prepared in the same manner as in Example 1, except that the mixing weight ratio of alumina and porous polyimide was 4:6 (2:3).

According to Comparative Example 4, when the ratio of the porous polyimide to alumina is relatively high, the adhesion of the separator is improved, but the heat shrinkage rate and resistance are increased.

Production example One: Lithium secondary battery Produce

Using the separator of Example 1, a lithium secondary battery was manufactured according to the method described below.

LiNi _{0 . 33} Co _{0 . 33} Mn _{0 . 33} O ₂ 97.45% by weight, 0.5% by weight of artificial graphite (SFG6, Timcal) powder as a conductive material, 0.7% by weight of carbon black (Ketjenblack, ECP), 0.25% by weight of modified acrylonitrile rubber (BM-720H, Zeon Corporation), After mixing 0.9% by weight of polyvinylidene fluoride (PVdF, S6020, Solvay) and 0.2% by weight of polyvinylidene fluoride (PVdF, S5130, Solvay) and adding it to the N-methyl-2-pyrrolidone solvent, a mechanical stirrer By stirring for 30 minutes to prepare a positive electrode active material slurry. The slurry was applied to a thickness of about 60 μm on an aluminum current collector having a thickness of 20 μm using a doctor blade, dried for 0.5 hours in a hot air dryer at 100° C., dried once again under vacuum and 120° C. for 4 hours, and rolled (roll press) to prepare a positive electrode plate.

The slurry prepared according to the above process was coated on an aluminum foil using a doctor blade to form a thin electrode plate, dried at 135° C. for 3 hours or more, and then subjected to rolling and vacuum drying processes to produce a positive electrode.

98% by weight of artificial graphite (BSG-L, Tianjin BTR New Energy Technology Co., Ltd.), 1.0% by weight of styrene-butadiene rubber (SBR) binder (ZEON), and 1.0% by weight of carboxymethylcellulose (CMC, NIPPON A&L) After mixing, the mixture was added to distilled water and stirred for 60 minutes using a mechanical stirrer to prepare a negative electrode active material slurry. The slurry was applied to a thickness of about 60 μm on a copper current collector having a thickness of 10 μm using a doctor blade, dried for 0.5 hours in a hot air dryer at 100° C., and dried again for 4 hours under vacuum and 120° C. conditions, The negative electrode was manufactured by rolling press.

As the electrolyte, a solution containing 1.5M LiPF ₆ dissolved in a solvent in which ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed in a weight ratio of 2:2:6 was used. .

The separator obtained in Example 1 was interposed between the positive electrode and the negative electrode, and an electrolyte was injected to prepare a prismatic lithium secondary battery.

Production example 2-4

A lithium secondary battery was manufactured in the same manner as in Preparation Example 1, except that the separators of Examples 2 to 4 were used instead of the separator of Example 1.

Comparative Production Example 1-4

A lithium secondary battery was manufactured in the same manner as in Preparation Example 1, except that the separators of Comparative Examples 1 to 4 were used instead of the separator of Example 1, respectively.

Evaluation example 1: ventilation

According to Examples 1 to 4 and Comparative Examples 1 to 4, the unit thickness air permeability of each separator was measured according to the following method using an air permeability meter (Asahi Seiko OKEN Type Air Permeation Tester: EGO1-55-1MR).

After making 10 specimens cut at 10 different points to a size that can fit a circle with a diameter of 1 inch (inch), ASAHI SEIKO OKEN TYPE Air Permeation Tester EG01-55-1MR (Asahi Seiko G) was used to measure the time for 100 cc of air to pass through each of the specimens. Each of the above times was measured five times, and then the average value was calculated to measure the air permeability.

[Setting conditions for air permeability measurement device]

Measurement pressure: 0.05 mPa, cylinder pressure: 2.5 kg/㎠, set time: 10 seconds

The average of the data was recorded by measuring at least 10 times at 10cm intervals for a 1m specimen.

Evaluation example 2: shrinkage rate

The shrinkage of the separators prepared in Examples 1 to 4 and Comparative Examples 1 to 4 was evaluated according to the following method.

[Condition 1]

Each of the separators was cut into 10 different points with a width (MD) of 50 mm and a length (TD) of 50 mm to prepare 10 samples. Each of the samples was left in an oven at 150° C. for 1 hour, and then the degree of shrinkage in the MD direction and the TD direction of each sample was measured to calculate the average thermal contraction rate.

[Condition 2]

Each of the separators was cut into 10 different points with a width (MD) of 50 mm and a length (TD) of 50 mm to prepare 10 samples. Each sample was left in an oven at 200° C. for 10 minutes, and then the degree of shrinkage in the MD direction and the TD direction of each sample was measured to calculate the average thermal contraction rate.

Evaluation example 3: adhesion

The adhesion of the separators prepared in Examples 1 to 4 and Comparative Examples 1 to 4 is measured by evaluating the adhesion between the polyethylene film and the coating film, which is a porous substrate. Specifically, using a tension meter (Tinius Olsen, HT400), the separator was attached to an adhesive tape having a width of 10 mm, and then bent at 180° to measure the force (N) required to remove the tape from the separator.

Evaluation example 4: resistance

Resistance of the separators of Examples 1 to 4 and Comparative Examples 1 to 4 was evaluated by measuring an AC impedance.

The air permeability, shrinkage, adhesion and resistance characteristics of the separator measured according to the above process are shown in Table 1 below. For reference, the air permeability of the polyethylene membrane, which is a porous substrate used in Examples and Comparative Examples, is 124sec/100cc.

division
Example
One
Example
2
Example
3
Example
4
Comparative example
One
Comparative example
2
Comparative example
3
Comparative example
4 Ventilation
(sec/100cc) 280 201
195
190 527 304
187 282 Shrinkage (%) 150℃/1hr MD 42.1 32.2 34.2 25.6 38.2 28.1 64.2 48.1 TD 48.2 35.2 39.4 23.5 42.5 25.7 66.7 52.0 200℃/1hr MD 38.2 31.5 36.2 22.9 36.1 26.5 65.0 45.3 TD 40.5 34.7 37.8 23.9 37.9 27.1 66.9 47.8 Adhesion (g/mm) 3.906 3.024 2.659 3.212 1.276 2.812 0.876 1.129 Resistance (Ω·cm ² ) 15.1 14.3 13.8 14.0 19.7 17.8 13.2 15.9

As shown in Table 1, the separators of Examples 1 to 4 were prepared according to Comparative Examples 1-3.

Compared to the prepared separator, it was found that air permeability and shrinkage were improved while the resistance properties were improved by using a porous polyimide, while adhesion was not lowered.

The separator of Comparative Example 1 exhibited excellent shrinkage, but the air permeability, shrinkage rate, and resistance characteristics were decreased compared to the separators of Examples 1 to 4. And the separator of Comparative Example 2 was excellent in shrinkage, adhesion, and resistance, but air permeability did not reach the desired level, and the separator of Comparative Example 3 had good air permeability, adhesion and resistance characteristics, but the shrinkage rate characteristics were reduced. In addition, when conducted according to Comparative Example 4, the resistance characteristics of the separator were the same as those of Examples 1 to 4, but the air permeability, shrinkage rate, and adhesion were decreased.

Although the above description has been made with reference to the preferred manufacturing examples, those skilled in the art will appreciate that various modifications and changes can be made without departing from the spirit and scope described in the following claims.

10: separator 40: anode
50: cathode 60: electrode assembly
70: battery case 100: lithium secondary battery

Claims (11)

It is a separator for a secondary battery having a porous substrate and a coating film containing porous polyimide and inorganic particles disposed on at least one side of the porous substrate,
A separator for a secondary battery in which the mixing weight ratio of the porous polyimide and inorganic particles in the coating film is 1:1.5 to 1:8. The method of claim 1,
In the coating film containing the porous polyimide, the inorganic particles and the binder, the mixed weight ratio of the porous polyimide and the inorganic particles is 1:1.5 to 1:4. The method of claim 1,
The weight average molecular weight of the porous polyimide is 300,000 to 500,000,
A separator for secondary batteries having a porosity of 15 to 50% of the porous polyimide. The method of claim 1,
A separator for a secondary battery having a porosity of 40 to 50% of the coating film. The method of claim 1,
A separator for a secondary battery further comprising at least one binder selected from polyvinylidene fluoride and acrylic polymer. The method of claim 1,
The content of the inorganic particles is 10 to 20 parts by weight based on 100 parts by volume of the total weight of the separator,
A separator for a secondary battery having an average particle diameter of the inorganic particles of 0.1 μm or less. The method of claim 1,
The inorganic particles are boehmite, alumina, aluminum oxyhydroside (AlOOH), zirconia, yttria, ceria, magnesia, titania, silica, aluminum carbide, titanium carbide, tungsten carbide, boron nitride, aluminum nitride. A separator for a secondary battery comprising calcium carbonate, barium sulfate, aluminum hydroxide, magnesium hydroxide, or a combination thereof. The method of claim 1,
The air permeability of the separator is 170 to 280 sec/100cc, the shrinkage is 20 to 50%, the adhesive strength is 2.5 to 4.0g/mm, and the resistance is 13 to 20 (Ω·cm ² ). It includes the step of forming a coating film by coating and drying a composition for forming a coating film containing a porous polyimide, inorganic particles and a solvent on at least one surface of the porous substrate,
A method of manufacturing a separator for a secondary battery in which the mixed volume ratio of the porous polyimide and the inorganic particles in the coating membrane is 1:1.5 to 1:8, wherein the separator for a secondary battery according to any one of claims 1 to 8 is manufactured. The method of claim 9,
The method of manufacturing a separator for a secondary battery, wherein the coating film-forming composition further comprises at least one binder selected from polyvinylidene fluoride and acrylic polymers. anode; cathode; And a separator according to any one of claims 1 to 8 interposed between the positive electrode and the negative electrode.

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