KR101796281B1 - Separator for electrochemical device comprising core-shell fillers, electrochemical device comprising the same, and method for preparing the separator - Google Patents

Abstract

The present invention relates to a separator for an electrochemical device including core-shell particles, an electrochemical device including the same, and a process for producing the separator. According to an aspect of the invention, the inorganic particle core (core), and is covered on the surface of the core, the melting point (T _m) is a number of cores comprising a shell (shell) of 170 ℃ than polymer-shell structure And a porous particle layer in which the particles are bonded to each other by fusion between the shells. The separator according to one aspect of the present invention exhibits a shutdown function by the shell structure when the combination with the porous particle layer separator or the porous substrate thereof is out of the normal operating temperature range of the cell, Safety can be maintained.

Description

TECHNICAL FIELD [0001] The present invention relates to a porous polyolefin separator comprising a filler of a core-shell structure, an electrochemical device including the same, and a separator for electrochemical device comprising core-shell fillers,

The present invention relates to a porous polyolefin separator comprising a filler of a core-shell structure, an electrochemical device comprising the same, and a process for producing the separator.

Recently, interest in energy storage technology among electrochemical devices is increasing. The development of rechargeable secondary batteries, especially lithium secondary batteries, has become a focus of attention as the application fields of cell phones, camcorders, laptops and even electric vehicles expand.

However, the porous separator of the secondary battery exhibits extreme heat shrinkage behavior at a temperature of about 100 캜 or more due to the characteristics of the manufacturing process including material properties and elongation, thereby causing a short circuit between the anode and the cathode. In order to solve the safety problem of such a battery, for example, Korean Patent Laid-Open Publication No. 2007-0083975 and Korean Patent Publication No. 2007-0019958 disclose a method in which a porous coating layer formed of a mixture of insulating filler particles and a binder polymer is provided on a porous substrate , And a material having a shut-down function is added to the porous coating layer. There still exists a demand for a separator excellent in structural and thermal stability in an electrochemical device such as a secondary cell.

Accordingly, it is an object of the present invention to provide a separation membrane having excellent structural and thermal stability, an electrochemical device including the separation membrane, and a process for producing the separation membrane.

According to an aspect of the present invention, there is provided a method of manufacturing a semiconductor device, comprising the steps of: forming a core of inorganic particles having a dielectric constant of 5 or more; coating a plurality of surfaces of the core with a shell of a high heat- Wherein the fillers of the core-shell structure of the porous polyolefin substrate are disposed in a porous polyolefin substrate.

According to another aspect of the present invention, a method for forming a plurality of core-shell structure fillers by preparing a plurality of inorganic particles having a dielectric constant of 5 or more, and coating the surface of the inorganic particles with a high heat resistant polymer by a chemical or physical coating method ; Forming a polyolefin solution by dissolving the polyolefin in a solvent; Mixing the polyolefin solution with the filler of the core-shell structure and stirring to form a base solution in which the filler is uniformly dispersed; And removing the solvent from the base solution. The present invention also provides a method for producing a porous polyolefin separator.

Other objects and advantages of the present invention will become apparent from the following description. It is also to be easily understood that the objects and advantages of the present invention can be realized by the means or method described in the claims, and the combination thereof.

The porous polyolefin separator according to one aspect of the present invention can improve heat resistance and electrical resistance as well as improve thermal and mechanical properties by the filler having a core-shell structure contained therein.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.
1 is an example of a filler of the core-shell structure of the present invention.

Hereinafter, the present invention will be described in detail. Prior to this, terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms, and the inventor may designate the concept of a term appropriately in order to describe its own invention in the best way possible. It should be interpreted as meaning and concept consistent with the technical idea of the present invention. Therefore, the embodiments described in this specification and the configurations shown in the drawings are merely the most preferred embodiments of the present invention and do not represent all the technical ideas of the present invention. Therefore, It is to be understood that equivalents and modifications are possible.

According to an aspect of the present invention, there is provided a porous polyolefin separator in which a plurality of core-shell structure fillers are disposed in a porous polyolefin substrate.

1 is an example of a filler of the core-shell structure of the present invention. Referring to FIG. 1, the filler of the core-shell structure is composed of a core and a shell coated on the surface of the core. The core is made of inorganic particles having a dielectric constant of 5 or more, preferably 10 or more, and the shell is made of a high heat-resistant polymer.

The inorganic particles may be inorganic particles having a dielectric constant of about 5 or more. The inorganic particles should not undergo oxidation and / or reduction reactions in the operating voltage range of the applied secondary battery (e.g., about 0 to about 5 V based on Li / Li ⁺ ). Particularly, when inorganic particles having a high dielectric constant are used as the inorganic particles, the dissociation of the electrolyte salt, for example, the lithium salt in the liquid electrolyte, can be increased, and the ion conductivity of the electrolyte can be improved. For the reasons stated above, it is preferred that the inorganic particles comprise high-permittivity inorganic particles having a dielectric constant of at least about 5, preferably inorganic particles having a dielectric constant of at least about 10. Non-limiting examples of a dielectric constant of about 5 or more inorganic particles, _{MgO, ZnO, ZrO 2, Al} 2 O 3 Or it may be selected from the group consisting of TiO _2.

The average particle size of the inorganic particles is not limited, but may be about 0.01 to about 0.9 占 퐉 as possible for the formation of a porous particle layer of uniform thickness and proper porosity. When the average particle size of the inorganic particles is in the range of about 0.01 to about 0.9 占 퐉, a separation membrane which does not have a problem of short-circuiting and an increase in separation membrane thickness is formed together with excellent dispersibility of the inorganic particles in addition to the high- .

The high heat-resistant polymer constituting the shell structure of the present invention is a polymer having a melting point (T _m ) of from about 100 캜 to about 250 캜, preferably from about 170 캜 to about 200 캜.

The high heat-resistant polymer may be at least one selected from the group consisting of polypropylene (PP), polyethylene terephthalate (PET), polyester, polyacetal, polyamide, polycarbonate, polyimide Polyetheretherketone, polyetherimide (PEI), polyamideimide, polyethersulfone (PES), polyphenylene oxide, polyphenylenesulfide, polyphenylene sulfide, And polyethylenenaphthalene, but are not limited thereto. Preferably, the high heat-resistant polymer is polypropylene (PP) or polyethylene terephthalate (PET).

The porous polyolefin substrate is not limited to polyethylene, for example, high density polyethylene, linear low density polyethylene, low density polyethylene or ultrahigh molecular weight polyethylene, polypropylene, polybutylene, polypentene and the like, or a combination of two or more thereof And the polyolefin substrate may have a porous structure by forming pores by a wet process known in the art.

Such a porous polyolefin substrate may be provided with various functions depending on the material thereof as a separation membrane. For example, in the case of polyethylene (PE) as the porous polyolefin substrate, the melting point thereof is approximately 105 to 140 ° C, so that a shutdown function can be imparted to the electrochemical device. The porous polyolefin substrate may have a thickness of from about 1 to about 20 microns.

The content of the filler may be 0.1 to 30 parts by weight, preferably 20 parts by weight or less, more preferably 10 parts by weight or less, based on 100 parts by weight of the total weight of the porous polyolefin separator.

The shell thickness of the high heat-resistant polymer is about 1 to about 10% based on the average radius of the inorganic particles.

In addition, the average particle diameter of the filler of the core-shell structure may be about 0.1 to about 1 mu m.

As a method of coating the surface of the inorganic particles with the high heat-resistant polymer, there is a chemical coating method or a physical coating method. The chemical coating method includes, but is not limited to, a polymerization method such as a catalytic polymerization method using a catalyst on the surface of inorganic particles, a method of bonding a high heat resistant polymer by surface treatment of inorganic particles, a chemical vapor deposition (CVD) The same chemical deposition. On the other hand, as the physical coating method, a conventional coating method of coating the surface of inorganic particles with a high heat-resistant polymer such as a melt spin coating, solution spin coating or electrospin coating, a method of bonding a high heat resistant polymer by heat fusion, Physical deposition such as physical vapor deposition (PVD), and the like.

Also, the above-mentioned porous polyolefin separator, a base film, a coating layer thereof, or other positive electrodes, cathodes, and electrolytes are as well known in the art, and they are commercially available, or are known in the art And can be easily produced by a process and / or method.

The separation membrane for an electrochemical device configured as a separation membrane or a coating layer for an electrochemical device of the porous particle layer of the present invention is interposed between a cathode and an anode to be manufactured from an electrochemical device.

According to the present invention, the negative electrode active material can be manufactured into a negative electrode according to a manufacturing method commonly used in the art. Also, the anode according to the present invention can be produced by a conventional method in the art, like the cathode. For example, the negative electrode active material of the present invention can be prepared by mixing and stirring a binder and a solvent, if necessary, with a conductive material and a dispersing agent to prepare a slurry, applying the slurry to a current collector, and compressing the electrode.

Accordingly, the present invention also provides a negative electrode for a lithium secondary battery comprising a current collector and a negative electrode active material layer formed on at least one surface of the current collector, the negative electrode active material comprising lithium A negative electrode for a secondary battery is provided.

Examples of the binder include vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, A wide variety of polymers can be used.

As the cathode active material, a lithium-containing transition metal oxide may be preferably used. For example, Li _x CoO ₂ (0.5 <x <1.3), Li _x NiO ₂ (0.5 <x <1.3), Li _x MnO _{2 x <1.3), Li x Mn} 2 O 4 (0.5 <x <1.3), Li x (Ni a Co b Mn c) O 2 (0.5 <x <1.3, 0 <a <1, 0 <b <1, Li _x Co _{1- y} Mn _y O ₂ (where 0 <c <1, a + b + c = 1), Li _x Ni _1-y Co _y O ₂ 0.5 <x <1.3, 0≤y < 1), Li x Ni 1 -y Mn y O 2 (0.5 <x <1.3, O≤y <1), Li x (Ni a Co b Mn c) O 4 ( (0.5 <x <1.3, 0 <a <2, 0 <b <2, 0 <c <2, a + b + c = 2), Li _x Mn _{2 -z} Ni _z O ₄ (0.5 <x <1.3, 0 <z <2), Li _x CoPO ₄ (0.5 <x <1.3) and Li _x FePO ₄ (0.5 <z <2), Li _x Mn _{2 -z} Co _z O ₄ x < 1.3), or a mixture of two or more thereof. The lithium-containing transition metal oxide may be coated with a metal such as aluminum (Al) or a metal oxide. In addition to the lithium-containing transition metal oxide, sulfide, selenide and halide may also be used.

When the electrode is manufactured, a lithium secondary battery having a separator interposed between the positive electrode and the negative electrode and an electrolyte, which is conventionally used in the art, can be manufactured using the electrode.

Accordingly, in the present invention, it is possible to provide a lithium secondary battery comprising a positive electrode, the negative electrode described above, and a separator interposed between the positive electrode and the negative electrode.

In the electrolyte used in the present invention, the lithium salt that may be included as the electrolyte may be any of those conventionally used in an electrolyte for a lithium secondary battery. For example, examples of the anion of the lithium salt include F ^- , Cl ^- , Br ^{- _{, I -, NO 3 -,}} N (CN) 2 -, BF 4 -, ClO 4 -, PF 6 -, (CF 3) 2 PF 4 -, (CF 3) 3 PF 3 -, (CF 3) 4 _{^{PF 2 -, (CF 3)}} 5 PF -, (CF 3) 6 P -, CF 3 SO 3 -, CF 3 CF 2 SO 3 -, (CF 3 SO 2) 2 N -, (FSO 2) 2 N _{^{-, CF 3 CF 2 (CF}} 3) 2 CO -, (CF 3 SO 2) 2 CH -, (SF 5) 3 C -, (CF 3 SO 2) 3 C -, CF 3 (CF 2) 7 SO ₃ ^- , CF ₃ CO ₂ ^- , CH ₃ CO ₂ ^- , SCN ^- and (CF ₃ CF ₂ SO ₂ ) ₂ N ^- .

As the organic solvent contained in the electrolytic solution used in the present invention, the organic solvent commonly used for the electrolyte for a lithium secondary battery can be used without limitation, and examples thereof include propylene carbonate (PC), ethylene carbonate (ethylene carbonate) EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl propyl carbonate, dipropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxy Ethane, vinylene carbonate, sulfolane, gamma-butyrolactone, propylene sulfite, and tetrahydrofuran, or a mixture of two or more thereof. In particular, ethylene carbonate and propylene carbonate, which are cyclic carbonates in the carbonate-based organic solvent, can be preferably used because they have high permittivity as a high-viscosity organic solvent and dissociate the lithium salt in the electrolyte well. To such a cyclic carbonate, dimethyl carbonate and diethyl When a low viscosity, low dielectric constant linear carbonate such as carbonate is mixed in an appropriate ratio, an electrolyte having a high electric conductivity can be prepared, and thus it can be more preferably used.

Alternatively, the electrolytic solution stored in accordance with the present invention may further contain additives such as an overcharge inhibitor or the like contained in a conventional electrolytic solution.

The electrochemical device according to one aspect of the present invention includes all devices that perform an electrochemical reaction, and specific examples thereof include capacitors such as all types of primary cells, secondary cells, fuel cells, solar cells, or super capacitor devices ). In particular, the secondary battery may be 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.

According to a further aspect of the present invention there is provided a method of forming a core-shell structure comprising the steps of forming a filler in a core-shell structure (S1), forming a polyolefin solution (S2), forming a base solution (S3) A process for producing a polyolefin separator is provided.

In the step S1, a plurality of inorganic particles are prepared in the step of forming the filler of the core-shell structure, and the surface of the plurality of inorganic particles is coated with the high heat-resistant polymer.

The description of the inorganic particles and the high heat-resistant polymer to be used here is the same as described above in connection with the porous polyolefin separator. In addition, the coating method is a chemical or physical coating method, and a description of this coating method is also as described above with respect to the porous polyolefin separator.

In step S2, a polyolefin solution is formed by dissolving the polyolefin in a solvent. The polyolefin is as hereinbefore described with respect to the polyolefin substrate with respect to the porous polyolefin separator.

The solvent may be selected from the group consisting of acetone, tetrahydrofuran, methylene chloride, chloroform, dimethylformamide, N-methyl-2-pyrrolidone, pyrrolidone, NMP), cyclohexane, and water, or a mixture of two or more thereof.

In step S3, a plurality of core-shell structure fillers formed in step S1 were mixed and stirred in the polyolefin solution formed in step S2. By such mixing and stirring, a base solution in which the filler is uniformly dispersed is formed.

It may further comprise pore-forming agents conventionally used in wet processes for making membranes in the art. The pore-forming agent used in the present invention is a material which is dispersed in polymer particles and exhibits a heterogeneity of a film produced through extrusion, drawing and the like, and is subsequently removed from such a film. Therefore, the site where the pore-forming agent is located in the polymer of the membrane remains in the form of pores. The pore former is preferably a liquid material in the extrusion process, but a material that maintains a solid state may be used.

The pore-forming agent may be an aliphatic hydrocarbon-based solvent such as liquid paraffin, paraffin oil, mineral oil or paraffin wax; Vegetable oils such as soybean oil, sunflower oil, rapeseed oil, palm oil, palm oil, coconut oil, corn oil, grape seed oil, cotton seed oil and the like; Or a plasticizer such as a dialkyl phthalate. In particular, the plasticizer is selected from the group consisting of di-2-ethylhexyl phthalate (DOP), di-butyl phthalate (DBP), di- isononyl phthalate Di-isodecyl phthalate (DIDP), butyl benzyl phthalate (BBP), and the like. Of these, liquid paraffin (LP, also referred to as &quot; liquid paraffin &quot;) is particularly preferable.

In addition, the content of such pore-former may be from about 50 to about 80 wt% based on the total amount of polyolefin substrate, solvent, filler and pore-former. When the content of the pore-forming agent falls within this limited range, pores are produced in a desired range, for example, a pore size of about 38% or more and / or a pore size of about 20 m or less, about 400 sec / 100 cc or less.

Further, the base solution can be extruded through an extruder. The extruder may be a twin-screw extruder and the temperature of the extrusion process may be from about 160 to about 240 &lt; 0 &gt; C. Through this extrusion process, an extruded sheet is formed.

The extruded sheet thus formed may be subjected to a stretching process. This stretching process results in the formation of a stretched film having improved mechanical strength.

The stretching process is carried out in machine direction (MD), machine direction, longitudinal direction) and / or transverse direction (TD), vertical direction. The tensile strength in the stretching direction is increased by the stretching process in all of these, or one of them. If desired, the separator of the present invention can be subjected to longitudinal (MD) stretching and / or transverse (TD) stretching alone (e.g., uniaxially stretching), simultaneously or sequentially (e.g., biaxially stretching) .

When a pore-forming agent is used, this pore-forming agent can be removed using a solvent. Specifically, the pore-former present in the stretched film is removed, for example, by extraction and drying with a solvent in one or more extraction tanks used. In addition, through this removal, the space occupied by the pore former is formed as pores.

In step S4, the solvent is removed from the base solution formed in step S3.

In addition, the anodes, cathodes, and electrolytes other than the above-described separator are as known in the art and they are commercially available or can be easily prepared by processes and / or methods known in the art have.

The separator of the present invention is interposed between the positive electrode and the negative electrode and is made of a secondary battery. In addition, the secondary battery of the present invention may be 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.

Claims (14)

A core of inorganic particles having a dielectric constant of 5 or more and a plurality of core-shell structure fillers coated on the surface of the core and comprising a shell of a high heat resistant polymer are disposed in the porous polyolefin substrate Wherein the high heat-resistant polymer is at least one selected from the group consisting of polyamide, polycarbonate, polyimide, polyetheretherketone, polyetherimide (PEI), polyamideimide ) Or a mixture of two or more selected from the group consisting of polyethersulfone (PES), polyphenylene oxide, polyphenylenesulfide, and polyethylene naphthalene. Polyolefin separator.
The method according to claim 1,
The inorganic particles are _{MgO, ZnO, ZrO 2, Al} 2 O 3 Or TiO &lt; ₂ &gt;. &Lt; / RTI &gt; delete The method according to claim 1,
Wherein the shell thickness of the high heat-resistant polymer is 1 to 10% based on the average radius of the inorganic particles.
The method according to claim 1,
Wherein the filler has an average particle diameter of 0.1 to 1 占 퐉.
The method according to claim 1,
Wherein the porous polyolefin substrate is formed of one selected from the group consisting of polyethylene, polypropylene, polybutylene, and polypentene, or a combination of two or more thereof.
An electrochemical device comprising the anode, the cathode, and the porous polyolefin separator of claim 1, 2, 4, 5, or 6 interposed between the anode and the cathode.
8. The method of claim 7,
Wherein the electrochemical device is a lithium secondary battery.
Preparing a plurality of inorganic particles having a dielectric constant of 5 or more and coating the surface of the inorganic particles with a high heat resistant polymer by a chemical or physical coating method to form a filler of a plurality of core-shell structures;
Forming a polyolefin solution by dissolving the polyolefin in a solvent;
Mixing the polyolefin solution with the filler of the core-shell structure and stirring to form a base solution in which the filler is uniformly dispersed; And
Removing the solvent from the base solution
/ RTI &gt;
The high-temperature-resistant polymer may be at least one selected from the group consisting of polyamide, polycarbonate, polyimide, polyetheretherketone, polyetherimide (PEI), polyamideimide, wherein the porous polyolefin membrane is one or a mixture of two or more selected from the group consisting of polyethersulfone (PES), polyphenylene oxide, polyphenylenesulfide, and polyethylene naphthalene. .
10. The method of claim 9,
Wherein the inorganic particles are selected from the group consisting of MgO, ZnO, ZrO ₂ , Al ₂ O ₃ , and TiO ₂ .
delete delete 10. The method of claim 9,
Wherein the polyolefin is at least one selected from the group consisting of polyethylene, polypropylene, polybutylene, and polypentene, or a combination of two or more thereof.
10. The method of claim 9,
Wherein the solvent is selected from the group consisting of acetone, tetrahydrofuran, methylene chloride, chloroform, dimethylformamide, N-methyl-2-pyrrolidone, wherein the porous polyolefin separator is a mixture of at least one selected from the group consisting of N-methylpyrrolidone (NMP), cyclohexane, and water.

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