KR20130073182A - A separator and electrochemical device having the same - Google Patents

Abstract

PURPOSE: A separator is provided to prevent emission of a flame retardant at room temperature by introducing a porous gel matrix, thereby preventing electrode reaction in an electric chemical device. CONSTITUTION: A separator includes an unwoven fabric substrate in which a porous gel matrix is formed inside thereof; and additionally includes a first porous coating layer which is formed in the outside of the nonwoven fabric and includes a crosslinking agent. The flame retardant includes at least one or more selected from a group consisting of trimethyl phosphate, triphenyl phosphate, and diphenyl octyl phosphate. An electrochemical device includes a positive electrode, negative electrode, separator inserted between the positive electrode and negative electrode, and electrolyte.

Description

Separator and electrochemical device having same {A SEPARATOR AND ELECTROCHEMICAL DEVICE HAVING THE SAME}

The present invention relates to a separator used in an electrochemical device such as a lithium secondary battery and an electrochemical device having the same, and more particularly, to a separator having a gel matrix containing a flame retardant on a nonwoven fabric substrate and an electrochemical device having the same. It is about.

Recently, interest in energy storage technology is increasing. As the application fields of cell phones, camcorders, notebook PCs and even electric vehicles are expanding, efforts for research and development of electrochemical devices are becoming more and more specified. Electrochemical devices have attracted the greatest attention in this respect, among which the development of rechargeable secondary batteries has become a focus of attention. In recent years, in order to improve the capacity density and specific energy in developing such batteries, And research and development on the design of the battery.

Among the currently applied secondary batteries, the lithium secondary battery developed in the early 1990s has advantages such as higher operating voltage and higher energy density than conventional batteries such as Ni-MH, Ni-Cd and sulfuric acid-lead batteries using an aqueous electrolyte solution . However, such a lithium ion battery has safety problems such as ignition and explosion when using an organic electrolytic solution, and it is disadvantageous in that it is difficult to manufacture. Recently, the lithium ion polymer battery has been considered as one of the next generation batteries by improving the weakness of the lithium ion battery, but the capacity of the battery is still relatively lower than that of the lithium ion battery, and the discharge capacity is improved due to insufficient discharge capacity at low temperatures. This is urgently needed.

In addition, such an organic electrolyte is to use a considerable amount of additives to improve the battery performance, due to the presence of these additives there is a problem that the electrode reaction is inhibited and the cycle characteristics are lowered. In particular, it is necessary to isolate the additive which needs to operate only when the battery reaches a high temperature so as not to participate in the reaction at room temperature.

Therefore, the problem to be solved by the present invention is to provide a separator that can achieve the isolation method of the additive to enable the additive to act selectively.

In order to solve the above problems, the present invention provides a separator comprising a non-woven substrate formed therein a porous gel matrix containing a flame retardant. The present invention may further include a first porous coating layer formed on an outer surface of the nonwoven fabric substrate and including a crosslinking agent. The separator of the present invention may further include a second porous coating layer formed on an outer surface of the first porous coating layer and including a mixture of inorganic particles and a polymer binder.

The kind of the porous gel matrix is not particularly limited, but may include gelatin, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene glycol, and the like. The flame retardant is not particularly limited in kind, but trimethyl phosphate, triphenyl phosphate, diphenyloctyl phosphate, and the like can be used.

The nonwoven substrate may be formed of polyester, polyacetal, polyamide, polycarbonate, polyimide, polyether ether ketone, polyether sulfone, polyphenylene oxide, polyphenylene sulfide, and polyethylene naphthalene. It is not specifically limited to this. The thickness of such a nonwoven substrate is 9 to 30 It is preferable to use one having a thickness of μm.

The inorganic particles used in the present invention are not particularly limited in kind, but inorganic particles having a dielectric constant of 5 or more, inorganic particles having a lithium ion transfer ability, and the like can be used. The inorganic particles having a dielectric constant of 5 or more include BaTiO ₃ , Pb (Zr _x , Ti _1-x ) O ₃ (PZT, 0 <x <1), Pb _{1 - x} La _x Zr _{1 -y} Ti _y O ₃ ( PLZT, 0 <x <1, 0 <y <1), (1-x) Pb (Mg _1/3 Nb _2/3 ) O ₃ -xPbTiO ₃ (PMN-PT, 0 <x <1), hafnia (HfO ₂ ), SrTiO ₃ , SnO ₂ , CeO ₂ , MgO, NiO, CaO, ZnO, ZrO ₂ , SiO ₂ , Y ₂ O ₃ , Al ₂ O ₃ , SiC, TiO _2, etc., are preferably used. It is not specifically limited to this. In addition, the inorganic particles having the lithium ion transport ability 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), lithium lanthanum titanate (Li _x La _y TiO _{3 ,} 0 <x <2, 0 <y <3), lithium germanium thiophosphate (Li _x Ge _y P _z S _w , 0 < x <4, 0 <y <1, 0 <z <1, 0 <w <5), Lithium Nitride (Li _x N _y , 0 <x <4, 0 <y <2), SiS ₂ (Li _x Si _y S _z , 0 <x <3, 0 <y <2, 0 <z <4) series glass and P ₂ S ₅ (Li _x P _y S _z , 0 <x <3, 0 <y <3, Although it is preferable to use 0 <z <7) series glass etc., it is not specifically limited to this.

Although the kind is not specifically limited as the polymeric binder of this invention, polyvinylidene fluoride-co-hexafluoropropylene (polyvinylidene fluoride-co-hexafluoropropylene), polyvinylidene fluoride- trichloroethylene (polyvinylidene fluoride-co- trichloroethylene), polymethylmethacrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, ethylene vinyl acetate copolymer ( polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, Cyanoethylflurane (cyanoe) thylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan and carboxyl methyl cellulose have.

Using the separator of the present invention, an electrochemical device including an anode, a cathode, a separator interposed between the anode and the cathode, and an electrolyte may be manufactured. The electrochemical device is preferably a lithium secondary battery.

The separator of the present invention can prevent the release of the flame retardant at room temperature by introducing a porous gel matrix containing a flame retardant, thereby preventing the electrode reaction in the electrochemical device can be prevented, thereby improving the performance of the electrochemical device. . In addition, when the electrochemical device reaches a high temperature, the flame retardant is released from the separator may contribute to secure the thermal safety of the electrochemical device.

Hereinafter, the present invention will be described in detail. The 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 appropriately define the concept of the term in order to best describe its invention It should be construed as meaning and concept consistent with the technical idea of the present invention.

The separator of the present invention comprises a nonwoven substrate having a porous gel matrix containing a flame retardant formed therein.

The separator of the present invention has a nonwoven base material having pores. Insulation on both electrodes is maintained due to the nonwoven substrate. The nonwoven substrate can be used as long as it is generally used as the substrate of the separator. Preferably, the microporous yarn having an average thickness of 0.5 to 10 um and more preferably 1 to 7 μm is used to form the longest diameter of the pores (the longest of the pores. It is preferable to form pores having a diameter) of 0.1 to 70 μm to include 50% or more based on the total number of pores. Nonwoven fabric having a large number of pores having a diameter of less than 0.1 μm is difficult to manufacture, and if the long diameter of the pore exceeds 70 μm, a problem of insulation degradation may occur due to the pore size. When the pores of the size described above are formed to contain 50% or more based on the total number of pores present in the nonwoven fabric, a separator suitable for high capacity electrochemical devices can be manufactured with good insulation.

The microfibers forming the nonwoven fabric base are polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyamides such as aramid, polyacetal, polycarbonate, polyimide, polyether ether ketone, poly It may be formed of ether sulfone, polyphenylene oxide, polyphenylene sulfide, polyethylene naphthalene and the like, but is not limited thereto. In particular, in order to improve the thermal stability of the nonwoven fabric base material, it is preferable that the melting temperature of the microfine yarn is 200 ° C or more. It is preferable that the thickness of a nonwoven fabric base material is 9-30 micrometers.

The porous gel matrix of the present invention is characterized in that the open three-dimensional pores are connected to each other by using the gel polymer as a matrix resin. The pores have an open structure connected in three dimensions. Such a porous gel matrix is prepared by applying or impregnating a gel polymer solution prepared by dissolving a gel polymer in a solvent to the nonwoven fabric and then drying. The gel polymer solution easily penetrates into pores in the nonwoven by capillary action. In addition, since the gel matrix of the present invention has an open structure, effective passage of lithium ions is possible.

Non-limiting examples of gel polymers that can be used include PVDF, PVDF copolymers (e.g. polyvinylidene fluoride-co-hexafluoropropylene, PVDF-co-HFP), polyvinylidene Polyvinylidene fluoride-co-trichloroethylene, PVDF-co-CTFE, etc.], gelatin, polyethylene glycol, carboxymethyl cellulose (CMC) polymer, polyethylene oxide (PEO) polymer, poly Acrylonitrile (polyacrylonitrile, PAN) polymer, polymethylmethacrylate (PMMA) polymer, or a mixture thereof. In addition, polyvinylpyrrolidone, polyvinylacetate, ethylene vinyl acetate copolymer, cellulose acetate, cellulose acetate butyrate, cellulose Cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan , Carboxyl methyl cellulose, acrylonitrile-styrene-butadiene copolymer, polyimide or mixtures thereof may also be used.

As the solvent for dissolving the gel polymer, it is preferable that the solubility index is similar to that of the gel polymer to be used, and the boiling point is low. This is to facilitate uniform mixing and subsequent solvent removal. Non-limiting examples of solvents that can be used include acetone, tetrahydrofuran, methylene chloride, chloroform, dimethylformamide, N-methyl-2-pyrrolidone (N-methyl-2-pyrrolidone, NMP), cyclohexane, or a mixture thereof.

And the gel matrix of the present invention contains a flame retardant.

The flame retardant serves to prevent the ignition of the electrochemical device at a high temperature, and generally inhibits the electrode reaction at room temperature. In the present invention, since the flame retardant is isolated inside the gel matrix, the electrode reaction is not inhibited at room temperature. In addition, when the electrochemical device reaches a high temperature, the structure of the gel matrix becomes fluid, and thus a flame retardant component isolated inside the gel matrix may be released to the outside, and the released flame retardant may prevent ignition of the electrochemical device. Can be.

As such flame retardant, trimethyl phosphate, triphenyl phosphate, diphenyloctyl phosphate and the like can be used.

The separator of the present invention may further include a first porous coating layer formed on an outer surface of the nonwoven fabric substrate and including a crosslinking agent. The first porous coating layer may be formed by applying or impregnating a crosslinking agent solution in which a crosslinking agent is dissolved in a solvent to the surface of a nonwoven fabric having a gel matrix. The first porous coating layer including the crosslinking agent may serve to control the temperature at which the gel matrix releases the flame retardant. As such a crosslinking agent, glutaraldehyde, isopropyl acrylamide, pentaerythritol tetraacrylate, or the like can be used.

The separator of the present invention may further include a second porous coating layer formed on an outer surface of the first porous coating layer and including a mixture of inorganic particles and a polymer binder. The inorganic particles included in the second porous coating layer are connected to and fixed to each other by the polymer binder, and the pores formed due to the interstitial volume formed between the inorganic particles in substantially contact with each other exist in the second porous coating layer. Done. Even when the nonwoven fabric substrate is partially damaged during thermal runaway of the electrochemical device, the porous coating layer maintains its shape as it is, and thus short circuit between the anode and the cathode can be suppressed, thereby improving the safety of the electrochemical device.

The inorganic particles used to form the second porous coating layer are not particularly limited as long as they are electrochemically stable. That is, the inorganic particles usable in the present invention are not particularly limited as long as oxidation and / or reduction reaction does not occur in the operating voltage range of the applied electrochemical device (for example, 0 to 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.

The inorganic particles are preferably used inorganic particles selected from the group consisting of inorganic particles having a dielectric constant of 5 or more, inorganic particles having a lithium ion transfer ability, and mixtures thereof.

The inorganic particles having a dielectric constant of 5 or more include BaTiO ₃ , Pb (Zr _x , Ti _{1 -x} ) O ₃ (PZT, 0 <x <1), Pb _{1 - x} La _x Zr _{1 -y} Ti _y O ₃ ( PLZT, 0 <x <1, 0 <y <1), (1-x) Pb (Mg 1/3 Nb 2/3) O 3 -xPbTiO 3 (PMN-PT, 0 <x <1), hafnia (HfO ₂ ), SrTiO ₃ , SnO ₂ , CeO ₂ , MgO, NiO, CaO, ZnO, ZrO ₂ , SiO ₂ , Y ₂ O ₃ , Al ₂ O ₃ , SiC, TiO _2, etc., are preferably used. It is not specifically limited to this. In addition, the inorganic particles having the lithium ion transport ability 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), lithium lanthanum titanate (Li _x La _y TiO _{3 ,} 0 <x <2, 0 <y <3), lithium germanium thiophosphate (Li _x Ge _y P _z S _w , 0 < x <4, 0 <y <1, 0 <z <1, 0 <w <5), Lithium Nitride (Li _x N _y , 0 <x <4, 0 <y <2), SiS ₂ (Li _x Si _y S _z , 0 <x <3, 0 <y <2, 0 <z <4) series glass and P ₂ S ₅ (Li _x P _y S _z , 0 <x <3, 0 <y <3, Although it is preferable to use 0 <z <7) series glass etc., it is not specifically limited to this.

Although the kind is not specifically limited as the polymeric binder of this invention, polyvinylidene fluoride-co-hexafluoropropylene (polyvinylidene fluoride-co-hexafluoropropylene), polyvinylidene fluoride- trichloroethylene (polyvinylidene fluoride-co- trichloroethylene), polymethylmethacrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, ethylene vinyl acetate copolymer ( polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, Cyanoethylflurane (cyanoe) thylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan and carboxyl methyl cellulose have.

The separator of the present invention is interposed between the positive electrode and the negative electrode to manufacture an electrochemical device. In this case, when a gelable polymer is used when the liquid electrolyte solution is impregnated with the binder polymer component, after the battery is assembled using the separator, the injected electrolyte solution and the polymer may react and gelate.

The electrochemical device of the present invention includes all devices that undergo an electrochemical reaction, and specific examples include capacitors such as all kinds of primary, secondary cells, fuel cells, solar cells, or supercapacitor elements. . Particularly, 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.

In the electrochemical device of the present invention, an electrolyte in which a salt having a structure such as A ⁺ B ⁻ is dissolved in an organic solvent may be selectively used. Wherein, A ⁺ is Li ^+, Na ^+, and comprising an alkali metal cation or an ion composed of a combination thereof, such as K ^+, B ^- is _{^{PF 6 -, BF 4 -,}} Cl -, Br -, I -, ClO _{^{4 -, AsF 6 -, CH}} 3 CO 2 -, CF 3 SO 3 -, N (CF 3 SO 2) 2 -, C (CF 2 SO 2) 3 - and include such anions or an ion composed of a combination of do. Organic solvents include propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane , Tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethylmethylcarbonate (EMC), gamma butyrolactone or mixtures thereof, but is not limited thereto.

The injection of the electrolyte may be performed at an appropriate step in the battery manufacturing process, depending on the manufacturing process and the required physical properties of the final product. That is, it can be applied before assembling the cell or at the final stage of assembling the cell.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with reference to examples. However, the embodiments according to the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The embodiments of the present invention are provided to enable those skilled in the art to more fully understand the present invention.

Example

Example  One. Flame retardant  Nonwoven Fabric With Gel Matrix Including Separator

After preparing an aqueous solution using gelatin as a gel polymer, trimethyl phosphate was added to the solution as a flame retardant to prepare a gel polymer solution.

The surface of the nonwoven fabric was coated with the gel polymer solution using a doctor blade.

After drying the nonwoven fabric coated with the gel polymer solution, a glutar aldehyde solution was applied with a crosslinking agent and then dried to prepare a separator.

Example  2. further comprising an organic-inorganic porous coating layer, Flame retardant  Nonwoven Fabric With Gel Matrix Including Separator

A solution in which a mixture of alumina particles and PVdF-co-HFP was dispersed in acetone was applied to the surface of the separator prepared in Example 1 to prepare a separator on which an organic-inorganic porous coating layer was formed.

Test Example  1. At room temperature In the separator  The release of flame retardants

In the separator prepared in Example 1-2, it was confirmed by gas chromatography whether the flame retardant was released at room temperature (25 ° C.), and there was no outflow of the flame retardant.

Test Example  2. at high temperature In the separator  The release of flame retardants

It was confirmed by gas chromatography whether the flame retardant was released at a high temperature (100 ° C.) in the separator prepared in Example 1-2. As the temperature of the separator was increased, it was confirmed that the flame retardant was released to exhibit a flame retardant effect.

Claims (14)

A separator comprising a nonwoven substrate having a porous gel matrix containing a flame retardant formed therein. The method of claim 1,
The separator is formed on the outer surface of the nonwoven fabric substrate, characterized in that it further comprises a first porous coating layer comprising a crosslinking agent. The method of claim 2,
A separator formed on an outer surface of the first porous coating layer, further comprising a second porous coating layer including a mixture of inorganic particles and a polymer binder. The method of claim 1,
The porous gel matrix is any one selected from the group consisting of gelatin, polyvinylidene fluoride polymer and polyethylene oxide. The method of claim 1,
The flame retardant is at least one separator selected from the group consisting of trimethyl phosphate, triphenyl phosphate and diphenyloctyl phosphate. The method of claim 1,
The nonwoven substrate is any one polymer selected from the group consisting of polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene oxide, polyphenylene sulfide, and polyethylene naphthalene Or a separator formed of a mixture of two or more of them. The method of claim 1,
The thickness of the nonwoven fabric substrate is 9 to 30 ㎛ separator. The method of claim 2,
The crosslinking agent is at least one selected from the group consisting of glutaraldehyde, isopropyl acrylamide and pentaerythritol tetraacrylate. The method of claim 3,
The inorganic particles further comprise inorganic particles selected from the group consisting of inorganic particles having a dielectric constant of 5 or more, inorganic particles having lithium ion transfer ability, and mixtures thereof. 10. The method of claim 9,
The inorganic particles having a dielectric constant of 5 or more include BaTiO ₃ , Pb (Zr _x , Ti _{1 -x} ) O ₃ (PZT, 0 <x <1), Pb _{1 - x} La _x Zr _{1 -y} Ti _y O ₃ (PLZT hafnia, 0 <x <1, 0 <y <1), (1-x) Pb (Mg 1/3 Nb 2/3) O 3 -xPbTiO 3 (PMN-PT, 0 <x <1), ( HfO ₂ ), SrTiO ₃ , SnO ₂ , CeO ₂ , MgO, NiO, CaO, ZnO, ZrO ₂ , SiO ₂ , Y ₂ O ₃ , Al ₂ O ₃ , SiC and TiO ₂ A separator, characterized in that the particles or a mixture of two or more thereof. 10. The method of claim 9,
The inorganic particles having a lithium ion transfer ability include lithium phosphate (Li ₃ PO ₄ ), lithium titanium phosphate (Li _x Ti _y (PO ₄ ) ₃ , 0 <x <2, 0 <y <3), and 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), lithium lanthanum titanate (Li _x La _y TiO _{3 ,} 0 <x <2, 0 <y <3), lithium germanium thiophosphate (Li _x Ge _y P _z S _w , 0 <x <4 , 0 <y <1, 0 <z <1, 0 <w <5), lithium nitride (Li _x N _y , 0 <x <4, 0 <y <2), SiS ₂ (Li _x Si _y S _z , 0 <x <3, 0 <y <2, 0 <z <4) Series glass and P ₂ S ₅ (Li _x P _y S _z , 0 <x <3, 0 <y <3, 0 <z <7) Any one inorganic particle selected from the group consisting of series glass or a mixture of two or more thereof. The method of claim 3,
The polymer binder may be polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethylmethacrylate, Polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, ethylene vinyl acetate copolymer, polyethylene oxide oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, cyanoethyl Polyvinyl alcohol (cyanoethylpolyviny) lalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, and carboxyl methyl cellulose, any one binder polymer selected from the group consisting of two or more thereof Separator, characterized in that the mixture. In the electrochemical device comprising a positive electrode, a negative electrode, a separator and an electrolyte interposed between the positive electrode and the negative electrode,
The separator is an electrochemical device according to any one of claims 1 to 12. The method of claim 13,
Wherein the electrochemical device is a lithium secondary battery.