KR101903189B1 - A separator, the manufacturing method thereof, and electrochemical device containing the same - Google Patents

Abstract

The separator of the present invention comprises a porous substrate having pores; A porous organic-inorganic coating layer formed on at least one surface of the porous substrate, the porous organic-inorganic coating layer including a mixture of inorganic particles and a binder polymer; And a poly dopamine coating layer dispersed so as to have a plurality of uncoated regions scattered on the surface of the organic-inorganic coating layer. INDUSTRIAL APPLICABILITY The separator of the present invention improves the binding force with the electrode, and exhibits the effect of improving the interfacial adhesion with the electrode and the wettability of the electrolyte. Accordingly, the safety, power density and cycle characteristics of the electrochemical device including the separator can be improved.

Description

TECHNICAL FIELD [0001] The present invention relates to a separator, a method of manufacturing the separator, and an electrochemical device having the separator,

The present invention relates to a separator of an electrochemical device such as a lithium secondary battery, a method for producing the separator, and an electrochemical device having the separator. More particularly, the present invention relates to a separator for a porous organic- And an electrochemical device having the separator.

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. The electrochemical device is one of the most sought-after fields in this respect, and development of a rechargeable battery capable of charging and discharging is the focus of attention. In recent years, in order to improve the capacity density and specific energy in the development of such a battery, research and development on the design of a new electrode and a battery have been carried out.

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.

Such electrochemical devices are produced in many companies, but their safety characteristics are different. It is very important to evaluate the safety and safety of such an electrochemical device. The most important consideration is that the electrochemical device should not injure the user in case of malfunction. For this purpose, the safety standard strictly regulates the ignition and fuming in the electrochemical device. In the safety characteristics of the electrochemical device, there is a high possibility that the electrochemical device is overheated and thermal explosion occurs or an explosion occurs when the separator is penetrated. Particularly, a polyolefin-based porous substrate commonly used as a separator of an electrochemical device exhibits extreme heat shrinkage behavior at a temperature of 100 DEG C or higher owing to the characteristics of the manufacturing process including material properties and elongation, . ≪ / RTI >

In order to solve the safety problem of such an electrochemical device, Korean Patent Laid-Open Publication No. 10-2007-231 discloses a method of coating a porous organic-inorganic hybrid material by coating a mixture of inorganic particles and a binder polymer on at least one surface of a porous substrate having a plurality of pores, A separator in which an inorganic coating layer is formed has been proposed. In the separator, the inorganic particles in the porous organic-inorganic coating layer coated on the porous substrate serve as a kind of spacer capable of maintaining the physical form of the porous organic-inorganic coating layer, so that the porous substrate is thermally shrunk . In addition, interstitial volumes exist between the inorganic particles to form micropores.

In this way, the porous organic-inorganic coating layer on the porous substrate greatly contributes to the improvement of the safety of the separator. However, in order for the porous organic-inorganic coating layer to suppress the heat shrinkage of the porous substrate, it is necessary to sufficiently contain the inorganic particles in a predetermined amount or more have. However, as the content of the inorganic particles increases, the content of the binder polymer becomes relatively small. Therefore, there is a possibility that the inorganic particles are desorbed by the stress generated in the assembling process of the electrochemical device due to deterioration of the bondability with the electrode. These desorbed inorganic particles act as local defects of the electrochemical device, adversely affecting the safety of the electrochemical device. In addition, if the both electrodes and the separator are not sufficiently adhered to each other, the performance of the electrochemical device may deteriorate. On the other hand, if the electrolytic solution is not easily dispersed in the porous organic-inorganic coating layer of the separator in the electrochemical device, there is a possibility that the electrolyte wettability characteristic becomes poor. Thus, the manufacturing process may be time-consuming and costly. Particularly, in manufacturing a large-capacity battery, it takes a long time to inject the electrolyte, so a solution is also needed.

SUMMARY OF THE INVENTION Accordingly, the present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a porous organic electrochemical device having improved adhesion to electrodes and improved safety of an electrochemical device, improved interfacial adhesion between a separator and an electrode, A separator having an inorganic coating layer, and an electrochemical device having the separator.

It is another object of the present invention to provide a method for easily manufacturing a separator having the above-mentioned object.

In order to solve the above problems, the separator of the present invention comprises

A porous substrate having pores;

A porous organic-inorganic coating layer formed on at least one surface of the porous substrate, the porous organic-inorganic coating layer including a mixture of inorganic particles and a binder polymer; And

And a poly-dopamine coating layer dispersed so as to have a plurality of uncoated regions scattered on the surface of the organic-inorganic coating layer.

In the separator of the present invention, the area of the polypodamine coating layer is preferably 5 to 80%, more preferably 10 to 60%, of the entire surface of the organic-inorganic coating layer. The thickness of the polypodamine coating layer is preferably 1 to 200 nm, more preferably 20 to 100 nm.

In the method for producing a separator of the present invention,

(S1) preparing a porous substrate having pores;

(S2) coating a coating solution in which inorganic particles are dispersed and a binder polymer dissolved in a solvent on at least one surface of the porous substrate and drying to form a porous organic-inorganic coating layer; And

(S3) coating a polypodamine solution on the surface of the organic-inorganic coating layer and drying.

The separator of the present invention is interposed between the positive electrode and the negative electrode and can be used in an electrochemical device such as a lithium secondary battery or a supercapacitor device.

INDUSTRIAL APPLICABILITY The separator of the present invention can improve the stability of the electrochemical device by controlling the inorganic particles which can be desorbed by the stress generated in the assembling process of the electrochemical device by improving the binding force with the electrode. Also, since the interfacial adhesion between the separator and the electrode is improved and the wettability of the electrolyte is improved, the output density and cycle characteristics of the electrochemical device including the separator can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate exemplary embodiments of the invention and, together with the description of the invention, It should not be construed as limited.
1 is an SEM photograph of a separator according to a comparative example.
2 is a SEM photograph of a separator according to the embodiment.
3 is a cycle test result of the lithium secondary batteries according to Examples and Comparative Examples according to the C-rate.
4 is a cycle test result of the lithium secondary batteries of Examples and Comparative Examples.

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. Therefore, the embodiments described in the present specification and the constitutions described in the drawings are only the most preferred embodiments, and not all of the technical ideas of the present invention are described. Therefore, various equivalents which can be substituted at the time of the present application It should be understood that variations can be made.

The separator of the present invention comprises a porous substrate having pores; And a porous organic-inorganic coating layer formed on at least one surface of the porous substrate, the porous organic-inorganic coating layer including a mixture of inorganic particles and a binder polymer; And a poly dopamine coating layer dispersed so as to have a plurality of uncoated regions scattered on the surface of the organic-inorganic coating layer.

In the present invention, the polydodamine coating layer is dispersed on at least one surface of the porous substrate so as to have a plurality of uncoated regions scattered on the surface of the porous organic-inorganic coating layer containing the inorganic particles and the binder polymer, and a more detailed description is as follows.

Polydodamine, which is a component of the dispersed coating layer, is a polymer produced by polymerization reaction of DOPA (3,4-dyhydroxy-L-phenylalanine), which is a catechol amine represented by the following formula (1). However, in the present invention, the polydodamine includes not only the polymer of DOPA but also polydopamine which conforms to the required properties by modifying the functional group of the polydodamine to the extent that the object of the present invention is not impaired.

The polypodamine coating layer formed on the surface of the porous organic-inorganic coating layer improves the adhesion between the porous organic-inorganic coating layer and the electrode. The material separator contacting the interface with the electrode is preferable when adhesion with the electrode is strong. Since the polydopamine coating layer according to the present invention has an adhesive force, the desorption phenomenon of the inorganic particles in the porous organic-inorganic coating layer is improved. In addition, the present invention provides strong adhesion of the interface between the separator and the electrode due to the formation of the polydodamine coating layer, thereby effectively transferring lithium ions and minimizing the internal resistance.

In addition, the polypodamine coating layer has a high affinity with the electrolyte solution, thereby improving the wettability to the separator. In the present invention, the compatibility with the electrolytic solution means that the electrolytic solution is impregnated with the separator at a high speed or impregnated with a large capacity. The present invention improves the ion transfer ability through the separator by providing a polydopamine coating layer.

That is, the polypodamine coating layer formed on the surface of the porous organic-inorganic coating layer can improve not only the safety but also the output density characteristics of the battery due to the improved interfacial adhesion between the separator and the electrode and high affinity with the electrolyte. In addition, the irreversible capacity is reduced and the C-rate is improved. This means that the time required for charging or discharging by the coating of the polypodamine coating layer is shortened and the charge / discharge cycle life is improved.

The polypodamine coating layer forms the outer periphery of the separator but does not completely cover the entire surface of the organic-inorganic coating layer. On the surface of the organic-inorganic coating layer, a plurality of uncoated regions where no polydopamine coating layer is formed are scattered. That is, the uncoated region and the polypodamine coating layer are dispersed on the surface of the organic-inorganic coating layer. As described above, since the poly-dopamine coating layer formed on the surface of the organic-inorganic coating layer is dispersed to have a plurality of uncoated regions, the ions can pass through the uncoated region. As a result, the adhesion of the separator to the electrode can be increased without substantially increasing the resistance.

In the separator of the present invention, the formation area of the polypodamine coating layer is preferably 5 to 80%, more preferably 10 to 60% of the entire surface of the organic-inorganic coating layer, More preferable. The thickness of the polypodamine coating layer is preferably 1 to 200 nm, more preferably 20 to 100 nm.

Hereinafter, the organic-inorganic coating layer including a mixture of inorganic particles and a binder polymer on which a polypodamine coating layer is formed will be described in detail as follows.

In the organic-inorganic coating layer of the present invention, the inorganic particles used for forming the porous organic-inorganic 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 ion transfer ability are used, the ion conductivity in the electrochemical device can be increased to improve the performance.

When inorganic particles having a high dielectric constant are used as the inorganic particles, dissociation of an electrolyte salt, for example, a lithium salt, in the liquid electrolyte is also increased, and ion conductivity of the electrolyte can be improved.

For the reasons stated above, it is preferable that the inorganic particles include high-permittivity inorganic particles having a dielectric constant of 5 or more, preferably 10 or more, inorganic particles having lithium ion-transporting ability, or a mixture thereof. Nonlimiting examples of inorganic particles having a dielectric constant of 5 or more include BaTiO ₃ , Pb (Zr, Ti) O ₃ (PZT), Pb _{1 - x} La _x Zr _{1 - y} Ti _y O ₃ (PLZT, <1, 0 <y <1 _{Im), Pb (Mg 1/3} 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, SiC, TiO 2 May be used alone or in combination of two or more.

Particularly, the above-mentioned BaTiO ₃ , Pb (Zr, Ti) O ₃ (PZT), Pb _{1 - x} La _x Zr _{1 - y} Ti _y O ₃ (PLZT, where 0 <x <1, 0 < ), inorganic particles, such as _{Pb (Mg 1/3 Nb 2} /3) O 3 -PbTiO 3 (PMN-PT), hafnia (HfO _2), not only exhibit a dielectric constant of 100 or more high dielectric constant characteristics, the predetermined pressure And a piezoelectricity is generated so that a potential difference is generated between both sides by generating a charge when being stretched or compressed so as to prevent the occurrence of an internal short circuit between the two electrodes due to an external impact so as to improve the safety of the electrochemical device can do. Further, when the above-mentioned high-permittivity inorganic particles and inorganic particles having lithium ion transferring ability are mixed, their synergistic effect can be doubled.

In the present invention, the inorganic particles having a lithium ion transferring ability refer to inorganic particles containing a lithium element but not lithium and having a function of transferring lithium ions. The inorganic particles having lithium ion transferring ability are contained in the particle structure Since lithium ions can be transferred and transferred due to a kind of defect present, the lithium ion conductivity in the battery is improved, thereby improving battery performance. Examples of the inorganic particles having lithium ion transferring ability include lithium phosphate (Li ₃ PO ₄ ), lithium titanium phosphate (Li _x Ti _y (PO ₄ ) ₃ , 0 <x <2, 0 <y < (Li _x Al _y Ti _z (PO ₄ ) ₃ , 0 <x <2, 0 <y <1, 0 <z <3), 14Li ₂ O-9Al ₂ O ₃ -38TiO ₂ -39P ₂ O ₅ (0 <x <4, 0 <y <13), lithium lanthanum titanate (Li _x La _y TiO ₃ , 0 <x <2, 0 <y <3), Li (LiAlTiP) _x O _y series glass _{3 .25} Ge _{0 .25} P _{0 .75} S ₄ Lithium, such as germanium Mani help thiophosphate lithium nitro, such as _{(Li x Ge y P z S} w, 0 <x <4, 0 <y <1, 0 <z <1, 0 <w <5), Li 3 N fluoride _{(Li x N y, 0 <} x <4, 0 <y <2), Li 3 PO 4 -Li 2 S-SiS 2 SiS 2 family, such as _{glass (Li x Si y S z} , 0 <x <3 , 0 <y <2, 0 <z <4), LiI-Li ₂ SP ₂ S ₅ There is P ₂ S ₅ based _{glass (Li x P y S z} , 0 <x <3, 0 <y <3, 0 <z <7) or a mixture thereof as such.

In the separator of the present invention, the inorganic particle size of the porous organic-inorganic coating layer is not limited. However, in order to form a coating layer having a uniform thickness and a proper porosity, it is preferable that the porous organic-inorganic coating layer is in the range of 0.001 to 10 μm. If it is more than 10 mu m, the thickness of the porous organic-inorganic coating layer may increase and the mechanical properties may be deteriorated. Also, if the pore size is too large, The probability of an internal short circuit occurring during charging and discharging of the battery increases.

In the organic-inorganic coating layer of the present invention, the binder polymer used for forming the porous organic-inorganic coating layer is not particularly limited as a binder polymer commonly used in the art.

In particular, a polymer having a glass transition temperature (T _g ) of -200 to 200 ° C can be used because it can improve the mechanical properties such as flexibility and elasticity of the finally formed organic-inorganic coating layer . Such a binder faithfully performs a binder function to connect and stably fix inorganic particles, thereby contributing to prevention of deterioration of mechanical properties of the separator into which the porous coating layer is introduced.

Further, the binder does not necessarily have the ion-conducting ability, but the performance of the electrochemical device can be further improved by using a polymer having ion-conducting ability. Therefore, a binder having a high permittivity constant can be used. Actually, the dissociation degree of the salt in the electrolytic solution depends on the permittivity constant of the solvent of the electrolyte. Therefore, the higher the permittivity constant of the polymer, the better the salt dissociation degree in the electrolyte. The permittivity constant of such a binder may be in the range of 1.0 to 100 (measurement frequency = 1 kHz), in particular, 10 or more.

In addition to the functions described above, the binder may be characterized by being capable of exhibiting a high degree of swelling of the electrolyte by gelation upon impregnation with a liquid electrolyte. Accordingly, the solubility parameter of the binder is from 15 to 45 MPa ^1/2 or 15 to 25 MPa ^1/2, and 30 to 45 MPa ^1/2 range. Therefore, hydrophilic polymers having many polar groups can be used more than hydrophobic polymers such as polyolefins. If the solubility is more than 15 MPa ^1/2 and less than 45 MPa ^1/2, because it can be difficult to swell (swelling) by conventional liquid electrolyte batteries.

Non-limiting examples of usable binder polymers include polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-cotrichloroethylene, polymethylmethacrylate, But are not limited to, polymethylmethacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide ), Cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylpolyvinylalcohol, Ethylcellulose (cyanoethylcell but are not limited to, polyvinyl alcohol, polyvinyl alcohol, polyvinylpyrrolidone, polyvinylpyrrolidone, polyvinylpyrrolidone, polyvinylpyrrolidone, polyvinylpyrrolidone, polyvinylpyrrolidone, polyvinylpyrrolidone, polyvinylpyrrolidone, polyvinylpyrrolidone, polyvinylpyrrolidone, And the like. In addition, any material including the above-mentioned characteristics may be used alone or in combination.

The content of the binder polymer in the porous organic-inorganic coating layer coated on the separator according to the present invention is preferably 2 to 30 parts by weight, more preferably 5 to 15 parts by weight, based on 100 parts by weight of the inorganic particles. When the content of the binder polymer is less than 2 parts by weight, problems such as elimination of an inorganic material may occur. When the content of the binder polymer is more than 30 parts by weight, the binder polymer blocks the pores of the porous substrate to increase the resistance and the porosity of the porous organic- Can be degraded.

The porous organic-inorganic hybrid layer formed on the porous substrate is characterized in that the binder polymer is located on a part or the entire surface of the inorganic particles as a coating layer and the inorganic particles are connected and fixed to each other by the coating layer in close contact, It is preferable that the pores are formed due to the void space existing between the inorganic particles. That is, the inorganic particles of the porous organic-inorganic hybrid layer exist in close contact with each other, and the empty space formed when the inorganic particles are in close contact becomes the pores of the porous organic-inorganic hybrid layer. The size of the void space existing between the inorganic particles is preferably equal to or smaller than the average particle size of the inorganic particles. The binder polymer located in a coating on a part or all of the surface of the inorganic particles connects and secures the inorganic particles together and fixes the inorganic particles in contact with the porous substrate to the porous substrate.

The thickness of the porous organic-inorganic coating layer composed of the inorganic particles and the binder polymer is not particularly limited, but is preferably in the range of 0.5 to 10 mu m.

In the separator of the present invention, the substrate on which the organic-inorganic coating layer formed with the polypodamine coating layer is formed is not particularly limited as a porous substrate having pores.

Examples of porous substrates having usable pores include polyolefins, polyethylene terephthalate, polybutylene terephthalate, polyacetals, polyamides, polycarbonates, polyimides, polyether ether ketones, polyethersulfones, A porous substrate formed of at least one of rhenium sulfide, rhenium sulfide, and polyethylene naphthalene, and the like can be used as long as it can be used as a separator of an electrochemical device. As the porous substrate, a membrane or a nonwoven fabric may be used. The thickness of the porous substrate is not particularly limited, but is preferably from 5 to 50 mu m, and the pore size and porosity present in the porous substrate are also not particularly limited, but are preferably 0.01 to 50 mu m and 10 to 95%, respectively.

Further, the present invention provides a preferable method for producing the separator according to the present invention.

A preferred method for producing the separator according to the present invention is

(S1) preparing a porous substrate having pores;

(S2) coating a coating solution in which inorganic particles are dispersed and a binder polymer dissolved in a solvent on at least one surface of the porous substrate and drying to form a porous organic-inorganic coating layer; And

(S3) coating a polypodamine solution on the surface of the organic-inorganic coating layer and drying.

First, a porous substrate having pores is prepared (step S1). The specific contents such as the kind of the porous substrate are as described above.

Next, inorganic particles are added to the solution of the binder polymer and dispersed. It is preferable that the solvent has a solubility index similar to that of the binder polymer to be used and a low boiling point. This is to facilitate uniform mixing and subsequent solvent removal. Non-limiting examples of usable solvents include acetone, tetrahydrofuran, methylene chloride, chloroform, dimethylformamide, N-methyl-2-pyrrolidone ( N-methyl-2-pyrrolidone, NMP), cyclohexane, water or a mixture thereof. It is preferable to add inorganic particles to the binder polymer solution and then crush the inorganic particles. In this case, the disintegration time is preferably 1 to 20 hours, and the particle size of the disintegrated inorganic particles is preferably 0.001 to 10 占 퐉 as mentioned above. As the crushing method, a conventional method can be used, and a ball mill method is particularly preferable.

A solution of the binder polymer in which the inorganic particles are dispersed is coated on the porous substrate and dried to form a porous organic-inorganic coating layer (step S2). The humidity condition at the time of coating is preferably 10 to 80%, and in the drying step, any method such as hot air drying can be used as long as the solvent can be volatilized.

A method of coating a solution of a binder polymer in which inorganic particles are dispersed on a porous substrate may be a conventional coating method known in the art. For example, a dip coating, a die coating, a roll coating, Various methods such as coating, comma coating, or a combination thereof can be used. In addition, the porous organic-inorganic coating layer can be selectively formed on both or only one side of the porous substrate.

Then, a polypodamine solution is coated on the organic-inorganic coating layer and dried (Step S3)

The polypodamine solution forms a solution of the polypodamine through self-polymerization of dopamine in a basic buffer solution. The coating of the polydodamine solution can be carried out by any of the coating methods of the binder polymer solution described above. As described above, the polypodamine coating layer forms the outer periphery of the separator, but does not completely cover the entire surface of the organic-inorganic coating layer. On the surface of the organic-inorganic coating layer, besides the polypodamine coating layer, a plurality of uncoated regions are dispersed between the polypodamine coating layers.

In the present specification, combinations of the above-described constituent elements described as preferred examples are not described, but all of the constituent elements may be combined in two or more of them and adopted in various configurations of the present invention.

The thus-produced separator of the present invention can be used as a separator of an electrochemical device. That is, the separator of the present invention can be usefully used as a separator interposed between an anode and a cathode. The electrochemical device includes all devices that perform an electrochemical reaction, and specific examples include capacitors such as all kinds of primary, secondary cells, fuel cells, solar cells, or super capacitor devices. 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.

The electrochemical device may be manufactured according to a conventional method known in the art, and may be manufactured, for example, by assembling the positive electrode and the negative electrode with the separator interposed therebetween, and then injecting an electrolyte solution .

The electrode to be used together with the separator of the present invention is not particularly limited, and the electrode active material may be bound to an electrode current collector according to a conventional method known in the art. Examples of the cathode active material include, but are not limited to, lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium iron oxide, or a combination thereof It is preferable to use a lithium composite oxide. As a non-limiting example of the negative electrode active material, a conventional negative electrode active material that can be used for a negative electrode of an electrochemical device can be used. In particular, lithium metal or a lithium alloy, carbon, petroleum coke, activated carbon, Lithium-adsorbing materials such as graphite or other carbon-based materials and the like are preferable. Non-limiting examples of the positive current collector include aluminum, nickel, or a combination thereof. Examples of the negative current collector include copper, gold, nickel, or a copper alloy or a combination thereof Foil to be manufactured, and the like.

Electrolyte that may be used in the present invention is A ⁺ B ^- A salt of the structure, such as, A ⁺ is Li ^+, Na ^+, K ⁺ comprises an alkaline metal cation or an ion composed of a combination thereof, such as, and B ^- is PF _{6 ^{-, BF 4 -, Cl -}} , Br -, I -, ClO 4 -, AsF 6 -, CH 3 CO 2 -, CF 3 SO 3 -, N (CF 3 SO 2) 2 -, C (CF 2 SO _{2) 3} ^- anion, or a salt containing an ion composed of a combination of propylene carbonate (PC like), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC) (NMP), ethylmethyl carbonate (EMC), gamma-butyrolactone, or mixtures thereof, in an inert solvent such as dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, But are not limited to, those dissolved or dissociated in an organic solvent.

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

Hereinafter, embodiments of the present invention will be described in detail to facilitate understanding of the present invention. 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 following embodiments. Embodiments of the invention are provided to more fully describe the present invention to those skilled in the art.

Example

1) Manufacture of separator

Organic-Inorganic Porous Coating Layer Separator ( PVdF - CTFE  / Al ₂ O ₃ Production

5% by weight of a polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP) polymer was added to acetone and dissolved at 50 ° C for about 12 hours or more to prepare a binder polymer solution. The Al ₂ O ₃ powder was added to the binder polymer solution so that the binder polymer / Al ₂ O ₃ ratio was 10/90 by weight, and the Al ₂ O ₃ powder was pulverized and dispersed for 12 hours or more using a ball mill Slurry. The slurry thus prepared was coated on both sides of a 12 μm thick polyethylene porous film (porosity of 45%) by dip coating method and dried to form an organic-inorganic coating layer.

Polydopamine  Coating layer formation

Dopamine was dissolved in a basic (pH 8.5, Tris-HCL buffer) buffer solution at a concentration of 2 mg / ml and self-polymerized to prepare a polypodamine solution. The polypodamine solution was coated on the porous membrane having the organic-inorganic porous coating layer formed thereon by a dip coating method and shaken uniformly for 24 hours. The organic-inorganic coating layer is discolored from white to brown to show whether a coating layer is formed. After sufficiently coated, the substrate was washed and dried to form a poly dopamine coating layer on the organic-inorganic coating layer.

2) Preparation of lithium secondary battery

Cathode manufacturing

(N-methyl-2-pyrrolidone) as a negative electrode active material, polyvinylidene fluoride (PVdF) as a binder and carbon black as a conductive material were respectively 96 wt%, 3 wt% and 1 wt% (NMP) to prepare a negative electrode mixture slurry. The negative electrode mixture slurry was applied to a copper (Cu) thin film as an anode current collector having a thickness of 10 탆 and dried to produce a negative electrode, followed by roll pressing.

Manufacture of anode

92 wt% of a lithium cobalt composite oxide as a positive electrode active material, 4 wt% of carbon black as a conductive material, and 4 wt% of PVDF as a binder were added to N-methyl-2-pyrrolidone (NMP) . The positive electrode mixture slurry was applied to an aluminum (Al) thin film of a positive electrode current collector having a thickness of 20 탆 and dried to produce a positive electrode, followed by roll pressing.

Manufacture of batteries

The electrodes thus prepared and the separators manufactured in Example 1) were assembled using a stacking method. The assembled battery was assembled with ethylene carbonate / ethyl methyl (LiPF6) dissolved in 1M of lithium hexafluorophosphate Carbonate (EC / EMC = 1: 2, volume ratio) based electrolyte was injected to prepare a lithium secondary battery.

Comparative Example

A lithium secondary battery was produced in the same manner as in the above example, except that polydodamine was not coated.

Experimental Example 1  - Separator  Surface observation

The surface of the separator of the lithium secondary batteries according to Examples and Comparative Examples was observed by a scanning electron microscope (SEM), and a photograph of a surface SEM according to a comparative example is shown in Fig. 2.

As a result of observing the surface of the separator, it can be seen that, in the case of the separator of the examples, even if the polypodamine coating layer is formed by the dip coating method, the pores on the surface are not completely blocked.

Experimental Example 2  - Performance evaluation of lithium secondary battery

In order to measure the charge / discharge capacity of the lithium secondary battery including the separator manufactured in the present invention, the following procedure was performed.

C- rate Discharge characteristics according to

The lithium secondary batteries of the examples and comparative examples were cut off at 3.0 V and discharged at a C-rate of 0.1 C, 0.3 C, 0.5 C, 1 C, 3 C, and 5 C, FIG. 3 shows a cycle chart according to the C-rate by plotting the residual capacity (%) of C-rate according to C-rate characteristics.

As a result of the tests, the lithium secondary batteries of the Examples are superior to the lithium secondary batteries of the comparative example in which the polypodamine layer is not provided. These characteristics are also exhibited at a low C-rate of 0.1 C, and the higher the C-rate is, the higher the improvement of the discharge characteristic is.

Evaluation of cycle characteristics

The lithium secondary batteries of Examples and Comparative Examples were discharged at 4.4 V, 1 C CC-CV charging / 3.0 V, 1 C CC, and the residual capacity (%) results thereof are shown in FIG.

As a result of experiments, it can be seen that the lithium secondary batteries of the embodiment are superior to the lithium secondary batteries of the comparative example which does not include the polypodamine layer, especially in that the residual capacity is higher as the number of cycles increases.

Claims (16)

A porous substrate having pores;
A porous organic-inorganic coating layer formed on at least one surface of the porous substrate, the porous organic-inorganic coating layer including a mixture of inorganic particles and a binder polymer; And
And a poly-dopamine coating layer dispersed so as to have a plurality of uncoated regions dispersed on the surface of the organic-inorganic coating layer,
Wherein the formation area of the polypodamine coating layer is 10 to 60% of the entire surface of the organic-inorganic coating layer, and the thickness of the polypodamine coating layer is 1 to 200 nm. The method according to claim 1,
Wherein the formation area of the polypodamine coating layer is 5 to 80% of the entire surface of the organic-inorganic coating layer. delete delete The method according to claim 1,
Wherein the inorganic particles have an average particle diameter of 0.001 to 10 mu m. The method according to claim 1,
Wherein the inorganic particles are selected from the group consisting of inorganic particles having a dielectric constant of 5 or more, inorganic particles having lithium ion transporting ability, and mixtures thereof. The method according to claim 6,
The inorganic particles having a dielectric constant of 5 or more include BaTiO ₃ , Pb (Zr, Ti) O ₃ (PZT), Pb _{1 -x} La _x Zr _{1 -y} Ti _y O ₃ (PLZT, <y <1 _{Im), Pb (Mg 1/3} 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 , SiC and TiO ₂ . The method according to claim 6,
The inorganic particles having lithium ion transferring 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 (13), lithium lanthanum titanate (Li _x La _y TiO _{3 ,} 0 <x <2, 0 <y <3), lithium germanium thiophosphate (LixGeyPzSw, 0 <x <4, 0 < 0 <x <3, 0 <y <2, 0), 0 <z <1, 0 <w <5), lithium nitride (LixNy, 0 <x <4, 0 <y <2), SiS ₂ z <4) series glass and P ₂ S ₅ (LixPySz, 0 <x <3, 0 <y <3, 0 <z <7) series glass. The method according to claim 1,
The binder polymer may be at least one selected from the group consisting of polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-cotylchlorethylene, polymethylmethacrylate, Polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide, cellulose (cellulose acetate) cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, hydroxypropylcellulose, hydroxypropylmethylcellulose, hydroxypropylmethylcellulose, hydroxypropylmethylcellulose, Cyanoethyl sucrose at least one selected from the group consisting of cyanoethylsucrose, pullulan, carboxyl methyl cellulose, acrylonitrile-styrene-butadiene copolymer, and polyimide, . The method according to claim 1,
Wherein the content of the binder polymer is 2 to 30 parts by weight based on 100 parts by weight of the inorganic particles. The method according to claim 1,
The binder polymer of the porous organic-inorganic coating layer is located on a part or the whole of the surface of the inorganic particles, the inorganic particles are connected and fixed to each other by the coating layer in close contact with each other, And the pores are formed due to the empty space. The method according to claim 1,
Wherein the porous organic-inorganic coating layer has a thickness of 0.5 to 10 占 퐉. The method according to claim 1,
The porous substrate may be formed of a material selected from the group consisting of polyolefin, polyethylene terephthalate, polybutylene terephthalate, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyether sulfone, polyphenylene oxide, polyphenylene sulfide and polyethylene naphthalene Wherein the separator is formed of at least one selected from the group consisting of the following. (S1) preparing a porous substrate having pores;
(S2) coating a coating solution in which inorganic particles are dispersed and a binder polymer dissolved in a solvent on at least one surface of the porous substrate and drying to form a porous organic-inorganic coating layer; And
(S3) coating a polypodamine solution on the surface of the organic-inorganic coating layer and drying the same, wherein the separator is the separator according to claim 1. An electrochemical device comprising a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode,
Wherein the separator is the separator according to any one of claims 1, 2, and 5 to 13. 16. The method of claim 15,
Wherein the electrochemical device is a lithium secondary battery.

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