KR101642334B1 - Separator for secondary battery - Google Patents

Abstract

The present invention relates to a separator for a secondary battery, comprising a first porous coating layer on a first surface of a porous substrate, the first porous coating layer comprising a mixture of a scavenger, a conductive material and a binder polymer capable of reducing manganese ions, The separator for a secondary battery of the present invention having a porous coating layer capable of capturing Mn on at least one surface of a base material can capture the Mn leaking from the Mn-based anode to alleviate degradation of the anode active material, It is possible to improve the life of the device. Further, since the separator of the present invention has a porous coating layer containing inorganic particles, it is excellent in heat resistance and can prevent heat shrinkage.

Description

SEPARATOR FOR SECONDARY BATTERY Technical Field [1] The present invention relates to a separator for a secondary battery,

The present invention relates to a separator for a secondary battery, and more particularly to a separator suitable for a manganese-based lithium secondary battery.

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 them, the development of rechargeable secondary batteries has become a focus of attention. In recent years, in order to improve capacity density and specific energy, 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. Recent lithium ion polymer batteries have been recognized as one of the next generation batteries by improving the weakness of such lithium ion batteries.

Lithium cobalt composite oxides, lithium nickel complex oxides, lithium manganese composite oxides, and the like are used as the cathode active materials used in such lithium secondary batteries. Of these, lithium manganese composite oxides, which are rich in resources and inexpensive, . In the Mn-based lithium secondary battery, manganese components are eluted and eluted on the surface of the negative electrode active material as the charge and discharge proceeds, and manganese precipitated on the surface of the negative electrode active material receives electrons from the negative active material, Thereby accelerating the decomposition of the electrolyte in the negative electrode active material, thereby increasing the resistance of the battery and degenerating the battery. This is a major cause of inhibiting the development of high performance (high output) manganese-based lithium secondary batteries.

Korean Patent Publication No. 2007-0082892 discloses a secondary battery using an anode active material coated with an Mn capturing agent. However, since a further step of coating an Mn capturing agent on the anode active material is required, the manufacturing method is complicated.

Accordingly, an object of the present invention is to provide a separator for maintaining the performance of a manganese-based lithium secondary battery.

In order to solve the above problems, the present invention provides a secondary battery separator comprising a first porous coating layer including a scavenger capable of reducing manganese ions, a conductive material, and a binder polymer on a first surface of a porous substrate, Lt; / RTI >

In the separator for a secondary battery of the present invention, a second porous coating layer containing inorganic particles and a binder polymer may be provided on the second surface of the porous substrate.

The Mn capturing agent may be TiO ₂ , TiS ₂ or a mixture thereof. As the conductive material, acetylene black, carbon black, Ketjen black, graphite, and carbon nanotube may be used. Such a conductive material is preferably used in an amount of 5 to 30% by weight relative to the Mn capturing agent.

The inorganic particles may be inorganic particles having a dielectric constant of 5 or more, inorganic particles having lithium ion transferring ability, and mixtures thereof.

As inorganic particles than such a dielectric constant is 5 _{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 and TiO ₂ Etc. may be used. 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), (LiAlTiP) _x O _y series glass 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 , x <4, 0 <y < 1, 0 <z <1, 0 <w <5), lithium nitrides _{(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) based glass, and _{P 2 S 5 (Li x P} y S z, 0 <x <3, 0 <y <3, 0 < z < 7) series glass, or a mixture of two or more thereof.

Examples of the binder polymer include polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichlorethylene, polymethylmethacrylate, Polybutyl acrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyvinyl alcohol, ethylene-vinyl acetate copolymer (polyethylene-co) polyvinyl acetate, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl Cyanoethylpullulan, cyano Cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, carboxyl methyl cellulose and a low molecular weight compound having a molecular weight of 10,000 g / mol or less A binder polymer selected from the group consisting of a mixture of two or more thereof, or the like can be used.

The thickness of the first porous coating layer is preferably 1.0 to 20.0 탆, and the thickness of the second porous coating layer is preferably 1.0 to 20.0 탆.

As the porous substrate of the present invention, a polyolefin-based porous substrate can be used. As the polyolefin-based porous substrate, polyethylene, polypropylene, polybutylene and polypentene are preferably used.

The present invention also provides a positive electrode comprising a manganese-based lithium metal oxide; cathode; And a separator and an electrolyte interposed between the anode and the cathode such that the first porous coating layer contacts the cathode.

The separator for a secondary battery of the present invention having a porous coating layer capable of capturing Mn on at least one surface of the porous substrate can capture Mn leaked from the Mn-based anode to alleviate degradation of the anode active material, The life of the battery can be improved.

Further, since the separator of the present invention has a porous coating layer containing inorganic particles, it is excellent in heat resistance and can prevent heat shrinkage.

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 present invention provides a separator for a secondary battery comprising a first porous coating layer on a first surface of a porous substrate, the first porous coating layer comprising a scavenger capable of reducing manganese ions, a conductive material and a binder polymer.

The Mn scavenger according to the present invention must be conductive or semiconductive in order to receive electrons. It is preferable that the material has affinity for manganese. Materials that can be used as Mn capture agent include electronically conductive titanium-based compounds, and non-limiting examples thereof include TiO ₂ and TiS ₂ . In some cases, mixed forms thereof may be used. Mn scavenger is preferably in the oxide form and, TiO ₂ is particularly preferred.

The Mn capturing agent coated on one surface of the separator can receive Mn from the surface of the Mn capturing agent by receiving electrons from the direct contacted conductive material. For example, since the coating of TiO ₂ having an ability as an Mn capturing agent is applied to the surface of the conductive material, deterioration of the carbon-based active material due to manganese deposited directly on the carbon surface of the negative electrode during long-term storage can be greatly alleviated .

Since the Mn capturing agent of the present invention is coated on the surface of the separator interposed between the positive electrode and the negative electrode, the manganese ions first come into contact with the manganese ions, and the manganese ions receive electrons from the contact surface, Manganese precipitates preferentially on the Mn scavenger since there is such an affinity that it does not migrate to the surface of the active material. As described above, since manganese precipitates preferentially on the surface of the Mn capturing agent, the Mn capturing agent film is formed in the manganese-based lithium secondary battery so that manganese is deposited on the Mn capturing agent film rather than on the carbon surface of the cathode to suppress degradation of the anode active material . Therefore, excellent battery performance can be maintained and the life of the battery can be improved.

The specific working principle is the Mn ^{2 +} TiO ₂ O-Ti-O-Mn or (TiO ₂ ) Mn while being stabilized in the form of O-Ti-O-Mn or MnO (TiO ₂ ) Mn while being directly reduced on the surface of the anode active material.

As the conductive material, acetylene black, carbon black, Ketjen black, graphite, carbon nanotubes, or the like can be used. It is preferable that the conductive material is used in an amount of 5 to 30% by weight relative to the Mn capturing agent. When the content of the conductive material is less than 5 wt%, it is difficult to supply electrons to the Mn trapping agent. When the content of the conductive material exceeds 30 wt%, the porosity of the first porous coating layer deteriorates.

In addition, the first porous coating layer of the present invention may contain inorganic particles as exemplified below in addition to the Mn capturing agent. Such inorganic particles are excellent in heat resistance, so that heat shrinkage of the porous substrate can be prevented.

The separator for a secondary battery of the present invention may include a second porous coating layer on the second surface of the porous substrate, the second porous coating layer including inorganic particles and a binder polymer.

In the second porous coating layer, the binder polymer adheres to each other (that is, the binder polymer bonds and fixes between the inorganic particles) so that the inorganic particles can remain bonded to each other, and the second porous coating layer is formed by the binder polymer And retains the state of binding with the porous substrate. In the second porous coating layer, the interstitial volume generated when the inorganic particles are in contact becomes the pores of the second porous coating layer. Likewise, the first porous coating layer also has porosity on a similar principle.

The inorganic particles may be inorganic particles having a dielectric constant of 5 or more, inorganic particles having lithium ion transferring ability, and mixtures thereof.

As inorganic particles than such a dielectric constant is 5 _{BaTiO 3, Pb (Zr x,} Ti 1 -x) O 3 (PZT), 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), 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 , and TiO ₂ Etc. may be used. 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), (LiAlTiP) _x O _y series glass 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 , x <4, 0 <y < 1, 0 <z <1, 0 <w <5), lithium nitrides _{(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) based glass, and _{P 2 S 5 (Li x P} y S z, 0 <x <3, 0 <y <3, 0 < z < 7) series glass, or a mixture of two or more thereof.

Examples of the binder polymer include polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichlorethylene, polymethylmethacrylate, Polybutyl acrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyvinyl alcohol, ethylene-vinyl acetate copolymer (polyethylene-co) polyvinyl acetate, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl Cyanoethylpullulan, cyano Cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, carboxyl methyl cellulose and a low molecular weight compound having a molecular weight of 10,000 g / mol or less A binder polymer selected from the group consisting of a mixture of two or more thereof, or the like can be used.

It is preferable that the thickness of the first porous coating layer is 1.0 to 20.0 占 퐉. If the thickness of the first porous coating layer is less than 1.0 占 퐉, it is difficult to realize a uniform coating property on the substrate. If the thickness of the first porous coating layer is more than 20.0 占 퐉, The energy density of the lithium secondary battery can be deteriorated due to the thickness. It is preferable that the thickness of the third porous coating layer is 1.0 to 20.0 占 퐉. If the thickness of the second porous coating layer is less than 1.0 占 퐉, the stability enhancement effect of the lithium secondary battery is not expected to be expected. If it exceeds 20.0 占 퐉 The thickness of the coating layer may deteriorate the energy density of the lithium secondary battery.

As the porous substrate to be used in the present invention, a polyolefin-based porous substrate may be used, and the polyolefin-based porous substrate may be formed of any one selected from the group consisting of polyethylene, polypropylene, polybutylene, and polypentene .

The present invention also provides a positive electrode comprising a manganese-based lithium metal oxide; cathode; And a separator and an electrolyte interposed between the anode and the cathode such that the first porous coating layer contacts the cathode.

The positive electrode of the present invention is preferably a positive electrode containing a manganese-based lithium metal oxide. The positive electrode and the negative electrode are not particularly limited, and the electrode active material may be used as an electrode current collector Or the like.

The cathode active material is a lithium manganese oxide having a spinel structure or a lithium manganese oxide having a spinel structure and other cathode active materials. In order for the Mn capturing agent to function in accordance with the present invention, it is preferable that the cathode contains at least 30 wt% of the manganese spinel-based cathode active material. 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 secondary battery of the present invention is A ⁺ B ^- A salt of the structure, such as, A ⁺ comprises Li ^+, Na ^+, an alkali metal cation or an ion composed of a combination thereof, such as K ⁺ 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 (DMP), dimethylsulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethylmethyl carbonate (EMC), gamma butyrolactone Butyrolactone), or a mixture thereof, but the present invention is not limited thereto. 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.

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 may 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  1. Carbon black Conductive material  Used Mn Capture agent  A double-sided porous coating layer Separator

1% by weight of PVdF-HFP (polyvinylidene fluoride-hexafluoropropylene) was dissolved in acetone. To the binder solution was added TiO ₂ having a diameter of 300 nm And a carbon black (Super P) were mixed at a weight ratio of 8: 2, and the polymer / inorganic particles were added so as to have a weight ratio of 10/90 and then dispersed by a ball mill method to prepare a first slurry. In addition, PVDF-CTFE (polyvinylidene fluoride-chlorotrifluoroethylene copolymer) and cyanoethylpullulan were mixed at a weight ratio of 10: 2 and dissolved in 5 wt% Al ₂ O ₃ particles having a diameter of 10/90 weight ratio were dispersed by a ball mill method to prepare a second slurry. The first slurry and the second slurry thus prepared were applied on a polyolefin separator (SK Energy, 312HT) having a thickness of 12 탆 by a multilayer coating method and simultaneously dried. The thickness of the first porous coating layer thus formed was 2.1 mu m on average and the average thickness of the second porous coating layer was 4.7 mu m.

A prepared coin cell was prepared by positioning the prepared separator between the manganese-based cathode active material and the graphite-based anode active material so that the first porous coating layer was oriented toward the anode active material. The prepared coin cell was allowed to stand at 60 ° C for 3 days, decomposed, and the component surface of the negative electrode surface was analyzed by ICP. As a result, Mn was not detected.

Example  2. Carbon nanotubes Conductive material  Used Mn Capture agent  A double-sided porous coating layer Separator

A separator having a porous coating layer was prepared in the same manner as in Example 1, except that carbon nanotubes were used instead of carbon black as a conductive material in the production of the first slurry. The thickness of the first porous coating layer thus formed was 2.1 mu m on average and the average thickness of the second porous coating layer was 4.7 mu m.

The prepared separator was placed between the manganese-based cathode active material and the graphite-based anode active material to prepare a coin cell. The prepared coin cell was allowed to stand at 60 ° C for 3 days, decomposed, and the component surface of the negative electrode surface was analyzed by ICP. As a result, Mn was not detected.

Example  3. Carbon nanotubes Conductive material  Used Mn Capture agent  A double-sided porous coating layer Separator

The first slurry and the second slurry were prepared in the same manner as in Example 2, and then a first slurry was coated on one surface of a polyolefin separator (SK Energy, 312HT) having a thickness of 12 탆 in a thickness of 2.8 탆 by a slot coating method to form a first porous And a second porous coating layer was formed by sequentially coating a second slurry on the opposite surface with a thickness of 4.0 탆 in a slot coating manner.

The prepared separator was placed between the manganese-based cathode active material and the graphite-based anode active material to prepare a coin cell. The prepared coin cell was allowed to stand at 60 ° C for 3 days and decomposed. The component surface of the negative electrode surface was analyzed by ICP. As a result, Mn was not detected.

Example  4. Carbon nanotubes Conductive material  Used Mn Capture agent  A cross-section porous coating layer Separator

A first slurry was prepared in the same manner as in Example 2, and then the first slurry was coated on one surface of a polyolefin separator (SK Energy, 312HT) having a thickness of 12 탆 in a thickness of 6.4 탆 by a slot coating method.

The prepared separator was sandwiched between the manganese-based cathode active material and the graphite-based anode active material to prepare a coin cell. The prepared coin cell was allowed to stand at 60 ° C for 3 days and decomposed. The component surface of the negative electrode surface was analyzed by ICP. As a result, Mn was not detected.

Comparative Example  One. Mn Capture agent  A cross-section porous coating layer having no coating layer Separator

A PVDF-CTFE (polyvinylidene fluoride-chrorotrifluoroethylene copolymer) and cyanoethylpullulan were mixed in a weight ratio of 10: 2 and dissolved in 5 wt%, to a binder solution having a diameter of 500 nm a has then added so as to have an Al ₂ 0 ₃ particles, polymer / inorganic particles weight ratio = 10/90 were dispersed in a ball mill method to prepare a second slurry. The prepared second slurry was coated on a 12 탆 thick polyolefin separator (SK Energy, 312HT) by a multi-layered slot coating method and dried at the same time. The thickness of the second porous coating layer thus formed was 7.0 mu m on average.

The prepared separator was placed between the manganese-based cathode active material and the graphite-based anode active material to prepare a coin cell. The prepared coin cell was left to stand at 60 ℃ for 3 days and decomposed. The component surface of the negative electrode surface was analyzed by ICP. As a result, 470 ppm of Mn was detected.

Claims (15)

A porous substrate;
A first porous coating layer provided on the first surface of the porous substrate, the first porous coating layer comprising a mixture of a scavenger, a conductive material and a binder polymer capable of reducing manganese ions; And
And a second porous coating layer on the second surface of the porous substrate, the second porous coating layer comprising a mixture of inorganic particles and a binder polymer,
Here, Mn is the scavenger is a mixture of TiO _2, TiS thereof,
Wherein the content of the conductive material is 5 to 30% by weight relative to the amount of the Mn capturing agent. delete delete The method according to claim 1,
Wherein the conductive material is at least one compound selected from the group consisting of acetylene black, carbon black, ketjen black, graphite, and carbon nanotube, or a mixture of two or more thereof. delete The method according to claim 1,
Wherein the inorganic particles are inorganic particles selected from the group consisting of inorganic particles having a dielectric constant of 5 or more, inorganic particles having a lithium ion transporting ability, and mixtures thereof. The method according to claim 6,
Inorganic particles is greater than or equal to the dielectric constant of 5, _{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 Particles or a mixture of two or more thereof. 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 (Li _x Ge _y P _z S _w , , 0 <y <1, 0 <z <1, 0 <w <5), lithium nitrides _{(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) based glass, and _{P 2 S 5 (Li x P} y S z, 0 <x <3, 0 <y <3, 0 <z &Lt; 7) series glass, or a mixture of two or more thereof. 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-co-trichlorethylene, polymethylmethacrylate, But are not limited to, polybutyl acrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyvinyl alcohol, polyethylene-co- polyvinyl acetate, vinyl acetate, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, Cyanoethylpullulan, cyanoethyl It is composed of cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, carboxyl methyl cellulose and a low molecular weight compound with a molecular weight of 10,000 g / mol or less , Or a mixture of two or more of them. 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-co-trichlorethylene, polymethylmethacrylate, But are not limited to, polybutyl acrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyvinyl alcohol, polyethylene-co- polyvinyl acetate, vinyl acetate, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, Cyanoethylpullulan, cyanoethyl It is composed of cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, carboxyl methyl cellulose and a low molecular weight compound with a molecular weight of 10,000 g / mol or less , Or a mixture of two or more of them. The method according to claim 1,
Wherein the thickness of the first porous coating layer is 10.0 to 20.0 탆. The method according to claim 1,
Wherein the thickness of the second porous coating layer is 1.0 to 20.0 탆. The method according to claim 1,
Wherein the porous substrate is a polyolefin-based porous substrate. 14. The method of claim 13,
Wherein the polyolefin-based porous substrate is formed of any one selected from the group consisting of polyethylene, polypropylene, polybutylene, and polypentene. A positive electrode containing a manganese-based lithium metal oxide; cathode; The secondary battery according to any one of claims 1, 4, and 6 to 14, wherein the separator and the electrolyte are interposed between the anode and the cathode such that the first porous coating layer is in contact with the cathode.