KR20190052588A - Separator, preparing method thereof, and non-aqueous electrolyte secondary battery including the same - Google Patents

Abstract

According to one embodiment of the present invention, provided is a separator for a non-aqueous electrolyte secondary battery, wherein a first layer which is a porous film containing a polyolefin-based resin, a second layer containing the polyolefin-based resin and an aqueous polymer, and a third layer containing a binder made of the polymer and a cellulose nanofiber are stacked inside the separator. Therefore, a separator which is excellent in heat resistance and mechanical strength and a manufacturing method thereof can be provided.

Description

Separator, a method of manufacturing the same, and a non-aqueous electrolyte secondary battery including the separator,

A separator, a method for producing the same, and a nonaqueous electrolyte secondary battery including the same.

BACKGROUND ART [0002] Secondary batteries are widely used in mobile electronic devices, electric vehicles, hybrid vehicles, and the like, and especially lithium ion secondary batteries have high energy density and are being actively developed.

At present, polyolefin-based microporous membranes which are inexpensive, chemically stable, and excellent in mechanical properties are mainly used as separators for lithium ion secondary batteries. In recent years, lithium ion secondary batteries have come to be used in automotive applications. In this case, heat resistance of 200 DEG C or more is required for the separator, but the polyolefin resin alone can not meet the demand. Therefore, a method of applying ceramic particles to a polyolefin-based microporous membrane or a method of using chemical crosslinking or the like has been studied for supplement. However, according to this method, although the heat-resistant temperature is improved, it is difficult to secure excellent heat-resistance at 200 ° C or more, and there is a problem that heat shrinks, and improvement is required.

One aspect is to provide a separator having excellent heat resistance and mechanical strength characteristics and a method of manufacturing the separator.

Another aspect is to provide a nonaqueous electrolyte secondary battery comprising the above-described separator.

According to an aspect, there is provided a laminate comprising: a first layer which is a porous film comprising a polyolefin-based resin; A second layer comprising a polyolefin resin and an aqueous polymer; And a third layer comprising an aqueous polymer and a cellulose nanofiber.

The cellulose nanofibers have a ratio of fibers having a fiber diameter of less than 1 占 퐉 of 80% by weight or more. The thickness of the third layer is 1/10 or more of the thickness of the first layer and the thickness of the second layer is 1/2 or less of the thickness of the first layer. The total thickness of the separator is 5 탆 to 50 탆.

The polyolefin-based resin is at least one of a polyethylene-based resin and a polypropylene-based resin. The content of the water-based polymer in the third layer is 0.1 to 40 parts by weight based on 100 parts by weight of the cellulose nanofiber.

The permeability of the separator may be 50 sec / 100cc to 2000 sec / 100cc.

The content of the cellulose nanofibers in the third layer is 60 parts by weight to 99.9 parts by weight based on 100 parts by weight of the total amount of the water-based polymer and the cellulose nanofibers. And the content of the water-based polymer in the second layer is 60 to 99.99 parts by weight based on 100 parts by weight of the total amount of the water-based polymer and the polyolefin resin.

According to another aspect, there is provided a non-aqueous electrolyte secondary battery comprising an anode, a cathode, and the above-described separator interposed therebetween.

Preparing a porous membrane comprising a polyolefin-based resin according to another aspect;

Supplying a composition comprising a cellulose nanofiber, an aqueous polymer, a water-soluble organic solvent and water to a porous membrane comprising the polyolefin-based resin; and

And drying the composition supplied to the porous membrane containing the polyolefin-based resin.

According to one embodiment, it is possible to provide a separator excellent in heat resistance and mechanical strength, having shutdown characteristics, and excellent in handling properties, and a nonaqueous electrolyte secondary battery having improved cell performance including the separator.

Figure 1 schematically illustrates a separator section according to one embodiment.
2 is a micrograph of a cross section of a separator according to one embodiment.
3 is a photomicrograph of the area A of FIG. 1 enlarged.
4 is a photomicrograph showing the measurement points of a Nano infrared ray (IR) spectrum.
Figure 5 is the Nano IR spectrum.
6 is a schematic view of a lithium battery according to one embodiment.

Hereinafter, a separator according to an embodiment, a method for manufacturing the same, and a nonaqueous electrolyte secondary battery including the same will be described in detail. The following description is merely exemplary in nature and is in no way intended to limit the application or uses thereof.

1, a separator 10 according to an embodiment comprises a porous layer 11 containing a polyolefin resin, a second layer 12 comprising a water-based polymer and a polyolefin resin as binders, and a second layer 12 comprising a cellulose nano- And a third layer 13 including a water-soluble or water-dispersible polymer. In this specification, the term "water-based polymer" refers to a water-soluble or water-dispersible polymer.

(Embodiment 1)

<Porous film made of polyolefin resin>

Examples of the polyolefin-based resin include homopolymers or copolymers obtained by polymerization of -olefins such as ethylene, propylene, 1-butene, 4-methyl-1-pentene and 1-hexene. Two or more such homopolymers or copolymers may also be mixed. Of these, at least one of a polyethylene-based resin and a polypropylene-based resin can be used.

Examples of the polyethylene-based resin include low density polyethylene, linear low density polyethylene, linear ultra low density polyethylene, medium density polyethylene, high density polyethylene, and copolymers containing ethylene as a main component. Examples of the copolymer containing ethylene as a main component include ethylene and an? -Olefin having 3 to 10 carbon atoms such as propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene and 1-octene; vinyl acetate and vinyl propionate Unsaturated carboxylic acid esters such as vinyl esters, methyl acrylate, ethyl acrylate, methyl methacrylate and ethyl methacrylate; unsaturated compounds such as conjugated dienes and non-conjugated dienes; Or a mixed composition thereof. The content of ethylene units in the ethylene-based aggregate is usually more than 50% by weight.

As such a polyethylene-based resin, at least one selected from low-density polyethylene, linear low-density polyethylene and high-density polyethylene can be used, and for example, a polyethylene resin, for example, high-density polyethylene is used.

Examples of the polypropylene resin include homo-propylene (propylene homopolymer), propylene and ethylene, and α-olefins such as 1-butene, 1-pentene, 1-hexene, - random copolymers or block copolymers with olefins. Of these, homopolypropylene is suitable from the viewpoint of maintaining the mechanical strength, heat resistance and the like of the porous film.

Examples of the polypropylene resin include polyvinyl chloride resins such as those available under the trade names of Novatek PP, WINTEC (manufactured by Japan Polypropylene Co., Ltd.), Nortio, Tafmer XR (manufactured by Mitsui Chemicals) , "Prime TPO" (manufactured by Sumitomo Chemical Co., Ltd.), "Sumoromonobrene", "Tough selenium" (manufactured by Sumitomo Chemical Co., Ltd.), "Prime polypropylene" (Commercially available from Dow Chemical Co., Ltd.) such as "Adflex", "Adsyl", "HMS-PP (PF814)" Products can be used.

In the separator according to one embodiment, an additive to be added to the resin composition can be suitably added to the porous film containing the polyolefin-based resin, within the range not deteriorating the effect of the separator in addition to the above-mentioned resin.

The porous film containing the polyolefin-based resin may have a single-layer structure or a multi-layered structure, and is not particularly limited.

<Cellulose nanofiber>

Cellulose nanofibers have attracted attention as separator materials because they are thermally stable up to about 300 占 폚 and are wood-derived materials that can be reproduced. On the other hand, in the separator using the cellulose fiber, since a large number of hydrogen bonds are generated between the fibers due to the hydroxyl groups present on the surface of the cellulose fiber, the separator becomes a hard and fragile separator. Particularly, there is a problem that the handling property is poor and the shutdown characteristic is not provided in a dry atmosphere.

The present inventors have completed the invention of providing a separator having excellent heat resistance, shutdown characteristics, and ease of handling in the light of the foregoing, a method for producing the same, and a nonaqueous electrolyte secondary battery comprising the same.

Cellulose nanofibers are used as a material for forming the separator.

The cellulose used as the raw material of the microcellulose fiber is not particularly limited, and for example, natural cellulose separated and purified from biosystheses such as plants, animals, and bacteria-producing gel can be used. More specifically, for example, nonwoven pulp such as softwood pulp, hardwood pulp, cotton linter, pulp such as straw pulp or bagasse pulp, bacterial cellulose or Ascidiacea, Cellulose separated from seaweed, and the like.

The cellulose nanofibers may have an average fiber diameter of from about 3 nm to about 300 nm, such as from about 5 nm to about 200 nm, such as from about 10 nm to about 100 nm, such as from about 20 nm to about 150 nm, such as from about 30 nm to about 100 nm, When the average fiber diameter is in the above range, the separator permeability is excellent. In addition, fibers having a fiber diameter of 1 탆 or more are not included as much as possible. Specifically, the proportion of fibers having a fiber diameter of less than 1 占 퐉 is 80% by weight or more, for example, 95% by weight or more, for example, 95 to 99% by weight. The proportion of fibers having a fiber diameter of 500 nm or less is 80% by weight or more, for example, 80 to 99% by weight. By reducing the proportion of fibers having a large fiber diameter, it is easy to control the thickness of the separator, micro pore diameter, permeability, and the like at the time of film formation.

Further, the fiber diameter can be measured by observing and observing a separator state or a dilute solution of cellulosic fiber in a cast film and drying it by a transmission electron microscope or a scanning electron microscope. (E type or B type clay type), tensile strength, and specific surface area of the porous film of a cellulose nanofiber water dispersion of not less than 0.1% by weight and less than 2% by weight, the ratio of fibers having a fiber diameter of less than 1 탆 Can be obtained. See, for example, International Publication No. 2013/054884.

<Water-based polymer for binder>

As a material for forming the separator, a binder made of a water-soluble or water-dispersible polymer is used together with a cellulose nanofiber. The water-soluble or water-dispersible polymer represents an aqueous polymer. The solubility of such a polymer in water depends on the temperature and the concentration. For example, when the polymer powder is added to water and stirred, if the water is partially melted, the surface of the polymer powder is dissolved in water, It becomes a dispersed state. By using such a polymer, the adhesion between the porous film made of a polyolefin-based resin and the cellulose nanofiber layer is improved.

In this specification, elongation at break refers to a value measured in accordance with JIS K7127.

The above-mentioned water-based polymer may be a polymer having a reactor capable of hydrogen bonding with the cellulose nanofiber. The polymer having a reactor capable of hydrogen bonding with the cellulose nanofiber may be a polymer having a hydroxyl group in the main chain, a hydroxyl group in the side chain and / or a functional group (-CO, -COO, -COOH, -CN, - NH ₂ and the like). When a polymer having a reactor capable of hydrogen bonding with the cellulose nanofibers is used as a binder, hydrogen bonding of the cellulose nanofibers is suppressed, and a separator having excellent strength and heat resistance can be produced.

Examples of the water-based polymer include a urethane resin, an acrylic resin, a phenol resin, a polyester resin, an epoxy resin, a polystyrene resin, a polyvinyl alcohol, a polyethylene resin, a polyacrylamide resin and the like. Polyvinyl alcohol is used. The polyvinyl alcohol has neither a degree of polymerization, a degree of saponification nor a modifying group, but it has a high degree of polymerization and a low degree of saponification so as not to lower the solubility in water from the viewpoint of interlayer adhesion. Specifically, the degree of polymerization is not less than 1.000, for example from 1,000 to 8,000, for example from 1,000 to 4,000, and the saponification degree is not more than 90%, for example from 60 to 90%, for example from 80 to 90% 90%.

&Lt; Lamination of the first layer which is a porous film and the third layer which comprises cellulose nanofibers &gt;

In the present embodiment, a first layer which is a porous film containing a polyolefin resin and a third layer which is a binder including a water-soluble or water-dispersible polymer and a cellulose nanofiber are laminated. The method of lamination is not particularly limited. For example, a method (coating method) in which a composition comprising a cellulose nanofiber and a binder comprising a water-soluble or water-dispersible polymer is applied onto a porous film (solvent is water) . This method is inexpensive and has high interlaminar adhesion.

The composition may be in the form of, for example, a suspension.

When the lamination is carried out by the coating method, since the suspension flows into the pores of the first layer though a small amount, the pores of the portion of the first layer that is in contact with the third layer in the dried layer (water- An acidic polymer) is introduced into a state where a second layer in which a polyolefin resin and a binder coexist is formed. The extent to which the binder is supported on the pores of the first layer may depend on the wettability of the coating composition and the molecular weight of the water-soluble or water-dispersible polymer used as the binder. The wettability of the coating composition may vary depending on the content of the water-soluble organic solvent contained in the coating composition, the kind of the binder, the content of the binder, and the like. The weight average molecular weight of the water-soluble or water-dispersible polymer usable as the binder is, for example, from 10,000 to 500,000, for example, from 20,000 to 300,000. When the weight average molecular weight of the water-soluble or water-dispersible polymer is in the above range, the thickness of the third layer may be at least 1/10 of the thickness of the first layer, for example, 0.1 to 5, for example, 0.5 to 2 . In this way, a part of the so-called third layer is pinched into the first layer to form the second layer, so that the laminated film is strongly and firmly bonded.

The thickness of the second layer may be less than or equal to 1/2 (0.5) of the thickness of the first layer, for example from 1/100 to 1/2, for example from 0.02 to 0.1.

The total thickness of the second layer and the third layer is 5 mu m or less, for example, 0.5 to 5 mu m.

In the third layer, the water-based polymer used as the binder does not contain a synthetic fiber (polyester fiber or the like) having a larger fiber diameter than that of the cellulose nanofiber. Thus, the lithium ion secondary battery manufactured by using such a separator has lithium The movement of the ions is not inhibited. As a result, good battery performance (cycle characteristics) can be realized.

The binder used in the formation of the third layer may have a non-fiber form, for example, and may enter the pores of the first layer to form the second layer.

The thickness of the third layer including the binder and the cellulose nanofibers is 1/10 or more of the thickness of the first layer, which is a porous film made of a polyolefin-based resin, and the heat resistance of the separator is not deteriorated.

In the third layer, the content of the water-based polymer as a binder is 0.1 to 40 parts by weight based on 100 parts by weight of the cellulose nanofiber. When the binder is in the above range, the mechanical strength (elongation at break) of the separator is insufficient and there is no risk of breakage, pores of the separator are clogged, ion conductivity is not lowered, and heat resistance and strength characteristics are excellent.

The content of the cellulose nanofibers in the third layer is 60 to 99.9 parts by weight based on 100 parts by weight of the total weight of the water-based polymer and the cellulose nanofibers. When the content of the cellulose nanofibers is within the above range, the ion conductivity of the separator is lowered, or the mechanical strength (elongation at break) of the separator is not lowered, and the heat resistance is excellent.

The content of the water-based polymer in the second layer is 60 to 99.9 parts by weight based on 100 parts by weight of the total amount of the water-based polymer and the polyolefin resin.

Also, even when the first layer and the third layer are laminated by using a method other than the coating method, for example, when heat is applied and compression is performed, the binder enters the pore portion of the portion of the first layer that is in contact with the third layer, Two layers are formed.

&Lt; Water soluble organic solvent &

The above-mentioned third layer can be produced by applying a suspension prepared by suspending the cellulose nanofibers, the binder and the water-soluble organic solvent in water to a porous film containing the above-mentioned polyolefin-based resin. This water-soluble organic solvent functions as a water-soluble pore-forming agent and forms a large number of openings in a film in which the coating liquid is dried by removing the water-soluble organic solvent, for example, by drying the coating liquid. As the water-soluble organic solvent functioning as such a water-soluble pore-forming agent, conventional ones can be used. For example, at least one organic solvent selected from an alcohol series, a lactone series, a glycol series, a glycol ether series, a glycerin series, a carbonate series, and N-methylpyrrolidone. Examples of the alcoholic organic solvent include 1,5-pentanediol, 1-methylamino-2,3-propanediol and the like, and lactone-based organic solvents include, for example,? -Caprolactone,? -Acetyl? -Butyrolactone And the like. Examples of the glycol-based organic solvent include diethylene glycol, 1,3-butylene glycol and propylene glycol. The glycol ether organic solvent includes, for example, triethylene glycol dimethyl ether, tripropylene glycol dimethyl ether, Diethylene glycol monobutyl ether, triethylene glycol monomethyl ether, triethylene glycol butyl methyl ether, tetraethylene glycol dimethyl ether, diethylene glycol monoethyl ether acetate, diethylene glycol monoethyl ether, triethylene glycol monobutyl ether, tetra Ethylene glycol monomethyl ether, ethylene glycol monobutyl ether, dipropylene glycol monomethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoisopropyl ether, ethylene glycol monoisobutyl ether, tripropylene glycol monomethyl ether, diethylene glycol methyl ethyl ether, And diethylene glycol diethyl ether . Examples of the carbonate-based organic solvent include propylene carbonate, ethylene carbonate, and the like. Examples of the water-insoluble organic solvent include glycerin, N-methylpyrrolidone, and mixtures thereof. According to one embodiment, triethylene glycol butyl methyl ether is used as a water-soluble organic solvent.

The water-soluble organic solvent may be removed in the drying process as described above and may be removed in the cleaning process by the organic solvent. Therefore, in the final nonaqueous secondary electrolyte separator, there is almost no water-soluble organic solvent.

<Separator for Non-aqueous Electrolyte Secondary Battery>

The separator for a nonaqueous electrolyte secondary battery of the present embodiment includes a laminated film in which the above-described first layer, second layer, and third layer are laminated. A layer other than the laminated film may be provided. The thickness of this separator is 5 탆 to 50 탆. When the thickness of the separator is within the above range, the tensile strength of the separator is not lowered, and the ratio of the separator in the battery becomes too large, so that the battery capacity is insufficient and the heat resistance and the strength property are excellent.

The separator of the present embodiment has a degree of air permeability of 50 sec / 100cc to 2000 sec / 100cc, for example, 20 sec / 100cc to 1000 sec / 100cc, for example, 50 sec / 100cc to 900 sec / 100cc, 100 sec / 100cc to 800 sec / 100cc, for example, 200 sec / 100cc to 800 sec / 100cc, for example, 300 sec / 100cc to 600 sec / 100cc. When the air permeability is in the above range, the pore distribution of the separator becomes large, so that the generation of the inert lithium can be prevented in advance, and the ion conductivity of the separator is excellent.

In this specification, the air permeability refers to a value measured in accordance with JIS P8117.

<Manufacturing Method of Separator>

Hereinafter, a method of manufacturing the separator according to one embodiment will be described.

A method for producing a separator includes a step of preparing a porous film containing a polyolefin resin, a coating step of applying a composition obtained by mixing a cellulose nanofiber, a binder, a water-soluble organic solvent and water onto a porous film, And a drying step of drying the coating liquid applied on the film.

The composition may have, for example, a suspension state.

The drying process may be performed at a temperature of, for example, 50 캜 or higher. After the drying process, a cleaning process using an organic solvent can be further performed. As the organic solvent, for example, toluene and the like can be used.

&Lt; Preparation process &gt;

A porous film containing the above-mentioned polyolefin-based resin is prepared. The thickness of the porous membrane is, for example, 5 탆 to 45 탆.

<Coating Step>

First, an aqueous suspension of a cellulose nanofiber having a predetermined concentration is prepared.

Subsequently, a mixed suspension prepared by adding the aqueous polymer for a binder described above to the aqueous suspension of the prepared cellulose nanofiber is adjusted.

At this time, as described above, the content of the water-based polymer as the binder is 0.1 to 50 parts by weight based on 100 parts by weight of the cellulose nanofiber.

The concentration of the cellulose nanofibers in the solution can be appropriately adjusted according to the film forming method. The solvent of the solution is preferably water from the viewpoint of handling and manufacturing cost, but may also be used by adding a solvent having a higher vapor pressure than water.

Subsequently, the above-mentioned water-soluble organic solvent is added to the suspension to adjust the suspension. The amount of the water-soluble organic solvent to be added in the suspension may be adjusted depending on the properties of the membrane, etc. However, from the viewpoint of ensuring the required pore size as the separator, the amount of the water-soluble organic solvent is preferably 5 parts by weight or more, For example up to 1000 parts by weight, for example from 5 to 1000 parts by weight.

In addition, the order of addition of the binder and the water-soluble organic solvent may be reversed, that is, the aqueous suspension of the cellulose nanofibers may be first added with the water-soluble organic solvent, and then the binder may be added.

The prepared suspension is then applied to the porous membrane. More specifically, the present invention relates to a method and apparatus for use in a roll forming machine, such as a comma coater, roll coater, reverse roll coater, direct gravure coater, reverse gravure coater, offset gravure coater, roll kiss coater, reverse kiss coater, micro gravure coater, A coating method, a coating method, a coater, a die coater, a dip coater, a blade coater, a brush coater, a curtain coater, a die slot coater, a cast coater or a combination of two or more coating methods. The coating method may be a batch method, a continuous method,

The porous film may also be subjected to surface treatment such as fluorine coating, corona treatment, plasma treatment, UV treatment, anchor coat, etc., in consideration of the adhesion to the porous film and the adhesion of the coated film after drying.

<Drying step>

Subsequently, the composition applied on the porous membrane is dried to form the second layer and the third layer. For example, it can be dried by hot air drying, infrared drying, hot plate drying, vacuum drying or the like. The third layer may also be referred to as a nonwoven fabric mainly composed of cellulose nanofibers.

The drying step is carried out at a temperature of, for example, 50 ° C or higher, for example, 60 ° C or higher, from the viewpoint of sufficiently reducing the amount of water and the water-soluble organic solvent remaining. From the viewpoint of preventing the deterioration of the porous film, it is carried out at 130 占 폚 or lower, for example, at 110 占 폚 or lower.

Further, water and a water-soluble organic solvent may be evaporated to form a third layer, and then the obtained third layer may be cleaned using an organic solvent or the like. Thus, the removal amount of the water-soluble organic solvent can be increased. The organic solvent is not particularly limited. For example, organic solvents having relatively high volatilization rates such as toluene, acetone, methyl ethyl ketone, ethyl acetate, n-hexane and propanol may be used alone or in combination of two or more, .

For the purpose of cleaning the residual water-soluble organic solvent, a solvent having high affinity with water such as ethanol and methanol is preferable. Since moisture in the air is absorbed to affect the physical properties of the third layer and the sheet shape of the separator, It is used in a controlled state of water content. A highly hydrophobic solvent such as n-hexane and toluene is suitable for cleaning the remaining water-soluble organic solvent because the water-soluble organic solvent has a poor cleaning effect but is hardly hygroscopic.

For the reasons described above, a method of gradually replacing the solvent while changing the type of the solvent so as to increase the hydrophobicity is repeated. For example, cleaning may be performed in the order of acetone, toluene, and n-hexane.

Subsequently, press processing of the laminated films of the first layer, the second layer and the third layer is carried out if necessary. This press treatment is not necessarily required.

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

The shape of the nonaqueous electrolyte secondary battery is not particularly limited, and may be, for example, a jelly roll type, a stack type, a stack folding type, or a lamination-stack type.

The nonaqueous electrolyte secondary battery according to one embodiment is manufactured in such a manner that an electrode assembly including a positive electrode, a negative electrode, and a separator according to one embodiment is included in a battery case together with an electrolyte solution. The electrode assembly has a structure in which an anode and a cathode are wound or laminated in a predetermined form with a separator according to one embodiment interposed therebetween.

The nonaqueous electrolyte secondary battery according to one embodiment may be, for example, a stacking battery. The nonaqueous electrolyte secondary battery may be a lithium secondary battery. The lithium secondary battery can be a lithium ion battery, a lithium polymer battery, a lithium sulfur battery, a lithium air battery, or the like.

First, a negative electrode is prepared according to a negative electrode manufacturing method.

The negative electrode may be prepared by mixing, for example, a negative electrode active material, a conductive material, a binder and a solvent, and directly coating the negative electrode active material composition with a current collector such as a copper foil to produce a negative electrode plate. Alternatively, the negative electrode active material composition may be cast on a separate support, and the negative electrode active material film peeled from the support may be laminated on a copper current collector to produce a negative electrode plate. The negative electrode is not limited to the above-described form, but may be in a form other than the above-described form.

The negative electrode active material may be any material that can be used as a negative electrode active material of a lithium battery in the related art. For example, at least one selected from the group consisting of a lithium metal, a metal capable of alloying with lithium, a transition metal oxide, a non-transition metal oxide, and a carbon-based material.

For example, the metal that can be alloyed with lithium is at least one element selected from the group consisting of Si, Sn, Al, Ge, Pb, Bi, Sb Si-Y alloys (Y is an alkali metal, an alkaline earth metal, a Group 13 to Group 16 element, Or a combination element thereof and not Si), a Sn-Y alloy (Y is an alkali metal, an alkaline earth metal, a Group 13 to Group 16 element, a transition metal, a rare earth element or a combination element thereof and not Sn) . The element Y may be at least one element selected from the group consisting of Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ti, Ge, P, As, Sb, Se, Te, Po, or a combination thereof.

For example, the transition metal oxide may be lithium titanium oxide, vanadium oxide, lithium vanadium oxide, or the like.

For example, the non-transition metal oxide may be SnO ₂ , SiO _x (0 <x <2), or the like.

The carbon-based material may be crystalline carbon, amorphous carbon, or a mixture thereof. The crystalline carbon may be graphite such as natural graphite or artificial graphite in the form of amorphous, plate-like, flake, spherical or fibrous type, and the amorphous carbon may be soft carbon or hard carbon carbon, mesophase pitch carbide, calcined coke, and the like.

As the conductive material, metal powders such as acetylene black, natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, copper, nickel, aluminum and silver, metal fibers and the like can be used. And derivatives thereof may be used alone or in combination of two or more. However, the present invention is not limited thereto, and any conductive material may be used as long as it can be used as a conductive material in the related art. In addition, the above-described crystalline carbon-based material can be added as a conductive material.

Examples of the binder include vinylidene fluoride / hexafluoropropylene copolymer, polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, polytetrafluoroethylene and mixtures thereof, and styrene butadiene rubber-based polymers May be additionally used, but are not limited thereto and may be additionally used as long as they can be used as binders in the art.

As the solvent, N-methylpyrrolidone, acetone, water or the like may be used, but not limited thereto, and any solvent which can be used in the technical field can be used.

The content of the negative electrode active material, the conductive material, the binder and the solvent is a level commonly used in a lithium battery. Depending on the use and configuration of the lithium battery, one or more of the conductive material and the solvent may be omitted.

Next, an anode is prepared according to the anode manufacturing method.

The positive electrode can be produced in the same manner as the positive electrode except that the positive electrode active material is used instead of the negative electrode active material. The conductive material, the binder and the solvent used in the cathode active material composition may be the same as those used for the cathode.

For example, a positive electrode active material composition is prepared by mixing a positive electrode active material, a conductive material, a binder, and a solvent, and then directly coated on the aluminum current collector to produce a positive electrode plate. Alternatively, the positive electrode active material composition may be cast on a separate support, and the positive electrode active material film peeled from the support may be laminated on an aluminum current collector to produce a positive electrode plate. The anode is not limited to those described above, but may be in a form other than the above.

The positive electrode active material may include at least one selected from the group consisting of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, and lithium manganese oxide. However, May be used.

For example, Li _a A _{1 - b} B _b D ₂ , wherein 0.90 ≤ a ≤ 1.8, and 0 ≤ b ≤ 0.5; Li _a E _{1 - b} B _b O _{2 - c} D _{c where} 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05; LiE _{2 - b} B _b O _{4 - c} D _{c where} 0? B? 0.5, 0? C? 0.05; Li _a Ni _{1 -b- c} Co _b B _c D _? Wherein, in the formula, 0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05, 0 <? Li _a Ni _{1 -b- c} Co _b B _c O _{2 - ?} F _? Wherein, in the formula, 0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05, 0 <? Li _a Ni _{1 -b- c} Co _b B _c O _{2 - ?} F ₂ wherein 0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05, 0 <? Li _a Ni _{1 -b- c} Mn _b B _c D _? Wherein, in the formula, 0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05, 0 <? Li _a Ni _{1 -b- c} Mn _b B _c O _{2 - ?} F _? Wherein, in the formula, 0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05, 0 <? Li _a Ni _{1 -b- c} Mn _b B _c O _{2 - ?} F ₂ wherein 0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05, 0 <? Li _a Ni _b E _c G _d O ₂ wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, and 0.001 ≤ d ≤ 0.1; Li _a Ni _b Co _c Mn _d GeO ₂ wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.5, and 0.001 ≤ e ≤ 0.1; Li _a NiG _b O ₂ (in the above formula, 0.90? A? 1.8, and 0.001? B? 0.1); Li _a CoG _b O ₂ wherein, in the above formula, 0.90? A? 1.8, and 0.001? B? 0.1; Li _a MnG _b O ₂ (in the above formula, 0.90? A? 1.8, 0.001? B? 0.1); Li _a Mn ₂ G _b O ₄ wherein, in the above formula, 0.90? A? 1.8, and 0.001? B? 0.1; QO _2; QS ₂ ; LiQS ₂ ; V ₂ O ₅ ; LiV ₂ O ₅ ; LiIO ₂ ; LiNiVO _4; Li _(3-f) J ₂ (PO ₄ ) ₃ (0? F? 2); Li _(3-f) Fe ₂ (PO ₄ ) ₃ (0? F? 2); In the formula of LiFePO ₄ may be used a compound represented by any one:

In the above formula, A is Ni, Co, Mn, or a combination thereof; B is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element or a combination thereof; D is O, F, S, P, or a combination thereof; E is Co, Mn, or a combination thereof; F is F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or combinations thereof; Q is Ti, Mo, Mn, or a combination thereof; I is Cr, V, Fe, Sc, Y, or a combination thereof; J is V, Cr, Mn, Co, Ni, Cu, or a combination thereof.

Of course, a compound having a coating layer on the surface of the compound may be used, or a compound having a coating layer may be mixed with the compound. The coating layer may comprise an oxide of a coating element, a hydroxide, an oxyhydroxide of the coating element, an oxycarbonate of the coating element, or a coating element compound of a hydroxycarbonate of the coating element. The compound constituting these coating layers may be amorphous or crystalline. The coating layer may contain Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr or a mixture thereof. The coating layer forming step may be any coating method as long as it can coat the above compound by a method that does not adversely affect physical properties of the cathode active material (for example, spray coating, dipping, etc.) by using these elements, It will be understood by those skilled in the art that a detailed description will be omitted.

For _{example, LiNiO 2, LiCoO 2, LiMn} x O 2x (x = 1 or _{2), LiNi 1 - x Mn} x O 2 (0 <x <1), LiNi 1 -xy Co x Mn y O 2 (0 ? 0.5, 0? Y? 0.5), LiFePO _4, or the like can be used.

An electrolyte is prepared in addition to the above-described separator. For example, the electrolyte may be an organic electrolyte. In addition, the electrolyte may be a solid. For example, boron oxide, lithium oxynitride, and the like, but not limited thereto, and any of them can be used as long as they can be used as solid electrolytes in the art. The solid electrolyte may be formed on the cathode by a method such as sputtering.

For example, an organic electrolytic solution can be prepared. The organic electrolytic solution can be prepared by dissolving a lithium salt in an organic solvent.

The organic solvent may be any organic solvent which can be used in the art. Examples of the solvent include propylene carbonate, ethylene carbonate, fluoroethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl isopropyl carbonate, dipropyl carbonate, dibutyl carbonate , N, N-dimethylformamide, dimethylacetamide, dimethylsulfoxide, tetrahydrofuran, tetrahydrofuran, acetonitrile, tetrahydrofuran, 2-methyltetrahydrofuran, , Dioxane, 1,2-dimethoxyethane, sulfolane, dichloroethane, chlorobenzene, nitrobenzene, diethylene glycol, dimethyl ether or mixtures thereof.

The lithium salt may also be used as long as it can be used in the art as a lithium salt. For example, LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , LiAlO ₂ , LiAlCl ₄ , _x F _{2x + 1} SO ₂ ) (C _y F _{2y + 1} SO ₂ ) (where x and y are natural numbers), LiCl, LiI, or a mixture thereof.

As shown in FIG. 6, the lithium battery 1 includes an anode 3, a cathode 2, and a separator 4. The anode 3, the cathode 2 and the separator 4 described above are wound or folded and housed in the battery case 5. Then, an organic electrolytic solution is injected into the battery case 5 and is sealed with a cap assembly 6 to complete the lithium battery 1. The battery case may have a cylindrical shape, a rectangular shape, a thin film shape, a pouch shape, a coin shape, or the like. The lithium battery may be a thin film battery. The lithium battery may be a lithium ion battery.

The nonaqueous electrolyte secondary battery can be classified into various batteries such as a lithium air battery, a lithium oxide battery, and a lithium total solid battery.

In addition, a plurality of battery structures are stacked to form a battery pack, and such a battery pack can be used for all devices requiring high capacity and high output. For example, a notebook, a smart phone, an electric vehicle, and the like.

In particular, non-aqueous electrolyte secondary batteries are excellent in electric vehicle (EV) because of their high-rate characteristics and long life characteristics. For example, a hybrid vehicle such as a plug-in hybrid electric vehicle (PHEV). It is suitable for electric bicycle (E-bike), electric scooter (escooter), electric golf cart, electric power storage system.

Hereinafter, the present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto.

(Example 1)

Triethyleneglycol butyl methyl ether (manufactured by Toho Chemical Industry Co., Ltd.) as a water-soluble organic solvent was added in an amount of 100: 1 (weight ratio) to an aqueous suspension of 0.5% by weight of the cellulose nanofibers and stirred to prepare a mixed solution. An aqueous solution of polyvinyl alcohol (polymerization degree: 3500, manufactured by Wako Pure Chemical Industries, Ltd.) adjusted to 0.5% by weight in the above mixed solution was added in an amount of 1 part by weight based on 100 parts by weight of the mixed solution and stirred to prepare a suspension.

The obtained suspension was applied on a polyethylene porous film (thickness: 7 m, permeability: 94 sec / 100 cc) using an applicator so that the thickness of the dried third layer became 6 m, and water was dried After thoroughly washing with toluene, the resultant was further dried in an oven at 85 캜 to obtain a separator 1. The thickness of the second layer containing polyethylene and polyvinyl alcohol in the separator 1 was about 500 nm.

Here, cellulose nanofiber originated from acetic acid bacteria, having an average fiber diameter of 50 nm, a fiber content of 1 占 퐉 or more, and a fiber average length of about 2.5 占 퐉 was used as the cellulose nanofiber.

 (Example 2)

The same material and the same method as in Example 1 were used to prepare the separator 2, except that the suspension was applied so that the thickness of the third layer after drying was 10 占 퐉. The thickness of the second layer containing polyethylene and polyvinyl alcohol in the separator 2 was about 500 nm.

(Example 3)

The separator 3 was produced using the same materials and the same method as in Example 1, except that the suspension was applied so that the thickness of the third layer after drying was 30 占 퐉 and the dried coating film was pressed at a pressure of about 50 MPa . By the press, the thickness of the third layer was 6 占 퐉. The thickness of the second layer in the separator 3 was about 500 nm.

(Example 4)

Separator 4 was prepared using the same materials and the same method as in Example 1, except that the suspension was applied so that the thickness of the third layer after drying was 45 占 퐉, and the dried coating film was pressed at 50 MPa. By the press, the thickness of the third layer became 11 탆. The thickness of the second layer in the separator 4 was about 500 nm.

(Example 5)

A separator 5 was prepared using the same materials and the same method as in Example 1 except that a polyethylene-emulsion modified with maleic acid in place of polyvinyl alcohol was added in a weight ratio of 100:20 with respect to the cellulose nanofiber. The thickness of the second layer in the separator 5 is about 500 nm.

(Example 6-7)

A separator was produced in the same manner as in Example 1 except that the content of polyvinyl alcohol was changed to about 1 part by weight and 40 parts by weight based on 100 parts by weight of the cellulose nanofibers, respectively.

(Comparative Example 1)

Only the polyethylene porous film (first layer) used in Example 1 was used as the separator 6.

(Comparative Example 2)

The suspension was applied on the PET film so that the thickness of the coated film after drying was 14 占 퐉 without using the polyethylene porous film (first layer). The PET film was peeled off after drying the suspension, and the dried film was used as the separator 7.

(Comparative Example 3)

A porous film having alumina-based ceramics particles coated with a thickness of 4 mu m on a polyethylene porous film having a thickness of 14 mu m was used as the separator 9. [

(Comparative Example 4)

An aqueous solution of 1% by weight of polyvinyl alcohol (degree of polymerization: 3500, manufactured by Wako Pure Chemical Industries, Ltd.) was applied to the polyethylene porous film (first layer) used in Example 1 so that the thickness of the dried film became 1 탆 and dried , A third layer containing cellulose nanofibers was formed on the coating film in the same manner as in Example 1. That is, the first layer and the third layer are not in direct contact with each other but a layer made of polyvinyl alcohol is formed between them.

(Comparative Example 5)

A 1% by weight aqueous solution of carboxymethyl cellulose (MAC350HC, manufactured by Nippon Paper Chemicals, Inc.) was applied to the polyethylene porous film (first layer) used in Example 1 so that the thickness of the coated film after drying was 1 占 퐉 and dried , A third layer containing cellulose nanofibers was formed on the coating film in the same manner as in Example 1. That is, the first layer and the third layer are not in direct contact with each other, but a layer of carboxymethyl cellulose is formed between them.

(Evaluation example)

Physical properties of the separator produced in accordance with Example 1-5 and Comparative Example 1-5 were evaluated according to the following measurement methods.

The thickness of the separator was measured using a micrometer.

The separator permeability was measured using a Gurley type specimen gauge (Gurley type Densometer, manufactured by Toyoda Seiki) specified in JISP8117, and a test piece fixedly attached to a circular hole having an outer diameter of 28.6 mm, Were measured. Further, the separator was heated to 200 占 폚 and measured before and after the separator.

The puncture strength was determined by fixing a separator between two metal plates with pores of 1 cm in diameter, and measuring a needle probe having a tip of 1 mm? (R = 0.5) using a compression mode of a texture analyzer (manufactured by Eiko Seiki Co., Ltd.) . A point at which the separator was broken was regarded as a puncture strength.

The average pore diameter was measured by mercury porosimetry (Autofor IV9510, Micromeritics Inc. Product).

The heat resistance was measured using a test piece made of a separator having a width of 3 mm and a length of 30 mm (measuring section 20 mm, TD direction being the major axis). The specimen was heated from 10 ° C / min to 350 ° C and measured using a thermomechanical analyzer (EXSTAR 6000, manufactured by Seiko Instruments Inc.) so that a force of 2 mN / Temperature.

The cycle characteristics were measured and carried out as described below. A test cell was fabricated using the fabricated separator. The positive electrode of the test cell was made of lithium nickel cobalt aluminum oxide (LiNo _0.85 Co _0.14 Al _0.01 O ₂ ) and the negative electrode was made of artificial graphite. A laminated battery was prepared in a constant temperature chamber set at 25 ° C, and the mixture was subjected to charge / discharge (4.35-2.75 V) at a rate of 10 hours to be converted into a solid. Thereafter, one cycle of constant current constant voltage charging at a two hour rate and constant current discharge at a five hour rate was carried out, and the initial capacity of the obtained value was confirmed. Thereafter, charge / discharge (4.35-2.8 V) was performed 200 times at an hour rate. One cycle of constant-current constant-voltage charging at a two-hour rate and constant-current discharge at a five-hour rate was carried out every 100 cycles of 1 hour rate, and the ratio of the obtained value to the initial capacity was defined as the capacity retention rate.

The cycle characteristics were measured in the same manner as in Example 1, and in Examples 2 and 4 and Comparative Examples 1, 2 and 4 shown below.

The results of the above physical properties measurement are shown in Table 1 below.

division
Thickness (㎛) Specularity
(Sec / 100cc) Sting intensity
(gf)
Heat resistance temperature
(° C)
PE CNF total Other CNF / PE One 2 Example 1 7 6 13 0 0.86 240.7 ∞ 322 321 Example 2 7 10 17 0 1.42 277.2 ∞ 331 322 Example 3 7 6 13 0 0.86 622 ∞ 335 325 Example 4 7 11 18 0 1.57 922 ∞ 339 324 Example 5 - - - - - 330.2 ∞ 330 320 Comparative Example 1 7 0 7 0 0 94 Heat shrinkage 340.1 143 Comparative Example 2 0 14 14 0 - 210 221 106 320 Comparative Example 3 14 0 18 4 0 198 Heat shrinkage 350 165 Comparative Example 4 7 6 14 One 0.86 ∞ ∞ 320 321 Comparative Example 5 7 6 14 One 0.86 ∞ ∞ 325 323

In Table 1, 1 represents heating before heating, 2 after heating, PE is the thickness of the first layer, CNF is the total thickness of the second and third layers, and CNF / PE ratio is the third layer / .

Microscopic observation and NanoIR spectral observation were performed. The observation results are shown in Figs. 2 to 5. Fig. FIGS. 2 and 3 are the results of analysis using Tecnai G2 F20 from FEI, and FIG. 4 were analyzed using nano-IR2 from Anasys Instruments.

The IR spectra at the upper side of FIG. 5 and the IR spectra at the lower side of FIG. 5 were observed at the upper observation point shown in FIG. 4 and the lower observation points of FIG. It was observed that the separators of Examples 1 to 5 contained polyvinyl alcohol or maleic acid-denatured polyethylene in the pores of the polyethylene on the side of the coated surface of the polyethylene porous film. In this embodiment, the stamper strength is as high as 300 gf or more, the heat-resistant temperature is 300 占 폚 or more, and has high sticking strength (mechanical strength) and high heat-resistant temperature (heat resistance). The separators of Examples 1 to 5 also had a shutdown characteristic and a capacity retention ratio of greater than 90%. In Examples 3 and 5, the capacity retention rate was not measured.

On the other hand, the separators of Comparative Examples 1 and 3 had a high stamper strength of 300 gf or more but a low heat-resistant temperature of less than 200 캜. The separator of Comparative Example 2 had a heat-resistant temperature exceeding 300 but a stuck strength as low as 106 gf. In addition, the separators of Comparative Examples 4 and 5 were so highly permeable that the movement of lithium ions was greatly inhibited.

The physical properties of the separator obtained in accordance with Example 6-7 were evaluated according to the same measurement method as the physical properties of the separator prepared in Example 1-5.

As a result of the evaluation, the physical properties of the separator of Example 6-7 were equivalent to those of the separator of Example 1.

(Other Embodiments)

The above-described embodiment is illustrative and is not limited to this example, and well-known techniques, tolerance techniques, and publicly known techniques may be combined or partially substituted in these examples. Modification inventions which can be easily obtained by those skilled in the art are also included.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the exemplary embodiments or constructions. It will be apparent to those skilled in the art that various modifications and variations are possible in light of the above teachings will be. Accordingly, the scope of protection of the invention should be determined by the appended claims.

1: Lithium battery 2: cathode
3: anode 4: separator
5: Battery case 6: Cap assembly

Claims (24)

A first layer which is a porous film comprising a polyolefin-based resin;
A second layer comprising a polyolefin resin and an aqueous polymer; And
A separator comprising a third layer comprising an aqueous polymer and a cellulose nanofiber. The method according to claim 1,
Wherein the cellulose nanofibers have a ratio of fibers having a fiber diameter of less than 1 占 퐉 of 80% by weight or more. The method according to claim 1,
Wherein the thickness of the third layer is 1/10 or more of the thickness of the first layer. The method according to claim 1,
Wherein the thickness of the separator is 5 占 퐉 to 50 占 퐉. The method according to claim 1,
Wherein the thickness of the second layer is 1/2 or less of the thickness of the first layer. The method according to claim 1,
Wherein the polyolefin-based resin is a polyethylene-based resin, a polypropylene-based resin, or a combination thereof. The method according to claim 1,
Wherein the content of the water-based polymer in the third layer is 0.1 to 40 parts by weight based on 100 parts by weight of the cellulose nanofiber. The method according to claim 1,
And the air permeability of the separator is 50 sec / 100 cc to 2000 sec / 100 cc. The method according to claim 1,
Wherein the content of the cellulose nanofibers in the third layer is 60 parts by weight to 99.9 parts by weight based on 100 parts by weight of the total weight of the water-based polymer and the cellulose nanofibers. The method according to claim 1,
Wherein the content of the water-based polymer in the second layer is 60 parts by weight to 99.9 parts by weight based on 100 parts by weight of the total weight of the polyolefin resin and the water-based polymer. The method according to claim 1,
Wherein the water-based polymer is a polymer having a reactor capable of forming a hydrogen bond with the cellulose nanofiber. The method according to claim 1,
Wherein the water-based polymer is a polymer having a hydroxyl group in its main chain, a polymer having at least one selected from the group consisting of hydroxyl, -CO, -COO, -COOH, -CN, and -NH ₂ in the side chain or a combination thereof. The method according to claim 1,
Wherein the water-based polymer is at least one selected from the group consisting of a urethane resin, an acrylic resin, a phenol resin, a polyester resin, an epoxy resin, a polystyrene resin, polyvinyl alcohol, a polyethylene resin, a polyacrylamide resin and the like. The method according to claim 1,
Wherein the water-based polymer has a non-fiber form. anode; cathode; And a separator according to any one of claims 1 to 14 interposed between the separator and the nonaqueous electrolyte secondary battery. Preparing a porous membrane comprising a polyolefin-based resin;
Supplying a composition comprising a cellulose nanofiber, an aqueous polymer, a water-soluble organic solvent and water to a porous membrane comprising the polyolefin-based resin; and
And drying the composition supplied to the porous film containing the polyolefin-based resin. 17. The method of claim 16,
The water-soluble organic solvent is at least one selected from the group consisting of an alcohol series, a lactone series, a glycol series, a glycol ether series, glycerin, propylene carbonate, and N-methylpyrrolidone,
Wherein the content of the water-soluble organic solvent is 5 parts by weight or more based on 100 parts by weight of the cellulose nanofiber. 17. The method of claim 16,
The water-soluble organic solvent may be selected from the group consisting of 1,5-pentanediol, 1-methylamino-2,3-propanediol, epsilon -caprolactone,? -Acetyl? -Butyrolactone, diethylene glycol, Propylene glycol dimethyl ether, tripropylene glycol dimethyl ether, diethylene glycol monobutyl ether, triethylene glycol monomethyl ether, triethylene glycol butyl methyl ether, tetraethylene glycol dimethyl ether, diethylene glycol monoethyl ether acetate, Diethylene glycol monoethyl ether, diethylene glycol monoethyl ether, triethylene glycol monobutyl ether, tetraethylene glycol monobutyl ether, dipropylene glycol monomethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoisopropyl ether, ethylene glycol monoisobutyl ether, Tripropylene glycol monomethyl ether, diethylene glycol The method of butyl ether, and diethylene glycol diethyl ether, glycerol, the separator comprising propylene carbonate, ethylene carbonate, and N- methylpyrrolidinone at least one selected from a money. 17. The method of claim 16,
The water-based polymer is a polymer having a reactor capable of forming a hydrogen bond with the cellulose nanofiber,
Wherein said aqueous polymer is a polymer having a hydroxyl group in its main chain, a polymer having at least one selected from hydroxyl group, -CO, -COO, -COOH, -CN, and -NH ₂ in its side chain or a combination thereof. 17. The method of claim 16,
Wherein the water-based polymer is at least one selected from urethane resin, acrylic resin, phenol resin, polyester resin, epoxy resin, polystyrene resin, polyvinyl alcohol, polyethylene resin, polyacrylamide resin,
Wherein the content of the water-based polymer is 0.1 wt% to 50 wt% based on 100 wt% of the cellulose nanofiber. 17. The method of claim 16,
Wherein the drying is carried out at 50 DEG C or higher. 17. The method of claim 16,
Wherein the step of drying the composition supplied to the porous film containing the polyolefin resin further performs a cleaning process with an organic solvent. 17. The method of claim 16,
Wherein the cellulose nanofibers have a ratio of fibers having a fiber diameter of less than 1 占 퐉 of 80% by weight or more. 17. The method of claim 16,
Wherein the polyolefin-based resin is a polyethylene-based resin, a polypropylene-based resin, or a combination thereof.

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