KR20170088271A - Separator for Nonaqueous Electrolyte Secondary battery - Google Patents

Abstract

Provided is a separator for a nonaqueous electrolyte secondary battery which comprises: a cellulose nanofiber; and a crosslinking agent having at least one of aluminum and boron as a main component. The main component couples to a hydroxyl group of the cellulose nanofiber, and performs crosslinking between the cellulose nanofibers. Through the separator for the nonaqueous electrolyte secondary battery, the withstand voltage can be improved with the str.

Description

Separator for Nonaqueous Electrolyte Secondary Battery [0002]

The present invention relates to a separator for a nonaqueous electrolyte secondary battery, a nonaqueous electrolyte secondary battery using the same, and a method of manufacturing the same.

In a non-aqueous electrolyte secondary battery such as a lithium ion battery, a separator for separating the positive electrode and the negative electrode to prevent a short circuit is used. The separator is required to have basic performance such as resistance to electrolyte and low internal resistance. In addition, in recent years, the demand for heat resistance is also increasing for using non-aqueous electrolyte secondary batteries in automobiles and the like.

As a separator for a nonaqueous electrolyte secondary battery, a porous film made of polyolefin such as polyethylene or polypropylene is widely used. However, when used in automobiles, heat resistance to a temperature of 200 DEG C or more may be required, and thus it is difficult to use polyolefin as a separator.

In recent years, a nonwoven fabric using cellulose as a separator having high heat resistance is expected. Among them, it has been studied to obtain a separator having excellent electrical characteristics by using cellulose nano fibers having a fiber diameter of 1 占 퐉 or less (see, for example, Patent Document 1).

However, the cellulose nonwoven fabric has a problem of low strength. The general nonwoven fabric is one in which the cellulose fibers are bonded to each other by hydrogen bonding, and if wetted by the electrolyte solution, fibrillation occurs, and the strength of the nonwoven fabric is greatly lowered. In order to improve the strength of the separator using the cellulose nanofibers, it has been studied to use a binder made of a hydrophilic polymer having a carboxyl group or a hydroxyl group (see, for example, Patent Document 2).

[Patent Document 1] Japanese Laid-Open Patent Publication No. 2006-049797 [Patent Document 2] JP-A-2014-210987

However, the separator using the cellulose nano fiber has a problem that the withstand voltage is low other than the strength. Recently, it has been required to charge the battery with a voltage of 4.3 V or more in order to increase the specific capacity of the electrode active material. However, the cellulose nanofibers have a large number of hydroxyl groups, and the hydroxyl groups exposed on the surface of the fibers are disadvantageously decomposed by increasing the voltage, which causes deterioration of the battery.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a separator for a nonaqueous electrolyte secondary battery which has improved strength withstanding voltage and strength, a nonaqueous electrolyte secondary battery using the same, and a method of manufacturing the same.

According to one aspect of the present invention,

Cellulose nanofibers; And

And a cross-linking agent containing at least one of aluminum and boron as a main component,

Wherein the main component binds to a hydroxyl group of the cellulose nanofiber and crosses the cellulosic nanofibers,

A separator for a nonaqueous electrolyte secondary battery is provided.

According to another aspect of the present invention,

There is provided a nonaqueous electrolyte secondary battery comprising the separator for the nonaqueous electrolyte secondary battery.

According to another aspect of the present invention,

A step of casting a mixture of the cellulose nanofibers and the water-soluble pore-forming agent to obtain a porous membrane; And

And impregnating the porous membrane with a solution containing a crosslinking agent to crosslink the porous membrane,

Wherein the cross-linking agent comprises at least one of aluminum and boron as a main component,

Wherein the main component binds to the hydroxyl groups of the cellulose nanofibers and crosses the cellulosic nanofibers,

A method of manufacturing a separator for a nonaqueous electrolyte secondary battery is provided.

INDUSTRIAL APPLICABILITY According to the separator for a nonaqueous electrolyte secondary battery of the present invention and the method for producing the same, it is possible to improve the characteristics of the nonaqueous electrolyte secondary battery by providing a separator with improved strength and withstanding voltage.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a spectrum showing the results of measurement of absorption of total infrared radiation of Examples 1 to 3 and Comparative Examples 1 and 2; FIG.

Hereinafter, a separator for a nonaqueous electrolyte secondary battery according to exemplary embodiments will be described in more detail.

The separator for a nonaqueous electrolyte secondary battery according to the following embodiments can be used as a separator for a nonaqueous electrolyte secondary battery such as a lithium ion battery.

The separator for a nonaqueous electrolyte secondary battery according to an embodiment includes a cellulose nano fiber; And a cross-linking agent containing at least one of aluminum and boron as a main component. The main component binds to a hydroxyl group of the cellulose nanofibers and cross-links the cellulose nanofibers.

Here, the cellulose nanofiber is a fine-sized cellulosic fiber. For example, natural cellulose fibers such as pulp or refined cellulose fibers subjected to fibrillation treatment, fine liners derived from refined linter or ascidiacea, and the like , And bacterial cellulose produced by a cellulose-producing bacterium can be used. Of these, natural cellulose fibers are preferably fined by fibrillating treatment in that they are easily available.

In one specific example, the cellulose nanofiber preferably has an average fiber diameter of about 20 nm to 300 nm. It is also preferable that the fibers do not contain fibers having a fiber diameter of 1 占 퐉 or more. Specifically, the proportion of fibers having a fiber diameter of less than 1 占 퐉 is preferably 90% by weight or more, and more preferably 95% by weight or more. It is also preferable that the proportion of fibers having a fiber diameter of 500 nm or less is 80% by weight or more. By reducing the proportion of fibers having a large fiber diameter as described above, it is easy to control the thickness, pore size and gurley permeability of the separator at the time of film formation. The fiber diameter can be measured by observing with a transmission electron microscope (TEM) and a scanning electron microscope (SEM) a separator state or a film in which a dilute solution of cellulose fiber is cast and dried. The ratio of the fibers having a fiber diameter of less than 1 占 퐉 can be obtained by comprehensively evaluating the viscosity (E type or B type viscometer), tensile strength and surface area of the porous film of 0.1 to 2 weight% of the cellulose fiber water dispersion (for example, , International Publication No. 2013/054884).

The crosslinking agent is composed mainly of a compound containing aluminum or boron which can easily form an ionic bond with the hydroxyl group of the cellulose nanofiber. For example, an inorganic compound that is easily ionized in water and an organic compound that is easily hydrolyzed in water can be used.

In one specific example, the crosslinking agent may comprise at least one of a water-soluble inorganic salt and an organic compound to be hydrolyzed.

According to one embodiment, the cross-linking agent may comprise a metal salt or a non-metal salt including polyvalent cations and anions. The crosslinking agent may include at least one of aluminum sulfate, aluminum oxyacid, boron sulfate and boron oxyacid. For example, the cross-linking agent, but may include aluminum sulfate _{(Al 2 (SO 4) 3} ), sodium aluminate _{(NaAlO 2), B 2 (} SO 4) 3, boric acid (B (OH) ₃₎ or the like, But is not limited thereto.

According to another embodiment, the crosslinking agent may comprise at least one of an aluminum compound and a boron compound.

For example, the crosslinking agent may include at least one of an aluminum compound and a boron compound represented by any one of the following formulas (1) to (5), but is not limited thereto:

MR (OH) ₂ (1)

_{(HO) 2 MM (OH)} 2 ... (2)

(RO) ₂ MOM (OR) ₂ (3)

M (O (C = O) R '(4)

M (OH) _3-x (OR'C (= O) O) _x (5)

In the formulas (1) to (5), M is aluminum or boron, R is hydrogen, a linear or branched alkyl group having 1 to 8 carbon atoms or a cycloalkyl group, and R ' Branched alkyl group, oxygen-containing glycol ether group or diol group, and 1? X? 3.

In the present specification, a and b of "carbon number a to b" mean the carbon number of a specific functional group. That is, the functional group may include a carbon atom from a to b. For example, "alkyl group of 1 to 4 carbon atoms" is an alkyl group having from 1 to 4 carbon atoms, _{i.e., CH 3 -, CH 3 CH} 2 -, CH 3 CH 2 CH 2 -, (CH 3) 2 CH-, CH ₃ CH ₂ CH ₂ CH ₂ -, CH ₃ CH ₂ CH (CH ₃ ) - and (CH ₃ ) ₃ C -.

As used herein, the term "alkyl group" refers to a branched or unbranched aliphatic hydrocarbon group. Specifically, "straight chain alkyl group" means an unbranched aliphatic hydrocarbon group, and "branched alkyl group" means branched aliphatic hydrocarbon group. In one embodiment, the alkyl group may be substituted or unsubstituted. The alkyl group includes alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, hexyl, But are not necessarily limited thereto, and each of them may be optionally substituted or unsubstituted. In one embodiment, the alkyl group may have from 1 to 8 carbon atoms. Examples of the alkyl group having 1 to 8 carbon atoms include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, pentyl, A til group, and the like, but are not limited thereto.

As used herein, the term "cycloalkyl group" means a fully saturated carbocycle ring or ring system. For example, a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, and a cyclooctyl group.

Specific examples of the aluminum compound or the boron compound include aluminum isopropoxide, aluminum sec-butoxide, bis (2-ethylhexanoate), hydroxyaluminum, aluminum 2-ethylhexanoate, ethyl (tri- Butoxy) diamine, ethylboronic acid, butylboronic acid, n-octylboronic acid, cyclohexylboronic acid, tetrahydroxyboronic acid, tripropyl borate, tributyl borate, triisoborate (4,4,5,5-tetramethyl-1,3,2-dioxanoborane-2-yl) methane, bis (neopentylglycolato) diboron, bis Diboron, and the like, but the present invention is not limited thereto.

These compounds can be used singly or in various combinations. For example, two or more inorganic compounds may be used in combination, two or more organic compounds may be used in combination, and at least one inorganic compound and at least one organic compound may be used in combination. Specifically, a compound containing aluminum and a compound containing boron may be used in combination.

Aluminum and boron, which are the main components of the crosslinking agent, can bind to the hydroxyl groups of the cellulose nanofibers. Therefore, the hydroxyl groups of the cellulose nanofibers, that is, the hydroxyl groups exposed on the surfaces of the cellulose nanofibers, can be masked with aluminum or boron, which is a main component of the crosslinking agent, and can be masked with aluminum or boron. Here, the term "masking" means a method of capping or blocking a functional group of a compound with a predetermined masking agent to protect it from the outside. Therefore, in the present invention, Means that the hydroxyl group is protected from the outside by aluminum or boron.

Further, since one aluminum or boron can bind to at least one hydroxyl group, aluminum and boron can cross-link between adjacent cellulose nanofibers.

Therefore, the separator according to an embodiment of the present invention has a much higher tensile strength than cellulose nanofibers are bonded by hydrogen bonds between conventional hydroxyl groups due to cross-linking of the cellulose nanofibers through aluminum or boron .

In addition, when not treated with a crosslinking agent containing aluminum or boron as a main component, a free hydroxyl group that does not participate in the hydrogen bonding between the cellulose nanofibers is present on the surface of the cellulose nanofibers. Since such a free hydroxyl group is easily decomposed at the time of charging, in the case of a battery including such a hydroxyl group, the capacity retention rate may be drastically lowered when the battery is charged to about 4.3V. However, since the separator according to one embodiment of the present invention is masked by aluminum or boron, the separator of the present invention is hardly decomposed at the time of charging, and exhibits a high capacity retention rate even when the battery containing the same is charged to about 4.3V. Specifically, even when charged to about 4.4 V, the capacity retention ratio is 70% or more.

In one specific example, the separator of the present invention can be produced by casting a mixture of cellulose nanofibers and water-soluble starch agent. Specifically, first, a casting solution is prepared by adding a water-soluble agent to a water suspension of the cellulose nanofibers. Thereafter, the casting solution is applied on a flat surface and then dried to form a porous film. The obtained porous membrane is washed to remove the pore-forming agent, dried, immersed in a solution containing a crosslinking agent, heated and dried, and the crosslinking reaction is allowed to proceed.

The concentration of the cellulose nanofibers in the casting solution can be appropriately adjusted by a vapor deposition method. The solvent of the casting solution is preferably water because it is easy to handle and is inexpensive, but a solvent having a higher vapor pressure than water may be added.

As the water-soluble pelletizer, those well known in the art can be used. For example, higher alcohols such as 1,5-pentanediol and 1-methylamino-2,3-propanediol, lactones such as epsilon -caprolactone and -acetyl- gamma -butyllactone, diethylene glycol, 1,3-butylene glycol and propylene glycol, 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, tetraethylene glycol monobutyl ether, dipropylene glycol monomethyl ether, diethylene glycol monomethyl ether, ethylene glycol mono Isopropyl ether, ethylene glycol monoisobutyl ether, tripropylene glycol monomethyl ether, di Glycol and the like can be used methyl ethyl ether and diethylene glycol diethyl ether and glycol ethers, glycerine, propylene carbonate, and N- methylpyrrolidone. Particularly, triethylene glycol butyl methyl ether is preferable.

The addition amount of the water-soluble crosslinking agent in the casting solution can be adjusted according to the properties of the required film. In order to ensure the pores required for the separator, the amount may preferably be 5 parts by weight or more based on 100 parts by weight of the cellulose nano- May be 100 parts by weight or more, preferably 3000 parts by weight or less, and more preferably 1000 parts by weight or less.

The solution containing the cellulose nanofibers can be applied by a method known in the art. For example, it can be applied on a flat surface by using a slot die coater, a curtain coater, an MB coater, an MB reverse coater or a comma coater.

In order to sufficiently reduce the residual amount of the solvent and the water-soluble release agent, the drying temperature of the casting solution may be preferably at least 50 ° C, and more preferably at least 60 ° C . On the other hand, in order to prevent deterioration of the cellulose nanofibers, the casting solution may be dried at a temperature of preferably 200 ° C or lower, more preferably 150 ° C or lower, still more preferably 120 ° C or lower . At this time, a heating heater, infrared irradiation, or hot air may be used. The casting solution can also be dried in a reduced pressure environment.

In one specific example, water and a water-soluble pore-forming agent are evaporated to form a porous membrane, and then the obtained porous membrane can be washed with an organic solvent or the like. The organic solvent is not particularly limited. For example, the organic solvent having a relatively high volatilization rate such as toluene, acetone, methyl ethyl ketone, ethyl acetate, n-hexane or propanol may be used singly or in combination, Can be used over. For the purpose of washing the residual thixotropic agent, a solvent having high affinity with water such as ethanol and methanol is preferable. However, water in the coating base material is converted into a solvent or absorbs moisture in the air, so that the properties of the cellulose microporous membrane, It is preferable to use it in a state in which the moisture content is controlled. A highly hydrophobic solvent such as n-hexane or toluene has a disadvantage of deteriorating the cleaning effect of the hydrophilic pore-forming agent, but can be suitably used in order to make it difficult to absorb moisture. For this reason, a method of repeating the washing while changing the type of the solvent so as to increase the hydrophobicity gradually is preferable. For example, cleaning can be done in the order of acetone, toluene, and n-hexane.

As described above, the cross-linking agent may include at least one of a water-soluble inorganic salt and an organic compound to be hydrolyzed. According to one embodiment, the cross-linking agent may comprise at least one of aluminum sulfate, aluminum oxyacid, boron sulfate and boron oxyacid. For example, the crosslinking agent may include at least one of an organoaluminum compound and an organic boron compound, but is not limited thereto.

The cross-linking agent solution may be a solution of a compound containing aluminum or boron, as described above. The concentration of the crosslinking agent can be adjusted depending on the characteristics of the required membrane and the kind of the crosslinking agent. However, in order to improve the strength of the membrane and to improve the withstanding voltage of the masked hydroxyl group, May be preferably 0.01 part by weight or more, more preferably 0.015 part by weight or more, and still more preferably 0.02 part by weight or more. In order to maintain the porosity of the membrane, the concentration of the cross-linking agent may be preferably 0.21 parts by weight or less, more preferably 0.2 parts by weight or less, still more preferably 0.18 parts by weight or less, Parts by weight. For example, in the step of crosslinking the porous membrane with the use of the crosslinking agent satisfying the concentration range, the crosslinking agent may be contained in the cellulose nano fiber in an amount of 0.01 wt% to 0.2 wt%.

The amount of the crosslinking agent in the finally obtained separator is, for example, allowed to stand for 3 days in a room having a low humidity of -30 DEG C or less and the dried porous film is cut into A4 size. The weight difference between the porous film and the non- The weight can be measured by comparing the weight with the weight. In addition, the porous membrane is boiled in an aqueous solution of hydrochloric acid + nitric acid (1: 1) to extract aluminum or boron and then analyzed by inductively coupled plasma mass spectrometry (ICP-MS) or inductively coupled plasma emission spectroscopy (ICP-AES) can do.

The solvent of the crosslinking agent solution may be selected depending on the kind of the crosslinking agent. For example, when the crosslinking agent is an inorganic salt, water may be used as a solvent. When the crosslinking agent is an organic compound, an organic solvent may be used. If necessary, water and an organic solvent may be mixed, or various organic solvents may be mixed.

The temperature of the drying step of the crosslinking agent solution can be controlled depending on the type of the solvent. However, in order to sufficiently promote the crosslinking and to sufficiently reduce the amount of the solvent remaining, the temperature may preferably be 50 ° C or higher, . In order to prevent deterioration of the cellulose nanofibers, the temperature of the step of drying the crosslinking agent solution may be preferably 200 ° C or lower, more preferably 150 ° C or lower, still more preferably 120 ° C or lower have. At this time, a heating heater, infrared irradiation, or hot air may be used. The crosslinking agent solution can also be dried in a reduced pressure environment.

In one specific example, after crosslinking, the porous membrane may be washed using an organic solvent or the like. In this case, the organic solvent is not particularly limited, but toluene, for example, may be used.

In one specific example, the porous membrane can be pressed after crosslinking. By performing the press as described above, after the cross-linking treatment and the drying treatment are carried out, the surface of the porous membrane can be smooth or adjusted to a desired porosity. The pressure at the time of pressing can be adjusted according to the characteristics of the required film, but it can be preferably 2 MPa or more and 50 MPa or less.

In one specific example, the casting solution may contain an alkali salt or ammonium salt of carboxymethylcellulose, a cellulose derivative binder such as methylhydroxyethylcellulose, hydroxypropylcellulose, or hydroxypropylmethylcellulose. By adding the binder, the strength of the film can be further improved. When the binder is added, the amount of the binder to be added may be 1 part by weight or more, preferably 1 part by weight or more, based on 100 parts by weight of the cellulose nanofibers in order to improve the strength. In order to maintain the flexibility of the film, have.

In one specific example, a water soluble padding agent may be added to the crosslinking agent solution. When the water-soluble crosslinking agent is added, it is possible to easily maintain the porosity and crosslink. When the water-soluble crosslinking agent is added to the crosslinking agent solution, the amount thereof may be preferably about 100 parts by weight to about 600 parts by weight based on 100 parts by weight of the cellulose nanofibers.

The pore size of the porous membrane after crosslinking may be less than or equal to about 2 탆 so as to avoid shorting during assembly and charging of the cell. The porosity can be adjusted depending on the characteristics of the required separator, but may be preferably 30% to 60%, and the gauge permeability may preferably be 300 seconds / 100 mL or less. The pore size can be measured by mercury porosimetry or bubble point method. It can be calculated from the specific gravity of the porous cellulose nanofibers and the density of the membrane. The gully permeability can be measured by a method in accordance with JIS P8117.

The thickness of the porous film after crosslinking can be adjusted according to the characteristics of the required separator, but it may preferably be 10 탆 or more, and more preferably be 14 탆 or more, in order to improve the insulating property and the ease of manufacture. Further, for ion conduction between the anode and the cathode, it may preferably be 25 占 퐉 or less, and more preferably 20 占 퐉 or less. The thickness can be measured by a micrometer or the like.

Considering the strength required for the separator, the tensile strength of the porous membrane after crosslinking, that is, the separator for the nonaqueous electrolyte secondary battery may be preferably 200 kgf / cm ^{2 or} more, more preferably 250 kgf / cm ^{2 or} more , Still more preferably not less than 300 kgf / cm ² . The tensile strength is preferably as high as possible, but it may preferably be 1200 kgf / cm ² or less, considering the winding property, slit property and porosity. The tensile strength can be measured by a tensile test.

After the crosslinking, the porous membrane, that is, the separator for the nonaqueous electrolyte secondary battery, at 3300 cm ^-1 in the ATR spectrum, the peak strength of the crosslinked separator may be 50% or less of the peak strength of the ungraded separator.

In the porous membrane after crosslinking, that is, in the separator for the nonaqueous electrolyte secondary battery, the cellulose nanofiber may have a ratio of fibers having a fiber diameter of less than 1 탆 of 90% by weight or more.

The porous membrane after crosslinking may preferably have a low content of impurities, considering the performance as a separator. For example, the Na content in the separator may preferably be less than 1 ppm. For example, the water content in the separator may preferably be less than 1000 ppm, and more preferably less than 300 ppm. For example, the residual amount of the water-soluble release agent in the separator may preferably be 500 ppm or less. It is also desirable to minimize the halogen content of the separator other than fluorine. However, the components contained in the electrolytic solution may be contained in the separator. Further, a quaternary ammonium salt, a phosphonium salt or a pyrrolidinium salt of a fluorine-containing organic acid such as bis (trifluoromethanesulfonium) amide or the like can be added to the crosslinking agent solution for the removal of static electricity and the like to be contained in the separator .

The present invention will be described in more detail by way of the following examples and comparative examples. However, the examples are for illustrating the present invention, and the scope of the present invention is not limited thereto.

[Example]

<Tensile Strength>

A width of 15 mm and a length of 50 mm was prepared and the tensile strength was measured by a tensile tester (digital material tester, manufactured by INSTRON). The measurement was carried out ten times, and the average value was used.

<Porosity>

The porosity was determined by multiplying the value obtained by dividing the difference in specific gravity and density of the porous membrane by the specific gravity, and multiplying by 100. The specific gravity of the porous membrane was the specific gravity of the cellulose fibers. The density of the porous membrane was calculated from the basis weight and thickness of the porous membrane. The thickness of the porous membrane was measured in micrometers.

<Gully speculation>

The time when 100 mL of air passed through the specimen secured in close contact with a circular hole having an outer diameter of 28.6 mm was measured by using a gully dynamometer (Gully type densimeter, manufactured by Dongyang Precision Machinery Co., Ltd.) prescribed in JISP8117.

<Capacity retention rate>

The prepared porous membrane was used as a separator to prepare a battery. Lithium cobalt oxide was used as the positive electrode of the battery, and artificial graphite was used as the negative electrode. (4.2 to 2.75 V) at a rate of 10 hours in an environment of 25 캜. Thereafter, the cell was charged twice to a constant voltage at a rate of 5 hours, and discharged to 2.75 V to confirm the initial capacity. The battery was charged three times from the 5 hour rate to the constant voltage and stored in a thermostat set at 60 占 폚 for 15 days in the charged state. After 15 days, the battery was taken out from the thermostat, cooled to 25 ° C, and discharged at a rate of 5 hours to 2.75V. The ratio of the obtained value to the initial capacity was defined as the capacity retention rate.

<Cellulose nanofibers>

The cellulose nanofibers were derived from pulp and had an average fiber diameter of 100 nm and a content of fibers having a fiber diameter of 1 占 퐉 or more of 5%.

&Lt; Measurement of Infrared Absorption Spectrum &

An infrared total absorption absorption (ATR) spectrum measurement was performed on the obtained sample. The measurement was carried out by Nicolet is 10 from Thermo Scientific. The prism was made of diamond. The absorption intensity was normalized by a peak near 1430 cm ^-1 .

(Example 1)

Carboxymethylcellulose (SANROZ MAC500LC, manufactured by Japan Kagaku Co., Ltd.) and triethylene glycol butyl methyl ether (manufactured by Orient Chemical Industries, Ltd.) were added as a binder to a water suspension of 2 wt% of the cellulose nanofibers and stirred, Solution. The binder was added in an amount of 1 part by weight based on 100 parts by weight of the cellulose nanofibers and 250 parts by weight in terms of 100 parts by weight of the cellulose nanofibers. The prepared casting solution was cast in a chalet, and then the solvent and triethylene glycol butyl methyl ether were evaporated on a hot plate at 85 DEG C to form a porous film. The resulting porous membrane was washed with toluene and again dried on a hot plate at 85 캜.

Thereafter, the porous membrane was immersed in the crosslinking agent solution filled in the chalet, and crosslinking was carried out while evaporating the solvent and triethylene glycol butyl methyl ether on a hot plate at 85 캜. The crosslinking agent solution was prepared so that 0.03 parts by weight of aluminum sulfate (manufactured by Wako Pure Chemical Industries, Ltd.) and 250 parts by weight of triethylene glycol butyl methyl ether were added based on 100 parts by weight of the cellulose nanofibers contained in the porous membrane Aqueous solution was used. After the crosslinking reaction, it was washed with toluene and pressed at a pressure of 20 MPa to obtain a crosslinked porous film.

The thickness of the crosslinked porous membrane was 18 탆, the gauge permeability was 205.2 sec / 100 mL, and the tensile strength was 278 kgf / cm ² . The capacity retention ratio of the cell obtained using the obtained crosslinked porous film as a separator was measured at a constant voltage of 4.4 V and found to be 76%.

(Example 2)

A crosslinked porous membrane was prepared in the same manner as in Example 1 except that 0.13 parts by weight of aluminum sulfate contained in the crosslinking agent solution was added.

The cross-linked porous membrane had a thickness of 18 탆, a gauge permeability of 205.2 sec / 100 mL, and a tensile strength of 304 kgf / cm ² . The capacity retention rate was measured at a constant voltage of 4.4 V and found to be 76%.

(Example 3)

A crosslinked porous membrane was prepared in the same manner as in Example 1 except that 0.21 part by weight of aluminum sulfate contained in the crosslinking agent solution was added.

The thickness of the crosslinked porous membrane was 15 mu m, the gluing rate was 232.4 sec / 100 mL, and the tensile strength was 368 kgf / cm &lt; ^{2 &} gt ;. The capacity retention ratio was measured at a constant voltage of 4.4 V and found to be 71%.

(Example 4)

A crosslinked porous membrane was prepared in the same manner as in Example 3, except that 440 parts by weight of triethylene glycol butyl methyl ether contained in the crosslinking agent solution was added.

The thickness of the crosslinked porous membrane was 20 mu m, the gluing rate was 244.8 sec / 100 mL, and the tensile strength was 323 kgf / cm &lt; ^{2 &} gt ;. The capacity retention ratio at a constant voltage of 4.4 V was measured and found to be 74%.

(Example 5)

Except that the crosslinking agent solution was changed to a solution prepared so that 0.02 part by weight of sodium aluminate (manufactured by Hikari Pure Chemical Industries, Ltd.) and 440 parts by weight of triethylene glycol butyl methyl ether were added to 100 parts by weight of the cellulose nano fiber contained in the porous membrane Using the same method as in Example 1, a crosslinked porous membrane was prepared.

The cross-linked membrane thickness is 20 ㎛, Gurley gas permeability was 213.2 seconds / 100mL, tensile strength was 388 kgf / cm ^2. The capacity retention rate was measured at a constant voltage of 4.4 V and found to be 76%.

(Example 6)

A cross-linked porous membrane was prepared in the same manner as in Example 5 except that 0.10 part by weight of sodium aluminate contained in the cross-linking agent solution was added.

The thickness of the crosslinked porous membrane was 14 mu m, the gauge permeability was 206.4 sec / 100 mL, and the tensile strength was 394 kgf / cm &lt; ^{2 &} gt ;. The capacity retention rate was measured at a constant voltage of 4.4 V and found to be 76%.

(Example 7)

A crosslinked porous membrane was prepared in the same manner as in Example 1 except that 0.19 parts by weight of aluminum sulfate contained in the crosslinking agent solution was added.

The thickness of the crosslinked porous membrane was 14 mu m, the gauge permeability was 222.4 sec / 100 mL, and the tensile strength was 394 kgf / cm &lt; ^{2 &} gt ;. The capacity retention ratio was measured at a constant voltage of 4.4 V and found to be 82%.

The crosslinking conditions and measurement results of Examples 1 to 7 are summarized in Table 1 below. In all embodiments, high tensile strengths of 250 kgf / cm &lt; ² &gt; or more were exhibited and high capacity retention ratios of 70% or more at a constant voltage of 4.4 V were exhibited.

(Example 8)

Propanol / toluene solution prepared so that 0.02 part by weight of aluminum isopropoxide (produced by Tokyo Chemical Industry Co., Ltd.) and 200 parts by weight of triethylene glycol butyl methyl ether were added to the cross-linking agent solution based on 100 parts by weight of the cellulose nano fiber contained in the porous membrane , A crosslinked porous film was prepared using the same method as in Example 1. [

The cross-linked membrane thickness is 20 ㎛, Gurley gas permeability was 214.0 seconds / 100mL, tensile strength was 360 kgf / cm ^2. The capacity retention rate was measured at a constant voltage of 4.4 V and found to be 76%.

(Example 9)

A crosslinked porous film was prepared in the same manner as in Example 8 except that the aluminum isopropoxide contained in the crosslinking agent solution was changed to 0.18 part by weight and the triethylene glycol butyl methyl ether was changed to 340 parts by weight.

The thickness of the crosslinked porous membrane was 14 mu m, the gluing rate was 218.3 sec / 100 mL, and the tensile strength was 321 kgf / cm &lt; ^{2 &} gt ;. The capacity retention ratio was measured at a constant voltage of 4.4 V and found to be 77%.

(Example 10)

0.1 part by weight of Al (C ₅ H ₇ O ₂ ) (C ₆ H ₉ O ₃ ) (manufactured by Tokyo Chemical Industry Co., Ltd.), 0.1 part by weight of triethylene glycol butylmethyl (meth) acrylate based on 100 parts by weight of the cellulose nanofibers contained in the porous membrane, A crosslinked porous membrane was prepared in the same manner as in Example 1 except that the isopropanol solution was changed so that the amount of ether was 200 parts by weight.

The thickness of the crosslinked porous membrane was 19 mu m, the gauge permeability was 213.6 sec / 100 mL, and the tensile strength was 359 kgf / cm &lt; ^{2 &} gt ;. The capacity retention ratio was measured at a constant voltage of 4.4 V and found to be 78%.

The crosslinking conditions and measurement results of Examples 8 to 10 are summarized in Table 2 below. In all embodiments, high tensile strengths of 250 kgf / cm &lt; ² &gt; or more were exhibited and high capacity retention ratios of 70% or more at a constant voltage of 4.4 V were exhibited.

(Example 11)

Except that the crosslinking agent solution was changed to an aqueous solution prepared so that 0.01 part by weight of boric acid (manufactured by Hikari Pure Chemical Industries, Ltd.) and 350 parts by weight of triethylene glycol butyl methyl ether were added based on 100 parts by weight of the cellulose nano fibers contained in the porous membrane. Using the same method, a crosslinked porous membrane was prepared.

The thickness of the cross-linked porous membrane was 16 μm, the gauge permeability was 208.8 sec / 100 mL, and the tensile strength was 344 kgf / cm ² . The capacity retention ratio was measured at a constant voltage of 4.4 V and found to be 77%.

(Example 12)

A crosslinked porous film was prepared in the same manner as in Example 11 except that the boric acid contained in the crosslinking agent solution was changed to 0.14 parts by weight.

The cross-linked porous membrane had a thickness of 14 탆, a gauge permeability of 221.6 sec / 100 mL, and a tensile strength of 353 kgf / cm ² . The capacity retention ratio at a constant voltage of 4.4 V was measured and found to be 74%.

(Example 13)

The crosslinking agent solution was added to 0.04 part by weight of (HO) ₂ BB (OH) ₂ (manufactured by Tokyo Chemical Industry Co., Ltd.) and 470 parts by weight of triethylene glycol butylmethyl ether based on 100 parts by weight of the cellulose nanofibers contained in the porous membrane. , A crosslinked porous film was prepared using the same method as in Example 1. [

The thickness of the crosslinked porous membrane was 16 mu m, the gauge permeability was 210.0 sec / 100 mL, and the tensile strength was 355 kgf / cm &lt; ^{2 &} gt ;. The capacity retention ratio was measured at a constant voltage of 4.4 V and found to be 77%.

(Example 14)

A cross-linked porous membrane was prepared in the same manner as in Example 13 except that (HO) ₂ BB (OH) ₂ contained in the cross-linking agent solution was changed to 0.10 part by weight.

The thickness of the crosslinked porous membrane was 15 mu m, the gauge permeability was 221.6 sec / 100 mL, and the tensile strength was 368 kgf / cm &lt; ^{2 &} gt ;. The capacity retention rate was measured at a constant voltage of 4.4 V and found to be 72%.

(Example 15)

0.18 part by weight of (HO) ₂ BB (OH) ₂ (manufactured by Tokyo Chemical Industry Co., Ltd.), 0.02 part by weight of boric acid, and 500 parts by weight of triethylene glycol butylmethylether, based on 100 parts by weight of the cellulose nano- Was changed to a water / ethanol solution prepared so as to be added in the same manner as in Example 1, to prepare a crosslinked porous film.

The cross-linked porous membrane had a thickness of 14 탆, a gauge permeability of 201.6 sec / 100 mL, and a tensile strength of 370 kgf / cm ² . The capacity retention ratio was measured at a constant voltage of 4.4 V and found to be 77%.

The crosslinking conditions and measurement results of Examples 11 to 15 are summarized in Table 3 below. In all embodiments, high tensile strengths of 250 kgf / cm &lt; ² &gt; or more were exhibited and high capacity retention ratios of 70% or more at a constant voltage of 4.4 V were exhibited.

(Example 16)

The crosslinking agent solution was changed to a toluene solution prepared so that 0.13 part by weight of isobornyl borate (produced by Tokyo Chemical Industry Co., Ltd.) and 300 parts by weight of triethylene glycol butyl methyl ether were added based on 100 parts by weight of the cellulose nano fiber contained in the porous membrane , A crosslinked porous film was prepared using the same method as in Example 1.

The thickness of the crosslinked porous membrane was 20 mu m, the gluing rate was 224.2 sec / 100 mL, and the tensile strength was 341 kgf / cm &lt; ^{2 &} gt ;. The capacity retention ratio at the constant voltage of 4.4 V was measured and found to be 73%.

(Example 17)

A crosslinked porous membrane was prepared in the same manner as in Example 17 except that 0.2 part by weight of boric acid isopropoxide contained in the crosslinking agent solution was used.

The cross-linked membrane thickness is 20 ㎛, Gurley gas permeability was 235.7 seconds / 100mL, tensile strength was 411 kgf / cm ^2. The capacity retention ratio was measured at a constant voltage of 4.4 V and found to be 70%.

(Example 18)

The crosslinking agent solution was mixed with 0.04 part by weight of bis (neopentylglycolato) diboron (manufactured by Tokyo Chemical Industry Co., Ltd.) and 200 parts by weight of triethylene glycol butylmethyl ether based on 100 parts by weight of the cellulose nanofibers contained in the porous membrane. , A crosslinked porous film was prepared using the same method as in Example 1. [

The thickness of the crosslinked porous membrane was 17 mu m, the gauge permeability was 217.2 sec / 100 mL, and the tensile strength was 350 kgf / cm &lt; ^{2 &} gt ;. The capacity retention ratio at a constant voltage of 4.4 V was measured and found to be 74%.

The crosslinking conditions and measurement results of the above Examples 16 to 18 are summarized in Table 4. In all embodiments, high tensile strengths of 250 kgf / cm &lt; ² &gt; or more were exhibited and high capacity retention ratios of 70% or more at a constant voltage of 4.4 V were exhibited.

(Comparative Example 1)

An uncrosslinked porous membrane was prepared using the same method as in Example 1, except that the crosslinking was not carried out.

The uncrosslinked porous membrane had a thickness of 22 mu m, a gauge permeability of 199.2 sec / 100 mL, and a tensile strength of 159 kgf / cm &lt; ^{2 &} gt ;. The capacity retention ratio at the constant voltage of 4.4 V was 52%, and the capacity retention ratio at the constant voltage of 4.2 V was 75%.

(Comparative Example 2)

A cross-linked porous membrane was prepared in the same manner as in Example 1, except that the cross-linking agent solution was changed to an aqueous solution prepared so that 0.007 parts by weight of aluminum sulfate was contained based on 100 parts by weight of the cellulose nanofibers contained in the porous membrane.

The thickness of the cross-linked porous membrane was 15 mu m, the gluing rate was 232.4 sec / 100 mL, and the tensile strength was 162 kgf / cm &lt; ^{2 &} gt ;. The capacity retention ratio was measured at a constant voltage of 4.4 V and found to be 54%.

(Comparative Example 3)

A crosslinked porous film was prepared in the same manner as in Example 1 except that the aluminum sulfate contained in the crosslinking agent solution was changed to 0.23 parts by weight.

The thickness of the cross-linked porous membrane was 15 mu m, the gluing strength was 1,634 sec / 100 mL, and the tensile strength was 304 kgf / cm &lt; ^{2 &} gt ;. The capacity retention ratio at a constant voltage of 4.4 V was measured and found to be 66%.

The data of each comparative example are summarized in Table 5 below. In Comparative Example 1 in which the porous membrane was not crosslinked, the tensile strength was less than 200 kgf / cm ² . It also showed a capacity retention rate of 75% at a voltage of 4.2V, but when the voltage was increased to 4.4V, the capacity retention rate dropped to 52%.

In Comparative Example 2 in which the amount of the crosslinking agent was small, the tensile strength was less than 200 kgf / cm ² , and the capacity retention rate was less than 70%. On the other hand, in Comparative Example 3 in which the amount of the crosslinking agent was large, the tensile strength showed a large value, but the capacity retention rate was less than 70%.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a spectrum showing the results of measurement of absorption of total infrared radiation of Examples 1 to 3 and Comparative Examples 1 and 2; FIG.

Referring to FIG. 1, in Comparative Example 1 in which the porous membrane was not crosslinked, a peak corresponding to a bond involved in hydrogen bonding between cellulosic nanofibers was observed at around 1600 cm ^-1 . Also, at 3300 cm ^-1 to 3400 cm ^-1 , a peak corresponding to the hydroxyl group (OH) was observed. In Comparative Example 2 in which crosslinking was carried out with a small amount of aluminum sulfate, the peak around 1600 cm ^-1 and the peak between 3300 cm ^-1 and 3400 cm ^-1 were both small.

On the other hand, in Examples 1 to 3 bridged by aluminum sulfate, the peak near 1600 cm ^-1 and the peak at 3300 cm ^-1 to 3400 cm ^-1 became much smaller than those in Comparative Example 1, It is considered that the hydrogen bonds are bonded through aluminum and most of the hydroxyl groups formed on the surface of the cellulose nanofibers are masked by aluminum.

Claims (20)

Cellulose nanofibers; And
And a cross-linking agent containing at least one of aluminum and boron as a main component,
Wherein the main component binds to a hydroxyl group of the cellulose nanofiber and crosses the cellulosic nanofibers,
Separator for non-aqueous electrolyte secondary battery. The separator for a nonaqueous electrolyte secondary battery according to claim 1, wherein the crosslinking agent comprises at least one of a water-soluble inorganic salt and an organic compound to be hydrolyzed. The separator for a nonaqueous electrolyte secondary battery according to claim 1, wherein the crosslinking agent comprises a metal salt or a nonmetal salt including a polyvalent cation and an anion. The separator for a nonaqueous electrolyte secondary battery according to claim 1, wherein the cross-linking agent comprises at least one of aluminum sulfate, aluminum oxyacid, boron sulfate and boron oxyacid. The separator for a nonaqueous electrolyte secondary battery according to claim 1, wherein the crosslinking agent comprises at least one of an organoaluminum compound and an organic boron compound. The separator for a nonaqueous electrolyte secondary battery according to claim 1, wherein the crosslinking agent comprises at least one of an aluminum compound and a boron compound represented by any one of the following formulas (1) to (5)
MR (OH) ₂ (1)
_{(HO) 2 MM (OH)} 2 ... (2)
(RO) ₂ MOM (OR) ₂ (3)
M (O (C = O) R '(4)
M (OH) _3-x (OR'C (= O) O) _x (5)
In the formulas (1) to (5), M is aluminum or boron, R is hydrogen, a linear or branched alkyl group having 1 to 8 carbon atoms or a cycloalkyl group, and R ' Branched alkyl group, oxygen-containing glycol ether group or diol group, and 1? X? 3. The separator for a nonaqueous electrolyte secondary battery according to claim 1, wherein the crosslinking agent is contained in an amount of 0.01 wt% to 0.22 wt% with respect to the cellulose nanofibers. The separator for a nonaqueous electrolyte secondary battery according to claim 1, wherein the cellulose nanofibers have a fiber ratio of 90% by weight or more to fibers having a fiber diameter of less than 1 占 퐉. The separator for a nonaqueous electrolyte secondary battery according to claim 1, wherein the hydroxyl groups of the cellulose nanofibers are masked by aluminum or boron. The separator for a nonaqueous electrolyte secondary battery according to claim 1, having a tensile strength of 200 kgf / cm ² or more. The separator for a nonaqueous electrolyte secondary battery according to claim 1, wherein the peak intensity of the crosslinked separator is 50% or less of the peak intensity of the ungraded separator at 3300 cm ^-1 in the ATR spectrum. 12. A nonaqueous electrolyte secondary battery comprising the separator for a nonaqueous electrolyte secondary battery according to any one of claims 1 to 11. The nonaqueous electrolyte secondary battery according to claim 12, wherein the capacity retention ratio at a constant voltage of 4.4 V is 70% or more. A step of casting a mixture of the cellulose nanofibers and the water-soluble pore-forming agent to obtain a porous membrane; And
And impregnating the porous membrane with a solution containing a crosslinking agent to crosslink the porous membrane,
Wherein the cross-linking agent comprises at least one of aluminum and boron as a main component,
Wherein the main component binds to the hydroxyl groups of the cellulose nanofibers and crosses the cellulosic nanofibers,
A method for manufacturing a separator for a nonaqueous electrolyte secondary battery. 15. The method for producing a separator for a nonaqueous electrolyte secondary battery according to claim 14, wherein the water soluble separating agent is contained in an amount of 5 parts by weight or more and 3,000 parts by weight or less based on 100 parts by weight of the cellulose nano fiber. 15. The method for producing a separator for a nonaqueous electrolyte secondary battery according to claim 14, wherein the crosslinking agent comprises at least one of a water-soluble inorganic salt and an organic compound to be hydrolyzed. 15. The method for producing a separator for a nonaqueous electrolyte secondary battery according to claim 14, wherein the crosslinking agent comprises at least one of aluminum sulfate, aluminum oxyacid, boron sulfate and boron oxyacid. 15. The method for producing a separator for a nonaqueous electrolyte secondary battery according to claim 14, wherein the crosslinking agent comprises at least one of an aluminum compound and a boron compound. 15. The method for producing a separator for a nonaqueous electrolyte secondary battery according to claim 14, wherein in the step of crosslinking the porous membrane, the crosslinking agent is contained in an amount of not less than 0.01% by weight and not more than 0.2% by weight based on the cellulose nano fiber. 15. The method for producing a separator for a nonaqueous electrolyte secondary battery according to claim 14, wherein the cellulose nanofibers have a fiber ratio of 90% by weight or more.

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