KR101965915B1 - Separator and method for producing same - Google Patents

Abstract

The present invention provides a separator and a method for producing the separator. The separator is a separator in which a porous film containing fine particles and a water-soluble polymer and a polyolefin porous film are laminated to each other, wherein the fine particles have a mean particle diameter of less than 0.1 μm and a specific surface area of 50 m 2 / Wherein the weight ratio of the fine particles (b) to the fine particles (a) is 0.05 to 50, and the weight ratio of the fine particles to the water soluble polymer is 1 to 100. The method comprises a step of coating a slurry containing a water-soluble polymer, fine particles and a medium on a polyolefin porous film, and a step of laminating a porous film containing a water-soluble polymer and fine particles on the polyolefin porous film by removing the medium from the resultant coated film Wherein the fine particles are substantially composed of fine particles (a) having an average particle diameter of less than 0.1 m and a specific surface area of not less than 50 m 2 / g and fine particles (b) having an average particle diameter of not less than 0.2 m, Wherein the weight ratio of the fine particles (b) to the fine particles (a) is 0.05 to 50, the weight ratio of the fine particles to the water soluble polymer is 1 to 100, and the concentration of the water soluble polymer in the water soluble polymer and medium is 0.4 wt% 1.3% by weight or less.

Description

SEPARATOR AND METHOD FOR PRODUCING SAME

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

Background Art Non-aqueous electrolyte secondary batteries, particularly lithium ion secondary batteries, are widely used as batteries for use in personal computers, cellular phones, portable information terminals, and the like because of their high energy density.

The nonaqueous electrolyte secondary battery typified by these lithium ion secondary batteries has a high energy density. If an internal short circuit or an external short circuit occurs due to breakage of a battery or breakage of a device using the battery, an excessive heat may flow due to a large current flow. For this reason, it is required to prevent heat generation at a certain level or more in the nonaqueous electrolyte secondary battery and ensure high safety. Upon abnormal heat generation, the separator generally has a shutdown function for blocking the passage of ions between the positive and negative electrodes to prevent additional heat generation. Examples of the separator having a shutdown function include a separator having a porous film made of a material that melts at the time of abnormal heat generation. That is, in the battery using the separator, the porous film is melted and non-porous (non-porous) at the time of abnormal heat generation, so that passage of ions can be blocked and further heat generation can be suppressed.

As such a separator having a shutdown function, for example, a porous film made of polyolefin is used. The separator made of the polyolefin porous membrane is melted and nonporous at about 80 to 180 DEG C in the abnormal heat generation of the battery, so that the passage of ions can be shut off (shutdown), and further heat generation can be suppressed. However, when the temperature becomes higher, the separator made of the polyolefin porous membrane may be short-circuited due to direct contact between the positive electrode (positive electrode) and the negative electrode (negative electrode) due to contraction or rupture. As described above, the shape stability of a separator made of a polyolefin-made porous film is insufficient when the temperature is further increased, and abnormal heat generation due to a short circuit can not be suppressed in some cases.

On the other hand, a method of imparting shape stability at a high temperature to a separator by laminating a porous film made of a material having heat resistance to the polyolefin porous film has been studied. As such a separator having high heat resistance, for example, a separator in which a porous film obtained by immersing a regenerated cellulose film in an organic solvent and a polyolefin porous film are laminated to each other has been proposed (for example, see Patent Document 1). Such a separator is excellent in shape stability at a high temperature and can provide a nonaqueous electrolyte secondary battery having higher safety, but there is a problem that load characteristics of the nonaqueous electrolyte secondary battery obtained using the separator become insufficient.

Patent Document 2 discloses a separator in which a porous film containing fine particles and a water-soluble polymer and a polyolefin porous film are laminated as a separator having excellent shape stability at a high temperature in addition to shutdown. A nonaqueous electrolyte secondary battery excellent in load characteristics, cycle characteristics, and safety is obtained by using the separator in a nonaqueous electrolyte secondary battery. The separator comprises a step of coating a slurry containing a water-soluble polymer, fine particles and a medium on a polyolefin porous film, and a step of laminating a porous film containing a water-soluble polymer and fine particles on the polyolefin porous film by removing the medium from the resulting coated film Lt; / RTI > However, in some of the obtained separators, it was difficult to say that the balance of shutdown property and shape stability at high temperature was sufficient. That is, there remains a room for improvement from the standpoint of stably producing a separator excellent in shutdown property and shape stability at a high temperature.

Japanese Patent Application Laid-Open No. 10-3898 Japanese Patent Application Laid-Open No. 2004-227972

An object of the present invention is to provide a separator for a nonaqueous electrolyte secondary battery which is excellent in shutdown performance and shape stability at a high temperature, and a method for producing the separator with good reproducibility.

The present invention provides the following.

≪ 1 > A separator comprising a porous film containing fine particles and a water-soluble polymer and a polyolefin porous film laminated to each other,

Wherein the fine particles are substantially composed of fine particles (a) having an average particle diameter of less than 0.1 탆 and a specific surface area of 50 m 2 / g or more and fine particles (b) having an average particle diameter of 0.2 탆 or more,

The weight ratio of the fine particles (b) to the fine particles (a) is 0.05 to 50,

The weight ratio of the fine particles to the water-soluble polymer is 1 to 100.

<2> The separator of <1>, wherein the specific surface area of the fine particles (b) is 20 m 2 / g or less.

(3) The separator of (1) or (2), wherein the water-soluble polymer is at least one polymer selected from the group consisting of cellulose ether, polyvinyl alcohol and sodium alginate.

&Lt; 4 > A separator according to < 3 >, wherein the cellulose ether is carboxymethylcellulose.

(5) The separator according to any one of (1) to (4), wherein the polyolefin porous membrane is a polyethylene porous membrane.

<6> A nonaqueous electrolyte secondary battery having any one of <1> to <5>.

<7> A step of coating a slurry containing a water-soluble polymer, fine particles and a medium on a polyolefin porous film, and a step of laminating a porous film containing a water-soluble polymer and fine particles on the polyolefin porous film by removing the medium from the obtained coating film The method comprising:

Wherein the fine particles are substantially composed of fine particles (a) having an average particle diameter of less than 0.1 탆 and a specific surface area of 50 m 2 / g or more and fine particles (b) having an average particle diameter of 0.2 탆 or more,

The weight ratio of the fine particles (b) to the fine particles (a) is 0.05 to 50,

Wherein the weight ratio of the fine particles to the water-soluble polymer is 1 to 100,

And the concentration of the water-soluble polymer in the total of the water-soluble polymer and the medium is 0.4 wt% or more and 1.3 wt% or less.

<8> The method for producing a separator according to <7>, wherein the specific surface area of the fine particles (b) is 20 m 2 / g or less.

<9> The method for producing a separator of <7> or <8>, wherein the solid content in the slurry is 6 to 50% by weight.

<10> The method for producing a separator according to any one of <7> to <9>, wherein the water-soluble polymer is at least one polymer selected from the group consisting of cellulose ether, polyvinyl alcohol and sodium alginate.

<11> The method for producing a separator according to <11>, wherein the cellulose ether is carboxymethylcellulose.

&Lt; 12 > A process for producing a separator according to any one of < 7 > to < 11 >, wherein the polyolefin porous membrane is a polyethylene porous membrane.

<Separator>

The separator of the present invention is a separator in which a porous film containing a water-soluble polymer and fine particles (hereinafter sometimes referred to as "A film") and a polyolefin porous film (hereinafter sometimes referred to as "B film" , A step of coating a slurry containing a water-soluble polymer, fine particles and a medium on a polyolefin porous film (B film) as described later, and a step of removing the medium from the obtained coated film by drying or the like have. The A film has heat resistance at a high temperature at which shutdown occurs, and imparts a shape stability function to the separator. The B film is melted and nonporous at the time of abnormal heat generation, thereby giving the separator a shutdown function. The A film and the B film may be laminated to each other, or may be three or more layers. For example, the A film may be laminated on both sides of the B film.

First, the A film in the separator will be described. The A film is a porous film containing fine particles and a water-soluble polymer. Examples of the water-soluble polymer include polyvinyl alcohol, polyethylene glycol, cellulose ether, sodium alginate, polyacrylic acid, polyacrylamide and polymethacrylic acid, and cellulose ether, polyvinyl alcohol and sodium alginate are preferable, Ether is more preferable. Specific examples of the cellulose ether include carboxymethylcellulose (CMC), hydroxyethylcellulose (HEC), carboxyethylcellulose, methylcellulose, ethylcellulose, cyanylethylcellulose, and oxyethylcellulose. CMC is particularly preferable because the deterioration in use is small.

As the fine particles in the present invention, fine particles made of an inorganic material or an organic material can be used. Specific examples of the organic material include homopolymers such as styrene, vinyl ketone, acrylonitrile, methyl methacrylate, ethyl methacrylate, glycidyl methacrylate, glycidyl acrylate, and methyl acrylate, Copolymer; Fluorinated resins such as polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-ethylene copolymer and polyvinylidene fluoride; Melamine resin; Urea resin; Polyethylene; Polypropylene; Polymethacrylates, and the like. Examples of the inorganic material include calcium carbonate, talc, clay, kaolin, silica, hydrotalcite, diatomaceous earth, magnesium carbonate, barium carbonate, calcium sulfate, magnesium sulfate, barium sulfate, aluminum hydroxide, magnesium hydroxide, Magnesium, titanium oxide, alumina, mica, zeolite, glass and the like. As the material of the fine particles, an inorganic material is preferable, and alumina is more preferable. The materials of these fine particles may be used alone. Two or more kinds of materials may be mixed and used.

The fine particles constituting the A film are substantially composed of fine particles (a) having an average particle diameter of less than 0.1 μm and a specific surface area of 50 m 2 / g or more and fine particles (b) having an average particle diameter of 0.2 μm or more, The weight ratio of the fine particles (b) is 0.05 to 50. The materials of the fine particles (a) and the fine particles (b) may be the same or different from each other.

Among the two types of fine particles, the fine particles (b) having a large particle diameter become the main skeleton in the A film, contributing to the shape stability of the A film at high temperature. The fine particles (a) having a small particle diameter have the function of appropriately filling the gaps between the fine particles (b) to increase the mechanical strength of the A film, and as described later, excessively entering the B film pores of the water- . The A film contains both of the fine particles (a) and the fine particles (b). In the case of using only one of the fine particles (a) and the fine particles (b), it is difficult to combine shape stability at high temperature and shutdown at a practical level while maintaining sufficient air permeability (ion permeability).

The fine particles (a) have an average particle diameter of less than 0.1 탆, preferably less than 0.05 탆, and a specific surface area of the fine particles (a) of 50 m 2 / g or more, and preferably 70 m 2 / g or more. Regarding the lower limit of the average particle diameter, the average particle diameter of the fine particles (a) is usually about 0.01 탆 or more. Regarding the upper limit of the specific surface area, the specific surface area of the fine particles (a) is usually about 150 m 2 / g or less. Examples of the shape of the fine particles (a) include a spherical shape, a gourd shape, and the like. If the fine particles (a) do not satisfy both of the average particle diameter of less than 0.1 탆 and the specific surface area of 50 m 2 / g or more, the shutdown performance (neutralization of the B film) of the separator becomes insufficient. Here, the specific surface area of the fine particles (a) is a value measured by a BET measurement method. The average particle diameter d (占 퐉) of the fine particles (a) is a value obtained by the following equation using the BET specific surface area B (m 2 / g) and the true density D (g / m 3) of the fine particles.

Average particle diameter d (占 퐉) = 6 占⁰⁶ / (B 占 D)

On the other hand, the fine particles (b) have an average particle diameter of 0.2 탆 or more, preferably 0.25 탆 or more. When the average particle size of the fine particles (b) is less than 0.2 탆, shrinkage upon heating of the A film can not be sufficiently suppressed, and the shape stability at high temperature becomes insufficient. The specific surface area of the fine particles (b) is not particularly limited, but is preferably 20 m 2 / g or less, and particularly preferably 10 m 2 / g or less. Regarding the upper limit of the average particle diameter, the average particle diameter of the fine particles (b) is usually about 1.0 占 퐉 or less. Regarding the lower limit of the specific surface area, the specific surface area of the fine particles (a) is usually about 4.0 m 2 / g or more. Examples of the shape of the fine particles (b) include a spherical shape, a gourd shape, and the like. The average particle diameter of the fine particles (b) is a value obtained by arbitrarily extracting 25 particles by a scanning electron microscope (SEM), measuring the particle diameter (diameter) of each particle, and calculating the average value of 25 particle diameters. When the shape of the fine particles (b) is other than spherical, the particle diameter is defined as the length in the direction indicating the maximum length of the particles. The specific surface area of the fine particles (b) is a value measured by a BET measurement method.

In the film A, the weight ratio of the fine particles (b) to the fine particles (a) (the weight ratio of the fine particles (b) when the fine particles (a) are taken as 1) is 0.05 to 50, preferably 0.1 to 15 Particularly preferably from 0.2 to 10. If the weight ratio is less than 0.05, the heat shrinkage of the A film can not be sufficiently suppressed, and the shape stability at high temperature becomes insufficient. If the weight ratio is more than 50, shutdown of the separator is impaired.

The fine particles (a) and the fine particles (b) other than the fine particles (hereinafter sometimes referred to as &quot; other fine particles &quot;) may be contained in such a range that the effect of the present invention is not significantly impaired. The proportion of the content of other fine particles in the A film is preferably 100% by weight or less (including 0% by weight) relative to the total weight of the fine particles (a) and the fine particles (b) 0% by weight).

The thickness of the A film is usually 0.1 占 퐉 or more and 20 占 퐉 or less, preferably 2 占 퐉 or more and 15 占 퐉 or less. If the thickness is too large, the load characteristics of the battery may be deteriorated when the nonaqueous electrolyte secondary battery is manufactured. When the battery is excessively thin, when abnormal heat generation of the battery occurs, the battery can not resist heat shrinkage of the polyolefin porous film, There is a risk of contraction. When the film A is formed on both surfaces of the film B, the thickness of the film A is the total thickness of both surfaces.

The A film is a porous film, but the hole diameter is preferably not more than 3 탆, more preferably not more than 1 탆, as the diameter of the sphere when the hole is approximated as a sphere. When the average size or the pore diameter of the pore diameter exceeds 3 탆, there is a possibility that a short circuit occurs when the carbon powder, which is the main component of the positive electrode or the negative electrode, or the small particle thereof falls off. The porosity of the membrane A is preferably 30 to 90% by volume, more preferably 40 to 85% by volume.

Next, the B film in the separator will be described. The B film is a porous film of polyolefin and is not dissolved in the electrolyte solution in the nonaqueous electrolyte secondary battery. The B film preferably contains a high molecular weight component having a molecular weight of 5 x 10 ⁵ to 15 x 10 ⁶ . Examples of the polyolefin include homopolymers or copolymers obtained by polymerizing ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene or the like. The B film preferably contains polyethylene or polypropylene, more preferably contains a high molecular weight polyethylene having a weight average molecular weight of at least 1 x 10 ^5, and more preferably contains an ultrahigh molecular weight polyethylene having a weight average molecular weight of at least 5 x 10 ⁵ More preferable.

The porosity of the B film is preferably 20 to 80% by volume, more preferably 30 to 70% by volume. If the porosity is less than 20% by volume, the amount of the electrolytic solution to be retained may be small. If the porosity exceeds 80% by volume, the non-airtightening at a high temperature at which shutdown occurs may be insufficient, There is a concern.

The thickness of the B film is usually 4 to 50 탆, preferably 5 to 30 탆. If the thickness is less than 4 탆, shutdown may be insufficient, and if it exceeds 50 탆, the thickness of the entire separator may become thick, and the electric capacity of the battery may be reduced. The pore diameter of the B film is preferably 3 占 퐉 or less, more preferably 1 占 퐉 or less.

The B film has a structure having pores connected to the inside thereof, and gas or liquid can permeate from one side to the other side. The permeability of the B membrane is usually from 50 to 400 sec / 100 cc, preferably from 50 to 300 sec / 100 cc, as a gelling value.

The method for producing the B film is not particularly limited, and for example, a method of adding a plasticizer to a polyolefin and forming the film into a polyolefin, followed by removing the plasticizer with an appropriate solvent as described in, for example, JP-A 7-29563, As disclosed in Japanese Patent Application Laid-Open No. 7-304110, by using a film made of a polyolefin produced by a known method, a structurally weak amorphous portion of the film is selectively stretched to form a fine hole Method. When the B film is formed of a polyolefin containing ultra-high-molecular-weight polyethylene and a low-molecular-weight polyolefin having a weight-average molecular weight of 10,000 or less, for example, the B film is preferably produced by the following method from the viewpoint of production cost.

(1) 100 parts by weight of ultrahigh molecular weight polyethylene, 5-200 parts by weight of a low molecular weight polyolefin having a weight average molecular weight of 10,000 or less, and 100-400 parts by weight of an inorganic filler such as calcium carbonate are kneaded to obtain a polyolefin resin composition

(2) a step of molding a sheet using the polyolefin resin composition

(3) a step of removing the inorganic filler from the sheet obtained in the step (2)

(4) a step of stretching the sheet obtained in the step (3) to obtain a B film

, Or

(1) 100 parts by weight of ultrahigh molecular weight polyethylene, 5 to 200 parts by weight of a low molecular weight polyolefin having a weight average molecular weight of 10,000 or less, and 100 to 400 parts by weight of an inorganic filler to obtain a polyolefin resin composition

(2) a step of molding a sheet using the polyolefin resin composition

(3) a step of stretching the sheet obtained in the step (2) to obtain a stretched sheet

(4) a step of removing the inorganic filler from the stretched sheet obtained in the step (3) to obtain a B film

.

A commercially available product having the above-described characteristics can be used for the B film.

The A film and the B film are laminated to each other to constitute a separator. The separator may contain, for example, a porous film such as an adhesive film or a protective film other than the A film and the B film within a range that does not significantly disturb the object of the present invention.

The total thickness of the separator (the sum of the thickness of the A film and the thickness of the B film) is usually 5 to 80 占 퐉, preferably 5 to 50 占 퐉, and particularly preferably 6 to 35 占 퐉. When the total thickness of the separator is less than 5 m, the membrane tends to be easily broken. When the thickness exceeds 80 m, the electric capacity of the battery may be reduced. The porosity of the whole separator is usually 30 to 85% by volume, preferably 35 to 80% by volume. When the nonaqueous electrolyte secondary battery is manufactured using the separator of the present invention, high load characteristics are obtained, but the air permeability of the separator is preferably 50 to 2000 sec / 100 cc, more preferably 50 to 1000 sec / 100 cc Do. If the air permeability is 2000 sec / 100 cc or more, the ion permeability of the separator and the load characteristics of the battery may be lowered.

The dimensional retention of the separator at a high temperature at which shutdown occurs is at least 90%, preferably at least 95%. The dimension retention ratio of the separator may be different depending on the MD direction and the TD direction of the B film. In this case, a smaller value is used among the dimension retention ratio in the MD direction and the dimension retention ratio in the TD direction. Here, the MD direction refers to the longitudinal direction at the time of sheet forming, and the TD direction refers to the width direction at the time of sheet forming. If the dimensional retention ratio is less than 90%, a short circuit may occur between the positive and negative electrodes due to thermal shrinkage of the separator at a high temperature at which shutdown occurs, which may result in insufficient shutdown function. The high temperature at which shutdown occurs is a temperature of 80 to 180 캜, usually about 130 to 150 캜.

<Manufacturing Method of Separator>

Next, a method of manufacturing the separator will be described.

The separator of the present invention is produced by a method including a step of coating a slurry containing a water-soluble polymer, fine particles and a medium (slurry for forming an A film) on a B film, and a step of removing the medium from the obtained coating film . The coating film is a film coated on the B film. By removing the medium from the coating film, a porous film (A film) containing a water-soluble polymer and fine particles is obtained, and the A film is laminated on the B film. When the coating film is dried, it is presumed that a gap is formed around the fine particles and an A film is formed. If the slurry does not contain fine particles, a porous film can not be obtained. The slurry may be coated on both sides of the B film to form the A film on both sides of the B film.

The slurry in the method of the present invention can be obtained, for example, by dissolving or swelling a water-soluble polymer in a medium (or by swelling a water-soluble polymer if it can be applied), and further adding fine particles thereinto And mixing them. The mixing method is not particularly limited, and for example, conventionally known dispersing machines such as three one-motor, homogenizer, media type disperser, pressure type disperser and the like can be used.

The fine particles in the slurry are substantially composed of fine particles (a) having an average particle diameter of less than 0.1 μm and a specific surface area of 50 m 2 / g or more and fine particles (b) having an average particle diameter of 0.2 μm or more, The weight ratio of the fine particles (b) is 0.05 to 50, and the weight ratio of the fine particles to the water-soluble polymer is 1 to 100.

As the medium, water or an organic solvent such as ethanol and isopropanol, or a mixed solvent of water and an organic solvent such as ethanol is used.

The water-soluble polymer, the fine particles (a) and the fine particles (b) contained in the slurry for forming an A film are the same as those described in the separator described above. As the water-soluble polymer, cellulose ether, polyvinyl alcohol and sodium alginate are preferable, and CMC is particularly preferable. As the fine particles (a) and the fine particles (b), fine particles made of an inorganic material or an organic material can be used. As the material of the fine particles, an inorganic material is preferable, and alumina is particularly preferable. The materials of the fine particles (a) and the fine particles (b) may be the same or different from each other.

Further, other fine particles other than the fine particles (a) and the fine particles (b) may be contained within a range not significantly inhibiting the object of the present invention. The content of other fine particles in the slurry is preferably not more than 100% by weight (including 0% by weight) based on the total weight of the fine particles (a) and the fine particles (b) % By weight). In addition, a surfactant, a pH adjuster, a dispersant, a plasticizer and the like may be added to the slurry within a range not significantly inhibiting the object of the present invention.

As described above, when the slurry containing the water-soluble polymer, the fine particles and the medium is coated on the polyolefin porous film in the conventional production process of the separator, the water-soluble polymer in the slurry is excessively charged into the pores of the polyolefin porous membrane And there is a problem in that the water-soluble polymer is precipitated in the pores by drying in this state. In the method of the present invention, since the fine particles (a) contained in the slurry have a large specific surface area, the medium and the water-soluble polymer can be adsorbed and retained on the surface of the fine particles (a). Due to the size of the fine particles (a) themselves, it is difficult to physically enter the pores of the B membrane. As a result, the slurry contains the fine particles (a), thereby preventing the fine particles (a) from excessively entering the B-film pores of the water-soluble polymer. On the other hand, in the case where the slurry contains only the fine particles (a) without containing the fine particles (b), the thickness of the slurry becomes too large with respect to the apparent weight of the formed A film, The porosity of the A film becomes large, and the dimensional retention and mechanical strength at the high temperature of the A film are impaired. Therefore, the weight ratio of the fine particles (b) to the fine particles (a) (the weight ratio of the fine particles (b) when the fine particles (a) are taken as 1) is 0.05 to 50, preferably 0.1 to 15, Is 0.2 to 10. When the weight ratio of the fine particles (b) to the fine particles (a) is in the above range, the thickness of the A film can be appropriately maintained, heat shrinkage of the A film can be suppressed, and the A film can have sufficient mechanical strength.

The concentration of the water-soluble polymer in the total of the water-soluble polymer and the medium of the slurry is 0.4 wt% or more and 1.3 wt% or less (based on the weight of the water-soluble polymer and the medium), preferably 0.4 wt% or more and 1.0 wt% or less. If the concentration of the water-soluble polymer is less than 0.4% by weight, the effect of adsorbing and retaining the water-soluble polymer by the above-mentioned fine particles (a) becomes insufficient and the adhesion of the coating film becomes poor, peeling of the coating film occurs, There is a fear that a film can not be formed. If the content exceeds 1.3% by weight, the shutdown property of the obtained separator may be deteriorated. The molecular weight and the like of the water-soluble polymer can be appropriately selected so as to obtain a slurry viscosity suitable for coating.

The solid concentration in the slurry (the total concentration of the fine particles (a) and the fine particles (b) relative to the slurry) is preferably 6 to 50 wt%, and more preferably 9 to 25 wt%. When the solid content is less than 6% by weight, it is difficult to remove the slurry when the medium is removed from the slurry. When the solid content is more than 50% by weight, the slurry must be thinly coated on the B film.

In producing the A film, when the slurry for forming the A film is coated on the B film, the slurry enters the pores (voids) of the B film and the water-soluble polymer in the slurry is precipitated. The film is bonded. At this time, if the slurry excessively enters the pores of the B film, the water-soluble polymer penetrates into the pores of the B film and precipitates, thereby deteriorating the smooth melting of the B film during shutdown. This problem can be avoided by suppressing excessive penetration of the slurry containing the water-soluble polymer into the pores (voids) of the B film.

By containing the fine particles (a) having a sufficient specific surface area, the water-soluble polymer is adsorbed and retained on the fine particles (a), and the water-soluble polymer in the slurry can be prevented from penetrating into the pores (voids) of the B film. In order to obtain the effect, the S value represented by the following formula is preferably 200 m 2 / g or more, and more preferably 300 m 2 / g or more.

S = [(specific surface area of particulate (a) / (number of particulates (a)) PHR + specific surface area of particulate (m 2 / g) ))] / (Number of water-soluble polymer (PHR))

On the other hand, when the film A contains fine particles (b) having a sufficient size as a filler, the film A can suppress the heat shrinkage of the film B at a high temperature at which shutdown occurs. The average particle diameter of the fine particles (b) is 0.2 占 퐉 or more, preferably 0.25 占 퐉 or more. It is difficult to obtain a separator having sufficient dimensional retentivity by suppressing the heat shrinkage of the B film effectively if the A film does not contain the fine particles (b) having an average particle diameter of 0.2 탆 or more. The upper limit value of the fine particles (b) is not limited as long as it can maintain the shape of the A film, but is usually 20 占 퐉 or less, preferably 5 占 퐉 or less, more preferably 1 占 퐉 or less, 0.8 μm or less.

The method of applying the slurry to the B film to obtain the coating film is not particularly limited as long as it can uniformly wet-coat it, and conventionally known methods can be employed. For example, a coating method such as a capillary coating method, a spin coating method, a slit to coat method, a spray coating method, a dip coating method, a roll coating method, a screen printing method, a flexo printing method, a bar coater method, And the like. The thickness of the A film can be controlled by adjusting the thickness of the coating film, the concentration of the water-soluble polymer in the slurry, and the ratio of the fine particles to the water-soluble polymer. As the support for supporting the B film, a resin film, a metal belt, a drum, or the like can be used.

The removal of the medium from the coating film is generally carried out by drying. As an example of the removal method, a solvent which can be dissolved in the medium but does not dissolve the water-soluble polymer is prepared, the coating film is immersed in the solvent and the medium is replaced with the solvent to precipitate the water-soluble polymer, And the solvent is removed by drying. When the slurry is coated on the B film, it is preferable that the drying temperature of the medium or the solvent does not lower the permeability of the B film.

<Non-aqueous electrolyte secondary battery>

Next, the nonaqueous electrolyte secondary battery of the present invention will be described. The battery of the present invention includes the separator of the present invention. Hereinafter, an example of a lithium ion secondary battery as a nonaqueous electrolyte secondary battery will be described. Particularly, components other than the separator will be described, but the present invention is not limited thereto.

As the non-aqueous electrolyte, for example, a nonaqueous electrolyte solution in which a lithium salt is dissolved in an organic solvent can be used. Examples of the lithium salt include LiClO ₄ , LiPF ₆ , LiAsF ₆ , LiSbF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , Li ₂ B ₁₀ Cl ₁₀ , A lower aliphatic carboxylic acid lithium salt, LiAlCl _4, and the like, or a mixture of two or more of them. Of _{these, LiPF 6, LiAsF 6, LiSbF} 6, LiBF 4, LiCF 3 SO 3, LiN (CF 3 SO 2) 2, and LiC (CF ₃ SO ₂₎ at least a fluorine-containing one kind of element selected from among the group consisting of ₃ Lithium salts are preferred.

Examples of the nonaqueous electrolytic solution include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, 4-trifluoromethyl-1,3-dioxolane- Carbonates such as methoxycarbonyloxy) ethane; 1,2-dimethoxyethane, 1,3-dimethoxypropane, pentafluoropropylmethylether, 2,2,3,3-tetrafluoropropyldifluoromethylether, tetrahydrofuran, 2-methyltetrahydro Ethers such as furan; Esters such as methyl formate, methyl acetate, and Y-butyrolactone; Nitriles such as acetonitrile and butyronitrile; Amides such as N, N-dimethylformamide and N, N-dimethylacetamide; Carbamates such as 3-methyl-2-oxazolidone; Sulfolane, dimethylsulfoxide, and 1,3-propanesultone, or those obtained by introducing a fluorine group into the above-mentioned materials, but usually two or more of them are used in combination.

Among them, it is preferable to contain a carbonate, and a mixture of a cyclic carbonate and a non-cyclic carbonate or a mixture of a cyclic carbonate and an ether is more preferable. The mixture of the cyclic carbonate and the non-cyclic carbonate is preferably a mixture of ethylene carbonate, dimethyl carbonate and ethylmethyl carbonate in view of resistance to decomposition even when a graphite material such as natural graphite or artificial graphite is used as the active material of the negative electrode, A mixture containing carbonate is preferred.

As the positive electrode sheet, a positive electrode current collector containing a positive electrode active material, a conductive material and a binder is usually carried on a positive electrode current collector. Examples of a method of supporting the positive electrode mixture on the positive electrode collector include a method of press molding; A method of obtaining a positive electrode material mixture paste by further using an organic solvent, coating the positive electrode material mixture paste on the positive electrode current collector, and pressing the obtained sheet to fix the positive electrode material mixture to the positive electrode current collector. Specifically, as the positive electrode active material, a material containing a material capable of doping and dedoping lithium ions, containing a carbonaceous material as a conductive material, and containing a thermoplastic resin or the like as a binder may be used. As the positive electrode current collector, a conductor such as Al, Ni, or stainless steel can be used, but Al is preferable because it is easy to process into a thin film and is inexpensive. Examples of the material capable of doping and dedoping the lithium ion include a lithium composite oxide containing at least one transition metal such as V, Mn, Fe, Co, and Ni. Among them, a lithium composite oxide having an? -NaFeO ₂ type structure such as lithium nickel oxide, lithium cobalt oxide and the like, a lithium composite oxide having a spinel structure such as lithium manganese spinel is preferably used because of its high average discharge potential .

The lithium composite oxide may contain various metal elements and may be at least one metal selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Cu, Ag, Mg, Al, Ga, The use of the composite nickel oxide containing the metallic element such that the amount of the at least one kind of metallic element is 0.1 to 20 mol% with respect to the sum of the number of moles of the element and the number of moles of Ni in the lithium nickel oxide is used, The cyclic properties of the polymer can be improved.

Examples of the binder include polyvinylidene fluoride, a copolymer of vinylidene fluoride, polytetrafluoroethylene, a copolymer of tetrafluoroethylene-hexafluoropropylene, a copolymer of tetrafluoroethylene-perfluoroalkyl vinyl ether A copolymer of ethylene-tetrafluoroethylene, a copolymer of vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene, a thermoplastic polyimide, and a thermoplastic resin such as polyethylene and polypropylene.

Examples of the conductive agent include carbonaceous materials such as natural graphite, artificial graphite, cokes, and carbon black. Each of them may be used alone as a conductive material, for example, a mixture of artificial graphite and carbon black may be used.

As the negative electrode sheet, for example, a material capable of doping and dedoping lithium ions, lithium metal, lithium alloy, or the like can be used. Examples of the material capable of doping and dedoping lithium ions include carbonaceous materials such as natural graphite, artificial graphite, cokes, carbon black, pyrolytic carbon materials, carbon fibers, and fired organic polymer compounds; And chalcogen compounds such as oxides and sulfides which are doped and doped. As a carbonaceous material, a carbonaceous material containing a graphite material such as natural graphite or artificial graphite as a main component is preferable in that a large energy density can be obtained when the carbonaceous material is combined with a positive electrode because of high dislocation flatness and low average discharge potential .

Cu, Ni, stainless steel or the like can be used as the collector of the negative electrode. However, Cu is preferable in the lithium ion secondary battery because it is difficult to produce lithium and an alloy and is easy to be processed into a thin film. As a method of supporting the negative electrode mixture containing the negative electrode active material on the negative electrode collector, there are a method of press molding; A solvent or the like is further used to obtain a negative electrode material mixture paste, the paste is coated on a negative electrode collector and dried, and the obtained sheet is pressed to fix the negative electrode material mixture to the negative electrode collector.

The shape of the battery is not particularly limited, and may be paper, coin, cylinder, square, or the like.

When the nonaqueous electrolyte secondary battery of the present invention is manufactured using the separator for a nonaqueous electrolyte secondary battery, the separator exhibits a shutdown function to suppress additional heat generation even when abnormal heat generation occurs, A nonaqueous electrolyte secondary battery can be obtained which can avoid the contact between the positive electrode and the negative electrode due to shrinkage of the separator even if the temperature becomes higher.

Example

Hereinafter, the present invention will be described more specifically by way of examples, but the present invention is not limited thereto.

The physical properties and the like of the separator in Examples and Comparative Examples were measured by the following methods.

(1) Thickness measurement (unit: 占 퐉)

The thickness of the separator was measured according to JIS standard (K7130-1992).

(2) Apparent weight (unit: g / ㎡)

A sample of the obtained separator was cut into a square having a length of 10 cm on one side, and a weight W (g) was measured. Apparent weight (g / m 2) = W / (0.1 x 0.1). The apparent weight of the A film was calculated by subtracting the apparent weight of the polyolefin porous film (B film), which is the base, from the apparent weight of the laminated porous film (separator).

(3) porosity (unit: volume%)

The film was cut into a square having a length of 10 cm on one side and weighed: W (g) and thickness: D (cm) were measured. The weight of the material in the sample was calculated, and the weight of each material: Wi (g) was divided by the true specific gravity, and the volume of each material was calculated, and the porosity (volume%) was calculated by the following equation.

Porosity (volume%)

= 100 - [(W1 / true specific gravity 1) + (W2 / true specific gravity 2) + 占 쏙옙 占 (Wn / true specific gravity n)} / (10 占 0 占 D)

(4) Air permeability (unit: sec / 100 cc)

The permeability of the separator was measured by a digital timer type Julian Densometer manufactured by Toyooko Kikai KK based on JIS P8117.

(5) Measurement of shutdown reaching resistance

The shutdown temperature was measured with a cell for measurement of shutdown (hereinafter referred to as &quot; cell &quot;). A rectangular film of 2 x 3 cm in length and width was impregnated with an electrolytic solution, sandwiched between two electrodes made of SUS, and fixed with a clip to prepare a cell. The electrolytic solution was prepared by dissolving 1 mol / l of LiBF ₄ in a mixed solvent of 50 vol% of ethylene carbonate and 50 vol% of diethyl carbonate. The terminal of the impedance analyzer was connected to the anode of the assembled cell. The resistance value at 1 kHz was measured. The resistance was measured while raising the temperature in the oven at a rate of 15 ° C / min. The maximum resistance value was taken as the reaching resistance value. The shutdown performance was evaluated based on the following criteria.

Evaluation of shutdown property:

◎: The arrival resistance value is 500 Ω or more

○: The arrival resistance value is 200 Ω or more, less than 500 Ω

×: reach resistance value is less than 200 Ω

(6) Dimensional retention ratio (heating shape retention ratio)

The film was cut into a square of 15 cm in length and 15 cm in length, and a square marking line was drawn at an interval of 10 cm in the center, sandwiched between two aluminum plates each having a thickness of 0.5 mm coated with a releasing agent and heated in an oven . The temperature of the oven was raised to 150 DEG C at a rate of 1 DEG C / min and held for 10 minutes, and then taken out to measure the square dimensions and calculate the dimensional retention ratios. The calculation method of the dimensional retention rate is as follows.

Marking line length before heating in the MD direction: L1

Marking line length before heating in the TD direction: W1

Marking line length in MD direction after heating: L2

Marking line length in TD direction after heating: W2

Dimensional retention ratio (%) = ((L2 x W2) / (L1 x W1)) x 100

The water-soluble polymer, the fine particles (a), the fine particles (b), and the B film used for the A film formation are as follows.

<A closing

&Quot; Water-soluble polymer &quot;

Carboxymethylcellulose (CMC): Cellogen 4H manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.

&Quot; Fine Particles (a) &quot;:

Fine particles (a1): AKP-G008 manufactured by Sumitomo Chemical Co., Ltd.

Average particle diameter: 0.024 탆

Specific surface area: 70 m 2 / g

Particle shape: roughly spherical

Fine particles (a2): AKP-G15 manufactured by Sumitomo Chemical Co.,

Average particle diameter: 0.013 mu m

Specific surface area: 149 m 2 / g

Particle shape: non-spherical

&Quot; Fine Particles (b) &quot;:

Fine particles (b1): Sumiko Random AA-03 manufactured by Sumitomo Chemical Co.,

Average particle diameter: 0.42 탆

Specific surface area: 4.8 m &lt; 2 &gt; / g

Particle shape: roughly spherical

Fine particles (b2): AKP-3000 manufactured by Sumitomo Chemical Co.,

Average particle diameter: 0.54 mu m

Specific surface area: 4.3 m &lt; 2 &gt; / g

Particle shape: Gourd type

<B membrane>

Polyethylene porous membrane

"B1":

Thickness: 15 탆

Apparent weight: 7 g / ㎡

Specularity: 105 sec / 100 cc

"B2":

Thickness: 13 탆

Apparent weight: 6.5 g / ㎡

Specularity: 120 sec / 100 cc

Example 1

(1) Preparation of slurry

The slurry of Example 1 was prepared in the following procedure.

First, CMC was dissolved in a water-ethanol mixed solvent (water: ethanol = 2: 1 (weight ratio)) to obtain a CMC solution having a CMC concentration of 0.6 wt% (for [water soluble polymer + medium]). Subsequently, 1000 parts by weight of the fine particles (a1) and 3000 parts by weight of the fine particles (b1) were added to the CMC solution (CMC 100 parts by weight), mixed and treated three times in a high pressure dispersion condition (60 MPa) using a Gorlin homogenizer To thereby prepare a slurry of Example 1. Table 1 shows the composition of the slurry of Example 1. The ratio of the total specific surface area (m 2 / g) to the CMC weight (g) of the fine particles (a1) calculated from the amounts of the fine particles (a1)

(2) Preparation and evaluation of separator

The above B1 was used as the B film. The B film (100 cm in the MD direction and 30 cm in the TD direction) was fixed to the drum, and 0.6 kg of weight was suspended in the other side so as to apply an even load to the B film. A stainless steel coating bar having a diameter of 20 mm was arranged at the top of the drum so as to have a clearance of 40 mu m with the drum. The drum was rotated and stopped so that the end of the side of the B film fixed with the tape came between the drum and the coating bar. While supplying the slurry prepared as described above onto the B film in front of the coating bar, the drum was rotated at 0.5 rpm to apply slurry to one surface of the B film. After coating, the rotation of the drum was stopped, and the resultant was kept in an atmosphere of 70 deg. C for 30 minutes and sufficiently dried to obtain the separator of Example 1 in which the A film was laminated on one surface of the B film. In the resulting separator, the A film was in close contact with the B film, and no peeling was observed.

Table 2 shows the solid weight ratio and physical properties of the separator obtained by the above evaluation method.

Examples 2 to 8

(1) Preparation of slurry

The slurries of Examples 2 to 8 were obtained in the same manner as in the preparation of the slurry of Example 1 except that the fine particles (a) and the fine particles (b) shown in Table 1 were used in the ratios shown in Table 1, respectively. The concentrations of the respective components in the slurries of Examples 2 to 8 are shown in Table 1.

(2) Preparation and evaluation of separator

The same operations as in Example 1 were carried out except that the slurries of Examples 2 to 8 were used to prepare separators of Examples 2 to 8. Table 2 shows the B film used. Table 2 shows the solid weight ratio and physical properties of the obtained separator. In the separators of Examples 2 to 8, the A film was in close contact with the B film, and no peeling was observed.

Example 9

(1) Preparation of slurry

A slurry of Example 9 was obtained in the same manner as in the preparation of the slurry of Example 1 except that the fine particles (a1) and the fine particles (b1) were changed to the ratios shown in Table 1. The concentrations of the respective components in the slurry of Example 9 are shown in Table 1.

(2) Preparation and evaluation of separator

The same operation as in Example 1 was carried out except that the slurry of Example 9 was used to laminate the A film on one surface of the B film. Table 2 shows the B film used. Subsequently, the A film was laminated on the other surface of the B film in the same manner to obtain the separator of Example 9 in which the A film was laminated on both surfaces of the B film. In the separator of Example 9, the film A was in close contact with the film B, and peeling was not observed. Table 2 shows the solid weight ratio and physical properties of the obtained separator. The thickness of the A film is the total thickness of the A film formed on both sides.

Examples 10 to 12

(1) Preparation of slurry

A slurry of each of Examples 10 to 12 was obtained in the same manner as in the preparation of the slurry of Example 1 except that the ratio of the fine particles (a) and the fine particles (b) shown in Table 1 were changed to those shown in Table 1, respectively. The concentrations of the respective components in the slurries of Examples 10 to 12 are shown in Table 1.

(2) Preparation and evaluation of separator

The same operation as in Example 9 was carried out except that the slurries of Examples 10 to 12 were used to obtain separators of Examples 10 to 12 in which the A film was laminated on both surfaces of the B film. Table 2 shows the B film used. In the separators of Examples 10 to 12, the A film was in close contact with the B film, and no peeling was observed. Table 2 shows the solid weight ratio and physical properties of the obtained separator. The thickness of the A film is the total thickness of the A film formed on both sides.

Comparative Example 1

(1) Preparation of slurry

A slurry of Comparative Example 1 was obtained in the same manner as in the production of the slurry of Example 1 except that only the fine particles (b1) were used as the fine particles and the other components were changed to the ratios shown in Table 1. The concentration of each component in the slurry of Comparative Example 1 is shown in Table 1.

(2) Preparation and evaluation of separator

A separator of Comparative Example 1 was produced in the same manner as in Example 1 except that the slurry of Comparative Example 1 was used. Table 2 shows the B film used. Table 2 shows the solid weight ratio and physical properties of the obtained separator. In the separator of Comparative Example 1, the film A was in close contact with the film B, and no peeling was observed.

Comparative Example 2

(1) Preparation of slurry

A slurry of Comparative Example 1 was obtained in the same manner as the slurry production method of Example 1 except that only the fine particles (a1) were used as fine particles and the other components were used in the ratios shown in Table 1. [ The concentration of each component in the slurry of Comparative Example 1 is shown in Table 1.

(2) Preparation and evaluation of separator

A separator of Comparative Example 2 was produced in the same manner as in Example 1 except that the slurry of Comparative Example 2 was used. Table 2 shows the B film used. Table 2 shows the solid weight ratio and physical properties of the obtained separator. In the separator of Comparative Example 2, the A film was in close contact with the B film, and no peeling was observed.

Comparative Example 3

(1) Preparation of slurry

A slurry of Comparative Example 3 was obtained in the same manner as in the production of the slurry of Example 1 except that the fine particles (a) and the fine particles (b) shown in Table 1 were used and the other components were changed to the ratios shown in Table 1. The concentration of each component in the slurry of Comparative Example 1 is shown in Table 1.

(2) Preparation and evaluation of separator

A separator of Comparative Example 3 was produced in the same manner as in Example 1 except that the slurry of Comparative Example 3 was used. Table 2 shows the B film used. Table 2 shows the solid weight ratio and physical properties of the obtained separator. In the separator of Comparative Example 3, the A film was remarkably peeled off and a continuous film could not be formed on the B film.

Comparative Example 4

(1) Preparation of slurry

A slurry of Comparative Example 4 was obtained in the same manner as in the production of the slurry of Example 1 except that only the fine particles (b2) were used as fine particles and the other components were changed to the ratios shown in Table 1. The concentration of each component in the slurry of Comparative Example 1 is shown in Table 1.

(2) Preparation and evaluation of separator

The same operation as in Example 9 was carried out except that the slurry of Comparative Example 4 was used to obtain a separator of Comparative Example 4 in which the A film was laminated on both sides of the B film. Table 2 shows the B film used. Table 2 shows the solid weight ratio and physical properties of the obtained separator. The thickness of the A film is the total thickness of the A film formed on both sides. In the separator of Comparative Example 4, the A film was in close contact with the B film, and no peeling was observed.

The dimensional retention ratios (heating shape retention ratios) and SD characteristics were evaluated for Examples 1, 7, 9, 10 and 12 and Comparative Examples 1, 2 and 4. The results are shown in Table 3.

Industrial availability

According to the present invention, there is provided a separator for a nonaqueous electrolyte secondary battery which is excellent in shape stability at a high temperature, and is also excellent in shuttability and permeability. By using the separator of the present invention, it is possible to prevent direct contact between the positive electrode and the negative electrode when the abnormal heat is generated, and to maintain the insulating property by quickly making the porous membrane of polyolefin nonporous, . Further, according to the method of the present invention, the separator can be manufactured with good reproducibility.

Claims (12)

A separator comprising a porous film containing fine particles and a water-soluble polymer, and a polyolefin porous film laminated to each other,
(A) having an average particle diameter of less than 0.1 mu m and a specific surface area of 50 m &lt; 2 &gt; / g or more and fine particles (b) having an average particle diameter of 0.25 mu m or more,
The ratio of the content of other fine particles is not more than 100% by weight (including 0% by weight) based on the total weight of the fine particles (a) and the fine particles (b)
The weight ratio of the fine particles (b) to the fine particles (a) is 0.05 to 50,
The total weight ratio of the fine particles (a), the fine particles (b) and other fine particles to the water-soluble polymer is 1 to 100,
Wherein the polyolefin porous membrane is a polyolefin porous membrane having a pore diameter of 1 m or less. The method according to claim 1,
And the specific surface area of the fine particles (b) is 20 m &lt; 2 &gt; / g or less. 3. The method according to claim 1 or 2,
Wherein the water-soluble polymer is at least one polymer selected from the group consisting of cellulose ether, polyvinyl alcohol and sodium alginate. The method of claim 3,
Wherein the cellulose ether is carboxymethylcellulose. 2. A separator for a nonaqueous electrolyte secondary battery, wherein the cellulose ether is carboxymethylcellulose. 3. The method according to claim 1 or 2,
Wherein the polyolefin porous film is a polyethylene porous film. A nonaqueous electrolyte secondary battery having the separator for a nonaqueous electrolyte secondary battery according to claim 1 or 2. A step of coating a slurry containing a water-soluble polymer, fine particles and a medium on a polyolefin porous film, and a step of laminating a porous film containing a water-soluble polymer and fine particles on the polyolefin porous film by removing the medium from the resulting coated film As a method for producing a separator,
Wherein the fine particles contain fine particles (a) having an average particle diameter of less than 0.1 mu m and a specific surface area of 50 m &lt; 2 &gt; / g or more and fine particles (b) having an average particle diameter of 0.25 mu m or more,
The ratio of the content of other fine particles is not more than 100% by weight (including 0% by weight) based on the total weight of the fine particles (a) and the fine particles (b)
The weight ratio of the fine particles (b) to the fine particles (a) is 0.05 to 50,
The total weight ratio of the fine particles (a), the fine particles (b) and other fine particles to the water-soluble polymer is 1 to 100,
The concentration of the water-soluble polymer in the total of the water-soluble polymer and the medium is 0.4 wt% to 1.3 wt%
Wherein the polyolefin porous film is a polyolefin porous film having a pore diameter of 1 m or less. 8. The method of claim 7,
Wherein the specific surface area of the fine particles (b) is 20 m &lt; 2 &gt; / g or less. 9. The method according to claim 7 or 8,
Wherein the solid content concentration in the slurry is from 6 to 50% by weight. 9. The method according to claim 7 or 8,
Wherein the water-soluble polymer is at least one polymer selected from the group consisting of cellulose ether, polyvinyl alcohol and sodium alginate. 11. The method of claim 10,
Wherein the cellulose ether is carboxymethylcellulose. 2. A method for producing a separator for a non-aqueous electrolyte secondary battery, 9. The method according to claim 7 or 8,
Wherein the polyolefin porous membrane is a polyethylene porous membrane.