JP6425484B2 - Battery separator - Google Patents

Description

  The present invention relates to a battery separator and the like.

  Conventionally, in order to improve the heat resistance of a battery separator such as a lithium ion secondary battery, for a battery provided with a porous layer containing an inorganic filler and a resin binder on at least one surface of a porous substrate film mainly composed of a polyolefin resin A separator has been proposed.

  In order to realize high capacity of the battery, thinning of the battery separator, in particular, thinning of the porous layer is required. However, as the porous layer is made thinner, sufficient heat resistance can not be given to the battery separator, and the safety of the battery is lowered.

  Even if the porous layer is made thin, using an inorganic filler having a small primary particle diameter makes the porous layer more dense, enhances the heat shrinkage suppressing effect at high temperature, and improves the safety of the battery. Be expected. However, an inorganic filler having a small primary particle diameter tends to aggregate in the coating liquid, and it is difficult to stably maintain the dispersed state of the inorganic filler. If the dispersion state of the inorganic filler can not be kept stable in the coating liquid, aggregation or sedimentation of the fine particles occurs, and the coating surface becomes uneven when the coating liquid is applied to the porous substrate film. It is difficult to form a uniform and dense porous layer. The dense porous layer means that the pore diameter of the porous layer is small.

  A coating liquid containing an inorganic filler, a dispersion medium, a thickener, and a dispersing agent in order to keep the dispersed state of the inorganic filler stable in the coating liquid, and the viscosity of the coating liquid is 5 to 500 mPa · s Among the particles contained in the inorganic filler, a coating liquid in which the proportion of particles having a particle size of 1 μm or less is 30% by volume or more and the proportion of particles having a particle size of 3 μm or more is 10% by volume or less It is proposed (patent document 1).

In order to achieve both battery safety and charge / discharge efficiency, 50% cumulative value D ₅₀ is 100 nm to ₅₀₀ nm, and 10% cumulative value D ₁₀ is 0.5 D ₅₀ or more in the particle size distribution of the inorganic filler particles. In addition, an inorganic filler dispersion having a 90% cumulative value D ₉₀ of 2D ₅₀ or less has also been proposed (Patent Document 2).

  In order to provide a separator with a low thermal contraction rate, a porous layer in which the average particle diameter of the inorganic filler is 0.10 μm or more and 3.0 μm or less has also been proposed (Patent Document 3).

WO 2009/096451 Patent No. 5470255 gazette International Publication No. 2014/069410

  Although the coating liquid described in Patent Documents 1 and 2 improves the uniform dispersion of the filler in the medium, it is difficult to maintain the storage stability in which the uniformly dispersed state is maintained. The coating liquid described in Patent Document 3 has room for further study on the dispersibility of the inorganic filler and the particle size distribution.

  Accordingly, an object of the present invention is to provide a battery separator having a dense porous layer and capable of improving the high temperature storage characteristics of the battery.

The invention is as follows:
[1] A battery separator comprising a porous layer (B) containing an inorganic filler, a resin binder, and a dispersing agent on at least one side of a porous substrate membrane (A),
The median diameter of the inorganic filler is 0.55 μm or more and 1.2 μm or less,
The dispersant is present in a ratio of 0.1 parts by mass to 5 parts by mass with respect to 100 parts by mass of the inorganic filler,
When the mass average molecular weight of the dispersant is 300 or more and 10,000 or less and the dispersant is dispersed or dissolved in water so that the solid content is 10% by mass, the pH at 25 ° C. is 3 to 3 Is 9,
The battery separator.
[2] The battery separator according to [1], wherein the dispersant is a water-soluble polymer dispersant.
[3] The battery separator according to [2], wherein the water-soluble polymer dispersant is a polycarboxylate.
[4] The battery separator according to any one of [1] to [3], wherein the inorganic filler is selected from the group consisting of alumina, silica, kaolin and boehmite.
[5] A non-aqueous electrolyte battery comprising the battery separator according to any one of [1] to [4], a positive electrode, a negative electrode, and an electrolytic solution.

  According to the present invention, the inorganic filler is uniformly dispersed in the resin binder, and the dense inorganic filler-containing porous layer (B) is formed on the porous substrate membrane (A). It is possible to provide a battery separator excellent in characteristics and a lithium ion secondary battery excellent in storage characteristics and charge / discharge cycle characteristics.

  Hereinafter, modes for carrying out the present invention (hereinafter, abbreviated as “the present embodiment”) will be described in detail. The present invention is not limited to the following embodiments, and various modifications can be made within the scope of the present invention.

<Battery separator>
The battery separator of the present invention will be described.
The battery separator of the present invention comprises a porous substrate film (A) and a porous layer (B) laminated on at least one surface of the porous substrate film (A), and the porous layer (B) is an inorganic material It contains a filler, a resin binder and a water soluble polymer dispersant.

  The above-mentioned separator is excellent in heat resistance and has a shutdown function, so it is suitable as a battery separator which isolates the positive electrode and the negative electrode in the battery. In particular, since the separator is difficult to short circuit even at high temperatures, it can be safely used as a separator for high electromotive force batteries.

  In the separator according to the present embodiment, the median diameter of the inorganic filler is 0.55 μm or more and 1.2 μm or less, preferably 0.6 μm or more and 1.1 μm or less, and is 0.7 μm or more and less than 1.0 μm. Is more preferred. When the median diameter of the inorganic filler is 0.55 μm or more, the battery separator tends to be excellent in air permeability and to suppress heat shrinkage at high temperatures. When the median diameter of the inorganic filler is 1.2 μm or less, the inorganic filler is uniformly dispersed in the resin binder, and a dense inorganic filler-containing porous layer (B) is formed on the porous substrate film (A) There is a tendency.

  The median diameter measurement of the inorganic filler can be performed by the method described in the examples. The median diameter measurement is performed using a dispersion of an inorganic filler or using a coating liquid containing an inorganic filler, a resin binder and a dispersant.

  In the separator according to the present embodiment, the median diameter of the inorganic filler is 0.55 μm or more and 1.2 μm or less by the use of the dispersant in the inorganic filler-containing coating liquid, or the heat treatment, surface treatment and pulverization treatment of the inorganic filler. It can be adjusted. The use of the water-soluble polymer dispersant, and the heat treatment, surface treatment and grinding treatment of the inorganic filler will be described later.

  The porous substrate film (A) and the porous layer (B) containing an inorganic filler, a resin binder and a dispersant are described below.

[Porous substrate membrane (A)]
The porous substrate membrane (A) in the present invention will be described.
The porous substrate film (A) is preferably one having small electron conductivity, ion conductivity, high resistance to an organic solvent, and a fine pore diameter.
As such a porous base film (A), for example, a porous base film containing a polyolefin resin, polyethylene terephthalate, polycycloolefin, polyether sulfone, polyamide, polyimide, polyimide amide, polyaramid, nylon, polytetrafluoroethylene And porous base film containing resin, woven fabric of polyolefin fiber (woven fabric), nonwoven fabric of polyolefin fiber, paper, and aggregate of insulating material particles. Among these, when obtaining a battery separator through a coating process, the coating property of the coating solution is excellent, the film thickness of the separator is thinner, and the active material ratio in a storage device such as a battery is increased. From the viewpoint of increasing the capacity per volume, a porous substrate film containing a polyolefin resin (hereinafter, also referred to as a “polyolefin resin porous substrate film”) is preferable.

The polyolefin resin porous substrate membrane will be described.
The polyolefin resin porous substrate film occupies 50% by mass or more and 100% by mass or less of the resin component constituting the porous substrate film (A) from the viewpoint of improving the shutdown performance etc. when used as a battery separator It is preferable that it is a porous base film (A) formed of a polyolefin resin composition. The proportion of the polyolefin resin in the polyolefin resin composition is more preferably 60% by mass to 100% by mass, and still more preferably 70% by mass to 100% by mass.

The polyolefin resin contained in the polyolefin resin composition is not particularly limited. For example, ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, and 1-octene are used as monomers. The obtained homopolymer, copolymer, multistage polymer, etc. are mentioned. These polyolefin resins may be used alone or in combination of two or more.
Among them, polyethylene, polypropylene, copolymers thereof, and mixtures thereof are preferable as the polyolefin resin from the viewpoint of shutdown characteristics when used as a battery separator.
Specific examples of polyethylene include low density polyethylene, linear low density polyethylene, medium density polyethylene, high density polyethylene, ultra high molecular weight polyethylene, etc.
Specific examples of polypropylene include isotactic polypropylene, syndiotactic polypropylene, atactic polypropylene, etc.
As a specific example of a copolymer, an ethylene-propylene random copolymer, an ethylene propylene rubber, etc. are mentioned.

Among them, it is preferable to use polyethylene, particularly high density polyethylene, as the polyolefin resin from the viewpoint of satisfying the required performance of low melting point and high strength when used as a battery separator. In the present invention, high density polyethylene refers to polyethylene having a density of 0.942 to 0.970 g / cm ³ . The density of high density polyethylene is preferably 0.950 to 0.969 (g / cm ³ ) from the viewpoint of the strength of the porous substrate membrane (A). In the present invention, the density of polyethylene refers to a value measured according to D) density gradient tube method described in JIS K7112 (1999).

  In the case of a polyolefin resin porous substrate film, it is preferable to use a mixture of polyethylene and polypropylene as the polyolefin resin from the viewpoint of improving the heat resistance of the porous substrate film (A). In this case, the ratio of polypropylene to the total polyolefin resin in the polyolefin resin composition is preferably 1 to 35% by mass, more preferably 3 to 20%, from the viewpoint of achieving both heat resistance and a good shutdown function. %, More preferably 4 to 10% by mass.

  The polyolefin resin composition can contain any additive. Additives include, for example, polymers other than polyolefin resins; inorganic materials; antioxidants such as phenol type, phosphorus type and sulfur type; metal soaps such as calcium stearate and zinc stearate; UV absorbers; light stabilizers Antistatic agents; antifogging agents; color pigments and the like. The total addition amount of these additives is preferably 20 parts by mass or less with respect to 100 parts by mass of the polyolefin resin from the viewpoint of improving the shutdown performance etc., more preferably 10 parts by mass or less, still more preferably 5 parts Part or less.

The porous substrate film (A) has a porous structure in which a large number of very small holes are gathered to form a dense communicating hole, so that the ion conductive property is very excellent and the withstand voltage characteristics are also good. Moreover, it has a feature of high strength.
The porous substrate film (A) may be a single layer film made of the above-described material, or may be a laminated film.

  The film thickness of the porous substrate film (A) is preferably 0.1 μm to 100 μm, more preferably 1 μm to 50 μm, and still more preferably 3 μm to 25 μm. 0.1 micrometer or more is preferable from a viewpoint of mechanical strength, and 100 micrometers or less are preferable from a viewpoint of the high capacitation of a battery. The film thickness of the porous substrate film (A) can be adjusted by controlling the die lip interval, the stretching ratio in the stretching step, and the like.

The average pore diameter of the porous substrate membrane (A) is preferably 0.03 μm or more and 0.70 μm or less, more preferably 0.04 μm or more and 0.20 μm or less, still more preferably 0.05 μm or more and 0.10 μm or less, particularly preferably It is 0.06 micrometers or more and 0.09 micrometers or less. From the viewpoint of high ion conductivity and withstand voltage, 0.03 μm or more and 0.70 μm or less is preferable. The average pore diameter of the porous substrate membrane (A) can be measured by the measurement method described later.
The average pore diameter can be adjusted by controlling the composition ratio, the cooling rate of the extruded sheet, the stretching temperature, the stretching ratio, the heat setting temperature, the stretching ratio during heat setting, and the relaxation rate during heat setting, or by combining these. Can.

The porosity of the porous substrate membrane (A) is preferably 25% to 95%, more preferably 30% to 65%, and still more preferably 35% to 55%. 25% or more is preferable from a viewpoint of ion conductivity improvement, and 95% or less is preferable from a viewpoint of a withstand voltage characteristic. The porosity of the porous substrate membrane (A) can be measured by the method described later.
The porosity of the porous substrate film (A) is controlled by controlling the mixing ratio of the polyolefin resin composition and the plasticizer, the stretching temperature, the stretching ratio, the heat setting temperature, the stretching ratio during heat setting, and the relaxation rate during heat setting. Or, it can be adjusted by combining these.

  When the porous substrate film (A) is a polyolefin resin porous substrate film, the viscosity average molecular weight of the polyolefin resin porous substrate film is preferably 30,000 or more and 12,000,000 or less, more preferably 50. It is more than 1,000 and less than 2,000,000, more preferably more than 100,000 and less than 1,000,000. When the viscosity average molecular weight is 30,000 or more, the melt tension at the time of melt molding is increased, the moldability is improved, and entanglement between polymers tends to result in high strength, which is preferable. On the other hand, when the viscosity average molecular weight is 12,000,000 or less, it becomes easy to melt and knead uniformly, which is preferable because it tends to be excellent in sheet formability, particularly thickness stability. Furthermore, when it is set as a battery separator, it is preferable for the viscosity average molecular weight to be less than 1,000,000 because the pores tend to be clogged when the temperature rises and a good shutdown function tends to be obtained. The viscosity average molecular weight of the polyolefin resin porous substrate membrane can be measured by the method described later.

There is no restriction | limiting in particular as a method to manufacture a porous base film (A), A well-known manufacturing method is employable. When the porous substrate film (A) is a polyolefin resin porous substrate film, for example,
(1) A method of forming a sheet by melt-kneading a polyolefin resin composition and a pore-forming material, stretching as required, and then extracting the pore-forming material to make it porous
(2) A method in which the polyolefin resin composition is melt-kneaded and extruded at a high draw ratio, and then the polyolefin crystal interface is peeled off by heat treatment and stretching to make it porous;
(3) A method in which the polyolefin resin composition and the inorganic filler are melt-kneaded and formed on a sheet, and then the interface between the polyolefin and the inorganic filler is peeled off by stretching to make it porous.
(4) After dissolving the polyolefin resin composition, the polyolefin resin composition is immersed in a poor solvent for the polyolefin to coagulate the polyolefin and simultaneously remove the solvent to make it porous.
Etc.

  Hereinafter, as an example of a method of manufacturing a porous substrate film (A), a method of extracting a pore forming material after melt-kneading a polyolefin resin composition and a pore forming material into a sheet shape will be described.

  First, the polyolefin resin composition and the above-mentioned pore forming material are melt-kneaded. As the melt-kneading method, for example, a polyolefin resin and, if necessary, other additives are introduced into a resin-kneading apparatus such as an extruder, a kneader, a laboplast mill, a kneading roll, or a Banbury mixer while heating and melting resin components. The method of introduce | transducing and knead | mixing a hole formation material by arbitrary ratios is mentioned.

  As the above-mentioned pore formation material, a plasticizer, an inorganic material, or their combination can be mentioned.

  Although it does not specifically limit as a plasticizer, It is preferable to use the non-volatile solvent which can form a uniform solution above the melting point of polyolefin. Specific examples of such non-volatile solvents include, for example, hydrocarbons such as liquid paraffin and paraffin wax; esters such as dioctyl phthalate and dibutyl phthalate; higher alcohols such as oleyl alcohol and stearyl alcohol . These plasticizers may be recovered by distillation or the like after extraction and reused. Furthermore, preferably, before being introduced into the resin kneading apparatus, the polyolefin resin, the other additives and the plasticizer are preliminarily kneaded at a predetermined ratio in advance using a Henschel mixer or the like. More preferably, in the pre-kneading, only a part of the plasticizer is introduced, and the remaining plasticizer is kneaded while being appropriately heated and side-fed to the resin kneading apparatus. By using such a kneading method, the dispersibility of the plasticizer is enhanced, and when stretching a sheet-like molded product of a resin composition and a melt-kneaded product of the plasticizer in a later step, high magnification can be obtained without film breakage. Tend to be stretched by

  Among the plasticizers, liquid paraffin is highly compatible with polyethylene or polypropylene when the polyolefin resin is polyethylene or polypropylene, and even if the melt-kneaded product is stretched, interfacial peeling between the resin and the plasticizer hardly occurs, and uniform stretching is achieved. Is preferable because it tends to be easy to implement.

  The ratio of the polyolefin resin composition to the plasticizer is not particularly limited as long as they can be melt-kneaded uniformly and molded into a sheet. For example, the mass fraction of the plasticizer in the composition comprising the polyolefin resin composition and the plasticizer is preferably 20 to 90% by mass, more preferably 30 to 80% by mass. When the mass fraction of the plasticizer is 90% by mass or less, the melt tension at the time of melt-forming becomes sufficient, so that the formability tends to be improved. On the other hand, when the mass fraction of the plasticizer is 20% by mass or more, the polyolefin molecular chain is not cut even when the mixture of the polyolefin resin composition and the plasticizer is drawn at a high ratio, and a uniform and fine pore structure Are easy to form and the strength is also easy to increase.

  The inorganic material is not particularly limited, and, for example, oxide ceramics such as alumina, silica (silicon oxide), titania, zirconia, magnesia, ceria, yttria, zinc oxide, iron oxide, etc .; silicon nitride, titanium nitride, nitride Silicon nitride, ceramics such as boron, silicon carbide, calcium carbonate, aluminum sulfate, aluminum hydroxide, potassium titanate, talc, kaolin clay, kaolinite, halloysite, pyrophyllite, montmorillonite, sericite, mica, amesite, bentonite , Asbestos, zeolite, calcium silicate, magnesium silicate, kieselguhr, silica sand, etc .; glass fiber. These may be used alone or in combinations of two or more. Among them, silica, alumina and titania are preferable from the viewpoint of electrochemical stability, and silica is particularly preferable from the viewpoint of easy extraction.

  The ratio of the polyolefin resin composition to the inorganic material is preferably 5% by mass or more, more preferably 10% by mass or more, based on the total mass thereof, from the viewpoint of obtaining good separability. From the viewpoint of securing the strength, the content is preferably 99% by mass or less, and more preferably 95% by mass or less.

  Next, the melt-kneaded product is formed into a sheet. As a method of producing a sheet-like molded product, for example, a melt-kneaded product is extruded into a sheet form through a T die or the like, brought into contact with a heat conductor, and cooled to a temperature sufficiently lower than the crystallization temperature of the resin component. There is a method of solidifying. Examples of the heat conductor used for cooling and solidification include metals, water, air, and plasticizers. Among these, it is preferable to use a metal roll because the heat conduction efficiency is high. In addition, when the extruded kneaded material is brought into contact with a metal roll, sandwiching between the rolls further increases the efficiency of heat conduction, orients the sheet and increases the film strength, and also improves the surface smoothness of the sheet. It is more preferable because it tends to It is preferable that it is 200 micrometers or more and 3,000 micrometers or less, and, as for the die-lip space | interval at the time of extruding a melt-kneaded thing into a sheet form from T die, it is more preferable that they are 500 micrometers or more and 2,500 micrometers or less. When the die-lip spacing is 200 μm or more, texture and the like are reduced, the influence on film quality such as streaks and defects is small, and risk of film breakage and the like can be reduced in the subsequent stretching step. On the other hand, when the die lip distance is 3,000 μm or less, the cooling rate is fast, cooling unevenness can be prevented, and the thickness stability of the sheet can be maintained.

  In addition, the sheet-like formed body may be rolled. The rolling can be carried out by, for example, a press method using a double belt press or the like. By rolling, in particular, the orientation of the surface layer can be increased. The rolling area magnification is preferably more than one and not more than three times, and more preferably more than one and not more than two times. When the rolling ratio exceeds 1 time, the plane orientation tends to increase and the film strength of the finally obtained porous substrate film (A) tends to increase. On the other hand, when the rolling ratio is 3 times or less, the difference in orientation between the surface layer portion and the inside of the center is small, and a uniform porous structure tends to be formed in the thickness direction of the film.

  Then, the pore-forming material is removed from the sheet-like molded product to obtain a porous substrate film (A). As a method of removing a hole formation material, the sheet-like molded object is immersed in an extraction solvent, for example, the method of extracting a hole formation material and making it fully dry is mentioned. The method of extracting the pore-forming material may be either a batch system or a continuous system. In order to suppress the shrinkage of the porous substrate membrane (A), it is preferable to restrain the end of the sheet-like compact during a series of steps of immersion and drying. In addition, it is preferable that the amount of remaining pore-forming material in the porous base film (A) be less than 1% by mass with respect to the mass of the whole porous base film (A).

  When the porous substrate film (A) is a polyolefin resin porous substrate film, the extraction solvent used when extracting the pore forming material is a poor solvent for the polyolefin resin and a good solvent for the pore forming material It is preferable to use one having a boiling point lower than the melting point of the polyolefin resin. Examples of such extraction solvents include hydrocarbons such as n-hexane and cyclohexane; halogenated hydrocarbons such as methylene chloride and 1,1,1-trichloroethane; non-chlorinated such as hydrofluoroether and hydrofluorocarbon Halogenated solvents; alcohols such as ethanol and isopropanol; ethers such as diethyl ether and tetrahydrofuran; and ketones such as acetone and methyl ethyl ketone. These extraction solvents may be recovered by distillation or the like and reused. Moreover, when using an inorganic material as a hole formation material, aqueous solution, such as sodium hydroxide and potassium hydroxide, can be used as an extraction solvent.

Moreover, it is preferable to stretch the said sheet-like molded object or porous base film (A). Stretching may be performed before extracting the pore-forming material from the sheet-like compact. Moreover, you may carry out with respect to the porous base film (A) which extracted the hole formation material from the said sheet-like molded object. Furthermore, it may be performed before and after extracting the pore-forming material from the sheet-like compact.
As the stretching treatment, both uniaxial stretching and biaxial stretching can be suitably used, but biaxial stretching is preferable from the viewpoint of improving the strength and the like of the obtained porous substrate film (A). When the sheet-like molded product is biaxially stretched at high magnification, the molecules are oriented in the surface direction, and the finally obtained porous substrate film (A) becomes difficult to tear, and has high piercing strength. Examples of the stretching method include methods such as simultaneous biaxial stretching, sequential biaxial stretching, multistage stretching, multiple stretching, and the like. Simultaneous biaxial stretching is preferable from the viewpoint of improvement in puncture strength, uniformity of stretching, and shutdown properties. Further, from the viewpoint of controllability of plane orientation, sequential biaxial stretching is preferred.

  Here, simultaneous biaxial stretching means stretching in the MD (machine direction when continuously forming the porous base film (A)) and TD (transverse direction of the MD of the porous base film (A) at an angle of 90 °. A stretching method in which the stretching in (a) is simultaneously applied, and the stretching ratio in each direction may be different. Sequential biaxial stretching refers to a stretching method in which stretching of MD and TD is performed independently, and when MD or TD is stretched, the other direction is fixed in a non-constrained state or a fixed length It will be in the state.

  The stretching ratio is preferably in the range of 20 times to 100 times in terms of area ratio, and more preferably in the range of 25 times to 70 times. The stretching ratio in each axial direction is preferably 4 to 10 times in MD, 4 to 10 times in TD, 5 to 8 times in MD, 5 to 8 times in TD More preferably, it is in the range of When the total area magnification is 20 times or more, the obtained porous substrate film (A) tends to be able to have sufficient strength, while when the total area magnification is 100 times or less, the membrane breakage in the stretching step is It tends to prevent and to obtain high productivity.

  In order to suppress the shrinkage of the porous substrate membrane (A), heat treatment can also be performed for the purpose of heat fixation after the stretching step or after the formation of the porous substrate membrane (A). In addition, the porous substrate film (A) may be subjected to post-treatments such as hydrophilization treatment with a surfactant or the like, crosslinking treatment with an ionizing radiation or the like.

  From the viewpoint of suppressing shrinkage, the porous substrate film (A) is preferably subjected to heat treatment for the purpose of heat setting. As a method of heat treatment, for the purpose of adjusting physical properties, stretching operation performed at a predetermined temperature atmosphere and a predetermined drawing rate, and / or relaxation performed at a predetermined temperature atmosphere and a predetermined relaxation rate for the purpose of reduction of drawing stress Operation is mentioned. The relaxation operation may be performed after the stretching operation. These heat treatments can be performed using a tenter or a roll drawing machine.

In the stretching operation, the MD and / or TD of the membrane is stretched 1.1 times or more, more preferably 1.2 times or more, to obtain a porous substrate membrane (A) having higher strength and high porosity. From the viewpoint of
A relaxation operation is a reduction operation of the membrane to MD and / or TD. The relaxation rate is a value obtained by dividing the dimension of the film after the relaxation operation by the dimension of the film before the relaxation operation. In addition, when both MD and TD are eased, it is the value which multiplied the relaxation rate of MD and the relaxation rate of TD. The relaxation rate is preferably 1.0 or less, more preferably 0.97 or less, and still more preferably 0.95 or less. The relaxation rate is preferably 0.5 or more from the viewpoint of film quality. The relaxation operation may be performed in both MD and TD directions, but may be performed only in one of MD and TD.
The stretching and relaxation operation after this plasticizer extraction is preferably performed in the TD. The temperature in the stretching and relaxation operation is preferably lower than the melting point of the polyolefin resin (the melting peak temperature of the DSC 2nd run of the main raw material, hereinafter referred to as "Tm"), and the range is 1 ° C to 25 ° C lower than Tm. More preferable. It is preferable from the viewpoint of the balance of a thermal contraction rate reduction and the porosity that the temperature in extending | stretching and relaxation operation is the said range.

[Porous layer (B) containing an inorganic filler, a resin binder and a dispersant]
The porous layer (B) containing an inorganic filler, a resin binder and a dispersant will be described below.

[Inorganic filler]
The inorganic filler used for the porous layer (B) is not particularly limited, but those having high heat resistance and electrical insulation and being electrochemically stable in the use range of the lithium ion secondary battery are preferable.
As an inorganic filler, an aluminum compound, a magnesium compound, and other compounds are mentioned, for example.
Examples of aluminum compounds include aluminum oxide, aluminum silicate, aluminum hydroxide, aluminum hydroxide oxide, sodium aluminate, aluminum sulfate, aluminum phosphate, hydrotalcite and the like.
Examples of the magnesium compound include magnesium sulfate and magnesium hydroxide.
Other compounds include oxide ceramics, nitride ceramics, clay minerals, silicon carbide, calcium carbonate, barium titanate, asbestos, zeolite, calcium silicate, magnesium silicate, diatomaceous earth, silica sand, glass fiber Etc. Examples of oxide ceramics include silica, titania, zirconia, magnesia, ceria, yttria, zinc oxide, iron oxide and the like. Examples of nitride ceramics include silicon nitride, titanium nitride, boron nitride and the like. Examples of clay minerals include talc, montmorillonite, sericite, mica, amesite, bentonite and the like.
These may be used alone or in combination of two or more.

  Among the above, aluminum oxide, aluminum hydroxide oxide, and aluminum silicate are preferable from the viewpoint of electrochemical stability and heat resistance. Alumina is mentioned as a specific example of aluminum oxide. An example of aluminum hydroxide oxide is boehmite. Specific examples of aluminum silicate include kaolinite, dickite, nacrite, halloysite and pyrophyllite.

  As the aluminum oxide, alumina is more preferable from the viewpoint of electrochemical stability. By employing particles mainly composed of alumina as the inorganic filler constituting the porous layer (B), it is possible to realize a very light-weight porous layer (B) while maintaining high permeability, and also thinner. Even with the thickness of the porous layer (B), the thermal contraction of the separator at high temperature is suppressed, and the heat resistance tends to be excellent. There are many crystal forms of alumina, such as α-alumina, β-alumina, γ-alumina, θ-alumina, etc. Any of them can be suitably used. Among these, α-alumina is most preferable because it is thermally and chemically stable.

  As the aluminum hydroxide oxide, boehmite is more preferable from the viewpoint of preventing internal short circuit caused by generation of lithium dendrite. By using particles containing boehmite as a main component as the inorganic filler constituting the porous layer (B), it is possible to realize a very light weight porous layer (B) while maintaining high permeability, and further thinner. Even with the thickness of the porous layer (B), the thermal contraction of the separator at high temperature is suppressed, and the heat resistance tends to be excellent. More preferred is synthetic boehmite capable of reducing ionic impurities that adversely affect the properties of the electrochemical device.

  Among the aluminum silicates, kaolinite (hereinafter also referred to as kaolin) mainly composed of kaolin minerals is preferable from the viewpoint of lightness and air permeability. Kaolin includes wet kaolin and calcined kaolin obtained by subjecting the kaolin to calcination, however, in addition to the fact that water of crystallization is released during calcination, calcined kaolin removes impurities, so that in terms of electrochemical stability. Particularly preferred. By employing particles containing calcined kaolin as the main component as the inorganic filler constituting the porous layer (B), it is possible to realize a very lightweight porous layer (B) while maintaining high permeability, Even with a thin porous layer thickness (B), the thermal contraction of the separator at high temperatures is suppressed, and the heat resistance tends to be excellent.

  It is preferable to adjust the median diameter of the inorganic filler to the above range from the viewpoint of the air permeability of the separator, the thermal contraction at a high temperature, and the formation of the dense inorganic filler-containing porous layer (B). The median diameter of the inorganic filler is a particle diameter corresponding to 50% by volume of accumulation in the cumulative graph of the particle size distribution of the inorganic filler.

As a volume particle size distribution of the inorganic filler, the inorganic filler having a particle diameter of 0.10 μm or less is preferably less than 10%, more preferably less than 5%, and still more preferably less than 3%.
It is preferable to adjust the volume particle size distribution of the inorganic filler to the above range from the viewpoint of suppressing the thermal contraction at high temperature or improving the uniform dispersibility of the inorganic filler by the combination of the inorganic filler and the dispersant. .

  The shape of the inorganic filler may, for example, be plate-like, scaly, polyhedron, needle-like, columnar, spherical, spindle-like, or massive. A plurality of inorganic fillers having the above-mentioned shape may be used in combination. Among these, plate-like, scale-like, and polyhedron are preferable from the viewpoint of permeability improvement.

  The proportion of the inorganic filler in the porous layer (B) can be appropriately determined from the viewpoint of the permeability and heat resistance of the separator. The ratio can be 50% by mass or more, more preferably 70% by mass or more, still more preferably 80% by mass or more, particularly preferably 95% by mass or more, and most preferably 97% by mass or more . The ratio is preferably less than 100% by mass, more preferably 99.9% by mass or less, still more preferably 99.5% by mass or less, and particularly preferably 99% by mass or less.

  In order to adjust the median diameter of the inorganic filler to 0.55 μm or more and 1.2 μm or less, it is preferable to subject the inorganic filler to heat treatment, surface treatment or pulverization treatment as described above.

(Heat treatment of inorganic filler)
Examples of the heat treatment method of the inorganic filler include drying with warm air, hot air or low humidity; vacuum drying; and drying with irradiation of (far) infrared rays, electron beams and the like. For example, the inorganic filler is preferably heat-treated at 120 to 500 ° C., more preferably at 180 to 300 ° C., for 1 minute or more. By the heat treatment, the surface adsorbed water can be removed, and the hydroxyl groups present on the surface can be dehydrated and condensed to enhance its hydrophobicity.

(Surface treatment of inorganic filler)
It is preferable to perform the surface treatment of the inorganic filler with a surface treatment agent from the viewpoint of controlling the density of the water adsorption point, the adsorption ability and the like. Specific examples of surface treatment agents include fatty acid-based, oil-based, surfactant-based, wax-based, carboxylic acid-based, and phosphoric acid-based coupling agents; silane coupling agents; titanate coupling agents, etc. Be From the viewpoint of battery suitability, fatty acid type, surfactant type and carboxylic acid type coupling agents are preferable.

  The surface treatment method may be, for example, a general dry treatment in which the above-mentioned surface treatment agent is directly mixed with the powder using a mixer such as a super mixer or a Henschel mixer, and the surface treatment is carried out by heating as required. The above-mentioned surface treatment agent may be dissolved in water or hot water, added to the water coating solution of the inorganic filler being stirred and subjected to surface treatment, then dewatering and drying may be general wet treatment, dry treatment and wet treatment It may be a composite of From the viewpoint of the degree of treatment on the surface of the inorganic filler and from the economical point of view, mainly the wet method is preferably used alone.

(Pulverization treatment of inorganic filler)
As a method of pulverizing the inorganic filler, for example, a ball mill, a bead mill, a jet mill or the like can be used. By controlling the particle size of the inorganic filler by grinding, the moisture adhering to the surface of the inorganic filler can be reduced. Grinding using a bead mill is preferable from the viewpoint of controlling the density of the water adsorption point, adsorption capacity and the like, and it is more preferable to use beads having a bead diameter of about 0.01 mmφ to about 1 mmφ from the viewpoint of uniform control.

  Furthermore, the density of the water adsorption point, the adsorption capacity, and the like can be appropriately adjusted by the bead loading amount, the rotation speed, and the like. The crushing degree of the inorganic filler is preferably 0.3 to 1.0, and more preferably 0.5 to 0.99. The degree of crushing is represented by (average particle size after crushing / average particle size before crushing).

[Resin binder]
The resin binder is a resin that plays a role of binding the above-mentioned inorganic fillers to one another. Moreover, it is preferable that it is resin which plays the role of mutually binding an inorganic filler and a porous base film (A).
As the type of the resin binder, it is preferable to use one that is insoluble in the electrolyte of the lithium ion secondary battery when it is used as a separator, and is electrochemically stable in the usage range of the lithium ion secondary battery.

Specific examples of the resin binder include the following 1) to 7).
1) Polyolefin: for example, polyethylene, polypropylene, ethylene propylene rubber, and modified products thereof;
2) Conjugated diene polymers: for example, styrene-butadiene copolymer and its hydride, acrylonitrile-butadiene copolymer and its hydride, acrylonitrile-butadiene-styrene copolymer and its hydride;
3) Acrylic polymers: for example, methacrylic acid ester-acrylic acid ester copolymer, styrene-acrylic acid ester copolymer, acrylonitrile-acrylic acid ester copolymer;
4) Polyvinyl alcohol-based resin: for example, polyvinyl alcohol, polyvinyl acetate;
5) Fluorine-containing resin: for example, polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polytetrafluoroethylene, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer United;
6) Cellulose derivatives: for example, ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose;
7) Melting point and / or resin having a glass transition temperature of 180 ° C. or more or a polymer having no melting point but having a decomposition temperature of 200 ° C. or more: for example, polyphenylene ether, polysulfone, polyether sulfone, polyphenylene sulfide, polyether imide, polyamide imide , Polyamide, polyester. In particular, wholly aromatic polyamides, in particular polymetaphenylene isophthalamide is preferable from the viewpoint of durability.
Among them, the above 2) conjugated diene polymers are preferable from the viewpoint of compatibility with electrodes, and the above 3) acrylic polymers and 5) fluorine-containing resins are preferable from the viewpoint of voltage resistance.

The above 2) conjugated diene polymer is a polymer containing a conjugated diene compound as a monomer unit.
Examples of the conjugated diene compound include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene, substituted linear Conjugated pentadienes, substituted and side chain conjugated hexadienes, etc. may be mentioned, and one of these may be used alone, or two or more may be used in combination. Among these, 1,3-butadiene is particularly preferable.

The above 3) acrylic polymer is a polymer containing a (meth) acrylic compound as a monomer unit. The (meth) acrylic compound indicates at least one selected from the group consisting of (meth) acrylic acid and (meth) acrylic acid ester.
As (meth) acrylic acid used for said 3) acrylic polymer, acrylic acid and methacrylic acid can be mentioned, for example.
Examples of the (meth) acrylic acid ester used for the above 3) acrylic polymer include
(Meth) acrylic acid alkyl esters such as methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, phenyl acrylate, phenyl methacrylate, cyclohexyl acrylate, cyclohexyl methacrylate, Hydroxyethyl acrylate, hydroxyethyl methacrylate;
Epoxy group-containing (meth) acrylic acid esters such as glycidyl acrylate and glycidyl methacrylate may be mentioned, and one of these may be used alone, or two or more may be used in combination.

The 2) conjugated diene polymer and 3) the acrylic polymer may be obtained by copolymerizing other monomers copolymerizable therewith. As another copolymerizable monomer to be used, for example, unsaturated carboxylic acid alkyl ester, aromatic vinyl monomer, vinyl cyanide monomer, unsaturated monomer containing a hydroxyalkyl group, unsaturated carboxylic acid amide monomer, Examples thereof include crotonic acid, maleic acid, maleic anhydride, fumaric acid, itaconic acid, etc. These may be used alone or in combination of two or more. Among the above, unsaturated carboxylic acid alkyl ester monomers are particularly preferred. Examples of unsaturated carboxylic acid alkyl ester monomers include dimethyl fumarate, diethyl fumarate, dimethyl maleate, diethyl maleate, dimethyl itaconate, monomethyl fumarate, monoethyl fumarate and the like, and these may be used alone or in combination. Even if it uses, you may use 2 or more types together.
The 2) conjugated diene polymer may be obtained by copolymerizing the (meth) acrylic compound as another monomer.

Dispersant
In the present embodiment, a water-soluble polymer dispersant is used to improve the dispersibility of the inorganic filler.

  The mass average molecular weight of the dispersant is 300 to 10,000, preferably 500 to 9,000, and more preferably 500 to 7,000.

  The aqueous dispersion of the dispersing agent obtained by dispersing the dispersing agent in water, or the aqueous dispersing agent solution obtained by dissolving the dispersing agent in water has a solid content of 10% by mass and a temperature of 25 ° C. Under certain conditions, it is preferred to have a pH of 3 to 9, and a pH of 4 to 8.

  In the battery separator according to the present embodiment, the water-soluble polymer dispersant is preferably 0.1 parts by mass to 5 parts by mass, preferably 0.3 parts by mass to 3 parts by mass with respect to 100 parts by mass of the inorganic filler. It is present in the following proportion, more preferably in the proportion of 0.5 parts by mass or more and 1.5 parts by mass or less, still more preferably in the proportion of about 1% by mass.

  When the proportion of the dispersant, the mass average molecular weight and the pH are within the above ranges, the dispersant adheres to the surface of the inorganic filler, whereby the dispersibility of the inorganic filler in the coating liquid for forming the porous layer (B) Is further improved, aggregation of the inorganic fillers is prevented, and the dispersion state of the inorganic fillers can be more stably maintained, whereby the storage stability of the coating liquid is improved.

  Among dispersants, since the action of dispersing fine particles is strong, ion dissociative acid group (carboxyl group, sulfonic acid group, amino acid group, maleic acid group etc.) or ion dissociative acid group (carboxylic acid group, sulfone) Dispersants containing a plurality of acid bases, maleate bases and the like) are preferred, and polycarboxylates, polyacrylates or polymethacrylates are more preferred.

  Furthermore, for example, in the case where the inorganic filler is plate-like particles, the plate surface of each particle may be obtained in an overlapping state depending on the production method thereof (for example, plate-like boehmite etc.). Thus, when the porous layer (B) is formed using the coating liquid for forming the porous layer (B) in which each particle is present in a laminated state, the above-mentioned short circuit preventing effect by the use of plate-like particles is sufficiently obtained. There is no such thing. However, if a coating liquid for forming a porous layer (B) is prepared using a dispersing agent together with such aggregated particles, individual particles can be separated and uniformly dispersed in the coating liquid. Therefore, according to the coating solution for forming a porous layer (B) using a dispersing agent, it is possible to form a porous layer (B) in which the effect is exhibited better even when plate-like particles are used. it can.

  Specific examples of the above-mentioned dispersant include various anionic, cationic and nonionic surfactants; polycarboxylic acid, polyacrylic acid, polymethacrylic acid, polycarboxylate, polyacrylate, polymethacrylate and the like And the like. More specifically, Adekal (trade name) series, Adekal (trade name) series manufactured by ADEKA, SN Dispersant (trade name) series manufactured by San Nopco, and Polity (Lion) Product Name Series), Armin (product name) series, Duomin (product name) series, Kao Corporation's Homogenol (product name) series, Leodol (product name) series, Amet (product Name) Series, "Falback (trade name) series" manufactured by NOF Corporation, "Ceramidol (trade name) series", "Polyster (trade name) series", "Ajispar (trade name)" manufactured by Ajinomoto Fine Techno Co., Ltd. Series, "Aron dispersant (trade name) series" manufactured by Toagosei Co., Ltd., and the like. When the polymer dispersant is a salt (when having an acid base), it is preferably an ammonium salt. As the dispersant, those exemplified above may be used alone or in combination of two or more.

  The content of the dispersant in the coating liquid for forming the porous layer (B) is 0.1 parts by mass (solid content conversion) or more with respect to 100 parts by mass of the inorganic filler from the viewpoint of exerting the function more effectively It is preferable that it is 0.3 mass parts (solid content conversion) or more. When the content of the dispersant in the coating liquid is too large, not only the effect is saturated, but also the ratio of other components in the insulating porous layer (B) decreases, and the effect by them decreases There is a risk. Therefore, the content of the dispersant in the coating liquid for forming a separator is preferably 5 parts by mass or less, and more preferably 3 parts by mass (solid content conversion) or less, with respect to 100 parts by mass of the inorganic filler. .

(Polymer dispersant)
As the polymeric dispersant, a water soluble polymer dispersant or a non-water soluble polymer dispersant may be used, but it is preferable to use at least a water soluble polymer dispersant. Examples of the water-soluble polymer dispersant include hydrophilic polymer compounds. For example, as natural hydrophilic polymer compounds, vegetable polymers such as gum arabic, gum traga gum, guar gum, karaya gum, locust bean gum, arabinogalacton, pectin, quince seed starch, etc .; seaweeds such as alginic acid, carrageenan, agar Polymers; animal-based polymers such as gelatin, casein, albumin, and collagen; microbial-based polymers such as xanthene gum and dextran; and natural polymers such as shellac.

  Also, among hydrophilic polymer compounds obtained by modifying raw materials for natural products, cellulose polymers such as methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose and carboxymethyl cellulose; starch polymers such as sodium starch glycolate and sodium starch phosphate ester Polymers include seaweed polymers such as sodium alginate and alginic acid propylene glycol ester.

  Furthermore, as synthetic hydrophilic polymer compounds, vinyl polymers such as polyvinyl alcohol, polyvinyl pyrrolidone, polyvinyl methyl ether, etc .; non-crosslinked polyacrylamide, polyacrylic acid or alkali metal salt thereof, water-soluble styrene acrylic resin, etc. Acrylic resin; water soluble styrene maleic resin, water soluble vinyl naphthalene acrylic resin, water soluble vinyl naphthalene maleic resin, polyvinyl pyrrolidone, polyvinyl alcohol, alkali metal salt of β-naphthalene sulfonic acid formalin condensate, quaternary ammonium or amino The high molecular compound etc. which have the salt of cationic functional groups, such as group, in a side chain are mentioned.

  Among these, water-soluble dispersants having a carboxyl group introduced therein are hydrophilic polymers, such as homopolymers of acrylic acid, methacrylic acid, styrene acrylic acid, and copolymers with monomers having other hydrophilic groups. Preferred as a compound. As the hydrophilic polymer compound, a polycarboxylate is more preferable.

  Among the polymer dispersants, as the non-water-soluble dispersant, polymers having both a hydrophobic part and a hydrophilic part can be used. For example, styrene- (meth) acrylic acid copolymer, styrene-(meth) acrylic acid-(meth) acrylic acid ester copolymer, (meth) acrylic acid ester-(meth) acrylic acid copolymer, polyethylene glycol ( Examples include meta) acrylate- (meth) acrylic acid copolymer, vinyl acetate-maleic acid copolymer, and styrene-maleic acid copolymer.

  The polymer dispersant preferably contains a polymer having a carboxyl group from the viewpoint of self-dispersibility and aggregation rate when contacted with a curable treatment liquid, and has a carboxyl group and an acid value of 100 mg KOH / g or less It is preferably a polymer, and more preferably a polymer having an acid value of 25 to 100 mg KOH / g.

[Structure and Formation Method of Porous Layer]
The filling ratio of the inorganic filler in the porous layer (B) is preferably 95% by volume or less, more preferably 80% by volume or less, still more preferably 70% by volume or less, from the viewpoint of lightness and high permeability. The following are particularly preferred. From the viewpoint of heat shrinkage suppression and dendrite suppression, the lower limit is preferably 20% by volume or more, more preferably 30% by volume or more, and still more preferably 40% by volume or more. The filling rate of the inorganic filler can be calculated from the layer thickness of the porous layer (B) and the mass and specific gravity of the inorganic filler.

  The porous layer (B) may be formed only on one side or both sides of the porous substrate membrane (A).

  As a method of forming the porous layer (B), a coating liquid containing an inorganic filler, a resin binder, and a dispersing agent is applied to at least one surface of the porous substrate film (A) to form the porous layer (B) Can be mentioned.

  The form of the resin binder in the coating liquid may be an aqueous solution dissolved or dispersed in water or an organic medium solution dissolved or dispersed in a general organic medium, but a resin latex is preferable . "Resin latex" indicates a resin in a state of being dispersed in a medium. When a resin latex is used as a resin binder, when the porous layer (B) containing an inorganic filler and a resin binder is laminated on at least one surface of the porous substrate film (A), the ion permeability is unlikely to decrease and the high output characteristics are It is easy to obtain. In addition, even when the temperature rise during abnormal heat generation is fast, smooth shutdown characteristics are exhibited, and high safety can be easily obtained.

  The average particle diameter of the resin binder in the resin latex is preferably 50 to 1,000 nm, more preferably 60 to 500 nm, and still more preferably 80 to 250 nm. When the average particle diameter is 50 nm or more, when a porous layer (B) containing an inorganic filler and a resin binder is laminated on at least one surface of the porous substrate film (A), a good binding property is expressed, In the case of heat shrinkage, the heat shrinkage tends to be good and the safety tends to be excellent. When the average particle size is 1,000 nm or less, it is difficult to reduce the ion permeability and to easily obtain high output characteristics. In addition, even when the temperature rise during abnormal heat generation is fast, smooth shutdown characteristics are exhibited, and high safety can be easily obtained. The average particle size can be controlled by adjusting the polymerization time, polymerization temperature, raw material composition ratio, raw material feeding order, pH, stirring speed and the like when producing the resin binder.

  As a medium of the coating liquid, one capable of uniformly and stably dispersing or dissolving the above-mentioned inorganic filler and the above-mentioned resin binder is preferable. For example, N-methylpyrrolidone, N, N-dimethylformamide, N, N-dimethylacetamide, Water, ethanol, toluene, hot xylene, methylene chloride, hexane and the like can be mentioned.

  In the coating liquid, various additives such as a surfactant, etc .; a thickener; a wetting agent; an antifoaming agent; An agent may be added. The total addition amount of these additives is preferably not more than 20 parts by mass with respect to 100 parts by mass of the inorganic filler, as the active ingredient (the mass of the additive component dissolved when the additive is dissolved in the solvent) More preferably, it is 10 parts by mass or less, more preferably 5 parts by mass or less.

  The method for dispersing or dissolving the inorganic filler and the resin binder in the medium of the coating liquid is not particularly limited as long as it can realize the dispersion property of the coating liquid necessary for the coating process. For example, a ball mill, a bead mill, a planetary ball mill, a vibrating ball mill, a sand mill, a colloid mill, an attritor, a roll mill, a high speed impeller dispersion, a disperser, a homogenizer, a high speed impact mill, ultrasonic dispersion, mechanical agitation by stirring blades etc. may be mentioned.

  There is no particular limitation on the method of applying the coating liquid to the porous substrate film (A) as long as the required layer thickness and coating area can be realized, for example, the gravure coater method, the small diameter gravure coater method , Reverse roll coater method, transfer roll coater method, kiss coater method, dip coater method, knife coater method, air doctor coater method, blade coater method, rod coater method, squeeze coater method, cast coater method, die coater method, screen printing method And spray coating methods.

  Furthermore, prior to the application of the coating solution, when the surface of the porous substrate film (A) is subjected to surface treatment, the coating solution can be easily applied, and the inorganic filler-containing porous layer (B) after application Since adhesiveness with the porous substrate membrane (A) surface is improved, it is preferable. The method of surface treatment is not particularly limited as long as it does not significantly impair the porous structure of the porous substrate membrane (A), and, for example, corona discharge treatment, plasma discharge treatment, mechanical surface roughening method, solvent Treatment methods, acid treatment methods, ultraviolet oxidation methods and the like can be mentioned.

  The method for removing the medium from the coating film after coating is not particularly limited as long as the porous substrate film (A) is not adversely affected. For example, while fixing the porous substrate film (A), the method is not particularly limited. The method of drying at the temperature below melting | fusing point, the method of vacuum-drying at low temperature, extraction drying etc. are mentioned. In addition, as long as the battery characteristics are not significantly affected, part of the solvent may be left. From the viewpoint of controlling the shrinkage stress in the MD direction of the porous base film (A) in which the porous base film (A) and the porous layer (B) are laminated, the drying temperature, the winding tension and the like are preferably adjusted appropriately.

<Coating fluid containing inorganic filler, resin binder and dispersant>
To provide a coating liquid containing the inorganic filler, the resin binder and the dispersant described above in order to form a porous layer (B) on at least one surface of a porous substrate film (A) containing a polyolefin resin as a main component. Is also preferred. The coating liquid is preferably used to form the porous layer (B).

  Examples of the dispersion medium for the coating liquid include those containing water as a main component, and organic solvents (aromatic hydrocarbons such as toluene; furans such as tetrahydrofuran; ketones such as methyl ethyl ketone and methyl isobutyl ketone; etc.) However, what has water as a main component is preferable. The "dispersion medium" as used in the field of this invention refers to the remaining part except the solid content which remains at the time of drying at the time of insulating porous layer (B) formation in a coating liquid. Moreover, "having water as a main component" refers to containing 70% by mass or more of the components of the dispersion medium, and preferably 90% by mass or more. When water is a main component, examples of the dispersion medium other than water include alcohols added to control the interfacial tension of the coating liquid. From the viewpoint of environmental protection, it is particularly preferable to use only water as the dispersion medium.

  The viscosity of the coating liquid is 5 mPa · s or more, preferably 10 mPa · s or more, and 20 mPa · s or more from the viewpoint of suppressing the sedimentation of the inorganic filler and improving the stability of the dispersion. More preferable. In addition, when the viscosity of the coating liquid is too high, it becomes difficult to coat uniformly with the required thickness, so the viscosity is 500 mPa · s or less, preferably 300 mPa · s or less, More preferably, it is 200 mPa · s or less. The viscosity in the coating liquid of the present invention is a viscosity measured by an E-type viscometer by a method according to Japanese Industrial Standard (JIS) R 1652, and a condition of a temperature of 23 ° C. and a shear rate of 1,000 / s. It refers to what was measured below.

(Apparatus for producing coating fluid)
In the manufacturing method of the present embodiment, the method of dissolving or dispersing the inorganic filler, the resin binder and the dispersant in a solvent is not particularly limited. For example, a ball mill, bead mill, planetary ball mill, vibration ball mill, sand mill, colloid mill, attritor Roll mill, high-speed impeller dispersion, disperser, homogenizer, high-speed impact mill, ultrasonic dispersion, mechanical agitation by a stirring blade, etc. may be mentioned.

(Coating device)
In the production method of the present embodiment, the method of applying the coating liquid containing the inorganic filler, the resin binder and the dispersant to the porous substrate film (A) is a method which can realize the required layer thickness or coating area. There is no particular limitation as long as it is. For example, gravure coater method, small diameter gravure coater method, reverse roll coater method, transfer roll coater method, kiss coater method, dip coater method, knife coater method, air doctor coater method, blade coater method, rod coater method, squeeze coater method, cast Examples of the method include a dip coater method, a die coater method, a screen printing method, and a spray coating method.

  In addition, depending on the application, a coating liquid containing an inorganic filler, a resin binder, and a dispersant may be coated on only one side of the porous substrate film (A), or may be coated on both sides.

(Characteristics of porous layer (B), etc.)
The layer thickness of the porous layer (B) in this embodiment is preferably 0.1 μm to 50 μm, more preferably 0.5 μm to 20 μm, still more preferably 1 μm to 10 μm, particularly preferably 1.5 μm to 7 μm. When the thickness of the porous layer (B) is 0.1 μm or more, the heat resistance tends to be further improved. In addition, when the layer thickness of the porous layer (B) is 50 μm or less, the capacity of the battery is further increased, the ion permeability of the separator is further improved, and the powder loss of the inorganic filler at the time of use tends to be further suppressed. is there.

<Other physical properties of separators>
The separator which concerns on this embodiment has a porous base film (A) and a porous layer (B) distribute | arranged to the single side | surface or both surfaces of this porous base film (A). The air permeability of the separator of the present embodiment is not particularly limited, but is preferably 10 seconds / 100 cc to 650 seconds / 100 cc, more preferably 20 seconds / 100 cc to 500 seconds / 100 cc, and still more preferably It is 300 seconds / 100 cc or more and 450 seconds / 100 cc or less, and particularly preferably 50 seconds / 100 cc or more and 400 seconds / 100 cc or less. When the air permeability is 10 seconds / 100 cc or more, the self-discharge resistance tends to be further improved. In addition, when the air permeability is 650 seconds / 100 cc or less, the charge and discharge characteristics tend to be further improved.

  The final film thickness of the separator according to the present embodiment is not particularly limited, but is preferably 2 μm to 200 μm, more preferably 5 μm to 100 μm, and still more preferably 7 μm to 30 μm, particularly preferably Is 9 μm or more and 20 μm or less. When the film thickness is 2 μm or more, mechanical strength tends to be further improved. In addition, when the film thickness is 200 μm or less, the capacity of the battery tends to be further increased.

  The thermal shrinkage at 150 ° C. of the separator is preferably 0% or more and 15% or less in both MD and TD directions, more preferably 0% or more and 10% or less, and still more preferably 0% or more and 5% or less . It is preferable that the thermal contraction rate is 15% or less in both the MD direction and the TD direction, since breakage of the separator at the time of abnormal heat generation of the battery is suppressed and short circuit is less likely to occur.

  The shutdown temperature of the separator is preferably 120 ° C. or more and 160 ° C. or less, and more preferably in the range of 120 ° C. or more and 150 ° C. or less. It is preferable that the shutdown temperature is 160 ° C. or less because current interruption is promptly promoted even when the battery generates heat, etc., and better safety performance can be obtained. On the other hand, when the shutdown temperature is 120 ° C. or higher, the battery can be used at around 100 ° C., which is preferable.

The short circuit temperature of the separator is preferably 160 ° C. or more and 1,000 ° C. or less, more preferably 180 ° C. or more and 1,000 ° C. or less, and still more preferably 200 ° C. or more and 1,000 ° C. or less. If the short circuit temperature is 160 ° C. or more, even if abnormal heat generation occurs in the battery, the short circuit does not occur immediately, so that heat can be dissipated during that time, and better safety performance can be obtained.
The shorting temperature can be controlled to a desired value by adjusting the content of polypropylene, the type of polyolefin other than polypropylene, the type of inorganic particles, the thickness of the porous layer (B), and the like.

<Storage device>
Hereinafter, the storage device will be described. The storage device includes the separator, and the other configuration may be the same as conventionally known. The storage device is not particularly limited, and examples thereof include batteries such as non-aqueous electrolyte batteries, capacitors and capacitors. Among them, non-aqueous electrolyte batteries are preferable, non-aqueous electrolyte secondary batteries are more preferable, and lithium ion secondary batteries are more preferable, from the viewpoint that the benefits of the effects according to the present invention can be obtained more effectively. Hereinafter, the suitable aspect about the case where an electrical storage device is a non-aqueous electrolyte battery is demonstrated.

There is no limitation on the positive electrode, the negative electrode, and the non-aqueous electrolyte, and known ones can be used.
Examples of positive electrode materials include lithium-containing composite oxides such as LiCoO ₂ , LiNiO ₂ , spinel-type LiMnO ₄ , olivine-type LiFePO _{4 and the} like, and examples of negative electrode materials include, for example, graphitic, non-graphitizable carbonaceous, easy-to-graphite Carbon materials such as carbon oxides and composite carbons; silicon, tin, lithium metal, various alloy materials and the like.

In addition, as the non-aqueous electrolytic solution, an electrolytic solution in which an electrolyte is dissolved in an organic solvent can be used. As the organic solvent, for example, propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate etc. are electrolytes Examples of L include lithium salts such as LiClO ₄ , LiBF ₄ , LiPF _{6 and the} like.

Although the said electrical storage device is not specifically limited, For example, it manufactures as follows. That is, the said separator is produced as an oblong separator with a width of 10 to 2,000 mm (preferably 80 to 1,000 mm) and a length of 200 to 4,000 m (preferably 1.000 to 4,000 m). Next, the separator is slit to a width of 10 to 500 mm as necessary. The obtained separator is stacked with a positive electrode and a negative electrode in the order of positive electrode-separator-negative electrode-separator or negative electrode-separator-positive electrode-separator to obtain a laminate. Then, the laminate is wound into a cylindrical or flat spiral shape to obtain a wound body. And the electrical storage device is obtained by passing through the process of accommodating the said wound body in an exterior body, and also inject | pouring electrolyte solution.
In the above electricity storage device, the separator, the positive electrode, and the negative electrode are formed into a flat plate, and then laminated in the order of positive electrode-separator-negative electrode-separator-positive electrode or negative electrode-separator-positive electrode-separator-negative electrode to obtain a laminate. After that, it can also be manufactured through steps such as being contained in an outer package and injecting an electrolytic solution there.
In addition, as the said exterior body, a battery can and a bag-like film can be used.

  Next, the present embodiment will be more specifically described by way of examples, but the present embodiment is not limited to the following examples as long as the gist thereof is not exceeded. Physical properties and evaluations in Examples and Comparative Examples were performed according to the following methods.

(1) Viscosity average molecular weight (Mv) of polyolefin
The intrinsic viscosity [D] (dl / g) at 135 ° C. in decalin solvent was determined based on ASTM-D4020.
For polyethylene, Mv was calculated by the following equation.
[Η] = 6.77 × 10 ^-4 Mv ^0.67
For polypropylene, Mv was calculated by the following equation.
[Η] = 1.10 × 10 ^-4 Mv ^0.80

(2) Film Thickness of Porous Substrate Film (A), Layer Thickness of Porous Layer (B) Samples of MD10 mm × TD10 mm were cut out from the porous substrate film (A) and the separator, respectively, and 9 locations (3 points × Select 3 points), measure the film thickness using a dial gauge (PEACOCK No. 25 (registered trademark) made by Ozaki Mfg. Co., Ltd.), and average the measured values of 9 points with the porous substrate film (A) and the separator Film thickness (μm). Further, the difference between the film thickness of the separator and the porous substrate film (A) thus measured was calculated as the layer thickness (μm) of the porous layer (B).

(3) Porosity of porous substrate membrane (A) (%)
A sample of 10 cm × 10 cm square is cut from the porous substrate membrane (A), its volume (cm ³ ) and mass (g) are determined, and the density of the porous substrate membrane (A) is 0.95 (g / cm ³ ) It calculated using following Formula as.
Porosity (%) = (1-mass / volume / 0.95) x 100

(4) Air permeability of porous base membrane (A) (sec / 100 cc)
Using a Gurley-type air permeability meter (G-B2 (trade name) manufactured by Toyo Seiki Co., Ltd .; inner cylinder weight: 567 g) according to JIS P-8117, a porous substrate film (circle 28.6 mm in diameter) of 645 mm ² The time (seconds) in which 100 cc of air passes through A) was measured, and these were respectively used as the air permeability of the porous substrate membrane (A) and the separator.

(5) Average particle diameter of inorganic filler After adding an inorganic filler to distilled water and adding a small amount of sodium hexametaphosphate aqueous solution and dispersing for 1 minute with an ultrasonic homogenizer, a laser type particle size distribution measuring device (manufactured by Nikkiso Co., Ltd.) The particle diameter distribution was measured using Microtrac MT3300EX), and the particle diameter (median diameter) at which the cumulative frequency was 50% was defined as the average particle diameter (μm).

(6) Stability in standing of coating liquid After sufficiently stirring the coating liquid in which the inorganic filler, the resin binder, and the dispersing agent are uniformly dispersed in water as described in the Examples and the like described later, 500 mL of the coating liquid Pour into a 500 mL graduated graduated cylinder. After the injection was completed, the height of the deposited layer of sediment after standing at 25 ° C. for 24 hours was measured on a scale, and the ratio to the height of the coating liquid at the completion of injection was evaluated (%).

(7) Molecular Weight of Dispersant The mass average molecular weight of the dispersant was measured by gel permeation chromatography (GPC) using a calibration curve prepared using standard polystyrene.

(8) pH of dispersant
The dispersant is dispersed in water to obtain a dispersant aqueous dispersion, or the dispersant is dissolved in water to obtain an aqueous dispersant solution, and the solution is adjusted to a solid content of 10% by mass, and the digital pH is adjusted at 25 ° C. The pH of the dispersant aqueous dispersion or dispersant aqueous solution was measured using a meter.

(9) Thermal contraction rate of separator (%)
The sample was cut into a square of 100 mm each for MD / TD. The cut out sample was sandwiched between two sheets of paper and allowed to stand in an oven at 150 ° C. for 1 hour. After the sample was taken out of the oven and cooled, the dimensional shrinkage (%) of the sample was determined in each of the MD direction and the TD direction.

(10) High temperature storage test (gas generation test)
The aluminum laminate sheet was cut into a fixed size, and made into a pack (6 cm × 8 cm) by an impulse sealer. The separator sample cut into 10 cm × 10 cm was folded, inserted into the laminate pack, and vacuum dried at 80 ° C. for 12 hours. Next, in an electrolytic solution in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed at a volume ratio of EC: EMC = 1: 2, a solution of LiPF ₆ dissolved at 1 mol / L as an electrolyte is contained in an argon box 0.4 mL was poured into the vacuum-dried aluminum laminate pack, and the opening of the aluminum laminate pack was sealed with a heat sealer. This was stored in an oven set at 150 ° C. for 72 hours, the mass before and after the test was measured, and the volume was calculated by the Archimedes method. The mass was converted by the density of water (20 ° C .: 0.9982 g / cm ³ ).
(Archimedes method: F = −ρVg)
Gas generation amount (mL) = volume after test−volume before test The number of defects of 20 batteries was calculated according to the following evaluation criteria.
Pass: When the amount of gas generation (mL) is less than 2 mL.
Bad: When gas generation amount (mL) is 2 mL or more.

(11) Charge-discharge cycle characteristics a. Preparation of positive electrode 90.4% by mass of nickel, manganese, cobalt composite oxide (NMC) (Ni: Mn: Co = 1: 1: 1 (element ratio), density 4.70 g / cm ³ ) as a positive electrode active material, 1.6% by mass of graphite powder (KS6) (density 2.26 g / cm ³ , number average particle diameter 6.5 μm) as conductive aid and acetylene black powder (AB) (density 1.95 g / cm ³ , number average) In N-methyl pyrrolidone (NMP), a particle diameter of 48 nm) is mixed at a ratio of 3.8% by mass and polyvinylidene fluoride (PVDF) (density 1.75 g / cm ³ ) as a binder at a ratio of 4.2% by mass The slurry was dispersed to prepare a slurry. This slurry was coated on one side of a 20 μm thick aluminum foil as a positive electrode current collector with a die coater, dried at 130 ° C. for 3 minutes, and then compression molded using a roll press. The active material coating amount at this time was 109 g / m ² .

b. Preparation of Negative Electrode As a negative electrode active material, 87.6% by mass of graphite powder A (density 2.23 g / cm ³ , number average particle diameter 12.7 μm) and graphite powder B (density 2.27 g / cm ³ , number average particle diameter 9.7% by mass of a 6.5 μm), and 1.4% by mass (in terms of solid content) of an ammonium salt of carboxymethylcellulose as a binder (in terms of solid content) (solid content concentration 1.83% by mass aqueous solution) and styrene-butadiene copolymer latex 1. A slurry was prepared by dispersing 7% by mass (in terms of solid content) (solid content concentration 40% by mass aqueous solution) in purified water. The slurry was coated on one side of a copper foil having a thickness of 12 μm, which is a negative electrode current collector, with a die coater, dried at 120 ° C. for 3 minutes, and compression molded using a roll press. At this time, the active material coating amount of the negative electrode was 5.2 g / m ² .

c. Preparation of Nonaqueous Electrolyte LiPF ₆ was dissolved as a solute in a mixed solvent of ethylene carbonate: ethyl methyl carbonate = 1: 2 (volume ratio) to a concentration of 1.0 mol / L.

d. Battery Assembly The separator was cut into a circle of 24 mm in diameter and the positive electrode and the negative electrode in a circle of 16 mm, and the negative electrode, the separator and the positive electrode were stacked in this order so that the active material faces of the positive electrode and the negative electrode face each other. The container and the lid were insulated, and the container was in contact with the copper foil of the negative electrode, and the lid was in contact with the aluminum foil of the positive electrode. In the container, 0.4 ml of the non-aqueous electrolyte was injected and sealed, to prepare a battery for evaluation.

e. Pretreatment After charging the battery assembled as described above to a voltage of 4.2 V at a current value of 1/3 C and performing constant voltage charging of 4.2 V for 8 hours, the battery was then subjected to a 1/3 C current 3. Discharge was performed to a final voltage of 0 V. Next, after constant current charging to a voltage of 4.2 V with a current value of 1 C, constant voltage charging of 4.2 V was performed for 3 hours, and then discharging was performed to a final voltage of 3.0 V with a current of 1 C. Finally, after performing constant current charge to 4.2 V with a current value of 1 C, constant voltage charge of 4.2 V was performed for 3 hours, and pretreatment was completed. Here, 1 C represents a current value at which the reference capacity of the battery is discharged in one hour.

f. Cycle Characteristics The battery subjected to the above pretreatment was discharged to a discharge termination voltage of 3 V at a discharge current of 1 A at a temperature of 25 ° C., and then charged to a charge termination voltage of 4.2 V at a charge current of 1 A. The charge and discharge were repeated by setting this as one cycle, the capacity retention after 200 cycles to the initial capacity was checked, and the cycle characteristics were evaluated based on the following criteria. The number of failures of 20 batteries was calculated according to the following evaluation criteria.
(Evaluation criteria)
Pass: When the capacity retention rate is 90% or more Defect: When the capacity retention rate is less than 90%

<Method of Producing Polyolefin Resin Porous Substrate Membrane (A)>
Mv of 700,000, 47.5 parts by mass of homopolymer high density polyethylene,
Mv of 300,000, 47.5 parts by mass of homopolymer high density polyethylene,
5 parts by mass of homopolymer polypropylene having an Mv of 400,000
And 1 part by mass of tetrakis- [methylene- (3 ', 5'-di-t-butyl-4'-hydroxyphenyl) propionate] methane as an antioxidant and dry blending using a tumbler blender, A mixture was obtained.

The resulting mixture was fed by a feeder to a twin screw extruder under a nitrogen atmosphere.
Also, liquid paraffin (kinetic viscosity 7.59 × 10 −5 m ² / s at 37.78 ° C.) was injected into the extruder cylinder by a plunger pump.

  The operating conditions of the feeder and pump were adjusted so that the proportion of liquid paraffin in the total mixture extruded was 65 parts by mass, that is, the polymer concentration was 35 parts by mass.

  Then, they are melt-kneaded while heating to 230 ° C. in a twin-screw extruder, and the resulting melt-kneaded product is extruded through a T-die onto a cooling roll controlled to a surface temperature of 80 ° C. A sheet-like molded product was obtained by contacting with a cooling roll, casting, and cooling and solidifying.

  The sheet was stretched in a simultaneous biaxial stretching machine at a magnification of 7 × 6.4 times and a temperature of 112 ° C., and then immersed in methylene chloride. Next, after extracting and removing liquid paraffin from the sheet-like molded product, it was dried.

  Further, the sheet is stretched 2.0 times in the transverse direction at a temperature of 128 ° C. by a tenter stretcher, and then this stretched sheet is heat treated by relaxing about 10% in the width direction at a temperature of 131 ° C. Thus, a polyolefin resin porous substrate film (A1) having a porosity of 40% by volume and an air permeability of 130 seconds / 100 cc was obtained.

<Method of producing resin binder>
Synthesis Example Production of Acrylic Polymer Latex 70.4 parts by mass of ion-exchanged water in a reaction vessel equipped with a stirrer, reflux condenser, dropping tank, and thermometer, “Aqualon KH1025” (trade name, first 0.1 parts by mass (in terms of solid content) made by Kogyo Seiyaku Co., Ltd. (25% by mass aqueous solution) and 0.1 parts by mass (solid form, 25% by mass aqueous solution made by ADEKA, trade name) The reaction vessel inside temperature is raised to 80 ° C., and 0.15 parts by mass (solid content conversion) of ammonium persulfate (2 mass% aqueous solution) is added while maintaining the temperature of 80 ° C. did.

  After 5 minutes of addition of an aqueous ammonium persulfate solution, methyl methacrylate: 38.5 parts by mass, n-butyl acrylate: 19.6 parts by mass, 2-ethylhexyl acrylate: 31.9 parts by mass, methacrylic acid: 0.1 Acrylic acid: 0.1 parts by mass, 2-hydroxyethyl methacrylate: 2 parts by mass, acrylamide: 5 parts by mass, glycidyl methacrylate: 2.8 parts by mass, γ-methacryloxypropyltrimethoxysilane: 0. 3 parts by mass, trimethylolpropane triacrylate (A-TMPT, manufactured by Shin-Nakamura Chemical Co., Ltd.): 0.7 parts by mass, "Aqualon KH1025" (trade name, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., 25% by mass aqueous solution) : 0.75 parts by mass (in terms of solid content), "Adekaria soap SR 1025" (trade name, manufactured by ADEKA Co., Ltd., 25% by mass) Solution): 0.75 parts by mass (in terms of solid content), sodium p-styrenesulfonate: 0.05 parts by mass, ammonium persulfate (2% by mass aqueous solution): 0.15 parts by mass (in terms of solid content), and ion exchange Water: A mixture of 52 parts by mass was mixed for 5 minutes with a homomixer, and an emulsion obtained by preparing an emulsion was dropped from the dropping tank to the reaction vessel over 150 minutes.

  After completion of the dropwise addition of the emulsion, the temperature inside the reaction vessel was maintained for 90 minutes while being kept at 80 ° C., and then cooled to room temperature to obtain an emulsion. An aqueous ammonia solution (ammonia content: 25% by mass) was added to the obtained emulsion to adjust to pH = 9.0, whereby a latex containing an acrylic polymer having a solid content concentration of 40% by mass was obtained.

  The average particle diameter of the obtained acrylic polymer was 145 nm, and the glass transition temperature was -20 ° C.

Example 1
[Formation of Porous Layer (B), and Production of Separator]
95.0 parts by mass of aluminum hydroxide oxide (D ₅₀ = 0.7 μm) as an inorganic filler, and the acrylic polymer latex obtained above as a resin binder (solid content concentration 40%, average particle diameter 145 nm, minimum film forming temperature 100 parts by mass of 4.0 parts by mass (in terms of solid content) and 1.0 parts by mass of an aqueous solution of ammonium polycarboxylate (Mw = 90, pH = 6.8) as a dispersant The coating solution was uniformly dispersed.

  Next, after corona discharge treatment (discharge amount 50 W) was performed on the surface of the substrate, the above-mentioned coating liquid was applied to the treated surface using a microgravure coater.

  The coated layer was dried at 60 ° C. to form a porous layer (B) having a thickness of 2 μm on the polyolefin resin porous substrate membrane (A1) to obtain a separator.

Example 2
A separator was obtained in the same manner as Example 1, except that an aqueous solution of ammonium polycarboxylate (Mw = 7,000, pH = 6.5) was used as the dispersant.

[Example 3]
A separator was obtained in the same manner as Example 1, except that a sodium polycarboxylate aqueous solution (Mw = 3,000, pH = 6.3) was used as a dispersant.

Example 4
A separator was obtained in the same manner as Example 1, except that a sodium polycarboxylate aqueous solution (Mw = 400, pH = 7.2) was used as the dispersant.

[ Reference Example 5]
A separator was obtained in the same manner as Example 1, except that an aqueous solution of ammonium polyacrylate (Mw = 7,000, pH = 4.3) was used as a dispersant.

[ Reference Example 6]
A separator was prepared in the same manner as Example 1, except that calcined kaolin (D ₅₀ = 0.7 μm) was used as the inorganic filler, and an aqueous solution of ammonium polymethacrylate (Mw = 7,000, pH = 8.4) was used as the dispersant. I got

[Example 7]
A separator was obtained in the same manner as Example 1, except that a sodium polycarboxylate aqueous solution (Mw = 500, pH = 8.7) was used as a dispersant.

[Example 8]
A separator was prepared in the same manner as in Example 1, except that aluminum hydroxide oxide (D ₅₀ = 0.55 μm) was used as the inorganic filler and sodium polycarboxylate aqueous solution (Mw = 500, pH = 4.1) was used as the dispersant. I got

[Example 9]
Using aluminum hydroxide oxide (D ₅₀ = 1.1 μm) as the inorganic filler and sodium polycarboxylate aqueous solution (Mw = 7,000, pH = 6.5) as the dispersant, the thickness of the porous layer (B) A separator was obtained in the same manner as Example 1 except that the thickness was 4 μm.

Comparative Example 1
A separator was obtained in the same manner as Example 1, except that aluminum hydroxide oxide (D ₅₀ = 0.3 μm) was used as the inorganic filler.

Comparative Example 2
A separator was obtained in the same manner as Example 1, except that aluminum hydroxide oxide (D ₅₀ = 1.4 μm) was used as the inorganic filler.

Comparative Example 3
A separator was obtained in the same manner as Example 1, except that an aqueous solution of ammonium polycarboxylate (Mw = 12,000, pH = 6.8) was used as a dispersant.

Comparative Example 4
A separator was obtained in the same manner as Example 1, except that an aqueous sodium polycarboxylate solution (Mw = 250, pH = 7.2) was used as the dispersant, and the thickness of the porous layer (B) was 4 μm.

Comparative Example 5
A separator was obtained in the same manner as Example 1, except that an aqueous ammonium polyacrylate solution (Mw = 6,000, pH = 2.5) was used as a dispersant and the thickness of the porous layer (B) was 4 μm. .

Comparative Example 6
A separator was obtained in the same manner as Example 8, except that an aqueous solution of ammonium polycarboxylate (Mw = 5,000, pH = 9.8) was used as the dispersant.

The evaluation results of the separators obtained in Examples 1 to 4 and 7 to 7 and Reference Examples 5 to 6 and Comparative Examples 1 to 6 are shown in Table 1 below.

Claims (4)

A battery separator comprising a porous layer (B) containing an inorganic filler, a resin binder, and a dispersing agent on at least one side of a porous substrate membrane (A),
The median diameter of the inorganic filler is 0.55 μm or more and 1.2 μm or less,
The dispersant is present in a ratio of 0.1 parts by mass to 5 parts by mass with respect to 100 parts by mass of the inorganic filler,
The dispersant is a polycarboxylate having a mass average molecular weight of 300 to 9,000 (excluding poly (meth) acrylate) , and the solid content of the dispersant is 10% by mass. The pH at 25 ° C when dispersed or dissolved in water is 3 to 9,
The battery separator.   The battery separator according to claim 1, wherein the dispersant is a water-soluble polymer dispersant.   The battery separator according to claim 1, wherein the inorganic filler is selected from the group consisting of alumina, silica, kaolin and boehmite.   A non-aqueous electrolyte battery comprising the battery separator according to any one of claims 1 to 3, a positive electrode, a negative electrode, and an electrolytic solution.