JP6444122B2 - Power storage device separator, separator slurry, and non-aqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to an electrical storage device separator and the like.

  Conventionally, in order to improve the heat resistance of a battery separator such as a lithium ion secondary battery, an inorganic coating film containing an inorganic filler and a resin binder is provided on at least one surface of a porous base film mainly composed of a polyolefin resin. Battery separators have been proposed.

  Inorganic fillers are used to form inorganic layers to improve the heat resistance of battery separators, but when battery separators with an inorganic coating film are used, the initial charge / discharge defects of batteries tend to increase. is there. For example, it is known that the decrease in charge / discharge cycle characteristics of the battery is caused by the amount of water contained in the separator in advance.

In order to manage the moisture content in the battery separator, for example, in Patent Document 1, the moisture content per unit volume when held in an atmosphere at 20 ° C. and 60% relative humidity for 24 hours is 1 mg / cm 2. Battery separators of ³ or less have been proposed.

  In the separator described in Patent Document 1, for example, by adjusting the upper limit of the average particle size of the inorganic filler to 10 μm or less, the gap between the inorganic fillers is increased to some extent to shorten the ion conduction path in the separator, Improves battery characteristics.

  In Patent Document 2, for example, the ratio of the inorganic filler having a particle diameter of 1 μm or less is 30% by volume or more, the ratio of the inorganic filler having a particle diameter of 3 μm or more is 10% by volume or less, and the median of the inorganic filler It has been proposed to form a battery separator provided with an inorganic coating film using an aqueous dispersion having a diameter of 0.54 μm or 0.71 μm.

  In Patent Document 3, it is proposed to form a battery separator having an inorganic coating film on a porous substrate using a dispersion liquid having a median diameter of an inorganic filler of 0.1 μm to 0.5 μm. Yes.

JP 2009-224341 A International Publication No. 2009/096451 Japanese Patent No. 5470255

  However, the separator described in Patent Document 1 does not sufficiently consider an inorganic filler having a relatively small particle size. An inorganic filler having a relatively small particle size has a large surface area, so that it easily adsorbs moisture, and increases initial charge / discharge failure of the battery due to moisture even when coated on a substrate such as a substrate.

  Since the separator described in Patent Document 2 still has room for study on the proportion of inorganic filler having a fine particle size, for example, a particle size of 0.2 μm or less, further improves the heat resistance of the separator and the initial charge / discharge characteristics of the battery. There is room to make it happen.

  Since the porous base material is a nonwoven fabric, the separator of patent document 3 is inferior to a shutdown characteristic.

  Therefore, the problem to be solved by the present invention is a storage device separator that has excellent heat resistance and can improve the initial charge / discharge characteristics of the battery, a non-aqueous electrolyte secondary battery including the separator, and the separator Providing a slurry for the production of

As a result of intensive studies, the present inventors have found that the above problems can be solved by controlling the primary particle size distribution of the inorganic filler to form the inorganic coating film of the separator for the electricity storage device, and completed the present invention. I let you. That is, the present invention is as follows.
[1] An electricity storage device separator including a porous layer containing an inorganic filler and a resin binder on at least one surface of a porous substrate film containing a polyolefin resin,
In the primary particle size distribution measurement based on the volume of the inorganic filler, the content of particles having a primary particle size of 0.2 μm or less is less than 10% by mass based on the mass of the inorganic filler, and The median diameter of the inorganic filler is more than 0.5 μm and not more than 0.8 μm.
The separator for an electricity storage device.
[2] In the primary particle size distribution measurement based on the volume of the inorganic filler, the content of particles having a primary particle size of 0.2 μm or less is less than 3% by mass based on the mass of the inorganic filler. The separator for an electricity storage device according to [1].
[3] The inorganic filler has a total desorption ammonia (NH ₃ ) amount of from 10 μmol / g to 1,000 μmol / g from 150 ° C. to 400 ° C. in an ammonia temperature-programmed desorption method, [1] or [ 2] The separator for electrical storage devices described in [2].
[4] The primary particle size distribution measurement is performed using an aqueous dispersion obtained by dispersing an inorganic filler in water, or a slurry containing an inorganic filler and a resin binder, [1] to [3]. The separator for electrical storage devices of any one of these.
[5] The thermal contraction rate at 150 ° C. of the electricity storage device separator is 0% or more and 15% or less in both the MD direction and the TD direction, according to any one of [1] to [4]. Electric storage device separator.
[6] The separator for an electricity storage device according to any one of [1] to [5],
A positive electrode;
A negative electrode,
A non-aqueous electrolyte secondary battery comprising a non-aqueous electrolyte.
[7] A slurry for a battery separator containing an inorganic filler and a resin binder,
In the primary particle size distribution measurement based on the volume of the inorganic filler, the content of particles having a primary particle size of 0.2 μm or less is less than 10% by mass based on the mass of the inorganic filler,
The median diameter of the inorganic filler is more than 0.5 μm and 0.8 μm or less, and the viscosity of the battery separator slurry at 25 ° C. and a solid content concentration of 30% by mass is 300 mPa · s or less.
The battery separator slurry.

  According to the present invention, an inorganic filler with few active sites, particularly an inorganic filler with few acid sites to which moisture can adhere, can be used. Therefore, it is possible to provide a separator for an electricity storage device that can suppress the initial charge / discharge failure of a battery. Further, according to the present invention, it is possible to suppress the deterioration reaction of the battery or the decomposition of the electrolytic solution due to the moisture in the battery.

It is a graph which shows the primary particle diameter distribution of a resin binder liquid, an inorganic filler preliminary dispersion liquid, and an inorganic filler dispersion liquid. It is a graph which shows the primary particle diameter distribution of an inorganic filler preliminary dispersion liquid, an inorganic filler dispersion liquid, and a slurry coating liquid containing an inorganic filler and a resin binder.

  Hereinafter, a mode for carrying out the present invention (hereinafter abbreviated as “this embodiment”) will be described in detail. In addition, this invention is not limited to the following embodiment, It can implement by changing variously within the range of the summary.

<Separator for electricity storage device>
The separator for an electricity storage device of the present invention will be described.
The separator for an electricity storage device of the present invention includes a porous substrate film containing a polyolefin resin and a porous layer laminated on at least one surface of the porous substrate film, and the porous layer contains an inorganic filler and a resin binder.

  The separator is excellent in heat resistance and has a shutdown function, and thus is suitable as a separator for an electricity storage device that separates a positive electrode and a negative electrode in a battery. In particular, since the separator is difficult to short-circuit even at high temperatures, it can be safely used as a separator for a high electromotive force battery.

  In the separator according to this embodiment, in the primary particle size distribution measurement based on the volume of the inorganic filler, the content of particles having a primary particle size of 0.2 μm or less is 10 based on the mass of the inorganic filler. It is less than 5% by mass, preferably less than 5% by mass, more preferably less than 1% by mass, further preferably 0.5% by mass or less, and most preferably 0% by mass.

  In the separator according to this embodiment, in the primary particle size distribution measurement based on the volume of the inorganic filler, the median diameter of the inorganic filler is preferably more than 0.5 μm, or 0.6 μm or more. The median diameter is preferably 0.8 μm or less, or 0.7 μm or less.

  Although not wishing to be bound by theory, in the separator according to the present embodiment, in the primary particle size distribution measurement based on the volume of the inorganic filler, the content of particles having a primary particle size of 0.2 μm or less Is less than 10% by mass based on the mass of the inorganic filler, and the median diameter of the inorganic filler is more than 0.5 μm and not more than 0.8 μm, the active point of the inorganic filler contained in the porous layer Is considered to be properly controlled.

  The active point is also called an acid point such as Bronsted acid point or Lewis acid point. When the acid point in the separator increases, the number of protons donating or accepting electrons increases between the positive electrode and the negative electrode, so that a predetermined electrochemical reaction between the positive electrode and the negative electrode or a predetermined ion of the electrolyte May adversely affect conduction.

Furthermore, the more acid points in the separator, the greater the amount of water that can be drawn to the separator. For example, when water is present in a non-aqueous secondary battery such as a lithium ion secondary battery, the lowest empty orbital (LUMO) level of water is lower than the Fermi level of a general negative electrode. Electrons flow into the LUMO, water molecules are activated due to the electrons, and a reductive decomposition reaction of water occurs instead of a predetermined electrochemical reaction between the positive electrode and the negative electrode, generating hydrogen. Water reacts with electrolytes such as LiPF ₆ and LiBF ₄ to generate hydrofluoric acid (HF), which may corrode batteries and separators.

  In any case, since active sites or water in the separator often leads to initial charge / discharge failure of the battery, it is important to reduce the amount of active sites of the inorganic filler contained in the separator. In particular, particles having a relatively small particle size, that is, particles having a relatively large surface area are considered to have many active sites. Therefore, assuming that the separator or battery contains a certain amount of water, an inorganic filler having a relatively small particle size is more likely to cause an initial charge / discharge failure of the battery than an inorganic filler having a relatively large particle size.

  In the present embodiment, from the above viewpoint, in order to reduce the amount of active sites of the inorganic filler, in the primary particle size distribution measurement based on the volume of the inorganic filler, particles having a primary particle size of 0.2 μm or less are separated. And the inorganic filler having a relatively small particle size is removed from the separator by adjusting the median diameter of the inorganic filler to a range of more than 0.5 μm and 0.8 μm or less.

The amount of active sites of the inorganic filler is believed to be calculated from the total desorption of ammonia (NH ₃₎ the amount described later.

  The primary particle size distribution measurement based on the volume of the inorganic filler can be performed by the method described in Examples. The primary particle size distribution measurement is preferably performed using an aqueous dispersion obtained by dispersing an inorganic filler in water, or using a slurry containing an inorganic filler and a resin binder.

  The volume of the inorganic filler is reduced by filtration treatment for removing particles having a relatively small particle size from the material for forming the porous layer containing the inorganic filler and / or heat treatment, surface treatment, pulverization treatment or granulation treatment of the inorganic filler. In the primary particle size distribution measurement as a reference, the content of particles having a primary particle size of 0.2 μm or less is adjusted to less than 10% by mass based on the mass of the inorganic filler, and the median diameter of the inorganic filler is adjusted. It can be adjusted within a range of more than 0.5 μm and 0.8 μm or less. Although the reason is not certain, it is considered that the adsorption ability or moisture adsorption point density of the inorganic filler is appropriately controlled by these treatments. These treatments will be described in detail in the description of the inorganic filler below.

  The porous substrate film and the porous layer containing an inorganic filler and a resin binder will be described below.

[Porous substrate film]
The porous substrate film in the present invention will be described.
As the porous substrate film, those having a small electron conductivity, an ionic conductivity, a high resistance to an organic solvent, and a fine pore diameter are preferable.
Examples of such a porous substrate film include a porous substrate film containing a polyolefin resin, a resin such as polyethylene terephthalate, polycycloolefin, polyethersulfone, polyamide, polyimide, polyimideamide, polyaramid, nylon, and polytetrafluoroethylene. , A woven fabric of polyolefin fibers (woven fabric), a nonwoven fabric of polyolefin fibers, paper, and an aggregate of insulating substance particles. Among these, when obtaining a multilayer porous substrate film through a coating process, that is, a battery separator, the coating liquid is excellent in coating properties, the separator film thickness is reduced, From the viewpoint of increasing the active material ratio and increasing the volume per volume, a porous substrate film containing a polyolefin resin (hereinafter also referred to as “polyolefin resin porous substrate film”) is preferable.

The polyolefin resin porous substrate film will be described.
The polyolefin resin porous substrate membrane is a polyolefin resin composition in which the polyolefin resin occupies 50% by mass or more and 100% by mass or less of the resin component constituting the porous substrate membrane from the viewpoint of improving shutdown performance when used as a battery separator. A porous substrate film formed of a product is preferable. The proportion of the polyolefin resin in the polyolefin resin composition is more preferably 60% by mass or more and 100% by mass or less, and further preferably 70% by mass or more and 100% by mass or less.

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. Examples thereof include a homopolymer, a copolymer, or a multistage polymer. Moreover, these polyolefin resins may be used independently or may be used in mixture of 2 or more types.
Among these, 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.
Specific examples of the copolymer include an ethylene-propylene random copolymer and ethylene propylene rubber.

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

  Further, from the viewpoint of improving the heat resistance of the porous substrate film, it is preferable to use a mixture of polyethylene and polypropylene as the polyolefin resin. 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% by mass from the viewpoint of achieving both heat resistance and a good shutdown function. %, More preferably 4 to 10% by mass.

  Arbitrary additives can be contained in the polyolefin resin composition. Examples of additives include polymers other than polyolefin resins; inorganic materials; antioxidants such as phenols, phosphorus and sulfur; metal soaps such as calcium stearate and zinc stearate; ultraviolet absorbers; light stabilizers An antistatic agent, an antifogging agent, a coloring pigment, 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 and the like, more preferably 10 parts by mass or less, and still more preferably 5 parts by mass. Or less.

The porous substrate film has a porous structure in which a large number of very small holes are gathered to form dense communication holes, so it has excellent ion conductivity and good withstand voltage characteristics, and high strength. It has the characteristic of being.
The porous substrate film may be a single layer film made of the above-described material or a laminated film.

  The thickness of the porous substrate film is preferably 0.1 μm or more and 100 μm or less, more preferably 1 μm or more and 50 μm or less, and further preferably 3 μm or more and 25 μm or less. From the viewpoint of mechanical strength, 0.1 μm or more is preferable, and from the viewpoint of increasing the capacity of the battery, 100 μm or less is preferable. The film thickness of the porous substrate film can be adjusted by controlling the die lip interval, the draw ratio in the drawing step, and the like.

The average pore diameter of the porous substrate membrane 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, further preferably 0.05 μm or more and 0.10 μm or less, particularly preferably 0.06 μm. It is 0.09 μm or less. From the viewpoint of high ion conductivity and withstand voltage, 0.03 to 0.70 μm is preferable. The average pore diameter of the porous substrate film can be measured by a measurement method described later.
The average pore diameter should be adjusted by controlling the composition ratio, the extrusion sheet cooling rate, the stretching temperature, the stretching ratio, the heat setting temperature, the stretching ratio at the time of heat setting, the relaxation rate at the time of heat setting, or a combination thereof. Can do.

The porosity of the porous substrate film is preferably 25% or more and 95% or less, more preferably 30% or more and 65% or less, and further preferably 35% or more and 55% or less. 25% or more is preferable from the viewpoint of improving ion conductivity, and 95% or less is preferable from the viewpoint of withstand voltage characteristics. The porosity of the porous substrate film can be measured by the method described later.
The porosity of the porous substrate film can be 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 fixing, the relaxation rate during heat fixing, Can be adjusted by combining.

  When the porous substrate film 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 50,000 or more. It is less than 2,000,000, more preferably 100,000 or more and less than 1,000,000. A viscosity average molecular weight of 30,000 or more is preferred because the melt tension during melt molding increases, moldability is improved, and the strength tends to increase due to entanglement between polymers. On the other hand, a viscosity average molecular weight of 12,000,000 or less is preferable because uniform melt kneading is facilitated and the formability of the sheet, particularly thickness stability, tends to be excellent. Furthermore, when it is used as a battery separator, it is preferable that the viscosity average molecular weight is less than 1,000,000 because it tends to close a hole 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 of manufacturing a porous base film, A well-known manufacturing method is employable. For example,
(1) A method in which a polyolefin resin composition and a pore-forming material are melt-kneaded and formed into a sheet, and then stretched as necessary, and then the pore-forming material is extracted to make it porous.
(2) A method in which a polyolefin resin composition is melt-kneaded and extruded at a high draw ratio and then made porous by peeling off the polyolefin crystal interface by heat treatment and stretching,
(3) A method in which a polyolefin resin composition and an inorganic filler are melt-kneaded and formed on a sheet, and thereafter the surface is made porous by peeling the interface between the polyolefin and the inorganic filler by stretching,
(4) After dissolving the polyolefin resin composition, it is immersed in a poor solvent for polyolefin to solidify the polyolefin, and at the same time remove the solvent to make it porous.
Etc.

  Hereinafter, as an example of a method for producing a porous substrate film, a method for extracting a pore-forming material after melt-kneading a polyolefin resin composition and a pore-forming material to form a sheet will be described.

  First, the polyolefin resin composition and the hole forming material are melt-kneaded. As the melt-kneading method, for example, the polyolefin resin and, if necessary, other additives are put into a resin kneading apparatus such as an extruder, kneader, lab plast mill, kneading roll, Banbury mixer, etc., while the resin component is heated and melted. A method of introducing and kneading the pore-forming material at an arbitrary ratio is mentioned.

  Examples of the pore forming material include a plasticizer, an inorganic material, or a combination thereof.

  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 melting | fusing point of polyolefin. Specific examples of such a non-volatile solvent 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. . Note that these plasticizers may be recovered and reused after extraction by an operation such as distillation. Further, preferably, before being put into the resin kneading apparatus, the polyolefin resin, other additives, and the plasticizer are previously kneaded at a predetermined ratio using a Henschel mixer or the like in advance. More preferably, in pre-kneading, only a part of the plasticizer is added, and the remaining plasticizer is appropriately heated in a resin kneader and kneaded while side-feeding. By using such a kneading method, the dispersibility of the plasticizer is increased, and when the sheet-shaped molded body of the melt-kneaded product of the resin composition and the plasticizer is stretched in a later step, a high magnification is obtained without breaking the film. Tend to stretch.

  Among the plasticizers, liquid paraffin is highly compatible with polyolefin resins such as polyethylene and polypropylene, and even when the melt-kneaded product is stretched, the interface between the resin and the plasticizer does not easily peel, and uniform stretching is possible. Is preferable because it tends to be easily implemented.

  The ratio of the polyolefin resin composition and the plasticizer is not particularly limited as long as they can be uniformly melt-kneaded and formed into a sheet shape. For example, the mass fraction of the plasticizer in the composition comprising the polyolefin resin composition and the plasticizer is preferably 20 to 90 mass%, more preferably 30 to 80 mass%. When the mass fraction of the plasticizer is 90% by mass or less, the melt tension at the time of melt molding becomes sufficient, and the moldability tends to be improved. On the other hand, when the mass fraction of the plasticizer is 20% by mass or more, even when the mixture of the polyolefin resin composition and the plasticizer is stretched at a high magnification, the polyolefin molecular chain is not broken, and the pore structure is uniform and fine. Are easily formed, and the strength is also easily increased.

  The inorganic material is not particularly limited. For example, oxide ceramics such as alumina, silica (silicon oxide), titania, zirconia, magnesia, ceria, yttria, zinc oxide, iron oxide; silicon nitride, titanium nitride, nitride Nitride ceramics such as boron; silicon carbide, calcium carbonate, aluminum sulfate, aluminum hydroxide, potassium titanate, talc, kaolin clay, kaolinite, halloysite, pyrophyllite, montmorillonite, sericite, mica, amicite, bentonite Ceramics such as asbestos, zeolite, calcium silicate, magnesium silicate, diatomaceous earth, and silica sand; glass fibers. These may be used alone or in combination of two or more. Among these, 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 between the polyolefin resin composition and the inorganic material is preferably 5% by mass or more, more preferably 10% by mass or more with respect to the total mass from the viewpoint of obtaining good separability. From the viewpoint of ensuring 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 shape. As a method for producing a sheet-like molded product, for example, a melt-kneaded product is extruded into a sheet shape via a T-die or the like, and brought into contact with a heat conductor to cool to a temperature sufficiently lower than the crystallization temperature of the resin component. And then solidify. Examples of the heat conductor used for cooling and solidifying include metals, water, air, and plasticizers. Among these, it is preferable to use a metal roll because of its high heat conduction efficiency. In addition, when the extruded kneaded product is brought into contact with a metal roll, sandwiching between the rolls further increases the efficiency of heat conduction, and the sheet is oriented to increase the film strength, and the surface smoothness of the sheet is also improved. This is more preferable. The die lip interval when the melt-kneaded product is extruded from the T die into a sheet is preferably 200 μm or more and 3,000 μm or less, and more preferably 500 μm or more and 2,500 μm or less. When the die lip interval is 200 μm or more, the mess and the like are reduced, and there is little influence on the film quality such as streaks and defects, and the risk of film breakage and the like in the subsequent stretching process can be reduced. On the other hand, when the die lip interval is 3,000 μm or less, the cooling rate is fast and cooling unevenness can be prevented, and the thickness stability of the sheet can be maintained.

  Moreover, you may roll a sheet-like molded object. Rolling can be performed, for example, by a pressing method using a double belt press or the like. By performing rolling, the orientation of the surface layer portion can be particularly increased. The rolling surface magnification is preferably more than 1 and 3 or less, more preferably more than 1 and 2 or less. When the rolling ratio exceeds 1, the plane orientation increases and the film strength of the finally obtained porous substrate film tends to increase. On the other hand, when the rolling ratio is 3 times or less, the orientation difference between the surface layer portion and the center is small, and a uniform porous structure tends to be formed in the thickness direction of the film.

  Next, the pore-forming material is removed from the sheet-like molded body to obtain a porous substrate film. As a method for removing the hole forming material, for example, a method of extracting the hole forming material by immersing the sheet-shaped molded body in an extraction solvent and sufficiently drying it may be mentioned. The method for extracting the hole forming material may be either a batch type or a continuous type. In order to suppress the shrinkage of the porous substrate film, it is preferable to constrain the end of the sheet-like molded body during a series of steps of immersion and drying. Moreover, it is preferable that the residual amount of pore forming material in the porous substrate film is less than 1% by mass with respect to the mass of the entire porous substrate film.

  As the extraction solvent used when extracting the pore-forming material, it is preferable to use a solvent that is a poor solvent for the polyolefin resin and a good solvent for the pore-forming material and has a boiling point lower than the melting point of the polyolefin resin. . Examples of such an extraction solvent include hydrocarbons such as n-hexane and cyclohexane; halogenated hydrocarbons such as methylene chloride and 1,1,1-trichloroethane; non-chlorine such as hydrofluoroether and hydrofluorocarbon. Halogenated solvents; alcohols such as ethanol and isopropanol; ethers such as diethyl ether and tetrahydrofuran; ketones such as acetone and methyl ethyl ketone. These extraction solvents may be recovered and reused by an operation such as distillation. Moreover, when using an inorganic material as a pore formation material, aqueous solution, such as sodium hydroxide and potassium hydroxide, can be used as an extraction solvent.

Moreover, it is preferable to extend | stretch the said sheet-like molded object or a porous base material film. The stretching may be performed before extracting the hole forming material from the sheet-like molded body. Moreover, you may carry out with respect to the porous base material film which extracted the hole formation material from the said sheet-like molded object. Furthermore, it may be performed before and after extracting the hole forming material from the sheet-like molded body.
As the stretching treatment, either uniaxial stretching or biaxial stretching can be suitably used, but biaxial stretching is preferred from the viewpoint of improving the strength and the like of the obtained porous substrate film. When the sheet-like molded body is stretched at a high magnification in the biaxial direction, the molecules are oriented in the plane direction, and the finally obtained porous substrate film is hardly torn and has a high puncture strength. Examples of the stretching method include simultaneous biaxial stretching, sequential biaxial stretching, multistage stretching, and multiple stretching. Simultaneous biaxial stretching is preferred from the viewpoints of improvement of puncture strength, uniformity of stretching, and shutdown property. Further, sequential biaxial stretching is preferred from the viewpoint of easy control of plane orientation.

  Here, simultaneous biaxial stretching means stretching in MD (machine direction when continuously forming a microporous substrate film) and stretching in TD (direction crossing MD of the microporous substrate film at an angle of 90 °). It refers to the stretching method applied simultaneously, and the stretching ratio in each direction may be different. Sequential biaxial stretching refers to a stretching method in which MD and TD are stretched independently. When MD or TD is stretched, the other direction is fixed in an unconstrained state or a constant length. State.

  The draw ratio is preferably in the range of 20 times to 100 times in terms of surface magnification, and more preferably in the range of 25 times to 70 times. The draw ratio in each axial direction is preferably in the range of 4 to 10 times in MD, 4 to 10 times in TD, 5 to 8 times in MD, and 5 to 8 times in TD. More preferably, it is the range. When the total area magnification is 20 times or more, there is a tendency that sufficient strength can be imparted to the resulting porous substrate film. On the other hand, when the total area magnification is 100 times or less, film breakage in the stretching process is prevented and high. Productivity tends to be obtained.

  In order to suppress the shrinkage of the porous substrate film, a heat treatment can be performed for the purpose of heat setting after the stretching step or after the formation of the porous substrate film. Further, the porous substrate film may be subjected to a post-treatment such as a hydrophilic treatment with a surfactant or the like, or a crosslinking treatment with ionizing radiation or the like.

  The porous substrate film is preferably subjected to heat treatment for the purpose of heat setting from the viewpoint of suppressing shrinkage. As a heat treatment method, a stretching operation performed at a predetermined temperature atmosphere and a predetermined stretching rate for the purpose of adjusting physical properties and / or a relaxation performed at a predetermined temperature atmosphere and a predetermined relaxation rate for the purpose of reducing stretching 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 stretching machine.

From the viewpoint of obtaining a porous substrate membrane having a further high strength and high porosity, the stretching operation may be performed by stretching the membrane MD and / or TD by 1.1 times or more, more preferably 1.2 times or more. preferable.
The relaxation operation is an operation for reducing the film 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. When both MD and TD are relaxed, it is a value obtained by multiplying the MD relaxation rate and the TD relaxation rate. The relaxation rate is preferably 1.0 or less, more preferably 0.97 or less, and even 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 the MD and TD directions, but only one of the MD and TD may be performed.
The stretching and relaxation operations after this plasticizer extraction are preferably performed at 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 main raw material DSC 2nd run, hereinafter also referred to as “Tm”), and is in the range of 1 ° C. to 25 ° C. lower than Tm. More preferred. When the temperature in the stretching and relaxation operation is in the above range, it is preferable from the viewpoint of the balance between the reduction in thermal shrinkage and the porosity.

[Porous layer containing inorganic filler and resin binder]
A porous layer containing an inorganic filler and a resin binder will be described.

[Inorganic filler]
The inorganic filler used in the porous layer is not particularly limited, but is preferably one that has high heat resistance and electrical insulation and is electrochemically stable within the range of use of the lithium ion secondary battery.
As an inorganic filler, an aluminum compound, a magnesium compound, and another compound are mentioned, for example.
Examples of the aluminum compound include aluminum oxide, aluminum silicate, aluminum hydroxide, aluminum hydroxide oxide, sodium aluminate, aluminum sulfate, aluminum phosphate, and hydrotalcite.
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, and glass fiber. Etc. Examples of the 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 the clay mineral include talc, montmorillonite, sericite, mica, amicite, bentonite and the like.
These may be used alone or in combination.

  Among these, aluminum oxide, aluminum hydroxide oxide, and aluminum silicate are preferable from the viewpoints of electrochemical stability and heat resistance. A specific example of aluminum oxide is alumina. Specific examples of the aluminum hydroxide oxide include 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 adopting particles mainly composed of alumina as the inorganic filler that constitutes the porous layer, it is possible to realize a very lightweight porous layer while maintaining high permeability. Thermal contraction of the material film at a high temperature is suppressed, and excellent heat resistance tends to be exhibited. Alumina has many crystal forms such as α-alumina, β-alumina, γ-alumina, and θ-alumina, and any of them can be suitably used. Of 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 an internal short circuit due to generation of lithium dendrite. By adopting boehmite-based particles as the inorganic filler constituting the porous layer, it is possible to achieve a very lightweight porous layer while maintaining high permeability, and even with a thinner porous layer thickness, Thermal contraction of the material film at a high temperature is suppressed, and excellent heat resistance tends to be exhibited. Synthetic boehmite that can reduce ionic impurities that adversely affect the characteristics of the electrochemical device is more preferred.

  Among the aluminum silicates, kaolinite (hereinafter, also referred to as kaolin) mainly composed of kaolin mineral is preferable from the viewpoint of lightness and air permeability. Kaolin includes wet kaolin and calcined kaolin, which is calcined. However, calcined kaolin releases crystal water during the calcining process and removes impurities. Particularly preferred. By adopting particles containing calcined kaolin as the main component for the inorganic filler that constitutes the porous layer, it is possible to realize a very lightweight porous layer while maintaining high permeability, and it is porous even with a thinner porous layer thickness. There is a tendency that thermal contraction of the base material film at a high temperature is suppressed and excellent heat resistance is exhibited.

  The average particle size of the inorganic filler is preferably more than 0.5 μm and not more than 0.8 μm, and more preferably not less than 0.6 μm and not more than 0.7 μm. It is preferable to adjust the average particle size of the inorganic filler to the above range from the viewpoint of suppressing the air permeability and heat shrinkage at high temperature.

As for the particle size distribution of the inorganic filler, the minimum particle size is preferably 0.05 μm or more, more preferably 0.2 μm or more.
D ₅₀ (particle diameter at 50% by volume in the cumulative graph of particle size distribution) corresponds to the median diameter of the inorganic filler described above.
Adjusting the particle size distribution of the inorganic filler to the above range is preferable from the viewpoint of suppressing the thermal contraction of the separator at a high temperature. Examples of the method for adjusting the particle size distribution of the inorganic filler include a method of pulverizing the inorganic filler using a ball mill, a bead mill, a jet mill or the like to adjust the particle size distribution to a desired particle size distribution. In addition, the particle size distribution can be adjusted by mixing fillers having different particle size distributions.

  Examples of the shape of the inorganic filler include a plate shape, a scale shape, a polyhedron, a needle shape, a columnar shape, a spherical shape, a spindle shape, and a lump shape. A plurality of inorganic fillers having the above shapes may be used in combination. Among these, a plate shape, a scale shape, and a polyhedron are preferable from the viewpoint of improving permeability.

  The proportion of the inorganic filler in the porous layer can be appropriately determined from the viewpoints of permeability and heat resistance. The proportion is preferably 50% by mass or more, more preferably 70% by mass or more, further preferably 80% by mass or more, particularly preferably 95% by mass or more, and most preferably 97% by mass or more. . The proportion 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 primary particle size distribution measurement based on the volume of the inorganic filler, the content of particles having a primary particle size of 0.2 μm or less is adjusted to less than 10% by mass based on the mass of the inorganic filler, and inorganic In order to adjust the median diameter of the filler within the range of more than 0.5 μm and 0.8 μm or less, as described above, the material for forming the porous layer containing the inorganic filler is subjected to filtration treatment and / or inorganic The filler is preferably subjected to heat treatment, surface treatment, pulverization treatment or granulation treatment.

(Filtration treatment of material to form porous layer containing inorganic filler)
The material for forming the porous layer containing the inorganic filler is not limited as long as it can be filtered and contains the inorganic filler. For example, slurry, dispersion, emulsion, liquid, fluid, powder Etc.

  The filtration treatment is not particularly limited, but, for example, atmospheric pressure filtration or pressure filtration using a filter is representative. As a filter, it is preferable to use a filter medium whose 90% collection particle diameter is 10 to 100 times the average particle diameter of the inorganic filler used in the present embodiment. Examples of the filter medium include paper and metal. When the 90% collection particle size is 10 times or more the average particle size of the inorganic filler, it is possible to suppress the pressure required for liquid feeding from becoming too high, or to prevent the filter from being clogged in a short period of time. . When the 90% collection particle diameter is 100 times or less of the average particle diameter of the inorganic filler, it is preferable from the viewpoint of satisfactorily removing the aggregate of particles or the undissolved resin binder.

(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 air; vacuum drying; drying by irradiation with (far) infrared rays or electron beams. For example, it is preferable to heat-treat the inorganic filler at 120 to 500 ° C., more preferably 180 to 300 ° C. for 1 minute or longer. 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 increase the hydrophobicity.

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

  The surface treatment method may be 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 performed by heating as necessary. The above-mentioned surface treatment agent is dissolved in water or hot water and added to the stirring water slurry of the inorganic filler, and after the surface treatment, a general wet process of dehydration and drying may be used, or a combination of a dry process and a wet process. But you can. In view of the degree of treatment on the surface of the inorganic filler and the economical viewpoint, the wet method is mainly preferably used alone.

(Inorganic filler grinding)
As a means for 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 pulverization, water adhering to the surface of the inorganic filler can be reduced. Pulverization using a bead mill is preferred from the viewpoint of controlling the density of moisture adsorption points, adsorption capacity, etc., and beads having a bead diameter of about 0.01 mmφ to about 1 mmφ are more preferred from the viewpoint of uniform control.

Furthermore, the density of moisture adsorption points, the adsorption capacity, etc. can be adjusted as appropriate depending on the bead filling amount, the number of rotations, 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 diameter after crushing / average particle diameter before crushing).
Moreover, when it grind | pulverizes using said mill etc., the particle size distribution of the inorganic filler after crushing can be narrowed compared with before crushing. When the particle size distribution change rate before and after crushing is defined as the following formula, the particle size distribution change rate due to crushing of the inorganic filler is preferably 0.01 or more and 0.9 or less, and 0.01 or more and 0.5 or less. More preferably, it is 0.01 or more and 0.1 or less. By changing the particle size distribution change rate from 0.01 to 0.9, the amount of water adhering to the surface of the inorganic filler can be reduced, the pore diameter in the porous layer can be made uniform, and the cycle of the battery incorporating the separator Properties can be improved Particle size distribution = (Volume average particle size) / (Number average particle size)
Change rate of particle size distribution = (particle size distribution after crushing) / (particle size distribution before crushing)

(Granulation of inorganic filler)
When the starting material of the inorganic filler has a remarkably small size such as, for example, a nanoparticle having a particle size of less than 100 nm, the starting material is subjected to a granulation treatment, and the primary particle size of the inorganic filler The distribution and median diameter may be adjusted to an appropriate range.

  A known granulation technique may be used for the granulation treatment of the inorganic filler. For example, the granulation treatment can be performed by kneading an aggregate of nanoparticles or a mixture of inorganic fillers and nanoparticles having appropriate dimensions together with a binder such as a thermoplastic resin or a talc compound. You may heat-melt at the time of kneading | mixing.

  In the present embodiment, it is preferable that pseudoboehmite having a primary particle size of 1 nm or more and less than 100 nm is subjected to granulation to obtain a pseudoboehmite granule having a primary particle size of 0.1 μm to 0.2 μm. . Furthermore, it is also preferable to mix the pseudo boehmite granulated product with boehmite or aluminum hydroxide having a median diameter of 1 to 5 μm to obtain an inorganic filler mixture.

(Total amount of ammonia removed from inorganic filler)
In the ammonia temperature-programmed desorption method, the total desorbed ammonia (NH ₃ ) amount of the inorganic filler from 150 ° C. to 400 ° C. is also preferably 10 μmol / g or more and 1,000 μmol / g or less.

Ammonia temperature-programmed desorption method is to measure the amount of desorbed ammonia and desorption temperature by adsorbing ammonia (NH ₃ ) to the sample and then controlling the temperature at a constant temperature increase rate to raise the temperature continuously. It is a method to do. The acid amount of the inorganic filler can be measured from the amount of NH ₃ desorbed. Further, NH ₃ adsorbed on a weak acid point desorbed at low temperatures, NH ₃ adsorbed on strong acid from the desorption at high temperature, can be measured acid strength of the inorganic filler.

In general, inorganic fillers have two peaks of desorbed NH ₃ content. A large amount of desorbed NH ₃ at a low temperature indicates that there are many weak acid sites in the inorganic filler, and the inorganic filler tends to release moisture. Therefore, of the peaks of the two desorption NH ₃ amount of the inorganic filler, the desorption amount of NH ₃ from 0.99 ° C. on the low temperature side to 400 ° C., corresponding to a weak acid point, in terms of the amount of water the inorganic filler is released It is preferably 10 μmol / g or more and 1000 μmol / g or less.

If the amount of total desorbed ammonia (NH ₃ ) when the inorganic filler is heated from 150 ° C. to 400 ° C. in the ammonia temperature-programmed desorption method is larger than 1000 μmol / g, the amount of moisture adsorbed by the inorganic filler increases. This causes malfunctions in battery performance. Furthermore, since the acid point of the inorganic filler becomes an active site and the electrolyte is thermally decomposed to generate gas, if the amount of desorbed NH ₃ is larger than 1000 μmol / g, the amount of gas generated increases and cell swelling occurs. This causes an increase or a decrease in battery performance. The total desorbed ammonia (NH ₃ ) amount is more preferably 800 μmol / g or less, and still more preferably 600 μmol / g or less.

When the total amount of desorbed ammonia (NH ₃ ) is less than 10 μmol / g when the inorganic filler is heated from 150 ° C. to 400 ° C. in the ammonia temperature-programmed desorption method, the binding force between the inorganic filler and the porous substrate film is low. Since it is weak, the inorganic filler is detached from the separator, and the expected physical properties of the separator do not appear, and the process troubles such as the device becoming dirty with the powder dropped when assembling into the battery occur. The total desorbed ammonia (NH ₃ ) amount is more preferably 20 μmol / g or more, and further preferably 50 μmol / g or more.

[Resin binder]
The resin binder is a resin that plays the role of binding the inorganic fillers described above. Moreover, it is preferable that it is resin which plays the role which bind | concludes an inorganic filler and a porous substrate film mutually.
As the type of the resin binder, it is preferable to use a resin binder that is insoluble in the electrolyte solution of the lithium ion secondary battery when used as a separator and is electrochemically stable within the use 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 polymer: for example, styrene-butadiene copolymer and its hydride, acrylonitrile-butadiene copolymer and its hydride, acrylonitrile-butadiene-styrene copolymer and its hydride;
3) Acrylic polymer: For example, methacrylic acid ester-acrylic acid ester copolymer, styrene-acrylic acid ester copolymer, acrylonitrile-acrylic acid ester copolymer;
4) Polyvinyl alcohol resin: for example, polyvinyl alcohol, polyvinyl acetate;
5) Fluorine-containing resin: For example, polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer Coalescence;
6) Cellulose derivatives: for example, ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose;
7) A resin having a melting point and / or glass transition temperature of 180 ° C. or higher or a polymer having no melting point but a decomposition temperature of 200 ° C. or higher: for example, polyphenylene ether, polysulfone, polyether sulfone, polyphenylene sulfide, polyetherimide, polyamideimide , Polyamide, polyester. In particular, from the viewpoint of durability, wholly aromatic polyamides, particularly polymetaphenylene isophthalamide, are preferred.
Among these, 2) conjugated diene polymers are preferable from the viewpoint of compatibility with electrodes, and 3) acrylic polymers and 5) fluorine-containing resins are preferable from the viewpoint of voltage resistance.

The 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, and substituted linear chains. Examples thereof include conjugated pentadienes, substituted and side chain conjugated hexadienes, and these may be used alone or in combination of two or more. Among these, 1,3-butadiene is particularly preferable.

The 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.
Examples of (meth) acrylic acid used in the above 3) acrylic polymer include acrylic acid and methacrylic acid.
As the (meth) acrylic acid ester used in the above 3) acrylic polymer, for example,
(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 used, and these may be used alone or in combination of two or more.

The above 2) conjugated diene polymer and 3) acrylic polymer may be obtained by copolymerizing other monomers copolymerizable therewith. Examples of other copolymerizable monomers used include unsaturated carboxylic acid alkyl esters, aromatic vinyl monomers, vinyl cyanide monomers, and unsaturated monomers containing a hydroxyalkyl group. , Unsaturated carboxylic acid amide monomer, crotonic acid, maleic acid, maleic anhydride, fumaric acid, itaconic acid and the like. These may be used alone or in combination of two or more. Good. Among the above, an unsaturated carboxylic acid alkyl ester monomer is particularly preferable. 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. It may be used alone or in combination of two or more.
The 2) conjugated diene polymer may be obtained by copolymerizing the (meth) acrylic compound as another monomer.

[Structure and forming method of porous layer]
The layer thickness of the porous layer is preferably 1 μm or more from the viewpoint of improving heat resistance and insulation, more preferably 1.0 μm or more, further preferably 1.2 μm or more, still more preferably 1.5 μm or more, Especially preferably, it is 1.8 micrometers or more, Most preferably, it is 2.0 micrometers or more. In addition, the thickness is preferably 50 μm or less, more preferably 20 μm or less, still more preferably 10 μm or less, and particularly preferably 7 μm or less from the viewpoint of increasing the capacity and permeability of the battery.

  The filling rate of the inorganic filler in the porous layer is preferably 95% by volume or less, more preferably 80% by volume or less, further preferably 70% by volume or less, and particularly preferably 60% by volume or less, from the viewpoint of lightness and high permeability. preferable. In light 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 and the weight and specific gravity of the inorganic filler.

  The porous layer may be formed only on one side of the porous substrate film or on both sides.

  Examples of the method for forming a porous layer include a method in which a porous layer is formed by applying a coating liquid containing an inorganic filler and a resin binder on at least one surface of a porous substrate film containing a polyolefin resin as a main component. be able to.

  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. preferable. “Resin latex” refers to a resin dispersed in a medium. When a resin latex is used as a binder, when a porous layer containing an inorganic filler and a binder is laminated on at least one surface of a polyolefin porous substrate film, ion permeability is not easily lowered and high output characteristics are easily obtained. In addition, even when the temperature rises rapidly during abnormal heat generation, smooth shutdown characteristics are exhibited, and high safety is easily obtained.

  The average particle size of the resin latex binder 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 size is 50 nm or more, when a porous layer containing an inorganic filler and a binder is laminated on at least one surface of the polyolefin porous substrate film, it exhibits good binding properties, and heat shrinkage occurs when used as a separator. It tends to be good and excellent in safety. When the average particle diameter is 1,000 nm or less, the ion permeability is unlikely to decrease and high output characteristics are easily obtained. In addition, even when the temperature rises rapidly during abnormal heat generation, smooth shutdown characteristics are exhibited, and high safety is easily obtained. The average particle size can be controlled by adjusting a polymerization time, a polymerization temperature, a raw material composition ratio, a raw material charging order, a pH, a stirring speed, and the like when manufacturing the resin binder.

  As the medium of the coating liquid, those capable of uniformly and stably dispersing or dissolving the inorganic filler and the resin binder are 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.

  Various additives such as surfactants, thickeners, wetting agents, antifoaming agents, pH adjusting agents including acids and alkalis are added to the coating solution to stabilize dispersion and improve coating properties. An agent may be added. The total addition amount of these additives is preferably 20 parts by weight or less of the active ingredient (the weight of the additive component dissolved when the additive is dissolved in the solvent) with respect to 100 parts by weight of the inorganic filler. More preferably, it is 10 parts by weight or less, and further preferably 5 parts by weight 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 is a method capable of realizing the dispersion characteristics of the coating liquid necessary for the coating process. Examples thereof include 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, and mechanical stirring using a stirring blade.

  The method for coating the coating liquid on the porous substrate film is not particularly limited as long as the required layer thickness or coating area can be realized. For example, a gravure coater method, a small diameter gravure coater method, a 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, spray coating A construction method etc. are mentioned.

  Furthermore, when the surface treatment is performed on the surface of the porous substrate film prior to the application of the coating liquid, the coating liquid can be easily applied, and the inorganic filler-containing porous layer after coating and the surface of the porous substrate film This is preferable because of improving the adhesiveness. The surface treatment method is not particularly limited as long as it does not significantly impair the porous structure of the porous substrate film. For example, corona discharge treatment method, plasma discharge treatment method, mechanical surface roughening method, solvent treatment method, Examples include an acid treatment method and an ultraviolet oxidation method.

  The method for removing the medium from the coating film after coating is not particularly limited as long as it does not adversely affect the porous substrate film, for example, at a temperature below its melting point while fixing the porous substrate film. Examples include a drying method, a low-pressure drying method at low temperature, and extraction drying. Further, a part of the solvent may be left as long as the battery characteristics are not significantly affected. From the viewpoint of controlling the shrinkage stress in the MD direction of the porous substrate film in which the porous substrate film and the porous layer are laminated, it is preferable to appropriately adjust the drying temperature, the winding tension, and the like.

<Slurry for battery separator>
In order to form a battery separator, it is also preferable to provide a battery separator slurry containing the inorganic filler and resin binder described above. The battery separator slurry is preferably used as the coating liquid described above or to form a coating liquid.

  The slurry for the battery separator has a content of particles having a primary particle size of 0.2 μm or less in the primary particle size distribution measurement based on the volume of the inorganic filler, less than 10% by mass based on the mass of the inorganic filler. And the median diameter of the inorganic filler is preferably more than 0.5 μm and not more than 0.8 μm.

  The battery separator slurry is preferably 10 mPa · s or more and 3,000 mPa · s or less, more preferably 30 mPa · s or more and 2,000 mPa · s or less, and 30 mPa · s or more and 1,000 mPa · s or less. More preferably, it has a viscosity of 30 mPa · s or more and 300 mPa · s or less. In addition, the viscosity of a slurry is a value in 25 degreeC and solid content concentration of 30 mass%.

<Other physical properties of separator>
The air permeability of the separator is preferably 10 seconds / 100 cc or more and 650 seconds / 100 cc or less, more preferably 20 seconds / 100 cc or more and 500 seconds / 100 cc or less, further preferably 30 seconds / 100 cc or more and 450 seconds / 100 cc. Hereinafter, it is 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, self-discharge tends to decrease when used as a battery separator, and when it is 650 seconds / 100 cc or less, good charge / discharge characteristics tend to be obtained.

  The rate of increase in the air permeability of the separator due to the formation of the porous layer is preferably 0% or more and 200% or less, more preferably 0% or more and 100% or less, and 0% or more and 75% or less. More preferably, it is more preferably 0% or more and 50% or less. However, when the air permeability of the porous substrate film is less than 100 seconds / 100 cc, it can be preferably used if the air permeability increase rate of the separator after forming the porous layer is 0% or more and 500% or less.

  The final film thickness of the separator is preferably 2 μm to 200 μm, more preferably 5 μm to 100 μm, and even more preferably 7 μm to 30 μm. When the film thickness is 2 μm or more, the mechanical strength tends to be sufficient, and when the film thickness is 200 μm or less, the occupied volume of the separator is reduced, which tends to be advantageous in terms of increasing the battery capacity.

  The thermal shrinkage rate of the separator at 150 ° C. is preferably 0% or more and 15% or less in both the MD direction and the TD direction, more preferably 0% or more and 10% or less, and further preferably 0% or more and 5% or less. . It is preferable that the thermal shrinkage rate is 15% or less in both the MD direction and the TD direction because the film breakage of the separator at the time of abnormal heat generation of the battery is suppressed and a short circuit tends not to occur.

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

The short-circuit temperature of the separator is preferably 180 ° C. or higher and 1000 ° C. or lower, more preferably 200 ° C. or higher and 1000 ° C. or lower. When the short-circuit temperature is 180 ° C. or higher, even if abnormal heat generation occurs in the battery, a short circuit does not occur immediately, so heat can be dissipated during that time, and better safety performance can be obtained.
The short 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 inorganic particle-containing layer, and the like.

<Power storage device>
Hereinafter, the electricity storage device will be described. The electricity storage device includes the separator, and other configurations may be the same as those conventionally known. The power storage device is not particularly limited, and examples thereof include batteries such as non-aqueous electrolyte batteries, capacitors, and capacitors. Among these, a non-aqueous electrolyte battery is preferable, a non-aqueous electrolyte secondary battery is more preferable, and a lithium ion secondary battery is still more preferable from the viewpoint of more effectively obtaining the benefits of the operational effects of the present invention. Hereinafter, a suitable aspect in the case where the electricity storage device is a non-aqueous electrolyte battery will be described.

There is no limitation in a positive electrode, a negative electrode, and a non-aqueous electrolyte, A well-known thing can be used.
Examples of the positive electrode material include lithium-containing composite oxides such as LiCoO ₂ , LiNiO ₂ , spinel type LiMnO ₄ , and olivine type LiFePO ₄ , and examples of the negative electrode material include graphite, non-graphitizable carbonaceous, and easy graphite. Carbonaceous materials such as carbonaceous carbon and composite carbon bodies; silicon, tin, metallic lithium, various alloy materials, and the like.

As the non-aqueous electrolyte, an electrolyte in which an electrolyte is dissolved in an organic solvent can be used. Examples of the organic solvent include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. Examples thereof include lithium salts such as LiClO ₄ , LiBF ₄ , and LiPF ₆ .

Although the said electrical storage device is not specifically limited, For example, it manufactures as follows. That is, the separator is produced as a vertically long separator having a width of 10 to 500 mm (preferably 80 to 500 mm) and a length of 200 to 4000 m (preferably 1000 to 4000 m). Next, the separator is stacked together with the positive electrode and the negative electrode in the order of positive electrode-separator-negative electrode-separator or negative electrode-separator-positive electrode-separator to obtain a laminate. Next, the laminate is wound into a cylindrical or flat spiral shape to obtain a wound body. And an electrical storage device is obtained by passing the process of accommodating the said winding body in an exterior body, and also inject | pouring electrolyte solution.
In addition, the electricity storage device is formed by forming a separator, a positive electrode, and a negative electrode in a flat plate shape, and then laminating in order of positive electrode-separator-negative electrode-separator-positive electrode or negative electrode-separator-positive electrode-separator-negative electrode. After that, it can be manufactured through a process such as housing in an exterior body and injecting an electrolytic solution therein.
In addition, a battery can or a bag-like film can be used as the exterior body.

  Next, the present embodiment will be described more specifically with reference to examples. However, the present embodiment is not limited to the following examples as long as the gist of the present embodiment is not exceeded. In addition, the physical property and evaluation in an Example or a comparative example were performed in accordance with the following method.

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

(2) Thickness of porous substrate film and layer thickness of porous layer Samples of MD10 mm × TD10 mm were cut out from the porous substrate film and the separator, respectively, and nine locations (3 points × 3 points) were selected in a lattice shape. Were each measured using a dial gauge (PEACOCK No. 25 (registered trademark) manufactured by Ozaki Seisakusho), and the average value of the measured values at 9 locations was defined as the film thickness (μm) of the porous substrate film and the separator. Further, the difference in the film thickness between the separator and the porous substrate film thus measured was calculated as the layer thickness (μm) of the porous layer containing the inorganic filler and the resin binder.

(3) Porosity of porous substrate film (%)
A sample of 10 cm × 10 cm square was cut from the porous substrate film, its volume (cm ³ ) and mass (g) were determined, and the density of the porous substrate film was 0.95 (g / cm ³ ), and the following equation was used: Calculated.
Porosity (%) = (1−mass / volume / 0.95) × 100

(4) Average pore diameter (μm) of porous substrate membrane
It is known that the fluid inside the capillary follows a Knudsen flow when the mean free path of the fluid is larger than the pore size of the capillary, and a Poiseuille flow when it is smaller. Therefore, it is assumed that the air flow in the measurement of the air permeability of the porous substrate membrane follows the Knudsen flow, and the water flow in the measurement of the water permeability of the porous substrate membrane follows the Poiseuille flow.
In this case, the average pore diameter d (μm) of the porous substrate membrane is determined by changing the air permeation rate constant R _gas (m ³ / (m ² · sec · Pa)) and the water permeation rate constant R _liq (m ³ / (m ² · sec · Pa)), the molecular velocity of air ν (m / sec), the viscosity of water η (Pa · sec), and the standard pressure P _s (= 101,325 Pa), were obtained using the following equation.
d = 2ν × (R _liq / R _gas ) × (16η / 3Ps) × 10 ⁶
Here, R _gas was obtained from the air permeability (sec) using the following equation.
R _gas = 0.0001 / (air permeability × (6.424 × 10 ⁻⁴ ) × (0.01276 × 101325))
R _liq was determined from the water permeability (cm ³ / (cm ² · sec · Pa)) using the following equation.
R _liq = water permeability / 100
The water permeability was determined as follows.
A porous base material membrane previously immersed in alcohol is set in a stainless steel permeation cell having a diameter of 41 mm, and after the alcohol of the membrane is washed with water, water is permeated at a differential pressure of about 50000 Pa for 120 sec. The water permeability per unit time, unit pressure, and unit area was calculated from the water permeability (cm ³ ) at the time, and this was used as the water permeability.
Further, the molecular velocity ν of air is obtained from the gas constant R (= 8.314), the absolute temperature T (K), the circumference ratio π, and the average molecular weight M of air (= 2.896 × 10 ⁻² kg / mol). It calculated | required using following Formula.
ν = ((8R × T) / (π × M)) ^1/2

(5) Air permeability (second / 100 cc) of porous substrate membrane and separator, rate of increase in air permeability due to formation of porous layer (%)
Using a Gurley type air permeability meter (G-B2 (trademark) manufactured by Toyo Seiki, inner cylinder mass: 567 g) compliant with JIS P-8117, a porous substrate membrane having an area of 645 mm ² (a circle having a diameter of 28.6 mm) and Each separator was measured for the time (seconds) through which 100 cc of air passed, and these were taken as the air permeability of the porous substrate membrane and the separator, respectively.
The rate of increase in air permeability due to the formation of the porous layer was calculated by the following formula.
Air permeability increase rate (%) = {(air permeability of battery separator−air permeability of porous substrate film) / air permeability of porous substrate film} × 100

(6) Ammonia (NH ₃ ) desorption amount of inorganic filler Ammonia temperature-programmed desorption method using a catalyst analyzer (trade name: fully automatic temperature-programmed desorption device TPD-1-ATw, manufactured by Nippon Bell Co., Ltd.) Thus, the acid amount of the inorganic filler powder was measured under the following measurement conditions.
<Measurement conditions>
(Preprocessing)
An inorganic filler accurately weighed 0.05 g was placed in the TPD measurement cell, and helium was circulated at 50 mL / min. The temperature was raised to 400 ° C. at 10 ° C./min and held for 1 hour.
(NH ₃ adsorption treatment)
After the pretreatment, it was cooled to 100 ° C., 0.5 vol% NH ₃ / helium was circulated and held for 30 minutes, and NH ₃ was adsorbed.
(Stabilization process)
After the NH ₃ adsorption treatment, helium was circulated at 100 ° C. at 50 mL / min and held for 30 minutes.
(TPD measurement)
The inorganic filler after stabilization treatment was placed in the catalyst analyzer, helium was circulated at 50 ml / min in the apparatus, and the temperature was increased to 800 ° C. at a temperature increase rate of 10 ° C./min. Peak detection is performed by quantifying ammonia with a m / z = 16 fragment of ammonia in the mass spectrum.

<Calculation and evaluation of desorbed NH ₃ amount>
A calibration gas (NH ₃ gas having a known concentration) was allowed to flow through the TPD measurement cell at a constant flow rate, and the NH ₃ amount per peak unit area was calculated from the peak area measured per unit time. From the peak area from 150 ° C. to 400 ° C., the total amount of desorbed NH ₃ from 150 ° C. to 400 ° C. was calculated.
(Desorbed NH ₃ amount [μmol / g]) = (peak area from 150 ° C. to 400 ° C. in TPD measurement) × (NH ₃ amount per unit area of peak) / sample weight Samples were evaluated according to the following criteria: :
○: The amount of desorbed NH ₃ is 10 μmol / g or more and 1,000 μmol / g or less.
X: The amount of desorbed NH ₃ is less than 10 μmol / g or more than 1,000 μmol / g.

(7) Particle size distribution and median size (μm) of inorganic filler dispersion or slurry coating solution
The particle size distribution of the inorganic filler dispersion or paint slurry was measured using a laser type particle size distribution measuring device (Microtrack MT3300EX manufactured by Nikkiso Co., Ltd.). If necessary, the particle size distribution of the inorganic filler dispersion or the slurry coating solution was adjusted using the particle size distribution of water or a resin binder as a baseline. The particle diameter at which the cumulative frequency was 50% was defined as the median diameter.

(8) Average particle diameter of resin (latex) binder The volume average particle diameter (nm) was measured using a particle size measuring apparatus (LECR & NORTHRUP MICROTRACTMUPA150) by a light scattering method to obtain an average particle diameter.

(9) Viscosity of Coating Liquid Using an E-type viscometer, the viscosity (mPa · s) of the coating liquid at 25 ° C. was measured under conditions of a shear rate of 1,000 s ⁻¹ . The solid content concentration of the coating liquid was adjusted to 30% by mass and evaluated.

(10) Evaluation of 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) and acetylene black powder (AB) (density 1.95 g / cm ³ , number average) as a conductive additive Particle size 48 nm) was mixed with 3.8% by mass, polyvinylidene fluoride (PVDF) (density 1.75 g / cm ³ ) as a binder at a ratio of 4.2% by mass (in terms of solid content), and N-methylpyrrolidone ( NMP) to prepare a slurry. This slurry was applied to one side of a 20 μm thick aluminum foil serving as a positive electrode current collector with a die coater, dried at 130 ° C. for 3 minutes, and then compression molded with a roll press. The active material coating amount at this time was 109 g / m ² .

b. Graphite powder A (density 2.23 g / cm ^3, number average particle diameter of 12.7 [mu] m) as creating a negative electrode active material of the negative electrode 87.6% by weight of graphite powder B (density 2.27 g / cm ^3, number average particle diameter 6.5 μm) is 9.7% by mass, ammonium salt of carboxymethyl cellulose as a binder is 1.4% by mass (in terms of solid content) (solid content concentration is 1.83% by mass aqueous solution), and styrene-diene copolymer latex is 1.7% by mass. (Solid content conversion) (Solid content concentration 40 mass% aqueous solution, particle size 80 nm, glass transition temperature -40 ° C) was dispersed in purified water to prepare a slurry. This slurry was coated on one side of a 12 μm thick copper foil serving as a negative electrode current collector with a die coater, dried at 120 ° C. for 3 minutes, and then compression molded with 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 Electrolytic Solution Prepared by dissolving LiPF ₆ 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 mmφ and the positive electrode and the negative electrode were cut into 16 mmφ, and the negative electrode, the separator, and the positive electrode were stacked in this order so that the active material surfaces of the positive electrode and the negative electrode were opposed to each other, and stored in a stainless steel container with a lid. The container and the lid were insulated, and the container was in contact with the negative electrode copper foil and the lid was in contact with the positive electrode aluminum foil. An evaluation battery was produced by injecting 0.4 ml of the non-aqueous electrolyte into the container and sealing it.

e. Pretreatment The battery assembled as described above was charged with a constant current up to a voltage of 4.2 V at a current value of 1/3 C, then charged with a constant voltage of 4.2 V for 8 hours, and then charged with a current of 1/3 C. Discharge was performed to a final voltage of 0V. Next, after constant current charging to a voltage of 4.2 V with a current value of 1 C, 4.2 V constant voltage charging 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 constant current charging to 4.2 V with a current value of 1 C, 4.2 V constant voltage charging was performed for 3 hours, and the pretreatment was completed. 1C represents a current value for discharging the reference capacity of the battery in one hour.

f. Cycle characteristics The battery subjected to the above pretreatment was discharged with a discharge current of 1 A to a discharge end voltage of 3 V under a temperature of 25 ° C., and then charged with a charge current of 1 A to a charge end voltage of 4.2 V. Charging / discharging was repeated with this as one cycle, the capacity retention after 200 cycles with respect to the initial capacity was examined, and the cycle characteristics were evaluated according to the following criteria. The number of defects of 20 batteries was calculated according to the following evaluation criteria. Two or less defects (defect rate of 10% or less) were evaluated as acceptable.
(Evaluation criteria)
Pass: When the capacity retention is 90% or more Defect: When the capacity retention is less than 90%

(11) High temperature storage test (gas generation test)
The aluminum laminate sheet was cut into a certain size and formed into a pack shape (6 cm × 8 cm) using an impulse sealer. The separator sample cut to 10 cm × 10 cm was folded, inserted into a Lamipack, and vacuum-dried at 80 ° C. for 12 hours. Next, an electrolytic solution in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a volume ratio of EC: EMC = 1: 2 was prepared by dissolving LiPF ₆ as an electrolyte at 1 mol / L in an argon box. 0.4 mL was poured into the aluminum lami pack which was vacuum-dried inside, and the opening of the aluminum lami pack was sealed with a heat sealer. This was stored in an oven set at 85 ° C. for 72 hours, the weight before and after the test was measured, and the volume was calculated by the Archimedes method. The weight 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 gas generation amount of the sample was evaluated according to the following criteria:
○: Gas generation amount is 3.3 mL or less.
X: Gas generation amount exceeds 3.3 mL.

(12) Thermal contraction rate of separator (%)
The sample was cut into a 100 mm MD / TD square. The cut sample was sandwiched between two sheets of paper and allowed to stand in an oven at 150 ° C. for 1 hour. After removing the sample from the oven and cooling, the dimensional shrinkage (%) of the sample was determined. A thermal shrinkage rate of 5% or less for both MD / TD was evaluated as acceptable.

[Manufacture of resin binder]
(Synthesis example) Manufacture of acrylic polymer latex In a reaction vessel equipped with a stirrer, reflux condenser, dripping tank, and thermometer, 70.4 parts by mass of ion-exchanged water and “AQUALON KH1025” (trade name, No. 1 Kogyo Seiyaku Co., Ltd., 25 mass% aqueous solution) 0.1 mass part (solid content conversion) and "Adekaria soap SR1025" (trade name, manufactured by ADEKA Corporation, 25 mass% aqueous solution) 0.1 mass part (solid ), And the temperature inside the reaction vessel is raised to 80 ° C., while maintaining the temperature at 80 ° C., 0.15 parts by mass (in terms of solid content) of ammonium persulfate (2 mass% aqueous solution) is added. did.
5 minutes after adding the ammonium persulfate aqueous 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 Parts by mass, 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), “ADEKA rear soap SR1025” (trade name, manufactured by ADEKA Corporation, 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 solids), and ion exchange Water: A mixture of 52 parts by mass was mixed with a homomixer for 5 minutes to prepare an emulsion, and the obtained emulsion was added dropwise from a dropping tank to a reaction vessel over 150 minutes.
After completion of the dropwise addition of the emulsion, the reaction container was maintained at an internal temperature of 80 ° C. for 90 minutes and then cooled to room temperature to obtain an emulsion. By adding an aqueous ammonia solution (ammonia content 25% by mass) to the obtained emulsion and adjusting the pH to 9.0, a latex containing an acrylic polymer having a solid concentration of 40% by mass was obtained.
The obtained acrylic polymer had an average particle size of 145 nm and a glass transition temperature of -20 ° C.

[Production of porous substrate film]
Mv is 700,000, 47.5 parts by mass of homopolymer high-density polyethylene,
Mv is 300,000, 47.5 parts by mass of homopolymer high-density polyethylene,
5 parts by mass of a homopolymer polypropylene having an Mv of 400,000
Was dry blended using a tumbler blender.

  1 part by mass of tetrakis- [methylene- (3 ′, 5′-di-t-butyl-4′-hydroxyphenyl) propionate] methane as an antioxidant was added to 99 parts by mass of the obtained polyolefin mixture, and again a tumbler blender. Was used for dry blending to obtain a mixture.

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

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

  Next, they are melt-kneaded while being heated to 230 ° C. in a twin-screw extruder, and the obtained melt-kneaded product is extruded through a T-die onto a cooling roll controlled at a surface temperature of 80 ° C. A sheet-like molded product was obtained by bringing into contact with a cooling roll and molding by cooling.

  The sheet was stretched by a simultaneous biaxial stretching machine under conditions of a magnification of 7 × 6.4 and a temperature of 112 ° C., and then immersed in methylene chloride to extract and remove liquid paraffin, followed by drying.

  Further, the sheet was stretched 2.0 times in the transverse direction at 128 ° C. with a tenter stretching machine, and then this stretched sheet was subjected to heat treatment by relaxing about 10% in the width direction at 131 ° C. to obtain a porous substrate film. Base material B1 was obtained.

  About the obtained base material B1, various physical properties were measured by the said method. The results are shown in Table 1.

<Example 1 and Comparative Examples 1-5>
[Production of inorganic filler, preliminary dispersion or dispersion]
Comparative Example 1
Preliminary dispersion was obtained by mixing boehmite and water before crushing. The median diameter of boehmite was measured and found to be 1.27 μm.

Example 1
Boehmite was subjected to a crushing process. The crushing treatment was performed using a bead mill (0.1 mmφ zirconia beads, bead filling rate 60%). The rotation speed and flow rate were adjusted to 2,600 rpm and 30 Hz, respectively, and the degree of crushed boehmite was adjusted to about 0.56. The crushed boehmite and water are mixed, and if necessary, an aqueous solution of ammonium polycarboxylate (SN Dispersant 5468 manufactured by San Nopco) is added as a dispersant, and dispersed in 2 passes. The primary particle diameter is 0.2 μm or less, the same applies hereinafter.) A dispersion having a content and a median diameter was obtained.

Comparative Example 2
The mill rotation speed and flow rate are adjusted to 3,500 rpm and 20 Hz, respectively, and the boehmite is subjected to a crushing process. The crushed boehmite is mixed with water, and if necessary, a dispersant is added to disperse in 3 passes. As a result, a dispersion having the fine particle content and median diameter shown in Table 1 was obtained.

Comparative Example 3
The mill rotation speed and flow rate are adjusted to 3,500 rpm and 20 Hz, respectively, and the boehmite is subjected to crushing treatment. The crushed boehmite is mixed with water, and if necessary, a dispersing agent is added to disperse in one pass. As a result, a dispersion having the fine particle content and median diameter shown in Table 1 was obtained.

Comparative Example 4
Pseudoboehmite having a particle diameter of 0.1 μm was added to the filler obtained in Example 1 to adjust the fine particle content to 10.7% by mass. The pseudo boehmite used was obtained by granulating pseudo boehmite having a primary particle diameter of 25 nm so as to have a primary particle diameter of 0.1 μm.

Comparative Example 5
Pseudoboehmite having a particle diameter of 0.1 μm was added to aluminum hydroxide having a median diameter of 6 μm, and the fine particle content was adjusted to 10.7% by mass. The pseudo boehmite used was obtained by granulating pseudo boehmite having a primary particle diameter of 25 nm so as to have a primary particle diameter of 0.1 μm.

[Formation of inorganic coating layer and production of multilayer porous substrate film (separator)]
The inorganic filler dispersion liquid obtained in Example 1 and Comparative Examples 2 to 5 was used.
A dispersion, a resin binder, a dispersant, and water were mixed and dispersed to obtain a slurry coating liquid (solid content concentration of 30% by mass) having the following composition.
95.0 parts by weight of inorganic filler;
Acrylic latex as a resin binder (solid content concentration 40%, average particle size 145 nm, minimum film forming temperature 0 ° C. or less) 4.0 parts by mass (in terms of solid content);
Aqueous polycarboxylate aqueous solution (SN Dispersant 5468, manufactured by San Nopco) as a dispersant 1.0 part by mass (in terms of solid content);

  Next, after the corona discharge treatment (discharge amount 50 W) was performed on the surface of the base material B1, the coating liquid was applied to the treated surface with a microgravure coater, dried at 60 ° C., and then on the base material B1. An inorganic porous layer was formed to obtain multilayer porous substrate films of Example 1 and Comparative Examples 2 to 5, respectively. The obtained multilayer porous substrate film was used as a separator to evaluate the separator.

[Evaluation of Example 1 and Comparative Examples 2 to 5]
The evaluation results of Example 1 and Comparative Examples 2 to 5 are shown in Table 1.
The particle size distribution of acrylic latex (synthesis example, solid content concentration 40%, average particle size 145 nm, minimum film formation temperature 0 ° C. or lower) used as a resin binder is shown in FIG. 1 as a reference example.
The particle size distributions of the preliminary dispersion of Comparative Example 1, the dispersion of Example 1, and the dispersions of Comparative Examples 2 and 3 are shown in FIG.
From the comparison between the resin binder and the dispersion in FIG. 1, it can be seen that the particle size distribution of the dispersion is not excessively influenced by the particle size distribution of the resin binder.
As shown in Table 1 and FIG. 1, the dispersion liquid of Example 1 is located between the preliminary dispersion liquid of Comparative Example 1 and the dispersion liquids of Comparative Examples 2 and 3 in terms of particle size distribution. Since the content is less than 10% by mass and the median diameter is more than 0.5 μm and not more than 0.8 μm, the separator formed using the dispersion liquid of Example 1 may be optimal in terms of its characteristics. I understand.

<Example 2 and Comparative Example 6>
[Preparation of Preliminary Dispersion, Dispersion, or Slurry Coating Solution]
Comparative Example 6
Preliminary dispersion was obtained by mixing boehmite and water before crushing. The median diameter of boehmite was measured and found to be 1.46 μm.

Example 2
Boehmite was subjected to a crushing process. The crushing treatment was performed using a bead mill (0.1 mmφ zirconia beads, bead filling rate 60%). The boehmite was crushed by adjusting the rotation speed and flow rate to 2,600 rpm and 20 Hz, respectively. Crushed boehmite and water are mixed, and if necessary, an aqueous solution of ammonium polycarboxylate (SN Dispersant 5468, manufactured by San Nopco) is added as a dispersant, and dispersed in one pass to contain the fine particles shown in Table 1. A dispersion having a rate and a median diameter was obtained. In addition, it confirmed that the median diameter of the obtained dispersion liquid was 0.74 micrometer.

The obtained dispersion, resin binder, dispersant, and water were mixed and dispersed to obtain a slurry coating solution (solid content concentration of 30% by mass) having the following composition.
95.0 parts by weight of inorganic filler;
Acrylic latex as a resin binder (solid content concentration 40%, average particle size 145 nm, minimum film forming temperature 0 ° C. or less) 4.0 parts by mass (in terms of solid content);
Aqueous polycarboxylate aqueous solution (SN Dispersant 5468, manufactured by San Nopco) as a dispersant 1.0 part by mass (in terms of solid content);

  The obtained slurry coating solution was confirmed to have a median diameter of 0.738 μm and a viscosity (25 ° C., solid content concentration of 30 mass%) of 300 mPa · s or less.

  Next, after the corona discharge treatment (discharge amount 50 W) was performed on the surface of the base material B1, the coating liquid was applied to the treated surface with a microgravure coater, dried at 60 ° C., and then on the base material B1. Inorganic porous layers were formed to obtain multilayer porous substrate films, respectively. The obtained multilayer porous substrate film was used as a separator to evaluate the separator.

[Evaluation of Example 2 and Comparative Example 6]
The evaluation results of Example 2 are shown in Table 1.
The particle size distribution of the preliminary dispersion liquid of Comparative Example 6, the dispersion liquid of Example 2, and the coating liquid of Example 2 is shown in FIG.
From the comparison of the dispersion liquid of Example 2 in FIG. 2 and the coating liquid, even if the primary particle size distribution of the inorganic filler according to the embodiment of the present invention is measured using an aqueous dispersion, the slurry coating liquid It can be seen that it is approximated even if measured using.
Furthermore, as shown in Table 1 and FIG. 2, the dispersion liquid and the coating liquid of Example 2 have a primary particle size distribution suitable for the electricity storage device separator as compared with the preliminary dispersion liquid of Comparative Example 1. I understand.

<Example 3>
The dispersion and coating solution of Example 3 were obtained in the same manner as in Example 2 except that the number of passes was changed from Example 2 to 3 and crushing / dispersing was performed. It was confirmed that the obtained dispersion had a median diameter of 0.51 μm, D ₁₀ of the dispersion was 0.25 μm, and the fine particle content was 0.3% by mass. Evaluation was performed in the same manner as in Example 2, and the evaluation results are shown in Table 1.

Claims (9)

A separator for an electricity storage device comprising a porous layer containing an inorganic filler and a resin binder on at least one surface of a porous substrate film containing a polyolefin resin,
In the primary particle size distribution measurement based on the volume of the inorganic filler, the content of particles having a primary particle size of 0.2 μm or less is less than 10% by mass based on the mass of the inorganic filler, and
The inorganic filler is boehmite;
The median diameter of the inorganic filler is greater than 0.5 [mu] m, and Ri der below 0.8 [mu] m,
The inorganic filler, the total elimination of ammonia from 0.99 ° C. to 400 ° C. in the ammonia temperature-programmed desorption method (NH ₃₎ the amount of Ru der less 10 .mu.mol / g or more 1,000μmol / g,
The separator for an electricity storage device.   In primary particle size distribution measurement based on the volume of the inorganic filler, the content of particles having a primary particle size of 0.2 μm or less is less than 3% by mass based on the mass of the inorganic filler. Item 10. The electricity storage device separator according to Item 1. The electrical storage device according to claim 1 or 2 , wherein the primary particle size distribution measurement is performed using an aqueous dispersion obtained by dispersing an inorganic filler in water, or a slurry containing an inorganic filler and a resin binder. Separator for use. The electricity storage device separator according to any one of claims 1 to 3 , wherein the electricity shrinkage rate of the electricity storage device separator at 150 ° C is 0% or more and 15% or less in both the MD direction and the TD direction. The average pore diameter of the said porous base material film is a separator for electrical storage devices of any one of Claims 1-4 which are 0.03 micrometer or more and 0.70 micrometer or less. The separator for an electricity storage device according to any one of claims 1 to 5, wherein the porosity of the porous substrate film is 30% or more and 65% or less. 7. The electricity storage device separator according to claim 1, wherein an air permeability of the electricity storage device separator is 10 seconds / 100 cc or more and 400 seconds / 100 cc or less. A separator device according to any one of claim 1 to 7
A positive electrode;
A negative electrode,
A non-aqueous electrolyte secondary battery comprising a non-aqueous electrolyte. A slurry for a battery separator containing an inorganic filler and a resin binder,
In the primary particle size distribution measurement based on the volume of the inorganic filler, the content of particles having a primary particle size of 0.2 μm or less is less than 10% by mass based on the mass of the inorganic filler,
The inorganic filler is boehmite;
The median diameter of the inorganic filler is more than 0.5 μm and not more than 0.8 μm,
The inorganic filler has a total desorbed ammonia (NH ₃ ) amount of 10 μmol / g or more and 1,000 μmol / g or less from 150 ° C. to 400 ° C. in the ammonia temperature- programmed desorption method , and 25 of the battery separator slurry. The viscosity at 30 ° C. and a solid content concentration of 30% by mass is 300 mPa · s or less.
The battery separator slurry.

Images