JP7664744B2 - Laminated separator for non-aqueous electrolyte secondary battery and manufacturing method thereof - Google Patents

Description

The present invention relates to a laminated separator for a non-aqueous electrolyte secondary battery and a method for manufacturing the same.

Non-aqueous electrolyte secondary batteries, especially lithium-ion secondary batteries, have a high energy density and are widely used in personal computers, mobile phones, portable information terminals, etc., and recently they have been developed as batteries for use in vehicles.

For example, Patent Document 1 discloses a non-aqueous electrolyte battery separator containing a heat-resistant nitrogen-containing aromatic polymer and a ceramic powder. According to the document, the heat-resistant nitrogen-containing aromatic polymer may have an intrinsic viscosity of 1.0 to 2.8 dL/g. In addition, the ceramic powder may have an average primary particle size of 1.0 μm or less.

JP 2000-030686 A

However, the above-mentioned conventional techniques leave room for improvement in terms of making the separator thinner. Specifically, the challenge remains of making the separator thinner while maintaining its heat resistance and ion permeability.

One aspect of the present invention aims to provide a method for manufacturing a laminated separator for a non-aqueous electrolyte secondary battery that can achieve both thinness, heat resistance, and ion permeability.

The present invention includes the following configurations.
＜1＞
A method for producing a laminated separator for a non-aqueous electrolyte secondary battery, comprising the steps of: forming a heat-resistant layer containing a resin and a filler on a polyolefin porous film,
The intrinsic viscosity of the resin is 1.5 to 1.9 dL/g;
The average particle size of the filler is 500 nm or less (here, the average particle size is the average value of the equivalent sphere particle size of 50 filler particles, and the equivalent sphere particle size is a value actually measured by a transmission electron microscope),
The method for producing a laminated separator for a non-aqueous electrolyte secondary battery, wherein the thickness of the laminated separator for a non-aqueous electrolyte secondary battery is 15 μm or less.
＜2＞
The manufacturing method according to <1>, wherein in the filler, a proportion of particles having an equivalent spherical particle diameter of 1 μm or more is 1% or less on a particle number basis.
＜3＞
A laminate separator for a non-aqueous electrolyte secondary battery, comprising a polyolefin porous film and a heat-resistant layer laminated on one or both sides of the film,
The heat-resistant layer contains a heat-resistant resin and a filler,
The thickness of the laminated separator for a non-aqueous electrolyte secondary battery is 15 μm or less,
The laminated separator for a nonaqueous electrolyte secondary battery has a heat shape retention rate in the TD direction of 75% or more when heated at 200° C. for 5 minutes,
The air permeability of the heat-resistant layer is 100 s/100 mL or less.
Laminated separator for non-aqueous electrolyte secondary batteries.
＜4＞
The laminate separator for a nonaqueous electrolyte secondary battery according to <3>, wherein the heat-resistant layer contains one or more resins selected from the group consisting of (meth)acrylate-based resins, fluorine-containing resins, polyamide-based resins, polyimide-based resins, polyamideimide-based resins, polyester-based resins, and water-soluble polymers.
＜5＞
The laminate separator for a nonaqueous electrolyte secondary battery according to <4>, wherein the heat-resistant layer contains an aramid resin.
＜6＞
A positive electrode and
<3> to <5>, and a laminate separator for a nonaqueous electrolyte secondary battery according to any one of <3> to <5>.
A negative electrode;
are arranged in this order.
＜７＞
A nonaqueous electrolyte secondary battery comprising the laminate separator for a nonaqueous electrolyte secondary battery according to any one of <3> to <5> or the member for a nonaqueous electrolyte secondary battery according to <6>.

According to one aspect of the present invention, a method for manufacturing a laminated separator for a non-aqueous electrolyte secondary battery that can simultaneously achieve thinness, heat resistance, and ion permeability can be provided.

One embodiment of the present invention will be described below, but the present invention is not limited to this. The present invention is not limited to the configurations described below, and various modifications are possible within the scope of the claims. The technical scope of the present invention also includes embodiments obtained by appropriately combining the technical means disclosed in different embodiments. In this specification, unless otherwise specified, "A to B" representing a numerical range means "greater than or equal to A and less than or equal to B."

In this specification, the term "laminated separator for non-aqueous electrolyte secondary batteries" may be referred to simply as "laminated separator."

[1. Manufacturing method of laminated separator for non-aqueous electrolyte secondary battery]
A method for producing a laminate separator for a non-aqueous electrolyte secondary battery according to one embodiment of the present invention includes the steps of:
The method includes forming a heat-resistant layer containing a resin and a filler on a polyolefin porous film,
The intrinsic viscosity of the resin is 1.5 to 1.9 dL/g;
The average particle size of the filler is 500 nm or less,
The thickness of the laminated separator for a non-aqueous electrolyte secondary battery is 15 μm or less.

Here, the average particle size of the filler is the average of the spherical equivalent particle sizes of 50 fillers. The spherical equivalent particle size of each filler is measured using a transmission electron microscope.

In the present invention, a thinner laminate separator for a non-aqueous electrolyte secondary battery is achieved by reducing the average particle size of the filler. In this case, it is believed that the reduced heat resistance caused by reducing the average particle size of the filler is compensated for by using a resin whose intrinsic viscosity is in a specific range. Setting the intrinsic viscosity of the resin in a specific range is also believed to contribute to maintaining the ion permeability of the heat-resistant layer.

[Heat-resistant layer]
The heat-resistant layer contains a resin and a filler, and may contain other components (such as a binder resin).

The heat-resistant layer is preferably a porous layer. In this specification, a porous layer is a layer that has many pores inside and has a structure in which these pores are connected, allowing gas or liquid to pass from one surface to the other.

The thickness of the heat-resistant layer is preferably 0.5 μm or more and less than 8.0 μm, more preferably 1.0 μm or more and less than 5.0 μm, and even more preferably 1.0 μm or more and less than 3.0 μm. In this specification, the "thickness of the heat-resistant layer" means the average thickness per heat-resistant layer.

If the thickness of the heat-resistant layer is 0.5 μm or more, it is possible to sufficiently prevent internal short circuits in the battery and maintain the amount of electrolyte held in the heat-resistant layer. On the other hand, if the thickness of the heat-resistant layer is less than 8.0 μm, it is possible to make the heat-resistant layer thinner than that of conventional technology while maintaining heat resistance and battery characteristics at or above conventional levels. This can contribute to the miniaturization of laminated separators for non-aqueous electrolyte secondary batteries, and ultimately non-aqueous electrolyte secondary batteries.

The heat-resistant layer may be disposed between the polyolefin porous film and at least one of the positive electrode and the negative electrode as a component of the nonaqueous electrolyte secondary battery. The heat-resistant layer may be formed on one or both sides of the polyolefin porous film. The heat-resistant layer disposed between the polyolefin porous film and at least one of the positive electrode and the negative electrode may be one layer or two or more layers.

The heat-resistant layer according to one embodiment of the present invention is preferably disposed between the polyolefin porous film and the positive electrode active material layer of the positive electrode. The description of the physical properties of the heat-resistant layer refers to at least the physical properties of the heat-resistant layer disposed between the polyolefin porous film and the positive electrode active material layer of the positive electrode when a non-aqueous electrolyte secondary battery is formed.

The porosity of the heat-resistant layer is preferably 20 to 90% by volume, and more preferably 30 to 80% by volume, so that sufficient ion permeability can be obtained. The pore size of the heat-resistant layer is preferably 1.0 μm or less, and more preferably 0.5 μm or less. By setting the pore size to these sizes, the nonaqueous electrolyte secondary battery can obtain sufficient ion permeability.

(resin)
The resin contained in the heat-resistant layer has a lower limit of intrinsic viscosity of 1.5 dL/g or more. The resin contained in the heat-resistant layer has an upper limit of intrinsic viscosity of 1.9 dL/g or less, preferably 1.8 dL/g or less, and more preferably 1.7 dL/g or less. A heat-resistant layer containing a resin having an intrinsic viscosity of 1.5 dL/g or more can impart sufficient heat resistance to a laminated separator for a non-aqueous electrolyte secondary battery. A heat-resistant layer containing a resin having an intrinsic viscosity of 1.9 dL/g or less has sufficient ion permeability.

In this specification, "intrinsic viscosity" refers to a value calculated by the following formula. In the formula, "resin solution" refers to a solution in which a resin is dissolved in an appropriate solvent (such as concentrated sulfuric acid). Furthermore, "flow time" refers to the time required for a liquid to flow through a capillary tube, and is measured by an Ubbelohde capillary viscometer.
Intrinsic viscosity = ln (T/T ₀ )/C (unit: dL/g)
T: flow time of the resin solution. T ₀ : flow time of the solvent without resin. C: concentration of the resin in the resin solution (g/dL).

It is known that the intrinsic viscosity of a resin is correlated with the molecular weight of the resin. In the present invention, a resin with a lower intrinsic viscosity than usual is used in order to achieve a laminated separator for a nonaqueous electrolyte secondary battery that is thin, heat-resistant, and has good ion permeability. That is, the laminated separator for a nonaqueous electrolyte secondary battery according to one embodiment of the present invention contains a resin with a higher content of low-molecular-weight components than usual in the heat-resistant layer.

A resin with an intrinsic viscosity of 1.5 to 1.9 dL/g can be synthesized by adjusting the molecular weight distribution of the resin by appropriately setting the synthesis conditions (monomer input amount, synthesis temperature, synthesis time, etc.). Alternatively, a commercially available resin with an intrinsic viscosity of 1.5 to 1.9 dL/g may be used in the production method according to one embodiment of the present invention.

In the manufacturing method according to one embodiment of the present invention, the resin having an intrinsic viscosity of 1.5 to 1.9 dL/g is preferably a heat-resistant resin. In this specification, a "heat-resistant resin" is a resin having a melting point or glass transition temperature of 180°C or higher, and preferably a resin having a melting point or glass transition temperature of 200°C or higher. Examples of heat-resistant resins include aromatic polyamides such as fully aromatic polyamides and semi-aromatic polyamides, aromatic polyimides, aromatic polyamideimides, polybenzimidazole, polyurethane, and melamine resins.

Among them, the heat-resistant resin is preferably a wholly aromatic polyamide. In this specification, the wholly aromatic polyamide is also referred to as an aramid resin. Examples of wholly aromatic polyamides include para-aramid and meta-aramid, with para-aramid being more preferred.

The method for preparing the para-aramid is not particularly limited, but may be a condensation polymerization method of a para-oriented aromatic diamine and a para-oriented aromatic dicarboxylic acid halide. In this case, the obtained para-aramid is substantially composed of repeating units in which the amide bonds are bonded at the para position of the aromatic ring or at a position equivalent thereto (for example, positions extending coaxially or parallel in opposite directions such as 4,4'-biphenylene, 1,5-naphthalene, 2,6-naphthalene, etc.). Examples of the para-aramid include para-oriented or para-oriented para-aramids having a structure similar to the para-oriented type, such as poly(paraphenylene terephthalamide), poly(parabenzamide), poly(4,4'-benzanilide terephthalamide), poly(paraphenylene-4,4'-biphenylenedicarboxylic acid amide), poly(paraphenylene-2,6-naphthalenedicarboxylic acid amide), poly(2-chloro-paraphenylene terephthalamide), and paraphenylene terephthalamide/2,6-dichloroparaphenylene terephthalamide copolymer.

There is no particular limitation on the method for preparing meta-aramid. Examples include (1) a condensation polymerization method of a meta-oriented aromatic diamine and a meta-oriented aromatic dicarboxylic acid halide or a para-oriented aromatic dicarboxylic acid halide, and (2) a condensation polymerization method of a meta-oriented aromatic diamine or a para-oriented aromatic diamine and a meta-oriented aromatic dicarboxylic acid halide. In this case, the obtained metalla-aramid contains repeating units in which the amide bond is bonded at the meta position of the aromatic ring or at a position equivalent thereto.

To adjust the intrinsic viscosity of the wholly aromatic polyamide to 1.5 to 1.9 dL/g, for example, the monomer feed ratio or the amount of water contained in the polymerization system (water content of the solvent, humidity of the polymerization environment, etc.) may be controlled. As for the monomer feed ratio, the intrinsic viscosity tends to increase when the feed ratio of the dicarboxylic acid halide is increased. Also, the intrinsic viscosity tends to decrease as the amount of water contained in the polymerization system increases. For a more specific example, see the synthesis method of poly(paraphenylene terephthalamide) (PPDA) described in the Examples.

The resin content in the heat-resistant layer is preferably 25 to 80% by weight, and more preferably 30 to 70% by weight. Here, the resin content in the heat-resistant layer is calculated assuming the total weight of the heat-resistant layer to be 100% by weight.

(Filler)
The average particle size of the filler contained in the heat-resistant layer is 500 nm or less, preferably 300 nm or less, more preferably 200 nm or less, more preferably 100 nm or less, and more preferably 50 nm or less. Here, the average particle size of the filler is the average value of the equivalent sphere particle size of 50 filler particles. The equivalent sphere particle size of the filler is a value actually measured by a transmission electron microscope. An example of a specific measurement method is as follows.
1. Using a transmission electron microscope (TEM; JEOL Ltd., JEM-2100F), images are taken at an accelerating voltage of 200 kV and a magnification of 10,000 times using a Gatan Imaging Filter.
2. For the obtained image, the contours of the particles are traced using image analysis software (ImageJ) to measure the spherical equivalent particle diameter of the filler particles (primary particles).
3. The above measurement is carried out on 50 randomly selected filler particles. The arithmetic average of the spherical equivalent particle diameters of the 50 filler particles is regarded as the average particle diameter of the particles.

By setting the average particle size of the filler to 500 nm or less, the laminate separator for a nonaqueous electrolyte secondary battery can be made thinner. The lower limit of the average particle size of the filler is not particularly limited, but can be, for example, 5 nm or more.

The ratio of particles having a spherical equivalent diameter of 1 μm or more among the fillers contained in the heat-resistant layer is preferably 1% or less, more preferably 0.5% or less, based on the number of particles. Since such fillers contain almost no large particles, it is easy to form a thin heat-resistant layer. Here, the ratio of particles having a spherical equivalent diameter of 1 μm or more is a value measured by a transmission electron microscope for 500 fillers. A specific measurement method is as follows.
1. Using a transmission electron microscope (TEM; JEOL Ltd., JEM-2100F), images are taken at an accelerating voltage of 200 kV and a magnification of 10,000 times using a Gatan Imaging Filter.
2. For the obtained image, the contours of the particles are traced using image analysis software (ImageJ) to measure the spherical equivalent particle diameter of the filler particles (primary particles).
3. The above measurement is carried out on 500 randomly selected filler particles. Among the 500 filler particles, the ratio of filler particles having an equivalent spherical particle size of 1 μm or more is calculated.

Types of fillers include organic fillers and inorganic fillers.

Examples of organic fillers include styrene, vinyl ketone, acrylonitrile, methyl methacrylate, ethyl methacrylate, glycidyl methacrylate, glycidyl acrylate, methyl acrylate, and the like, either alone or in copolymers of two or more kinds; fluororesins such as polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-ethylene copolymer, and polyvinylidene fluoride; melamine resins; urea resins; polyolefins; polymethacrylates, and the like. The organic fillers may be used alone or in a mixture of two or more kinds. Among these organic fillers, polytetrafluoroethylene powder is preferred in terms of chemical stability.

Examples of inorganic fillers include materials made of inorganic substances such as metal oxides, metal nitrides, metal carbides, metal hydroxides, carbonates, and sulfates. Specific examples include powders of alumina, boehmite, silica, titanium dioxide, aluminum hydroxide, and calcium carbonate. The inorganic fillers may be used alone or in combination of two or more types. Among these inorganic fillers, alumina powder is preferred in terms of chemical stability.

The shape of the filler can be roughly spherical, plate-like, columnar, needle-like, whisker-like, fibrous, etc., and any type of particle can be used. Roughly spherical particles are preferred because they are easier to form uniform pores.

The filler content in the heat-resistant layer is preferably 20 to 80% by weight, and more preferably 30 to 70% by weight. The filler content in the heat-resistant layer is calculated assuming that the total weight of the heat-resistant layer is 100% by weight. By setting the filler content in the above range, a porous layer with sufficient ion permeability can be easily obtained.

[Polyolefin Porous Film]
The laminated separator for a non-aqueous electrolyte secondary battery according to one embodiment of the present invention includes a polyolefin porous film. The polyolefin porous film has many interconnected pores inside, allowing gas and liquid to pass from one side to the other side. The polyolefin porous film can be a substrate for the laminated separator for a non-aqueous electrolyte secondary battery. The polyolefin porous film can be melted when the battery generates heat, rendering the laminated separator for a non-aqueous electrolyte secondary battery non-porous, thereby imparting a shutdown function to the laminated separator for a non-aqueous electrolyte secondary battery.

Here, a "polyolefin porous film" is a porous film whose main component is a polyolefin resin. Also, "whose main component is a polyolefin resin" means that the proportion of polyolefin resin in the porous film is 50% by volume or more, preferably 90% by volume or more, and more preferably 95% by volume or more of the total material constituting the porous film.

The polyolefin resin, which is the main component of the polyolefin porous film, is not particularly limited, but examples thereof include homopolymers and copolymers formed by polymerizing monomers such as ethylene, propylene, 1-butene, 4-methyl-1-pentene, and/or 1-hexene, which are thermoplastic resins. That is, examples of homopolymers include polyethylene, polypropylene, and polybutene, and examples of copolymers include ethylene-propylene copolymers. The polyolefin porous film may be a layer containing these polyolefin resins alone, or a layer containing two or more of these polyolefin resins. Of these, polyethylene is more preferable because it can prevent (shut down) the flow of excessive current at a lower temperature, and in particular, high molecular weight polyethylene mainly composed of ethylene is preferable. Note that the polyolefin porous film may contain components other than polyolefins as long as the function is not impaired.

Examples of polyethylene include low-density polyethylene, high-density polyethylene, linear polyethylene (ethylene-α-olefin copolymer), and ultra-high molecular weight polyethylene. Among these, ultra-high molecular weight polyethylene is more preferred, and it is even more preferred that the polyethylene contains a high molecular weight component having a weight-average molecular weight of 5×10 ⁵ to 15×10 ^6. In particular, it is more preferred that the polyolefin resin contains a high molecular weight component having a weight-average molecular weight of 1,000,000 or more, since this improves the strength of the polyolefin porous film and the laminate separator for non-aqueous electrolyte secondary batteries.

The thickness of the polyolefin porous film is preferably 5 to 20 μm, more preferably 7 to 15 μm, and even more preferably 9 to 15 μm. If the thickness is 5 μm or more, the functions required of the polyolefin porous film (such as a shutdown function) can be sufficiently obtained. If the thickness is 20 μm or less, a thin laminate separator for a nonaqueous electrolyte secondary battery can be obtained.

The pore size of the pores in the polyolefin porous film is preferably 0.1 μm or less, and more preferably 0.06 μm or less. This allows for sufficient ion permeability and better prevents the particles that make up the electrode from entering.

The weight basis weight per unit area of the polyolefin porous film is usually preferably 4 to 20 g/ ^m2 , more preferably 5 to 12 g/ ^m2 , so that the gravimetric energy density and volumetric energy density of the battery can be increased.

The polyolefin porous film preferably has an air permeability of 30 to 500 s/100 mL in Gurley value, and more preferably 50 to 300 s/100 mL. This allows the laminated separator for non-aqueous electrolyte secondary batteries to have sufficient ion permeability.

The porosity of the polyolefin porous film is preferably 20 to 80% by volume, and more preferably 30 to 75% by volume. This increases the amount of electrolyte retained and also enables the flow of excessive current to be reliably prevented (shutdown) at a lower temperature.

The method for producing the polyolefin porous film can be a known method and is not particularly limited. For example, as described in Japanese Patent No. 5476844, a method in which a filler is added to a thermoplastic resin, a film is formed, and then the filler is removed can be mentioned.

Specifically, for example, when the polyolefin porous film is formed from a polyolefin resin containing ultra-high molecular weight polyethylene and a low molecular weight polyolefin having a weight average molecular weight of 10,000 or less, from the viewpoint of production costs, it is preferable to produce it by a method including the following steps (1) to (4).

(1) A process for obtaining a polyolefin-based resin composition by kneading 100 parts by weight of ultra-high molecular weight polyethylene, 5 to 200 parts by weight of a low molecular weight polyolefin having a weight average molecular weight of 10,000 or less, and 100 to 400 parts by weight of an inorganic filler such as calcium carbonate;
(2) forming a sheet using the polyolefin resin composition;
(3) removing the inorganic filler from the sheet obtained in step (2);
(4) A step of stretching the sheet obtained in step (3).
In addition, the methods described in the above-mentioned patent documents may be used.

In addition, commercially available products having the above-mentioned characteristics may be used as the polyolefin porous film.

[Other ingredients]
The heat-resistant layer may contain components other than the above-mentioned components. For example, the heat-resistant layer may contain a binder resin. The binder resin has a function of bonding the components constituting the heat-resistant layer together, and bonding between the heat-resistant layer and the polyolefin porous film and/or between the heat-resistant layer and the electrode plate.

It is preferable that the binder resin is insoluble in the battery's electrolyte and is electrochemically stable within the range of use of the battery.

Examples of binder resins include polyolefins; (meth)acrylate resins; fluorine-containing resins; polyamide resins; polyimide resins; polyamideimide resins; polyester resins; rubbers; resins with a melting point or glass transition temperature of 180°C or higher; water-soluble polymers; polycarbonate, polyacetal, polyether ether ketone, etc.

Among the above-mentioned resins, (meth)acrylate resins, fluorine-containing resins, polyamide resins, polyimide resins, polyamideimides, polyester resins and water-soluble polymers are preferred.

Preferred polyolefins include polyethylene, polypropylene, polybutene, and ethylene-propylene copolymers.

Examples of fluorine-containing resins include polyvinylidene fluoride (PVDF), polytetrafluoroethylene, vinylidene fluoride-hexafluoropropylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-trichloroethylene copolymer, vinylidene fluoride-vinyl fluoride copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, and ethylene-tetrafluoroethylene copolymer, as well as fluorine-containing rubbers having a glass transition temperature of 23°C or lower among the above fluorine-containing resins.

As polyamide-based resins, aramid resins such as aromatic polyamides and fully aromatic polyamides are preferred.

Specific examples of aramid resins include poly(paraphenylene terephthalamide), poly(metaphenylene isophthalamide), poly(parabenzamide), poly(metabenzamide), poly(4,4'-benzanilide terephthalamide), poly(paraphenylene-4,4'-biphenylenedicarboxylic acid amide), poly(metaphenylene-4,4'-biphenylenedicarboxylic acid amide), poly(paraphenylene-2,6-naphthalene dicarboxylic acid amide), poly(metaphenylene-2,6-naphthalene dicarboxylic acid amide), poly(2-chloroparaphenylene terephthalamide), paraphenylene terephthalamide/2,6-dichloroparaphenylene terephthalamide copolymer, metaphenylene terephthalamide/2,6-dichloroparaphenylene terephthalamide copolymer, etc. Of these, poly(paraphenylene terephthalamide) is more preferred.

Preferred polyester resins are aromatic polyesters such as polyarylates and liquid crystal polyesters.

Examples of rubbers include styrene-butadiene copolymers and their hydrogenated products, methacrylate copolymers, acrylonitrile-acrylate copolymers, styrene-acrylate copolymers, ethylene propylene rubber, polyvinyl acetate, etc.

Examples of resins with a melting point or glass transition temperature of 180°C or higher include polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyamideimide, polyetheramide, etc.

Examples of water-soluble polymers include polyvinyl alcohol, polyethylene glycol, cellulose ether, sodium alginate, polyacrylic acid, polyacrylamide, polymethacrylic acid, etc.

Note that only one type of binder resin may be used, or two or more types may be used in combination.

[Method of manufacturing laminated separator]
The manufacturing method according to one embodiment of the present invention includes a step of forming a heat-resistant layer containing a resin and a filler on a polyolefin porous film. The preferred embodiments of the resin, the filler and the porous film used in this step are as described above.

The heat-resistant layer can be formed using a coating liquid in which a resin having a specified intrinsic viscosity, a filler having a specified average particle size, and optionally other components are dissolved or dispersed in a solvent. Methods for forming the coating liquid include, for example, mechanical stirring, ultrasonic dispersion, high-pressure dispersion, and media dispersion. Examples of solvents that can be used include N-methylpyrrolidone, N,N-dimethylacetamide, and N,N-dimethylformamide.

As a method for forming the heat-resistant layer, for example, the above-mentioned coating liquid is prepared, the coating liquid is applied to a polyolefin porous film, and the heat-resistant layer is formed by drying.

The coating liquid can be applied to the polyolefin porous film using known coating methods such as knife, blade, bar, gravure, or die.

The solvent (dispersion medium) is generally removed by drying. Examples of drying methods include natural drying, air drying, heat drying, and reduced pressure drying, but any method that can sufficiently remove the solvent (dispersion medium) is acceptable. The solvent (dispersion medium) contained in the paint may also be replaced with another solvent before drying. A specific example of a method for replacing the solvent (dispersion medium) with another solvent before removing it is to replace it with a low-boiling point poor solvent such as water, alcohol, or acetone, precipitate it, and then dry it.

[2. Laminated separator for non-aqueous electrolyte secondary batteries]
A laminate separator for a non-aqueous electrolyte secondary battery according to one embodiment of the present invention comprises a heat-resistant layer laminated on one or both sides of a polyolefin porous film,
The heat-resistant layer contains a heat-resistant resin and a filler,
The thickness of the laminated separator for a non-aqueous electrolyte secondary battery is 15 μm or less,
The laminated separator for a nonaqueous electrolyte secondary battery has a heat shape retention rate in the TD direction of 75% or more when heated at 200° C. for 5 minutes,
The heat-resistant layer has an air permeability of 100 s/100 mL or less.

In the manufacturing method according to one embodiment of the present invention, a resin with an intrinsic viscosity of 1.5 to 1.9 dL/g and a filler with an average particle size of 500 nm or less are used as the raw materials for the heat-resistant layer. As a result, it is now possible to provide a laminated separator for non-aqueous electrolyte secondary batteries that has the above-mentioned physical properties that could not be obtained with conventional technology.

The heat-resistant layer and the polyolefin porous film are as explained in Section [1], so a repeated explanation will be omitted. The heat-resistant resin and filler contained in the heat-resistant layer are as explained in Section [1], so a repeated explanation will be omitted.

The thickness of the laminated separator for a non-aqueous electrolyte secondary battery according to one embodiment of the present invention is preferably 15 μm or less, more preferably 14.5 μm or less, and even more preferably 14 μm or less. If the thickness is 15 μm or less, it can be said that the laminated separator for a non-aqueous electrolyte secondary battery is sufficiently thin. The lower limit of the thickness is not particularly limited, but can be, for example, 7 μm or more.

The thickness of the laminated separator for non-aqueous electrolyte secondary batteries can be adjusted by selecting the polyolefin porous film used and adjusting the basis weight of the porous layer.

When the laminated separator for a nonaqueous electrolyte secondary battery according to one embodiment of the present invention is heated at 200°C for 5 minutes, the heat shape retention rate in the TD direction is 75% or more, more preferably 76% or more, and even more preferably 77% or more. If the heat shape retention rate is 75% or more, it can be said to have sufficient heat resistance. There is no particular limit to the upper limit of the heat shape retention rate, but it can be, for example, 95% or less.

In this specification, "heat shape retention" refers to the retention of sample width in the TD direction after a sample of a laminated separator for a non-aqueous electrolyte secondary battery is heated at 200°C for 5 minutes. In other words, it is a value calculated by "(sample width after heating/sample width before heating) x 100". For more detailed information on the method for measuring the heat shape retention, see the examples.

The heat shape retention rate in the TD direction when the laminated separator for a nonaqueous electrolyte secondary battery is heated at 200° C. for 5 minutes also depends on the basis weight of the heat-resistant layer. In consideration of this point, when the sample width before heating is 54 mm, the heat deformation amount per heat-resistant basis weight is preferably 10 mm/(g/m ² ) or less, more preferably 9.8 mm/(g/m ² ) or less, and even more preferably 9.5/(g/m ² ) or less. The heat deformation amount per heat-resistant basis weight is a value calculated by "(sample width before heating (=54 mm) - sample width after heating) / basis weight of the heat-resistant layer".

The heat shape retention rate can be adjusted, for example, by the intrinsic viscosity of the resin, the resin content of the heat-resistant layer, and the basis weight of the heat-resistant layer. The amount of heat deformation per heat-resistant basis weight can be adjusted, for example, by the intrinsic viscosity of the resin, and the resin content of the heat-resistant layer. In general, the heat shape retention rate tends to increase as the intrinsic viscosity of the resin increases. Also, the heat shape retention rate tends to increase as the resin content of the heat-resistant layer increases. Furthermore, the heat shape retention rate tends to increase as the basis weight of the heat-resistant layer increases.

In the laminate separator for a nonaqueous electrolyte secondary battery according to one embodiment of the present invention, the air permeability of the heat-resistant layer is preferably 100 s/100 mL or less, more preferably 90 s/100 mL or less, and even more preferably 80 s/100 mL or less, in Gurley value. If the air permeability is 100 s/100 mL or less, it can be said that the heat-resistant layer has sufficient ion permeability.

The air permeability of the heat-resistant layer also depends on the basis weight of the heat-resistant layer. In consideration of this point, the air permeability of the heat-resistant layer per unit weight is preferably 60 s/100 mL/(g/ ^m2 ) or less, more preferably 67 s/100 mL/(g/ ^m2 ) or less, and even more preferably 55 s/100 mL/(g/ ^m2 ) or less. The "air permeability of the heat-resistant layer per unit weight" refers to the value obtained by dividing the air permeability of the heat-resistant layer by the unit weight of the heat-resistant layer.

The air permeability of the heat-resistant layer can be adjusted, for example, by the intrinsic viscosity of the resin and the basis weight of the heat-resistant layer. The air permeability of the heat-resistant layer per unit weight of the heat-resistant layer can be adjusted, for example, by the intrinsic viscosity of the resin. In general, as the intrinsic viscosity of the resin decreases, the Gurley value tends to decrease. Also, as the basis weight of the heat-resistant layer decreases, the Gurley value tends to decrease.

The air permeability of the laminated separator for a non-aqueous electrolyte secondary battery according to one embodiment of the present invention is preferably 50 to 500 s/100 mL, more preferably 50 to 300 s/100 mL, in Gurley value. If the laminated separator for a non-aqueous electrolyte secondary battery has the above air permeability, sufficient ion permeability can be obtained in the non-aqueous electrolyte secondary battery.

In the laminate separator for a nonaqueous electrolyte secondary battery according to one embodiment of the present invention, the basis weight of the porous layer is preferably 0.5 to 2.0 g/ ^m2 , more preferably 1.0 to 2.0 g/ ^m2 , and even more preferably 1.0 to 1.8 g/ ^m2 , in terms of solid content.

The laminated separator for a non-aqueous electrolyte secondary battery according to one embodiment of the present invention is a laminated separator in which a heat-resistant layer is laminated on a polyolefin porous film. In this case, the heat-resistant layer may be laminated on one side or both sides of the polyolefin porous film.

The laminate separator for a nonaqueous electrolyte secondary battery according to one embodiment of the present invention may contain, in addition to the polyolefin porous film and the heat-resistant layer, a known porous film such as an adhesive layer or a protective layer, as necessary, to the extent that the object of the present invention is not impaired.

3. Non-aqueous electrolyte secondary battery components and non-aqueous electrolyte secondary batteries
A nonaqueous electrolyte secondary battery member according to one embodiment of the present invention comprises a positive electrode, the above-mentioned laminated separator for nonaqueous electrolyte secondary batteries, and a negative electrode arranged in this order. A nonaqueous electrolyte secondary battery according to one embodiment of the present invention includes the above-mentioned laminated separator for nonaqueous electrolyte secondary batteries. The nonaqueous electrolyte secondary battery generally has a structure in which a negative electrode and a positive electrode face each other via the above-mentioned laminated separator for nonaqueous electrolyte secondary batteries. In the nonaqueous electrolyte secondary battery, a battery element in which the structure is impregnated with an electrolyte is enclosed in an exterior material. For example, the nonaqueous electrolyte secondary battery is a lithium ion secondary battery that obtains electromotive force by doping and dedoping lithium ions.

[Positive electrode]
As the positive electrode, for example, a positive electrode sheet having a structure in which an active material layer containing a positive electrode active material and a binder is formed on a current collector can be used. The active material layer may further contain a conductive agent.

The positive electrode active material may be, for example, a material capable of doping and dedoping lithium ions. Such a material may be, for example, a lithium composite oxide containing at least one transition metal such as V, Mn, Fe, Co, or Ni.

Examples of the conductive agent include carbonaceous materials such as natural graphite, artificial graphite, cokes, carbon black, pyrolytic carbons, carbon fibers, and fired organic polymer compounds.

Examples of the binder include polyvinylidene fluoride, vinylidene fluoride copolymers, polytetrafluoroethylene, vinylidene fluoride-hexafluoropropylene copolymers, tetrafluoroethylene-hexafluoropropylene copolymers, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymers, ethylene-tetrafluoroethylene copolymers, vinylidene fluoride-tetrafluoroethylene copolymers, vinylidene fluoride-trifluoroethylene copolymers, vinylidene fluoride-trichloroethylene copolymers, vinylidene fluoride-vinyl fluoride copolymers, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymers, thermoplastic polyimide, polyethylene, polypropylene, and other thermoplastic resins, acrylic resins, and styrene-butadiene rubber. The binder also functions as a thickener.

Examples of the positive electrode current collector include conductors such as Al, Ni, and stainless steel. Among these, Al is more preferred because it is easy to process into a thin film and is inexpensive.

Examples of methods for manufacturing a sheet-shaped positive electrode include a method of pressurizing and molding the positive electrode active material, conductive agent, and binder that will become the positive electrode mixture on a positive electrode current collector; a method of forming the positive electrode active material, conductive agent, and binder into a paste using an appropriate organic solvent to obtain a positive electrode mixture, and then coating the positive electrode mixture on a positive electrode current collector and drying the resulting sheet-shaped positive electrode mixture, which is then pressed to adhere to the positive electrode current collector.

[Negative electrode]
As the negative electrode, for example, a negative electrode sheet having a structure in which an active material layer containing a negative electrode active material and a binder is formed on a current collector can be used. The active material layer may further contain a conductive agent.

Examples of the negative electrode active material include materials capable of doping and dedoping lithium ions, lithium metals, and lithium alloys. Examples of the material include carbonaceous materials such as natural graphite, artificial graphite, cokes, carbon black, pyrolytic carbons, carbon fibers, and organic polymer compound sintered bodies; chalcogen compounds such as oxides and sulfides that perform doping and dedoping of lithium ions at a potential lower than that of the positive electrode; metals such as aluminum (Al), lead (Pb), tin (Sn), bismuth (Bi), and silicon (Si) that are alloyed with alkali metals, cubic intermetallic compounds (AlSb, Mg ₂ Si, NiSi ₂ ) that can insert alkali metals between lattices, and lithium nitrogen compounds (Li _3-x M _x N (M: transition metal)).

Examples of negative electrode current collectors include Cu, Ni, and stainless steel. Among these, Cu is more preferable, especially in lithium-ion secondary batteries, because it is difficult to form an alloy with lithium and it is easy to process into a thin film.

Examples of methods for producing a sheet-shaped negative electrode include a method of pressurizing and molding a negative electrode active material that will become a negative electrode mixture on a negative electrode current collector; a method of forming a negative electrode active material into a paste using an appropriate organic solvent to obtain a negative electrode mixture, applying the negative electrode mixture to a negative electrode current collector, drying the mixture, and pressing the sheet-shaped negative electrode mixture obtained to adhere to the negative electrode current collector. The paste preferably contains the conductive agent and the binder.

[Non-aqueous electrolyte]
The non-aqueous electrolyte may be, for example, a non-aqueous electrolyte obtained by dissolving a lithium salt in _{an organic} solvent. Examples of the lithium salt include LiClO4, _LiPF6 , _LiAsF6 , _LiSbF6 , _LiBF4 , _LiCF3SO3 , _LiN ( _CF3SO2 ) ₂ , LiC( _{CF3SO2 ) 3} , _{Li2B10Cl10 ,} lithium salts of lower aliphatic carboxylic acids, _{and LiAlCl4} . Among the above lithium salts, at least one fluorine _- containing lithium salt selected from the group consisting _{of LiPF6} , _LiAsF6 , _LiSbF6 , _LiBF4 , _LiCF3SO3 , LiN( _{CF3SO2 ) 2} and LiC( _CF3SO2 ) ₃ is more preferred.

Examples of organic solvents include carbonates such as ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, 4-trifluoromethyl-1,3-dioxolan-2-one, and 1,2-di(methoxycarbonyloxy)ethane; ethers such as 1,2-dimethoxyethane, 1,3-dimethoxypropane, pentafluoropropyl methyl ether, 2,2,3,3-tetrafluoropropyl difluoromethyl ether, tetrahydrofuran, and 2-methyltetrahydrofuran; esters such as methyl formate, methyl acetate, and γ-butyrolactone; nitriles such as acetonitrile and butyronitrile; amides such as N,N-dimethylformamide and N,N-dimethylacetamide; carbamates such as 3-methyl-2-oxazolidone; sulfur-containing compounds such as sulfolane, dimethyl sulfoxide, and 1,3-propane sultone; and fluorine-containing organic solvents obtained by introducing a fluorine group into the above organic solvents. Among the above organic solvents, carbonates are more preferred, and a mixed solvent of a cyclic carbonate and an acyclic carbonate, or a mixed solvent of a cyclic carbonate and an ether is even more preferred. As a mixed solvent of a cyclic carbonate and an acyclic carbonate, a mixed solvent containing ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate is even more preferred. The mixed solvent has a wide operating temperature range, and is difficult to decompose even when a graphite material such as natural graphite or artificial graphite is used as the negative electrode active material.

[Members for non-aqueous electrolyte secondary batteries and methods for producing non-aqueous electrolyte secondary batteries]
As a method for producing a member for a non-aqueous electrolyte secondary battery, for example, there is a method in which a positive electrode, the above-mentioned laminated separator for a non-aqueous electrolyte secondary battery, and a negative electrode are arranged in this order.

In addition, the following method can be used as a method for manufacturing a nonaqueous electrolyte secondary battery. First, a nonaqueous electrolyte secondary battery component is placed in a container that will become the housing of the nonaqueous electrolyte secondary battery. Next, the container is filled with nonaqueous electrolyte, and the container is sealed while reducing the pressure. In this way, a nonaqueous electrolyte secondary battery can be manufactured.

The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. The technical scope of the present invention also includes embodiments obtained by appropriately combining the technical means disclosed in different embodiments.

The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[Methods for measuring various physical properties]
In the examples and comparative examples described later, the various physical properties were measured by the following methods.

(1) Intrinsic Viscosity The flow time was measured using an Ubbelohde capillary viscometer for (i) a solution in which 0.5 g of resin (aramid resin in this example) was dissolved in 100 mL of concentrated sulfuric acid (96 to 98%), and (ii) concentrated sulfuric acid (96 to 98%) in which no resin was dissolved. The temperature during measurement was 30°C. The intrinsic viscosity was calculated from the calculated flow time using the following formula.
Intrinsic viscosity = ln (T/T ₀ )/C (unit: dL/g)
T: flow time of concentrated sulfuric acid solution of aramid resin T ₀ : flow time of concentrated sulfuric acid C: concentration of aramid resin in concentrated sulfuric acid solution of aramid resin (g/dL).

(2) Film Thickness The film thickness of the laminate separator was measured using a high-precision digital length measuring machine manufactured by Mitutoyo Corporation. Furthermore, a peeling tape was attached to the surface of the laminate separator on which the heat-resistant layer was formed, and then peeled off to peel off the heat-resistant layer from the polyethylene porous film. The film thickness of the polyethylene porous film after peeling off the heat-resistant layer was measured in the same manner as the laminate separator. In addition, the film thickness of the heat-resistant layer was calculated from the difference between the film thickness of the laminate separator and the film thickness of the polyethylene porous film after peeling.

(3) Weight per unit area of heat-resistant layer The laminated separator was cut into a square with a side length of 8 cm to prepare a sample, and the weight W1 [g] of this sample was measured. Furthermore, a release tape was attached to the surface of the sample on which the heat-resistant layer was formed, and then peeled off to peel the heat-resistant layer from the polyethylene porous film. The weight W2 [g] of the polyethylene porous film after peeling off the heat-resistant layer was measured. The weight per unit area of the heat-resistant layer [g/ ^m2 ] was calculated according to the following formula.
Weight of heat-resistant layer=(W1−W2)/(0.08×0.08).

(4) Air permeability The air permeability of the laminated separator and the polyolefin porous film was measured using a digital timer type Gurley densometer (manufactured by Yasuda Seiki Seisakusho Co., Ltd.) based on JIS P 8117. The air permeability of the heat-resistant layer was calculated by subtracting the air permeability of the polyethylene porous film from the air permeability of the laminated separator. The value obtained by dividing the air permeability of the heat-resistant layer by the basis weight of the heat-resistant layer was defined as the "air permeability of the heat-resistant layer per unit weight of the heat-resistant layer."

(5) Heat Shape Retention Rate A laminated separator cut to a length of 108 mm and a width of 54 mm was placed on a glass plate with the polyethylene porous film side facing down. Both ends of the laminated separator in the longitudinal direction were fixed to the glass plate with polyimide adhesive tape (manufactured by Nitto Denko). At this time, the end of the laminated separator was covered by the adhesive tape by 4 mm in the longitudinal direction on each side. In other words, the length of the measurement part of the laminated separator not covered by the adhesive tape was 100 mm. In this state, the width (L1) of the central part of the laminated separator was measured. Since L1 corresponds to the width of the laminated separator in the cut-out state, L1 = 54 mm.

Next, the glass plate was placed in a heating oven set at 200°C and heated for 5 minutes. The glass plate was then removed from the heating oven and left to stand until it reached room temperature. Next, the width (L2) of the center part of the laminated separator was measured.

L1 - L2 was defined as the "heat deformation amount." The value calculated by (L2/L1) x 100 was defined as the "heat shape retention rate." The value calculated by dividing the heat deformation amount by the basis weight of the heat-resistant layer was defined as the "heat deformation amount per heat-resistant basis weight."

If the heat shape retention rate is 75% or more, it can be said to have excellent heat resistance. Also, if the heat deformation amount per unit area is 10 mm/(g/m ² ) or less, it can be said to have excellent heat resistance.

Synthesis Example 1
Poly(paraphenylene terephthalamide), a type of aramid resin, was synthesized as the resin contained in the heat-resistant layer. A 3-L separable flask equipped with a stirring blade, a thermometer, a nitrogen inlet, and a powder addition port was used as a synthesis vessel. 2200 g of N-methyl-2-pyrrolidone (NMP) was charged into a thoroughly dried flask. 151.07 g of calcium chloride powder was added thereto, and the mixture was heated to 100°C to completely dissolve it. The calcium chloride powder used was previously vacuum-dried at 200°C for 2 hours.

Then, the liquid temperature was returned to room temperature, and 68.23 g of paraphenylenediamine was added and completely dissolved. While keeping this solution at 20°C ± 2°C, 124.25 g of terephthalic acid dichloride was added in four portions at approximately 10 minute intervals. After that, the solution was aged for 1 hour while continuing to stir at 150 rpm and kept at 20°C ± 2°C, to obtain aramid polymerization liquid (1) containing 6% by weight of poly(paraphenylene terephthalamide). The intrinsic viscosity of the poly(paraphenylene terephthalamide) contained in the aramid polymerization liquid (1) was 1.5 g/dL.

Synthesis Example 2
Except for changing the amount of terephthalic acid dichloride added to 124.48 g, an aramid polymerization liquid (2) was obtained in the same manner as in Synthesis Example 1. The intrinsic viscosity of poly(paraphenylene terephthalamide) contained in the aramid polymerization liquid (2) was 1.6 g/dL.

[Synthesis Example 3]
Except for changing the amount of terephthalic acid dichloride added to 124.61 g, an aramid polymerization liquid (3) was obtained in the same manner as in Synthesis Example 1. The intrinsic viscosity of poly(paraphenylene terephthalamide) contained in the aramid polymerization liquid (3) was 1.7 g/dL.

Synthesis Example 4
Except for changing the amount of terephthalic acid dichloride added to 124.97 g, an aramid polymerization liquid (4) was obtained in the same manner as in Synthesis Example 1. The intrinsic viscosity of poly(paraphenylene terephthalamide) contained in the aramid polymerization liquid (4) was 1.9 g/dL.

Synthesis Example 5
Except for changing the amount of terephthalic acid dichloride added to 123.98 g, an aramid polymerization liquid (5) was obtained in the same manner as in Synthesis Example 1. The intrinsic viscosity of poly(paraphenylene terephthalamide) contained in the aramid polymerization liquid (5) was 1.4 g/dL.

Synthesis Example 6
Except for changing the amount of terephthalic acid dichloride added to 125.10 g, an aramid polymerization liquid (6) was obtained in the same manner as in Synthesis Example 1. The intrinsic viscosity of poly(paraphenylene terephthalamide) contained in the aramid polymerization liquid (6) was 2.0 g/dL.

Example 1
100 g of the aramid polymerization liquid (1) was weighed into a flask, and 6.0 g of alumina A (average particle size: 13 nm) was added. At this time, the weight ratio of poly(paraphenylene terephthalamide) to alumina A was 1:1. Next, NMP was added so that the solid content was 4.5 wt %, and the mixture was stirred for 240 minutes. The "solid content" here refers to the total weight of poly(paraphenylene terephthalamide) and alumina A. Next, 0.73 g of calcium carbonate was added and the mixture was stirred for 240 minutes to neutralize the solution. The solution was degassed under reduced pressure to prepare a slurry-like coating liquid (1).

The coating liquid (1) was applied by doctor blade method onto a polyolefin porous film (thickness: 10.4 μm, air permeability: 116 s/100 mL) made of polyethylene. The obtained coating (1) was left to stand in air at 50° C. and a relative humidity of 70% for 1 minute to precipitate poly(paraphenylene terephthalamide). Next, the coating (1) was immersed in ion-exchanged water to remove calcium chloride and the solvent. Next, the coating (1) was dried in an oven at 70° C. to obtain a laminated separator for nonaqueous electrolyte secondary batteries (1). The physical properties of the laminated separator for nonaqueous electrolyte secondary batteries (1) are shown in Table 1.

Example 2
Except for using the aramid polymerization solution (2) instead of the aramid polymerization solution (1), a laminate separator (2) for a nonaqueous electrolyte secondary battery was obtained in the same manner as in Example 1. The physical properties of the laminate separator (2) for a nonaqueous electrolyte secondary battery are shown in Table 1.

Example 3
Except for using the aramid polymerization solution (3) instead of the aramid polymerization solution (1), a laminate separator (3) for a nonaqueous electrolyte secondary battery was obtained in the same manner as in Example 1. The physical properties of the laminate separator (3) for a nonaqueous electrolyte secondary battery are shown in Table 1.

Example 4
Except for using the aramid polymerization solution (4) instead of the aramid polymerization solution (1), a laminate separator for a nonaqueous electrolyte secondary battery (4) was obtained in the same manner as in Example 1. The physical properties of the laminate separator for a nonaqueous electrolyte secondary battery (4) are shown in Table 1.

Example 5
A laminated separator for a non-aqueous electrolyte secondary battery (5) was obtained in the same manner as in Example 4, except that the amount of alumina A added was changed to 7.5 g. The physical properties of the laminated separator for a non-aqueous electrolyte secondary battery (5) are shown in Table 1.

Example 6
A laminated separator for a nonaqueous electrolyte secondary battery (6) was obtained in the same manner as in Example 4, except that the amount of alumina A added was changed to 9.1 g. The physical properties of the laminated separator for a nonaqueous electrolyte secondary battery (6) are shown in Table 1.

Example 7
A laminated separator for a nonaqueous electrolyte secondary battery (7) was obtained in the same manner as in Example 4, except that the basis weight of the heat-resistant layer was made larger than that of Example 4. The physical properties of the laminated separator for a nonaqueous electrolyte secondary battery (7) are shown in Table 1.

Comparative Example 1
Except for using the aramid polymerization solution (5) instead of the aramid polymerization solution (1), a comparative laminate separator for non-aqueous electrolyte secondary batteries (1) was obtained in the same manner as in Example 1. The physical properties of the comparative laminate separator for non-aqueous electrolyte secondary batteries (1) are shown in Table 1.

Comparative Example 2
Except for using the aramid polymerization liquid (6) instead of the aramid polymerization liquid (1) and using another polyolefin porous film (thickness: 10.2 μm, air permeability: 165 s/100 mL), a comparative laminate separator for nonaqueous electrolyte secondary batteries (2) was obtained in the same manner as in Example 1. The physical properties of the comparative laminate separator for nonaqueous electrolyte secondary batteries (2) are shown in Table 1.

Comparative Example 3
100 g of the aramid polymerization solution (4) was weighed into a flask, and 6.0 g of alumina A (average particle size: 13 nm) and 6.0 g of alumina B (average particle size: 640 nm) were added. At this time, the weight ratio of poly(paraphenylene terephthalamide), alumina A, and alumina B was 1:1:1. Next, a coating liquid was prepared so that the solid content was 6.0 wt%. A comparative laminate separator for nonaqueous electrolyte secondary batteries (3) was obtained by the same procedure as in Example 4 except for the above. In Comparative Example 3, the average particle size of the filler as a whole was 530 nm. The physical properties of the comparative laminate separator for nonaqueous electrolyte secondary batteries (3) are shown in Table 1.

In Examples 1 to 7 and Comparative Examples 1 and 2, the percentage of particles with a spherical equivalent diameter of 1 μm or more in the filler was 0.2%. On the other hand, in Comparative Example 3, the percentage of particles with a spherical equivalent diameter of 1 μm or more in the filler was 1.2%.

〔result〕
The laminated separators for non-aqueous electrolyte secondary batteries (1) to (7) and the comparative laminated separators for non-aqueous electrolyte secondary batteries (1) to (3) were all produced to be thin separators having a thickness of 15 μm or less.

A comparison between Example 1 and Comparative Example 1 suggests that when the intrinsic viscosity of the resin is less than 1.5 dL/g, the heat shape retention rate tends to be too low. A comparison between Example 4 and Comparative Example 2 suggests that when the intrinsic viscosity of the resin is more than 1.9 dL/g, the heat resistant layer tends to have too high air permeability (note that although the types of polyolefin porous film are different between Example 4 and Comparative Example 2, the air permeability of the heat resistant layer does not depend on the type of polyolefin porous film). A comparison between Example 4 and Comparative Example 3 suggests that when the average particle size of the filler is more than 500 nm, the heat shape retention rate tends to be too low.

In this way, the manufacturing method according to one embodiment of the present invention makes it possible to obtain a laminated separator for a non-aqueous electrolyte secondary battery that is thin, heat-resistant, and ion-permeable at the same time, something that could not be achieved with conventional technology.

The present invention can be used, for example, in non-aqueous electrolyte secondary batteries.

Claims (7)

A method for producing a laminated separator for a non-aqueous electrolyte secondary battery, comprising the steps of: forming a heat-resistant layer containing a resin and a filler on a polyolefin porous film,
The intrinsic viscosity of the resin is 1.6 to 1.9 dL/g;
The average particle size of the filler is 500 nm or less (here, the average particle size is the average value of the equivalent sphere particle size of 50 filler particles, and the equivalent sphere particle size is a value actually measured by a transmission electron microscope),
The thickness of the laminated separator for a non-aqueous electrolyte secondary battery is 15 μm or less .
Here, the intrinsic viscosity of the resin is measured by the following procedure:
1. Measure the flow time T of a solution (resin concentration: C (g/dL)) obtained by dissolving 0.5 g of resin in 100 mL of concentrated sulfuric acid (96 to 98%) at 30° C. using an Ubbelohde capillary viscometer;
2. For concentrated sulfuric acid (96-98%) in which no resin is dissolved, the flow time T ₀ is measured at 30° C. using an Ubbelohde capillary viscometer;
3. From the flow time thus determined, the intrinsic viscosity is calculated according to the following formula:
Intrinsic viscosity (dL/g) = ln(T/T ₀ )/C. The manufacturing method according to claim 1, wherein the proportion of particles having a spherical equivalent diameter of 1 μm or more in the filler is 1% or less based on the number of particles. A laminate separator for a non-aqueous electrolyte secondary battery, comprising a polyolefin porous film and a heat-resistant layer laminated on one or both sides of the film,
The heat-resistant layer contains a heat-resistant resin and a filler,
The average particle size of the filler is 50 nm or less,
The thickness of the laminated separator for a non-aqueous electrolyte secondary battery is 15 μm or less,
The laminated separator for a nonaqueous electrolyte secondary battery has a heat shape retention rate in the TD direction of 75% or more when heated at 200° C. for 5 minutes,
The air permeability of the heat-resistant layer is 100 s/100 mL or less.
Laminated separator for non-aqueous electrolyte secondary batteries. The laminate separator for a non-aqueous electrolyte secondary battery according to claim 3, wherein the heat-resistant layer contains one or more resins selected from the group consisting of (meth)acrylate-based resins, fluorine-containing resins, polyamide-based resins, polyimide-based resins, polyamideimide-based resins, polyester-based resins, and water-soluble polymers. The laminated separator for a non-aqueous electrolyte secondary battery according to claim 4, wherein the heat-resistant layer contains an aramid resin. A positive electrode and
A laminate separator for a nonaqueous electrolyte secondary battery according to any one of claims 3 to 5,
A negative electrode;
are arranged in this order. A nonaqueous electrolyte secondary battery comprising the laminate separator for a nonaqueous electrolyte secondary battery according to any one of claims 3 to 5, or the member for a nonaqueous electrolyte secondary battery according to claim 6.