JP2022026936A - Separator for non-aqueous secondary battery and non-aqueous secondary battery - Google Patents

Abstract

To provide a separator for a non-aqueous secondary battery having a heat-resistant porous layer on a porous base material which is excellent in heat resistance and prevents peeling of the heat-resistant porous layer from the porous base material.SOLUTION: A separator for a non-aqueous secondary battery has a porous base material, and a heat-resistant porous layer that is provided on one surface or both surfaces of the porous base material and contains a heat-resistant binder resin, inorganic particles and heat-resistant resin particles, in which an average primary particle diameter of the inorganic particles contained in the heat-resistant porous layer is 0.01 μm to 3 μm, and an average primary particle diameter of the heat-resistant resin particles contained in the heat-resistant porous layer is 0.6 μm to 10 μm.SELECTED DRAWING: None

Description

The present disclosure relates to a separator for a non-aqueous secondary battery and a non-aqueous secondary battery.

The separator, which is one of the members that make up a non-aqueous secondary battery, is required to have heat resistance that does not easily break or shrink even when the inside of the battery becomes hot, in order to ensure the safety of the battery. Will be done. As a separator having enhanced heat resistance, a separator having a porous layer containing a heat resistant resin and / or inorganic particles on a porous substrate is known.
For example, Patent Document 1 or 2 discloses a separator having a porous layer containing barium sulfate particles on a porous substrate.
For example, Patent Document 3 or 4 discloses a separator provided with a porous layer containing a resin such as a total aromatic polyamide and inorganic particles on a porous substrate.
For example, Patent Document 5 discloses a separator provided with a porous layer containing a resin such as a total aromatic polyamide and barium sulfate particles on a porous substrate.

In addition, a separator having a layer containing resin particles on a porous substrate is disclosed.
For example, Patent Document 6 discloses a separator having a porous layer containing fluorine-based resin particles on a porous substrate.
For example, Patent Document 7 discloses a separator having a porous layer containing a resin such as a total aromatic polyamide, inorganic particles, and polyimide particles on a porous substrate.
For example, Patent Document 8 discloses a separator having a porous layer containing silicone resin particles on a porous substrate.
For example, Patent Document 9 discloses a separator provided with a lubricating layer containing a fluorine-containing resin filler on a porous substrate.
For example, Patent Document 10 discloses a separator provided with a porous layer containing a resin such as a total aromatic polyamide and acrylic resin particles on a porous substrate.
For example, Patent Document 11 or 12 discloses a separator having a porous layer containing a polyvinylidene fluoride-based resin and an acrylic resin filler on a porous substrate.

Japanese Patent No. 524911 International Publication No. 2014/148536 Japanese Unexamined Patent Publication No. 2012-119224 Japanese Unexamined Patent Publication No. 2019-216033 Japanese Patent No. 6526359 Japanese Unexamined Patent Publication No. 2010-02718 Japanese Unexamined Patent Publication No. 2010-146839 Japanese Unexamined Patent Publication No. 2010-176936 Japanese Unexamined Patent Publication No. 2010-244875 Japanese Unexamined Patent Publication No. 2019-029313 International Publication No. 2013/58371 International Publication No. 2014/21293

In order to ensure the safety of the battery, the separator is required to have adhesiveness that does not easily peel off from the electrode even if it receives an impact from the outside or the electrode expands and contracts due to charging and discharging. In order to ensure the adhesiveness of the separator to the electrode, in addition to the adhesiveness of the separator surface to the electrode, it is also necessary that the layers constituting the separator are not easily peeled off from each other. It is important from the viewpoint of increasing the manufacturing yield of the battery that the layers constituting the separator are not easily peeled off from each other.

The embodiments of the present disclosure have been made under the above circumstances.
The embodiment of the present disclosure is a separator for a non-aqueous secondary battery provided with a heat-resistant porous layer on a porous substrate, which has excellent heat resistance and the heat-resistant porous layer is not easily peeled off from the porous substrate. An object of the present invention is to provide a separator for a non-aqueous secondary battery.

Specific means for solving the above-mentioned problems include the following aspects.

<1> Porous substrate and
A heat-resistant porous layer provided on one or both sides of the porous substrate and containing a heat-resistant binder resin, inorganic particles and heat-resistant resin particles is provided.
The average primary particle size of the inorganic particles contained in the heat-resistant porous layer is 0.01 μm to 3 μm.
The average primary particle size of the heat-resistant resin particles contained in the heat-resistant porous layer is 0.6 μm to 10 μm.
Separator for non-aqueous secondary batteries.
<2> When the heat-resistant porous layer is provided on one side of the porous base material, the following formula (1) is satisfied on one side.
The separator for a non-aqueous secondary battery according to <1>, wherein when the heat-resistant porous layer is provided on both sides of the porous base material, the heat-resistant porous layer satisfies the following formula (1) on both sides.
Equation (1) 0.5 ≦ r / a ≦ 3
Here, in one heat-resistant porous layer, a is the thickness (μm) of the heat-resistant porous layer, and r is the average primary particle size of the heat-resistant resin particles contained in the heat-resistant porous layer (s). μm).
<3> The separator for a non-aqueous secondary battery according to <1> or <2>, wherein the volume ratio of the heat-resistant resin particles to the solid content of the heat-resistant porous layer is 1% by volume to 40% by volume. ..
<4> The heat-resistant resin particles are made of crosslinked poly (meth) acrylic acid particles, crosslinked poly (meth) acrylic acid ester particles, crosslinked polystyrene particles, and copolymerized crosslinked resin particles of (meth) acrylic acid ester and styrene. The separator for a non-aqueous secondary battery according to any one of <1> to <3>, which comprises at least one selected from the group.
<5> The separator for a non-aqueous secondary battery according to any one of <1> to <4>, wherein the heat-resistant binder resin contains a total aromatic polyamide.
<6> At least the inorganic particles selected from the group consisting of metal sulfate particles, metal hydroxide particles, metal oxide particles, metal carbonate particles, metal nitride particles, metal fluoride particles, and clay mineral particles. The separator for a non-aqueous secondary battery according to any one of <1> to <5>, which comprises one type.
<7> The non-aqueous secondary according to any one of <1> to <6>, wherein the volume ratio of the inorganic particles to the solid content of the heat-resistant porous layer is 5% by volume to 95% by volume. Battery separator.
<8> The separator for a non-aqueous secondary battery according to any one of <1> to <7>, wherein the heat-resistant porous layer has a porosity of 15% to 70%.
<9> The method according to any one of <1> to <8>, wherein the mass per unit area of the heat-resistant porous layer is 1.0 g / m ² to 30.0 g / m ² in total on both sides. Separator for non-aqueous secondary batteries.
<10> The positive electrode, the negative electrode, and the separator for a non-aqueous secondary battery according to any one of <1> to <9> arranged between the positive electrode and the negative electrode are provided, and the lithium ion is provided. A non-aqueous secondary battery that obtains electromotive force by doping and dedoping.

According to the present disclosure, it is a separator for a non-aqueous secondary battery provided with a heat-resistant porous layer on a porous base material, and has excellent heat resistance and the heat-resistant porous layer is not easily peeled off from the porous base material. Separator for water-based secondary battery is provided.

Hereinafter, embodiments of the present disclosure will be described. These explanations and examples are examples of embodiments and do not limit the scope of the embodiments.

The numerical range indicated by using "-" in the present disclosure indicates a range including the numerical values before and after "-" as the minimum value and the maximum value, respectively.
In the numerical range described stepwise in the present disclosure, the upper limit value or the lower limit value described in one numerical range may be replaced with the upper limit value or the lower limit value of the numerical range described in another stepwise description. .. Further, in the numerical range described in the present disclosure, the upper limit value or the lower limit value of the numerical range may be replaced with the value shown in the examples.

In the present disclosure, the term "process" is included in this term not only as an independent process but also as long as the intended purpose of the process is achieved even if it cannot be clearly distinguished from other processes.

When referring to the amount of each component in the composition in the present disclosure, if a plurality of substances corresponding to each component are present in the composition, unless otherwise specified, the plurality of species present in the composition. It means the total amount of substances.

In the present disclosure, a plurality of types of particles corresponding to each component may be contained. When a plurality of particles corresponding to each component are present in the composition, the particle size of each component means a value for a mixture of the plurality of particles present in the composition, unless otherwise specified.

In the present disclosure, MD (Machine Direction) means a long direction in a porous base material and a separator manufactured in a long shape, and TD (transverse direction) means a plane direction of a porous base material and a separator. Means the direction orthogonal to the MD. In the present disclosure, TD is also referred to as "width direction".

In the present disclosure, when the stacking relationship of each layer constituting the separator is expressed by "upper" and "lower", the layer closer to the porous substrate is referred to as "lower", and the layer is referred to as "lower" with respect to the porous substrate. The distant layer is called "upper".

<Separator for non-water-based secondary batteries>
The separators for non-aqueous secondary batteries of the present disclosure (also referred to as "separators" in the present disclosure) are a porous substrate, heat-resistant binder resin, inorganic particles and inorganic particles provided on one or both sides of the porous substrate. It is provided with a heat-resistant porous layer containing heat-resistant resin particles.

In the separator of the present disclosure, the average primary particle size of the inorganic particles contained in the heat-resistant porous layer is 0.01 μm to 3 μm, and the average primary particle size of the heat-resistant resin particles contained in the heat-resistant porous layer is 0. It is 6 μm to 10 μm.

In the present disclosure, the heat-resistant resin refers to a resin having a melting point of 200 ° C. or higher, or a resin having no melting point and a decomposition temperature of 200 ° C. or higher. That is, the heat-resistant resin in the present disclosure is a resin that does not melt or decompose in a temperature range of less than 200 ° C.
In the present disclosure, the heat-resistant binder resin contained in the heat-resistant porous layer refers to a heat-resistant resin, which binds inorganic particles and / or heat-resistant resin particles. In the present disclosure, the heat-resistant resin particles contained in the heat-resistant porous layer refer to particles made of heat-resistant resin.

The average primary particle size of the inorganic particles contained in the heat-resistant porous layer is 3 μm or less from the viewpoint of enhancing the heat resistance of the heat-resistant porous layer. When the average primary particle size of the inorganic particles is 3 μm or less, the heat resistance of the heat-resistant porous layer is enhanced. The mechanism is that the smaller particle size of the inorganic particles increases the surface area (ie, specific surface area) of the inorganic particles per unit volume, and thus increases the contact points between the inorganic particles and the heat resistant binder resin. Therefore, it is presumed that the heat-resistant porous layer is less likely to break when exposed to high temperatures. Further, it is presumed that the heat-resistant porous layer is less likely to break when exposed to a high temperature due to the connection of a large number of inorganic particles having a small particle size.
The average primary particle size of the inorganic particles contained in the heat-resistant porous layer is 0.01 μm or more from the viewpoint of suppressing aggregation of the inorganic particles and forming a highly uniform heat-resistant porous layer.

The heat-resistant porous layer having an average primary particle size of the inorganic particles of 3 μm or less has excellent heat resistance, but since the particle size of the inorganic particles is relatively small, the surface of the heat-resistant porous layer tends to be flat, and the heat resistance is high. The porous layer is easily peeled off from the porous substrate. In order to suppress this phenomenon, a part of the filler of the heat-resistant porous layer is made into heat-resistant resin particles. The average primary particle size of the heat-resistant resin particles contained in the heat-resistant porous layer is such that appropriate irregularities are formed on the interface between the heat-resistant porous layer and the porous base material due to the heat-resistant resin particles, and the heat-resistant porous layer has appropriate irregularities with respect to the porous base material. It is 0.6 μm or more from the viewpoint of enhancing the adhesiveness of the heat-resistant porous layer and making it difficult for the heat-resistant porous layer to peel off from the porous substrate.
The average primary particle size of the heat-resistant resin particles contained in the heat-resistant porous layer is 10 μm or less from the viewpoint of enhancing the heat resistance of the heat-resistant porous layer. When the average primary particle size of the heat-resistant resin particles is 10 μm or less, the surface area (that is, the specific surface area) of the heat-resistant resin particles per unit volume becomes large, and therefore, the heat-resistant resin particles, the inorganic particles, and the heat-resistant binder resin Since the number of contact points with the particles increases, it is presumed that the heat-resistant porous layer is less likely to break when exposed to high temperatures. Further, from the viewpoint of making it difficult for the heat-resistant porous layer to be peeled off from the porous substrate, the average primary particle size of the heat-resistant resin particles is 10 μm or less.

Due to the synergistic action of each of the above configurations, the separator of the present disclosure has excellent heat resistance, and the heat-resistant porous layer is not easily peeled off from the porous substrate.

Hereinafter, the details of the porous substrate and the heat-resistant porous layer included in the separator of the present disclosure will be described.

[Porous substrate]
In the present disclosure, the porous base material means a base material having pores or voids inside. As such a base material, a microporous film; a porous sheet made of a fibrous material such as a non-woven fabric or paper; a composite porous structure in which one or more other porous layers are laminated on the microporous film or the porous sheet. Quality sheet; etc. In the present disclosure, a microporous membrane is preferable from the viewpoint of thinning and strength of the separator. The microporous membrane means a membrane having a large number of micropores inside and having a structure in which the micropores are connected so that a gas or a liquid can pass from one surface to the other.

As the material of the porous base material, a material having electrical insulation is preferable, and either an organic material or an inorganic material may be used.

The porous substrate preferably contains a thermoplastic resin in order to impart a shutdown function to the porous substrate. The shutdown function is a function of blocking the movement of ions by melting the constituent materials and closing the pores of the porous substrate when the battery temperature rises to prevent thermal runaway of the battery. As the thermoplastic resin, a thermoplastic resin having a melting point of less than 200 ° C. is preferable. Examples of the thermoplastic resin include polyesters such as polyethylene terephthalate; polyolefins such as polyethylene and polypropylene; and the like, among which polyolefins are preferable.

As the porous substrate, a microporous membrane containing polyolefin (referred to as “polyolefin microporous membrane” in the present disclosure) is preferable. Examples of the polyolefin microporous membrane include a polyolefin microporous membrane applied to a conventional battery separator, and it is desirable to select one having sufficient mechanical properties and ion permeability from these.

The polyolefin microporous membrane is preferably a microporous membrane containing polyethylene from the viewpoint of exhibiting a shutdown function, and the polyethylene content is preferably 95% by mass or more with respect to the total mass of the polyolefin microporous membrane.

The microporous polyolefin membrane is preferably a microporous polypropylene film from the viewpoint of having heat resistance that does not easily break when exposed to high temperatures.

The microporous polyolefin membrane is preferably a microporous polyolefin membrane containing polyethylene and polypropylene from the viewpoint of having a shutdown function and heat resistance that does not easily break when exposed to high temperatures. Examples of the polyolefin microporous membrane containing polyethylene and polypropylene include a microporous membrane in which polyethylene and polypropylene are mixed in one layer. From the viewpoint of achieving both a shutdown function and heat resistance, the microporous membrane preferably contains 95% by mass or more of polyethylene and 5% by mass or less of polypropylene. Further, from the viewpoint of achieving both a shutdown function and heat resistance, a polyolefin microporous membrane having a laminated structure of two or more layers, at least one layer containing polyethylene and at least one layer containing polypropylene is also preferable.

As the polyolefin contained in the polyolefin microporous membrane, a polyolefin having a weight average molecular weight (Mw) of 100,000 to 5,000,000 is preferable. When the Mw of the polyolefin is 100,000 or more, sufficient mechanical properties can be imparted to the microporous membrane. On the other hand, when the Mw of the polyolefin is 5 million or less, the shutdown characteristics of the microporous membrane are good, and the microporous membrane can be easily formed.

As a method for producing a microporous polyolefin film, a molten polyolefin resin is extruded from a T-die to form a sheet, which is crystallized and then stretched, and then heat-treated to form a microporous film: liquid paraffin or the like. Examples thereof include a method in which a polyolefin resin melted together with a plasticizer is extruded from a T-die, cooled to form a sheet, stretched, and then the plasticizer is extracted and heat-treated to form a microporous film.

Examples of the porous sheet made of a fibrous material include polyesters such as polyethylene terephthalate; polyolefins such as polyethylene and polypropylene; heat resistant materials such as total aromatic polyamide, polyamideimide, polyimide, polyethersulfone, polysulfone, polyetherketone, and polyetherimide. Examples thereof include porous sheets such as non-woven fabrics and paper made of fibrous materials such as sex resin; cellulose;

Examples of the composite porous sheet include a sheet in which a functional layer is laminated on a porous sheet made of a microporous membrane or a fibrous material. Such a composite porous sheet is preferable from the viewpoint that further functions can be added by the functional layer. Examples of the functional layer include a porous layer made of a heat-resistant resin and a porous layer made of a heat-resistant resin and an inorganic filler from the viewpoint of imparting heat resistance. Examples of the heat-resistant resin include one or more heat-resistant resins selected from total aromatic polyamide, polyamideimide, polyimide, polyethersulfone, polysulfone, polyetherketone and polyetherimide. Examples of the inorganic filler include metal oxides such as alumina; metal hydroxides such as magnesium hydroxide; and the like. As a method of compositing, a method of applying a functional layer to a microporous membrane or a porous sheet, a method of joining a microporous membrane or a porous sheet and a functional layer with an adhesive, a method of joining a microporous membrane or a porous sheet with an adhesive, and the like. Examples thereof include a method of thermocompression bonding with the functional layer.

The surface of the porous substrate is subjected to various surface treatments in order to improve the wettability with the coating liquid for forming the heat-resistant porous layer, as long as the properties of the porous substrate are not impaired. You may. Examples of the surface treatment include corona treatment, plasma treatment, flame treatment, ultraviolet irradiation treatment and the like.

[Characteristics of porous substrate]
The thickness of the porous substrate is preferably 18 μm or less, more preferably 15 μm or less, further preferably 12 μm or less from the viewpoint of increasing the energy density of the battery, and 4 μm or more from the viewpoint of the manufacturing yield of the separator and the manufacturing yield of the battery. Is preferable, 6 μm or more is more preferable, and 8 μm or more is further preferable.

The galley value (JIS P8117: 2009) of the porous substrate is preferably 40 seconds / 100 mL to 300 seconds / 100 mL, preferably 50 seconds / 100 mL to 200 seconds / from the viewpoint of the balance between ion permeability and suppression of short circuit of the battery. 100 mL is more preferable.

The porosity of the porous substrate is preferably 20% to 60% from the viewpoint of obtaining appropriate film resistance and shutdown function. The porosity ε (%) of the porous substrate is calculated by the following formula.
ε = {1-Ws / (ds · t)} × 100
Here, Ws is the basis weight of the porous substrate (g / m ² ), ds is the true density of the porous substrate (g / cm ³ ), and t is the thickness of the porous substrate (μm). Metsuke is the mass per unit area.

The average pore size of the porous substrate is preferably 20 nm to 100 nm from the viewpoint of ion permeability or suppression of short circuit of the battery. The average pore size of the porous substrate is measured according to ASTM E1294-89 using a palm poromometer (CFP-1500-A manufactured by PMI).

The puncture strength of the porous substrate is preferably 150 gf or more, more preferably 200 gf or more, from the viewpoint of the manufacturing yield of the separator and the manufacturing yield of the battery. The piercing strength of the porous substrate is measured by performing a piercing test using a KES-G5 handy compression tester manufactured by Kato Tech Co., Ltd. under the conditions of a radius of curvature of the needle tip of 0.5 mm and a piercing speed of 2 mm / sec. Refers to strength (gf).

[Heat-resistant porous layer]
The heat-resistant porous layer has a large number of micropores inside and has a structure in which the micropores are connected, and is a layer through which a gas or a liquid can pass from one surface to the other.

The heat-resistant porous layer may be on only one side of the porous base material, or may be on both sides of the porous base material. When the heat-resistant porous layer is provided on both sides of the porous substrate, the heat resistance of the separator is more excellent, and the safety of the battery can be further enhanced. In addition, curl is less likely to occur on the separator, and it is excellent in handleability during battery manufacturing. When the heat-resistant porous layer is present on only one side of the porous substrate, the ion permeability of the separator is more excellent. In addition, the thickness of the entire separator can be suppressed, and a battery having a higher energy density can be manufactured.

The heat-resistant porous layer contains at least a heat-resistant binder resin, inorganic particles, and heat-resistant resin particles. The heat-resistant porous layer may contain other components other than these.

-Heat-resistant binder resin-
The type of the heat-resistant binder resin is not limited as long as it is a resin that does not melt or decompose in a temperature range of less than 200 ° C. Examples of the heat-resistant binder resin include total aromatic polyamide, polyamideimide, poly-N-vinylacetamide, polyacrylamide, copolymerized polyether polyamide, polyimide, and polyetherimide. As the heat-resistant binder resin, one type may be used alone, or two or more types may be used in combination.

Among the heat-resistant binder resins, all-aromatic polyamide is preferable from the viewpoint of durability. The total aromatic polyamide means a polyamide in which the main chain is composed only of a benzene ring and an amide bond. However, a small amount of aliphatic monomer may be copolymerized with the total aromatic polyamide. Total aromatic polyamides are also called aramids.

The total aromatic polyamide may be a meta type or a para type. Among all aromatic polyamides, meta-type total aromatic polyamides are preferable from the viewpoint of easily forming a porous layer and having excellent oxidation-reduction resistance in an electrode reaction. Specifically, the total aromatic polyamide is preferably polymetaphenylene isophthalamide or polyparaphenylene terephthalamide, and more preferably polymethaphenylene isophthalamide.

When the heat-resistant porous layer is on both sides of the porous substrate, the type of the heat-resistant binder resin contained in one of the heat-resistant porous layers and the type of the heat-resistant binder resin contained in the other heat-resistant porous layer. May be the same or different.

The content of the heat-resistant binder resin contained in the heat-resistant porous layer is preferably 85% by mass to 100% by mass, preferably 90% by mass to 100% by mass, based on the total amount of the binder resin contained in the heat-resistant porous layer. Is more preferable, and 95% by mass to 100% by mass is further preferable.

The volume ratio of the heat-resistant binder resin to the solid content of the heat-resistant porous layer is preferably 5% by volume or more, more preferably 10% by volume or more, from the viewpoint that the heat-resistant porous layer does not easily peel off from the porous substrate. 15% by volume or more is more preferable. The volume ratio of the heat-resistant binder resin to the solid content of the heat-resistant porous layer is preferably 95% by volume or less, preferably 80% by volume or less, from the viewpoint of relatively increasing the volume ratio of the inorganic particles and improving the heat resistance of the separator. Is more preferable, and 70% by volume or less is further preferable.

-Other resins-
The heat-resistant porous layer may contain a binder resin other than the heat-resistant binder resin, that is, a binder resin that melts or decomposes in a temperature range of less than 200 ° C. Examples of other binder resins include polyvinylidene fluoride-based resins, acrylic resins, fluororubbers, styrene-butadiene copolymers, homopolymers or copolymers of vinylnitrile compounds (acrylonitrile, methacrylonitrile, etc.), and the like. Examples thereof include carboxymethyl cellulose, hydroxyalkyl cellulose, polyvinyl alcohol, polyvinyl butyral, polyvinylpyrrolidone, polyether (polyethylene oxide, polypropylene oxide, etc.), polysulfone, polyketone, polyetherketone, polyethersulfone, and mixtures thereof.

The type and content of the other binder resin can be selected from the viewpoints of improving the adhesiveness of the heat-resistant porous layer to the electrode, the function of binding inorganic particles, and the moldability of the heat-resistant porous layer.

The content of the other binder resin contained in the heat-resistant porous layer is preferably 0% by mass to 15% by mass, preferably 0% by mass to 10% by mass, based on the total amount of the binder resin contained in the heat-resistant porous layer. Is more preferable, and 0% by mass to 5% by mass is further preferable.

-Inorganic particles-
Examples of the inorganic particles include metal sulfate particles such as barium sulfate, strontium sulfate, calcium sulfate, calcium sulfate dihydrate, myoban stone, and jarosite; magnesium hydroxide, aluminum hydroxide, calcium hydroxide, and chromium hydroxide. , Metal hydroxide particles such as zirconium hydroxide, cerium hydroxide, nickel hydroxide, boron hydroxide; magnesium oxide, alumina (Al ₂ O ₃ ), boehmite (alumina monohydrate), titania (TiO ₂ ), Metal oxide particles such as silica (SiO ₂ ), zirconia (ZrO ₂ ), barium titanate (BaTIO ₃ ), zinc oxide; metal carbonate particles such as calcium carbonate and magnesium carbonate; magnesium nitride, aluminum nitride, calcium nitride, Examples thereof include metal nitride particles such as titanium nitride; metal fluoride particles such as magnesium fluoride and calcium fluoride; clay mineral particles such as calcium silicate, calcium phosphate, apatite and talc; and the like. The inorganic particles may be inorganic particles whose surface is modified with a silane coupling agent or the like. As the inorganic particles, one kind may be used alone, or two or more kinds may be used in combination.

As the inorganic particles, barium sulfate particles are preferable from the viewpoint that the electrolytic solution or the electrolyte is less likely to be decomposed and therefore gas is less likely to be generated. As the inorganic particles, magnesium hydroxide particles are preferable from the viewpoint of excellent heat resistance.

When the heat-resistant porous layer is on both sides of the porous substrate, the type of inorganic particles contained in one heat-resistant porous layer and the type of inorganic particles contained in the other heat-resistant porous layer are the same. But it can be very different.

The particle shape of the inorganic particles is not limited, and may be spherical, plate-shaped, needle-shaped, or indefinite. The inorganic particles are preferably spherical or plate-shaped particles from the viewpoint of suppressing short circuits in the battery or forming a highly uniform heat-resistant porous layer.

The average primary particle size of the inorganic particles contained in the heat-resistant porous layer is 3 μm or less, preferably 2.8 μm or less, and more preferably 2.5 μm or less, from the viewpoint of enhancing the heat resistance of the heat-resistant porous layer. The average primary particle size of the inorganic particles contained in the heat-resistant porous layer is 0.01 μm or more, 0.05 μm or more, from the viewpoint of suppressing aggregation of the inorganic particles and forming a highly uniform heat-resistant porous layer. The above is preferable, and 0.1 μm or more is more preferable.

The average primary particle size of the inorganic particles is determined by measuring the major axis of 100 randomly selected inorganic particles in observation with a scanning electron microscope (SEM) and averaging the major axis of 100 particles. The sample to be used for SEM observation is an inorganic particle which is a material for forming the heat-resistant porous layer, or an inorganic particle taken out from the heat-resistant porous layer of the separator.
There is no limitation on the method of extracting the inorganic particles from the heat-resistant porous layer of the separator. In this method, for example, the heat-resistant porous layer peeled off from the separator is immersed in an organic solvent that dissolves the resin, the resin is dissolved with the organic solvent, and the inorganic particles are taken out; the heat-resistant porous layer peeled off from the separator is obtained. A method of removing the resin by heating to about 800 ° C. and taking out the inorganic particles; etc.

When the heat-resistant porous layer is on both sides of the porous substrate, the average primary particle size of the inorganic particles contained in one heat-resistant porous layer and the average primary particle size of the inorganic particles contained in the other heat-resistant porous layer. The particle size may be the same or different.

The volume ratio of the inorganic particles to the solid content of the heat-resistant porous layer is preferably 5% by volume or more, more preferably 10% by volume or more, still more preferably 15% by volume or more, from the viewpoint of heat resistance of the separator. The volume ratio of the inorganic particles to the solid content of the heat-resistant porous layer is preferably 95% by volume or less, more preferably 90% by volume or less, and more preferably 85 volumes, from the viewpoint that the heat-resistant porous layer does not easily peel off from the porous substrate. % Or less is more preferable.

The volume ratio Va (volume%) of the inorganic particles to the solid content of the heat-resistant porous layer is calculated by the following formula.
Va = {(Xa / Da) / (Xa / Da + Xb / Db + Xc / Dc + ... + Xn / Dn)} × 100
Here, among the constituent materials of the heat-resistant porous layer, the inorganic particles are a, the other constituent materials are b, c, ..., N, and each constituent material contained in the heat-resistant porous layer having a predetermined area. The masses of are Xa, Xb, Xc, ..., Xn (g), and the true densities of the constituent materials are Da, Db, Dc, ..., Dn (g / cm ³ ).
Xa or the like substituted into the above formula is the mass (g) of the constituent material used for forming the heat-resistant porous layer having a predetermined area, or the mass (g) of the constituent material taken out from the heat-resistant porous layer having a predetermined area. ).
Da etc. substituted in the above formula is the true density (g / cm 3) of the constituent material used to form the heat-resistant porous layer, or the true density (g / cm ³ ) of the constituent material taken out from the heat-resistant porous layer. cm ³ ).

When the heat-resistant porous layer is on both sides of the porous substrate, the volume ratio of the inorganic particles in the solid content of one heat-resistant porous layer and the inorganic particles in the solid content of the other heat-resistant porous layer. The volume ratio may be the same or different.

-Heat-resistant resin particles-
Examples of the heat-resistant resin particles include crosslinked poly (meth) acrylic acid particles, crosslinked poly (meth) acrylic acid ester particles, crosslinked polystyrene particles, copolymerized crosslinked resin particles of (meth) acrylic acid ester and styrene, and melamine resin. Examples thereof include particles, nylon particles, polyimide particles, polyamideimide particles, phenol resin particles, polytetrafluoroethylene particles, fluororesin particles, silicone resin particles and the like. These heat-resistant resin particles may be used alone or in combination of two or more. In the present disclosure, the notation "(meth) acrylic" means that it may be either "acrylic" or "methacrylic".

The heat-resistant resin particles include crosslinked poly (meth) acrylic acid particles, crosslinked poly (meth) acrylic acid ester particles, and crosslinked polystyrene particles from the viewpoint of stability with respect to an electrolytic solution and compatibility with inorganic particles and electrodes. And at least one selected from the group consisting of copolymerized crosslinked resin particles of (meth) acrylic acid ester and styrene is preferable.

Examples of the (meth) acrylic acid ester contained in the resin constituting the heat-resistant resin particles include methyl (meth) acrylic acid, ethyl (meth) acrylic acid, isopropyl (meth) acrylic acid, and n-butyl (meth) acrylic acid. Isobutyl (meth) acrylate, n-hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, cyclohexyl (meth) acrylate, (meth) acrylic Dicyclopentanyl acid, isobornyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 2- (diethylamino) (meth) acrylate ) Ethyl, methoxypolyethylene glycol (meth) acrylate and the like.

As the (meth) acrylic acid ester contained in the resin constituting the heat-resistant resin particles, a (meth) acrylic acid alkyl ester is preferable. The alkyl group of the (meth) acrylic acid alkyl ester preferably has 1 to 6 carbon atoms, and more preferably 1 to 4 carbon atoms.
The (meth) acrylic acid alkyl ester contained in the resin constituting the heat-resistant resin particles is preferably methyl (meth) acrylate, more preferably methyl methacrylate, and the crosslinked poly (meth) acrylic acid ester particles are crosslinked. Methyl poly (meth) acrylate particles are preferred, and crosslinked polymethyl methacrylate particles are more preferred.

Examples of the styrene-based monomer contained in the resin constituting the heat-resistant resin particles include styrene, metachlorostyrene, parachlorostyrene, parafluorostyrene, paramethoxystyrene, meta-tert-butoxystyrene, and para-tert-. Examples thereof include butoxystyrene, rosevinyl benzoic acid, paramethyl-α-methylstyrene and the like, and styrene is preferable.

Examples of the resin cross-linking agent include organic peroxides such as diacyl peroxide, alkyl peroxy ester, peroxy dicarbonate, monoperoxy carbonate, peroxyketal, dialkyl peroxide, hydroperoxide, and ketone peroxide. ..

Commercially available heat-resistant resin particles include the product name "Crosslinked acrylic monodisperse particle MX series" (manufactured by Soken Kagaku), the product name "Eposter MA series" (manufactured by Nippon Shokubai), and the product name "Techpolymer SSX series" (manufactured by Nippon Shokubai). Sekisui Plastics) and the like.

When the heat-resistant porous layer is on both sides of the porous substrate, the type of heat-resistant resin particles contained in one heat-resistant porous layer and the type of heat-resistant resin particles contained in the other heat-resistant porous layer. May be the same or different.

The average primary particle size of the heat-resistant resin particles contained in the heat-resistant porous layer is 10 μm or less, preferably 8 μm or less, and more preferably 6 μm or less, from the viewpoint of enhancing the heat resistance of the heat-resistant porous layer. The average primary particle size of the heat-resistant resin particles contained in the heat-resistant porous layer is from the viewpoint of enhancing the adhesion of the heat-resistant porous layer to the porous substrate and making it difficult for the heat-resistant porous layer to peel off from the porous substrate. Therefore, it is 0.6 μm or more, preferably 0.8 μm or more, and more preferably 1.0 μm or more.

The average primary particle size of the heat-resistant resin particles is determined by measuring the major axis of 100 heat-resistant resin particles randomly selected by observation with a scanning electron microscope (SEM) and averaging the major axis of 100 particles. The sample to be used for SEM observation is heat-resistant resin particles which are materials for forming the heat-resistant porous layer, or heat-resistant resin particles taken out from the heat-resistant porous layer of the separator.
There is no limitation on the method of extracting the heat-resistant resin particles from the heat-resistant porous layer of the separator. The method is, for example, a method of immersing the heat-resistant porous layer peeled off from the separator in an organic solvent that dissolves the binder resin, dissolving the binder resin with the organic solvent, and taking out the heat-resistant resin particles.

When the heat-resistant porous layer is on both sides of the porous substrate, the average primary particle size of the heat-resistant resin particles contained in one heat-resistant porous layer and the heat-resistant resin contained in the other heat-resistant porous layer. The average primary particle size of the particles may be the same or different.

The volume ratio of the heat-resistant resin particles to the solid content of the heat-resistant porous layer is preferably 1% by volume or more, more preferably 5% by volume or more, from the viewpoint that the heat-resistant porous layer does not easily peel off from the porous substrate. 8% by volume or more is more preferable. The volume ratio of the heat-resistant resin particles to the solid content of the heat-resistant porous layer is preferably 40% by volume or less, preferably 30% by volume or less, from the viewpoint of increasing the volume ratio of the inorganic particles and improving the heat resistance of the separator. Is more preferable, and 25% by volume or less is further preferable.

The volume ratio Vb (volume%) of the heat-resistant resin particles to the solid content of the heat-resistant porous layer is calculated by the following formula.
Vb = {(Xb / Db) / (Xa / Da + Xb / Db + Xc / Dc + ... + Xn / Dn)} × 100
Here, among the constituent materials of the heat-resistant porous layer, the heat-resistant resin particles are b, and the other constituent materials are a, c, ..., N, which are contained in the heat-resistant porous layer having a predetermined area. The masses of the constituent materials are Xa, Xb, Xc, ..., Xn (g), and the true densities of the constituent materials are Da, Db, Dc, ..., Dn (g / cm ³ ).
Xa or the like substituted into the above formula is the mass (g) of the constituent material used for forming the heat-resistant porous layer having a predetermined area, or the mass (g) of the constituent material taken out from the heat-resistant porous layer having a predetermined area. ).
Da etc. substituted in the above formula is the true density (g / cm 3) of the constituent material used to form the heat-resistant porous layer, or the true density (g / cm ³ ) of the constituent material taken out from the heat-resistant porous layer. cm ³ ).

When the heat-resistant porous layer is on both sides of the porous substrate, the volume ratio of the heat-resistant resin particles to the solid content of one heat-resistant porous layer and the heat resistance to the solid content of the other heat-resistant porous layer. The volume ratio of the sex resin particles may be the same or different.

The total volume ratio of the inorganic particles and the heat-resistant resin particles to the solid content of the heat-resistant porous layer is preferably 95% by volume or less, preferably 90% by volume, from the viewpoint that the heat-resistant porous layer does not easily peel off from the porous substrate. The following is more preferable, and 85% by volume or less is further preferable. The total volume ratio of the inorganic particles and the heat-resistant resin particles to the solid content of the heat-resistant porous layer is preferably 5% by volume or more, more preferably 20% by volume or more, and more preferably 30% by volume from the viewpoint of heat resistance of the separator. The above is more preferable.

The ratio of the volume ratio of the inorganic particles to the volume ratio of the heat-resistant resin particles in the heat-resistant porous layer is preferably the volume ratio of the inorganic particles: the volume ratio of the heat-resistant resin particles = 99: 1 to 10:90, 95: 5 to 20:80 is more preferable, and 90:10 to 50:50 is even more preferable.

-Other ingredients-
The heat-resistant porous layer may contain other organic fillers other than the heat-resistant resin particles (that is, an organic filler that melts or decomposes in a temperature range of less than 200 ° C.). The heat-resistant porous layer may contain additives such as a dispersant such as a surfactant, a wetting agent, a defoaming agent, and a pH adjuster. The dispersant is added to the coating liquid for forming the heat-resistant porous layer for the purpose of improving dispersibility, coatability or storage stability. Wetting agents, defoaming agents, and pH adjusters are used in the coating liquid for forming a heat-resistant porous layer, for example, for the purpose of improving the compatibility with the porous base material, and for the purpose of air entrainment in the coating liquid. It is added for the purpose of suppressing or adjusting the pH.

[Characteristics of heat-resistant porous layer]
The thickness of the heat-resistant porous layer is preferably 0.5 μm or more on one side, more preferably 1.0 μm or more on one side, further preferably 1.5 μm or more on one side, and ion permeability from the viewpoint of heat resistance or handleability of the separator. From the viewpoint of the energy density of the battery, one side is preferably 8.0 μm or less, one side is more preferably 6.0 μm or less, and one side is more preferably 4.0 μm or less.

When the heat-resistant porous layer is on both sides of the porous substrate, the total thickness of the heat-resistant porous layer is preferably 1.0 μm or more, more preferably 2.0 μm or more, and more preferably 3.0 μm or more. Is more preferable, 16.0 μm or less is preferable, 12.0 μm or less is more preferable, and 8.0 μm or less is further preferable.

When the heat-resistant porous layer is on both sides of the porous substrate, the difference (μm) between the thickness of one heat-resistant porous layer and the thickness of the other heat-resistant porous layer is preferably smaller, and the total of both sides is total. It is preferably 20% or less of the thickness (μm).

The mass per unit area of the heat-resistant porous layer is the total of both sides from the viewpoint of heat resistance or handleability of the separator regardless of whether the heat-resistant porous layer is on one side or both sides of the porous base material. 1.0 g / m ² or more is preferable, 2.0 g / m ² or more is more preferable, 3.0 g / m ² or more is further preferable, and from the viewpoint of ion permeability and energy density of the battery, the total of both sides is 30. 0 g / m ² or less is preferable, 20.0 g / m ² or less is more preferable, and 10.0 g / m ² or less is further preferable.

When the heat-resistant porous layer is on both sides of the porous substrate, the difference between the mass per unit area of one heat-resistant porous layer and the mass per unit area of the other heat-resistant porous layer (g /). The smaller m ² ) is preferable from the viewpoint of suppressing curl of the separator or improving the cycle characteristics of the battery, and it is preferably 20% or less of the total amount (g / m ² ) of both sides.

From the viewpoint of ion permeability, the porosity of the heat-resistant porous layer is preferably 15% or more, more preferably 20% or more, further preferably 30% or more, and the heat resistance and mechanical strength of the heat-resistant porous layer. From the viewpoint of the above, 70% or less is preferable, 65% or less is more preferable, and 60% or less is further preferable. The porosity ε (%) of the heat-resistant porous layer is calculated by the following formula.
ε = {1- (Wa / da + Wb / db + Wc / dc + ... + Wn / dn) / t} × 100
Here, the constituent materials of the heat-resistant porous layer are a, b, c, ..., N, and the mass per unit area of each constituent material is Wa, Wb, Wc, ..., Wn (g / cm ² ). The true densities of each constituent material are da, db, dc, ..., Dn (g / cm ³ ), and the thickness of the heat-resistant porous layer is t (cm).

The average pore size of the heat-resistant porous layer is preferably 10 nm to 200 nm. When the average pore diameter is 10 nm or more, when the heat-resistant porous layer is impregnated with the electrolytic solution, the pores are less likely to be closed even if the resin contained in the heat-resistant porous layer swells. When the average pore diameter is 200 nm or less, the uniformity of ion transfer in the heat-resistant porous layer is high, and the cycle characteristics and load characteristics of the battery are excellent.

The average pore diameter (nm) of the heat-resistant porous layer is calculated by the following formula, assuming that all pores are columnar.
d = 4V / S
In the formula, d represents the average pore diameter (diameter) of the heat-resistant porous layer, V represents the pore volume per 1 m ² of the heat-resistant porous layer, and S represents the pore surface area per 1 m ² of the heat-resistant porous layer.
The pore volume V per 1 m ² of the heat-resistant porous layer is calculated from the porosity of the heat-resistant porous layer.
The pore surface area S per 1 m ² of the heat-resistant porous layer is determined by the following method.
First, the specific surface area (m ² / g) of the porous substrate and the specific surface area (m ² / g) of the separator are calculated from the amount of nitrogen gas adsorbed by applying the BET formula to the nitrogen gas adsorption method. These specific surface areas (m ² / g) are multiplied by each basis weight (g / m ² ) to calculate the pore surface area per 1 m ² of each. Then, the pore surface area per 1 m ² of the porous substrate is subtracted from the pore surface area per 1 m ² of the separator to calculate the pore surface area S per 1 m ² of the heat-resistant porous layer. Metsuke is the mass per unit area.

The peel strength between the porous substrate and the heat-resistant porous layer is preferably 0.30 N / 12 mm or more, more preferably 0.35 N / 12 mm or more, and more preferably 0.40 N, from the viewpoint of the adhesive strength of the separator to the electrode. / 12 mm or more is more preferable. From the above viewpoint, the higher the peel strength between the porous substrate and the heat-resistant porous layer, the more preferable, but the peel strength is usually 2.00 N / 12 mm or less. When the separator has a heat-resistant porous layer on both sides of the porous substrate, the peel strength between the porous substrate and the heat-resistant porous layer may be in the above range on both sides of the porous substrate. preferable.

The peel strength (N / 12 mm) between the porous substrate and the heat-resistant porous layer is determined by a T-shaped peel test in which the separator is peeled in the MD direction. The dimensions of the test piece are a rectangle with MD 70 mm and TD 12 mm, and the tensile speed of the T-shaped peeling test is 300 mm / min.

The heat-resistant porous layer forms appropriate irregularities due to the heat-resistant resin particles at the interface between the heat-resistant porous layer and the porous substrate, enhances the adhesion of the heat-resistant porous layer to the porous substrate, and is porous. From the viewpoint of making it difficult for the heat-resistant porous layer to peel off from the material substrate, it is preferable to satisfy the following formula (1).

Equation (1) 0.5 ≦ r / a ≦ 3
Here, in one heat-resistant porous layer, a is the thickness (μm) of the heat-resistant porous layer, and r is the average primary particle size of the heat-resistant resin particles contained in the heat-resistant porous layer (s). μm).

The above r / a is more preferably 0.6 or more, further preferably 0.7 or more, further preferably 2.5 or less, still more preferably 2 or less.

When the heat-resistant porous layer is provided on one side of the porous base material, it is preferable that the formula (1) is satisfied on that one side. When the heat-resistant porous layer is provided on both sides of the porous substrate, it is preferable that both sides satisfy the formula (1).

From the viewpoint of improving the slipperiness of the exposed surface of the heat-resistant porous layer and increasing the manufacturing efficiency of the battery, the heat-resistant porous layer preferably satisfies the formula (1). When the heat-resistant porous layer satisfies the formula (1), the friction coefficient of the exposed surface of the heat-resistant porous layer can be controlled in an appropriate range.

[Characteristics of separator]
The thickness of the separator is preferably 8 μm or more, more preferably 10 μm or more, further preferably 12 μm or more, preferably 25 μm or less, and more preferably 22 μm or less from the viewpoint of battery energy density. , 20 μm or less is more preferable.

The puncture strength of the separator is preferably 150 gf to 1000 gf, more preferably 200 gf to 600 gf, from the viewpoint of the mechanical strength of the separator or the short circuit resistance of the battery. The method for measuring the puncture strength of the separator is the same as the method for measuring the puncture strength of the porous substrate.

The porosity of the separator is preferably 30% to 70%, more preferably 35% to 65%, and 40% to 60% from the viewpoint of adhesiveness to the electrode, handleability of the separator, ion permeability or mechanical strength. Is more preferable.

The galley value of the separator (JIS P8117: 2009) is preferably 80 seconds / 100 mL to 400 seconds / 100 mL, more preferably 120 seconds / 100 mL to 300 seconds / 100 mL, from the viewpoint of the mechanical strength of the separator and the ion permeability.

The separator of the present disclosure may further have a layer other than the porous substrate and the heat-resistant porous layer. Examples of the other layer include an adhesive layer provided as an outermost layer mainly for the purpose of adhering to the electrode. The separator of the present disclosure may have an adhesive layer as an outermost layer on one side or both sides thereof.

[Manufacturing method of separator]
The separator of the present disclosure can be produced, for example, by forming a heat-resistant porous layer on a porous substrate by a wet coating method or a dry coating method. In the present disclosure, the wet coating method is a method of solidifying the coating layer in a coagulating liquid, and the dry coating method is a method of drying and solidifying the coating layer. An embodiment of the wet coating method will be described below.

In the wet coating method, a coating liquid containing heat-resistant binder resin, inorganic particles and heat-resistant resin particles is applied onto a porous substrate and immersed in a coagulation liquid to solidify the coating layer, and then the coagulation liquid is used. It is a method of performing salvage washing and drying.

The coating liquid for forming the heat-resistant porous layer is prepared by dissolving or dispersing the heat-resistant binder resin, the inorganic particles and the heat-resistant resin particles in a solvent. In the coating liquid, if necessary, other components other than the heat-resistant binder resin, the inorganic particles and the heat-resistant resin particles are dissolved or dispersed.

The solvent used for preparing the coating liquid includes a solvent that dissolves the heat-resistant binder resin (hereinafter, also referred to as “good solvent”). Examples of the good solvent include polar amide solvents such as N-methylpyrrolidone, dimethylacetamide and dimethylformamide.

The solvent used for preparing the coating liquid may contain a phase separation agent that induces phase separation from the viewpoint of forming a porous layer having a good porous structure. Therefore, the solvent used for preparing the coating liquid may be a mixed solvent of a good solvent and a phase separation agent. The phase separation agent is preferably mixed with a good solvent in an amount that can secure an appropriate viscosity for coating. Examples of the phase separation agent include water, methanol, ethanol, propyl alcohol, butyl alcohol, butane diol, ethylene glycol, propylene glycol, tripropylene glycol and the like.

When the solvent used for preparing the coating liquid is a mixed solvent of a good solvent and a phase separating agent, from the viewpoint of forming a good porous structure, the good solvent is contained in an amount of 60% by mass or more and the phase separating agent is contained in an amount of 5% by mass or more. A mixed solvent containing 40% by mass is preferable.

The resin concentration of the coating liquid is preferably 1% by mass to 20% by mass from the viewpoint of forming a good porous structure. The concentration of inorganic particles in the coating liquid is preferably 0.5% by mass to 50% by mass from the viewpoint of forming a good porous structure.

The coating liquid may contain a dispersant such as a surfactant, a wetting agent, an antifoaming agent, a pH adjusting agent and the like. These additives may remain in the heat-resistant porous layer as long as they are electrochemically stable in the range of use of the non-aqueous secondary battery and do not inhibit the reaction in the battery.

Examples of the means for applying the coating liquid to the porous substrate include a Meyer bar, a die coater, a reverse roll coater, a roll coater, a gravure coater and the like. When the heat-resistant porous layer is formed on both sides of the porous substrate, it is preferable to apply the coating liquid to the porous substrate at the same time on both sides from the viewpoint of productivity.

The solidification of the coating layer is performed by immersing the porous base material on which the coating layer is formed in a coagulating liquid and solidifying the resin while inducing phase separation in the coating layer. As a result, a laminated body composed of a porous base material and a heat-resistant porous layer is obtained.

The coagulation liquid generally contains a good solvent and a phase separation agent used for preparing the coating liquid, and water. It is preferable in terms of production that the mixing ratio of the good solvent and the phase separation agent is adjusted to the mixing ratio of the mixed solvent used for preparing the coating liquid. The content of water in the coagulation liquid is preferably 40% by mass to 90% by mass from the viewpoint of forming a porous structure and productivity. The temperature of the coagulant is, for example, 20 ° C to 50 ° C.

After the coating layer is solidified in the coagulation liquid, the laminate is withdrawn from the coagulation liquid and washed with water. The coagulant is removed from the laminate by washing with water. Further, by drying, water is removed from the laminate. The water washing is performed, for example, by transporting the laminated body in a water bath. Drying is performed, for example, by transporting the laminate in a high temperature environment, blowing air on the laminate, bringing the laminate into contact with a heat roll, and the like. The drying temperature is preferably 40 ° C to 80 ° C.

The separator of the present disclosure can also be manufactured by a dry coating method. The dry coating method is a method of forming a heat-resistant porous layer on a porous substrate by applying a coating liquid to a porous substrate and drying the coating layer to volatilize and remove a solvent. ..

The separator of the present disclosure can also be produced by producing a heat-resistant porous layer as an independent sheet, superimposing the heat-resistant porous layer on a porous substrate, and compounding the heat-resistant porous layer by thermocompression bonding or an adhesive. Examples of the method for producing the heat-resistant porous layer as an independent sheet include a method of forming the heat-resistant porous layer on the release sheet by applying the above-mentioned wet coating method or dry coating method.

<Non-water-based secondary battery>
The non-aqueous secondary battery of the present disclosure is a non-aqueous secondary battery that obtains an electromotive force by doping and dedoping lithium ions, and includes a positive electrode, a negative electrode, and a separator for the non-aqueous secondary battery of the present disclosure. Dope means occlusion, support, adsorption, or insertion, and means a phenomenon in which lithium ions enter the active material of an electrode such as a positive electrode.

The non-aqueous secondary battery of the present disclosure has, for example, a structure in which a battery element in which a negative electrode and a positive electrode face each other via a separator is enclosed in an exterior material together with an electrolytic solution. The non-aqueous secondary battery of the present disclosure is suitable for a non-aqueous electrolyte secondary battery, particularly a lithium ion secondary battery.

Hereinafter, morphological examples of the positive electrode, the negative electrode, the electrolytic solution, and the exterior material included in the non-aqueous secondary battery of the present disclosure will be described.

Examples of the embodiment of the positive electrode include a structure in which an active material layer containing a positive electrode active material and a binder resin is formed on a current collector. The active material layer may further contain a conductive additive. Examples of the positive electrode active material include lithium-containing transition metal oxides, specifically, LiCoO ₂ , LiNiO ₂ , LiMn _1/2 Ni _1/2 O ₂ , LiCo _1/3 Mn _1/3 Ni _{1 /.} Examples thereof include ₃ O ₂ , LiMn ₂ O ₄ , LiFePO ₄ , LiCo _1/2 Ni _1/2 O ₂ , LiAl _1/4 Ni _3/4 O ₂ . Examples of the binder resin include polyvinylidene fluoride-based resins and styrene-butadiene copolymers. Examples of the conductive auxiliary agent include carbon materials such as acetylene black, ketjen black, and graphite powder. Examples of the current collector include aluminum foil, titanium foil, stainless steel foil and the like having a thickness of 5 μm to 20 μm.

Examples of the embodiment of the negative electrode include a structure in which an active material layer containing a negative electrode active material and a binder resin is formed on a current collector. The active material layer may further contain a conductive additive. Examples of the negative electrode active material include materials capable of electrochemically occluding lithium ions, and specific examples thereof include carbon materials; alloys of silicon, tin, aluminum and the like with lithium; wood alloys; and the like. Examples of the binder resin include polyvinylidene fluoride-based resins and styrene-butadiene copolymers. Examples of the conductive auxiliary agent include carbon materials such as acetylene black, ketjen black, graphite powder, and ultrafine carbon fibers. Examples of the current collector include copper foil, nickel foil, stainless steel foil and the like having a thickness of 5 μm to 20 μm. Further, instead of the above-mentioned negative electrode, a metallic lithium foil may be used as the negative electrode.

The electrolytic solution is a solution in which a lithium salt is dissolved in a non-aqueous solvent. Examples of the lithium salt include LiPF ₆ , LiBF ₄ , LiClO ₄ , and the like. Examples of the non-aqueous solvent include cyclic carbonates such as ethylene carbonate, propylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, and vinylene carbonate; and chain carbonates such as dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, and fluorine-substituted products thereof; Cyclic esters such as γ-butyrolactone and γ-valerolactone; may be used alone or in combination. As the electrolytic solution, the cyclic carbonate and the chain carbonate are mixed at a mass ratio (cyclic carbonate: chain carbonate) of 20:80 to 40:60, and the lithium salt is in the range of 0.5 mol / L to 1.5 mol / L. A solution dissolved in is suitable.

Examples of the exterior material include metal cans and aluminum laminated film packs. The shape of the battery includes a square shape, a cylindrical shape, a coin shape, and the like, and the separator of the present disclosure is suitable for any shape.

In the non-aqueous secondary battery of the present disclosure, after manufacturing a laminated body in which the separator of the present disclosure is arranged between the positive electrode and the negative electrode, the laminated body is used, for example, any of the following (1) to (3). Can be manufactured by Hereinafter, performing a hot pressing process by impregnating a separator with an electrolytic solution is referred to as "wet heat pressing", and performing a hot pressing process without impregnating a separator with an electrolytic solution is referred to as "dry heat pressing".

(1) After heat-pressing (dry heat-pressing) the laminate to bond the electrode and the separator, it is housed in an exterior material (for example, an aluminum laminated film pack; the same applies hereinafter), and an electrolytic solution is injected therein to form an exterior. After the inside of the material is put into a vacuum state, the laminate is further heat-pressed (wet heat-pressed) from above the exterior material to bond the electrode and the separator and to seal the exterior material.

(2) The laminate is housed in the exterior material, an electrolytic solution is injected therein, the inside of the exterior material is evacuated, and then the laminate is hot-pressed (wet heat-pressed) from above the exterior material to form an electrode and a separator. Adhesion with and sealing of the exterior material.

(3) After heat-pressing (dry heat-pressing) the laminate to bond the electrode and the separator, it is housed in the exterior material, an electrolytic solution is injected into it, the inside of the exterior material is evacuated, and then the exterior material is used. Is sealed.

As the conditions for the wet heat press in the above manufacturing method, the press temperature is preferably 70 ° C. to 110 ° C., and the press pressure is preferably 0.5 MPa to 2 MPa. As the conditions for the dry heat press in the above manufacturing method, the press temperature is preferably 20 ° C to 100 ° C, and the press pressure is preferably 0.5 MPa to 9 MPa. The press time is preferably adjusted according to the press temperature and the press pressure, for example, in the range of 0.5 minutes to 60 minutes.

When manufacturing a laminate in which a separator is arranged between a positive electrode and a negative electrode, the method of arranging the separator between the positive electrode and the negative electrode is a method of laminating at least one layer of the positive electrode, the separator, and the negative electrode in this order (so-called). (Stack method) may be used, or a method in which a positive electrode, a separator, a negative electrode, and a separator are stacked in this order and wound in the length direction may be used.

Hereinafter, the separator and the non-aqueous secondary battery of the present disclosure will be described in more detail with reference to examples. The materials, amounts, ratios, treatment procedures, etc. shown in the following examples may be appropriately changed as long as they do not deviate from the gist of the present disclosure. Therefore, the scope of the separators and non-aqueous secondary batteries of the present disclosure should not be construed as limiting by the specific examples shown below.

<Measurement method, evaluation method>
The measurement methods and evaluation methods applied to the examples and comparative examples are as follows.

[Average primary particle size of inorganic particles]
Using inorganic particles before addition to the coating liquid for forming the heat-resistant porous layer as a sample, the major axis of 100 randomly selected particles was measured by observation with a scanning electron microscope (SEM), and the average thereof was measured. The value was calculated and used as the average primary particle size (μm) of the inorganic particles. The SEM magnification was 50,000 to 300,000 times.

[Average primary particle size of heat-resistant resin particles]
Using heat-resistant resin particles before addition to the coating liquid for forming the heat-resistant porous layer as a sample, the major axis of 100 randomly selected particles was measured by observation with a scanning electron microscope (SEM). The average value was calculated and used as the average primary particle size (μm) of the heat-resistant resin particles. The SEM magnification was 50,000 to 300,000 times.

[Contents of inorganic particles or heat-resistant resin particles]
Based on the amount and true density of the inorganic particles, heat-resistant resin particles, and heat-resistant binder resin used in the coating liquid for forming the heat-resistant porous layer, the volume ratio Va (volume%) of the inorganic particles is calculated by the following formula. And the volume ratio Vb (volume%) of the heat-resistant resin particles were determined.
Va = {(Xa / Da) / (Xa / Da + Xb / Db + Xc / Dc)} × 100
Vb = {(Xb / Db) / (Xa / Da + Xb / Db + Xc / Dc)} × 100
Here, the inorganic particles are a, the heat-resistant resin particles are b, the heat-resistant binder resin is c, and the amounts of the constituent materials used are Xa, Xb, and Xc (g). The true densities are Da, Db, and Dc (g / cm ³ ).

[Thickness of porous substrate and separator]
The thickness (μm) of the porous substrate and the separator was determined by measuring 20 points in a 10 cm square with a contact type thickness gauge (Mitutoyo Co., Ltd., LITEMACTIC VL-50S) and averaging them. A spherical measuring element with a radius of 10 mm (Mitutoyo Co., Ltd., super hard spherical surface measuring element φ10.5) was used as the measurement terminal, and the measurement was adjusted so that a load of 0.19N was applied during the measurement.

[Thickness of heat-resistant porous layer]
The thickness of the heat-resistant porous layer (total on both sides, μm) was determined by subtracting the thickness (μm) of the porous substrate from the thickness of the separator (μm).

[Mass of heat-resistant porous layer]
The separator was cut into 10 cm × 10 cm, the mass was measured, and the mass was divided by the area to obtain the basis weight (g / m ² ) of the separator. The porous base material used for producing the separator was cut into 10 cm × 10 cm, and the mass was measured, and the mass was divided by the area to obtain the basis weight (g / m ² ) of the porous base material. By subtracting the basis weight of the porous substrate from the basis weight of the separator, the mass per unit area of the heat-resistant porous layer (total on both sides, g / m ² ) was obtained.

[Porosity of porous substrate]
The porosity ε (%) of the porous substrate was calculated by the following formula.
ε = {1-Ws / (ds · t)} × 100
Here, Ws is the basis weight of the porous substrate (g / m ² ), ds is the true density of the porous substrate (g / cm ³ ), and t is the thickness of the porous substrate (μm).

[Porosity of heat-resistant porous layer]
The porosity ε (%) of the heat-resistant porous layer was calculated by the following formula.
ε = {1- (Wa / da + Wb / db + Wc / dc + ... + Wn / dn) / t} × 100
Here, the constituent materials of the heat-resistant porous layer are a, b, c, ..., N, and the mass per unit area of each constituent material is Wa, Wb, Wc, ..., Wn (g / cm ² ). The true densities of each constituent material are da, db, dc, ..., Dn (g / cm ³ ), and the thickness of the heat-resistant porous layer is t (cm).

[Gare value]
The Gale value (seconds / 100 mL) of the porous substrate and the separator was measured using a Gale type densometer (Toyo Seiki Co., Ltd., GB2C) according to JIS P8117: 2009.

[Peeling strength between the porous substrate and the heat-resistant porous layer]
A T-shaped peeling test was performed on the separator. Specifically, an adhesive tape (3M, # 550, 12 mm width) is attached to one surface of the separator (when the adhesive tape is attached, the length direction of the adhesive tape is matched with the MD of the separator), and the separator is adhered. Each tape was cut into a rectangle with MD 70 mm and TD 12 mm. The adhesive tape was slightly peeled off together with the heat-resistant porous layer directly underneath, and the two separated ends were gripped by Tencilon (Orientec, RTC-1210A) to perform a T-shaped peeling test. The adhesive tape is used as a support for peeling the heat-resistant porous layer from the porous substrate. The tensile speed of the T-shaped peeling test was set to 300 mm / min, and a load (N / 12 mm) from 10 mm to 40 mm was collected at intervals of 0.4 mm after the start of measurement, and the average value was calculated. Further, the load (N / 12 mm) of 10 test pieces was averaged.

[Spot heating]
The separator was cut into a square having an MD of 50 mm and a TD of 50 mm, and used as a test piece. The test piece was placed on a horizontal table, and a soldering iron having a tip diameter of 2 mm was heated to bring the tip temperature to 260 ° C., and the tip of the soldering iron was brought into point contact with the separator surface for 60 seconds. The area of the holes (mm ² ) formed in the separator by the point contact was measured, and the areas of the holes of 10 test pieces were averaged. The higher the heat resistance of the separator, the smaller the area of holes formed in the separator.

[Static friction coefficient, dynamic friction coefficient]
The coefficient of static friction and the coefficient of dynamic friction on the surface of the separator were measured using a Haydon surface tester (Type: 14FW manufactured by Shinto Kagaku). A cylindrical terminal (length 2 cm, diameter 2 cm) was used as the measurement terminal, and the cylinder was attached so that the length direction was perpendicular to the moving direction. The load cell was set to 9.8 N, the weight used to adjust the balance of the main body was set to 50 gf, the moving speed of the sample table was set to 100 mm / min, and the moving distance was set to 1 mm. The separator was cut into a rectangle having an MD of 40 mm and a TD of 100 mm as a test piece, and set on a sample table so that the long side direction was the moving direction. The average values of the static friction coefficient and the dynamic friction coefficient when the measurement was performed at N = 5 were obtained.

<Making a separator>
[Example 1]
As a material for the heat-resistant porous layer, a meta-type total aromatic polyamide, barium sulfate particles, and crosslinked polymethyl methacrylate particles (crosslinked PMMA particles) were prepared. These physical properties are as shown in Table 1.

The meta-type total aromatic polyamide is dissolved in dimethylacetamide (DMAc) so that the resin concentration is 6.5% by mass, and barium sulfate particles and crosslinked PMMA particles are further mixed by stirring to prepare the coating liquid (1). Obtained.

The coating liquid (1) was applied to one side of a polyethylene microporous membrane (thickness 10 μm, porosity 48%, galley value 72 seconds / 100 mL) using a Meyer bar. This was immersed in a coagulating liquid (DMAc: water = 50: 50 [mass ratio], liquid temperature 40 ° C.) to solidify the coating layer, and then washed in a water washing tank having a water temperature of 40 ° C. and dried. In this way, a separator having a heat-resistant porous layer formed on one side of the polyethylene microporous membrane was obtained.

[Examples 2 to 17, Comparative Examples 1 to 6]
In the same manner as in Example 1, however, the material, composition, coated surface or coated amount of the heat-resistant porous layer was changed to the specifications shown in Table 1 to prepare each separator. When the coating liquid was applied to both sides of the polyethylene microporous membrane, the coating was applied so that the amount of coating on the front and back surfaces of the polyethylene microporous membrane was equal.

Tables 1 and 2 show the compositions, physical properties, and evaluation results of each of the separators of Examples 1 to 17 and Comparative Examples 1 to 6. The meta-type total aromatic polyamides used to form the heat-resistant porous layer are listed as "aramid" in Table 1.

Claims (10)

Porous substrate and
A heat-resistant porous layer provided on one or both sides of the porous substrate and containing a heat-resistant binder resin, inorganic particles and heat-resistant resin particles is provided.
The average primary particle size of the inorganic particles contained in the heat-resistant porous layer is 0.01 μm to 3 μm.
The average primary particle size of the heat-resistant resin particles contained in the heat-resistant porous layer is 0.6 μm to 10 μm.
Separator for non-aqueous secondary batteries. When the heat-resistant porous layer is provided on one side of the porous base material, the following formula (1) is satisfied on one side.
The separator for a non-aqueous secondary battery according to claim 1, wherein when the heat-resistant porous layer is provided on both surfaces of the porous substrate, the following formula (1) is satisfied on both surfaces.
Equation (1) 0.5 ≦ r / a ≦ 3
Here, in one heat-resistant porous layer, a is the thickness (μm) of the heat-resistant porous layer, and r is the average primary particle size of the heat-resistant resin particles contained in the heat-resistant porous layer (s). μm). The separator for a non-aqueous secondary battery according to claim 1 or 2, wherein the volume ratio of the heat-resistant resin particles to the solid content of the heat-resistant porous layer is 1% by volume to 40% by volume. The heat-resistant resin particles consist of a group consisting of crosslinked poly (meth) acrylic acid particles, crosslinked poly (meth) acrylic acid ester particles, crosslinked polystyrene particles, and copolymerized crosslinked resin particles of (meth) acrylic acid ester and styrene. The separator for a non-aqueous secondary battery according to any one of claims 1 to 3, which comprises at least one selected. The separator for a non-aqueous secondary battery according to any one of claims 1 to 4, wherein the heat-resistant binder resin contains a total aromatic polyamide. The inorganic particles are at least one selected from the group consisting of metal sulfate particles, metal hydroxide particles, metal oxide particles, metal carbonate particles, metal nitride particles, metal fluoride particles, and clay mineral particles. The separator for a non-aqueous secondary battery according to any one of claims 1 to 5, which comprises. The separator for a non-aqueous secondary battery according to any one of claims 1 to 6, wherein the volume ratio of the inorganic particles to the solid content of the heat-resistant porous layer is 5% by volume to 95% by volume. .. The separator for a non-aqueous secondary battery according to any one of claims 1 to 7, wherein the heat-resistant porous layer has a porosity of 15% to 70%. The non-aqueous system according to any one of claims 1 to 8, wherein the mass per unit area of the heat-resistant porous layer is 1.0 g / m ² to 30.0 g / m ² in total on both sides. Separator for next battery. The non-aqueous secondary battery separator according to any one of claims 1 to 9, which is provided between a positive electrode, a negative electrode, and the positive electrode and the negative electrode, is provided with lithium ion doping and desorption. A non-aqueous secondary battery that obtains electromotive force by doping.