JP7474115B2 - Separator for non-aqueous secondary battery and non-aqueous secondary battery - Google Patents

Description

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

The separator, which is one of the components that make up a non-aqueous secondary battery, is required to have heat resistance so that it does not easily break or shrink even when the temperature inside the battery becomes high, in order to ensure the safety of the battery. A separator with improved heat resistance is known to have a porous layer containing inorganic particles on a porous substrate. For example, Patent Documents 1 and 2 disclose a separator with a porous layer containing resin and inorganic particles on a porous substrate.

International Publication No. 2019/146155 JP 2016-033913 A

One way to improve the heat resistance of the porous layer provided on the porous substrate is to increase the content of inorganic particles in the porous layer. However, if the content of inorganic particles is high, the viscosity of the coating liquid used to form the porous layer may increase, or the viscosity of the coating liquid may increase over time. If the viscosity of the coating liquid is high, it becomes difficult to form the porous layer, and the productivity of the separator decreases.

The embodiments of the present disclosure have been made under the above circumstances.
An object of the embodiments of the present disclosure is to provide a separator for a nonaqueous secondary battery that is excellent in heat resistance and can be easily produced, and an object of the present disclosure is to achieve this object.

Specific means for solving the above problems include the following:

<1> A porous substrate,
A heat-resistant porous layer containing a resin and inorganic particles provided on one or both sides of the porous substrate,
a mass ratio of the inorganic particles in the heat-resistant porous layer is 50 mass% or more and 90 mass% or less;
The inorganic particles include first inorganic particles which are metal sulfate particles and second inorganic particles which are not metal sulfate particles.
Separator for non-aqueous secondary batteries.
<2> The separator for a nonaqueous secondary battery according to <1>, wherein a mass ratio of the first inorganic particles to the second inorganic particles (first inorganic particles:second inorganic particles) contained in the heat-resistant porous layer is 90:10 to 10:90.
<3> The separator for a nonaqueous secondary battery according to <1> or <2>, wherein the first inorganic particles have an average primary particle size of 0.01 μm or more and 0.3 μm or less.
<4> The separator for a nonaqueous secondary battery according to any one of <1> to <3>, wherein the second inorganic particles have an average primary particle size of 0.4 μm or more and 2.0 μm or less.
<5> The separator for a nonaqueous secondary battery according to any one of <1> to <4>, wherein the second inorganic particles are metal hydroxide particles.
<6> The separator for a nonaqueous secondary battery according to any one of <1> to <5>, wherein a mass ratio of the first inorganic particles to the second inorganic particles (first inorganic particles:second inorganic particles) contained in the heat-resistant porous layer is 80:20 to 40:60.
<7> The separator for a nonaqueous secondary battery according to any one of <1> to <6>, wherein a mass ratio of the inorganic particles in the heat-resistant porous layer is 60 mass % or more and 80 mass % or less.
<8> The separator for a nonaqueous secondary battery according to any one of <1> to <7>, wherein the resin contains a polyvinylidene fluoride resin having no carboxy group and no ester bond.
<9> A nonaqueous secondary battery comprising: a positive electrode; a negative electrode; and the separator for a nonaqueous secondary battery according to any one of <1> to <8>, the separator being disposed between the positive electrode and the negative electrode, the nonaqueous secondary battery generating electromotive force by doping and dedoping lithium ions.

This disclosure provides a separator for a non-aqueous secondary battery that has excellent heat resistance and is highly manufacturable.

Embodiments of the present disclosure are described below. These descriptions and examples are intended to illustrate the embodiments and are not intended to limit the scope of the embodiments.

In the present disclosure, a numerical range indicated using "to" indicates a range that includes the numerical values before and after "to" as the minimum and maximum values, respectively.
In the numerical ranges described in the present disclosure in stages, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. In addition, in the numerical ranges described in the present disclosure, the upper or lower limit value of the numerical range may be replaced with a value shown in the examples.

In this disclosure, the term "process" includes not only independent processes, but also processes that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved.

In this disclosure, when referring to the amount of each component in a composition, if there are multiple substances corresponding to each component in the composition, this refers to the total amount of those multiple substances present in the composition, unless otherwise specified.

In this disclosure, the particles corresponding to each component may include multiple types. When multiple types of particles corresponding to each component are present in the composition, the particle size of each component means the value for the mixture of the multiple types of particles present in the composition, unless otherwise specified.

In this disclosure, MD (machine direction) refers to the longitudinal direction of the porous substrate and separator that are manufactured in a long shape, and TD (transverse direction) refers to the direction perpendicular to the MD in the planar direction of the porous substrate and separator. In this disclosure, TD is also referred to as the "width direction."

In this disclosure, when the stacking relationship of the layers constituting the separator is expressed as "upper" and "lower," the layer closer to the porous substrate is referred to as "lower," and the layer farther from the porous substrate is referred to as "upper."

In this disclosure, a heat-resistant resin refers to a resin with a melting point of 200°C or higher, or a resin that does not have a melting point and has a decomposition temperature of 200°C or higher. In other words, a heat-resistant resin in this disclosure is a resin that does not melt or decompose in a temperature range below 200°C.

<Separator for non-aqueous secondary battery>
The nonaqueous secondary battery separator of the present disclosure (also simply referred to as "separator" in the present disclosure) includes a porous substrate and a heat-resistant porous layer provided on one or both sides of the porous substrate.

In the separator of the present disclosure, the heat-resistant porous layer contains a resin and inorganic particles,
The mass ratio of the inorganic particles in the heat-resistant porous layer is 50 mass% or more and 90 mass% or less,
The inorganic particles include first inorganic particles which are metal sulfate particles and second inorganic particles other than metal sulfate particles.

In the separator of the present disclosure, the mass ratio of inorganic particles in the heat-resistant porous layer is 50% by mass or more from the viewpoint of the heat resistance of the separator, and is 90% by mass or less from the viewpoint of keeping the viscosity of the coating liquid for forming the heat-resistant porous layer low, the viewpoint of preventing the heat-resistant porous layer from peeling off from the porous substrate, and the viewpoint of excellent adhesion of the heat-resistant porous layer to the electrode.

In the separator of the present disclosure, the heat-resistant porous layer contains first inorganic particles that are metal sulfate particles and second inorganic particles other than metal sulfate particles. In this embodiment, in order to increase the heat resistance of the heat-resistant porous layer, the mass ratio of the inorganic particles in the heat-resistant porous layer is 50 mass% or more, and in order to suppress the increase in viscosity over time of the coating liquid for forming the heat-resistant porous layer, some of the inorganic particles are metal sulfate particles. However, if all of the inorganic particles are metal sulfate particles, the viscosity of the coating liquid immediately after preparation is relatively high, so some of the inorganic particles are inorganic particles other than metal sulfate particles.

As a result of the action of each of the above components, the separator of the present disclosure has excellent heat resistance, i.e., is less likely to shrink at high temperatures (e.g., below 150°C), and the heat-resistant porous layer is easy to form, making it highly productive.

The porous substrate and heat-resistant porous layer of the separator of the present disclosure are described in detail below.

[Porous substrate]
In the present disclosure, the porous substrate means a substrate having pores or gaps inside. Examples of such substrates include microporous membranes; porous sheets such as nonwoven fabrics and paper made of fibrous materials; composite porous sheets obtained by laminating one or more other porous layers on these microporous membranes or porous sheets; and the like. In the present disclosure, from the viewpoint of thinning and strength of the separator, microporous membranes are preferred. The microporous membrane means a membrane having a large number of micropores inside, a structure in which these micropores are connected, and which allows gas or liquid to pass from one surface to the other surface.

The material for the porous substrate is preferably an electrically insulating material, and may be either an organic material or an inorganic material.

The porous substrate desirably contains a thermoplastic resin to provide the porous substrate with a shutdown function. The shutdown function refers to a function in which, when the battery temperature rises, the constituent materials dissolve and block the pores of the porous substrate, thereby blocking the movement of ions and preventing thermal runaway of the battery. The thermoplastic resin is preferably a thermoplastic resin with a melting point of less than 200°C. Examples of the thermoplastic resin include polyesters such as polyethylene terephthalate; polyolefins such as polyethylene and polypropylene; and the like; among which polyolefins are preferred.

As the porous substrate, a microporous membrane containing polyolefin (referred to as a "polyolefin microporous membrane" in this disclosure) is preferable. Examples of polyolefin microporous membranes include polyolefin microporous membranes that are used in conventional battery separators, and it is desirable to select one from these that has sufficient mechanical properties and ion permeability.

From the viewpoint of exhibiting a shutdown function, the polyolefin microporous membrane is preferably a microporous membrane containing polyethylene, and the polyethylene content is preferably 95% by mass or more based on the total mass of the polyolefin microporous membrane.

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

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

The polyolefin contained in the polyolefin microporous membrane is preferably a polyolefin having a weight average molecular weight (Mw) of 100,000 to 5,000,000. When the Mw of the polyolefin is 100,000 or more, the microporous membrane can be given sufficient mechanical properties. On the other hand, when the Mw of the polyolefin is 5,000,000 or less, the microporous membrane has good shutdown properties and is easy to mold.

Methods for producing a microporous polyolefin membrane include a method in which molten polyolefin resin is extruded through a T-die to form a sheet, which is crystallized, stretched, and then heat-treated to form a microporous membrane; a method in which molten polyolefin resin together with a plasticizer such as liquid paraffin is extruded through a T-die, cooled to form a sheet, stretched, the plasticizer is extracted, and the sheet is heat-treated to form a microporous membrane; and the like.

Examples of porous sheets made of fibrous materials include nonwoven fabrics, paper, and other porous sheets made of fibrous materials such as polyesters such as polyethylene terephthalate; polyolefins such as polyethylene and polypropylene; heat-resistant resins such as wholly aromatic polyamide, polyamideimide, polyimide, polyethersulfone, polysulfone, polyetherketone, and polyetherimide; and cellulose.

Examples of composite porous sheets include sheets in which a functional layer is laminated on a porous sheet made of a microporous membrane or a fibrous material. Such composite porous sheets are preferable from the viewpoint of enabling the addition of further functions by the functional layer. From the viewpoint of imparting heat resistance, examples of functional layers include a porous layer made of a heat-resistant resin, and a porous layer made of a heat-resistant resin and an inorganic filler. Examples of heat-resistant resins include one or more heat-resistant resins selected from wholly aromatic polyamide, polyamideimide, polyimide, polyethersulfone, polysulfone, polyetherketone, and polyetherimide. Examples of inorganic fillers include metal oxides such as alumina; metal hydroxides such as magnesium hydroxide; and the like. Examples of methods for compounding include a method of coating a functional layer on a microporous membrane or a porous sheet, a method of bonding a microporous membrane or a porous sheet to a functional layer with an adhesive, and a method of thermocompression bonding a microporous membrane or a porous sheet to a functional layer.

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

[Characteristics of porous substrate]
From the viewpoint of increasing the energy density of the battery, the thickness of the porous substrate is preferably 25 μm or less, more preferably 20 μm or less, and even more preferably 15 μm or less, and from the viewpoint of the production yield of the separator and the production yield of the battery, the thickness is preferably 3 μm or more, and more preferably 5 μm or more.

The Gurley value (JIS P8117:2009) of the porous substrate is preferably 50 sec/100 mL to 400 sec/100 mL, more preferably 80 sec/100 mL to 300 sec/100 mL, from the viewpoint of ion permeability or suppression of short circuits in the battery.

The porosity of the porous substrate is preferably 20% to 60% from the viewpoint of obtaining an appropriate membrane 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 (g/m ² ) of the porous substrate, ds is the true density (g/cm ³ ) of the porous substrate, and t is the thickness (μm) of the porous substrate. The basis weight is the mass per unit area.

From the viewpoint of separator manufacturing yield and battery manufacturing yield, the puncture strength of the porous substrate is preferably 160 gf (1.6 N) or more, and more preferably 200 gf (2.0 N) or more. The puncture strength of the porous substrate refers to the maximum puncture strength (gf) measured by a puncture test using a Kato Tech KES-G5 handy compression tester under conditions of a needle tip curvature radius of 0.5 mm and a puncture speed of 2 mm/sec.

The average pore diameter of the porous substrate is preferably 15 nm to 100 nm. When the average pore diameter of the porous substrate is 15 nm or more, ions can easily move, and good battery performance can be easily obtained. From this viewpoint, the average pore diameter of the porous substrate is more preferably 25 nm or more, and even more preferably 30 nm or more. When the average pore diameter of the porous substrate is 100 nm or less, the peel strength between the porous substrate and the heat-resistant porous layer can be improved, and a good shutdown function can also be exhibited. From this viewpoint, the average pore diameter of the porous substrate is more preferably 90 nm or less, and even more preferably 80 nm or less. The average pore diameter of the porous substrate is a value measured using a perm porometer, and is measured using a perm porometer (CFP-1500-A manufactured by PMI) according to ASTM E1294-89.

[Heat-resistant porous layer]
The heat-resistant porous layer has a large number of micropores therein, and these micropores are structured to be interconnected, allowing gas or liquid to pass from one surface to the other.

The heat-resistant porous layer is preferably provided on one or both sides of the porous substrate as the outermost layer of the separator, and is preferably a layer that adheres to the electrode when the separator and electrode are stacked and pressed or hot pressed.

The heat-resistant porous layer may be present on only one side of the porous substrate, or on both sides of the porous substrate. When the heat-resistant porous layer is present on both sides of the porous substrate, the separator has good adhesion to both electrodes of the battery. In addition, the separator is less likely to curl, and is easy to handle during battery production. When the heat-resistant porous layer is present on only one side of the porous substrate, the separator has better ion permeability. In addition, the overall thickness of the separator can be reduced, and a battery with a higher energy density can be produced.

In the separator of the present disclosure, the heat-resistant porous layer contains a resin and inorganic particles, and the inorganic particles include first inorganic particles that are metal sulfate particles and second inorganic particles that are not metal sulfate particles. The heat-resistant porous layer may contain other components such as an organic filler.

[resin]
The resin contained in the heat-resistant porous layer is preferably a resin that is stable in an electrolytic solution, electrochemically stable, has a function of connecting inorganic particles, and can adhere to an electrode. The heat-resistant porous layer may contain only one type of resin, or may contain two or more types of resins.

The type of resin contained in the heat-resistant porous layer is not limited. Examples of the resin include polyvinylidene fluoride resin, acrylic resin, fluorine-based rubber, styrene-butadiene copolymer, homopolymer or copolymer of vinyl nitrile compounds (acrylonitrile, methacrylonitrile, etc.), carboxymethyl cellulose, hydroxyalkyl cellulose, polyvinyl alcohol, polyvinyl butyral, polyvinylpyrrolidone, polyether (polyethylene oxide, polypropylene oxide, etc.), polyamide, wholly aromatic polyamide, polyimide, polyamideimide, polysulfone, polyketone, polyether ketone, polyether sulfone, polyether imide, and mixtures thereof.

Examples of polyvinylidene fluoride resins include homopolymers of vinylidene fluoride (i.e., polyvinylidene fluoride); copolymers of vinylidene fluoride with halogen-containing monomers such as hexafluoropropylene, tetrafluoroethylene, trifluoroethylene, chlorotrifluoroethylene, vinyl fluoride, and trichloroethylene; and mixtures thereof. One type of polyvinylidene fluoride resin may be used alone, or two or more types may be used in combination.

As the polyvinylidene fluoride resin, from the viewpoint of suppressing an increase in the viscosity of the coating liquid for forming the heat-resistant porous layer, a polyvinylidene fluoride resin that is unlikely to interact with the functional groups of the inorganic particles is preferred, and specifically, a polyvinylidene fluoride resin that does not have a carboxy group or an ester bond is preferred.

[Inorganic particles]
In the separator of the present disclosure, the mass ratio of the inorganic particles in the heat-resistant porous layer is 50 mass % or more, more preferably 55 mass % or more, and even more preferably 60 mass % or more, from the viewpoint of the heat resistance of the separator.
In the separator of the present disclosure, the mass proportion of the inorganic particles in the heat-resistant porous layer is 90 mass% or less, more preferably 85 mass% or less, and even more preferably 80 mass% or less, from the viewpoint of keeping low the viscosity of the coating liquid for forming the heat-resistant porous layer, from the viewpoint of preventing the heat-resistant porous layer from peeling off from the porous substrate, and from the viewpoint of excellent adhesion of the heat-resistant porous layer to the electrode.

There is no limitation on the particle shape of the inorganic particles, and they may be spherical, elliptical, plate-like, needle-like, or amorphous. From the viewpoint of suppressing short circuits in the battery or being easily packed densely into the heat-resistant porous layer, it is preferable that the inorganic particles are plate-like or spherical particles, or non-aggregated primary particles.

The average primary particle size of the inorganic particles is determined by measuring the major axis of 100 inorganic particles randomly selected in observation with a scanning electron microscope (SEM) and averaging the major axis sizes of the 100 particles.
The sample used for measuring the average primary particle size is inorganic particles that are the material forming the heat-resistant porous layer, or inorganic particles taken out from the heat-resistant porous layer of the separator.
When inorganic particles, which are materials forming the heat-resistant porous layer, are used as the measurement sample, the average primary particle size of each of the prepared first inorganic particles and second inorganic particles is measured.
When inorganic particles taken out from the heat-resistant porous layer of the separator are used as the measurement sample, the average primary particle size is determined based on the position of the peak that appears in the particle size distribution of the average primary particle size.
There is no limitation on the method for extracting the inorganic particles from the heat-resistant porous layer of the separator, and for example, a method of immersing the heat-resistant porous layer peeled off from the separator in an organic solvent that dissolves the resin and extracting the inorganic particles with the organic solvent may be mentioned. Alternatively, the heat-resistant porous layer peeled off from the separator may be heated to about 800° C. to remove the resin and extract the inorganic particles.

-First inorganic particles (metal sulfate particles)-
The first inorganic particles are metal sulfate particles. Examples of metal sulfate particles include barium sulfate (BaSO ₄ ) particles, strontium sulfate (SrSO ₄ ) particles, calcium sulfate (CaSO ₄ ) particles, calcium sulfate dihydrate (CaSO ₄ .2H ₂ O) particles, alumite (KAl ₃ (SO ₄ ) ₂ (OH) ₆ ) particles, and jarosite (KFe ₃ (SO ₄ ) ₂ (OH) ₆ ) particles. Among them, barium sulfate (BaSO ₄ ) particles are preferred. The metal sulfate particles may be used alone or in combination of two or more.

The first inorganic particles preferably have an average primary particle size of 0.01 μm to 0.3 μm.
The average primary particle size of the first inorganic particles is preferably 0.3 μm or less, more preferably 0.2 μm or less, and even more preferably 0.1 μm or less, from the viewpoint of increasing the surface area (specific surface area) of the inorganic particles per unit volume and densely packing the inorganic particles to suppress thermal shrinkage of the heat-resistant porous layer.
The average primary particle size of the first inorganic particles is preferably 0.01 μm or more, more preferably 0.03 μm or more, and even more preferably 0.05 μm or more, from the viewpoints of a practical size of the inorganic particles and keeping the viscosity of the coating liquid for forming the heat-resistant porous layer low.
The first inorganic particles may be a combination of two or more types of metal sulfate particles having different average primary particle sizes, and each of the average primary particle sizes preferably falls within the above range.

-Second inorganic particles (inorganic particles other than metal sulfate particles)-
The second inorganic particles are inorganic particles other than metal sulfate particles. Examples of the second inorganic particles include metal hydroxide particles, metal oxide particles, metal carbonate particles, metal nitride particles, metal fluoride particles, clay mineral particles, etc. The second inorganic particles may be used alone or in combination of two or more. As the second inorganic particles, metal hydroxide particles are preferred from the viewpoint of flame retardancy.

Examples of metal hydroxide particles include particles of magnesium hydroxide, aluminum hydroxide, calcium hydroxide, chromium hydroxide, zirconium hydroxide, cerium hydroxide, nickel hydroxide, etc. Among these, magnesium hydroxide (Mg(OH) ₂ ) particles are preferred.

Examples of metal oxide particles include particles of magnesium oxide, alumina, boehmite (alumina monohydrate), titania, silica, zirconia, barium titanate, zinc oxide, etc. Examples of metal carbonate particles include particles of magnesium carbonate, calcium carbonate, etc. Examples of metal nitride particles include particles of magnesium nitride, aluminum nitride, calcium nitride, titanium nitride, etc. Examples of metal fluoride particles include particles of magnesium fluoride, calcium fluoride, etc. Examples of clay mineral particles include particles of calcium silicate, calcium phosphate, apatite, talc, etc.

The second inorganic particles preferably have an average primary particle size of 0.4 μm to 2.0 μm.
The average primary particle size of the second inorganic particles is preferably 0.4 μm or more, more preferably 0.5 μm or more, and even more preferably 0.6 μm or more, from the viewpoint of keeping the viscosity of the coating liquid for forming the heat resistant porous layer low.
The average primary particle size of the second inorganic particles is preferably 2.0 μm or less, more preferably 1.5 μm or less, and even more preferably 1.0 μm or less, from the viewpoints of increasing the surface area (specific surface area) of the inorganic particles per unit volume and densely packing the inorganic particles to suppress thermal shrinkage of the heat-resistant porous layer.
The second inorganic particles may be a combination of two or more types of inorganic particles having different average primary particle diameters, and each of the average primary particle diameters preferably falls within the above range.

The average primary particle size of the second inorganic particles/average primary particle size of the first inorganic particles is preferably more than 1 and not more than 200, more preferably more than 3 and not more than 100, and even more preferably more than 5 and not more than 50.

The mass ratio of the first inorganic particles to the second inorganic particles (first inorganic particles:second inorganic particles) contained in the heat-resistant porous layer is preferably 90:10 to 10:90, more preferably 80:20 to 40:60, and even more preferably 75:25 to 45:55, from the viewpoint of keeping the viscosity of the coating liquid low immediately after preparation while also suppressing an increase in viscosity over time.

-Organic filler-
Examples of the organic filler include particles made of crosslinked polymers such as crosslinked poly(meth)acrylic acid, crosslinked poly(meth)acrylic acid ester, crosslinked polysilicone, crosslinked polystyrene, crosslinked polydivinylbenzene, styrene-divinylbenzene copolymer crosslinked product, melamine resin, phenolic resin, and benzoguanamine-formaldehyde condensate; particles made of heat-resistant polymers such as polysulfone, polyacrylonitrile, aramid, and polyacetal; and the like. These organic fillers may be used alone or in combination of two or more. In the present disclosure, the term "(meth)acrylic" means that it may mean either "acrylic" or "methacrylic".

-Other ingredients-
In the separator of the present disclosure, the heat-resistant porous layer may contain additives such as a dispersant such as a surfactant, a wetting agent, an antifoaming 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. The wetting agent, antifoaming agent, and pH adjuster are added to the coating liquid for forming the heat-resistant porous layer for the purpose of improving compatibility with the porous substrate, suppressing air entrapment in the coating liquid, or adjusting the pH, for example.

[Characteristics of heat-resistant porous layer]
The thickness of the heat-resistant porous layer is preferably 1 μm or more on one side, more preferably 1.5 μm or more on one side, and even more preferably 2.0 μm or more on one side, from the viewpoints of heat resistance of the separator and adhesion to the electrodes, and is preferably 8 μm or less on one side, more preferably 7.0 μm or less on one side, and even more preferably 6.0 μm or less on one side, from the viewpoints of ion permeability and energy density of the battery.

The thickness of the heat-resistant porous layer, calculated as the total thickness of both sides, is preferably 2 μm or more, more preferably 4 μm or more, even more preferably 6 μm or more, and is preferably 16 μm or less, more preferably 12 μm or less, and even more preferably 10 μm or less.

When a heat-resistant porous layer is provided on both sides of a porous substrate, the difference between the thickness of the heat-resistant porous layer on one side and the thickness of the heat-resistant porous layer on the other side is preferably 25% or less of the total thickness of both sides, and the lower the better.

The mass of the heat-resistant porous layer per unit area, in terms of both sides in total, is preferably 2.0 g/ ^m2 or more, more preferably 3.0 g/ ^m2 or more, and even more preferably 4.0 g/ ^m2 or more, from the viewpoints of the heat resistance of the separator and the adhesion to the electrodes, and from the viewpoints of ion permeability and the energy density of the battery, the mass of both sides in total is preferably 30.0 g/ ^m2 or less, more preferably 25.0 g/ ^m2 or less, and even more preferably 20.0 g/ ^m2 or less.

When the heat-resistant porous layer is provided on both sides of the porous substrate, the difference in mass of the heat-resistant porous layer between one side and the other side is preferably 25% by mass or less of the total of both sides, from the viewpoint of suppressing curling of the separator or improving the cycle characteristics of the battery.

The porosity of the heat-resistant porous layer is preferably 25% or more, more preferably 30% or more, and even more preferably 35% or more from the viewpoints of ion permeability and adhesion to the electrode, and is preferably 60% or less, more preferably 55% or less, and even more preferably 50% or less from the viewpoints of the mechanical strength and heat resistance of the heat-resistant porous layer. 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, the masses per unit area of each constituent material are Wa, Wb, Wc, ..., Wn (g/ ^cm2 ), the true densities of each constituent material are da, db, dc, ..., dn (g/ ^cm3 ), 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 or more, more preferably 20 nm or more, from the viewpoint of preventing pore blockage even if the resin contained in the heat-resistant porous layer swells when the heat-resistant porous layer is impregnated with an electrolyte, and is preferably 300 nm or less, more preferably 200 nm or less, from the viewpoint of adhesion of the heat-resistant porous layer to the electrode or excellent cycle characteristics and load characteristics of the battery.

The average pore size (nm) of the heat-resistant porous layer is calculated by the following formula, assuming that all pores are cylindrical.
d=4V/S
In the formula, d represents the average pore size (diameter) of the heat-resistant porous layer, V represents the pore volume per ^m2 of the heat-resistant porous layer, and S represents the pore surface area per ^m2 of the heat-resistant porous layer.
The pore volume V per 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 ^m2 of the heat-resistant porous layer is determined by the following method.
First, the specific surface area ( ^m2 /g) of the porous substrate and the specific surface area ( ^m2 /g) of the separator are calculated from the nitrogen gas adsorption amount by applying the BET equation to the nitrogen gas adsorption method. These specific surface areas ( ^m2 /g) are multiplied by their respective basis weights (g/ ^m2 ) to calculate the pore surface area per ^m2 . Then, the pore surface area per ^m2 of the porous substrate is subtracted from the pore surface area per ^m2 of the separator to calculate the pore surface area S per ^m2 of the heat-resistant porous layer. The basis weight is the mass per unit area.

[Separator characteristics]
The thickness of the separator of the present disclosure is preferably 5 μm or more, more preferably 8 μm or more, and even more preferably 10 μm or more from the viewpoint of the mechanical strength of the separator, and is preferably 30 μm or less, more preferably 25 μm or less, and even more preferably 20 μm or less from the viewpoint of the energy density of the battery.

From the viewpoint of the mechanical strength of the separator or the short circuit resistance of the battery, the puncture strength of the separator of the present disclosure is preferably 160 gf (1.6 N) to 1000 gf (9.8 N), and more preferably 200 gf (2.0 N) to 600 gf (5.9 N). 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 of the present disclosure is preferably 30% to 65%, and more preferably 35% to 60%, from the viewpoints of adhesion to the electrode, ease of handling of the separator, ion permeability, and mechanical strength.

From the viewpoint of mechanical strength and the load characteristics of the battery, the Gurley value (JIS P8117:2009) of the separator of the present disclosure is preferably 100 sec/100 mL to 600 sec/100 mL, and more preferably 120 sec/100 mL to 500 sec/100 mL.

From the viewpoint of ion permeability, the separator of the present disclosure preferably has a Gurley value of the separator minus the Gurley value of the porous substrate of 400 seconds/100 mL or less, more preferably 300 seconds/100 mL or less, and even more preferably 200 seconds/100 mL or less. The lower limit of the Gurley value of the separator minus the Gurley value of the porous substrate is not particularly limited, but in the separator of the present disclosure, it is preferably 10 seconds/100 mL or more.

The separator of the present disclosure preferably has an MD shrinkage rate of 30% or less, more preferably 20% or less, and even more preferably 15% or less, when heat-treated at 150°C for 1 hour.

The separator of the present disclosure preferably has a TD shrinkage rate of 30% or less, more preferably 20% or less, and even more preferably 15% or less, when heat-treated at 150°C for 1 hour.

The separator of the present disclosure preferably has an area shrinkage rate of 50% or less, more preferably 40% or less, and even more preferably 30% or less, when heat-treated at 150°C for 1 hour.

The area shrinkage rate when the separator is heat-treated at 150° C. for 1 hour is determined by the following measurement method.
The separator is cut into a rectangle of 180 mm MD x 60 mm TD to prepare a test specimen. Marks are made on this test specimen at points 20 mm and 170 mm from one end on the line that divides the TD in half (referred to as points A and B, respectively). Furthermore, marks are made on the line that divides the MD in half at points 10 mm and 50 mm from one end (referred to as points C and D, respectively). A clip is attached to the marked test specimen (the clip is attached between the end closest to point A and point A), and the specimen is hung in an oven with the temperature adjusted to 150°C, and heat treated for 1 hour in a tensionless state. The lengths between A and B and between CD are measured before and after heat treatment, and the area shrinkage is calculated using the following formula.
Area shrinkage rate (%)={1-(AB length after heat treatment/AB length before heat treatment)×(CD length after heat treatment/CD length before heat treatment)}×100

The separator of the present disclosure may further have layers other than the porous substrate and the heat-resistant porous layer. Examples of a configuration having additional layers include a configuration having a heat-resistant porous layer on one surface of the porous substrate, and an adhesive porous layer provided on the other surface of the porous substrate for the main purpose of bonding to an electrode.

[Separator manufacturing method]
The separator of the present disclosure can be manufactured, 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 in which a coating layer is solidified in a coagulating liquid, and the dry coating method is a method in which a coating layer is dried and solidified. An embodiment example of the wet coating method will be described below.

The wet coating method involves applying a coating liquid containing resin and inorganic particles onto a porous substrate, immersing the substrate in a coagulating liquid to solidify the coating layer, and then removing the substrate from the coagulating liquid, rinsing the substrate with water, and drying the substrate.

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

The solvent used to prepare the coating liquid includes a solvent that dissolves the resin (hereinafter, also referred to as a "good solvent"). Examples of good solvents include polar amide solvents such as N-methylpyrrolidone, dimethylacetamide, and dimethylformamide.

The solvent used to prepare the coating liquid preferably contains a phase separation agent that induces phase separation, from the viewpoint of forming a porous layer having a good pore structure. Therefore, the solvent used to prepare the coating liquid is preferably a mixed solvent of a good solvent and a phase separation agent. The phase separation agent is preferably mixed with the good solvent in an amount that ensures a suitable viscosity for coating. Examples of phase separation agents include water, methanol, ethanol, propyl alcohol, butyl alcohol, butanediol, ethylene glycol, propylene glycol, and tripropylene glycol.

From the viewpoint of forming a good porous structure, the solvent used to prepare the coating liquid is preferably a mixed solvent of a good solvent and a phase separation agent, containing 60% by mass or more of the good solvent and 5% by mass to 40% by mass of the phase separation agent.

The resin concentration of the coating liquid is preferably 3% to 10% by mass from the viewpoint of forming a good porous structure. The inorganic particle concentration of the coating liquid is preferably 2% 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 adjuster, etc. These additives may remain in the heat-resistant porous layer as long as they are electrochemically stable within the range of use of the non-aqueous secondary battery and do not inhibit the reaction within the battery.

From the viewpoint of suitability for application to porous substrates, the viscosity of the coating liquid is preferably 100 mPa·s to 2500 mPa·s, and more preferably 500 mPa·s to 2000 mPa·s. The viscosity (Pa·s) of the coating liquid is the viscosity measured on a sample at a temperature of 20°C using a B-type rotational viscometer.

Means for applying the coating liquid to the porous substrate include a Mayer bar, a die coater, a reverse roll coater, a roll coater, a gravure coater, etc. When forming a heat-resistant porous layer on both sides of the porous substrate, it is preferable from the viewpoint of productivity to apply the coating liquid to both sides of the porous substrate simultaneously.

The coating layer is solidified by immersing the porous substrate on which the coating layer is formed in a coagulation liquid, and solidifying the resin while inducing phase separation in the coating layer. This results in a laminate consisting of the porous substrate and the heat-resistant porous layer.

The solidification liquid generally contains the good solvent and phase separation agent used in preparing the coating liquid, and water. From the viewpoint of production, it is preferable that the mixing ratio of the good solvent and the phase separation agent is the same as the mixing ratio of the mixed solvent used in preparing the coating liquid. From the viewpoint of forming a porous structure and productivity, it is preferable that the water content in the solidification liquid is 40% by mass to 90% by mass. The temperature of the solidification liquid is, for example, 20°C to 50°C.

After the coating layer is solidified in the coagulating liquid, the laminate is lifted out of the coagulating liquid and washed with water. The coagulating liquid is removed from the laminate by washing with water. Furthermore, water is removed from the laminate by drying. The washing with water is performed, for example, by transporting the laminate through a water bath. The drying is performed, for example, by transporting the laminate through a high-temperature environment, by blowing air on the laminate, by contacting the laminate with a heat roll, etc. 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 in which a coating liquid is applied to a porous substrate, the coating layer is dried, and the solvent is removed by evaporation, thereby forming a heat-resistant porous layer on the porous substrate. However, the dry coating method tends to produce a denser porous layer than the wet coating method, so the wet coating method is preferred from the viewpoint of obtaining a good porous structure.

The separator of the present disclosure can also be manufactured by a method in which the heat-resistant porous layer is prepared as an independent sheet, and this heat-resistant porous layer is layered on a porous substrate and composited by thermocompression or adhesive. Examples of a method for preparing the heat-resistant porous layer as an independent sheet include a method in which the heat-resistant porous layer is formed on a release sheet by applying the above-mentioned wet coating method or dry coating method.

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

The nonaqueous secondary battery of the present disclosure has a structure in which, for example, a battery element in which a negative electrode and a positive electrode face each other with a separator interposed therebetween is enclosed in an exterior material together with an electrolyte. The nonaqueous secondary battery of the present disclosure is suitable for nonaqueous electrolyte secondary batteries, particularly lithium ion secondary batteries.

From the viewpoint of adhesion to the separator, it is preferable that the active material layer of the electrode contains a large amount of binder resin, and from the viewpoint of increasing the energy density of the battery, it is preferable that the active material layer contains a large amount of active material and the amount of binder resin is relatively small. The separator of the present disclosure has excellent adhesion to the electrode, so it is possible to reduce the amount of binder resin in the active material layer and increase the amount of active material, thereby increasing the energy density of the battery.

Below, examples of the positive electrode, negative electrode, electrolyte, and exterior material of the nonaqueous secondary battery disclosed herein are described.

An example of the positive electrode is 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 assistant. 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 _1/3 O ₂ , LiMn ₂ O ₄ , LiFePO ₄ , LiCo _1/2 Ni _1/2 O ₂ , LiAl _1/4 Ni _3/4 O ₂ , etc. Examples of the binder resin include polyvinylidene fluoride resins, styrene-butadiene copolymers, etc. Examples of the conductive assistant include carbon materials such as acetylene black, ketjen black, and graphite powder. The current collector may be, for example, an aluminum foil, a titanium foil, a stainless steel foil, or the like having a thickness of 5 μm to 20 μm.

In the nonaqueous secondary battery of the present disclosure, the polyvinylidene fluoride resin contained in the heat-resistant porous layer of the separator of the present disclosure has excellent oxidation resistance, and therefore, by disposing the heat-resistant porous layer in contact with the positive electrode of the nonaqueous secondary battery, it is easy to use LiMn1 _{/ 2Ni1/ 2O2} , LiCo1 _/ 3Mn1 _{/ 3Ni1/ 3O2} , or the like, which are capable of operating at a high voltage of 4.2 V or more, as the positive electrode active material.

An example of an embodiment of the negative electrode is 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 assistant. The negative electrode active material may be a material capable of electrochemically absorbing lithium ions, specifically, for example, a carbon material; an alloy of lithium with silicon, tin, aluminum, etc.; Wood's alloy; and the like. Examples of the binder resin include polyvinylidene fluoride resin, styrene-butadiene copolymer, and the like. Examples of the conductive assistant 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. In addition, instead of the above negative electrode, a metallic lithium foil may be used as the negative electrode.

The electrolyte 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 , and LiClO _4. Examples of the non-aqueous solvent include cyclic carbonates such as ethylene carbonate, propylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, and vinylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and fluorine-substituted derivatives thereof; and cyclic esters such as γ-butyrolactone and γ-valerolactone; which may be used alone or in combination. As the electrolyte, a solution in which a cyclic carbonate and a chain carbonate are mixed in a mass ratio (cyclic carbonate:chain carbonate) of 20:80 to 40:60 and a lithium salt is dissolved in the range of 0.5 mol/L to 1.5 mol/L is suitable.

Examples of exterior materials include metal cans and packs made of aluminum laminated film. Battery shapes include rectangular, cylindrical, and coin shapes, and the separator of the present disclosure is suitable for any shape.

The nonaqueous secondary battery of the present disclosure can be manufactured by, for example, any of the following (1) to (3) using a laminate in which the separator of the present disclosure is disposed between a positive electrode and a negative electrode. Hereinafter, the process of impregnating the separator with an electrolyte and then performing a heat press process is referred to as "wet heat press," and the process of performing a heat press process without impregnating the separator with an electrolyte is referred to as "dry heat press."

(1) The laminate is heat pressed (dry heat pressed) to bond the electrodes and separator, then housed in an exterior material (e.g., an aluminum laminate film pack; the same applies below), electrolyte is injected into it, and the interior of the exterior material is evacuated. After that, the laminate is further heat pressed (wet heat pressed) on top of the exterior material to bond the electrodes and separator and seal the exterior material.

(2) The laminate is placed in an exterior packaging material, an electrolyte is injected into it, and a vacuum is created inside the exterior packaging material. The laminate is then heat pressed (wet heat pressed) onto the exterior packaging material to bond the electrodes and separator together and seal the exterior packaging material.

(3) The laminate is heat pressed (dry heat pressed) to bond the electrodes and separator, then it is housed in an exterior packaging material, the electrolyte is injected into it, a vacuum is created inside the exterior packaging material, and the exterior packaging material is then sealed.

In the manufacturing methods (1) to (3) above, the heat pressing conditions are preferably a pressure of 0.1 MPa to 15.0 MPa and a temperature of 60°C to 100°C for both dry heat pressing and wet heat pressing.

When manufacturing a laminate in which a separator is disposed between a positive electrode and a negative electrode, the method of disposing the separator between the positive electrode and the negative electrode may be a method of stacking at least one layer of a positive electrode, a separator, and a negative electrode in this order (so-called stack method), or a method of stacking a positive electrode, a separator, a negative electrode, and a separator in this order and winding them in the length direction.

The separator and nonaqueous secondary battery of the present disclosure will be described in more detail below with reference to examples. The materials, amounts used, ratios, processing procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present disclosure. Therefore, the scope of the separator and nonaqueous secondary battery of the present disclosure should not be interpreted as being limited by the specific examples shown below.

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

[Thickness of porous substrate and separator]
The thickness (μm) of the porous substrate and the separator was measured at 20 points within a 10 cm square using a contact thickness meter (Mitutoyo Corporation, LITEMATIC VL-50-B) and the average was obtained. A spherical probe with a sphere radius of 10 mm (Mitutoyo Corporation, superhard spherical probe φ10.5) was used as the measurement terminal, and the load was adjusted to be about 0.2 N during the measurement.

[Thickness of heat-resistant porous layer]
The thickness (μm) of the heat-resistant porous layer was calculated by subtracting the thickness (μm) of the porous substrate from the thickness (μm) of the separator to determine the total thickness of both sides, and then dividing this in half to determine the thickness of one side.

[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 (g/m ² ) of the porous substrate, ds is the true density (g/cm ³ ) of the porous substrate, and t is the thickness (μm) of the porous substrate.

[Gurley value of porous substrate]
The Gurley value (sec/100 mL) of the porous substrate was measured using a Gurley densometer (Toyo Seiki Co., Ltd.) in accordance with JIS P8117:2009.

[Average primary particle size of inorganic particles]
The inorganic particles before being added to a coating liquid for forming a heat-resistant porous layer were used as a sample.
The average primary particle size of the inorganic particles was determined by measuring the major axis of 100 particles randomly selected in observation with a scanning electron microscope (SEM) and averaging the major axis sizes of the 100 particles.

[Area shrinkage rate]
The separator was cut into a rectangle of 180 mm MD x 60 mm TD to prepare a test specimen. Marks were made on the test specimen at 20 mm and 170 mm from one end on the line dividing the TD in half (referred to as points A and B, respectively). Marks were also made on the line dividing the MD in half at 10 mm and 50 mm from one end (referred to as points C and D, respectively). A clip was attached to the marked test specimen (the clip was attached between the end closest to point A and point A), and the specimen was hung in an oven with the temperature adjusted to 150°C, and heat-treated for 1 hour in a tensionless state. The lengths between A and B and between CD were measured before and after the heat treatment, and the area shrinkage rate (%) was calculated using the following formula, and the area shrinkage rates (%) of 10 test specimens were averaged.

Area shrinkage rate (%) = {1 - (AB length after heat treatment ÷ AB length before heat treatment) x (CD length after heat treatment ÷ CD length before heat treatment)} x 100

[Viscosity of coating liquid]
The viscosity (Pa s) of the coating liquid was measured using a B-type rotational viscometer (Brookfield, product number RVDV+I, spindle: SC4-18). A sample was taken from the coating liquid homogenized by stirring, and the measurement was performed under the conditions of a sample amount of 7 mL, a sample temperature of 20° C., and a spindle rotation speed of 10 rpm.
The viscosity of the coating liquid immediately after preparation is taken as the reference value for Example 1, and the viscosities of the other Examples and Comparative Examples are shown as percentages relative to Example 1.

The prepared coating liquid was left to stand for 24 hours in a thermostatic chamber at a temperature of 25° C. After 24 hours, the sample was stirred to homogenize it, and the viscosity was measured by the above-mentioned method. For each of the examples and comparative examples, the viscosity increase rate (%) was calculated by the following formula.
Viscosity increase rate (%) = (viscosity after 24 hours - viscosity immediately after preparation) ÷ viscosity immediately after preparation × 100

<Preparation of separator>
[Example 1]
As materials for the heat-resistant porous layer, a copolymer of vinylidene fluoride and hexafluoropropylene (VDF-HFP copolymer. This copolymer is a polyvinylidene fluoride-based resin having no carboxy groups or ester bonds), barium sulfate particles, and magnesium hydroxide particles were prepared. The physical properties of the barium sulfate particles and magnesium hydroxide particles are shown in Table 1.

The VDF-HFP copolymer was dissolved in dimethylacetamide (DMAc), and barium sulfate particles and magnesium hydroxide particles were further dispersed therein to obtain coating liquid (1). Coating liquid (1) had a VDF-HFP copolymer concentration of 5% by mass, a mass ratio of the VDF-HFP copolymer to the inorganic particles (VDF-HFP copolymer:inorganic particles) of 20:80, and a mass ratio of the barium sulfate particles to the magnesium hydroxide particles (barium sulfate particles:magnesium hydroxide particles) of 70:30.

Coating liquid (1) was applied to both sides of a polyethylene microporous membrane (thickness 12 μm, porosity 40%, Gurley value 200 sec/100 mL). The coating was applied so that the amount of coating on both sides was equal. This was immersed in a coagulation liquid (water:DMAc = 70:30 [mass ratio], liquid temperature 40°C) to solidify the coating layer, and then washed with water and dried. In this way, a separator was obtained in which a heat-resistant porous layer was formed on both sides of the polyethylene microporous membrane. The thickness of the heat-resistant porous layer was 4 μm on each side.

[Examples 2 to 12, Comparative Examples 1 to 6]
Each separator was produced in the same manner as in Example 1, except that the material and composition of the heat-resistant porous layer were set to the specifications shown in Table 1.

The composition, physical properties, and evaluation results of each separator in Examples 1 to 12 and Comparative Examples 1 to 6 are shown in Table 1.

Claims (8)

A porous substrate;
A heat-resistant porous layer containing a resin and inorganic particles provided on one or both sides of the porous substrate,
a mass ratio of the inorganic particles in the heat-resistant porous layer is 50 mass% or more and 90 mass% or less;
The inorganic particles include first inorganic particles which are metal sulfate particles and second inorganic particles which are metal hydroxide particles .
Separator for non-aqueous secondary batteries. 2. The separator for a nonaqueous secondary battery according to claim 1 , wherein the first inorganic particles have an average primary particle size of 0.01 μm or more and 0.3 μm or less. 3. The separator for a nonaqueous secondary battery according to claim 1 , wherein the second inorganic particles have an average primary particle size of 0.4 μm or more and 2.0 μm or less. 4. The separator for a non-aqueous secondary battery according to claim 1, wherein a mass ratio of said inorganic particles in said heat-resistant porous layer is 60 mass % or more and 80 mass % or less. The separator for a non-aqueous secondary battery according to any one of claims 1 to 4, wherein the mass ratio of the first inorganic particles to the second inorganic particles contained in the heat-resistant porous layer (first inorganic particles:second inorganic particles) is 90:10 to 10:90. The separator for a non-aqueous secondary battery according to any one of claims 1 to 5, wherein the mass ratio of the first inorganic particles to the second inorganic particles contained in the heat-resistant porous layer (first inorganic particles:second inorganic particles) is 80:20 to 40:60. The separator for a non-aqueous secondary battery according to any one of claims 1 to 6, wherein the resin includes a polyvinylidene fluoride-based resin having no carboxy groups or ester bonds. A non-aqueous secondary battery comprising a positive electrode, a negative electrode, and a separator for a non-aqueous secondary battery according to any one of claims 1 to 7, which is disposed between the positive electrode and the negative electrode, and which obtains electromotive force by doping and dedoping lithium ions.