JP7545216B2 - 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.

Non-aqueous secondary batteries, such as lithium-ion secondary batteries, are widely used as power sources for portable electronic devices, such as notebook computers, mobile phones, digital cameras, and camcorders. Conventionally known separators for non-aqueous secondary batteries include a separator in which a layer containing polyamide (also called aramid) is applied to a substrate such as a polyethylene film, and a separator in which nylon is kneaded into a polyethylene film.

For example, as in Patent Document 1, in a separator in which a layer containing aramid is applied to a polyethylene film, the aramid is usually applied to both sides of the polyethylene film. Since the aramid is applied to both sides of the polyethylene film, the separator produced inevitably has a certain thickness, and it is difficult to make it thinner.

In addition, aramid or nylon has polar groups in the molecule. Therefore, separators using aramid or nylon have the characteristics of being easily charged with static electricity and having poor slip properties. If the separator becomes charged with static electricity, foreign matter may adhere to the separator during the manufacturing process, causing problems. In addition, if the separator's slip properties become poor, for example, during the manufacturing process in which the separator and electrodes are stacked and wound around a core to form a wound body, the wound body may stretch out like a bamboo shoot and lose its shape, or wrinkles may form on the wound body.

In view of the above, when a coating film is provided on a substrate, it is preferable that the coating film is provided only on one side of the substrate. A nonaqueous electrolyte battery separator has been disclosed that has a layer containing a heat-resistant nitrogen-containing aromatic polymer on one side of the substrate (see, for example, Patent Document 2).

International Publication No. 2008/062727 Patent No. 3175730

However, in an embodiment in which the coating film is provided on only one side of a substrate such as a polyethylene film, there is a problem that the electrolyte is less likely to penetrate into the separator than in an embodiment in which the coating film is provided on both sides of the polyethylene film. If the electrolyte does not penetrate sufficiently into the separator, the resistance value (membrane resistance) of the separator increases, and the technology described in Patent Document 2 cannot be expected to provide the desired battery characteristics.

The present disclosure has been made in consideration of the above circumstances.
An object of one embodiment of the present disclosure is to provide a separator for a nonaqueous secondary battery that is easily permeated by an electrolyte solution.
Another problem to be solved by another embodiment of the present disclosure is to provide a nonaqueous secondary battery having excellent battery characteristics.

Specific means for solving the problems include the following aspects.
<1> A porous substrate including a microporous polyolefin membrane; and a porous layer including a resin having at least one bond group selected from the group consisting of an amide bond, an imide bond, and a sulfonyl bond, provided on only one surface of the porous substrate;
When 1.0 μL of an electrolyte solution in which 1 mol/l of _LiPF4 is dissolved in a mixed solvent of ethylene carbonate and propylene carbonate (mixing ratio 1:1 [mass ratio]) is dropped onto the surface of the porous layer, the contact angle at the time 65 milliseconds after the electrolyte solution lands is 5° or more and 40° or less,
When 1.0 μL of the electrolyte solution is dropped onto the surface of the porous substrate opposite to the surface having the porous layer, the contact angle at 65 milliseconds after the electrolyte solution is dropped is 30° or more and 75° or less.
A separator for a non-aqueous secondary battery.

<2> The porous layer is a separator for a non-aqueous secondary battery described in <1>, which contains inorganic particles.

<3> The non-aqueous secondary battery separator according to <1> or <2>, wherein the resin contains a wholly aromatic polyamide.

<4> The separator for a nonaqueous secondary battery according to any one of <1> to <3>, wherein a MacMillan number Mn calculated by the following formula is 20 or less:
Mn=(σe)/(σs)
σs=t/Rm
In the formula, σe represents the conductivity (S/m) at 20°C of an electrolyte solution in which 1 mol/l of _LiPF6 is dissolved in a mixed solvent of ethylene carbonate and propylene carbonate (mixing ratio 1:1 [mass ratio]), σs represents the conductivity (S/m) at 20°C of a separator impregnated with the electrolyte solution, t represents the membrane thickness (m), and Rm represents the membrane resistance (ohm· ^cm2 ) of the separator.

<5> The nonaqueous secondary battery separator according to any one of <1> to <4>, wherein the porous layer has a thickness of 0.3 μm to 5.0 μm.

<6> A separator for a non-aqueous secondary battery according to any one of <1> to <5>, in which the resin is present inside the pores of the porous substrate and on the surface of the porous substrate opposite to the side having the porous layer.

<7> A non-aqueous secondary battery that includes a positive electrode, a negative electrode, a separator for a non-aqueous secondary battery according to any one of <1> to <6> that is disposed between the positive electrode and the negative electrode, and an electrolyte solution in which a lithium salt is dissolved in a solvent that contains 90% by mass or more of a cyclic carbonate relative to the total mass of the solvent, and that obtains an electromotive force by doping and dedoping lithium.

According to one embodiment of the present disclosure, a separator for a nonaqueous secondary battery is provided that is easily permeable by an electrolyte solution.
According to another embodiment of the present disclosure, a nonaqueous secondary battery having excellent battery characteristics is provided.

The contents of the present disclosure will be described in detail below.
The following description of the configuration elements may be based on representative embodiments of the present disclosure, but the present disclosure is not limited to such embodiments.

In this specification, a numerical range indicated using "~" means a range that includes the numerical values before and after "~" as the lower and upper limits, respectively. In the numerical ranges described in this disclosure in stages, the upper or lower limit value described in a certain 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 this disclosure, the upper or lower limit value described in a certain numerical range may be replaced with a value shown in the examples.

In this specification, when referring to the amount of each component in a composition, if there are multiple substances corresponding to each component in the composition, it means the total amount of the multiple components present in the composition, unless otherwise specified.

The term "solid content" in this specification means components excluding the solvent, and liquid components such as low molecular weight components other than the solvent are also included in the "solid content" in this specification.
In this specification, the term "solvent" is used to mean water, an organic solvent, and a mixed solvent of water and an organic solvent.

In this specification, 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, combinations of preferred aspects are more preferred aspects.

The weight average molecular weight (Mw) in this disclosure is a value measured by gel permeation chromatography (GPC).
Specifically, a polyethylene microporous membrane sample is heated and dissolved in o-dichlorobenzene, and measured by GPC (Alliance GPC 2000 model, Waters Corporation, columns: GMH6-HT and GMH6-HTL) at a column temperature of 135° C. and a flow rate of 1.0 mL/min to obtain Mw. Molecular weight calibration can be performed using monodisperse polystyrene (Tosoh Corporation).

<Separator for non-aqueous secondary battery>
The separator for a nonaqueous secondary battery according to the present disclosure (hereinafter also referred to as "the separator according to the present disclosure" or "separator") comprises a porous substrate including a polyolefin microporous membrane, and a porous layer including a resin having at least one bonding group selected from the group consisting of an amide bond, an imide bond, and a sulfonyl bond, on only one side of the porous substrate, in which the contact angle when 65 milliseconds have elapsed since the electrolyte solution is dropped on the surface of the porous layer when 1.0 μL of the electrolyte solution is dropped on the surface of the porous substrate is 5° or more and 40° or less, and the contact angle when 65 milliseconds have elapsed since the electrolyte solution is dropped on the surface of the porous substrate opposite the side having the porous layer is 30° or more and 75° or less.
The electrolyte solution was prepared by dissolving 1 mol/l of LiPF ₆ in a mixed solvent of ethylene carbonate and propylene carbonate (mixing ratio 1:1 [mass ratio]).

Conventionally, a three-layer structure in which layers containing aramid are coated on both sides of a polyethylene film has been known as a separator for use in a non-aqueous secondary battery. Separators using aramid or nylon tend to be electrostatically charged and have poor slipperiness. Due to such characteristics, foreign matter may adhere to the separator during the manufacturing process, causing problems, or the wound body manufactured by winding the separator and electrodes around the core may lose its shape or wrinkles may form.
In view of this situation, in the separator for non-aqueous secondary batteries of the present disclosure, a porous layer containing a specific resin is formed only on one side of the porous substrate, and the entire separator is made thin. This suppresses the occurrence of defects due to static electricity, deformation, wrinkles, etc. However, when the porous layer is formed only on one side of the porous substrate and no porous layer is formed on the other side, and the surface of the porous substrate is exposed, there is a concern that the separator will not be impregnated with the amount of electrolyte required from the viewpoint of battery characteristics due to poor affinity with the electrolyte. If the impregnation of the electrolyte is insufficient, the desired battery characteristics cannot be expected.
In view of this, in the separator for a non-aqueous secondary battery of the present disclosure, a porous layer containing a resin having a bond group selected from the group consisting of an amide bond, an imide bond, and a sulfonyl bond is provided, the contact angle of the surface of the porous layer is set to 5° to 40°, and the contact angle of the surface of the porous substrate is set to 30° to 75°. This improves the affinity of the inside of the pores of the porous substrate and the surface on the side not having the porous layer with the electrolyte, and the contact angle is adjusted to a predetermined range. As a result, the electrolyte is more likely to penetrate. When the electrolyte is more likely to penetrate, the amount of electrolyte impregnated in the separator is improved.

(Porous substrate)
The porous substrate in the present disclosure is a substrate including at least a polyolefin microporous membrane, and may be a substrate made of a polyolefin microporous membrane.

A porous substrate has a structure in which a plurality of pores are connected to each other within the layer, allowing gas or liquid to pass from one side of the layer to the other side. The same is true for polyolefin microporous membranes.

~Contact angle of porous substrate~
The surface of the porous substrate opposite the side having the porous layer has a contact angle (e.g., the contact angle on the surface of the porous substrate) of 30° or more and 75° or less 65 milliseconds after 1.0 μL of the electrolyte solution is dropped onto the surface.
The "point in time 65 milliseconds after the electrolyte lands on the surface" refers to the period from the point in time when the electrolyte lands on the surface to the point in time (end point) when 65 milliseconds have elapsed.

The contact angle on the side of the porous substrate opposite to the side having the porous layer is preferably kept low in terms of ease of penetration of the electrolyte solution. If the contact angle exceeds 75°, it is difficult for the electrolyte solution to penetrate the separator entirely, and the electrolyte solution impregnated therein is insufficient.
A contact angle of 75° or less indicates that the resin of the porous layer provided on one side of the porous substrate passes through the inside of the pores of the porous substrate to reach the other side, and that the resin is present on the surface of the porous substrate. That is, it indirectly indicates that the inside of the pores of the porous substrate is impregnated with the resin, for example, that the inner surface of the pores of the porous substrate is partially or entirely covered with the resin.

The contact angle of the porous substrate is preferably 72° or less, more preferably 70° or less, even more preferably 68° or less, and particularly preferably 65° or less.

The lower limit of the contact angle of the porous substrate can be in the range of 30° or more, since the contact angle will not be substantially lower than that of the porous layer.

When the porous substrate has a porous layer on only one side, the absolute value of the difference between the contact angle of the surface of the porous layer and the contact angle of the surface of the porous substrate opposite the side having the porous layer is preferably 60° or less, more preferably 45° or less, and particularly preferably 40° or less. When the absolute value of the difference is within the above range, that is, when the difference between the contact angle of the coated surface and the contact angle of the opposite side of the coated surface is small, it is easy to obtain a state in which the aramid has penetrated into the porous substrate.

As described above, the contact angle of the porous substrate itself, on whose surface no resin is present, is about 85° to 90°.
The difference between the contact angle of the surface of the porous substrate opposite the side having the porous layer and the contact angle of the surface of the porous substrate itself where no resin is present on the surface of the porous substrate is preferably greater than 0 degrees, more preferably 10° or more, and even more preferably 20° or more.

The contact angle of the porous substrate can be adjusted by appropriately selecting the porous substrate to be used, the resin to be coated, the solvent of the coating liquid, the resin concentration of the coating liquid, and the coating method of the coating liquid (e.g., a method of applying by pressing, such as a method using a reverse coater) and the coating conditions.
The contact angle can also be adjusted by applying a solvent to the surface of the porous substrate opposite the side on which the porous layer is to be formed, allowing the solvent to soak into the pores of the porous substrate, and then applying a coating liquid for forming the porous layer.

The contact angle of the porous substrate is a value measured using a contact angle meter (for example, Kyowa Interface Science Co., Ltd.'s contact angle meter DMo-701) under the following measurement conditions.
(Measurement conditions)
Environmental conditions: temperature 20°C, relative humidity 40%
Dropping solution: Electrolyte solution in which 1 mol/l LiPF ₆ is dissolved in a mixed solvent of ethylene carbonate and propylene carbonate (mixing ratio 1:1 [mass ratio]) Dropping amount: 1.0 μL
Measurement timing: Measured 65 milliseconds after the electrolyte hits the surface

The porous substrate is preferably a microporous film containing polyolefin (referred to herein as a "polyolefin microporous film").
The polyolefin microporous membrane may be selected from polyolefin microporous membranes that have sufficient mechanical properties and ion permeability and are used in separators for conventional non-aqueous secondary batteries.

From the viewpoint of mechanical properties and shutdown properties, it is preferable that the polyolefin microporous membrane contains polyethylene (i.e., a polyethylene microporous membrane). It is preferable that the polyethylene content of the resin components in the polyethylene microporous membrane is 95 mass% or more.

The polyolefin contained in the polyolefin microporous membrane is preferably a polyolefin having a weight-average molecular weight of 100,000 to 5,000,000. If the weight-average molecular weight is 100,000 or more, good mechanical properties can be ensured. On the other hand, if the weight-average molecular weight is 5,000,000 or less, the membrane is easy to mold.

A microporous polyolefin membrane can be produced, for example, by the following methods: a method in which molten polyolefin resin is extruded through a T-die to form a sheet, which is then crystallized, stretched, and heat-treated to form a microporous membrane; or a method in which molten polyolefin resin together with a plasticizer such as liquid paraffin is extruded through a T-die into a sheet, the extruded resin is cooled and stretched, the plasticizer is extracted, and the resin is heat-treated to form a microporous membrane.

The average pore size of the porous substrate is preferably in the range of 20 nm or more and 100 nm or less. When the average pore size of the porous substrate is 20 nm or more, ions are easily moved, and good battery performance is easily obtained. From this viewpoint, the average pore size of the porous substrate is more preferably 30 nm or more, and even more preferably 40 nm or more. On the other hand, when the average pore size of the porous substrate is 100 nm or less, the peel strength between the porous substrate and the porous layer is improved. From this viewpoint, the average pore size of the porous substrate is more preferably 90 nm or less, and even more preferably 80 nm or less.
The average pore size of the porous substrate is a value measured using a perm porometer, and can be measured, for example, using a perm porometer (CFP-1500-A manufactured by PMI) in accordance with ASTM E1294-89.

From the viewpoint of obtaining good mechanical properties and internal resistance, the thickness of the porous substrate is preferably in the range of 3 μm to 25 μm. In particular, the thickness of the porous substrate is more preferably in the range of 5 μm to 20 μm.

The Gurley value (JIS P8117:2009) of the porous substrate is preferably in the range of 50 sec/100 ml to 400 sec/100 ml inclusive, from the viewpoint of obtaining ion permeability.

The porosity of the porous substrate is preferably in the range of 20% to 60% in order to obtain an appropriate membrane resistance.

From the viewpoint of improving production yield, it is preferable that the puncture strength of the porous substrate is 200 g or more.

It is preferable that the porous substrate is subjected to various surface treatments. By performing the surface treatment, it is possible to improve the wettability with the coating liquid for forming the porous layer described below. Specific examples of the surface treatment include corona treatment, plasma treatment, flame treatment, ultraviolet irradiation treatment, etc., and the treatment can be performed within a range that does not impair the properties of the porous substrate.

(Porous Layer)
The porous layer in the present disclosure contains a resin having at least one bond group selected from the group consisting of amide bond, imide bond and sulfonyl bond (hereinafter also referred to as specific resin) on only one side of the porous substrate. The porous layer in the present disclosure preferably contains inorganic particles, and may further contain other components such as resins other than the specific resin and additives as necessary.

A porous layer has multiple pores inside the layer, and the multiple pores are interconnected, allowing gas or liquid to pass from one side of the layer to the other.

~Contact angle of porous layer~
The surface of the porous layer (i.e., the exposed surface of the porous layer that does not face the porous substrate) has a contact angle of 5° or more and 40° or less 65 milliseconds after the electrolyte solution is dropped on the surface when 1.0 μL of the electrolyte solution, in which ₁ mol/L LiPF6 is dissolved in a mixed solvent of ethylene carbonate and propylene carbonate (mixing ratio 1:1 [mass ratio]), is dropped on the surface of the porous layer.
The term "65 milliseconds after the electrolytic solution has landed" has the same meaning as in the case of the porous substrate described above.

The contact angle of the porous layer of the separator for a non-aqueous secondary battery of the present disclosure is preferably kept low in terms of ease of penetration of the electrolyte. If the contact angle of the porous layer is 40° or less, the electrolyte can easily penetrate throughout the separator, and the electrolyte can be impregnated well.

A contact angle of 5° or more for the porous layer means that this is the measurement limit.
The contact angle of the porous layer is preferably 30° or less for the same reasons as above.

The contact angle of the porous layer is a value measured using a contact angle meter (for example, Kyowa Interface Science Co., Ltd.'s contact angle meter DMo-701) under the following measurement conditions.
(Measurement conditions)
Environmental conditions: temperature 20°C, relative humidity 40%
Dropping solution: Electrolyte solution in which 1 mol/l LiPF ₆ is dissolved in a mixed solvent of ethylene carbonate and propylene carbonate (mixing ratio 1:1 [mass ratio]) Dropping amount: 1.0 μL
Measurement timing: Measured 65 milliseconds after the electrolyte hits the surface

-resin-
The porous layer contains at least one resin (specific resin) having at least one bond group selected from the group consisting of amide bonds, imide bonds, and sulfonyl bonds. Since the resin has a bond group selected from amide bonds, imide bonds, and sulfonyl bonds, it has good affinity with the porous substrate (particularly a polyethylene film) and also has high affinity with the electrolyte, so that the electrolyte permeability into the porous layer is good. As a result, the non-aqueous secondary battery separator of the present disclosure is easily permeated with the electrolyte and is easily impregnated with the electrolyte. As a result, it contributes to improving the battery characteristics when a secondary battery is produced.

The resin in this disclosure is a polymer having at least one bond selected from the group consisting of an amide bond, an imide bond, and a sulfonyl bond, and may have any structure as long as it is a polymer having the above bond.

Resins having an amide bond include nylon, wholly aromatic polyamide, polyamideimide, and the like.
Resins having imide bonds include polyamideimide, polyimide, and the like.
Resins having a sulfonyl bond include polysulfone, polyethersulfone, and the like.

Among the above resins, fully aromatic polyamide is preferred because it has good affinity with the porous substrate (especially polyethylene film) and the electrolyte, and also has excellent heat resistance. Fully aromatic polyamide can be dissolved at an appropriate concentration in a polar organic solvent, such as an amide-based solvent. Therefore, a solution (coating liquid) in which fully aromatic polyamide is dissolved in an organic solvent is applied to a porous substrate including a polyolefin microporous membrane, and the coating film is solidified, washed with water, and dried to easily form a porous layer. In addition, the porous structure is easily controlled. Furthermore, since the coating liquid easily penetrates into the pores of the porous substrate, the electrolyte impregnation of the porous substrate can also be improved.
Moreover, since the melting point of the wholly aromatic polyamide is 200° C. or higher, the heat resistance of the separator is increased, and the safety of the secondary battery is improved.

Fully aromatic polyamides include meta-type polyamides (also referred to as meta-aramids in this specification) and para-type polyamides. Of these, meta-type polyamides are preferred in that they are easier to form a porous layer from the standpoint of crystallinity compared to para-type polyamides.

Examples of meta-type polyamides include polymetaphenylene isophthalamide, etc. Examples of para-type polyamides include copolyparaphenylene-3,4'-oxydiphenylene-terephthalamide, polyparaphenylene terephthalamide, etc.
The wholly aromatic polyamide may be a commercially available product, such as Teijin Techno Products' Conex (registered trademark; meta type), Technora (registered trademark; para type), or Twaron (registered trademark; para type).

The content of the wholly aromatic polyamide in the porous layer is preferably 10% by mass to 40% by mass, and more preferably 15% by mass to 35% by mass, based on the total solid content of the porous layer.

-particle-
The porous layer preferably contains particles, and the particles include both inorganic particles and organic particles. The porous layer preferably contains inorganic particles.

By including inorganic particles in the porous layer, it is possible to improve heat resistance, reduce film resistance (improving the ease of electrolyte penetration and the ease of pore formation), and reduce the coefficient of friction.

Examples of inorganic particles include metal oxides such as alumina, zirconia, yttria, ceria, magnesia, titania, and silica; metal nitrides such as boron nitride and aluminum nitride; metal salts such as calcium carbonate and barium sulfate; and metal hydroxides such as magnesium hydroxide.

Among the above, as the inorganic particles, from the viewpoints of improving heat resistance, reducing film resistance (improving the ease of electrolyte penetration and the ease of pore formation), and reducing friction coefficient, bivalent metal-containing particles are preferred, and bivalent metal sulfate particles or bivalent metal hydroxide particles are more preferred. For example, magnesium-containing particles or barium-containing particles are preferred.
As the magnesium-containing particles, particles of magnesium sulfate, magnesium hydroxide, magnesium oxide, etc. are preferred, and magnesium hydroxide particles are more preferred.
The barium-containing particles are preferably barium sulfate particles.

The average primary particle size of the inorganic particles is preferably 0.01 μm to 2.0 μm.
When the average primary particle size is 0.01 μm or more, a porous structure is easily formed in the separator manufacturing process, and when the average primary particle size is 2.0 μm or less, it is advantageous for thinning the porous layer, and the packing density of the inorganic particles and the resin in the heat-resistant porous layer is increased.
The average primary particle size of the inorganic particles is more preferably from 0.02 μm to 1.5 μm, and further preferably from 0.03 μm to 0.9 μm.

The average primary particle size is obtained by measuring the major axis of 100 inorganic particles randomly selected in observation with a scanning electron microscope (SEM) and averaging the major axis of the 100 particles. The sample used for SEM observation is inorganic particles that are the material of the heat-resistant porous layer, or inorganic particles taken out from a separator. There is no limitation on the method for taking out the inorganic particles from the separator, and examples of the method include a method of heating the separator to about 800°C to remove the binder resin and take out the inorganic particles, and a method of immersing the separator in an organic solvent to dissolve the binder resin with the organic solvent and take out the inorganic particles.
When the average primary particle size of the inorganic particles is small, or when the inorganic particles are significantly aggregated and the major axis of the inorganic particles cannot be measured, the specific surface area of the inorganic particles is measured by the BET method, and the particle size is calculated from the specific gravity and specific surface area of the inorganic particles according to the following formula, assuming that the inorganic particles are true spheres.
Average primary particle diameter (μm) = 6÷[specific gravity (g/cm ³ )×BET specific surface area (m ² /g)]
In measuring the specific surface area by the BET method, an inert gas is used as the adsorbate and is adsorbed onto the surface of inorganic particles at the boiling point of liquid nitrogen (-196°C). The amount of gas adsorbed onto the sample is measured as a function of the pressure of the adsorbate, and the specific surface area of the sample is calculated from the amount of adsorption.

There are no limitations on the shape of the inorganic particles, and they may be spherical or nearly spherical, plate-like, or fibrous.

-Other ingredients-
In addition to the above components, the porous layer in the present disclosure may contain other components, such as resins other than the specific resin and additives, as necessary.
Resins other than the specific resin may be appropriately selected from any known resin depending on the purpose or case, as long as the effects of the present disclosure are not significantly impaired.
Examples of the additives include dispersants such as surfactants, wetting agents, antifoaming agents, and pH adjusters.

The porous layer can be formed by preparing a coating liquid for forming the porous layer and applying the coating liquid to the porous substrate. From the viewpoint of adjusting the contact angle to the above range, the coating can be performed by a coating method in which the substrate is pressed against the substrate, such as a method using a reverse coater.

~Properties of the porous layer~
[Thickness]
The thickness of the porous layer on one side of the porous substrate is preferably 0.3 μm or more and 5.0 μm or less. When the thickness of the porous layer is 0.3 μm or more, the layer becomes smooth and homogeneous, and the cycle characteristics of the battery are further improved. From the same viewpoint, the thickness of one side of the porous layer is more preferably 1.5 μm or more. On the other hand, when the thickness of one side of the porous layer is 5.0 μm or less, the ion permeability becomes better, and the load characteristics of the battery become more excellent. From the same viewpoint, the thickness of one side of the porous layer is more preferably 4.0 μm or less, further preferably 3.0 μm or less, and particularly preferably 2.5 μm or less.

[Porosity]
The porosity of the porous layer is preferably in the range of 30% to 80%. When the porosity is 80% or less, it is easy to ensure mechanical properties, and the surface opening ratio is not too high, which is suitable for ensuring adhesive strength. On the other hand, when the porosity is 30% or more, ion permeability is improved.
The porosity (ε) is a value calculated from the following formula.
ε={1-Ws/(ds・t)}×100
In the formula, ε represents porosity (%), Ws represents basis weight (g/m ² ), ds represents true density (g/cm ³ ), and t represents film thickness (μm).

[Average pore size]
The average pore size of the porous layer is preferably in the range of 10 nm to 300 nm. When the average pore size is 300 nm or less, the non-uniformity of the pores is suppressed, the bonding points are relatively evenly distributed, and the adhesiveness is further improved. When the average pore size is 300 nm or less, the uniformity of the movement of ions is high, and the cycle characteristics and load characteristics are further improved. On the other hand, when the average pore size is 10 nm or more, when the porous layer is impregnated with an electrolyte, the resin constituting the porous layer swells and blocks the pores, so that the phenomenon of ion permeability being inhibited is unlikely to occur.

The average pore size (diameter, unit: nm) of the porous layer is calculated from the pore surface area S of the porous layer made of a wholly aromatic polyamide calculated from the nitrogen gas adsorption amount, and the pore volume V of the porous layer calculated from the porosity, based on the assumption that all pores are cylindrical, according to the following formula:
d = 4 V/S
In the formula, d represents the average pore diameter (nm) of the porous layer, V represents the pore volume per ^m2 of the porous layer, and S represents the pore surface area per ^m2 of the porous layer.
The pore surface area S per ^m2 of the porous layer is determined by the following method.
The specific surface area ( ^m2 /g) of the porous substrate and the specific surface area ( ^m2 /g) of the composite membrane formed by laminating the porous substrate and the porous layer are measured by applying the BET method in the nitrogen gas adsorption method. Each specific surface area is multiplied by each basis weight (g/ ^m2 ) to calculate each pore surface area per ^m2 . Next, 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 porous layer.

～Separator properties～

[McMillan number (Mn)]
In terms of ion permeability, the nonaqueous secondary battery separator of the present disclosure preferably has a MacMillan number (Mn) calculated by the following formula of 20 or less.
The McMillan number is an index of ion permeability, and is the value obtained by dividing the conductivity of the electrolyte alone by the conductivity when the separator is impregnated with the electrolyte. In other words, if Mn is too large, the ion permeability is insufficient.
Mn is more preferably 15 or less, further preferably 12 or less, and further preferably 10 or less. The lower limit of Mn can be 1 or more, and more preferably 4 or more.

Mn=(σe)/(σs)
σs=t/Rm

σe represents the electrical conductivity (S/m) at 20° C. of an electrolyte solution in which 1 mol/l of _LiPF6 is dissolved in a mixed solvent of ethylene carbonate and propylene carbonate (mixing ratio 1:1 [mass ratio]). σe is a value measured using a CM-41X electrical conductivity meter and a CT-58101B electrical conductivity cell manufactured by DKK-TOA Corporation.
σs represents the electrical conductivity (S/m) of the separator impregnated with the electrolyte at 20° C. σs is a value measured by dividing the membrane thickness by the membrane resistance.
t represents the film thickness (m), which is determined in the same manner as in [Thickness] below.
Rm represents the membrane resistance (ohm·cm ² ) of the separator. Rm is a value determined in the same manner as in “[Membrane resistance (ion permeability)]” below.

[Thickness]
The nonaqueous secondary battery separator of the present disclosure preferably has a thickness of 7.5 μm or more and 20 μm or less.
When the thickness of the separator is 7.5 μm or more, the separator can easily maintain a sufficient strength for handling, and when the thickness of the separator is 20 μm or less, the ion permeability can be well maintained, the dischargeability and low-temperature characteristics of the battery can be well maintained, and the energy density of the battery can be well maintained.
For the same reason, the thickness of the separator is more preferably 7.6 μm to 14 μm.
The thickness is measured using a contact thickness gauge (Mitutoyo Corporation, LITEMATIC) with a cylindrical measuring probe having a diameter of 5 mm. During the measurement, a load of 0.01 N is applied, and measurements are taken at any 20 points within a 10 cm x 10 cm area, and the average value is calculated.

[Membrane resistance (ion permeability)]
In order to ensure the load characteristics of the battery, the membrane resistance of the separator is preferably in the range of 1 ohm·cm ² to 10 ohm·cm ² .
The membrane resistance refers to the resistance value when the separator is impregnated with the electrolyte, and is a value measured by an AC method. The membrane resistance is measured at 20° C. using an electrolyte solution in which 1 mol/l LiPF ₆ is dissolved in a mixed solvent of ethylene carbonate and propylene carbonate (mixture ratio 1:1 [mass ratio]). The detailed measurement method will be described in the examples.

It is preferable that the porous substrate has a resin inside the pores and on the surface of the porous substrate opposite to the side having the porous layer, whereby the separator can be entirely impregnated with the electrolyte.
The term "having a resin inside the pores of a porous substrate" refers to a state in which the resin has permeated part or all of the inside of the pores of the porous substrate.
The term "having a resin on the surface opposite to the porous layer of the porous substrate" refers to a state in which, when the coating liquid for forming a porous layer is applied to one side of the porous substrate, the resin in the coating liquid penetrates from one side of the porous substrate, passes through the inside of the pores in the porous substrate, and reaches the other side, so that the presence of the resin can be confirmed. The presence of the resin can be confirmed by checking that the contact angle after the coating liquid for forming a porous layer is applied is lower than the contact angle on the surface of the porous substrate before the coating liquid for forming a porous layer is applied.

The larger the absolute value of the difference between the contact angle of the surface of the porous substrate opposite the side having the porous layer and the contact angle of the surface of the porous substrate before the coating liquid for forming the porous layer is applied, the more the resin adheres to the inner surface of the pores of the porous substrate, the higher the affinity with the electrolyte, and the easier it is to be impregnated with the electrolyte. Specifically, the absolute value of the difference is preferably 15° or more, and more preferably 20° or more.

The presence of resin on the inner surface of the pores of the porous substrate can be confirmed by observing using energy dispersive X-ray spectroscopy (SEM-EDX; Energy Dispersive X-ray Spectroscopy), secondary ion mass spectrometry (SIMS; Secondary Ion Mass Spectrometry), X-ray photoelectron spectroscopy (ESCA; Electron Spectroscopy for Chemical Analysis), dyeing the resin, etc.

In addition, if the contact angle on the surface of the porous substrate opposite the porous layer is smaller 60 seconds after the electrolyte is deposited than 65 milliseconds after the electrolyte is deposited, it can be determined that this condition has occurred.

<Non-aqueous secondary battery>
The nonaqueous secondary battery of the present disclosure includes a positive electrode, a negative electrode, the above-described nonaqueous secondary battery separator of the present disclosure disposed between the positive electrode and the negative electrode, and an electrolyte solution in which a lithium salt is dissolved in a solvent containing 90 mass % or more of cyclic carbonate with respect to the total mass of the solvent, and generates an electromotive force by doping and dedoping of lithium.

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 is preferably a lithium ion secondary battery having a structure in which a separator is disposed between a positive electrode and a negative electrode, and includes (1) a secondary battery in which battery elements such as a positive electrode, a negative electrode, and a separator are enclosed in an exterior material together with an electrolyte, and (2) an all-resin battery in which all battery elements including the electrodes are made of resin.

For the secondary battery (1) above, reference can be made to the materials described in paragraphs 0056 to 0061 of International Publication No. WO 2008/062727.

The all-resin battery (2) above is a secondary battery in which an electrode active material covered with a gel-like polymer that has absorbed an electrolyte is mixed with a conductive assistant and conductive fibers to form a composite material, and the composite material for the positive electrode and the composite material for the negative electrode are stacked with a separator in between, and preferably a current collector is provided on the surface of the composite material.

The positive electrode may be a positive electrode layer formed from a composite material that includes a positive electrode active material, a gel electrolyte that covers the positive electrode active material, and conductive fibers. The positive electrode layer may further include a conductive assistant.

The negative electrode may be a negative electrode layer formed from a composite material that includes a negative electrode active material, a gel electrolyte that covers the negative electrode active material, and conductive fibers. The negative electrode layer may further include a conductive assistant.

Examples _{of the} positive electrode active material include lithium-containing transition metal oxides, such as _LiCoO2 , _LiNiO2 , LiMn1/ _{2Ni1 / 2O2 ,} LiCo1/ _3Mn1 /3Ni1/3O2, LiMn2O4, _LiFePO4 , LiCo1 _{/ 2Ni1/ 2O2 ,} and LiAl1 _{/ 4Ni3 / 4O2} .

An example of the negative electrode active material is hard carbon (non-graphitizable carbon).

Gel electrolytes include those in which an electrolyte solution is absorbed into a gel-like polymer (polymer gel).

The electrolyte is a solution in which a lithium salt is dissolved in a non-aqueous solvent.
Examples of lithium salts include LiPF ₆ , LiBF ₄ , and LiClO ₄ .
Examples of the non-aqueous solvent include propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and γ-butyrolactone. The non-aqueous solvent may be used alone or in combination of two or more. The non-aqueous solvent is preferably one having a high relative dielectric constant and a low melting point, more preferably a cyclic carbonate, and more preferably a mixed solvent containing 90% by mass or more of the cyclic carbonate relative to the total mass of the non-aqueous solvent.

The cyclic carbonate-based non-aqueous solvents such as EC and PC have a relatively high viscosity.
An electrolyte solution containing a cyclic carbonate-based non-aqueous solvent such as EC or PC is preferred in that it is easy to retain a large amount of electrolyte and has excellent electrochemical stability. Conventionally, when the permeability of the electrolyte solution into the separator is not necessarily sufficient, the electrolyte solution impregnated becomes insufficient, so that a high-concentration electrolyte solution containing a large amount of electrolyte was generally used after dilution. In this respect, the non-aqueous secondary battery of the present disclosure is provided with the non-aqueous secondary battery separator of the present disclosure, which has excellent electrolyte permeability, as described above, so that a cyclic carbonate with a relatively high viscosity can be used as a solvent. And, a high-concentration electrolyte solution using a cyclic carbonate can be used in a non-aqueous secondary battery, and the impregnation of the electrolyte is excellent, resulting in excellent battery characteristics.

The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to the following examples as long as it does not deviate from the gist of the invention. Note that "parts" are by weight unless otherwise specified.

(measurement)
The following measurements were carried out on the porous substrates and separators produced in the examples and comparative examples described below.

[Film thickness]
The thickness (μm) of the porous substrate and the separator was measured at 20 points using a contact thickness meter (Mitutoyo Corporation, LITEMATIC VL-50) and the average was calculated. A cylindrical terminal with a diameter of 5 mm was used as the measurement terminal, and the terminal was adjusted so that a load of 0.01 N was applied during the measurement.

[Film thickness of porous layer]
The difference between the thickness of the separator and the thickness of the porous substrate was defined as the thickness of the porous layer.

[Film resistance]
The prepared separator is cut into a sample piece of 2.6 cm x 2.0 cm size. A 20 μm thick aluminum foil is cut into 2.0 cm x 1.4 cm, and a lead tab is attached. Two sheets of this aluminum foil are prepared, and the cut sample piece is sandwiched between the aluminum foils so that the aluminum foil does not short circuit. The sample piece is impregnated with an electrolyte solution in which 1 mol/l LiPF ₆ is dissolved in a mixed solvent of ethylene carbonate and propylene carbonate (mixture ratio 1:1 [mass ratio]) which is an electrolyte solution. This is sealed under reduced pressure in an aluminum laminate pack so that the tab is outside the aluminum pack to form a cell. Such cells are prepared so that one, two, and three sample pieces (separators) are placed in the aluminum foil. The cell is placed in a thermostatic chamber at 20 ° C., and the resistance of the cell is measured by an AC impedance method at an amplitude of 10 mV and a frequency of 100 kHz. The measured cell resistance values were plotted against the number of separators, and the plot was linearly approximated to obtain a slope, which was multiplied by the electrode area (2.0 cm x 1.4 cm) to obtain the membrane resistance (ohm·cm ² ) per separator.

[Macmillan number]
The McMillan number (Mn) was calculated from the following formula.
Mn=(σe)/(σs)
σs=t/Rm
In the formula, σe represents the conductivity (S/m) at 20°C of an electrolyte solution obtained by dissolving 1 mol/l _LiPF6 in a mixed solvent of ethylene carbonate and propylene carbonate (mixing ratio 1:1 [mass ratio]), σs represents the conductivity (S/m) of a separator impregnated with the electrolyte solution at 20°C, t represents the membrane thickness (m), and Rm represents the membrane resistance (ohm·cm ² ) of the separator. σe was measured using an electric conductivity system CM-41X and an electric conductivity cell CT-58101B manufactured by DKK-TOA Corporation, and σs was measured by dividing the membrane thickness by the membrane resistance. t and Rm were measured in the same manner as the above [film thickness of the porous layer] and [membrane resistance], respectively.

[Contact angle]
The separator was fixed on a flat plate, and 1.0 μL of an electrolyte solution prepared by dissolving 1 mol/l LiPF ₆ in a mixed solvent of ethylene carbonate and propylene carbonate (mixing ratio 1:1 [mass ratio]) was dropped onto the separator, and the contact angle was measured 65 ms after the drop landed. The measurement was performed in an environment with a temperature of 20 degrees and a relative humidity of 40%, using a contact angle meter "DMo-701" manufactured by Kyowa Scientific.

[Prototype of non-aqueous secondary battery]
A slurry was prepared by kneading 94 parts by mass of lithium cobalt oxide (LiCoO ₂ ; manufactured by Nippon Chemical Industry Co., Ltd.) powder, 3 parts by mass of acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd.; product name: Denka Black), and 3 parts by mass of polyvinylidene fluoride (manufactured by Kureha Chemical Co., Ltd.) using N-methyl-2-pyrrolidone solvent. The obtained slurry was applied onto an aluminum foil with a thickness of 20 μm, dried, and then pressed to obtain a positive electrode of 100 μm.
87 parts by mass of hard carbon powder (Bellfine LN-0001: manufactured by AT Electrode Co., Ltd.), 3 parts by mass of acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd.; product name: Denka Black), and 10 parts by mass of polyvinylidene fluoride (manufactured by Kureha Chemical Co., Ltd.) were kneaded using an N-methyl-2-pyrrolidone solvent to prepare a slurry. The obtained slurry was applied onto a copper foil having a thickness of 18 μm, dried, and then pressed to obtain a negative electrode having a thickness of 90 μm.
The positive and negative electrodes were opposed to each other with a separator interposed therebetween. The electrodes were impregnated with an electrolyte and enclosed in an exterior made of an aluminum laminate film to prepare a non-aqueous secondary battery. The electrolyte used was a solution of 1 mol/l _LiPF6 dissolved in a mixed solvent of ethylene carbonate and propylene carbonate (mixture ratio 1:1 [mass ratio]).
Here, this prototype battery has a positive electrode area of 5.0×3.0 cm ² , a negative electrode area of 5.2×3.2 cm ² , and a set capacity of 10 mAh (range of 4.2 V-2.5 V).

(evaluation)
[Dischargeability]
The dischargeability of the battery prepared by the above method was evaluated. Five charge/discharge cycles were performed: 15 hours of constant current/voltage charging at 1 mA and 4.2 V, followed by constant current discharging at 1 mA and 2.5 V. The discharge capacity obtained in the second cycle was divided by the discharge capacity of the battery in the fifth cycle, and the resulting value was used as an index of dischargeability and was evaluated according to the following evaluation criteria.
<Evaluation criteria>
A: 85% or more B: 70% or more but less than 85% C: Less than 70%

[Heat resistance]
The prepared separator is cut into a size of 18 cm (MD; Machine Direction) x 6 cm (TD; Transverse Direction). Marks are made on the line dividing the TD in half at points 2 cm and 17 cm from the top (points A and B). Marks are also made on the line dividing the MD in half at points 1 cm and 5 cm from the left (points C and D). A clip is attached to this (the clip is attached within 2 cm from the top of the MD), and it is hung in an oven adjusted to 120°C and heat-treated for 60 minutes without tension. The lengths between the two points A and B and between the two points CD were measured before and after heat treatment, and the thermal shrinkage was calculated from the following formula.
MD heat shrinkage rate (%) = {(length of AB before heat treatment - length of AB after heat treatment) / length of AB before heat treatment} x 100
TD heat shrinkage rate (%)={(CD length before heat treatment−CD length after heat treatment)/CD length before heat treatment}×100
<Evaluation criteria>
A: Both the MD heat shrinkage rate and the TD heat shrinkage rate are less than 5%.
B: Either the MD heat shrinkage rate or the TD heat shrinkage rate is 5% or more.

Example 1
Meta-type wholly aromatic polyamide (meta-aramid) was dissolved in dimethylacetamide (DMAc) so that the concentration was 4.5% by mass, and further barium sulfate particles (average primary particle diameter 0.05 μm) were mixed while stirring to obtain a coating liquid (A). Next, the coating liquid (A) was applied to one side of a polyethylene microporous membrane A (thickness 7 μm, porosity 36%, Gurley value 120 seconds/100 mL) using a reverse roll coater to form a coating film. The coating film was immersed in a coagulation liquid (DMAc: water = 50: 50 [mass ratio], liquid temperature 40 ° C.) to solidify the coating layer. Next, the coating layer was washed in a water washing tank with a water temperature of 40 ° C. and dried. As a result of the evaluation, the ratio of meta-aramid: barium sulfate in the porous layer was 20: 80 (mass ratio). In this way, a separator in which a porous layer having a thickness of 2.0 μm was formed on one side of a polyethylene microporous membrane was produced.

Example 2
A separator was prepared in the same manner as in Example 1, except that the polyethylene microporous membrane A was changed to a polyethylene microporous membrane B (thickness: 12 μm, porosity: 40%, Gurley value: 200 sec/100 mL).

Example 3
A separator was produced in the same manner as in Example 1, except that the barium sulfate particles in Example 1 were changed to magnesium hydroxide particles (average primary particle diameter: 0.88 μm).

Example 4
A separator was prepared in the same manner as in Example 1, except that a coating liquid was prepared without adding barium sulfate particles, and a separator was prepared in which a porous layer with a thickness of 0.5 μm was formed on one side of a polyethylene microporous membrane.

(Comparative Example 1)
A separator was produced in the same manner as in Example 1, except that the coating liquid (A) was applied to both sides of the polyethylene microporous membrane A to form coating films on the front and back of the polyethylene microporous membrane A.

(Comparative Example 2)
A separator was produced in the same manner as in Example 2, except that the coating liquid (A) was applied to both surfaces of the polyethylene microporous membrane B to form coating films on the front and back of the polyethylene microporous membrane A.

(Comparative Example 3)
A polyvinylidene fluoride resin (VDF-HFP copolymer, VDF:HFP (molar ratio) = 97.6:2.4, weight average molecular weight 1,130,000) was dissolved in a mixed solvent of dimethylacetamide (DMAc) and tripropylene glycol (TPG) (DMAc:TPG = 80:20 [mass ratio]) to a concentration of 4 mass%, and barium sulfate particles (average primary particle diameter 0.05 μm) were further mixed with the solution while stirring to obtain a coating liquid (P).
The coating liquid (P) was applied to one side of the polyethylene microporous membrane B using a reverse roll coater to form a coating film. The coating film was immersed in a coagulation liquid (DMAc:TPG:water=30:8:62 [mass ratio], liquid temperature 40°C) to solidify the coating film. The coating film was then washed in a water washing tank with water temperature of 40°C and dried. In this way, a separator having a porous layer formed on one side of the polyethylene microporous membrane was obtained.

(Comparative Example 4)
A meta-type wholly aromatic polyamide was dissolved in dimethylacetamide (DMAc) so that the concentration was 4.5% by mass, and barium sulfate particles (average primary particle diameter 0.05 μm) were further stirred and mixed to obtain a coating liquid (A). When the coating liquid (A) was applied to one side of a polyethylene microporous membrane B (thickness 12 μm, porosity 40%, Gurley value 200 seconds/100 mL) using a reverse roll coater, dimethylacetamide was simultaneously applied to the opposite side. This was immersed in a coagulation liquid (DMAc:water=50:50 [mass ratio], liquid temperature 40° C.) to solidify the coating film. Next, the coating film was washed in a water washing tank with a water temperature of 40° C. and dried. In this way, a porous layer was formed on one side of the polyethylene microporous membrane, and a separator in which the coating liquid did not penetrate into the polyethylene microporous membrane was obtained.

As shown in Table 1, in the examples, the porous layer contains a specific resin, and thus the contact angle is significantly lower not only on the surface of the porous layer but also on the surface of the porous substrate opposite the side having the porous layer, compared to the comparative examples. This is thought to be because the resin of the porous layer passes through the inside of the pores from one side of the porous substrate to the other side and reaches the other side, and the specific resin is present inside the pores of the porous substrate and on the surface opposite the side having the porous layer of the porous substrate. In other words, the change in the contact angle supports the idea that the resin of the porous layer is present inside the pores of the porous substrate and on the surface opposite the side having the porous layer of the porous substrate. As a result, the affinity of the separator with the electrolyte is improved, and the impregnation of the electrolyte is enhanced. Therefore, the discharge characteristics of the examples are also higher than those of the comparative examples.

Claims (6)

A porous substrate comprising a polyolefin microporous membrane;
a porous layer on only one surface of the porous substrate, the porous layer comprising a resin having at least one bond group selected from the group consisting of an amide bond, an imide bond, and a sulfonyl bond;
Equipped with
When 1.0 μL of an electrolyte solution in which 1 mol/l of _LiPF4 is dissolved in a mixed solvent of ethylene carbonate and propylene carbonate (mixing ratio 1:1 [mass ratio]) is dropped onto the surface of the porous layer, the contact angle at the time 65 milliseconds after the electrolyte solution lands is 5° or more and 40° or less,
When 1.0 μL of the electrolyte solution is dropped onto the surface of the porous substrate opposite to the surface having the porous layer, the contact angle at 65 milliseconds after the electrolyte solution lands is 30° or more and 75° or less;
The porous layer has a thickness of 0.5 μm to 2.5 μm;
The resin is present inside the pores of the porous substrate, and the resin is present from one surface of the porous substrate to the other surface of the porous substrate.
Separator for non-aqueous secondary batteries. The separator for a non-aqueous secondary battery according to claim 1, wherein the porous layer contains inorganic particles. The separator for a non-aqueous secondary battery according to claim 1 or 2, wherein the resin contains a wholly aromatic polyamide. 4. The separator for a non-aqueous secondary battery according to claim 1, wherein a MacMillan number Mn calculated by the following formula is 20 or less:
Mn=(σe)/(σs)
σs=t/Rm
In the formula, σe represents the conductivity (S/m) at 20° C. of an electrolyte solution in which 1 mol/l of _LiPF6 is dissolved in a mixed solvent of ethylene carbonate and propylene carbonate (mixing ratio 1:1 [mass ratio]), σs represents the conductivity (S/m) at 20° C. of a separator impregnated with the electrolyte solution, t represents the membrane thickness (m), and Rm represents the membrane resistance of the separator (ohm cm ²
) 5. The separator for a non-aqueous secondary battery according to claim 1, wherein the absolute value of the difference between the contact angle of the surface of the porous layer and the contact angle of the surface of the porous substrate opposite to the side having the porous layer is 45 ° or less. The battery includes a positive electrode, a negative electrode, a non-aqueous secondary battery separator disposed between the positive electrode and the negative electrode, and an electrolyte solution in which a lithium salt is dissolved in a solvent containing 90 mass % or more of a cyclic carbonate with respect to a total mass of the solvent,
The nonaqueous secondary battery separator comprises a porous substrate including a polyolefin microporous membrane, and a porous layer including a resin having at least one bonding group selected from the group consisting of an amide bond, an imide bond, and a sulfonyl bond, on only one surface of the porous substrate;
When 1.0 μL of an electrolyte solution in which 1 mol/l of _LiPF4 is dissolved in a mixed solvent of ethylene carbonate and propylene carbonate (mixing ratio 1:1 [mass ratio]) is dropped onto the surface of the porous layer, the contact angle at the time 65 milliseconds after the electrolyte solution lands is 5° or more and 40° or less,
When 1.0 μL of the electrolyte solution is dropped onto the surface of the porous substrate opposite to the surface having the porous layer, the contact angle at 65 milliseconds after the electrolyte solution lands is 30° or more and 75° or less;
The resin is present inside the pores of the porous substrate, and the resin is present from one surface of the porous substrate to the other surface of the porous substrate;
A non-aqueous secondary battery that obtains electromotive force by doping and dedoping lithium.