JP2021061143A - Separator of nonaqueous electrolyte secondary battery, member for nonaqueous electrolyte secondary battery, and nonaqueous electrolyte secondary battery - Google Patents

Abstract

To suppress the occurrence of a short circuit owing to the growth of dendrite, which precipitates on a negative electrode in a nonaqueous electrolyte secondary battery.SOLUTION: A separator of a nonaqueous electrolyte secondary battery comprises a polyolefin porous film. In the nonaqueous electrolyte secondary battery separator, a path length, which is the product of a tortuosity factor and a film thickness is 22 μm or more and 38 μm or less; and the moisture percentage is 0.2 wt% or more and 0.7 wt% or less to a total weight of the nonaqueous electrolyte secondary battery separator.SELECTED DRAWING: None

Description

The present invention relates to a separator for a non-aqueous electrolyte secondary battery, a member for a non-aqueous electrolyte secondary battery provided with the separator for the non-aqueous electrolyte secondary battery, and a non-aqueous electrolyte secondary battery.

Non-aqueous electrolyte secondary batteries, particularly lithium ion secondary batteries, have high energy densities and are therefore widely used as batteries used in personal computers, mobile phones, mobile information terminals, automobiles, and the like.

In recent years, the demand for high-power lithium-ion secondary batteries has been increasing. In order to meet the above demand, the development of a lithium ion secondary battery provided with a separator having excellent ion permeability is underway.

On the other hand, the lithium ion secondary battery has a problem that a voltage drop due to a minute short circuit is likely to occur. The micro short circuit contributes to a decrease in long-term reliability of the battery.

Patent Document 1 discloses, as a separator for solving the above-mentioned problem, a separator composed of an insulating layer composed of a layer having a high bending ratio and a layer having a low bending ratio.

Japanese Unexamined Patent Publication No. 2009-199730 (published on September 3, 2009)

As will be described later, when the lithium ion secondary battery is repeatedly charged and discharged, lithium is deposited on the negative electrode and dendrites are generated. When the grown dendrites pass through the holes of the separator and reach the positive electrode, a voltage drop due to a minute short circuit can occur.

The separator disclosed in Patent Document 1 aims to suppress a voltage drop due to a minute short circuit by inhibiting the growth of dendrites in a layer having a high curvature rate and ensuring ion permeability in a layer having a low curvature ratio. It is supposed to be.

However, since the separator disclosed in Patent Document 1 has a structure in which a layer having a high bending ratio and a layer having a low bending ratio are overlapped, the region covered by the layer having a high bending ratio is one of the regions from the negative electrode to the positive electrode. Stop at the club. Therefore, the structure of the separator disclosed in Patent Document 1 is not yet sufficient to sufficiently suppress the growth of dendrites.

Further, it is known that the shape of the dendrite becomes closer to a needle shape as the dendrite grows, and the closer the shape is to the needle shape, the easier it is for the dendrite to extend in the hole of the separator. Therefore, it is important to control the shape of the dendrite in order to prevent a short circuit due to the growth of the dendrite.

However, Patent Document 1 focuses only on the curvature ratio and does not consider the control of the shape of the dendrite. From this point as well, it is considered that the structure of the separator disclosed in Patent Document 1 is not yet sufficient to sufficiently suppress the growth of dendrites.

The present invention includes the inventions shown in the following [1] to [5].
[1] A separator for a non-aqueous electrolytic solution secondary battery containing a polyolefin porous film, wherein the path length, which is the product of the curvature ratio and the film thickness, is 22 μm or more and 38 μm or less, and the water content is high. A separator for a non-aqueous electrolyte secondary battery, which is 0.2% by weight or more and 0.7% by weight or less with respect to the total weight of the separator for a non-aqueous electrolyte secondary battery.
[2] The separator for a non-aqueous electrolytic solution secondary battery according to [1], which has a structure in which a porous layer and the polyolefin porous film are laminated, and the porous layer contains a resin.
[3] The separator for a non-aqueous electrolytic solution secondary battery according to [2], wherein the resin is a nitrogen-containing aromatic resin.
[4] Non-aqueous electrolyte secondary battery in which the positive electrode, the separator for the non-aqueous electrolyte secondary battery according to any one of [1] to [3], and the negative electrode are arranged in this order. Materials.
[5] A non-aqueous electrolyte secondary battery comprising the separator for a non-aqueous electrolyte secondary battery according to any one of [1] to [3].

The separator for a non-aqueous electrolytic solution secondary battery according to an embodiment of the present invention has excellent ion permeability, and the occurrence of a short circuit due to the growth of dendrite deposited on the negative electrode is sufficiently suppressed. It has the effect of being able to provide an electrolytic solution secondary battery.

An embodiment of the present invention will be described below, but the present invention is not limited thereto. The present invention is not limited to the configurations described below, and various modifications can be made within the scope of the claims, and the technical means disclosed in the different embodiments may be appropriately combined. The obtained embodiments are also included in the technical scope of the present invention. Unless otherwise specified in the present specification, "A to B" representing a numerical range means "A or more and B or less".

[Embodiment 1: Separator for non-aqueous electrolyte secondary battery]
The separator for a non-aqueous electrolytic solution secondary battery according to the first embodiment of the present invention (hereinafter, also referred to as “separator 1”) is a separator for a non-aqueous electrolytic solution secondary battery containing a polyolefin porous film, and is curved. The path length, which is the product of the road ratio and the film thickness, is 22 μm or more and 38 μm or less, and the water content is 0.2% by weight or more and 0, based on the total weight of the separator for the non-aqueous electrolyte secondary battery. It is 0.7% by weight or less.

(1. Structure of separator 1)
The separator 1 contains a polyolefin porous film, preferably made of a polyolefin porous film.

Here, the "polyolefin porous film" is a porous film containing a polyolefin-based resin as a main component. Further, "mainly composed of a polyolefin resin" means that the ratio of the polyolefin resin to the porous film is 50% by volume or more, preferably 90% by volume or more of the whole material constituting the porous film. More preferably, it means that it is 95% by volume or more.

The polyolefin porous film contains an olefin resin as a main component and has a large number of pores connected to the inside thereof, so that gas and liquid can pass from one surface to the other. .. Hereinafter, the polyolefin porous film is also simply referred to as a "porous film".

Wherein the polyolefin is more preferably contains high molecular weight component having a weight average molecular weight of ^{5 × 10 5 ~15 × 10 6} . In particular, it is more preferable that the polyolefin contains a high molecular weight component having a weight average molecular weight of 1 million or more because the strength of the separator for a non-aqueous electrolytic solution secondary battery according to one embodiment of the present invention is improved.

Examples of the polyolefin include homopolymers and copolymers obtained by polymerizing monomers such as ethylene, propylene, 1-butene, 4-methyl-1-pentene and 1-hexene.

Examples of the homopolymer include polyethylene, polypropylene, and polybutene. Further, as the copolymer, for example, an ethylene-propylene copolymer can be mentioned.

Of these, polyethylene is more preferable as the polyolefin because it can prevent an excessive current from flowing at a lower temperature. Note that this "preventing the flow of excessive current" is also referred to as shutdown.

Examples of the polyethylene include low-density polyethylene, high-density polyethylene, linear polyethylene (ethylene-α-olefin copolymer), ultra-high molecular weight polyethylene having a weight average molecular weight of 1 million or more, and the like. Of these, as the polyethylene, ultra-high molecular weight polyethylene having a weight average molecular weight of 1 million or more is more preferable.

The basis weight of the porous film can be appropriately determined in consideration of strength, film thickness, weight and handleability. However, to be able to increase the weight energy density and volume energy density of the nonaqueous electrolyte secondary battery, wherein the basis weight is preferably 4~20g / ^{m 2,} is 4~12g / ^{m 2} More preferably, it is more preferably 5 to 10 g / m ² .

The air permeability of the porous film is preferably 30 to 500 s / 100 mL, more preferably 50 to 300 s / 100 mL in terms of Gale value. When the porous film has an air permeability within the above range, the porous film can obtain sufficient ion permeability.

The porosity of the porous film is preferably 20 to 80% by volume so that the retention amount of the electrolytic solution can be increased and the function of reliably blocking the flow of an excessive current at a lower temperature can be obtained. , 30-75% by volume, more preferably.

Further, the pore diameter of the pores of the porous film is 0.3 μm or less so that sufficient ion permeability can be obtained and particles can be prevented from entering the positive electrode and the negative electrode. It is preferably 0.14 μm or less, and more preferably 0.14 μm or less.

The separator 1 may further include other layers such as an adhesive layer, a heat-resistant layer, and a protective layer in addition to the polyolefin porous film.

(2. Method for producing porous polyolefin film)
Examples of the method for producing the porous film include the following methods. That is, first, a polyolefin-based resin, a pore-forming agent such as an inorganic filler or a plasticizer, and optionally an antioxidant or the like are kneaded to obtain a polyolefin-based resin composition. Then, the polyolefin-based resin composition is extruded to prepare a sheet-shaped polyolefin resin composition. Then, the pore-forming agent is removed from the sheet-shaped polyolefin resin composition with an appropriate solvent. Then, the polyolefin resin composition from which the pore-forming agent has been removed is stretched to produce a polyolefin porous film.

The inorganic filler is not particularly limited, and examples thereof include an inorganic filler, specifically calcium carbonate and the like. The plasticizer is not particularly limited, and examples thereof include low molecular weight hydrocarbons such as liquid paraffin.

Examples of the method for producing the porous film include a method including the following steps.
(I) Kneading an ultra-high molecular weight polyethylene having a weight average molecular weight of 1 million or more, a low molecular weight polyethylene having a weight average molecular weight of 10,000 or less, a pore-forming agent such as calcium carbonate or a plasticizer, and an antioxidant. A step of obtaining a polyolefin resin composition.
(Ii) A step of stepwise cooling the obtained polyolefin resin composition to form a sheet.
(Iii) A step of removing the pore-forming agent from the obtained sheet with an appropriate solvent.
(Iv) A step of stretching a sheet from which the pore-forming agent has been removed at an appropriate stretching ratio.

(3. Path length)
The path length in one embodiment of the present invention is the product of the bending ratio of the separator for a non-aqueous electrolyte secondary battery according to the embodiment of the present invention and the film thickness of the separator for a non-aqueous electrolyte secondary battery. This means the average path length of the holes of the separator for the non-aqueous electrolyte secondary battery, that is, the average path length of the through holes.

Examples of the method for measuring the path length include the methods shown in (a) and (b) below.
(A) The curvature ratio is calculated from the resistance value of the separator for a non-aqueous electrolyte secondary battery.
(B) The path length is calculated by multiplying the calculated curvature ratio by the film thickness (μm) of the separator for a non-aqueous electrolyte secondary battery.

Here, the curvature ratio is the average path length of the through holes per unit film thickness of the separator for a non-aqueous electrolyte secondary battery, and is also called the “waviness degree”. That is, the curvature ratio of the separator for a non-aqueous electrolyte secondary battery is a value obtained by dividing the path length of the separator for a non-aqueous electrolyte secondary battery by the film thickness of the separator for a non-aqueous electrolyte secondary battery.

The curvature ratio can be measured by, for example, the method shown below. First, a measurement cell in a state in which the separator for a non-aqueous electrolytic solution secondary battery is completely immersed in the electrolytic solution is prepared. Next, using the measurement cell, the resistance value of the separator for a non-aqueous electrolyte secondary battery is measured by the AC impedance method. A commercially available AC impedance measuring device can be used for measuring the resistance value.

After that, the measured resistance value R (Ω · cm ² ), the specific resistance r (Ω · cm) of the electrolytic solution, and the void ratio ε (%) and the film thickness d of the separator for the non-aqueous electrolytic solution secondary battery. Using (cm), the curve resistivity (T) is calculated based on the following formula (1).
T = [{(R × ε) / 100} / (r × d)] ^1/2 ... (1)
When, for example, a lithium ion secondary battery is used as the non-aqueous electrolyte secondary battery and charging and discharging are repeated, lithium (Li) is deposited on the negative electrode. As a result, dendrites composed of precipitated Li are generated at the negative electrode. Here, dendrite means a dendritic crystal. Hereinafter, the dendrite composed of the precipitated Li is also referred to as "Li dendrite".

When charging and discharging are repeated further, Li is further precipitated at the negative electrode, and the Li dendrite grows. At that time, Li preferentially precipitates at the terminal portion of the branch in the Li dendrite, so that the Li dendrite extends in the branch direction.

As a result, it is considered that a fine short circuit occurs when the portion of the lidendrite extending in the branch direction reaches the positive electrode through the hole in the lithium ion secondary battery separator, that is, the through hole.

When the path length is 22 μm or more, the curve ratio and length of the through hole are such that the dendrite does not easily extend in the through hole. Therefore, it is possible to make it difficult for a minute short circuit to occur. From the viewpoint of more efficiently suppressing the occurrence of micro short circuits, the path length is more preferably 27 μm or more, and particularly preferably 27.5 μm or more.

On the other hand, the through hole is also a path for ions to move between the positive electrode and the negative electrode. Therefore, if the path length becomes excessively large, the moving distance of ions between the positive and negative electrodes becomes excessively long, so that the ion conductivity of the separator may decrease and the ion permeability may deteriorate. As a result, the battery performance of the lithium ion secondary battery provided with the separator may deteriorate.

Therefore, the path length is 38 μm or less, preferably 35 μm or less, and more preferably 30 μm or less.

Further, the curvature ratio is preferably 1.3 or more and 2.5 or less in order to efficiently inhibit the dendrite from extending in the through hole while having excellent ion permeability. It is more preferably 5 or more and 2.0 or less, and particularly preferably 1.6 or more and 1.9 or less.

The bending ratio of the separator 1 is the bending ratio of the polyolefin porous film or the bending ratio of the separator provided with the polyolefin porous film and the other layer (adhesive layer or the like).

Further, the film thickness of the separator for the non-aqueous electrolyte secondary battery is such that the moving distance of the dendrite required until the fine short circuit occurs is sufficiently long and the film thickness can maintain good ionic conductivity. It is preferable to have.

From this point of view, the film thickness of the separator 1 is preferably 9 μm or more and 29 μm or less, more preferably 9 μm or more and 20 μm or less, and particularly preferably 9 μm or more and 15 μm or less.

The film thickness of the polyolefin porous film when the separator 1 does not include the other layers is also preferably 9 μm or more and 29 μm or less, more preferably 9 μm or more and 20 μm or less, and 9 μm or more and 15 μm or less. Is particularly preferred.

The film thickness of the separator 1 is the film thickness of the polyolefin porous film or the film thickness of the polyolefin porous film and the film thickness of the other layers (adhesive layer, etc.).

As described above, the path length represents the complexity and pore length of the pore structure of the separator and the ionic conductivity of the separator. The separator for a non-aqueous electrolyte secondary battery having a path length of 22 μm or more and 38 μm or less has a through hole having a suitable bending ratio and length for inhibiting dendrite elongation, and is good. It can be said that it is a separator having excellent ion conductivity, that is, excellent ion permeability.

(4. Moisture content)
The water content in one embodiment of the present invention means the ratio of the weight of water contained in the separator to the total weight (total weight) of the separator for a non-aqueous electrolyte secondary battery according to the embodiment of the present invention. To do. Therefore, the unit of the water content is% by weight.

When, for example, a lithium ion secondary battery is used as a non-aqueous electrolyte secondary battery and charging and discharging are repeated, the branch portion of the lidendrite generated at the negative electrode becomes thin in an environment with low water content, and the lidendrite becomes a needle. It becomes close to the shape. On the other hand, in an environment with a large amount of water, the branch portion of the Lidendrite generated at the negative electrode becomes thicker, and the Lidendrite becomes nearly spherical.

Here, the closer the Lidendrite is to a needle shape, the easier it is for the Lidendrite to extend toward the end of the needle, that is, in the branch direction when the Lidendrite grows. On the contrary, the closer the Lidendrite is to a spherical shape, the more difficult it is for the Lidendrite to grow in the branch direction.

Therefore, when the water content is large, the growth rate of the Lidendrite in the positive electrode direction becomes slow, so that the time until the Lidendrite reaches the positive electrode can be lengthened. As a result, the occurrence of fine short circuits can be suppressed.

When the water content is 0.2% by weight or more, the shape of the dendrite can be made closer to a spherical shape instead of a needle shape. Therefore, it is possible to make it difficult for a minute short circuit to occur.

From the viewpoint of more efficiently suppressing the occurrence of micro short circuits, the water content is more preferably 0.3% by weight or more, and particularly preferably 0.4% by weight or more.

On the other hand, it is known that the performance of a non-aqueous electrolyte secondary battery may deteriorate in an environment in which water is present. Therefore, when the water content is excessively large, the battery performance of the non-aqueous electrolyte secondary battery provided with the separator for the non-aqueous electrolyte secondary battery according to the embodiment of the present invention may deteriorate.

Therefore, the water content is 0.7% by weight or less, preferably 0.65% by weight or less, and more preferably 0.62% by weight or less.

The moisture content can be measured using, for example, a commercially available Karl Fischer titer.

(5. Adjustment of path length and water content)
The method for producing a porous film described in "2. Method for producing a polyolefin porous film" may include a step of washing the stretched film with an appropriate solvent and drying it after the step (iv). Further, after the step of drying the film, a step of heat-fixing the dried film may be further included.

By suitably controlling the stretching conditions such as the stretching ratio, the stretching temperature, and the ratio of the strain rate during stretching in the step (iv), the complexity and length of the pores inside the obtained porous film can be controlled. Can be done.

Further, when the heat fixing step is included, the complexity and length of the holes can be controlled by suitably controlling the heat fixing conditions such as the heat fixing temperature and the heat fixing time. .. As a result, the path length of the porous film can be controlled to a suitable value.

The draw ratio is preferably 3.0 times or more and 7.0 times or less, and more preferably 4.5 times or more and 6.0 times or less.

The stretching temperature is preferably 80 ° C. or higher and 125 ° C. or lower, and more preferably 100 ° C. or higher and 120 ° C. or lower.

The strain rate ratio (MD / TD) during stretching is preferably 0.2 or more and 2.8 or less, and more preferably 0.5 or more and 1.5 or less.

In addition, in this specification, MD (Machine Direction) of a porous film means the transport direction at the time of manufacturing a porous film. Further, the TD (Transverse Direction) of the porous film means a direction perpendicular to the MD of the porous film.

The heat fixing temperature is preferably 100 ° C. or higher and 150 ° C. or lower, and more preferably 110 ° C. or higher and 140 ° C. or lower.

The heat fixing time is preferably 1 minute or more and 60 minutes or less, and more preferably 1 minute or more and 30 minutes or less.

Polyolefin is known to be a resin having low water absorption performance. Therefore, the porous film containing polyolefin as a main component usually has a low water content. On the other hand, by subjecting the porous film to a hydrophilic treatment, the water content of the porous film can be improved and controlled to a suitable value.

Examples of the hydrophilization treatment include one or more methods selected from a hydrophilization treatment such as corona treatment, plasma treatment, electron beam irradiation treatment, ozone treatment, and a treatment of spraying water containing a surfactant. be able to.

By the method described above, the path length and the water content of the separator 1 can be controlled within the above ranges.

[Embodiment 2: Separator for non-aqueous electrolyte secondary battery provided with a porous layer]
The separator for a non-aqueous electrolytic solution secondary battery according to the second embodiment has a structure in which a porous layer and a polyolefin porous film included in the separator 1 are laminated, and the porous layer is a non-aqueous layer containing a resin. This is a separator for an electrolyte secondary battery. Hereinafter, the separator for a non-aqueous electrolytic solution secondary battery according to the second embodiment is also referred to as “separator 2”.

(1. Structure of separator 2)
The separator 2 has a structure in which a porous layer is laminated on one side or both sides of a polyolefin porous film. The polyolefin porous film is as described in the first embodiment.

The porous layer is a member constituting the separator for the non-aqueous electrolyte secondary battery according to the embodiment of the present invention. In the non-aqueous electrolyte secondary battery, the porous polyolefin film and at least one of a positive electrode and a negative electrode are used. It can be placed between one and the other.

The porous layer can be formed on at least one of the active material layer of the positive electrode and the negative electrode in the non-aqueous electrolytic solution secondary battery. The porous layer may be arranged between the polyolefin porous film and at least one of a positive electrode and a negative electrode so as to be in contact with them. The porous layer arranged between the polyolefin porous film and at least one of the positive electrode and the negative electrode may be one layer or two or more layers.

The porous layer contains a resin. The porous layer is preferably an insulating porous layer containing an insulating resin.

When the porous layer is laminated on one side of the polyolefin porous film, the porous layer preferably faces the positive electrode among the surfaces of the polyolefin porous film in the non-aqueous electrolyte secondary battery. It is laminated on the surface to be used. More preferably, the porous layer is laminated on the surface in contact with the positive electrode in the non-aqueous electrolyte secondary battery.

(2. Resin)
It is preferable that the resin is insoluble in the electrolytic solution of the battery and is electrochemically stable in the range of use of the battery.

Examples of the resin include polyolefin; (meth) acrylate-based resin; nitrogen-containing aromatic resin; fluorine-containing resin; polyamide-based resin; polyimide-based resin; polyester-based resin; rubbers; melting point or glass transition temperature of 180 ° C. or higher. Resin; water-soluble polymer; polycarbonate, polyacetal, polyether ether ketone and the like.

Among the above-mentioned resins, one or more resins selected from the group consisting of polyolefins, (meth) acrylate-based resins, fluorine-containing resins, nitrogen-containing aromatic resins, polyamide-based resins, polyester-based resins, and water-soluble polymers are preferable.

Further, the resin is particularly preferably a nitrogen-containing aromatic resin. Since the nitrogen-containing aromatic resin has a nitrogen-mediated bond such as an amide bond, it is excellent in water absorption. Therefore, when the resin is a nitrogen-containing aromatic resin, the water content of the porous layer can be suitably improved. As a result, the water content of the separator for a non-aqueous electrolytic solution secondary battery containing the porous layer can be controlled within a suitable range.

As the polyolefin, polyethylene, polypropylene, polybutene, ethylene-propylene copolymer and the like are preferable.

Examples of the fluororesin include polyvinylidene fluoride (PVDF), polytetrafluoroethylene, vinylidene fluoride-hexafluoropropylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and tetrafluoroethylene-perfluoroalkyl vinyl ether. Polymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-trichloroethylene copolymer, vinylidene fluoride-vinyl fluoride copolymer, vinylidene fluoride-hexa Examples thereof include fluoropropylene-tetrafluoroethylene copolymers, ethylene-tetrafluoroethylene copolymers, and the fluoropolymers among the fluororesins having a glass transition temperature of 23 ° C. or lower.

The polyamide-based resin is preferably a polyamide-based resin corresponding to a nitrogen-containing aromatic resin, and particularly preferably an aramid resin such as an aromatic polyamide and a totally aromatic polyamide.

Examples of the aramid resin include poly (paraphenylene terephthalamide), poly (metaphenylene isophthalamide), poly (parabenzamide), poly (metabenzamide), poly (4,4'-benzanilide terephthalamide), and poly. (Paraphenylene-4,4'-biphenylenedicarboxylic acid amide), poly (metaphenylene-4,4'-biphenylenedicarboxylic acid amide), poly (paraphenylene-2,6-naphthalenedicarboxylic acid amide), poly (metaphenylene) -2,6-naphthalenedicarboxylic acid amide), poly (2-chloroparaphenylene terephthalamide), paraphenylene terephthalamide / 2,6-dichloroparaphenylene terephthalamide copolymer, metaphenylene terephthalamide / 2,6-dichloro Examples thereof include paraphenylene terephthalamide copolymers. Of these, poly (paraphenylene terephthalamide) is more preferable.

As the polyester-based resin, aromatic polyesters such as polyarylate and liquid crystal polyesters are preferable.

Examples of the rubbers include a styrene-butadiene copolymer and its hydride, a methacrylate copolymer, an acrylonitrile-acrylic acid ester copolymer, a styrene-acrylic acid ester copolymer, an ethylene propylene rubber, and polyvinyl acetate. Can be mentioned.

Examples of the resin having a melting point or a glass transition temperature of 180 ° C. or higher include polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyamideimide, and polyetheramide.

Examples of the water-soluble polymer include polyvinyl alcohol, polyethylene glycol, cellulose ether, sodium alginate, polyacrylic acid, polyacrylamide, polymethacrylic acid and the like.

As the resin, only one type of resin may be used, or two or more types of resins may be used in combination. The content of the resin in the porous layer is preferably 25 to 80% by weight, more preferably 30 to 70% by weight, assuming that the total weight of the porous layer is 100% by weight.

Since the resin is more excellent in water absorption than the filler described later, the more the portion composed of the resin, the easier it is to adjust the water content of the porous layer. In the porous layer according to the embodiment of the present invention, it is preferable that the content of the resin is within the above range from the viewpoint of controlling the water content of the porous layer within a suitable range.

(3. Filler)
In one embodiment of the present invention, the porous layer preferably contains a filler. The filler can be an inorganic filler or an organic filler. As the filler, an inorganic filler composed of one or more inorganic oxides selected from the group consisting of silica, calcium oxide, magnesium oxide, titanium oxide, alumina, mica, zeolite, aluminum hydroxide, boehmite and the like is more preferable.

In addition, in order to improve the water absorption of the inorganic filler, the surface of the inorganic filler may be hydrophilized with a silane coupling agent or the like.

The content of the filler in the porous layer is preferably 20 to 80% by weight, more preferably 30 to 70% by weight, assuming that the total weight of the porous layer is 100% by weight. When the content of the filler is in the above range, it is easy to obtain a porous layer having sufficient ion permeability.

The porous layer is preferably arranged between the polyolefin porous film and the positive electrode active material layer included in the positive electrode. The physical properties of the porous layer in the following description are the physical properties of the porous layer arranged between the polyolefin porous film and the positive electrode active material layer included in the positive electrode when a non-aqueous electrolyte secondary battery is constructed. At least point.

The basis weight, that is, the weight per unit area of the porous layer can be appropriately determined in consideration of the strength, film thickness, weight and handleability of the porous layer. The basis weight of the porous layer is preferably 0.5 to 3.5 g / m ² and more preferably ^{1.0 to 3.0 g / m 2 per layer of the porous layer.}

By setting the texture of the porous layer in these numerical ranges, the weight energy density and the volumetric energy density of the non-aqueous electrolyte secondary battery provided with the porous layer can be further increased. When the basis weight of the porous layer exceeds the above range, the non-aqueous electrolytic solution secondary battery provided with the porous layer tends to be heavy.

The porosity of the porous layer is preferably 20 to 90% by volume, more preferably 30 to 80% by volume so that sufficient ion permeability can be obtained.

The pore size of the pores of the porous layer is preferably 1.0 μm or less, and more preferably 0.5 μm or less. By setting the pore diameter of the pores to these sizes, the non-aqueous electrolyte secondary battery provided with the porous layer can obtain sufficient ion permeability.

The air permeability of the porous layer is preferably 30 to 80 s / 100 mL, more preferably 40 to 75 s / 100 mL in terms of Gale value. If the air permeability of the porous layer is within the above range, it can be said that the porous layer has sufficient ion permeability.

(4. Method for producing a porous layer)
A porous layer can be formed by using a coating liquid in which the resin described in "2. Resin" is dissolved or dispersed in a solvent. Further, the coating liquid obtained by dissolving or dispersing the resin in a solvent and dispersing the filler can be used to form a porous layer containing the resin and the filler.

The solvent may be a solvent that dissolves the resin. Further, the solvent may be a dispersion medium for dispersing the resin or the filler. Examples of the method for forming the coating liquid include a mechanical stirring method, an ultrasonic dispersion method, a high-pressure dispersion method, a media dispersion method, and the like.

As a method for forming the porous layer, for example, a method of directly applying the coating liquid to the surface of the base material and then removing the solvent; after applying the coating liquid to an appropriate support, the solvent is applied. A method of removing the porous layer to form the porous layer, crimping the porous layer with the base material, and then peeling off the support; after applying the coating liquid to an appropriate support, the coating surface is coated with the above. A method of crimping the base material and then removing the solvent after peeling off the support; and a method of removing the solvent after performing dip coating by immersing the base material in the coating liquid and the like. Can be mentioned.

The solvent is preferably a solvent that does not adversely affect the base material, dissolves the resin uniformly and stably, and disperses the filler uniformly and stably. Examples of the solvent include one or more solvents selected from the group consisting of N-methyl-2-pyrrolidone, N, N-dimethylacetamide, N, N-dimethylformamide, acetone, water and the like.

The coating liquid may appropriately contain a dispersant, a plasticizer, a surfactant, a pH adjuster and the like as components other than the resin and the filler.

As the base material, in addition to the above-mentioned porous polyolefin film, other films, positive electrodes, negative electrodes, and the like can be used.

As a method for applying the coating liquid to the substrate, a conventionally known method can be adopted, and specific examples thereof include a gravure coater method, a dip coater method, a bar coater method, and a die coater method. Be done.

When the coating liquid contains an aramid resin, the aramid resin can be precipitated by giving humidity to the coated surface. As a result, the porous layer may be formed.

As a method of removing the solvent from the coating liquid coated on the base material, for example, a method of removing the solvent from the coating film which is a film of the coating liquid by ventilation drying, heat drying, or the like. Can be mentioned.

Further, by changing the amount of the solvent in the coating liquid, the porosity and the average pore size of the obtained porous layer can be adjusted.

The suitable solid content concentration of the coating liquid may vary depending on the type of filler and the like, but is generally more than 3% by weight and preferably 40% by weight or less.

The coating shear rate when the coating liquid is applied onto the substrate can vary depending on the type of filler and the like, but is generally preferably 2 (1 / s) or more, and 4 (1 / s). It is more preferably s) to 50 (1 / s).

(5. Adjustment of path length and water content)
The separator 2 is a laminate having a structure in which a porous layer and a polyolefin porous film are laminated. The separator 2 is a laminate having a structure in which a porous layer and a polyolefin porous film of the separator 1 are laminated, and the separator 1 has the other layers (adhesive layer and the like) described above. May be good.

The path length of the separator 2 is the product of the curving ratio of the laminated body and the film thickness of the laminated body, and is 22 μm or more and 38 μm or less. The water content of the separator 2 is the ratio of the weight of water contained in the separator 2 to the total weight of the laminate (the weight of the entire laminate), which is 0.2% by weight or more and 0.7% by weight or less. ..

The polyolefin porous film included in the separator 2 is the same as the polyolefin porous film described in the first embodiment. The method for adjusting the path length and the water content of the polyolefin porous film included in the separator 2 is the same as the method described in the first embodiment.

In the method for producing a porous layer, a porous structure of the porous layer is formed when the solvent is removed to precipitate the resin. Therefore, as a manufacturing method for controlling the path length of the porous layer within a preferable range, for example, steam at a temperature of 53 to 57 ° C. is used at the stage of removing the solvent in the coating liquid coated on the substrate. A method of spraying the coating liquid coated on the base material with an air flow rate of 50 to 80 m ^{3 / min can be mentioned.}

Further, from the viewpoint of controlling the path length of the separator 2 to a preferable range, when producing the porous layer, the coating liquid is applied, and then the solvent in the coating liquid is removed to obtain the above. It is preferable to control the time until the resin is precipitated.

The time from the coating of the coating liquid to the precipitation of the resin is preferably 1 second or more and 13 seconds or less, more preferably 1 second or more and 10 seconds or less, and 1 second or more and 8 seconds or less. It is more preferable to have.

When the time from the coating of the coating liquid to the precipitation of the resin is 1 second or more and 13 seconds or less, the coating liquid soaks into the pores near the surface of the polyolefin porous film and soaks into the coating liquid. Precipitates in the pores. Here, the porous layer precipitated in the pores is referred to as the porous layer A.

Since the resin forming the porous layer is more likely to shrink after drying than the polyolefin porous film, the porous layer A is near the surface of the polyolefin porous film on the side where the porous layer is formed. The pores in the film are shrunk after drying. By such shrinkage, the curving ratio in the vicinity of the surface of the polyolefin porous film on the side where the porous layer is formed can be controlled.

That is, the path length of the separator 2 can be controlled by controlling the time from coating the coating liquid to removing the solvent in the coating liquid and precipitating the resin. On the contrary, when the time from the coating of the coating liquid to the precipitation of the resin exceeds 13 seconds, the coating liquid is precipitated in a state of being soaked in a large amount in the polyolefin porous film. Since the pores are easily clogged, the pathway length may become too long and the ion permeability may decrease.

In addition, the method for producing the porous layer may include a step of washing the porous layer precipitated on the polyolefin porous film with water and then drying it. In the step, the moisture content of the porous layer can be suitably controlled by controlling the drying time and the drying temperature of the porous layer.

The drying temperature is preferably 60 ° C. or higher and 130 ° C. or lower, and more preferably 80 ° C. or higher and 120 ° C. or lower.

The drying time is preferably 5 seconds or more and 60 seconds or less, and more preferably 10 seconds or more and 40 seconds or less.

Further, in the drying step of the porous layer, the moisture content of the porous layer is also preferable by drying while alternately contacting both sides of the polyolefin porous film on which the porous layer is formed with a plurality of heating rolls. Can be controlled. The temperature of the heating roll is preferably set within the temperature range described in the drying temperature.

By the method described above, the path length and the water content of the porous layer can be suitably controlled.

The film thickness and curving ratio of the porous layer and the film thickness and curving ratio of the polyolefin porous film affect the path length of the separator 2. Since the path length is 22 μm or more and 38 μm or less, the film thickness of the porous layer is preferably 1.0 μm or more and 6.0 μm or less, and more preferably 1.5 μm or more and 5.0 μm or less. , 2.0 μm or more and 5.0 μm or less is particularly preferable.

Further, the curvature ratio of the porous layer is preferably 1.3 or more and 2.5 or less, and more preferably 1.5 or more and 2.0 or less because the path length is 22 μm or more and 38 μm or less. It is preferable, and it is particularly preferable that it is 1.5 or more and 1.9 or less.

The film thickness of the polyolefin porous film is preferably 8.0 μm or more and 23 μm or less, more preferably 8.0 μm or more and 20 μm or less, because the path length of the separator 2 is 22 μm or more and 38 μm or less. It is particularly preferable that the thickness is 0 μm or more and 15.5 μm or less.

Further, the bending ratio of the polyolefin porous film is preferably 1.3 or more and 2.5 or less, and preferably 1.5 or more and 2.0 or less because the path length is 22 μm or more and 38 μm or less. It is more preferable, and it is particularly preferable that it is 1.6 or more and 1.9 or less.

The water content of the porous layer is 0.2% by weight or more, more preferably 0.3% by weight or more, and more preferably 0.4% by weight or more, similarly to the water content of the polyolefin porous film. Is particularly preferable. The water content of the porous layer is 0.7% by weight or less, preferably 0.65% by weight or less, and more preferably 0.62% by weight or less, similar to the water content of the polyolefin porous film. Is more preferable.

As described above, in the separator 2, the path length and the water content of the polyolefin porous film are controlled, and the path length and the water content of the porous layer are controlled so that the path length of the separator 2 is 22 μm or more and 38 μm or less. And the water content can be 0.2% by weight or more and 0.7% by weight with respect to the total weight of the separator 2.

(6. Method for preparing aramid resin)
The method for preparing the aramid resin is not particularly limited, and examples thereof include a condensation polymerization method of a para-oriented aromatic diamine and a para-oriented aromatic dicarboxylic acid halide. In that case, the resulting aramid resin is substantially made up of repeating units in which the amide bond is bonded at the para position of the aromatic ring or a similar orientation position. The orientation position according to the para position is an orientation position extending coaxially or parallelly in the opposite direction, for example, 4,4'-biphenylene, 1,5-naphthalene, 2,6-naphthalene, or the like.

Specific methods for preparing a solution of poly (paraphenylene terephthalamide) include, for example, a method including the steps shown in (I) to (IV) below.
(I) N-methyl-2-pyrrolidone is charged in a dried flask, calcium chloride dried at 200 ° C. for 2 hours is added, and the temperature is raised to 100 ° C. to completely dissolve the calcium chloride.
(II) After returning the temperature of the solution obtained in step (I) to room temperature, para-phenylenediamine is added to completely dissolve the para-phenylenediamine.
(III) While maintaining the temperature of the solution obtained in step (II) at 20 ± 2 ° C., terephthalic acid dichloride is divided into 10 portions and added every about 5 minutes.
(IV) The solution obtained in step (III) was aged for 1 hour while maintaining the temperature at 20 ± 2 ° C., and then stirred under reduced pressure for 30 minutes to remove air bubbles, thereby poly (paraphenylene terephthal). A solution of amide) is obtained.

[Embodiment 3: Non-aqueous electrolyte secondary battery member, Embodiment 4: Non-aqueous electrolyte secondary battery]
In the non-aqueous electrolytic solution secondary battery member according to the third embodiment of the present invention, the positive electrode, the separator 1 or the separator 2, and the negative electrode are arranged in this order.

The non-aqueous electrolytic solution secondary battery according to the fourth embodiment of the present invention includes the separator 1 or the separator 2.

The shape of the non-aqueous electrolyte secondary battery is not particularly limited, and may be a thin plate (paper) type, a disk type, a cylindrical type, a prismatic type such as a rectangular parallelepiped, or the like. The non-aqueous electrolyte secondary battery is, for example, a non-aqueous secondary battery that obtains an electromotive force by doping and dedoping lithium, and the positive electrode, the separator 1, the separator 2, and the negative electrode are in this order. It is provided with a member for a non-aqueous electrolyte secondary battery that is laminated. The components of the non-aqueous electrolytic solution secondary battery other than the separator 1 or the separator 2 are not limited to the components described below.

In the non-aqueous electrolytic solution secondary battery, a battery element in which a negative electrode and a positive electrode are usually opposed to each other via the separator 1 or the separator 2 is impregnated with the electrolytic solution is sealed in an exterior material. Has a structure. The dope means occlusion, support, adsorption, or insertion, and means a phenomenon in which lithium ions enter the active material of an electrode such as a positive electrode.

Since the non-aqueous electrolyte secondary battery member includes the separator 1 or the separator 2, when incorporated into the non-aqueous electrolyte secondary battery, the non-aqueous electrolyte secondary battery is micro-short-circuited. Can be suppressed and its safety can be improved. Further, since the non-aqueous electrolytic solution secondary battery includes the separator 1 or the separator 2, the occurrence of fine short circuits is suppressed, and the safety is excellent.

As a method for producing the non-aqueous electrolyte secondary battery, a conventionally known production method can be adopted. For example, the member for the non-aqueous electrolytic solution secondary battery is formed by arranging the positive electrode, the separator 1, or the separator 2 and the negative electrode in this order. Next, the member for the non-aqueous electrolyte secondary battery is placed in a container that serves as a housing for the non-aqueous electrolyte secondary battery. Further, after filling the container with a non-aqueous electrolytic solution, the container is sealed while reducing the pressure. Thereby, the non-aqueous electrolyte secondary battery can be manufactured.

<Positive electrode>
The positive electrode in one embodiment of the present invention is not particularly limited as long as it is generally used as a positive electrode of a non-aqueous electrolyte secondary battery. For example, as the positive electrode, a positive electrode sheet having a structure in which an active material layer containing a positive electrode active material and a binder is formed on a positive electrode current collector can be used. The active material layer may further contain a conductive agent and / or a binder.

Examples of the positive electrode active material include materials capable of doping and dedoping lithium ions. Specific examples of the material include a lithium composite oxide containing at least one transition metal such as V, Mn, Fe, Co and Ni.

Examples of the conductive agent include carbonaceous materials such as natural graphite, artificial graphite, cokes, carbon black, pyrolytic carbons, carbon fibers and calcined organic polymer compounds. Only one type of the conductive agent may be used, or two or more types may be used in combination.

Examples of the binder include fluororesins such as polyvinylidene fluoride (PVDF), acrylic resins, and styrene-butadiene rubber. The binder also has a function as a thickener.

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

As a method for producing the positive electrode sheet, for example, a method of press-molding a positive electrode active material, a conductive agent and a binder on a positive electrode current collector; a positive electrode active material, a conductive agent and a binder using an appropriate organic solvent. Is formed into a paste, the paste is applied to the positive electrode current collector, dried, and then pressurized to be fixed to the positive electrode current collector; and the like.

<Negative electrode>
The negative electrode in one embodiment of the present invention is not particularly limited as long as it is generally used as a negative electrode of a non-aqueous electrolyte secondary battery. For example, as the negative electrode, a negative electrode sheet having a structure in which an active material layer containing a negative electrode active material and a binder is formed on a negative electrode current collector can be used. The active material layer may further contain a conductive agent and / or a binder.

Examples of the negative electrode active material include materials capable of doping and dedoping lithium ions. Examples of the material include carbonaceous materials and the like. Examples of carbonaceous materials include natural graphite, artificial graphite, cokes, carbon black and pyrolytic carbons.

Examples of the negative electrode current collector include Cu, Ni and stainless steel. Cu is more preferable because it is difficult to form an alloy with lithium and it is easy to process it into a thin film.

As a method for manufacturing the negative electrode sheet, for example, a method of press-molding the negative electrode active material on the negative electrode current collector; after making the negative electrode active material into a paste using an appropriate organic solvent, the paste is used as the negative electrode current collector. A method of applying the paste to the negative electrode, drying it, and then pressurizing it to fix it to the negative electrode current collector; etc. The paste preferably contains the conductive agent and the binder.

<Non-aqueous electrolyte>
The non-aqueous electrolytic solution according to the embodiment of the present invention is not particularly limited as long as it is a non-aqueous electrolytic solution generally used for a non-aqueous electrolytic solution secondary battery such as a lithium ion secondary battery. As the non-aqueous electrolytic solution, for example, a non-aqueous electrolytic solution obtained by dissolving a lithium salt in an organic solvent can be used. Examples of lithium salts include LiClO ₄ , LiPF ₆ , _{LiAsF 6} , LiSbF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , Li ₂ B ₁₀ Cl. _10. Lower aliphatic carboxylic acid lithium salt and LiAlCl _{4 and the} like can be mentioned. Only one type of the lithium salt may be used, or two or more types may be used in combination.

Examples of the organic solvent constituting the non-aqueous electrolyte solution include carbonates, ethers, esters, nitriles, amides, carbamates and sulfur-containing compounds, and a fluorine group introduced into these organic solvents. Fluorine organic solvent and the like can be mentioned. Only one kind of the organic solvent may be used, or two or more kinds may be used in combination.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

[Measurement of physical properties]
In Examples and Comparative Examples, the physical characteristics of the separator for a non-aqueous electrolytic solution secondary battery and the porous polyolefin film were measured by the following methods.

(1) Film thickness The film thickness of the separator for a non-aqueous electrolyte secondary battery was measured using a high-precision digital length measuring machine (manufactured by Mitutoyo Co., Ltd.). Specifically, each of the separators for a non-aqueous electrolyte secondary battery was cut into squares having a side length of 8 cm, five-point measurements were performed in that range, and the film thickness was determined from the average value thereof.

(2) Moisture content Using a Karl Fischer titer meter (manufactured by Metrohm Shibata Co., Ltd.), the moisture content of the separator for a non-aqueous electrolyte secondary battery was measured based on the Karl Fischer method.

(3) Path length of separator for non-aqueous electrolyte secondary battery and bending rate of porous layer (3-1) Measurement of resistance value of separator for non-aqueous electrolyte secondary battery For non-aqueous electrolyte secondary battery Twenty-three circular measurement samples having a diameter of 17 mm were cut out from the separator as measurement samples. Further, as members of the 2032 type coin cell, an upper lid, a lower lid, a gasket, two circular spacers having a diameter of 15.5 mm and a thickness of 0.5 mm, and a wave washer were prepared.

First, a spacer, a sample for measurement, and a spacer were placed on the lower lid in this order from the lower lid side in a glove box filled with argon gas and having a dew point temperature of −80 ° C. or lower. The number of measurement samples arranged between the spacers was 5, 8, and 10, and two cells in which each of the measurement samples was arranged were prepared. A gasket was placed so as to fix a circular measurement sample having a diameter of 17 mm, and a wave washer was installed on the spacer.

Next, an electrolytic solution (manufactured by Kishida Chemical Co., Ltd.) was injected into the cell in which the wave washer was installed. The electrolytic solution is a mixed solvent prepared by mixing ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) at EC / DMC / EMC = 30/35/35 (volume ratio). This is a non-aqueous electrolytic solution containing _{LiPF 6} so that the concentration of _{LiPF 6 is 0.1 M.}

After the injection, the cell was allowed to stand for 10 minutes under a pressure of about −80 kPa, and the measurement sample was impregnated with the electrolytic solution. Then, the cell was covered with an upper lid and sealed with a coin cell caulking device to obtain a sample cell.

The obtained sample cell was placed in a constant temperature bath at 25 ° C. and left for 24 hours, and then the resistance of the sample cell was measured in the range of an amplitude of 5 mV and a frequency of 1 MHz to 10 kHz using an AC impedance measuring device. The value of the real axis when the value of the imaginary axis in the measured impedance curve was 0 was taken as the value of the resistance component of the sample cell.

The value of the resistance component of the obtained sample cell was plotted against the number of measurement samples placed in the sample cell. Then, the obtained plot was linearly approximated to obtain the slope of the plot. The value obtained by multiplying this slope by the area of the spacer was taken as the resistance value R (Ω · cm ² ) of the separator for the non-aqueous electrolyte secondary battery. Here, the area of the spacer was (1.55 cm / 2) ² × π = 1.88 cm ² .

(3-2) Curve rate of non-aqueous electrolyte secondary battery separator The resistance value R (Ω · cm ² ) of the non-aqueous electrolyte secondary battery separator measured in (3-1) above, of the electrolyte Using the specific resistance r (Ω · cm), the void ratio ε (%) and the film thickness d (cm) of the separator for a non-aqueous electrolyte secondary battery, the non-aqueous electrolyte solution is based on the following formula (1). The curvature T of the separator for the secondary battery was measured.
T = [{(R × ε) / 100} / (r × d)] ^1/2 ... (1)
The resistivity r of the electrolytic solution was measured with a conductivity meter (manufactured by Yokogawa Electric).

The void ratio of the separator for the non-aqueous electrolyte secondary battery is the weight W (g) of the separator for the non-aqueous electrolyte secondary battery having a constant volume (8 cm × 8 cm × film thickness dcm), and the non-aqueous electrolyte solution. It was calculated based on the following formula (2) using the thickness d (μm) of the separator for the secondary battery and the true specific gravity ρ (g / cm ^{3) of the separator for the non-aqueous electrolytic solution secondary battery.}
Porosity (%) = (1-{(W / ρ) / (8 × 8 × d)}) × 100 ・ ・ (2)
(3-3) Path length of separator for non-aqueous electrolyte secondary battery Multiply the curvature ratio T measured in (3-2) above by the film thickness (μm) of the separator for non-aqueous electrolyte secondary battery. The path length of the separator for the non-aqueous electrolyte secondary battery was calculated.

(3-4) Curvature ratio T'of the porous layer
The path length A of the polyolefin porous film was calculated by the measurement methods (3-1) to (3-3). Next, the path length B of the laminated separator in which the porous layer was formed on the polyolefin porous film was calculated, and the bending ratio T'of the porous layer was calculated by the following formula (3).
T'= (BA) / (film thickness of porous layer) ... (3)
Here, the film thickness of the porous layer was calculated by subtracting the film thickness of the polyolefin porous film from the film thickness of the laminated separator.

The path length of the porous layer can also be measured by the following method.

By measuring the film thickness of the separator for a non-aqueous electrolytic solution secondary battery having a porous layer (the "separator 2") and the same measurement as in (3-1) to (3-3) above. , The film thickness D1 and the path length B of the separator 2 are obtained.

Subsequently, a separator 2 not used for measuring the path length B is prepared, and a release tape is attached to the porous layer side. Then, by peeling the release tape, the porous layer is peeled from the polyethylene porous film. By measuring the film thickness of the polyethylene porous film from which the porous layer has been peeled off and performing the same measurements as in (3-1) to (3-3) above, the film thickness D2 and the path length of the polyethylene porous film are measured. Get A. Here, since the value obtained by subtracting D2 from D1 corresponds to the film thickness of the porous layer in the above formula (3), the curvature ratio T'of the porous layer can be calculated by the above formula (3). ..

(4) Ion permeability (air permeability) evaluation of separator for non-aqueous electrolyte secondary battery The air permeability of the separator for non-aqueous electrolyte secondary battery cut out to a size of 60 mm x 60 mm is manufactured by Asahi Seiko Co., Ltd. The measurement was performed using a digital Oken type air permeability tester EGO1. When the value of air permeability was 300 s / 100 ml or less, the ion permeability was good, and when it exceeded 300 s / 100 ml, the ion permeability was poor.

(5) Evaluation of short-circuit time by dendrite A separator for a non-aqueous electrolyte secondary battery cut into a disk shape of φ19 mm, Li foil with a thickness of 0.5 mm and φ15.5 mm, and Cu foil with a thickness of 20 μm and φ14.5 mm. I sandwiched it with. Then, a non-aqueous electrolytic solution was injected to prepare a bipolar coin cell (CR2032 type).

As the non-aqueous electrolytic solution, EC, DMC and EMC are mixed in a mixed solvent at EC / EMC / DEC = 3/5/2 (volume ratio) so that the concentration of _{LiPF 6 is 1 M.} , A non-aqueous electrolyte solution containing _{LiPF 6 was used.}

The manufactured coin cell is installed in a constant temperature bath (inside temperature: 25 ° C.), and the voltage when a current of 6 mA ^{/ cm 2 is applied using a charge / discharge evaluation device (TOSCAT-3000) manufactured by Toyo System Co., Ltd. is timed.} It was measured. In the above measurement, the time immediately before the measured voltage becomes unstable intermittently was defined as the short-circuit time by dendrite.

[Example 1]
Poly (paraphenylene terephthalamide) was prepared using a separable flask with a capacity of 3 L, which had a stirring blade, a thermometer, a nitrogen inflow pipe and a powder addition port.

First, the separable flask was sufficiently dried and charged with 2200 g of N-methyl-2-pyrrolidone (NMP). Further, 151.07 g of calcium chloride powder vacuum-dried at 200 ° C. for 2 hours was added, and the temperature was raised to 100 ° C. to completely dissolve the calcium chloride powder.

After returning the obtained NMP solution of calcium chloride to room temperature, 68.23 g of para-phenylenediamine was added and completely dissolved. While keeping the obtained solution at 20 ° C. ± 2 ° C., 124.97 g of terephthalic acid dichloride was divided into 10 portions and added to the solution about every 5 minutes.

After that, the solution was aged for 1 hour while keeping the temperature at 20 ° C. ± 2 ° C. while continuing stirring. The aged solution was then filtered using a 1500 mesh stainless wire mesh. The concentration of poly (paraphenylene terephthalamide) in the obtained solution was 6% by weight.

100 g of the poly (paraphenylene terephthalamide) solution was weighed into a flask, and 300 g of NMP was added to adjust the poly (paraphenylene terephthalamide) concentration to 1.5% by weight.

Then, the obtained solution was stirred for 60 minutes. Alumina C (manufactured by Nippon Aerodil Co., Ltd .; average particle size (D50) = 0.15 μm; particles having a particle size of 1.0 μm or more occupy 100% of the total number of particles of the filler in this solution. 5%) and 6 g of Advanced Alumina AKP3000 (manufactured by Sumitomo Chemical Co., Ltd .; average particle size (D50) = 0.7 μm; the ratio of particles having a particle size of 1.0 μm or more is 100% of the total number of particles of the filler. 22.0%) was mixed, and the mixture was further stirred for 240 minutes.

The obtained solution was filtered using a 1000 mesh wire mesh, and then 0.73 g of calcium carbonate was added to the obtained filtrate and stirred for 240 minutes to neutralize the filtrate. Then, the neutralized filtrate was defoamed under reduced pressure to prepare a slurry coating liquid.

The coating liquid was applied onto a polyethylene porous film having a film thickness of 12.2 μm using a coating bar. Subsequently, the formed coating film was led to a precipitation step in an atmosphere of 50 ° C. and 70% relative humidity to precipitate poly (paraphenylene terephthalamide). The time from applying the coating liquid to precipitating poly (paraphenylene terephthalamide) was 2 seconds. In addition, steam at a temperature of 55 ° C. and an air flow rate of 50 m ³ / min was applied to the surface of the coating film formed by applying the coating liquid for several seconds in the initial stage of the precipitation.

Finally, the coating film on which poly (paraphenylene terephthalamide) was precipitated was washed with water and then dried to obtain a separator for a non-aqueous electrolyte secondary battery. The drying time in the drying after washing was 24 seconds, and the drying temperature was 110 ° C.

The film thickness of the obtained separator for a non-aqueous electrolyte secondary battery was 16.5 μm. The resistance value of the non-aqueous electrolyte secondary battery separator was measured, and the curvature ratio calculated from the measured resistance value was 1.68. The water content of the separator for the non-aqueous electrolyte secondary battery was 0.465% by weight.

[Example 2]
The non-aqueous procedure was the same as in Example 1 except that the coating amount of the coating solution was changed so that the thickness of the obtained non-aqueous electrolytic solution secondary battery separator was 17.5 μm. A separator for an electrolytic solution secondary battery was prepared. The film thickness of the obtained separator for a non-aqueous electrolyte secondary battery was 17.5 μm, and the curvature ratio was 1.67. The water content of the separator for the non-aqueous electrolyte secondary battery was 0.603% by weight.

[Example 3]
As a filler, the non-aqueous electrolytic solution secondary was carried out in the same procedure as in Example 1 except that only alumina C (12 g) was added instead of the mixture of alumina C (6 g) and advanced alumina AKP3000 (6 g). A battery separator was produced. The film thickness of the obtained separator for a non-aqueous electrolyte secondary battery was 15.1 μm, and the curvature ratio was 1.82. The water content of the non-aqueous electrolyte secondary battery separator was 0.547% by weight.

[Example 4]
A separator for a non-aqueous electrolyte secondary battery was used in the same procedure as in Example 1 except that a polyethylene porous film having a thickness of 13.1 μm was used instead of the polyethylene porous film having a thickness of 12.2 μm. Was produced.

The film thickness of the obtained separator for a non-aqueous electrolyte secondary battery was 17.2 μm, and the curvature ratio was 1.72. The water content of the non-aqueous electrolyte secondary battery separator was 0.522% by weight.

[Comparative Example 1]
A separator for a non-aqueous electrolytic solution secondary battery made of a polyethylene porous film having a film thickness of 12.2 μm alone was prepared. The resistance value of the obtained separator for a non-aqueous electrolyte secondary battery was measured, and the curvature ratio calculated from the measured resistance value was 1.74. The water content of the non-aqueous electrolyte secondary battery separator was 0.007% by weight.

[Conclusion]
Tables 1 and 2 below show the physical property values of the separators for non-aqueous electrolyte secondary batteries and the short-circuit time due to dendrites obtained in Examples and Comparative Examples.

As shown in Table 2, the range of "path length is 22 μm or more and 38 μm or less and water content is 0.2% by weight or more and 0.7% by weight or less" prepared in Examples 1 to 4 is defined. The satisfied non-aqueous electrolyte secondary battery separator has a significantly longer short-circuit time due to dendrite than the non-aqueous electrolyte secondary battery separator produced in Comparative Example 1.

Further, the separators for non-aqueous electrolyte secondary batteries produced in Examples 1 to 4 had an air permeability of 300 s / 100 ml or less, and their ion permeability was good.

Therefore, the separator for a non-aqueous electrolyte secondary battery according to an embodiment of the present invention has excellent ion permeability and has a fine short circuit when the non-aqueous electrolyte secondary battery is charged and discharged. It was found that the outbreak can be sufficiently suppressed.

The separator for a non-aqueous electrolyte secondary battery according to an embodiment of the present invention is used for manufacturing a non-aqueous electrolyte secondary battery which is excellent in safety because the occurrence of micro short circuits during charging and discharging is suppressed. be able to.

Claims (5)

A separator for a non-aqueous electrolyte secondary battery containing a porous polyolefin film.
The path length, which is the product of the curve ratio and the film thickness, is 22 μm or more and 38 μm or less.
A separator for a non-aqueous electrolyte secondary battery having a water content of 0.2% by weight or more and 0.7% by weight or less with respect to the total weight of the separator for a non-aqueous electrolyte secondary battery. It has a structure in which a porous layer and the polyolefin porous film are laminated.
The separator for a non-aqueous electrolytic solution secondary battery according to claim 1, wherein the porous layer contains a resin. The separator for a non-aqueous electrolyte secondary battery according to claim 2, wherein the resin is a nitrogen-containing aromatic resin. A member for a non-aqueous electrolyte secondary battery in which a positive electrode, a separator for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, and a negative electrode are arranged in this order. A non-aqueous electrolyte secondary battery comprising the separator for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 3.