JP2023098268A - Separator for non-aqueous electrolyte secondary battery, member for non-aqueous electrolyte secondary battery, and non-aqueous electrolyte secondary battery - Google Patents

Abstract

To provide a separator for a non-aqueous electrolyte secondary battery which is excellent in impact resistance.SOLUTION: A separator for a non-aqueous electrolyte secondary battery contains a polyolefin porous film, and has an elongation rate after immersion in ethanol of 0.85% or more and 1.5% or less, and piercing strength of 300 gf or more.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to a non-aqueous electrolyte secondary battery separator, a non-aqueous electrolyte secondary battery member, and a non-aqueous electrolyte secondary battery.

Non-aqueous electrolyte secondary batteries, especially lithium-ion secondary batteries, have high energy density and are widely used in personal computers, mobile phones, personal digital assistants, etc. Recently, they are also being developed as batteries for vehicles. It is getting worse.

As an example of a separator in such a non-aqueous electrolyte secondary battery, Patent Document 1 discloses a separator having an elongation rate of 0.3% or more when immersed in a non-aqueous electrolyte and swollen. Patent Document 1 discloses that the separator can prevent depletion of the electrolyte in the non-aqueous electrolyte secondary battery and extend the life of the non-aqueous electrolyte secondary battery. Specifically, in Examples of Patent Document 1, a separator having an elongation rate of 0.54% is disclosed as a separator capable of extending the life of a non-aqueous electrolyte secondary battery.

JP 2017-103091 A

However, the non-aqueous electrolyte secondary battery including the separator described in Patent Document 1 has room for further improvement in terms of impact resistance.

Accordingly, an object of one embodiment of the present invention is to provide a non-aqueous electrolyte secondary battery with excellent impact resistance.

As a result of intensive research, the present inventors have found that in a separator for a non-aqueous electrolyte secondary battery having a puncture strength of a specific value or more, the elongation rate after immersion in an organic solvent such as ethanol is the same as the life of the battery. The inventors first found that there is a relationship between impact resistance of non-aqueous electrolyte secondary batteries, which is completely different from the above, and came up with the present invention.

One aspect of the present invention includes the following inventions [1] to [6].
[1] A separator for a non-aqueous electrolyte secondary battery comprising a polyolefin porous film,
Elongation after immersion in ethanol is 0.85% or more and 1.5% or less, and
A separator for a non-aqueous electrolyte secondary battery, having a puncture strength of 300 gf or more.
(Here, the elongation rate after the ethanol immersion is calculated by the following formula (1);
Elongation after immersion in ethanol (%)={(X ₁ −X ₀ )/X ₀ }×100 (1),
In the formula (1), X ₀ is the length (mm) in the TD direction before the separator for the non-aqueous electrolyte secondary battery is immersed in ethanol, and X ₁ is the non-aqueous electrolyte secondary battery. is the length (mm) in the TD direction after the separator for immersion in ethanol for 24 hours,
The puncture strength is calculated by the following methods (i) and (ii);
(i) After fixing the separator for the non-aqueous electrolyte secondary battery, a pin (pin diameter 1 mmΦ, tip 0.5R) is pierced at a speed of 200 mm / min, and the non-aqueous electrolyte secondary Pierce the battery separator.
(ii) The maximum stress (gf) when the pin is pierced into the non-aqueous electrolyte secondary battery separator in (i) is measured, and the measured value is defined as the piercing strength. ).
[2] The non-aqueous electrolyte secondary according to [1], wherein the separator for a non-aqueous electrolyte secondary battery has a heat shrinkage rate of 20% or less when heated at a temperature of 150 ° C. for 1 hour. Battery separator.
(Here, it is calculated by the following formula (2).
Heat shrinkage = {(A ₀ −A ₁ )/A ₀ }×100 (2)
In formula (2), A ₀ is the area of the non-aqueous electrolyte secondary battery separator before heating the non-aqueous electrolyte secondary battery separator, and A ₁ is the non-aqueous electrolyte secondary battery separator. It is the area of the separator for the non-aqueous electrolyte secondary battery after heating the separator for the secondary battery at a temperature of 150° C. for 1 hour. )
[3] The separator for a non-aqueous electrolyte secondary battery according to [1] or [2], wherein porous layers containing a resin are laminated on both sides of the polyolefin porous film.
[4] The separator for a non-aqueous electrolyte secondary battery according to [3], wherein the resin contains an aramid resin.
[5] 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 [1] to [4], and a negative electrode are arranged in this order. Element.
[6] A nonaqueous electrolyte secondary battery comprising the separator for a nonaqueous electrolyte secondary battery according to any one of [1] to [4].

The non-aqueous electrolyte secondary battery separator according to one embodiment of the present invention is said to be able to improve the impact resistance of a non-aqueous electrolyte secondary battery comprising the non-aqueous electrolyte secondary battery separator. Effective.

An embodiment of the invention will be described below, but the invention is not limited thereto. The present invention is not limited to the configurations described below, and can be modified in various ways within the scope of the claims, by appropriately combining technical means disclosed in different embodiments. The resulting embodiment is also included in the technical scope of the present invention. In this specification, unless otherwise specified, "A to B" representing a numerical range means "A or more and B or less".

In the present specification, the MD direction (Machine Direction) means the direction in which the sheet-shaped polyolefin resin composition, the sheet and the polyolefin porous film are conveyed in the method for producing the polyolefin porous film described below. The TD direction (Transverse Direction) means a direction parallel to the surface of the sheet-shaped polyolefin resin composition, the sheet, or the polyolefin porous film and perpendicular to the MD direction. Further, in the non-aqueous electrolyte secondary battery separator according to one embodiment of the present invention, the same direction as the MD direction and the TD direction in the polyolefin porous film constituting the non-aqueous electrolyte secondary battery separator is It is defined as the MD direction and the TD direction of the separator for non-aqueous electrolyte secondary batteries.

[Embodiment 1: Separator for non-aqueous electrolyte secondary battery]
A non-aqueous electrolyte secondary battery separator according to Embodiment 1 of the present invention is a non-aqueous electrolyte secondary battery separator containing a polyolefin porous film, and has an elongation rate after immersion in ethanol of 0.85%. Above, it is 1.5% or less, and the puncture strength is 300 gf or more.

Here, the elongation rate after the ethanol immersion is calculated by the following formula (1);
Elongation after ethanol immersion (%)={(X ₁ −X ₀ )/X ₀ }×100 (1)
In the formula (1), X ₀ is the length (mm) in the TD direction before the separator for the non-aqueous electrolyte secondary battery is immersed in ethanol, and X ₁ is the non-aqueous electrolyte secondary battery. It is the length (mm) in the TD direction after the separator for immersion in ethanol for 24 hours.

Further, the puncture strength is calculated by the following methods (i) and (ii);
(i) After fixing the separator for the non-aqueous electrolyte secondary battery, a pin (pin diameter 1 mmΦ, tip 0.5R) is pierced at a speed of 200 mm / min, and the non-aqueous electrolyte secondary Pierce the battery separator.
(ii) The maximum stress (gf) when the pin is pierced into the non-aqueous electrolyte secondary battery separator in (i) is measured, and the measured value is defined as the piercing strength.

A separator for a non-aqueous electrolyte secondary battery according to one embodiment of the present invention includes a polyolefin porous film. Hereinafter, the separator for a non-aqueous electrolyte secondary battery is also simply referred to as "separator", and the polyolefin porous film is simply referred to as "porous film".

A separator according to an embodiment of the present invention may be a separator made of the porous film. Moreover, the separator according to one embodiment of the present invention may be a separator that is a laminate including the porous film and a porous layer described later. In addition, the separator, which is a laminate including the porous film and the porous layer described below, is hereinafter also referred to as a "laminated separator". The laminated separator may be a separator in which the porous layer is laminated on one side or both sides of the porous film. The laminated separator may preferably be a separator in which the porous layers are laminated on both sides of the porous film.

In the non-aqueous electrolyte secondary battery, the separator is in a state in which the non-aqueous electrolyte permeates inside by being immersed in the non-aqueous electrolyte. Here, the separator after being immersed in ethanol for 24 hours is in a state in which the ethanol permeates inside. Ethanol is an organic solvent similar to the non-aqueous electrolyte. Therefore, that the separator has a specific range of elongation after being immersed in ethanol means that the separator has a similar elongation in the non-aqueous electrolyte secondary battery.

Since the separator according to one embodiment of the present invention has an elongation rate of 0.85% or more after being immersed in ethanol, it can be elongated to some extent in the non-aqueous electrolyte secondary battery. Here, when an external force is applied to the separator that is stretched to some extent, it has a margin to absorb the external force. Therefore, the separator according to one embodiment of the present invention is such that the non-aqueous electrolyte secondary battery is damaged even when a strong impact is applied to the non-aqueous electrolyte secondary battery including the separator. can reduce risk. That is, the separator according to one embodiment of the present invention can improve the impact resistance of a non-aqueous electrolyte secondary battery including the separator. The elongation after immersion in ethanol is preferably 1.0% or more, more preferably 1.2% or more.

The separator according to one embodiment of the present invention has an elongation rate of 1.5% or less after being immersed in ethanol, and is not excessively elongated in the non-aqueous electrolyte secondary battery. Here, in a non-aqueous electrolyte secondary battery, a separator is positioned between the electrodes, that is, the positive electrode and the negative electrode. In the non-aqueous electrolyte secondary battery, since the separator does not stretch excessively, displacement between the electrode and the separator is less likely to occur even when a strong impact is applied. Therefore, the impact resistance of the non-aqueous electrolyte secondary battery is improved. The elongation after immersion in ethanol is preferably 1.45% or less, more preferably 1.40% or less.

The separator according to one embodiment of the present invention has a high puncture strength of 300 gf or more. Therefore, the separator according to one embodiment of the present invention is difficult to break. Therefore, by using the separator according to one embodiment of the present invention, a non-aqueous electrolyte secondary battery can be assembled more easily. Further, the separator according to one embodiment of the present invention has a puncture strength of 300 gf or more, so that it is difficult to break even when an external force is applied, and a non-aqueous electrolyte secondary battery including the separator is resistant to damage. It can also improve impact resistance.

From the viewpoints of ease of assembly and impact resistance of the non-aqueous electrolyte secondary battery, the puncture strength is preferably 400 gf or more, more preferably 500 gf or more. Moreover, the upper limit of the puncture strength is not particularly limited, and may be, for example, 650 gf or less, or 700 gf or less.

The separator according to one embodiment of the present invention preferably has a heat shrinkage rate of 30% or less, more preferably 20% or less when heated at a temperature of 150° C. for 1 hour. Here, the heat shrinkage rate is a parameter representing the degree of shrinkage of the separator by heating at a temperature of 150° C. for 1 hour. The heat shrinkage rate is calculated by the following formula (2) using the area _A0 of the separator before heating and the area _A1 of the separator after heating at a temperature of 150°C for 1 hour.
Heat shrinkage = {(A ₀ −A ₁ )/A ₀ }×100 (2)
In formula (2), A ₀ is the area of the non-aqueous electrolyte secondary battery separator before heating the non-aqueous electrolyte secondary battery separator, and A ₁ is the non-aqueous electrolyte secondary battery separator. It is the area of the separator for the non-aqueous electrolyte secondary battery after heating the separator for the secondary battery at a temperature of 150° C. for 1 hour.

Since the heat shrinkage rate of the separator is low, shrinkage of the separator due to heat generation of the non-aqueous electrolyte secondary battery is suppressed. Therefore, deterioration in adhesion between the separator and the electrode due to shrinkage of the separator is also suppressed. Therefore, even when a strong impact is applied to the non-aqueous electrolyte secondary battery, displacement between the electrodes and the separator is unlikely to occur. Therefore, the impact resistance of the non-aqueous electrolyte secondary battery is improved. From the viewpoint of impact resistance of the non-aqueous electrolyte secondary battery, the heat shrinkage rate is preferably within the range described above. Moreover, the lower limit of the heat shrinkage rate is 0% or more, and may be 0.1% or more.

The separator according to one embodiment of the present invention preferably has a heat shrinkage rate of 15% or less, more preferably 10% or less in the MD direction when heated at a temperature of 150° C. for 1 hour. The heat shrinkage rate in the MD direction is calculated by the following formula (3).
Heat shrinkage rate in MD direction = {(D _MD0 −D _MD1 )/D _MD0 }×100 (3)
In equation (3), _DMD0 is the length in the MD direction of the separator before heating, and _DMD1 is the length in the MD direction of the separator after heating at a temperature of 150° C. for 1 hour.

The separator according to one embodiment of the present invention preferably has a heat shrinkage rate of 15% or less, more preferably 10% or less in the TD direction when heated at a temperature of 150° C. for 1 hour. The heat shrinkage rate in the TD direction is calculated by the following formula (4).
Heat shrinkage rate in TD direction = {(D _TD0 −D _TD1 )/D _TD0 }×100 (4)
In equation (4), D _TD0 is the length in the TD direction of the separator before heating, and D _TD1 is the length in the TD direction of the separator after heating at a temperature of 150° C. for 1 hour.

<Polyolefin porous film>
The porous film contains a polyolefin-based resin, and is generally a porous film containing a polyolefin-based resin as a main component. In addition, "mainly composed of a polyolefin resin" means that the proportion of the polyolefin resin in the porous film is 50% by weight or more, preferably 90% by weight or more, of the entire material constituting the porous film, It means that it is more preferably 95% by weight or more.

The porous film has a large number of interconnected pores in its interior, allowing gas and liquid to pass from one surface to the other surface.

The thickness of the porous film is 4 to 40 μm, preferably 5 to 20 μm. When the thickness of the porous film is 4 μm or more, it is possible to sufficiently prevent the internal short circuit of the battery. On the other hand, if the thickness of the porous film is 40 μm or less, it is possible to prevent the size of the non-aqueous electrolyte secondary battery from increasing.

More preferably, the polyolefin resin contains a high molecular weight component having a weight average molecular weight of 5×10 ⁵ to 15×10 ⁶ . In particular, when the polyolefin resin contains a high-molecular-weight component having a weight-average molecular weight of 1,000,000 or more, the obtained porous film and the separator including the porous film have improved strength, which is more preferable.

The polyolefin resin is not particularly limited, but is, for example, a homopolymer or copolymer obtained by polymerizing monomers such as ethylene, propylene, 1-butene, 4-methyl-1-pentene and 1-hexene. Thermoplastic resins such as Examples of the homopolymer include polyethylene, polypropylene, and polybutene. Further, examples of the copolymer include an ethylene-propylene copolymer.

Among these, polyethylene is more preferable because it can prevent an excessive current from flowing through the separator at a lower temperature. It should be noted that blocking the flow of this excessive current is also called shutdown. Examples of the polyethylene include low-density polyethylene, high-density polyethylene, linear polyethylene (ethylene-α-olefin copolymer), and ultra-high molecular weight polyethylene having a weight average molecular weight of 1,000,000 or more. Among them, ultra-high molecular weight polyethylene having a weight average molecular weight of 1,000,000 or more is more preferable.

The porosity of the porous film is preferably 20 to 80% by volume so as to increase the retention amount of the electrolytic solution and to obtain the function of reliably preventing the flow of excessive current at a lower temperature. It is more preferably 30 to 75% by volume. In addition, 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. is preferable, and 0.14 μm or less is more preferable.

<Porous layer>
In one embodiment of the present invention, the porous layer can be arranged between the polyolefin porous film and at least one of the positive electrode and the negative electrode as a member constituting the non-aqueous electrolyte secondary battery. The porous layer may be formed on one side or both sides of the polyolefin porous film. Alternatively, the porous layer may be formed on the active material layer of at least one of the positive electrode and the negative electrode. Alternatively, the porous layer may be arranged between and in contact with the polyolefin porous film and at least one of the positive electrode and the negative electrode. 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 layers or more. The porous layer is preferably an insulating porous layer containing a resin.

When the porous layer is laminated on one side of the polyolefin porous film, the porous layer is preferably laminated on the surface of the polyolefin porous film facing the positive electrode. More preferably, the porous layer is laminated on the surface in contact with the positive electrode.

Resins constituting the porous layer include, for example, polyolefins; (meth)acrylate resins; fluorine-containing resins; polyamide resins; polyimide resins; polyester resins; Resin; water-soluble polymer and the like.

Among the above resins, polyolefins, polyester resins, acrylate resins, fluorine-containing resins, polyamide resins and water-soluble polymers are preferred. As the polyamide-based resin, a wholly aromatic polyamide (aramid resin) is preferable. Polyarylates and liquid crystal polyesters are preferred as the polyester-based resin. As the fluorine-containing resin, a polyvinylidene fluoride resin is preferable.

Examples of the aramid resin include para-aramid and meta-aramid, with para-aramid being more preferred. Examples of para-aramid include poly(paraphenylene terephthalamide), poly(parabenzamide), poly(4,4'-benzanilide terephthalamide), poly(paraphenylene-4,4'-biphenylenedicarboxylic acid amide), poly(para phenylene-2,6-naphthalenedicarboxylic acid amide), poly(2-chloro-paraphenylene terephthalamide), paraphenylene terephthalamide/2,6-dichloro-paraphenylene terephthalamide copolymer, poly(4,4'-diphenyl sulfonyl terephthalamide), para-orientation type such as para-phenylene terephthalamide/4,4′-diphenylsulfonyl terephthalamide copolymer, or para-aramid having a structure conforming to para-orientation type.

The porous layer may contain fillers. The fillers can be inorganic fillers or organic fillers. More preferred fillers are inorganic fillers made of inorganic oxides such as silica, calcium oxide, magnesium oxide, titanium oxide, alumina, mica, zeolite, aluminum hydroxide, and boehmite. In the porous layer, the filler content may be 10 to 99% by weight, or 20 to 75% by weight, based on the total amount of the resin and filler.

In particular, when the resin constituting the porous layer is an aramid resin, by setting the content of the filler in the above range of 20 to 75% by weight, the increase in the weight of the separator due to the filler can be suppressed, and the ion permeability is improved. A good separator can be obtained.

The porous layer in the present embodiment is preferably arranged between the polyolefin porous film and the positive electrode active material layer of the positive electrode. In the following description of the physical properties of the porous layer, at least the physical properties of the porous layer disposed between the polyolefin porous film and the positive electrode active material layer of the positive electrode when used as a non-aqueous electrolyte secondary battery. .

The average film thickness of the porous layer is preferably in the range of 0.5 μm to 10 μm per one porous layer, and in the range of 1 μm to 5 μm, from the viewpoint of ensuring adhesion with the electrode and high energy density. is more preferable. When the film thickness of the porous layer is 0.5 μm or more per layer, it is possible to sufficiently suppress internal short circuits due to breakage of the non-aqueous electrolyte secondary battery, etc., and the amount of electrolyte retained in the porous layer. is sufficient. On the other hand, if the film thickness of the porous layer exceeds 10 μm per layer, the permeation resistance of lithium ions increases in the non-aqueous electrolyte secondary battery, and the positive electrode may deteriorate after repeated cycles. Therefore, in the non-aqueous electrolyte secondary battery, the rate characteristics and cycle characteristics may deteriorate. In addition, since the distance between the positive electrode and the negative electrode increases, the internal volumetric efficiency of the non-aqueous electrolyte secondary battery may decrease.

The basis 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 per unit area of the porous layer is preferably 0.5 to 20 g/m ² and more preferably 0.5 to 10 g/m ² per one porous layer. By setting the basis weight per unit area of the porous layer within these numerical ranges, the weight energy density and volume energy density of the non-aqueous electrolyte secondary battery can be increased. If the basis weight of the porous layer exceeds the above range, the non-aqueous electrolyte secondary battery 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 as to obtain sufficient ion permeability. Moreover, the pore size of the pores of the porous layer is preferably 1.0 μm or less, more preferably 0.5 μm or less. By setting the pore diameters of the pores to these sizes, the non-aqueous electrolyte secondary battery can obtain sufficient ion permeability.

The air permeability of the laminated separator obtained by laminating the porous layer on the porous film is preferably 30 to 1000 sec/100 mL, more preferably 50 to 800 sec/100 mL in terms of Gurley value. By having the air permeability, the laminated separator can obtain sufficient ion permeability in a non-aqueous electrolyte secondary battery.

<Laminated separator>
A separator according to an embodiment of the present invention may be a laminated separator.

The film thickness of the laminated separator is preferably 5.5 μm to 45 μm, more preferably 6 μm to 25 μm.

The air permeability of the laminated separator is preferably 100 to 350 sec/100 mL, more preferably 100 to 300 sec/100 mL in Gurley value.

In addition, the separator according to one embodiment of the present invention may contain another porous layer other than the porous film and the porous layer, if necessary, within a range that does not impair the object of the present invention. . Examples of the other porous layer include known porous layers such as a heat-resistant layer, an adhesive layer, and a protective layer.

<Method for manufacturing separator for non-aqueous electrolyte secondary battery>
(Method for producing polyolefin porous film)
The method for producing the porous film is not particularly limited. For example, a sheet-like polyolefin resin composition is produced by kneading a polyolefin resin, a pore-forming agent such as an inorganic filler or a plasticizer, and optionally an antioxidant or the like and then extruding the mixture. Then, the pore-forming agent is removed from the sheet-like polyolefin resin composition with an appropriate solvent. Thereafter, by stretching the polyolefin resin composition from which the pore-forming agent has been removed, a polyolefin porous film can be produced.

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

Specific examples of the method for producing the porous film include a method including the following steps.
(A) A step of kneading an ultra-high molecular weight polyethylene, 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 to obtain a polyolefin resin composition.
(B) A step of rolling the obtained polyolefin resin composition with a pair of rolling rollers, cooling it step by step while pulling it with winding rollers with different speed ratios, and forming a sheet.
(C) A step of removing the pore-forming agent from the obtained sheet with a suitable solvent.
(D) A step of stretching the sheet from which the pore-forming agent has been removed at an appropriate stretching ratio.

(Method for producing porous layer and laminated separator)
As a method for producing the porous layer in one embodiment of the present invention and the laminated separator according to one embodiment of the present invention, for example, a coating liquid containing a resin contained in the porous layer is applied to one side of the porous film or A method of forming the porous layer on the porous film by removing the solvent by coating on both sides and drying, and applying a coating liquid containing a resin contained in the porous layer to the porous film After coating on one or both sides of the porous film, the resin contained in the porous layer is precipitated on the porous film under the conditions of a specific temperature and a specific relative humidity, and then the solvent is removed by drying. a method of forming the porous layer on the porous film by

When forming the porous layers on both sides of the porous film, (a) the porous layers may be formed simultaneously on both sides of the porous film, and (b) one side of the porous film may be formed. to form a porous layer on one side of the porous film, apply the coating liquid to the other side of the porous film, and apply the coating liquid to the other side of the porous film A porous layer may be formed on one side.

In addition, before applying the coating liquid to one or both sides of the porous film, one side or both sides of the polyolefin porous film to be coated with the coating liquid may be subjected to hydrophilic treatment as necessary. can be done.

The coating liquid contains a resin contained in the porous layer. In addition, the coating liquid may contain fine particles described later that may be contained in the porous layer. The coating liquid can usually be prepared by dissolving the resin that can be contained in the porous layer described above in a solvent and dispersing the fine particles. Here, the solvent for dissolving the resin also serves as a dispersion medium for dispersing the fine particles. Further, the resin may be made into an emulsion by the solvent.

The solvent is not particularly limited as long as it can uniformly and stably dissolve the resin and uniformly and stably disperse the fine particles without adversely affecting the polyolefin porous film. Specific examples of the solvent include water and organic solvents. Only one type of the solvent may be used, or two or more types may be used in combination.

The coating liquid may be formed by any method as long as it satisfies the conditions such as the resin solid content (resin concentration) and the amount of fine particles necessary for obtaining a desired porous layer. Specific 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. Further, the coating liquid may contain additives such as a dispersant, a plasticizer, a surfactant, and a pH adjuster as components other than the resin and the fine particles as long as the object of the present invention is not impaired. . The amount of the additive to be added may be within a range that does not impair the object of the present invention.

The method of applying the coating liquid to the porous film, that is, the method of forming the porous layer on the surface of the porous film is not particularly limited. Methods for forming the porous layer include, for example, a method of directly applying a coating liquid to the surface of a porous film and then removing the solvent; After forming a porous layer, the porous layer and the porous film are pressed against each other, and then the support is peeled off. Next, a method of removing the solvent after peeling off the support, and the like can be mentioned.

As a method for applying the coating liquid, a conventionally known method can be employed, and specific examples thereof include a gravure coater method, a dip coater method, a bar coater method, a die coater method, and the like.

Drying is generally used to remove the solvent. Alternatively, drying may be performed after replacing the solvent contained in the coating liquid with another solvent.

(Method of controlling “elongation after ethanol immersion” and “penetration strength”)
In one embodiment of the present invention, as a method of controlling the "elongation rate after immersion in ethanol" within a suitable range, for example, the following methods (a) to (d) are used to form the porous film that constitutes the separator. can include a method of adjusting the residual stress of.
(a) A method of controlling the draw ratio in the step (D) in the method for producing a porous film described above within a suitable range.
(b) A method of heat-treating at a suitable temperature after step (D) in the method for producing a porous film described above.
(c) After coating the coating solution on the porous film to form a coating layer, under conditions of a suitable temperature and a suitable relative humidity, the A method of precipitating a resin constituting the porous layer while stretching a laminate composed of the porous film and the coating layer in the MD direction.
(d) after depositing the resin constituting the porous layer on the porous film, drying the porous film in which the resin constituting the porous layer is deposited at a specific heating temperature, A method of removing the solvent contained in the coating liquid to form the porous layer, and then heat-treating the laminate composed of the porous film and the porous layer at a suitable temperature.

In method (a), the preferred range of draw ratio may vary depending on the composition of the porous film and the like. Specifically, the preferred range of the draw ratio is, for example, preferably 3 times to 20 times, more preferably 6 times to 9 times. By controlling the draw ratio within a suitable range, the residual stress in the obtained porous film can be controlled within a suitable range. As a result, the "elongation rate after immersion in ethanol" of the separator containing the porous film can be controlled within a suitable range.

By performing heat treatment in the method (b), the sheet stretched in the step (D) is shrunk to reduce the internal strain and reduce the residual stress in the resulting porous film. can be done. As a result, the "elongation rate after immersion in ethanol" of the separator containing the porous film can be reduced and controlled within a suitable range. Here, the heat treatment temperature in the heat treatment is preferably, for example, 50°C to 100°C, more preferably 60°C to 90°C.

In the method (c), a suitable temperature, a suitable relative humidity, and a suitable elongation rate when depositing the porous layer vary depending on the composition of the porous layer film and the porous layer. obtain. Specifically, the preferred temperature for depositing the porous layer is preferably 45°C to 65°C, more preferably 50°C to 60°C. A suitable relative humidity when depositing the porous layer is preferably 65% to 80%, more preferably 70% to 75%. The preferred elongation is preferably 1.0% to 6.5%, more preferably 4.5% to 6.5%, throughout the deposition process. The elongation rate in elongation when depositing the porous layer is calculated by the following formula (5).
Elongation rate (%) = {(d ₁ -d ₀ )/d ₀ } x 100 (%) (5)
In equation (5), _d0 is the transport speed of the laminate before stretching, and _d1 is the transport speed of the laminate after stretching.

In addition, when depositing the porous layer, the laminate may be stretched once during the deposition, or may be stretched twice or more. When extending twice or more, it is preferable that the elongation rate calculated from the total value of the elongation amount in each elongation is within the preferred range described above. By adjusting the elongation rate within the preferred range described above, the residual stress in the porous film constituting the resulting laminated separator can be controlled within a preferred range. As a result, the "elongation rate after immersion in ethanol" of the laminated separator can be controlled within a suitable range.

In the method (d), the heating temperature for removing the solvent and forming the porous layer may vary depending on the type of the solvent. Specifically, the heating temperature is preferably 70°C to 100°C, more preferably 85°C to 98°C. After the solvent is removed, the temperature in the heat treatment (heat treatment temperature) is preferably 85°C to 135°C, more preferably 85°C to 90°C.

By performing the heat treatment at the suitable temperature, as in the method (b), the strain inside the porous film constituting the laminated separator obtained is reduced, and the residual stress in the porous film is reduced. can be done. As a result, the "elongation rate after immersion in ethanol" of the laminated separator can be reduced and controlled within a suitable range.

In the method (d), roller heating can be used as the heating for removing the solvent and the means for the heat treatment. In roller heating, the porous film on which the resin is deposited is dried by bringing the porous film on which the resin is deposited into contact with a heated roller. A method of heating the roller includes, for example, a method of supplying a heating medium inside the roller and circulating the medium. In this case, the heating temperature and heat treatment temperature described above represent the temperature of the heat medium. Further, by performing the heating and the heat treatment using a plurality of rollers using different types of heat medium, the heat treatment can be performed at a temperature different from the heating temperature. As the heat medium, for example, hot water, oil, steam, or the like is used. For example, the cold rollers may be supplied with hot water and the hot rollers with steam.

In one embodiment of the present invention, as a method of controlling the "penetration strength" within a suitable range, for example, a method of controlling the air permeability, shutdown (SD) temperature and weight basis weight of the porous film within a suitable range. can be mentioned.

In addition, after adopting at least one method of (a) to (d), for example, by laminating the porous layer on both sides of the porous film, the "elongation rate after ethanol immersion ” can be increased to control within a more suitable range. Specifically, as shown above, heating the stretched sheet in step (D) reduces the residual stress in the resulting porous film. Here, when the porous layer is laminated on the porous film, the porous film is usually heated in order to deposit the porous layer from the coating liquid, and the residual stress is reduced. . On the other hand, the porous film tends to undergo elastic deformation in the MD direction when heated. Therefore, when the porous layer is laminated on both sides of the porous film, the porous layer has less elasticity than when the porous layer is laminated on one side of the porous film. fixes the size of the porous film. Therefore, it becomes more difficult to reduce the residual stress in the porous film due to the shrinkage. As a result, the "elongation rate after immersion in ethanol" of the separator containing the porous film is increased. Therefore, by adopting at least one method of (a) to (d) and laminating the porous layer on both sides of the porous film, the "elongation rate after ethanol immersion" , can be controlled to a more suitable range.

From the viewpoint of controlling the "puncture strength" in the range of 300 gf or more, the air permeability of the porous film is preferably 55 sec/100 mL to 90 sec/100 mL, and 80 sec/100 mL to 85 sec/100 mL. is more preferred. The SD temperature of the porous film is preferably 135°C to 147°C, more preferably 138°C to 145°C. Furthermore, the weight basis weight of the porous film is preferably 4.0 g/m ² to 5.0 g/m ² , more preferably 4.5 g/m ² to 4.8 g/m ² .

[2. Non-aqueous electrolyte secondary battery member, non-aqueous electrolyte secondary battery]
A non-aqueous electrolyte secondary battery member according to one embodiment of the present invention is a non-aqueous electrolyte secondary battery member in which a positive electrode, the above separator or laminated separator, and a negative electrode are arranged in this order. be. Further, a non-aqueous electrolyte secondary battery according to one embodiment of the present invention includes the separator or laminated separator described above.

A non-aqueous electrolyte secondary battery member according to an embodiment of the present invention is said to be able to improve impact resistance of a non-aqueous electrolyte secondary battery including the non-aqueous electrolyte secondary battery member. Effective. A non-aqueous electrolyte secondary battery according to an embodiment of the present invention has an effect of being excellent in impact resistance.

As a method for manufacturing the non-aqueous electrolyte secondary battery according to one embodiment of the present invention, a conventionally known manufacturing method can be adopted. For example, a non-aqueous electrolyte secondary battery member is formed by arranging a positive electrode, a polyolefin porous film and a negative electrode in this order. Here, the porous layer may exist between the polyolefin porous film and at least one of the positive electrode and the negative electrode. Next, the non-aqueous electrolyte secondary battery member is placed in a container that serves as a housing for the non-aqueous electrolyte secondary battery. After filling the inside of the container with the non-aqueous electrolyte, the container is sealed while reducing the pressure. Thereby, a non-aqueous electrolyte secondary battery according to one embodiment of the present invention 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 for non-aqueous electrolyte secondary batteries. For example, a positive electrode sheet having a structure in which an active material layer containing a positive electrode active material and a binder is formed on a positive electrode current collector can be used as the positive electrode. The active material layer may further contain a conductive agent.

Examples of the positive electrode active material include materials that can be doped/dedoped with metal ions such as lithium ions or sodium ions. Specific examples of such materials include lithium composite oxides containing at least one type of transition metal such as V, Mn, Fe, Co and Ni.

Examples of the conductive agent include natural graphite, artificial graphite, cokes, carbon black, pyrolytic carbons, carbon fibers, and carbonaceous materials such as organic polymer compound sintered bodies. 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 fluorine-based resins such as polyvinylidene fluoride (PVDF), acrylic resins, and styrene-butadiene rubber. In addition, 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. Among them, Al is more preferable because it is easy to process into a thin film and is inexpensive.

Methods for producing the positive electrode sheet include, for example, a method of pressure-molding a positive electrode active material, a conductive agent and a binder on a positive electrode current collector; is made into a paste, the paste is applied to the positive electrode current collector, and after drying, pressure is applied to fix it to the positive electrode current collector;

<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 for non-aqueous electrolyte secondary batteries. For example, a negative electrode sheet having a structure in which an active material layer containing a negative electrode active material and a binder is formed on a negative electrode current collector can be used as the negative electrode. The active material layer may further contain a conductive agent.

Examples of the negative electrode active material include materials capable of doping/dedoping metal ions such as lithium ions or sodium ions. Examples of such materials include carbonaceous materials. 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 is easy to process into a thin film.

Examples of the method for producing the negative electrode sheet include a method of pressure-molding a negative electrode active material on a negative electrode current collector; a method in which the coating is applied to the surface, dried, and then pressed to adhere to the negative electrode current collector; and the like. The paste preferably contains the conductive agent and the binder described above.

<Non-aqueous electrolyte>
The non-aqueous electrolyte in one embodiment of the present invention is not particularly limited as long as it is a non-aqueous electrolyte generally used for non-aqueous electrolyte secondary batteries. As the non-aqueous electrolyte, for example, a non-aqueous electrolyte 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 salts and _LiAlCl4 . Only one type of the lithium salt may be used, or two or more types may be used in combination.

Organic solvents constituting the non-aqueous electrolyte include, for example, carbonates, ethers, esters, nitriles, amides, carbamates, sulfur-containing compounds, and fluorine groups introduced into these organic solvents. Fluorinated organic solvents and the like are included. Only one type of the organic solvent may be used, or two or more types may be used in combination.

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

[Measuring method]
Various measurements in Examples and Comparative Examples were performed by the following methods.

<Measurement of film thickness>
The film thicknesses of the porous films and separators in Examples and Comparative Examples described later were measured using a high-precision digital length measuring machine (VL-50) manufactured by Mitutoyo Corporation.

<Measurement of weight basis weight>
A square sample with a side length of 8 cm was cut out from the porous films in Examples and Comparative Examples described later, and the weight W (g) of the sample was measured. Then, the weight basis weight of the porous film was calculated according to the following formula (6).
Weight basis weight (g/m ² ) = W/(0.08 x 0.08) (6)
<Measurement of air permeability>
The air permeability (Gurley value) of the porous films in Examples and Comparative Examples described later was measured according to JIS P8117.

<Measurement of SD temperature>
The SD temperature of porous films in Examples and Comparative Examples described later was measured by the following method.

A circular measurement sample with a diameter of 19.4 mm was punched from the polyolefin porous film to obtain a measurement sample. In addition, 2032 type coin cell parts (upper lid, lower lid, gasket, Kapton ring (outer diameter 16.4 mm, inner diameter 8 mm, thickness 0.05 mm), spacer (diameter 15.5 mm, thickness 0.5 mm circular spacer ) and an aluminum ring (outer diameter 16 mm, inner diameter 10 mm, thickness 1.6 mm) (manufactured by Hosen Co., Ltd.) were prepared.

Then, a measurement sample and a gasket ring are installed in order from the lower lid, impregnated with 10 μmL of electrolytic solution, then a Kapton ring, a spacer, an aluminum ring, and an upper lid are installed in order from the top of the measurement sample, and a coin cell caulking device ( Hosen Co., Ltd.) to prepare a coin cell for measurement. Here, as the electrolytic solution, a non _- aqueous electrolytic solution ( LiBF ₄ concentration: 1.0 mol/L) was used. While the temperature inside the coin cell for measurement is raised from room temperature to 150°C at a rate of 15°C/min, the temperature inside the coin cell is measured with a digital multimeter (manufactured by ADC Co., Ltd.; 7352A) at 1 kHz in the coin cell. was continuously measured by an LCR meter (manufactured by Hioki Electric Co., Ltd.; IM3523).

When the resistance value of the coin cell at 1 kHz was 2000Ω or more during the measurement, it was confirmed that the coin cell has a shutdown function.

At this time, from the graph of the relationship between the cell temperature and the resistance value, the intersection point of the tangent line of the resistance value of 2000Ω and the resistance value straight line of the base before the resistance greatly increased was taken as the shutdown temperature (SD temperature) of the polyolefin porous film.

<Measurement of immersion elongation>
A test piece having a length of 250 mm and a width of 27 mm was cut out from the separators obtained in Examples and Comparative Examples described later. In addition, in a test piece, the TD direction with the largest elongation rate was set to 250 mm in length. The test piece was placed in a 50 mL plastic container with a lid, and ethanol was injected into the plastic container. Ethanol was added until the specimen was completely submerged in the liquid. After sealing the plastic container, it was allowed to stand in an environment of 23°C. After 24 hours, the test piece was taken out from the plastic container, and aluminum sheets of length 250 mm, width 27 mm, and thickness 0.5 mm were arranged on a glass plate so that one short side was aligned, while taking care not to create wrinkles. . After a glass plate was superimposed on the short side opposite to the aligned short side and brought into close contact, the amount of elongation in the longitudinal direction of the test piece was measured through the glass plate. A scale loupe 10×S manufactured by PEAK was used to measure the amount of elongation. The amount of elongation was measured within 3 minutes after the test piece was removed from the plastic container. The amount of elongation was measured by sampling three samples per sample, and the average value was taken as the average amount of elongation. Moreover, the elongation rate was calculated from the following formula (1').
Elongation rate (%) = {average elongation amount (mm) / 250 mm} x 100 (1')
<Measurement of puncture strength>
A test piece having a length of 15 mm and a width of 300 mm was cut out from the separators obtained in Examples and Comparative Examples described later. Using the test piece, the puncture strength of the separator was measured by the following methods (i) and (ii).
(i) After fixing the test piece with a 12 mmΦ washer, a pin (pin diameter 1 mmΦ, tip 0.5R) was pierced into the test piece at a piercing speed of 200 mm/min.
(ii) The maximum stress (gf) when the pin was pierced into the test piece in (i) was measured, and the measured value was defined as the piercing strength of the separator.

<Measurement of heat shrinkage>
A separator obtained in Examples and Comparative Examples described later was cut into a square having an area of 8 m × 8 m and an area of 64 cm ² . A sample for measurement was prepared by pulling. The area of the part surrounded by the drawn line in the measurement sample: 6 cm × 6 cm = 36 cm ² was taken as the area of the measurement sample before heating. The sample for measurement was sandwiched between paper and placed in an oven heated to 150°C. After 1 hour, the measurement sample was taken out from the oven, and the length of the line drawn in the MD direction and the length of the line drawn in the TD direction of the measurement sample were measured using a digital caliper. The product of the length of the drawn line in the TD direction and the length of the drawn line in the MD direction was defined as the area of the measurement sample after heating. The measured area of the measurement sample after heating: A (cm ² ), the length of the line drawn in the MD direction _DM (cm), and the length of the line drawn in the TD direction: D _TD ( cm), the heat shrinkage rate when the separator is heated at a temperature of 150 ° C. for 1 hour, the heat shrinkage rate in the MD direction, and the heating in the TD direction from the following equations (2') to (4'). Shrinkage was calculated.
Heat shrinkage = {(36-A)/36} x 100 (2')
Heat shrinkage rate in MD direction = {(6-D _MD )/6} x 100 (3')
Heat shrinkage rate in TD direction = {(6-D _TD )/6} x 100 (4')
<Measurement of elastic modulus in TD direction>
The elastic modulus in the TD direction of separators obtained in Examples and Comparative Examples described later was measured by the following method.

Two mini-dumbbell-shaped test pieces conforming to JIS K7127 were cut from each of the separators obtained in Examples and Comparative Examples described later. For each test piece, at a temperature of 23 ° C., in accordance with the test method of JIS K6850, with a tensile speed of 10 mm / min, a tensile tester (manufactured by A&D, Tensilon universal tester RTG-1310) A tensile test was performed using The test piece was pulled in the length direction (TD direction) in the tensile test. The elastic modulus in the TD direction was calculated from the slope of the obtained stress-strain curve in the range where the strain was 0.1% to 1.0%. The above measurements were performed on two test pieces cut from one separator. That is, the measurement was performed twice for one separator. The average value of the elastic moduli in the two TD directions obtained for a certain separator was calculated, and the average value was adopted as the elastic modulus in the TD direction of the separator.

<Crush test>
(Preparation of non-aqueous electrolyte secondary battery)
Non-aqueous electrolyte secondary batteries were produced by the following method using the separators obtained in Examples and Comparative Examples described later. The separator was a laminated separator roll having a width of 275 mm. The laminated separator roll was dried at a dew point of -40°C for 24 hours. Subsequently, the laminated separator roll was placed in a battery laminating device. The laminated separator unwound from the laminated separator roll was periodically folded in the MD direction at a length of 97 mm to fold in a zigzag shape. Positive electrodes with tabs (265 mm×90 mm) and negative electrodes with tabs (270 mm×95 mm) were alternately laminated on the valleys of the folded laminated separator. That is, the tabbed negative electrode is placed in the first valley, the tabbed positive electrode is placed in the next valley, the tabbed negative electrode is placed in the next valley, and the tabbed positive electrode is placed in the next valley. I repeated the placement process. A total of 18 positive electrodes with tabs and 19 negative electrodes with tabs were used. After arranging the positive electrode with a tab and the negative electrode with a tab, an electrode laminate was obtained by fixing the end portion of the laminated separator with a tape. The fixed electrode laminate was inserted into an aluminum exterior material. Next, three sides of this exterior material were thermocompressed, dried in vacuum at 85° C. for 24 hours, and then a non-aqueous electrolyte was injected into the exterior material. The non-aqueous electrolytic solution is _{an electrolytic solution at 25 ° C. (LiBF 4 concentration} : 1.0 mol/L) was used. After the injection, the pressure was reduced and the remaining side of the exterior material was thermocompression bonded to produce a non-aqueous electrolyte secondary battery.

(Implementation of crushing test)
After the non-aqueous electrolyte secondary battery thus produced was fully charged, a crushing test was conducted according to the method described in WO2007/023609. Specifically, under conditions of 25 ° C., using an iron round bar with a diameter of 10 mm, the longitudinal direction of the round bar is parallel to the TD direction of the separator in the non-aqueous electrolyte secondary battery. A pressure was applied to the central portion of the separator of the non-aqueous electrolyte secondary battery in the direction corresponding to the MD direction. Then, the thickness of the non-aqueous electrolyte secondary battery was crushed by the pressure until it reached 50% of the initial thickness before the crush test. At this time, the non-aqueous electrolyte secondary battery was crushed so that the thickness of the non-aqueous electrolyte secondary battery decreased at a speed of 50 mm per second.

Subsequently, a new non-aqueous electrolyte secondary battery identical to the non-aqueous electrolyte secondary battery was fabricated by the method described above. Under the condition of 25 ° C., using an iron round bar with a diameter of 10 mm, the longitudinal direction of the round bar is parallel to the MD direction of the separator in the new non-aqueous electrolyte secondary battery. , pressure was applied to the central portion of the separator of the new non-aqueous electrolyte secondary battery in the direction corresponding to the TD direction. Then, the thickness of the new non-aqueous electrolyte secondary battery was crushed by the pressure until it reached 50% of the thickness before the crush test, that is, the initial thickness. At this time, the new non-aqueous electrolyte secondary battery was crushed so that the thickness of the new non-aqueous electrolyte secondary battery decreased at a rate of 50 mm per second.

A crush test was performed by the method described above, and as a result of the crush test, both the non-aqueous electrolyte secondary battery and the new non-aqueous electrolyte secondary battery did not ignite. When at least one of the non-aqueous electrolyte secondary battery and the new non-aqueous electrolyte secondary battery ignited, it was evaluated as x.

[Example 1]
<Preparation of coating solution>
As the resin constituting the porous layer, poly(paraphenylene terephthalamide) (hereinafter referred to as "PPTA"), which is a kind of aramid resin, was synthesized by the following method.

A separable flask with a capacity of 3 L having a stirring blade, a thermometer, a nitrogen inlet tube and a powder addition port was used as a synthesis vessel. A well-dried flask was charged with 2200 g of N-methyl-2-pyrrolidone (NMP). To this, 151.07 g of calcium chloride powder was added, and the temperature was raised to 100° C. to dissolve completely, thereby obtaining an NMP solution of calcium chloride. The calcium chloride powder used was preliminarily vacuum-dried at 200° C. for 2 hours.

Next, the temperature of the NMP solution of calcium chloride was returned to room temperature, and 68.23 g of paraphenylenediamine was added and completely dissolved to obtain solution (1). While maintaining the temperature of solution (1) at 20°C ± 2°C, 124.25 g of terephthaloyl dichloride was added to solution (1) in 4 portions at intervals of about 10 minutes. After that, while continuing to stir at 150 rpm, the solution (1) was aged for 1 hour while maintaining the temperature at 20° C.±2° C. to obtain an aramid polymerization solution (1) containing 6% by weight of PPTA. The intrinsic viscosity of PPTA contained in the aramid polymerization liquid (1) was 1.5 g/dL.

100 g of aramid polymerization liquid (1) was weighed into a flask, and 6.0 g of alumina A (average particle size: 13 nm) was added to obtain mixed liquid A (1). In mixed liquid A(1), the weight ratio of PPTA and alumina A was 1:1. Next, NMP was added to mixed liquid A(1) so that the solid content was 4.5% by weight, and the mixture was stirred for 240 minutes to obtain mixed liquid B(1). The "solid content" referred to herein is the total weight of PPTA and Alumina A. Next, 0.73 g of calcium carbonate was added to mixed liquid B(1), and the mixture was stirred for 240 minutes to neutralize the solution and obtain neutralized liquid (1). Thereafter, the neutralized liquid (1) was defoamed under reduced pressure to prepare a slurry-like coating liquid (1).

<Preparation of separator for non-aqueous electrolyte secondary battery>
While conveying the polyethylene porous film (hereinafter also simply referred to as "porous film"), the first continuous coating of the slurry coating liquid (1) is performed on one side of the porous film, A coating film was formed. The thickness, air permeability, SD temperature and weight basis weight of the porous film are shown in Table 1 below. Subsequently, while conveying the porous film on which the coating film was formed, the first elongation was performed at the deposition temperature, deposition relative humidity, and elongation rate shown in Table 2 below. PPTA was deposited at . Next, calcium chloride and the solvent were removed by washing the coating film on which PPTA had precipitated with water. Here, the elongation rate is represented by the following formula (7).
Elongation rate (%) = {a ₂ /(a ₁ -1)} x 100 (7)
In the formula (7), _a1 is the transport speed (m/min) of the porous film when the slurry coating liquid (1) is continuously applied, and _a2 is the It is the conveying speed (m/min) of the porous film on which the coating film is formed. That is, the PPTA was precipitated by controlling _a1 and _a2 such that the elongation rate was the value shown in Table 2 below.

After that, the coating film from which calcium chloride and the solvent have been removed is subjected to a drying treatment using a heating roller group ₁ at a heating temperature R1 shown in Table 2 below. The drying treatment was carried out using the heating roller group 2 at the heating temperature R ₂ described in . That is, the first drying process for continuously drying the coating film was performed. As a result, a single layered separator roll (1) was obtained in which a porous layer was formed on one side of the porous film. In the heating roller group 2, different temperatures were set for the first half roller and the second half roller. Hereinafter, the heating temperature of the first half roller is R _2a and the heating temperature of the second half roller is R _2b . Note that the front-half roller is a roller positioned upstream in the heating roller group 2, and the rear-half roller is a roller positioned downstream. In other words, the coating film was dried at the heating temperature _R1 , then at the heating temperature _R2a , and then at the heating temperature _R2b . Here, the drying at the heating temperature _R1 and the drying at the heating temperature _R2a correspond to the step of removing the solvent from the coating film, and the drying at the heating temperature _R2b corresponds to the heat treatment step.

After that, the slurry coating liquid (1) is continuously applied for the second time to the surface opposite to the coating surface of the single-layer separator, followed by stretching for the second time. A coating film in which PPTA was deposited was formed on the surface. The second elongation was performed under the same conditions of temperature and relative humidity as the first elongation, at the elongation rates listed in Table 2. Calcium chloride and the solvent were removed by washing the coating film with the precipitated PPTA with water. The coating film from which calcium chloride and the solvent have been removed is subjected to a second drying treatment under the same conditions as in the preparation of the single-sided layer separator, forming porous layers on both sides of the porous film. Thus, a double-sided laminated separator roll (1) was obtained. The double-sided laminated separator roll (1) was used as a separator (1).

[Example 2]
The porous film was changed to a porous film having the thickness, air permeability, SD temperature and weight basis weight shown in Table 1 below, and the conditions for depositing PPTA and the drying treatment A double-sided laminated separator roll (2) was obtained in the same manner as in Example 1, except that the conditions were changed as shown in Table 2 below. The double-sided laminated separator roll (2) was used as a separator (2).

[Example 3]
The porous film was changed to a porous film having the thickness, air permeability, SD temperature and weight basis weight shown in Table 1 below, and the conditions for depositing PPTA and the drying treatment A double-sided laminated separator roll (3) was obtained in the same manner as in Example 1, except that the conditions were changed as shown in Table 2 below. The double-sided laminated separator roll (3) was used as a separator (3).

[Comparative Example 1]
The porous film was changed to a porous film having the thickness, air permeability, SD temperature and weight basis weight shown in Table 1 below, and the conditions for depositing PPTA and the drying treatment A single laminated separator roll (1) for comparison was obtained in the same manner as in Example 1, except that the conditions were changed as shown in Table 2 below. In Comparative Example 1, the porous layer was formed only on one side of the porous film, that is, the second continuous coating, the second stretching, and the second drying treatment were not performed. The comparative single-layered separator roll (1) was used as a comparative separator (1).

[Comparative Example 2]
The porous film was changed to a porous film having the thickness, air permeability, SD temperature and weight basis weight shown in Table 1 below, and the conditions for depositing PPTA and the drying treatment A comparative single-layer separator roll (2) was obtained in the same manner as in Comparative Example 1, except that the conditions were changed as shown in Table 2 below. The comparative single-layered separator roll (2) was used as a comparative separator (2).

[Comparative Example 3]
The porous film was changed to a porous film having the thickness, air permeability, SD temperature and weight basis weight shown in Table 1 below, and the conditions for depositing PPTA and the drying treatment A double-sided laminated separator roll (3) for comparison was obtained in the same manner as in Example 1, except that the conditions were changed as shown in Table 2 below. The comparative double-sided laminated separator roll (3) was used as a comparative separator (3). An attempt was made to produce a non-aqueous electrolyte secondary battery by the above-described method using the comparative separator (3), but the comparative separator (3) was broken, resulting in a non-aqueous electrolyte secondary battery. could not be produced.

[result]
The results of measuring the physical properties of the separators produced in Examples and Comparative Examples by the methods described above, and the results of evaluating the non-aqueous electrolyte secondary batteries comprising the separators by the methods described above are shown below. Table 3 shows.

As shown in Table 3, the separators (1) to (3) described in Examples 1 to 3 had an immersion elongation of 0.85% or more and 1.5% or less, and a puncture strength of 300 gf or more. Further, when the separators (1) to (3) are used to assemble the non-aqueous electrolyte secondary battery by the method described above, the non-aqueous electrolyte secondary battery can be assembled without breaking the separator. I was able to Furthermore, the non-aqueous electrolyte secondary batteries produced using the separators (1) to (3) did not ignite in the crush test.

On the other hand, the comparative separators (1) to (3) described in Comparative Examples 1 to 3 had an immersion elongation rate outside the range of 0.85% or more and 1.5% or less, or had a puncture strength of It was less than 300gf. In the non-aqueous electrolyte secondary batteries manufactured using the comparative separators (1) to (3), the separator was broken during assembly, or caught fire in the crush test.

From the above, the separator according to one embodiment of the present invention has an immersion elongation of 0.85% or more and 1.5% or less and a puncture strength of 300 gf or more. It was found that the non-aqueous electrolyte secondary battery can be easily assembled using the separator, and the impact resistance of the non-aqueous electrolyte secondary battery provided with the separator can be improved.

A separator according to an embodiment of the present invention can be used for manufacturing a non-aqueous electrolyte secondary battery having excellent impact resistance.

Claims (6)

A separator for a non-aqueous electrolyte secondary battery comprising a polyolefin porous film,
Elongation after immersion in ethanol is 0.85% or more and 1.5% or less, and
A separator for a non-aqueous electrolyte secondary battery, having a puncture strength of 300 gf or more.
(Here, the elongation rate after the ethanol immersion is calculated by the following formula (1);
Elongation after immersion in ethanol (%)={(X ₁ −X ₀ )/X ₀ }×100 (1),
In the formula (1), X ₀ is the length (mm) in the TD direction before the separator for the non-aqueous electrolyte secondary battery is immersed in ethanol, and X ₁ is the non-aqueous electrolyte secondary battery. is the length (mm) in the TD direction after the separator for immersion in ethanol for 24 hours,
The puncture strength is calculated by the following methods (i) and (ii);
(i) After fixing the separator for the non-aqueous electrolyte secondary battery, a pin (pin diameter 1 mmΦ, tip 0.5R) is pierced at a speed of 200 mm / min, and the non-aqueous electrolyte secondary Pierce the battery separator.
(ii) The maximum stress (gf) when the pin is pierced into the non-aqueous electrolyte secondary battery separator in (i) is measured, and the measured value is defined as the piercing strength. ) 2. The separator for a non-aqueous electrolyte secondary battery according to claim 1, wherein the separator for a non-aqueous electrolyte secondary battery has a heat shrinkage rate of 20% or less when heated at a temperature of 150° C. for 1 hour. .
(Here, the heat shrinkage rate is calculated by the following formula (2).
Heat shrinkage = {(A ₀ −A ₁ )/A ₀ }×100 (2)
In formula (2), A ₀ is the area of the non-aqueous electrolyte secondary battery separator before heating the non-aqueous electrolyte secondary battery separator, and A ₁ is the non-aqueous electrolyte secondary battery separator. It is the area of the separator for the non-aqueous electrolyte secondary battery after heating the separator for the secondary battery at a temperature of 150° C. for 1 hour. ) 3. The separator for a non-aqueous electrolyte secondary battery according to claim 1, wherein porous layers containing a resin are laminated on both sides of said polyolefin porous film. 4. The separator for a non-aqueous electrolyte secondary battery according to claim 3, wherein said resin contains an aramid resin. A member for a non-aqueous electrolyte secondary battery, comprising a positive electrode, the separator for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 4, and a negative electrode arranged in this order. A nonaqueous electrolyte secondary battery comprising the separator for a nonaqueous electrolyte secondary battery according to any one of claims 1 to 4.