JP5882549B1 - Nonaqueous secondary battery separator, method for producing the same, and nonaqueous secondary battery - Google Patents

Abstract

A porous base material containing a thermoplastic resin, and a porous layer containing a polyvinylidene fluoride resin provided on one or both sides of the porous base material, wherein the porous layer is open in a direction perpendicular to the surface of the porous layer A separator for a non-aqueous secondary battery comprising: a porous layer having a structure in which a large number of cells are arranged adjacent to each other in the plane direction of the porous layer, and a water contact angle of 115 to 140 ?.

Description

  The present invention relates to a separator for a non-aqueous secondary battery, a manufacturing method thereof, and a non-aqueous secondary battery.

  Non-aqueous secondary batteries typified by lithium ion secondary batteries are widely used as power sources for portable electronic devices such as notebook computers, mobile phones, digital cameras, and camcorders.

  In recent years, with the miniaturization and weight reduction of portable electronic devices, the exterior and exterior of non-aqueous secondary batteries have been simplified, and aluminum cans have been developed instead of stainless steel cans as exterior materials. In addition, aluminum laminated film packs have been developed in place of metal cans. However, since a pack made of aluminum laminate film is soft, a battery (so-called soft pack battery) using the pack as an outer packaging material (so-called soft pack battery) is subjected to an impact from the outside or expansion and contraction of the electrode due to charge and discharge. A gap is easily formed between the two and the cycle life may be reduced.

  In order to solve the above problems, a technique for improving the adhesion between the electrode and the separator has been proposed. As one of such techniques, a separator having a porous layer containing a polyvinylidene fluoride-based resin on a substrate made of a polyolefin microporous film or the like is known (see, for example, Patent Documents 1 to 4). When this separator is pressed or hot pressed over the electrode, it adheres well to the electrode through the porous layer, so that the cycle life of the battery can be improved.

JP 2004-356102 A International Publication No. 2005/049318 Japanese Patent No. 4988972 JP 2013-54972 A

  However, since the polyvinylidene fluoride-based resin is a resin that is easily charged, a porous layer containing the polyvinylidene fluoride-based resin is easily charged with static electricity, and a separator provided with the porous layer may have poor handling properties. As a result, when a battery element is produced by stacking and winding a separator having a porous layer containing a polyvinylidene fluoride-based resin and winding the electrode, the electrode and the separator are unwound and the production efficiency of the battery is reduced. There was a problem.

  On the other hand, when the electrolytic solution is injected after the battery element is inserted into the packaging material, a separator with high wettability of the electrolytic solution is preferable in order to impregnate the separator with high uniformity in a short time.

The embodiment of the present invention has been made under the above circumstances.
An object of the embodiment of the present invention is to provide a separator for a non-aqueous secondary battery that realizes excellent handling properties and high affinity with an electrolyte in a well-balanced manner.
Furthermore, an embodiment of the present invention aims to provide a non-aqueous secondary battery with high production efficiency.

Specific means for solving the problems include the following aspects.
[1] A porous substrate containing a thermoplastic resin, and a porous layer containing a polyvinylidene fluoride resin provided on one or both surfaces of the porous substrate, the surface being perpendicular to the porous layer open cell has a number aligned structure adjacent the surface direction of the porous layer comprises a porous layer contact angle of water is 115 ° to 140 °, and in the porous layer on the A separator for a non-aqueous secondary battery having a measured charge decay half-life of 300 seconds or less .
[2] The separator for a nonaqueous secondary battery according to [1], wherein an average diameter of the opening of the cell is 0.1 μm to 10 μm.
[3] The non-aqueous secondary battery separator according to [1] or [2], wherein the porosity of the porous layer is 40% to 80% .
[ 4 ] The dynamic wetting tension is 1.5 mN when immersed in an electrolytic solution in which LiBF ₄ is dissolved at a concentration of 1M in a solvent in which ethylene carbonate and methyl ethyl carbonate are mixed at a mass ratio of 3: 7. The separator for a non-aqueous secondary battery according to any one of [1] to [ 3 ], wherein the time until it is 10 seconds or less.
[ 5 ] The porous layer further includes a surfactant having an HLB value of 5.0 to 8.0, and the polyvinylidene fluoride resin and the surfactant are mixed in the porous layer. The separator for nonaqueous secondary batteries according to any one of [1] to [ 4 ].
[6] In the above porous layer, the mass ratio of the surfactant and the polyvinylidene fluoride resin is 99.9: 0.1 to 95.0: A 5.0 non according to [5] Separator for water-based secondary battery.
[ 7 ] The non-aqueous system according to any one of [1] to [ 6 ], wherein a peel strength between the porous substrate and the porous layer is 0.1 N / cm to 2.0 N / cm. Secondary battery separator.
[ 8 ] The separator for a nonaqueous secondary battery according to any one of [1] to [ 7 ], wherein the porous layer further contains a filler.
[ 9 ] The separator for a nonaqueous secondary battery according to any one of [1] to [ 8 ], which has the porous layer on both surfaces of the porous substrate.
[ 10 ] The separator for a nonaqueous secondary battery according to any one of [1] to [ 9 ], wherein the porous substrate is a polyolefin microporous membrane containing polyethylene.
[ 11 ] The separator for a nonaqueous secondary battery according to any one of [1] to [ 10 ], wherein the porous substrate is a polyolefin microporous film containing polyethylene and polypropylene.
[ 12 ] A method for producing the separator for a non-aqueous secondary battery according to any one of [ 5 ] to [ 11 ], wherein the polyvinylidene fluoride resin and the HLB value are 5.0 to 8.0. A step of applying a solution obtained by dissolving an activator in a solvent to one or both sides of a porous substrate to form a coating layer; and removing the solvent from the coating layer to form a porous layer Forming the separator for a non-aqueous secondary battery.
[ 13 ] A positive electrode, a negative electrode, and a separator for a nonaqueous secondary battery according to any one of [1] to [ 11 ] disposed between the positive electrode and the negative electrode, and lithium doping / dedoping A non-aqueous secondary battery that obtains an electromotive force.

According to the embodiment of the present invention, there is provided a separator for a non-aqueous secondary battery that realizes excellent handling properties and high affinity with an electrolyte in a well-balanced manner.
Furthermore, according to the embodiment of the present invention, a non-aqueous secondary battery is provided with high manufacturing efficiency.

It is the image obtained by observing the separator of Example A1 from a surface perpendicular direction with a scanning electron microscope. It is the image obtained by observing the separator of Comparative Example A2 from the surface perpendicular direction with a scanning electron microscope.

  Hereinafter, embodiments of the present invention will be described. These descriptions and examples are illustrative of the invention and are not intended to limit the scope of the invention.

  In the present specification, a numerical range indicated using “to” indicates a range including the numerical values described before and after “to” as the minimum value and the maximum value, respectively.

  In the present specification, “machine direction” means the long direction in the long porous substrate and separator, and “width direction” means the direction orthogonal to the “machine direction”. In this specification, “machine direction” is also referred to as “MD direction”, and “width direction” is also referred to as “TD direction”.

<Separator for non-aqueous secondary battery>
A separator for a non-aqueous secondary battery according to the present disclosure (also simply referred to as “separator”) includes a porous base material containing a thermoplastic resin, and a polyvinylidene fluoride system provided on one or both surfaces of the porous base material. It is a porous layer containing resin, and has a structure in which a large number of cells opened in the surface vertical direction of the porous layer are arranged adjacent to each other in the surface direction of the porous layer (hereinafter also referred to as “honeycomb structure”). And a porous layer having a water contact angle of 115 ° to 140 °. In the separator of the present disclosure, the porous layer is a layer that exists as an outermost layer of the separator and is in contact with the electrode.

  The separator of the present disclosure is a separator having a porous layer containing a polyvinylidene fluoride-based resin on at least one surface of a porous substrate containing a thermoplastic resin, and has a good balance between excellent handling properties and high affinity with an electrolytic solution. Realize. According to the separator of the present disclosure, it is possible to suppress the generation of defective products when the battery element is manufactured by overlapping and winding the separator and the electrode, and the manufacturing efficiency of the battery can be improved.

  In the separator of the present disclosure, the porous layer containing the polyvinylidene fluoride resin has a honeycomb structure and the contact angle of water is 115 ° to 140 °. The wettability of the surface of the porous layer to the liquid is high. Therefore, it is considered that when the battery element is manufactured by overlapping and winding the separator and the electrode of the present disclosure, the position shift of the separator is suppressed. Further, it is considered that when the core is pulled out from the battery element, the core is easily slipped, and the battery element is prevented from being deformed. Furthermore, when impregnating the electrolytic solution into the battery element manufactured by overlapping and winding the separator and the electrode of the present disclosure, the impregnation can be performed in a short time and with high uniformity. Therefore, according to the separator of the present disclosure, the manufacturing efficiency of the battery can be improved.

  The chargeability of the surface of the porous layer of the separator can be compared by measuring the charge decay half-life on the porous layer. The smaller the charge decay half-life, the lower the chargeability.

  Since the separator of this indication has the porous layer containing polyvinylidene fluoride system resin as the outermost layer at least on one side, it is excellent in adhesiveness with an electrode. Therefore, the non-aqueous secondary battery to which the separator of the present disclosure is applied has an improved battery cycle life.

  Hereinafter, the detail of the porous base material and porous layer which the separator of this indication has is demonstrated.

[Porous substrate]
In the present disclosure, the porous substrate means a substrate having pores or voids therein. Examples of such a substrate include a microporous film; a porous sheet made of a fibrous material such as a nonwoven fabric and paper; In the present disclosure, a microporous membrane is preferable from the viewpoint of thinning and strength of the separator. A microporous membrane means a membrane that has a large number of micropores inside and has a structure in which these micropores are connected, allowing gas or liquid to pass from one surface to the other. To do.

  The porous substrate includes a thermoplastic resin. Examples of the thermoplastic resin include polyesters such as polyethylene terephthalate; polyolefins such as polyethylene and polypropylene; The thermoplastic resin is preferably a thermoplastic resin having a melting point of less than 200 ° C. from the viewpoint of imparting a shutdown function to the porous substrate. The shutdown function refers to a function of preventing the thermal runaway of the battery by blocking the movement of ions by dissolving the material and closing the pores of the porous base material when the battery temperature rises.

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

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

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

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

  The polyolefin microporous membrane can be produced, for example, by the following method. That is, it is a method in which a melted polyolefin resin is extruded from a T-die to form a sheet, which is crystallized and then stretched, and then heat treated to form a microporous film. Alternatively, by extruding a polyolefin resin melted with a plasticizer such as liquid paraffin from a T-die, cooling it into a sheet, stretching, and then extracting the plasticizer and heat treating it into a microporous membrane. is there.

  Examples of the porous sheet made of a fibrous material include porous sheets made of a thermoplastic resin fibrous material such as a nonwoven fabric and paper.

  The surface of the porous substrate may be subjected to corona treatment, plasma treatment, flame treatment, ultraviolet irradiation treatment, etc. for the purpose of improving wettability with the coating liquid for forming the porous layer.

  The thickness of the porous substrate is preferably 3 μm to 25 μm, more preferably 5 μm to 20 μm, from the viewpoint of obtaining good mechanical properties and internal resistance.

  The Gurley value (JIS P8117 (2009)) of the porous substrate is preferably 50 seconds / 100 cc to 400 seconds / 100 cc from the viewpoint of preventing short circuit of the battery and obtaining sufficient ion permeability.

  The porosity of the porous substrate is preferably 20% to 60% from the viewpoint of obtaining appropriate membrane resistance and a shutdown function. A method for measuring the porosity of the porous substrate in the present disclosure will be described later.

  The puncture strength of the porous substrate is preferably 200 g or more from the viewpoint of improving the production yield. In the present disclosure, the puncture strength of the porous substrate is measured by performing a puncture test using a KES-G5 handy compression tester manufactured by Kato Tech Co. under the conditions of a radius of curvature of the needle tip of 0.5 mm and a puncture speed of 2 mm / sec. Refers to the maximum piercing load (g).

[Porous layer]
In the present disclosure, the porous layer includes a polyvinylidene fluoride-based resin, and is a layer provided as an outermost layer of the separator on one side or both sides of the porous base material. When the separator and the electrode are stacked and pressed or hot pressed It is a layer that adheres to the electrode.

  In the present disclosure, the porous layer is preferably present on both sides rather than only on one side of the porous substrate from the viewpoint of improving the cycle life of the battery. This is because when the porous layer is on both sides of the porous substrate, both sides of the separator are well bonded to both electrodes via the porous layer.

  In the present disclosure, the porous layer has a structure in which a large number of cells opened in the direction perpendicular to the surface of the porous layer (that is, the direction perpendicular to the surface of the separator) are arranged adjacent to each other in the surface direction of the porous layer (that is, the surface direction of the separator). Have That is, the porous layer is partitioned into cells having a large number of openings by a mesh-like partition wall standing in a direction perpendicular to the plane of the porous layer (that is, a direction perpendicular to the plane of the separator).

  The shape of the cell in the lateral direction (the shape of the cross section that appears when the cell is cut in the plane direction of the porous layer) is not limited. Examples of the shape of the cell in the lateral direction include a circle, an ellipse, a triangle, a quadrangle, a pentagon, a hexagon, an octagon, and the like, and a plurality of types of shapes may be mixed. The shape of the cell in the vertical direction (the shape of the cross section that appears when the cell is cut in the direction perpendicular to the plane of the porous layer) is not limited. Examples of the vertical shape of the cell include a columnar shape, a conical shape, a tapered shape, and an inverted tapered shape, and a plurality of types of shapes may be mixed.

  In the present specification, a structure in which a large number of cells opened in the direction perpendicular to the plane of the porous layer are arranged adjacent to each other in the plane direction of the porous layer is also referred to as a “honeycomb structure”. In the present specification, when the structure is referred to as a “honeycomb structure”, the shape in the horizontal direction and the vertical direction of the cells constituting the structure are not limited, and the shape in the horizontal direction may be a circle, an ellipse, a triangle, a quadrangle, and the like. , Pentagons, hexagons, octagons, and the like, and vertical shapes include columnar shapes, conical shapes, tapered shapes, reverse tapered shapes, and the like.

  In the present disclosure, it is considered that the porous layer has a honeycomb structure so that it is less likely to be charged with static electricity and the wettability with respect to the electrolytic solution is improved.

  In the present disclosure, the average diameter of the openings of the cells constituting the honeycomb structure is preferably 0.1 μm to 10 μm, more preferably 0.5 μm to 10 μm, and still more preferably 1 μm to 10 μm. It is preferable that the average diameter of the opening of the cell is 0.1 μm or more because the handleability becomes better. It is preferable that the average diameter of the opening of the cell is 10 μm or less because the wettability of the electrolytic solution becomes better. The average diameter of the opening of the cell is determined by observing the surface of the porous layer with a scanning electron microscope, selecting 20 cells arbitrarily from the obtained image, and setting the maximum diameter and the minimum diameter for each inner edge of the opening of each cell. Then, {(maximum diameter + minimum diameter) / 2)} is calculated, and the average value of 20 is set as the average diameter of the opening of the cell.

  In the present disclosure, the cells constituting the honeycomb structure may be holes that penetrate the porous layer, or may be recesses that do not penetrate the porous layer. When the cell is a depression not penetrating the porous layer, a thin layered region containing a polyvinylidene fluoride resin as a part of the porous layer between the pores of the cell and the surface of the porous substrate Exists. From the viewpoint of adhesion between the porous layer and the porous substrate, the cell is preferably a depression that does not penetrate the porous layer.

  In the separator of the present disclosure, the pores of the cells constituting the honeycomb structure in the porous layer and the micropores of the porous base material are connected, and gas or liquid flows from one side of the separator to the other side. It is possible to pass. When the cell is a depression that does not penetrate the porous layer, the layered region between the cell pores and the porous substrate surface has a large number of micropores inside, and the micropores It is preferable that the pores of the cell and the micropores of the porous substrate are connected.

  As a preferable example of the embodiment of the porous layer in the present disclosure, a layered region in contact with the porous substrate, a layered region having a large number of micropores therein, and a honeycomb structure existing on the layered region, , And a porous layer.

  In the separator of the present disclosure, it can be confirmed with reference to the Gurley value that gas or liquid can pass from one surface to the other surface. Specifically, the value obtained by subtracting the Gurley value of the porous substrate from the Gurley value of the separator is preferably 1800 seconds / 100 cc or less, more preferably 1500 seconds / 100 cc or less, and 1000 seconds / 100 cc. Or less, more preferably 900 seconds / 100 cc or less, and still more preferably 800 seconds / 100 cc or less.

  In the present disclosure, the thickness of the partition walls constituting the honeycomb structure (that is, the partition walls partitioning the porous layer into a large number of cells) is, for example, 0.1 μm to 2 μm. The partition walls constituting the honeycomb structure preferably have a large number of micropores, and the pores of adjacent cells are preferably connected by the micropores.

  In the present disclosure, the porous layer has a water contact angle of 115 ° to 140 ° on the surface thereof. When the contact angle of water on the surface of the porous layer is smaller than 115 °, it is easily charged with static electricity and handling properties are difficult. In this respect, the contact angle of water is 115 ° or more, and more preferably 120 ° or more. On the other hand, when the contact angle of water on the porous layer surface is larger than 140 °, the wettability with the electrolytic solution is not sufficient. In this respect, the contact angle of water is 140 ° or less, and more preferably 135 ° or less.

  In the present disclosure, the contact angle of water is a contact angle meter (for example, DropMaster DM-301 manufactured by Kyowa Interface Science Co., Ltd.), distilled water is used as water, and 1 μL of water droplets are applied to the surface of the porous layer using a syringe. Form and measure.

  The presence or absence of a honeycomb structure in the porous layer, the size of the cells constituting the honeycomb structure, and the contact angle of water on the surface of the porous layer can be controlled by various conditions when the porous layer is formed on the porous substrate. It is. Details will be described in the description of the separator manufacturing method described later.

  In the present disclosure, the porous layer preferably has a porosity of 40% to 80% from the viewpoint of wettability with the electrolytic solution and ion permeability. A method for measuring the porosity of the porous layer in the present disclosure will be described later.

  The thickness of the porous layer is preferably 0.5 μm or more, more preferably 1 μm or more, and even more preferably 1.5 μm or more, on one side of the porous substrate, from the viewpoint of adhesion with the electrode and ion permeability. 5 micrometers or less are preferable, 4 micrometers or less are more preferable, and 3 micrometers or less are still more preferable.

  In the present disclosure, the porous layer is a porous layer that is provided on one side or both sides of the porous substrate and contains at least polyvinylidene fluoride resin. In the present disclosure, the porous layer may further include other components such as other resins and fillers other than the polyvinylidene fluoride resin.

Mass of polyvinylidene fluoride resin contained in the porous layer, from the viewpoint of adhesiveness and ion permeability of the electrode, on one side of the porous ^{substrate, 0.5g / m 2 ~3.0g / m} 2 is Preferably, 0.5 g / m ^{2 to} 1.5 g / m ² is more preferable. When forming a porous layer on both surfaces of the porous substrate, the mass of polyvinylidene fluoride resin contained in the porous layer, as the sum of both ^{sides, 1.0g / m 2 ~6.0g / m} 2 is preferably ^{, 1.0g / m 2 ~3.0g / m} 2 is more preferable.

[Polyvinylidene fluoride resin]
In the present disclosure, as the polyvinylidene fluoride resin, a homopolymer of vinylidene fluoride (that is, polyvinylidene fluoride); a copolymer of vinylidene fluoride and another copolymerizable monomer (polyvinylidene fluoride copolymer) A mixture thereof. Examples of the monomer copolymerizable with vinylidene fluoride include tetrafluoroethylene, hexafluoropropylene, trifluoroethylene, trichloroethylene, vinyl fluoride, and the like, and one kind or two or more kinds can be used. The polyvinylidene fluoride-based resin preferably contains 70 mol% or more of vinylidene fluoride as a structural unit, and contains 94 mol% or more of vinylidene fluoride from the viewpoint of securing sufficient mechanical properties in the bonding step with the electrode. Is preferred.

  In the present disclosure, the polyvinylidene fluoride resin preferably has a weight average molecular weight (Mw) in the range of 100,000 to 3,000,000. When the weight average molecular weight is 100,000 or more, the adhesive force of the porous layer to the electrode tends to be better. In this respect, the weight average molecular weight is more preferably 400,000 or more. On the other hand, when the weight average molecular weight is 3 million or less, the viscosity of the coating liquid is suppressed, the moldability is good, and the porous layer is porous. In this respect, the weight average molecular weight is more preferably 2 million or less, and further preferably 1.2 million or less. The weight average molecular weight of the polyvinylidene fluoride resin can be determined by gel permeation chromatography (GPC method). The polyvinylidene fluoride resin having a relatively high molecular weight can be obtained by emulsion polymerization or suspension polymerization, and is preferably obtained by suspension polymerization.

[Other resins]
In the present disclosure, the porous layer may include other resins other than the polyvinylidene fluoride resin. Other resins include fluorine rubber, acrylic resin, styrene-butadiene copolymer, homopolymers or copolymers of vinyl nitrile compounds (acrylonitrile, methacrylonitrile, etc.), carboxymethyl cellulose, hydroxyalkyl cellulose, polyvinyl alcohol , Polyvinyl butyral, polyvinyl pyrrolidone, polyether (polyethylene oxide, polypropylene oxide, etc.).

  The content of the other resin in the porous layer is preferably 5% by mass or less, more preferably 3% by mass or less, still more preferably 1% by mass or less, and the other resin is not substantially contained. preferable.

[Other additives]
In the present disclosure, the porous layer may contain a filler made of an inorganic substance or an organic substance or other additives for the purpose of improving the slipperiness and heat resistance of the separator. In that case, it is preferable to make it content and particle size of the grade which does not inhibit the effect of this indication.

  It is preferable that the average particle diameter of a filler is 0.01 micrometer-10 micrometers. The lower limit is more preferably 0.1 μm or more, and the upper limit is more preferably 5 μm or less.

  The particle size distribution of the filler is preferably 0.1 μm <d90−d10 <3 μm. Here, d10 represents an average particle diameter (μm) of 10% cumulative in the weight cumulative particle size distribution calculated from the small particle side, and d90 represents an average particle diameter (μm) of 90% cumulative. The particle size distribution is measured using, for example, a laser diffraction particle size distribution measuring apparatus (Mastersizer 2000 manufactured by Sysmex Corporation), using water as a dispersion medium, and using a small amount of a nonionic surfactant Triton X-100 as a dispersant. A method is mentioned.

[Inorganic filler]
The inorganic filler in the present disclosure is preferably an inorganic filler that is stable with respect to the electrolytic solution and electrochemically stable. Specifically, for example, metal hydroxides such as aluminum hydroxide, magnesium hydroxide, calcium hydroxide, chromium hydroxide, zirconium hydroxide, cerium hydroxide, nickel hydroxide, boron hydroxide; silica, alumina, zirconia, Metal oxides such as magnesium oxide; carbonates such as calcium carbonate and magnesium carbonate; sulfates such as barium sulfate and calcium sulfate; clay minerals such as calcium silicate and talc; The inorganic filler preferably contains at least one of a metal hydroxide and a metal oxide, and more preferably contains at least one metal hydroxide from the viewpoint of imparting flame retardancy and a charge removal effect. It is more preferable to include. These inorganic fillers may be used alone or in combination of two or more. The inorganic filler may be surface-modified with a silane coupling agent or the like.

  The particle shape of the inorganic filler is not limited, and may be a shape close to a sphere or a plate shape, but from the viewpoint of suppressing short circuit of the battery, it should be a plate-like particle or a non-aggregated primary particle. Is preferred.

  In the present disclosure, the content of the inorganic filler in the porous layer is preferably 1% by mass to 95% by mass, more preferably 5% by mass to 80% by mass, and 10% by mass to 50% by mass. More preferably it is.

[Organic filler]
Examples of the organic filler in the present disclosure include cross-linked acrylic resins such as cross-linked polymethyl methacrylate, and cross-linked polystyrene. Cross-linked polymethyl methacrylate is preferable.

[Surfactant having an HLB value of 5.0 to 8.0]
The porous layer in the present disclosure includes a surfactant having an HLB value of 5.0 to 8.0 from the viewpoint of improving the ion permeability of the separator, and the surfactant and the polyfluoride are contained in the porous layer. It is preferable that vinylidene resin is mixed. It is considered that the ion permeability of the separator is improved by the presence and function of the surfactant at the interface between the porous layer and the porous substrate.

  In the present disclosure, the HLB value (hydrophile-lipophile balance value) is a value that represents the degree of hydrophilicity and lipophilicity of a surfactant, and is a value calculated by the following equation.

  HLB value = 20 × sum of formula weight of hydrophilic part / molecular weight

  In the present disclosure, the surfactant having an HLB value of 5.0 to 8.0 may be a mixed surfactant obtained by mixing a plurality of types of surfactants. The HLB value of the mixed surfactant is an arithmetic average obtained by weighting the HLB value of each component surfactant by a mass percentage.

  In the present disclosure, for example, polyoxyethylene fatty acid diester, polyoxyethylene fatty acid monoester, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene alkyl ether, polyoxyalkylene alkyl ether, polyoxyethylene polyoxypropylene block A surfactant having an HLB value of 5.0 to 8.0 by selecting a surfactant having an HLB value of 5.0 to 8.0 from a polymer or the like, or by combining a plurality of the above compounds and the like It is preferable to prepare In the present disclosure, a surfactant having an HLB value of 5.0 to 8.0 is selected from sorbitan fatty acid esters, or a plurality of sorbitan fatty acid esters are combined to have an HLB value of 5.0 to 8. It is more preferred to prepare a surfactant that is zero.

  The mass ratio of the polyvinylidene fluoride resin in the porous layer to the surfactant having an HLB value of 5.0 to 8.0 is preferably 99.9: 0.1 to 95.0: 5.0. When the mass ratio of the surfactant is 0.1 or more, the ion permeability of the porous layer is improved. From this viewpoint, the mass ratio of the surfactant is more preferably 0.2 or more. On the other hand, when the mass ratio of the surfactant is 5.0 or less, the peel strength between the porous substrate and the porous layer is ensured. From this viewpoint, the mass ratio of the surfactant is more preferably 3.0 or less. Accordingly, the mass ratio is preferably 99.9: 0.1 to 95.0: 5.0, more preferably 99.9: 0.1 to 97.0: 3.0, and 99.8: 0. 2-97.0: 3.0 is more preferable.

  The porous layer in the present disclosure may contain various dispersants, and the dispersant is, for example, dispersibility, coatability, and storage stability with respect to a coating liquid for forming the porous layer. It is added for the purpose of improving. In addition, the porous layer in the present disclosure may contain various additives such as a wetting agent, an antifoaming agent, and a pH adjusting agent. It is added for the purpose of improving familiarity, the purpose of suppressing air entrainment in the coating liquid, or the purpose of a pH adjuster.

[Characteristics of separators for non-aqueous secondary batteries]
The film thickness of the separator of the present disclosure is preferably 30 μm or less and more preferably 25 μm or less from the viewpoint of the energy density and output characteristics of the battery.

  The puncture strength of the separator of the present disclosure is preferably 250 g to 1000 g, and more preferably 300 g to 600 g. The method for measuring the puncture strength of the separator is the same as the method for measuring the puncture strength of the porous substrate.

  The porosity of the separator of the present disclosure is preferably 30% to 60% from the viewpoints of adhesion to the electrode, handling properties, ion permeability, and mechanical properties. The method for measuring the porosity of the separator in the present disclosure is the same as the method for measuring the porosity of the porous substrate (described later).

  The Gurley value (JIS P8117 (2009)) of the separator of the present disclosure is preferably 50 seconds / 100 cc to 1500 seconds / 100 cc, and 100 seconds / 100 cc to 1500 seconds / 100 cc from the viewpoint of the balance between ion permeability and mechanical strength. Is more preferable, and 500 seconds / 100 cc to 1500 seconds / 100 cc is still more preferable.

  The water content (mass basis) contained in the separator of the present disclosure is preferably 1000 ppm or less. The smaller the moisture content of the separator, the more the reaction between the electrolyte and water in the battery can be suppressed, the gas generation in the battery can be suppressed, and the cycle characteristics of the battery are improved. In this respect, the water content (mass basis) contained in the separator is more preferably 800 ppm or less, and further preferably 500 ppm or less.

  In the separator of the present disclosure, the peel strength between the porous layer and the porous substrate is preferably 0.1 N / cm to 2.0 N / cm from the viewpoint of adhesion to the electrode and ion permeability. When the peel strength is 0.1 N / cm or more, the adhesion between the porous layer and the porous substrate is excellent, and as a result, the adhesion between the electrode and the separator is improved. In this respect, the peel strength is preferably equal to or greater than 0.1 N / cm, more preferably equal to or greater than 0.2 N / cm, still more preferably equal to or greater than 0.3 N / cm, and still more preferably equal to or greater than 0.4 N / cm. When the peel strength is 2.0 N / cm or less, the separator has excellent ion permeability. In this respect, the peel strength is preferably 2.0 N / cm or less, and more preferably 1.5 N / cm or less. A method for measuring peel strength in the present disclosure will be described later.

  The separator of the present disclosure preferably has a charge decay half-life measured on the porous layer of 300 seconds or less. When the charge decay half-life measured on the porous layer is 300 seconds or less, it is possible to suppress deterioration in handling properties due to static electricity. As a result, when a battery element is manufactured by overlapping and winding the separator and the electrode, the generation of defective products can be suppressed, and the manufacturing efficiency of the battery can be improved. From this viewpoint, the value of the charge decay half-life measured on the porous layer is preferably as low as possible.

In the present disclosure, the method for measuring the charge decay half-life of the separator is as follows.
Three separators are cut into a size of 45 mm in the MD direction × 45 mm in the TD direction, and this is used as a test piece. The test piece was left in a dry room (dew point -60 ° C.) for 1 hour, then neutralized with a static eliminator for 10 seconds, and then charged on the porous layer using STATIC HONESTETTER TYPE H-0110 manufactured by Sicid Electrostatic Co., Ltd. Measure the decay half-life (seconds). For each of the three test pieces, the charge decay half-life is measured, and the measured values are averaged.

  From the viewpoint of impregnating the electrolytic solution with high uniformity and obtaining sufficient battery performance, the separator of the present disclosure has a time of 10 seconds until the dynamic wetting tension becomes 1.5 mN when immersed in the electrolytic solution. Or less, more preferably 5 seconds or less. In this respect, the shorter the time, the better.

In the present disclosure, the method for measuring the time is as follows.
Three separators are cut into a size of 25 mm in the MD direction × 25 mm in the TD direction, and this is used as a test piece. Using a dynamic wettability tester (WET-6200 manufactured by Reska Co., Ltd.) to which the Wilhelmy method is applied, the time until the dynamic wetting tension becomes 1.5 mN by immersing the test piece in the electrolyte at room temperature ( Second). As the electrolytic solution, 1M LiBF4-ethylene carbonate: methyl ethyl carbonate = 3: 7 (mass ratio) is used. The above time is measured for each of the three test pieces, and the measured values are averaged.

  The charge decay half-life and wettability of the separator are controlled by, for example, providing the porous layer with a honeycomb structure, the size of the cells constituting the honeycomb structure, the components contained in the porous layer, the thickness of the porous layer, etc. Is possible.

<Method for producing separator for non-aqueous secondary battery>
The separator of the present disclosure is formed by, for example, applying a coating solution containing at least a polyvinylidene fluoride resin on a porous substrate to form a coating layer, and then solidifying the polyvinylidene fluoride resin contained in the coating layer By making it, it can manufacture by the method of forming a porous layer on a porous base material. Specific examples of the method for forming a porous layer having a honeycomb structure include the following methods (i) to (iii), and the following method (i) is preferable.

(I) Dissolving polyvinylidene fluoride resin in a mixed solvent in which a good solvent and a poor solvent are mixed to produce a coating solution, and coating the coating solution on a porous substrate to form a coating layer And removing the poor solvent from the coating layer after inducing a phase separation phenomenon by selectively removing the good solvent from the coating layer.

(Ii) Dissolving the polyvinylidene fluoride resin in a good solvent containing a pore-forming agent to produce a coating solution, and coating the coating solution on a porous substrate to form a coating layer. And, after the polyvinylidene fluoride resin and the pore-forming agent are solidified by selectively removing the good solvent from the coating layer, the pore-forming agent is removed with the good solvent of the pore-forming agent. .

(Iii) dissolving a polyvinylidene fluoride resin in a good solvent to prepare a coating solution, coating the coating solution on a porous substrate to form a coating layer, and Removing the good solvent from the coating layer after inducing a phase separation phenomenon by controlling the ambient temperature and humidity.

  In the case of the method (i), examples of the good solvent used in the coating liquid include methyl ethyl ketone, acetone, tetrahydrofuran, a fluorine-based solvent, and a mixture thereof. Of these, methyl ethyl ketone, acetone, and tetrahydrofuran are preferable. The poor solvent used in the coating solution is not particularly limited as long as it does not dissolve the polyvinylidene fluoride resin, and water, methanol, ethanol, propyl alcohol, butyl alcohol, butanediol, ethylene glycol, propylene glycol, tripropylene Examples include glycol, toluene, ortho-xylene, meta-xylene, para-xylene, ethylbenzene, and mixtures thereof. It is preferable to add an appropriate amount of the poor solvent that can secure a coating solution that can be stably applied. From the viewpoint of selectively removing the good solvent from the coating layer, the good solvent is preferably volatilized before the poor solvent in a dry atmosphere. Therefore, the boiling point of the good solvent is preferably lower than the boiling point of the poor solvent. .

  In the case of the method (i), the content of the polyvinylidene fluoride resin in the coating liquid is preferably 1% by mass to 20% by mass. The mass ratio of the good solvent and the poor solvent in the coating liquid is preferably 80:20 to 99.5: 0.5, and more preferably 90:10 to 99: 1. In the method (i) above, the type of solvent, the type of polyvinylidene fluoride resin, the composition of the coating solution, the thickness of the porous layer, the coating amount of the porous layer, the drying atmosphere and the drying conditions (temperature, speed) ) Etc. can be appropriately selected to control the honeycomb structure and the fine porous structure.

  In the case of the above method (ii), the good solvent used in the coating solution is not particularly limited as long as it is a solvent that dissolves the polyvinylidene fluoride resin. For example, N-methylpyrrolidone, dimethylacetamide, dimethylformamide, dimethyl Examples thereof include sulfoxide, γ-butyrolactone, ethylene carbonate, methyl ethyl ketone, acetone, ethyl acetate, tetrahydrofuran, and a fluorine-based solvent. Among these, N-methylpyrrolidone, dimethylacetamide, dimethylformamide, dimethyl sulfoxide, γ-butyrolactone, methyl ethyl ketone, acetone, and tetrahydrofuran are preferable. The pore-forming agent used in the coating liquid is not particularly limited as long as it does not dissolve in a good solvent, inorganic salts that dissolve in water such as NaCl, metal oxides that dissolve in strong acids such as silica, and mixtures thereof. Is mentioned.

  In the case of the method (ii), the content of the polyvinylidene fluoride resin in the coating solution is preferably 1% by mass to 20% by mass. The mass ratio of the polyvinylidene fluoride resin and the pore-forming agent in the coating solution is preferably 10:90 to 90:10, and more preferably 20:80 to 80:20. In the above method (ii), the type of solvent, the type of polyvinylidene fluoride resin, the type of pore forming agent, the composition of the coating solution, the thickness of the porous layer, the coating amount of the porous layer, the dry atmosphere, and A honeycomb structure and a fine porous structure can be controlled by appropriately selecting drying conditions (temperature, speed) and the like.

  In the case of the method (iii), examples of the good solvent used for the coating liquid include methyl ethyl ketone, acetone, tetrahydrofuran, a fluorine-based solvent, and a mixture thereof. Among these, a fluorinated solvent is preferable. In the case of the above method (iii), concentration of water droplets, growth of water droplets, and packing of water droplets due to capillary phenomenon occur on the surface of the coating layer, and a honeycomb structure template is formed. Subsequently, after the good solvent volatilizes, the water droplets volatilize to form a honeycomb structure. Therefore, the good solvent used for the coating liquid is preferably a solvent that is not compatible with water and has a lower boiling point than water.

  In the case of the method (iii), the content of the polyvinylidene fluoride resin in the coating solution is preferably 1% by mass to 20% by mass. In the above method (iii), the type of solvent, the type of polyvinylidene fluoride resin, the composition of the coating solution, the thickness of the porous layer, the coating amount of the porous layer, the drying atmosphere and the drying conditions (temperature, speed) ) Etc. can be appropriately selected to control the honeycomb structure and the fine porous structure.

  In the above methods (i) to (iii), when the porous layer contains a filler or other additives, it may be dissolved or dispersed in the coating solution. The coating liquid may contain a dispersant such as a surfactant, a thickener, a wetting agent, an antifoaming agent, a pH adjusting agent, and the like. These additives may remain as long as they are electrochemically stable in the use range of the non-aqueous secondary battery and do not inhibit the reaction in the battery.

  When forming a porous layer in which a polyvinylidene fluoride resin and a surfactant having an HLB value of 5.0 to 8.0 are mixed as the porous layer, the above (i) to (iii) ), A polyvinylidene fluoride resin and a surfactant having an HLB value of 5.0 to 8.0 may be dissolved in a solvent to prepare a coating solution.

  In the above methods (i) to (iii), the coating method of the coating liquid onto the porous substrate includes knife coater method, gravure coater method, Mayer bar method, die coater method, reverse roll coater method, roll Examples include a coater method, a screen printing method, an ink jet method, a spray method, and a dip method. When the porous layer is formed on both sides of the porous substrate, the coating solution may be applied on each side, but it is preferable from the viewpoint of productivity to apply the coating solution on both sides simultaneously.

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

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

  The non-aqueous secondary battery of the present disclosure can be manufactured with high manufacturing efficiency by using the separator of the present disclosure as the separator.

  Hereinafter, exemplary embodiments of the positive electrode, the negative electrode, the electrolytic solution, and the exterior material included in the nonaqueous secondary battery of the present disclosure will be described.

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

In the non-aqueous secondary battery according to the present disclosure, when the porous layer of the separator is disposed on the positive electrode side, the layer is excellent in oxidation resistance, and thus LiMn _1/2 Ni ₁ operable at a high voltage of 4.2 V or higher. It is easy to apply positive electrode active materials such as _{/ 2} O ₂ and LiCo _1/3 Mn _1/3 Ni _1/3 O ₂ .

  The negative electrode has, for example, a structure in which an active material layer containing a negative electrode active material and a binder resin is formed on a current collector. The active material layer may further contain a conductive additive. Examples of the negative electrode active material include materials that can occlude lithium electrochemically, and specific examples include carbon materials; alloys of silicon, tin, aluminum, and the like with lithium. Examples of the binder resin include polyvinylidene fluoride resin and styrene-butadiene rubber. Examples of the conductive aid include carbon materials such as acetylene black, ketjen black, and graphite powder. Examples of the current collector include copper foil, nickel foil, and stainless steel foil having a thickness of 5 to 20 μm. Moreover, it may replace with said negative electrode and may use metal lithium foil as a negative electrode.

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

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

  The non-aqueous secondary battery of the present disclosure is, for example, impregnated with an electrolytic solution in a laminate in which the separator of the present disclosure is disposed between a positive electrode and a negative electrode and accommodated in an exterior material (for example, an aluminum laminate film pack). The laminate can be manufactured by hot pressing from above the exterior material.

  When manufacturing a non-aqueous secondary battery, the method of disposing a separator between the positive electrode and the negative electrode may be a method of stacking at least one layer of the positive electrode, the separator, and the negative electrode in this order (so-called stack method). The separator, the negative electrode, and the separator may be stacked in this order and wound in the length direction.

  The separator and non-aqueous secondary battery of the present disclosure will be described more specifically with reference to examples. However, the separator and the non-aqueous secondary battery of the present disclosure are not limited to the following examples.

<Measurement method>
The measurement methods applied in each example and comparative example are as follows.

[Film thickness]
The film thickness (μm) of the porous substrate and the separator was determined by measuring 20 points using a contact-type thickness meter (LITEMATIC manufactured by Mitutoyo Corporation) and averaging these. A cylindrical terminal having a diameter of 5 mm was used as a measurement terminal, and the load was adjusted so that a load of 7 g was applied during the measurement.
The coating thickness (μm) of the porous layer was obtained by subtracting the thickness of the porous substrate from the thickness of the separator.

[Unit weight]
The basis weight (mass per 1 m ² ) was determined by cutting the separator into 10 cm × 30 cm, measuring the mass, and dividing this mass by the area.

[Coating amount of porous layer]
The coating amount (g / m ² ) of the porous layer was determined by subtracting the basis weight of the porous substrate from the basis weight of the separator.

[Gurley value]
The Gurley value (second / 100 cc) of the porous substrate and the separator was measured using a Gurley type densometer (G-B2C manufactured by Toyo Seiki Co., Ltd.) according to JIS P8117 (2009).

[Porosity]
The porosity of the porous substrate and the porous layer was determined according to the following calculation method.
The constituent materials are a, b, c,..., N, the mass of each constituent material is Wa, Wb, Wc,..., Wn (g / cm ² ), and the true density of each constituent material is Da, db, dc,..., dn (g / cm ³ ), and when the thickness is t (cm), the porosity ε (%) is obtained from the following equation.
ε = {1− (Wa / da + Wb / db + Wc / dc +... + Wn / dn) / t} × 100

[Average diameter of cell openings]
The surface of the separator was observed using a scanning electron microscope (Keyence 3D Real Surface View Microscope VE-8800). 20 cells are arbitrarily selected from the obtained images, the maximum diameter and the minimum diameter are obtained for each inner edge of the opening of each cell, {(maximum diameter + minimum diameter) / 2)} is calculated, and the average of 20 cells is calculated. The value was defined as the average diameter of the cell opening.

[Contact angle of water]
Using a contact angle meter DropMaster DM-301 manufactured by Kyowa Interface Science Co., Ltd., the contact angle of water on the surface of the porous layer was measured. Distilled water was used as water, 1 μL of water droplets were formed on the surface of the separator using a syringe, and the contact angle was measured. The contact angle was measured for 10 water droplets, and the average value was calculated.

[Charging decay half-life]
Three separators were cut into a size of 45 mm in the MD direction × 45 mm in the TD direction, and used as test pieces. The test piece was left in a dry room (dew point -60 ° C.) for 1 hour, then neutralized with a static eliminator for 10 seconds, and then charged decay half-life (seconds) using STATIC HONESTEMETER TYPE H-0110 manufactured by Sicid Electrostatic Co. ) Was measured. The measured values of the three test pieces were averaged to obtain the charge decay half-life (seconds) of the separator.

[Wettability with electrolyte]
Three separators were cut into a size of 25 mm in the MD direction × 25 mm in the TD direction and used as test pieces. The test piece is immersed in an electrolytic solution (1M LiBF ₄ -ethylene carbonate: methyl ethyl carbonate = 3: 7 (mass ratio)) at room temperature using a dynamic wettability tester (WET-6200 manufactured by Reska Co., Ltd.). The time (seconds) until the dynamic wetting tension became 1.5 mN was measured. The measured values of three test pieces were averaged and used as an indicator of the wettability of the separator.

[Peel strength]
Mending tape made by 3M was pasted on both sides of the separator so that the length direction coincided with the MD direction of the separator. Three separators with a mending tape attached on both sides were cut out to a width of 10 mm and used as test pieces. The mending tape is peeled off together with the porous layer directly below from one end in the length direction of the test piece (that is, the MD direction of the separator), and the two separated ends are held by Tensilon (Orientec RTC-1210A). T-peel test was conducted. The tensile speed of the T-shaped peel test is 20 mm / min, the load (N) when the porous layer peels from the porous substrate is measured, and the load from 10 mm to 40 mm is sampled at intervals of 0.4 mm after the measurement is started. The average was calculated, and the measured values of the three test pieces were averaged to obtain the peel strength (N / cm) of the separator.

<Example A1>
A polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP, KYNAR2800 manufactured by Arkema Inc.) was dissolved in a mixed solvent in which acetone and water were mixed at a mass ratio of 95: 5 to prepare a coating solution. The density | concentration of PVDF-HFP with respect to the coating liquid was 10 mass%.
This coating solution was coated on both sides of a porous microporous polyethylene film (film thickness: 9.1 μm, Gurley value: 160 sec / 100 cc, porosity: 33%) using a bar coater # 6. The coating layer was formed on both surfaces of the porous substrate. This coating layer was dried at 60 ° C. to obtain a separator having a porous layer on both sides of a polyethylene microporous membrane. The surface of this separator was observed with a scanning electron microscope (SEM), and it was confirmed that the porous layer had a honeycomb structure. An SEM image obtained by observing the surface of the separator from the direction perpendicular to the plane is shown in FIG.

<Example A2>
A separator having a porous layer on both sides of a polyethylene microporous membrane was obtained in the same manner as in Example A1, except that the mass ratio of acetone to water in the mixed solvent was changed to 97.5: 2.5. The surface of this separator was observed with an SEM, and it was confirmed that the porous layer had a honeycomb structure.

<Comparative Example A1>
Based on the examples described in JP-A-2004-356102, a separator was produced as follows.
A polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP, KYNAR2800 manufactured by Arkema) is dissolved in a mixed solvent in which acetone, isopropanol, and water are mixed at a mass ratio of 89.4: 7.1: 3.5. A coating solution was prepared. The density | concentration of PVDF-HFP with respect to the coating liquid was 2.6 mass%.
This coating solution was coated on both sides of a porous microporous polyethylene film (film thickness: 9.1 μm, Gurley value: 160 sec / 100 cc, porosity: 33%) using a bar coater # 6. The coating layer was formed on both surfaces of the porous substrate. This coating layer was dried at 60 ° C. to obtain a separator having a porous layer on both sides of a polyethylene microporous membrane. The surface of this separator was observed by SEM, and it was confirmed that the porous layer did not have a honeycomb structure. In this separator, the porous layer is easily peeled off, it is difficult to measure various physical properties of the porous layer and the separator, and a battery cannot be produced using this separator.

<Comparative Example A2>
A separator having a porous layer on both sides of a polyethylene microporous membrane was obtained in the same manner as in Comparative Example A1, except that the PVDF-HFP concentration in the coating solution was changed to 10% by mass. The surface of this separator was observed by SEM, and it was confirmed that the porous layer did not have a honeycomb structure. FIG. 2 shows an SEM image obtained by observing the surface of the separator from the direction perpendicular to the plane.

<Comparative Example A3>
A polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP, KYNAR2800 manufactured by Arkema Co., Ltd.) was dissolved in a mixed solvent in which dimethylacetamide and tripropylene glycol were mixed at a mass ratio of 8: 2 to prepare a coating solution. The concentration of PVDF-HFP with respect to the coating solution was 8% by mass.
This coating solution is applied to both sides of a porous microporous polyethylene film (film thickness: 9.1 μm, Gurley value: 160 sec / 100 cc, porosity: 33%). A coating layer was formed. A composite film having a coating layer on both sides of a porous substrate is dipped in a coagulation liquid (water: dimethylacetamide: tripropylene glycol = 57: 30: 13 [mass ratio], liquid temperature 40 ° C.) and applied to the coating layer. The contained resin was solidified. Next, the composite membrane was washed with water and dried to obtain a separator having porous layers on both sides of the polyethylene microporous membrane. The surface of this separator was observed by SEM, and it was confirmed that the porous layer did not have a honeycomb structure.

<Comparative Example A4>
A separator having a porous layer on both sides of a polyethylene microporous membrane was obtained in the same manner as in Example A1, except that PVDF-HFP was changed from KYNAR2800 manufactured by Arkema to Solef 21216 manufactured by Solvay. The surface of this separator was observed with an SEM, and it was confirmed that the porous layer had a honeycomb structure.

<Example B1>
In a mixed solvent obtained by mixing acetone and water at a mass ratio of 95: 5, polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP, KYNAR2800 manufactured by Arkema) and sorbitan monopalmitate (HLB value) as a surfactant are used. 6.7) was dissolved to prepare a coating solution. The mass ratio of PVDF-HFP and sorbitan monopalmitate contained in the coating solution was 99.8: 0.2, and the total concentration of both was 10% by mass with respect to the coating solution.
This coating solution was coated on both sides of a porous microporous polyethylene film (film thickness: 9.1 μm, Gurley value: 160 sec / 100 cc, porosity: 33%) using a bar coater # 6. The coating layer was formed on both surfaces of the porous substrate. This coating layer was dried at 60 ° C. to obtain a separator having a porous layer on both sides of a polyethylene microporous membrane. The surface of this separator was observed with an SEM, and it was confirmed that the porous layer had a honeycomb structure and a fine porous structure.

<Example B2>
A porous layer is provided on both sides of a polyethylene microporous membrane in the same manner as in Example B1 except that the mass ratio of PVDF-HFP and sorbitan monopalmitate contained in the coating liquid is changed to 99.5: 0.5. A separator was obtained. The surface of this separator was observed with an SEM, and it was confirmed that the porous layer had a honeycomb structure and a fine porous structure.

<Example B3>
A separator having a porous layer on both sides of a polyethylene microporous membrane was obtained in the same manner as in Example B1, except that the mass ratio of PVDF-HFP and sorbitan monopalmitate contained in the coating solution was changed to 99: 1. . The surface of this separator was observed with an SEM, and it was confirmed that the porous layer had a honeycomb structure and a fine porous structure.

<Example B4>
A separator having a porous layer on both sides of a polyethylene microporous membrane was obtained in the same manner as in Example B1 except that the mass ratio of PVDF-HFP and sorbitan monopalmitate contained in the coating solution was changed to 98: 2. . The surface of this separator was observed with an SEM, and it was confirmed that the porous layer had a honeycomb structure and a fine porous structure.

<Example B5>
In a mixed solvent obtained by mixing acetone and water at a mass ratio of 95: 5, polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP, KYNAR2800 manufactured by Arkema) and sorbitan monopalmitate (HLB value) as a surfactant are used. 6.7). The mass ratio of PVDF-HFP and sorbitan monopalmitate contained in this solution was 99: 1, and the total concentration of both in this solution was 10% by mass.
Further, magnesium hydroxide (Kisuma Chemical Co., Ltd., Kisuma 5P) was dispersed as an inorganic filler in the above solution to prepare a coating solution. The mass ratio of PVDF-HFP and magnesium hydroxide contained in the coating solution was 80:20.
This coating solution was coated on both sides of a porous microporous polyethylene film (film thickness: 9.1 μm, Gurley value: 160 sec / 100 cc, porosity: 33%) using a bar coater # 6. The coating layer was formed on both surfaces of the porous substrate. This coating layer was dried at 60 ° C. to obtain a separator having a porous layer on both sides of a polyethylene microporous membrane. The surface of this separator was observed with an SEM, and it was confirmed that the porous layer had a honeycomb structure and a fine porous structure.

<Example B6>
A separator having a porous layer on both sides of a polyethylene microporous membrane was obtained in the same manner as in Example B5 except that the mass ratio of PVDF-HFP and magnesium hydroxide contained in the coating solution was changed to 60:40. The surface of this separator was observed with an SEM, and it was confirmed that the porous layer had a honeycomb structure and a fine porous structure.

<Example B7>
As a surfactant, sorbitan monopalmitate (HLB value 6.7) and sorbitan trioleate (HLB value 1.8) were used at a mass ratio of 65.3: 34.7, and PVDF-HFP contained in the coating solution A separator having a porous layer on both sides of a polyethylene microporous membrane was obtained in the same manner as in Example B1, except that the surfactant mass ratio was changed to 99: 1. The surface of this separator was observed with an SEM, and it was confirmed that the porous layer had a honeycomb structure and a fine porous structure.

<Example B8>
As a surfactant, sorbitan monopalmitate (HLB value 6.7) and Tween 80 (PEG-20 sorbitan monooleate, HLB value 15.0) were used at a mass ratio of 84.3: 15.7 and included in the coating liquid. A separator having a porous layer on both sides of a polyethylene microporous membrane was obtained in the same manner as in Example B1, except that the mass ratio of PVDF-HFP and the surfactant was changed to 99: 1. The surface of this separator was observed with an SEM, and it was confirmed that the porous layer had a honeycomb structure and a fine porous structure.

<Example B9>
The surfactant was changed from sorbitan monopalmitate (HLB value 6.7) to sorbitan monostearate (HLB value 4.7), and the mass ratio of PVDF-HFP and surfactant contained in the coating solution was 99: A separator having a porous layer on both sides of a polyethylene microporous membrane was obtained in the same manner as in Example B1, except that the number was changed to 1. The surface of this separator was observed with an SEM, and it was confirmed that the porous layer had a honeycomb structure and a fine porous structure.

<Example B10>
A separator having a porous layer on both sides of a polyethylene microporous membrane was obtained in the same manner as in Example B1 except that the coating liquid did not contain sorbitan monopalmitate. This separator was immersed in a solution obtained by adding sorbitan monopalmitate (HLB value 6.7) as water as a surfactant to obtain a separator having a surfactant added to the porous layer. In the porous layer of the separator, the polyvinylidene fluoride resin and the surfactant are not mixed, and the surfactant is interposed between the polyethylene microporous membrane and the porous layer. Not done. The surface of this separator was observed with an SEM, and it was confirmed that the porous layer had a honeycomb structure and a fine porous structure.

<Comparative Example B1>
A separator having a porous layer on both sides of a polyethylene microporous membrane was obtained in the same manner as in Example B1, except that the mass ratio of PVDF-HFP and sorbitan monopalmitate contained in the coating solution was changed to 90:10. . The surface of this separator was observed with an SEM, and it was confirmed that the porous layer did not have a honeycomb structure and had a structure in which micropores were slightly formed.

<Comparative Example B2>
In a mixed solvent in which acetone, isopropanol, and water are mixed at a mass ratio of 89.4: 7.1: 3.5, a polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP, KYNAR2800 manufactured by Arkema) and an interface Sorbitan monopalmitate (HLB value 6.7) was dissolved as an activator to prepare a coating solution. The mass ratio of PVDF-HFP and sorbitan monopalmitate contained in the coating solution was 99: 1, and the total concentration of both was 10% by mass with respect to the coating solution.
This coating solution was coated on both sides of a porous microporous polyethylene film (film thickness: 9.1 μm, Gurley value: 160 sec / 100 cc, porosity: 33%) using a bar coater # 6. The coating layer was formed on both surfaces of the porous substrate. This coating layer was dried at 60 ° C. to obtain a separator having a porous layer on both sides of a polyethylene microporous membrane. The surface of the separator was observed with an SEM, and it was confirmed that the porous layer did not have a honeycomb structure, and the porous structure had fine pores distributed with high uniformity.

<Comparative Example B3>
A separator having a porous layer on both sides of a polyethylene microporous membrane was obtained in the same manner as in Example B5 except that the mass ratio of PVDF-HFP and magnesium hydroxide contained in the coating solution was changed to 40:60. The surface of the separator was observed with an SEM, and it was confirmed that the porous layer did not have a honeycomb structure, and the porous structure had fine pores distributed with high uniformity.

<Battery manufacturing efficiency test>
Two separators (width 108 mm) were prepared and overlapped, and one end in the MD direction was wound around a stainless steel core. A positive electrode (width: 106.5 mm) was sandwiched between two separators, a negative electrode (width: 107 mm) was placed on one separator, and this laminate was wound to produce 50 continuous wound electrode bodies. did. The amount of protrusion of the separator from the positive electrode is in the range of 1.5 mm ± 0.3 mm, the amount of protrusion of the separator from the negative electrode is in the range of 1.0 mm ± 0.3 mm, and the lamination of the two separators The case where the part did not slip | deviated was judged as the pass. On the other hand, when it did not correspond to the above, it was judged as a failure. And the number ratio (%) of the passed winding electrode body was computed, and it classified as follows.
A: The percentage of the number that passed is 100%
B: Passed number ratio is 90% or more and less than 100% C: Passed number ratio is less than 90%

<Battery performance test>
[Production of negative electrode]
300 g of artificial graphite as negative electrode active material, 7.5 g of water-soluble dispersion containing 40% by mass of modified styrene-butadiene copolymer as binder, 3 g of carboxymethyl cellulose as thickener, and appropriate amount of water The mixture was stirred and mixed with a type mixer to prepare a negative electrode slurry. This negative electrode slurry was applied to a 10 μm thick copper foil as a negative electrode current collector, dried and pressed to obtain a negative electrode having a negative electrode active material layer.

[Production of positive electrode]
89.5 g of lithium cobaltate powder as a positive electrode active material, 4.5 g of acetylene black as a conductive auxiliary agent, and 6 g of polyvinylidene fluoride as a binder are mixed with N-methyl so that the concentration of polyvinylidene fluoride is 6% by mass. -It melt | dissolved in the pyrrolidone and stirred with the double arm type mixer, and produced the slurry for positive electrodes. This positive electrode slurry was applied to a 20 μm thick aluminum foil as a positive electrode current collector, dried and pressed to obtain a positive electrode having a positive electrode active material layer.

[Production of battery]
Lead tabs were welded to the positive electrode and the negative electrode, respectively, and the positive electrode and the negative electrode were joined via a separator to produce a battery element. This battery element was accommodated in an aluminum pack, infiltrated with an electrolytic solution, and sealed using a vacuum sealer. As the electrolytic solution, 1M LiPF ₆ -ethylene carbonate: ethyl methyl carbonate (mass ratio 3: 7) was used. Thereafter, the aluminum pack containing the battery element and the electrolytic solution was subjected to hot pressing (load: 20 kg per 1 cm ^{2 of} electrode, temperature: 90 ° C., pressing time: 2 minutes) with a hot press machine, and a secondary test was performed. A battery was obtained.

[Cycle characteristic test]
The secondary battery for test was charged and discharged 100 cycles, the capacity retention rate (%) after 100 cycles was determined, and this was used as an index of cycle characteristics. In this test, charging was constant current constant voltage charging of 0.5 C or 1.0 C and 4.2 V, and discharging was constant current discharging of 0.5 C or 1.0 C and 2.75 V cutoff. In Example A1 etc., the charge / discharge current was set to 0.5C, and in Example B1 etc., the charge / discharge current was set to 1.0C.

[Confirmation of adhesion between separator and electrode]
The secondary battery for test after the cycle characteristic test was disassembled, and the adhesion between the separator and the electrode was confirmed from the viewpoints of adhesive strength and uniformity.

-Adhesive strength-
The battery element was taken out from the aluminum pack and cut into two pieces to obtain two test pieces. One test piece was subjected to a 180 ° peel test on the positive electrode, and another test piece was subjected to a 180 ° peel test on the negative electrode. The 180-degree peel test was conducted using Tensilon (RTC-1210A manufactured by Orientec Co., Ltd.) under the condition of a tensile speed of 20 mm / min. The load (N) when the positive electrode or the negative electrode was peeled from the test piece was measured, and the load from 10 mm to 40 mm was sampled at intervals of 0.4 mm after the start of measurement, and the average value was calculated. And about each of the positive electrode and the negative electrode, the average value of Example A1 or Example B1 was set to 100, and the relative value of the other Example and the comparative example was computed.

-Uniformity-
About the positive electrode and negative electrode after finishing a 180 degree | times peeling test, the surface of the side which was in contact with the separator was observed visually, and it classified as follows.
G1: Almost all porous layers of the separator were attached to the electrode surface. Uniformity is good.
G2: Most of the porous layer of the separator adheres to the electrode surface, but is partially damaged.
NG: Most of the porous layer of the separator was remarkably damaged during the 180-degree peel test, and hardly adhered to the electrode surface. The uniformity is poor.

Tables 1 and 3 show various physical property values of the separators of Examples and Comparative Examples. In the comparative example in which the porous layer does not have a honeycomb structure, the average diameter of the micropores existing on the surface of the porous layer is described instead of the average diameter of the cell opening.
Tables 2 and 4 show the evaluation results of the secondary batteries prepared using the separators of the examples and comparative examples.

  For the disclosure of Japanese application No. 2014-104352 filed on May 20, 2014 and the disclosure of Japanese application No. 2014-168462 filed on August 21, 2014, reference is made in its entirety. Is incorporated herein by reference.

  All documents, patent applications, and technical standards mentioned in this specification are to the same extent as if each individual document, patent application, and technical standard were specifically and individually stated to be incorporated by reference, Incorporated herein by reference.

Claims (13)

A porous substrate containing a thermoplastic resin;
A porous layer comprising a polyvinylidene fluoride resin provided on one or both surfaces of the porous substrate, wherein cells open in a direction perpendicular to the surface of the porous layer are adjacent to the surface direction of the porous layer A porous layer having a structure in which a large number of the layers are arranged and having a water contact angle of 115 ° to 140 °,
A separator for a non-aqueous secondary battery having a charge decay half-life measured on the porous layer of 300 seconds or less .   The separator for non-aqueous secondary batteries according to claim 1, wherein an average diameter of the opening of the cell is 0.1 μm to 10 μm.   The separator for nonaqueous secondary batteries according to claim 1 or 2, wherein the porosity of the porous layer is 40% to 80%. When the dynamic wetting tension becomes 1.5 mN when immersed in an electrolyte solution in which LiBF ₄ is dissolved at a concentration of 1M in a solvent in which ethylene carbonate and methyl ethyl carbonate are mixed at a mass ratio of 3: 7 . The separator for a nonaqueous secondary battery according to any one of claims 1 to 3 , wherein the time is 10 seconds or less. The porous layer further includes a surfactant having an HLB value of 5.0 to 8.0,
The separator for nonaqueous secondary batteries according to any one of claims 1 to 4 , wherein the polyvinylidene fluoride resin and the surfactant are mixed in the porous layer. The non-aqueous secondary according to claim 5 , wherein in the porous layer, a mass ratio of the polyvinylidene fluoride resin and the surfactant is 99.9: 0.1 to 95.0: 5.0. Battery separator. The non-aqueous secondary according to any one of claims 1 to 6 , wherein a peel strength between the porous substrate and the porous layer is 0.1 N / cm to 2.0 N / cm. Battery separator. The separator for a nonaqueous secondary battery according to any one of claims 1 to 7 , wherein the porous layer further contains a filler. The separator for a nonaqueous secondary battery according to any one of claims 1 to 8 , wherein the porous layer is provided on both surfaces of the porous substrate. The separator for non-aqueous secondary batteries according to any one of claims 1 to 9 , wherein the porous substrate is a polyolefin microporous film containing polyethylene. The separator for non-aqueous secondary batteries according to any one of claims 1 to 10 , wherein the porous substrate is a polyolefin microporous film containing polyethylene and polypropylene. A method for producing the separator for a non-aqueous secondary battery according to any one of claims 5 to 11 ,
A coating layer is formed by applying a solution obtained by dissolving a polyvinylidene fluoride resin and a surfactant having an HLB value of 5.0 to 8.0 in a solvent to one or both sides of a porous substrate. And a process of
Removing the solvent from the coating layer to form a porous layer;
The manufacturing method of the separator for non-aqueous secondary batteries which has these. A positive electrode, a negative electrode, and the separator for a non-aqueous secondary battery according to any one of claims 1 to 11 disposed between the positive electrode and the negative electrode, and by lithium doping / dedoping Non-aqueous secondary battery for obtaining electromotive force.