JP6371905B2 - Non-aqueous secondary battery separator and non-aqueous secondary battery - Google Patents

Description

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

Non-aqueous secondary batteries represented 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. With the reduction in size and weight of portable electronic devices, the exterior of non-aqueous secondary batteries has been simplified. Specifically, a battery can made of an aluminum can has been proposed instead of the stainless steel battery can originally used as an exterior, and more recently, a soft pack such as an aluminum laminate pack has been developed instead of a battery can. .
However, in soft packs such as aluminum laminate packs, the exterior is soft, so a gap may be formed between the electrode and the separator due to impact from the outside or expansion or contraction of the electrode during charge / discharge, resulting in a cycle life. May worsen.

As techniques related to adhesiveness, various techniques for improving the adhesiveness between electrodes and separators in secondary batteries have been studied. As one of the techniques, a technique using a separator in which an adhesive porous layer made of a polyvinylidene fluoride resin is formed on a polyolefin microporous film has been proposed (for example, Japanese Patent No. 4127899 and International (See Publication No. 2014/021293). When this separator is hot-pressed over an electrode containing an electrolyte solution, the adhesion between the electrode and the separator is improved through the adhesive porous layer, and the cycle of a soft pack battery using a soft pack is improved. Lifespan can be improved.
Also disclosed is an organic / inorganic composite porous film in which a mixed solution containing PVdF-HFP and BaTiO ₃ is coated on a Teflon sheet substrate (see, for example, Japanese Patent No. 5889271).
Further, as a technique related to heat resistance, for example, a separator in which a porous layer containing a heat-resistant resin such as a filler such as aluminum hydroxide and a meta-type wholly aromatic polyamide is formed, and magnesium hydroxide and polyvinylidene fluoride are used. A separator in which a porous layer containing a resin is formed has been proposed (see, for example, International Publication No. 2008/062727, International Publication No. 2008/156033, and International Publication No. 2014/021293).

  In recent years, non-aqueous secondary batteries represented by lithium ion secondary batteries have been studied for application as batteries for power storage or vehicles such as electric vehicles because of their high energy density. For example, in addition to the situation where a thin and wide-area battery is required with the miniaturization of portable electronic devices, the battery area is also increased in order to ensure capacity even in batteries suitable for vehicles and the like. It tends to be. However, even in a separator having an adhesive porous layer containing a polyvinylidene fluoride resin, depending on the composition of the monomer unit forming the polyvinylidene fluoride resin, the adhesion between the electrode and the separator may be Insufficient ion conductivity may not be stably maintained, resulting in a decrease in battery capacity, a decrease in charge / discharge characteristics (cycle characteristics), battery swelling, and insufficient battery strength.

A battery having a separator having an adhesive porous layer containing a polyvinylidene fluoride resin generally has a process in which the electrode and the separator are overlapped and wound or the electrode and the separator are alternately stacked. This laminate can be manufactured by performing a heat press treatment (hereinafter also referred to as “wet heat press”) in a state where the laminate is housed in an exterior material and an electrolyte is injected. According to the wet heat press, the polyvinylidene fluoride resin is hot pressed in a swollen state in contact with the electrolytic solution, so that the adhesion between the electrode and the separator is improved, and good charge / discharge characteristics are easily obtained. .
The adhesive porous layer in the separator generally contains a filler from the viewpoint of improving heat resistance and enhancing the rigidity of the layer by improving the rigidity of the layer. Among various fillers, in particular, inorganic fillers tend to act on the electrolyte in the layer impregnated with the electrolytic solution and impair the stability of the solution.
As described above, when producing a battery through wet heat press, although there is an advantage that the adhesiveness is improved by being hot pressed in a swollen state of the polyvinylidene fluoride-based resin, as the temperature rises, The stability of the liquid by the inorganic filler is further lowered, and the inorganic filler is more easily induced to decompose the electrolytic solution and the electrolyte. When the decomposition of the electrolytic solution and the electrolyte is induced, the amount of gas generated in the battery increases and the battery tends to swell. In particular, when a battery is enlarged in a jelly roll battery or the like, or when the internal stress remaining in the separator is high, such a phenomenon is likely to occur.

  Furthermore, negative electrodes using water-based binders have become widespread due to demands for higher capacity and higher energy density for non-aqueous secondary batteries. Between negative electrodes containing water-based binders and separators containing polyvinylidene fluoride resin The improvement of the adhesiveness is desired.

  The present disclosure has been made in view of the above, and is a separator including an adhesive porous layer containing a polyvinylidene fluoride-based resin, which has excellent heat resistance and adhesion to an electrode by wet heat press, and is a battery. Separator for non-aqueous secondary battery that increases the battery strength when the battery is manufactured and suppresses deformation due to swelling, and non-aqueous secondary battery with excellent charge / discharge characteristics (cycle characteristics) and suppressed deformation due to swelling It is an object to provide this and to achieve the object.

The present disclosure focuses on the monomer units and fillers of the polyvinylidene fluoride resin, and is based on the knowledge that the content ratio of the specific monomer units and the type of filler are important for achieving the above object. Thus, the above problems are solved.
Specific means for achieving the above object includes the following aspects.

<1> A hexagonal material having a ratio of 1.5 mol% to 5 mol% of a porous substrate and the vinylidene fluoride monomer unit and the total monomer units provided on one or both surfaces of the porous substrate. A non-aqueous two-component resin comprising a polyvinylidene fluoride resin having a fluoropropylene monomer unit and a weight average molecular weight of 600,000 to 3,000,000 and an adhesive porous layer containing barium titanate particles. This is a secondary battery separator.
<2> The non-aqueous secondary material according to <1>, wherein the content of the barium titanate particles in the adhesive porous layer is 5% by mass or more based on the solid content of the adhesive porous layer. It is a battery separator.
<3> The non-aqueous secondary battery separator according to <1> or <2>, wherein the barium titanate particles have an average particle size of 0.1 μm to 1 μm.
<4> The adhesive porous layer further includes an inorganic filler selected from metal hydroxides and metal oxides other than barium titanate, and the content of the barium titanate particles relative to the content of the inorganic filler. Is a separator for a non-aqueous secondary battery according to any one of <1> to <3>, wherein the mass ratio is 5 mass% or more and 40 mass% or less.
<5> The non-aqueous secondary battery separator according to <4>, wherein the inorganic filler is at least one filler selected from magnesium hydroxide, aluminum hydroxide, aluminum oxide, boehmite, and magnesium oxide. .
<6> A positive electrode, a negative electrode, and the separator for a nonaqueous secondary battery according to any one of <1> to <5> disposed between the positive electrode and the negative electrode, lithium It is a non-aqueous secondary battery which obtains an electromotive force by doping and dedoping.

According to the present disclosure, a separator having an adhesive porous layer containing a polyvinylidene fluoride-based resin, which has excellent heat resistance and adhesion to an electrode by wet heat press, and has a battery strength when a battery is manufactured. There is provided a separator for a non-aqueous secondary battery that enhances and suppresses deformation due to swelling.
Moreover, according to this indication, the non-aqueous secondary battery which was excellent in charging / discharging characteristics (cycle characteristics), and the deformation | transformation accompanying a swelling was suppressed is provided.

Embodiments of the present invention will be described below. It should be noted that the description of the embodiment and the examples illustrate the present invention and do not limit the scope of the present invention.
In the present specification, numerical ranges indicated using “to” indicate ranges including the numerical values described before and after “to” as the minimum value and the maximum value, respectively.

<Separator for non-aqueous secondary battery>
The separator for a non-aqueous secondary battery according to the present disclosure includes at least a porous substrate and an adhesive porous layer provided on one or both surfaces of the porous substrate. The adhesive porous layer provided on the porous substrate has a vinylidene fluoride monomer unit and a hexafluoropropylene monomer unit, and the hexafluoropropylene monomer unit is based on all monomer units. A polyvinylidene fluoride resin having a ratio of 1.5 mol% to 5 mol% and a weight average molecular weight of 600,000 to 3,000,000 and barium titanate particles are contained. The separator for a non-aqueous secondary battery of the present disclosure may further include another layer, and the adhesive porous layer may include other components other than the polyvinylidene fluoride resin and the barium titanate particles. Good.

Conventionally, various studies have been made on the adhesion between the separator and the electrode, and a separator having an adhesive porous layer containing a polyvinylidene fluoride resin has been proposed. Adhesion between electrodes and separators required for batteries using recent exterior materials or between negative electrodes and separators using aqueous binders is high, and further improvements are required. In this respect, battery strength is one of the technical problems that should be improved.
In addition, the battery contains a filler for the purpose of increasing heat resistance and battery rigidity. For example, an inorganic filler such as a metal oxide acts on the electrolyte in the layer impregnated with the electrolyte. Thus, the stability of the liquid is impaired, and the decomposition of the electrolytic solution and the electrolyte is induced to contribute to the generation of gas.
In view of the above situation, in the separator for a non-aqueous secondary battery of the present disclosure, the adhesive porous layer in contact with the electrode is composed of a polyvinylidene fluoride resin having a specific structure and molecular weight and a specific filler. To form. As a result, the adhesiveness between the electrodes by wet heat pressing is dramatically improved, the battery strength is increased, and the strength (cell strength) required for, for example, a soft pack battery is secured, and the quality stability is also improved. It will be excellent. Furthermore, the generation of gas due to the decomposition of the electrolytic solution and the electrolyte due to the inorganic filler is suppressed, and the swelling of the battery (battery deformation) is suppressed. Moreover, since an inorganic filler is included, it is excellent also in heat resistance.

Hereinafter, the separator for a non-aqueous secondary battery of the present disclosure will be described in detail.
[Porous substrate]
The non-aqueous secondary battery separator includes a porous substrate. The porous substrate means a substrate having pores or voids inside.
As a porous substrate, a porous sheet such as a nonwoven fabric and paper made of a microporous film and a fibrous material, and a composite in which one or more other porous layers are laminated on a microporous film or a porous sheet Examples thereof include a porous sheet. Here, the microporous membrane is a membrane that has a large number of micropores inside and that allows the passage of gas or liquid from one surface to the other by virtue of the structure in which the micropores are connected to each other. Refers to that.

The porous substrate includes an organic material and / or an inorganic material having electrical insulation.
The porous substrate preferably contains a thermoplastic resin from the viewpoint of imparting a shutdown function to the porous substrate. The shutdown function refers to a function of preventing 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 increases. As the thermoplastic resin, a thermoplastic resin having a melting point of less than 200 ° C. is preferable, and polyolefin is particularly preferable.

As the porous substrate, a microporous membrane containing polyolefin (referred to as “polyolefin microporous membrane” in the present specification) is preferable.
As the polyolefin microporous membrane, one having sufficient mechanical properties and ion permeability may be selected from among polyolefin microporous membranes applied to conventional non-aqueous secondary battery separators.

  The polyolefin microporous membrane preferably contains polyethylene (that is, a polyethylene microporous membrane) 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 will 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. Such a 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. Further, 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, at least one layer contains polyethylene and at least one layer contains polypropylene. Is also preferable.

  The polyolefin contained in the polyolefin microporous membrane is preferably a polyolefin having a weight average molecular weight of 100,000 to 5,000,000. When the weight average molecular weight is 100,000 or more, good 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, a melted polyolefin resin is extruded from a T-die to form a sheet, which is crystallized and then stretched, and further heat treated to form a microporous film, or melted together with a plasticizer such as liquid paraffin. In this method, a polyolefin resin is extruded from a T-die into a sheet shape, the extruded resin is cooled and stretched, and then a plasticizer is extracted and heat-treated to form a microporous film.

Examples of porous sheets made of fibrous materials include polyesters such as polyethylene terephthalate; polyolefins such as polyethylene and polypropylene; heat resistant resins such as aromatic polyamide, polyimide, polyethersulfone, polysulfone, polyetherketone, and polyetherimide; Nonwoven fabric, paper, etc. made of the fibrous material of
The heat resistant resin means a polymer having a melting point of 200 ° C. or higher, or a polymer having no melting point and a decomposition temperature of 200 ° C. or higher.

  Examples of the composite porous sheet include a sheet in which a functional layer is laminated on a porous sheet made of a microporous film or a fibrous material. Such a composite porous sheet is preferable in that a further function can be added by the functional layer. As the functional layer, for example, from the viewpoint of imparting heat resistance, a porous layer containing a heat resistant resin or a porous layer containing a heat resistant resin and an inorganic filler is preferable. Examples of the heat resistant resin include one or more heat resistant resins selected from aromatic polyamide, polyimide, polyethersulfone, polysulfone, polyetherketone and polyetherimide. Examples of the inorganic filler include metal oxides such as alumina and metal hydroxides such as magnesium hydroxide. As a method of providing a functional layer on a microporous membrane or a porous sheet, a method of applying a functional layer to a microporous membrane or a porous sheet, a method of bonding a microporous membrane or a porous sheet and a functional layer with an adhesive And a method of thermocompression bonding a microporous membrane or a porous sheet and a functional layer.

The average pore diameter of the porous substrate is preferably in the range of 20 nm to 100 nm. When the average pore diameter of the porous substrate is 20 nm or more, ions easily move and good battery performance is easily obtained. From such a viewpoint, the average pore diameter of the porous substrate is more preferably 30 nm or more, and further preferably 40 nm or more. On the other hand, when the average pore size of the porous substrate is 100 nm or less, the peel strength between the porous substrate and the porous layer is improved, and a good shutdown function can be exhibited. From such a viewpoint, the average pore diameter of the porous substrate is more preferably 90 nm or less, and further preferably 80 nm or less.
In addition, the average hole diameter of a porous base material is a value measured using a palm porometer, For example, based on ASTM E1294-89, a palm porometer (CFP-1500-A made from PMI) is used. Can be measured.

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

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

  The porosity of the porous substrate is preferably in the range of 20% or more and 60% or less from the viewpoint of obtaining appropriate film resistance and a shutdown function.

  The puncture strength of the porous substrate is preferably 200 g or more from the viewpoint of improving the production yield.

  The porous substrate is preferably subjected to various surface treatments. By performing the surface treatment, wettability with a coating solution for forming an adhesive porous layer described later can be improved. Specific examples of the surface treatment include corona treatment, plasma treatment, flame treatment, ultraviolet irradiation treatment, and the like, and the treatment can be performed within a range that does not impair the properties of the porous substrate.

[Adhesive porous layer]
The separator for a non-aqueous secondary battery includes an adhesive porous layer on a porous substrate.
The adhesive porous layer is a porous layer that is disposed on one or both sides of a porous substrate and includes a polyvinylidene fluoride resin having a specific structure and molecular weight, and particles of barium titanate that is a filler. . The adhesive porous layer has a large number of micropores inside, and has a structure in which the micropores are connected to each other so that gas or liquid can pass from one surface to the other surface.

  The adhesive porous layer may contain other resins or fillers other than the polyvinylidene fluoride resin and barium titanate particles.

  In addition, the adhesive porous layer is a layer that is disposed as the outermost layer of the separator on one side or both sides of the porous substrate, and is bonded to the electrode when the separator and the electrode are hot pressed. .

  When the adhesive porous layer is disposed on both sides of the porous substrate, the battery has excellent cycle characteristics (capacity retention rate). This is presumably because when the adhesive porous layer is disposed on both sides of the porous substrate, the separator adheres well to both the positive electrode and the negative electrode via the adhesive porous layer on both sides.

(Polyvinylidene fluoride resin)
The adhesive porous layer is composed of a vinylidene fluoride monomer unit (VDF unit) and a hexafluoropropylene monomer unit (HFP unit) having a ratio of 1.5 mol% to 5 mol% with respect to the total monomer units. And at least one polyvinylidene fluoride resin (hereinafter also referred to as VDF-HFP copolymer) having a weight average molecular weight of 600,000 to 3,000,000.
Since the adhesive porous layer contains a specific VDF-HFP copolymer together with the barium titanate particles described later, the battery is manufactured with excellent heat resistance and adhesion to electrodes by wet heat press. In this case, for example, good strength (cell strength) suitable for a soft pack battery can be obtained, and swelling (battery deformation) due to gas generation accompanying decomposition of the electrolyte and electrolyte in the battery is suppressed. .

Among the above, the adhesiveness by wet heat press is easily influenced by the weight average molecular weight of the VDF-HFP copolymer and the content of HFP units.
That is, in order to improve the adhesion during wet heat pressing, it is important to have an appropriate fluidity, that is, an appropriate weight average molecular weight. In addition, it is important that the ratio of HFP units is in an appropriate range in order to give flexibility to the resin and allow the electrolyte to swell in a range that does not dissolve the separator.

  Further, the VDF-HFP copolymer is obtained by copolymerizing hexafluoropropylene and vinylidene fluoride, and includes a VDF unit derived from vinylidene fluoride (VDF) and an HFP unit derived from hexafluoropropylene (HFP). The crystallinity and heat resistance of the resin can be controlled within an appropriate range. Thereby, it can suppress that an adhesive porous layer flows at the time of the heat press process at the time of making a separator adhere with an electrode.

In the present disclosure, particularly from the viewpoint of improving the adhesion by heat press at an appropriate temperature, attention is paid to the copolymer component of the VDF-HFP copolymer, and in particular, the copolymerization ratio of the HFP unit in the polyvinylidene fluoride resin is determined. It is set as the range of 1.5 mol% or more and 5 mol% or less with respect to all the monomer units.
When the copolymerization ratio of the HFP unit in the VDF-HFP copolymer is less than 1.5 mol%, it is difficult to swell when impregnated with the electrolytic solution, so that the adhesiveness by wet heat pressing at an appropriate temperature is lowered. The strength (cell strength) required for the battery cannot be secured. On the other hand, when the copolymerization ratio of the HFP unit exceeds 5 mol%, the HFP unit is easily dissolved in the electrolytic solution and is difficult to apply to the adhesive porous layer.
From the same viewpoint as described above, the content of HFP units in the VDF-HFP copolymer is preferably 2.0 mol% or more and 4.0 mol% or less.

  As a VDF-HFP copolymer, in addition to the copolymer which consists only of a VDF unit and an HFP unit, the other copolymerization component copolymerizable with vinylidene fluoride may be contained. Examples of monomers copolymerizable with vinylidene fluoride other than hexafluoropropylene include tetrafluoroethylene, trifluoroethylene, trichloroethylene, chlorotrifluoroethylene, vinyl fluoride, and the like, and one or more are used. be able to.

The weight average molecular weight (Mw) of the polyvinylidene fluoride resin is in the range of 600,000 to 3,000,000. When the weight average molecular weight is less than 600,000, it is difficult to obtain an adhesive porous layer having mechanical properties that can withstand the heat press treatment at the time of adhesion to the electrode, and adhesion between the electrode and the adhesive porous layer The adhesiveness is lowered, and in particular, the adhesiveness by wet heat press is inferior. From the viewpoint of easily obtaining an adhesive porous layer having mechanical properties that can withstand heat press treatment, and particularly excellent adhesion by wet heat pressing between the electrode and the adhesive porous layer, a polyvinylidene fluoride resin is used. The weight average molecular weight is more preferably 800,000 or more, and even more preferably 1,000,000 or more.
On the other hand, when the weight average molecular weight exceeds 3 million, the viscosity at the time of molding becomes too high, the moldability and crystal formation deteriorate, and it becomes difficult to make it porous. Therefore, the weight average molecular weight of the polyvinylidene fluoride resin is preferably 2.5 million or less from the viewpoint of improving the moldability and crystal formability and increasing the adhesion to the electrode (particularly the adhesion by dry heat press). 2 million or less is more preferable.

The weight average molecular weight (Mw) of the polyvinylidene fluoride resin is a molecular weight measured by gel permeation chromatography (hereinafter also referred to as GPC) under the following conditions and converted to polystyrene.
<Condition>
・ GPC: GPC-900 (manufactured by JASCO)
Column: TSKgel Super AWM-H x 2 (Tosoh Corporation)
-Mobile phase solvent: dimethylformamide (DMF)
Standard sample: Monodispersed polystyrene (manufactured by Tosoh Corporation)
-Column temperature: 140 ° C
・ Flow rate: 10ml / min

The polyvinylidene fluoride resin can be obtained by emulsion polymerization or suspension polymerization.
The acid value of the polyvinylidene fluoride resin is preferably in the range of 3 mgKOH / g to 20 mgKOH / g.
The acid value can be controlled, for example, by introducing a carboxyl group into the polyvinylidene fluoride resin. The introduction and introduction amount of the carboxyl group into the polyvinylidene fluoride-based resin is a monomer having a carboxyl group as a polymerization component of the VDF-HFP copolymer that is the polyvinylidene fluoride-based resin (for example, carboxylic acid ester, maleic acid, It can be controlled by adjusting the polymerization ratio using (maleic anhydride).

-Resins other than polyvinylidene fluoride resin-
The adhesive porous layer of the present disclosure may include a resin other than the polyvinylidene fluoride resin.
Examples of the resin other than the polyvinylidene fluoride resin include, for example, a fluorine-based rubber, an acrylic resin, a styrene-butadiene copolymer, a homopolymer or a copolymer of a vinyl nitrile compound (acrylonitrile, methacrylonitrile, etc.), Examples thereof include carboxymethyl cellulose, hydroxyalkyl cellulose, polyvinyl alcohol, polyvinyl butyral, polyvinyl pyrrolidone, and polyether (polyethylene oxide, polypropylene oxide, etc.).

  The total content of the resin other than the polyvinylidene fluoride-based resin in the adhesive porous layer is preferably 5% by mass or less, and preferably 3% by mass or less with respect to the total amount of the resin contained in the adhesive porous layer. More preferably, it is more preferably 1% by mass or less, and particularly preferably below the detection limit. That is, the polyvinylidene fluoride resin occupies 95% by mass or more (more preferably 97% by mass or more, more preferably 99% by mass or more, particularly preferably 100% by mass) of the total resin contained in the adhesive porous layer. It is preferable.

(Barium titanate particles)
The adhesive porous layer contains particles of barium titanate (BaTiO ₃ ) (hereinafter referred to as BaTiO ₃ particles) as a filler. By selectively containing BaTiO ₃ particles as a filler, not only the slipperiness and heat resistance of the separator are improved, but also swelling (battery deformation) due to the generation of gas accompanying decomposition of the electrolyte and electrolyte is specific. It is suppressed. The swelling suppression effect is considered to be because BaTiO ₃ has a function of trapping chemical species such as hydrogen fluoride that cause gas generation in the battery. Since such chemical species also cause cycle deterioration, the addition of BaTiO ₃ also has an effect of improving cycle characteristics.

The average particle diameter of the BaTiO ₃ particles is preferably in the range of 0.1 μm to 1 μm. When the average particle size is 0.1 μm or more, the effect of suppressing gas generation is excellent. Further, when the average particle diameter is 1 μm or less, the adhesive porous layer is easily thinned. The average particle diameter of the BaTiO ₃ particles is more preferably in the range of 0.1 μm to 0.5 μm.
The average particle diameter is a value measured using a laser diffraction particle size distribution measuring apparatus, and is measured using, for example, a master sizer 2000 manufactured by Sysmex Corporation. Specifically, the center particle diameter (D50) in the volume particle size distribution of a dispersion obtained by mixing and dispersing BaTiO ₃ particles, water (dispersion medium), and nonionic surfactant (Triton X-100; dispersant). ) Is the average particle size.

The particle size distribution of the BaTiO ₃ particles is preferably 0.1 <d90-d10 <3 μm. Here, “d10” represents a particle diameter (μm) at a cumulative weight of 10% by mass calculated from the small particle side in the particle size distribution in the laser diffraction method, and “d90” represents a particle at a cumulative total of 90% by weight. Represents the diameter (μm). The particle size distribution is a value measured using a laser diffraction particle size distribution measuring apparatus, and is measured using, for example, a master sizer 2000 manufactured by Sysmex Corporation. The measurement can be performed using water as a dispersion medium and using a dispersion in which water, BaTiO ₃ particles, and a nonionic surfactant (Triton X-100; dispersant) are mixed and dispersed.

The form of the BaTiO ₃ particles may be any form, for example, a spherical shape, a plate shape, or a needle shape. The form of the BaTiO ₃ particles is preferably primary particles that are not aggregated.

The content of the BaTiO ₃ particles in the adhesive porous layer is preferably 5% by mass or more based on the solid content of the adhesive porous layer. When the content of BaTiO ₃ particles is 5% by mass or more, heat resistance is imparted and, for example, good strength suitable for soft pack batteries and the like is obtained, and gas generation accompanying decomposition of the electrolyte and electrolyte It is excellent due to the suppression effect.
The content of the BaTiO ₃ particles is preferably 10% by mass or more, more preferably 20% by mass or more, particularly preferably more than 50% by mass, most preferably 70% by mass or more with respect to the solid content of the adhesive porous layer. preferable. Furthermore, the content of the barium titanate particles is preferably 95% by mass or less, more preferably 90% by mass or less, based on the solid content of the adhesive porous layer.

Further, the adhesive porous layer within a range not to impair the effects of the present invention, in addition to BaTiO ₃ particles, may contain other filler consisting of inorganic or organic. By appropriately containing other fillers, it is possible to further improve the slipperiness and heat resistance of the separator. When other fillers are used in combination, it is preferably contained in a content and a particle size as long as the effects of the present invention are not impaired.

Other fillers include inorganic fillers and organic fillers. Examples of inorganic fillers include metal hydroxides such as aluminum hydroxide, magnesium hydroxide, calcium hydroxide, chromium hydroxide, zirconium hydroxide, cerium hydroxide, nickel hydroxide, boron hydroxide; alumina, titania, magnesia Metal oxides such as silica and zirconia (excluding barium titanate); carbonates such as calcium carbonate and magnesium carbonate; sulfates such as barium sulfate and calcium sulfate; clay minerals such as calcium silicate and talc .
Among them, the adhesive porous layer, in addition to BaTiO ₃ particles, preferably contains an inorganic filler selected from the group consisting of metal oxides (except barium titanate) and metal hydroxides. The adhesive porous layer can be expected to have a more excellent heat resistance effect by containing a specific inorganic filler. On the other hand, inorganic fillers generally selected from metal hydroxides and metal oxides tend to act on the electrolyte in the layer impregnated with the electrolytic solution, impair the stability of the liquid, and induce decomposition of the electrolytic solution and the electrolyte. It tends to contribute to the generation of gas. When the inorganic filler and a predetermined amount of BaTiO ₃ particles are used in combination, the generation of gas accompanying the decomposition of the electrolytic solution and the electrolyte is suppressed, and the swelling due to the gas (battery deformation) is suppressed.
Moreover, as an example of an organic filler, bridge | crosslinking acrylic resins, such as bridge | crosslinking polymethyl methacrylate, or bridge | crosslinking polystyrene is mentioned, A bridge | crosslinking polymethyl methacrylate is preferable.
Among the other fillers, a filler selected from magnesium hydroxide, aluminum hydroxide, aluminum oxide, boehmite (alumina monohydrate), and magnesium oxide is preferable from the viewpoint that the effect of improving heat resistance and battery strength can be achieved at low cost. . In particular, from the viewpoint of imparting flame retardancy and a charge removal effect, a metal hydroxide is preferable, and magnesium hydroxide is preferable.
In addition, other fillers may be used alone or in combination of two or more. Moreover, you may use the filler surface-modified by the silane coupling agent etc.

When other filler is included together with the BaTiO ₃ particles, the content of the other filler in the adhesive porous layer is preferably in the range of 70% by mass or less, and 60% by mass with respect to the solid content of the adhesive porous layer. The following ranges are more preferable.
In addition, the content ratio of BaTiO ₃ particles in the case of containing BaTiO ₃ particles and other fillers is such that the adhesion with the electrode is ensured and the gas accompanying the decomposition of the electrolyte and electrolyte caused by the other fillers is ensured. of suppressing the generation viewpoint, based on the total weight of BaTiO ₃ particles and other fillers, preferably at least 5 wt%, more preferably at least 10 mass%.
When BaTiO ₃ particles and other fillers are included, the total amount of BaTiO ₃ particles and other fillers is the total resin (including polyvinylidene fluoride resin), BaTiO ₃ particles and other fillers from the viewpoint of improving heat resistance. Is preferably 30% by mass or more, more preferably 50% by mass or more, and still more preferably 60% by mass or more.

Furthermore, when including BaTiO ₃ particles and other fillers, the content ratio of the BaTiO ₃ particles to the content of other filler other than BaTiO ₃ particles, preferably in the range of less than 5 wt% to 40 wt%.
When the mass ratio of the BaTiO ₃ particles is 5% by mass or more, the effect of suppressing the generation of gas accompanying decomposition of the electrolytic solution and electrolyte induced by the inorganic filler is improved. Further, if the mass ratio of the BaTiO ₃ particles is 40 wt% or less, the heat effect by using the inorganic filler selected from metal hydroxides and metal oxides can be more effectively achieved.
The content ratio of the BaTiO ₃ particles to the inorganic filler, for the same reason as described above, preferably in the range of 10 wt% to 40 wt% or less, and more preferably in the range of less than 15 wt% to 40 wt%.
The adhesive porous layer in the present disclosure uses, as a filler, an inorganic filler selected from metal hydroxides and metal oxides (excluding barium titanate) together with barium titanate particles, and the content ratio of the barium titanate particles. Is formed as the above-mentioned specific range, the generation of gas accompanying decomposition of the electrolyte and electrolyte caused by metal hydroxide and metal oxide is suppressed, and swelling due to the generated gas (battery deformation) Is more suppressed. Moreover, since the separator for non-aqueous secondary batteries of this indication contains a filler, it becomes the thing excellent in heat resistance.

In general, when the adhesive porous layer contains a filler, the adhesion with the electrode tends to deteriorate, but a VDF-HFP copolymer having a specific structure and molecular weight as a resin component is used in combination with BaTiO ₃ particles. Therefore, the adhesive strength with the electrode can be maintained well.

(Other ingredients)
The adhesive porous layer may contain other additives such as a dispersant, if necessary, as long as the effects of the present invention are not impaired.
The adhesive porous layer may contain a dispersant such as a surfactant. By including the dispersant, the dispersibility, the coatability, and the storage stability can be improved.
Further, the adhesive porous layer includes a wetting agent for improving familiarity with the porous substrate, an antifoaming agent for suppressing air entrainment in the coating liquid, and a pH adjusting agent containing acid or alkali. Various additives such as may be contained. The additive may remain as long as it is electrochemically stable in the range of use of the lithium ion secondary battery and does not inhibit the reaction in the battery.

When the adhesive porous layer is formed by coating, the coating amount is preferably 1.0 g / m ² or more and 10.0 g / m ² or less as the total of both surfaces of the porous substrate.
“Total of both surfaces of porous substrate” refers to the amount of coating on one surface when the adhesive porous layer is provided on one surface of the porous substrate. When it is provided on both sides of the material, it indicates the total coating amount on both sides.
When the coating amount is 1.0 g / m ² or more, the adhesion with the electrode becomes better and the cycle characteristics of the battery are further improved. On the other hand, when the coating amount is 10.0 g / m ² or less, the ion permeability is improved, and the load characteristics of the battery are further improved. The coating amount is more preferably 1.5 g / m ² or more and 8.0 g / m ² or less as the total of both surfaces of the porous substrate.
Further, the coating amount on one side of the porous substrate is preferably 0.5 g / m ² or more and 5.0 g / m ² or less, and preferably 0.75 g / m ² or more and 4.0 g / m ² or less. More preferably.

  When the adhesive porous layer is provided on both sides of the porous substrate, the difference between the coating amount on one side and the coating amount on the other side is 20% by mass or less based on the total coating amount on both sides. It is preferable that When the difference in the coating amount is 20% by mass or less, the separator is difficult to curl, so that the handling property is excellent.

  The thickness of the adhesive porous layer is preferably 0.5 μm or more and 6 μm or less on one side of the porous substrate. When the thickness of the adhesive porous layer is 0.5 μm or more, the adhesion with the electrode becomes better, and the cycle characteristics of the battery are further improved. From such a viewpoint, the thickness of the adhesive porous layer is more preferably 1 μm or more on one side of the porous substrate. On the other hand, when the thickness of the adhesive porous layer is 6 μm or less, the ion permeability becomes better and the load characteristics of the battery are more excellent. From such a viewpoint, the thickness of the adhesive porous layer is more preferably 5.5 μm or less, and further preferably 5.0 μm or less, on one side of the porous substrate.

The porosity of the adhesive porous layer is preferably in the range of 30% to 80%. When the porosity is 80% or less, it is easy to ensure the mechanical properties that can be withstood at the time of hot pressing to adhere to the electrode, and the surface aperture ratio does not become too high, which is suitable for securing the adhesive force. On the other hand, if the porosity is 30% or more, the ion permeability becomes better.
The porosity (ε) is a value obtained from the following formula.
ε = {1-Ws / (ds · t)} × 100
In the formula, ε represents porosity (%), Ws represents basis weight (g / m ² ), ds represents true density (g / cm ³ ), and t represents film thickness (μm).

  The average pore size of the adhesive porous layer is preferably in the range of 10 nm to 200 nm. When the average pore diameter is 200 nm or less, the nonuniformity of the pores is suppressed, the adhesion points are dispersed relatively evenly, and the adhesiveness is further improved. Moreover, when the average pore diameter is 200 nm or less, the uniformity of ion movement is high, and the cycle characteristics and load characteristics are further improved. On the other hand, when the average pore diameter is 10 nm or more, when the adhesive porous layer is impregnated with the electrolyte, the resin constituting the adhesive porous layer swells to block the pores, thereby inhibiting the ion permeability. This phenomenon is less likely to occur.

The average pore diameter (diameter, unit: nm) of the adhesive porous layer is determined from the pore surface area S of the adhesive porous layer made of polyvinylidene fluoride resin calculated from the nitrogen gas adsorption amount and the porosity. Using the calculated pore volume V of the adhesive porous layer, it is calculated from the following equation assuming that all the holes are cylindrical.
d = 4 · V / S
Wherein, d represents the average pore size of the adhesive porous layer (nm), V represents a pore volume of 1 m ² per adhesive porous layer, S is empty 1 m ² per adhesive porous layer Represents the pore surface area.
Further, the pore surface area S per 1 m ^{2 of} the adhesive porous layer is obtained by the following method.
By applying the BET equation in a nitrogen gas adsorption method, a specific surface area of the porous substrate (m 2 ^{/ g),} specific surface area of the composite film obtained by laminating a porous substrate and adhesive porous layer (m ² / g) and are measured. The specific surface area is multiplied by the basis weight (g / m ² ), and the pore surface area per 1 m ² is calculated. Next, the pore surface area per 1 m ^{2 of the} porous substrate is subtracted from the pore surface area per 1 m ² of the separator to calculate the pore surface area S per 1 m ² of the adhesive porous layer.

-Various properties of non-aqueous secondary battery separator-
The porosity of the non-aqueous secondary battery separator is preferably in the range of 30% or more and 60% or less from the viewpoint of improving the effects of the present invention and the mechanical properties of the separator.

  The Gurley value based on Japanese Industrial Standard (JIS P8117: 2009) of the separator for non-aqueous secondary batteries is preferably in the range of 50 seconds / 100 ml to 800 seconds / 100 ml in terms of excellent balance between mechanical strength and membrane resistance. .

  The separator for a non-aqueous secondary battery preferably has a porous structure from the viewpoint of ion permeability. Specifically, a value obtained by subtracting the Gurley value of the porous substrate from the Gurley value of the non-aqueous secondary battery separator in a state where the adhesive porous layer is formed (hereinafter referred to as Gurley value difference) is 300 seconds / 100 ml. Or less, more preferably 150 seconds / 100 ml or less, and even more preferably 100 seconds / 100 ml or less. When the Gurley value difference is 300 seconds / 100 ml or less, the adhesive porous layer is not too dense, the ion permeability is kept good, and excellent battery characteristics are obtained. On the other hand, the Gurley value difference is preferably 0 second / 100 ml or more, and preferably 10 seconds / 100 ml or more in order to increase the adhesive force between the adhesive porous layer and the porous substrate.

Membrane resistance of the separator for a nonaqueous secondary battery, in view of the load characteristics of the battery, 1ohm · cm ² or more 10 ohm · cm ² preferably in the following range. The membrane resistance is a resistance value when the separator is impregnated with an electrolytic solution, and is measured by an alternating current method. Since the value of the membrane resistance varies depending on the type and temperature of the electrolytic solution, the value of the membrane resistance is a mixture of 1M (mol / L) LiBF ₄ -propylene carbonate / ethylene carbonate (= 1/1; mass ratio) as the electrolytic solution. It is a value measured at 20 ° C. using a solvent.

  The curvature of the non-aqueous secondary battery separator is preferably in the range of 1.5 to 2.5 from the viewpoint of ion permeability.

The amount of water contained in the nonaqueous secondary battery separator is preferably 1000 ppm or less. The smaller the moisture content of the non-aqueous secondary battery separator, the more the reaction between the electrolytic solution and water is suppressed when the battery is configured, and the gas generation in the battery can be more effectively suppressed. Thereby, the cycle characteristics of the battery are further improved.
From such a viewpoint, the amount of water contained in the non-aqueous secondary battery separator is more preferably 800 ppm or less, and further preferably 500 ppm or less.

  The film thickness of the non-aqueous secondary battery separator 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 non-aqueous secondary battery separator is preferably in the range of 250 g to 1000 g, and more preferably in the range of 300 g to 600 g.

-Manufacturing method of separator for non-aqueous secondary battery-
The nonaqueous electrolyte battery separator is, for example, a coating containing polyvinylidene fluoride resin, BaTiO ₃ particles, and an inorganic filler selected from metal oxides other than metal hydroxide and barium titanate as necessary. Manufactured by a method in which the adhesive porous layer is integrally formed on the porous substrate by coating the liquid on the porous substrate to form a coating layer and then solidifying the resin of the coating layer. Is done.
Specifically, the adhesive porous layer containing the polyvinylidene fluoride resin and BaTiO ₃ particles can be formed by, for example, the following wet coating method.

The wet coating method includes (i) a step of preparing a coating solution by dissolving polyvinylidene fluoride resin in an appropriate solvent, and dispersing BaTiO ₃ particles and, if necessary, an inorganic filler, (ii) this coating solution. (Iii) a step of solidifying the polyvinylidene fluoride resin while inducing phase separation by immersing the porous substrate in an appropriate coagulating liquid, and (iv) washing with water This is a film forming method in which a step and (v) a drying step are performed to form an adhesive porous layer on the porous substrate. Details of the wet coating method suitable for the embodiment of the present invention are as follows.

As a solvent (hereinafter also referred to as “good solvent”) for dissolving the polyvinylidene fluoride resin used for the preparation of the coating solution and dispersing the BaTiO ₃ particles and, if necessary, the inorganic filler, N-methylpyrrolidone, Polar amide solvents such as dimethylacetamide, dimethylformamide and dimethylformamide are preferably used.

  From the viewpoint of forming a good porous structure, it is preferable to mix a phase separation agent that induces phase separation in addition to a good solvent. Examples of the phase separation agent include water, methanol, ethanol, propyl alcohol, butyl alcohol, butanediol, ethylene glycol, propylene glycol, and tripropylene glycol. The phase separation agent is preferably added in a range that can ensure a viscosity suitable for coating.

  The solvent is preferably a mixed solvent containing 60% by mass or more of a good solvent and 40% by mass or less of a phase separation agent from the viewpoint of forming a good porous structure.

  The concentration of the resin in the coating liquid is preferably 1% by mass to 20% by mass with respect to the total mass of the coating liquid from the viewpoint of forming a good porous structure. When the adhesive porous layer contains a filler and other components, it may be mixed or dissolved in the coating solution.

  The coagulating liquid is generally composed of a good solvent used for preparing the coating liquid, a phase separation agent, and water. It is preferable in production that the mixing ratio of the good solvent and the phase separation agent is adjusted to the mixing ratio of the mixed solvent used for dissolving the resin. It is appropriate that the concentration of water is 40% by mass to 90% by mass from the viewpoint of formation of a porous structure and productivity. Further, the phase separation rate can be adjusted by controlling the concentration of water, and the crystal structure of the polyvinylidene fluoride resin in the adhesive porous layer can be controlled.

  A conventional coating method such as a Meyer bar, a die coater, a reverse roll coater, or a gravure coater may be applied to the coating liquid on the porous substrate. In the case where the adhesive porous layer is formed on both surfaces of the porous substrate, it is preferable from the viewpoint of productivity to apply the coating liquid to both surfaces simultaneously on both surfaces.

The adhesive porous layer can be produced by a dry coating method in addition to the wet coating method described above. The dry coating method is, for example, by applying a coating liquid containing a polyvinylidene fluoride resin, BaTiO ₃ particles and a solvent to a porous substrate, and drying the coating layer to volatilize and remove the solvent. This is a method for obtaining a porous layer. However, since the dry coating method tends to be denser than the wet coating method, the wet coating method is preferred in that a good porous structure can be obtained.

<Non-aqueous secondary battery>
A non-aqueous secondary battery according to an embodiment of the present invention includes the above-described separator for a non-aqueous secondary battery. Specifically, the non-aqueous secondary battery includes a positive electrode, a negative electrode, and the separator for a non-aqueous secondary battery of the present disclosure that is disposed between the positive electrode and the negative electrode, and is doped with lithium. An electromotive force can be obtained by doping.

  In a non-aqueous secondary battery, a separator is disposed between a positive electrode and a negative electrode, and these battery elements are enclosed in an exterior together with an electrolytic solution. As the non-aqueous secondary battery, a lithium ion secondary battery is suitable.

  The dope means occlusion, support, adsorption, or insertion, and means a phenomenon in which lithium ions enter the active material of an electrode such as a positive electrode.

The positive electrode may have 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, and specifically include 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 assistant 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 a non-aqueous secondary battery, when the adhesive porous layer of the separator is disposed on the positive electrode side, the adhesive porous layer is excellent in oxidation resistance, so LiMn _1/2 that can operate at a high voltage of 4.2 V or higher A positive electrode active material such as Ni _1/2 O ₂ , LiCo _1/3 Mn _1/3 Ni _1/3 O ₂ is easy to apply and is advantageous.

The negative electrode may have 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. Examples thereof 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 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 non-aqueous solvents include cyclic carbonates such as ethylene carbonate, propylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, and vinylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and fluorine-substituted products thereof. Cyclic esters such as γ-butyrolactone and γ-valerolactone; A non-aqueous solvent may be used individually by 1 type, or may be mixed and used.
As an electrolytic solution, cyclic carbonate and chain carbonate are mixed at a mass ratio of 20/80 to 40/60 (= cyclic carbonate / chain carbonate), and lithium salt is in the range of 0.5 mol to 1.5 mol. What was melt | dissolved in is suitable.

Examples of the exterior material include a metal can and a soft pack such as an aluminum laminate film. Since the separator for a non-aqueous secondary battery as described above has an adhesive resin layer containing a polyvinylidene fluoride resin having a specific structure and molecular weight and BaTiO ₃ particles, the adhesion to the electrode, specifically, wet heat Excellent adhesion by pressing. Thereby, the strength of the battery to be produced is improved, and gap formation due to poor adhesion between the electrode and the separator due to external impact, expansion and contraction of the electrode accompanying charging / discharging, charging due to charging / discharging, etc. Suppressed and excellent in charge / discharge characteristics (cycle characteristics). In addition, the separator for non-aqueous secondary batteries is suitable for a soft pack battery using a soft pack (for example, an aluminum laminate film pack) as an exterior material because swelling (deformation of the battery) due to gas generated in the battery is suppressed. It is. In addition, the non-aqueous secondary battery separator is favorably bonded to the electrode under an appropriate hot press temperature condition, and this also contributes to improving the quality stability of the soft pack battery.

  The shape of the battery includes a square shape, a cylindrical shape, a coin shape, and the like, but the above-described separator for a non-aqueous secondary battery is suitable for any shape.

The non-aqueous secondary battery of the present disclosure is manufactured by manufacturing a laminated body in which the separator of the present disclosure is disposed between a positive electrode and a negative electrode, and then using the laminated body, for example, by the following manufacturing methods 1) to 2) Can be manufactured.
1) After heat-pressing (dry heat-pressing) the laminate and bonding the electrode and the separator, the laminate is housed in an exterior material (for example, an aluminum laminate film pack; the same applies hereinafter), and an electrolyte is injected therein, and the exterior material The laminate is further hot-pressed (wet heat press) from above, and adhesion between the electrode and the separator and sealing of the exterior material are performed.
2) The laminated body is accommodated in an exterior material, an electrolyte is injected therein, the laminated body is hot-pressed (wet heat press) from above the exterior material, adhesion between the electrode and the separator, sealing of the exterior material, I do.

According to the manufacturing method of 1) above, since the electrode and the separator are bonded prior to housing the laminate in the exterior material, deformation of the laminate that occurs during transportation for housing in the exterior material is suppressed, Excellent battery strength and dimensional stability, and battery characteristics.
In addition, the wet heat press may be performed under such a mild condition that the adhesion between the electrode and the separator, which has been somewhat attenuated by impregnation with the electrolytic solution, is recovered, that is, the temperature of the wet heat press can be set to a relatively low temperature. Therefore, gas generation due to decomposition of the electrolytic solution and electrolyte in the battery during battery manufacture is further suppressed, and the battery strength and dimensional stability and battery characteristics are excellent.
In addition, since the laminate is further hot-pressed in a state where the polyvinylidene fluoride-based resin is swollen in the electrolytic solution, the adhesion between the electrode and the separator becomes stronger, and the battery strength and battery characteristics are excellent.

  According to the production method of 2), since the laminate is hot-pressed in a state where the polyvinylidene fluoride resin is swollen in the electrolytic solution, the electrode and the separator are well bonded, and the cell strength and battery characteristics are excellent.

  Since the separator of the present disclosure is excellent in adhesion to the electrode, and particularly excellent in adhesion by wet heat press, the non-aqueous secondary battery to which the separator of the present disclosure is applied is selected, for example, from any of the manufacturing methods described above can do. From the viewpoint of suppressing deformation of the laminated body and further suppressing peeling of the electrode and the separator in response to an increase in the area of the battery, the production method 1) is preferable.

  As the wet heat press conditions in the production methods 1) and 2) above, the press pressure is preferably in the range of 0.5 MPa to 2 MPa, and the temperature is preferably in the range of 70 ° C to 110 ° C. Moreover, as for the conditions of dry heat pressing, the press pressure is preferably in the range of 0.5 MPa to 5 MPa, and the temperature is preferably in the range of 20 to 100 ° C.

  The separator of the present disclosure can be bonded by overlapping with the electrode. Therefore, although pressing is not an essential step in battery production, it is preferable to perform pressing from the viewpoint of strengthening the adhesion between the electrode and the separator. Furthermore, from the viewpoint of further strengthening the adhesion between the electrode and the separator, the press is preferably a press while heating (hot press).

  When manufacturing a laminated body, the system which arrange | positions a separator between a positive electrode and a negative electrode may be a system (what is called a stack system) which laminates | stacks a positive electrode, a separator, and a negative electrode one layer at a time in this order (so-called stack system). Alternatively, the separators may be stacked in this order and rolled in the longitudinal direction. The “longitudinal direction” means the longitudinal direction of the separator manufactured in a long shape, and the direction orthogonal to the longitudinal direction of the separator is the “width direction”.

  Hereinafter, embodiments of the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples.

[Measurement and evaluation]
In the following examples and comparative examples, the following measurements and evaluations were performed. The results of measurement and evaluation are shown in Table 1 below.

(HFP content of polyvinylidene fluoride resin)
The content ratio (HFP content) of hexafluoropropylene monomer units (HFP units) in the polyvinylidene fluoride resin was determined from the NMR spectrum. Specifically, 20 mg of a polyvinylidene fluoride resin was dissolved in 0.6 ml of heavy dimethyl sulfoxide at 100 ° C., and the ¹⁹ F-NMR spectrum was measured at 100 ° C. to obtain.

(Weight average molecular weight of polyvinylidene fluoride resin)
The weight average molecular weight of the polyvinylidene fluoride resin was measured by gel permeation chromatography (GPC) under the following conditions, and calculated in terms of polystyrene.
<Condition>
・ GPC: GPC-900 (manufactured by JASCO)
・ Column: TSKgel Super AWM-H (2 pieces) (manufactured by Tosoh Corporation)
-Mobile phase solvent: dimethylformamide (DMF)
Standard sample: Monodispersed polystyrene (manufactured by Tosoh Corporation)
-Column temperature: 40 ° C
・ Flow rate: 10ml / min

(Coating amount of adhesive porous layer)
The separator was cut into 10 cm × 10 cm, the mass was measured, and this mass was divided by the area to determine the basis weight of the separator. Moreover, the porous base material used for preparation of a separator was cut out to 10 cm x 10 cm, the mass was measured, and this mass was divided | segmented by the area, and the fabric weight of the porous base material was calculated | required. And the total coating amount of both surfaces of the adhesive porous layer was calculated | required by subtracting the fabric weight of a porous base material from the fabric weight of a separator.

(Film thickness)
The thickness of the separator was measured using a contact-type thickness meter (LITEMATIC, manufactured by Mitutoyo Corporation). The measurement terminal was a cylindrical one having a diameter of 5 mm, and was adjusted so that a load of 7 g was applied during the measurement, and the average value of the thickness at 20 points was obtained.

(Heat-resistant)
The heat resistance of the separator was evaluated by applying a soldering iron having a tip diameter of 2 mm and a tip temperature of 260 ° C. to the separator and measuring the area (mm ² ) of the holes generated when the soldering iron was applied.

(Gas generation test)
The separator is cut out to a size of 600 cm ² to make a sample piece. The sample piece is placed in an aluminum laminate film pack, the electrolyte is injected into the pack, the separator is impregnated with the electrolyte, and then sealed. A cell was produced. Here, the electrolytic solution was 1 mol / L LiPF ₆ -ethylene carbonate: ethyl methyl carbonate [mass ratio 3: 7].
The prepared test cell was placed in a temperature environment of 85 ° C. and heat-treated for a certain period. Then, the volume of the test cell before and after the heat treatment is measured, and the gas generation amount V (= V2−V1, unit: ml) is obtained by subtracting the volume V1 of the test cell before the heat treatment from the volume V2 of the test cell after the heat treatment. It was.
The heat treatment period was 3 days in Examples 1 to 4 and Comparative Examples 1 to 5 described later, and 20 days in Examples 5 to 12 and Comparative Examples 6 to 7 described later.

(Wet adhesive strength with electrode)
91 g of lithium cobaltate powder as a positive electrode active material, 3 g of acetylene black as a conductive additive, and 3 g of polyvinylidene fluoride as a binder are dissolved in N-methyl-pyrrolidone so that the concentration of polyvinylidene fluoride is 5% by mass. Then, the mixture was stirred with a double arm mixer to prepare a positive electrode slurry. This positive electrode slurry was applied to one side of an aluminum foil with a thickness of 20 μm, dried and pressed to obtain a positive electrode (single side coating) having a positive electrode active material layer as an electrode for evaluating the wet adhesion between the separator and the electrode. .
The electrode and the aluminum foil (thickness 20 μm) obtained above were cut into a width of 1.5 cm and a length of 7 cm, respectively, and each separator obtained in the following examples and comparative examples was 1.8 cm in width and 7.5 cm in length. Cut into. An electrode-separator-aluminum foil is laminated in order to produce a laminate, and an electrolytic solution (1 mol / L LiBF ₄ -ethylene carbonate: propylene carbonate [mass ratio 1: 1]) is soaked in the laminate to obtain aluminum. Housed in a laminate film pack. Next, the inside of the pack was evacuated using a vacuum sealer, and the laminate was hot-pressed together with the pack using a hot press machine to bond the electrode and the separator. The conditions for hot pressing were a pressure of 1 MPa, a temperature of 90 ° C., and a pressing time of 2 minutes. Thereafter, the pack was opened, the laminate was taken out, and the one obtained by removing the aluminum foil from the laminate was used as a measurement sample.
The uncoated surface of the electrode of the measurement sample was fixed to a metal plate with double-sided tape, and the metal plate was fixed to the lower chuck of Tensilon (manufactured by A & D, STB-1225S). At this time, the metal plate was fixed to Tensilon so that the length direction of the measurement sample was the gravity direction. The separator was peeled from the electrode by about 2 cm from the lower end, and the end was fixed to the upper chuck so that the tensile angle (angle of the separator with respect to the measurement sample) was 180 °. The separator was pulled at a pulling speed of 20 mm / min, and the load when the separator was peeled off from the electrode was measured. Loads from 10 mm to 40 mm at the start of measurement were sampled at intervals of 0.4 mm. The same measurement was performed 3 times, the average was calculated, and it was set as the wet adhesive force (N / 15mm, the adhesive force between the electrode and separator by wet heat press) with an electrode.

(Battery strength)
91 g of lithium cobaltate powder as a positive electrode active material, 3 g of acetylene black as a conductive additive, and 3 g of polyvinylidene fluoride as a binder are dissolved in N-methyl-pyrrolidone so that the concentration of polyvinylidene fluoride is 5% by mass. Then, the mixture was stirred with a double arm mixer to prepare a positive electrode slurry. This positive electrode slurry was applied to one side of an aluminum foil having a thickness of 20 μm, dried and pressed to obtain a positive electrode having a positive electrode active material layer.
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.

The positive electrode and the negative electrode were overlapped and wound through the separators obtained in the following examples and comparative examples, and lead tabs were welded to obtain battery elements. This battery element is housed in an aluminum laminate film pack and impregnated with an electrolytic solution, and then heat press (wet heat press) is performed at a pressure of 1 MPa, a temperature of 90 ° C. for 2 minutes to seal the exterior. Thus, a secondary battery for test (length 65 mm, width 35 mm, thickness 2.5 mm: capacity 700 mAh) was obtained. Here, 1 mol / L LiPF ₆ -ethylene carbonate: diethyl carbonate (mass ratio 3: 7) was used as the electrolytic solution.
About the secondary battery for a test obtained above, the three-point bending test was done based on ISO-178, and cell strength was calculated | required.

(Cycle characteristics)
A test secondary battery was produced in the same manner as in the production method for “battery strength”.
Charge / discharge cycle under the conditions of 4.2V constant current at 1C, constant voltage charge for 2 hours, and constant current discharge with 3V cut-off at 1C in a 25 ° C environment using the fabricated test secondary battery The ratio of the discharge capacity obtained after the end of the predetermined cycle is obtained as a percentage with reference to the discharge capacity obtained in the first cycle (%; = discharge capacity after the end of the predetermined cycle / at the time of the first cycle) Discharge capacity × 100), and the obtained value was used as an index for evaluating the cycle characteristics.
The charge / discharge cycle was 300 cycles in Examples 1 to 4 and Comparative Examples 1 to 5 described later, and 500 cycles in Examples 5 to 12 and Comparative Examples 6 to 7 described later.

[Example 1]
As a polyvinylidene fluoride resin that is an adhesive resin, a copolymer of vinylidene fluoride (VDF) and hexafluoropropylene (HFP) (VDF-HFP copolymer, VDF / HFP (molar ratio)) = 97.6 / 2.4, weight average molecular weight = 1.13 million). This VDF-HFP copolymer was dissolved in a mixed solvent (dimethylacetamide / tripropylene glycol = 80/20 [mass ratio]) so as to have a concentration of 5% by mass, and barium titanate particles (BaTiO ₃ as a filler). , BT-05, manufactured by Sakai Chemical Industry Co., Ltd., average particle size: 0.2 μm), and uniformly stirred, the mass ratio of VDF-HFP copolymer to BaTiO ₃ is 15:85 (= VDF-HFP) A coating solution which was a copolymer: BaTiO ₃ ) was produced.
The prepared coating solution was applied to both sides of a polyethylene microporous membrane (film thickness: 9 μm, porosity: 40%, Gurley value: 152 seconds / 100 ml) as a porous substrate, and a coagulation solution (dimethylacetamide) / Tripropylene glycol / water = 30/8/62 [mass ratio], temperature 40 ° C.) and solidified.
Next, the coated polyethylene microporous membrane was washed with water and further dried to obtain a separator in which an adhesive porous layer having a thickness of 4 μm was formed on both sides of the polyethylene microporous membrane. Here, the solid component of the adhesive porous layer because it is VDF-HFP copolymer and BaTiO _3, the ratio of BaTiO ₃ to the total of VDF-HFP copolymer and BaTiO ₃ is 85 mass%.
Said measurement and evaluation were performed with respect to the obtained separator. The results of measurement and evaluation are shown in Table 1 below.

[Example 2]
In Example 1, except that the copolymerization ratio of hexafluoropropylene (HFP) in the VDF-HFP copolymer was changed from 2.4 mol% to 2.0 mol%, the same procedure as in Example 1 was carried out. A separator having an adhesive porous layer formed on both sides of the microporous membrane was obtained, and the obtained separator was measured and evaluated. The results of measurement and evaluation are shown in Table 1 below.

[Example 3]
In Example 1, except that the copolymerization ratio of hexafluoropropylene (HFP) in the VDF-HFP copolymer was changed from 2.4 mol% to 4.5 mol%, the same procedure as in Example 1 was followed. A separator having an adhesive porous layer formed on both sides of the microporous membrane was obtained, and the obtained separator was measured and evaluated. The results of measurement and evaluation are shown in Table 1 below.

[Example 4]
In Example 1, an adhesive porous layer was formed on both sides of the polyethylene microporous membrane in the same manner as in Example 1 except that the weight average molecular weight of the VDF-HFP copolymer was changed from 1.13 million to 2 million. The obtained separator was obtained, and the obtained separator was measured and evaluated. The results of measurement and evaluation are shown in Table 1 below.

[Comparative Example 1]
In Example 1, an adhesive porous layer was formed on both sides of the polyethylene microporous membrane in the same manner as in Example 1 except that the weight average molecular weight of the VDF-HFP copolymer was changed from 1.13 million to 380,000. A comparative separator was obtained. The above measurement and evaluation were performed on the obtained separator in the same manner as in Example 1. The results of measurement and evaluation are shown in Table 1 below.

[Comparative Example 2]
In Example 1, the VDF-HFP copolymer was changed to a VDF-HFP copolymer having a weight average molecular weight of 1,500,000 and a copolymerization ratio of hexafluoropropylene (HFP) of 0 mol%. Except for the above, a separator for comparison in which an adhesive porous layer was formed on both sides of a polyethylene microporous membrane was obtained in the same manner as in Example 1. The above measurement and evaluation were performed on the obtained separator in the same manner as in Example 1. The results of measurement and evaluation are shown in Table 1 below.

[Comparative Example 3]
In Example 1, the VDF-HFP copolymer was changed to a VDF-HFP copolymer having a weight average molecular weight of 890,000 and a hexafluoropropylene (HFP) copolymerization ratio of 5.8 mol%. A separator for comparison in which an adhesive porous layer was formed on both sides of a polyethylene microporous membrane was obtained in the same manner as in Example 1 except that. The above measurement and evaluation were performed on the obtained separator in the same manner as in Example 1. The results of measurement and evaluation are shown in Table 1 below.

[Comparative Example 4]
In Example 1, except that the barium titanate particles used as the inorganic filler were not added, a comparative porous layer in which an adhesive porous layer was formed on both sides of the polyethylene microporous film was the same as in Example 1. A separator was obtained. The above measurement and evaluation were performed on the obtained separator in the same manner as in Example 1. The results of measurement and evaluation are shown in Table 1 below.

[Comparative Example 5]
In the same manner as in Example 1, except that the barium titanate particles used as the inorganic filler in Example 1 were replaced with the same amount of Al ₂ O ₃ particles (average primary particle size 0.5 μm), polyethylene A comparative separator having an adhesive porous layer formed on both sides of the microporous membrane was obtained. The above measurement and evaluation were performed on the obtained separator in the same manner as in Example 1. The results of measurement and evaluation are shown in Table 1 below.

As shown in Table 1, implementation comprising selectively containing a polyvinylidene fluoride resin containing a hexafluoropropylene monomer unit in a specific ratio and having a weight average molecular weight of 600,000 or more, and barium titanate The separator of the example was excellent in adhesion by wet heat press, and was excellent in strength when used as a battery. Moreover, since the adhesive porous layer contains barium titanate as a filler, it showed good heat resistance. Furthermore, due to the inclusion of barium titanate, gas generation accompanying decomposition of the electrolytic solution was not confirmed, and the cycle characteristics were also good.
On the other hand, in Comparative Example 1 in which the weight average molecular weight of the polyvinylidene fluoride-based resin is less than 600,000, an adhesive force with a good electrode could not be obtained, and the effect of the combined use with barium titanate was lowered.
Further, in Comparative Examples 2 to 3 in which the copolymerization ratio of the hexafluoropropylene monomer unit deviates from a predetermined range (1.5 mol% or more and 5 mol% or less), the result is inferior in adhesiveness by wet heat press. The strength was also very low.
In Comparative Example 4 in which barium titanate was not used in combination with the polyvinylidene fluoride resin, the heat resistance was low, and the battery strength and cycle characteristics were inferior. Moreover, in the comparative example 5 comprised only with inorganic fillers other than a barium titanate, the result that gas generation | occurrence | production by reaction with electrolyte solution was recognized was seen.

[Example 5]
As a polyvinylidene fluoride resin which is a binder resin, a copolymer of vinylidene fluoride (VDF) and hexafluoropropylene (HFP) (VDF-HFP copolymer, VDF: HFP (molar ratio)) = 97.6: 2 .4, weight average molecular weight = 1.13 million). This VDF-HFP copolymer was dissolved in a mixed solvent (dimethylacetamide / tripropylene glycol = 80/20 [mass ratio]) so as to have a concentration of 5% by mass, and barium titanate particles (BaTiO 3) were further used as a filler. ₃ , BT-05, manufactured by Sakai Chemical Industry Co., Ltd., average particle size: 0.2 μm), and magnesium hydroxide (Mg (OH) ₂ , Kyowa Chemical Industry Co., Ltd. Kisuma 5P, average primary particle size: 0.8 μm) And the mass ratio of VDF-HFP copolymer, BaTiO ₃ and Mg (OH) ₂ is 40:12:48 (= VDF-HFP copolymer: BaTiO ₃ : Mg (OH) ₂ ) A coating solution was prepared. The ratio of the content of BaTiO ₃ particles to the content of Mg (OH) ₂ that is an inorganic filler is 20% by mass.

The prepared coating solution was applied to both sides of a polyethylene microporous membrane (film thickness: 9 μm, porosity: 40%, Gurley value: 152 seconds / 100 ml) as a porous substrate, and a coagulation solution (dimethylacetamide) / Tripropylene glycol / water = 30/8/62 [mass ratio], temperature 40 ° C.) and solidified.
Next, the coated polyethylene microporous membrane was washed with water and further dried to obtain a separator in which a heat-resistant porous layer having a thickness of 5 μm was formed on both sides of the polyethylene microporous membrane. In the formed heat resistant porous layer, the total volume ratio of BaTiO ₃ and Mg (OH) _{2 in} the heat resistant porous layer was 50% by volume.
Moreover, said measurement and evaluation were performed with respect to the obtained separator. The results of measurement and evaluation are shown in Table 2 below.

[Example 6]
In Example 5, except that magnesium hydroxide (Mg (OH) ₂ ) was replaced with magnesium oxide (MgO, PUREMAG (registered trademark) FNM-G manufactured by Tateho Chemical Industry Co., Ltd., average primary particle size 0.5 μm). In the same manner as in Example 5, a separator having a heat-resistant porous layer formed on both surfaces of a polyethylene microporous membrane was obtained, and the obtained separator was measured and evaluated. The results of measurement and evaluation are shown in Table 2 below.

[Example 7]
Example 5 is the same as Example 5 except that the ratio of the content of BaTiO ₃ particles to the content of magnesium hydroxide (Mg (OH) ₂ ), which is an inorganic filler, was changed from 20% by mass to 7% by mass. Similarly, a separator having a heat-resistant porous layer formed on both surfaces of a polyethylene microporous membrane was obtained, and the obtained separator was measured and evaluated. The results of measurement and evaluation are shown in Table 2 below.

[Example 8]
Example 5 is the same as Example 5 except that the ratio of the content of BaTiO ₃ particles to the content of magnesium hydroxide (Mg (OH) ₂ ), which is an inorganic filler, was changed from 20% by mass to 32% by mass. Similarly, a separator having a heat-resistant porous layer formed on both surfaces of a polyethylene microporous membrane was obtained, and the obtained separator was measured and evaluated. The results of measurement and evaluation are shown in Table 2 below.

[Example 9]
In Example 5, a heat-resistant porous layer was formed on both sides of the polyethylene microporous membrane in the same manner as in Example 5 except that the weight average molecular weight of the VDF-HFP copolymer was changed from 1.13 million to 2 million. The obtained separator was obtained, and the obtained separator was measured and evaluated. The results of measurement and evaluation are shown in Table 2 below.

[Example 10]
In Example 5, except that the total volume ratio of BaTiO ₃ particles and magnesium hydroxide (Mg (OH) ₂ ) in the heat-resistant porous layer was changed from 50% by volume to 45% by volume, Example 5 In the same manner as above, a separator having a heat-resistant porous layer formed on both sides of a polyethylene microporous membrane was obtained, and the obtained separator was measured and evaluated. The results of measurement and evaluation are shown in Table 2 below.

[Example 11]
Example 5 is the same as Example 5 except that the total volume ratio of BaTiO ₃ particles and magnesium hydroxide (Mg (OH) ₂ ) in the heat-resistant porous layer is changed from 50% by volume to 73% by volume. In the same manner as above, a separator having a heat-resistant porous layer formed on both sides of a polyethylene microporous membrane was obtained, and the obtained separator was measured and evaluated. The results of measurement and evaluation are shown in Table 2 below.

[Example 12]
Example 5 is the same as Example 5 except that the ratio of the content of BaTiO ₃ particles to the content of magnesium hydroxide (Mg (OH) ₂ ), which is an inorganic filler, was changed from 20% by mass to 83% by mass. Similarly, a separator having a heat-resistant porous layer formed on both surfaces of a polyethylene microporous membrane was obtained, and the obtained separator was measured and evaluated. The results of measurement and evaluation are shown in Table 2 below.

[Comparative Example 6]
In Example 5, except that the barium titanate particles used as the inorganic filler were not added, a comparative heat resistant porous layer was formed on both sides of the polyethylene microporous membrane in the same manner as in Example 5. A separator was obtained. The above measurement and evaluation were performed on the obtained separator in the same manner as in Example 5. The results of measurement and evaluation are shown in Table 2 below.

[Comparative Example 7]
Example 5 and Example 5 except that the VDF-HFP copolymer was replaced with Conex (registered trademark; manufactured by Teijin Techno Products), which is a similar meta-type wholly aromatic polyamide (meta-aramid resin). Similarly, a separator having a heat-resistant porous layer formed on both surfaces of a polyethylene microporous membrane was obtained, and the obtained separator was measured and evaluated. The results of measurement and evaluation are shown in Table 2 below.

As shown in Table 2, the separator of the example in which the inorganic filler selected from the metal hydroxide and the metal oxide and the BaTiO ₃ particles are used together in a predetermined ratio shows good heat resistance and helps to decompose the electrolytic solution. The generation of the accompanying gas was suppressed, and the change (deformation) of the battery shape accompanying the swelling was also suppressed. Moreover, in the Example containing a VDF-HFP copolymer as binder resin, compared with the comparative example 7 containing the aramid which is other resin, the adhesiveness by wet heat press becomes more favorable, and the intensity | strength of the produced battery It was also excellent.
Furthermore, BaTiO ₃ Example 5 like the ratio of the content is not more than 40 wt% of the particles to the content of magnesium hydroxide, as compared to Example 12 where the ratio of the content of the BaTiO ₃ particles exceeds 40 wt% The heat resistance was better.
In contrast, as in Comparative Example 6, containing only inorganic filler other than BaTiO _3, the composition containing no BaTiO ₃ particles, although the effect of improving the heat resistance and battery strength by filler appears, decomposition of the electrolyte solution A lot of generated gas was confirmed. Moreover, in Comparative Example 7 not including a specific VDF-HFP copolymer as the binder resin, the adhesiveness and battery strength by wet heat press were remarkably inferior.

The disclosures of Japanese application 2015-221601 and Japanese application 2015-221602 are incorporated herein by reference in their entirety.
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 described to be incorporated by reference, Incorporated herein by reference.

Claims (4)

A porous substrate;
Provided on one or both sides of the porous substrate, and having a vinylidene fluoride monomer unit and a hexafluoropropylene monomer unit having a ratio of 1.5 mol% to 5 mol% with respect to the total monomer units. An adhesive porous layer comprising a polyvinylidene fluoride resin having a weight average molecular weight of 600,000 to 3,000,000 and barium titanate particles;
With
The adhesive porous layer further includes at least one inorganic filler selected from magnesium hydroxide, aluminum hydroxide, aluminum oxide, boehmite, and magnesium oxide, and the barium titanate with respect to the content of the inorganic filler. A separator for a non-aqueous secondary battery, wherein the mass ratio of the content of particles is 5% by mass or more and 20 % by mass or less (excluding 20% by mass) .   The separator for a non-aqueous secondary battery according to claim 1, wherein the content of the barium titanate particles in the adhesive porous layer is 5% by mass or more based on the solid content of the adhesive porous layer.   The separator for a non-aqueous secondary battery according to claim 1, wherein the barium titanate particles have an average particle diameter of 0.1 μm to 1 μm. A positive electrode, a negative electrode, and the separator for a non-aqueous secondary battery according to any one of claims 1 to 3 disposed between the positive electrode and the negative electrode. A non-aqueous secondary battery that obtains an electromotive force.