JP2012089346A - Separator for nonaqueous secondary battery, and nonaqueous secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separator for a nonaqueous secondary battery comprising a microporous polyolefin film and a heat-resistant porous layer and achieving high productivity and a high level of safety of a battery.SOLUTION: The separator for a nonaqueous secondary battery comprises a microporous polyolefin film, a heat-resistant porous layer on one side or both sides of the microporous polyolefin film, and an adhesive layer provided between the microporous polyolefin film and the heat-resistant porous layer and containing at least one kind of ingredient selected from thermoplastic elastomers and rubbers.

Description

  The present invention 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 main power sources for portable electronic devices such as mobile phones and laptop computers. Non-aqueous secondary batteries are required to have higher energy density, but ensuring safety is a technical issue.
With regard to ensuring the safety of non-aqueous secondary batteries, separators have mechanical characteristics that do not break during repeated charging and discharging, and characteristics that shut down battery reactions quickly when abnormally heated (shutdown characteristics) ), Performance (short-circuit resistance), etc., that maintains the shape even at high temperatures and prevents a dangerous situation in which the positive electrode material and the negative electrode material directly react with each other are required.

  Under such circumstances, conventionally, a separator in which a porous layer containing a heat-resistant polymer (heat-resistant porous layer) is formed on one or both surfaces of a polyolefin microporous film has been proposed (for example, a patent) References 1-3). According to these proposals, the effect of improving the shutdown characteristics and short circuit resistance of the separator can be obtained.

JP 2005-209570 A JP 2000-030686 A JP 2009-205959 A

  It is desirable that a part of the heat resistant porous layer of the separator does not peel off or fall off during the battery manufacturing process or use. If the heat-resistant porous layer is missing, the battery yield will decrease, and the heat-resistant and short-circuit resistance of the separator will be lost where the heat-resistant porous layer is missing. This is because a problem may occur. Therefore, in a separator having a heat-resistant porous layer on the surface of the polyolefin microporous membrane, the heat-resistant porous layer needs to be well retained.

  The present invention relates to a separator for a non-aqueous secondary battery including a polyolefin microporous membrane and a heat-resistant porous layer, and an object thereof is to provide a separator for a non-aqueous secondary battery that increases battery productivity and safety. .

Specific means for achieving the above object are as follows.
<1> A polyolefin microporous membrane, a heat-resistant porous layer provided on one or both surfaces of the polyolefin microporous membrane, and provided between the polyolefin microporous membrane and the heat-resistant porous layer, are thermoplastic. A separator for a non-aqueous secondary battery comprising: an adhesive layer containing at least one selected from an elastomer and a rubber component.
<2> The adhesive layer, a non-aqueous secondary battery separator according to the coating weight of 0.05 g / ^{m 2} or more 1.0 g / ^{m 2} or less <1>.
<3> A positive electrode, a negative electrode, and the separator for a nonaqueous secondary battery according to <1> or <2> disposed between the positive electrode and the negative electrode, and an electromotive force generated by doping or dedoping lithium. Get non-aqueous secondary battery.

  ADVANTAGE OF THE INVENTION According to this invention, the separator for non-aqueous secondary batteries provided with the polyolefin microporous membrane and the heat-resistant porous layer can be provided with the separator for non-aqueous secondary batteries which improves battery productivity and safety. .

Hereinafter, although the form for implementing this invention is demonstrated in detail, this invention is not limited to this, A various deformation | transformation can be implemented within the range of the meaning.
In the present specification, a numerical range represented by using “to” means a range including numerical values described before and after “to” as a lower limit value and an upper limit value.

<Separator for non-aqueous secondary battery>
The separator for a non-aqueous secondary battery according to the present invention includes a polyolefin microporous membrane, a heat resistant porous layer provided on one or both sides of the polyolefin microporous membrane, the polyolefin microporous membrane, and the heat resistant porous layer. And a bonding layer containing at least one selected from a thermoplastic elastomer and a rubber component, and a separator for a non-aqueous secondary battery.
The separator for a non-aqueous secondary battery of the present invention is provided with an adhesive layer containing at least one selected from a thermoplastic elastomer and a rubber component between the polyolefin microporous membrane and the heat-resistant porous layer, thereby providing heat resistance. Improves retention of the porous layer and suppresses peeling and dropping of the heat-resistant porous layer during the battery manufacturing process and when using the battery, thus improving the yield during battery manufacturing and the safety during battery use Can be made.

In the present invention, the mechanism that achieves the above effect is not constrained by a specific theory, but is presumed as follows.
The adhesive layer containing at least one selected from a thermoplastic elastomer and a rubber component has flexibility resulting from the thermoplastic elastomer and the rubber component. It is assumed that the adhesive layer has flexibility, so that when a mechanical external force is applied to the separator, the impact is alleviated and the heat-resistant porous layer is prevented from peeling or falling off from the separator. The As a result, it is considered that the yield at the time of manufacturing the battery and the safety at the time of using the battery are improved.

(Adhesive layer)
In the separator for a non-aqueous secondary battery of the present invention, the adhesive layer is provided between the polyolefin microporous membrane and the heat-resistant porous layer, and prevents the heat-resistant porous layer from peeling or falling off from the separator. .
In the separator for a non-aqueous secondary battery of the present invention, the heat-resistant porous layer is provided on one side or both sides of the polyolefin microporous membrane, but when the heat-resistant porous layer is provided on both sides of the polyolefin microporous membrane, The adhesive layer is provided between the polyolefin microporous membrane and the heat-resistant porous layer on both sides of the polyolefin microporous membrane.
In the present invention, the adhesive layer contains at least one selected from a thermoplastic elastomer and a rubber component.

[Thermoplastic elastomer]
The general structure of a thermoplastic elastomer consists of a soft layer (soft segment) and a hard layer (hard segment). The soft layer and the hard layer combine to have rubber elasticity unique to thermoplastic elastomers. Although it does not restrict | limit especially as a thermoplastic elastomer, A styrene type thermoplastic elastomer, an olefin type thermoplastic elastomer, etc. are mentioned.

  Examples of the styrenic thermoplastic elastomer include styrene-butadiene-styrene copolymer, styrene-isoprene-styrene copolymer, styrene-ethylenebutylene-styrene copolymer, styrene-ethylenepropylene-styrene copolymer, styrene- An ethylene ethylene propylene-styrene copolymer, a styrene thermoplastic elastomer compound, etc. are mentioned. These may be used alone or in combination of two or more as required.

  Examples of commercially available styrene-based thermoplastic elastomers are listed below. Examples of styrene-butadiene-styrene copolymers include tufprene (A125, 126S, etc.), Asaprene T (411, 414, etc.) (Asahi Kasei Corporation) Company), and Clayton D (1101, 1102 etc.) (Clayton Polymer Japan Co., Ltd.). Examples of the styrene-isoprene-styrene copolymer include Clayton D1124 (Clayton Polymer Japan Co., Ltd.). Examples of styrene-ethylenebutylene-styrene copolymers include Tuftec H (1031, 1041 etc.) (Asahi Kasei Corporation), Septon (8004, 8006 etc.) (Kuraray Co., Ltd.), and Kraton G (1650, 1651 etc.). (Clayton Polymer Japan Co., Ltd.). Examples of the styrene-ethylenepropylene-styrene copolymer include Septon (2002, 2005, etc.) (Kuraray Co., Ltd.). Examples of the styrene-ethylene ethylene propylene-styrene copolymer include Septon 4033 (Kuraray Co., Ltd.).

Examples of the olefinic thermoplastic elastomer include ethylene-α olefin copolymer, propylene-α olefin copolymer, ethylene-α olefin copolymer (metallocene catalyst), amorphous polyα olefin, high density polyethylene, low Examples include density polyethylene, ultra-low density polyethylene, and polypropylene. These may be used alone or in combination of two or more as required.
Examples of commercially available olefin-based thermoplastic elastomers include, for example, Miralastomer (7030, 8030, etc.) (Mitsui Chemicals, Inc.), Tuffmer (A-4085, P-0180, P-0480, etc.) (Mitsui Chemicals, Inc.) Etc.

[Rubber component]
Although it does not restrict | limit especially as a rubber component, For example, SBR (styrene-butadiene rubber), BR (butadiene rubber), EPM (ethylene propylene rubber), EPDM (ethylene propylene diene terpolymer), ACM (acrylic rubber) Etc. These may be used alone or in combination of two or more as required.

  Examples of SBR include JSR (0202, T5582, etc .: JSR Corporation), and Nipol (1721, 2057S, etc .: Nippon Zeon Corporation). Examples of BR include JSR (RB810, RB820, RB830, etc .: JSR Corporation) and Nipol (BR1220, BR1241, etc .: Nippon Zeon Corporation). Examples of EPM include JSR EP57P (JSR Corporation). Examples of the EPDM include JSR EP24 and EP27 (JSR Corporation). Examples of the ACM include Nipol (AR31, AR32, etc .: Nippon Zeon Co., Ltd.).

The rubber component may have a core / shell structure. The core-shell structure in the rubber component has a structure composed of a core part and an outer shell part, and the resin composition differs between the core part and the outer shell part. A rubber component having a core / shell structure relates to a resin constituting a core portion and a resin constituting an outer shell portion, and (i) a combination of a resin having a high glass transition temperature (Tg) and a resin having a low glass transition temperature (Tg) can be controlled. Yes, (ii) By changing the resin of the outer shell, compatibility and adhesion to other materials can be adjusted. (Iii) Viscoelasticity control by combining a highly viscous resin and a highly elastic resin There are advantages such as being able to.
Specific examples of the rubber component having a core / shell structure include parapets (SA-NW001, etc.) (Kuraray Co., Ltd.) and RP-101 (Negami Kogyo Co., Ltd.) having a core / shell structure.
The rubber component having a core / shell structure may be used alone, in combination of two or more kinds, or in combination with other rubber components described above.

  In the present invention, the thermoplastic elastomer and rubber component contained in the adhesive layer preferably have a glass transition temperature (Tg) of 120 ° C. or lower. When the glass transition temperature (Tg) is 120 ° C. or lower, the flexibility of the adhesive layer is good, and the effect of preventing the heat-resistant porous layer from peeling off or falling off is high. In addition, when the glass transition temperature (Tg) is 120 ° C. or lower, the flexibility of the adhesive layer is not easily lost even when the battery is used for a long time by repeated charge and discharge or when the temperature rises during use. The glass transition temperature (Tg) is preferably −50 to 120 ° C., more preferably −40 to 100 ° C.

  In the present invention, the adhesive layer may contain other components other than the thermoplastic elastomer and the rubber component, but other components (for example, inevitably mixed in the manufacturing process) from the viewpoint of preventing impurities from being eluted. The content of the component to be) is preferably small and more preferably not contained.

In the present invention, the adhesive layer is preferably coated amount is 0.05 g / ^{m 2} or more 1.0 g / ^{m 2} or less. When the coating amount is 0.05 g / m ² or more, the flexibility of the adhesive layer is good, and the lack of the heat-resistant porous layer is well suppressed. On the other hand, when the coating amount is 1.0 g / m ² or less, the adhesive layer does not easily block the micropores of the polyolefin microporous membrane and the heat-resistant porous layer, and the battery performance is not affected. The coating amount is more preferably 0.08 g / m ² or more and 1.0 g / m ² or less, and further preferably 0.1 g / m ² or more and 1.0 g / m ² or less.
In addition, the coating amount said about an adhesive layer in this invention is a coating amount after drying.

[Method of forming adhesive layer]
The method for forming the adhesive layer on the polyolefin microporous membrane is not particularly limited, and examples thereof include the following methods (a) and (b). Hereinafter, in the description of the method for forming the adhesive layer, the thermoplastic elastomer and the rubber component may be referred to as “polymer”.

(A) A liquid obtained by dissolving at least one polymer in a solvent or dispersed as an aqueous emulsion is applied to a polyolefin microporous film to form a coating film, and then the solvent and water are removed from the coating film. Forming an adhesive layer.
(B) A liquid obtained by dissolving at least one polymer in a solvent or dispersed as an aqueous emulsion is applied to a substrate to form a coating film, and the coating film is transferred from the substrate onto a polyolefin microporous film. To form an adhesive layer.

  In the above (a) and (b), the solvent is not particularly limited as long as it dissolves the polymer. Specifically, an aprotic polar solvent is preferable, for example, methyl ethyl ketone, dimethyl sulfoxide, dimethylacetamide, N-methyl-2-pyrrolidone and the like can be mentioned.

  In the above (a) and (b), the polymer obtained by dissolving the polymer in a solvent or dispersing as a water-based emulsion preferably has a polymer concentration of 1% by mass to 20% by mass. When the polymer concentration is 1% by mass or more, the flexibility of the adhesive layer formed using the liquid material is good, and the lack of the heat-resistant porous layer is well suppressed. On the other hand, when the polymer concentration is 20% by mass or less, the adhesive layer formed using the liquid material does not easily block the micropores of the polyolefin microporous film and the heat-resistant porous layer.

(Polyolefin microporous membrane)
In the present invention, the polyolefin microporous membrane has a large number of micropores inside and has a structure in which these micropores are connected, and gas or liquid can pass from one surface to the other. Means a thick film. Such a microporous membrane is preferably a microporous membrane that softens at 130 to 150 ° C., closes the porous voids, exhibits a shutdown function, and does not dissolve in the electrolyte solution of the nonaqueous secondary battery.

The thickness of the polyolefin microporous membrane is preferably 5 μm to 25 μm, more preferably 5 μm to 20 μm. When the thickness is 5 μm or more, the shutdown function is good. On the other hand, when the thickness is 25 μm or less, it is appropriate as the thickness of the separator for a non-aqueous secondary battery to which the heat-resistant porous layer is added, and high electric capacity can be achieved.
The porosity of the polyolefin microporous membrane is preferably 30 to 80% from the viewpoints of permeability, mechanical strength, and handling properties. When the porosity is 30% or more, the permeability and the amount of electrolyte retained are appropriate. On the other hand, when the porosity is 80% or less, it is preferable in terms of mechanical strength of the polyolefin microporous membrane, and the shutdown function is good. The porosity is more preferably 40 to 60%.
The Gurley value (JIS P8117) of the polyolefin microporous membrane is preferably 50 to 500 sec / 100 cc from the viewpoint of obtaining a good balance between mechanical strength and membrane resistance.

The membrane resistance of the polyolefin microporous membrane is preferably 0.5 to ⁵ ohm · cm ² from the viewpoint of load characteristics of the non-aqueous secondary battery.
The puncture strength of the polyolefin microporous membrane is preferably 250 g or more. When the puncture strength is 250 g or more, when a non-aqueous secondary battery is produced, pinholes or the like are hardly generated in the separator due to unevenness or impact of the electrodes, and the possibility that the non-aqueous secondary battery is short-circuited is low.
The tensile strength of the polyolefin microporous membrane is preferably 10 N or more. When the tensile strength is 10 N or more, the separator is difficult to break when winding the separator when producing a non-aqueous secondary battery.

[Polyolefin]
Examples of the polyolefin resin used for the polyolefin microporous membrane include polymers obtained by polymerizing monomers such as ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, and 1-octene. Polymer, copolymer, multistage polymer, etc.), low density polyethylene, linear low density polyethylene, medium density polyethylene, high density polyethylene, ultra high molecular weight polyethylene, isotactic polypropylene, atactic polypropylene, polybutene, Examples include ethylene propylene rubber.

  The said polyolefin resin may be used individually by 1 type, and 2 or more types may be mixed and used for it. For example, it is possible to make a mixture of high density polyethylene and medium density polyethylene with an emphasis on shutdown behavior. In addition, it is possible to make a mixture of high-density polyethylene and ultrahigh molecular weight polyethylene by paying attention to improvement of short circuit resistance or mechanical properties (such as puncture strength). In addition, it is possible to make a mixture of polyethylene and polypropylene by paying attention to heat resistance.

  From the viewpoint of lowering the melting point of the polyolefin microporous membrane, the polyolefin resin preferably contains high-density polyethylene. The proportion of the high-density polyethylene in the polyolefin resin is preferably 10% by mass or more, more preferably 30% by mass or more.

[Production method of polyolefin microporous membrane]
In the present invention, the method for producing the microporous polyolefin membrane is not particularly limited, but for example, a solution method, a melting method, or the like can be applied. Specifically, the method is produced through the following steps (1) to (6). It is preferable.

(1) Preparation of polyolefin solution A polyolefin solution is prepared by dissolving a predetermined amount of polyolefin in a solvent. At this time, a solvent may be mixed to prepare a polyolefin solution. Examples of the solvent include paraffin, liquid paraffin, paraffin oil, mineral oil, castor oil, tetralin, ethylene glycol, glycerin, decalin, toluene, xylene, diethyltriamine, ethyldiamine, dimethyl sulfoxide, hexane, and the like.

The concentration of the polyolefin solution is preferably 1 to 35% by mass, more preferably 10 to 30% by mass. When the concentration of the polyolefin solution is 1% by mass or more, the gel-like molded product obtained by cooling gelation can be maintained so as not to be highly swollen with a solvent, so that it is difficult to be deformed and the handleability is good. On the other hand, when the concentration of the polyolefin solution is 35% by mass or less, since the pressure during extrusion can be suppressed, the discharge amount can be maintained and the productivity is excellent. In addition, the alignment in the extrusion process is difficult to proceed, which is advantageous for ensuring stretchability and uniformity.
The polyolefin solution is preferably used after filtration for removing foreign substances. There are no particular limitations on the filtration device, the shape of the filtration filter, the filtration mode, and the like, and conventionally known devices and modes can be used. The hole diameter of the filter is preferably 1 μm to 50 μm from the viewpoint of filterability.

(2) Extrusion of polyolefin solution The prepared polyolefin solution is kneaded with a single screw extruder or a twin screw extruder, and extruded with a T die or an I die at a temperature not lower than the melting point and not higher than the melting point + 60 ° C. A twin screw extruder is preferably used. Then, the extruded polyolefin solution is passed through a chill roll or a cooling bath to form a gel composition. At this time, it is preferable to rapidly cool below the gelation temperature to cause gelation. In particular, when a volatile solvent and a non-volatile solvent are used in combination as the solvent, the cooling rate of the gel composition is preferably 30 ° C./min or more from the viewpoint of controlling the crystal parameters.

(3) Desolvation treatment Next, the solvent is removed from the gel composition. When a volatile solvent is used, the solvent can also be removed from the gel composition by evaporating by heating or the like, which also serves as a preheating step. In the case of a non-volatile solvent, the solvent can be removed by squeezing out under pressure. The solvent need not be completely removed.

(4) Stretching of the gel-like composition After the solvent removal treatment, the gel-like composition is stretched. Here, a relaxation treatment may be performed before the stretching treatment. In the stretching treatment, the gel-like molded product is heated and biaxially stretched at a predetermined magnification by a normal tenter method, roll method, rolling method, or a combination of these methods. Biaxial stretching may be simultaneous or sequential. Moreover, it can also be set as longitudinal multistage extending | stretching and 3 thru | or 4 step extending | stretching.
The stretching temperature is preferably 90 ° C. or higher and lower than the melting point of the polyolefin used for film formation, and more preferably 100 to 120 ° C. When the heating temperature is lower than the melting point, the gel-like molded product is difficult to dissolve, so that stretching can be performed satisfactorily. Further, when the heating temperature is 90 ° C. or higher, the gel-like molded product is sufficiently softened and can be stretched at a high magnification without being broken during stretching.

Although a draw ratio changes with thickness of an original fabric, it is preferable to carry out at least 2 times or more in a uniaxial direction, preferably 4 to 20 times. In particular, the draw ratio is preferably 4 to 10 times in the machine direction (MD direction) and 6 to 15 times in the machine direction (TD direction). The stretching speed is preferably set to 200% / second or less from the viewpoint of suitably improving charge / discharge cycle stability and short-circuit resistance.
After stretching, heat setting is performed as necessary to provide thermal dimensional stability. By repeating the stretching and heat setting two more steps or more, the heat shrinkability can be suppressed and the short-circuit resistance can be improved more suitably. At this time, the drawability ratio in the MD and / or TD direction is preferably relatively low, 1.5 to 3 times.

(5) Extraction and removal of solvent The stretched gel composition is immersed in an extraction solvent to extract the solvent. Examples of the extraction solvent include hydrocarbons such as pentane, hexane, heptane, cyclohexane, decalin, and tetralin, chlorinated hydrocarbons such as methylene chloride, carbon tetrachloride, and methylene chloride, fluorinated hydrocarbons such as ethane trifluoride, diethyl, and the like. Easily volatile compounds such as ethers such as ether and dioxane can be used. These solvents are appropriately selected according to the solvent used for dissolving the polyolefin resin, and can be used alone or in combination. The extraction of the solvent removes the solvent in the microporous membrane to less than 1% by mass.

(6) Annealing of microporous film The microporous film is heat-set by annealing. The annealing temperature is preferably 80 to 150 ° C., more preferably 115 to 135 ° C., from the viewpoint of the heat shrinkage rate of the microporous film.
The annealing time is preferably 1 minute or more from the viewpoint of reducing the thermal shrinkage rate of the microporous film, and can be 1 minute to 1 hour. From the viewpoint of suppressing the deformation of the microporous film, annealing for a long time is preferable. In order to further reduce the thermal shrinkage of the microporous film, it is possible to extend the annealing time from about 1 hour to about 5 hours.

(Heat resistant porous layer)
In the present invention, the heat-resistant porous layer has a large number of micropores inside and has a structure in which these micropores are connected, and gas or liquid can pass from one surface to the other. Means the layer that became.

In the present invention, the heat-resistant porous layer may be formed on both sides or one side of the polyolefin microporous membrane, but it was formed on both sides of the polyolefin microporous membrane from the viewpoints of handling properties, durability, and the effect of suppressing heat shrinkage. Embodiments are preferred.
In the present invention, when the heat-resistant porous layer is formed on both surfaces of the polyolefin microporous membrane, the total thickness of the heat-resistant porous layer is preferably 3 μm or more and 12 μm or less. When formed only on one side of the polyolefin microporous membrane, the thickness of the heat-resistant porous layer is preferably 3 μm or more and 12 μm or less. Such a thickness range is preferable in terms of handling properties, durability, an effect of suppressing heat shrinkage, and resistance to liquid withstand.
In the present invention, the porosity of the heat-resistant porous layer is preferably in the range of 30 to 90%, more preferably 30 to 70%, from the viewpoint of being hard to dry up.

[Heat resistant polymer]
In the present invention, the heat resistant polymer constituting the heat resistant porous layer is preferably a crystalline polymer having a melting point of 200 ° C. or higher, or a polymer having no melting point but having a decomposition temperature of 200 ° C. or higher. Examples thereof include at least one resin selected from the group consisting of aromatic polyamide, polyimide, polyamideimide, polysulfone, polyketone, polyetherketone, polyetherimide and cellulose.
Such a polymer (hereinafter also referred to as “heat-resistant resin”) may be a homopolymer, and may further contain some copolymer components depending on a desired purpose such as exhibiting flexibility. That is, for example, in a wholly aromatic polyamide, it is possible to copolymerize a small amount of an aliphatic component, for example.
Further, such a heat-resistant resin is insoluble in the electrolyte solution and is preferably a wholly aromatic polyamide due to its high durability. From the viewpoint that it is easy to form a porous layer and has excellent oxidation-reduction resistance, the meta type More preferred is polymetaphenylene isophthalamide, which is an aromatic polyamide.

[Inorganic filler]
In the present invention, the heat resistant porous layer preferably contains an inorganic filler. The inorganic filler is not particularly limited, but metal oxides such as alumina, titania, silica and zirconia, metal carbonates such as calcium carbonate, metal phosphates such as calcium phosphate, metals such as aluminum hydroxide and magnesium hydroxide A hydroxide or the like is preferably used. Such an inorganic filler is preferably highly crystalline from the viewpoints of impurity elution and durability.

As an inorganic filler, what produces an endothermic reaction in 200-400 degreeC is preferable. In non-aqueous secondary batteries, heat generation associated with the decomposition of the positive electrode is considered to be the most dangerous, and this decomposition occurs in the vicinity of 300 ° C. For this reason, if the generation temperature of the endothermic reaction is in the range of 200 to 400 ° C., it is effective in preventing heat generation of the non-aqueous secondary battery.
Examples of the inorganic filler that generates an endothermic reaction at 200 to 400 ° C. include an inorganic filler made of a metal hydroxide, a boron salt compound, a clay mineral, or the like. Specific examples include aluminum hydroxide, magnesium hydroxide, calcium aluminate, dosonite, and zinc borate. Among these inorganic fillers, aluminum hydroxide, dawsonite, and calcium aluminate undergo a dehydration reaction in the range of 200 to 300 ° C, and magnesium hydroxide and zinc borate undergo a dehydration reaction in the range of 300 to 400 ° C. It is preferable to use at least one of them.
The said inorganic filler can be used individually or in combination of 2 or more types. In addition, these flame retardant inorganic fillers are appropriately mixed with other inorganic fillers such as metal oxides such as alumina, zirconia, silica, magnesia, and titania, metal nitrides, metal carbides, and metal carbonates. You can also.

In the present invention, the average particle diameter of the inorganic filler is preferably 0.1 μm to 2 μm from the viewpoint of short circuit resistance at high temperature, moldability, and the like. The content of the inorganic filler in the heat-resistant porous layer is preferably 50 to 95% by mass from the viewpoint of heat resistance improvement effect, permeability and handling properties.
In addition, the inorganic filler in the heat-resistant porous layer is present in a state of being trapped by the heat-resistant resin when the heat-resistant porous layer is in the form of a microporous film, and when the heat-resistant porous layer is a nonwoven fabric or the like It may be present in the constituent fibers or fixed to the nonwoven fabric surface or the like with a binder such as a resin.

[Method for forming heat-resistant porous layer]
In the present invention, the method for forming the heat-resistant porous layer is not particularly limited, but specifically, it is preferably formed through the following steps (1) to (5). In addition, before implementing the process of following (1), the contact bonding layer is formed on the surface in which the heat resistant porous layer of the polyolefin microporous film used as a base material is formed.

(1) Preparation of coating slurry A heat-resistant resin is dissolved in a solvent to prepare a coating slurry. The solvent is not particularly limited as long as it dissolves the heat-resistant resin, but is preferably a polar solvent, and examples thereof include N-methylpyrrolidone, dimethylacetamide, dimethylformamide, and dimethyl sulfoxide. In addition to the polar solvent, the solvent may be a solvent that becomes a poor solvent for the heat-resistant resin. By applying such a poor solvent, a microphase separation structure is induced and the formation of a heat-resistant porous layer is facilitated. As the poor solvent, alcohols are preferable, and polyhydric alcohols such as glycol are particularly preferable.
The concentration of the heat-resistant resin in the coating slurry is preferably 4 to 9% by mass. Moreover, an inorganic filler is disperse | distributed to this as needed, and it is set as the slurry for coating. In dispersing the inorganic filler in the coating slurry, when the dispersibility of the inorganic filler is not preferable, a method of surface-treating the inorganic filler with a silane coupling agent or the like to improve the dispersibility is also applicable.

(2) Coating of slurry The slurry is coated on at least one surface of the polyolefin microporous membrane. When forming a heat-resistant porous layer on both surfaces of a polyolefin microporous film, it is preferable from a viewpoint of shortening of a process to apply simultaneously on both surfaces of a base material. Examples of the method for coating the slurry for coating include a knife coater method, a gravure coater method, a die coater method, a reverse roll coater method, a roll coater method, a Mayer bar method, a screen printing method, an inkjet method, and a spray method. . The reverse roll coater method is preferable from the viewpoint of uniformly forming a coating film.
When coating on both sides of the polyolefin microporous membrane simultaneously, for example, by passing the polyolefin microporous membrane between a pair of Meyer bars, an excess coating slurry is applied to both sides, and this is applied to a pair of reverse roll coaters. It is possible to employ a method of precise measurement by scraping off excess slurry through
The slurry for coating is preferably filtered prior to coating in order to remove fine foreign matters. There are no particular limitations on the shape of the filtration device, the filter, and the installation position, and a conventionally known device and filter can be installed and used at predetermined positions. The hole diameter of the filter is preferably 1 μm or more and 100 μm or less from the viewpoint of filterability and productivity.

(3) Solidification of the slurry The coating of the polyolefin microporous film with the slurry for coating is treated with a coagulation liquid capable of coagulating the heat resistant resin, so that the heat resistant resin is solidified. A porous layer is formed. Treatment methods include spraying the coagulating liquid onto the surface coated with the coating slurry, or immersing the polyolefin microporous film coated with the coating slurry in a bath (coagulating bath) containing the coagulating liquid. The method of doing is mentioned. Here, when installing a coagulation bath, it is preferable to install it below the coating apparatus.
The coagulation liquid is not particularly limited as long as it can coagulate the heat-resistant resin, but water or a solution obtained by mixing an appropriate amount of water with the solvent used in the slurry is preferable. Here, the mixing amount of water is preferably 40 to 80% by mass with respect to the coagulating liquid from the viewpoint of coagulation efficiency and porosity.

(4) Removal of coagulating liquid The coagulating liquid used for coagulating the slurry is removed by washing with water.

(5) Drying Water is removed by drying from a sheet in which a heat-resistant resin coating layer is formed on a polyolefin microporous membrane. The drying method is not particularly limited, but the drying temperature is preferably 50 to 80 ° C. When a high drying temperature is applied, a method of contacting with a roll is applied in order to prevent dimensional change due to heat shrinkage. It is preferable.

(Separator characteristics)
The separator for a non-aqueous secondary battery of the present invention preferably has a total film thickness of 30 μm or less from the viewpoint of the energy density of the battery when a non-aqueous secondary battery is produced.
The porosity of the separator for a non-aqueous secondary battery of the present invention is preferably 30 to 70%, more preferably 40 to 60% from the viewpoints of permeability, mechanical strength, and handling properties.
The Gurley value (JIS P8117) of the non-aqueous secondary battery separator of the present invention is preferably 100 to 500 sec / 100 cc from the viewpoint of a good balance between mechanical strength and membrane resistance.
The membrane resistance of the non-aqueous secondary battery separator of the present invention is preferably 1.5 to 10 ohm · cm ² from the viewpoint of load characteristics of the non-aqueous secondary battery.

The puncture strength of the separator for a non-aqueous secondary battery of the present invention is preferably 250 to 1000 g. When the puncture strength is 250 g or more, when a non-aqueous secondary battery is produced, pinholes or the like hardly occur in the separator, and the occurrence of a short circuit in the non-aqueous secondary battery can be suppressed.
The tensile strength of the nonaqueous secondary battery separator of the present invention is preferably 10 N or more. When the tensile strength is 10 N or more, the separator is difficult to break when winding the separator when producing a non-aqueous secondary battery.

  The thermal contraction rate at 105 ° C. of the separator for non-aqueous secondary batteries of the present invention is preferably 0.5 to 10%. When the thermal contraction rate is within this range, the shape stability and shutdown characteristics of the separator are well balanced. More preferably, it is 0.5 to 5%.

<Non-aqueous secondary battery>
The non-aqueous secondary battery of the present invention is a non-aqueous secondary battery that obtains an electromotive force by doping and dedoping lithium, and includes a positive electrode, a negative electrode, and a separator for a non-aqueous secondary battery having the above-described configuration. . A non-aqueous secondary battery has a structure in which an electrolytic solution is impregnated in a battery element in which a negative electrode and a positive electrode face each other via a separator, and this is enclosed in an exterior.

The negative electrode has a structure in which a negative electrode mixture composed of a negative electrode active material, a conductive additive and a binder is formed on a current collector. Examples of the negative electrode active material include materials capable of electrochemically doping lithium, and examples thereof include carbon materials, silicon, aluminum, tin, and wood alloys. The negative electrode active material preferably has a volume change rate of 3% or more in the process of dedoping lithium from the viewpoint that the separator is unlikely to dry up. Examples of the negative electrode active material include Sn, SnSb, Ag ₃ Sn, artificial graphite, graphite, Si, SiO, V ₅ O _{4 and the} like. Examples of the conductive assistant include carbon materials such as acetylene black and ketjen black. The binder is made of an organic polymer, and examples thereof include polyvinylidene fluoride and carboxymethyl cellulose. A copper foil, a stainless steel foil, a nickel foil or the like can be used for the current collector.

The positive electrode has a structure in which a positive electrode mixture composed of a positive electrode active material, a conductive additive and a binder is formed on a current collector. Examples of the positive electrode active material include lithium-containing transition metal oxides. Specifically, LiCoO ₂ , LiNiO ₂ , LiMn _0.5 Ni _0.5 O ₂ , LiCo _1/3 Ni _1/3 Mn _1/3 Examples include O ₂ , LiMn ₂ O ₄ , LiFePO ₄ , LiCo _0.5 Ni _0.5 O ₂ , LiAl _0.25 Ni _0.75 O _{2, and the} like. The positive electrode active material preferably has a volume change rate of 1% or more in the process of dedoping lithium from the viewpoint that the separator does not easily drain. Examples of such a positive electrode active material include LiMn ₂ O ₄ , LiCoO ₂ , LiNiO ₂ , LiCo _0.5 Ni _0.5 O ₂ , LiAl _0.25 Ni _0.75 O _{2 and the} like. Examples of the conductive assistant include carbon materials such as acetylene black and ketjen black. The binder is made of an organic polymer, and examples thereof include polyvinylidene fluoride. For the current collector, aluminum foil, stainless steel foil, titanium foil, or the like can be used.

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 the non-aqueous solvent include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, γ-butyrolactone, vinylene carbonate, and the like. These may be used alone or in combination.

  Examples of the exterior material include a metal can or an aluminum laminate pack. The shape of the battery includes a square shape, a cylindrical shape, a coin shape, and the like. The nonaqueous secondary battery separator of the present invention can be suitably applied to any shape.

  The present invention will be described more specifically with reference to the following examples. The materials, amounts used, ratios, processing procedures, and the like shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the specific examples shown below.

The measurement methods applied in the examples and comparative examples of the present invention are as follows.
(1) Coating amount of adhesive layer A sample in which an adhesive layer is provided on one side or both sides of a polyolefin microporous membrane is cut into 10 cm x 10 cm and the mass is measured. Separately, a polyolefin microporous film not provided with an adhesive layer is cut into 10 cm × 10 cm and the mass is measured. The coating amount (g / m ² ) of the adhesive layer was determined by subtracting the latter mass from the former mass and dividing by the area.
(2) Film thickness The film thickness of the polyolefin microporous membrane and the separator for the non-aqueous secondary battery was determined by measuring 20 points with a contact-type film thickness meter (manufactured by Mitutoyo Corporation) and averaging them. Here, a cylindrical contact terminal having a diameter of 0.5 cm was used as the contact terminal.
(3) Weight per unit area (mass per 1 m ² ) of the separator for a non-aqueous secondary battery was obtained by cutting a sample into 10 cm × 10 cm, measuring the mass, and dividing this mass by the area.
(4) Gurley value The Gurley value of the separator for non-aqueous secondary batteries was determined according to JIS P8117.
(5) Gelboflex test The gelboflex test of the separator for non-aqueous secondary batteries was carried out using a gelboflex tester (manufactured by Tester Kogyo) at room temperature (25 ° C) and 1000 cycles.

Example 1
[Production of polyethylene microporous membrane]
As polyethylene powder, GUR2126 (weight average molecular weight 41.50 million, melting point 141.degree. C.) and GRX143 (weight average molecular weight 560,000, melting point 135.degree. C.) manufactured by Ticona were prepared. GUR2126 and GURX143 were dissolved in a mixed solvent of liquid paraffin and decalin so that the mixing ratio (GUR2126: GURX143) was 1: 9 (mass ratio) and the polyethylene concentration was 30% by mass to prepare a polyethylene solution. The composition of the polyethylene solution was polyethylene: liquid paraffin: decalin = 30: 45: 25 (mass ratio).
This polyethylene solution was extruded from a die at 148 ° C., cooled in a water bath, and dried at 60 ° C. for 8 minutes and at 95 ° C. for 15 minutes to produce a gel tape (base tape). The base tape was stretched by biaxial stretching in which longitudinal stretching and lateral stretching were sequentially performed. Here, the longitudinal stretching was performed at a stretching ratio of 5.5 times, the stretching temperature was 90 ° C., the transverse stretching was performed at a stretching ratio of 11.0 times, and the stretching temperature was 105 ° C. After transverse stretching, heat setting was performed at 125 ° C. Next, this was immersed in a methylene chloride bath to extract liquid paraffin and decalin. Then, it dried at 50 degreeC and obtained the polyethylene microporous film by annealing at 120 degreeC. The properties of this polyethylene microporous membrane were a film thickness of 11.5 μm, a porosity of 36%, and an air permeability of 301 seconds / 100 cc.

[Formation of adhesive layer]
On one side of the polyethylene microporous membrane obtained above, a methyl ethyl ketone solution (concentration of styrene-butadiene-styrene copolymer of 5% by mass) of styrene-butadiene-styrene copolymer (TAFPRENE A125 manufactured by Asahi Kasei Kogyo) was dried. It was coated with a gravure roll so that the coating amount was 0.05 g / m ² and dried at 60 ° C. for 1 hour to form an adhesive layer. Subsequently, an adhesive layer having a coating amount of 0.05 g / m ² at the time of drying was similarly formed on the other surface of the polyethylene microporous membrane.

[Formation of heat-resistant porous layer]
Conex (registered trademark; manufactured by Teijin Techno Products), which is a meta-type wholly aromatic polyamide, and magnesium hydroxide having an average particle size of 0.8 μm (Kisuma 5P manufactured by Kyowa Chemical Co., Ltd.) were prepared. The meta-type wholly aromatic polyamide is such that the mixing ratio (meta-type wholly aromatic polyamide: magnesium hydroxide) is 25:75 (mass ratio) and the meta-type wholly aromatic polyamide concentration is 5.5% by mass. And magnesium hydroxide were mixed in a mixed solvent (mass ratio 50:50) of dimethylacetamide (DMAc) and tripropylene glycol (TPG) to prepare a coating slurry.
Apply a suitable amount of the above slurry to a pair of Meyer bars (count # 6) facing each other with a clearance of 20 μm, and pass a polyethylene microporous film with an adhesive layer on both sides between the Mayer bars, and apply to both sides. An industrial slurry was applied.
This was immersed in a coagulation liquid at 40 ° C. (water: DMAc: TPG = 50: 25: 25 [mass ratio]). Next, washing with water and drying were performed to obtain a separator for a non-aqueous secondary battery in which heat-resistant porous layers were provided on both sides of a polyethylene microporous membrane. Table 1 shows the physical properties of this separator.

[Manufacture of non-aqueous secondary batteries]
89.5 parts by mass of lithium cobaltate (LiCoO ₂ ) (manufactured by Nippon Chemical Industry Co., Ltd.), 4.5 parts by mass of acetylene black (Denka black manufactured by Denki Kagaku Kogyo Co., Ltd.), 6 parts by mass of polyvinylidene fluoride (manufactured by Kureha Chemical Co., Ltd.) These were kneaded using N-methyl-2-pyrrolidone to prepare a slurry. This slurry was applied onto an aluminum foil having a thickness of 20 μm, dried and pressed to obtain a positive electrode having a thickness of 100 μm.
N-methyl so that it becomes 87 parts by mass of mesophase carbon microbeads (manufactured by Osaka Gas Chemical Co., Ltd.), 3 parts by mass of acetylene black (Denka Black manufactured by Denki Kagaku Kogyo Co., Ltd.), and 10 parts by mass of polyvinylidene fluoride (manufactured by Kureha Chemical Co., Ltd.). These were kneaded using -2-pyrrolidone to prepare a slurry. This slurry was applied on a copper foil having a thickness of 18 μm, dried and pressed to obtain a negative electrode having a thickness of 90 μm.

The separator for non-aqueous secondary batteries obtained above was used as a separator, and the positive electrode and the negative electrode obtained above were arranged to face each other. This was impregnated with an electrolytic solution and sealed in an exterior made of an aluminum laminate film to produce a non-aqueous secondary battery. As the electrolytic solution, a 1M LiPF ₆ / [ethylene carbonate / ethyl methyl carbonate (mass ratio 3: 7)] solution (manufactured by Kishida Chemical Co., Ltd.) was used. This non-aqueous secondary battery has a positive electrode area of 2 × 1.4 cm ² , a negative electrode area of 2.2 × 1.6 cm ² , and a set capacity of 8 mAh (in the range of 4.2V-2.75V).
The non-aqueous secondary battery obtained above was satisfactory in terms of practical use in terms of discharge capacity, load characteristics, and cycle characteristics.

(Example 2)
In Example 1, the methyl ethyl ketone solution of the styrene-butadiene-styrene copolymer used for forming the adhesive layer was changed to a methyl ethyl ketone solution (ethylene-α olefin) of ethylene-α olefin copolymer (Tafmer A-4085 manufactured by Mitsui Chemicals, Inc.). A nonaqueous secondary battery separator was obtained in the same manner as in Example 1 except that the copolymer concentration was changed to 5% by mass. Table 1 shows the physical properties of this separator.

(Example 3)
In Example 1, the methyl ethyl ketone solution of the styrene-butadiene-styrene copolymer used for forming the adhesive layer was changed to a methyl ethyl ketone solution (EPDM concentration) of EPDM (ethylene propylene diene terpolymer) (JSR EP24 manufactured by JSR Corporation). A separator for a non-aqueous secondary battery was obtained in the same manner as in Example 1 except that the content was changed to 5% by mass). Table 1 shows the physical properties of this separator.

Example 4
A separator for a non-aqueous secondary battery was obtained in the same manner as in Example 1 except that the coating amount of the adhesive layer was changed to 0.1 g / m ² in Example 1. Table 1 shows the physical properties of this separator.

(Example 5)
A separator for a non-aqueous secondary battery was obtained in the same manner as in Example 1 except that the coating amount of the adhesive layer was changed to 0.5 g / m ² in Example 1. Table 1 shows the physical properties of this separator.

(Example 6)
A separator for a non-aqueous secondary battery was obtained in the same manner as in Example 1 except that the coating amount of the adhesive layer was changed to 1.0 g / m ² in Example 1. Table 1 shows the physical properties of this separator.

(Comparative Example 1)
A separator for a non-aqueous secondary battery was obtained in the same manner as in Example 1 except that the adhesive layer was not formed in Example 1. Table 1 shows the physical properties of this separator.

As shown in Table 1, in Examples 1 to 6, the Gurley value was not particularly increased, and the permeability of the separator was not impaired.
In Examples 1 to 6, it is apparent that the number of pinholes generated in the gelboflex test is extremely small as compared with Comparative Example 1, and the lack of the heat-resistant porous layer is suppressed.
Therefore, according to the present invention, a separator for a non-aqueous secondary battery having a polyolefin microporous membrane and a heat-resistant porous layer is provided, and the separator for a non-aqueous secondary battery that improves battery productivity and safety is provided. Can do.

Claims (3)

A polyolefin microporous membrane,
A heat-resistant porous layer provided on one side or both sides of the polyolefin microporous membrane;
An adhesive layer provided between the polyolefin microporous membrane and the heat-resistant porous layer, comprising at least one selected from a thermoplastic elastomer and a rubber component;
A separator for a non-aqueous secondary battery. The adhesive layer is a non-aqueous secondary battery separator of claim 1 coating weight of 0.05 g / ^{m 2} or more 1.0 g / ^{m 2} or less.   A non-aqueous secondary battery separator according to claim 1 or 2, which is disposed between the positive electrode and the negative electrode, and between the positive electrode and the negative electrode, and obtains an electromotive force by doping or dedoping lithium. Water-based secondary battery.