JP2012119225A - Separator for nonaqueous electrolyte battery, and nonaqueous electrolyte battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separator for a nonaqueous electrolyte battery resisting cutting when being wound and offering high heat resistance, and a nonaqueous electrolyte battery comprising the separator for a nonaqueous electrolyte battery.SOLUTION: The separator for a nonaqueous electrolyte battery comprises a porous base material containing polyolefin, and a heat-resistant porous layer disposed on one side or both sides of the porous base material and containing a heat-resistant resin. The lower value of the tear strength in the longitudinal direction and the tear strength in the cross direction measured by the test method of JIS K7128-1, is in the range of 0.5 to 5 mN/μm.

Description

  The present invention relates to a separator for a nonaqueous electrolyte battery and a nonaqueous electrolyte battery.

  Non-aqueous electrolyte secondary batteries represented by lithium ion secondary batteries are widely used as the main power source for portable electronic devices such as mobile phones and laptop computers. Applications are expanding to power storage systems. With the spread of non-aqueous electrolyte secondary batteries, securing stable battery characteristics and safety has become an important issue.

  The role of the separator is important in ensuring the safety of the nonaqueous electrolyte secondary battery. From the viewpoint of the shutdown function, a porous film mainly composed of polyolefin (especially polyethylene) is currently used. In the technical field of non-aqueous electrolyte secondary batteries, the shutdown function refers to the function that the polyolefin melts and the pores of the porous membrane are blocked by blocking the current when the temperature of the battery rises abnormally. It works to stop thermal runaway.

  However, when the battery temperature further increases after the shutdown function is activated, the entire polyolefin porous film is melted (so-called meltdown). As a result, a short circuit occurs inside the battery, and a large amount of heat is generated along with this, which may lead to smoke, ignition, or explosion of the battery. For this reason, in addition to the shutdown function, the separator is required to have heat resistance enough not to melt down even at a temperature higher than the temperature at which the shutdown function is manifested.

  In response to this requirement, conventionally, proposals have been made to coat a porous layer containing a heat-resistant polymer on one or both surfaces of a polyolefin porous membrane (see, for example, Patent Documents 1 and 2). These proposals can be expected to ensure the safety of the battery at high temperatures in terms of both a shutdown function and heat resistance.

International Publication No. 08/062727 Pamphlet International Publication No. 08/156033 Pamphlet

However, in the market, further improvement is demanded regarding the heat resistance of the separator.
The separator is also required to have good mechanical properties. In particular, if the cutting of the separator, which is likely to occur at the time of winding work in which tension is applied to the separator, can be suppressed, the yield in manufacturing the battery can be improved.

In view of the above, an object of the present invention is to provide a separator for a nonaqueous electrolyte battery in which cutting during winding is suppressed and heat resistance is excellent.
Another object of the present invention is to provide a non-aqueous electrolyte battery that is provided with the separator for non-aqueous electrolyte batteries and has excellent battery characteristics.

Specific means for achieving the above object are as follows.
<1> A porous substrate containing polyolefin, and a heat-resistant porous layer containing a heat-resistant resin provided on one or both surfaces of the porous substrate, and measured by a test method specified in JIS K7128-1. A separator for a non-aqueous electrolyte battery, wherein the lower value of the tear strength in the length direction and the tear strength in the width direction is 0.5 mN / μm or more and 5 mN / μm or less.
<2> The heat-resistant resin is at least one selected from the group consisting of aromatic polyamide, polyimide, polysulfone, polyethersulfone, polyetherketone, polyetherimide, and polyvinylidene fluoride, according to <1>. Nonaqueous electrolyte battery separator.
<3> A positive electrode, a negative electrode, and the separator for a nonaqueous electrolyte battery according to <1> or <2> disposed between the positive electrode and the negative electrode, and generating electromotive force by doping or dedoping lithium. Non-aqueous electrolyte battery to get.

According to the present invention, it is possible to provide a separator for a nonaqueous electrolyte battery in which cutting during winding is suppressed and heat resistance is excellent.
Moreover, according to this invention, the nonaqueous electrolyte battery excellent in the battery characteristic provided with the said separator for nonaqueous electrolyte batteries can be provided.

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 electrolyte battery>
A separator for a nonaqueous electrolyte battery according to the present invention includes a porous substrate containing polyolefin and a heat-resistant porous layer containing a heat-resistant resin provided on one or both surfaces of the porous substrate. JIS K7128-1 The lower value of the tear strength in the length direction and the tear strength in the width direction, measured by the test method specified in 1., is 0.5 mN / μm or more and 5 mN / μm or less.
Here, regarding the non-aqueous electrolyte battery separator, the “length direction” refers to the length direction of the separator manufactured in a long shape, and the “width direction” refers to the direction orthogonal to the length direction. .
In the present invention, the tear strength in the length direction is measured using a test piece in which the length direction of the separator manufactured in a long shape is the test direction, and the tear strength in the width direction is long. It is measured using a test piece in which the direction perpendicular to the longitudinal direction of the separator to be manufactured is the test direction.
Hereinafter, the “length direction” is also referred to as “MD direction”, and the “width direction” is also referred to as “TD direction”.

The separator for a non-aqueous electrolyte battery of the present invention has a shutdown function obtained by a porous substrate containing polyolefin, and has a heat resistance that prevents the separator from melting even at a temperature higher than the melting point of the polyolefin by a heat resistant porous layer containing a heat resistant resin. Is obtained.
The nonaqueous electrolyte battery separator of the present invention has a lower value of 0.5 mN, which is the lower of the tear strength in the length direction and the tear strength in the width direction, measured by the test method specified in JIS K7128-1. By being / μm or more and 5 mN / μm or less, the cutting of the separator is suppressed and the heat resistance is improved in the winding process at the time of manufacturing the battery. Therefore, the non-aqueous electrolyte battery separator of the present invention has a good yield during battery production and high safety during battery use.
In addition, the non-aqueous electrolyte battery provided with the separator for non-aqueous electrolyte battery of the present invention has a good shutdown performance, and the battery capacity is remarkably lowered even if it is repeatedly charged and discharged when used for a long time. And cycle characteristics are stable.

  Conventionally, the breaking strength of the separator disclosed in the prior art document is measured by measuring the stress at the time of breaking after the separator itself is deformed nearly 100% in the tensile test. It does not occur in separators during normal manufacturing. This physical property as the breaking strength is considered to be a physical property having no correlation with the tear strength measured by the test method specified in JIS K7128-1.

The separator for a nonaqueous electrolyte battery according to the present invention has a lower value of 0.5 mN / t in either the MD direction tear strength or the TD direction tear strength measured by a test method specified in JIS K7128-1. μm to 5 mN / μm.
If the lower one of the tear strength in the MD direction and the tear strength in the TD direction is less than 0.5 mN / μm, the separator is likely to tear during handling or winding in the battery manufacturing process. .
On the other hand, if the lower one of the tear strength in the MD direction and the tear strength in the TD direction is more than 5 mN / μm, the heat resistance may be inferior.
In addition, if the lower one of the tear strength in the MD direction and the tear strength in the TD direction is 5 mN / μm or less, the state of the pores or voids of the porous substrate containing polyolefin is suitable. When used as a battery, the ion permeability is good.
In the separator for a non-aqueous electrolyte battery of the present invention, the lower value of the tear strength in the MD direction and the tear strength in the TD direction is preferably 0.7 mN / μm to 4 mN / μm, more preferably 1.0 mN / μm to 3 mN / μm.

  In the separator for a nonaqueous electrolyte battery of the present invention, there is no particular limitation on the higher value of the tear strength in the MD direction and the tear strength in the TD direction, which is measured by the test method specified in JIS K7128-1. . The tear strength in the MD direction and the tear strength in the TD direction may be the same value.

In the separator for a nonaqueous electrolyte battery of the present invention, in particular, a method of controlling so that the lower value of the tear strength in the MD direction or the tear strength in the TD direction is 0.5 mN / μm to 5 mN / μm. There is no limit.
For example, stretching conditions for producing a porous substrate containing polyolefin (hereinafter also referred to as “polyolefin porous substrate”, “porous substrate” and “substrate”), particularly stretching in the MD and TD directions. Controlling the magnification and stretching order can be mentioned.
When producing a polyolefin porous substrate, if the stretching ratio in the TD direction is increased, the tear strength in the MD direction increases, but the tear strength in the TD direction tends to decrease. On the contrary, when the MD direction stretch ratio is increased, the tear strength in the TD direction increases, but the tear strength in the MD direction tends to decrease. In order to set the lower one of the tear strength in the MD direction and the tear strength in the TD direction to 0.5 mN / μm to 5 mN / μm, a suitable balance of stretch ratio is selected.
The stretching conditions suitable for the present invention are as described in detail in the section of [Method for producing porous substrate containing polyolefin] described later.

In addition, as a method of controlling the lower value of the tear strength in the MD direction and the tear strength in the TD direction to be 0.5 mN / μm to 5 mN / μm, it is used for polyolefin porous substrates. And controlling the weight average molecular weight (Dalton) of the polyolefin to 300,000 to less than 3 million.
If the weight average molecular weight of the polyolefin is less than 3 million, it is easy to control the lower one of the tear strength in the MD direction and the tear strength in the TD direction to 5 mN / μm or less. Further, the polyolefin porous base material has good stretchability, which is advantageous because it can suppress the occurrence of stretch spots. If the occurrence of stretch spots can be suppressed in a polyolefin porous substrate, breakage and pinholes are unlikely to occur. In addition, if the weight average molecular weight of the polyolefin is less than 3 million, the porosity of the polyolefin porous substrate is in an appropriate range, and the ion permeability is good when a battery is obtained.
On the other hand, if the weight average molecular weight of the polyolefin is 300,000 or more, it is possible to obtain a handleable porous base material having a balance between strength and elongation in operations such as conveyance, winding and slitting by stretching. . This is advantageous in that the tear strength of the present invention is easily exhibited. From this viewpoint, the weight average molecular weight of the polyolefin is more preferably 950,000 or more.

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

In the present invention, the thickness of the polyolefin porous substrate 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 including the heat-resistant porous layer, and high electric capacity can be achieved.
The porosity of the polyolefin porous substrate 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 porous substrate, and the shutdown function is good. The porosity is more preferably 40 to 60%.
The Gurley value (JIS P8117) of the polyolefin porous substrate 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 porous substrate is preferably 0.5 to ⁵ ohm · cm ² from the viewpoint of load characteristics of the nonaqueous electrolyte battery.
The thermal shrinkage rate at 105 ° C. of the polyolefin porous substrate is preferably 1 to 20% in the MD direction and 1 to 15% in the TD direction. When the thermal contraction rate is in the above range, the separator has a good balance between shape stability and shutdown characteristics.
The puncture strength of the polyolefin porous substrate is preferably 250 g or more. When the pin puncture strength is 250 g or more, pinholes or the like are hardly generated in the separator due to the unevenness of the electrode or impact when the battery is used, and the possibility that the nonaqueous electrolyte battery is short-circuited is low.

  In the present invention, the polyolefin porous substrate preferably has a breaking strength of 10 N or more in both the MD direction and the TD direction, and the breaking elongation exceeds 50%. When the breaking strength and breaking elongation are within the above ranges, the separator is less likely to be damaged when the separator is wound in the battery manufacturing process, and the cycle characteristics of the shutdown are less likely to change when the battery is manufactured.

In the present invention, the polyolefin porous substrate preferably has crystallinity. When the polyolefin porous substrate has crystallinity, it is excellent in mechanical strength such as puncture strength when it is used as a separator, and the polyolefin flows appropriately at high temperatures to obtain good shutdown characteristics.
The crystallinity of the polyolefin porous substrate can be easily measured as the crystallinity by, for example, X-ray diffraction. The degree of crystallinity is preferably higher, preferably 30 to 80%, more preferably 40 to 70%, and still more preferably 50 to 60%.

[Polyolefin]
Examples of the polyolefin resin used for the polyolefin porous substrate include polymers obtained by polymerizing monomers such as ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, and 1-octene ( Homopolymers, copolymers, multistage polymers, etc.).
Examples of the polyolefin resin include low density polyethylene (density less than 0.93 g / cm ³ ), linear low density polyethylene, medium density polyethylene (density 0.93 to 0.94 g / cm ³ ), and high density polyethylene ( Density 0.94 g / cm ^{3 or} more), ultra high molecular weight polyethylene, isotactic polypropylene, atactic polypropylene, ethylene propylene rubber and the like.
A polyolefin resin may be used individually by 1 type, and 2 or more types may be mixed and used for it.

The polyolefin resin preferably has a weight average molecular weight (Dalton) of 50,000 to 10,000,000 from the viewpoint of improving the mechanical properties (breaking strength, scratch resistance, etc.) of the polyolefin porous substrate and / or separator. More preferably, it is 10,000 to 3,000,000. A weight average molecular weight of 50,000 or more is from the viewpoint of maintaining high melt tension during heat stretching and ensuring good moldability, or from the viewpoint of increasing the strength of the polyolefin porous substrate by imparting sufficient entanglement. preferable. On the other hand, it is preferable that the weight average molecular weight is 10 million or less from the viewpoint of realizing the production of a uniform solution and improving the sheet formability, particularly the thickness stability. Setting the weight average molecular weight to 3 million or less is preferable from the viewpoints of improving uniformity during molding and lowering stretching tension.
The weight average molecular weight is a molecular weight measured by gel permeation chromatography (GPC) and expressed in terms of polystyrene. When several polyolefin resin is used, the value measured about each polyolefin resin is meant.

As the polyolefin resin, high-density polyethylene and medium-density polyethylene are preferably used from the viewpoint of increasing the strength of the polyolefin porous substrate and / or the separator. They can be used alone or as a mixture.
Further, from the viewpoint of moldability and stretchability of the polyolefin porous substrate, it is preferable to contain 90% by mass or less of ultrahigh molecular weight polyethylene having a weight average molecular weight of 700,000 or more (preferably 800,000 to 3,000,000).
In addition, it is also preferable to use polyethylene alone from the viewpoint of improving the permeability and mechanical strength of the polyolefin porous substrate.

The polyolefin resin preferably contains a polypropylene resin from the viewpoint of securing moldability, heat resistance and permeability. The weight average molecular weight of the polypropylene resin is preferably 100,000 to 600,000, more preferably 100,000 to 500,000 from the viewpoints of ensuring moldability and ensuring moldability and permeability.
Specific examples of polypropylene include propylene homopolymer, ethylene-propylene random copolymer, and ethylene-propylene block copolymer. Among these, polypropylene homopolymer is preferably used.
In the case of using a copolymer as polypropylene, the content of ethylene as a comonomer is 1.0% by mass or less from the viewpoint of not lowering the crystallinity of polypropylene and thus not lowering the permeability of the base material. Is preferred. Moreover, in all the polypropylenes used, the ethylene content as a comonomer is preferably 1 mol% or less, and all are preferably propylene homopolymers.
The proportion of polypropylene in the polyolefin resin is preferably 1 to 40% by mass, more preferably 1 to 20% by mass, still more preferably 1 to 10% by mass, and particularly preferably 1 to 8% by mass. Setting the ratio to 1% by mass or more is preferable from the viewpoint of improving the heat resistance of the substrate or the separator. On the other hand, setting the ratio to 40% by mass or less is preferable from the viewpoint of realizing good shutdown characteristics, permeability, and puncture strength.

[Method for producing porous substrate containing polyolefin]
In the present invention, the method for producing the polyolefin porous substrate is not particularly limited, but specifically, it is preferably produced through the following steps (1) to (6). The polyolefin used for the raw material is as described above.

(1) Preparation of polyolefin solution A polyolefin solution in which polyolefin is dissolved in a solvent is prepared. 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 filtered to remove foreign substances. There are no particular restrictions on the filtration device, filter shape, mode, etc., 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 and productivity.

(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. At this time, 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-like formed product. At this time, it is preferable to rapidly cool below the gelation temperature to cause gelation. In particular, when a combination of a volatile solvent and a non-volatile solvent is used as the solvent, the cooling rate of the gel-like product 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-like product. When a volatile solvent is used, the solvent can also be removed from the gel-like product 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 product Next to the solvent removal treatment, the gel-like product is stretched. Here, a relaxation treatment may be performed before the stretching treatment. In the stretching treatment, the gel-like formed 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 production, more preferably 100 to 120 ° C. from the viewpoint of stretchability and the like. When the heating temperature is less than the melting point, the gel-like formed product is difficult to dissolve, so that the stretching can be performed satisfactorily. Further, when the heating temperature is 90 ° C. or higher, the gel-like product is sufficiently softened and can be stretched at a high magnification without being broken during stretching.

The draw ratio varies depending on the thickness of the original fabric, but is preferably at least 2 times or more, preferably 4 to 20 times in one axial direction. In particular, from the viewpoint of the purpose of the present invention and improvement of production efficiency, the draw ratio is preferably 4 to 10 times in the machine direction (MD direction) and 6 to 15 times in the vertical direction (TD direction) of the machine direction. The magnification is preferably 10 to 100 times, more preferably 20 to 80 times, and still more preferably 30 to 60 times. The ratio of the draw ratio in the MD direction and the TD direction is preferably 2/1 to 1/2, more preferably 1.5 / 1 to 1/2, still more preferably 1.2 / 1 to 1 /. 1.5. From the viewpoint of tear strength when a separator is used, the TD direction is preferably selected as the final stretching direction.
Furthermore, for the purpose of the present invention, the stretching speed is preferably 200% / second or less, and from the viewpoint of productivity, the stretching speed is 1% / second or more. More preferably, 150 to 5% / second, still more preferably 100 to 10% / second is selected.

(5) Extraction / removal of solvent The stretched gel-like product 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. Solvent extraction removes the solvent in the polyolefin porous substrate to less than 1% by weight.

(6) Annealing of polyolefin porous substrate A polyolefin porous substrate is heat-set by annealing. From the viewpoint of the heat shrinkage ratio of the polyolefin porous substrate and the tear strength when used as a separator, the annealing temperature is preferably 80 to 150 ° C, more preferably 80 ° C to 140 ° C, Preferably it is 90 to 135 ° C. The annealing time is preferably 1 minute or more from the viewpoint of reducing the thermal shrinkage rate of the polyolefin porous substrate, and can be 1 minute to 1 hour. From the viewpoint of suppressing deformation of the polyolefin porous substrate, long-time annealing is preferable. In order to further reduce the thermal shrinkage of the polyolefin porous substrate, 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 on at least one side of the polyolefin porous substrate, but from the viewpoint of the handling properties of the separator, durability, and the effect of suppressing heat shrinkage, it is on both sides of the polyolefin porous substrate. Embodiments are preferred.

In the present invention, when the heat-resistant porous layer is formed on both surfaces of the polyolefin porous substrate, the total thickness of the heat-resistant porous layer is preferably 3 μm to 12 μm, and the heat-resistant porous layer is When it is formed only on one side of the polyolefin porous substrate, the heat-resistant porous layer preferably has a thickness of 3 μm to 12 μm. Such a thickness range is preferable in terms of handling properties, durability, mechanical strength, an effect of suppressing heat shrinkage, and resistance to liquid drainage.
The total thickness of the heat resistant porous layer is preferably 10 to 80% of the thickness of the polyolefin porous substrate. When the thickness of the heat resistant porous layer is in the above range, the short circuit resistance and the shutdown efficiency are good. The total thickness of the heat-resistant porous layer is more preferably 15 to 70% of the thickness of the polyolefin porous substrate, further preferably 20 to 60%, and particularly preferably 25 to 50%. preferable.

  In the present invention, the porosity of the heat resistant porous layer is preferably from 30 to 90%, more preferably from 40 to 70%, from the viewpoint of preventing liquid withstand.

[Heat resistant resin]
In the present invention, the heat resistant resin 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 include fluorine-containing polymer compounds that swell with an electrolyte solution such as aromatic polyamide, polyimide, polyamideimide, polysulfone, polyethersulfone, polyketone, polyetherketone, polyetherimide, cellulose, and polyvinylidene fluoride. In the present invention, at least one resin selected from the group consisting of aromatic polyamide, polyimide, polysulfone, polyethersulfone, polyetherketone, polyetherimide, and polyvinylidene fluoride (PVdF) is preferable.
Such a 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.
Furthermore, such a heat-resistant resin is insoluble in the electrolyte solution, and is highly durable due to its high durability. From the viewpoint that it is easy to form a porous layer and has excellent oxidation-reduction resistance in the electrode reaction. Polymetaphenylene isophthalamide and polyparaphenylene terephthalamide, which are meta-type wholly aromatic polyamides, are more preferred, and polymetaphenylene isophthalamide is particularly preferred.

In the present invention, the molecular weight of the heat resistant resin constituting the heat resistant porous layer is, for example, polymetaphenylene isophthalamide from the viewpoint of tear strength when used as a separator, and the weight average molecular weight (Mw) (Dalton) is Preferably it is 25,000-300,000, More preferably, it is 30,000-250,000, More preferably, it is 30,000-200,000, and molecular content (Ms) (Dalton) is 1 million or more molecular content (% By mass) is preferably 10 to 30% by mass, more preferably 12 to 25% by mass, and still more preferably 15 to 25% by mass.
The weight average molecular weight (Mw) and the molecular weight (Ms) are molecular weights measured by gel permeation chromatography (GPC) and converted to polystyrene.

[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 viewpoint of elution of impurities and durability.

As an inorganic filler, what produces an endothermic reaction in 200-400 degreeC is preferable. In the nonaqueous electrolyte battery, heat generation due to 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 the heat generation of the nonaqueous electrolyte 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. Among these, metal hydroxides are preferable from the viewpoints of flame retardancy improvement effect, handling properties, static elimination effect, and battery durability improvement effect, and aluminum hydroxide or magnesium hydroxide is particularly preferable.
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 viewpoints of the electrochemical stability of the nonaqueous electrolyte battery separator, short circuit resistance at high temperature, moldability, and the like.
In this invention, it is preferable that content of the inorganic filler in a heat resistant porous layer is 50-95 mass% from a viewpoint of a heat resistant improvement effect, permeability, and handling property.
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 it is preferably formed through the following steps (1) to (5).
In order to fix the heat-resistant porous layer on the substrate, a method in which the heat-resistant porous layer is directly formed on the substrate by a coating method is preferable. A technique of adhering the quality layer sheet on the base material using an adhesive or the like, a technique such as heat fusion or pressure bonding can also be employed.

(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 amide solvent or a polar urea solvent, such as dimethyl sulfoxide, N, N-dimethylformamide, N, N-dimethylacetamide. , N-methyl-2-pyrrolidone, tetramethyl and the like. 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 porous substrate. When forming a heat resistant porous layer on both surfaces of a polyolefin porous substrate, it is preferable from a viewpoint of shortening of a process to apply simultaneously on both surfaces of a substrate. Examples of the method for coating the slurry for coating include a knife coater method, a gravure coater method, a Mayer bar method, a die coater method, a reverse roll coater method, a roll coater method, a screen printing method, an ink jet method, and a spray method. . Among these, the reverse roll coater method is preferable from the viewpoint of uniformly forming the coating layer. When applying to both surfaces of a polyolefin porous substrate at the same time, for example, by passing the substrate between a pair of Meyer bars, an excess coating slurry is applied to both surfaces of the substrate, and this is applied to a pair of reverse It is possible to employ a method of precise weighing by scraping excess slurry through a roll coater.
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 slurry By applying a slurry for coating on a polyolefin porous substrate with a coagulation liquid capable of coagulating the heat resistant resin, the heat resistant resin is coagulated and heat resistant. Forming a porous layer.
As a method of treating with the coagulating liquid, a method of spraying the coagulating liquid onto the surface coated with the coating slurry or a polyolefin porous substrate coated with the coating slurry on a bath containing the coagulating liquid (coagulating liquid) The method of immersing in bath) etc. 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 mixture of an appropriate amount of water in 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. When the mixing amount of water is 40% by mass or more, the time required for solidifying the heat-resistant resin does not become too long. In addition, the tear strength is good without generating insufficiently solidified portions. On the other hand, when the mixing amount of water is 80% by mass or less, the solidification of the surface of the heat-resistant resin layer in contact with the coagulating liquid proceeds at an appropriate rate, the surface is sufficiently porous, and the degree of crystallization is moderate. And the tear strength is good. Furthermore, the cost of solvent recovery can be kept low.
In the present invention, in order to suppress shrinkage from the viewpoint of tear strength when a separator is used, it is preferable to apply a certain tension to the base material coated with the coating slurry when treated with the coagulating liquid. Specifically, a method of holding both ends of the substrate coated with the coating slurry with a chuck and applying a constant low tension, preferably in the TD direction is exemplified.

(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 porous substrate. The drying method is not particularly limited, but the drying temperature is preferably 50 to 90 ° C., and a method of contacting with a roll in order to prevent dimensional change due to heat shrinkage, or holding both ends of the separator with a chuck or the like. It is preferable to apply a method or the like. In the drying process, by suppressing deformation in the MD direction and the TD direction, the heat-resistant porous layer can be uniformly crystallized with a uniform thickness, and various physical properties can be suitably realized.
The time for the drying treatment is preferably 2 minutes to 5 hours, more preferably 5 minutes to 3 hours, from the viewpoint of the thermal contraction rate of the separator. The drying heat treatment is also preferably carried out in an atmosphere at atmospheric pressure or lower. At this time, the treatment time can be appropriately selected between 1 minute and 10 hours.

(Separator characteristics)
The shutdown temperature of the nonaqueous electrolyte battery separator of the present invention is preferably 130 to 155 ° C. When the shutdown temperature is 130 ° C. or higher, the melt does not melt at a low temperature and the safety is high. On the other hand, when the shutdown temperature is 155 ° C. or lower, various materials of the battery are not exposed to high temperatures. The shutdown temperature is preferably 135 to 150 ° C.

The separator for a nonaqueous electrolyte battery of the present invention preferably has a total film thickness of 30 μm or less from the viewpoint of energy density when used as a battery.
The porosity of the non-aqueous electrolyte battery separator 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 separator for a nonaqueous electrolyte battery of the present invention is preferably 100 to 500 sec / 100 cc from the viewpoint of good balance between mechanical strength and membrane resistance.
The membrane resistance of the nonaqueous electrolyte battery separator of the present invention is preferably 1.5 to 10 ohm · cm ² from the viewpoint of the load characteristics of the battery.

  The puncture strength of the nonaqueous electrolyte battery separator of the present invention is preferably 250 g to 1000 g. When the pin puncture strength is 250 g or more, when the battery is used, pinholes or the like hardly occur in the separator, and the occurrence of a short circuit in the nonaqueous electrolyte battery can be suppressed.

  The separator for a nonaqueous electrolyte battery of the present invention preferably has a breaking strength of 10 N or more in both the MD direction and the TD direction, and the breaking elongation exceeds 50%. When the breaking strength and breaking elongation are within the above ranges, the separator is less likely to be damaged when the separator is wound in the battery manufacturing process, and the cycle characteristics of the shutdown are less likely to change when the battery is manufactured.

  The thermal shrinkage rate at 105 ° C. of the nonaqueous electrolyte battery separator 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%.

<Nonaqueous electrolyte battery>
The non-aqueous electrolyte battery of the present invention is a non-aqueous electrolyte battery that obtains an electromotive force by doping or dedoping lithium, and includes a positive electrode, a negative electrode, and a separator for a non-aqueous electrolyte battery having the above-described configuration. A non-aqueous electrolyte battery has a structure in which a battery element in which a negative electrode and a positive electrode face each other with a separator interposed therebetween is impregnated with an electrolytic solution, and this is enclosed in an exterior.
The nonaqueous electrolyte battery having such a configuration has a shutdown function and heat resistance, and is excellent in cycle characteristics.

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, but the nonaqueous electrolyte 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) Weight average molecular weight of polyolefin The weight average molecular weight of the polyolefin used in the present Example was measured by the following gel permeation chromatography (GPC).
To 15 mg of the sample, 20 ml of a mobile phase for GPC measurement was added, completely dissolved at 145 ° C., and filtered through a stainless sintered filter (pore size: 1.0 μm). 400 μl of the filtrate was injected into the apparatus for measurement, and the weight average molecular weight of the sample was determined.
-Apparatus: Gel permeation chromatograph Alliance GPC2000 (manufactured by Waters)
Column: manufactured by Tosoh Corporation, TSKgel GMH6-HT × 2 + TSKgel GMH6-HT × 2
Column temperature: 140 ° C
・ Mobile phase: o-dichlorobenzene ・ Detector: Differential refractometer (RI)
・ Molecular weight calibration: Tosoh Corporation monodisperse polystyrene

(2) Tear Strength The tear strength (mN / μm) of the nonaqueous electrolyte battery separator was measured by the tear strength test method specified in JIS K7128-1.
(3) Film thickness The film thickness of the polyolefin porous substrate and the separator for the non-aqueous electrolyte 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.
(4) Porosity The porosity of the heat resistant porous layer was determined according to the following calculation method.
The constituent components of the layer of interest are a, b, c,..., N, and the masses of the constituent components are Wa, Wb, Wc,..., Wn (g / cm ² ). When the density is xa, xb, xc,..., Xn (g / cm ³ ) and the film thickness of the layer of interest is t (cm), the porosity ε (%) is obtained from the following equation. It is done.
ε = {1− (Wa / xa + Wb / xb + Wc / xc +... + Wn / xn) / t} × 100

(5) Winding (cutting during winding)
The winding property of the separator for nonaqueous electrolyte batteries was evaluated using a winding machine KMW-2BY manufactured by Minato Seisakusho. Using a model electrode, the separator was rolled at a winding speed of 500 mm / sec for a total of 1000 m, and whether or not the separator was cut was confirmed. Those in which cutting did not occur were judged as good (◯), and those in which cutting occurred were judged as bad (x).

(6) Heat resistance (shutdown characteristics)
A separator for a non-aqueous electrolyte battery was punched into a circle having a diameter of 19 mm, immersed in a methanol solution in which a nonionic surfactant (Emulgen 210P manufactured by Kao Corporation) was dissolved at a concentration of 3% by mass, and air-dried. This sample was sandwiched between electrodes of two SUS plates having a thickness of 0.4 mm and a diameter of 15.5 mm, and an electrolyte solution of 1M LiBF ₄ / [propylene carbonate / ethylene carbonate (mass ratio 1/1)] solution (Kishida Chemical Co., Ltd.) was impregnated. This was enclosed in a 2032 type coin cell to form a coin type battery. I took the lead from the coin cell, put a thermocouple, and put it in the oven. The temperature inside the coin-type battery was raised at a rate of temperature rise of 1.6 ° C./min. At the same time, an alternating voltage with an amplitude of 10 mV and a frequency of 1 kHz was applied to measure the resistance value (ohm · cm ² ) of the coin-type battery. . When the resistance value reached 10 ⁴ ohm · cm ² , the shutdown was regarded as the shutdown temperature.
After the shutdown, in the temperature range from the shutdown temperature to + 20 ° C., when the resistance value is continuously 10 ⁴ ohm · cm ² or more, it is determined that the heat resistance is good (◯), and the resistance value is 10 ⁴ ohm · cm ^2. When it decreased to less than, it was determined that the heat resistance was poor (x).

(7) Charging / discharging cycle characteristics-Production of test battery-
-Preparation of positive electrode-
A powder of lithium cobaltate (LiCoO ₂ , manufactured by Nippon Chemical Industry Co., Ltd.), acetylene black, and an N-methyl-2-pyrrolidone solution of PVdF having a concentration of 6% by mass were prepared. A mixed solution was prepared so that the mass ratio (LiCoO ₂ : acetylene black: PVdF [dry mass]) was 89.5: 4.5: 6, and this was used as a positive electrode paste. The positive electrode paste was applied onto an aluminum foil having a thickness of 20 μm, dried and pressed to obtain a positive electrode having a thickness of 97 μm.
-Production of negative electrode-
As the negative electrode active material, powder of mesophase carbon microbeads (MCMB, manufactured by Osaka Gas Chemical Co., Ltd.), acetylene black, and an N-methyl-2-pyrrolidone solution of PVdF having a concentration of 6% by mass were prepared. A mixed solution was prepared so that the mass ratio (MCMB: acetylene black: PVdF [dry mass]) was 87: 3: 10, and this was used as a negative electrode paste. The negative electrode paste was applied onto a 18 μm thick copper foil, dried and pressed to obtain a 90 μm thick negative electrode.
~ Production of button battery ~
A button battery (CR2032) having an initial capacity of about 4.5 mAh was manufactured using the separator and the positive electrode and the negative electrode. As the electrolytic solution, a 1M LiPF ₆ / [ethylene carbonate / diethyl carbonate / methyl ethyl carbonate (mass ratio 1/2/1)] solution was used.
-Evaluation method-
The button battery was repeatedly charged and discharged at a charge voltage of 4.2 V and a discharge voltage of 2.75 V, and the numerical value obtained by dividing the discharge capacity at the 100th cycle by the initial capacity was taken as the capacity retention rate. The charge / discharge cycle characteristics were evaluated.
~Evaluation criteria~
A: The average value of the capacity retention rate of 10 button batteries is 85% or more. In this case, it was determined to be acceptable (◯) without any practical problem.
X: The average value of the capacity retention of 10 button batteries is less than 85%. In this case, there was a problem in practical use, and it was determined to be rejected (x).

<Preparation of raw polyethylene>
As raw materials for the polyolefin porous substrate used in Examples and Comparative Examples of the present invention, PE-1 to PE-5 polyethylene produced by the following method was used.

(Synthesis Example 1)
[Production of polyethylene PE-1]
<Preparation of solid catalyst component>
A 2-liter round bottom flask equipped with a stirrer and thoroughly substituted with nitrogen gas was charged with 100 g of diethoxymagnesium and 130 ml of tetraisopropoxytitanium, and the suspension was treated at 130 ° C. for 6 hours with stirring. . Next, after cooling to 90 ° C., 800 ml of toluene preheated to 90 ° C. was added and stirred for 1 hour to obtain a uniform solution. 90 ml of this solution was stirred at a stirring speed of 500 rpm in 150 ml of n-heptane at 0 ° C. and 50 ml of silicon tetrachloride charged in a 500 ml round bottom flask equipped with a stirrer while maintaining the temperature in the system at 0 ° C. However, it was added over 1 hour. Thereafter, the temperature was raised to 55 ° C. over 1 hour and reacted for 1 hour to obtain a white finely divided solid composition. Next, after removing the supernatant, 40 ml of toluene was added to form a slurry. To this, 20 ml of room temperature titanium tetrachloride in which 0.5 g of sorbitan distearate was previously dissolved was added with stirring, and 1.5 ml of di-n-butyl phthalate was further added to 110 ° C. over 3 hours. The temperature was raised and the treatment was performed for 2 hours. Finally, by washing 7 times with 100 ml of room temperature n-heptane, about 10 g of solid catalyst component was obtained.

<Polymerization>
700 ml of n-heptane was charged into a stainless steel autoclave with a stirrer having an internal volume of 1500 ml that was completely replaced with ethylene gas, and 0.70 mmol of triethylaluminum was charged at 20 ° C. while maintaining an ethylene gas atmosphere. Next, after raising the temperature to 70 ° C., 0.006 mmol of the solid catalyst component as titanium atoms was charged, and polymerization was carried out for 10 hours while supplying ethylene so that the pressure in the system was 5 kg / cm ² · G. After separation by filtration, it was dried under reduced pressure to obtain polyethylene powder (PE-1). The weight average molecular weight (Mw) of the obtained polymer was 6 million or more.

(Synthesis Example 2)
[Production of polyethylene PE-2]
In the polymerization of Synthesis Example 1, the same as Synthesis Example 1, except that 0.0052 mmol of the solid catalyst component was charged as titanium atom, the pressure in the system was 3.8 kg / cm ² · G, and the polymerization time was 3 hours. Thus, polyethylene powder (PE-2) was obtained. The weight average molecular weight (Mw) of the obtained polymer was 2,040,000.

(Synthesis Example 3)
[Production of polyethylene PE-3]
Silica (W.R Grace and Company grade 952) was loaded with 1.0 mass% chromium trioxide and calcined at 800 ° C. to obtain a solid catalyst. This solid catalyst was put into a polymerization vessel (reaction volume 170 L), and an organoaluminum compound obtained by reacting methanol and aluminum trihexyl in a molar ratio of 0.92: 1 had a concentration of the compound in the polymerization vessel of 0. 0. It was supplied at a rate of 0.7 g / hr so as to be 08 mmol / l. Subsequently, purified hexane is supplied to the polymerization vessel at a rate of 60 L / hr, ethylene is supplied at a rate of 12 kg / hr, and hydrogen is supplied as a molecular weight regulator so that the gas phase concentration becomes 2.5 mol%. Polymerization was performed. The polymer in the polymerization vessel was obtained as a pellet after passing through a drying step and a granulation step. The obtained polymer (PE-3) had a weight average molecular weight (Mw) of 420,000.

(Synthesis Example 4)
[Production of polyethylene PE-4]
In the polymerization of Synthesis Example 1, the same as Synthesis Example 1 except that 0.0048 mmol of titanium catalyst was used as the solid catalyst component, the pressure in the system was 4 kg / cm ² · G, and the polymerization time was 1.5 hours. Thus, polyethylene powder (PE-4) was obtained. The weight average molecular weight (Mw) of the obtained polymer was 810,000.

(Synthesis Example 5)
[Production of polyethylene PE-5]
Polyethylene (PE-5) was obtained in the same manner as in Synthesis Example 3 except that the hydrogen gas phase concentration was adjusted to 2.8 mol%. The weight average molecular weight (Mw) of the obtained polymer was 290,000.

<Manufacture of polyolefin porous substrate>
(Production Example 1)
PE-1, PE-2 and PE-3 were mixed at a ratio of 7.2 / 45 / 47.8 (parts by mass). Using this polyethylene mixture, it is dissolved in a mixed solvent of liquid paraffin (Smoyl P-350P, boiling point 480 ° C. by Matsumura Oil Research Co., Ltd.) and decalin so that the polyethylene concentration becomes 30% by mass to prepare a polyethylene solution. did. The composition of this polyethylene solution was polyethylene: liquid paraffin: decalin = 30: 45: 25 (mass ratio).
This polyethylene solution was extruded from a die at 148 ° C. and cooled in a water bath to prepare a gel tape (base tape). This base tape was dried at 60 ° C. for 8 minutes and at 95 ° C. for 15 minutes. Subsequently, the base tape was stretched by biaxial stretching in which longitudinal stretching and lateral stretching were sequentially performed, and heat setting was performed at 125 ° C. after the lateral stretching to obtain a sheet. Here, the longitudinal stretching (MD direction) was a stretching ratio of 5.5 times and a stretching temperature of 90 ° C., and the transverse stretching (TD direction) was a stretching ratio of 11 times and a stretching temperature of 105 ° C.
Next, the sheet obtained above was immersed in a methylene chloride bath to extract and remove liquid paraffin and decalin. Then, it dried at 50 degreeC and annealed at 120 degreeC, and obtained the polyethylene porous base material. This polyethylene porous substrate could be produced satisfactorily without any operational problems in film formation, stretching and post-treatment. Hereinafter, this polyethylene porous substrate may be abbreviated as PO1.

(Production Examples 2 to 5)
Polyethylene porous substrates PO2 to PO5 were obtained in the same manner as in Production Example 1 except that the mixing ratio of PE-1 to PE-5 and the draw ratio were changed as shown in Table 1. PO2 to PO5 could be satisfactorily produced without any operational problems in film formation, stretching and post-treatment.

<Manufacture of heat-resistant resin>
(Polymerization example 1)
[Polymerphenylene isophthalamide polymerization by interfacial polymerization]
A solution was prepared by dissolving 160.5 g of isophthalic acid chloride in 1120 ml of tetrahydrofuran. Separately, 85.2 g of metaphenylenediamine was dehydrated and dried with a molecular sieve and dissolved in 1120 ml of tetrahydrofuran to prepare a solution. While stirring the former solution, the latter solution was gradually added as a trickle to obtain a cloudy milky white solution. Stirring was continued for about 5 minutes. Then, with further stirring, an aqueous solution in which 167.6 g of sodium carbonate and 317 g of sodium chloride were dissolved in 3400 ml of water was quickly added, and the mixture was stirred for 5 minutes. The reaction increased in viscosity after a few seconds and then decreased to give a white suspension. This was allowed to stand, and the separated transparent aqueous solution layer was removed and filtered to obtain 185.3 g of polymetaphenylene isophthalamide (hereinafter sometimes referred to as PMIA (1)).
PMIA (1) had a weight average molecular weight (polystyrene equivalent) (Dalton) of 75,000, and the content of molecules having a molecular weight of 1 million or more was 20% by mass.

<Manufacture of separators for non-aqueous electrolyte batteries>
Example 1
-Preparation of slurry for coating heat resistant porous layer-
PMIA (1) of Polymerization Example 1 and magnesium hydroxide having an average particle diameter of 0.8 μm (Kisuma Chemical Kisuma 5P) were prepared as inorganic fillers. Dimethylacetamide (DMAc) and tripropylene glycol so that the mixing ratio of the two (PMIA (1): magnesium hydroxide) is 50:50 (mass ratio) and the concentration of PMIA (1) is 5.5% by mass. It was mixed with a mixed solvent (DMAc: TPG = 50: 50 [mass ratio]) with (TPG) to prepare a slurry for coating.

-Formation of heat-resistant porous layer-
An appropriate amount of the slurry for coating was placed on a pair of Meyer bars (count # 6) facing each other with a clearance of about 20 μm. The polyethylene porous substrate PO1 was passed between Mayer bars, and the slurry for coating was applied to both sides of PO1 without rotating the Mayer bar (non-rotating method). Then, both ends of the coated separator were held with a chuck and immersed in a coagulating liquid (water: DMAc: TPG = 50: 25: 25 [mass ratio]) at 40 ° C. Next, washing with water and drying were performed to obtain a separator for a non-aqueous electrolyte battery in which a heat-resistant porous layer (both sides each 3 μm) was provided on both sides of PO1.

(Example 2)
In Example 1, PMIA (1) was changed to polyvinylidene fluoride (Kynar 720), magnesium hydroxide (Kisuma 5P manufactured by Kyowa Chemical Co., Ltd.) was not used, and the polyethylene porous substrate PO1 was changed to PO2, and the heat resistant porous material was changed. A separator for a nonaqueous electrolyte battery was obtained in the same manner as in Example 1 except that the thickness of each layer was 2 μm on both sides.

(Comparative Examples 1-3)
A separator for a nonaqueous electrolyte battery was obtained in the same manner as in Example 1 except that the polyolefin porous substrate was changed as shown in Table 2.

  As can be easily understood from Table 2, the separators of Example 1 and Example 2 according to the present invention have a tear strength within a suitable range, and the cutting during winding is suppressed and the heat resistance is excellent.

  The separator for a nonaqueous electrolyte battery according to the present invention is suitable for lithium secondary battery applications because cutting at the time of winding is suppressed and heat resistance is excellent.

Claims (3)

A porous substrate containing polyolefin; and a heat-resistant porous layer containing a heat-resistant resin provided on one or both surfaces of the porous substrate,
A non-aqueous electrolyte in which the lower one of the tear strength in the length direction and the tear strength in the width direction is 0.5 mN / μm or more and 5 mN / μm or less as measured by the test method specified in JIS K7128-1 Battery separator.   The non-water according to claim 1, wherein the heat-resistant resin is at least one selected from the group consisting of aromatic polyamide, polyimide, polysulfone, polyethersulfone, polyetherketone, polyetherimide, and polyvinylidene fluoride. Electrolyte battery separator.   A non-aqueous electrolyte comprising a positive electrode, a negative electrode, and the non-aqueous electrolyte battery separator according to claim 1 disposed between the positive electrode and the negative electrode, wherein an electromotive force is obtained by doping or dedoping lithium. Electrolyte battery.