JPH11329392A - Nonaqueous electrolyte separator and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To cause no absorptive problem, ensure a high heat resistance, and keep a sufficient affinity with respect to electrolyte under a high temperature by sticking a polymer being a wetting improver having a specified level or less of melt flow rate and a critical surface tension to a surface of fine structure of a polymer porous film of a substrate. SOLUTION: This is a nonaqueous separator where a polymer having a melt flow rate of 15 g/min. or less and a critical surface tension of (28 deg.C) 28 dyn/cm or less is stuck to a fine structural surface. Preferably, the polymer is selected from one kind or more of vinyliden homopolymer, vinyliden/olefin fluoride copolymer, vinyl fluoride homopolymer, and vinyl fluoride/olefine fluoride copolymer, while the separator has the porous film of polytetrafluoroethylene, and the separator has a polyolefin porous layer at least one surface thereof. The porous layer shows a shutdown function to lose the porous structure caused by fusion and compression or shrinkage when it is heated with an abnormal current.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte separator used as a battery separator, a capacitor separator and the like, a surface treating agent for producing the same, and a method for producing the non-aqueous electrolyte separator.

[0002]

2. Description of the Related Art Conventionally, porous materials or thin sheet-like porous films, woven fabrics, nonwoven fabrics, papers, and the like have been used for battery separators, filtration filters, and the like. As the demands for these uses become more sophisticated, higher strength, smaller pore size, higher permeability, etc. are required for the porous body. In addition, various types of batteries have been put to practical use in the field of batteries, in particular, in which progress has been remarkable in recent years.

[0003] Among them, a lithium battery has been put to practical use as a battery for a portable electronic device such as a mobile phone or a notebook personal computer because of its high energy density and high electromotive force. In addition, as a means to solve environmental issues and energy issues that have been actively discussed in recent years,
The use of high-performance lithium batteries for batteries for electric vehicles such as HEVs and large storage batteries for power storage is also being studied.

In such a battery, an external short circuit or a positive
If an abnormal current flows due to improper connection or misuse of the negative electrode, the temperature inside the battery rises significantly due to heat generation,
There is a risk that the device incorporating the battery may be thermally damaged. Therefore, when an abnormal current flows and heat is generated in the separator built in the battery as described above, the porous structure is lost due to melting and compression or shrinkage, etc., and the battery reaction is stopped. A shutdown (hereinafter referred to as "SD") characteristic for preventing dangers such as smoking and ignition is required. Further, in order to further secure safety when a lithium battery has higher performance and larger size, a higher SD speed and a lower SD start temperature are required for the separator.

[0005]

However, the above S
The D function alone is not sufficient. For example, in a large battery for electric power storage or a battery for an electric vehicle, the temperature rises further under the above-mentioned circumstances, so that contact between the electrodes due to melting of the separator at a high temperature is reduced. Heat resistance for prevention is also required. For this reason, for example, Japanese Patent Application Laid-Open No. 7-60084 discloses a method for producing a polyolefin-based porous membrane comprising at least a mixture of polyethylene and polymethylpentene, but the melting point of polymethylpentene (about 240 ° C.) or higher is used. At this temperature, the membrane breaks down, so it cannot be said that safety is sufficient.

As a porous film that can withstand use in such a high temperature environment, polytetrafluoroethylene (hereinafter referred to as “P
It is known to use a porous film using a fluororesin material represented by "TFE"). However, when the above material is used for a non-aqueous solvent electrolyte, the material has a low surface tension (critical surface tension (20 ° C.) 18 dyn / cm).
For this reason, a phenomenon such as poor affinity with the electrolytic solution and impermeability of the electrolytic solution occurs, and the electrolyte cannot be used as it is, so that a lyophilic lyophilic treatment (hereinafter referred to as “lyophilic treatment”) is required. .

[0007] As one of the treatment methods, there is known a method of immersing a surfactant in a solution and then removing the solvent to attach the surfactant to the porous film. However,
In this method, especially in a system where the environment is used at a higher temperature than a secondary battery used for consumer use, such as a large battery, a dropout of a surfactant or the like causes The affinity is lost, and the battery does not function as a battery separator.

[0008] A hydrophilic fluororesin porous material obtained by attaching a copolymer of a fluorine-containing monomer and a hydrophilic group-containing monomer has also been reported (JP-A-7-1927).
In the case of a lithium battery, water is particularly strictly prohibited, and the fact that the separator is water-absorbing also affects the safety of the battery.

Accordingly, an object of the present invention is to solve the above problems, to reduce the problem of water absorption, to have high heat resistance,
An object of the present invention is to provide a separator for a non-aqueous electrolyte, which can sufficiently maintain an affinity for an electrolyte even when used at a high temperature, a surface treatment agent for producing the same, and a method for producing the separator for a non-aqueous electrolyte.

[0010]

Means for Solving the Problems The present inventors have intensively studied various surface treatment agents to achieve the above object, and found that the melt flow rate was 15 g / min. The present invention has been accomplished by finding that the above object can be achieved by using a surface treatment agent containing a polymer having a critical surface tension (20 ° C.) of 28 dyn / cm or less. .

That is, the separator for a non-aqueous electrolyte according to the present invention is a separator for a non-aqueous electrolyte in which a polymer as a wettability improver is adhered to the surface of a microstructure of a polymer porous membrane as a substrate. In the above, the polymer has a melt flow rate of 15 g / min. And critical surface tension (20
C) is 28 dyn / cm or less.

In the above, the material of the polymer porous membrane serving as the base material and the type of the polymer are exemplified by various types as described later, and the material of the polymer porous membrane is critical. A fluororesin having a surface tension (20 ° C.) of 23 dyn / cm or less, wherein the polymer is vinylidene fluoride homopolymer, vinylidene fluoride / olefin copolymer, vinyl fluoride homopolymer, and vinyl fluoride It is preferable that the main component is one or more selected from the group consisting of a fluorinated olefin copolymer.

The nonaqueous electrolyte separator of the present invention may be a single-layer film or a composite film, but is preferably a composite film having a polyolefin porous layer on at least one surface.

The material of the porous membrane is exemplified by various materials as described below, and is preferably polytetrafluoroethylene.

On the other hand, the surface treatment agent of the present invention contains a polymer which is a wetting agent and a solvent for improving the wettability of the base polymer porous membrane of the non-aqueous electrolyte separator. , The polymer has a melt flow rate of 15 g / min. And a critical surface tension (20 ° C.) of 28 dyn / cm or less.

On the other hand, in the production method of the present invention, after the surface treatment of the polymer porous membrane with a surfactant in advance, the solvent is removed while the surface treating agent is in contact with and held therein,
The polymer is caused to adhere to the surface of the microstructure of the polymer porous membrane.

In the above, as the surfactant,
Although various types are exemplified as described below, it is preferably a fluorine-based surfactant.

The non-aqueous electrolyte separator of the present invention includes a non-aqueous electrolyte separator obtainable by the above-described production method, but is substantially the same as that obtained by the above-mentioned production method. As long as they are the same, they are not limited to those obtained by such a manufacturing method.

[Effect] According to the separator for a non-aqueous electrolyte of the present invention, in addition to having a small problem of water absorption, it has high heat resistance, The affinity with the electrolytic solution can be sufficiently maintained even when used below. That is, the melt flow rate is 15 g
/ Min. Or less, and a polymer having a critical surface tension (20 ° C.) of 28 dyn / cm or less has a low affinity for a non-aqueous electrolyte because of its low critical surface tension, and has sufficient affinity with a non-aqueous electrolyte. It is considered that the stability of the adhered state and the heat resistance are high and the polymer does not easily fall off even at a high temperature, so that the affinity with the electrolytic solution can be sufficiently maintained.

The material of the polymer porous membrane is a fluororesin having a critical surface tension (20 ° C.) of 23 dyn / cm or less, and the polymer is a vinylidene fluoride homopolymer, a vinylidene fluoride / fluorinated olefin copolymer. The reason why the main component is preferably one or more selected from the group consisting of a polymer, a vinyl fluoride homopolymer, and a vinyl fluoride / fluorinated olefin copolymer is as follows.
That is, a fluororesin porous membrane having a critical surface tension (20 ° C.) of 23 dyn / cm or less has high heat resistance, but is hardly wetted by a normal nonaqueous electrolyte, and is composed of vinylidene fluoride homopolymer, vinylidene fluoride / fluorine. By attaching a polymer mainly composed of one or more selected from the group consisting of a fluorinated olefin copolymer, a vinyl fluoride homopolymer, and a vinyl fluoride / fluorinated olefin copolymer, Due to the high molecular weight, the stability of the adhered state is high, and the polymer is less likely to fall off. In addition, these polymers have a high affinity for non-aqueous electrolytes, are suitable for heat resistance, and have high chemical and physical stability to non-aqueous electrolytes. It is considered that the affinity with the liquid can be sufficiently maintained.

When the separator for a non-aqueous electrolyte of the present invention has a polyolefin porous layer on at least one side, when heat is generated due to an abnormal current or the like, the porous structure is melted and compressed or contracted to lose its porous structure.
D) Function can be exhibited. At that time, as shown in the results of the examples described below, the adhesion of the polymer of the present invention,
There is no particular hindrance to the SD function.

When the material of the porous film is polytetrafluoroethylene, heat resistance as a substrate, film forming property,
In addition to the good solvent resistance, the effect of the surface treatment with the polymer is high, and the present invention is particularly advantageous.

On the other hand, according to the surface treating agent of the present invention, since the above-mentioned polymer is contained, a separator for a non-aqueous electrolyte which can obtain the above-mentioned effects can be suitably produced. .

On the other hand, according to the production method of the present invention, since the polymer porous membrane has been previously surface-treated with a surfactant,
The wettability with the above surface treatment agent is improved, and the subsequent treatment can be performed satisfactorily and reliably. Then, in a state where the surface treatment agent is in contact with and held therein, the solvent is removed, and the polymer is attached to the surface of the microstructure of the polymer porous membrane. The separator for non-aqueous electrolyte which can be manufactured can be manufactured suitably.

When the surfactant is a fluorine-based surfactant, the fluorine-based surfactant has a high heat resistance, a good affinity with the porous film of the base material, a high adhesion, and a more reliable The above manufacturing method can be easily performed.

The separator for a non-aqueous electrolyte obtained by the above production method has a high initial wettability improving effect because both the surfactant and the polymer are adhered to the porous substrate film. At the same time, the effect can be maintained for a longer time.

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION The separator for a non-aqueous electrolyte, a surface treating agent, and a method for producing the separator for a non-aqueous electrolyte according to the present invention will be described below in order.

(Separator for non-aqueous electrolyte solution of the present invention) As the material of the polymer porous membrane serving as a substrate, any of various polymer materials capable of forming a membrane can be used.
It is a fluororesin having a critical surface tension (20 ° C.) of 23 dyn / cm or less, and preferably a fluororesin of 20 dyn / cm or less in consideration of the relative height of the wettability improving effect. More specifically, polytetrafluoroethylene P
Examples include TFE (18 dyn / cm), poly (ethylene hexafluoride) propylene (16 dyn / cm), and poly (ethylene trifluoride) (22 dyn / cm). For the above-mentioned reason, PTFE is most suitable.

The pore size and thickness of the porous membrane serving as the base material are appropriately determined according to the characteristics required for the separator as described later.

The polymer which is a wetting agent has a melt flow rate of 15 g / min. And the critical surface tension (20 ° C.) is 28 dyn / cm or less, but vinylidene fluoride homopolymer (PVDF), vinylidene fluoride / olefin copolymer, vinyl fluoride homopolymer, And those mainly composed of at least one member selected from the group consisting of vinyl fluoride / fluorinated olefin copolymers are preferred for the above-mentioned reasons. Examples of the vinylidene fluoride / olefin copolymer include at least one copolymer selected from vinylidene fluoride and vinyl fluoride, ethylene trifluoride, ethylene tetrafluoride, propylene hexafluoride, and the like. . The vinyl fluoride / fluorinated olefin copolymer also includes one or more copolymers selected from vinyl fluoride and ethylene trifluoride, ethylene tetrafluoride, propylene hexafluoride, and the like. Among them, it is most preferable to use a vinylidene fluoride homopolymer. As can be seen from the fact that vinylidene fluoride homopolymer is actually used also as a binder of an active material of a lithium ion battery, solvent resistance to an electrolyte, wettability as well as thermal stability, non-reducing properties,
It has excellent non-oxidizing properties and is suitable for use in lithium batteries.

The melt flow rate of the polymer is 15 g
/ Min. The following (according to JIS K 7210) is preferred. Melt flow rate is 15 g / min. If it exceeds, dispersion (dropping) into the electrolyte tends to easily occur due to heating or the like.

The separator for a non-aqueous electrolyte of the present invention preferably has a polyolefin porous layer on at least one surface as described above. The mode of forming the polyolefin porous layer is as follows. And those in which a porous layer is directly formed on a porous substrate film. Examples of the material for the polyolefin porous layer include polypropylene, polymethylpentene, ultrahigh molecular weight polyethylene, and high-density polyethylene alone or as a mixture. Further, a structure in which a polyolefin porous membrane is laminated via an adhesive porous layer may be used.In this case, the adhesive porous layer may be a thermoplastic elastomer, polypropylene, ultra high molecular weight polyethylene, high density polyethylene,
A simple substance or a mixture of low-density polyethylenes may be used. These may be separately produced and then laminated, or both may be integrally extruded and produced together, and may be employed as appropriate. The method for making each forming material porous is not particularly limited, and examples thereof include a method by stretching and a method by solvent extraction.

The features of the battery separator and the like corresponding to the non-aqueous electrolyte separator of the present invention will be described below. The porosity of the separator is preferably 10 to 90%, more preferably 30 to 70%. If the porosity is less than 10%, the amount of the electrolyte impregnated is small, and the internal resistance of the battery tends to increase. If the porosity exceeds 90%, the mechanical strength tends to decrease, and there is a tendency that problems occur in terms of workability and winding properties during battery assembly. The thickness of this battery separator is 5
To 100 μm, more preferably 1 to 100 μm.
5 to 50 μm. If it is less than 5 μm, the mechanical strength of the separator becomes weak, and short-circuiting may easily occur. On the other hand, if it exceeds 100 μm, the electric resistance tends to be high, and it tends to be difficult to function as a separator. The electrical resistance per sheet of the separator is preferably 10 Ω · cm ² or less, more preferably 5 Ω · cm ² or less. Also, 70
The electric resistance change rate after 72 hours in an atmosphere of
Preferably it is less than 00%. The type and concentration of the non-aqueous solvent and solute of the target non-aqueous electrolyte are appropriately selected according to the type of the battery and the like and required characteristics.

A series of production methods for a nonaqueous electrolyte separator having a porous polyolefin layer will be described below. The production method is roughly divided into steps of producing a polyolefin porous membrane and a fluorine-based resin porous membrane, laminating these porous membranes, and attaching polyvinylidene fluoride and the like.

The polyolefin-based porous membrane is formed, for example, by forming a polyolefin-based resin into a sheet while heating and melting the sheet, heat-treating the sheet to increase the crystal orientation, and then stretching the sheet in only one axis or in two axes. can get. Fluororesin porous membranes are described, for example, in JP-B-58-25332, JP-B-51-18991, and JP-B-42-13.
It can be obtained by a stretching method described in, for example, Japanese Patent Publication No. 560 or the like.

As a method of laminating the fluororesin porous film and the polyolefin porous film, a method by heat fusion or the like can be considered. At this time, it is preferable from the viewpoint of membrane permeability and the like to perform the lamination by setting the pressure to such an extent that the collapse does not occur. Further, the aforementioned adhesive porous layer may be interposed.

As a method for attaching polyvinylidene fluoride or the like to the composite porous membrane or the like, the production method of the present invention is suitable, and this will be described later, but is not limited to this method. These adhesion treatments may be performed by treating the fluororesin porous membrane and then laminating it with a polyolefin porous membrane, or by laminating these membranes and then treating them.

(Surface Treatment Agent of the Present Invention) The surface treatment agent of the present invention contains a polymer as a wettability improver and a solvent thereof, and is used as a base polymer porous membrane for a non-aqueous electrolyte separator. In the surface treatment agent for improving wettability, the polymer has a melt flow rate of 15 g / min. And a critical surface tension (20 ° C.) of 28 dyn / cm or less, which is suitably used for producing the separator of the present invention. Accordingly, the types of the base polymer porous membrane and the polymer are the same as described above, and only different points will be described.

Examples of the solvent for the polymer include dimethylacetamide (hereinafter referred to as "DMAc") and N-methylpyrrolidone (hereinafter referred to as "NMP") having good solubility such as polyvinylidene fluoride. The concentration of polyvinylidene fluoride or the like is preferably 0.1 to 10% by weight in DMAc or NMP at the time of use, and more preferably 1 to 5% by weight.

(Production Method of the Present Invention) In the production method of the present invention, after the surface treatment of the polymer porous membrane with a surfactant in advance, the solvent Is removed to allow the polymer to adhere to the surface of the microstructure of the polymer porous membrane, and is suitably used for producing the separator of the present invention. Therefore, the components and compositions of the surface treatment agent are as described above, and only the differences will be described.

Preliminary surface treatment with a surfactant is performed because the surface treatment agent has poor permeability to a fluororesin porous membrane or the like, and the above-described effects can be obtained. Examples of the surfactant include an aliphatic higher alcohol-based surfactant, a sulfone-based surfactant, a fluorine-based surfactant, and the like, and it is preferable to use a fluorine-based surfactant for the above-described reason. In particular, a perfluoroalkyl-based surfactant having 10 to 25 carbon atoms is preferable. The method of the surface treatment with the surfactant is not particularly limited.
After dilution to 10% by weight, preferably 1-5% by weight,
A method of immersing the fluororesin porous membrane in a surfactant solution or applying the solution and drying the membrane is conceivable. The organic solvent used for the dilution is not particularly limited, but, for example, ethanol, isopropyl alcohol and the like are preferably used.

On the other hand, as a method for bringing the surface treating agent of the present invention into contact with and holding on the porous membrane, a dipping method, application by spraying or the like is preferable, but from the viewpoint of reducing the volatilization of the solvent component. The dipping method is preferably used. By using the surface treatment agent as described above, the treatment agent can penetrate into the inside by capillary action due to contact with the fluororesin porous membrane or the like. In addition, as a method for removing the solvent, various drying methods and solvent extraction methods may be mentioned, such as drying temperature and time, depending on the type of the solvent,
It is set appropriately.

[0043]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment showing the specific structure and effect of the present invention will be described below. In addition, the physical property value shown below is a value measured as follows.

[Air permeability] According to JIS K-8117,
Gurley type densometer No. manufactured by Yasuda Seiki Seisakusho 32
Using 3-Auto, the membrane area of 642 mm ² was changed to 10 cc of air.
Was measured, and the value was determined by multiplying the value by 10 times.

[Porosity] 15.45 cm of five samples stacked on top of each other
² and the thickness and weight of the five sheets were measured and calculated from the density of the porous membrane and the battery separator.

[Thickness] The thickness was measured with a dial gauge of 1/1000 mm.

[Membrane Resistance] The porous membrane and the battery separator were cut into a square having a side of about 50 mm, and five samples were stacked on each other to form a resistance meter (Hewlett Packa).
10kHz by 4262A LCR meter manufactured by rd
Is measured and the electrical resistance R (Ω ·
cm ² ) was calculated.

R = (Rb−Ra) × S In the formula, Ra is the electric resistance value (Ω) of the electrolytic solution (liquid temperature 20 ° C.), and Rb is the electric resistance value measured with the sample immersed in the electrolytic solution. (Ω) and S are the area (cm ² ) of the sample.
As the electrolytic solution, a solution obtained by dissolving anhydrous lithium perchlorate so as to have a concentration of 1M as an electrolytic solution in a solution obtained by mixing propylene carbonate and 1,2-dimethoxyethane in equal amounts was used. The details of the measurement state are shown in FIG.
Denotes a sample holder, 2 denotes a polypropylene cell, 3 denotes a thermostat, 4 denotes a platinum electrode, 5 denotes an electrolytic solution, and 6 denotes a sample.

[SD Characteristics] A porous membrane immersed in an electrolytic solution was fixed so that the length in the stretching direction was constant, and this was sandwiched between platinum electrodes, and a thermocouple was sandwiched therebetween. I do. The platinum electrode is connected to a resistance meter (KCR-535C, manufactured by Kokuyo Denki Kogyo Co., Ltd.), and the thermocouple is connected to a digital multimeter. This cell was placed in a dryer maintained at a predetermined temperature, and the AC resistance at 1 kHz was measured at each temperature while heating for several tens minutes. In this specification, the temperature when the electric resistance exceeds 100 Ω · cm 2 is referred to as “SD start temperature”. As the electrolytic solution, a solution obtained by dissolving lithium borofluoride to a concentration of 1 M as an electrolyte in a solution obtained by mixing propylene carbonate and 1,2-dimethoxyethane in equal volumes was used. The details of the cell are shown in FIG. 2, where 11 is a thermocouple and 12 is PTFE.
Reference numeral 13 denotes a nonwoven fabric, 14 denotes a platinum electrode, 15 denotes a silicone rubber packing, 16 denotes a platinum wire, and 17 denotes a sample.

[Resistivity of Resistance] After fixing the four sides of the sample to a jig and holding it in a dryer set at a temperature of 70 ° C. for 72 hours, the electrical resistance of the film of the sample was measured. It calculated by the formula of.

Resistance change rate (%) = (Rd−Rc) / Rc × 100 In the formula, Rc is the electric resistance of the film of the sample before storage at 70 ° C., and Rd is stored in a drier at 70 ° C. for 72 hours. This is the electrical resistance of the film of the later sample.

[Heat-Resistant Film Shape Retention] One side of a sample was fixed to a jig and placed in a drier in which the temperature was set to each temperature shown in Table 1.
After the sample was held for 5 minutes, the sample was evaluated for shape retention.

(Example 1) A two-layer laminated porous body obtained by co-extrusion of high-density polyethylene and polypropylene and then heat-treating to increase the crystal orientation was stretched to obtain a PTFE porous membrane (NTF-1033) manufactured by Nitto Denko Corporation. One side was laminated so that the polyethylene surface and the PTFE film faced each other. This composite porous membrane is immersed in a 2% by weight solution of a fluorinated surfactant (Unidyne DS-401, manufactured by Daikin Industries, Ltd.) in isopropyl alcohol and dried, and then PVDF (K, manufactured by Kureha Chemical Co., Ltd.)
F- # 1100, melt flow rate 4 g / min. )
Was immersed in a 2% by weight solution of NMP and dried in the same manner. This was further dried in a vacuum dryer at 60 ° C.

Example 2 The polyolefin-based porous membrane used in Example 1 was replaced with a Nitto Denko PTFE porous membrane (N
TF-1033) was laminated on both sides such that the polyethylene surface and the PTFE film faced each other. This composite porous membrane was impregnated with a fluorine-based surfactant and PVDF and dried in the same manner as in Example 1.

(Example 3) A porous film obtained by extruding a high-density polyethylene and then heat-treating to increase the crystal orientation was stretched to obtain a PTFE porous film (NTF-1 manufactured by Nitto Denko Corporation).
033). This composite porous membrane was impregnated with a fluorine-based surfactant and PVDF and dried in the same manner as in Example 1.

Comparative Example 1 The composite porous membrane used in Example 1 was immersed in a 2% by weight solution of the same fluorinated surfactant as in Example 1 and dried.

Comparative Example 2 10 parts by weight of ultra-high molecular weight polyethylene having a viscosity average molecular weight of 2,000,000 and 5 parts by weight of high-density polyethylene were mixed with 85 parts by weight of decalin, and heated and stirred to prepare a uniform solution. Rolled on a roll at a temperature of 140 ° C., formed into a sheet having a thickness of 100 μm, then immersed in methanol at 30 ° C. to extract decalin, and then contacted with a hot roll at a temperature of 70 ° C. to dry the solvent It produced by doing.

(Comparative Example 3) A polypropylene sheet formed by extrusion molding was heated to increase the crystal orientation, and then formed into a film by stretching.

Comparative Example 4 In Example 1, the melt flow rate was 4 g / min. A separator was obtained in the same manner as in Example 1 except that PVDF having a melt flow rate of 18 g / min was used instead of using PVDF.

(Comparative Example 5) In Example 1, PVDF was used.
A separator was obtained in the same manner as in Example 1, except that polyethylene having a weight average molecular weight of 5000 was used instead of

Tables 1 and 2 show the results of the above examples and the like.

[0062]

[Table 1]

[Table 2] As shown in the results of Tables 1 and 2, according to the separators of Examples, the rate of change in film resistance could be kept small without impairing the SD function or the like. On the other hand, in the case where only the surfactant treatment was performed (Comparative Example 1), since the surfactant was dropped, the film resistance change rate was large, the wettability to the electrolytic solution could not be maintained, and the fluorine When the resin porous membrane was not used as a substrate (Comparative Examples 2 and 3), the heat-resistant shape retention at high temperatures was insufficient. In the case of using PVDF having a large melt flow rate (Comparative Example 4),
The rate of change in membrane resistance is large, the wettability to the electrolyte cannot be sufficiently maintained, and even in the case of using polyethylene (Comparative Example 5), the rate of change in membrane resistance is slightly large, and high temperature use (70 ° C.)
In this case, the wettability to the electrolyte could not be sufficiently maintained.

The separator having a polyolefin porous layer as described above among the separators of the present invention has an SD function and has a high temperature exceeding 200 ° C. when it generates heat due to an internal short circuit of a battery. It prevents direct contact between the positive electrode and the negative electrode, and has excellent heat resistance.
Further, during normal use, the resistance is hardly reduced even in a use environment at 70 ° C., and the composition has excellent high-temperature preservability. Thus, the separator of the present invention has excellent characteristics and is useful as a separator for batteries such as lithium ion secondary batteries.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a measurement state of a film resistance in an embodiment.

FIG. 2 is a schematic configuration diagram showing a cell for measuring SD characteristics in an embodiment.

[Explanation of symbols]

 Reference Signs List 1 sample holder 2 polypropylene cell 3 constant temperature bath 4 platinum electrode 5 electrolytic solution 6 sample 11 thermocouple 12 PTFE plate 13 nonwoven fabric 14 platinum electrode 15 silicon rubber packing 16 platinum wire 17 sample

Claims (8)

[Claims] 1. A non-aqueous electrolyte separator in which a polymer as a wettability improving agent is adhered to a fine structure surface of a polymer porous membrane serving as a base material, wherein the polymer has a melt flow rate. 15 g / min.
And the critical surface tension (20 ° C.) is 28 dyn
/ Cm or less, a separator for a non-aqueous electrolyte. 2. The polymer which is a wetting property improving agent is a vinylidene fluoride homopolymer, a vinylidene fluoride / fluorinated olefin copolymer, a vinyl fluoride homopolymer, or a vinyl fluoride / fluorinated olefin copolymer. 2. The non-aqueous electrolyte separator according to claim 1, wherein the separator mainly comprises at least one member selected from the group consisting of polymers. 3. The non-aqueous electrolyte separator according to claim 1, which has a polyolefin porous layer on at least one surface. 4. The non-aqueous electrolyte separator according to claim 1, wherein the material of the polymer porous membrane is polytetrafluoroethylene. 5. A surface treatment agent for improving the wettability of a base polymer porous membrane of a separator for a non-aqueous electrolyte, comprising a polymer as a wettability improver and a solvent thereof, The coalescence has a melt flow rate of 15 g / min.
And the critical surface tension (20 ° C.) is 28 dyn
/ Cm or less. 6. After the surface treatment of the polymer porous membrane with a surfactant in advance, the solvent is removed in a state where the surface treatment agent according to claim 5 is kept in contact with the polymer porous membrane, and the polymer is removed. A method for producing a separator for a non-aqueous electrolyte, which is attached to the surface of the microstructure of the polymer porous membrane. 7. The method according to claim 6, wherein the surfactant is a fluorine-based surfactant. 8. A non-aqueous electrolyte separator obtainable by the production method according to claim 6. Description: