JP2011108515A - Separator for nonaqueous secondary battery, and nonaqueous secondary battery employing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a separator capable of improving cycle characteristics of battery and preventing sufficiently gas swelling of the battery. <P>SOLUTION: The separator for a nonaqueous secondary battery has a fluorine-based compound layer of a thickness of 1 nm-500 nm on the surface of the separator. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a separator for a non-aqueous secondary battery and a non-aqueous secondary battery using the same, and particularly to a technique for improving battery characteristics.

  Non-aqueous secondary batteries represented by lithium ion secondary batteries have a high energy density and are widely used as main power sources for portable electronic devices such as mobile phones and notebook computers. This lithium ion secondary battery is required to have a higher energy density and further improved battery characteristics.

In general, lithium ion secondary batteries use highly reactive electrolytes such as lithium hexafluorophosphate, but such electrolytes easily react with a small amount of moisture present in the battery, Thereby, hydrogen fluoride is generated. For this reason, the separator disposed between the positive and negative electrodes may be oxidized and deteriorated by hydrogen fluoride while charging and discharging are repeated, and the cycle characteristics of the battery may be deteriorated. In particular, the surface of the separator that is in contact with the electrode is easily affected by oxidative degradation, and if the separator surface is oxidatively degraded, the cycle characteristics of the battery are significantly reduced. Further, since the generated hydrogen fluoride can react with the constituent materials of the electrolyte and the separator in a chained manner, there is a concern that the battery may swell.
In view of such a problem, techniques for preventing oxidative deterioration of the separator surface have been conventionally known (see, for example, Patent Documents 1 and 2).

  In Patent Document 1, in a separator for a non-aqueous electrolyte secondary battery having a shutdown layer and a heat-resistant porous layer, a point on the surface of the heat-resistant porous layer on which the shutdown layer is not disposed, A configuration in which a spacer in the form of a line, a line, a mesh, or a porous film is provided (see claim 1). Specific examples of the spacers include those obtained by applying a suspension of polypropylene, polyethylene, tetrafluoroethylene-hexafluoropropylene copolymer or the like to the surface of the heat-resistant porous layer and drying (Examples 1 to 3). reference).

  However, such a configuration in which the particle layer obtained by drying the suspension as the spacer layer is attached to the separator surface is liable to powder off and has a handling problem. In addition, since oxidative degradation may occur from the gap portion of the spacer layer, there is a possibility that the oxidative degradation of the separator cannot be suitably prevented, and there is a concern about the problem of battery gas expansion due to a chain reaction with hydrogen fluoride.

On the other hand, in Patent Document 2, a battery separator having a three-layer structure having an intermediate layer made of polyethylene resin and a layer made of polypropylene resin disposed on both outer surfaces, the layer made of polypropylene resin, A configuration including an antioxidant having a melting point of 60 ° C. or higher and an oxidation potential of less than +4.5 V with respect to lithium is shown.
With such a configuration, there is no concern about the problem of powder falling, but there is a concern about the problem of gas expansion of the battery due to a chain reaction with hydrogen fluoride.

JP 2002-151044 A Japanese Patent No. 3838492

As described above, in the past, there has been no technology that can suitably prevent the oxidative deterioration of the separator to improve the cycle characteristics of the battery, and can sufficiently prevent the gas from expanding. is there.
Therefore, an object of the present invention is to provide a separator that can improve the cycle characteristics of the battery and can sufficiently prevent gas expansion of the battery.

In the present invention, the following configuration is adopted in order to solve the above problems.
1. A separator for a non-aqueous secondary battery, wherein the separator has a fluorine-based compound layer having a thickness of 1 nm to 500 nm on the surface of the separator.
2. 2. The separator for a non-aqueous secondary battery as described in 1 above, wherein the separator is a polyolefin microporous membrane.
3. 2. The separator according to 1 above, wherein the separator is a composite membrane comprising a polyolefin microporous membrane and a heat resistant porous layer containing a heat resistant resin laminated on one or both surfaces of the microporous membrane. Non-aqueous secondary battery separator.
4). 4. The non-aqueous system according to 3 above, wherein the heat resistant resin is at least one resin selected from the group consisting of aromatic polyamide, polyimide, polyethersulfone, polysulfone, polyetherketone and polyetherimide. Secondary battery separator.
5. The separator for a non-aqueous secondary battery according to 3 or 4 above, wherein the heat-resistant porous layer contains an inorganic filler.
6). 6. The separator for a non-aqueous secondary battery according to 5 above, wherein the inorganic filler is a metal oxide or a metal hydroxide.
7). A non-aqueous secondary battery for obtaining an electromotive force by doping or dedoping of lithium, wherein the non-aqueous secondary battery separator according to any one of the above 1 to 6 is used. .

  ADVANTAGE OF THE INVENTION According to this invention, the separator which can improve the cycling characteristics of a battery and can fully prevent the gas expansion of a battery can be provided.

[Separator for non-aqueous secondary battery]
The present invention relates to a separator for a non-aqueous secondary battery, wherein the separator has a fluorine compound layer having a thickness of 1 nm to 500 nm on the surface of the separator. .
According to the present invention, the fluorine-based compound layer comes into contact with the electrode on the entire surface, and the separator surface is hardly oxidized and deteriorated microscopically, so that the cycle characteristics of the battery can be improved. In addition, since the chain reaction with hydrogen fluoride generated on the separator surface can be prevented by the fluorine-based compound layer, it is possible to sufficiently prevent gas expansion of the battery.

  Here, the fluorine-based compound in the present invention is a compound containing fluorine and may be organic or inorganic. For example, a fluorinated polyolefin represented by polytetrafluoroethylene or polyvinylidene fluoride may be used, or a functional group introduced into these side chains. Further, an inorganic salt such as aluminum fluoride or magnesium fluoride may be used. Further, a part of the surface of the organic or inorganic substance may be fluorinated by exposure to fluorine gas or vapor deposition, sputtering, CVD, or the like. The fluorinated compound layer in the present invention includes both a configuration in which a fluorinated compound is adhered to the surface of the separator and a configuration in which the separator surface is directly fluorinated.

  In the present invention, the thickness of the fluorine-based compound layer needs to be 1 nm or more and 500 nm or less. If the thickness of the fluorine-based compound layer is less than 1 nm, the effect of preventing the separator from oxidative deterioration and the effect of preventing gas expansion cannot be obtained sufficiently. In particular, the thickness of the fluorine-based compound layer is preferably 5 nm or more. On the other hand, when the thickness of the fluorine-based compound layer is larger than 500 nm, an effect of preventing gas bulging can be obtained, but cycle characteristics are deteriorated, which is not preferable. In addition, the thickness of the fluorine-type compound layer said here means that the thickness of the one side of the fluorine-type compound layer formed in the single side | surface or both surfaces of a separator is 1 nm or more and 500 nm or less, and a fluorine-type compound When the layer is formed on both sides of the separator, the total thickness of the fluorine-based compound layer is 2 nm or more and 1000 nm or less.

  In the present invention, the fluorine-based compound layer may be formed on both sides or one side of the separator. However, from the viewpoint of the effect of preventing the oxidative deterioration and the effect of preventing gas expansion of the separator, the fluorine-based compound layer is preferably formed on both sides. .

  In the present invention, the sheet configuration of the separator for the non-aqueous secondary battery is not particularly limited. For example, a polyolefin microporous film, a polyolefin microporous film, and a heat resistant laminated on one or both surfaces of the microporous film. It is preferable that it is a composite film provided with the heat resistant porous layer containing a conductive resin.

  The above-mentioned polyolefin microporous membrane is configured to contain polyolefin, has a large number of micropores inside, and has a structure in which these micropores are connected. From one surface to the other, a gas or liquid Is a membrane that can pass through. Such a microporous membrane is preferable from the viewpoint of shutdown characteristics, handling properties and strength. Examples of the polyolefin include polyethylene, polypropylene, and polymethylpentene. Among them, those containing 90% by weight or more of polyethylene are preferable from the viewpoint of obtaining good shutdown characteristics. As the polyethylene, low density polyethylene, high density polyethylene, ultra high molecular weight polyethylene, and the like are preferably used. Particularly, high density polyethylene and ultra high molecular weight polyethylene are preferable. What consists of a mixture of high molecular weight polyethylene is still more preferable. The molecular weight of polyethylene is preferably 100,000 to 10,000,000 in terms of weight average molecular weight, and particularly preferably a polyethylene composition containing at least 1% by weight of ultrahigh molecular weight polyethylene having a weight average molecular weight of 1,000,000 or more. In addition, the porous substrate in the present invention may be constituted by mixing other polyolefins such as polypropylene and polymethylpentene in addition to polyethylene, or two or more layers of a polyethylene microporous membrane and a polypropylene microporous membrane. You may comprise as a laminated body of.

  The film thickness of the above-mentioned polyolefin microporous film is preferably in the range of 5 to 20 μm from the viewpoints of handling properties, strength, battery energy density, and the like. The porosity of the polyolefin microporous membrane is preferably 10 to 60% from the viewpoints of electrolyte retention characteristics, battery charge / discharge characteristics, shutdown characteristics, strength, and the like. The puncture strength of the polyolefin microporous membrane is preferably 200 g or more from the viewpoint of the effect of preventing a short circuit between the positive and negative electrodes. The Gurley value (JIS P8117) of the polyolefin microporous membrane is preferably in the range of 100 to 500 seconds / 100 cc from the viewpoints of ion permeability, battery load characteristics, shutdown characteristics, mechanical strength, and the like. The average pore size of the polyolefin microporous membrane is preferably 10 to 100 nm from the viewpoint of the impregnation property of the electrolytic solution, shutdown characteristics, and the like.

  The above heat-resistant porous layer is composed of a heat-resistant resin, has a large number of pores or voids inside, and has a porous structure in which these pores are connected to each other It is. The heat-resistant resin is not particularly limited as long as it is a resin having sufficient heat resistance that does not melt or thermally decompose even at a temperature exceeding the melting point of the polyolefin microporous film. For example, a resin having a melting point of 200 ° C. or higher, or a resin having substantially no melting point can be suitably used as long as its thermal decomposition temperature is 200 ° C. or higher. Examples of such a heat resistant resin include at least one resin selected from the group consisting of aromatic polyamide, polyimide, polyethersulfone, polysulfone, polyetherketone, and polyetherimide. Among these, aromatic polyamides are preferable from the viewpoint of durability such as ease of forming a porous layer, binding property with an inorganic filler, strength of the porous layer and accompanying oxidation resistance. As for aromatic polyamides, meta-type aromatic polyamides are preferred, and metaphenylene isophthalamide is particularly preferred from the viewpoint that the meta-type is easier to mold than the para-type.

  The porosity of the heat resistant porous layer is preferably in the range of 30 to 80% from the viewpoint of shutdown characteristics and ion permeability. When the heat-resistant porous layer is formed on both sides of the polyolefin microporous membrane, the total thickness of the heat-resistant porous layer is preferably 2 μm or more and 12 μm or less. When the porous porous layer is formed only on one side, it is preferably 2 μm or more and 12 μm or less. The thickness of the composite membrane is preferably in the range of 7 to 25 μm, the porosity of the composite membrane is preferably 20 to 70%, and the puncture strength of the composite membrane is preferably 200 g or more. The Gurley value (JIS P8117) of the composite membrane is preferably in the range of 150 to 600 seconds / 100 cc from the viewpoint of ion permeability, shutdown characteristics, mechanical strength, and the like.

  The heat resistant porous layer preferably further contains an inorganic filler. When an inorganic filler is contained in the heat resistant porous layer, thermal shrinkage when the separator is exposed to a high temperature is suppressed, and the compressive strength of the separator is further strengthened. As a result, an effect of improving the heat resistance of the separator occurs. Moreover, it is also preferable in that a specific function of the inorganic filler itself (for example, heat resistance, thermal conductivity, flame retardancy, gas absorbability, etc.) can be added to the function of the separator.

  The composition of the heat-resistant porous layer in the case of containing an inorganic filler is such that the weight ratio of heat-resistant resin: inorganic filler = 10: 90 to 80:20 from the viewpoint of moldability, ion permeability, heat shrinkage suppression effect, and the like. A range is preferred. The average particle diameter of the inorganic filler is preferably in the range of 0.1 μm or more and 1 μm or less from the viewpoint of short-circuit prevention effect, moldability, and the like. The type of inorganic filler is not particularly limited, and examples thereof include metal oxides, metal nitrides, metal carbides, metal carbonates, and metal hydroxides. Of these, metal oxides such as alumina, zirconia, silica, magnesia, and titania, and metal hydroxides such as aluminum hydroxide and magnesium hydroxide are preferable.

[Method for producing separator for non-aqueous secondary battery]
The method for producing the separator for a non-aqueous secondary battery of the present invention is not particularly limited. For example, in the case of a configuration in which a fluorine compound layer is provided on the surface of a polyolefin microporous membrane, after forming the polyolefin microporous membrane, A method for carrying out the compound layer forming step may be mentioned. Moreover, in the case of a configuration in which a fluorine-based compound layer is provided on the surface of a composite membrane including a polyolefin microporous membrane and a heat-resistant porous layer, it can be manufactured by a manufacturing method including the following steps (i) to (v) . That is, (i) a step of producing a coating slurry containing a heat-resistant resin and a water-soluble organic solvent, and (ii) a step of coating the obtained coating slurry on one or both sides of the polyolefin microporous membrane; , (Iii) a step of coagulating the heat-resistant resin in the coated slurry, (iv) a step of washing and drying the sheet after the coagulation step, and (v) a step of forming a fluorine-based compound layer This is a manufacturing method.

  The step of forming the fluorine-based compound layer is not particularly limited. For example, after the fluorine-based polymer solution is attached to the separator by a method such as dipping or spraying, the solvent is removed and the surface is fixedly formed on the surface. Can be mentioned. Alternatively, the separator may be exposed to a fluorine gas atmosphere to fluorinate the separator surface. Alternatively, a method using a fluorinated silane coupling agent, or a method in which the fluorine-based compound layer is fixedly formed on the separator surface by a vapor deposition method, a CVD method, or a sputtering method may be used.

  The method for producing the polyolefin microporous membrane is not particularly limited. For example, a base tape is prepared by extruding a gel-like mixture of polyolefin and liquid paraffin from a die and then cooling, and then stretching the base tape. This is heat fixed. Thereafter, liquid paraffin can be extracted by dipping in an extraction solvent such as methylene chloride, and then the extraction solvent can be dried.

  In the above step (i), the water-soluble organic solvent is not particularly limited as long as it is a good solvent for the heat-resistant resin. Specifically, for example, N-methylpyrrolidone, dimethylacetamide, dimethylformamide, Polar solvents such as dimethyl sulfoxide can be used. Further, in the slurry, a solvent that becomes a poor solvent for the heat-resistant resin can be partially mixed and used. 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 preferred, and polyhydric alcohols such as glycol are particularly preferred. In addition, what is necessary is just to disperse | distribute an inorganic filler in a slurry in this process (i), when an inorganic filler is included in a heat resistant porous layer.

In the step (ii), the amount of slurry applied to the polyolefin microporous membrane is preferably about ² to 3 g / m ² . Examples of the coating method include a knife coater method, a gravure coater method, a screen printing method, a Meyer bar method, a die coater method, a reverse roll coater method, an ink jet method, a spray method, and a roll coater method. Among them, the reverse roll coater method is preferable from the viewpoint of uniformly applying the coating film.

  In the step (iii), the heat-resistant resin in the slurry can be coagulated by spraying a coagulating liquid onto the polyolefin microporous film after coating, or a bath containing a coagulating liquid (coagulating bath) ) And the like in which the substrate is immersed. The coagulation liquid is not particularly limited as long as it can coagulate the heat-resistant resin, but water or a mixed liquid in which an appropriate amount of water is contained in a good solvent used in the slurry is preferable. Here, the mixing amount of water is preferably 40 to 80% by weight with respect to the coagulation liquid.

  In said process (iv), although a drying method is not specifically limited, 50-80 degreeC is suitable for drying temperature. In the case of applying a high drying temperature, it is preferable to apply a method of contacting the roll in order to prevent dimensional change due to heat shrinkage.

[Non-aqueous secondary battery]
The non-aqueous secondary battery of the present invention uses the above-described separator for a non-aqueous secondary battery of the present invention in a non-aqueous secondary battery that obtains an electromotive force by doping or dedoping lithium. Next battery. Such a non-aqueous secondary battery of the present invention is excellent in cycle characteristics and hardly causes gas expansion of the battery.

  The type and configuration of the non-aqueous secondary battery to which the present invention is applied are not limited in any way, but an electrolytic solution is impregnated in a battery element in which a positive electrode, a separator, and a negative electrode are sequentially laminated, and this is enclosed in an exterior. Any structure can be used as long as it has a different structure.

  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 (copper foil, stainless steel foil, nickel foil, etc.). As the negative electrode active material, a material capable of electrochemically doping lithium, for example, a carbon material, silicon, aluminum, or tin is used.

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 such as LiCoO ₂ , LiNiO ₂ , LiMn _0.5 Ni _0.5 O ₂ , LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ , LiMn ₂ O. ₄ and LiFePO ₄ are used.

The electrolytic solution has a configuration in which a lithium salt, for example, LiPF ₆ , LiBF ₄ , or LiClO ₄ is dissolved in a non-aqueous solvent. Examples of the non-aqueous solvent include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, γ-butyrolactone, and vinylene carbonate.

  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 separator of the present invention can be suitably applied to any shape.

  Hereinafter, the present invention will be described in detail by way of examples. Various measurement methods in the present invention are as follows.

[Film thickness]
It was determined by measuring 20 points with a contact-type film thickness meter (manufactured by Mitutoyo Co., Ltd.) and averaging them. Here, the contact terminal used was a cylindrical one having a bottom surface of 0.5 cm in diameter, and measurement was performed under a condition that a load of 1.2 kg / cm ² was applied to the contact terminal.

[Thickness of fluorine compound layer]
The thickness of the fluorine compound layer on the separator surface was observed with EF-TEM (TECNAI 12 BIO TWIN manufactured by FEI), and the thickness of the observed fluorine compound layer was measured at 20 points and averaged. Asked.

[Gurley value]
The Gurley value (sec / 100 cc) was measured according to JIS P8117.

[Porosity]
Construction materials a, b, c ..., consist n, weight Wa of the constituent materials, Wb, Wc ..., a Wn (g / cm ^2), each true density da, db, dc ..., dn ( g / cm ³ ), where the film thickness of the layer of interest is t (cm), the porosity ε (%) was obtained from the following equation.
ε = {1− (Wa / da + Wb / db + Wc / dc +... + Wn / dn) / t} × 100

[Membrane resistance]
A separator as a sample was cut into a size of 2.6 cm × 2.0 cm. The cut-out separator was immersed in a methanol solution in which 3% by weight of a nonionic surfactant (manufactured by Kao Corporation; Emulgen 210P) was dissolved and air-dried. A 20 μm thick aluminum foil was cut into 2.0 cm × 1.4 cm, and a lead tab was attached. Two aluminum foils were prepared, and a separator cut between the aluminum foils was sandwiched between the aluminum foils so that the aluminum foils were not short-circuited. The separator was impregnated with 1M LiBF ₄ .propylene carbonate / ethylene carbonate (1/1 weight ratio) as an electrolytic solution. This was sealed in an aluminum laminate pack under reduced pressure so that the tabs came out of the aluminum pack. Such cells were prepared so that there were one, two, and three separators in the aluminum foil, respectively. The cell was placed in a constant temperature bath at 20 ° C., and the resistance of the cell was measured by an AC impedance method at an amplitude of 10 mV and a frequency of 100 kHz. The measured resistance value of the cell was plotted against the number of separators, and the plot was linearly approximated to obtain the slope. The inclination was multiplied by the electrode area of 2.0 cm × 1.4 cm to determine the membrane resistance (ohm · cm ² ) per separator.

[Battery cycle characteristics]
In order to evaluate the cycle characteristics of the batteries, non-aqueous secondary batteries were produced as follows using the separators produced in the following Examples and Comparative Examples.

1) Positive electrode 6 wt% PVdF so that the lithium cobalt oxide (LiCoO ₂ , Nippon Chemical Industry Co., Ltd.) powder 89.5 parts by weight, acetylene black 4.5 parts by weight and PVdF dry weight 6 parts by weight A positive electrode paste was prepared using the NMP solution. The obtained 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.

2) Negative electrode 6 wt% PVdF so that the dry weight of mesophase carbon microbeads (MCMB, manufactured by Osaka Gas Chemical Co., Inc.) powder 87 parts by weight, acetylene black 3 parts by weight and PVdF 10 parts by weight as the negative electrode active material An NMP solution was used to prepare a negative electrode agent paste. The obtained paste was applied onto a copper foil having a thickness of 18 μm, dried and pressed to prepare a negative electrode having a thickness of 90 μm.

3) electrolytic solution of ethylene carbonate and ethyl methyl carbonate of 3: a mixed solution with 7 weight ratio, were used as LiPF ₆ was dissolved at a 1 mol / L.

4) Trial manufacture of non-aqueous secondary battery The above-mentioned positive electrode (2 cm × 1.4 cm) and negative electrode (2.2 cm × 1.6 cm) were prepared in the separators (2.6 cm × 2. 2 cm). This was impregnated with the above electrolytic solution (0.2 g) and sealed in an exterior made of an aluminum laminate film to produce a non-aqueous secondary battery.

5) Cycle characteristics The cycle characteristics of the non-aqueous secondary battery were evaluated using a charge / discharge measuring device (HJ-101SM6 manufactured by Hokuto Denko). In the measurement, the battery was charged at 1.6 mA / h to 4.2 V, and then discharged at 1.6 mA / h to 2.75 V, which was defined as one cycle. For the battery using each separator, the ratio (%) of the discharge capacity after 20 cycles when the discharge capacity at the first cycle was 100 was used for evaluation of the cycle characteristics.

[Battery gas expansion]
In the evaluation of the cycle characteristics described above, the swelling of the battery cells after the 20-cycle test was visually observed. It was judged that the larger the blister, the more gas was generated.

[Example 1]
As polyethylene powder, GUR2126 (weight average molecular weight 41.50 million, melting point 141 ° C.) and GRX143 (weight average molecular weight 560,000, melting point 135 ° C.) manufactured by Ticona were used. GUR2126 and GURX143 are made to be 1: 9 (weight ratio), and liquid paraffin (manufactured by Matsumura Oil Research Co., Ltd .; Smoyl P-350P; boiling point 480 ° C.) and decalin so that the polyethylene concentration becomes 30% by weight. A polyethylene solution was prepared by dissolving in a mixed solvent. The composition of this polyethylene solution was polyethylene: liquid paraffin: decalin = 30: 45: 25 (weight 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). The base tape was dried at 60 ° C. for 8 minutes and at 95 ° C. for 15 minutes, and then the base tape was stretched by biaxial stretching that was performed in the order of longitudinal stretching and lateral stretching. Here, the longitudinal stretching was 5.5 times, the stretching temperature was 90 ° C., the transverse stretching was 11.0 times the stretching ratio, and the stretching temperature was 105 ° C. After transverse stretching, heat setting was performed at 125 ° C. Next, this was immersed in a methylene chloride bath to extract liquid paraffin and decalin. Then, it dried at 50 degreeC and annealed at 120 degreeC, and obtained the polyethylene microporous film.

The polyethylene microporous membrane obtained as described above was exposed to fluorine gas at room temperature for 1 minute to fluorinate the polyethylene surface, thereby obtaining a separator for a non-aqueous secondary battery of the present invention. The separator had a thickness of 12 μm, a Gurley value of 231 sec / 100 cc, and a membrane resistance of 2.3 ohm · cm ² . Moreover, the thickness of the fluorine-type compound layer of this separator was 3 nm. This separator had no powder fall off of the fluorine-based compound layer, and there was no handling problem.
The various physical properties and characteristics of Example 1 are summarized in Table 1 below. The following Examples 2 to 4 and Comparative Examples 1 to 3 are also shown in Table 1 in the same manner.

[Example 2]
A separator for a non-aqueous secondary battery of the present invention was obtained in the same manner as in Example 1, except that the fluorine gas exposure treatment was performed for 120 minutes. The separator had a thickness of 12 μm, a Gurley value of 231 sec / 100 cc, and a membrane resistance of 2.3 ohm · cm ² . Moreover, the thickness of the fluorine-type compound layer of this separator was 400 nm. This separator had no powder fall off of the fluorine-based compound layer, and there was no handling problem.

[Example 3]
The weight ratio of dimethylacetamide (DMAc) and tripropylene glycol (TPG) is 60:40 such that Cornex (registered trademark; manufactured by Teijin Techno Products), a meta-type wholly aromatic polyamide, is 6.0% by weight. The mixture was mixed with a mixed solvent to prepare a coating solution. Two Meyer bars were placed opposite each other, and an appropriate amount of coating solution was put between them. The polyethylene microporous film produced in Example 1 was passed between Mayer bars carrying the coating liquid, and the coating liquid was applied to the front and back surfaces of the polyethylene microporous film. Here, the clearance between the Mayer bars was 20 μm, and the number of the Mayer bars was # 6. This was immersed in a coagulating liquid having a weight ratio of water: DMAc: TPG = 50: 30: 20 at 40 ° C., then washed with water and dried, and heat-resistant porous on the front and back surfaces of the polyethylene microporous membrane. A layer was formed.

The separator obtained as described above was exposed to fluorine gas at room temperature for 2 minutes, and both surfaces of the heat-resistant porous layer were fluorinated to obtain a separator for a non-aqueous secondary battery of the present invention. The separator had a thickness of 17 μm, a Gurley value of 355 sec / 100 cc, and a membrane resistance of 2.9 ohm · cm ² . Moreover, the thickness of the fluorine-type compound layer of this separator was 7 nm. This separator had no powder fall off of the fluorine-based compound layer, and there was no handling problem.

[Example 4]
The weight ratio of dimethylacetamide (DMAc) and tripropylene glycol (TPG) is 60:40 such that Cornex (registered trademark; manufactured by Teijin Techno Products), a meta-type wholly aromatic polyamide, is 6.0% by weight. 200 g of a coating solution was prepared by mixing with the mixed solvent. To this, 48 g of α-alumina (manufactured by Showa Denko KK, AL160SG-3, average particle size 0.8 μm) was added and stirred for 2 hours to obtain a coating solution. Next, two Meyer bars were opposed to each other, and an appropriate amount of this coating solution was put between them. The polyethylene microporous film produced in Example 1 was passed between Mayer bars carrying the coating liquid, and the coating liquid was applied to the front and back surfaces of the polyethylene microporous film. Here, the clearance between the Mayer bars was 20 μm, and the number of the Mayer bars was # 6. This was immersed in a coagulating liquid having a weight ratio of water: DMAc: TPG = 50: 30: 20 at 40 ° C., then washed with water and dried, and heat-resistant porous on the front and back surfaces of the polyethylene microporous membrane. A layer was formed.

The separator obtained as described above was exposed to fluorine gas at room temperature for 60 minutes to fluorinate both surfaces of the heat-resistant porous layer, thereby obtaining the separator for a non-aqueous secondary battery of the present invention. The separator had a thickness of 18 μm, a Gurley value of 353 sec / 100 cc, and a membrane resistance of 2.8 ohm · cm ² . Moreover, the thickness of the fluorine-type compound layer of this separator was 200 nm. This separator had no powder fall off of the fluorine-based compound layer, and there was no handling problem.

[Comparative Example 1]
A non-aqueous secondary battery separator of Comparative Example 1 was obtained in the same manner as in Example 1 except that the fluorine gas exposure treatment was performed for 180 minutes. The separator had a thickness of 13 μm, a Gurley value of 231 sec / 100 cc, and a membrane resistance of 2.3 ohm · cm ² . Moreover, the thickness of the fluorine-type compound layer of this separator was 700 nm. This separator had no powder fall off of the fluorine-based compound layer, and there was no handling problem.

[Comparative Example 2]
In Example 1, the polyethylene microporous membrane before the fluorine gas exposure treatment was used as the separator for the non-aqueous secondary battery of Comparative Example 2. The separator had a thickness of 12 μm, a Gurley value of 231 sec / 100 cc, and a membrane resistance of 2.3 ohm · cm ² .

[Comparative Example 3]
A nonaqueous secondary battery separator was obtained in the same manner as in Example 4 except that the fluorine gas exposure treatment was not performed. The separator had a thickness of 12 μm, a Gurley value of 231 sec / 100 cc, and a membrane resistance of 2.3 ohm · cm ² .

[Comparative Example 4]
A polyethylene microporous membrane was prepared in the same manner as in Example 1, and then a polytetrafluoroethylene particle dispersion (Fluorolink 5032 manufactured by Solvay Solexis Co., Ltd .: solid content 25%, average particle size 50 nm) on both sides of the microporous membrane. Was applied and dried to obtain a separator for a non-aqueous secondary battery of Comparative Example 4. The separator had a thickness of 12 nm, a Gurley value of 320 sec / 100 cc, and a membrane resistance of 2.8 ohm · cm ² . Moreover, the thickness of the fluorine-type compound layer of this separator was 100 nm. In addition, this separator had many powder falling of the fluorine-type compound layer, and had the problem of handling.

  When Examples 1 and 3 are compared with Comparative Examples 2 and 3, if the thickness of the fluorine-based compound layer is 1 nm or more, the cycle characteristics of the battery are good, and the effect of preventing the gas expansion of the battery can be obtained. I understand. Further, when Examples 2 and 4 are compared with Comparative Example 1, it can be seen that when the thickness of the fluorine-based compound layer is 500 nm or less, there is no gas expansion and the cycle characteristics of the battery are improved.

Claims (7)

  A separator for a non-aqueous secondary battery, wherein the separator has a fluorine-based compound layer having a thickness of 1 nm to 500 nm on the surface of the separator.   The said separator is a polyolefin microporous film, The separator for non-aqueous secondary batteries of Claim 1 characterized by the above-mentioned.   The separator is a composite membrane comprising a polyolefin microporous membrane and a heat resistant porous layer containing a heat resistant resin laminated on one or both sides of the microporous membrane. The separator for non-aqueous secondary batteries as described.   The non-heat-resistant resin according to claim 3, wherein the heat-resistant resin is at least one resin selected from the group consisting of aromatic polyamide, polyimide, polyethersulfone, polysulfone, polyetherketone, and polyetherimide. Separator for water-based secondary battery.   The separator for a non-aqueous secondary battery according to claim 3 or 4, wherein the heat-resistant porous layer contains an inorganic filler.   The separator for a non-aqueous secondary battery according to claim 5, wherein the inorganic filler is a metal oxide or a metal hydroxide.   A non-aqueous secondary battery for obtaining an electromotive force by doping or dedoping of lithium, wherein the non-aqueous secondary battery separator according to claim 1 is used. battery.