JP2015170448A - Separator for nonaqueous secondary battery, method of manufacturing the same, and nonaqueous secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyvinylidene fluoride-based resin separator for a nonaqueous secondary battery, whose handleability and piercing strength are both improved.SOLUTION: The separator for a nonaqueous secondary battery includes a porous substrate and a porous layer coated on one surface or both surfaces of the porous substrate and containing a polyvinylidene fluoride-based resin. The porous layer further contains a copolymer resin containing a polyether skeleton and a polyolefin skeleton. The copolymer resin is contained in an amount of 1-20 pts.mass based on 100 pts.mass of the solid content of the porous layer.

Description

  The present invention relates to a separator for a non-aqueous secondary battery, a manufacturing method thereof, and a non-aqueous secondary battery.

Non-aqueous secondary batteries typified by lithium ion secondary batteries are widely used for mobile power and storage purposes because of their high energy density, flexible and lightweight structure, and longer life than other batteries. .
Conventionally, there has been a polyolefin porous membrane as a separator for a lithium ion secondary battery, and there has been a technique for improving cycle characteristics by further improving the adhesion between the electrode and the separator by coating a polyvinylidene fluoride resin (for example, Patent Document 1). .

JP 2013-161707 A

However, a separator including a polyvinylidene fluoride resin has a handling problem such that the separator is difficult to slip in a battery manufacturing process and the like because the polyvinylidene fluoride resin has a property of being easily charged with static electricity.
On the other hand, a lithium ion secondary battery has a problem of short circuit due to lithium dendride, and a technique capable of preventing the short circuit is required. One solution is to improve the puncture strength of the separator.
However, conventionally, there has been no proposal for improving both handling property and piercing strength in a separator including a polyvinylidene fluoride resin.
Accordingly, an object of the present invention is to improve both the handling property and the piercing strength in a separator containing a polyvinylidene fluoride resin.

The present invention adopts the following configuration in order to solve the above problems.
1. A porous substrate, and a porous layer containing a polyvinylidene fluoride-based resin coated on one or both sides of the porous substrate, and the porous layer further includes a polyether skeleton and a polyolefin skeleton. The separator for non-aqueous secondary batteries containing the copolymer resin to contain.
2. The separator for a non-aqueous secondary battery according to 1 above, wherein the porous layer contains 1 to 20 parts by mass of the copolymer resin in 100 parts by mass of the solid content of the porous layer.
3. 3. The non-aqueous secondary battery according to 1 or 2 above, wherein the copolymer resin is dispersed in the porous layer as a particulate aggregate having an average primary particle size of 0.1 μm to 5 μm. Separator.
4). A method for producing the non-aqueous secondary battery separator according to any one of 1 to 3,
A step of dispersing the copolymer resin in a solvent, dissolving the polyvinylidene fluoride-based resin in the dispersion, and preparing a coating liquid;
Applying the coating liquid onto the porous substrate to form a coating layer;
Removing the solvent from the coating layer to form the porous layer;
The manufacturing method of the separator for non-aqueous secondary batteries which implements sequentially.
5. A positive electrode, a negative electrode, and the separator for a non-aqueous secondary battery according to any one of 1 to 3 disposed between the positive electrode and the negative electrode, and an electromotive force by doping and dedoping of lithium Get a non-aqueous secondary battery.

  ADVANTAGE OF THE INVENTION According to this invention, in the separator containing a polyvinylidene fluoride resin, both handling property and piercing strength can be improved.

<Separator for non-aqueous secondary battery>
The present invention comprises a porous substrate and a porous layer containing a polyvinylidene fluoride-based resin coated on one or both surfaces of the porous substrate, and the porous layer further includes a polyether skeleton. And a separator for a non-aqueous secondary battery containing a copolymer resin containing a polyolefin skeleton.

  According to the present invention as described above, in the separator including the polyvinylidene fluoride resin, both the handling property and the piercing strength can be improved. Specifically, in the present invention, by adding a copolymer resin containing a polyether skeleton and a polyolefin skeleton to the porous layer, charging of the porous layer can be prevented and the handling property of the separator can be improved. Thereby, when slitting a separator or manufacturing a battery, manufacturing efficiency can be improved. It was also found that the puncture strength of the separator was improved by adding the copolymer resin to the porous layer. This is presumably because the copolymer resin forms a composite with the polyvinylidene fluoride resin in the porous layer, and the three-dimensional network structure of the porous layer is strengthened. Furthermore, it was also found that by adding the copolymer resin to the porous layer, the cycle characteristics of the battery can be improved, and the thermal shrinkage characteristics in the width direction (TD direction) of the separator can be improved. If the separator of this invention is used, the safety | security and cycling characteristics of a battery can be improved and manufacturing efficiency can be improved.

  In the present invention, the film thickness of the separator is preferably 5 μm to 35 μm from the viewpoint of mechanical strength and energy density when used as a battery. The porosity of the separator is preferably 30% to 60% from the viewpoints of adhesion to the electrode, mechanical strength, and ion permeability. The Gurley value (JIS P8117) of the separator is preferably 50 seconds / 100 cc to 800 seconds / 100 cc from the viewpoint of mechanical strength and film resistance.

[Porous substrate]
In the present invention, the porous substrate means a substrate having pores or voids therein. Examples of such a substrate include a microporous film; a porous sheet made of a fibrous material such as a nonwoven fabric or a paper-like sheet; In particular, a microporous membrane is preferable from the viewpoint of thinning and increasing the strength of the separator. A microporous membrane means a membrane that has a large number of micropores inside and has a structure in which these micropores are connected, allowing gas or liquid to pass from one surface to the other. To do.
The material constituting the porous substrate may be either an organic material or an inorganic material as long as it is an electrically insulating material.

  The material constituting the porous substrate is preferably a thermoplastic resin from the viewpoint of imparting a shutdown function to the porous substrate. Here, the shutdown function refers to a function of preventing the thermal runaway of the battery by blocking the movement of ions by dissolving the constituent materials and closing the pores of the porous base material when the battery temperature increases. . Examples of the thermoplastic resin include polyesters such as polyethylene terephthalate; polyolefins such as polyethylene and polypropylene; The thermoplastic resin is preferably a polyolefin from the viewpoint of providing a shutdown function.

The thickness of the porous substrate is preferably 3 μm to 25 μm, more preferably 5 μm to 25 μm, from the viewpoint of obtaining good mechanical properties and internal resistance.
The Gurley value of the porous substrate (JIS P8117 (2009)) is preferably 50 seconds / 100 cc to 800 seconds / 100 cc, and 50 seconds / 100 cc to 400 seconds / 100 cc from the viewpoint of preventing short circuit of the battery and obtaining ion permeability. Is more preferable.
The porosity of the porous substrate is preferably 20% to 60% from the viewpoint of obtaining appropriate film resistance and a shutdown function.
The puncture strength of the porous substrate is preferably 300 g or more from the viewpoint of improving the production yield.
The surface of the porous substrate may be subjected to corona treatment, plasma treatment, flame treatment, ultraviolet irradiation treatment, etc. for the purpose of improving wettability with the coating liquid for forming the porous layer.

[Porous layer]
In the present invention, the porous layer is a porous layer that is coated on one or both surfaces of a porous substrate and contains a polyvinylidene fluoride resin. This porous layer has a structure in which a large number of micropores are connected and these micropores are connected, and gas or liquid can pass from one surface to the other.

  In the present invention, the porous layer preferably contains 1 to 20 parts by mass of a copolymer resin in 100 parts by mass of the solid content of the porous layer. By including 1 part by mass or more of the copolymer resin, the handling property is further improved. From such a viewpoint, it is preferable that 2 parts by mass or more of the copolymer resin is contained, and further, 5 parts by mass or more of the copolymer resin is preferably contained. Moreover, piercing strength will become more excellent because copolymer resin is contained 20 mass parts or less. From such a viewpoint, the copolymer resin is preferably contained in an amount of 15 parts by mass or less, more preferably 10 parts by mass or less.

In the present invention, the copolymer resin is preferably dispersed in the porous layer as a particulate aggregate having an average primary particle size of 0.1 μm to 5 μm. Since the aggregate of the copolymer resin is dispersed in the porous layer, the conductive unit including the hydrophilic segment of the copolymer resin can form a conductive circuit in the porous layer. By forming a conductive circuit, which is a path of charge, in the porous layer, static electricity can be leaked to the outside of the material, and antistatic properties can be imparted.
The porous layer is preferably on both sides rather than only on one side of the porous substrate from the viewpoint of excellent cycle characteristics of the battery. This is because when the porous layer is on both sides of the porous substrate, both sides of the separator are well bonded to both electrodes via the porous layer.

In this invention, it is preferable that the film thickness of a porous layer is 0.5-5 micrometers in the single side | surface of a porous base material from a viewpoint of ensuring adhesiveness with an electrode and a high energy density. The porosity of the porous layer is preferably 30 to 60% from the viewpoints of ion permeability and adhesiveness.
In addition, it is also possible to mix the filler which consists of an inorganic substance or an organic substance, and another additive in the range which does not inhibit the effect of this invention in a porous layer. By mixing such a filler, it is possible to improve the slipperiness and heat resistance of the separator. As the inorganic filler, for example, a metal oxide such as alumina or a metal hydroxide such as magnesium hydroxide can be used. As the organic filler, for example, an acrylic resin or the like can be used.

(Polyfluorinated vinylidene resin)
In the present invention, the polyvinylidene fluoride resin is not particularly limited as long as it is a resin containing vinylidene fluoride as a monomer component, but for example, a homopolymer of vinylidene fluoride, vinylidene fluoride and other monomers Examples include copolymers containing components. Examples of such other monomer components include one kind or two or more kinds such as hexafluoropropylene, tetrafluoroethylene, trifluoroethylene, trichloroethylene, and vinyl fluoride. Among them, it is preferable to use a copolymer consisting only of vinylidene fluoride and hexafluoropropylene from the viewpoints of adhesion between the electrode and the separator and ion permeability.
The polyvinylidene fluoride resin as described above can be obtained by emulsion polymerization or suspension polymerization, particularly preferably suspension polymerization.

(Copolymer resin containing polyether skeleton and polyolefin skeleton)
The copolymer resin containing a polyether skeleton and a polyolefin skeleton in the present invention is not particularly limited. For example, a hydrophilic polymer segment (hydrophilic portion) and a hydrophobic polymer segment (hydrophobic portion) are alternately bonded. The amphiphilic block copolymer which has is mentioned. The hydrophobic part is preferably an olefin polymer and the hydrophilic part is preferably an ether polymer.

Examples of the olefin constituting the olefin polymer include olefins such as ethylene, propylene, butene, pentene, and hexene. Examples of the monomer that constitutes the ether polymer include alkylene oxides such as ethylene oxide, propylene oxide, and butylene oxide. The chemical bond between the olefin polymer and the ether polymer is not particularly limited, and examples thereof include an ester bond, an amide bond, and an ether bond.
Commercial products may be used as the copolymer resin containing the polyether skeleton and the polyolefin skeleton used in the present invention. For example, Pelestat (registered trademark) or Peletron (registered trademark) manufactured by Sanyo Chemical Industries, Ltd. can be used as the copolymer resin.

<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 as long as it is a method for obtaining the above-described separator. For example, the production includes the following steps (i) to (iii): The method is preferred.
That is, (i) a step of dispersing a copolymer resin in a solvent and dissolving a polyvinylidene fluoride-based resin in the dispersion to prepare a coating liquid; and (ii) the coating liquid being the porous substrate. A separator for a non-aqueous secondary battery, in which a step of coating on and forming a coating layer, and (iii) a step of removing the solvent from the coating layer and forming the porous layer are sequentially performed. It is a manufacturing method.

  In the step (i), as a method for dispersing the copolymer resin, the copolymer resin is dispersed by stirring in a solvent whose temperature is raised to the melting point of the copolymer resin or higher. After dispersing the copolymer resin, a polyvinylidene fluoride resin is added to the dispersion to prepare a coating solution. In this case, the coating liquid may be prepared by dissolving the polyvinylidene fluoride resin in the dispersion liquid in which the copolymer resin is dispersed, or the polyvinylidene fluoride resin in the dispersion liquid in which the copolymer resin is dispersed. Another polymer solution in which is dissolved may be mixed to adjust the coating solution. The solvent is not particularly limited as long as it is a good solvent for the polyvinylidene fluoride resin. Specifically, for example, a polar solvent such as N-methylpyrrolidone, dimethylacetamide, dimethylformamide, dimethylsulfoxide is used. be able to. Moreover, the solvent which becomes a poor solvent with respect to a polyvinylidene fluoride-type resin can also be partially mixed and used for a coating liquid. By applying such a poor solvent, a microphase separation structure is induced and the formation of a porous layer facilitates the formation of a porous layer. As the poor solvent, water and alcohols are preferable, and polyhydric alcohols such as methanol, ethanol, propyl alcohol, butyl alcohol, butanediol, ethylene glycol, propylene glycol, or tripropylene glycol are particularly preferable. It is preferable that the density | concentration of resin in a coating liquid is 1-9 mass%.

In step (ii), the coating amount of the coating solution on the porous substrate is preferably about 1 to 30 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. Moreover, a porous layer can be stably obtained by adjusting the slurry temperature at the time of coating. Here, the slurry temperature is not particularly limited, but a range of 5 ° C to 40 ° C is preferable.

In step (iii), a porous layer containing a copolymer resin and a polyvinylidene fluoride resin is formed by removing the solvent from the resin solution applied to the porous substrate. As a method for removing the solvent, Any method that does not adversely affect the porous substrate can be used without particular limitation. For example, a method of drying at a temperature below the melting point while fixing the porous substrate, a method of drying under reduced pressure at a low temperature, a method of coagulating the resin by dipping in a poor solvent for the resin and extracting the solvent at the same time It is done.
After step (iii), post-treatment such as washing with water, drying and heat treatment may be performed as necessary.

<Non-aqueous secondary battery>
The non-aqueous secondary battery of the present invention includes a positive electrode, a negative electrode, and the above-described non-aqueous electrolyte secondary battery separator disposed between the positive electrode and the negative electrode, and is generated by doping and dedoping of lithium. It is characterized by obtaining electric power.
Generally, a non-aqueous secondary battery is configured to include a positive electrode, a negative electrode, a separator disposed between these electrodes, and an electrolytic solution. Such a battery element is enclosed in an exterior. Yes.

  As a positive electrode, the structure which formed the electrode layer which consists of a positive electrode active material, binder resin, and a conductive support agent on a positive electrode collector can be employ | adopted. Examples of the positive electrode active material include lithium cobaltate, lithium nickelate, spinel structure lithium manganate, and olivine structure lithium iron phosphate. Examples of the binder resin include polyvinylidene fluoride resin. Examples of the conductive assistant include acetylene black, ketjen black, and graphite powder. Examples of the current collector include aluminum foil having a thickness of 5 to 20 μm.

  As a negative electrode, the structure which formed the negative electrode active material and the electrode layer which consists of binder resin on the negative electrode electrical power collector can be employ | adopted, and you may add a conductive support agent in an electrode layer as needed. As the negative electrode active material, for example, a carbon material that can occlude lithium electrochemically, a material that forms an alloy with lithium such as silicon or tin, and the like can be used. Examples of the binder resin include polyvinylidene fluoride resin and styrene-butadiene rubber. Examples of the conductive assistant include acetylene black, ketjen black, and graphite powder. Examples of the current collector include copper foil having a thickness of 5 to 20 μm. Moreover, it can replace with said negative electrode and can also use metal lithium foil as a negative electrode.

The electrolytic solution has a structure in which a lithium salt is dissolved in an appropriate solvent. Examples of the lithium salt include LiPF ₆ , LiBF ₄ , LiClO _{4, and the} like. Examples of the solvent include cyclic carbonates such as ethylene carbonate, propylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, chain carbonates such as dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and fluorine-substituted products thereof, γ-butyrolactone, γ -Cyclic esters such as valerolactone or a mixed solvent thereof can be suitably used. In particular, what melt | dissolved 0.5-1.5M lithium salts in the solvent of cyclic carbonate / chain carbonate = 20-40 / 80-60 mass ratio is suitable.

  Although the separator for non-aqueous secondary batteries of the present invention can be applied to a battery with a metal can exterior, it is suitably used for a soft pack battery with an aluminum laminate film exterior because of its good adhesion to the electrode. In the method of manufacturing such a battery, the positive electrode and the negative electrode are joined via a separator, impregnated with an electrolytic solution, and enclosed in an aluminum laminate film. A non-aqueous secondary battery can be obtained by hot-pressing it. With such a configuration of the present invention, an electrode and a separator can be bonded well, and a non-aqueous secondary battery excellent in cycle life can be obtained. In addition, since the adhesion between the electrode and the separator is good, the battery is excellent in safety. There are a stack method in which the electrode and the separator are laminated, a method in which the electrode and the separator are wound together, and the present invention is applicable to any method. 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 with reference to examples. However, the present invention is not limited to the following examples.

[Measuring method]
(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 such a condition that a load of 1.2 kg / cm ² was applied to the contact terminal.

(Weight)
A sample was cut into 10 cm × 10 cm and its mass was measured. The basis weight was determined by dividing the mass by the area.

(Coating amount of porous layer)
The basis weight of the separator coated with the porous layer and the polyethylene microporous film used therefor was measured, and the coating amount of the porous layer was determined from these differences.

(Porosity)
The constituent materials are a, b, c..., N, and the constituent materials have the masses Wa, Wb, Wc..., Wn (g · cm ² ), and their true densities are da, db, dc. 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

(Puncture properties)
Using a KES-G5 handy compression tester manufactured by Kato Tech Co., Ltd., a piercing test was conducted under the conditions of a radius of curvature of the needle tip of 0.5 mm and a piercing speed of 2 mm / sec, and the maximum piercing load was defined as the piercing strength. Here, the silicon rubber packing was also sandwiched and fixed in a metal frame (sample holder) having a hole with a diameter of 11.3 mm.

(Heat shrinkage)
A separator serving as a sample was cut into 18 cm (MD direction) × 6 cm (TD direction). On the line that bisects the TD direction, points (point A, point B) of 2 cm and 17 cm from the top were marked. In addition, on the line that bisects the MD direction, the points (point C, point D) of 1 cm and 5 cm from the left were marked. A clip was attached to this (the place where the clip is attached is within the upper 2 cm in the MD direction), and it was hung in an oven adjusted to 105 ° C., 120 ° C., and 135 ° C., and each was heat-treated for 30 minutes under no tension. . The length between the two points AB and the CD was measured before and after the heat treatment, and the thermal shrinkage rate was determined from the following formula, which was used as an index of heat resistance.
MD direction thermal shrinkage = {(AB length before heat treatment−AB length after heat treatment) / AB length before heat treatment} × 100
TD direction thermal contraction rate = {(length of CD before heat treatment−length of CD after heat treatment) / length of CD before heat treatment} × 100

(Gurre value)
According to JIS P8117, measurement was performed with a Gurley type densometer (G-B2C manufactured by Toyo Seiki Co., Ltd.).

(Water content of separator)
About the separator which left still for one hour under the environment of temperature 20 degreeC and humidity 18%, after vaporizing water at 120 degreeC in a moisture vaporizer (Mitsubishi Analytech Co., Ltd. model VA-100 type), Karl Fischer moisture meter ( The moisture content was measured using Mitsubishi Chemical (CA-100).

(Withstand voltage half-life)
The withstand voltage half-life was measured using an Honest meter (Sisid electrostatic company make: HO110 type). The measurement environment was a temperature of 20 ° C. and a humidity of 18%. A separator as a sample was fixed to a sample holder, a distance between the voltage application device and the sample was 20 mm, and a voltage was applied under the condition of an applied voltage of 10 kV. The voltage decay behavior for 3 minutes after the charging was saturated was confirmed, and the half-life was calculated from this decay curve. In addition, it can be said that the shorter the withstand voltage half-life, the lower the charge, and the better the handling property.

(Handling test)
When the separator is spread horizontally and the surface is rubbed about 10 times with a metal or resin rod, the separator is attached to the rod or the surface is broken when the rod is lifted vertically. If the separator was not defective and the change was not observed, it was judged that the handling property was good.

(Charge / discharge cycle test)
Lithium ion batteries using the non-aqueous secondary battery separators of each example and comparative example were produced as follows and subjected to a cycle test.

(1) Preparation of positive electrode NMP so that lithium cobaltate powder which is a positive electrode active material is 89.5 mass%, acetylene black is 4.5 mass% which is a conductive additive, and polyvinylidene fluoride which is a binder is 6 mass%. It melt | dissolved and stirred with the double arm type mixer, and produced the positive electrode slurry. This positive electrode slurry was applied to a 20 μm thick aluminum foil as a positive electrode current collector, and the resulting coating film was dried and pressed to produce a positive electrode having a positive electrode active material layer.

(2) Production of negative electrode 300 g of artificial graphite as a negative electrode active material, 7.5 g of a water-soluble dispersion containing 40% by mass of a modified styrene-butadiene copolymer as a binder, 3 g of carboxymethyl cellulose as a thickener, and An appropriate amount of water was stirred with a double-arm mixer to prepare a slurry for negative electrode. This negative electrode slurry was applied to a 10 μm thick copper foil as a negative electrode current collector, dried and pressed to obtain a negative electrode having a negative electrode active material layer.

(3) Production of Battery A lead tab was welded to the positive electrode and the negative electrode, the positive and negative electrodes were joined via a separator, and the electrolyte solution was infiltrated and sealed in an aluminum pack using a vacuum sealer. Here, 1 M LiPF ₆ ethylene carbonate / ethyl methyl carbonate = 30/70 mass ratio was used as the electrolytic solution.

(4) Cycle test The cycle test was implemented using the produced non-aqueous secondary battery. After performing constant current-constant voltage charging (total charging time: 4 hours) with a constant current of 1 C and a constant current of voltage 4.2 V at room temperature (25 ° C.), constant current discharge (discharging end voltage: 2) at 1 C .75V). With this as one cycle, 100 cycles of charge and discharge were repeated under the above conditions, and the capacity retention ratio (= electric capacity at 100th cycle / electric capacity at the first cycle × 100%) was calculated.

[Example 1]
PELECTRON (registered trademark) manufactured by Sanyo Chemical Industries, Ltd. was used as a copolymer resin containing a polyether skeleton and a polyolefin skeleton. The copolymer resin was added to dimethylacetamide at 2% by mass and then stirred to prepare a dispersion. As the polyvinylidene fluoride resin, KF polymer # 9300 (vinylidene fluoride / hexafluoropropylene = 98.9 / 1.1 mol% mass average molecular weight 1.95 million) manufactured by Kureha Chemical Co., Ltd. and KYNAR 2801 (fluorinated fluoride) manufactured by ARKEMA Vinylidene / hexafluoropropylene = 95.2 / 4.8 mol% (mass average molecular weight: 470,000) was used as a 50/50 mass ratio. After the mixed polyvinylidene fluoride resin is dissolved in a mixed solvent having a dimethylacetamide / tripropylene glycol = 3/1 mass ratio at 8% by mass, the resin component is added by 5% by mass to the previous dispersion. A working solution was prepared. The breakdown of the resin component was copolymer resin / polyvinylidene fluoride resin = 10/90 mass ratio.

A pair of Meyer bars (count # 6) were confronted with a clearance of 30 μm. An appropriate amount of the above slurry for coating was placed on a Mayer bar, a polyethylene microporous membrane was passed between a pair of Mayer bars, and the coating slurry was coated on both sides of the polyethylene microporous membrane. And what was coated was immersed in the coagulating liquid which is 40 degreeC by water: DMAc: TPG = 62.5: 30: 7.5 by mass ratio. Next, a separator for a non-aqueous secondary battery having a porous layer made of a copolymer resin containing a polyether skeleton and a polyolefin skeleton and a polyvinylidene fluoride resin on both surfaces (front and back surfaces) of the polyethylene microporous membrane is washed and dried. Got.
For this separator, the measurement results of the mass ratio of the resin constituting the porous layer, the film thickness and basis weight of the separator, the porosity of the separator, the mass of the porous layer, the piercing physical properties of the separator, the heat shrinkage rate, and the Gurley value Table 1 shows. In addition, Table 2 shows the moisture content of the separator, the withstand voltage half-life with an Honest meter, the handling test results, and the charge / discharge cycle test results. The separators of the following examples and comparative examples are similarly shown in Tables 1 and 2.

[Example 2]
A non-aqueous secondary battery separator of the present invention was obtained in the same manner as in Example 1 except that copolymer resin / polyvinylidene fluoride resin = 2/98 mass ratio as a breakdown of the resin component.

[Example 3]
A non-aqueous secondary battery separator of the present invention was obtained in the same manner as in Example 1 except that copolymer resin / polyvinylidene fluoride resin = 5/95 mass ratio was used as the breakdown of the resin component.

[Example 4]
A non-aqueous secondary battery separator of the present invention was obtained in the same manner as in Example 1 except that copolymer resin / polyvinylidene fluoride resin = 20/80 mass ratio was used as the breakdown of the resin component.

[Comparative Example 1]
As the polyvinylidene fluoride resin, KF polymer # 9300 manufactured by Kureha Chemical Co., Ltd. and KYNAR 2801 manufactured by ARKEMA were used in a 50/50 mass ratio. Example: A mixed polyvinylidene fluoride resin was dissolved in a mixed solvent having a dimethylacetamide / tripropylene glycol = 8/2 mass ratio at 5% by mass, and then a coating liquid having a resin component of 5% by mass was prepared. In the same manner as in Example 1, a non-aqueous secondary battery separator was obtained.

[Comparative Example 2]
As the polyvinylidene fluoride resin, KF polymer # 9300 manufactured by Kureha Chemical Co., Ltd. and KYNAR 2801 manufactured by ARKEMA were used in a 50/50 mass ratio. Example: A mixed polyvinylidene fluoride resin was dissolved in a mixed solvent having a dimethylacetamide / tripropylene glycol = 7/3 mass ratio at 5% by mass, and then a coating solution having a resin component of 5% by mass was prepared In the same manner as in Example 1, a non-aqueous secondary battery separator was obtained.

[Interpretation of piercing properties]
In Examples 1 to 3, the puncture strength was higher than that in Comparative Examples 1 and 2, and the results showed that the strength was improved. However, in Example 4, the puncture strength was reduced as compared with Comparative Examples 1 and 2. When the content of the copolymer resin containing the polyether skeleton and the polyolefin skeleton is 0 to 10% by mass, the puncture strength tends to increase proportionately, but when the content is 20% by mass, the decrease starts. Thereby, it is not preferable from the viewpoint of strength to make the content of the copolymer resin containing the polyether skeleton and the polyolefin skeleton 20% by mass or more.

[Interpretation of heat shrinkage]
As the content of the copolymer resin containing the polyether skeleton and the polyolefin skeleton increased, the thermal contraction rate in the TD direction tended to decrease. For the MD direction, no correlation with the content was found.

[Interpretation of Gurley values]
Good values were shown in both Examples and Comparative Examples.

[Interpretation of moisture content]
It turned out that the moisture content of a separator becomes high compared with Comparative Examples 1-2 in Example 1, 3-4. When the content of the copolymer resin containing the polyether skeleton and the polyolefin skeleton was 5% by mass or more, the water content of the separator increased in proportion to the content.

[Interpretation of half-life of charged voltage]
Compared with Comparative Examples 1-2, in Examples 1-4, the antistatic performance was high. The chargeability was reduced by dispersing a copolymer resin containing a polyether skeleton and a polyolefin skeleton in the porous layer. In Examples, it was found that the charged half-life decreased as the content of the copolymer resin containing a polyether skeleton and a polyolefin skeleton increased, and the antistatic effect was improved accompanyingly.

[Interpretation of handling test results]
In Examples 1 to 4, the handleability was good. On the other hand, in Comparative Examples 1 and 2, the separator stuck to the rod, and the handling property was poor. In Comparative Examples 1 and 2, strong chargeability is shown from the results of initial electrostatic voltage measurement of static electricity, and the separator surface was rubbed with a metal or resin rod, so that the surface was stuck and sticked to the rod Conceivable. In Examples 1 to 4, since the separator has no charging property, it is not charged even when the surface of the separator is rubbed with a metal or resin rod.

[Interpretation of cycle test results]
In Examples 1 to 4, the capacity retention was 91 to 93% after 100 cycles of charge and discharge. On the other hand, in Comparative Examples 1 and 2, the capacity retention was 83 to 85%. For this reason, in lithium ion batteries made using a battery separator made of a polyvinylidene fluoride resin and a copolymer resin containing a polyether skeleton and a polyolefin skeleton, the potential distribution is uniform in the porous film layer. It was shown that the cycle characteristics were improved.

[Agglomerates of copolymer resin]
The cross sections of the separators produced in Examples 1 to 4 were subjected to selective visualization treatment of the copolymer resin by osmium tetroxide staining, and observed by TEM to investigate the dispersion state of the copolymer resin in the porous layer. In each Example, it was found that the copolymer resin was dispersed in the form of particulate aggregates having an average primary particle size of 0.1 μm to 5 μm in the porous layer of the separator.

  The present invention can be effectively used as a technique for improving the safety and battery characteristics of a non-aqueous secondary battery.

Claims (5)

A porous base material, and a porous layer containing polyvinylidene fluoride-based resin coated on one or both surfaces of the porous base material,
A separator for a non-aqueous secondary battery, wherein the porous layer further contains a copolymer resin containing a polyether skeleton and a polyolefin skeleton.   The separator for a non-aqueous secondary battery according to claim 1, wherein the porous layer contains 1 to 20 parts by mass of the copolymer resin in 100 parts by mass of the solid content of the porous layer.   The non-aqueous secondary according to claim 1 or 2, wherein the copolymer resin is dispersed in the porous layer as a particulate aggregate having an average primary particle size of 0.1 µm to 5 µm. Battery separator. A method for producing a separator for a non-aqueous secondary battery according to any one of claims 1 to 3,
A step of dispersing the copolymer resin in a solvent, dissolving the polyvinylidene fluoride-based resin in the dispersion, and preparing a coating liquid;
Applying the coating liquid onto the porous substrate to form a coating layer;
Removing the solvent from the coating layer to form the porous layer;
The manufacturing method of the separator for non-aqueous secondary batteries which implements sequentially.   A positive electrode, a negative electrode, and the separator for a non-aqueous secondary battery according to any one of claims 1 to 3 disposed between the positive electrode and the negative electrode. A non-aqueous secondary battery that obtains an electromotive force.