JP2012089283A - Method for manufacturing separator for nonaqueous secondary battery, separator for nonaqueous secondary battery, and secondary battery prepared therewith - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a separator for a nonaqueous secondary battery achieving an excellent balance between air permeability and mechanical strength and causing only a small amount of dust fall, a separator for a nonaqueous secondary battery, and a nonaqueous secondary battery.SOLUTION: When the components of a separator for a nonaqueous secondary battery containing a polypropylene resin and at least one kind of air permeability enhancing agent are heated to 280°C, the air permeability enhancing agent is in a compatible state. The air permeability enhancing agent is precipitated in a nonspherical shape during a temperature drop of the components of the separator for a nonaqueous secondary battery from the compatible state at 280°C to 100°C at -10°C/min. In the process of manufacturing the separator for a nonaqueous secondary battery, the draw ratio at the extrusion into a film is in the range of 50 to 500. The method for manufacturing the separator for a nonaqueous secondary battery includes at least two drawing steps in the film making direction, and the temperature during the second drawing is higher than the temperature during the first drawing.

Description

  The present invention relates to a method for producing a separator for a non-aqueous secondary battery having good air permeability characteristics and an improved balance with mechanical strength, a separator for a non-aqueous secondary battery, and a secondary battery using the same.

  In recent years, non-aqueous secondary batteries have been actively researched, as typified by lithium ion secondary batteries mounted on electric vehicles and the like.

  A lithium ion secondary battery is composed of a positive electrode, a negative electrode, and a separator, and serves as a battery by lithium ion movement between the positive electrode and the negative electrode.

  The separator is a film having micropores using a polyolefin resin typified by polyethylene and polypropylene, and serves as a path for movement of lithium ions between electrodes and at the same time, insulates between the positive and negative electrodes.

  As a technique for forming fine pores in a separator using a polyolefin resin, for example, a technique using a polypropylene-based resin containing an inorganic filler (for example, see Patent Documents 1 and 2). In the methods described in Patent Documents 1 and 2, the crystal orientation of the polyolefin resin is controlled by highly controlling the conditions at the time of melt extrusion, and further, the method is based on the generation and growth of cleavage initiation points between lamellar crystals ( This is a composite pore forming technique in which pores are formed by cleaving (stretching method), inorganic filler, and polyolefin resin (interfacial peeling method).

  Porosity formation by the stretching method makes it easy to form non-communication holes due to the limitation of control of the manufacturing method, it is difficult to balance air permeability and mechanical strength, and relatively large voids formed by interfacial cleavage method. Even combining the methods of connecting the independent holes with the holes to increase the communication hole ratio is not sufficient to achieve a high balance between air permeability and mechanical strength.

  In addition, the use of fillers typified by the inorganic filler used in the interfacial debonding method has fundamental problems of process contamination due to deterioration in film surface quality and powder falling off of the film, and a method to solve these problems is required. I got it.

JP 2009-211943 A JP 2008-94911 A

  The present invention has been made in view of the above problems, and its object is to provide a method for producing a separator for a non-aqueous secondary battery in which air permeability and mechanical strength are highly balanced and powder fall is improved. A secondary battery separator and a nonaqueous secondary battery using the same.

The above object of the present invention can be achieved by the following configuration. As a separator for a non-aqueous secondary battery, it contains a polypropylene resin and at least one air permeability increasing agent, and the air permeability increasing agent is in phase when the non-aqueous secondary battery separator is heated to 280 ° C. A separator for a non-aqueous secondary battery in which the air permeability increasing agent is non-spherically precipitated while being in a molten state and falling from the compatible state of 280 ° C. to 100 ° C. at −10 ° C./min, and The method for producing a separator for a non-aqueous secondary battery includes a step in which when the film is extruded and formed, the draw ratio is 50 or more and 500 or less and the film is drawn at least twice in the film forming direction. A method for producing a separator for a non-aqueous secondary battery, characterized in that the second stretching temperature is higher than the second stretching temperature.

  2. A separator for a non-aqueous secondary battery manufactured by the method for manufacturing a separator for a non-aqueous secondary battery described in 1 above.

  3. 3. The separator for a non-aqueous secondary battery according to 2, wherein the air permeability increasing agent is deposited in a needle shape or a fiber shape having an aspect ratio of 2 or more.

  4). The air permeability increasing agent is an amide compound, an ester amide having at least one ester bond and an amide bond in the molecule, a substituted urea compound having a urea bond in the molecule, a sorbitol compound, an amino acid derivative, and a cyclic peptide derivative The separator for a non-aqueous secondary battery according to 2 or 3 above, wherein the separator is at least one selected from cyclohexane derivatives.

  5. A non-aqueous secondary battery using the separator for a non-aqueous secondary battery according to any one of 2 to 4 above.

  According to the present invention, it is possible to provide a separator for a non-aqueous secondary battery in which air permeability and mechanical strength are highly balanced, and a secondary battery using the separator.

It is a schematic diagram which shows the behavior at the time of precipitation of the air permeability increasing agent of this invention. Fig.1 (a) shows the shape of the air permeability increasing agent at the time of casting. FIG. 1 (b) shows the shape of the air permeability increasing agent after casting.

  The best mode for carrying out the present invention will be described in detail below, but the present invention is not limited thereto.

[Polypropylene resin]
Specific examples of the polypropylene resin of the present invention include homopropylene (propylene homopolymer), or propylene and ethylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1 -Random copolymers or block copolymers with α-olefins such as nonene or 1-decene. Among these, homopolypropylene is more preferably used from the viewpoint of mechanical strength as a separator.

  The polypropylene resin preferably has an isotactic pentad fraction (mmmm fraction) exhibiting stereoregularity of 80 to 99%. More preferably, it is 83-98%, More preferably, it is 85-97%. If the isotactic pentad fraction is too low, the mechanical strength as a separator may be reduced. On the other hand, the upper limit of the isotactic pentad fraction is defined by the upper limit that can be obtained industrially at the present time, but this is not the case when a more regular resin is developed in the industrial level in the future. is not.

  The isotactic pentad fraction (mmmm fraction) is the same direction for all five methyl groups that are side chains with respect to the main chain of carbon-carbon bonds composed of arbitrary five consecutive propylene units. Means the three-dimensional structure located at or its proportion. Signal assignment of the methyl group region is as follows. It conforms to Zambelli et al (Macromolecules 8, 687, (1975)).

  Moreover, it is preferable that Mw / Mn which is a parameter which shows molecular weight distribution of a polypropylene resin is 2.0-10.0. More preferably, it is 2.0-8.0, More preferably, it is 2.0-6.0. This means that the smaller the Mw / Mn is, the narrower the molecular weight distribution is. However, when the Mw / Mn is less than 2.0, problems such as a decrease in extrusion moldability occur, and it is difficult to produce industrially. . On the other hand, when Mw / Mn exceeds 10.0, the low molecular weight component increases, and the mechanical strength as a separator tends to decrease. Mw / Mn is obtained by GPC (gel permeation chromatography) method.

  Further, the melt flow rate (MFR) of the polypropylene resin is not particularly limited, but usually the MFR is preferably 0.5 to 15 g / 10 minutes, and preferably 1.0 to 10 g / 10 minutes. Is more preferable. When the MFR is less than 0.5 g / 10 min, the resin has a high melt viscosity at the time of molding and the productivity is lowered. On the other hand, if it exceeds 15 g / 10 minutes, the mechanical strength of the film is insufficient, and problems are likely to occur in practice. MFR is measured according to JIS K7210 under conditions of a temperature of 230 ° C. and a load of 2.16 kg.

  The method for producing the polypropylene resin is not particularly limited, and a known polymerization method using a known olefin polymerization catalyst, for example, a multisite catalyst represented by a Ziegler-Natta type catalyst or a metallocene catalyst. And a polymerization method using a single site catalyst.

(Air permeability increasing agent)
The air permeability increasing agent of the present invention is contained in a separator for a non-aqueous secondary battery (hereinafter also simply referred to as a separator). When the separator is heated to 280 ° C., the separator is in a compatible state, and when the temperature is lowered from the compatible state by 10 ° C./min. Further, the air permeability increasing agent of the present invention preferably has a non-spherical precipitation shape.

  Usually, in the production of a separator by a stretching method, first, a polyolefin resin typified by a polypropylene resin is cast on a cooling roll at a high draft ratio, and then cooled and solidified to produce a separator precursor. Secondly, by stretching the separator precursor with highly oriented lamellar crystals while adjusting the magnification and temperature conditions, etc., formation of independent micropores by cleavage between crystals and formation of connecting pores from the expansion of micropores To produce separator film.

  In Patent Document 1 and Patent Document 2 described above, formation of a connecting hole is promoted by containing a filler, but the results are still insufficient. This was considered to be due to the fact that when the filler contained was cast, the maximum diameter direction of the filler coincided with the casting direction of the separator, resulting in a low formation rate of the connecting holes, which led to the present invention.

  The air permeability increasing agent of the present invention is compatible at the time of extrusion in melt film formation (for example, in a T-die) in the process of manufacturing a separator, and the direction in the film is fixed at the stage of fixing the film shape by cooling. It is considered to be in a random state and non-spherical (more preferably fibrous or needle-like).

  In the process of micropore origin formation by subsequent cleavage between lamellar crystals of polypropylene by stretching and the subsequent micropore connection process, cleavage between the air permeability increasing agent and the polypropylene resin occurs and the micropore connection can be performed more efficiently. I think I can do it.

  The structure of the air permeability increasing agent of the present invention is not limited as long as it has a function of precipitating non-spherically during the cooling process.

  Examples of air permeability increasing agents include amide compounds represented by monoamide, bisamide, and trisamide, ester amides having at least one ester bond and amide bond in the molecule, and substituted urea having a urea bond in the molecule. Compounds, sorbitol compounds, amino acid derivatives, cyclic peptide derivatives, cyclohexane derivatives, and the like.

  These compounds are provided as commercial products from Shin Nippon Rika Co., Ltd., Nippon Kasei Co., Ltd., and the like.

  The precipitation shape of the air permeability increasing agent of the present invention is non-spherical. The non-spherical shape in the present invention means that the maximum and minimum distances are larger than 1.5 times in consideration of the distance of the contact point between the straight line passing through the center of gravity of the precipitate and the surface of the precipitation component.

  From the viewpoint of increasing the air permeability by connecting independent pores, the air permeability increasing agent is more preferably the shape of the precipitation component is needle-like or fibrous, and the aspect ratio is 2 or more. preferable.

(Non-aqueous secondary battery)
The non-aqueous secondary battery according to the present invention includes at least one unit electrode in which a positive electrode, a separator, and a negative electrode are stacked in this order, a lead that extracts electricity from the positive electrode and the negative electrode, and an electrolyte that is a substance that transmits ions between the positive electrode and the negative electrode These are composed of exterior materials that enclose these components. A stacked electrode group configured by stacking a plurality of sets of unit electrodes via separators may be included.

[Positive electrode]
As the positive electrode constituting the non-aqueous secondary battery of the present invention, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, manganese dioxide, metal oxide such as vanadium pentoxide or chromium oxide, molybdenum disulfide, etc. Metal sulfides are used as the active material, and a mixture of these positive electrode active materials with appropriate addition of a conductive additive or a binder such as polytetrafluoroethylene is used as a collector material such as a stainless steel net. A finished product is used as the core material.

As an example of the method for forming the positive electrode, phosphorous graphite as a conductive additive is added to lithium cobalt oxide (LiCoO ₂ ) at a mass ratio of 90: 5 (lithium cobalt oxide: phosphorous graphite) and mixed. The mixture and a solution of polyvinylidene fluoride dissolved in N-methylpyrrolidone are mixed to form a slurry. This positive electrode mixture slurry is passed through a 70-mesh net to remove large particles, and then uniformly applied to both sides of a positive electrode current collector made of an aluminum foil having a thickness of 20 μm, dried, and then compressed by a roll press. After forming, a method of cutting and forming a strip-like positive electrode plate can be mentioned.

[Negative electrode]
As the negative electrode forming material, an alkali metal or a compound containing an alkali metal integrated with a current collecting material such as a stainless steel net is used. Examples of the alkali metal include lithium, sodium, and potassium. Examples of the compound containing an alkali metal include an alloy of an alkali metal and aluminum, lead, indium, potassium, cadmium, tin or magnesium, a compound of an alkali metal and a carbon material, a low potential alkali metal and a metal oxide. An active material is a compound with a product or a sulfide.

  When a carbon material is used for the negative electrode, the carbon material may be any material that can be doped and dedoped with lithium ions. For example, graphite, pyrolytic carbons, cokes, glassy carbons, and fired bodies of organic polymer compounds Mesocarbon microbeads, carbon fibers, activated carbon and the like can be used.

  As an example of a method for forming a negative electrode, a carbon material having an average particle size of 10 μm is mixed with a solution in which vinylidene fluoride is dissolved in N-methylpyrrolidone to form a slurry, and the slurry of the negative electrode mixture is formed into a mesh of 70 mesh. After passing through and removing large particles, the negative electrode current collector made of a strip-shaped copper foil having a thickness of 18 μm was uniformly coated and dried, then compression-molded by a roll press machine, cut, and strip-shaped A method for forming a negative electrode plate can be given.

[Electrolyte]
As the electrolytic solution, an electrolytic solution in which a lithium salt is used as an electrolyte and this is dissolved in an organic solvent is used. The organic solvent is not particularly limited, but examples include esters such as propylene carbonate, ethylene carbonate, butylene carbonate, γ-butyrolactone, γ-valerolactone, dimethyl carbonate, methyl propionate or butyl acetate, and acetonitrile. Nitriles, 1,2-dimethoxyethane, 1,2-dimethoxymethane, dimethoxypropane, 1,3-dioxolane, ethers such as tetrahydrofuran, 2-methyltetrahydrofuran or 4-methyl-1,3-dioxolane, or sulfolane These may be used alone or in combination of two or more.

As an example of the electrolytic solution, a solution obtained by dissolving lithium hexafluorophosphate (LiPF ₆ ) at a rate of 1.4 mol / L in a solvent in which 2 parts by mass of methyl ethyl carbonate is mixed with 1 part by mass of ethylene carbonate. be able to.

[Method for producing porous film used in separator for non-aqueous secondary battery]
The manufacturing method of the porous film used for the separator for non-aqueous secondary batteries is: (1) a step of obtaining a raw film by mixing and extruding a thermoplastic resin, and (2) making the original film porous by stretching. Performing a heat treatment.

[Step (1)]
Step (1) is a step of obtaining a raw film by mixing and extruding the polypropylene-based resin listed above, the air permeability increasing agent, and, if necessary, additives other than those described above.

  In this step, the constituent components of the separator may be mixed and dispersed in advance and supplied to the extruder for melt extrusion molding, or may be directly supplied to the extruder for melt extrusion molding. As a method of mixing and dispersing in advance, a known method can be used. For example, a method of obtaining pellets by melt kneading using a single screw extruder, a twin screw extruder, a mixing roll, etc., a Henschel mixer, a tumbler The method of performing air blending etc. is mentioned. For the melt extrusion molding, a known uniaxial or biaxial extruder can be used, and a known die used for film production, such as a T die or a circular die, can also be used.

  When a raw film is obtained by a melt molding method using a T die, the draw ratio, which is the thickness after extrusion molding with respect to the thickness of the discharge port of the molten resin composition, is preferably 50 to 500, more preferably 200 to 300. It is.

  When the draw ratio is 50 to 500, the film is sufficiently oriented in the flow direction (MD), the formation of pores by stretching is easy, there is no thickness unevenness, and there is no need to use special equipment.

[Step (2)]
Step (2) is a step in which the raw film obtained in step (1) is made porous by stretching and heat-treated.

  It is also preferable to subject the raw film obtained in the step (1) to an annealing treatment in order to enhance crystal orientation.

  The annealing temperature is preferably −80 ° C. or higher and melting point −5 ° C. or lower with respect to the melting point of the separator component used.

  If the annealing temperature is too high, the raw film may be dissolved and the crystal structure itself may be broken.If the annealing temperature is too low, the effect of increasing the orientation tends to be low. The orientation can be increased without breaking the crystal structure.

  In the present invention, the stretching treatment is carried out twice or more under different temperature conditions, and the stretching temperature performed after the stretching temperature performed earlier in time series is higher. Each of the stretching methods in at least twice stretching may be a uniaxial stretching method or a biaxial stretching method, and the biaxial stretching method may be a simultaneous biaxial stretching method or a sequential biaxial stretching method.

  From the viewpoint that the lamellar crystals are easily oriented in the MD direction (film transport direction) by casting the separator, it is preferable to perform the above-described stretching twice or more in the MD direction.

  The stretching temperature is preferably not lower than the glass transition temperature and not higher than the melting point of the thermoplastic resin to be used, and more preferably not lower than the glass transition temperature and not higher than the melting point−10 ° C. When the film is stretched in this temperature range, the original film can be stretched without breaking, and a porous structure in which the pores are highly connected tends to be obtained.

(Pore size and pore size distribution)
As for the pore diameter of the porous membrane of the separator of the present invention, the maximum pore diameter is preferably within a range of 0.01 to 3 μm, and more preferably within a range of 0.01 to 0.5 μm. When the maximum pore diameter is less than 0.01 μm, the electrolyte solution tends to be insufficiently diffused, and the internal resistance of the battery may be increased. Moreover, when the maximum pore diameter exceeds 3 μm, for example, when used as a separator of a lithium ion secondary battery, it becomes difficult to suppress the generation of lithium dendriide (lithium needle crystals that are generated during battery reaction) Short circuit may occur.

  The average pore diameter is preferably 0.01 to 0.1 μm, more preferably 0.03 to 0.1 μm.

  Here, the average value (average pore diameter) of the pores formed in the separator is obtained by, for example, the bubble point method (JIS K 3832 or JIS B 8356-2). The measurement of the pore diameter (average pore diameter or pore diameter distribution) based on the bubble point method can be easily performed using, for example, a commercially available Porometer 3G device manufactured by Nippon Bell Co., Ltd.

(Porosity)
The porosity of the separator of the present invention is preferably 40 to 70%, more preferably 40 to 65%, and still more preferably 40 to 60%. When the porosity is 40% or more, the transmission performance tends to be excellent, and when the porosity is 70% or less, the mechanical strength is excellent and the winding property at the time of slitting tends to be good. The porosity can be measured according to ASTM D-2873, for example, by measuring the mass of the sample before and after immersion in a hexadecane solvent and measuring the volume of the sample.

(density)
The density of the material used for the separator of the present invention can be measured by the position of the sample in the concentration gradient tube according to JISK-7112.

(Puncture strength)
The membrane puncture strength of the separator of the present invention is preferably 2 to 10 N, more preferably 3 to 10 N, from the viewpoint of improving battery failure due to a short circuit between the electrodes. The piercing strength can be measured according to ASTM D3763.

(Breaking strength, elastic modulus)
The breaking strength of the separator of the present invention is preferably 500 kg / cm ² or more in both the MD direction and the TD direction from the viewpoint of battery assembly. From the viewpoint of separator tearing and meandering during battery assembly, the ratio of the breaking strength in the MD direction and the TD direction is preferably 0.1 or more and 8.0 or less. More preferably, it is 0.1 or more and 5.0 or less, More preferably, it is 0.5 or more and 2.0 or less.

  The elastic modulus of the separator is preferably in the range of 10 MPa to 600 MPa, more preferably 20 MPa to 550 MPa, and still more preferably 40 MPa to 500 MPa. When the tensile modulus is 10 MPa or more, when used as a battery separator, when wound together with the electrode, defects such as film breakage hardly occur and excellent winding properties. When it is 600 MPa or less, defects such as winding tightening after winding. Is preferable because it is difficult to occur.

  Breaking strength and elastic modulus are conditioned in accordance with JIS K-7127, for example, at 23 ° C. and 55% RH for 24 hours, using commercially available tensile tester Tensilon RTA-100 manufactured by Orientec Co., Ltd. However, the shape of the test piece is No. 1 type test piece, and the test speed can be measured under the condition of 10 mm / min.

(Heat shrink)
The thermal shrinkage rate of the separator of the present invention is preferably 0% or more and 5% or less in both the MD direction and the TD direction at 90 ° C. With the recent increase in capacity of lithium ion batteries, it is more preferable that the MD direction and the TD direction are 0% or more and 15% or less, more preferably 0% or more and 10% or less, more preferably 0, at 150 ° C. % Or more and 5% or less. When the thermal contraction rate is 15% or less in both the MD direction and the TD direction, it is preferable from the viewpoint of preventing a short circuit from occurring due to suppression of film breakage of the multilayer porous film during abnormal heat generation of the battery.

(Torsion / Linearity)
The linearity of the separator of the present invention is preferably 0.5 mm / m, and preferably 0.2 mm / m. For example, when assembling as a cylindrical battery, it is preferable because problems such as meandering are unlikely to occur when winding with an electrode.

  As the evaluation of the linearity of the separator, it can be measured on a flat table under conditions of humidity control at 25 ° C. and 50%.

(Shutdown characteristics, meltdown resistance)
The separator of the present invention may require a shutdown (SD) function in order to ensure safety. The SD function is a function for preventing the temperature increase by stopping the battery reaction by rapidly increasing the electrical resistance of the separator when the internal temperature of the battery is excessively increased due to a short circuit or the like. As a mechanism for expressing the SD function, for example, in the case of a separator made of a microporous film, when the battery internal temperature rises to a predetermined temperature, the porous structure is lost to make it non-porous, and ion permeation is blocked. Can be mentioned. However, even if the pores are made non-porous in this way and the ion permeation is blocked, if the temperature further rises and the entire film melts and breaks, the electrical insulation cannot be maintained. Therefore, the temperature at which this film cannot maintain its shape and ion passage cannot be blocked is called the meltdown temperature, and the higher the temperature, the better the heat resistance of the separator. Moreover, it can be said that it is excellent in safety, so that the difference of the said meltdown temperature and SD start temperature is large.

(Electrolyte absorption)
The electrolyte solution absorbability of the separator of the present invention is required to be quickly absorbed in order to quickly assemble in the electrolyte solution process during battery productivity. The absorption rate of the electrolytic solution can be measured, for example, by a method of dropping one drop of the electrolytic solution to be used on the separator surface and measuring the time (the time for clearing) the electrolytic solution is absorbed visually.

  The relationship between the liquid penetrating the capillary and the capillary diameter is expressed by the Lucas-Washburn equation (Equation 1) (l: penetration depth, d: capillary diameter, γ: surface tension, θ: contact angle, η: Liquid viscosity, t: time) is known. According to the formula, the penetration depth is proportional to the square root of the capillary diameter and the square root of time, and inversely proportional to the square root of the liquid viscosity. Therefore, when this is applied to a microporous membrane, it is theoretically assumed that the larger pore diameter is superior in liquid permeation.

(Liquid retention)
The electrode of the non-aqueous secondary battery of the present invention expands and contracts as lithium is inserted and removed, but the expansion rate tends to increase as the capacity of the battery increases. Since the parator is pressed by the electrode as the electrode expands and contracts along with charging and discharging, the separator is required to have a small decrease in the amount of electrolyte retained by the pressing.

(Chemical stability)
When the charge voltage of the non-aqueous secondary battery of the present invention is increased, the positive electrode has a high potential, so that the separator is exposed to a strong oxidizing environment and is susceptible to oxidative decomposition. When the molecular weight is lowered by oxidative decomposition, mechanical properties are remarkably lowered, and film breakage or the like is likely to occur. In particular, since the oxidation of the separator is more likely to proceed in a high temperature environment, film breakage or the like is more likely to occur when stored at a high temperature, and therefore a separator having high chemical stability is required.

(Dynamic friction coefficient)
From the viewpoint of performing stable production without causing problems such as wrinkles and creases in the assembly process of the nonaqueous secondary battery of the present invention, the static friction coefficient μs between separators (when both separator surfaces are superimposed) is A range of 0.3 to 1.8 is preferable. If the static friction coefficient μs is less than 0.3, the separator may slip excessively, and winding slippage or wrinkles may occur when winding in a long length. On the other hand, when μs exceeds 1.8, the surface layer polymer falls off or the separator breaks due to the friction between the separators or between the separator and the roll in the film production (film formation) and the secondary processing step, and the productivity is increased. May decrease. The dynamic friction coefficient of the separator is more preferably 0.3 to 1.5, and still more preferably 0.5 to 1.5.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

Example 1
Porous film production method As a polypropylene resin, 100% by mass of Sun Allomer PL500A (manufactured by Sun Allomer Co., Ltd.) (MFR: 3.3, Tm: 162 ° C.) and the air permeability increasing agent described in Table 1 are listed in Table 1. In addition, a resin composition was obtained that was melt-kneaded at 280 ° C. and processed into a pellet using a twin-screw extruder manufactured by Toshiba Machine Co., Ltd. (caliber φ40 mm, L / D = 32).

  The above resin composition was extruded from a T-die with an extruder and taken up with a 90 ° C. casting roll under a draw ratio of 300 to obtain a separator raw film.

  The obtained raw film for separator was uniaxially stretched 1.2 times at 25 ° C. in the casting direction, then further uniaxially stretched 2.5 times at 120 ° C. and thermally relaxed 4% at 100 ° C. Secondary battery separators 1-1 to 1-8 were produced.

(Production of non-aqueous secondary battery)
A unit electrode was produced by stacking the positive electrode plate, the separator, and the negative electrode plate so that the positive electrode active material layer and the negative electrode active material layer face each other with the separators 1-1 to 1-8 interposed therebetween. Nine unit electrodes were laminated with a separator interposed between the unit electrodes to produce a laminated electrode group. After connecting an aluminum positive electrode lead and a nickel negative electrode lead having a tab made of polypropylene (PP) resin to this laminated electrode group, it is inserted into an outer case made of an aluminum laminate sheet, and a PP tab is arranged at the sealing portion. In this way, heat welding was performed. Thereafter, a non-aqueous electrolyte was injected, and the opening of the outer case was welded while vacuum-reducing the inside of the outer case, thereby producing non-aqueous secondary batteries 1-1 to 1-8 respectively corresponding to the separators.

(Evaluation method)
[Compatibility, precipitation temperature, shape observation]
About separators 1-1 to 1-8, using a polarizing microscope (BX51-P (manufactured by Olympus Corporation)) and a hot stage for a microscope (type: 10033L (manufactured by Japan Hightech Co., Ltd.)), from room temperature to 10 ° C. The temperature was raised to 280 ° C. at a rate of temperature rise / minute, then lowered to 130 ° C. under the condition of −10 ° C./min on a horizontal glass plate at a thickness of 5.0 μm, and 280 ° C. with a polarizing microscope. The compatibility and temperature-fall precipitation were confirmed.

  The compatibility at 280 ° C. was judged by observation after holding at 280 ° C. for 5 minutes. Those that were compatible were marked with ◯, and those that were not compatible were marked with ×. The temperature at which precipitation was observed by visual observation when the temperature was lowered from 280 ° C. to 100 ° C. at 10 ° C./min was indicated as “◯”, and the case where precipitation was not observed was indicated as “x”.

[Air permeability / (Gurley air permeability)]
Gurley air permeability is one of the indexes of air permeability of a sheet, and is shown in JIS P 8117 (1998). The Gurley value (air permeability) was measured using a commercial Toyo Seiki Gurley Densometer and evaluated as follows.
A: 400 to 499 (seconds / 100 ml)
○: 500 to 599 (seconds / 100 ml)
Δ: 600 to 699 (seconds / 100 ml)
×: 700 or more (seconds / 100 ml)
[Puncture strength]
The puncture strength was measured according to ASTM D3763 and evaluated as follows.
A: 2.2 N or more B: 2.0 N or more Δ: 1.8 N or more X: less than 1.8 N [Strength at break]
The strength at break was measured by a method according to JIS K-7127. Humidity was adjusted for 24 hours in an environment of 23 ° C. and 55% RH, a commercially available tensile tester, Tensilon RTA-100 manufactured by Orientec Co., Ltd. was used, and the shape of the test piece was No. 1 type test piece. The test speed was measured under the condition of 10 mm / min.
◎: 33 MPa or more ○: 30 MPa or more Δ: 27 MPa or more ×: less than 27 MPa [powder falling]
100 non-aqueous secondary batteries 1-1 to 1-8 were produced and checked for the presence or absence of powder fall, and those without powder fall were marked with ◯ and those with powder fall confirmed with x.

  From the results shown in Table 1, the separators 1-1, 1-2, 1-4, and 1-5 of the present invention have reduced air permeability, mechanical properties, and process contamination (powder) compared to the separator 1-8 of the comparative example. It can be seen that this is a highly balanced separator. Since the separators 1-3 and 1-6 of the comparative examples were phase-separated at the time of melting, they did not precipitate non-spherically during the cooling process, and thus the balance between the increase in air permeability and mechanical properties was considered insufficient. It is done. In addition, it is considered that the separator 1-7 was powdered off because the filler was removed from the separator surface.

Example 2
(Preparation of separators 2-1 to 2-12 for non-aqueous secondary batteries)
Non-aqueous secondary battery separators 2-1 to 2-12 were produced in the same manner as non-aqueous secondary battery separators 1-1 to 1-8. However, the air permeability increasing agent was synthesized according to the method described in Table 2 in the type and amount described in Table 2.

  The obtained separators 2-1 to 2-12 for the nonaqueous secondary battery were evaluated in the same manner as the separators 1-1 to 1-8, and the results are shown in Table 2.

  From Table 2, it can be seen that separators 2-1 to 2-12 of the present invention have obtained good results in terms of air permeability, mechanical strength, and powder falling. When separators 2-1 to 2-3 and 2-4 to 2-6 are compared, the increase in the aspect ratio of the precipitated shape is a result of a better rate of increase in the air permeability, and the high aspect ratio is effective for efficiently connecting the communication holes. It is thought that the air permeability was formed and increased.

  When separators 2-7 to 2-12 are compared, the lower the deposition temperature, the better the balance between air permeability and mechanical properties. This is considered to be because a compound that precipitates at a low temperature can reduce the influence of orientation upon melt casting.

Example 3
(Preparation of separators 3-1 to 3-8 for non-aqueous secondary batteries)
Non-aqueous secondary battery separators 3-1 to 3-8 were produced in the same manner as non-aqueous secondary battery separators 1-1 to 1-8. However, the draw ratio and the stretching temperature during extrusion were performed under the conditions described in Table 3.

  As is apparent from Table 3, the draw ratio at the time of extrusion is 50 or more and 500 or less, including the step of stretching twice, and the second stretching temperature being high is the condition for obtaining a good separator. I understand.

1 Air permeability increasing agent 2 Cleavage hole

Claims (5)

  As a separator for a non-aqueous secondary battery, it contains a polypropylene resin and at least one air permeability increasing agent, and the air permeability increasing agent is in phase when the non-aqueous secondary battery separator is heated to 280 ° C. A separator for a non-aqueous secondary battery in which the air permeability increasing agent is non-spherically precipitated while being in a molten state and falling from the compatible state of 280 ° C. to 100 ° C. at −10 ° C./min, and The method for producing a separator for a non-aqueous secondary battery includes a step in which when the film is extruded and formed, the draw ratio is 50 or more and 500 or less and the film is drawn at least twice in the film forming direction. A method for producing a separator for a non-aqueous secondary battery, characterized in that the second stretching temperature is higher than the second stretching temperature.   A separator for a non-aqueous secondary battery manufactured by the method for manufacturing a separator for a non-aqueous secondary battery according to claim 1.   The separator for a non-aqueous secondary battery according to claim 2, wherein the deposition shape of the air permeability increasing agent is a needle shape or a fiber shape having an aspect ratio of 2 or more.   The air permeability increasing agent is an amide compound, an ester amide having at least one ester bond and an amide bond in the molecule, a substituted urea compound having a urea bond in the molecule, a sorbitol compound, an amino acid derivative, and a cyclic peptide derivative The separator for a non-aqueous secondary battery according to claim 2 or 3, wherein the separator is at least one selected from cyclohexane derivatives.   A non-aqueous secondary battery using the non-aqueous secondary battery separator according to claim 2.

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