JP2014113734A - Laminate porous film, separator for nonaqueous electrolyte secondary battery, and nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laminate porous film to be suitably used as a separator for an on-vehicle battery, the film which has safety in an overcharged state without decreasing air permeability.SOLUTION: The laminate porous film includes a polyolefin resin porous layer 2 having at least a polypropylene resin porous layer 2B having β-crystal activity, and a conductive layer 4 having a thickness of 0.1 nm to 50 nm layered via an easy adhesion treatment surface 3 applied on a surface of the polypropylene resin porous layer. A difference ratio of the air permeability of the laminate porous film to the air permeability of the polyolefin resin porous layer not laminated with the conductive layer is 1% or more and 30% or less.

Description

  The present invention relates to a laminated porous film, a separator for a non-aqueous electrolyte secondary battery using the laminated porous film, and a non-aqueous electrolyte secondary battery provided with the separator, and more particularly to provide safety under overcharge. In the laminated porous film in which the conductive layer is laminated on the porous resin layer, the deterioration of the air permeability characteristics is prevented.

  High capacity, high output lithium ion secondary batteries are used in electric vehicles (EV), hybrid electric vehicles (HEV), and the like. The working voltage of the lithium ion secondary battery is usually designed with an upper limit of 4.1 to 4.2V. Since an aqueous solution causes electrolysis at such a high voltage and cannot be used as an electrolytic solution, a non-aqueous electrolyte secondary battery using an organic solvent is used as an electrolytic solution that can withstand even a high voltage.

Since the lithium ion secondary battery, which is a non-aqueous electrolyte secondary battery for EV or HEV, requires a high voltage of several hundred volts for driving the motor, it is necessary to connect a large number of single cells in series. Producing high voltage. At this time, for the convenience of assembly and management, a module battery is usually constructed by connecting several to 10 single cells in series, and a whole battery system is constructed by combining multiple module batteries. doing.
Since the control of the battery input / output and the like is normally performed in module battery units, a voltage of several tens of volts is applied to the module battery, and when a defective cell is mixed in the module battery, the worst situation is Is in an overcharged state where a voltage of several tens of volts of the entire module battery is applied to one single cell, which may cause a short circuit or the like. Therefore, it is necessary to take measures to prevent a short circuit that occurs in an overcharged state and maintain safety.

  In order to prevent short circuit and to ensure safety, for example, in JP 2009-167287 A (Patent Document 1), a porous film having an inorganic thin film having a thickness of 55 to 300 nm on at least one surface of a porous polyolefin film is disclosed. Proposed. Specifically, as described in Examples 1 to 6 of Patent Document 1, a single layer of porous polypropylene film or polyethylene film was loaded into a vacuum deposition machine, and the thickness was 55 to 300 nm (Examples). 1 to 6 (60 to 290 nm) is formed by vapor deposition of an inorganic thin film (alumina, aluminum, silica in the examples).

  Japanese Patent Application Laid-Open No. 2011-65984 (Patent Document 2) discloses a non-overcharge countermeasure provided by providing a conductive layer having a required volume resistivity and a film thickness of less than 5 μm on the surface of a resin porous film. A separator for an aqueous electrolyte secondary battery is provided. The conductive layer is formed on the surface of the resin porous layer by a method such as sputtering, ion plating, or vacuum deposition.

JP 2009-167287 A JP2011-65984A

Although the porous film proposed in Patent Document 1 shows improvement in dimensional stability at high temperatures, the air permeability of the porous film on which the inorganic thin film is laminated is that the thickness of the inorganic thin film is 55. Since it is relatively thick at ˜300 nm, it is considerably deteriorated compared with the air permeability characteristics of the porous film before lamination of the inorganic thin film.
Further, in the technique disclosed in Patent Document 2, since the conductive layer is directly provided on the base material composed of the resin porous layer, the conductive layer is peeled off due to wear in the process of handling the separator or deterioration over time. There is room for improvement in terms of easy loss.
In other words, if alumina or the like is directly deposited on the surface of the porous film as the base material, the surface of the porous film is easily damaged physically and chemically, and the pores are crushed and the air permeability characteristics are reduced. And pin puncture strength tends to decrease.

  The present invention has been made in view of the above problems, and even when a conductive layer such as an inorganic thin film is laminated on a porous film to prevent a short circuit and the safety is improved, the conductive layer is not laminated ( That is, the rate of increase in numerical value from the air permeability of the porous film before lamination is small, the air permeability is excellent, the pin penetration strength is not reduced, and the conductive layer is firmly bonded to the porous film. It is an object of the present invention to provide a laminated porous film that does not easily peel off and has good battery assembly.

In order to solve the above problems, the present invention provides a polyolefin resin porous layer including a polypropylene resin porous layer having at least β crystal activity,
A conductive layer having a thickness of 0.1 nm to 50 nm, which is laminated via an easy adhesion treatment surface applied to the surface of the polypropylene resin porous layer;
The present invention provides a laminated porous film in which the ratio of the air permeability of the polyolefin resin porous layer not laminated with the conductive layer is 1% or more and 30% or less.

  The numerical value of the air permeability in the state where the conductive layer is laminated on the polyolefin resin porous layer of the present invention is that the easy adhesion treatment surface is not provided and the conductive layer is not laminated (that is, before the lamination of the conductive layer). 1) The value is increased only by 1% or more and 30% or less with respect to the numerical value of the air permeability of the polyolefin resin porous layer.

  The difference from the air permeability of the polyolefin resin porous layer in which the conductive layer is not laminated is preferably 150 seconds / 100 mL or less.

The polyolefin-based resin porous layer may be a single layer composed only of the polypropylene-based resin porous layer having the β-crystal activity, or another polyolefin with the polypropylene-based resin porous layer having the β-crystal activity positioned outside at least one of the other layers. It consists of a multilayer laminated with a porous resin layer, and in the case of the multilayer, it is laminated on the outer surface of the polypropylene resin porous layer located outside the polyolefin resin porous layer.
Specifically, the polyolefin resin porous layer is composed of a polypropylene resin porous layer having β crystal activity and an A layer, and a polyethylene resin porous layer as a B layer. It is good also as a structure of 3 layers etc. which arrange | position A layer on both outer surfaces on both sides of a layer and B layer.

  The air permeability of the entire laminated porous film of the present invention in which the conductive layer is laminated on the polyolefin resin porous layer is preferably in the range of 10 to 1000 seconds / 100 mL. If it is this range, a lamination | stacking porous film will have the outstanding air permeability.

  The easy adhesion treatment surface is preferably a treatment surface selected from any one of corona treatment, plasma treatment, sputter etching treatment, sulfonation treatment, grafting treatment, ultraviolet irradiation treatment, and electron beam irradiation treatment.

The conductive layer is preferably made of at least one selected from the group consisting of aluminum, tungsten, molybdenum, titanium, tantalum, indium tin oxide (ITO), copper, nickel, iron, and chromium.
When the laminated porous film of the present invention is used as a separator for a non-aqueous electrolyte secondary battery including a lithium ion secondary battery, the conductive layer facing the positive electrode is formed of aluminum, tungsten, molybdenum, titanium, or tantalum, The conductive layer facing the negative electrode is preferably formed of indium tin oxide (ITO), copper, nickel, titanium, iron, or chromium.

As a second invention, a method for producing a laminated porous film of the first invention is provided. That is, after forming the polyolefin resin porous layer, the surface of the polypropylene resin porous layer located outside is subjected to an easy adhesion treatment,
Next, the present invention provides a method for producing a laminated porous film in which the conductive layer is formed on the surface subjected to the easy adhesion treatment by sputtering, ion plating, or vacuum deposition.

The easy adhesion treatment is performed by corona discharge treatment, the treatment speed is preferably 1 m / min to 100 m / min, and the discharge power is preferably 0.1 kw to 10 kw.
If the treatment speed is within the above range within the discharge power range, the surface tension of the polypropylene resin porous layer can be reduced without crushing the surface, and the surface tension can be reduced, improving the adhesion with the conductive layer. It can be performed.

  Furthermore, as a third invention, there is provided a separator for a non-aqueous electrolyte secondary battery using the laminated porous film described in the first invention.

  Furthermore, as a fourth invention, there is provided a non-aqueous electrolyte secondary battery using the non-aqueous electrolyte secondary battery separator of the third invention.

  According to the laminated porous film of the present invention, the conductive layer is laminated on the outer surface of the polyolefin-based resin porous layer via the easy adhesion treatment surface, so that the 0.1 to 50 nm ultrathin conductive layer is firmly adhered. Can be laminated. In particular, since the conductive layer is as extremely thin as 0.1 to 50 nm, there is an advantage that the rate of increase in air permeability from a state where no conductivity is provided can be reduced to 1% or more and 30% or less. Therefore, even when a defective cell is mixed in the module battery and an overcharged state in which a voltage of several tens of volts of the entire module battery is applied to one or a few single cells, a short circuit or the like occurs in the conductive layer. Since generation | occurrence | production can be prevented, it can be used as a highly safe separator, and since the air permeability is not lowered, battery characteristics can be maintained. In addition, the conductive layer is not formed directly on the surface of the polyolefin resin porous layer by vapor deposition or the like, and an easy-adhesion treated surface is interposed, which may cause physical or chemical damage to the surface of the polyolefin resin porous layer. No required pin stab strength and porosity can be maintained.

(A) (B) is a schematic sectional drawing of embodiment of the lamination | stacking porous film of this invention. It is the photograph which observed the form of the surface of the conductive layer of the lamination | stacking porous film obtained in Example 1 by 10,000 times of magnification with the scanning electron microscope (SEM). It is the photograph which observed the form of the surface of the conductive layer of the lamination | stacking porous film obtained in the comparative example 1 with the magnification of 10,000 times with the scanning electron microscope (SEM).

The present invention will be described in detail below.
In the present invention, the expression “main component” includes the intention to allow other components to be contained within a range that does not interfere with the function of the main component, unless otherwise specified. Although the content ratio of the main component is not limited, the main component is, for example, 50% by mass or more, preferably 70% by mass or more, particularly preferably 90% by mass or more (including 100% by mass) in the composition. It is intended to include the meaning.

  In addition, when expressed as “X to Y” (X and Y are arbitrary numbers), “X is preferably greater than X” and “preferably Y”, with the meaning of “X to Y” unless otherwise specified. It is meant to include “less than”. Here, the upper limit value and the lower limit value of the numerical range in the present invention are not limited to those within the numerical range specified by the present invention. It is included in the equivalent range.

Below, the lamination | stacking porous film of this invention is demonstrated.
As shown in FIG. 1, the laminated porous film 1 of the present invention includes a polyolefin resin porous layer 2 having a polypropylene resin porous layer 2A having β crystal activity as at least one outer layer, and the polypropylene resin porous layer 2A. The conductive layer 4 is laminated via the easy adhesion treatment surface 3 applied to the surface of the conductive layer 4, and the conductive layer 4 is an ultrathin film having a thickness of 0.1 nm to 50 nm.
As shown in FIG. 1 (A), the polyolefin resin porous layer 2 may have a three-layer structure in which a polyethylene resin porous layer 2B is sandwiched between polypropylene resin porous layers 2A and 2A on both sides. As shown in (B), a two-layer structure in which a polypropylene resin porous layer 2A and a polyethylene resin porous layer 2B are laminated may be used. Furthermore, it is good also as a single layer which consists only of 2 A of polypropylene resin porous layers which have (beta) crystal activity.

The air permeability of the laminated porous film 1 of the present invention is such that the ratio of the difference from the air permeability of the polyolefin resin porous layer 2 on which the conductive layer 4 is not laminated is 1% or more and 30% or less. The difference from the air permeability of the polyolefin resin porous layer 2 is 150 seconds / 100 mL or less.
Moreover, it is preferable that the air permeability of the whole laminated porous film 1 of the present invention in which the conductive layer 4 is laminated on the polyolefin resin porous layer 2 is in the range of 10 to 1000 seconds / 100 mL.

<Polyolefin resin porous layer>
The polyolefin resin porous layer is a layer containing a polyolefin resin as a main component, and includes at least one polypropylene resin porous layer having β crystal activity. That is, from the viewpoint of maintaining the mechanical strength, heat resistance, etc. of the laminated porous film of the present invention, and from the viewpoint of expressing β crystal activity, a polypropylene resin is essential as a polyolefin resin, and if necessary Another polyolefin resin is further used to form a polyolefin resin porous layer.

(Polypropylene resin)
As the polypropylene resin used for the polyolefin resin porous layer of the present invention, homopropylene (propylene homopolymer), or propylene and ethylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, Examples include random copolymers or block copolymers with α-olefins such as 1-nonene and 1-decene. Among these, homopolypropylene, a block copolymer of propylene and an α-olefin are preferable, and homopropylene is particularly preferable from the viewpoints of air permeability, mechanical strength, heat resistance and the like of the laminated porous film.

  Moreover, as a polypropylene resin, it is preferable that the isotactic pendant fraction (mmmm fraction) which shows stereoregularity is 80 to 99%, More preferably, it is 83 to 99%, More preferably, it is 85 to 99. % Is used. If the isotactic pendant fraction is too low, the mechanical strength of the resulting laminated porous film may be reduced. The upper limit of the isotactic pendant fraction is defined by the upper limit value 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. Not. The isotactic pendant fraction (mmmm fraction) means that five methyl groups as side chains are located in the same direction with respect to the main chain of carbon-carbon bonds composed of arbitrary five consecutive propylene units. It means the ratio of the three-dimensional structure. The assignment of the signal of the methyl group region is as follows. It conformed to Zambelli et at al (macromolecules 8, 687, (1975)).

  Moreover, as a polypropylene resin, it is preferable that Mw / Mn which is a parameter which shows molecular weight distribution is 2.0-10.0. More preferably, 2.0 to 8.0, and still more preferably 2.0 to 6.0 is used. This means that the smaller the Mw / Mn, the narrower the molecular weight distribution. However, if the Mw / Mn is less than 2.0, for example, when forming a film by melt extrusion molding, the extrusion moldability may be lowered, Production may be difficult. On the other hand, when Mw / Mn exceeds 10.0, generally low molecular weight components increase, and the mechanical strength of the laminated porous film tends to decrease. Mw / Mn is obtained by GPC (gel permeation chromatography) method.

  The melt flow rate (MFR) of the polypropylene resin is not particularly limited, but is usually preferably 0.5 to 15 g / 10 minutes, more preferably 1.0 to 10 g / 10 minutes. preferable. When the MFR is 0.5 g / 10 min or more, for example, when forming a film by melt extrusion molding, the back pressure during the molding process does not become too high, and sufficient productivity can be ensured. On the other hand, the mechanical strength of the obtained laminated porous film can be sufficiently maintained by setting it to 15 g / 10 min or less. MFR is measured in accordance with JIS K7210 (1999) under conditions of a temperature of 230 ° C. and a load of 2.16 kg.

  The method for producing the polypropylene-based resin is not particularly limited, and is a known polymerization method using a known olefin polymerization catalyst, for example, a multisite catalyst typified by a Ziegler-Natta type catalyst or a metallocene-based catalyst. Examples thereof include slurry polymerization, melt polymerization method, bulk polymerization method, gas phase polymerization method, and bulk polymerization method using a radical initiator.

  Examples of the polypropylene resin include trade names “Novatech PP”, “WINTEC” (manufactured by Nippon Polypro Co., Ltd.), “Zeras”, “Thermoran” (manufactured by Mitsubishi Chemical Corporation), “Sumitomo Noblen”, “Tough Selenium”. (Above, manufactured by Sumitomo Chemical Co., Ltd.), “Prime Polypro”, “Prime TPO” (above, manufactured by Prime Polymer Co., Ltd.), “Adflex”, “Adsyl”, “HMS-PP (PF814)”, “Quoria” (above , Sun Aroma Co., Ltd.), “Notio”, “Toughmer XR” (above, made by Mitsui Chemicals), “Versify”, “Inspire” (above, made by Dow Chemical) can be used.

  Examples of polyolefin resins other than the polypropylene resin include homopolymers or copolymers obtained by polymerizing α-olefins such as ethylene, 1-butene, 4-methyl-1-pentene, and 1-hexene. Also, two or more of these homopolymers or copolymers can be mixed. Among these, it is preferable to use a polyethylene resin.

(Polyethylene resin)
Examples of the polyethylene resin used for the polyolefin resin porous layer of the present invention include low density polyethylene, linear low density polyethylene, linear ultra low density polyethylene, medium density polyethylene, high density polyethylene, and a copolymer mainly composed of ethylene. That is, α-olefin having 3 to 10 carbon atoms such as ethylene and propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene; vinyl esters such as vinyl acetate and vinyl propionate; acrylic Copolymers with one or more comonomers selected from unsaturated carboxylic acid esters such as methyl acrylate, ethyl acrylate, methyl methacrylate and ethyl methacrylate, and unsaturated compounds such as conjugated and non-conjugated dienes. Examples thereof include a polymer, a multi-component copolymer, and a mixed composition thereof. The ethylene unit content of the ethylene polymer is usually more than 50% by mass.

  Among these polyethylene resins, at least one polyethylene resin selected from low density polyethylene, linear low density polyethylene, and high density polyethylene is preferable, and high density polyethylene is more preferable.

Density of the polyethylene resin is preferably 0.910~0.970g / cm ^3, more preferably 0.930~0.970g / cm ^3, 0.940~0.970g / cm ³ is more preferable. A density of 0.910 g / cm ³ or more is preferable because an appropriate shutdown characteristic can be obtained. On the other hand, 0.970 g / cm ³ or less is preferable in that it can have an appropriate shutdown characteristic and can maintain stretchability.
The density can be measured according to JIS K7112 (1999) using a density gradient tube method.

Further, the melt flow rate (MFR) of the polyethylene resin is not particularly limited, but usually the MFR is preferably 0.03 to 30 g / 10 minutes, and preferably 0.3 to 10 g / 10 minutes. It is more preferable. If the MFR is 0.03 g / 10 min or more, the melt viscosity of the resin during the molding process is sufficiently low, which is excellent in productivity and preferable. On the other hand, if it is 30 g / 10 minutes or less, since sufficient mechanical strength can be obtained, it is preferable.
MFR is measured in accordance with JIS K7210 (1999) under conditions of a temperature of 190 ° C. and a load of 2.16 kg.

  The production method of the polyethylene resin is not particularly limited, and is 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. A polymerization method using a single site catalyst may be mentioned. As a polymerization method of the polyethylene resin, there are a one-stage polymerization, a two-stage polymerization, or a multistage polymerization more than that, and any method of the polyethylene resin can be used.

(Β crystal activity)
In the polyolefin resin porous layer, it is important that the polypropylene resin porous layer has β crystal activity. The β crystal activity can be regarded as an index indicating that β crystals were generated in the film-like material before stretching. If β crystals are generated in the film before stretching, even if no fillers or other additives are used, micropores can be easily formed by stretching, so a laminate with air permeability A porous film can be obtained.
Further, since the polypropylene-based resin porous layer has β crystal activity, the surface of the resulting polyolefin-based resin porous layer can form a uniform nano-order sized continuous porous structure. Even if the adhesion treatment is performed, there is little risk of physical and chemical damage, and the pin puncture strength and shutdown characteristics required for the non-aqueous electrolyte secondary battery separator are sufficiently maintained.

  In the laminated porous film of the present invention, the presence or absence of “β crystal activity” is determined when the crystal melting peak temperature derived from β crystal is detected by a differential scanning calorimeter described later and / or wide angle X-ray diffraction described later. When a diffraction peak derived from the β crystal is detected by measurement using an apparatus, it is determined that the crystal has “β crystal activity”.

  The presence or absence of “β crystal activity” is determined by holding the laminated porous film with a differential scanning calorimeter from 25 ° C. to 240 ° C. at a scanning speed of 10 ° C./min for 1 minute and then from 240 ° C. to 25 ° C. When the temperature is lowered at 10 ° C./min and held for 1 minute, and further heated again from 25 ° C. to 240 ° C. at a scanning speed of 10 ° C./min, the crystal melting peak temperature (Tmβ ) Is detected, it is judged to have β crystal activity

In addition, the β crystal activity of the laminated porous film is calculated by the following formula using the detected crystal heat of fusion (ΔHmα) and crystal heat of fusion (ΔHmβ) of the polypropylene resin. ing.
β crystal activity (%) = [ΔHmβ / (ΔHmβ + ΔHmα)] × 100

  For example, when the polypropylene resin is homopolypropylene, the amount of heat of crystal melting derived from the β crystal (ΔHmβ) detected mainly in the range from 145 ° C. to less than 160 ° C., and the detection mainly in the range from 160 ° C. to 170 ° C. It can be calculated from the heat of crystal melting (ΔHmα) derived from the α crystal. Further, for example, in the case of random polypropylene copolymerized with 1 to 5 mol% of ethylene, the crystal melting heat amount (ΔHmβ) derived from the β crystal detected mainly in the range of 120 ° C. or higher and lower than 140 ° C. It can be calculated from the crystal melting calorie (ΔHmα) derived from the α crystal detected in the range of from 0 ° C. to 165 ° C.

The β-crystal activity of the laminated porous film is preferably larger, specifically 20% or more, more preferably 40% or more, and particularly preferably 60% or more. If the laminated porous film has a β crystal activity of 20% or more, it indicates that a large number of β crystals of polypropylene resin can be produced in the film-like material before stretching, and fine and uniform pores are formed by stretching. As a result, a laminated porous film, particularly a battery separator, having high mechanical strength and excellent air permeability can be obtained.
The upper limit value of the β crystal activity is not particularly limited, but the higher the β crystal activity, the more effective the effect is obtained, so the closer it is to 100% is preferable.

The presence or absence of the β crystal activity can also be determined by a diffraction profile obtained by wide-angle X-ray diffraction measurement of a laminated porous film subjected to a specific heat treatment.
Specifically, the laminated porous film subjected to heat treatment at 170 ° C. to 190 ° C., which is a temperature exceeding the melting point of the polypropylene resin, and gradually cooled to produce and grow β crystals, was subjected to wide-angle X-ray measurement, When the diffraction peak derived from the (300) plane of the β-crystal of the polypropylene resin is detected in the range of 2θ = 16.0 ° to 16.5 °, it is determined that there is β-crystal activity.

  For details on the β crystal structure and wide-angle X-ray diffraction measurement of polypropylene resins, see Macromol. Chem. 187, 643-352 (1986), Prog. Polym. Sci. Vol. 16, 361-404 (1991), Macromol. Symp. 89, 499-511 (1995), Macromol. Chem. 75, 134 (1964) and references cited therein. A detailed evaluation method of the β crystal activity using wide-angle X-ray diffraction will be described in Examples described later.

  As the method for obtaining the β crystal activity described above, there is a method in which a substance that promotes the generation of α crystal of the polypropylene resin is not added, or a treatment for generating a peroxide radical as described in Japanese Patent No. 3739481. Examples thereof include a method of adding the applied polypropylene and a method of adding a β crystal nucleating agent to the composition.

(Β crystal nucleating agent)
Examples of the β crystal nucleating agent used in the present invention include the following, but are not particularly limited as long as they increase the formation and growth of β crystals of polypropylene resin, and two or more types are mixed. May be used.

  Examples of the β crystal nucleating agent include amide compounds; tetraoxaspiro compounds; quinacridones; iron oxides having a nanoscale size; potassium 1,2-hydroxystearate, magnesium benzoate or magnesium succinate, magnesium phthalate, etc. Alkali or alkaline earth metal salts of carboxylic acids represented by: aromatic sulfonic acid compounds represented by sodium benzenesulfonate or sodium naphthalenesulfonate; di- or triesters of dibasic or tribasic carboxylic acids; phthalocyanine blue Phthalocyanine pigments typified by, etc .; two-component compounds consisting of component A, which is an organic dibasic acid, and component B, which is an oxide, hydroxide or salt of a Group 2 metal in the periodic table; cyclic phosphorus compounds and magnesium Composition comprising a compound Etc., and the like. In addition, specific types of nucleating agents are described in JP-A No. 2003-306585, JP-A Nos. 06-228966, and JP-A Nos. 09-194650.

  As a commercial product of β crystal nucleating agent, β crystal nucleating agent “NJESTER NU-100” manufactured by Shin Nippon Rika Co., Ltd., specific examples of polypropylene resin to which β crystal nucleating agent is added include polypropylene “Bepol” manufactured by Aristech. B-022SP ”, polypropylene manufactured by Borealis“ Beta (β) -PP BE60-7032 ”, polypropylene manufactured by Mayzo“ BNX BETAPP-LN ”, and the like.

  The proportion of the β-crystal nucleating agent added to the polypropylene-based resin needs to be appropriately adjusted depending on the type of the β-crystal nucleating agent or the composition of the polypropylene-based resin, but the polypropylene-based constituting the polypropylene-based resin layer. It is preferable to mix | blend in the ratio of 0.0001 mass part to 5 mass parts with respect to 100 mass parts of resin. Moreover, 0.001 mass part to 3 mass parts is more preferable, and 0.01 mass part to 1 mass part is still more preferable. If it is 0.0001 parts by mass or more, β-crystals of polypropylene resin can be sufficiently generated and grown during film formation, and sufficient β-crystal activity can be secured even when a porous film is formed. Ventilation performance can be obtained. Addition of 5 parts by mass or less is preferable because it is economically advantageous and there is no bleeding of the β crystal nucleating agent on the surface of the laminated porous film.

(Other ingredients)
In the present invention, in addition to the components described above, the amount generally added to the resin composition can be appropriately added within a range that does not significantly impair the effects of the present invention. Examples of the additive include recycling resin, silica, talc, kaolin, calcium carbonate, and the like, which are added for the purpose of improving and adjusting molding processability, productivity, and various physical properties of the porous film. Inorganic particles such as, pigments such as titanium oxide and carbon black, flame retardants, weathering stabilizers, heat stabilizers, antistatic agents, melt viscosity improvers, crosslinking agents, lubricants, nucleating agents, plasticizers, anti-aging agents, Examples thereof include additives such as antioxidants, light stabilizers, ultraviolet absorbers, neutralizers, antifogging agents, antiblocking agents, slip agents, and coloring agents. Further, in order to promote the opening and impart moldability, the modified polyolefin resin, the aliphatic saturated hydrocarbon resin or a modified product thereof, an ethylene polymer, as long as the effects of the present invention are not significantly impaired. Wax or low molecular weight polypropylene may be added.

(Layer structure of polyolefin resin porous layer)
The polyolefin resin porous layer of the present invention may be a single layer or multiple layers as long as at least one outermost layer of the polypropylene resin porous layer having β crystal activity is provided. is not. Among them, a single layer of the polypropylene resin porous layer having the β crystal activity (hereinafter may be referred to as “A layer”), the A layer and other layers (hereinafter “ Lamination is sometimes preferred. For example, when used as a separator for a non-aqueous electrolyte secondary battery, a low melting point resin layer is provided to close the hole in a high temperature atmosphere as described in JP-A No. 04-181651 and to ensure the safety of the battery. Can be made.

Specific examples include a two-layer structure in which A layers / B layers are stacked, and a three-layer structure in which A layers / B layers / A layers are stacked. In addition, a form such as a three-layer three-layer is possible in combination with a layer having other functions. In this case, the order of stacking with other functions is not limited. Further, the number of layers may be increased as necessary to 4 layers, 5 layers, 6 layers, and 7 layers.
In addition, the physical property of the polyolefin resin porous layer used for this invention can be freely adjusted with a layer structure, a lamination ratio, a composition of each layer, and a manufacturing method.

(Manufacturing method of polyolefin resin porous layer)
Next, although the manufacturing method of the polyolefin resin porous layer of this invention is demonstrated, this invention is not limited only to the polyolefin resin porous layer manufactured by this manufacturing method.

  Specifically, using the polyolefin-based resin, a non-porous film-like product was produced by melt extrusion, and a number of fine pores having communication in the thickness direction were formed by stretching the non-porous film-like product. A porous film can be obtained.

  The method for producing the non-porous film is not particularly limited, and a known method may be used. For example, a method of melting a thermoplastic resin composition using an extruder, extruding from a T die, and cooling and solidifying with a cast roll. Is mentioned. Further, a method of cutting a film-like material manufactured by a tubular method into a flat shape can be applied.

  The method for making the nonporous film-like material is not particularly limited, and a known method such as wet uniaxial stretching or porous uniaxial stretching or porous uniaxial stretching may be used. As the stretching method, there are methods such as a roll stretching method, a rolling method, a tenter stretching method, and a simultaneous biaxial stretching method, and these methods are used alone or in combination of two or more to perform uniaxial stretching or biaxial stretching. Among these, sequential biaxial stretching is preferable from the viewpoint of controlling the porous structure. Moreover, the method of extracting and drying the plasticizer contained in the polyolefin-type resin composition with a solvent before and behind extending | stretching as needed is also applied.

Further, in the present invention, a method for laminating a plurality of polyolefin resin porous layers is roughly classified into the following four types depending on the order of perforation and lamination.
(1) A method of laminating each porous layer after laminating each porous layer or by adhering with an adhesive or the like.
(2) A method of laminating each layer to produce a laminated nonporous film-like material and then making the nonporous film-like material porous.
(3) A method in which one of the layers is made porous and then laminated with another layer of non-porous film to make it porous.
(4) A method for forming a laminated porous film by preparing a porous layer and then coating with inorganic / organic particles or depositing metal particles.
In the present invention, it is preferable to use the method (2) from the viewpoint of simplicity of the process and productivity, and in particular, in order to ensure the interlayer adhesion between the two layers, a laminated nonporous film-like material is formed by coextrusion. A method of making it porous after production is particularly preferred.

Below, the specific example of the manufacturing method of a polyolefin resin porous layer is demonstrated.
First, a mixed resin composition of the polyolefin resin and, if necessary, a thermoplastic resin and an additive is prepared. For example, a raw material such as a polypropylene resin, a β crystal nucleating agent, and other additives as required, preferably using a Henschel mixer, a super mixer, a tumbler type mixer, or the like, or by hand-blending all ingredients in a bag After mixing, the mixture is melt-extruded and cut by a single-screw or twin-screw extruder, a kneader, etc., preferably a twin-screw extruder, to obtain pellets.

  The pellets are put into an extruder and extruded from a T-die extrusion die to form a nonporous film. The type of T die is not particularly limited. For example, when the polyolefin-based resin porous layer has a laminated structure of two types and three layers, the T die may be a multi-manifold type for two types and three layers or a feed block type for two types and three layers.

  The gap of the T die to be used is finally determined from the required film thickness, stretching conditions, draft rate, various conditions, etc., but is generally about 0.1 to 3.0 mm, preferably 0.5. -1.0 mm. If it is 0.1 mm or more, there is little possibility that the back pressure at the time of melt extrusion becomes high or melt fracture occurs, and therefore, it is preferable from the viewpoint of production stability. Moreover, if it is 3.0 mm or less, since the draft rate does not increase too much, there is little fear of the occurrence of draw resonance, etc., which is preferable from the viewpoint of production stability.

  In extrusion molding, the extrusion temperature is appropriately adjusted depending on the flow characteristics and moldability of the resin composition, but is generally preferably 180 to 350 ° C, more preferably 200 to 330 ° C, and further preferably 200 to 300 ° C. A temperature of 180 ° C. or higher is preferable because the viscosity of the molten resin is sufficiently low and the moldability is excellent and the productivity is improved. On the other hand, by setting the temperature to 350 ° C. or lower, it is possible to suppress the deterioration of the resin composition, and hence the mechanical strength of the laminated porous film obtained.

  The cooling and solidification temperature by the cast roll is very important in the present invention, and the ratio of β crystals of the polypropylene resin in the non-porous film can be adjusted. The cooling and solidification temperature of the cast roll is preferably 80 to 150 ° C, more preferably 90 to 140 ° C, and still more preferably 100 to 130 ° C. It is preferable to set the cooling and solidification temperature to 80 ° C. or higher because the ratio of β crystals in the film can be sufficiently increased. Further, by setting the temperature to 150 ° C. or lower, it is preferable that troubles such as the extruded molten resin stick to and roll around the cast roll hardly occur, and it is possible to efficiently form a nonporous film-like material.

  By setting the cast roll in the temperature range, it is preferable to adjust the β crystal ratio of the polypropylene resin of the non-porous film-like material before stretching to 30 to 100%. 40-100% is more preferable, 50-100% is still more preferable, and 60-100% is the most preferable. By setting the β crystal ratio of the non-porous film-like material before stretching to 30% or more, a porous polyolefin resin porous layer having good air permeability can be obtained because it can be easily made porous by a subsequent stretching operation.

The β crystal ratio of the non-porous film before stretching was determined by heating the non-porous film from 25 ° C. to 240 ° C. at a heating rate of 10 ° C./min using a differential scanning calorimeter. It is calculated by the following formula using the detected heat of crystal melting (ΔHmα) and the heat of crystal melting (ΔHmβ) derived from the β crystal of the polypropylene resin to be detected.
β crystal ratio (%) = [ΔHmβ / (ΔHmα + ΔHmβ)] × 100

  Next, it is more preferable to stretch at least the obtained non-porous film-like product. In the stretching step, uniaxial stretching may be performed in the longitudinal direction or the transverse direction, or biaxial stretching may be performed. In addition, when biaxial stretching is performed, simultaneous biaxial stretching or sequential biaxial stretching may be performed, but stretching conditions (magnification, temperature) can be easily selected in each stretching process, and a porous structure Sequential biaxial stretching is more preferred because it is easy to control. The longitudinal direction of the non-porous membrane and film is referred to as “longitudinal direction”, and the direction perpendicular to the longitudinal direction is referred to as “lateral direction”. Further, stretching in the longitudinal direction is referred to as “longitudinal stretching”, and stretching in the direction perpendicular to the longitudinal direction is referred to as “lateral stretching”.

  When sequential biaxial stretching is used, the stretching temperature needs to be appropriately changed depending on the composition of the resin composition to be used, the crystal melting peak temperature, the crystallization temperature, the crystallinity, etc., but the stretching temperature in the longitudinal stretching is generally from 0 to 130. The temperature is preferably controlled in the range of 10 to 120 ° C, more preferably 20 to 120 ° C. The draw ratio is preferably 2 to 10 times, more preferably 3 to 8 times, still more preferably 4 to 7 times. By performing longitudinal stretching within the above range, it is possible to develop an appropriate pore starting point while controlling breakage during stretching.

  On the other hand, the stretching temperature in transverse stretching is generally 100 to 160 ° C, preferably 110 to 150 ° C, and more preferably 120 to 140 ° C. Moreover, a preferable draw ratio is 1.2-10 times, More preferably, it is 1.5-8 times, More preferably, it is 2-7 times. By transversely stretching within the above range, the pore starting point formed by longitudinal stretching can be appropriately expanded, and a fine porous structure can be expressed.

  The stretching speed in the stretching step is preferably 500 to 12000% / min, more preferably 1000 to 10,000% / min, and further preferably 1500 to 8000% / min.

  The film to be the polyolefin resin porous layer thus obtained is preferably heat-treated for the purpose of improving dimensional stability. In this case, the effect of dimensional stability can be expected by setting the temperature to preferably 100 ° C. or higher, more preferably 120 ° C. or higher, and still more preferably 140 ° C. or higher. On the other hand, the heat treatment temperature is preferably 170 ° C. or lower, more preferably 165 ° C. or lower, and further preferably 160 ° C. or lower. When the heat treatment temperature is within the above range, it is preferable that the polyolefin resin hardly melts by the heat treatment and the porous structure can be maintained. Moreover, you may perform a 1-20% relaxation process as needed during the heat processing process. In addition, after heat processing, a polyolefin resin porous layer is obtained by cooling uniformly and winding up.

<Easy adhesion treatment>
On the surface of the polypropylene resin porous layer 2A having β crystal activity, which is provided in at least one outermost layer of the polyolefin resin porous layer 2 of the present invention comprising the film produced by the production method, a thickness of 0.1 nm to The conductive layer 4 of 50 nm is formed, but before forming the conductive layer 4, the surface of the polypropylene resin porous layer 2 </ b> A is subjected to an easy adhesion treatment, and the easy adhesion treatment surface 3 is formed between the conductive layer 4 and the conductive layer 4. is important.
The easy adhesion treatment is a treatment for modifying the surface of the polypropylene resin porous layer so as to improve the adhesion to the conductive layer. As the treatment method, for example, corona treatment, plasma treatment, sputter etching treatment, sulfonation treatment, graft treatment, ultraviolet irradiation treatment, electron beam irradiation treatment, or the like can be used. Among these, corona treatment, plasma treatment, or sputter etching treatment is preferable from the viewpoint of processing performance and ease of processing (productivity), and corona treatment is particularly preferable in view of simplicity of equipment and work. is there.

  As a condition for performing the corona treatment as the easy adhesion treatment, the treatment speed is preferably 1 m / min or more from the viewpoint of productivity, and preferably 100 m / min or less from the viewpoint of stability of the surface treatment. . Further, the discharge power in the treatment is preferably 0.1 kw or more from the viewpoint of easy adhesion, and preferably 10 kw or less from the viewpoint of preventing damage to the polypropylene resin porous layer.

  When a laminated porous film in which a conductive layer is formed on the surface of the polypropylene resin porous layer without applying an easy adhesion treatment as a battery separator is used to produce a battery, the feeding speed of the laminated porous film fed from the reel is increased. The vibration and load applied to the laminated porous film are increased, and the conductive layer may be peeled off from the laminated porous film. When the conductive layer is peeled off, the pores of the polyolefin resin porous layer are partially blocked by the peeled conductive layer, resulting in a problem that a stable battery reaction is hindered. On the other hand, when the conductive layer is formed after the surface of the polypropylene resin porous layer is subjected to the easy adhesion treatment, the adhesive strength of the conductive layer is increased, the peeling of the conductive layer can be prevented, and the occurrence of the above problems can be prevented.

  Furthermore, by subjecting the surface of the polypropylene resin porous layer having β crystal activity to an easy adhesion treatment, the surface of the polypropylene resin porous layer is less likely to be physically and chemically damaged during the formation of the conductive layer. Pin puncture strength and shutdown characteristics required for the electrolyte secondary battery separator are sufficiently maintained. On the other hand, even if an easy adhesion treatment is performed on a polypropylene resin porous layer having no β crystal activity, the distribution of the porous size on the surface of the obtained polypropylene resin porous layer is increased. Since there is an increased risk of being damaged chemically and chemically, there remains a problem in terms of improving safety when used as a separator for a non-aqueous electrolyte secondary battery.

<Conductive layer>
In the laminated porous film of the present invention, the conductive layer 4 having a thickness of 0.1 to 50 nm is formed on at least one surface of the polyolefin resin porous layer 2 from the viewpoint of overcharge resistance. As described above, the overcharge resistance is an overcharged state in which defective cells are mixed in the module battery and a voltage of several tens of volts of the entire module battery is applied to one or a few single cells. This is a characteristic that can prevent short circuit and explosion. The reason why the overcharge resistance can be greatly improved is presumed to be that the conductive layer 4 provided on at least one side of the laminated polyolefin resin porous layer 2 homogenizes the electric field inside the battery in the overcharged state. The

  The material constituting the conductive layer 4 according to the present invention (hereinafter may be abbreviated as “conductive material”) is not particularly limited as long as it has conductivity. For example, a metal or its oxidation is used. Or a carbonaceous material can be used.

  When the laminated porous film according to the present invention is used as a separator of a lithium ion secondary battery, the metal material selection criteria are different between the conductive layer facing the positive electrode and the conductive layer facing the negative electrode. That is, when the conductive layer faces the positive electrode, the conductive layer has a high potential, and therefore gold or alloys having a high oxidation potential are preferably used. Moreover, the valve metal which produces a passive film by anodic oxidation is also used suitably. Examples of the valve metal include aluminum, tungsten, molybdenum, titanium, and tantalum. Further, stainless steel having a chromium oxide film can also be suitably used.

  On the other hand, for the conductive layer facing the negative electrode, it is necessary to select a metal material that does not form an alloy with lithium. Examples of such a metal or oxide thereof include copper, nickel, titanium, iron, molybdenum, chromium, and indium tin oxide (hereinafter referred to as ITO), and any of them can be suitably used.

A method for forming the conductive layer is not particularly limited, and a known method is used.
As an example, a method of forming a conductive layer on at least one surface of the polypropylene resin porous layer by a method such as sputtering, ion plating, or vacuum deposition may be mentioned. Moreover, in the laminated porous film of the present invention, when the conductive layer is formed on the inner side, a method of laminating another porous film on the conductive layer side of the separator in which the conductive layer is formed on one side described above is integrated. It is done.

<Shape and physical properties of laminated porous film>
The total thickness of the laminated porous film 1 of the present invention is preferably 5 to 100 μm. More preferably, it is 8-50 micrometers, More preferably, it is 10-30 micrometers. When used as a separator for a non-aqueous electrolyte secondary battery, within the above range, substantially necessary electrical insulation can be obtained. For example, even when a large force is applied to the protruding portion of the electrode, The problem that the porous film is broken and short-circuited does not occur, and the electric resistance can be within the actual use range.

  The thickness of the conductive layer 4 is 0.1 nm or more, preferably 0.5 nm or more, more preferably 1 nm or more, from the viewpoint of overcharge resistance. On the other hand, the upper limit is 50 nm or less, preferably 30 nm or less, more preferably 20 nm or less, from the viewpoint of air permeability of the laminated porous film.

In the laminated porous film of the present invention, the porosity is preferably 30% or more, more preferably 35% or more, and further preferably 40% or more. If the porosity is 30% or more, it is possible to obtain a laminated porous film that ensures communication and has excellent air permeability.
On the other hand, the upper limit is preferably 70% or less, more preferably 65% or less, and still more preferably 60% or less. If the porosity is 70% or less, the strength of the laminated porous film is hardly lowered, which is preferable from the viewpoint of handling. In addition, the porosity of this invention is measured by the method as described in an Example.

  The air permeability of the laminated porous film of the present invention is preferably 1000 seconds / 100 mL or less, more preferably 10 to 800 seconds / 100 mL, still more preferably 50 to 700 seconds / 100 mL. If it is 1000 seconds / 100 mL or less, the air permeability as a separator of a lithium ion secondary battery can be maintained.

  The air permeability represents the difficulty of air removal in the film thickness direction, and is specifically expressed by the number necessary for 100 mL of air to pass through the film. Therefore, the smaller the value, the easier it is for air to pass through, and the larger the value, the harder it is to pass. That is, the smaller the value, the better the communication in the thickness direction of the film. Communicability is the degree of connection of holes in the thickness direction of the film. If the air permeability of the laminated porous film of the present invention is low, it can be used for various applications. For example, when used as a separator for a non-aqueous electrolyte secondary battery, a low air permeability means that lithium ions can be easily transferred, which is preferable because battery performance is excellent.

  The ratio of the difference between the air permeability of the laminated porous film 1 of the present invention and the air permeability of the polyolefin resin porous layer 2 before the conductive layer 4 is laminated is used as a separator for a non-aqueous electrolyte secondary battery. From the viewpoint of the ease of movement of lithium ions in this case, it is 1% or more and 30% or less, more preferably 5% or more and 20% or less, and further preferably 5% or more and 16% or less.

  Further, the difference between the air permeability of the laminated porous film 1 of the present invention and the air permeability of the film composed of the polyolefin resin porous layer 2 before the conductive layer 4 is laminated is preferably 150 seconds / 100 mL or less. More preferably, it is 120 seconds / 100 mL or less, More preferably, it is 90 seconds / 100 mL or less. The lower limit is 0 second / 100 mL or more. However, when the conductive layer 4 is provided, the air permeability is mostly increased slightly, and it is considered that the lower limit is usually 1 second / 100 mL or more.

<Battery>
A nonaqueous electrolyte secondary battery comprising a lithium ion secondary battery containing the laminated porous film 1 of the present invention as a battery separator will be described.
Both electrodes of the positive electrode plate and the negative electrode plate are arranged so as to overlap each other via a battery separator.

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. Although it does not specifically limit as an organic solvent, For example, propylene carbonate, ethylene carbonate, butylene carbonate, (gamma) -butyrolactone, (gamma) -valerolactone, dimethyl carbonate, methyl propionate, or esters, such as butyl acetate, acetonitrile, etc. Nitriles, ethers such as 1,2-dimethoxyethane, 1,2-dimethoxymethane, dipetoxypropane, 1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, or 4-methyl-1,3-dioxolane Or sulfolane. These may be used alone or in admixture of two or more.
Among them, an electrolytic solution obtained by dissolving lithium hexafluorophosphate (LiPF ₆₎ at a rate of 1.0 mol / L in a solvent obtained by mixing 2 parts by mass of methyl ethyl carbonate relative to ethylene carbonate 1 part by weight is preferred.

As the negative electrode, 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, and the like. Or a compound with a sulfide or the like.
When using a carbon material for the negative electrode, the carbon raw material may be any material that can be doped and dedoped with lithium ions, such as graphite, pyrolytic carbons, cokes, glassy carbons, a fired body of an organic polymer compound, Mesocarbon microbeads, carbon fibers, activated carbon and the like can be used.

  In this embodiment, as a negative electrode, a carbon material having an average particle size of 10 μm is mixed with a solution in which polyvinylidene fluoride is dissolved in N-methylpyrrolidone to form a slurry, and this negative electrode mixture slurry is passed through a mesh of 70 mesh. After removing the large particles, the negative electrode current collector made of a strip-shaped copper foil having a thickness of 18 μm is uniformly coated and dried, then compression molded by a roll press machine, and then cut.

  As a positive electrode, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, manganese dioxide, metal oxide such as vanadium pentoxide or chromium oxide, metal sulfide such as molybdenum disulfide, and the like are used as active materials. , These positive electrode active materials are combined with conductive additives and binders such as polytetrafluoroethylene as appropriate, and finished with a current collector material such as a stainless steel mesh as a core material. It is done.

In the present embodiment, a positive electrode plate manufactured as follows is used as the positive electrode. In other words, lithium graphite oxide (LiCoO ₂ ) was added with phosphorous graphite as a conductive additive at a mass ratio of 95: 5 (lithium cobalt oxide: phosphorous graphite) and mixed, and this mixture and polyvinylidene fluoride were mixed with N -Mix with a solution dissolved in methylpyrrolidone to make 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 aluminum foil having a thickness of 20 μm and dried, and then compression molded by a roll press. And then cut to make a positive electrode plate

Examples and comparative examples are shown below. In addition, this invention is not limited to an Example.
The longitudinal direction of the laminated porous film 1 is referred to as “longitudinal direction”, and the direction perpendicular to the longitudinal direction is referred to as “lateral direction”.

(1) Thickness With a dial gauge of 1/1000 mm, 30 areas in the surface where the conductive layer is formed on the laminated polyolefin resin porous layer are unspecified, and the average value is the thickness of the laminated porous film. It was.

(2) Air permeability (Gurley value)
The air permeability (seconds / 100 mL) was measured according to JIS P8117 (2009).

(3) Pin puncture strength A needle having a curvature radius of 0.5 mm was pierced at a puncture speed of 300 mm / min, and the maximum load when a hole was formed was measured. The obtained maximum load was defined as pin puncture strength. The pin puncture strength was obtained as a converted value per 25 μm thickness.

(4) Overcharge resistance test For a new battery that has not undergone a charge / discharge cycle, a current value of 5 C (1) is maintained until the SOC reaches 230% in an environment adjusted so that the temperature inside the battery becomes 95 ° C. CC charge is performed at a rated capacity based on the discharge capacity at a time rate of 1 C, and the current value is 1 C (the same applies hereinafter), and then switched to constant voltage (CV) charge. The initial application is 30 V and 1 minute. Retained. When no short circuit was observed, the voltage was increased in increments of 5V and the same cycle was repeated until a short circuit was observed, and the voltage at which the short circuit was observed was measured and evaluated according to the following criteria.
○: When the short-circuit voltage is 65 V or more ×: When the short-circuit voltage is less than 65 V

(5) Differential scanning calorimetry (DSC)
Using a differential scanning calorimeter (DSC-7) manufactured by Perkin Elmer, the obtained laminated porous film was heated to 25-240 ° C. at a scanning rate of 10 ° C./min and held for 1 minute, and then 240-240 The temperature was lowered to 25 ° C. at a scanning speed of 10 ° C./min and held for 1 minute, and then heated again to 25-240 ° C. at a scanning speed of 10 ° C./min. The presence or absence of β crystal activity was evaluated according to the following criteria depending on whether or not a peak was detected at 145 to 160 ° C., which is a crystal melting peak temperature (Tmβ) derived from β crystal of polypropylene resin after the temperature rise. .
○: When Tmβ is detected within the range of 145 to 160 ° C (with β crystal activity)
X: When Tmβ is not detected within the range of 145 to 160 ° C. (no β crystal activity)
The β crystal activity was measured with a sample amount of 10 mg in a nitrogen atmosphere.

(6) Wide angle X-ray diffraction measurement (XRD)
The laminated porous film was cut into a 60 mm long × 60 mm wide square, and as shown in FIG. 2 (A), an aluminum plate having a circular hole with a central portion of 40 mmφ (material: JIS A5052, size: 60 mm long, 60 mm wide, (Thickness 1 mm) was sandwiched between two sheets, and the surrounding four sides were fixed with clips. A sample in which the laminated porous film is constrained by two aluminum plates is placed in a ventilation constant temperature and temperature chamber (model: DKN602, manufactured by Yamato Kagaku Co., Ltd.) having a measurement temperature of 180 ° C. and a display temperature of 180 ° C., and set for 3 minutes. The temperature was changed to 100 ° C., and a slow cooling to 100 ° C. was performed by applying a temperature of 10 minutes or more. When the display temperature reached 100 ° C., the sample was taken out and cooled in an atmosphere of 25 ° C. for 5 minutes while being restrained by two aluminum plates to obtain a sample. The obtained sample was subjected to wide-angle X-ray diffraction measurement for a circular portion of 40 mmφ at the center under the following measurement conditions.
-Wide-angle X-ray diffraction measurement device: manufactured by Mac Science Co., Ltd., model number: XMP18A
X-ray source: CuKα ray, output: 40 kV, 200 mA
Scanning method: 2θ / θ scan, 2θ range: 5 to 25 °, scanning interval: 0.05 °, scanning speed: 5 ° / min For the obtained diffraction profile, β-crystal (300) plane of polypropylene resin The presence or absence of β crystal activity was evaluated from the peak derived from the following.
◯: When a peak is detected in the range of 2θ = 16.0 to 16.5 ° (with β crystal activity)
X: When a peak is not detected in the range of 2θ = 16.0 to 16.5 ° (no β crystal activity)
In addition, when a laminated porous film piece cannot be cut out to a 60 mm x 60 mm square, it may adjust so that a laminated porous film may be installed in the circular hole of 40 mmphi in the center part, and may produce a sample.

(Preparation of non-aqueous electrolyte)
Under a dry argon atmosphere, sufficiently dried lithium hexafluorophosphate (LiPF ₆ ) was dissolved in a solvent in which ethylene carbonate and ethyl methyl carbonate were mixed in a volume ratio of 3/7 so that the ratio was 1.0 mol / L. A non-aqueous electrolyte was used.

(Preparation of positive electrode)
LiNi _1/3 Mn _1/3 Co _1/3 O ₂ was used as the positive electrode active material, LiNi _1/3 Mn _1/3 Co _1/3 O ₂ was 90 parts by weight, 5 parts by weight of acetylene black and polyfluorinated 5 parts by mass of vinylidene (“KF-1000” manufactured by Kureha Chemical) was added and mixed, and the mixture was dispersed in N-methyl-2-pyrrolidone to form a slurry. The obtained slurry was uniformly applied to both surfaces of a 15 μm-thick aluminum foil as a positive electrode current collector, dried, and then rolled to a thickness of 81 μm by a press machine. A positive electrode was cut out into a shape having an uncoated part with a thickness of 100 mm and a width of 30 mm. The density of the positive electrode active material was 2.35 g / cm ³ .

(Preparation of negative electrode)
Natural graphite powder is used as a negative electrode active material, natural graphite powder is 98 parts by weight, carboxymethylcellulose sodium aqueous solution (concentration of 1% by weight of sodium carboxymethylcellulose) is used as a thickener, and styrene-butadiene rubber is used as a binder. 2 parts by weight of an aqueous dispersion (styrene / butadiene rubber concentration 50% by weight) was added and mixed to form a slurry. The obtained slurry was applied to both sides of a rolled copper foil having a thickness of 10 μm as a negative electrode current collector, dried, and then rolled to a thickness of 75 μm with a pressing machine. A negative electrode was cut into a shape having an uncoated part with a thickness of 104 mm and a width of 30 mm. The density of the negative electrode active material layer was 1.35 g / cm ³ .

(Production of battery)
The positive electrode plate and the negative electrode plate produced as described above were alternately arranged, and the separators obtained in Examples and Comparative Examples were laminated between the electrodes so that the conductive layer side was opposed to the positive electrode side. At this time, the positive electrode active material surface was faced so as not to deviate from the negative electrode active material surface. A current collector tab is welded to the uncoated portion of each of the positive electrode and the negative electrode to form an electrode body, and a laminate sheet (total thickness) in which a polypropylene film, an aluminum foil having a thickness of 0.04 mm, and a nylon film are laminated in this order. 0.1 mm) was sandwiched with a laminate sheet so that the polypropylene film was on the inner surface side, and the area without electrodes was heat-sealed except for one piece for injecting the electrolyte solution. Thereafter, 200 μL of a non-aqueous electrolyte was injected into the active material layer, sufficiently infiltrated into the electrode, and sealed to produce a laminate cell.

[Example 1]
(Polyolefin resin porous layer)
Polypropylene resin (manufactured by Nippon Polypro, Novatec PP FY6HA, MFR: 2.4 g / 10 min) as the material of the resin composition constituting the A layer, and 3,9-bis [4- ( N-cyclohexylcarboyl) phenyl] -2,4,8,10-tetraoxaspiro [5.5] undecane and “IRGANOX-B225” manufactured by Ciba Specialty Chemicals as an antioxidant were prepared. Each raw material was dry blended at a ratio of 0.2 parts by mass of β crystal nucleating agent and 0.1 parts by mass of antioxidant with respect to 100% by mass of this polypropylene resin, Put into a shaft extruder (caliber: 40 mmφ, L / D: 32), melt and knead at a set temperature of 300 ° C, cool and solidify the strands in a water bath, cut the strands with a pelletizer, and make polypropylene resin pellets Produced.

  Next, as a resin composition constituting the B layer, a high-density polyethylene (manufactured by Prime Polymer Co., Ltd., Hi-Zex 3600F, MFR: 1.0 g / 10 min) is added to 97% by mass of a low molecular weight polypropylene (manufactured by Sanyo Chemical Industries, Ltd., Viscol). 330P, weight average molecular weight 73200, number average molecular weight 18800) was dry blended at a ratio of 3% by mass, and 200 using a unidirectional twin screw extruder (caliber: 40 mmφ, L / D: 32) manufactured by Toshiba Machine Co., Ltd. A resin composition that was melt-kneaded at 0 ° C. and processed into a pellet was obtained.

  Using the above-mentioned two kinds of raw materials, using a separate extruder so that the outer layer is the A layer and the intermediate layer is the B layer, it is extruded from a T-die die for lamination molding through a feed block of two types and three layers. The mixture was cooled and solidified with a casting roll at 0 ° C. to obtain a two-layer / three-layer non-porous film-like material of A layer / B layer / A layer.

  The non-porous film-like material is stretched 4.2 times in the longitudinal direction using a longitudinal stretching machine, and then stretched 2.1 times in the transverse direction at 195 ° C. with a transverse stretching machine, followed by heat setting / relaxation treatment. By carrying out, the polyolefin resin porous film was obtained.

One side of the polyolefin resin porous film was subjected to corona treatment using a corona treatment apparatus manufactured by Kasuga Electric Co., Ltd. under treatment conditions of a line speed of 50 m / min and a treatment output of 2 kw. Subsequently, the treatment conditions were adjusted so that the temperature of the polyolefin resin porous film was 80 ° C. or lower, and corona treatment was performed.
A conductive layer was provided on the easy-adhesion-treated surface formed by corona treatment by performing aluminum sputtering so that the thickness was 5 nm. Table 1 shows the physical properties of the obtained laminated porous film. Further, FIG. 2 shows a photograph of the surface state on the conductive layer side observed with a scanning electron microscope (SEM) at a magnification of 10,000.

[Example 2]
An aluminum sputtering treatment was performed to provide a conductive layer so that the thickness was 10 nm. A laminated porous film was obtained in the same manner as in Example 1 except that the thickness of the conductive layer was different. Table 1 shows the physical properties of the obtained laminated porous film.

[Example 3]
An aluminum sputtering process was performed to provide a conductive layer so that the thickness was 20 nm. A laminated porous film was obtained in the same manner as in Example 1 except that the thickness of the conductive layer was different. Table 1 shows the physical properties of the obtained laminated porous film.

[Example 4]
The conductive material was changed from aluminum to ITO, and an ITO sputtering process was performed to provide a conductive layer so that the thickness was 10 nm. Otherwise, a laminated porous film was obtained in the same manner as in Example 1. Table 1 shows the physical properties of the obtained laminated porous film.

[Example 5]
An aluminum sputtering treatment was performed to provide a conductive layer so that the thickness was 50 nm. Otherwise, a laminated porous film was obtained in the same manner as in Example 1. Table 1 shows the physical properties of the obtained laminated porous film.

[Comparative Example 1]
A laminated porous film was obtained in the same manner as in Example 4 except that an ITO sputtering process was performed so that the thickness was 100 nm and a conductive layer was provided. Table 1 shows the physical properties of the obtained laminated porous film. Further, FIG. 2 shows a photograph of the surface state on the conductive layer side observed with a scanning electron microscope (SEM) at a magnification of 10,000.
The ratio of the difference between the air permeability of the laminated porous film obtained in Comparative Example 1 and the air permeability of the polyolefin-based resin porous layer before lamination of the conductive layer is greater than 30%, and the air permeability is 200 seconds / 100 mL or more. It turns out that it is not preferable in terms of air permeability.

[Comparative Example 2]
An overcharge resistance test was conducted using only the polyolefin resin porous film produced in Example 1 without providing a conductive layer. The results are shown in Table 1. A short circuit was observed in about 6 seconds when 50 V was applied.

  As is clear from the above, the laminated porous films of the present invention of Examples 1 to 5 have excellent overcharge resistance and sufficient gas permeability to be used as a separator for a nonaqueous electrolyte secondary battery. It turns out that it is a laminated porous film which has.

  On the other hand, since the laminated porous film of Comparative Example 1 has a conductive layer that is too thick, the polyolefin resin porous layer before lamination of the conductive layer has a large air permeability difference and is used as a separator for a nonaqueous electrolyte secondary battery. Was insufficient. This is clear even when the micrograph shown in FIG. 2 of Example 1 and the micrograph shown in FIG. 3 of Comparative Example 1 are compared, and Comparative Example 1 (FIG. In 3), it was confirmed that the pores of the laminated polyolefin resin porous layer were closed by the conductive layer. Moreover, when it did not have a conductive layer from the comparative example 2, it was recognized not to have overcharge resistance.

  In addition, when using the polyolefin resin porous layer which does not have (beta) crystal activity, it is estimated that a polyolefin resin porous layer deteriorates a little in corona treatment or the vapor deposition process of an electroconductive layer, and pin pinning intensity | strength falls.

Claims (10)

A polyolefin resin porous layer comprising a polypropylene resin porous layer having at least β crystal activity;
A conductive layer having a thickness of 0.1 nm to 50 nm, which is laminated via an easy adhesion treatment surface applied to the surface of the polypropylene resin porous layer;
A laminated porous film, wherein a ratio of a difference in air permeability of the polyolefin resin porous layer not laminated with the conductive layer is 1% or more and 30% or less.   The laminated porous film according to claim 1, wherein a difference between the air permeability of the polyolefin-based resin porous layer on which the conductive layer is not laminated is 150 seconds / 100 mL or less.   The laminated porous film according to claim 1 or 2, wherein the air permeability is in a range of 10 to 1000 seconds / 100 mL.   The surface of the easy adhesion treatment is a treatment surface selected from any one of corona treatment, plasma treatment, sputter etching treatment, sulfonation treatment, grafting treatment, ultraviolet irradiation treatment, and electron beam irradiation treatment. Item 4. The laminated porous film according to any one of Items 3 above.   5. The conductive layer according to claim 1, wherein the conductive layer is made of at least one selected from the group consisting of aluminum, tungsten, molybdenum, titanium, tantalum, indium tin oxide (ITO), copper, nickel, iron, and chromium. 2. The laminated porous film according to item 1.   The polyolefin resin porous layer consists of a single layer consisting only of the polypropylene resin porous layer having the β crystal activity, or a multilayer obtained by laminating the polypropylene resin porous layer and another polyolefin resin porous layer, The laminated porous film according to any one of claims 1 to 5, wherein the polyolefin resin porous layer of the multilayer has the polypropylene resin porous layer disposed on at least one outer side. It is a manufacturing method of the lamination | stacking porous film of any one of Claim 1 thru | or 6, Comprising: After forming the said polyolefin resin porous layer, it is easy on the surface of the said polypropylene resin porous layer located outside. Apply the adhesive treatment,
Next, a method for producing a laminated porous film in which the conductive layer is formed on the surface subjected to the easy adhesion treatment by sputtering, ion plating, or vacuum deposition.   The method for producing a laminated porous film according to claim 7, wherein the easy adhesion treatment is performed by corona discharge treatment, the treatment speed is 1 m / min to 100 m / min, and the discharge power is 0.1 kw to 10 kw.   A separator for a non-aqueous electrolyte secondary battery using the laminated porous film according to claim 1.   A non-aqueous electrolyte secondary battery using the separator for a non-aqueous electrolyte secondary battery according to claim 9.