JP2006137789A - Polyolefinic microporous membrane, separator for battery and non-aqueous electrolyte battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a non-combustible separator having shut-down characteristics and to provide a microporous membrane suitable for the separator. <P>SOLUTION: A polyolefinic microporous membrane is characterized as having 0.5-75 μm thickness, 30-85% porosity and <135°C permeability cutoff temperature (shut-down temperature) and comprising an ultrahigh-molecular weight polyolefin having ≥7×10<SP>5</SP>Mw (weight-average molecular weight), an LDPE (low-density polyolefin) and a non-combustibility imparting substance containing phosphorus. The separator for batteries is composed of the polyolefinic microporous membrane. A phosphazene compound, a phosphonate compound and a phosphinate compound are preferred as the non-combustibility imparting substance. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a polyolefin microporous membrane, a battery separator comprising the microporous membrane, and a non-aqueous electrolyte battery using the separator, and more particularly to a nonflammable polyolefin microporous membrane.

  Currently, a porous film of polyolefin such as polyethylene or polypropylene is used as a separator provided to prevent a short circuit between positive and negative electrodes between positive and negative electrodes of various batteries. The separator is provided with a large number of holes for allowing ions to pass during charging and discharging of the battery, and does not hinder the passage of ions under a normal use environment.

  On the other hand, non-aqueous electrolyte batteries such as lithium batteries and lithium ion secondary batteries have recently been widely used as power supplies having high voltage and high energy density, such as cameras, electronic watches, It is used as a memory backup power source, a drive power source for notebook computers and mobile phones, and a main power source or auxiliary power source for electric vehicles and fuel cell vehicles.

  In the non-aqueous electrolyte battery, since lithium in the negative electrode reacts violently with a compound having active protons such as water or alcohol, a flammable aprotic organic solvent is used for the electrolyte of the battery. However, the aprotic organic solvent has a drawback of high risk of ignition and ignition. Therefore, the separator for the non-aqueous electrolyte battery has an abnormal current flowing due to a short circuit, etc., and when the temperature in the battery rises, the separator itself melts and the hole of the separator is closed, It has the function of blocking the passage of ions between the positive and negative electrodes, that is, blocking the current and stopping the temperature rise (shutdown effect), reducing the risk of ignition and ignition of aprotic organic solvents in the electrolyte. Yes.

  As separators as described above, JP-A-5-25305 (Patent Document 1) and JP-A-5-94812 (Patent Document 2) disclose microporous polyolefin made of a specific weight-average molecular weight and molecular weight distribution. A membrane is disclosed, and the microporous membrane is excellent in mechanical strength and permeation performance, and at the relatively low temperature, the microporous can be blocked to exhibit a shutdown effect.

JP-A-5-25305 Japanese Patent Laid-Open No. 5-94812

  However, although the separator made of the microporous membrane disclosed in the above-mentioned JP-A-5-25305 and JP-A-5-94812 can cut off the current at a relatively low temperature and stop the temperature rise in the battery, Since the microporous membrane itself is flammable, the separator itself may burn when the battery abnormally generates heat due to a short circuit or the like. In this case, the temperature rise of the battery is promoted, and the battery is thermally runaway. There is a risk. In particular, non-aqueous electrolyte batteries, which are being increased in size and increased in energy density for use as a main power source or auxiliary power source for electric vehicles and fuel cell vehicles, require higher safety than before. Therefore, there is a demand for a separator with higher safety than conventional polyolefin separators.

  Accordingly, an object of the present invention is to solve the above-mentioned problems of the prior art and provide a nonflammable separator having a shutdown characteristic and a microporous membrane suitable for the separator. Another object of the present invention is to provide a highly safe non-aqueous electrolyte battery using such a non-flammable separator.

  As a result of intensive studies to achieve the above object, the present inventor can make the microporous membrane itself nonflammable by adding a nonflammability imparting substance containing phosphorus to the polyolefin microporous membrane. The present inventors have found that the safety of the battery can be greatly improved by using the nonflammable microporous membrane for a separator of a non-aqueous electrolyte battery, and the present invention has been completed.

That is, the polyolefin microporous membrane of the present invention has a thickness of 0.5 to 75 μm, a porosity of 30 to 85%, a permeability cutoff temperature of less than 135 ° C., and a weight average molecular weight of 7 × 10 ⁵ or more. The ultrahigh molecular weight polyolefin, low density polyolefin, and nonflammability imparting substance containing phosphorus are included. Here, the permeability cutoff temperature is 10 ⁴ sec / 100 mL of the air permeability indicated by the Gurley value (according to JIS P8117, the number of seconds in which 100 mL of air passes through the membrane at 0.879 g / mm ² pressure). It is the temperature when exceeding.

  In a preferred example of the polyolefin microporous membrane of the present invention, the nonflammability imparting substance is a phosphazene compound.

  In another preferred embodiment of the polyolefin microporous membrane of the present invention, the nonflammability imparting substance is at least one selected from the group consisting of phosphonate compounds and phosphinate compounds.

  In the polyolefin microporous membrane of the present invention, the nonflammability imparting substance is preferably solid at 25 ° C.

  In another preferred embodiment of the polyolefin microporous membrane of the present invention, the ultrahigh molecular weight polyolefin is ultrahigh molecular weight polyethylene.

  In another preferred embodiment of the polyolefin-based microporous membrane of the present invention, the low density polyolefin is low density polyethylene.

  The battery separator of the present invention comprises the above polyolefin-based microporous membrane, and the non-aqueous electrolyte battery of the present invention comprises the battery separator, a positive electrode, a negative electrode, and a non-aqueous electrolyte. Features.

  ADVANTAGE OF THE INVENTION According to this invention, the nonflammable polyolefin microporous film containing a phosphorus containing nonflammability provision substance can be provided. Moreover, the non-flammable separator which consists of this microporous film and has a shutdown characteristic, and the highly safe nonaqueous electrolyte battery provided with this separator can be provided.

The present invention is described in detail below. The polyolefin microporous membrane of the present invention has a thickness of 0.5 to 75 μm, a porosity of 30 to 85%, a permeability cutoff temperature of less than 135 ° C., and a weight average molecular weight of more than 7 × 10 ⁵ It contains high molecular weight polyolefin, low density polyolefin, and nonflammability imparting substance containing phosphorus. Since the polyolefin microporous membrane of the present invention contains a phosphorus-containing nonflammability imparting substance, it is nonflammable, and when the separator made of the microporous membrane is applied to a battery, the battery abnormally generates heat due to a short circuit or the like. At this time, the separator itself does not burn, and the thermal runaway of the battery can be reliably prevented.

  The polyolefin microporous membrane of the present invention is required to have a thickness of 0.5 to 75 μm and a porosity of 30 to 85%. When the thickness of the microporous membrane is less than 0.5 μm, the short-circuit failure rate of the battery increases when the microporous membrane is used as a battery separator. On the other hand, when the thickness exceeds 75 μm, the microporous membrane becomes a battery separator. When used, the battery performance deteriorates. In addition, when the porosity of the microporous membrane is less than 30%, when the separator made of the microporous membrane is used for a battery, the impregnation and amount of the electrolyte are insufficient, and the internal resistance of the battery increases. On the other hand, if it exceeds 85%, the mechanical strength of the microporous membrane is insufficient and it cannot be used as a battery separator or the like. The average pore diameter of the microporous membrane is not particularly limited, but is preferably in the range of 0.02 to 5 μm, and more preferably in the range of 0.05 to 3 μm.

  The polyolefin microporous membrane of the present invention requires a permeability cutoff temperature, so-called shutdown temperature, of less than 135 ° C., and is preferably in the range of 100 to 130 ° C. When the permeability cutoff temperature of the microporous membrane is 135 ° C. or higher, when a separator made of the microporous membrane is used for a battery, the safety of the battery in the event of an abnormality such as a short circuit cannot be sufficiently improved.

The ultrahigh molecular weight polyolefin used for the polyolefin microporous membrane of the present invention requires a weight average molecular weight (Mw) of 7 × 10 ⁵ or more, and may be in the range of 1 × 10 ^{6 to} 1.5 × 10 ^7. preferable. When the weight average molecular weight of the ultrahigh molecular weight polyethylene is less than 7 × 10 ⁵ , the maximum draw ratio becomes low, and thus a microporous film suitable as a battery separator cannot be obtained. The ultrahigh molecular weight polyolefin is not particularly limited, but preferably has a density in the range of 0.93 to 0.95 g / cm ³ . Here, as the ultra-high molecular weight polyolefin, homopolymers, copolymers, and mixtures of olefins such as ethylene, propylene, 1-butene, 4-methyl-1-pentene, and 1-hexene can be used. Ultra high molecular weight polyethylene is particularly preferred. The content of the ultrahigh molecular weight polyolefin in the polyolefin microporous membrane of the present invention is preferably in the range of 30 to 65% by mass. When the content of the ultrahigh molecular weight polyolefin in the microporous film is less than 30% by mass, the interlamellar cleavage does not occur even when stretched, and it becomes difficult to sufficiently form the microporous, whereas it exceeds 65% by mass. Then, it becomes difficult to make the permeability cutoff temperature of the microporous membrane less than 135 ° C.

Low density polyolefins for use in the polyolefin microporous membrane of the present invention is preferably a density in the range of less than 0.91 g / cm ³ or more and 0.93 g / cm ^3. The weight molecular weight of the low density polyolefin is not particularly limited and may be less than 7 × 10 ⁵ . As the low-density polyolefin, homopolymers and copolymers of olefins such as ethylene, propylene, 1-butene, 4-methyl-1-pentene, and 1-hexene, and mixtures thereof can be used. (LDPE) is particularly preferred. Examples of the low-density polyethylene include branched polyethylene produced by a high-pressure method and linear low-density polyethylene (LLDPE) produced by a medium-low pressure method. The content of the low density polyolefin in the polyolefin microporous membrane of the present invention is preferably in the range of 15 to 67% by mass. If the content of the low density polyolefin in the microporous membrane is less than 15% by mass, it becomes difficult to make the permeability cutoff temperature of the microporous membrane less than 135 ° C. Cleavage between lamellae does not occur, and it becomes difficult to sufficiently form micropores.

  The nonflammability imparting substance used for the polyolefin microporous membrane of the present invention needs to contain phosphorus and is preferably solid at 25 ° C. (room temperature). Moreover, specifically as a said nonflammability provision substance, a phosphazene compound, a phosphonate compound, and a phosphinate compound are preferable, and these phosphorus containing compounds may be used individually by 1 type, and may be used in combination of 2 or more type. Good. These compounds containing phosphorus in the molecule generate phosphate esters when the microporous membrane burns, and make the microporous membrane incombustible by the action of the phosphate esters. Moreover, since phosphorus has the effect | action which suppresses the chain decomposition of polyolefin which is a raw material of a microporous film, the danger of the combustion of a microporous film can be reduced effectively.

  The content of the nonflammability-imparting substance in the polyolefin microporous membrane of the present invention is preferably in the range of 3 to 17% by mass. If the content of the nonflammability imparting substance is less than 3% by mass, the effect of reducing the risk of polyolefin combustion is small, and if it exceeds 17% by mass, the mechanical strength of the microporous membrane decreases and it is used as a battery separator. It becomes difficult to do.

［式中、Ｒ¹は、それぞれ独立して一価の置換基又はハロゲン元素を表し；Ｙ¹は、それぞれ独立して２価の連結基、２価の元素又は単結合を表し；Ｘは、炭素、ケイ素、ゲルマニウム、スズ、窒素、リン、ヒ素、アンチモン、ビスマス、酸素、硫黄、セレン、テルル及びポロニウムからなる群から選ばれる元素の少なくとも１種を含む置換基を表す］で表される鎖状ホスファゼン化合物、及び下記式(II)：
(ＮＰＲ² ₂)_n ・・・ (II)
［式中、Ｒ²はそれぞれ独立して一価の置換基又はハロゲン元素を表し；ｎは３〜１５を表す］で表される環状ホスファゼン化合物が好適に挙げられる。これらホスファゼン化合物は、１種単独で用いてもよく、２種以上を混合して用いてもよい。リンに加え、窒素を含むホスファゼン化合物を不燃性付与物質として微多孔膜に含ませることで、万が一の燃焼時に誘導される窒素ガスの作用によって、微多孔膜の不燃性を更に向上させることができる。 As the phosphazene compound, the following formula (I):

[Wherein, R ¹ each independently represents a monovalent substituent or a halogen element; Y ¹ each independently represents a divalent linking group, a divalent element or a single bond; Chain representing a substituent containing at least one element selected from the group consisting of carbon, silicon, germanium, tin, nitrogen, phosphorus, arsenic, antimony, bismuth, oxygen, sulfur, selenium, tellurium and polonium] Phosphazene compound and the following formula (II):
(NPR ² ₂ ) _n ... (II)
Preferable examples include cyclic phosphazene compounds represented by the formula: wherein R ² each independently represents a monovalent substituent or a halogen element; n represents 3 to 15. These phosphazene compounds may be used alone or in combination of two or more. By adding a phosphazene compound containing nitrogen as a nonflammability imparting substance to the microporous membrane in addition to phosphorus, the nonflammability of the microporous membrane can be further improved by the action of nitrogen gas induced in the unlikely event of combustion. .

R ^{1 in} formula (I) is not particularly limited as long as it is a monovalent substituent or a halogen element, and each R ¹ may be the same or different. Here, examples of the monovalent substituent include an alkoxy group, an alkyl group, a carboxyl group, an acyl group, and an aryl group, and among these, an alkoxy group is preferable. On the other hand, preferred examples of the halogen element include fluorine, chlorine, bromine and the like. Examples of the alkoxy group include methoxy group, ethoxy group, propoxy group, butoxy group, and alkoxy-substituted alkoxy groups such as methoxyethoxy group and methoxyethoxyethoxy group. Among these, methoxy group, ethoxy group, methoxy group, etc. An ethoxy group and a methoxyethoxyethoxy group are preferable, and a methoxy group and an ethoxy group are more preferable. Examples of the alkyl group include a methyl group, an ethyl group, a propyl group, a butyl group, and a pentyl group. Examples of the acyl group include a formyl group, an acetyl group, a propionyl group, a butyryl group, an isobutyryl group, and a valeryl group. Examples of the aryl group include a phenyl group, a tolyl group, and a naphthyl group. The hydrogen element in these monovalent substituents is preferably substituted with a halogen element. As the halogen element, fluorine, chlorine and bromine are preferred, fluorine is most preferred, and chlorine is then preferred.

Y ^{1 in} formula (I) is not particularly limited as long as it is a divalent linking group, a divalent element, or a single bond, and each Y ¹ may be the same or different. Here, as the divalent linking group, in addition to the CH ₂ group, oxygen, sulfur, selenium, nitrogen, boron, aluminum, scandium, gallium, yttrium, indium, lanthanum, thallium, carbon, silicon, titanium, tin, germanium Divalent containing at least one element selected from the group consisting of zirconium, lead, phosphorus, vanadium, arsenic, niobium, antimony, tantalum, bismuth, chromium, molybdenum, tellurium, polonium, tungsten, iron, cobalt, nickel From the viewpoint of effectively reducing the risk of ignition / flammability of the microporous membrane, a divalent linking group containing sulfur and / or selenium elements is preferable. Examples of the divalent element include oxygen, sulfur, and selenium.

［式(III)、式(IV)及び式(V)中、Ｒ³、Ｒ⁴及びＲ⁵は、それぞれ独立に一価の置換基又はハロゲン元素を表し；Ｙ³、Ｙ⁴及びＹ⁵は、それぞれ独立に２価の連結基、２価の元素又は単結合を表し；Ｚは２価の基又は２価の元素を表す］で表される置換基が更に好ましい。 X in formula (I) is a substituent containing at least one element selected from the group consisting of carbon, silicon, germanium, tin, nitrogen, phosphorus, arsenic, antimony, bismuth, oxygen, sulfur, selenium, tellurium and polonium. As long as it is, there is no particular limitation. From the viewpoint of consideration for toxicity, environment, etc., X in formula (I) is preferably a substituent containing at least one element selected from the group consisting of carbon, silicon, nitrogen, phosphorus, oxygen and sulfur, The following formula (III), formula (IV) or formula (V):

[In Formula (III), Formula (IV) and Formula (V), R ³ , R ⁴ and R ⁵ each independently represents a monovalent substituent or a halogen element; Y ³ , Y ⁴ and Y ⁵ are And each independently represents a divalent linking group, a divalent element or a single bond; and Z represents a divalent group or a divalent element].

R ³ of formula (III), R ⁵ of formula (IV) R ⁴ and formula (V), substituent or a halogen element similar monovalent to that described in R ¹ of formula (I) is either Are also preferred. Further, two R ^{3 s} in the formula (III) and two R ^{5 s in} the formula (V) may be the same or different, and may be bonded to each other to form a ring.

Y ³ of the formula (III), Y ⁴ and Y ⁵ of formula (V) of the formula (IV), the divalent linking group or bivalent element similar to that described by Y ¹ in the formula (I) Are preferably mentioned. Similarly, in the case of a divalent linking group containing sulfur and / or selenium elements, the risk of ignition / flammability of the microporous membrane is greatly reduced, which is particularly preferable. Further, two Y ³ in the formula (III) and two Y ^{5 in} the formula (V) may be the same or different.

Z in the formula (III) is not particularly limited as long as it is a divalent group or a divalent element. Here, as the divalent group, CH ₂ group, CHR group (where R represents an alkyl group, alkoxy group, phenyl group, etc.), NR group, oxygen, sulfur, selenium, boron, aluminum , Scandium, gallium, yttrium, indium, lanthanum, thallium, carbon, silicon, titanium, tin, germanium, zirconium, lead, phosphorus, vanadium, arsenic, niobium, antimony, tantalum, bismuth, chromium, molybdenum, tellurium, polonium, tungsten , A divalent group containing at least one element selected from the group consisting of iron, cobalt, and nickel; and examples of the divalent element include oxygen, sulfur, and selenium. Among these, Z in the formula (III) is preferably a divalent group containing at least one element selected from the group consisting of oxygen, sulfur and selenium in addition to the CH ₂ group, CHR group and NR group. In particular, a divalent group containing an element of sulfur and / or selenium is preferable because the risk of ignition / flammability of the microporous film is greatly reduced.

  As these substituents, a substituent containing phosphorus as represented by the formula (III) is particularly preferable in that the risk of ignition / flammability can be particularly effectively reduced.

R ^{2 in} formula (II) is not particularly limited as long as it is a monovalent substituent or a halogen element. Here, examples of the monovalent substituent include an alkoxy group, an aryloxy group, an alkyl group, a carboxyl group, an acyl group, an aryl group, a substituted or unsubstituted amino group, an alkylthio group, and an arylthio group. Among these, An alkoxy group and an aryloxy group are preferable. On the other hand, preferred examples of the halogen element include fluorine, chlorine, bromine and the like, and among these, fluorine is particularly preferred. Examples of the alkoxy group include a methoxy group, an ethoxy group, a propoxy group, a butoxy group, an allyloxy group containing a double bond, an alkoxy-substituted alkoxy group such as a methoxyethoxy group and a methoxyethoxyethoxy group, and the like. Examples of the aryloxy group include a phenoxy group, a methylphenoxy group, and a methoxyphenoxy group. Examples of the alkyl group include a methyl group, an ethyl group, a propyl group, a butyl group, and a pentyl group. Includes a phenyl group, a tolyl group, a naphthyl group, and the substituted or unsubstituted amino group includes an amino group, a methylamino group, a dimethylamino group, an ethylamino group, a diethylamino group, an aziridyl group, and a pyrrolidyl group. Examples of the alkylthio group include methylthio group, ethylthio group Include groups such as the above-described arylthio group, a phenylthio group, and the like. The hydrogen element in these monovalent substituents is preferably substituted with a halogen element, and preferred examples of the halogen element include fluorine, chlorine, bromine and the like. And a trifluoroethoxy group. In addition, each R ² in the formula (II) may be bonded to each other to form a ring.

［式中、Ｒ^6aは、それぞれ独立して一価の置換基を示し；Ｒ^6bは、一価の置換基又はハロゲン元素を示す］で表される化合物が好ましく、上記ホスフィネート化合物としては、下記式(VII)：

［式中、Ｒ^7aは、一価の置換基を示し；Ｒ^7bは、それぞれ独立して一価の置換基又はハロゲン元素を示す］で表される化合物が好ましい。これらホスホネート化合物及びホスフィネート化合物は、１種単独で用いても、２種以上を混合して用いてもよく、ホスホネート化合物とホスフィネート化合物とを組み合わせて用いてもよい。 Examples of the phosphonate compound include the following formula (VI):

[Wherein R ^6a independently represents a monovalent substituent; R ^6b represents a monovalent substituent or a halogen element] is preferable, and examples of the phosphinate compound include the following: Formula (VII):

[Wherein, R ^7a represents a monovalent substituent; R ^7b independently represents a monovalent substituent or a halogen element] is preferable. These phosphonate compounds and phosphinate compounds may be used singly or in combination of two or more, or a phosphonate compound and a phosphinate compound may be used in combination.

Examples of the monovalent substituent in R ^6a and R ^{6b in} the above formula (VI) and R ^7a and R ^7b in the formula (VII) include an alkoxy group, an aryloxy group, an alkyl group, an aryl group, an acyl group, a substituted or non-substituted group. Examples thereof include a substituted amino group, an alkylthio group, and an arylthio group. Among these, an alkoxy group and an aryloxy group are preferable in terms of excellent nonflammability. Examples of the alkoxy group include a methoxy group, an ethoxy group, a propoxy group, a butoxy group, an allyloxy group containing a double bond, an alkoxy-substituted alkoxy group such as a methoxyethoxy group and a methoxyethoxyethoxy group, and the like. Examples of the aryloxy group include a phenoxy group, a methylphenoxy group, and a methoxyphenoxy group. Examples of the alkyl group include a methyl group, an ethyl group, a propyl group, a butyl group, and a pentyl group. Includes a phenyl group, a tolyl group, a naphthyl group, and the substituted or unsubstituted amino group includes an amino group, a methylamino group, a dimethylamino group, an ethylamino group, a diethylamino group, an aziridyl group, and a pyrrolidyl group. Examples of the alkylthio group include methylthio group, ethylthio group Include groups such as the above-described arylthio group, a phenylthio group, and the like. The hydrogen element in these monovalent substituents may be substituted with a halogen element, and is preferably substituted with fluorine.

On the other hand, examples of the halogen element in R ^{6b of} the above formula (VI) and R ^7b of the formula (VII) include fluorine, chlorine, bromine, etc. Among these, fluorine is preferable.

  Specific examples of the phosphonate compound of the above formula (VI) include dimethyl fluorophosphate, diethyl fluorophosphate, bistrifluoroethyl fluorophosphate, dipropyl fluorophosphate, diallyl fluorophosphate, dibutyl fluorophosphate, and fluorophosphoric acid. Examples thereof include diphenyl and difluorophenyl fluorophosphate.

  On the other hand, as the phosphinate compound of the above formula (VII), specifically, methyl chlorofluorophosphate, ethyl chlorofluorophosphate, trifluoroethyl chlorofluorophosphate, propyl chlorofluorophosphate, allyl chlorofluorophosphate, chloro Butyl fluorophosphate, methoxyethyl chlorofluorophosphate, methoxyethoxyethyl chlorofluorophosphate, phenyl chlorofluorophosphate, fluorophenyl chlorofluorophosphate, methyl difluorophosphate, ethyl difluorophosphate, trifluoroethyl difluorophosphate, Propyl difluorophosphate, allyl difluorophosphate, butyl difluorophosphate, methoxyethyl difluorophosphate, methoxyethoxyethyl difluorophosphate, phenyl difluorophosphate, fluorinated difluorophosphate Phenyl, and the like. Among these, methyl difluorophosphate, ethyl difluorophosphate, trifluoroethyl difluorophosphate, propyl difluorophosphate, and phenyl difluorophosphate are preferable.

  The polyolefin microporous membrane of the present invention can be produced by a conventional method for producing a microporous membrane, and examples thereof include a wet process as shown below. In the wet process, for example, in the first step, a solvent, the ultrahigh molecular weight polyolefin and the low density polyolefin, and the phosphorus-containing nonflammability imparting substance are mixed and dissolved by heating to obtain a polyolefin solution. Here, the solvent is not particularly limited as long as it can sufficiently dissolve the polyolefin, and specific examples thereof include aliphatic hydrocarbons such as nonane, decane, undecane, dodecane, and paraffin oil, or alicyclic hydrocarbons. Among these, non-volatile solvents such as paraffin oil are preferable. Moreover, the temperature in heat dissolution is suitably selected according to the polyolefin and solvent to be used, and the range of 140-250 degreeC is preferable normally. The total concentration of the ultrahigh molecular weight polyolefin, the low density polyolefin and the phosphorus-containing nonflammability imparting substance in the polyolefin solution is preferably in the range of 10 to 50% by mass. If the total concentration is less than 10% by mass, the amount of solvent is large and not economical, and when forming into a sheet, swell and neck-in at the die outlet are large, making it difficult to form the sheet, and the concentration is 50% by mass. If it exceeds%, it is difficult to prepare a uniform solution.

  Next, in the second step, the obtained polyolefin solution is extruded into a film by an extruder. Examples of the die to be used include a sheet die, a double cylindrical hollow die, and an inflation die. In addition, the extrudate becomes a gel-like product by being cooled. Here, the extrudate is preferably cooled at a cooling rate of 50 ° C./min or lower until the gelation temperature or lower. If it is less than 50 degreeC / min, the crystallinity of a film will rise and it will become difficult to extend | stretch. In addition, as a cooling method, the method of making it contact directly with cold air, cooling water, and another cooling medium, the method of making it contact with the roll cooled with the refrigerant | coolant, etc. are mentioned.

  Next, in the third step, the extrudate is stretched uniaxially or biaxially with a stretching machine. Stretching can be performed by heating the extrudate and using a general method such as a tenter method, a roll method, an inflation method, or a rolling method. The stretching temperature is preferably the melting point of the polyolefin to be used + 10 ° C. or less. If the stretching temperature exceeds the melting point + 10 ° C., the molecular chain cannot be oriented due to the melting of the polyolefin. The draw ratio varies depending on the thickness of the extrudate, but is preferably 2 times or more, more preferably 3 to 30 times, more preferably 10 times or more, and further preferably 15 to 400 times in the uniaxial direction.

  Further, the solvent used in the first step is extracted from the film stretched in the fourth step with a volatile solvent, and further dried to form a microporous film. As the volatile solvent, pentane, hexane, heptane, dichloromethane, carbon tetrachloride, trifluoroethane, diethyl ether, dioxane and the like can be used, and these volatile solvents depend on the solvent used in the first step. It is selected appropriately. Moreover, drying can be performed by heat drying, air drying, or the like. In addition, you may anneal the microporous film after drying, and it is preferable to carry out at the temperature below melting | fusing point of the polyolefin to be used in this case.

  The polyolefin-based microporous membrane of the present invention has various uses, but is particularly suitable as a battery separator and is non-flammable, and thus is particularly suitable as a separator for a non-aqueous electrolyte battery.

  The non-aqueous electrolyte battery of the present invention comprises a battery separator comprising the above-mentioned microporous membrane, a positive electrode, a negative electrode, and a non-aqueous electrolyte, and, in addition, technical fields of non-aqueous electrolyte batteries as necessary. It is provided with other members that are normally used.

The positive electrode active material of the non-aqueous electrolyte battery of the present invention is partially different between the primary battery and the secondary battery. For example, as the positive electrode active material of the non-aqueous electrolyte primary battery, fluorinated graphite [(CF _x ) _n ], MnO ₂ (which may be electrochemical synthesis or chemical synthesis), V ₂ O ₅ , MoO ₃ , Ag ₂ CrO ₄ , CuO, CuS, FeS ₂ , SO ₂ , SOCl ₂ , TiS _2, etc. Among these, MnO ₂ and fluorinated graphite are preferable from the viewpoints of high capacity and high safety, and high discharge potential and excellent wettability of the electrolytic solution. These positive electrode active materials may be used individually by 1 type, and may use 2 or more types together.

On the other hand, as the positive electrode active material of the non-aqueous electrolyte secondary battery, metal oxides such as V ₂ O ₅ , V ₆ O ₁₃ , MnO ₂ , MnO ₃ , LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiFeO _{2 are used.} Preferable examples include lithium-containing composite oxides such as LiFePO ₄ , metal sulfides such as TiS ₂ and MoS ₂ , and conductive polymers such as polyaniline. The lithium-containing composite oxide may be a composite oxide containing two or three transition metals selected from the group consisting of Fe, Mn, Co, and Ni. In this case, the composite oxide includes: LiFe _x Co _y Ni (wherein, 0 ≦ x <1,0 ≦ y <1,0 <x + y ≦ 1) (1-xy) O 2, or represented by LiMn _x Fe _y O _2-xy like. Among these, LiCoO ₂ , LiNiO ₂ , and LiMn ₂ O ₄ are particularly preferable in terms of high capacity, high safety, and excellent electrolyte wettability. These positive electrode active materials may be used individually by 1 type, and may use 2 or more types together.

  The negative electrode active material of the nonaqueous electrolyte battery of the present invention is partially different between the primary battery and the secondary battery. For example, as the negative electrode active material of the nonaqueous electrolyte primary battery, lithium metal itself, lithium alloy, etc. Is mentioned. Examples of the metal that forms an alloy with lithium include Sn, Si, Pb, Al, Au, Pt, In, Zn, Cd, Ag, and Mg. Among these, Al, Zn, and Mg are preferable from the viewpoints of rich reserves and toxicity. These negative electrode active materials may be used individually by 1 type, and may use 2 or more types together.

  On the other hand, as the negative electrode active material of the non-aqueous electrolyte secondary battery, lithium metal itself, an alloy of lithium and Al, In, Sn, Si, Pb, Zn, or the like, or a carbon material such as graphite doped with lithium is preferable. Among these, carbon materials such as graphite are preferable, and graphite is particularly preferable in that it is higher in safety and excellent in wettability of the electrolytic solution. Here, examples of graphite include natural graphite, artificial graphite, mesophase carbon microbeads (MCMB), and the like, and widely include graphitizable carbon and non-graphitizable carbon. These negative electrode active materials may be used individually by 1 type, and may use 2 or more types together.

  The positive electrode and the negative electrode can be mixed with a conductive agent and a binder as necessary. Examples of the conductive agent include acetylene black, and the binder includes polyvinylidene fluoride (PVDF) and polytetrafluoro. Examples include ethylene (PTFE), styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), and the like. These additives can be used at a blending ratio similar to the conventional one.

  Moreover, there is no restriction | limiting in particular as a shape of the said positive electrode and a negative electrode, It can select suitably from well-known shapes as an electrode. For example, a sheet shape, a columnar shape, a plate shape, a spiral shape, and the like can be given.

  The non-aqueous electrolyte of the non-aqueous electrolyte battery of the present invention contains a non-aqueous solvent and a supporting salt as main components. Here, as the non-aqueous solvent, an aprotic organic solvent can be used, and one selected from the above-described phosphazene compounds, phosphonate compounds and phosphinate compounds can be used at 25 ° C. (room temperature). It is also possible to use a mixed solution of an aprotic organic solvent and at least one of a phosphazene compound, a phosphonate compound and a phosphinate compound. Specific examples of the aprotic organic solvent include dimethyl carbonate (DMC), diethyl carbonate (DEC), diphenyl carbonate, ethyl methyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), and vinylene carbonate. Carbonates such as (VC), 1,2-dimethoxyethane (DME), tetrahydrofuran (THF), diethyl ether (DEE), ethers such as phenyl methyl ether, γ-butyrolactone (GBL), γ-valerolactone, Examples thereof include carboxylic acid esters such as methyl formate (MF), nitriles such as acetonitrile, amides such as dimethylformamide, and sulfones such as dimethyl sulfoxide. These aprotic organic solvents may be used individually by 1 type, and 2 or more types may be mixed and used for them.

Moreover, as said support salt, the support salt used as the ion source of lithium ion is preferable. The supporting salt is not particularly limited, and for example, LiClO ₄ , LiBF ₄ , LiPF ₆ , LiCF ₃ SO ₃ , LiAsF ₆ , LiC ₄ F ₉ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N and Li ( Preferable examples include lithium salts such as C ₂ F ₅ SO ₂ ) ₂ N. Among these, LiPF ₆ is more preferable in terms of excellent nonflammability. These supporting salts may be used alone or in combination of two or more. The concentration of the supporting salt in the non-aqueous electrolyte is preferably 0.2 to 1.5 mol / L (M), more preferably 0.5 to 1 mol / L (M). If the concentration of the supporting salt is less than 0.2 mol / L, the conductivity of the electrolyte cannot be sufficiently ensured, and the discharge characteristics and charging characteristics of the battery may be hindered. Since the viscosity of the electrolytic solution increases and the mobility of lithium ions cannot be ensured sufficiently, the conductivity of the electrolytic solution cannot be sufficiently ensured in the same manner as described above, which may hinder battery discharge characteristics and charge characteristics. .

  The form of the non-aqueous electrolyte battery of the present invention described above is not particularly limited, and various known forms such as a coin-type, button-type, paper-type, square-type or spiral-type cylindrical battery are suitable. Can be mentioned. In the case of the button type, a non-aqueous electrolyte battery can be manufactured by preparing a sheet-like positive electrode and negative electrode and sandwiching a separator between the positive electrode and the negative electrode. In the case of a spiral structure, for example, a non-aqueous electrolyte battery can be manufactured by preparing a sheet-like positive electrode, sandwiching a current collector, and stacking and winding up a sheet-like negative electrode on the current collector. it can.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples.

Example 1
30 parts by mass of ultra high molecular weight polyethylene (density 0.964 g / cm ³ ) with a weight average molecular weight of 3 × 10 ⁶ and 65 parts by mass of low density polyethylene with a weight average molecular weight of 2 × 10 ⁴ and a density of 0.924 g / cm ³ And 5 parts by mass of phosphazene compound A [cyclic phosphazene compound in which n is 3 and all six R ² are Cl] in 50 parts by mass of liquid paraffin (specific gravity 0.875). A polyethylene mixed solution was prepared. Next, the polyethylene mixed solution was extruded from a T die with an extruder having a diameter of 40 mm, and a gel-like sheet was produced while being taken up by a cooling roll. Next, the sheet was set in a biaxial stretching machine and stretched 4 × 4 times at a temperature of 117 ° C. and a stretching speed of 0.65 m / min. The obtained stretched film was washed and extracted with methylene chloride, and further annealed at 100 ° C. for 40 seconds to produce a polyethylene microporous film. The obtained polyethylene microporous membrane had a thickness of 30 μm, a porosity of 46%, and a permeability cutoff temperature of 120 ° C. Further, the critical oxygen index of the obtained microporous membrane was evaluated by the following method and found to be 26.8.

<Limited oxygen index>
The critical oxygen index of the microporous membrane was measured according to JIS K7201. The larger the limiting oxygen index, the more difficult the microporous membrane burns. Specifically, a 127 mm × 12.7 mm test piece was prepared from the microporous membrane, and the test piece was perpendicular to the test piece support, and a combustion cylinder (inner diameter 75 mm, height 450 mm, diameter 4 mm of glass particles at the bottom) To 100 ± 5 mm thickness, with a metal mesh placed on top of it) and mounted at a distance of 100 mm or more, and then oxygen (JIS K 1101 or Equivalent or better) and nitrogen (JIS K 1107 grade 2 or better), and ignite the specimen under a predetermined oxygen concentration (the heat source is JIS K 2240 Type 1 No. 1) The combustion state was examined. However, the total flow rate in the combustion cylinder is 11.4 L / min. This test was performed three times and the average value was obtained. The oxygen index refers to the value of the minimum oxygen concentration expressed by the volume percent necessary for the material to continue burning. In this application, the test piece burns continuously for 3 minutes or longer, From the minimum oxygen flow rate required for burning 50 mm or more and the nitrogen flow rate at that time, the following formula:
Critical oxygen index = (oxygen flow rate) / [(oxygen flow rate) + (nitrogen flow rate)] × 100 (volume%)
The limiting oxygen index was calculated according to

(Example 2)
Except for using phosphazene B [cyclic phosphazene compound in which n is 3 and all six R ² are phenoxy groups (PhO)] in place of phosphazene A, the same procedure as in Example 1 was performed. Thus, a polyethylene microporous film was prepared. The obtained polyethylene microporous membrane had a thickness of 30 μm, a porosity of 45%, a permeability cutoff temperature of 118 ° C., and a limiting oxygen index of 25.7.

(Example 3)
[In the formula (II), n is 3, six four are fluorine R ^2, ethylene glycoxy group cyclic phosphazene compound introduced into one phosphorus atom phosphazene C in place of the phosphazene A except using Produced a polyethylene-based microporous membrane in the same manner as in Example 1. The obtained polyethylene microporous membrane had a thickness of 30 μm, a porosity of 45%, a permeability cutoff temperature of 117 ° C., and a limiting oxygen index of 25.4.

Example 4
A polyethylene-based microporous membrane was prepared in the same manner as in Example 1 except that the amount of phosphazene A was 10 parts by mass and the amount of low-density polyethylene was 60 parts by mass. The obtained polyethylene microporous membrane had a thickness of 27 μm, a porosity of 42%, a permeability cutoff temperature of 120 ° C., and a limiting oxygen index of 28.4.

(Example 5)
In the same manner as in Example 1, except that diethyl fluorophosphate [phosphonate compound in which two R ^6a are ethyl groups and R ^6b is fluorine] in the formula (VI) was used instead of phosphazene A, A porous membrane was produced. The obtained polyethylene microporous membrane had a thickness of 26 μm, a porosity of 50%, a permeability cutoff temperature of 115 ° C., and a limiting oxygen index of 26.4.

(Example 6)
In the same manner as in Example 1 except that ethyl difluorophosphate [a phosphinate compound in which R ^7a is an ethyl group and two R ^7b are fluorine] was used in place of phosphazene A, A porous membrane was produced. The obtained polyethylene microporous membrane had a thickness of 28 μm, a porosity of 50%, a permeability cutoff temperature of 113 ° C., and a limiting oxygen index of 26.0.

(Comparative Example 1)
A polyethylene-based microporous membrane was produced in the same manner as in Example 1 except that phosphazene A was not blended and the blending amount of low-density polyethylene was 70 parts by mass. The obtained polyethylene microporous membrane had a thickness of 30 μm, a porosity of 50%, a permeability cutoff temperature of 113 ° C., and a limiting oxygen index of 18.9.

(Comparative Example 2)
A polyethylene microporous membrane was prepared in the same manner as in Example 1 except that phosphazene A was not blended and the blending amount of ultrahigh molecular weight polyethylene was 35 parts by mass. The obtained polyethylene microporous membrane had a thickness of 30 μm, a porosity of 52%, a permeability cutoff temperature of 115 ° C., and a limiting oxygen index of 19.2.

  As is clear from Table 1, the microporous membrane of the comparative example was flammable and had a low critical oxygen index, whereas the microporous membrane of the example was nonflammable and had a very high critical oxygen index.

Claims (8)

An ultrahigh molecular weight polyolefin having a thickness of 0.5 to 75 μm, a porosity of 30 to 85%, a permeability cutoff temperature of less than 135 ° C., and a weight average molecular weight of 7 × 10 ⁵ or more, a low density polyolefin, A polyolefin-based microporous membrane comprising a nonflammability imparting substance containing phosphorus.   The polyolefin microporous membrane according to claim 1, wherein the nonflammability imparting substance is a phosphazene compound.   2. The polyolefin microporous membrane according to claim 1, wherein the nonflammability imparting substance is at least one selected from the group consisting of a phosphonate compound and a phosphinate compound.   The polyolefin microporous membrane according to any one of claims 1 to 3, wherein the nonflammability imparting substance is solid at 25 ° C.   The polyolefin microporous membrane according to claim 1, wherein the ultrahigh molecular weight polyolefin is ultrahigh molecular weight polyethylene.   The polyolefin microporous membrane according to claim 1, wherein the low-density polyolefin is low-density polyethylene.   A battery separator comprising the polyolefin microporous membrane according to claim 1.   A nonaqueous electrolyte battery comprising the battery separator according to claim 7, a positive electrode, a negative electrode, and a nonaqueous electrolyte.