JP2012072285A - Porous film, electrical insulation maintenance film, separator for non-aqueous electrolyte battery and electrochemical element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a porous film having such excellent abrasion resistance as not to deteriorate battery characteristics and battery safety even when used as a battery separator, and to also provide an electrical insulation maintenance film, a separator for a non-aqueous electrolyte battery and an electrochemical element.SOLUTION: The porous film comprises a porous base film containing at least a polyolefin and a coat formed on at least one surface of the base film. A surface hardness of the coat attached surface of the porous film by an indentation hardness test is ≥50 MPa. The electrical insulation maintenance film is made of the porous film. The separator for a non-aqueous electrolyte battery is made of the electrical insulation maintenance film. The electrochemical element comprises one pair of electrodes and the electrical insulation maintenance film disposed between the one pair of electrodes.

Description

  The present invention provides a porous film containing polyolefin, an electrical insulation sustaining film comprising the porous film, a separator for a nonaqueous electrolyte battery comprising the electrical insulation sustaining film, and an electrochemical element comprising the electrical insulation sustaining film And about.

  Since non-aqueous electrolyte batteries such as lithium ion batteries have high energy density and low self-discharge, the range of use has been greatly expanded against the background of high performance and miniaturization of electronic devices. As a configuration of such a non-aqueous electrolyte battery, a spiral wound body having a wide effective electrode area obtained by stacking and winding a strip-like positive electrode, a negative electrode, and a separator is used.

  The separator basically prevents a short circuit between both electrodes and allows a battery reaction by allowing ions to permeate due to its porous structure. Furthermore, in addition to such a function, a separator having a so-called shutdown function (SD function) is employed from the viewpoint of improving safety. The SD function means that when an abnormal current occurs due to an incorrect connection, etc., the resin constituting the separator is thermally deformed as the battery internal temperature rises, closing the holes forming the porous structure, and the battery reaction It is a function to stop. As such a separator having an SD function, for example, a polyolefin porous film, more specifically, a polyethylene porous film, a porous film having a multilayer structure of polyethylene and polypropylene, and the like are known.

  These porous films used as separators for non-aqueous electrolyte batteries include porous films having submicron micropores in consideration of maintaining insulation between electrodes and liquid retention of the electrolytic solution. Preferably used.

  As a configuration of the nonaqueous electrolyte battery, there is a method of alternately stacking sheet-like electrodes and separators. However, in general, from the viewpoint of production efficiency, as described above, a spirally wound body having a large effective electrode area obtained by laminating and winding a belt-like positive electrode, a negative electrode, and a separator is mainly used. ing. Improvement of production efficiency is progressing steadily, and under the situation where the operating speed of the device is dramatically increasing, the friction control between the separator and the battery manufacturing device (especially roll) during the production of the spiral wound body is controlled by the battery. It has become an important point that also affects the safety.

  As described above, the present inventors have examined the problems that occur during production, and it has been confirmed that there is a problem that micropores of the polyolefin porous film are blocked due to surface friction during production. . The blockage of the holes is not preferable from the viewpoint of battery characteristics and safety rooted in a homogeneous reaction because the function of the battery in that portion is lost or significantly deteriorated. For this reason, it is necessary to take measures not only for the battery manufacturing apparatus but also for the porous film.

  Furthermore, a porous film is used inside the nonaqueous electrolyte battery so as to be sandwiched between the positive electrode and the negative electrode. By the charge and discharge, the positive electrode and the negative electrode repeatedly expand and contract. Therefore, the porous film is in a state where it receives pressure and friction from the electrode inside the battery. Therefore, the above-mentioned load inside the battery sometimes causes pore closure or pore reduction of the porous film.

  Therefore, an improvement solution for the above problems has been desired for the porous film used as the separator for nonaqueous electrolyte batteries.

  For example, Patent Document 1 discloses a battery separator in which an inorganic thin film made of at least one of silicon oxide and aluminum oxide is formed on the surface of a porous film without blocking pores of the porous film. Yes. According to such a configuration, it is possible to obtain a battery separator having high mechanical strength that is difficult for conductive fine particles such as electrode powder to penetrate.

  Patent Document 2 discloses a porous film using a modified polyolefin resin in which a polysiloxane molecular chain is chemically bonded to a polyolefin resin. Since a porous film formed using such a material can realize good slipperiness, it can be suitably used as a battery separator.

Japanese Patent No. 3797729 JP 2000-7819 A

  However, in the porous film disclosed in Patent Document 1, since the inorganic thin film is formed by a coating technique using a coating liquid, the inorganic thin film is unevenly distributed in a part of the hole, and the hole is blocked. There is a risk of non-uniformity.

  Further, according to the technique disclosed in Patent Document 2, since the slipperiness of the porous film can be improved, damage to the porous film due to friction can be suppressed to some extent. However, since it is not a method for selectively imparting durability to the surface layer of the film, and because it is not a method for the purpose of improving the friction resistance, the friction at the time of manufacturing or the incorporation into the battery and the It was not possible to suppress pore blockage or pore shrinkage caused by pressure. Therefore, further improvement was eagerly desired.

  Therefore, an object of the present invention is to provide a porous film excellent in friction resistance, which does not deteriorate battery characteristics or battery safety even when used as a battery separator. Furthermore, another object of the present invention is to provide an electrical insulation sustaining film using such a porous film, a nonaqueous electrolyte battery separator and an electrochemical element using the electrical insulation sustaining film.

  As a result of intensive studies to achieve the above object, the present inventors have reached the present invention using the following means.

  The porous film of the present invention includes a porous substrate film containing at least polyolefin, and a coating formed on at least one surface of the substrate film, and the surface on which the coating is provided The surface hardness according to the indentation hardness test is 50 MPa or more.

  Furthermore, the present invention provides an electrical insulation sustaining film comprising the porous film of the present invention.

  Furthermore, the present invention provides a separator for a non-aqueous electrolyte battery comprising the electrical insulation sustaining film of the present invention.

  Furthermore, the present invention provides an electrochemical device comprising a pair of electrodes and the electrical insulation sustaining film of the present invention disposed between the pair of electrodes.

  Since the porous film of the present invention has a surface hardness of at least 50 MPa on at least one surface, it can realize excellent friction resistance. Thereby, even if it is a case where the porous film of this invention is a case where it is used, for example as a separator of a nonaqueous electrolyte battery, it can suppress that the obstruction | occlusion and shrinkage | contraction of a micropore occur by friction with a battery manufacturing apparatus at the time of manufacture. Further, even when incorporated in the battery, the micropores are not easily blocked or reduced. Thus, according to the present invention, it is possible to provide a porous film excellent in wear resistance without deteriorating battery characteristics and battery safety when used as a battery separator. Furthermore, an electrochemical element provided with such a porous film as an electrical insulation sustaining film, for example, a nonaqueous electrolyte battery provided with such a porous film as a separator, can realize excellent battery characteristics and safety.

It is a partial cross section figure which shows the structural example of the nonaqueous electrolyte battery which is an example of the battery of this invention.

  The porous film of the present invention is formed by providing a coating on at least one surface of the base film. The base film contains at least polyolefin and is porous. Moreover, it is preferable that the base film has micropores having an average pore diameter of 1 μm or less. On the surface provided with the coating film of the porous film of the present invention, the surface hardness according to the indentation hardness test is 50 MPa or more.

  Hereinafter, embodiments of the porous film of the present invention will be described with reference to the drawings. The following description does not limit the present invention.

<Base film>
First, the base film will be described.

  The porous substrate film used in the present embodiment can be produced by using a material containing at least polyolefin and undergoing processes such as molding, stretching, extraction, and washing.

  The base film preferably contains an ultrahigh molecular weight polyolefin resin such as ultrahigh molecular weight polyethylene having a weight average molecular weight of 500,000 or more as a polyolefin. By using a base film containing an ultrahigh molecular weight polyolefin resin, high mechanical strength can be realized. Among all the resin components contained in the base film, the content of the ultrahigh molecular weight polyolefin resin is preferably 10 to 100% by weight, and more preferably 20 to 100% by weight.

  The base film may further contain a first resin component and / or a second resin component described below as a resin component.

  The first resin component in the present embodiment is a polymer having a carbon-carbon double bond. The polymer having a carbon-carbon double bond here is one having a carbon-carbon double bond in the polymer main chain and / or side chain, and a part of the carbon-carbon double bond is hydrogen, halogen or the like. It may be eliminated by addition, or may be a derivative in which some hydrogen atoms of the carbon-carbon double bond are replaced with other substituents. The polymer preferably has a hydrogen atom bonded to the α-position of the carbon-carbon double bond. Specifically, for example, polynorbornene, polybutadiene, polyisoprene, natural rubber, acrylonitrile butadiene rubber, styrene butadiene Examples thereof include rubber, EPDM (ethylene propylene diene terpolymer), polychloroprene and the like. As described above, a part of these carbon-carbon double bonds may be modified, or a mixture of two or more types may be used. Of these, polynorbornene, polybutadiene, and EPDM are more preferably used from the viewpoint of supplying raw materials and dispersibility.

  More specifically, the polybutadiene is preferably a polybutadiene having a large number of cis-type 1,4-polybutadiene skeletons which can easily have a flexible structure and can easily undergo a reaction between carbon-carbon double bonds. In order to promote a good crosslinking reaction, polybutadiene having a cis-type 1,4-polybutadiene skeleton ratio of 30% or more is preferably used. In EPDM, a type using ethylidene norbornene having excellent copolymerizability as a raw material is preferred, and among them, the one having a larger amount of residual double bonds is preferred.

  When the base film contains the first resin component, the content thereof is preferably 50% by weight or less, more preferably 40% by weight or less, and more preferably 35% by weight or less based on the total resin components contained in the base film. Particularly preferred. By setting the upper limit of the content of the first resin component to 50% by weight, it is possible to maintain the characteristics (for example, SD function and mechanical strength) of the porous film required when used as a battery separator. it can.

  In the present embodiment, as the second resin component, one or more resins selected from the group consisting of polyolefins having a weight average molecular weight of less than 500,000, thermoplastic elastomers, and graft copolymers are used.

  Examples of polyolefins having a weight average molecular weight of less than 500,000 include polyolefin resins such as polyethylene and polypropylene, and modified polyolefin resins such as ethylene-acrylic monomer copolymers and ethylene-vinyl acetate copolymers.

  Examples of the thermoplastic elastomer include thermoplastic elastomers such as polystyrene, polyolefin, polydiene, vinyl chloride, and polyester.

  The graft copolymer is not particularly limited as long as it has a polyolefin chain. For example, a graft copolymer having a polyolefin in the main chain and an incompatible group in the side chain can be mentioned. Here, the incompatible group means a group incompatible with polyolefin, and examples thereof include a group derived from a vinyl polymer. As the graft component, polyacryls, polymethacrylics, polystyrene, polyacrylonitrile, and polyoxyalkylenes are preferable.

  These resins may be used alone or in combination of two or more.

  When the porous film of the present embodiment is used as a battery separator, among the above listed examples of the second resin component, a polyolefin resin having a weight average molecular weight of less than 500,000, particularly polyethylene having a low melting point, A polyolefin-based elastomer having crystallinity, a graft copolymer having a polymethacrylate having a low melting temperature in the side chain, and the like are preferable from the viewpoint of providing a low shutdown temperature.

  When the base film contains the second resin component, the content thereof is preferably 50% by weight or less, more preferably 5 to 45% by weight, and more preferably 5 to 40% by weight with respect to the total resin components contained in the base film. % Is particularly preferred. By setting the upper limit of the content of the second resin component to 50% by weight, it is possible to maintain the characteristics of the porous film required when used as a battery separator.

  The base film used in the present embodiment is porous and preferably has micropores having an average pore diameter of 1 μm or less (for example, an average pore diameter of 0.03 to 1 μm). When the porous film of the present invention is used as, for example, a battery separator, a substrate film having micropores with an average pore diameter of 1 μm or less is preferably used in consideration of the liquid retention of the electrolyte and the suppression of the passage of microscopic foreign matters. Although the base film having such micropores is likely to cause pore closure or pore reduction due to friction, the occurrence of such a problem is suppressed by adopting a configuration in which a coating is provided on the surface as in the present invention. it can.

  Note that additives such as antioxidants, ultraviolet absorbers, dyes, nucleating agents, pigments, antistatic agents, and inorganic fillers are added to the base film as necessary, as long as the object of the present invention is not impaired. Further, it may be included.

<Method for producing base film>
Next, the manufacturing method of the base film by this invention is demonstrated.

  For the production of the substrate film according to the present invention, a known method such as a wet film forming method can be used. For example, the resin component (ultra high molecular weight polyolefin resin, first resin component, second resin component, etc.) is mixed with a solvent, kneaded, formed into a sheet shape while being heated and melted, rolled, and stretched in more than one axis direction. And it can manufacture by removing a solvent by heating.

  Examples of the solvent include aliphatic or cyclic hydrocarbons such as nonane, decane, undecane, dodecane, decalin, liquid paraffin, and mineral oil fractions having boiling points corresponding to these. Nonvolatile solvents containing a large amount of alicyclic hydrocarbons such as liquid paraffin are preferred.

  Moreover, the process of kneading the mixture of the resin component and the solvent and forming the mixture into a sheet can be performed by a known method. For example, an extruder equipped with a T die or the like may be kneaded batch-wise using a Banbury mixer, a kneader, etc., and then cooled by being sandwiched between cooled metal plates and rapidly cooled to crystallize. Etc. may be used to obtain a sheet-like molded product. In addition, kneading | mixing should just be on suitable temperature conditions, Although it does not specifically limit, Preferably it is 100 to 200 degreeC.

  Although it does not specifically limit as thickness of the sheet-like molding obtained in this way, 1-20 mm is preferable and you may make it thickness of 0.5-3 mm by rolling processes, such as a heat press. Although it does not specifically limit as a heat press method, For example, the belt press machine described in Unexamined-Japanese-Patent No. 2000-230072 is used suitably. Moreover, the temperature of the rolling process is preferably 100 to 140 ° C.

  A method for stretching the sheet-shaped molded product is not particularly limited, and a known method such as a normal tenter method, a roll method, and an inflation method can be used, and a combination of these methods may be used. . Also, any system such as uniaxial stretching or biaxial stretching can be applied. In the case of biaxial stretching, either longitudinal and transverse simultaneous stretching or sequential stretching may be used. From the viewpoint of film uniformity and strength, the film is preferably formed by simultaneous biaxial stretching. It is preferable that the temperature of an extending | stretching process is 100 to 140 degreeC.

  The solvent removal treatment is a step of forming a porous structure by removing the solvent from the sheet-like molded product, and the method is not particularly limited. For example, the sheet-like molded product can be washed with a solvent to remove the remaining solvent. Solvents include hydrocarbons such as pentane, hexane, heptane and decane, chlorine hydrocarbons such as methylene chloride and carbon tetrachloride, fluorinated hydrocarbons such as ethane trifluoride, ethers such as diethyl ether and dioxane, methanol and Examples thereof include readily volatile solvents such as alcohols such as ethanol and ketones such as acetone and methyl ethyl ketone. These can be used individually or in mixture of 2 or more types. The cleaning method using such a solvent is not particularly limited, and examples thereof include a method of extracting a solvent by immersing a sheet-shaped molded product in a solvent, and a method of showering the solvent on the sheet-shaped molded product.

  After obtaining a porous substrate film by the above method, a crosslinking treatment may be performed. When a polymer having a carbon-carbon double bond (first resin component) is contained in the resin component of the base film, it is desirable to perform a crosslinking treatment because a crosslinked structure can be formed. For example, the base film can be subjected to a crosslinking treatment using at least one selected from the group consisting of heat, ultraviolet rays, electron beams and visible rays. Among the above-mentioned means for crosslinking treatment, crosslinking treatment using heat or ultraviolet rays is desirable from the viewpoint of the structural stability of the base film. By performing these cross-linking treatments, the base film has higher strength and higher heat resistance, and the film resistance at high temperatures is greatly improved.

  The reason for improving the film resistance at high temperature by the crosslinking treatment is that the polymer radical generated in each treatment is added to the carbon-carbon double bond, and the polymers having the carbon-carbon double bond, or the polymer and others. It is conceivable that a crosslinking reaction takes place with the resin component of the polymer chain, or that the glass transition temperature of the polymer chain itself greatly increases due to the disappearance of the carbon-carbon double bond in the main chain. The proportion at which the carbon-carbon double bond disappears is appropriately selected in consideration of the desired heat resistance, but a disappearance rate of 80 to 100% (calculated based on the peak size of IR (infrared absorption spectrum)) is preferable. And it is thought that heat resistance improves greatly by these. Further, when the resin component is kneaded, it is considered that pseudo-crosslinking occurs due to complicated entanglement between very long polyolefins or the crosslinking component and the polyolefin, thereby contributing to curing. When the polyolefin is a long chain, the entanglement point between the molecules increases, so that the heat resistance is improved similarly to the cross-linking. This improvement in heat resistance can be confirmed, for example, by an increase in meltdown temperature in shutdown measurement.

  When heat is used as the crosslinking treatment method, a one-stage heat treatment method in which heat treatment is performed at a time, a multi-stage heat treatment method in which heat treatment is first performed at a low temperature, and then heat treatment at a higher temperature is performed, or a heat treatment is performed while increasing the temperature. Although it is possible to use a warm heat treatment method, it is desirable to perform treatment so that heat does not impair the original properties of the base film such as air permeability. In the case of single-stage heat treatment, although it depends on the composition of the base film, it is preferably 40 ° C to 140 ° C. In addition, if heat treatment is started from a low temperature and then the treatment temperature is raised, the heat resistance gradually improves as the base film cures, so heating does not impair the original properties such as air permeability. It becomes possible to expose a base film to high temperature. Therefore, in order to complete the heat treatment in a short time without impairing various characteristics, a multistage type or a temperature rising type heat treatment method is preferable.

  When a multistage heat treatment method is used, the initial heat treatment temperature is preferably 40 to 90 ° C., although it depends on the composition of the base film. The heat treatment temperature in the second stage is preferably 90 to 140 ° C. although it depends on the composition of the base film.

  When ultraviolet rays are used for the crosslinking treatment, for example, the base film after film formation is impregnated in the air as it is, or the base film after film formation is impregnated in a methanol solution containing a polymerization initiator, and then the solvent is added. The dried product can be subjected to crosslinking treatment by irradiating with ultraviolet rays with a mercury lamp. Moreover, you may perform ultraviolet irradiation in water for the heat control at the time of irradiation.

  In the case of using an electron beam, for example, a crosslinking treatment can be performed by irradiating a base film after film formation with an electron beam having a radiation dose of 1 to 10 kGy (0.1 to 10 Mrad). The atmosphere at the time of irradiation may be air as in the heat treatment method, or an inert gas atmosphere such as nitrogen gas or argon gas for the purpose of controlling the crosslinking state.

  Further, following the crosslinking treatment step, the base film may be heat set (heat-fixed) in order to prevent thermal shrinkage. When the crosslinking treatment is performed using heat as described above, depending on the treatment conditions, the heat setting can be substantially performed by the crosslinking treatment. However, even in such a case, when the heat set is insufficient, the heat set may be performed by further heating after the crosslinking treatment in order to prevent heat shrinkage more reliably. The heat setting may be performed, for example, at 110 to 140 ° C. for about 0.5 to 2 hours. In addition, when the polymer which has a carbon-carbon double bond is not added to the base film, the crosslinking treatment can be omitted. Therefore, in that case, heat setting (heat setting) may be performed immediately after film formation.

  As for the thickness of the base film obtained as mentioned above, 1-60 micrometers is preferable and 5-50 micrometers is more preferable. The porosity is preferably 20 to 80%, more preferably 25 to 75%. The air permeability is preferably 100 to 1000 seconds / 100 cc, more preferably 100 to 900 seconds / 100 cc, for example, by a method based on JIS P8117. The shutdown temperature is preferably 150 ° C. or lower, more preferably 145 ° C. or lower. The mechanical strength is, for example, preferably 1N or more, more preferably 2N or more in terms of needle stick strength. In addition, the measuring method of this needle stick strength can mention the method as described in the below-mentioned Example.

<Coating>
The coating is provided on at least one surface of the base film. The coating is formed so that the surface hardness of the surface of the porous film provided with the coating is 50 MPa or more according to the indentation hardness test. Preferably, it is to form a coating that can realize a surface hardness of the porous film of 200 MPa or more.

  The material of the coating film is not particularly limited as long as the surface hardness of the porous film can be 50 MPa or more, preferably 200 MPa or more. For example, the coating can be formed using a metal oxide such as silica, zirconia, and alumina, diamond-like carbon, or the like.

  It is desirable that the coating is formed so as not to significantly reduce the air permeability of the base film. The amount of increase in the air permeability of the porous film due to the formation of the coating on the base film is, for example, a method based on JIS P8117, preferably 0 to 200 seconds / 100 cc, more preferably 0 to 100 seconds / 100 cc. preferable.

  The thickness of the coating is not particularly limited because it may be appropriately selected in consideration of the hardness of the material to be used, but is preferably 2 to 500 nm, and more preferably 5 to 200 nm.

  By forming the coating as described above, the friction resistance of the porous film can be improved. When the porous film is used as a separator for a non-aqueous electrolyte battery, hole blockage and hole reduction due to friction are unlikely to occur, and the change in air permeability is small in terms of characteristics. As an evaluation method, when a surface friction test described later is performed on the surface on which the film is formed, the increase in air permeability is preferably 50 seconds / 100 cc or less, more preferably 30 seconds / 100 cc or less. When the air permeability increases beyond 50 seconds / 100 cc, the charge / discharge characteristics of the battery may deteriorate.

  The method for forming the film can be appropriately selected from known thin film forming methods. For example, the formation of a silica film or a zirconia film by applying a coating agent for forming a silica film or a zirconia film, the formation of a film by applying a slurry to which nanoparticles such as alumina or silica are added, and then fixing the coating, Examples thereof include formation of a metal oxide film by sputtering (reactive sputtering) and CVD (Chemical Vapor Deposition), and formation of a diamond-like carbon coating by plasma CVD and ion plating. In particular, when diamond-like carbon, which is a suitable film, is formed by ion plating, a hydrocarbon gas such as benzene is introduced into a vacuum chamber to generate hydrocarbon ions in a direct current arc discharge plasma. There is a method in which ions are made to collide with a material to be coated having a negative charge to solidify and form.

  Among the films formed as described above, it can be formed on a base film containing a polyolefin having a low melting point, can achieve high hardness even when thin, and can selectively form a thin film on the surface of the base film, etc. From this point, a film using diamond-like carbon is preferably used.

  The coating may be formed on at least one surface of the base film, but may be formed on both surfaces. In consideration of the relationship with the roll of the production line when used as a battery separator, the pressure and friction state inside the battery, the reactivity with the electrode, etc., select the surface to form the film and the area to form the film as appropriate. That's fine. The coating does not need to be provided on the entire surface of the base film, and may be partially formed, for example, a striped coating or a dot coating.

<Nonaqueous electrolyte battery>
The porous film of the present invention can be used as an electrical insulation sustaining film. One example is a non-aqueous electrolyte battery separator. A battery can be assembled using this non-aqueous electrolyte battery separator in a state of being interposed between the positive electrode and the negative electrode in the same manner as a conventional separator. In the present embodiment, a nonaqueous electrolyte battery provided with the porous film of the present invention as a battery separator will be described as an example. The material of the positive electrode, negative electrode, battery case, electrolyte, etc. used in this nonaqueous electrolyte battery and the arrangement structure of these components are not particularly limited, and may be the same as in the prior art. For example, in JP-A 63-205048 It may be as shown.

  In the present embodiment, a cylindrical nonaqueous electrolyte battery 1 as shown in FIG. 1 will be described as an example of a nonaqueous electrolyte battery. In FIG. 1, some hatching is omitted for the purpose of making the drawing easier to see.

  As shown in FIG. 1, in the nonaqueous electrolyte battery 1, a positive electrode 2, a negative electrode 3, and a separator (separator for nonaqueous electrolyte battery) 4 disposed between the positive electrode 2 and the negative electrode 3 are integrally swirled. And is accommodated in a battery case 5 with a bottom. The separator 4 is a non-aqueous electrolyte battery separator made of the porous film of the present invention. A positive electrode lead (not shown) connected to the positive electrode 2 is electrically connected to the battery case 5 via a lower insulating sleeve (not shown). In the figure, reference numeral 5a denotes a positive terminal portion. The negative electrode tab 7 electrically connected to the negative electrode 3 is electrically connected to the negative electrode terminal portion 6 a through the cavity portion 8 a of the upper insulating sleeve 8. The battery is filled with a nonaqueous electrolyte (not shown). The battery case 5 is sealed by a lid body 6 including a negative electrode terminal portion 6a and a packing 9 that closes a gap between the lid body 6 and the battery case 5, so that the nonaqueous electrolyte cannot leak out of the battery. Yes. In addition, the separator 4 is impregnated with an electrolyte. As a result, the ion carrier is moved between the positive electrode 2 and the negative electrode 3 sandwiching the separator 4, so that the secondary battery can be discharged and charged. . In this example, two separators 4 are bonded together to form a bag shape, and the negative electrode 3 is inserted therein and wound together with the positive electrode 2. However, the separator 4 need not necessarily be formed in a bag shape because the separator 4 may be disposed between the positive electrode 2 and the negative electrode 3 adjacent to each other in the state after winding.

  The positive electrode 2 is formed of an active material that occludes and releases lithium ions, a binder, and a current collector. The positive electrode 2 can be produced, for example, by preparing a paste by mixing the active material in a solvent in which a binder is dissolved, applying the paste onto a current collector, and drying the paste. You may press further after drying.

As a positive electrode active material, the well-known compound used as a positive electrode active material of a lithium ion secondary battery can be used. Specifically, lithium-containing transition metal oxides such as LiCoO ₂ , LiMnO ₂ , LiNiO ₂ , or lithium-containing transition metal oxides in which a part of the transition metal is substituted with another transition metal, titanium disulfide, And chalcogen compounds such as molybdenum disulfide.

  As the binder, a known resin can be used as the binder constituting the positive electrode 2. For example, fluorine resins such as polyvinylidene fluoride (PVDF), hexafluoropropylene and polytetrafluoroethylene (PTFE), hydrocarbon resins such as styrene butadiene rubber and ethylene propylene terpolymer, or a mixture thereof can be used. . Moreover, you may add conductive powder, such as carbon black, as a conductive support agent.

  As the current collector of the positive electrode 2, a metal excellent in oxidation resistance is used. For example, aluminum processed into a foil shape or a mesh shape is preferably used.

  The negative electrode 3 is formed of a carbon-based active material or a lithium-containing alloy, a binder, and a current collector. The negative electrode 3 can also be produced by the same method as the positive electrode 2. Further, the same binder as the binder used in the positive electrode 2 can be used.

  Examples of the carbon-based active material include artificial graphite, natural graphite, fired bodies such as coke and pitch, and those obtained by sintering phenol resin, polyimide, cellulose, and the like. Examples of the lithium-containing metal include Al, Sn, and Si alloys.

  As the current collector of the negative electrode 3, a metal excellent in reduction stability is used. For example, copper processed into a foil shape or a mesh shape is preferably used.

The non-aqueous electrolyte includes a non-aqueous solvent and an electrolyte. Specifically, lithium ions such as an electrolytic solution in which a lithium salt (electrolyte) is dissolved in a non-aqueous solvent, a gel electrolytic solution containing the electrolytic solution, a solid electrolyte in which a lithium salt is dissolved and decomposed into a polymer such as polyethylene oxide, etc. The well-known non-aqueous electrolyte used for a secondary battery is mention | raise | lifted. Specific examples of the lithium salt used as the electrolyte include lithium borotetrafluoride (LiBF ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium perchlorate (LiClO ₄ ), and lithium trifluorosulfonate (LiCF ₃ SO). ₃ ) etc. can be used. Examples of the non-aqueous solvent include propylene carbonate (PC), ethylene carbonate (EC), methyl ethyl carbonate (MEC), 1,2-dimethoxyethane (DME), and γ-butyrolactone (γ-BL). Or a mixed solvent thereof can be used.

  For the separator 4, the above-described electrical insulation sustaining film of the present invention, that is, a porous film is used.

  In this embodiment, a cylindrical non-aqueous electrolyte battery has been described as an example of the non-aqueous electrolyte battery of the present invention. However, other configurations such as a cylindrical or laminated non-aqueous electrolyte battery may be used. However, the configuration of the present invention can be applied.

<Others>
Examples of the electrochemical element of the present invention that includes the porous film of the present invention as an electrical insulation sustaining film include solar cells, fuel cells, and the like in addition to non-aqueous electrolyte batteries typified by the lithium ion secondary battery.

  In general, a dye-sensitized solar cell is composed of a nano-sized titanium oxide porous thin film electrode to which a dye is chemisorbed and an electrolyte. Frame-like spacers were used for insulation between the electrodes, but by using the electrical insulation sustaining film made of the porous film of the present invention for insulation between the electrodes, the electrolyte layer was made thin, uniform, and large. The area can be easily increased, contributing to an improvement in output.

  In a fuel cell using a polymer as an electrolyte, for example, as shown in International Publication No. 01/022514, a state in which a polymer electrolyte membrane is interposed between a positive electrode and a negative electrode composed of a catalyst layer and a gas diffusion layer Then, the battery is assembled. By impregnating the porous film of the present invention with a polymer electrolyte and using it as a polymer electrolyte membrane, the electrolyte layer can be both reinforced and thinned, and the output can be improved.

Further, a capacitor can be assembled by interposing an electrical insulation sustaining film made of the porous film of the present invention between a pair of electrodes. In such a capacitor, materials such as electrodes, electrolyte, and case and the arrangement structure of these components are not particularly limited, and may be the same as a conventional capacitor. For example, in an electric double layer capacitor, an activated carbon electrode formed with PTFE as a binder can be used as an electrode, and a solution obtained by adding 0.5 M Et ₄ PBF ₄ to propylene carbonate can be used as an electrolyte.

  The present invention will be described in more detail based on examples and comparative examples, but the present invention is not limited to such examples. Various characteristics were measured as follows.

[Film thickness]
It was measured with a 1/10000 thickness gauge.

[Porosity]
A porous film to be measured was cut out into a circle having a diameter of 6 cm, and its volume (cm ³ ) and weight (g) were determined, and calculated from the obtained results using the following formula.
Porosity (%) = 100 × (volume (cm ³ ) −weight (g) / average density of components (g / cm ³ )) / volume (cm ³ )

[Air permeability]
It measured based on JISP8117.

[Needle strength]
A needlestick test was performed at room temperature (25 ° C.) using a compression tester “KES-G5” manufactured by Kato Tech Co., Ltd. The maximum load was read from the obtained load displacement curve and used as the needle stick strength. A needle having a diameter of 0.5 mm and a radius of curvature of the tip of 0.25 mm was used, and piercing was performed at a speed of 2 mm / second.

[Surface hardness]
Using a nano indenter (Nanoindenter DCM) manufactured by MTS, the hardness of the micro region was measured from the surface in the depth direction in the continuous stiffness measurement mode. As the surface hardness, the maximum value near the outermost surface was read.

[Surface friction test]
A porous film cut into a strip shape having a width of 50 mm and a length of 400 mm was fixed at two points, and installed so as to float in the air between the two points. Using a wire bar (RDS, No. 3), the surface of the film was rubbed over a length of 300 mm out of the floating state in the air using its own weight (103.5 g). The surface friction test was repeated 10 times at a speed of about 300 mm / sec.

Example 1
12 parts by weight of ultrahigh molecular weight polyethylene having a weight average molecular weight of 1,000,000 (melting point: 137 ° C.), 3 parts by weight of maleic anhydride-modified polyethylene having a weight average molecular weight of 250,000 (manufactured by Nippon Polyethylene, ADDEX ER403A), and polynorbornene (manufactured by Nippon Zeon) Nosolex NB) 0.5 parts by weight and 85 parts by weight of liquid paraffin are uniformly mixed in a slurry state, and melt-kneaded in a twin-screw extruder at a temperature of 160 ° C. to give a sheet having a thickness of 1.5 mm Extruded into a shape. The sheet molding was taken out under a certain tension, and then cooled and molded with a roll once cooled with cooling water at 10 ° C. to prepare a resin sheet. Thereafter, the resin sheet was biaxially stretched 5.0 × 4.5 times at a temperature of 123 ° C. in the vertical and horizontal directions to produce a stretched film. Next, the solvent was removed from the stretched film using heptane. In order to perform a crosslinking treatment and a heat setting treatment on the stretched film, it was placed in a thermostatic bath at 125 ° C. and treated for 2 hours while applying an air flow to produce a porous substrate film. A diamond-like carbon thin film was formed on one side of the obtained base film by ion plating using benzene as a hydrocarbon gas. However, for the purpose of preventing the deformation of the base film, the periphery of the base film was fixed with tape. As a result of cross-sectional observation using a transmission electron microscope (TEM), the coating thickness was 40 nm. About the obtained porous film, film thickness, porosity, surface hardness, needlestick strength and surface hardness were measured, and air permeability before and after the surface friction test was also measured. The results are shown in Table 1. The surface hardness and needlestick strength were measured on the surface provided with the coating.

(Comparative Example 1)
A porous film was produced in the same manner as in Example 1 except that no film was formed on the surface of the base film. That is, the porous film of Comparative Example 1 is the base film used in Example 1. The porous film of Comparative Example 1 was also measured for film thickness and the like in the same manner as in Example 1. The results are shown in Table 1.

(Example 2)
15 parts by weight of ultra high molecular weight polyethylene (melting point 137 ° C.) having a weight average molecular weight of 1 million and 85 parts by weight of liquid paraffin are uniformly mixed on the slurry, and melt kneaded at a temperature of 160 ° C. with a twin screw extruder. And extruded into a sheet having a thickness of 1.5 mm. The sheet molding was taken out under a certain tension, and then cooled and molded with a roll once cooled with cooling water at 10 ° C. to prepare a resin sheet. Thereafter, the resin sheet was biaxially stretched 5.0 × 4.5 times at a temperature of 124 ° C. in the vertical and horizontal directions to produce a stretched film. Next, the solvent was removed from the stretched film using decane. This stretched film was placed in a constant temperature bath at 128 ° C. and treated for 2 hours while applying an air current to produce a porous substrate film. A diamond-like carbon thin film was formed on one side of the obtained base film by ion plating using benzene as a hydrocarbon gas. As a result of cross-sectional observation by TEM, the coating thickness was 20 nm. About the obtained porous film, film thickness, porosity, surface hardness, needlestick strength and surface hardness were measured, and air permeability before and after the surface friction test was also measured. The results are shown in Table 1. The surface hardness and needlestick strength were measured on the surface provided with the coating.

(Comparative Example 2)
15 parts by weight of ultra high molecular weight polyethylene (melting point 137 ° C.) having a weight average molecular weight of 1 million and 85 parts by weight of liquid paraffin are uniformly mixed on the slurry, and melt kneaded at a temperature of 160 ° C. with a twin screw extruder. And extruded into a sheet having a thickness of 1.2 mm. The sheet molding was taken out under a certain tension, and then cooled and molded with a roll once cooled with cooling water at 10 ° C. to prepare a resin sheet. Thereafter, the resin sheet was biaxially stretched 5.0 × 4.5 times at a temperature of 124 ° C. in the vertical and horizontal directions to produce a stretched film. Next, the solvent was removed from the stretched film using decane. This stretched film was placed in a constant temperature bath at 128 ° C. and treated for 2 hours while applying an air current to produce a porous substrate film. About the base film in the state in which the film is not formed, film thickness etc. were measured similarly to Example 2. The results are shown in Table 1.

  The porous films of Examples 1 and 2 having a coating film on the surface obtained a higher surface hardness than Comparative Examples 1 and 2 without a coating film. Further, when the air permeability before and after the friction test was compared, in the porous film of Example 1 provided with the coating, no significant decrease in the air permeability due to the friction test was observed. On the other hand, in the porous film of Comparative Example 1 in which no coating was provided, the air permeability was greatly reduced after the friction test. Similarly, in the comparison between Example 2 and Comparative Example 2, there was no significant difference in air permeability before and after the friction test in Example 2, but in Example 2, the air permeability was significantly reduced by the friction test. From these results, it was confirmed that by providing the coating film, it was possible to suppress hole blockage or hole shrinkage due to friction and maintain good characteristics.

  Further, the porous films of Examples 1 and 2 have a structure in which a film is formed on the surface of the base film, but the porosity is almost the same as that of the porous films of Comparative Examples 1 and 2 where no film is formed. The initial air permeability (air permeability before the friction test) was obtained. Therefore, it was also confirmed that the porous film of the present invention can be used as a battery separator.

  The porous film of the present invention is not easily deteriorated in friction properties and has high friction resistance. Therefore, it can also be suitably used for battery separators that require high friction resistance. In addition, the porous film of the present invention can be used not only as an electrical insulation sustaining film such as a battery separator but also as a porous film that requires friction resistance. . In addition, for example, if the conductivity is adjusted by adjusting the coating material or the coating formation conditions, it can be used as a porous film with an electrode for filter applications.

1 Nonaqueous Electrolyte Battery 2 Positive Electrode 3 Negative Electrode 4 Separator (Porous Film)
5 Battery Case 5a Positive Terminal 6 Lid 6a Negative Terminal 7 Negative Tab 8 Upper Insulating Sleeve 8a Cavity 9 Packing

Claims (9)

A porous substrate film containing at least polyolefin;
A coating formed on at least one surface of the base film,
The porous film whose surface hardness by an indentation hardness test is 50 MPa or more about the surface in which the said film is provided.   The porous film according to claim 1, wherein the base film has micropores having an average pore diameter of 1 μm or less.   The porous film of Claim 1 or 2 whose surface hardness by the said indentation hardness test is 200 Mpa or more about the surface in which the said film is provided. The base film contains, as the polyolefin, ultra high molecular weight polyethylene having a weight average molecular weight of 500,000 or more,
The porous film of any one of Claims 1-3 whose content of the said ultra high molecular weight polyethylene is 10 weight% or more with respect to all the resin components contained in the said base film.   The porous film according to claim 1, wherein the coating is formed of diamond-like carbon.   The electrical insulation maintenance film | membrane consisting of the porous film of any one of Claims 1-5.   A separator for a non-aqueous electrolyte battery comprising the electrical insulation sustaining film according to claim 6.   An electrochemical element comprising a pair of electrodes and the electrical insulation sustaining film according to claim 6 disposed between the pair of electrodes.   The electrochemical element according to claim 8, which is a nonaqueous electrolyte battery.

Images