JPWO2013058061A1 - Porous membrane manufacturing method, porous membrane, battery separator and battery - Google Patents

Abstract

The porous membrane (A) to be processed is placed in the coating processing apparatus, a specific raw material is present in the apparatus in a gaseous state, and the coating treatment is performed in the presence of an additive gas, thereby the porous film ( A porous film (A ′) obtained by forming a film containing the constituent elements of the raw material and the additive gas on at least one surface of A). Superior heat shrinkage, shutdown, meltdown resistance, wettability with electrolyte, and electrochemical stability without reducing the ion permeability and mechanical properties required for battery separators The present invention provides a porous membrane having a property and a battery separator using the same.

Description

  The present invention relates to a porous film having both excellent shutdown characteristics and meltdown resistance, and excellent wettability with electrolyte and oxidation resistance. More specifically, it has excellent ion permeability, low heat shrinkage, shutdown characteristics and melt-down resistance near 200 ° C, so it has excellent safety, and also has good wettability with electrolyte and electrochemical stability. The present invention relates to a polyolefin porous membrane useful as an excellent battery separator, a method for producing the same, and a battery and a capacitor using the porous membrane.

  Thermoplastic resin porous membranes are widely used as material separation membranes, permselective membranes, partition materials and the like. For example, various filters such as reverse osmosis filtration membranes, ultrafiltration membranes, microfiltration membranes, moisture permeable waterproof clothing, battery separators used for lithium ion batteries, nickel metal hydride batteries, etc., diaphragms for electrolytic capacitors, etc. It is used. Among these, polyolefin (PO) porous membranes are used as separators for lithium ion batteries, and the performance of polyolefin (PO) porous membranes is deep in battery characteristics, battery productivity, and battery safety. Is involved. Therefore, excellent ion permeability, mechanical characteristics, low heat shrinkage, shutdown characteristics, meltdown resistance, etc. are required.

  Due to the high capacity and high energy density that can be achieved, lithium-ion batteries will continue to be used in consumer applications (mobile terminals, power tools, etc.), transportation applications (cars, buses, etc.), and power storage applications (smart grids, etc.). Is predicted. In these batteries, a separator made of an electrically insulating porous film is interposed between positive and negative electrodes, and an electrolyte solution in which a lithium salt is dissolved is impregnated in the gap of the film. A structure in which the layers are laminated or wound in a spiral manner is mainly used. Lithium secondary batteries need to take various safety measures against problems due to their high capacity and high energy density, for example, a large increase in battery temperature due to short circuit inside and outside the battery. In order to solve such problems, attempts have been made to add various devices to the separator.

  In particular, as a safety measure to which a separator can contribute, a shutdown characteristic and a melt-down resistance are attracting attention. For example, when the internal temperature of the battery rises due to troubles such as overcharge, external or internal short circuit, the part of the separator melts, the gap is closed, and the current is cut off is called shutdown (also called a fuse) This temperature is called the shutdown temperature. As the temperature rises further, the separator melts and flows, resulting in large holes. This is called meltdown, and the temperature at this time is called meltdown temperature. When the separator melts and flows, a short circuit occurs between the electrodes, resulting in a more dangerous state. Therefore, non-aqueous electrolyte battery separators are required to lower the shutdown temperature of the separator and increase the meltdown temperature.

  In response to such safety requirements, proposals have been made to improve the thermoplastic resin composition used in the separator and to provide an inorganic particle layer or a heat-resistant resin layer on the separator surface. For example, a polyolefin porous film (Patent Document 1) in which both surface layers are mainly composed of polypropylene and a layer mainly composed of polyethylene between both surface layers, porous film A1 made of a resin having a melting point of 150 ° C. or less, and glass transition A composite porous membrane integrated with a porous membrane B1 made of a resin having a temperature higher than 150 ° C. (Patent Document 2), and a thermal decomposition temperature in which organic powder and / or inorganic powder is dispersed is 200 ° C. or higher. A composite porous film (Patent Document 3) in which a porous film B2 made of a polymer and a porous film A2 made of a thermoplastic resin are laminated has been reported.

  However, in the improvement of the thermoplastic resin composition reported in Patent Document 1, sufficient meltdown resistance cannot be achieved due to the heat resistance limit of the thermoplastic resin as a raw material. Also, a porous film A made of a thermoplastic resin and a porous film B made of a heat resistant resin (organic and / or inorganic particles may be dispersed in the heat resistant resin) reported in Patent Document 2 or 3 are laminated. In the porous membrane, the interlayer adhesion between the porous membranes is low, and further, a solution, slurry, or gel for forming the porous membrane B in the pores of the porous membrane A from the production method There is a problem that the air permeability resistance (ion permeability) of the entire laminated porous membrane deteriorates due to the heat-resistant resin in the shape of entering and closing the pores. Further, since lamination is necessary, there is a limit to reducing the thickness of the entire laminated porous film, and there is a possibility that it will not be possible to cope with the higher capacity of the battery that will be developed in the future.

  On the other hand, physical / chemical vapor deposition has also been proposed as a surface treatment method for a porous film. For example, for the purpose of hydrophilic treatment of a porous material, a method of irradiating plasma in an inert gas or a mixed gas of an inert gas and a reactive gas and plasma-treating the surface of the porous material and the inside of the pores (Patent Document) 4) A PO microporous membrane whose surface is modified with a hydrophilic polymer by plasma treatment (Patent Document 5) has been reported. Similarly, by depositing inorganic particles on the organic porous film by physical vapor deposition, the PO film contacting the positive electrode is prevented from being carbonized, and a battery separator (Patent Document 6) is hard to be short-circuited even if charged for a long time. Has been. Thus, attempts have been made to improve various properties of the separator by physical / chemical vapor deposition, but no report has been made to improve the meltdown resistance.

  Furthermore, the requirements for the separator include wettability with an electrolytic solution and improvement in electrochemical stability. If the wettability with the electrolyte is poor, there is a problem that it takes time to inject the electrolyte when manufacturing the battery and the productivity is deteriorated, and the electrolyte is easily depleted (dry out) and the internal resistance is increased. There is a risk that the battery performance may be remarkably deteriorated due to the above. In addition, when the electrochemical stability is low, self-discharge is accelerated due to a decrease in insulation due to carbonization of the separator and the like, which may hinder the increase in battery capacity and energy density.

JP 2008-255307 A JP 2007-125821 A JP 2006-348280 A JP 2007-80588 A JP 2011-12238 A JP 2005-196999 A

  Therefore, the problem to be solved by the present invention is that it has excellent low heat shrinkage, shutdown characteristics, melt-down resistance, and electrolysis without deteriorating ion permeability and mechanical characteristics required for battery separators. A porous membrane having wettability with liquid and electrochemical stability and a battery separator using the same are provided.

In order to solve the above-mentioned problems, the porous membrane of the present invention has the following configuration (1) or (2). That is,
(1) The porous film (A) to be processed is placed in the plasma coating processing apparatus, and at least one raw material selected from the raw material group shown in the following group 1 is present in the gaseous state in the apparatus. Further, the porous film (A ′) obtained by forming a film containing the constituent elements of the raw material and the additive gas on at least one surface of the porous film (A) by performing the coating treatment in the presence of the additive gas. ,
Or
(2) The porous membrane (A) to be processed is placed in the plasma coating processing apparatus, and at least one raw material selected from the raw material group shown in group 1 below is present in the gaseous state in the apparatus. And a porous film obtained by forming a film containing the constituent elements of the raw material and the additive gas on the surface of the fiber, pulp or fibril forming the porous membrane (A) by performing the coating treatment in the presence of the additive gas. Membrane (A ′).

Here, the group 1 refers to the following raw material groups (1) to (9).
(1) A silane compound represented by SiR ¹ R ² R ³ R ⁴ (wherein R ¹ to R ⁴ are each hydrogen, halogen, an alkyl group having 1 to 10 carbon atoms, or an alkoxy group, The chain may be straight or branched, and each may have the same or different carbon number, and the carbon chain may be saturated or unsaturated, eg, Si and the substituents R ¹ and R ² And may form a ring.)
(2) a disiloxane compound represented by O— (SiR ¹ R ² R ³ ) ₂ (wherein R ¹ to R ³ are each hydrogen, halogen, or an alkyl group having 1 to 10 carbon atoms; The chain may be straight or branched, and each may have the same or different carbon number, and the carbon chain may be saturated or unsaturated, eg, Si and the substituents R ¹ and R ² And may form a ring.)
(3) a cyclic siloxane compound represented by — (OSiR ¹ R ² ) _n — (wherein R ¹ and R ² are each hydrogen, halogen, or an alkyl group having 1 to 10 carbon atoms, and the carbon chain is The chain may be linear or branched, and each may have the same or different carbon number, and the carbon chain may be saturated or unsaturated, for example, a ring with Si and substituents R ¹ and R ² In which n is an integer of 2 to 20)
(4) Silazane compound represented by N- (SiR ¹ R ² R ³ ) _m R ⁴ _3-m (where R ^{1 to} R ⁴ are each hydrogen, halogen, or an alkyl group having 1 to 10 carbon atoms) The carbon chain may be linear or branched, and each may have the same or different carbon number, and the carbon chain may be saturated or unsaturated, for example, Si and a substituent R ^A ring may be formed by ¹ and R ^{2. In the} formula, m is an integer of 1 to ^3. )
(5) a cyclic silazane compound represented by — (NR ¹ SiR ² R ² ) ₁ — (wherein R ¹ to R ³ are each hydrogen, halogen, or an alkyl group having 1 to 10 carbon atoms; The chain may be straight or branched, and each may have the same or different carbon number, and the carbon chain may be saturated or unsaturated, eg, Si and the substituents R ¹ and R ² And in the formula, l is an integer of 2 to 20.)
(6) A titanate compound represented by TiR ¹ R ² R ³ R ⁴ (wherein R ^{1 to} R ⁴ are each hydrogen, halogen, an alkyl group having 1 to 10 carbon atoms, or an alkoxy group, May be linear or branched, and may have the same or different carbon number, and the carbon chain may be saturated or unsaturated, for example, with Ti and substituents R ¹ and R ² A ring may be formed.)
(7) Aromatic hydrocarbon compounds
(8) Ar- (X) An aromatic compound having at least one polar group represented by _k (wherein Ar represents an aromatic hydrocarbon or heteroaromatic compound, -X represents -COOH, -SO ₃ H, —OR, —CO—R, —CONHR, —SO ₂ NHR, —NHCOOR, —NHCONHR, —NH ₂ , k is an integer of 1 to 3 and R is 1 to 10 carbon atoms The carbon chain of the alkyl group may be linear or branched, and may have the same or different carbon number, and the carbon chain may be saturated or unsaturated.
(9) Lactam Compound The battery separator of the present invention has the following configuration. That is,
A battery separator comprising the porous membrane (A ′).

The battery of the present invention has the following configuration. That is,
A battery comprising at least one positive electrode, a negative electrode, an electrolyte, and the battery separator according to claim 11.

  The porous membrane of the present invention is preferably coated by a roll-to-roll process.

  In the porous membrane of the present invention, the additive gas is preferably at least one selected from gases shown in Group 2 below.

Here, the group 2 refers to the following gas group.
Hydrogen, nitrogen, oxygen, carbon dioxide, nitrous oxide, nitrogen dioxide, hydrocarbon having 3 or less carbon atoms In the porous film of the present invention, the raw material that exists in a gaseous state at the time of coating treatment is solid at normal temperature and pressure, or The liquid is preferable.

  In the porous membrane of the present invention, the raw material is at least one selected from the raw material group shown in groups 1- (2), (4), (6) and (8), and the additive gas is nitrogen and carbon number. It is preferably either 3 or less hydrocarbon or carbon dioxide.

  The porous membrane of the present invention has an air resistance X (sec / 100 cc Air / 20 μm) of the porous membrane (A) before coating treatment and an air resistance of the porous membrane (A ′) on which the coating is formed. The relationship with X ′ (sec / 100 cc Air / 20 μm) preferably satisfies X ′ / X ≦ 2.0.

The porous membrane of the present invention, the weight W of the porous film (A) (g / m 2 ), ' the weight W of (g / m ²⁾ and the relationship coating formed porous film (A)' Preferably satisfies W′−W ≦ 2 (g / m ² ).

  In the porous membrane of the present invention, the porous membrane (A) is preferably produced by a wet method.

  According to the present invention, without lowering the ion permeability, mechanical properties, etc. required for battery separators, excellent, low heat shrinkability, shutdown characteristics, meltdown resistance, wettability with electrolyte, A porous membrane having electrochemical stability and a battery separator using the same can be provided.

  The porous membrane (A ′) in the present invention is required to have a coating film for improving the meltdown resistance. As a method of forming a film, a voltage is applied between electrodes in a plasma coating processing apparatus to ionize source molecules present in a gaseous state to form at least one surface of the porous film (A) or the porous film (A). There is a method of forming a chemical vapor deposition film by depositing chemical species containing constituent elements of a raw material gas on the surface of fibers, pulp or fibrils.

  The film in the present invention is a chemical vapor deposition film formed by chemical vapor deposition (hereinafter referred to as CVD), and excites the source gas by applying energy such as heat, light, electromagnetic waves, etc. to the source gas, Alternatively, it is a deposited film made of a chemical species containing a constituent element of the source gas, formed on the surface of the base material by a chemical reaction on the surface of the base material. Examples of the CVD method include thermal CVD, metal organic CVD, plasma CVD, photo CVD, and laser CVD. The present invention is a porous film in which a film is formed by plasma CVD. Among these, in the present invention, high-frequency plasma CVD is preferably used from the viewpoint of the cost of the processing apparatus.

  The coating in the present invention needs to be excellent in heat resistance in order to improve meltdown resistance. As the raw material for forming the film, it is necessary to use at least one kind of raw material selected from the raw material group shown in Group 1, and a plurality of kinds of raw materials can be used in an arbitrary ratio.

In the present invention, the silane compound represented by Group 1- (1): SiR ¹ R ² R ³ R ⁴ is silicon, hydrogen, halogen, an alkyl group having 1 to 10 carbon atoms, or an alkoxy group (here, a carbon chain) May be linear or branched, and may have the same or different carbon number, and the carbon chain may be saturated or unsaturated, for example, with Si and substituents R ¹ and R ² A ring that may form a ring). Specific examples include tetramethylsilane, diethoxydimethylsilane, and tetraethoxysilane.

In the present invention, the disiloxane compound represented by the group 1- (2): O— (SiR ¹ R ² R ³ ) ₂ is formed by bonding two silicon atoms to oxygen, and further hydrogen, halogen, carbon number to silicon. 1-10 alkyl groups or alkoxy groups (wherein the carbon chain may be linear or branched, and each may have the same or different carbon number. Furthermore, the carbon chain may be saturated or unsaturated. Further, for example, a compound in which Si and substituents R ¹ and R ² may form a ring) is bonded. Specific examples include hexamethyldisiloxane and hexaethyldisiloxane, and hexamethyldisiloxane is preferably used.

The cyclic siloxane compound represented by the group 1- (3) :-( OSiR ¹ R ² ) _n — in the present invention is the same number of oxygen and silicon bonded cyclically, and further halogen to silicon and carbon atoms of 1 to 10 An alkyl group or an alkoxy group (wherein the carbon chain may be linear or branched, and each may have the same or different carbon number. The carbon chain may be saturated or unsaturated. Further, for example, a compound in which Si and substituents R ¹ and R ² may form a ring is bonded. Specific examples include hexamethylcyclotrisiloxane and octamethylcyclotetrasiloxane. The number of silicon atoms in the molecule (n in the formula) is preferably in the range of 2 to 20, and more preferably in the range of 2 to 5 from the viewpoint of handleability.

The silazane compound represented by group 1- (4): N- (SiR ¹ R ² R ³ ) _m R ⁴ _3-m in the present invention is a compound in which 1 to 3 silicons are bonded to nitrogen, and further to silicon. Hydrogen, halogen, an alkyl group having 1 to 10 carbon atoms, or an alkoxy group (wherein the carbon chain may be linear or branched, and each may have the same or different carbon number. Further, the carbon chain is saturated) Or a compound in which Si and substituents R ¹ and R ² may form a ring. M in the formula is an integer of 1 to 3. Specific examples include hexamethyldisilazane and hexaethyldisiloxane, and hexamethyldisilazane is preferably used.

Group ^{1- (5) :-( NR 1 SiR} 2 R 2) l in the present invention _- and the cyclic silazane compound represented by the same number of nitrogen and silicon are bonded to the annular, further halogen each nitrogen and silicon, An alkyl group having 1 to 10 carbon atoms or an alkoxy group (wherein the carbon chain may be linear or branched, and each may have the same or different carbon number. Furthermore, the carbon chain may be saturated) It may be unsaturated, or a compound in which Si and substituents R ¹ and R ² may form a ring. Specific examples include hexamethylcyclotrisilazane and octamethylcyclotetrasilazane. The number of silicon atoms in the molecule (l in the formula) is preferably in the range of 2 to 20, and more preferably in the range of 2 to 5 from the viewpoint of handleability.

In the present invention, the group 1- (6): titanate compound represented by TiR ¹ R ² R ³ R ⁴ is titanium, hydrogen, halogen, an alkyl group having 1 to 10 carbon atoms, or an alkoxy group (here, a carbon chain) May be linear or branched, and may have the same or different carbon number, and the carbon chain may be saturated or unsaturated, for example, with Ti and substituents R ¹ and R ² A ring that may form a ring). Specific examples include tetramethyl titanium and tetraethoxy titanium.

  The group 1- (7): aromatic hydrocarbon compound in the present invention is a benzene aromatic compound, and specific examples thereof include benzene, naphthalene, anthracene, phenanthrene and the like. In the present invention, naphthalene and anthracene which are solid at room temperature and have sublimation properties can be preferably used from the viewpoints of handleability and meltdown resistance.

Group in the present invention 1- (8): Ar- (X ) is an aromatic compound having at least one polar group represented by _k, a hydrogen atom of an aromatic compound is -COOH, _-SO 3 H, - OR, —CO—R, —CONHR, —SO ₂ NHR, —NHCOOR, —NHCONHR, —NH ₂ (where R is an aromatic group or alkyl group having 1 to 10 carbon atoms, and the carbon chain is linear) However, it may be branched, and each may have the same or different number of carbon atoms, and may be saturated or unsaturated, and is a compound substituted with at least one polar group selected from , K is an integer of 1 to 3, Ar represents an aromatic hydrocarbon or heteroaromatic compound, and the total number of atoms of carbon, nitrogen, oxygen, sulfur, etc. constituting the aromatic compound is in the range of 5-10. is there. Specific examples include aromatic carboxylic acids such as benzoic acid and phthalic acid, aromatic sulfonic acids such as benzenesulfonic acid, and the like. In the present invention, compounds that are solid at room temperature and have sublimation properties, specifically, terephthalic acid, melamine, and the like can be preferably used from the viewpoints of handleability and meltdown resistance.

  The group 1- (9): lactam compound in the present invention is an intramolecular cyclic amino compound, specifically, α-lactam (three-membered ring), β-lactam (four-membered ring), γ-lactam (five Member ring) and the like. In the present invention, a lactam compound having a 7-membered ring or less can be preferably used from the viewpoint of meltdown resistance.

  When forming a film in the present invention, at least one kind of raw material selected from the raw material group shown in group 1 is present in a gas state in the coating processing apparatus, and at least one kind selected from group 2 described above. It is preferable that the additive gas is allowed to coexist in the coating processing apparatus from the viewpoints of melt-down resistance, adhesion between the porous membrane (A) and the coating, and flexibility of the coating. By forming the coating in the presence of the additive gas, the constituent elements of the additive gas are incorporated into the coating, and the flexibility of the coating is improved. At the same time, the adhesion between the porous membrane and the coating and the meltdown resistance are improved. Presumed to be.

  Here, the additive gas of group 2 is hydrogen, nitrogen, oxygen, carbon dioxide, nitrous oxide, nitrogen dioxide, and hydrocarbon having 3 or less carbon atoms, as described above. The hydrocarbon having 3 or less carbon atoms may be saturated or unsaturated, and specific examples include methane, ethane, propane, ethylene, propylene, acetylene and the like.

  In the coating process, as the additive gas, a plurality of kinds of gases selected from the group 2 are used in an arbitrary ratio in the coating processing apparatus coexisting with the raw material gas. The ratio of the total amount of raw materials shown in group 1 present in the coating apparatus and the total amount of additive gas selected from group 2 is not particularly limited, and the coating process can be performed in an arbitrary ratio in the coating apparatus. I can do it.

  Preferred combinations of the raw material (gas) shown in group 1 and the additive gas shown in group 2 include, for example, disiloxane compounds of group 1- (2), silazane compounds of group 1- (4), group 1- ( A combination of a titanate compound of 6) or an aromatic hydrocarbon having at least one polar group of Group 1- (8) and carbon dioxide, hydrocarbon or nitrogen is from the viewpoint of meltdown resistance and coating flexibility. It can be illustrated as a preferred combination. However, the combination of the raw material and the additive gas is not limited to this.

  There is no particular limitation on the method of introducing the raw material selected from the raw material group of group 1 and the additive gas selected from group 2 into the plasma coating apparatus, and the gaseous raw material is directly introduced into the apparatus. A method of vaporizing a liquid raw material by depressurization, heating or the like and introducing it into the apparatus, a method of vaporizing a solid raw material by heating or the like and introducing it into the apparatus, or a method of vaporizing the raw material by installing an evaporation source in the apparatus Etc. In the present invention, in order to make the various gas concentrations in the plasma coating processing apparatus constant, it is preferable to introduce various vaporized gases into the plasma coating processing apparatus via a flow meter or the like. When introduced into the apparatus, an additive gas selected from group 2 can also be used as a carrier gas for the raw material gas shown in group 1.

  The plasma coating process in the present invention is a so-called roll-to-roll process in which the porous film (A) is unwound, the coating process is continuously performed, and the porous film (A ′) on which the film is formed can be wound. -It is preferable to carry out by a roll process from a viewpoint of productivity and the quality stability of a film.

  As a specific example of the plasma coating treatment apparatus in the present invention, a decompression vessel connected to a decompression system for decompressing the inside of the treatment apparatus and a supply system for introducing raw materials and / or additive gas into the treatment apparatus is exemplified. The container may be provided with a porous membrane (A) unwinding device, a plasma generation source, and a porous membrane (A ′) winding device.

  In the present invention, the roll of the porous film (A) is set in the coating processing apparatus, the pressure inside the apparatus is reduced, and then the coating process is performed while the porous film is fed out. It is preferable to coat by a roll-to-roll process by winding up as a roll. The porous membranes (A) and (A ′) are usually wound around a core to form a roll. The core material used is a thermoplastic resin such as ABS (acrylonitrile butadiene styrene) resin or polyethylene resin. , And a thermosetting resin such as a resol resin can be preferably used because it has a small amount of volatile components from the core and does not contaminate the porous membrane surface or the inside of the coating processing apparatus.

  In the plasma coating treatment apparatus of the present invention, it is preferable that there is a support for supporting the porous membrane (A) in the region irradiated with plasma, and the support has a curved surface even if it is flat. Even if there is, it is not limited. The support preferably has a cooling function so that the surface of the support can be kept warm. When it has a cooling function, the temperature rise by plasma irradiation is prevented effectively, the porous membrane (A) is hard to be thermally contracted, and the flatness is not impaired.

  In the present invention, plasma discharge conditions are not particularly limited, but the pressure is preferably in the range of 0.01 to 1,000 Pa, more preferably in the range of 0.1 to 100 Pa. When the pressure is in this preferred range, plasma is efficiently generated, and a coating film is efficiently formed because the source gas is present in an appropriate amount.

  In the coating process of the present invention, when the film thickness uniformity cannot be maintained in the area to be coated, the shape of the plasma electrode is appropriately changed, and a shielding plate having an appropriate shape is installed between the electrodes. The film thickness uniformity of the film can be secured by adjusting the amount of plasma to be irradiated.

  Hereinafter, the characteristics of the porous membrane (A ′) of the present invention will be described in detail.

The porous membrane (A ′) of the present invention needs to have a coating formed of at least one raw material selected from Group 1 and at least one additive gas constituting element selected from Group 2. . The film deposition amount is preferably in the range of 0.05 g / m ² or more and 2 mg / m ² or less. When the deposition amount of the film is within this preferable range, the improvement of the meltdown resistance can be achieved, and the increase of the air resistance can be effectively prevented. Excellent discharge characteristics. The amount of deposition is W (g / m ² ) for the weight of the porous film (A), and W ′ (g / m ² ) for the weight of the porous film (A ′) on which the film is formed. It can be obtained by W′−W.

  The deposition amount of the porous film (A ′) of the present invention is the type and concentration of the raw material gas and additive gas in the processing apparatus, the pressure in the processing apparatus, the output of microwaves and high frequencies for generating plasma, It can be arbitrarily adjusted by adjusting the vapor deposition treatment area and the vapor deposition treatment speed.

  The air permeability resistance of the porous membrane (A ′) of the present invention is such that the air permeability resistance of the porous membrane (A) before the coating treatment is Xsec / 100 cc Air / 20 μm, and the porous membrane (A When the air resistance of ') is X'sec / 100ccAir / 20µm, it is preferable to satisfy X' / X≤2.0. When the value of X ′ / X is 2.0 or less, the charge / discharge characteristics are excellent without inhibiting the movement of ions in the battery. The value of X ′ / X is preferably 1.5 or less, more preferably 1.2 or less.

  The heat shrinkage rate of the porous membrane (A ′) of the present invention is preferably lower than that of the porous membrane (A). Furthermore, the heat shrinkage rate at 105 ° C. for 8 hours imitating the use of the battery at a high temperature and the heat shrinkage rate at 150 ° C. for 30 minutes near the meltdown temperature of the separator are both lower than those of the porous membrane (A). preferable. The lower the thermal shrinkage rate in the above evaluation conditions, the better from the viewpoint of safety, and the lower the MD and TD, the better from the viewpoint of safety.

  The porous membrane (A ′) of the present invention has shutdown characteristics, and preferably has a shutdown temperature in the range of 70 to 150 ° C. from the viewpoint of safety. Although the shutdown temperature of the porous membrane (A ′) can be adjusted by selecting the porous membrane (A), the shutdown temperature (T ′s) of the porous membrane (A ′) depends on the composition of the coating, the deposition amount, and the deposition state. ) May be higher than the shutdown temperature (Ts) of the porous membrane (A). From the viewpoint of safety, it is preferable that the increase range of the shutdown temperature (T′s−Ts) is small, preferably (T′s−Ts) ≦ 5 ° C., more preferably (T′s−Ts) ≈0 ° C. is there.

  The meltdown temperature (T′m) of the porous membrane (A ′) of the present invention is preferably higher than the meltdown temperature of the porous membrane (A). From the viewpoint of safety, the increase range of the meltdown temperature (T′m−Tm) is preferably large, preferably (T′m−Tm) ≧ 20 ° C., more preferably (T′m−Tm) ≧ 30 ° C. It is.

  The puncture strength of the porous membrane (A ′) of the present invention can be adjusted by the design and selection of the porous membrane (A). However, the puncture strength of the porous membrane (A ′) depends on the composition, deposition amount, and deposition state of the coating. The puncture strength (P ′) may be slightly lower than the puncture strength (P) of the porous membrane (A). From the viewpoint of workability, the rate of decrease in puncture strength (1-P ′ / P) is preferably small, preferably (1-P ′ / P) = 0.2 or less, more preferably (1-P ′ / P). ) = 0.1 or less. The rate of decrease in the puncture strength can be kept low by adjusting the additive gas, the microwave for generating the plasma, the output of the high frequency, etc. so that the porous film (A) is not etched by the plasma. .

  The wettability of the porous membrane (A ′) of the present invention with the electrolytic solution is preferably higher than that of the porous membrane (A). High wettability means that the electrolyte easily spreads on the surface of the porous membrane, and also means that it easily penetrates in the thickness direction of the porous membrane. High wettability shortens the time required to inject electrolyte during battery manufacture, and can be expected to improve productivity. Prevents electrolyte from depleting (dry out) and increases internal resistance. There is no fear of significantly lowering.

  The electrochemical stability of the porous membrane (A ′) of the present invention is preferably higher than that of the porous membrane (A). Electrochemical stability is a property related to the oxidation resistance of separators that are exposed to relatively high temperatures during storage or use. If the electrochemical stability is low, it is not preferable because it may cause a decrease in insulation due to carbonization of the separator and the like, which may accelerate self-discharge and hinder the increase in battery capacity and energy density.

  Next, the composition of the porous membrane (A) will be described.

  Examples of the porous membrane (A) in the present invention include a porous woven fabric, nonwoven fabric, paper or porous film made of electrically insulating organic, inorganic fibers or pulp. A porous film is preferable in terms of balance between properties and mechanical strength.

  The material of the porous membrane (A) in the present invention may be organic or inorganic as long as it is electrically insulating, and may be synthetic or natural. Organic fibers and / or inorganic fibers and / or pulps of organic fibers and / or Or the thing containing the pulp of an inorganic fiber is mention | raise | lifted. Specific examples of organic fibers include synthetic fibers made of thermoplastic polymers and natural fibers such as Manila hemp. Examples of the synthetic fiber made of the thermoplastic polymer include polyolefins such as polyethylene and polypropylene, and synthetic fibers such as rayon, vinylon, polyester, acrylic, polystyrene, and nylon. Examples of the inorganic fiber include glass fiber and alumina fiber.

  Preferred examples of the material for the porous membrane (A) include polyolefins such as polyethylene and polypropylene from the viewpoint of electrical insulation and shutdown characteristics. When the porous membrane (A) is composed of polyolefin, it may be a single substance or a mixture of two or more different polyolefin resins, for example, a mixture of polyethylene resin and polypropylene resin, or different olefins, such as ethylene. And a copolymer of propylene. Of the polyolefin resins, polyethylene and polypropylene are particularly preferred. This is because, in addition to basic characteristics such as electrical insulation and ion permeability, it has shutdown characteristics and electrochemical stability that cuts off the current and suppresses excessive temperature rise at abnormal battery temperature rise.

The mass average molecular weight (Mw) of the polyolefin resin is not particularly limited, but is usually within a range of 1 × 10 ⁴ to 1 × 10 ⁷ , preferably within a range of 1 × 10 ^{4 to} 5 × 10 ⁶ , and more. Preferably it exists in the range of 1 * 10 < ⁵ > -5 * 10 < ⁶ >.

  The polyolefin resin preferably contains polyethylene. Examples of polyethylene include ultra high molecular weight polyethylene, high density polyethylene, medium density polyethylene, and low density polyethylene. The polymerization catalyst is not particularly limited, and examples thereof include polyethylene produced by a polymerization catalyst such as a Ziegler-Natta catalyst, a Philips catalyst, or a metallocene catalyst. These polyethylenes may be not only ethylene homopolymers but also copolymers containing a small amount of other α-olefins. Examples of α-olefins other than ethylene include propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene, (meth) acrylic acid, esters of (meth) acrylic acid, styrene, etc. Can be suitably used.

  Polyethylene may be a single substance, but is preferably a mixture of two or more kinds of polyethylene. As the polyethylene mixture, a mixture of two or more types of ultrahigh molecular weight polyethylene having different Mw, a mixture of similar high density polyethylene, a mixture of similar medium density polyethylene, and a mixture of low density polyethylene may be used. A mixture of two or more polyethylenes selected from the group consisting of high-density polyethylene, medium-density polyethylene, and low-density polyethylene may be used.

The inter alia polyethylene mixture, 5 × 10 ⁵ or more ultra-high molecular weight polyethylene and Mw of 1 × 10 ⁴ or more, the mixture is preferably composed of a polyethylene of less than 5 × 10 ^5. The Mw of the ultra high molecular weight polyethylene is preferably in the range of 5 × 10 ⁵ to 1 × 10 ⁷ , more preferably in the range of 1 × 10 ⁶ to 1 × 10 ⁷ , and more preferably 1 × 10 ^{6 to} 5. It is particularly preferable that it is within the range of × 10 ⁶ . As the polyethylene having an Mw of 1 × 10 ⁴ or more and less than 5 × 10 ⁵ , any of high density polyethylene, medium density polyethylene and low density polyethylene can be used, and it is particularly preferable to use high density polyethylene. As polyethylene with Mw of 1 × 10 ⁴ or more and less than 5 × 10 ⁵ , two or more types having different Mw may be used, or two or more types having different densities may be used. By setting the upper limit of Mw of the polyethylene mixture to 1 × 10 ⁷ , melt extrusion can be facilitated. The content of ultrahigh molecular weight polyethylene in the polyethylene mixture is preferably 1% by weight or more, more preferably in the range of 10 to 80% by weight, based on the entire polyethylene mixture.

When the ultra-high molecular weight polyethylene having Mw of 5 × 10 ⁵ or more is contained in the polyethylene mixture, the pore diameter of the porous membrane may become smaller as the added amount of ultra-high molecular weight polyethylene increases. Here, for example, when improving the meltdown resistance by applying a solution of a high heat resistant resin on the porous film (A), a step for making the high heat resistant resin layer porous is required. In addition, there is a drawback that the air resistance is remarkably increased by the high heat-resistant resin entering the pores of the porous membrane (A). On the other hand, in the present invention, since it is possible to coat the surface of the fibril forming the porous membrane (A), the step of making porous is unnecessary, and it is easy to suppress the increase in the air resistance. is there. As described above, a porous film containing ultrahigh molecular weight polyethylene and having a small pore diameter can be used without any problem.

  The ratio of the Mw and the number average molecular weight (Mn) and the molecular weight distribution (Mw / Mn) of the polyolefin resin are not particularly limited, but are preferably in the range of 5 to 300, and in the range of 10 to 100. More preferred. When Mw / Mn is in this preferred range, the polyolefin solution is easy to extrude because the high molecular weight component is appropriate, and the strength of the porous film obtained is excellent because the low molecular weight component is appropriate. Mw / Mn is used as a measure of the molecular weight distribution. That is, in the case of a single polyolefin, the larger this value, the wider the molecular weight distribution. The Mw / Mn of a single polyolefin can be appropriately adjusted by multistage polymerization of polyolefin. The multistage polymerization method is preferably a two-stage polymerization in which a high molecular weight component is polymerized in the first stage and a low molecular weight component is polymerized in the second stage. When the polyolefin is a mixture, the larger the Mw / Mn, the larger the difference in Mw of each component to be mixed, and the smaller the Mw / Mn, the smaller the difference in Mw. Mw / Mn of the polyolefin mixture can be appropriately adjusted by adjusting the molecular weight and mixing ratio of each component.

When a polyethylene porous membrane is used, polypropylene may be included together with polyethylene for the purpose of improving the meltdown resistance and the high-temperature storage characteristics of the battery. The Mw of polypropylene is preferably in the range of 1 × 10 ⁴ to 4 × 10 ⁶ . As the polypropylene, a homopolymer or a block copolymer and / or a random copolymer containing another α-olefin can be used. Other α-olefins are preferably ethylene. The polypropylene content is preferably 80% by weight or less based on 100% by weight of the entire polyolefin mixture (polyethylene + polypropylene).

  In order to improve the characteristics as a battery separator, the polyethylene porous membrane may contain a polyolefin imparting shutdown characteristics. For example, low-density polyethylene can be used as the polyolefin imparting shutdown characteristics. As the low density polyethylene, at least one selected from the group consisting of branched, linear, and ethylene / α-olefin copolymers produced by a single site catalyst is preferable. The addition amount of the low density polyethylene is preferably 20% by weight or less, based on 100% by weight of the whole polyolefin. When the addition amount of the low density polyethylene is within this preferable range, breakage hardly occurs during stretching.

In the polyethylene composition containing the ultra high molecular weight polyethylene, as an optional component, Mw is poly 1-butene in the range of 1 × 10 ⁴ to 4 × 10 ⁶ , and Mw is in the range of 1 × 10 ³ to 4 × 10 ⁴ . And at least one polyolefin selected from the group consisting of ethylene / α-olefin copolymers having a Mw in the range of 1 × 10 ⁴ to 4 × 10 ⁶ may be added. The amount of these optional components added is preferably 20% by weight or less, based on 100% by weight of the polyolefin composition.

  Hereinafter, taking the case where the porous membrane (A) is a polyolefin porous membrane as an example, the production method and characteristics will be described.

  The method for producing the porous membrane (A) in the present invention is not particularly limited, and the phase structure according to the purpose can be freely given by the production method. As a method for producing the porous membrane (A), there are a foaming method, a phase separation method, a dissolution recrystallization method, a stretch pore-opening method, a powder sintering method, etc. Among these, the uniformity of micropores and the point of cost However, the phase separation method is preferable, but is not limited thereto.

  As a production method by the phase separation method, for example, a polyolefin and a film-forming solvent are melt-kneaded, the obtained molten mixture is extruded from a die, and cooled to form a gel-like molding, and the obtained gel-like molding is obtained. Examples thereof include a method of obtaining a porous film by stretching a material in at least a uniaxial direction and removing the film-forming solvent.

  The porous film (A) may be a single-layer film or a multilayer film composed of two or more layers (for example, a three-layer structure of polypropylene / polyethylene / polypropylene or a three-layer structure of polyethylene / polypropylene / polyethylene). Good.

  As a method for producing a multilayer film composed of two or more layers, for example, each of the polyolefins constituting the first layer and the second layer is melt-kneaded with a film-forming solvent, and the resulting molten mixture is sent from each extruder to one Either a method in which the gel sheets constituting each component are supplied to a die and integrated and coextruded, or a method in which the gel sheets constituting each layer are superposed and heat-sealed can be produced. The coextrusion method is more preferable because it is easy to obtain a high interlayer adhesive strength, and it is easy to form communication holes between layers, so that high permeability is easily maintained and productivity is excellent.

  The porous membrane (A) preferably has a shutdown characteristic in which the pores are closed when the charge / discharge reaction is abnormal from the viewpoint of safety when using the battery. Therefore, the melting point (softening point) of the constituent resin is preferably 70 to 150 ° C, more preferably 100 to 140 ° C. If the melting point (softening point) of the constituent resin is within this preferred range, there is no possibility that the shutdown function will be manifested during normal use and the battery will not be usable, while the shutdown function will be promptly manifested if an abnormal reaction occurs. Therefore, safety can be ensured.

  The film thickness of the porous membrane (A) is preferably 5 μm or more and less than 30 μm. The upper limit of the film thickness is more preferably 25 μm, still more preferably 20 μm. Further, the lower limit of the film thickness is more preferably 7 μm, and most preferably 10 μm. When the film thickness is within this preferred range, it is possible to have a film strength and a shutdown function that maintain practical workability, while the electrode area per unit volume in the battery case is not restricted. Therefore, it is possible to cope with the future increase in battery capacity. From the viewpoint of increasing the capacity of the battery, it is preferable that the thickness of the porous membrane (A) is thin as long as there is no problem in workability.

  The upper limit of the air permeability resistance (JIS P 8117) of the porous membrane (A) is preferably 800 sec / 100 cc Air / 20 μm, more preferably 700 sec / 100 cc Air / 20 μm, and most preferably 600 sec / 100 cc Air / 20 μm. The lower limit of the air resistance is preferably 50 sec / 100 cc Air, more preferably 70 sec / 100 cc Air, and most preferably 100 sec / 100 cc Air. From the viewpoint of increasing the output of the battery, it is preferable that the air resistance of the porous membrane (A) is as small as possible without causing problems in workability.

  The upper limit of the porosity of the porous membrane (A) is preferably 70%, more preferably 60%, and most preferably 55%. The lower limit of the porosity is preferably 25%, more preferably 30%, and most preferably 35%.

  The air permeability resistance and porosity of the porous membrane (A) are related to ion permeability (charge / discharge operating voltage), battery charge / discharge characteristics, battery life (closely related to the amount of electrolyte retained). If the influence is large and the upper limit of the air permeability resistance or the lower limit of the porosity is within the above preferable range, the battery function can be sufficiently exhibited. On the other hand, when the lower limit of the air permeability resistance or the upper limit of the porosity is within the above preferable range, sufficient mechanical strength and electrical insulation between the electrodes can be maintained, and a short circuit occurs during charging and discharging. There is nothing.

  Since the average pore diameter of the porous membrane (A) greatly affects the shutdown speed, it is preferably 0.01 to 1.0 μm, more preferably 0.02 to 0.5 μm, and most preferably 0.03 to 0.00. 3 μm.

  When the average pore diameter is within this preferred range, the air permeability resistance is not greatly deteriorated during film formation, while the response to the temperature of the shutdown phenomenon is quick, such as overcharge, external or internal short circuit, etc. Even when the internal temperature of the battery suddenly rises due to a trouble, the shutdown function works effectively.

  The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

[Porous membrane (A)]
Here, as the porous membrane (A), “Setela” (registered trademark) E20MMS manufactured by Toray Battery Separator Film Co., Ltd. was used, and the effect of the present invention was confirmed.

E20MMS is a polyethylene porous membrane, and various physical properties were measured as Comparative Example 1 for comparison with the present invention.
[Coating treatment equipment]
The coating processing apparatus includes a film unwinding shaft, a winding shaft, a cooling drum (Φ150 mm), and a plasma electrode in a container (chamber) that can be decompressed. A vacuum pump is connected to the coating processing apparatus, and the inside of the chamber can be depressurized.

  The film fed from the unwinding shaft side is conveyed while being held by the cooling drum facing the plasma electrode, and is wound on the winding shaft side. The unwinding and winding tension can be appropriately set by adjusting the shaft torque.

  The plasma electrode was a flat-plate magnetron type, and graphite was used as the electrode material. The effective size of the electrode is 50 mm in the film transport direction and 100 mm in the film width direction. In addition, a high frequency power source of 13.56 MHz is connected to the plasma electrode via a matching box.

  In addition, a liquid raw material vaporizer is connected to the coating processing apparatus. In this method, a liquid material is pressurized with argon gas and supplied to a vaporizer while being metered by a digital liquid mass flow controller to generate a material vapor. The raw material vapor is supplied between the cooling drum of the coating apparatus and the plasma electrode. The opposing axes of the cooling drum and the plasma electrode are horizontal, and the shortest distance is 100 mm.

  In addition, a gas introduction system using a mass flow controller is connected to the coating processing apparatus, and for example, an additive gas can be supplied between the cooling drum and the plasma electrode.

  Furthermore, a crucible for heating and vaporizing the solid raw material can be installed in this coating processing apparatus. By disposing the crucible between the cooling drum and the plasma electrode, the raw material vapor can be supplied from diagonally below the cooling drum.

  The crucible shape is a square with an opening of 50 mm × 50 mm, and the height is 40 mm. The material of the crucible is stainless steel SUS306 having a thickness of 1.0 mm. Below the crucible, a copper heater plate of 50 mm × 50 mm × 10 mm is disposed via a carbon sheet for increasing the thermal conductivity.

  A heater and a thermocouple are embedded in the heater plate, and the temperature can be controlled by PID. The heater plate is placed on the chamber base plate via an insulating alumina spacer.

  Moreover, the opening of the crucible was covered with an aluminum mesh having a pitch of 1.5 mm, so that when the plasma was generated at the top, the material surface in the crucible was prevented from being exposed to the plasma and denatured.

A quartz oscillator type film thickness meter is installed on the side of the cooling drum toward the plasma electrode side so that the coating process can be monitored.
(Example 1)
Hexamethyldisiloxane (HMDSO: manufactured by Shin-Etsu Chemical Co., Ltd.) was charged into the liquid raw material container, purged with argon gas after evacuation. On the other hand, a roll around which a porous film (A) having a thickness of 20 μm, a width of 50 mm, and a length of 20 m was wound was set in a coating apparatus, and the inside of the apparatus was evacuated to 3.0 × 10 ⁻³ Pa or less.

  Thereafter, HMDSO was supplied to the vaporizer at a flow rate of 0.65 cc / min, the vapor was introduced into the coating apparatus, and the exhaust valve was adjusted to set the pressure in the chamber to 1.0 Pa. The additive gas methane was added to the chamber by adjusting the setting of the mass flow controller of the gas introduction system so that the partial pressure ratio with HMDSO was the partial pressure ratio shown in Table 1.

  After setting the pressure, the high-frequency power supplied to the plasma electrode was set to 100 W, and plasma was generated. Further, winding of the film was started after 5 minutes from the generation of the plasma. The winding speed was set to be 0.1 m / min.

The raw materials and coating conditions in each Example and Comparative Example are as shown in Tables 1 and 2.
(Example 2)
The same procedure as in Example 1 was performed except that the additive gas was changed to carbon dioxide and the pressure in the chamber was set to 5.0 Pa.
(Comparative Example 2)
The same procedure as in Example 1 was performed except that the additive gas was not added and the pressure in the chamber was set to 10.0 Pa.
(Example 3)
Hexamethyldisilazane (HMDS: manufactured by Wako Pure Chemical Industries, Ltd.) was charged into the liquid raw material container and purged with argon gas after evacuation. The pressure in the chamber was set to 5.0 Pa, and the others were performed in the same manner as in Example 1.
Example 4
Hexamethyldisilazane (HMDS: manufactured by Wako Pure Chemical Industries, Ltd.) was charged into the liquid raw material container and purged with argon gas after evacuation. The additive gas was carbon dioxide, and the others were performed in the same manner as in Example 1.
(Comparative Example 3)
Hexamethyldisilazane (HMDS: manufactured by Wako Pure Chemical Industries, Ltd.) was charged into the liquid raw material container and purged with argon gas after evacuation. Furthermore, it carried out like Example 1 except not having added addition gas.
(Example 5)
Titanium isopropoxide (TTIP: manufactured by Wako Pure Chemical Industries, Ltd.) was put into the liquid raw material container, purged with argon gas after evacuation. Further, the same procedure as in Example 1 was performed except that the additive gas was changed to carbon dioxide.
(Examples 6 to 9 and Comparative Example 4)
20 g of terephthalic acid monomer powder (manufactured by Wako Pure Chemical Industries, Ltd.) was introduced into the crucible and uniformly spread in the crucible. Further, a roll around which a porous film (A) having a thickness of 20 μm, a width of 50 mm, and a length of 20 m was wound was set in a coating apparatus, and evacuation was started.

Then, the exhaust was exhausted to 3.0 × 10 ⁻³ Pa or less while the heater was heated to 200 ° C. during exhaust. At this temperature, it was confirmed with a crystal oscillator type film thickness meter that almost no monomer had evaporated at this temperature.

  After stabilizing for about 5 minutes in this state, the heater temperature was set to 400 ° C. to generate material vapor. Further, an additive gas was introduced, and the pressure in the chamber was 5 Pa to 10 Pa, and the high frequency power supplied to the plasma electrode was plasma applied in the range of 50 W to 100 W. In either case, the film conveyance speed was set in the range of 0.1 m / min to 0.4 m / min.

The addition method of the additive gas is the same as in Example 1, and the raw materials and coating conditions in each Example and Comparative Example are as shown in Tables 1 and 2.
(Examples 10 and 11 and Comparative Example 5)
20 g of melamine monomer powder (manufactured by Wako Pure Chemical Industries, Ltd.) was put into a crucible and spread uniformly in the crucible. Further, a roll around which a porous film (A) having a thickness of 20 μm, a width of 50 mm, and a length of 20 m was wound was set in a coating apparatus, and evacuation was started.

Then, the exhaust was exhausted to 3.0 × 10 ⁻³ Pa or less while the heater was heated to 200 ° C. during exhaust. At this temperature, it was confirmed with a crystal oscillator type film thickness meter that almost no monomer had evaporated at this temperature.

  After stabilizing for about 5 minutes in this state, the heater temperature was set to 350 ° C. to generate material vapor. Further, an additive gas was introduced, and the pressure in the chamber was 5 Pa to 10 Pa, and the high frequency power supplied to the plasma electrode was plasma applied in the range of 50 W to 100 W. In either case, the film conveyance speed was set to 0.1 m / min to 0.4 m / min.

The addition method of the additive gas is the same as in Example 1, and the raw materials and coating conditions in each Example and Comparative Example are as shown in Tables 1 and 2.
[result]
The physical properties of the porous membranes obtained in Examples 1 to 11 and Comparative Examples 1 to 5 were measured by the following methods. The results are shown in Tables 1 and 2.
-Film thickness: measured with a contact thickness meter (manufactured by Mitutoyo Corporation).
Air permeability resistance: Gurley value was measured according to JIS P 8117 (converted to a film thickness of 20 μm).
Weight per unit: The porous membrane was punched into 50 mm squares, and the weight of the porous membrane was measured to 0.1 mg. The weight was converted to g / m ² unit.
Puncture strength: The maximum load was measured when the porous membrane was punctured at a speed of 2 mm / sec using a needle having a diameter of 1 mm (0.5 mmR), and converted to a thickness of 20 μm.
Shutdown temperature: Using a heat / stress / strain measuring device (manufactured by Seiko Denshi Kogyo Co., Ltd., TMA / SS6000), a porous film sample of 10 mm (TD) × 3 mm (MD) is room temperature at a rate of 5 ° C./min The temperature was raised from the point 2 with a load of 2 g, and the inflection point observed near the melting point was taken as the shutdown temperature.
Melt down temperature: Using the above heat / stress / strain measuring apparatus, a 10 mm (MD) × 3 mm (TD) porous film sample was pulled with a load of 2 g while being heated from room temperature at a rate of 5 ° C./min. The temperature at which the film was broken by melting was taken as the meltdown temperature.
Flexibility: A new design cutter blade was inserted from the coating surface side of the porous membrane (A ′), and a cut of about 5 mm was made. The cut portion was observed with an electron microscope at a magnification of 1000 times, and the presence or absence of cracks on the coating surface (such as cracks on the coating surface derived from the cutting and peeling) was evaluated and qualitatively evaluated according to the following criteria.

Excellent: No crack
good: There seems to be a crack
failure: There is a large crack. Thermal contraction rate (105 ° C. × 8 h): Marking is performed at the midpoint (bisected point) of each side of the porous film having a size of 50 × 50 mm in the MD and TD directions. It heat-processes for 8 hours at 105 degreeC in a free state, without fixing a porous membrane, and measures each dimension of MD and TD after heat processing at the marked position.
The heat shrinkage ratio was calculated by subtracting the dimension after heating from the dimension before heating (50 mm) and further dividing by the dimension before heating (50 mm).
Heat shrinkage rate (150 ° C. × 30 minutes): When measuring the heat shrinkage rate in the TD direction, a porous film having a size of 50 × 50 mm in the MD and TD directions is applied to a frame having an opening of 50 × 35 mm. Both ends in the MD direction are fixed with tape or the like so as to be parallel to the TD direction. As a result, the MD direction is fixed at an interval of 35 mm, and the TD direction is positioned with the film end along the frame opening. The whole frame on which the porous membrane is fixed is heat-treated in an oven at 150 ° C. for 30 minutes and cooled. Due to thermal shrinkage in the TD direction, the end of the porous membrane that is parallel to the MD bends slightly inwardly (towards the center of the opening in the frame). The thermal shrinkage rate (%) in the TD direction was calculated by subtracting the shortest dimension in the TD direction after heating from the TD dimension (50 mm) before heating and further dividing by the TD dimension (50 mm) before heating.

When measuring the thermal contraction rate in the MD direction, the TD and MD directions are switched in the above method.
-Wettability with electrolyte solution On the surface on which the porous membrane (A) kept in a horizontal state and the porous membrane (A ') of the present invention were formed, the mixture No. 1 for the wetting tension test was used. One drop of 42.0 (manufactured by Wako Pure Chemical Industries, Ltd.) was dropped from the dropper, and the state of droplet spreading on the surface of the porous film 30 seconds after the dropping was observed. When the spread of the droplet on the surface on which the coating film of the porous film (A ′) was formed was larger than the porous film (A), it was indicated as “◯”.
Electrochemical stability A porous film having a MD direction of 70 mm × TD direction of 60 mm is prepared, and a battery is produced by sandwiching the porous film between a negative electrode and a positive electrode of the same size. At this time, the negative electrode was made of natural graphite, the positive electrode was made of LiCoO ₂ , and the electrolyte was a 1M solution in which LiPF ₆ was dissolved in a mixture of ethylene carbonate and dimethyl carbonate (3/7, v / v). In the case of the porous membrane (A ′), the membrane was disposed so that the coating surface was in contact with the positive electrode, and the electrolyte was impregnated into the porous membrane to complete the battery.

  Next, an applied voltage of 4.3 V was applied to the produced battery at 60 ° C., and “electrochemical stability” was judged by the magnitude of the integrated current flowing between the voltage source and the battery. It is generally desirable for the integrated current to be small, representing a small charge loss during overcharge.

  In the examples, the integrated current value (mAh) up to 120 hr after voltage application was described.

  As shown in Tables 1 and 2, the porous membrane (A) of the present invention having a coating formed from a raw material selected from the raw material group shown in Group 1 and an additive gas shown in Group 2 was excellent. It can be seen that it has characteristics.

  According to the present invention, without lowering the ion permeability, mechanical properties, etc. required for battery separators, excellent, low heat shrinkability, shutdown characteristics, meltdown resistance, wettability with electrolyte, A porous membrane having electrochemical stability can be provided, which can be used as a battery separator.

Claims (12)

A porous film (A) to be treated is placed in a plasma coating treatment apparatus, and at least one kind of raw material selected from the raw material group (1) to (9) shown in the following group 1 is gasified in the apparatus. The porous film obtained by forming a film containing the constituent elements of the raw material and the additive gas on at least one side surface of the porous film (A) by performing the coating treatment in the presence of the additive gas and coexisting with the additive gas ( A ′).
Group 1
(1) A silane compound represented by SiR ¹ R ² R ³ R ⁴ (wherein R ¹ to R ⁴ are each hydrogen, halogen, an alkyl group having 1 to 10 carbon atoms, or an alkoxy group, The chain may be straight or branched, and each may have the same or different carbon number, and the carbon chain may be saturated or unsaturated, eg, Si and the substituents R ¹ and R ² And may form a ring.)
(2) a disiloxane compound represented by O— (SiR ¹ R ² R ³ ) ₂ (wherein R ¹ to R ³ are each hydrogen, halogen, or an alkyl group having 1 to 10 carbon atoms; The chain may be straight or branched, and each may have the same or different carbon number, and the carbon chain may be saturated or unsaturated, eg, Si and the substituents R ¹ and R ² And may form a ring.)
(3) a cyclic siloxane compound represented by — (OSiR ¹ R ² ) _n — (wherein R ¹ and R ² are each hydrogen, halogen, or an alkyl group having 1 to 10 carbon atoms, and the carbon chain is The chain may be linear or branched, and each may have the same or different carbon number, and the carbon chain may be saturated or unsaturated, for example, a ring with Si and substituents R ¹ and R ² In which n is an integer of 2 to 20)
(4) Silazane compound represented by N- (SiR ¹ R ² R ³ ) _m R ⁴ _3-m (where R ^{1 to} R ⁴ are each hydrogen, halogen, or an alkyl group having 1 to 10 carbon atoms) The carbon chain may be linear or branched, and each may have the same or different carbon number, and the carbon chain may be saturated or unsaturated, for example, Si and a substituent R ^A ring may be formed by ¹ and R ^{2. In the} formula, m is an integer of 1 to ^3. )
(5) a cyclic silazane compound represented by — (NR ¹ SiR ² R ² ) ₁ — (wherein R ¹ to R ³ are each hydrogen, halogen, or an alkyl group having 1 to 10 carbon atoms; The chain may be straight or branched, and each may have the same or different carbon number, and the carbon chain may be saturated or unsaturated, eg, Si and the substituents R ¹ and R ² And in the formula, l is an integer of 2 to 20.)
(6) A titanate compound represented by TiR ¹ R ² R ³ R ⁴ (wherein R ^{1 to} R ⁴ are each hydrogen, halogen, an alkyl group having 1 to 10 carbon atoms, or an alkoxy group, May be linear or branched, and may have the same or different carbon number, and the carbon chain may be saturated or unsaturated, for example, with Ti and substituents R ¹ and R ² A ring may be formed.)
(7) Aromatic hydrocarbon compounds
(8) Ar- (X) An aromatic compound having at least one polar group represented by _k (wherein Ar represents an aromatic hydrocarbon or heteroaromatic compound, -X represents -COOH, -SO ₃ H, —OR, —CO—R, —CONHR, —SO ₂ NHR, —NHCOOR, —NHCONHR, —NH ₂ , k is an integer of 1 to 3 and R is 1 to 10 carbon atoms The carbon chain of the alkyl group may be linear or branched, and may have the same or different carbon number, and the carbon chain may be saturated or unsaturated.
(9) Lactam compounds A porous film (A) to be processed is placed in a plasma coating processing apparatus, and at least one kind of raw material selected from the raw material group shown in group 1 below is present in the apparatus in a gaseous state, and an additional gas The porous film (A ′) obtained by forming a film containing the constituent element of the additive gas on the surface of the fiber, pulp or fibril forming the porous film (A) by performing the coating treatment in the presence of.
Group 1
(1) A silane compound represented by SiR ¹ R ² R ³ R ⁴ (wherein R ¹ to R ⁴ are each hydrogen, halogen, an alkyl group having 1 to 10 carbon atoms, or an alkoxy group, The chain may be straight or branched, and each may have the same or different carbon number, and the carbon chain may be saturated or unsaturated, eg, Si and the substituents R ¹ and R ² And may form a ring.)
(2) a disiloxane compound represented by O— (SiR ¹ R ² R ³ ) ₂ (wherein R ¹ to R ³ are each hydrogen, halogen, or an alkyl group having 1 to 10 carbon atoms; The chain may be straight or branched, and each may have the same or different carbon number, and the carbon chain may be saturated or unsaturated, eg, Si and the substituents R ¹ and R ² And may form a ring.)
(3) a cyclic siloxane compound represented by — (OSiR ¹ R ² ) _n — (wherein R ¹ and R ² are each hydrogen, halogen, or an alkyl group having 1 to 10 carbon atoms, and the carbon chain is The chain may be linear or branched, and each may have the same or different carbon number, and the carbon chain may be saturated or unsaturated, for example, a ring with Si and substituents R ¹ and R ² In which n is an integer of 2 to 20)
(4) Silazane compound represented by N- (SiR ¹ R ² R ³ ) _m R ⁴ _3-m (where R ^{1 to} R ⁴ are each hydrogen, halogen, or an alkyl group having 1 to 10 carbon atoms) The carbon chain may be linear or branched, and each may have the same or different carbon number, and the carbon chain may be saturated or unsaturated, for example, Si and a substituent R ^A ring may be formed by ¹ and R ^{2. In the} formula, m is an integer of 1 to ^3. )
(5) a cyclic silazane compound represented by — (NR ¹ SiR ² R ² ) ₁ — (wherein R ¹ to R ³ are each hydrogen, halogen, or an alkyl group having 1 to 10 carbon atoms; The chain may be straight or branched, and each may have the same or different carbon number, and the carbon chain may be saturated or unsaturated, eg, Si and the substituents R ¹ and R ² And in the formula, l is an integer of 2 to 20.)
(6) A titanate compound represented by TiR ¹ R ² R ³ R ⁴ (wherein R ^{1 to} R ⁴ are each hydrogen, halogen, an alkyl group having 1 to 10 carbon atoms, or an alkoxy group, May be linear or branched, and may have the same or different carbon number, and the carbon chain may be saturated or unsaturated, for example, with Ti and substituents R ¹ and R ² A ring may be formed.)
(7) Aromatic hydrocarbon compounds
(8) Ar- (X) An aromatic compound having at least one polar group represented by _k (wherein Ar represents an aromatic hydrocarbon or heteroaromatic compound, -X represents -COOH, -SO ₃ H, —OR, —CO—R, —CONHR, —SO ₂ NHR, —NHCOOR, —NHCONHR, —NH ₂ , k is an integer of 1 to 3 and R is 1 to 10 carbon atoms The carbon chain of the alkyl group may be linear or branched, and may have the same or different carbon number, and the carbon chain may be saturated or unsaturated.
(9) Lactam compounds   The porous membrane (A ') according to claim 1 or 2, which is coated by a roll-to-roll process. The porous film (A ') according to any one of claims 1 to 3, wherein the additive gas is at least one selected from the gases shown in group 2 below.
Group 2
Hydrogen, nitrogen, oxygen, carbon dioxide, nitrous oxide, nitrogen dioxide, hydrocarbons with 3 or less carbon atoms   The porous film (A ') according to any one of claims 1 to 4, wherein the raw material present in a gaseous state at the time of coating treatment is a solid at normal temperature and pressure.   The porous membrane (A ') according to any one of claims 1 to 4, wherein the raw material present in a gaseous state during the coating treatment is a liquid at normal temperature and pressure.   The raw material is at least one selected from the raw material groups shown in groups 1- (2), (4), (6) and (8), and the additive gas is nitrogen, hydrocarbons having 3 or less carbon atoms or carbon dioxide The porous membrane (A ') according to any one of claims 1 to 6.   The air permeability resistance X (sec / 100 cc Air / 20 μm) of the porous film (A) before the coating treatment and the air resistance X ′ (sec / 100 cc Air / 20 μm) of the porous film (A ′) on which the film is formed. ) Satisfying X ′ / X ≦ 2.0, the porous film (A ′) according to claim 1. The relationship between the weight W (g / m ² ) of the porous membrane (A) and the weight W ′ (g / m ² ) of the porous membrane (A ′) on which the coating is formed is W′−W ≦ 2 ( the porous membrane according to claim 1 satisfying ^{g / m 2) (a '} ).   The porous membrane (A ') according to any one of claims 1 to 9, wherein the porous membrane (A) is produced by a wet method.   A battery separator comprising the porous membrane (A ') according to any one of claims 1 to 10.   A battery comprising at least one positive electrode, a negative electrode, an electrolyte, and the battery separator according to claim 11.