JP2012099349A - Separator for nonaqueous secondary battery, and nonaqueous secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separator for a nonaqueous secondary battery having excellent shutdown characteristics, heat resistance, and resistance to decomposition of an electrolyte.SOLUTION: The separator for a nonaqueous secondary battery comprises a polyolefin microporous membrane, and a heat-resistant porous layer containing a heat-resistant resin and an inorganic filler and formed on one side or both sides of the polyolefin microporous membrane. At least a portion of the surface of the inorganic filler is made of magnesium fluoride.

Description

  The present invention relates to a separator for a non-aqueous secondary battery and a non-aqueous secondary battery, and particularly relates to a technique for improving the safety of a non-aqueous secondary battery or the like.

  Conventionally, a separator for a non-aqueous secondary battery in which the surface of a polyolefin microporous membrane is coated with a heat-resistant porous layer made of a heat-resistant resin is known (for example, see Patent Documents 1 and 2). Patent Document 1 shows a configuration in which inorganic fine particles such as alumina are included in a heat-resistant porous layer made of a heat-resistant resin such as wholly aromatic polyamide to improve heat resistance in addition to a shutdown function. Has been. In Patent Document 2, metal hydroxide particles such as aluminum hydroxide are included in a heat-resistant porous layer made of a heat-resistant resin such as wholly aromatic polyamide, and in addition to a shutdown function and heat resistance, flame retardant The structure which improved the property is shown.

  Each of these structures has a function (so-called shutdown function) for preventing thermal runaway of the battery by melting the polyolefin at a high temperature to close the pores of the polyolefin microporous membrane and interrupting the current. In addition, even when the entire temperature of the polyolefin microporous membrane can be melted due to further temperature rise, the heat resistant porous layer exhibits excellent heat resistance, so that the shape of the entire separator can be maintained, and between the positive and negative electrodes Can be prevented. Thus, in the point which made the shutdown function and heat resistance compatible, the effect excellent in the viewpoint of the safety | security of a battery can be anticipated.

  However, the inorganic filler added for the purpose of improving heat resistance reacts with the moisture in the battery to produce hydrogen fluoride, which causes the electrolyte solution to be decomposed. There has been concern about a decrease in battery durability. In particular, since the heat-resistant resin such as wholly aromatic polyamide is a material that easily contains moisture, it can be said that the above-described problem is likely to appear remarkably.

On the other hand, a technique is known in which hydrogen fluoride in a battery is changed to a substance having a low reaction activity with a metal fluoride to prevent deterioration in battery characteristics caused by hydrogen fluoride (see Patent Document 3). In Patent Document 3, in a lithium secondary battery in which at least one of a positive electrode, a negative electrode, and a non-aqueous electrolyte contains a fluorine compound, at least one of the positive electrode, the negative electrode, the non-aqueous electrolyte, and the separator includes NaF, KF, CsF, A structure containing at least one metal fluoride selected from the group consisting of MgF ₂ , CaF ₂ , SrF ₂ and BaF ₂ is disclosed.

International Publication No. 2008/062727 Pamphlet International Publication No. 2008/156033 Pamphlet JP-A-8-321326

However, Patent Document 3 described above does not mention anything about the configuration using a heat-resistant resin such as wholly aromatic polyamide, and does not disclose a separator having both a polyolefin microporous film and a heat-resistant porous layer. Absent.
Accordingly, an object of the present invention is to provide a separator for a non-aqueous secondary battery that is excellent in an effect of suppressing decomposition of an electrolytic solution in addition to shutdown characteristics and heat resistance.

1. A separator for a non-aqueous secondary battery comprising a polyolefin microporous membrane, and a heat-resistant porous layer formed by containing a heat-resistant resin and an inorganic filler and laminated on one or both sides of the polyolefin microporous membrane. A separator for a non-aqueous secondary battery, wherein at least a part of the surface of the inorganic filler is magnesium fluoride.
2. 2. The separator for a non-aqueous secondary battery according to 1 above, wherein the entire calorific value of the separator at 350 to 400 ° C. is 0 to −200 J / g.
3. A non-aqueous secondary battery that is an non-aqueous secondary battery that obtains an electromotive force by doping or dedoping lithium, and uses the non-aqueous secondary battery separator described in 1 or 2 above.

  In the present invention, it is possible to provide a separator for a non-aqueous secondary battery that is excellent in the effect of suppressing the decomposition of the electrolytic solution in addition to the shutdown characteristics and heat resistance. According to the separator for a non-aqueous secondary battery of the present invention, the safety and battery characteristics of the non-aqueous secondary battery can be improved.

  Hereinafter, embodiments of the present invention will be sequentially described. In addition, these description and Examples illustrate this invention, and do not restrict | limit the scope of the present invention.

[Separator for non-aqueous secondary battery]
A separator for a non-aqueous secondary battery according to the present invention comprises a polyolefin microporous membrane, and a heat resistant porous layer formed by containing a heat resistant resin and an inorganic filler and laminated on one or both sides of the polyolefin microporous membrane. A separator for a non-aqueous secondary battery provided, wherein at least a part of the surface of the inorganic filler is magnesium fluoride.
According to such a separator for a non-aqueous secondary battery of the present invention, a polyolefin microporous membrane as a base material can provide a shutdown function, and the heat-resistant porous layer retains the polyolefin even at a temperature higher than the shutdown temperature. Therefore, meltdown can be prevented.

Here, a general inorganic filler such as alumina reacts with a small amount of hydrogen fluoride (HF) present in the battery to fluorinate the surface, and at that time, water is generated, and in the electrolyte solution Decomposes the carbonate component. The water generated here again decomposes an electrolyte such as LiPF ₆ in the electrolytic solution to generate hydrogen fluoride. The cycle in which hydrogen fluoride is generated repeatedly causes decomposition of the electrolytic solution to proceed in a chain manner. In that respect, according to the present invention, by applying passive magnesium fluoride to at least a part of the surface of the inorganic filler, the inorganic filler does not react with hydrogen fluoride in the battery, and the decomposition of the electrolyte is suppressed. Is done. Therefore, according to the separator of the present invention, it is possible to ensure safety at high temperatures, to prevent battery gas expansion and deterioration of cycle characteristics, and to obtain a nonaqueous secondary battery excellent in battery characteristics.

(Polyolefin microporous membrane)
In the present invention, the polyolefin microporous film has a large number of micropores inside and has a structure in which these micropores are connected, and gas or liquid can pass from one surface to the other. Polyolefin porous membrane.
Examples of the raw material for the polyolefin microporous membrane include polyolefin, that is, polyethylene, polypropylene, polymethylpentene, and copolymers thereof. Among these, polyethylene is preferable, and high-density polyethylene and a mixture of high-density polyethylene and ultrahigh molecular weight polyethylene are more preferable from the viewpoints of strength, heat resistance, and the like. The polyolefin microporous membrane used in the present invention is not limited as long as 90% by weight or more is made of polyolefin, and may contain 10% by weight or less of other components that do not affect the battery characteristics.

The film thickness of the polyolefin microporous membrane is preferably 5 to 25 μm from the viewpoint of mechanical strength, handling properties, and energy density. The porosity of the polyolefin microporous membrane is preferably 30 to 60% from the viewpoints of permeability, mechanical strength, and handling properties. The Gurley value (JIS P8117) of the polyolefin microporous membrane is preferably 50 to 500 sec / 100 cc from the viewpoint of the balance between mechanical strength and membrane resistance. The membrane resistance of the polyolefin microporous membrane is preferably 0.5 to ⁵ ohm · cm ² from the viewpoint of load characteristics of the non-aqueous secondary battery. The piercing strength of the polyolefin microporous membrane is preferably 250 g or more from the viewpoint of the strength of the separator, handling properties, and prevention of short circuit of the battery. The tensile strength of the polyolefin microporous membrane is preferably 10 N or more from the viewpoint of the strength and handling properties of the separator. The thermal shrinkage rate at 105 ° C. of the polyolefin microporous membrane is preferably 5 to 30% or less from the viewpoint of the balance between the shape stability of the separator and the shutdown characteristics.

(Heat resistant porous layer)
In the present invention, the heat-resistant porous layer is formed including a heat-resistant resin, has a number of micropores inside, and has a structure in which these micropores are connected. A layer that allows gas or liquid to pass through it.

  As the heat-resistant resin used in the present invention, a polymer having a melting point of 200 ° C. or higher or a polymer having no melting point but having a decomposition temperature of 200 ° C. or higher is suitable, and preferably a wholly aromatic polyamide, polyimide, polyamideimide, polyether It is at least one resin selected from the group consisting of sulfone, polysulfone, polyketone, polyetherketone and polyetherimide. In particular, wholly aromatic polyamides are preferable from the viewpoint of durability, and polymetaphenylene isophthalamide, which is a meta-type wholly aromatic polyamide, is more preferable from the viewpoint of easy formation of a porous layer and excellent redox resistance. is there.

  In the present invention, the heat-resistant porous layer may be formed on both surfaces or one surface of the polyolefin porous substrate, but from the viewpoints of handling properties, durability, and the effect of suppressing heat shrinkage, it is formed on both surfaces of the substrate. Is preferred.

  In the present invention, regarding the thickness of the heat resistant porous layer, when the heat resistant porous layer is formed on both surfaces of the substrate, the total thickness of the heat resistant porous layer may be 3 μm or more and 12 μm or less. Preferably, when the heat resistant porous layer is formed only on one side of the substrate, the thickness of the heat resistant porous layer is preferably 3 μm or more and 12 μm or less. The porosity of the heat resistant porous layer is preferably in the range of 60 to 90%.

(Inorganic filler)
In the present invention, the heat-resistant porous layer needs to contain an inorganic filler. The inorganic filler in the heat resistant porous layer is present in a state of being captured by the heat resistant resin. The inorganic filler in the present invention is not particularly limited as long as it has magnesium fluoride on a part of the surface, but specifically, metal oxides such as alumina, titania, silica, zirconia, metals such as calcium carbonate, etc. Metal phosphates such as carbonates and calcium phosphates, and metal hydroxides such as aluminum hydroxide and magnesium hydroxide are preferably used. Such an inorganic filler is preferably highly crystalline from the viewpoints of impurity elution and durability.

  Especially, as an inorganic filler, what produces an endothermic reaction in 200-400 degreeC is preferable. Although it does not specifically limit as an inorganic filler which has such a characteristic, It is an inorganic filler which consists of a metal hydroxide, a boron salt compound, or a clay mineral, Comprising: What produces an endothermic reaction in 200-400 degreeC is mentioned. Specific examples include aluminum hydroxide, magnesium hydroxide, calcium aluminate, dosonite, zinc borate and the like, and these can be used alone or in combination of two or more. In addition, these flame retardant inorganic fillers are appropriately mixed with other inorganic fillers such as metal oxides such as alumina, zirconia, silica, magnesia, and titania, metal nitrides, metal carbides, and metal carbonates. You can also.

  Here, in the non-aqueous secondary battery, heat generation accompanying the decomposition of the positive electrode is considered to be the most dangerous, and this decomposition occurs in the vicinity of 300 ° C. For this reason, if the generation | occurrence | production temperature of endothermic reaction is the range of 200 to 400 degreeC, it is effective in preventing the heat_generation | fever of a non-aqueous secondary battery. It should be noted that at 200 ° C. or higher, since the negative electrode almost loses its activity, it does not react with water generated from the metal hydroxide to cause heat generation and is safe. Moreover, when the endothermic reaction temperature of an inorganic filler exceeds 400 degreeC, since there exists a possibility that the heat_generation | fever of a non-aqueous secondary battery cannot be prevented suitably, it is unpreferable. For example, aluminum hydroxide, dawsonite, and calcium aluminate undergo a dehydration reaction in the range of 200 to 300 ° C, and magnesium hydroxide and zinc borate undergo a dehydration reaction in the range of 300 to 400 ° C. It is preferable to use at least one of them.

  In particular, in the present invention, the inorganic filler is preferably made of a metal hydroxide. Since the metal hydroxide undergoes a dehydration reaction accompanied by a large endotherm by heating, an effect of improving flame retardancy due to both the release of water and endotherm can be obtained. The release of water is effective in diluting the flammable electrolyte and making the battery itself incombustible. In addition, since metal hydroxide is a softer material than metal oxides such as alumina, the parts used in each process at the time of manufacturing are worn by the inorganic filler contained in the separator. There is no problem. In addition, when a metal hydroxide such as aluminum hydroxide or magnesium hydroxide is added to the heat-resistant porous layer, the charged charge decays quickly, so that the charge can be kept at a low level and handling properties are improved. Is improved. Furthermore, aluminum hydroxide and magnesium hydroxide have the function of adsorbing and co-precipitating hydrofluoric acid, so it is possible to maintain the hydrofluoric acid concentration in the electrolyte at a low level, and the durability of non-aqueous secondary batteries Can be improved. Therefore, the inorganic filler is preferably a metal hydroxide, and particularly preferably aluminum hydroxide or magnesium hydroxide. Among these, magnesium hydroxide is particularly preferable from the viewpoint of decomposition of the electrolytic solution because it forms magnesium fluoride which becomes passive on the surface by reaction with hydrogen fluoride.

  In the present invention, the method of applying magnesium fluoride to the surface of the inorganic filler is not particularly limited. However, when magnesium hydroxide is used for the base material described above, a method of surface treatment with hydrogen fluoride or the like is used. Can be mentioned. When inorganic particles other than magnesium hydroxide are used as the base material, magnesium fluoride is deposited on the surface of the inorganic filler by physical vapor deposition such as sputtering, and magnesium fluoride fine particles are attached to the surface of the inorganic filler using a binder. And a method in which an aqueous dispersion sol of magnesium fluoride fine particles is attached to the surface of the inorganic filler and dried.

  In the present invention, the average particle size of the inorganic filler is preferably in the range of 0.1 to 2 μm from the viewpoints of coating film strength, prevention of powder falling, and short circuit resistance at high temperatures. The content of the inorganic filler in the heat-resistant porous layer is preferably 50 to 95% by weight from the viewpoints of ion permeability, handling properties, and effects of improving heat resistance.

(Other configuration of separator)
In the separator for a non-aqueous secondary battery of the present invention, the calorific value of the whole separator at 350 ° C. to 400 ° C. is preferably 0 to −200 J / g. 350 ° C. to 400 ° C. is a temperature at which the thermal decomposition reaction of the electrolytic solution occurs, but if the calorific value of the separator at this temperature is 0 to −200 J / g, it indicates that the electrolytic solution decomposition reaction is very small and the temperature is high. It can be said that the effect of suppressing decomposition of the electrolyte below is higher. In addition, when the calorific value of the separator is 0 J / g or less, the effect of suppressing the decomposition reaction of the electrolytic solution becomes better, and when the calorific value of the separator is −200 J / g or more, the filler mixing amount is appropriate. Therefore, it is preferable from the viewpoint that the heat-resistant layer is difficult to peel off.

  As described above, there is no particular limitation on the method of suppressing the heat generation amount of the separator from 350 ° C. to 400 ° C., but the method of reducing the water in the inorganic filler by drying or the like, the method of reducing the water in the separator, the generated fluorination Examples thereof include a method of quenching hydrogen with an antioxidant and the like, a surface treatment of an inorganic filler, a method of forming a passive state on the surface of the inorganic filler, and the like.

The film thickness of the non-aqueous secondary battery separator is preferably 30 μm or less from the viewpoint of energy density. The porosity of the separator is preferably 30 to 70% from the viewpoints of mechanical strength, handling properties, and lithium ion mobility. The Gurley value (JIS P8117) of the separator is preferably 100 to 500 sec / 100 cc from the viewpoint of the balance between the mechanical strength and the membrane resistance of the separator. The membrane resistance of the separator is preferably 1.5 to 10 ohm · cm ² from the viewpoint of battery load characteristics. The puncture strength of the separator is preferably 250 g or more from the viewpoint of short circuit resistance, mechanical strength, and handling properties. The tensile strength of the separator is preferably 10 N or more from the viewpoint of short circuit resistance, mechanical strength, and handling properties.

It is preferable that the shutdown temperature of a separator is 130-155 degreeC. Here, the shutdown temperature is the temperature at which the resistance value is 10 ³ ohm · cm ² . When the shutdown temperature is less than 130 ° C., a phenomenon called meltdown, in which the polyolefin microporous film is completely melted and a short-circuit phenomenon occurs at the same time, is not preferable for safety. Moreover, when the shutdown temperature is higher than 155 ° C., a sufficient safety function at a high temperature cannot be expected, which is not preferable. Preferably it is 135-150 degreeC.

  The thermal contraction rate at 105 ° C. of the separator for a non-aqueous secondary battery of the present invention is preferably 0.5 to 10%. When the heat shrinkage rate is within this range, the shape stability and shutdown characteristics of the non-aqueous secondary battery separator are balanced. When it is 10% or more, the shape stability at high temperature is deteriorated, which is not preferable. More preferably, it is 0.5 to 5%.

[Production method of microporous polyolefin membrane]
In the present invention, the method for producing the polyolefin microporous membrane is not particularly limited, but specifically, it can be produced through the following steps (1) to (6).

(1) Preparation of polyolefin solution Polyolefin is dissolved in a solvent such as paraffin, liquid paraffin, paraffin oil, mineral oil, castor oil, tetralin, ethylene glycol, glycerin, decalin, toluene, xylene, diethyltriamine, ethyldiamine, dimethylsulfoxide, hexane, etc. Adjust the solution. At this time, a solution may be prepared by mixing solvents. The concentration of the polyolefin solution is preferably 1 to 35% by weight, more preferably 10 to 30% by weight. When the concentration of the polyolefin solution is less than 1% by weight, the gel-like molded product obtained by cooling and gelation is highly swollen with a solvent, so that it is easily deformed, which may hinder handling. On the other hand, if it exceeds 35% by weight, the pressure at the time of extrusion increases, so the discharge amount decreases and the productivity may not be increased. Moreover, the orientation in the extrusion process proceeds, and stretchability and uniformity may not be ensured.

(2) Extrusion of polyolefin solution The adjusted solution is kneaded with a single screw extruder or a twin screw extruder, and extruded with a T die or an I die at a temperature not lower than the melting point and not higher than the melting point + 60 ° C. A twin screw extruder is preferably used. Then, the extruded solution is passed through a chill roll or a cooling bath to form a gel composition. At this time, it is preferable to rapidly cool below the gelation temperature to cause gelation.

(3) Drying of gel-like composition When using the solvent which volatilizes at extending | stretching temperature, a gel-like composition is dried.

(4) Stretching of the gel composition The gel composition is stretched. Here, a relaxation treatment may be performed before the stretching treatment. In the stretching treatment, the gel-like molded product is heated and biaxially stretched at a predetermined magnification by a normal tenter method, roll method, rolling method, or a combination of these methods. Biaxial stretching may be simultaneous or sequential. Moreover, it can also be set as longitudinal multistage extending | stretching, 3 or 4 steps extending | stretching.
The stretching temperature is preferably 90 ° C. to less than the melting point of the polyolefin, more preferably 100 to 120 ° C. When the heating temperature exceeds the melting point, it cannot be stretched because the gel-like molded product is dissolved. On the other hand, when the heating temperature is less than 90 ° C., the gel-like molded product is not sufficiently softened, and the film is likely to be broken during stretching, making it difficult to stretch at a high magnification.
Moreover, although a draw ratio changes with thickness of an original fabric, it carries out by at least 2 times or more in a uniaxial direction, Preferably it is 4-20 times.
After stretching, heat setting is performed as necessary to provide thermal dimensional stability.

(5) Extraction and removal of solvent The stretched gel composition is immersed in an extraction solvent to extract the solvent. Extraction solvents include hydrocarbons such as pentane, hexane, heptane, cyclohexane, decalin and tetralin, chlorinated hydrocarbons such as methylene chloride, carbon tetrachloride and methylene chloride, fluorinated hydrocarbons such as ethane trifluoride, diethyl ether, Easily volatile substances such as ethers such as dioxane can be used. These solvents are appropriately selected according to the solvent used for dissolving the polyolefin composition, and can be used alone or in combination. Solvent extraction removes the solvent in the microporous membrane to less than 1% by weight.

(6) Annealing of microporous film The microporous film is heat-set by annealing. Annealing is performed at 80 to 150 ° C.

[Method for producing heat-resistant porous layer]
In the present invention, the method for producing a separator for a non-aqueous secondary battery is not particularly limited as long as the separator of the present invention having the above-described configuration can be produced. For example, it can be produced through the following steps (1) to (5). It is.

(1) Preparation of coating slurry A heat-resistant resin is dissolved in a solvent to prepare a coating slurry. The solvent is not particularly limited as long as it dissolves the heat-resistant resin, but specifically, a polar solvent is preferable, and examples thereof include N-methylpyrrolidone, dimethylacetamide, dimethylformamide, and dimethylsulfoxide. Moreover, the said solvent can add the solvent used as a poor solvent with respect to heat resistant resin in addition to these polar solvents. By applying such a poor solvent, a microphase separation structure is induced and the formation of a heat-resistant porous layer is facilitated. As the poor solvent, alcohols are preferable, and polyhydric alcohols such as glycol are particularly preferable. The concentration of the heat resistant resin in the coating slurry is preferably 4 to 9% by weight. Moreover, an inorganic filler is disperse | distributed to this as needed, and it is set as the slurry for coating. In dispersing the inorganic filler in the coating slurry, when the dispersibility of the inorganic filler is not preferable, a method of improving the dispersibility by surface-treating the inorganic filler with a silane coupling agent or the like is also applicable.

(2) Coating of slurry The slurry is coated on at least one surface of the polyolefin porous substrate. When forming a heat resistant porous layer on both surfaces of a polyolefin porous substrate, it is preferable from a viewpoint of shortening of a process to apply simultaneously on both surfaces of a substrate. Examples of the method for coating the slurry for coating include a knife coater method, a gravure coater method, a screen printing method, a Meyer bar method, a die coater method, a reverse roll coater method, an ink jet method, a spray method, and a roll coater method. . Among these, the reverse roll coater method is preferable from the viewpoint of uniformly forming a coating film. When applying simultaneously to both sides of the base material, for example, by passing the base material between a pair of Meyer bars, an excess coating slurry is applied to both sides of the base material, and this is applied to a pair of reverse roll coaters. There is a method of precise measurement by scraping off excess slurry in between.

(3) Solidification of slurry The base material on which the slurry is applied is treated with a coagulating liquid capable of coagulating the heat-resistant resin. Thereby, the heat resistant resin is solidified to form a heat resistant porous layer made of the heat resistant resin or a heat resistant porous layer in which the inorganic filler is bound to the heat resistant resin. As a method of treating with the coagulating liquid, a method of spraying the coagulating liquid on the substrate coated with the coating slurry, or a method of immersing the substrate in a bath (coagulating bath) containing the coagulating liquid. Etc. Here, when installing a coagulation bath, it is preferable to install it below the coating apparatus. The coagulation liquid is not particularly limited as long as it can coagulate the heat-resistant resin, but water or a solution obtained by mixing an appropriate amount of water with the solvent used in the slurry is preferable. Here, the mixing amount of water is preferably 40 to 80% by weight with respect to the coagulation liquid. When the amount of water is less than 40% by weight, there arises a problem that the time required for solidifying the heat-resistant resin becomes long or the solidification becomes insufficient. On the other hand, when the amount of water is more than 80% by weight, there arises a problem that the cost for solvent recovery becomes high, or the surface that comes into contact with the coagulation liquid is solidified too quickly and the surface is not sufficiently porous.

(4) Removal of coagulating liquid The coagulating liquid is removed by washing with water.

(5) Drying Dry and remove water from the sheet. Although there is no particular limitation on the drying method, the drying temperature is preferably 50 to 80 ° C. When a high drying temperature is applied, a method of contacting with a roll to prevent dimensional change due to heat shrinkage. It is preferable to apply.

[Non-aqueous secondary battery]
The non-aqueous secondary battery of the present invention is a non-aqueous secondary battery that obtains an electromotive force by doping or dedoping lithium, and is characterized by using the separator for a non-aqueous secondary battery having the above-described configuration. The non-aqueous secondary battery has a structure in which a battery element in which a negative electrode and a positive electrode face each other with a separator interposed therebetween is impregnated with an electrolytic solution, and this is enclosed in an exterior.

  The negative electrode has a structure in which a negative electrode mixture composed of a negative electrode active material, a conductive additive and a binder is formed on a current collector. Examples of the negative electrode active material include materials capable of electrochemically doping lithium, and examples thereof include carbon materials, silicon, aluminum, tin, and wood alloys. Examples of the conductive assistant include carbon materials such as acetylene black and ketjen black. The binder is made of an organic polymer, and examples thereof include polyvinylidene fluoride and carboxymethyl cellulose. As the current collector, a copper foil, a stainless steel foil, a nickel foil, or the like can be used.

The positive electrode has a structure in which a positive electrode mixture composed of a positive electrode active material, a conductive additive and a binder is formed on a current collector. Examples of the positive electrode active material include lithium-containing transition metal oxides. Specifically, LiCoO ₂ , LiNiO ₂ , LiMn _0.5 Ni _0.5 O ₂ , LiCo _1/3 Ni _1/3 Mn _{1/3 O 2, LiMn 2 O 4,} LiFePO 4 , and the like. Examples of the conductive assistant include carbon materials such as acetylene black and ketjen black. The binder is made of an organic polymer, and examples thereof include polyvinylidene fluoride. As the current collector, aluminum foil, stainless steel foil, titanium foil, or the like can be used.

The electrolytic solution has a structure in which a lithium salt is dissolved in a non-aqueous solvent. Examples of the lithium salt include LiPF ₆ , LiBF ₄ , LiClO _{4 and the} like. Examples of the non-aqueous solvent include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, γ-butyrolactone, vinylene carbonate, and the like. These may be used alone or in combination.

  Examples of the exterior material include a metal can or an aluminum laminate pack. The shape of the battery includes a square shape, a cylindrical shape, a coin shape, and the like, but the separator of the present invention can be suitably applied to any shape.

Examples are shown below, but the present invention is not limited thereto.
[Measuring method]
Each value in this example was determined according to the following method.
(1) The film thickness of the polyolefin microporous membrane and the separator for a non-aqueous secondary battery was determined by measuring 20 points with a contact-type film thickness meter (manufactured by Mitutoyo Corporation) and averaging them. Here, the contact terminal used was a cylindrical one having a bottom surface of 0.5 cm in diameter.

(2) The Gurley values of the polyolefin microporous membrane and the non-aqueous secondary battery separator were determined according to JIS P8117.

(3) The shutdown temperature of the polyolefin microporous membrane and the non-aqueous secondary battery separator was determined by the following method.
The sample was punched into Φ19 mm, and the sample cut out in a methanol solution (methanol: manufactured by Wako Pure Chemical Industries, Ltd.) in which 3% by weight of a nonionic surfactant (Emulgen 210P manufactured by Kao Corporation) was dissolved was immersed and air-dried. The sample was sandwiched between SUS plates with a diameter of 15.5 mm. The sample was impregnated with 1M LiBF ₄ propylene carbonate / ethylene carbonate (1/1 weight ratio) (manufactured by Kishida Chemical Co., Ltd.) as an electrolyte. This was enclosed in a 2032 type coin cell. I took the lead from the coin cell, put a thermocouple, and put it in the oven. The temperature of the cell was increased at a temperature increase rate of 1.6 ° C./min, and the resistance of the cell was measured at the same time by the AC impedance method at an amplitude of 10 mV and a frequency of 100 kHz. The temperature at which the resistance value reached 10 ³ ohm · cm ² or more was taken as the shutdown temperature.

(4) The thermal contraction rate of the polyolefin microporous membrane and the non-aqueous secondary battery separator was measured by heating the sample at 105 ° C. for 1 hour. Note that the measurement direction is the machine direction.

(5) The calorific value of the non-aqueous secondary battery separator between 350 ° C. and 400 ° C. was measured using DSC (TA-2920, manufactured by TA Instruments).

(6) The discharge property evaluation of the non-aqueous secondary battery was performed by the following method.
About the non-aqueous secondary battery produced by the Example and the comparative example, it is 1.6 mA, 4.2V for 8 hours constant current / constant voltage charge, 1.6 mA, 2.75V constant current discharge is performed 10 cycles. The discharge capacity obtained at the 10th cycle was defined as the discharge capacity of this battery. Next, constant current / constant voltage charging was performed at 1.6 mA and 4.2 V for 8 hours, and constant current discharging was performed at 16 mA and 2.75 V. The capacity obtained at this time was divided by the discharge capacity of the battery at the 10th cycle, and the obtained value was used as an index of load characteristics.

(7) About the decomposition | disassembly suppression effect of the electrolyte solution of a non-aqueous secondary battery separator, it verified with the following method.
After the discharge property evaluation described in (6) above, the nonaqueous secondary battery was charged at 1.6 mA and 4.2 V for 8 hours at a constant current and a constant voltage. After charging, it was put into an atmosphere furnace at 80 ° C. for 72 hours. After 72 hours, when the amount of increase in cell thickness was less than 1 mm, it was judged as good (◯), and when the cell thickness was increased by 1 mm or more, it was judged as defective (x). In addition, that it was favorable in said float characteristic evaluation means that there was little gas generation | occurrence | production, ie, the decomposition | disassembly inhibitory effect of electrolyte solution was excellent.

(8) The decomposition suppression effect and heat resistance of the electrolyte solution of the nonaqueous secondary battery separator were evaluated by the following nail penetration test.
About the non-aqueous secondary battery produced by the Example and the comparative example, it charged to 4.2V at 0.2C for 12 hours, and was set to the full charge state. Then, the charged battery was passed through a 2.5 mmφ iron nail. As a result, it was evaluated as x when ignition was confirmed, Δ when ignition was not confirmed but smoke rose, and ○ when neither ignition nor smoke was confirmed. The above evaluation was performed after 20 batteries of each example and comparative example were produced. Table 1 shows the number of ◯, Δ, and x in the 20 batteries. In addition, the fact that ignition and smoke were not confirmed in the above test means that the decomposition of the electrolytic solution is suppressed and the heat resistance is excellent even in a situation where the battery temperature is very high.

[Reference Example 1]
Ticona's GUR2126 (weight average molecular weight 4150,000, melting point 141 ° C.) and GURX143 (weight average molecular weight 560,000, melting point 135 ° C.) were used as polyethylene powder. Liquid paraffin (Smoyl P-350, boiling point 480 ° C., Matsumura Oil Research Co., Ltd.) and decalin (Wako Pure) so that GUR2126 and GURX143 become 2: 8 (weight ratio) and the polyethylene concentration becomes 30% by weight. A polyethylene solution was prepared by dissolving in a mixed solvent having a boiling point of 193 ° C. manufactured by Yakuhin Co., Ltd. The composition of the polyethylene solution is polyethylene: liquid paraffin: decalin = 30: 67.5: 2.5 (weight ratio).
This polyethylene solution was extruded from a die at 148 ° C. and cooled in a water bath to prepare a gel tape (base tape). The base tape was dried at 60 ° C. for 8 minutes and at 95 ° C. for 15 minutes, and the base tape was stretched by biaxial stretching in which longitudinal stretching and lateral stretching were sequentially performed. Here, the longitudinal stretching was 6 times, the stretching temperature was 90 ° C., the transverse stretching was 9 times the stretching ratio, and the stretching temperature was 105 ° C. After transverse stretching, heat setting was performed at 130 ° C. Next, this was immersed in a methylene chloride bath to extract liquid paraffin and decalin. Then, the polyolefin microporous film was obtained by drying at 50 degreeC and annealing at 120 degreeC. The resulting polyolefin microporous membrane had a structure in which fibrillar polyolefins were entangled in a network and constituted pores.
Table 1 shows the measurement results of the properties (film thickness, Gurley value, shutdown (SD) temperature, thermal shrinkage, calorific value between 350 ° C. and 400 ° C.) of the obtained polyolefin microporous membrane. The measurement results of the following examples and comparative examples are also summarized in Table 1.

[Example 1]
The polyolefin microporous membrane obtained in Reference Example 1 was used, and a heat-resistant porous layer made of a heat-resistant resin and an inorganic filler was laminated thereon to produce the non-aqueous secondary battery separator of the present invention.
Specifically, polymetaphenylene isophthalamide (manufactured by Teijin Techno Products, Conex) was used as the heat resistant resin. As the inorganic filler, a magnesium hydroxide (Kyowa Chemical Industry Co., Ltd., Kisuma-5P, average particle size 1.0 μm) surface treated with hydrogen fluoride and coated with magnesium fluoride was used. The heat resistant resin was dissolved in a mixed solvent of dimethylacetamide (DMAc) and tripropylene glycol (TPG) in a weight ratio of 50:50. An inorganic filler was dispersed in the polymer solution to prepare a coating slurry. The concentration of polymetaphenylene isophthalamide in the coating slurry was adjusted to 5.5% by weight, and the weight ratio of polymetaphenylene isophthalamide to inorganic filler was adjusted to 25:75. Then, two Meyer bars were opposed to each other, and an appropriate amount of coating liquid was put between them. Thereafter, the polyolefin microporous film was passed between Mayer bars on which the coating liquid was placed, and the coating liquid was applied to the front and back surfaces of the polyolefin microporous film. Here, the clearance between the Meyer bars was set to 20 μm, and # 6 was used for both the Mayer bars. This was immersed in a coagulating liquid having a weight ratio of water: DMAc: TPG = 50: 25: 25 and 40 ° C., followed by washing and drying. The drying temperature was set to 60 ° C. and the drying time was set to 120 minutes. This obtained the separator for non-aqueous secondary batteries in which the heat resistant porous layer was formed in the both surfaces of the polyolefin microporous film.

[Example 2]
A separator for a non-aqueous secondary battery was obtained in the same manner as in Example 1, except that the drying temperature of the separator was set to 60 ° C., the drying time was set to 120 minutes, and the atmosphere was set to a reduced pressure of 3 mmHg.

[Example 3]
A separator for a non-aqueous secondary battery was obtained in the same manner as in Example 1, except that the separator was dried at a drying temperature of 60 ° C. and a drying time of 5 minutes, and then conditioned for 2 days at 25 ° C. and a humidity of 80 RH%. .

[Example 4]
Lithium cobalt oxide (LiCoO ₂ : manufactured by Nippon Chemical Industry Co., Ltd.) 89.5 parts by weight, acetylene black (Denka Black manufactured by Denki Kagaku Kogyo Co., Ltd.) 4.5 parts by weight, polyvinylidene fluoride (manufactured by Kureha Chemical Co., Ltd.) 6 parts by weight Thus, these were kneaded using N-methyl-pyrrolidone to prepare a slurry. The obtained slurry was applied onto an aluminum foil having a thickness of 20 μm, dried and pressed to obtain a positive electrode having a thickness of 100 μm.
87 parts by weight of mesophase carbon micro beads (MCMB: manufactured by Osaka Gas Chemical Co., Ltd.), 3 parts by weight of acetylene black (trade name Denka Black, manufactured by Denki Kagaku Kogyo Co., Ltd.) and 10 parts by weight of polyvinylidene fluoride (manufactured by Kureha Chemical Co., Ltd.) These were kneaded using N-methyl-2pyrrolidone to prepare a slurry. The obtained slurry was applied onto a copper foil having a thickness of 18 μm, dried and pressed to obtain a negative electrode having a thickness of 90 μm.
The positive electrode and the negative electrode were opposed to each other through the non-aqueous secondary battery separator produced in Example 1. This was impregnated with an electrolytic solution and sealed in an exterior made of an aluminum laminate film to produce a non-aqueous secondary battery. Here, 1M LiPF ₆ ethylene carbonate / ethyl methyl carbonate (3/7 weight ratio) (manufactured by Kishida Chemical Co., Ltd.) was used as the electrolytic solution.
Here, this prototype battery has a positive electrode area of 2 × 1.4 cm ² , a negative electrode area of 2.2 × 1.6 cm ² , and a set capacity of 8 mAh (in the range of 4.2V-2.75V).
Table 2 shows the measurement results of the characteristics (discharge capacity, load characteristics, heat resistance) of the obtained nonaqueous secondary battery. The measurement results of the following examples and comparative examples are also summarized in Table 2.

[Example 5]
A non-aqueous secondary battery was produced in the same manner as in Example 4 except that the non-aqueous secondary battery separator produced in Example 2 was used.

[Example 6]
A non-aqueous secondary battery was prepared in the same manner as in Example 4 except that the non-aqueous secondary battery separator prepared in Example 3 was used.

[Comparative Example 1]
A nonaqueous secondary battery separator was obtained in the same manner as in Example 1 except that α-alumina (SA-1, manufactured by Iwatani Chemical Industry Co., Ltd., average particle size 0.8 μm) was used as the inorganic filler.

[Comparative Example 2]
A non-aqueous secondary battery was obtained in the same manner as in Example 4 except that the separator obtained in Comparative Example 1 was used as the separator for the non-aqueous secondary battery.

Claims (3)

A separator for a non-aqueous secondary battery comprising a polyolefin microporous membrane, and a heat resistant porous layer formed by containing a heat resistant resin and an inorganic filler and laminated on one or both sides of the polyolefin microporous membrane, ,
A separator for a non-aqueous secondary battery, wherein at least a part of the surface of the inorganic filler is magnesium fluoride.   2. The separator for a non-aqueous secondary battery according to claim 1, wherein a calorific value of the whole separator at 350 ° C. to 400 ° C. is 0 to −200 J / g.   A non-aqueous secondary battery using the separator for a non-aqueous secondary battery according to claim 1 or 2, wherein the non-aqueous secondary battery obtains an electromotive force by doping or dedoping lithium.