JP2011129304A - Separator for nonaqueous secondary battery, and nonaqueous secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a separator for a nonaqueous secondary battery having shutdown characteristics, heat resistance, and strength. <P>SOLUTION: In the separator for the nonaqueous secondary battery having a polyolefin micro-porous film and a heat-resistant porous layer formed by including a heat-resistant resin and laminated on one surface or both surfaces of the polyolefin micro-porous film, polyolefin included in the polyolefin micro-porous film includes high density polyethylene with weight-average molecular weight of 50,000-1,000,000, and the high density polyethylene is manufactured by using a chromium oxide catalyst. <P>COPYRIGHT: (C)2011,JPO&INPIT

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.

  Non-aqueous secondary batteries such as lithium-ion secondary batteries, which use lithium-containing transition metal oxides typified by lithium cobaltate as the positive electrode and carbon materials that can be doped or dedoped with lithium as the negative electrode, have high energy density. It is important as a power source for portable electronic devices typified by mobile phones because of its characteristics, and demand for these portable electronic devices is increasing with the rapid spread of these portable electronic devices.

  In addition, many automobiles that are environmentally conscious, such as hybrid cars, have been developed, but lithium ion secondary batteries having a high energy density have attracted a great deal of attention as one of the power sources to be mounted.

  Many lithium ion secondary batteries are composed of a laminate of a positive electrode, a separator containing an electrolytic solution, and a negative electrode. The separator is responsible for preventing a short circuit between the positive electrode and the negative electrode as a main function, but as required characteristics, there are mobility, strength, durability, and the like of lithium ions.

  At present, various polyolefin microporous membranes have been proposed as films suitable for lithium ion secondary battery separator applications. Among polyolefin microporous membranes, polyethylene microporous membranes meet the above-mentioned required characteristics, and have a function of preventing thermal runaway by shutting off current from hole blockage due to high temperatures, a so-called shutdown function, as a safety function at high temperatures. It is widely used as a separator for lithium ion secondary batteries.

  However, even if the pores of the microporous membrane are blocked due to the temperature rise and the current is interrupted once, if the battery temperature exceeds the melting point of polyethylene constituting the microporous membrane and exceeds the heat resistance limit of polyethylene, the microporous membrane The membrane itself melts and the shutdown function is lost. As a result, a short circuit between the electrodes causes a thermal runaway of the battery, which may cause destruction of a device incorporating the lithium ion secondary battery or occurrence of an accident due to ignition. For this reason, in order to ensure further safety, there is a demand for a separator that can maintain a shutdown function even at high temperatures.

  Thus, conventionally, a separator for a non-aqueous secondary battery in which the surface of a polyethylene microporous film is coated with a heat-resistant porous layer made of a heat-resistant polymer such as wholly aromatic polyamide has been proposed (for example, Patent Documents 1 and 2). reference). In Patent Document 1, a separator in which a heat-resistant porous layer made of wholly aromatic polyamide is coated on the surface of a polyethylene microporous membrane, or inorganic fine particles such as alumina in the heat-resistant porous layer is included to provide a shutdown function. In addition, a configuration for improving heat resistance is shown. Patent Document 2 discloses a configuration in which metal hydroxide particles such as aluminum hydroxide are included in the heat-resistant porous layer to improve the flame retardancy in addition to the shutdown function and heat resistance. . Any of these configurations can be expected to have an excellent effect in terms of battery safety in terms of both a shutdown function and heat resistance.

  However, in the configurations described in Patent Documents 1 and 2 above, the separator for non-aqueous secondary batteries has a structure in which the polyolefin microporous membrane is coated with a heat-resistant porous layer, and thus the shutdown function of the polyolefin microporous membrane is suppressed. There is a tendency. Therefore, in order to have a shutdown function comparable to that of a polyolefin microporous membrane, it is necessary to increase the porosity of the heat resistant porous layer. As a result, since the mechanical strength of the heat-resistant porous layer itself tends to decrease, the mechanical strength of the non-aqueous secondary battery separator is mainly borne by the polyolefin microporous membrane. For this reason, in order to increase the mechanical strength of the entire separator, it has been desired to further increase the mechanical strength of the polyolefin microporous membrane.

International Publication No. 2008/062727 Pamphlet International Publication No. 2008/156033 Pamphlet

  An object of the present invention is to provide a separator for a non-aqueous secondary battery that simultaneously satisfies heat resistance and strength while maintaining shutdown characteristics.

  As a result of intensive studies to combine shutdown characteristics, heat resistance and strength, the present inventors have found that high density polyethylene used for polyolefin microporous membranes can be produced by a specific catalyst. The headline, the present invention has been reached.

  That is, the present invention provides 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 laminated on one or both sides of the polyolefin microporous membrane. The polyolefin microporous membrane contains a high density polyethylene having a weight average molecular weight of 50,000 to 1,000,000, and the high density polyethylene is produced by a chromium oxide catalyst. This is a secondary battery separator.

Moreover, a separator for a non-aqueous secondary battery comprising a polyolefin microporous membrane and a heat resistant porous layer formed by including a heat resistant resin and laminated on one or both sides of the polyolefin microporous membrane, The polyolefin contained in the polyolefin microporous membrane includes ultra high molecular weight polyethylene having a weight average molecular weight of 1.5 million or more and high density polyethylene having a weight average molecular weight of 50,000 to 1,000,000, and the high density polyethylene was produced by a chromium oxide catalyst. This is a separator for a non-aqueous secondary battery.
Moreover, it is a non-aqueous secondary battery which obtains an electromotive force by doping and dedoping of lithium, wherein the non-aqueous secondary battery separator is used.

  In the present invention, a separator for a non-aqueous secondary battery having both shutdown characteristics, heat resistance, and mechanical strength can be provided. According to the separator for a non-aqueous secondary battery of the present invention, the safety 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 of the present invention includes a polyolefin microporous membrane, and a heat-resistant porous layer formed by including a heat-resistant resin and laminated on one or both surfaces of the polyolefin microporous membrane. A separator for an aqueous secondary battery, wherein the polyolefin contained in the polyolefin microporous membrane includes high-density polyethylene having a weight average molecular weight of 50,000 to 1,000,000, and the high-density polyethylene is produced by a chromium oxide catalyst. Features. Alternatively, the non-aqueous secondary battery separator of the present invention includes a polyolefin microporous membrane and a heat resistant porous layer formed by including a heat resistant resin and laminated on one or both sides of the polyolefin microporous membrane. A separator for a non-aqueous secondary battery, wherein the polyolefin contained in the polyolefin microporous membrane includes ultrahigh molecular weight polyethylene having a weight average molecular weight of 1.5 million or more and high density polyethylene having a weight average molecular weight of 50,000 to 1,000,000, The high-density polyethylene is produced with a chromium oxide catalyst.

  According to such a separator for a non-aqueous secondary battery of the present invention, an excellent shutdown function and mechanical strength can be obtained by the polyolefin microporous membrane as a base material, and at a temperature higher than the shutdown temperature by the heat-resistant porous layer. However, since the polyolefin microporous membrane is retained, safety at high temperatures can be secured. Therefore, according to the separator of the present invention, a non-aqueous secondary battery excellent in safety can be obtained.

  The separator for a non-aqueous secondary battery of the present invention preferably has a total film thickness of 30 μm or less. When a separator exceeds 30 micrometers, there exists a tendency for the energy density of a non-aqueous secondary battery to fall, and it is unpreferable.

  The porosity of the nonaqueous secondary battery separator of the present invention is preferably 30 to 70%. More preferably, it is 40% to 60%. When the porosity is less than 30%, the permeability may decrease and the mobility of lithium ions may decrease, which is not preferable. On the other hand, when the porosity exceeds 70%, the mechanical strength is insufficient and the handling property may be deteriorated.

  The Gurley value (JIS P8117) of the separator for a non-aqueous secondary battery of the present invention is preferably 100 to 500 sec / 100 cc. When the Gurley value is in this range, the separator mechanical strength and the membrane resistance are balanced. If it is less than 100 sec / 100 cc, the mechanical strength of the separator tends to decrease, which is not preferable. When it exceeds 500 sec / 100 cc, the membrane resistance of the separator for non-aqueous secondary batteries tends to decrease, which is not preferable.

The membrane resistance of the non-aqueous secondary battery separator of the present invention is preferably 1.5 to 10 ohm · cm ² . Since the membrane resistance of the non-aqueous secondary battery separator affects the load characteristics of the non-aqueous secondary battery, a smaller one is preferable.

  The puncture strength of the nonaqueous secondary battery separator of the present invention is preferably 300 to 1000 g. When the puncture strength is less than 300 g, when a lithium ion battery is produced, pinholes or the like may be generated in the separator due to unevenness or impact of the electrodes, and the lithium ion battery may be short-circuited. Being over 300 g means having sufficient strength as a battery separator for a non-aqueous secondary battery, and indicates that handling and durability at the time of manufacturing and processing are high.

  The tensile strength of the nonaqueous secondary battery separator of the present invention is preferably 10 N or more. If it is less than 10N, the separator is likely to be damaged when the separator is wound when the lithium ion battery is produced. 10N or more means that it has sufficient strength as a battery separator for non-aqueous secondary batteries, and indicates that it is easy to handle and process.

The shutdown temperature of the separator for a non-aqueous secondary battery of the present invention is preferably 130 to 155 ° C. In the present invention, the shutdown temperature is the temperature at which the resistance value becomes 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. In addition, it is preferable that the difference of the shutdown temperature of the separator for non-aqueous secondary batteries of this invention and the shutdown temperature of the polyolefin microporous film used for this is 0-5 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. Preferably it is 0.5 to 5%.

[Polyolefin microporous membrane]
In the polyolefin microporous membrane of the present invention, the microporous membrane has a structure in which a large number of micropores are connected to each other, and these micropores are connected to each other. Refers to a membrane that can pass through.

  As a raw material of the polyolefin microporous membrane in the present invention, a polyolefin containing high-density polyethylene having a weight average molecular weight of 50,000 to 1,000,000, or an ultrahigh molecular weight polyethylene having a weight average molecular weight of 1,500,000 or more and a weight average molecular weight of 50,000 to 100 are used. It must be a polyolefin containing a million high density polyethylene. Here, the polyolefin microporous membrane used in the present invention may be composed of 90% by weight or more of polyolefin, and may contain other components of 10% by weight or less that do not affect battery characteristics. . If the weight average molecular weight of the high-density polyethylene is less than 50,000, the meltdown temperature is lowered and the nonaqueous secondary battery may run out of heat at a high temperature. Moreover, when the weight average molecular weight of high density polyethylene exceeds 1 million, shutdown temperature becomes high and there exists a possibility that the safety | security of a non-aqueous secondary battery cannot fully be ensured. Further, in the case of a configuration containing ultra high molecular weight polyethylene, if the weight average molecular weight of the ultra high molecular weight polyethylene is less than 1,500,000, there is a problem that sufficient mechanical strength such as tensile strength of the polyolefin microporous membrane cannot be obtained. .

  The film thickness of the polyolefin microporous membrane used in the present invention is preferably 5 to 25 μm. When the thickness is less than 5 μm, the mechanical strength is insufficient and the handling property may be lowered. When it exceeds 25 μm, the energy density of the non-aqueous secondary battery decreases, and it may be difficult to achieve sufficient load characteristics, which is not preferable.

  The porosity of the polyolefin microporous membrane of the present invention is preferably 30 to 60%. More preferably, it is 40% to 60%. When the porosity is less than 30%, the permeability may decrease and the mobility of lithium ions may decrease, which is not preferable. On the other hand, when the porosity exceeds 60%, the mechanical strength is insufficient and the handling property may be deteriorated.

  The Gurley value (JIS P8117) of the polyolefin microporous membrane of the present invention is preferably 50 to 500 sec / 100 cc. When the Gurley value is in this range, the separator mechanical strength and the membrane resistance are balanced. If it is less than 50 sec / 100 cc, the mechanical strength of the separator tends to decrease, which is not preferable. When it exceeds 500 sec / 100 cc, the membrane resistance of the polyolefin microporous membrane tends to decrease, which is not preferable.

The membrane resistance of the microporous polyolefin membrane of the present invention is preferably 0.5 to ⁵ ohm · cm ² . Since the membrane resistance of the polyolefin microporous membrane affects the load characteristics of the non-aqueous secondary battery separator and non-aqueous secondary battery obtained by processing the polyolefin microporous membrane, a smaller one is preferable.

  The puncture strength of the polyolefin microporous membrane of the present invention is preferably 300 g or more. When it is less than 300 g, when a non-aqueous secondary battery is produced, pinholes or the like are generated in the separator due to the unevenness of the electrode or impact, and the possibility that the non-aqueous secondary battery is short-circuited increases. 300 g or more means having sufficient strength as a battery separator, and indicates that handling and durability at the time of manufacturing and processing are high.

  The tensile strength of the polyolefin microporous membrane of the present invention is preferably 10 N or more. When less than 10N, when winding a separator when producing a non-aqueous secondary battery, possibility that a separator will be damaged becomes high. 10N or more means having sufficient strength as a battery separator, and indicates high handling properties when manufacturing or processing.

  The heat shrinkage ratio at 105 ° C. of the polyolefin microporous membrane of the present invention is preferably 5 to 25% or less. When the thermal shrinkage is in this range, the shape stability and shutdown characteristics of the separator for a non-aqueous secondary battery obtained by processing the polyolefin microporous membrane are balanced. When the heat shrinkage rate is less than 5%, it means that the polyolefin has poor fluidity, and the shutdown characteristics are lowered, which is not preferable. When the thermal shrinkage rate exceeds 25%, the shape stability at high temperature is deteriorated, which is not preferable.

[Polyolefin polymerization catalyst]
In the present invention, a chromium oxide catalyst is used as a polymerization catalyst for high-density polyethylene or ultrahigh molecular weight polyethylene.
Here, when the polyolefin microporous membrane and the heat-resistant porous layer are combined, the mechanical strength of the combined non-aqueous secondary battery separator tends to be mainly borne by the polyolefin microporous membrane. Therefore, in order to increase the mechanical strength of the entire separator, it is preferable to improve the mechanical strength of the polyolefin microporous membrane.

  However, the Ziegler-Natta catalyst, which is generally used mainly for the polymerization of polyolefin, is characterized in that a polyolefin having a high molecular weight, a wide molecular weight distribution, and a wide crystal size distribution can be obtained. For this reason, when it is used as a microporous film, although it is excellent in moldability, it tends to be difficult to obtain high mechanical strength.

  On the other hand, the chromium oxide catalyst is characterized in that a polyolefin having a relatively low molecular weight, a wide molecular weight distribution, and a uniform crystal size can be obtained. For this reason, when it is used as a microporous membrane, a microporous membrane excellent in mechanical strength can be obtained. In addition, since the molecular weight distribution is relatively low, the shutdown characteristics can be exhibited at a relatively low temperature even in combination with the heat-resistant porous layer.

  In the present invention, the chromium oxide catalyst used for the polymerization is not particularly limited. Specifically, for example, a chromium compound (for example, chromium oxide, halide, oxyhalide, phosphate, Sulfates, oxalates, alcoholates, organic compounds, etc.) can be easily prepared by, for example, supporting them by various methods such as impregnation, distillation, sublimation and the like, followed by calcination. Preferred chromium compounds include chromium (IV) oxide, chromium (III) acetate, chromium (III) nitrate, chromium (III) acetoneate, chromium (III) sulfate, chromium (III) chloride, chromyl chloride, potassium chromate, Ammonium chromate, potassium dichromate, tris (2-ethylhexanoate) chromium, chromium acetylacetonate, bis (1,1-dimethylethyl) chromate, butylchromate, etc., among others, chromium (IV) oxide, Particularly preferred are chromium (III) nitrate, chromium (III) acetate, and chromium acetylacetonate.

[Polyolefin microporous membrane production method]
Hereinafter, a preferred method for producing a polyolefin microporous membrane used in the present invention will be described.
Although there is no restriction | limiting in particular in the manufacturing method of the polyolefin microporous film of this invention, Specifically, it can manufacture through the process of following (1)-(6).

(1) Preparation of polyolefin solution Polyolefin was dissolved in a solvent such as paraffin, liquid paraffin, paraffin oil, mineral oil, castor oil, tetralin, ethylene glycol, glycerin, decalin, toluene, xylene, diethylenetriamine, 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 40% by weight, more preferably 10 to 35% 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 40% by weight, the pressure at the time of extrusion becomes high, so the discharge amount becomes low and the productivity may not be improved. 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 | 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 of the polyolefin, the gel-like molded product is dissolved and may not be stretched. 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. The annealing is preferably performed at 80 to 150 ° C.

[Heat-resistant porous layer]
In the present invention, examples of the heat-resistant porous layer include microporous film-like, non-woven fabric, paper-like, and other layers having a three-dimensional network-like porous structure. From the viewpoint of being obtained, the layer is preferably a microporous film. Here, the microporous film-like layer has a large number of micropores inside, and has a structure in which these micropores are connected. Gas or liquid can pass from one surface to the other. It says the layer that became.

  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, preferably a wholly aromatic polyamide, polyimide, polyamideimide, polysulfone, It is at least one resin selected from the group consisting of polyketone, polyetherketone, polyetherimide and cellulose. 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 sides or one side of the polyolefin microporous membrane, but it is formed on both sides of the polyolefin microporous membrane from the viewpoint of handling properties, durability and the effect of suppressing heat shrinkage. Is preferred. In order to fix the heat-resistant porous layer on the polyolefin microporous membrane, a method in which the heat-resistant porous layer is directly formed on the polyolefin microporous membrane by a coating method is preferable. A technique of adhering the heat-resistant porous layer sheet to the polyolefin microporous film using an adhesive or the like, or a technique such as heat fusion or pressure bonding can also be employed.

  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 polyolefin microporous membrane, the total thickness of the heat resistant porous layer is 3 μm or more and 12 μm or less. In the case where the heat resistant porous layer is formed only on one side of the polyolefin microporous membrane, 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 preferably contains an inorganic filler. In this case, the inorganic filler in the heat resistant porous layer is present in a state of being captured by the heat resistant resin when the heat resistant porous layer is in the form of a microporous film, and the heat resistant porous layer is a nonwoven fabric or the like. In this case, it may be present in the constituent fibers or fixed to the surface of the nonwoven fabric with a binder such as a resin.

  The inorganic filler in the present invention is not particularly limited, but for example, metal hydroxide, metal oxide, metal nitride, carbonate, sulfate, clay mineral, or a combination of two or more of these. A thing etc. can be used conveniently. Specific examples of the metal hydroxide include aluminum hydroxide, magnesium hydroxide, calcium hydroxide, chromium hydroxide, zirconium hydroxide, nickel hydroxide, boron hydroxide, boehmite and the like. Specific examples of the metal oxide include aluminum oxide, titanium oxide, zinc oxide, silicon oxide, yttrium oxide, cerium oxide, tin oxide, and iron oxide. Specific examples of the metal nitride include aluminum nitride, boron nitride, and titanium nitride. Specific examples of the carbonate include calcium carbonate, magnesium carbonate, barium carbonate and the like. Specific examples of the sulfate include barium sulfate and calcium sulfate. Specific examples of the clay mineral include calcium silicate, talc, mica, montmorillonite, hydrotalcite, bentonite, zeolite, sepiolite, kaolin, hectorite, saponite, stevensite, beidellite and the like.

  As the inorganic filler in the present invention, among the above-mentioned inorganic fillers, those that cause an endothermic reaction at 200 to 400 ° C. are preferable in that they can impart flame retardancy to the battery. Examples of such inorganic fillers include inorganic fillers made of metal hydroxides, boron salt compounds, clay minerals, and the like, which cause an endothermic reaction at 200 to 400 ° C. 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.

  In the present invention, the average particle size of the inorganic filler is preferably in the range of 0.1 to 2 μm. When the average particle diameter of the inorganic filler exceeds 2 μm, the short circuit resistance at high temperature of the heat resistant porous layer is lowered, which is not preferable. Further, there is a problem that it hinders the formation of the heat-resistant porous layer with an appropriate thickness. In addition, when the average particle size of the inorganic filler is less than 0.1 μm, not only does the coating film strength decrease and the problem of powder falling occurs, but using such a small one is substantially from the viewpoint of cost. Have difficulty.

  In this invention, it is preferable that content of the inorganic filler in a heat resistant porous layer is 50 to 95 weight%. If the content of the inorganic filler is less than 50% by weight, the effect of improving heat resistance by the inorganic filler may not be sufficiently obtained, which is not preferable. On the other hand, if the content of the inorganic filler exceeds 95% by weight, the heat-resistant porous layer may be excessively densified and ion permeability may be reduced, or the heat-resistant porous layer may become brittle and handling properties may be reduced. This is not preferable.

[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, and an inorganic filler is dispersed in the solvent as necessary 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. 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 microporous membrane. When forming a heat-resistant porous layer on both surfaces of a polyolefin microporous film, it is preferable from a viewpoint of shortening of a process to apply simultaneously on both surfaces of a base material. 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 simultaneously coating both surfaces of the polyolefin microporous membrane, for example, by passing the polyolefin microporous membrane between a pair of Meyer bars, an excess coating slurry is applied to both surfaces of the polyolefin microporous membrane. There is a method of precise measurement by scraping off excess slurry through a pair of reverse roll coaters.

(3) Solidification of slurry The polyolefin microporous film coated with the slurry is treated with a coagulation 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 polyolefin microporous film coated with the coating slurry, or immersing the substrate in a bath (coagulating bath) containing the coagulating liquid. The method of doing is mentioned. 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 may be a problem that the time required for solidifying the heat-resistant resin becomes long or the solidification becomes insufficient. Also, if the amount of water is more than 80% by weight, there may be a problem that the cost for solvent recovery becomes high, or the surface that comes into contact with the coagulation liquid becomes too fast to solidify and the surface is not sufficiently porous. is there.

(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]
In addition, each value in a present Example was calculated | required 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 basis weight of the polyolefin microporous membrane and the separator for a non-aqueous secondary battery is obtained by cutting a sample into 10 cm × 10 cm and measuring the weight. By dividing this weight by the area, the basis weight which is the weight per 1 m ² was obtained.

(3) The porosity of the microporous polyolefin membrane is
It calculated | required from (epsilon) = {1-Ws / (ds * t)} * 100.
Here, ε: porosity (%), Ws: basis weight (g / m ² ), ds: true density (g / cm ³ ), and t: film thickness (μm).

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

(5) The membrane resistance of the polyolefin microporous membrane and the non-aqueous secondary battery separator was determined by the following method.
Cut the sample to a size of 2.6 cm × 2.0 cm. A sample cut out in a methanol solution (methanol: manufactured by Wako Pure Chemical Industries, Ltd.) in which 3% by weight of a nonionic surfactant (Emalgen 210P manufactured by Kao Corporation) is dissolved is immersed and air-dried. A 20 μm thick aluminum foil is cut into 2.0 cm × 1.4 cm and a lead tab is attached. Two aluminum foils are prepared, and a sample cut between the aluminum foils is sandwiched so that the aluminum foils are not short-circuited. The sample is impregnated with 1M LiBF ₄ propylene carbonate / ethylene carbonate (1/1 weight ratio) as an electrolyte. This is sealed under reduced pressure in an aluminum laminate pack so that the tab comes out of the aluminum pack. Such cells are prepared so that there are one, two, and three separators in the aluminum foil, respectively. The cell is placed in a constant temperature bath at 20 ° C., and the resistance of the cell is measured by an AC impedance method at an amplitude of 10 mV and a frequency of 100 kHz. The measured resistance value of the cell is plotted against the number of separators, and the plot is linearly approximated to obtain the slope. The film resistance (ohm · cm ² ) per separator was determined by multiplying the inclination by 2.0 cm × 1.4 cm which is the electrode area.

(6) The piercing strength of the polyolefin microporous membrane and the separator for the non-aqueous secondary battery was measured using a KES-G5 handy compression tester manufactured by Kato Tech Co., with a radius of curvature of the needle tip of 0.5 mm and a piercing speed of 2 mm / sec. The puncture test was performed under the conditions, and the maximum puncture load was defined as the puncture strength. Here, the sample was fixed by sandwiching a silicon rubber packing in a metal frame (sample holder) having a hole of Φ11.3 mm.

(7) Tensile strength of polyolefin microporous membrane and non-aqueous secondary battery separator was adjusted to 10 × 100 mm using a tensile tester (A & D, RTC-1225A), load cell load 5 kgf, distance between chucks Measurement was performed under the condition of 50 mm.

(8) 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 rate of temperature increase 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.

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

(10) The discharge property evaluation of the non-aqueous secondary battery was performed by the following method.
10 cycles of constant current / constant voltage charging at 1.6 mA, 4.2 V for 8 hours, and constant current discharge at 1.6 mA, 2.75 V were carried out 10 cycles, and the discharge capacity obtained at the 10th cycle was determined for this battery. Discharge capacity. 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.

[Reference Example 1]
A polyethylene powder having a weight average molecular weight of 500,000 (hereinafter referred to as polyethylene A) produced using a chromium oxide catalyst was used as the polyethylene powder. It is dissolved in a mixed solvent of liquid paraffin (Sumoyl P-350: boiling point 480 ° C. by Matsumura Oil Research Co., Ltd.) and decalin (Wako Pure Chemical Industries, boiling point 193 ° C.) so that the polyethylene concentration is 30% by weight. A solution was made. The composition of the polyethylene solution is polyethylene: liquid paraffin: decalin = 30: 45: 25 (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 5.5 times, the stretching temperature was 90 ° C., the transverse stretching was 11.0 times the stretching ratio, and the stretching temperature was 105 ° C. After transverse stretching, heat setting was performed at 125 ° 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 obtained polyethylene 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, basis weight, Gurley value, porosity, membrane resistance, puncture strength, tensile strength, shutdown temperature, thermal shrinkage rate) of the obtained polyolefin microporous membrane.

[Reference Example 2]
A polyethylene powder prepared by using a Ziegler-Natta catalyst with an ultra-high molecular weight polyethylene powder (hereinafter referred to as polyethylene B) having a weight average molecular weight of 41.50 million and polyethylene A mixed at 1: 9 (weight ratio). A polyethylene microporous membrane was obtained in the same manner as in Reference Example 1 except that it was used. Table 1 shows the measurement results of the properties (film thickness, basis weight, Gurley value, porosity, membrane resistance, puncture strength, tensile strength, shutdown temperature, thermal shrinkage rate) of the obtained polyolefin microporous membrane.

[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 Ltd., Conex), which is a meta-type aromatic polyamide, was used as the heat resistant resin. This heat resistant resin was dissolved in a mixed solvent of dimethylacetamide (DMAc) and tripropylene glycol (TPG) in a weight ratio of 50:50. In this polymer solution, magnesium hydroxide (average particle diameter: 1 μm) as an inorganic filler was dispersed 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 polyethylene 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. 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.
Table 2 shows the measurement results of the characteristics (film thickness, basis weight, Gurley value, porosity, membrane resistance, puncture strength, tensile strength, shutdown temperature, heat shrinkage rate) of the obtained nonaqueous secondary battery separator.

[Example 2]
A separator for a nonaqueous secondary battery was obtained in the same manner as in Example 1 except that the polyolefin microporous film obtained in Reference Example 2 was used.
Table 2 shows the measurement results of the characteristics (film thickness, basis weight, Gurley value, porosity, membrane resistance, puncture strength, tensile strength, shutdown temperature, heat shrinkage rate) of the obtained nonaqueous secondary battery separator.

[Example 3]
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 2. 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 3 shows the measurement results of the characteristics (discharge capacity, load characteristics) of the obtained nonaqueous secondary battery.

[Example 4]
A nonaqueous secondary battery was obtained in the same manner as in Example 3 except that the separator obtained in Example 2 was used as the separator for the nonaqueous secondary battery.
Table 3 shows the measurement results of the characteristics (discharge capacity, load characteristics) of the obtained nonaqueous secondary battery.

[Reference Example 3]
A polyolefin microporous membrane was prepared in the same manner as in Reference Example 1 except that high-density polyethylene powder (hereinafter referred to as polyethylene C) having a weight average molecular weight of 550,000 produced using a Ziegler-Natta catalyst was used as the polyethylene powder. Obtained.
Table 1 shows the measurement results of the properties (film thickness, basis weight, Gurley value, porosity, membrane resistance, puncture strength, tensile strength, shutdown temperature, thermal shrinkage rate) of the obtained polyolefin microporous membrane.

[Reference Example 4]
A polyolefin microporous membrane was obtained in the same manner as in Reference Example 1 except that polyethylene powder and polyethylene C mixed at 1: 9 (weight ratio) were used as polyethylene powder.
Table 1 shows the measurement results of the properties (film thickness, basis weight, Gurley value, porosity, membrane resistance, puncture strength, tensile strength, shutdown temperature, thermal shrinkage rate) of the obtained polyolefin microporous membrane.

[Comparative Example 1]
A separator for a non-aqueous secondary battery was obtained in the same manner as in Example 1 except that the polyolefin microporous film obtained in Reference Example 3 was used.
Table 2 shows the measurement results of the characteristics (film thickness, basis weight, Gurley value, porosity, membrane resistance, puncture strength, tensile strength, shutdown temperature, heat shrinkage rate) of the obtained nonaqueous secondary battery separator.

[Comparative Example 2]
A non-aqueous secondary battery separator was obtained in the same manner as in Example 1 except that the polyolefin microporous film obtained in Reference Example 4 was used.
Table 2 shows the measurement results of the characteristics (film thickness, basis weight, Gurley value, porosity, membrane resistance, puncture strength, tensile strength, shutdown temperature, heat shrinkage rate) of the obtained nonaqueous secondary battery separator.

[Comparative Example 3]
A non-aqueous secondary battery was obtained in the same manner as in Example 3 except that the separator obtained in Comparative Example 1 was used as the separator for the non-aqueous secondary battery.
Table 3 shows the measurement results of the characteristics (discharge capacity, load characteristics) of the obtained nonaqueous secondary battery.

[Comparative Example 4]
A non-aqueous secondary battery was obtained in the same manner as in Example 3 except that the separator obtained in Comparative Example 2 was used as the separator for the non-aqueous secondary battery.
Table 3 shows the measurement results of the characteristics (discharge capacity, load characteristics) of the obtained nonaqueous secondary battery.

Claims (7)

A non-aqueous secondary battery separator comprising a polyolefin microporous membrane, and a heat-resistant porous layer formed by including a heat-resistant resin and laminated on one or both sides of the polyolefin microporous membrane,
The polyolefin contained in the polyolefin microporous membrane contains high-density polyethylene having a weight average molecular weight of 50,000 to 1,000,000, and the high-density polyethylene is produced by a chromium oxide catalyst. . A non-aqueous secondary battery separator comprising a polyolefin microporous membrane, and a heat-resistant porous layer formed by including a heat-resistant resin and laminated on one or both sides of the polyolefin microporous membrane,
The polyolefin contained in the polyolefin microporous membrane includes ultra high molecular weight polyethylene having a weight average molecular weight of 1.5 million or more and high density polyethylene having a weight average molecular weight of 50,000 to 1,000,000, and the high density polyethylene was produced by a chromium oxide catalyst. A separator for a non-aqueous secondary battery.   2. The heat-resistant resin is at least one resin selected from the group consisting of wholly aromatic polyamide, polyimide, polyamideimide, polysulfone, polyketone, polyetherketone, polyetherimide, and cellulose. Or the separator for non-aqueous secondary batteries of 2.   The separator for a non-aqueous secondary battery according to any one of claims 1 to 3, wherein the heat-resistant porous layer contains an inorganic filler.   The separator for a non-aqueous secondary battery according to claim 4, wherein the inorganic filler is an inorganic filler that generates an endothermic reaction at 200 to 400 ° C.   The separator for a non-aqueous secondary battery according to claim 5, wherein the inorganic filler is aluminum hydroxide or magnesium hydroxide.   A non-aqueous secondary battery for obtaining an electromotive force by doping and dedoping of lithium, wherein the non-aqueous secondary battery separator according to any one of claims 1 to 6 is used. Secondary battery.