JP2011210574A - Polyolefin microporous film, separator for nonaqueous secondary battery, and the nonaqueous secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyolefin microporous film in which superior ionic conductivity and mechanical strength are obtained, and drying of the electrolytic liquid can be prevented, even when it is compounded with a heat-resistant porous layer.SOLUTION: The polyolefin microporous film has a fibril diameter of 40-100 nm, with the diameter of fine pores being 50-100 nm, and the tortuosity ratio as calculated from the membrane resistance being set in the range of 1.4-1.8.

Description

  The present invention relates to a polyolefin microporous membrane, and particularly relates to a technique for improving the safety and battery characteristics of a non-aqueous secondary battery.

  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. Polyolefin microporous membrane satisfies the above-mentioned required characteristics, and as a safety function at high temperatures, it may have a thermal runaway prevention function by shutting off current from hole blockage due to high temperature, so-called shutdown function 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.

  Therefore, Patent Document 1 proposes a separator for a nonaqueous secondary battery in which the surface of a polyethylene microporous membrane is covered with a heat resistant porous layer made of a heat resistant polymer such as wholly aromatic polyamide. Patent Document 2 discloses a configuration in which inorganic fine particles such as alumina are included in a heat-resistant porous layer to improve heat resistance in addition to a shutdown function. Patent Document 3 shows a structure 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. ing. 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, because the separator for non-aqueous secondary batteries has a structure in which a polyolefin microporous membrane is coated with a heat-resistant porous layer, the polyolefin microporous membrane has excellent ion conductivity in order to maintain good ion conductivity. Conductivity was sought. However, when the polyolefin microporous membrane is thinned in order to improve ionic conductivity, the mechanical strength of the polyolefin microporous membrane is lowered, and as a result, there is a problem that the mechanical strength of the separator for non-aqueous secondary batteries is lowered.

  By the way, in terms of increasing the capacity of lithium ion batteries, in recent years, various high capacity type positive electrode materials and negative electrode materials have been developed. However, such high-capacity positive and negative electrode materials often have large volume changes during charging and discharging, and thus a problem arises in that battery characteristics deteriorate due to large volume changes in electrodes. .

  That is, since the separator is disposed between the positive electrode and the negative electrode in the battery, when the battery is charged / discharged, a compressive force or a restoring force acts in the thickness direction of the separator due to the expansion / contraction of the electrode. . In the case of conventional low-capacity positive and negative electrode materials such as lithium cobaltate and hard carbon, since the volume change of the electrode is small, the deformation in the thickness direction of the separator is small, and the battery characteristics are not particularly affected. However, when an electrode material having a large volume change rate during charge / discharge, such as a high-capacity positive / negative active material, is used, the acting force applied from the electrode to the separator also increases. And, when the separator cannot follow the volume change of the electrode and the porous structure of the separator cannot be recovered from the compressed state, a sufficient amount of electrolyte is not retained in the pores of the separator, so-called There is a possibility that the problem of withering may occur. As a result, this liquid withdrawing phenomenon may deteriorate the repeated charge / discharge characteristics (cycle characteristics) of the battery.

  In order to solve this problem of liquid dripping, it is conceivable to control the physical properties such as elasticity of the polyolefin microporous membrane. However, as described above, the polyolefin microporous membrane is also required to have good ionic conductivity and mechanical strength. Therefore, if one physical property of the polyolefin microporous membrane is controlled, the other physical property is inevitably affected. Therefore, a technique that can improve these characteristics in a well-balanced manner is desired.

JP 2005-209570 A International Publication No. 2008/062727 Pamphlet International Publication No. 2008/156033 Pamphlet

  An object of the present invention is to provide a polyolefin microporous membrane that can provide excellent ionic conductivity and mechanical strength even when combined with a heat-resistant porous layer, and that can prevent the electrolyte from draining. It is in.

  As a result of intensive studies to solve the above problems, the present inventors have found that the problem can be solved by the following configuration, and have reached the present invention.

  That is, the present invention provides a polyolefin fine particle characterized in that the fibril diameter is 40 to 100 nm, the microporous diameter is 50 to 100 nm, and the curvature calculated from the membrane resistance is 1.4 to 1.8. It is a porous membrane.

  The present invention also provides a separator for a non-aqueous secondary battery in which the polyolefin microporous membrane is coated with a heat resistant porous layer. In addition, the present invention is a non-aqueous secondary battery that obtains an electromotive force by doping or dedoping lithium, wherein the non-aqueous secondary battery separator is used.

  According to the present invention, it is possible to provide a microporous polyolefin membrane that can provide excellent ionic conductivity and mechanical strength even when combined with a heat-resistant porous layer, and that can prevent the electrolyte from draining. Can do. According to the polyolefin microporous membrane of the present invention or the separator for a non-aqueous secondary battery using the same, 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.
[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.

Examples of the raw material for the polyolefin microporous membrane used in the present invention include polyolefins, for example, 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 molecular weight of polyethylene is preferably 500,000 to 5,000,000 in terms of weight average molecular weight, and a polyethylene composition containing 1% by weight or more of ultrahigh molecular weight polyethylene having a weight average molecular weight of 1,000,000 or more is particularly preferred. Furthermore, a polyethylene composition containing 10 to 90% by weight of ultrahigh molecular weight polyethylene having a weight average molecular weight of 1,000,000 or more is suitable. The density of the high density polyethylene is preferably 0.942 g / cm ³ (JIS K 6748-1981) or more. 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 polyolefin microporous membrane of the present invention has a fibril diameter of 40 to 100 nm, a microporous diameter of 50 to 100 nm, and a curvature calculated from membrane resistance of 1.4 to 1.8. When the fibril diameter, microporous membrane, and curvature are in this range, the ionic conductivity and mechanical strength of the separator for a non-aqueous secondary battery using the polyolefin microporous membrane of the present invention are balanced. In addition, since the polyolefin microporous membrane has an appropriate porous structure, the pore shape is sufficiently recovered against repeated deformation caused by the volume change of the charge / discharge electrode, thereby preventing the electrolyte from withering. be able to.

  When the fibril diameter is less than 40 nm, the mechanical strength of one fibril is low, and as a result, the mechanical strength of the polyolefin microporous membrane is lowered, which is not preferable. On the other hand, when the fibril diameter exceeds 100 nm, the microporous pore diameter of the polyolefin microporous membrane increases simultaneously, and the mechanical strength tends to decrease, which is not preferable. In addition, as a fibril diameter, it is more preferable in it being 50-80 nm.

  When the microporous diameter is less than 50 nm, the mobility of the electrolytic solution is lowered, and the battery characteristics tend to be lowered, which is not preferable. Conversely, when the microporous diameter exceeds 100 nm, the mechanical strength of the polyolefin microporous membrane tends to decrease, which is not preferable. In addition, as a microporous diameter, it is more preferable in it being 60-100 nm.

  Here, the fibril diameter in the present invention assumes that the entire structure of the polyolefin microporous membrane is a cylindrical fibril, and the microporous diameter in the present invention assumes that the pore structure is all cylindrical. And calculate as follows.

Let V _{s1 be} the total volume of fibril fiber, and V _{s2 be the} total pore volume. When the diameter of the fibril is R _s1 , the diameter of the cylindrical hole is R _s2 , the total length of the fibril is L _s1 , and the total length of the cylindrical hole is L _s2 , the following formulas (i) to (v) hold.
Ss · Ws = πR _s1 · L _s1 = πR _s2 · L _s2 (i)
V _s1 = π (R _s1 / 2) ² · L _s1 (ii)
V _s2 = π (R _s2 / 2) ² · L _s2 (iii)
V _s2 = ε · (V _s1 + V _s2 ) (iv)
V _s1 = Ws / ds … (V)
Here, Ss is a specific surface area (m ² / g), Ws is a basis weight (g / m ² ), ε is a porosity (%), and ds is a true density (g / cm ³ ).

From the equations (i) to (v), R _s1 (fibril diameter) and R _s2 (microporous diameter) can be obtained.

The specific surface area can be determined, for example from the N ₂ adsorption amount obtained by the gas adsorption method described below using the BET formula. (Method according to JIS Z 8830)
1 / [W · {(P ₀ / P) −1}] = {(C−1) / (Wm · C)} (P / P ₀ ) (1 / (Wm · C)... BET equation P is the gas pressure of the adsorbate in the adsorption equilibrium, P ₀ is the saturated vapor pressure of the adsorbate in the adsorption equilibrium, W is the adsorption amount at the adsorption equilibrium pressure P, Wm is the monomolecular adsorption amount, and C is the BET constant. Specific surface area measurement method by gas adsorption method (hereinafter sometimes referred to as “BET method”)
A plot (BET plot) is linear when the x-axis is relative pressure P ₀ / P and the y-axis is 1 / [W · {(P ₀ / P) −1}]. When the slope in this plot is A and the intercept is B, the monomolecular adsorption amount Wm is as follows.

Wm = 1 / (A + B)
Next, the specific surface area S _s is obtained by the following formula.

Ss = (Wm · N · Acs · M) / w
Here, N is the Avogadro number, M is the molecular weight, Acs is the adsorption cross section, and w is the sample weight. For example, in the case of N ₂ , the adsorption cross-sectional area is 0.16 nm ² .

  In the present invention, the curvature indicates the ratio of the length of the flow path penetrating from one side of the microporous surface to the opposite side and the film thickness. There are several methods for calculating the curvature, and specific examples include a method of calculating from the membrane resistance and a method of calculating from the specific surface area. When considering battery characteristics, a method of calculating from the membrane resistance is desirable. When the curvature is less than 1.4, the microporous material penetrates almost linearly from one surface of the microporous membrane to the opposite surface, which increases the possibility of a short circuit, which is not preferable. Conversely, when the curvature exceeds 1.8, the mobility of the electrolytic solution is lowered, and the battery characteristics tend to be lowered, which is not preferable.

  Further, the ratio of the curvature calculated from the Kozeny-Carman equation to the curvature calculated from the membrane resistance is preferably 1.3 to 1.6. The curvature calculated from the Kozeny-Carman equation is obtained using a fibril diameter, a specific surface area, etc., and indicates an average path from one surface of the microporous membrane to the opposite surface. On the other hand, the curvature calculated from the membrane resistance indicates the shortest path from one surface of the microporous membrane to the opposite surface. This is because there are portions where the micropores penetrating the microporous membrane are bonded to each other, and the membrane resistance, that is, ionic conductivity is measured by the shortest path. When the ratio of curvature is less than 1.3, it means that the average path and the shortest path are close in length, and it tends to be difficult to obtain excellent ion conduction. On the other hand, when the ratio of the curvature ratios exceeds 1.6, it means that there are very many short paths in the route, and there is a possibility that the mechanical strength is lowered, which is not preferable.

  The method for controlling the fibril diameter, the microporous diameter and the curvature is not particularly limited. Specifically, for example, the stretching conditions of the polyolefin microporous film are controlled, the molecular weight of the polyolefin used for the raw material and the branched structure are controlled. Control, control of the porosity of the microporous membrane, and control of the film take-up ratio in the drying step of the gel composition described below. Basically, the higher the molecular weight, the longer the branched structure, the stronger the stretching conditions, and the higher the porosity, the larger the fibril diameter and the microporous diameter.

  As a configuration close to the present invention, a polyolefin microporous membrane having an average fibril diameter of 40 to 80 nm, an average pore diameter of 15 to 50 nm, and a curvature of 1.2 to 1.8 has been disclosed. (See JP 2010-53245). However, this prior art does not consider at all about the compounding with the heat-resistant porous layer as in the present invention and the prevention of the electrolyte withering. The prior art is also different in that the average pore diameter of the pores is 15 to 50 nm, which is smaller than the microporous diameter of 50 to 100 nm of the present invention.

  The film thickness of the polyolefin microporous membrane of the present invention is preferably 5 to 25 μm from the viewpoint of energy density, load characteristics, mechanical strength and handling properties of the non-aqueous secondary battery.

  The porosity of the polyolefin microporous membrane of the present invention is preferably 30 to 60% from the viewpoints of permeability, mechanical strength and handling properties. More preferably, it is 40% to 60%.

  The Gurley value (JIS P8117) of the microporous polyolefin membrane of the present invention is preferably 50 to 500 sec / 100 cc from the viewpoint of obtaining a good balance between mechanical strength and membrane resistance.

The membrane resistance of the polyolefin microporous membrane of the present invention is preferably 0.5 to ⁵ ohm · cm ² from the viewpoint of load characteristics of the non-aqueous secondary battery.

  The puncture strength of the polyolefin microporous membrane of the present invention is preferably 300 g or more. If it is less than 300 g, when a non-aqueous secondary battery is produced, pinholes and the like are generated in the separator due to unevenness or impact of the electrode, and there is a high possibility that the non-aqueous secondary battery is short-circuited. is there.

  The tensile strength of the polyolefin microporous membrane of the present invention is preferably 10 N or more. If it is less than 10 N, there is a possibility that the separator will be damaged when winding the separator when a non-aqueous secondary battery is produced, which may not be preferable.

The shutdown temperature of the polyolefin microporous membrane of the present invention is preferably 130 to 150 ° C. The shutdown temperature is the temperature at which the resistance value is 10 ³ ohm · cm ² . When the shutdown temperature is lower than 130 ° C., the phenomenon called meltdown, in which the polyolefin microporous membrane completely melts and the short circuit phenomenon occurs, is generated at a low temperature. There may not be. On the other hand, if the shutdown temperature is higher than 150 ° C., a sufficient safety function at a high temperature cannot be expected, which is not preferable. Preferably it is 135-145 degreeC.

  The heat shrinkage rate at 105 ° C. of the polyolefin microporous membrane of the present invention is preferably 5 to 40% 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.

[Production method of microporous polyolefin membrane]
Although there is no restriction | limiting in particular in the manufacturing method of the polyolefin microporous membrane of this invention, Specifically, manufacturing through the following (1)-(6) processes is preferable. The polyolefin used as a raw material is as described above.
(1) Preparation of polyolefin solution A solution in which polyolefin is dissolved in a solvent is prepared. At this time, a solution may be prepared by mixing solvents. Examples of the solvent include paraffin, liquid paraffin, paraffin oil, mineral oil, castor oil, tetralin, ethylene glycol, glycerin, decalin, toluene, xylene, diethyltriamine, ethyldiamine, dimethyl sulfoxide, hexane, and the like. 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 may decrease and the productivity may not be increased. Further, the orientation in the extrusion process proceeds, and stretchability and uniformity cannot be ensured. There is a case.
(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) Desolvation treatment Next, the solvent is removed from the gel composition. When a volatile solvent is used, the solvent can also be removed from the gel composition by evaporating by heating or the like, which also serves as a preheating step. In particular, in the case of using a combination of a volatile solvent and a non-volatile solvent as a solvent, from the viewpoint of controlling the fibril diameter, the microporous diameter, and the curvature, when the gel composition is heated, the film draw ratio Is preferably 1 to 5 times. On the other hand, in the case of a non-volatile solvent, the solvent can be removed by squeezing under pressure. The solvent need not be completely removed.
(4) Stretching of the gel-like composition After the solvent removal treatment, the gel-like 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 is preferable to carry out by at least 2 times or more in a uniaxial direction, Preferably it is 4-20 times. In particular, from the viewpoint of controlling crystal parameters, the draw ratio is preferably 4 to 10 times in the machine direction and 6 to 15 times in the machine vertical direction.
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. Examples of the extraction solvent 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, and the like. Easily volatile compounds such as ethers and 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. In this invention, it is preferable that annealing temperature is 115-135 degreeC from a viewpoint that it has a predetermined | prescribed heat shrinkage rate.

[Separator for non-aqueous secondary battery]
A separator for a non-aqueous secondary battery according to the present invention includes the above-described 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. It is a separator for non-aqueous secondary batteries.

  According to such a separator for a non-aqueous secondary battery of the present invention, the polyolefin microporous membrane provides a shutdown function, and the heat-resistant porous layer holds the polyolefin even at a temperature higher than the shutdown temperature. It is hard to cause down and secures safety at high temperatures. 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 from the viewpoint of the energy density of the non-aqueous secondary battery.

  The porosity of the non-aqueous secondary battery separator of the present invention is preferably 30 to 70% from the viewpoints of permeability, mechanical strength, and handling properties. More preferably, it is 40% to 60%.

  The Gurley value (JIS P8117) of the non-aqueous secondary battery separator of the present invention is preferably 100 to 500 sec / 100 cc from the viewpoint of improving the balance between mechanical strength and membrane resistance.

The membrane resistance of the non-aqueous secondary battery separator of the present invention is preferably 1.5 to 10 ohm · cm ² from the viewpoint of load characteristics of the non-aqueous secondary battery.

  The puncture strength of the separator for a non-aqueous secondary battery of the present invention is preferably 250 to 1000 g. When the puncture strength is less than 250 g, when a non-aqueous secondary battery is produced, pinholes or the like may be generated in the separator due to electrode unevenness or impact, etc., which may cause a short circuit of the non-aqueous secondary battery. is there.

  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, there is a possibility that the separator is damaged when winding the separator when producing a non-aqueous secondary battery, which may not be preferable.

  The shutdown temperature of the separator for a non-aqueous secondary battery of the present invention is preferably 130 to 155 ° C. When the shutdown temperature is lower than 130 ° C., meltdown occurs at a low temperature, which may be unfavorable for safety. On the other hand, 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. More preferably, it is 0.5 to 5%.

[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.

  The heat-resistant resin used in the present invention is suitably 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. Preferable examples of such heat-resistant resins include at least one resin selected from the group consisting of wholly aromatic polyamides, polyimides, polyamideimides, polysulfones, polyketones, polyether ketones, polyether imides, and celluloses. 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 microporous membrane. However, from the viewpoint of handling properties, durability, and the effect of suppressing heat shrinkage, it is preferable to form the heat-resistant porous layer on both surfaces of the substrate. preferable. In order to fix the heat-resistant porous layer on the substrate, a method in which the heat-resistant porous layer is directly formed on the substrate by a coating method is preferable. A technique of adhering the quality layer sheet on the base material using an adhesive or the like, 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 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. Such a range of the film thickness is also preferable from the viewpoint of the effect of preventing liquid withstand.

  In the present invention, the porosity of the heat-resistant porous layer is preferably in the range of 30 to 90% from the viewpoint of the effect of preventing liquid withstand. More preferably, it is 30 to 70%.

[Inorganic filler]
In the present invention, the heat resistant porous layer preferably contains an inorganic filler. The inorganic filler is not particularly limited, but specifically, metal oxides such as alumina, titania, silica, zirconia, metal carbonates such as calcium carbonate, metal phosphates such as calcium phosphate, aluminum hydroxide, hydroxide A metal hydroxide such as magnesium is 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. 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 from the viewpoints of flame retardancy improving effect, handling property, charge eliminating effect, and battery durability improving effect. Of these, aluminum hydroxide or magnesium hydroxide is preferred.

  In the present invention, the average particle diameter of the inorganic filler is preferably in the range of 0.1 to 2 μm from the viewpoint of short circuit resistance at high temperature, moldability, and the like.

  In this invention, it is preferable that content of the inorganic filler in a heat resistant porous layer is 50 to 95 weight% from a heat resistant improvement effect, a permeability, and a viewpoint of handling property.

  In addition, the inorganic filler in the heat resistant porous layer is present in a state of being trapped 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 such a case, it may be present in the constituent fibers or fixed to the nonwoven fabric surface or the like with a binder such as a resin.

[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 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 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. The substrate coated with the coating slurry is treated with a coagulating liquid capable of coagulating the heat resistant resin, so that the heat resistant resin is solidified to form a heat resistant porous layer. 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. In particular, from the viewpoint of utilizing the effect of preventing the liquid withering by the separator of the present invention, it is preferable to use a negative electrode active material having a volume change rate of 3% or more in the process of dedoping lithium. Examples of the negative electrode active material include Sn, SnSb, Ag ₃ Sn, artificial graphite, graphite, Si, SiO, V ₅ O _{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 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 Examples include O ₂ , LiMn ₂ O ₄ , LiFePO ₄ , LiCo _0.5 Ni _0.5 O ₂ , LiAl _0.25 Ni _0.75 O _{2, and the} like. In particular, from the viewpoint of utilizing the effect of preventing liquid withering by the separator of the present invention, it is preferable to use a positive electrode active material having a volume change rate of 1% or more in the process of dedoping lithium. Examples of such a positive electrode active material include LiMn ₂ O ₄ , LiCoO ₂ , LiNiO ₂ , LiCo _0.5 Ni _0.5 O ₂ , LiAl _0.25 Ni _0.75 O _{2 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 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 polyolefin microporous membrane and the non-aqueous secondary battery separator was determined from the following formula.
ε = {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 fibril diameter and microporous diameter of the polyolefin microporous membrane were determined by the following method.
The BET specific surface area of the polyolefin microporous membrane was measured according to JIS K 8830. Specifically, NOVA-1200 (manufactured by Yuasa Ionics Co., Ltd.) was used for analysis and determination by a nitrogen gas adsorption method. The sample weight during measurement was 0.1 to 0.15 g. The analysis was carried out by a three-point method, and the specific surface area Ss (m ² / g) was determined from the BET plot.
The pore diameter is Vs ₁ , the total pore volume is Vs ₂ , the fibril diameter is Rs ₁ , the pore diameter is Rs ₂ , the fibril total length Ls ₁ , and the cylindrical hole total length is Ls _2. The following formulas (i) to (v) hold.
Ss · Ws = πRs ₁ · Ls ₁ = πRs ₂ · Ls ₂ (i)
^{_{Vs 1 = π (Rs 1/}} 2) 2 · Ls 1 ··· (ii)
^{_{Vs 2 = π (Rs 2/}} 2) 2 · Ls 2 ··· (iii)
Vs ₂ = ε · (Vs ₁ + Vs ₂ ) (iv)
Vs ₁ = Ws / ds (v)
Here, Ss: specific surface area (m ² / g), Ws: basis weight (g / m ² ), ε: porosity (%), ds: specific gravity (g / cm ³ ).
Rs ₁ and Rs ₂ can be obtained from the equations (i) to (v).

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

(6) The membrane resistance of the polyolefin microporous membrane and the non-aqueous secondary battery separator was determined by the following method.
First, a sample is cut out 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.

(7) The curvature τ _ion calculated from the membrane resistance of the polyolefin microporous membrane was obtained from the following formula.
τ _ion = {(Rm · ε) / (ρ · t)} ^(1/2)
Here, in the above formula, Rm: membrane resistance (ohm · cm ² ), ε: porosity (%), ρ: specific resistance of the electrolyte (ohm · cm), and t: film thickness (μm). As the electrolyte, 1M LiBF ₄ propylene carbonate / ethylene carbonate (1/1 weight ratio) (manufactured by Kishida Chemical Co., Ltd.) is used at 20 ° C. In this case, ρ is 2.663 × 10 ⁻² ohm · cm. It is.

(8) The curvature τ _KC calculated from the Kozeny-Carman equation of the polyolefin microporous membrane was determined from the following equation.
k = [4 ⁵ × ε / (300 × π ² × Rs ₁ ² × Ss ² )] × τ _KC
Here, in the above formula, k: Kozeny-Carman coefficient (using 5), ε: porosity (%), Rs ₁ : fibril diameter, Ss: specific surface area (m ² / g).

(9) The puncture 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 puncture 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 silicon rubber packing was also sandwiched and fixed together with a metal frame (sample holder) having a hole with a diameter of 11.3 mm.

(10) 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.

(11) The shutdown temperature of the polyolefin microporous membrane and the nonaqueous secondary battery separator was determined by the following method.
The sample was punched to a diameter of 19 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 having 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.

(12) The heat resistance of the separator for non-aqueous secondary batteries is such that when the shutdown temperature of (11) is measured, the resistance value is 10 ³ ohms until the cell temperature reaches 200 ° C. after the shutdown occurs. -Evaluated by whether or not to continue to maintain cm ² or more. When the resistance value was kept at 10 ³ ohm · cm ² or more, the heat resistance was judged as good (◯), and when the resistance value was below 10 ³ ohm · cm ² , the heat resistance was judged as poor (×).

(13) 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 1 hour.

(14) The liquid withstand prevention effect of the polyolefin microporous membrane and the non-aqueous secondary battery separator was evaluated by measuring the following pressure recovery rate.
First, the sample was cut into a size of 2.6 cm × 2.0 cm. The cut sample was immersed in a methanol solution in which 3% by weight of a nonionic surfactant (manufactured by Kao Corporation; Emulgen 210P) was dissolved and air-dried. A 20 μm thick aluminum foil was cut into 2.0 cm × 1.4 cm, and a lead tab was attached. Two aluminum foils were prepared, and a separator cut between the aluminum foils was sandwiched between the aluminum foils so that the aluminum foils were not short-circuited. As the electrolytic solution, a solution in which 1M LiBF ₄ was dissolved in a solvent in which propylene carbonate and ethylene carbonate were mixed at a weight ratio of 1: 1 was used, and the above sample was impregnated with the electrolytic solution. This was sealed in an aluminum laminate pack under reduced pressure so that the tabs came out of the aluminum pack. The resistance of this cell was measured by an alternating current impedance method at an amplitude of 10 mV and a frequency of 100 kHz, and a resistance value (A) (ohm · cm ² ) before pressurization was obtained. Next, this cell was pressurized with a flat plate press to 40 MPa for 5 minutes, and then the pressure was released. This operation was repeated 5 times, and the resistance value (B) (ohm · cm ² ) of the cell whose pressure was released after pressurization was measured. And the pressure recovery rate was calculated | required by the following Formula. In addition, it can be said that the higher the pressure recovery rate is, the better the effect of preventing liquid withering.
Pressure recovery rate = resistance value (B) / resistance value (A) × 100 (%)

[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. by Matsumura Oil Research Co., Ltd.) and decalin (Wako Pure) so that GUR2126 and GURX143 become 3: 7 (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. At this time, the take-up ratio during drying of the base tape was set to 1 time. Thereafter, 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 135 ° 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.
Properties of the resulting microporous polyolefin membrane (film thickness, basis weight, porosity, Gurley value, membrane resistance, fibril diameter, pore diameter, curvature calculated from membrane resistance (τ _ion ), calculated from Kozeny-Carman equation) Table 1 shows the measurement results of curvature ratio (τ _KC ), ratio of curvature ratio (τ _KC / τ _ion ), puncture strength, tensile strength, shutdown (SD) temperature, thermal contraction rate, pressure recovery rate). . The following Example 2 and Comparative Examples 1 and 2 are similarly shown in Table 1.

[Example 2]
A polyolefin microporous membrane was obtained in the same manner as in Example 1 except that the take-up ratio during drying of the gel-like base tape was 5 times.

[Comparative Example 1]
Polyolefin microporous membrane as in Example 1 except that the composition of the polyethylene solution was polyethylene: liquid paraffin: decalin = 20: 80: 0 (weight ratio) and the take-up ratio during drying of the gel-like base tape was 8 times. Got.

[Comparative Example 2]
Polyolefin microporous membrane as in Example 1, except that the composition of the polyethylene solution was polyethylene: liquid paraffin: decalin = 20: 20: 60 (weight ratio) and the take-up ratio during drying of the gel-like base tape was 8 times. Got.

[Example 3]
The polyolefin microporous membrane obtained in 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. 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 as an inorganic filler (Kyowa Chemical Industry Co., Ltd., Kisuma-5P, average particle size: 1.0 μm) was dispersed to prepare a slurry for coating. 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. 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.
Characteristics of the obtained non-aqueous secondary battery separator (film thickness, basis weight, porosity, Gurley value, membrane resistance, puncture strength, tensile strength, shutdown temperature, heat resistance, heat shrinkage rate, pressure recovery rate) The measurement results are shown in Table 2. The following Examples 4 to 9 and Comparative Examples 3 and 4 are similarly shown in Table 2.

[Example 4]
A separator for a non-aqueous secondary battery was obtained in the same manner as in Example 3 except that the polyolefin microporous film prepared in Example 2 was used.

[Example 5]
In Example 3, a separator for a non-aqueous secondary battery was obtained in the same manner as in Example 3 except that the clearance between the Meyer bars was set to 7 μm.

[Example 6]
In Example 3, the mixing ratio of DMAc and TPG was set to 40:60 (weight ratio), the clearance between the Meyer bars was set to 60 μm, and the composition of the coagulation liquid was adjusted to water: DMAc: TPG = 50: 30: 20 A separator for a non-aqueous secondary battery was obtained in the same manner as in Example 3 except that.

[Example 7]
In Example 3, the mixing ratio of DMAc and TPG was set to 40:60 (weight ratio), the clearance between Meyer bars was set to 75 μm, and the composition of the coagulation liquid was adjusted to water: DMAc: TPG = 50: 30: 20 A separator for a non-aqueous secondary battery was obtained in the same manner as in Example 3 except that.

[Example 8]
In Example 3, the mixing ratio of DMAc and TPG was set to 35:65 (weight ratio), the clearance between the Meyer bars was set to 60 μm, and the composition of the coagulation liquid was adjusted to water: DMAc: TPG = 50: 32: 18 A separator for a non-aqueous secondary battery was obtained in the same manner as in Example 3 except that.

[Example 9]
In Example 3, the mixing ratio of DMAc and TPG was set to 70:30 (weight ratio), and the composition of the coagulating liquid was adjusted to water: DMAc: TPG = 50: 15: 35. A separator for a non-aqueous secondary battery was obtained.

[Comparative Example 3]
A separator for a non-aqueous secondary battery was obtained in the same manner as in Example 3 except that the polyolefin microporous film prepared in Comparative Example 1 was used.

[Comparative Example 4]
A separator for a non-aqueous secondary battery was obtained in the same manner as in Example 3 except that the polyolefin microporous film prepared in Comparative Example 2 was used.

[Cycle characteristics]
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 polyolefin microporous film or non-aqueous secondary battery separator produced in Examples 1 to 9 and Comparative Examples 1 to 4 was sandwiched between the positive electrode and the negative electrode, respectively. This was impregnated with an electrolytic solution and sealed in an exterior made of an aluminum laminate film, and non-aqueous secondary batteries of Examples 10 to 18 and Comparative Examples 5 to 8 were produced. 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 had 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).
For each non-aqueous secondary battery thus obtained, 4.0 V constant current / constant voltage charging and 2.75 V constant current discharging were repeated 100 cycles, and then the discharge capacity was measured. The discharge capacity after 100 cycles was divided by the discharge capacity after 3 cycles, and the obtained discharge capacity retention rate (%) was used as an index of cycle characteristics. The measurement results are summarized in Table 3.

  The polyolefin microporous membrane of the present invention controls the fibril diameter, microporous diameter, and curvature so that excellent ionic conductivity and mechanical strength can be obtained even when this is combined with a heat-resistant porous layer. In addition, it is possible to prevent the electrolytic solution from draining. This ensures the safety and battery characteristics of the non-aqueous secondary battery using the non-aqueous secondary battery separator.

Claims (7)

The fibril diameter is 40-100 nm,
The microporous diameter is 50 to 100 nm,
A polyolefin microporous membrane having a curvature calculated from membrane resistance of 1.4 to 1.8.   The polyolefin microporous membrane according to claim 1, wherein the ratio of the curvature calculated from the Kozeny-Carman equation to the curvature calculated from the membrane resistance is 1.3 to 1.6.   The polyolefin microporous membrane according to claim 1, and a heat-resistant porous layer formed by containing a heat-resistant resin and laminated on one side or both sides of the polyolefin microporous membrane. Separator for non-aqueous secondary battery.   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. A separator for a non-aqueous secondary battery according to 1.   The separator for a non-aqueous secondary battery according to claim 3 or 4, wherein the heat-resistant porous layer contains an inorganic filler.   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 that obtains an electromotive force by doping or dedoping lithium, wherein the polyolefin microporous membrane according to any one of claims 1 to 6 or the separator for a non-aqueous secondary battery is used as a separator. A non-aqueous secondary battery characterized by