JP2012049018A - Separator for nonaqueous electrolyte battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separator for a nonaqueous electrolyte battery which has a cycle stability for charging and discharging, especially excellent capacity stability on repeated charging and discharging over a long period of time, and has high resistance to short-circuit.SOLUTION: A separator for a nonaqueous electrolyte battery comprises a base material layer containing a polyolefin and a heat-resistant porous layer containing a heat-resistant polymer, and satisfies the conditions (i) and (ii). (i) The heat-resistant porous layer contains 0.1 to 1000 ppm of one or two or more kinds of element selected from the group consisting of alkali metals, alkaline earth metals, transition metals, halogens, and silicon. (ii) The base material layer satisfies at least one of the conditions (A) to (E). (A)The base material layer contains 0.1 to 3 ppm of at least one kind of element selected from Fe, Cr, and Ni. (B) The base material layer contains 0.1 to 30 ppm of at least one kind of element selected from Ti and Zr. (C) The base material layer contains 0.1 to 50 ppm of at least one kind of element selected from Al and B. (D) The base material layer contains 1 to 70 ppm of at least one kind of element selected from alkali metals and alkaline earth metals. and (E) The base material layer contains 1 to 200 ppm of a halogen.

Description

  The present invention relates to a non-aqueous electrolyte battery separator that has excellent charge / discharge cycle characteristics over a long period of time and improved short-circuit resistance, and further relates to a non-aqueous electrolyte secondary battery using the above-described separator.

  Nonaqueous electrolyte batteries, particularly nonaqueous electrolyte secondary batteries represented by lithium ion secondary batteries, have high energy density and are widely used as the main power source for portable electronic devices such as mobile phones and laptop computers. . This lithium ion secondary battery is required to have a higher energy density, but ensuring safety is a technical issue. The role of the separator is important in ensuring the safety of the lithium ion secondary battery, and from the viewpoint of the shutdown function, polyolefins, particularly polyethylene microporous membranes are currently used. Here, the shutdown function refers to a function of blocking the current when the micropores of the porous film are closed when the temperature of the battery rises, and is effective in preventing the thermal runaway of the battery.

  On the other hand, lithium ion secondary batteries have been increased in energy density year by year, and higher heat resistance and short circuit resistance have been required in addition to a shutdown function to ensure safety. However, since the shutdown function is based on the principle of clogging of pores due to melting of the polyethylene microporous membrane, the shutdown function is not necessarily parallel to heat resistance and the like. That is, after the shutdown function is activated, the battery temperature further rises, so that the separator may be melted (so-called meltdown). As a result, a short circuit occurs inside the battery, and as a result, a large amount of heat is generated, and the battery is exposed to dangers such as smoke, ignition, and explosion.

  For this reason, in addition to the shutdown function, the separator does not cause a short circuit even at a temperature somewhat higher than the temperature at which the shutdown function is manifested, and further requires heat resistance that does not cause a short circuit even if held at a temperature higher than the shutdown. Has been. In this respect, the combined use of polyolefin having a shutdown function and polyolefin having heat resistance is well known, but the heat resistance of the polyolefin itself is not so high and sufficient heat resistance is not obtained.

  Furthermore, proposals for coating a heat-resistant porous layer on one or both sides of a polyolefin microporous membrane, and proposals for laminating a nonwoven fabric made of heat-resistant fibers have been made (see Patent Documents 1 to 4). These techniques provide sufficient heat resistance and achieve both a shutdown function and heat resistance, but do not consider the influence of impurities of the constituent material of the separator on the cycle characteristics of the battery.

  On the other hand, in a separator that improves heat resistance by installing an aramid porous layer as a heat-resistant porous layer on one or both sides of a polyolefin microporous membrane, a specific element in the aramid porous layer, that is, an alkali metal or an alkaline earth metal The non-aqueous electrolyte has excellent cycle characteristics and improved safety by setting the content of one or more elements selected from the group consisting of transition metals, halogens and silicon to 0.1 ppm or more and 1000 ppm or less A battery separator has been proposed (Patent Document 5). This proposal has some success with regard to short-term capacity characteristics of charge / discharge, but no report has been made regarding the capacity stability and short-circuit resistance of charge / discharge over a longer period of time.

JP 2002-355938 A JP 2005-209570 A JP 2005-285385 A JP 2000-030686 A JP 2009-205959 A

  The present inventors have solved the above-mentioned problems, and are excellent in cycle stability of charge / discharge, in particular, capacity stability when repeated charge / discharge over a long period of time, and are further maintained at a higher temperature resistance, that is, at a higher temperature. In this case, a nonaqueous electrolyte battery separator that is less likely to cause a short circuit and has higher heat resistance is proposed, and as another problem, a nonaqueous electrolyte secondary battery using the above separator is proposed.

  The present inventors include a base material layer formed by containing polyolefin and having pores or voids therein and having a shutdown function, and a heat-resistant porous layer laminated on one or both surfaces of the base material layer. In the non-aqueous electrolyte battery separator, as a result of research on the realization of capacity stability, higher short-circuit resistance and safety when charging and discharging are repeated for a long time, the inclusion of specific elements in the base material layer It has been found that controlling the amount effectively suppresses the alteration of the polyolefin and can solve the above-mentioned problems.

That is, the present invention employs the following configuration.
(1) A heat-resistant base material layer formed by containing polyolefin and having pores or voids therein and having a shutdown function, and heat-resistant polymer formed and laminated on one or both surfaces of the base material layer A nonaqueous electrolyte battery separator comprising a porous layer and satisfying the following conditions (i) and (ii): (I) The heat-resistant porous layer contains 0.1 to 1000 ppm of one or more elements selected from the group consisting of alkali metals, alkaline earth metals, transition metals, halogens, and silicon. (Ii) The base material layer satisfies at least one of the following conditions (A) to (E). (A) 0.1 to 3 ppm of at least one element of Fe, Cr and Ni, (B) 0.1 to 30 ppm of at least one element of Ti and Zr, (C) Al And B contains 0.1 to 50 ppm of at least one element, (D) contains 1 to 70 ppm of at least one element among alkali metal elements and alkaline earth metal elements, and (E) a halogen element. Contains 1 to 200 ppm.
(2) The nonaqueous electrolyte battery separator according to (1), wherein the base material layer satisfies all the following conditions (A) to (E). (A) At least one element of Fe, Cr and Ni is contained in an amount of 0.1 to 2 ppm, (B) Ti element is contained in an amount of 1 to 20 ppm, (C) Al element is contained in an amount of 1 to 20 ppm, (D) Na 1 to 50 ppm of at least one element among Ca, Mg, and 1 to 100 ppm of (E) halogen element.
(3) The polyolefin includes polyethylene polymerized by at least one catalyst selected from the group consisting of a chromium oxide catalyst, a metallocene catalyst, and a Ziegler-Natta catalyst, wherein the polyethylene has a weight average molecular weight of 100,000 to 10,000,000. The nonaqueous electrolyte battery separator according to any one of (1) and (2).
(4) The nonaqueous electrolyte battery separator according to any one of (1) to (3), wherein the heat-resistant porous layer is laminated by coating.
(5) The above (1) to (4), wherein the heat resistant polymer is one or more selected from the group consisting of aromatic polyamide, polyimide, polyethersulfone, polysulfone, polyetherketone and polyetherimide. The non-aqueous electrolyte battery separator according to any one of the above.
(6) The nonaqueous electrolyte battery separator according to (5), wherein the heat-resistant polymer is polymetaphenylene isophthalamide.
(7) A non-aqueous electrolyte secondary battery using the non-aqueous electrolyte battery separator according to any one of (1) to (6) to obtain an electromotive force by doping or dedoping lithium.

  According to the present invention, it is possible to provide a non-aqueous electrolyte battery separator having a shutdown function and excellent in capacity stability when charging and discharging are repeated over a long period of time and having further high short-circuit resistance. Furthermore, a non-aqueous electrolyte secondary battery using the same has excellent battery characteristics and is excellent in safety at high temperatures.

  The non-aqueous electrolyte battery separator of the present invention includes a base material layer that includes a polyolefin and has pores or voids therein and has a shutdown function, and includes a heat-resistant polymer and is provided on one side of the base material layer. A heat-resistant porous layer laminated on both sides, and satisfying the following conditions (i) and (ii). (I) The heat-resistant porous layer contains 0.1 to 1000 ppm of one or more elements selected from the group consisting of alkali metals, alkaline earth metals, transition metals, halogens, and silicon. (Ii) The base material layer satisfies at least one of the following conditions (A) to (E). (A) 0.1 to 3 ppm of at least one element of Fe, Cr and Ni, (B) 0.1 to 30 ppm of at least one element of Ti and Zr, (C) Al And B contains 0.1 to 50 ppm of at least one element, (D) contains 1 to 70 ppm of at least one element among alkali metal elements and alkaline earth metal elements, and (E) a halogen element. Contains 1 to 200 ppm.

  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.

[Base material layer]
In the present invention, examples of the base material layer having pores or voids therein and having a shutdown function include microporous membranes, nonwoven fabrics, paper sheets, and other sheets having a three-dimensional network structure. A microporous membrane is preferred.

Moreover, polyolefin-type resin is mentioned as a raw material which comprises the base material layer in this invention, Especially, polyethylene, a polypropylene, polymethylpentene, and those copolymers are illustrated as suitable resin. Among these, polyethylene is more preferable. When polyethylene is used as a raw material, its production method and catalyst system are not particularly limited, but with respect to the weight average molecular weight, ultrahigh molecular weight polyethylene, a mixture of ultrahigh molecular weight polyethylene and other polyethylene, or low molecular weight polyethylene is suitable. In terms of strength, durability, and resistance to scratching during handling (hereinafter sometimes referred to as operability), for example, 100,000 to 10 million, preferably 10 It is preferable to use polyethylene containing a weight average molecular weight of 10,000 to 5,000,000, more preferably 200,000 to 3,000,000. Moreover, it is preferable that the polyethylene includes high-density polyethylene, particularly high-density polyethylene having a density exceeding 0.94 g / cm ³ . From the shutdown temperature characteristics of the separator, polyethylene having a crystal melting temperature of polyolefin of 130 ° C. or higher, preferably 135 ° C. or higher, more preferably 140 ° C. or higher is preferable. In addition, the base material layer used in the present invention is mainly required to have about 90% by weight or more of polyolefin, and contains about 10% by weight or less of other components that do not affect the battery characteristics. It doesn't matter.

[Impurities in the base material layer]
When the base material layer in the present invention is laminated with a heat-resistant porous layer and repeated charge and discharge over a long period of time, the alteration of the polyolefin is suppressed, the capacity change is small, and the heat resistance, particularly short-circuit resistance is excellent. Functions as a non-aqueous electrolyte battery separator. For this reason, the impurity element group in the base material layer may change the base material layer itself and, at the same time, diffuse into the heat-resistant porous film and promote a decrease in heat resistance. It is classified into five groups (A) to (E).

Ie;
Group (A); group consisting of Fe, Cr, and Ni elements; these elements may deteriorate polyolefin, and may change the capacity change of charge / discharge, and further reduce short-circuit resistance.
Group (B); group consisting of Ti and Zr elements; these elements have a great effect of reducing the heat resistance when they are deteriorated in polyolefin and diffused into the heat resistant porous layer, but the degree of change in shutdown characteristics Is smaller than group (A).
Group (C); group consisting of Al and B elements; these elements have a slightly smaller effect on polyolefin than groups (A) and (B), but when diffused into the heat-resistant porous layer, heat-resistant polymer May greatly reduce the heat resistance.
Group (D); alkali metal and alkaline earth metal elements; these elements have a smaller effect on polyolefin than groups (A) and (B), but when diffused into the heat resistant porous layer, the heat resistant polymer May greatly reduce the heat resistance.
Group (E); Halogen element; Battery function, that is, promoting the dissolution of aluminum used as the positive electrode current collector, blocking the lithium insertion / extraction site of the positive electrode active material, and the possibility that the performance of the secondary battery is significantly impaired In addition, there is a possibility that the heat resistant polymer is decomposed and its heat resistance is greatly reduced.

  In general, the smaller the content of various impurities in the base material layer, the less undesirable effects caused by those components are reduced. However, it is industrially difficult to reduce the content to nearly 0 ppm. In many cases, an excessive cost is required, and as a result, the cost of the separator often becomes an unacceptable value. Therefore, separating the impurity elements into several groups and setting the content within a specific range is an effective method for reducing the cost.

  When such a specific group increases beyond the limit amount corresponding to that group, when charging and discharging are repeated over a long period of time, the polyolefin resin may change, leading to a reduction in battery capacity and deterioration in short-circuit resistance. is there. Furthermore, it may diffuse into the heat-resistant porous layer to reduce the heat resistance of the heat-resistant resin and reduce the desired effect. That is, this invention discovered that the above-mentioned problem can be suppressed by making the element amount of the specific group contained in a base material layer into a specific range.

That is, as a range where the separator manufacturing cost and the control of the problem are compatible;
(I) The heat-resistant porous layer contains 0.1 to 1000 ppm of one or more elements selected from the group consisting of alkali metals, alkaline earth metals, transition metals, halogens, and silicon,
(Ii) The base material layer satisfies at least one of the following conditions (A) to (E). (A) 0.1 to 3 ppm of at least one element of Fe, Cr and Ni, (B) 0.1 to 30 ppm of at least one element of Ti and Zr, (C) Al And B contains 0.1 to 50 ppm of at least one element, (D) contains 1 to 70 ppm of at least one element of alkali metal and alkaline earth metal, and (E) 1 to 1 halogen element. It is preferable to contain 200 ppm. Thereby, the capacity stability of charging / discharging over the long term mentioned above and favorable short circuit resistance can be expressed. When impurities are included exceeding the upper limit values of the conditions (i) and (ii), the above-mentioned problem cannot be controlled, and it is not realistic from the viewpoint of cost to reduce it to less than the lower limit value.

  Regarding the impurities in the heat-resistant porous layer (i), the amount of the heat-resistant resin contained in the heat-resistant porous layer is less than that of the polyolefin, and the impurities are strongly bound in the heat-resistant resin. Therefore, the influence is often small compared to (ii). Therefore, from the above viewpoint, preferably (ii) the base material layer satisfies all the following conditions (A) to (E). (A) At least one element of Fe, Cr and Ni is contained in an amount of 0.1 to 2 ppm, (B) Ti element is contained in an amount of 1 to 20 ppm, (C) Al element is contained in an amount of 1 to 20 ppm, (D) Na 1 to 50 ppm of at least one element among Ca, Mg, and 1 to 100 ppm of (E) halogen element.

[Method for reducing impurity elements in substrate layer]
The method for adjusting the content of the elements constituting the groups (A) to (E) in the substrate layer is not particularly limited, and specifically, for example, the following methods (1) to (4) Etc. are exemplified. In addition, as described in the section of the heat-resistant porous layer described later, in the production process of the heat-resistant porous layer, the groups (A) to (E) are related to both the base material layer and the heat-resistant porous layer. It is also possible to simultaneously remove elemental components constituting the above, and such a method is preferably selected from the viewpoint of simplification of the process and cost reduction.

(1) A method of reducing the content of the element derived from the catalyst system by using a highly active catalyst system during polyolefin polymerization. That is, by using a highly active catalyst, the content of the elements constituting the groups (A) to (E) in the polyolefin becomes low. Specifically, it is preferably polymerized with at least one kind of catalyst selected from the group of chromium oxide catalyst, metallocene catalyst and Ziegler-Natta catalyst. It is particularly preferred to contain a polyolefin polymerized with a Ziegler-Natta catalyst.

(2) A method of repeating solvent washing of the polyolefin resin particles after polymerization.

(3) A method of removing elemental components constituting the groups (A) to (E) by filtration or adsorption treatment of a polyolefin solution during the production of the base material layer. That is, by passing various known filter media such as celite and adsorbents such as molecular sieves, the elemental components constituting the groups (A) to (E) in the base material layer can be suitably reduced. . In addition, by extruding a polyolefin solution before passing through a die during extrusion of the polyolefin solution, it is also possible to remove elemental components constituting the groups (A) to (E) that are insoluble in the solution. The amount of the filter medium or adsorbent used must be appropriately selected depending on the content of the elements constituting the groups (A) to (E) contained in the solution, the ability of the filter medium or adsorbent, and the like.

(4) A method of subjecting the stretched polyolefin microporous membrane to a solvent extraction treatment. When a polyolefin microporous membrane is used as the base material layer, the extraction ability of the element components constituting the groups (A) to (E) is determined during the production from the stretching to the heat setting, and further after the heat setting. Solvent extraction treatment can be performed with a solvent having, for example, a volatile polar solvent, a polar solvent having a boiling point of room temperature to 200 ° C., preferably room temperature to 150 ° C. Specific examples include a method of washing with water or a solvent containing at least one polar solvent having at least one selected from alcoholic hydroxyl groups, ether groups, carbonyl groups, amide groups, sulfoxide groups and sulfonyl groups. The Examples of the solvent include lower alcohols such as water, methyl alcohol, ethyl alcohol, butyl alcohol, hexyl alcohol, and cyclohexanol, lower ethers such as diethyl ether, methyl ethyl ether, dibutyl ether, and acetone, methyl ethyl ketone, dibutyl ketone, Examples include lower ketones such as cyclohexanone, lower amides such as dimethylformamide and dimethylacetamide, lower sulfoxides such as dimethyl sulfoxide and sulfolane, and sulfones. Among these, use of a mixed solvent of water and these organic solvents is preferable. By these methods, it is possible to control the content of the elements constituting the groups (A) to (E) within a suitable range, but it is preferable to implement several methods in combination.

  As a resin user, it is difficult to carry out the method (1). As a specific combination method, the methods (2), (3) and (4), or some combination of these methods are used. The method to implement is preferable from the viewpoint of ease of implementation and effects. In particular, the elemental components constituting the groups (A) to (E) can be effectively reduced by a combination method including (3) and / or (4) as essential means. Particularly preferred is a method in which the methods (3) and (4) are combined.

[Purity of cleaning solvent]
In the present invention, as the cleaning solvent for cleaning the polyolefin resin particles or the microporous polyolefin membrane, it is possible to use a cleaning solvent having a low content of elemental components constituting the groups (A) to (E). preferable. The content of the elemental components constituting the groups (A) to (E) in the cleaning solvent is 0.01 to 50 ppm, preferably 0.02 to 30 ppm, more preferably 0.05 to 20 pm, particularly preferably. Examples are 1 to 10 ppm of solvent. A solvent having a small content of elemental components constituting such a specific group can be easily achieved by using an electronic solvent, but is not preferable from the viewpoint of cost. However, a general industrial solvent is subjected to simple distillation or multistage distillation under normal pressure or reduced pressure conditions, or the use of various filter media or adsorbents, preferably by a combination of these methods, to reduce the impurity content within the above-mentioned range. It is possible to control within. In the present invention, it is possible to use a halogen-based solvent for the elemental component constituting the group (E), but the halogen-based solvent may remain in the polyolefin microporous membrane, and such a solvent is used. Preferably not.

[Other characteristics of base material layer]
The characteristics when a polyolefin microporous membrane is used as the substrate layer in the present invention will be described below. The polyolefin microporous membrane in the present invention preferably has a pinhole count of 5 / m ² or less after a gelboflex test at 1000 cycles at room temperature. Thereby, the short circuit resistance of the separator for nonaqueous electrolyte batteries is excellent.

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

  The porosity of the polyolefin microporous membrane in 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 polyolefin microporous membrane in 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 in the present invention is preferably 0.5 to ⁵ ohm · cm ² from the viewpoint of the load characteristics of the nonaqueous electrolyte battery.

  The piercing strength of the polyolefin microporous membrane in the present invention is preferably 250 g or more. If it is less than 250 g, when a non-aqueous electrolyte battery is produced, pinholes or the like are generated in the separator due to unevenness or impact of the electrodes, and there is a high possibility that the non-aqueous electrolyte battery is short-circuited.

  The tensile strength of the polyolefin microporous membrane in the present invention is preferably 10 N or more. This is because when the value is less than 10 N, the separator is more likely to be damaged when the separator is wound when the non-aqueous electrolyte secondary battery is manufactured.

The shutdown temperature of the polyolefin microporous membrane in the present invention is preferably 130 to 150 ° C. The shutdown temperature refers to 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. Further, when the shutdown temperature is higher than 150 ° C., the safety function at high temperatures of the members constituting the battery including the separator cannot be expected. From this viewpoint, the range of 135 to 145 ° C is preferably selected.

  The heat shrinkage rate at 105 ° C. of the polyolefin microporous membrane in the present invention is preferably 5 to 40%. When the heat shrinkage is in this range, the shape stability and shutdown characteristics of the non-aqueous electrolyte secondary battery separator obtained by processing the polyolefin microporous membrane are balanced.

[Manufacturing method of base material layer]
When a polyolefin microporous membrane is used as the substrate layer in the present invention, the production method is not particularly limited, but specifically, it is preferably produced through the following steps (5) to (10).

(5) 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. In the present invention, the content of the elements constituting the groups (A) to (E) contained in the solvent is reduced by using an electronic solvent, a distillation method, or an adsorption method to molecular sieves or the like. It is preferable to use a solvent. 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.

(6) 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 from the melting point to the melting point + 60 ° C or lower. In the present invention, it is also exemplified as a preferred embodiment that a filtration filter is installed immediately before the T die or the I die and the element components constituting the groups (A) to (E) that are insoluble in the solution are filtered. The In the present invention, a twin screw extruder is preferably used as the extruder. 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.

(7) 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 the case of a non-volatile solvent, the solvent can be removed by squeezing out under pressure. The solvent need not be completely removed. At this time, as described above, the solvent (A) in the polyolefin microporous membrane can be obtained by using, as the volatile solvent, a solvent having the ability to extract elemental components constituting the groups (A) to (E). To (E) can be reduced.

(8) 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. Further, after stretching, heat setting is performed as necessary to provide thermal dimensional stability.

(9) 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.

(10) 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.

[Heat-resistant porous layer]
In the present invention, the heat-resistant porous layer has a large number of micropores inside and has a structure in which these micropores are connected, and gas or liquid can pass from one surface to the other. Means the layer that became.

  In the present invention, the combined use of the heat-resistant porous layer is essential, but the method for producing the heat-resistant porous layer is not particularly limited, and specifically, for example, in accordance with the method described in JP-A-2009-205959. The manufacturing method is preferred. That is, a step (11) of preparing a coating solution using a water-soluble organic solvent of a heat-resistant polymer, a step (12) of applying the coating solution to one or both sides of the substrate layer, and a coated substrate A step (13) of solidifying the heat-resistant polymer by immersing in water or a mixed solution of water and the water-soluble organic solvent, and a step of washing and drying the substrate after the solidification step A method through (14) is exemplified.

  The heat-resistant porous layer contains one or more elements selected from the group consisting of alkali metals, alkaline earth metals, transition metals, halogens and silicon in a range of 0.1 to 1000 ppm. It is illustrated as a preferable example that it is produced using a polymer. Specific and typical substances include Na or Li element as alkali metal, Mg or Ca element as alkaline earth metal, Fe element as transition metal, and chlorine element as halogen. Illustrated. The substance may affect the heat resistance of the nonaqueous electrolyte battery separator, in particular, the heat resistance and stability of the heat-resistant porous layer, as well as the shutdown characteristics due to diffusion into the base material layer, and the meltdown behavior. However, if the content in the heat-resistant porous layer is in the range of 0.1 to 1000 ppm, these effects can be avoided. As a result, it is possible to obtain a separator excellent in cycle characteristics and short-circuit resistance, that is, a battery.

  Alkali metals, especially Na element, also have the effect of renewing and removing the film at the negative electrode interface, which does not necessarily have an adverse effect, but the effect of thermally decomposing the heat-resistant resin is significant, so the heat resistance of the separator From the viewpoint of short circuit resistance, it is preferable to be within the above range. Since Mg, Ca, and Fe elements have a large effect of promoting thermal decomposition of the heat-resistant porous layer, the range is preferably 0.1 to 800 ppm, more preferably 0.1 to 700 ppm. Halogen, especially chlorine element, preferably promotes dissolution of aluminum used as the positive electrode current collector, plugs the lithium insertion / extraction site of the positive electrode active material, and may significantly impair the performance of the secondary battery. A range of 0.1 to 500 ppm, particularly preferably 0.1 to 300 ppm is exemplified.

  The method for setting the elemental component within a predetermined range is, for example, a method of treating the coating liquid produced in the step (11) with an adsorbent such as molecular sieves, or filtering with various filter media to remove the insoluble component. The method of doing is mentioned. Further, the element component can be reduced by using an aqueous coagulating liquid in the step (13) for coagulating the heat-resistant polymer, and by washing with water in the step (14) for washing and drying the substrate. . In particular, in the steps (13) and (14), the element components contained in the base material layer and the heat-resistant porous layer described above can be simultaneously reduced. Therefore, in the step (14), it is more preferable to repeat the water washing treatment.

  In the step (11) of preparing the coating liquid, the water-soluble organic solvent is not particularly limited, and a conventionally known solvent can be suitably used. Specifically, a polar solvent is preferable, for example, N-methyl Examples include pyrrolidone, dimethylacetamide, dimethylformamide, dimethylsulfoxide and the like. Moreover, in order to accelerate | stimulate porosity of a heat resistant porous layer, the solvent used as a poor solvent with respect to a heat resistant polymer can also be mixed and used for the said polar solvent. As the poor solvent, alcohols are preferable, and polyhydric alcohols such as glycol are particularly preferable.

  In the step (12) of applying the coating liquid, the coating method is not particularly limited, but specifically, knife coater method, gravure coater method, screen printing method, Mayer bar method, die coater method, reverse roll coater method. , Inkjet method, spray method, roll coater method and the like. From the viewpoint of uniformly applying the coating film, the reverse roll coater method is particularly suitable. For example, when coating a heat-resistant polymer coating solution on both surfaces of a substrate such as a polyethylene microporous membrane, apply the coating solution excessively on both surfaces or one surface of the substrate through a pair of Meyer bars. In addition, there is a method in which this is passed between a pair of reverse roll coaters and the excess coating solution is scraped off to precisely measure.

  In the step (13) of solidifying the heat-resistant polymer, the substrate coated with the heat-resistant polymer is immersed and solidified in a coagulating liquid to form a heat-resistant porous layer. The coagulation method is not particularly limited, and a conventionally known method can be used, and examples thereof include a method of spraying a coagulating liquid with a spray and a method of immersing in a bath (coagulating bath) containing the coagulating liquid. The coagulation liquid is not particularly limited as long as it can coagulate the heat-resistant polymer, but is preferably water or an organic solvent used for the coating liquid mixed with an appropriate amount of water. The mixing amount of water is preferably 40 to 80% by weight with respect to the coagulation liquid. When the amount is less than 40% by weight, there may be a problem that the time for solidifying the heat-resistant polymer becomes long and a problem that the solidification is insufficient. On the other hand, when the amount is more than 80% by weight, there may be a problem of high solvent recovery cost and a problem that surface solidification of the coating film is too fast and surface porosity becomes insufficient.

  The step (14) of washing and drying the substrate is a step of washing the obtained separator with water to remove the coagulating liquid and then drying, following the step (13). The drying method is not particularly limited, but a drying temperature of 50 to 80 ° C. is appropriate. When a high drying temperature is applied, a method of contacting with a roll in order to prevent a dimensional change due to heat shrinkage occurs. It is preferable to apply.

  Examples of the heat-resistant polymer used in the present invention include a polymer having a melting point of 200 ° C. or higher or a polymer having no melting point but a decomposition temperature of 200 ° C. or higher. One or two or more selected from the group consisting of ether sulfone, polysulfone, polyether ketone, and polyetherimide. Particularly preferable examples include wholly aromatic polyamides obtained from aromatic diamines and dichlorides of aromatic dicarboxylic acids. The wholly aromatic polyamide may be a homopolymer, a copolymer, or a copolymer of some aromatic aminocarboxylic acid chlorides. Furthermore, some aliphatic diamines, dicarboxylic acids, and aminocarboxylic acids may be contained. Among the wholly aromatic polyamides, polymetaphenylene isophthalamide is exemplified as a preferred example. Polyethylene and polymetaphenylene isophthalamide are a particularly preferred combination in the present invention because they are well known and exhibit good adhesion.

  The production method of the heat-resistant polymer is not particularly limited, and a conventionally known method is preferably used, but those obtained by solution polymerization or interfacial polymerization are preferable. For example, in solution polymerization of wholly aromatic polyamides, aromatic diamines and aromatic dicarboxylic acid chlorides are reacted in an organic polar solvent such as N-methylpyrrolidone, dimethylacetamide, dimethylformamide, dimethyl sulfoxide to give a wholly aromatic polyamide. Polyamide is obtained. In this case, the coating liquid can be produced directly. Further, the salts produced as a reaction by-product by solution polymerization may be removed or the coating solution may be adjusted while containing it. For example, in interfacial polymerization of a wholly aromatic polyamide, an aromatic diamine and an aromatic dicarboxylic acid chloride are reacted in an organic solvent (solvent) that is not a good solvent for the resulting polyamide, for example, tetrahydrofuran, and then a solution or dispersion. A liquid is made, and this is contacted with an aqueous solution of an acid acceptor such as sodium carbonate to complete the reaction. The obtained water-soluble organic solvent solution of wholly aromatic polyamide may be applied to one side or both sides of the base material layer.

  The heat-resistant porous layer should be mainly composed of heat-resistant polymer in an amount of about 90% by weight or more, and contains about 10% by weight or less of other components that do not affect the battery characteristics. You can leave.

  In the present invention, the heat-resistant porous layer is formed, for example, on one side or both sides of the base layer of the polyolefin microporous membrane. More preferred. When the heat resistant porous layer is formed on both surfaces of the base material layer, the total thickness of the heat resistant porous layer is suitably selected from 3 μm to 12 μm. Further, when the heat-resistant porous layer is formed only on one side of the base material layer, the thickness of the heat-resistant porous layer is suitably selected from 3 μm to 12 μm. In any case, when the total thickness of the heat-resistant porous layer is less than 3 μm, sufficient heat resistance, particularly a heat shrinkage suppressing effect cannot be obtained. On the other hand, when the total thickness of the heat-resistant porous layer exceeds 12 μm, it becomes difficult to achieve an appropriate separator thickness.

  The porosity of the heat resistant porous layer is preferably in the range of 60 to 90%. If the porosity exceeds 90%, the heat resistance tends to be insufficient, and if it is less than 60%, the cycle characteristics, storage characteristics, and discharge characteristics tend to decrease, which is not preferable.

  In the present invention, the heat-resistant porous layer can contain an inorganic filler in a weight fraction of 50 to 95% by weight depending on the desired purpose. The inorganic filler is an inorganic fine particle, and the kind thereof is not particularly limited, but is preferably an oxide such as alumina, titania, silica, zirconia, carbonate, phosphate, hydroxide, etc. is there. In particular, a metal hydroxide is preferable. As the metal hydroxide, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, chromium hydroxide, zirconium hydroxide, nickel hydroxide, boron hydroxide, or combinations of two or more thereof are suitable. The average particle diameter of the inorganic filler is preferably in the range of 0.1 to 1 μm.

  In the present invention, when an inorganic filler is added to the heat resistant porous layer, the alkali metal, alkaline earth metal, transition metal, halogen, and silicon contained in the heat resistant polymer used in the present invention are used. It may be difficult to distinguish one or two or more kinds of substances selected from the group consisting of 0.1 to 1000 ppm from the viewpoint of analysis / analysis, but the substances originally contained in the heat-resistant polymer are still Since it differs from the inorganic fine particles as described above, it may affect the essential properties and performance of the heat-resistant polymer.

  When the amount of the inorganic filler is in the range of 50 to 95% by weight, the inorganic filler is sufficiently compatible with the heat-resistant polymer and has good dispersibility. In addition, when the heat-resistant porous layer is formed by solidification in water due to the action of the inorganic filler, it is difficult for the low-molecular weight polymer of the heat-resistant polymer to flow out into the coagulation liquid, so that suitable pore formation is possible. And the effect that the below-mentioned Gurley value and film resistance become still lower is also acquired.

  The inorganic filler functions effectively in making the nonaqueous electrolyte battery separator of the present invention flame retardant. For example, when a metal hydroxide is used as the inorganic filler, when the metal hydroxide is heated, a dehydration reaction occurs to become an oxide, and water is released. Furthermore, this dehydration reaction is a reaction with a large endotherm. The release of water during this dehydration reaction and the endothermic effect of this reaction provide a flame retardant effect. In addition, an electrolyte that is flammable to release water is diluted with water and is effective not only for the separator but also for the electrolyte, and is effective in making the battery itself flame-retardant.

  The metal hydroxide as the inorganic filler is also preferable from the viewpoint of handling properties. In addition, since metal hydroxide is softer than metal oxide such as alumina, it is used in each process at the time of manufacture depending on the problem with conventional separators, that is, the inorganic filler contained in the separator. It is also preferable in that a problem relating to handling properties such as wear of parts is unlikely to occur.

  When producing a heat-resistant porous layer containing 50 to 95% by weight of inorganic filler by weight fraction, in step (11), the inorganic filler is dispersed in the water-soluble organic solvent solution of the heat-resistant polymer. The slurry for coating may be prepared. In the present invention, such a coating slurry is also included in the concept of the coating liquid in the step (11). When the dispersibility of the inorganic filler is not good, a method of improving the dispersibility by surface-treating the inorganic filler with a silane coupling agent or the like is also applicable.

[Nonaqueous electrolyte battery separator]
The film thickness of the nonaqueous electrolyte battery separator of the present invention is preferably 30 μm or less, more preferably 20 μm or less. When the thickness of the separator exceeds 30 μm, the energy density and output characteristics of a battery to which the separator is applied are lowered, which is not preferable. As the physical properties of the nonaqueous electrolyte battery separator, the Gurley value (JIS P8117) is 10 to 1000 sec / 100 cc, preferably 100 to 400 sec / 100 cc. When the Gurley value is less than 10 sec / 100 cc, the shutdown function is extremely impractical. When the Gurley value exceeds 1000 sec / 100 cc, the ion permeability becomes insufficient, resulting in a problem that the membrane resistance of the separator is increased and the output of the battery is lowered. The membrane resistance is 0.5 to 10 ohm · cm ² , preferably 1 to 5 ohm · cm ² . The puncture strength is in the range of 10 to 1000 g, preferably 200 to 600 g.

[Nonaqueous electrolyte battery]
The nonaqueous electrolyte battery separator of the present invention can be applied to any known nonaqueous electrolyte battery, and a battery excellent in cycle characteristics and short circuit resistance can be obtained. Such a non-aqueous electrolyte battery may be a primary battery or a secondary battery, and the type and configuration thereof are not limited in any way, but the non-aqueous electrolyte battery separator obtained by the production method of the present invention Can be suitably applied to a non-aqueous electrolyte secondary battery that obtains an electromotive force by doping or dedoping lithium. Among these, application to a lithium ion secondary battery is preferable.

In general, a nonaqueous electrolyte secondary battery refers to a battery element 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 sealed 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 (copper foil, stainless steel foil, nickel foil, etc.). As the negative electrode active material, a material capable of electrochemically doping lithium, for example, a carbon material, silicon, aluminum, or tin is 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 such as 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 and LiFePO ₄ are used. The electrolytic solution has a configuration in which a lithium salt, for example, LiPF ₆ , LiBF ₄ , or LiClO ₄ is dissolved in a non-aqueous solvent. Examples of the non-aqueous solvent include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, γ-butyrolactone, and vinylene carbonate. 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 obtained by the manufacturing method of the present invention can be suitably applied to any shape.

  EXAMPLES Hereinafter, although an Example explains this invention in detail, this invention is not restrict | limited to these. Various measurement methods in the present invention are as follows.

[Measurement method of impurity content]
Sulfuric acid was added to the sample and incinerated, and then melted with potassium hydrogen sulfate. After dissolving in dilute nitric acid and making a constant volume with pure water, the contents of various metal elements were measured by ICP emission analysis (ICP-AES method). In addition, the sample polymer is combusted by an automatic sample combustion apparatus AQF-100 (manufactured by Dia Instruments Co., Ltd.), and the generated gas is absorbed in 30 ppm of hydrogen peroxide water to be ion chromatograph (ICS-1500, manufactured by Dionex Co., Ltd.) Qualitative and quantitative determination of the halogen element was performed with a column (IonPacAG12A / AS12A).

[Film thickness]
The film thickness was obtained by measuring 20 points with a contact-type film thickness meter (manufactured by Mitutoyo Corporation) and averaging this. Here, the contact terminal used was a cylindrical one having a bottom surface of 0.5 cm in diameter, and measurement was performed under a condition that a load of 1.2 kg / cm ² was applied to the contact terminal.

[Porosity]
The porosity of the base material layer 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).

[Gurley value]
The Gurley value of the nonaqueous electrolyte secondary battery separator was determined according to JIS P8117.

[Membrane resistance]
The membrane resistance of the nonaqueous electrolyte secondary battery separator was determined by the following method.
A sample is cut into a size of 2.6 cm × 2.0 cm, immersed in a methanol solution (methanol: Wako Pure Chemical Industries, Ltd.) in which 3% by weight of a nonionic surfactant (Emulgen 210P manufactured by Kao Corporation) is dissolved, 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, and impregnated with 1M LiBF ₄ propylene carbonate / ethylene carbonate (1/1 weight ratio) as an electrolytic solution. . This is depressurized and sealed so that the tab comes out of the aluminum pack in the aluminum laminate 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.

[Puncture strength]
The puncture strength of the base material layer and the non-aqueous electrolyte secondary battery separator is a puncture test using a KES-G5 handy compression tester manufactured by Kato Tech Co. under the conditions of a radius of curvature of the needle tip of 0.5 mm and a puncture speed of 2 mm / sec. The maximum piercing load was taken as the piercing strength. Here, the silicon rubber packing was also sandwiched and fixed in a metal frame (sample holder) having a hole with a diameter of 11.3 mm.

[Heat shrinkage]
The thermal contraction rate of the base material layer and the nonaqueous electrolyte battery separator was measured by heating the sample at 105 ° C. for 1 hour.

[Gelboflex test]
The gel layer flex test of the base material layer and the non-aqueous electrolyte battery separator was carried out using a gelbo flex tester (manufactured by Tester Kogyo) under the conditions of room temperature (25 ° C.) and 1000 cycles.

[Evaluation of charge / discharge cycle characteristics]
1) Positive electrode 6 wt% PVdF so that the lithium cobalt oxide (LiCoO ₂ , Nippon Chemical Industry Co., Ltd.) powder 89.5 parts by weight, acetylene black 4.5 parts by weight and PVdF dry weight 6 parts by weight A positive electrode paste was prepared using the NMP solution. The obtained paste was applied onto an aluminum foil having a thickness of 20 μm, dried and pressed to obtain a positive electrode having a thickness of 97 μm.
2) Positive and negative electrodes 6% by weight so that the dry weight of 87 parts by weight of mesophase carbon microbeads (MCMB, manufactured by Osaka Gas Chemical Co., Ltd.), 3 parts by weight of acetylene black and 10 parts by weight of PVdF is used as the negative electrode active material. A negative electrode paste was prepared using an NMP solution of PVdF. The obtained paste was applied onto a copper foil having a thickness of 18 μm, dried and pressed to prepare a negative electrode having a thickness of 90 μm.
3) Production of button battery Using the produced composite porous membrane as a separator, a button battery (CR2032) having an initial capacity of about 4.5 mAh was produced using the positive electrode and the negative electrode. As the electrolytic solution, 1M LiPF ₆ EC / DEC / MEC (1/2/1 weight ratio) was used. The manufactured button battery was repeatedly charged and discharged at a charge voltage of 4.2 V and a discharge voltage of 2.75 V. The discharge capacity at the 500th cycle was divided by the initial capacity, and the change in capacity when charging and discharging were repeated over a long period of time. It was a parameter.

[Shutdown temperature]
A microporous polyolefin membrane sample with polymetaphenylene isophthalamide layers on both sides was punched to a diameter of 19 mm, and a methanol solution (methanol: Wako Pure Chemical Industries, Ltd.) in which 3% by weight of a nonionic surfactant (Emulgen 210P manufactured by Kao Corporation) was dissolved. The sample cut out was manufactured 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.

[Short-circuit resistance]
The manufactured button battery was charged and discharged at a charging voltage of 4.2 V and a discharging voltage of 2.75 V for 500 cycles, and then charged again to 4.2 V, placed in an oven, and placed with a 5 kg weight. In this state, the oven was set so that the battery temperature was raised at 2 ° C./min, and the temperature was raised to 150 ° C. and then held for 1 hour. At that time, the short-circuit resistance was evaluated to be poor (×) for those in which a sudden drop in battery voltage was observed near 150 ° C., and the short-circuit resistance was evaluated for those for which there was no significant change in battery voltage even at 150 ° C. Evaluated as good (◯).

[Reference Example 1]
Production of polyethylene microporous membrane (base material layer) As polyethylene powder, GUR2126 (weight average molecular weight 4150,000, melting point 141 ° C) and GURX143 (weight average molecular weight 560,000, melting point 135 ° C) manufactured by Ziegler-Natta catalyst. ) Was used. GUR2126 and GURX143 are made to be 1: 9 (weight ratio) and liquid paraffin (manufactured by Matsumura Oil Research Co., Ltd .; Smoyl P-350P; boiling point 480 ° C.) and decalin so that the polyethylene concentration becomes 30% by weight. A polyethylene solution was prepared by dissolving in a mixed solvent. The composition of this polyethylene solution was 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 then the base tape was stretched by biaxial stretching that was performed in the order of longitudinal stretching and lateral stretching. 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, it dried at 50 degreeC and annealed at 120 degreeC, and obtained the polyethylene microporous film.
The film thickness of this polyethylene microporous film is 12 μm, the porosity is 36%, the Gurley value is 355 sec / 100 cc, the membrane resistance is 2.7 ohm · cm ² , the thermal shrinkage rate (MD / TD) is 21 / 8.8%, and the puncture strength is 475 g. The gelboflex test was 4 / m ² . The abundance of each of Fe / Ti / (Na, Ca) / Al / chlorine element in the polyethylene microporous film was 4/40 / (5, 75) / 70/250 ppm.

[Reference Example 2]
Production of polymetaphenylene isophthalamide by interfacial polymerization method Dissolve 160.5 g of isophthalic acid chloride in 1120 ml of tetrahydrofuran, and gradually add a solution of 85.2 g of metaphenylenediamine in 1120 ml of tetrahydrofuran as a trickle while stirring. A cloudy milky white solution was obtained. Stirring was continued for about 5 minutes, and then an aqueous solution in which 167.6 g of sodium carbonate and 317 g of sodium chloride were dissolved in 3400 ml of water was rapidly added while stirring for 5 minutes. The reaction system increased in viscosity after a few seconds and then decreased again to obtain a white suspension. This was left to stand, the separated transparent aqueous solution layer was removed, and 185.3 g of a white polymer of polymetaphenylene isophthalamide was obtained by filtration. The abundance of each of the Fe / Na / chlorine elements in this polymetaphenylene isophthalamide was 2/100/30 ppm.

[Reference Example 3]
Production of polymetaphenylene isophthalamide by solution polymerization method Into a reaction vessel equipped with a thermometer, a stirrer and a raw material inlet, 753 g of NMP having a moisture content of 100 ppm or less is put, and 85.5 g of metaphenylenediamine is put in this NMP, Cooled to 0 ° C. To this cooled diamine solution, 160.5 g of isophthalic acid chloride was gradually added with stirring to react. This reaction increased the temperature of the solution to 70 ° C. After the change in viscosity stopped, 58.4 g of calcium hydroxide powder was added and stirred for another 40 minutes to complete the reaction, and the polymerization solution was taken out and reprecipitated in water to obtain 184.0 g of polymetaphenylene isophthalamide. . The abundance of each of Fe / Ca / chlorine elements in polymetaphenylene isophthalamide was 3/120/200 ppm.

[Comparative Example 1]
The inorganic filler made of polymetaphenylene isophthalamide of Reference Example 2 and aluminum hydroxide having an average particle size of 0.8 μm (Showa Denko KK; H-43M) was adjusted to a weight ratio of 25:75, These were mixed in a mixed solvent in which dimethylacetamide (DMAc) and tripropylene glycol (TPG) had a weight ratio of 50:50 so that the polymetaphenylene isophthalamide concentration was 5.5% by weight. A slurry was obtained.
A pair of Meyer bars (count # 6) was opposed to each other with a clearance of 20 μm. An appropriate amount of the above slurry for coating was placed on a Meyer bar, and the slurry for coating was applied to both sides of the polyethylene microporous membrane through the polyethylene microporous membrane of Reference Example 1 between a pair of Mayer bars. And what was coated was immersed in the coagulating liquid which is 40 degreeC by water: DMAc: TPG = 50: 25: 25 by weight ratio. Next, washing with water and drying were performed to form a heat-resistant porous layer composed of 2 μm on each side of the polymetaphenylene isophthalamide porous layer on both surfaces (front and back surfaces) of the polyethylene microporous membrane to obtain a nonaqueous electrolyte battery separator.
The abundance of each of Fe / Ti / (Na, Ca) / Al / chlorine elements in the polyethylene microporous film of this separator was 4/40 / (4, 70) / 70/210 ppm, and in the heat-resistant porous layer The abundance of each of Fe / Na / chlorine element was 2/80/25 ppm. Further, the charge / discharge cycle characteristics of the battery using the separator were 65%, the shutdown temperature was 145 ° C., and the short-circuit resistance characteristics were x.

[Comparative Example 2]
The inorganic filler made of polymetaphenylene isophthalamide of Reference Example 3 and aluminum hydroxide having an average particle size of 0.8 μm (Showa Denko KK; H-43M) was adjusted to a weight ratio of 25:75, These were mixed in a mixed solvent in which dimethylacetamide (DMAc) and tripropylene glycol (TPG) had a weight ratio of 50:50 so that the polymetaphenylene isophthalamide concentration was 5.5% by weight. A slurry was obtained.
A pair of Meyer bars (count # 6) was opposed to each other with a clearance of 20 μm. An appropriate amount of the above slurry for coating was placed on a Meyer bar, and the slurry for coating was applied to both sides of the polyethylene microporous membrane through the polyethylene microporous membrane of Reference Example 1 between a pair of Mayer bars. And what was coated was immersed in the coagulating liquid which is 40 degreeC by water: DMAc: TPG = 50: 25: 25 by weight ratio. Next, washing with water and drying were performed, and heat-resistant porous layers made of polymetaphenylene isophthalamide were formed on both sides (front and back surfaces) of the polyethylene microporous membrane to form 2 μm on each side to obtain a nonaqueous electrolyte battery separator.
The abundance of each of Fe / Ti / (Na, Ca) / Al / chlorine elements in the polyethylene microporous film of this separator was 4/40 / (4, 70) / 70/210 ppm, and in the heat-resistant porous layer The abundance of each of Fe / Ca / chlorine element was 3/110/190 ppm. Further, the charge / discharge cycle characteristics of the battery using the separator were 50%, the shutdown temperature was 145 ° C., and the short-circuit resistance characteristics were x.

[Example 1]
In Reference Example 1, a polyethylene microporous membrane was produced in the same manner except that the polyethylene solution was contacted with molecular sieves (4A) for 10 hours and filtered. This polyethylene microporous film has a film thickness of 12 μm, a porosity of 37%, a Gurley value of 351 sec / 100 cc, a membrane resistance of 2.6 ohm · cm ² , a heat shrinkage rate (MD / TD) of 21.0 / 8.5%, and a piercing The strength was 475 g, and the gelbo flex test was 4 / m ² . The abundance of each of Fe / Ti / (Na, Ca) / Al / chlorine element was 1/15 / (3, 40) / 17/130 ppm.
This polyethylene microporous membrane was used in the same manner as in Comparative Example 1, except that it was immersed in a coagulation solution, washed repeatedly with ion-exchanged water, dried, and heat-resistant polymetaphenylene isophthalamide of 2 μm on each side. A porous layer was formed to obtain a nonaqueous electrolyte battery separator.
The abundance of each of Fe / Ti / (Na, Ca) / Al / chlorine element in the polyethylene microporous film of the separator is 1/15 / (2,35) / 17/95 ppm, in the heat-resistant porous layer. The abundance of each of Fe / Na / chlorine element was 2/45/20 ppm. The battery using the separator had a charge / discharge cycle characteristic of 85%, a shutdown temperature of 143 ° C., and a short-circuit resistance characteristic of ◯.

[Example 2]
In Reference Example 1, the polyethylene solution was contacted with molecular sieves (4A) for 10 hours, filtered, liquid paraffin and decalin were extracted with methylene chloride, and the same treatment was repeated except that the extraction treatment was repeated with ion-exchanged water. A microporous membrane was produced. This polyethylene microporous film has a film thickness of 12 μm, a porosity of 37%, a Gurley value of 351 sec / 100 cc, a membrane resistance of 2.6 ohm · cm ² , a heat shrinkage rate (MD / TD) of 21.0 / 8.5%, and a piercing The strength was 475 g, and the gelbo flex test was 4 / m ² . The abundance of each of Fe / Ti / (Na, Ca) / Al / chlorine element was 1/10 / (2, 30) / 15/100 ppm.
This polyethylene microporous membrane was used in the same manner as in Comparative Example 2, except that it was immersed in a coagulation liquid, washed repeatedly with ion-exchanged water, dried, and heat-resistant polymetaphenylene isophthalamide of 2 μm on each side. A porous layer was formed to obtain a nonaqueous electrolyte battery separator.
The amount of each of Fe / Ti / (Na, Ca) / Al / chlorine elements in the polyethylene microporous film of the separator is 1/10 / (2,25) / 15/80 ppm, heat resistance of polymetaphenylene isophthalamide The abundance of each of Fe / Ca / chlorine elements in the porous layer was 3/90/160 ppm. The battery using the separator had a charge / discharge cycle characteristic of 84%, a shutdown temperature of 143 ° C., and a short-circuit resistance characteristic of ◯.

  As seen from the above examples, the separator of the present invention is excellent in cycle characteristics of charge / discharge, particularly capacity stability when charging / discharging is repeated over a long period of time, and also exhibits excellent short-circuit resistance.

  The present invention makes it possible to use a non-aqueous electrolyte battery separator having good cycle characteristics and short-circuit-proof characteristics, and further to use a non-aqueous electrolyte secondary battery that obtains an electromotive force by doping and dedoping lithium. It becomes possible.

Claims (7)

A base material layer that contains polyolefin and has pores or voids inside and has a shutdown function, and a heat-resistant porous layer that contains a heat-resistant polymer and is laminated on one or both sides of the base material layer And a non-aqueous electrolyte battery separator that satisfies the following conditions (i) and (ii):
(I) The heat-resistant porous layer contains 0.1 to 1000 ppm of one or more elements selected from the group consisting of alkali metals, alkaline earth metals, transition metals, halogens, and silicon.
(Ii) The base material layer satisfies at least one of the following conditions (A) to (E).
(A) 0.1 to 3 ppm of at least one element of Fe, Cr and Ni (B) 0.1 to 30 ppm of at least one element of Ti and Zr (C) Al and B 0.1 to 50 ppm of at least one element among them (D) 1 to 70 ppm of at least one element among alkali metals and alkaline earth metals (E) 1 to 200 ppm of halogen elements The non-aqueous electrolyte battery separator according to claim 1, wherein the base material layer satisfies all of the following conditions (A) to (E).
(A) 0.1 to 2 ppm of at least one element among Fe, Cr and Ni (B) 1 to 20 ppm of Ti element (C) 1 to 20 ppm of Al element (D) Na, Ca and 1 to 50 ppm containing at least one element of Mg (E) 1 to 100 ppm halogen element   The polyolefin includes polyethylene polymerized by at least one catalyst selected from the group consisting of a chromium oxide catalyst, a metallocene catalyst, and a Ziegler-Natta catalyst, the polyethylene having a weight average molecular weight of 100,000 to 10 million. The nonaqueous electrolyte battery separator according to claim 1, wherein the battery separator is a nonaqueous electrolyte battery separator.   The non-aqueous electrolyte battery separator according to claim 1, wherein the heat-resistant porous layer is laminated by coating.   The heat-resistant polymer is one or more selected from the group consisting of aromatic polyamide, polyimide, polyethersulfone, polysulfone, polyetherketone, and polyetherimide. The nonaqueous electrolyte battery separator according to any one of the above.   6. The nonaqueous electrolyte battery separator according to claim 5, wherein the heat resistant polymer is polymetaphenylene isophthalamide.   A non-aqueous electrolyte secondary battery using the non-aqueous electrolyte battery separator according to claim 1 to obtain an electromotive force by doping or dedoping lithium.