JP2012099370A - Separator for nonaqueous electrolyte secondary battery and nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separator for nonaqueous electrolyte secondary battery in which tension fluctuation in the winding work during manufacture and occurrence of failures incident thereto, e.g. creases, streaks and rupture, are minimized, production efficiency is enhanced, and excellent cycle characteristics of shutdown and short circuit resistance are ensured.SOLUTION: The separator for nonaqueous electrolyte secondary battery comprises a polyolefin porous base material containing polyolefin and internally having pores, and a heat resistant porous layer containing a heat resistant resin provided at least on one side of the polyolefin porous base material. Under following conditions, average value of stress at a proof stress point in the longitudinal direction is 6-30 MPa, and average value of stress at a proof stress point in the width direction perpendicular to the longitudinal direction is 4-20 MPa. <conditions> tension rate: 20 mm/min, temperature: 25°C, humidity: 65%RH, sample size: width 1.0 cm, length 7 cm.

Description

  The present invention relates to a separator for a nonaqueous electrolyte secondary battery and a nonaqueous electrolyte secondary battery.

  Non-aqueous electrolyte batteries, particularly non-aqueous 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. Yes. While this lithium ion secondary battery is required to have higher energy density and improved safety, improvement of safety and productivity has been an issue with the expansion of the range of use.

  The lithium ion secondary battery includes a separator between the positive and negative electrodes, and the separator plays an important role in ensuring safety against fuming, ignition, and the like. In particular, a porous film of polyolefin, particularly polyethylene, is used from the viewpoint of providing a shutdown function for stopping permeation of a substance at a high temperature to a lithium ion secondary battery. However, the battery temperature may further increase after the shutdown function is activated. In this case, when the melting of the separator (so-called meltdown) proceeds excessively, a short circuit occurs inside the battery, and this may generate a large amount of heat, which may increase the risk of smoking, ignition, explosion, etc. .

  Therefore, in view of such a situation, techniques such as coating a porous layer containing a heat-resistant resin on one side or both sides of a polyolefin porous substrate or laminating a nonwoven fabric made of fibers of a heat-resistant resin are proposed. (For example, see Patent Documents 1 to 5). According to these techniques, a certain degree of improvement effect can be expected with respect to heat resistance and, consequently, short circuit resistance.

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

  In this way, although the technology for improving the heat resistance while providing a shutdown function by attaching a heat resistant resin to the polyolefin used as the base material is known, in actuality, in the manufacturing process of the separator It may be difficult to keep the tension at a predetermined pressure during the winding operation or the like, and the manufacturing suitability may be inferior. In such a case, failure such as wrinkles or breakage is likely to occur in the separator, and it is easy to cause defects in terms of deformation, adhesion, dimensions, etc., when a battery is manufactured by incorporating the separator. There is a problem that cannot be secured.

  Therefore, if an anomaly that occurs in the separator during manufacturing is avoided, the effect on the battery characteristics due to the separator is eliminated, more stable quality is maintained, and cycle characteristics and short-circuit resistance are better than before. Become.

  The present invention has been made in view of the above, and the occurrence of failure such as wrinkles, streaks, breakage and the like in the winding operation during the manufacturing process such as the slitting process is suppressed, and the production efficiency is high. To provide a non-aqueous electrolyte secondary battery separator with excellent shutdown cycle characteristics and short-circuit resistance, and a highly safe non-aqueous electrolyte secondary battery with excellent heat resistance and suppressed thermal runaway and ignition. It is an object to achieve this purpose.

Specific means for achieving the above object are as follows.
<1> A polyolefin porous substrate containing polyolefin and having pores therein, and a heat-resistant porous layer provided on at least one side of the polyolefin porous substrate and containing a heat-resistant resin, The average value of stress at a plurality of proof stress points measured in the longitudinal direction when the tensile treatment is performed under the conditions of 6 to 30 MPa, and the proof stress measured in the width direction orthogonal to the longitudinal direction. This is a separator for a non-aqueous electrolyte secondary battery having an average value of stress at a point of 4 to 20 MPa.
<Condition>
・ Tensing speed: 20mm / min ・ Temperature: 25 ℃
・ Humidity: 65% RH
・ Sample size: width 1.0cm, length 7cm

  <2> The separator for a nonaqueous electrolyte secondary battery according to <1>, wherein the elongation of stress at the proof stress in the longitudinal direction and the width direction is 0.6 to 3%, respectively.

  <3> A positive electrode, a negative electrode, and the non-aqueous electrolyte secondary battery separator according to <1> or <2> disposed between the positive electrode and the negative electrode, and lithium doping / dedoping This is a non-aqueous electrolyte secondary battery that obtains an electromotive force.

According to the present invention, fluctuations in tension (winding) in winding operations during manufacturing such as a slit process and the occurrence of failures such as wrinkles, streaks, and breaks are suppressed, production efficiency is high, and cycle characteristics of shutdown are achieved. And the separator for nonaqueous electrolyte secondary batteries excellent in short circuit resistance can be provided. Also,
According to the present invention, it is possible to provide a highly safe non-aqueous electrolyte secondary battery that has excellent heat stability and thermal runaway and ignition are suppressed.

It is a graph for demonstrating a proof stress from the relationship between the displacement of a separator, and stress.

  Hereinafter, although the form for implementing this invention is demonstrated in detail, this invention is not restrict | limited to the said form, Various deformation | transformation can be implemented within the range of the summary.

[Separator for non-aqueous electrolyte secondary battery]
The separator for a non-aqueous electrolyte secondary battery according to the present invention includes a polyolefin porous substrate having polyolefin therein and pores therein, and is provided on at least one side of the polyolefin porous substrate, and includes a heat resistant resin. When the tensile treatment is performed under the following conditions, the average value of stress at a plurality of proof stress points measured in the longitudinal direction is set to 6 to 30 MPa, and is orthogonal to the longitudinal direction. The average value of stress at a plurality of proof stress points measured in the width direction is 4 to 20 MPa.
<Condition>
・ Tensile speed: 20mm / min ・ Temperature: 25 ℃
・ Humidity: 65% RH
・ Sample size: width 1.0cm, length 7cm

In the present invention, as a method of pulling the separator, treatment using a tensile tester RTC-1225A (chuck length: 5.0 cm) manufactured by A & D is applied. Here, the sample size is as described above, but the sample thickness is about 8 to 30 μm. Further, a distance between chucks: 5 cm and a chuck width: 1.0 cm are preferable.
The pulling process uses a plurality of sample pieces arbitrarily cut from the long separator in the longitudinal direction or the width direction, and the tensile strength at the time of performing the pulling process on a plurality of samples in each direction. The average value obtained by averaging the stresses is used as the stress at the proof stress.

In the present invention, a laminate in which a heat-resistant porous layer is provided on one side or both sides of a polyolefin porous base material having a shutdown function (hereinafter sometimes referred to as “base material” or “porous base material”). When a plurality of specimens that have a structure and are arbitrarily cut out are subjected to a pulling process, a proof stress exists, and a longitudinal direction (MD: Machine Direction; hereinafter abbreviated as “MD direction”) and width. By comparing the stress at each proof stress point in the direction (TD: Transverse Direction; hereinafter abbreviated as “TD direction”) with an average value within a predetermined range, a predetermined comparison corresponding to the stress at the proof stress point Tension fluctuations that tend to occur during winding operations such as the slit process when winding with a low tension are suppressed, and films such as wrinkles, streaks, and film breaks that occur due to unstable winding due to this tension fluctuation Abnormal Occurrence is suppressed. Thereby, it can roll efficiently while suppressing winding failure, and manufacturing efficiency improves. That is, the winding operation of the long separator is important for the stress balance between the MD direction and the TD direction to wind the long object stably without meandering.
In addition, because there is little fluctuation in tension when winding the separator, membrane abnormalities (such as wrinkles and folds) due to separator breakage and winding failure are suppressed, resulting in abnormalities in the separator film during battery manufacturing. Stress fluctuations and stress concentration at the corners of, for example, a prismatic battery are prevented. As a result, the cycle stability of the shutdown function is excellent, a stable heat resistance performance is obtained, the occurrence of thermal runaway or ignition is avoided, and a non-aqueous electrolyte secondary battery that is safer than before can be obtained.

Here, the proof stress referred to in the present invention will be described with reference to FIG.
FIG. 1 shows the relationship between the stress applied to the separator and its displacement, where the horizontal axis is the amount (displacement) of the separator that is stretched and the vertical axis is the tensile force (stress) required to obtain the displacement. This relationship is represented by a curve indicated by a solid line. At this time, a tangent line that touches the curve through the origin is drawn, and a point where a straight line obtained by translating a displacement corresponding to 1% in a direction in which the displacement increases is defined as a proof point. The displacement when stretched by stretching at the stress at the proof stress means the stretch amount stretched by the stress at the proof stress, and the ratio of the stretch amount to the stretch amount 100 at break is the elongation (%). Means.

In the present invention, when the average stress of the proof stress exceeds 30 MPa in the longitudinal direction (MD direction) or exceeds 20 MPa in the width direction (TD direction), the elongation of the separator is small. The phenomenon that the fluctuation range and number of times of tension become steep and increase in frequency is likely to occur, and when winding into a roll, fluctuations such as winding and loosening occur greatly, and defects such as breakage, wrinkles and streaks of the separator occur. appear.
In addition, when the average value of stress at the proof stress is less than 6 MPa in the longitudinal direction (MD direction) or less than 4 MPa in the width direction (TD direction), the slack of the separator due to tension fluctuations, etc., just by applying some tension. Abnormalities are likely to occur, resulting in defects such as wrinkles and streaks.

In the present invention, the standard deviation is preferably 5% or less with respect to the average value of the proof stress. When the standard deviation is 5% or less, it is possible to prevent the fluctuation of tension from being promoted and greatly swinging. As a result, the quality of the separator is further improved, and desired battery characteristics can be stably obtained in battery manufacture. Among these, the standard deviation is more preferably 4% or less with respect to the average value.
The standard deviation can be controlled to a desired degree by changing the draw ratio at the time of drawing.

  Furthermore, when the average value of stress at the proof stress exceeds 30 MPa in the MD direction and less than 4 MPa in the TD direction, or conversely, less than 6 MPa in the MD direction and exceeds 20 MPa in the TD direction, The above characteristics (physical properties) cannot be expressed, and winding failure such as meandering is caused. At this time, the standard deviation is preferably 5% or less with respect to the average value. When the standard deviation is 5% or less, it is possible to prevent the winding failure from being promoted.

  In the above, since the stress balance in the MD direction and the TD direction greatly affects the tension fluctuation during winding in the above, the stress range in each direction in which the stress balance can be achieved differs depending on the case. For example, the average value of stress at the proof stress in the MD direction is preferably in the range of 7 to 25 MPa, and the average value of stress at the proof stress in the TD direction is preferably in the range of 4.5 to 15 MPa.

Further, the elongation at the proof point, that is, the elongation percentage when stretched by the stress at the proof point (%; percentage of the elongation amount with respect to the elongation amount 100 at break) is 0.6 to 3%. It is preferable. If the elongation is within the above range, the tension fluctuation is further reduced. Specifically, since the elongation at the proof stress is 3% or less, the separator is not easily stretched or deformed by the tension during winding. Moreover, when the elongation at the proof stress is 0.6% or more, it is difficult to cause stress concentration of the wound body due to the tension fluctuation. Therefore, the winding can be performed with higher accuracy by setting the elongation within the above range.
Among them, the elongation at the proof stress is more preferably 0.7 to 2% for the same reason.
The elongation can be controlled by the stretching conditions of the polyolefin.

The control of the proof stress in the MD direction and the TD direction in the separator for a nonaqueous electrolyte secondary battery of the present invention is performed so as to satisfy a predetermined range by, for example, a method of controlling the draw ratio of the polyolefin porous substrate. Can do.
Among the above, (1) when the yield strength is controlled by controlling the stretching conditions, the stretching conditions may be 4 to 12 times in the MD direction and 5 to 20 times in the TD direction. More preferably, the MD direction draw ratio is 5 to 10 times, and the TD direction draw ratio is 5 to 15 times.
The stretching temperature is preferably in the range from 90 ° C. to the melting point of the polyolefin, and more preferably in the range from 100 ° C. to 120 ° C.

  Among the above, the separator for a nonaqueous electrolyte secondary battery of the present invention has a proof stress, an average value of stress in the MD direction is 7 to 25 MPa, and an elongation at the proof stress is 0.7 to 2. It is particularly preferable that the average value of the stress in the TD direction is 4.5 to 15 MPa and the elongation at the proof stress is 0.7 to 2%.

  As described above, the separator for a non-aqueous electrolyte secondary battery of the present invention has an advantage that roll winding can be performed stably and efficiently with a constant low tension corresponding to the stress at the proof stress. At this time, the stress variation of the proof stress and the variation of the stress and the elongation in the MD and TD directions of the separator are within a small range within 10% as standard deviation. As a result, tension fluctuations and associated stress fluctuations during winding can be kept small, and the winding can be performed more quickly and efficiently, so variation in the cycle characteristics of the shutdown function is suppressed and excellent heat resistance performance. Is obtained, and the battery characteristics become more stable. In particular, when a cylindrical battery is used, the short circuit resistance can be kept higher.

(Polyolefin porous substrate)
The separator for a non-aqueous electrolyte secondary battery of the present invention is configured by providing a polyolefin porous substrate containing polyolefin. Examples of the porous substrate include microporous membranes, nonwoven fabrics, papers, and other layers having a porous structure of a three-dimensional network, but in terms of achieving better fusion, A microporous membrane-like layer is preferable. Here, the microporous film-like layer (hereinafter, also simply referred to as “microporous film”) has a structure in which a large number of micropores are connected and these micropores are connected to each other. A layer that allows gas or liquid to pass from one surface to the other.
The microporous membrane is preferably a porous substrate that softens at 130 to 150 ° C., closes the porous voids, exhibits a shutdown function, and does not dissolve in the electrolyte of the nonaqueous electrolyte battery.

  Examples of the polyolefin in the present invention include polymers obtained by polymerizing monomers such as ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, and 1-octene (homopolymers and copolymers). Polymer, multistage polymer, etc.). Specific examples of the polyolefin include low density polyethylene, linear low density polyethylene, medium density polyethylene, high density polyethylene, ultrahigh molecular weight polyethylene, isotactic polypropylene, atactic polypropylene, polybutene, and ethylene propylene rubber. it can. These polymers can be used alone or in combination of two or more.

  The polyolefin porous substrate is mainly formed of polyolefin. Here, “mainly” means that the proportion of polyolefin in the porous substrate is 50% by mass or more, preferably 70% by mass or more, more preferably 90% by mass or more, and 100% by mass. % May mean.

As the polyolefin, a single type of polyolefin may be used or a plurality of types of polyolefins may be mixed and used depending on the desired purpose. Polyolefins, e.g., high density polyethylene such as density exceeds 0.94 g / cm ^3, low low density polyethylene than the density is 0.94 g / cm ^3, a weight average molecular weight 1,000,000 more than such ultra-high molecular weight polyethylene Is mentioned.
Specifically, for example, a mixture of high density polyethylene and low density polyethylene may be used as the polyolefin with emphasis on the shutdown behavior. Furthermore, a mixture of high-density polyethylene and ultra-high molecular weight polyethylene may be used by paying attention to improvement in mechanical properties such as strength, short circuit resistance or puncture strength. Furthermore, in view of heat resistance, a mixture of polyethylene and polypropylene can be used. Moreover, it is preferable that the said polyolefin contains a high density polyethylene from a viewpoint of reducing melting | fusing point of a polyolefin porous base material. The proportion of the high-density polyethylene in the polyolefin in the porous substrate is preferably 10% by mass or more, and more preferably 30% by mass or more.

Further, as the polyolefin, a modified polyolefin having a carboxyl group and / or a group derived from a carboxylic acid derivative is also suitable. Examples of modified polyolefins include those commercially available under the trade names such as “Modic” (registered trademark) manufactured by Mitsubishi Chemical Corporation and “Admer” (registered trademark) manufactured by Mitsui Chemicals, Inc. Examples thereof include “Modic-AP H511” and “Modic-AP L503” manufactured by Mitsubishi Chemical Corporation.
In this case, by selecting aramid as the heat-resistant resin used for the heat-resistant porous layer, particularly 30-70 equivalents / ton-polymer aramid of the amino group as a terminal group, the chemistry with the modified polyolefin is selected. The adhesive force between the porous substrate and the porous substrate is further improved by the mechanical affinity. Examples of such aramid include Cornex (manufactured by Teijin Techno Products) and Nomex (manufactured by DuPont).

  Among these, high-density polyethylene and medium-density polyethylene are preferably used from the viewpoint of increasing the film strength of the porous substrate and / or the strength of the separator. They can be used singly or as a mixture of plural kinds. From the viewpoint of improving the permeability and mechanical strength of the porous substrate, it is also preferable to use polyethylene alone.

Furthermore, from the viewpoint of improving the slit property of the separator, the porous base material has an ultrahigh molecular weight polyethylene having a weight average molecular weight (Dalton) of 700,000 or more, preferably 800,000 to 5,000,000, to the total mass of the porous base material. On the other hand, an embodiment containing 5 to 90% by mass, more preferably 10 to 90% by mass, and still more preferably 20 to 80% by mass is preferable.
Furthermore, from the viewpoint of improving the film strength of the porous base material and / or the strength of the separator, the porous base material has an ultrahigh molecular weight of 700,000 or more, preferably 800,000 to 3,000,000 in weight average molecular weight (Dalton). An embodiment in which polyethylene is contained in a range of preferably 5% by mass to 90% by mass with respect to the total mass of the porous substrate is preferable.

The weight average molecular weight (Dalton) of the polyolefin is preferably 50,000 or more, more preferably 100,000 or more. The upper limit is preferably 10 million, more preferably 3 million. When the weight average molecular weight is within the above range, the mechanical properties (breaking strength, scratch resistance, etc.) of the porous substrate or the separator can be improved.
Here, when several polyolefin is used, let the weight average molecular weight measured about each polyolefin be in the said range.
The weight average molecular weight (Dalton) of polyolefin is a molecular weight measured by gel permeation chromatography (hereinafter also referred to as GPC) and expressed in terms of polystyrene.

  Since the weight average molecular weight is not less than 50,000 (Dalton), the melt tension at the time of hot stretching is maintained high, good film-forming properties are ensured, or good entanglement is imparted. The strength of the quality base material can be increased. On the other hand, when the polyolefin solution is prepared at the time of film formation, the weight average molecular weight is 10 million (Dalton) or less, so that uniform solution preparation can be performed and the film formability, particularly the film thickness uniformity is improved. be able to. Furthermore, it is preferable that the weight average molecular weight is 3 million (Dalton) or less from the viewpoint of improving the uniformity of the formed film and reducing the stretching tension.

  The thickness of the polyolefin porous substrate is preferably 5 to 25 μm, more preferably 5 to 20 μm. When the thickness of the polyolefin porous substrate is 5 μm or more, the shutdown function is good, and when the thickness is 25 μm or less, when the separator for a non-aqueous electrolyte secondary battery including a heat-resistant porous layer is used, The thickness does not become too large, and the range where high electric capacity can be realized can be maintained.

  The porosity of the polyolefin porous substrate is preferably 30 to 80% from the viewpoints of permeability, mechanical strength, and handling properties. When the porosity is 30% or more, the permeability and the amount of electrolyte retained are appropriate. When the porosity is 80% or less, the mechanical strength as a base material when formed into a film can be maintained, and the shutdown function can be made to function with good responsiveness. The porosity is more preferably 40 to 60%.

The Gurley value (JIS P8117) of the polyolefin porous substrate 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 porous substrate is preferably 0.5 to ⁵ ohm · cm ² from the viewpoint of the load characteristics of the nonaqueous electrolyte secondary battery.
The puncture strength of the polyolefin porous substrate is preferably 250 g or more. When the puncture strength is 250 g or more, when a non-aqueous electrolyte battery is produced, it has excellent resistance to electrode irregularities and impacts, prevents the occurrence of pinholes and the like in the separator, and short-circuits the non-aqueous electrolyte secondary battery. Can be avoided more effectively.
The tensile strength of the polyolefin porous substrate is preferably 10 N or more. A tensile strength of 10 N or more is preferable in that the separator can be wound well so as not to damage the separator in producing the nonaqueous electrolyte secondary battery.

The polyolefin porous substrate preferably has a breaking strength of 10 N or more in both the MD direction and the TD direction, and the breaking elongation is preferably more than 50%.
By making the breaking strength 10N or more and the elongation at break exceeding 50%, the separator is not damaged when the separator is wound when manufacturing the non-aqueous electrolyte secondary battery. As a result, the fluctuation of the cycle characteristic of the shutdown function can be suppressed.
The breaking strength refers to the force when the separator is broken and stretched, and the breaking elongation refers to the amount of elongation when the separator is stretched and stretched.

-Polyolefin porous substrate manufacturing method-
Although there is no restriction | limiting in particular in the manufacturing method of the polyolefin porous base mentioned above, Specifically, it can manufacture by the method including the process of the following (1)-(6), for example.

(1) Preparation of polyolefin solution A solution in which polyolefin of a predetermined quantitative ratio is dissolved in a solvent is prepared. At this time, a solvent may be mixed to prepare a solution. 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 in the polyolefin solution is preferably 1 to 35% by mass, more preferably 10 to 30% by mass. When the concentration of the polyolefin solution is 1% by mass or more, the gel-like molded product obtained by cooling gelation can be maintained so as not to be highly swollen with a solvent, so that it is difficult to be deformed and the handleability is good. On the other hand, since the pressure during extrusion, which is 35% by mass or less, can be suppressed, the discharge amount can be maintained and the productivity is excellent. In addition, the alignment in the extrusion process is difficult to proceed, which is advantageous for ensuring stretchability and uniformity. The polyolefin solution is preferably used for filtration to remove foreign substances. There are no particular limitations on the filtration device, filter shape, mode, etc., and conventionally known devices and modes can be used. In this case, the hole diameter (filtration diameter) of the filter is preferably 1 μm or more and 50 μm or less from the viewpoint of filterability. When the hole diameter is 50 μm or less, the filterability is excellent and the foreign matter removal efficiency is good. Further, when the hole diameter is 1 μm or more, good filterability can be obtained, and productivity can be maintained high.

(2) Extrusion of polyolefin solution The prepared 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. In particular, when a volatile solvent and a non-volatile solvent are used in combination as the solvent, the cooling rate of the gel composition is preferably 30 ° C./min or more from the viewpoint of controlling the crystal parameters.

(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 the case of a non-volatile solvent, the solvent can be removed by squeezing out under pressure. The solvent need not be completely removed.

(4) Stretching of the gel-like composition Following 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-stage extending | stretching, and 4-stage extending | stretching.
The stretching temperature is preferably in the range of 90 ° C. or higher and lower than the melting point of polyolefin, more preferably 100 to 120 ° C. When the heating temperature is lower than the melting point, the gel-like molded product is difficult to dissolve, so that the stretching can be performed satisfactorily. Further, when the heating temperature is 90 ° C. or higher, the gel-like molded product is sufficiently softened, so that it is difficult to break the film during stretching, and stretching at a high magnification can be performed.
Moreover, although a draw ratio changes with thickness of a raw fabric, it is preferable to carry out at least 2 times or more in a uniaxial direction, Preferably it is 4 to 20 times. In particular, from the viewpoint of the effect of the present invention, the draw ratio is preferably 4 to 10 times in the machine direction (MD direction) and 6 to 15 times in the direction perpendicular to the machine direction (TD direction). Further, from the viewpoint of suitably improving charge / discharge cycle stability and short-circuit resistance, the stretching speed is preferably set to 1% / second or more and 200% / second or less. When the stretching speed is maintained in the range of 1% / second or more, good productivity can be obtained, which is suitable for industrial production. From this viewpoint, the stretching speed is more preferably selected from 150% / second to 5% / second, more preferably from 100% / second to 10% / second. After stretching, heat setting is performed as necessary to provide thermal dimensional stability. By repeating the stretching and heat setting two more steps or more, the heat shrinkability can be suppressed and the short-circuit resistance can be improved more suitably. From this viewpoint, it is preferable that the drawability ratio in the MD and / or TD direction at this time is relatively low, 1.5 to 3 times.

(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, and fluorinated hydrocarbons such as ethane trifluoride, Easily volatile compounds such as ethers such as diethyl ether and 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 admixture of two or more. Solvent extraction removes the solvent in the porous substrate to less than 1% by weight.

(6) Annealing of microporous film The microporous film is heat-set by annealing. The annealing is preferably performed in the temperature range of 80 to 150 ° C. from the viewpoint of the heat shrinkage rate. In the present invention, annealing is carried out at an annealing temperature of preferably 80 to 140 ° C., more preferably 90 to 135 ° C. in order to realize stress and elongation at a predetermined proof stress point in the tensile treatment. The annealing time is preferably 1 minute or more, more preferably 1 minute to 1 hour, from the viewpoint of reducing the heat shrinkage rate, and from a viewpoint of suppressing deformation of the porous substrate, the annealing time is a long length. Time annealing is preferred. In order to further reduce the heat shrinkage, the annealing time can be extended to about 1 to 5 hours.

(Heat resistant porous layer)
The separator for nonaqueous electrolyte secondary batteries of the present invention is provided on at least one side of the polyolefin porous substrate, and is provided with a heat resistant porous layer containing a heat resistant resin. Examples of the heat-resistant porous layer include microporous film-like, nonwoven fabric-like, paper-like, and other layers having a three-dimensional network-like porous structure, but more excellent heat resistance can be obtained. The layer is preferably a microporous membrane. A “microporous membrane layer” has a structure in which a large number of micropores are connected to each other and these micropores are connected, and gas or liquid can pass from one surface to the other. The layer that became.
Here, “heat resistance” refers to a property that does not cause melting or decomposition in a temperature range of less than 200 ° C.

-Heat resistant resin-
As the heat-resistant resin constituting the heat-resistant porous layer, a crystalline polymer having a melting point of 200 ° C. or higher or a polymer having no melting point but having a decomposition temperature of 200 ° C. or higher is suitable, and preferably a wholly aromatic polyamide , Polyimide, polyamideimide, polysulfone, polyketone, polyetherketone, polyetherimide, and at least one resin selected from the group consisting of cellulose.

The heat-resistant resin may be a homopolymer, and may contain some copolymer components in accordance with a desired purpose such as exhibiting flexibility. That is, for example, in a wholly aromatic polyamide, it is possible to copolymerize a small amount of an aliphatic component, for example.
Furthermore, the heat-resistant resin is insoluble in the electrolyte solution and highly durable because it is highly durable. From the viewpoint of easily forming a porous layer and excellent in redox resistance, More preferred is polymetaphenylene isophthalamide, which is a meta-type wholly aromatic polyamide.

In the present invention, the molecular weight of the heat-resistant resin is preferably in a specific range from the viewpoint of cycle characteristics due to repeated charge and discharge, short circuit resistance, and dimensional stability of the separator during heating. This specific range varies slightly depending on the type of resin, especially the molecular weight of the repeating unit, but the average degree of polymerization (hereinafter simply referred to as the degree of polymerization) at which polymer entanglement is observed in the melt or concentrated solution of the resin. Or a degree of polymerization slightly higher than that.
Specifically, it is preferable that the number average molecular weight (Mn; Dalton) is a relatively low degree of polymerization of 10000 to 100,000. Furthermore, in the wholly aromatic polyamide, the range of 20,000 to 80,000 is preferable, the range of 20,000 to 70,000 is more preferable, and the range of 30,000 to 50,000 is more preferable. When the number average molecular weight (Mn) of the heat resistant resin is 10000 (Dalton) or more, the strength of the heat resistant porous layer can be maintained and peeling can be prevented. When Mn is 100,000 (Dalton) or less, the interfacial stress with the polyolefin porous substrate is kept low, and the surface property of the separator can be kept high.

  The heat-resistant porous layer can be formed on both sides or one side of the polyolefin porous substrate, but from the viewpoints of handling properties, durability, and the effect of suppressing thermal shrinkage, both sides of the polyolefin porous substrate are provided. The formed form is preferred.

  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.

  When the heat resistant porous layer is formed on both sides of the polyolefin porous substrate, the total thickness of the heat resistant porous layer is preferably 3 μm or more and 12 μm or less. When the heat resistant porous layer is formed only on one side of the polyolefin porous substrate, the thickness of the heat resistant porous layer is preferably 3 μm or more and 12 μm or less. Such a range of thickness is also preferable from the viewpoint of the effect of preventing liquid withering.

  The porosity of the heat-resistant porous layer in the present invention 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-
The heat-resistant porous layer in the present invention preferably contains at least one 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, The inorganic filler which consists of a metal hydroxide, a boron salt compound, or a clay mineral etc., 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 electrolyte 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 an endothermic reaction is the range of 200 to 400 degreeC, it is effective in preventing the heat_generation | fever of a nonaqueous electrolyte 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 filler.
In particular, the inorganic filler is preferably in the form of using a metal hydroxide from the viewpoints of flame retardant improvement effect, handling property, static elimination effect, battery durability improvement effect, and the like. Among these, the inorganic filler is preferably aluminum hydroxide or magnesium hydroxide.

  The average particle diameter of the inorganic filler is preferably in the range of 0.1 to 2 μm from the viewpoints of short circuit resistance at high temperature and moldability. From the said viewpoint, More preferably, they are 0.1 micrometer-1.5 micrometers, More preferably, they are 0.15 micrometer-1 micrometer.

  As content of the inorganic filler in a heat resistant porous layer, it is preferable that it is 50-95 mass% from a heat resistant improvement effect, a viewpoint of permeability and 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 ~
The method for producing the separator for a nonaqueous electrolyte secondary battery of the present invention is not particularly limited as long as the separator of the present invention having the above-described configuration can be produced. For the heat resistant porous layer, for example, the following (1) to (5) It is possible to manufacture through the process of).

(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 mass. Moreover, an inorganic filler is disperse | distributed to this as needed, and it is set as the slurry for coating. In dispersing the inorganic filler in the coating slurry, when the dispersibility of the inorganic filler is not preferable, a method of improving the dispersibility by surface-treating the inorganic filler with a silane coupling agent or the like is also applicable.

(2) Coating of slurry The slurry is coated on at least one surface of the polyolefin porous substrate. When forming a heat resistant porous layer on both surfaces of a polyolefin porous substrate, it is preferable from a viewpoint of shortening of a process to apply simultaneously on both surfaces of a substrate. Examples of the method for coating the slurry for coating include a knife coater method, a gravure coater method, a screen printing method, a Meyer bar method, a die coater method, a reverse roll coater method, an ink jet method, a spray method, and a roll coater method. . Among these, the reverse roll coater method is preferable from the viewpoint of uniformly forming a coating film. When simultaneously applying to both sides of the polyolefin porous substrate, for example, by applying the polyolefin porous substrate between a pair of Meyer bars, apply an excess coating slurry on both sides of the porous substrate, There is a method in which this is passed between a pair of reverse roll coaters to scrape off excess slurry and precisely weighed.
The slurry is preferably filtered prior to coating to remove fine foreign matters. There are no particular limitations on the shape of the filtration device and the filter, and the installation position, and a conventionally known device and filter can be installed and used at a predetermined position. The hole diameter (filtration diameter) of the filter is preferably 1 μm or more and 100 μm or less. When the hole diameter is 100 μm or less, the filterability is excellent and the foreign matter removal efficiency is good. Further, when the hole diameter is 1 μm or more, good filterability can be obtained, and productivity can be maintained high.

(3) Solidification of slurry The heat resistance of the heat-resistant resin is obtained by coagulating the heat-resistant resin by treating the substrate coated with the slurry with a coagulation liquid capable of coagulating the heat-resistant resin. A porous layer is formed. In solidification, it is preferable to suppress deformation of the porous substrate in the MD direction and the TD direction. By suppressing the deformation of the porous substrate, the heat resistant resin layer can be formed uniformly, and the stress at the proof stress and the elongation can be adjusted more suitably. Specifically, a method of applying a constant tension to the substrate coated with the coating slurry, a method of gripping both ends with a chuck, preferably a method of applying a constant low tension in the TD direction, etc. .
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 mass with respect to the coagulating liquid. If the amount of water is 40% by mass or more, the time required for solidifying the heat-resistant resin can be kept shorter, the solidification can be performed well, and the stress and elongation at the proof stress point do not become too large. Can be adjusted. In addition, when the amount of water is 80% by mass or less, the surface of the heat-resistant resin layer in contact with the coagulation liquid is not solidified too quickly, and the surface is well porous and the crystallization proceeds appropriately. The strength can be maintained, and the stress and elongation at the proof stress can be kept high. Furthermore, the cost for solvent recovery can be kept low.

(4) Removal of coagulating liquid The coagulating liquid is removed by washing with water.
(5) Drying Dry and remove water from the sheet. The drying method is not particularly limited, but the drying temperature is preferably 50 to 90 ° C., and in order to prevent dimensional change due to heat shrinkage, a method of contacting the roll, or both ends of the separator with a chuck or the like. It is preferable to apply a gripping method or the like. In the drying process, by suppressing the deformation in the MD direction and the TD direction, the heat-resistant resin layer can be obtained with a highly uniform thickness, and can be crystallized with a high degree of uniformity, so that the above-described physical properties are suitably achieved. be able to.

  The drying treatment time is preferably 2 minutes to 5 hours, more preferably 5 minutes to 3 hours, from the viewpoint of the thermal contraction rate of the separator. It is also preferable to carry out drying and heat treatment in an atmosphere at atmospheric pressure or lower. The processing time at this time can be suitably selected in the range of 1 minute to 10 hours.

  The shutdown temperature of the nonaqueous electrolyte secondary battery separator of the present invention is preferably 130 to 155 ° C. When the shutdown temperature is 130 ° C. or higher, the phenomenon that meltdown occurs at a low temperature can be prevented, which is preferable in terms of safety. Moreover, when the shutdown temperature is 155 ° C. or lower, it is possible to expect a safety function at various temperatures when the various materials are mounted on the battery. The shutdown temperature is preferably 135 to 150 ° C.

In the nonaqueous electrolyte secondary battery separator of the present invention, the total ratio of the thickness of the heat-resistant porous layer to the thickness of the polyolefin porous substrate is preferably in the range of 10 to 80%. When the total thickness is 10% or more, the short circuit resistance can be improved. On the contrary, when the total thickness is 80% or less, rapid expansion of the separator can be expected, and the separator is easily broken. That is, the short circuit resistance can be effectively expressed.
From the above points, the ratio of the total thickness of the heat-resistant porous layer to the thickness of the polyolefin porous substrate is preferably in the range of 15 to 70%, more preferably in the range of 20 to 60%. Preferably it is 25 to 50% of range.

The separator for a non-aqueous electrolyte secondary battery of the present invention includes a polyolefin porous substrate, and a heat resistant porous layer containing a heat resistant resin, which is disposed (preferably by coating) on at least one surface of the polyolefin porous substrate. From the viewpoint of the energy density of the nonaqueous electrolyte secondary battery, the thickness of the entire separator is preferably 30 μm or less.
In the separator for a nonaqueous electrolyte secondary battery of the present invention, when the heat resistant resin layer is formed by coating, the heat resistant resin layer is more closely bonded to the polyolefin porous substrate, and the heat shrinkage of the porous substrate, etc. The deformation and the elongation at the proof stress can be made within a suitable range for constituting the nonaqueous electrolyte secondary battery.

The porosity of the nonaqueous electrolyte secondary battery separator of the present invention is preferably 30 to 70% from the viewpoints of permeability, mechanical strength, and handling properties. More preferably, the porosity is 40% to 60%.
The Gurley value (JIS P8117) of the separator for a nonaqueous electrolyte secondary battery 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 nonaqueous electrolyte secondary battery separator of the present invention is preferably 1.5 to 10 ohm · cm ² from the viewpoint of load characteristics of the nonaqueous electrolyte secondary battery.
The puncture strength of the nonaqueous electrolyte secondary battery separator of the present invention is preferably 250 to 1000 g. When the puncture strength is 250 g or more, when a non-aqueous electrolyte battery is produced, it has excellent resistance to electrode irregularities and impacts, prevents the occurrence of pinholes and the like in the separator, and short-circuits the non-aqueous electrolyte secondary battery. Can be avoided more effectively.
The separator for a nonaqueous electrolyte secondary battery of the present invention preferably has a breaking strength of 10 N or more and a breaking elongation of 50% or more in both the MD direction and the TD direction. When the breaking strength is 10 N or more and the breaking elongation is 50% or more, it is easy to avoid breakage of the separator when winding a long separator in producing a nonaqueous electrolyte secondary battery.
The thermal shrinkage rate at 105 ° C. of the separator for a nonaqueous electrolyte secondary battery of the present invention is preferably 0.6 to 3%. When the thermal contraction rate is within this range, the shape stability and shutdown characteristics of the nonaqueous electrolyte secondary battery separator are balanced. The thermal contraction rate is more preferably 0.7 to 2%.

[Nonaqueous electrolyte secondary battery]
The non-aqueous electrolyte secondary battery of the present invention is a non-aqueous electrolyte secondary battery that obtains an electromotive force by doping or dedoping lithium, and uses the non-aqueous electrolyte secondary battery separator having the above-described configuration. And The non-aqueous electrolyte secondary battery has a structure in which a battery element in which a negative electrode and a positive electrode are opposed to 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 comprising 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, 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 comprising 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 the liquid withering by the separator, 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 the 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 Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples unless it exceeds the gist thereof. Unless otherwise specified, “part” is based on mass.

[Measuring method]
Each value in this example was determined according to the following method.
(1) Tensile treatment and proof stress (stress, elongation, etc.)
Ten sample pieces (n = 10) in the MD direction and the TD direction were cut out from the nonaqueous electrolyte secondary battery separator each having a size of 7 cm in length and 1.0 cm in width, and 10 according to the tension conditions shown below. A tensile treatment was performed on each sample piece. From the result, as shown in FIG. 1, a graph showing the relationship between stress and displacement was created to determine the proof stress, and the stress, elongation, and standard deviation at that time were calculated.
<Tensioning conditions>
・ Tensile testing machine: RTC-1225A (manufactured by A & D)
・ Chuck length: 5.0cm
・ Tensing speed: 20mm / min ・ Temperature: 25 ℃
・ Humidity: 65% RH
・ Sample size: width 1.0cm, length 7cm

(2) Molecular weight of polyolefin The weight average molecular weight and number average molecular weight of polyolefin were measured by gel permeation chromatography (GPC).
20 ml of a mobile phase for GPC measurement was added to 15 mg of the sample and completely dissolved at 145 ° C., followed by filtration with a stainless steel sintered filter (pore diameter: 1.0 μm). 400 μl of the filtrate was injected into the apparatus for measurement, and the weight average molecular weight and number average molecular weight of the sample were determined.
-Apparatus: Gel permeation chromatograph Alliance GPC2000 (manufactured by Waters)
Column: TSKgel GMH6-HT × 2 + TSKgel GMH6-HT × 2 (manufactured by Tosoh Corporation)
Column temperature: 140 ° C
・ Mobile phase: o-dichlorobenzene ・ Detector: Differential refractometer (RI)
・ Molecular weight calibration: monodisperse polystyrene (manufactured by Tosoh Corporation)

(3) Film thickness The thickness of the non-aqueous electrolyte secondary battery separator (total thickness of the polyolefin microporous film and heat-resistant porous layer) and the thickness of the polyolefin microporous film are determined by a contact-type film thickness meter (manufactured by Mitutoyo Corporation). It was determined by measuring 20 points and averaging them. Here, the contact terminal used was a cylindrical one having a bottom surface of 0.5 cm in diameter.
(4) Porosity The porosity of the nonaqueous electrolyte secondary battery separator and the polyolefin microporous membrane 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).
(5) Gurley value The Gurley value of the separator for a nonaqueous electrolyte secondary battery and the polyolefin microporous membrane was determined according to JIS P8117.

(6) Membrane resistance The membrane resistance of the polyolefin microporous membrane was determined by the following method.
Cut the sample to a size of 2.6 cm × 2.0 cm. A sample cut out in a methanol solution (methanol: manufactured by Wako Pure Chemical Industries, Ltd.) in which 3% by mass of a nonionic surfactant (Emulgen 210P manufactured by Kao Corporation) is dissolved is immersed in air and dried. An aluminum foil with a thickness of 20 μm 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 an electrolytic solution (manufactured by Kishida Chemical Co., Ltd.) in which 1M LiBF ₄ is mixed with a mixed solvent of propylene carbonate (PC) / ethylene carbonate (EC) (PC / EC = 1/1 [mass ratio]). 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 this 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) Puncture strength The puncture strength of the separator for a nonaqueous electrolyte secondary battery and the polyolefin microporous membrane was measured using a KES-G5 handy compression tester manufactured by Kato Tech Co., Ltd., with a radius of curvature of 0.5 mm and a puncture speed of 2 mm. The puncture test was conducted under the conditions of / sec, and the maximum puncture load was defined as the puncture strength. Here, the sample was fixed by sandwiching a silicone rubber packing in a metal frame (sample holder) having a hole of φ11.3 mm.
(8) Heat shrinkage rate The heat shrinkage rate of the separator for a nonaqueous electrolyte secondary battery and the polyolefin microporous membrane is measured by heating at 105 ° C. for 1 hour in the MD and TD directions of the sample, and averaging the values. Determined by
(9) Tensile strength The tensile strength of the polyolefin microporous membrane was measured on a sample cut into 10 mm x 100 mm using a tensile tester (manufactured by A & D, RTC-1225A) under the conditions of a load cell load of 5 kgf and a distance between chucks of 50 mm. did.

(10) Winding property The winding property of the separator for the nonaqueous electrolyte secondary battery is determined by using a winding machine KMW-2BY manufactured by Minato Seisakusho Co., Ltd. The state in which the separator was wound by adjusting to 50 mm / second was judged visually. The determination was made according to the following criteria. The evaluation was performed by using a model electrode having a length of 60 cm and forming a separator for a nonaqueous electrolyte secondary battery into a size having a length of 50 cm.
<Standard>
A: Defects such as streaks and wrinkles were hardly recognized and were good.
○: The occurrence of defects such as streaks and wrinkles was slightly recognized, but it was in a practically unaffected level (passed).
X: Defects such as streaks and wrinkles clearly appeared, and were in a practically troublesome state (failed).

(11) Slit property The slit property of the non-aqueous electrolyte secondary battery separator was evaluated by using a slitter TH4C manufactured by Nishimura Seisakusho Co., Ltd. and visually observing the slit and roll at a running speed of 60 m / min. In the evaluation, when the occurrence of wrinkles, streaks and winding deviations was remarkable, the result was poor (×), and when wrinkles, streaks and winding deviations were not found or were slightly recognized, there was no problem in practical use ( ○), the case where it was difficult to recognize the occurrence of wrinkles, streaks, and winding deviation was judged as a good pass (（).

(12) Shutdown temperature The shutdown temperature (SD temperature) of the polyolefin microporous membrane was determined by the following method.
A circular sample having a diameter of 19 mm is punched out from a polyolefin microporous membrane having polymetaphenylene isophthalamide layers on both sides, and 3% by mass of the obtained sample is dissolved with a nonionic surfactant (Emulgen 210P, manufactured by Kao Corporation). Was immersed in a methanol solution (methanol: Wako Pure Chemical Industries, Ltd.) and air-dried. This sample was sandwiched between two circular stainless steel plates (SUS plates) having a diameter of 15.5 mm used as electrode plates. Next, the sample was impregnated with an electrolytic solution (made by Kishida Chemical Co., Ltd.) in which 1M LiBF ₄ was mixed with a mixed solvent of propylene carbonate (PC) / ethylene carbonate (EC) (PC / EC = 1/1 [mass ratio]). And sealed 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 was 10 ³ ohm · cm ² or more was defined as the shutdown temperature.

(13) Charging / discharging cycle characteristics 89.5 parts by mass of lithium cobalt oxide (LiCoO ₂ , manufactured by Nippon Kagaku Kogyo Co., Ltd.), 4.5 parts by mass of acetylene black, and polyvinylidene fluoride (PVdF; hereinafter the same) are in dry mass. A positive electrode paste was prepared using a 6 mass% N-methyl-2-pyrrolidone (NMP; hereinafter the same) solution of PVdF in an amount of 6 parts by mass. The obtained paste was applied onto an aluminum foil having a thickness of 20 μm, dried, and then pressed to obtain a positive electrode having a thickness of 97 μm.
Next, 87 mass parts of mesophase carbon microbeads (MCMB, manufactured by Osaka Gas Chemical Co., Ltd.) as negative electrode active material, 3 mass parts of acetylene black, and 6 mass% of PVdF in an amount such that PVdF is 6 mass parts by dry mass. An NMP solution was used to produce a negative electrode agent paste. The obtained paste was applied on a copper foil having a thickness of 18 μm, dried, and then pressed to prepare a negative electrode having a thickness of 90 μm.
10 button batteries (CR2032) having an initial capacity of about 4.5 mAh are sandwiched between the positive electrode and the negative electrode obtained above, and separators prepared in the following examples and comparative examples are impregnated with an electrolyte. Was made. At this time, 1 M LiPF ₆ was blended with a mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC) and methyl ethyl carbonate (MEC) (EC / DEC / MEC = 1/2/1 [mass ratio]). An electrolytic solution was used.
The produced 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 100th cycle was divided by the initial capacity, and the capacity retention rate when the charge and discharge were repeated The average value and the fluctuation range (%) were evaluated as cycle characteristics.
In the evaluation, when the capacity retention rate is 85% or more, when the fluctuation range is 7% or less, it is judged that there is no practical problem, and it is judged as “◯ (pass)”, and the capacity retention rate is less than 85% The cases where the fluctuation range exceeded 7% were judged to be practically hindered, and “x (failed)” was judged.

(14) Short circuit resistance Ten button batteries similar to the above (13) were prototyped, charged to 4.2 V, and then placed in an oven to place 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 this time, when there was a battery voltage drop suddenly confirmed at around 150 ° C, the short-circuit resistance was evaluated as poor (x), and there was no significant change in the voltage of all the batteries at 150 ° C. The short circuit resistance was evaluated as good (◯).

(Reference Example 1): Polymerization of poly (metaphenylene terephthalamide) by the interfacial polymerization method 160.5 g of isophthalic acid chloride was dissolved in 1120 ml of tetrahydrofuran, and a solution of 85.2 g of metaphenylenediamine in 1120 ml of tetrahydrofuran was stirred. When gradually added as a trickle, 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 standing, the separated transparent aqueous solution layer was removed, and filtration was performed to obtain 185.3 g of a white polymer of poly (metaphenylene isophthalamide) (hereinafter sometimes abbreviated as PMIA). The number average molecular weight of the obtained PMIA was 20,000.

(Reference Example 2): Preparation of polyolefin microporous membrane Hi-Zex Million 340M and Hi-Zex Million 030S (both manufactured by Mitsui Chemicals, Inc.) were mixed at a ratio (mass ratio) of 20/80, respectively. A polyolefin solution was prepared by dissolving in a mixed solvent of liquid paraffin (manufactured by Matsumura Oil Research Co., Ltd .; Smoyl P-350P; boiling point 480 ° C.) and decalin so as to be 30% by mass and filtering with a filter having a pore size of 5 μm. The composition of this polyolefin solution was polyolefin: liquid paraffin: decalin = 30: 45: 25 (mass ratio).
The obtained polyolefin 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 biaxially stretched by sequentially performing longitudinal stretching and transverse stretching. Here, in the longitudinal stretching, the stretching ratio was 5.5 times and the stretching temperature was 90 ° C. In the transverse stretching, the stretching ratio was 11.0 times, the stretching temperature was 105 ° C, and the surface stretching ratio was 60.5 times. 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 produced the polyolefin microporous film. At this time, there was no particular problem in the operations of film formation, stretching, and post-treatment, and the microporous film could be produced satisfactorily. The characteristics of the membrane are shown in Table 1 below.

(Reference Example 3)
In Reference Example 2, a polyolefin microporous membrane was produced in the same manner as in Reference Example 2, except that the longitudinal stretching and the lateral stretching were 8 times and 7.5 times, respectively, and the surface stretching ratio was 60 times. At this time, there was no particular problem in the operations of film formation, stretching, and post-treatment, and the microporous film could be produced satisfactorily. The characteristics of the membrane are shown in Table 1 below.

(Reference Example 4)
In Reference Example 2, a polyolefin microporous membrane was prepared in the same manner as Reference Example 2, except that the longitudinal stretching and lateral stretching were 3.8 times and 16 times, respectively, and the surface draw ratio was 60.8 times. did. At this time, there was no particular problem in the operations of film formation, stretching, and post-treatment, and the microporous film could be produced satisfactorily. The characteristics of the membrane are shown in Table 1 below.

(Reference Example 5)
In Reference Example 2, a polyolefin microporous membrane was produced in the same manner as in Reference Example 2, except that the longitudinal stretching and the lateral stretching were 8 times and 3.8 times, respectively, and the surface stretching ratio was 30.4 times. did. At this time, there was no particular problem in the operations of film formation, stretching, and post-treatment, and the microporous film could be produced satisfactorily. The characteristics of the membrane are shown in Table 1 below.

Example 1
PMIA obtained in Reference Example 1 and aluminum hydroxide having an average particle diameter of 0.8 μm (made by Showa Denko KK; H-43M) are used in a mass ratio of 25:75 by mass ratio of the aluminum hydroxide and the PMIA. And adjusting to a PMIA concentration of 5.5% by mass while mixing with a mixed solvent having a mass ratio of dimethylacetamide (DMAc) and tripropylene glycol (TPG) of 50:50. A slurry for coating was obtained.
A pair of Meyer bars (count # 6) were opposed to each other with a clearance of about 20 μm. Put an appropriate amount of the slurry for coating on a Mayer bar and pass the polyethylene microporous film of Reference Example 2 between a pair of Mayer bars while rotating in the reverse direction of the traveling direction. Coated. The both ends of the polyethylene microporous film after coating are gripped with a chuck so as not to loosen, and the polyethylene microporous film after coating is coagulated with water: DMAc: TPG = 50: 25: 25 by mass ratio. It was immersed in (40 ° C.). Next, washing with water and drying were carried out while gripping with a chuck, and heat-resistant porous layers of 2 μm each on the front and back sides were formed on both surfaces (front and back surfaces) of the polyethylene microporous membrane, thereby forming a separator for a non-aqueous electrolyte battery.

The obtained separator has a total thickness of 16 μm and possesses a proof stress by tensile treatment. The proof stress in the MD direction is 9 MPa, the stress in the TD direction is 5 MPa, and the elongation at the proof stress is in the MD direction. The stress was MD4%, TD5%, and the elongation was 10% or less. Further, the slit property and winding property of this separator were both “◎”.
Moreover, about the physical property of the obtained separator, a result is put together and it shows in following Table 2. FIG.

(Example 2)
In Example 1, a separator for a nonaqueous electrolyte battery was obtained in the same manner as in Example 1 except that the polyethylene microporous membrane of Reference Example 3 was used. The obtained separator has a total thickness of 16 μm and possesses a proof stress in the tensile treatment, the proof stress in the MD direction is 16 MPa, the stress in the TD direction is 6 MPa, and the elongation at the proof stress is in the MD direction. The standard deviation was 1.1%, 0.9% in the TD direction, and the stress was MD5%, TD5%, and the elongation was 10% or less. Further, the slit property and winding property of this separator were both “◯”. The physical properties of the obtained separator are summarized in Table 2 below.

(Comparative Example 1)
In Example 1, a separator for a non-aqueous electrolyte battery was obtained in the same manner as in Example 1 except that the polyethylene microporous membrane of Reference Example 4 was used. The obtained separator has a total thickness of 16 μm and possesses a proof stress by tensile treatment. The proof stress in the MD direction is 7 MPa, the stress in the TD direction is 15 MPa, and the elongation at the proof stress is in the MD direction. 3.1%, 0.5% in the TD direction, and their standard deviations were stress of MD 10%, TD 6%, and elongation of 15% or less. Further, both the slit property and the winding property of this separator were “x”. The physical properties of the obtained separator are summarized in Table 2 below.

(Comparative Example 2)
In Example 1, a separator for a nonaqueous electrolyte battery was obtained in the same manner as in Example 1 except that the polyethylene microporous membrane of Reference Example 5 was used. The obtained separator has a total thickness of 16 μm and possesses a proof stress by tensile treatment. The proof stress in the MD direction is 5 MPa, the stress in the TD direction is 3.5 MPa, and the elongation at the proof stress is MD. The direction deviation was 2.8%, the TD direction was 3.5%, and the standard deviation was MD10%, TD15%, and elongation 15% or less. Further, both the slit property and the winding property of this separator were “x”. The physical properties of the obtained separator are summarized in Table 2 below.

  As shown in Table 2, the example was superior to the comparative example in cycle characteristics and short-circuit resistance when a lithium secondary battery was used.

  The non-aqueous electrolyte secondary battery separator of the present invention is excellent in good cycle stability and short-circuit resistance, has high production efficiency, and can be suitably used for lithium battery applications.

Claims (3)

A polyolefin porous substrate containing polyolefin and having pores therein, and a heat-resistant porous layer provided on at least one side of the polyolefin porous substrate and containing a heat-resistant resin, satisfying the following conditions: The average value of stress at a plurality of proof stress points measured in the longitudinal direction when the tensile treatment is performed is 6 to 30 MPa, and at a plurality of proof stress points measured in the width direction orthogonal to the longitudinal direction. The separator for nonaqueous electrolyte secondary batteries whose average value of stress is 4-20 Mpa.
<Condition>
・ Tensing speed: 20mm / min ・ Temperature: 25 ℃
・ Humidity: 65% RH
・ Sample size: width 1.0cm, length 7cm   The separator for a non-aqueous electrolyte secondary battery according to claim 1, wherein the elongation of stress at the proof stress in the longitudinal direction and the width direction is 0.6 to 3%, respectively.   A positive electrode, a negative electrode, and the separator for a nonaqueous electrolyte secondary battery according to claim 1 disposed between the positive electrode and the negative electrode, and obtaining an electromotive force by doping or dedoping of lithium. Non-aqueous electrolyte secondary battery.