JP2007095575A - Separator for non-aqueous electrolyte secondary battery, method for manufacturing non-aqueous electrolyte secondary battery, and non-aqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a separator with which a non-aqueous electrolyte secondary battery not having high electric resistance can be obtained since a microporous membrane and a heat-resisting porous body are adhered in a body in order to get heat resistance, hence maintaining of opening of the micropores of the membrane. <P>SOLUTION: The separator for the non-aqueous electrolyte secondary battery is formed by adhering the microporous membrane made of resin having a melting point of 100 to 180°C to the heat-resisting porous body using adhering resin having a melting point less than that of the resin which forms the microporous membrane, and has gas permeability decreasing rate (Gd) of 5% or less wherein the micropores of the membrane are not closed. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

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

  In recent years, portable information devices including personal computers, mobile phones, portable information terminals, and the like have been widely used. Since these devices as multimedia are desired to be multifunctional, secondary batteries used for power sources are required to have a small capacity, light weight, large capacity, that is, high energy density. Yes. Lithium ion secondary batteries are expected as secondary batteries that can satisfy such requirements.

  In this lithium ion secondary battery, since the inherent energy is large, high safety is required in the event of an abnormality such as an internal short circuit or external short circuit. For this safety measure, a polyolefin microporous membrane is used as a separator. Has been. This is because this polyolefin-based microporous film is considered to have a function (shutdown function) that is made non-porous at the time of abnormal heat generation and does not flow electricity. If abnormal heat generation does not stop even if such safety measures are taken, the polyolefin microporous membrane may break, causing the electrodes to come into contact with each other, resulting in a short circuit, which may ignite.

  Therefore, in order to improve the heat resistance of the separator and enhance the safety of the lithium ion secondary battery, it has been proposed to integrate the polyolefin microporous film with the heat resistant porous body. For example, “a separator for a lithium ion secondary battery characterized by comprising a polyolefin porous membrane and a polyester resin porous membrane” (Patent Document 1) or “a heat-resistant barrier film and a liquid retaining layer film are bonded. Has been proposed, and a piercing strength is 400 gf or more. "(Patent Document 2) has been proposed.

  However, as a method for integrating with the heat-resistant porous body in order to improve the heat resistance of the separator, a method using an adhesive or a method using thermal fusion is disclosed, but according to the former method using an adhesive, the adhesive Clogged the micropores of the polyolefin-based microporous membrane, resulting in a problem that the electrical resistance was increased. On the other hand, according to the method by thermal fusion, the thermal fusion force of the polyolefin microporous membrane is inevitably used due to the relationship of the constituent resins. Closed, and in this case, there was a problem that the electrical resistance was increased.

JP 2002-190291 A (claims, paragraph number 0016, etc.) JP 2004-363048 A (claims, paragraph number 0054, etc.)

  The present invention has been made to solve the above problems, and the microporous membrane and the heat-resistant porous body are bonded and integrated so as to be excellent in heat resistance, and the micropores of the microporous membrane are maintained. It is an object of the present invention to provide a separator that can provide a non-aqueous electrolyte secondary battery that does not increase in electrical resistance, and to provide a method for manufacturing the separator, and a non-aqueous electrolyte secondary battery including the separator. And

The invention according to claim 1 of the present invention is such that “a microporous film made of a resin having a melting point of 100 ° C. to 180 ° C. and a heat-resistant porous body are bonded by an adhesive resin having a melting point lower than that of the resin constituting the microporous film”. A separator for a non-aqueous electrolyte secondary battery, which is an integrated separator for a non-aqueous electrolyte secondary battery and has a gas permeability resistance reduction rate (Gd) defined below of 5% or less.
Gd = {(Ga−Gb) / Gb} × 100
Here, Gd is the air resistance reduction rate (%), Ga is the air resistance (s) of the nonaqueous electrolyte secondary battery separator, and Gb is the heat resistant porous material from the nonaqueous electrolyte secondary battery separator. It means the air permeability resistance (s) of the microporous membrane from which the adhesive resin has been removed.

The invention according to claim 2 of the present invention is “the separator for a non-aqueous electrolyte secondary battery according to claim 1, wherein the adhesive resin amount is 0.01 to 4 g / m ² ”.

  The invention according to claim 3 of the present invention is “the separator for a non-aqueous electrolyte secondary battery according to claim 1, wherein a heat shrinkage rate at 150 ° C. is 10% or less.” It is.

  The invention according to claim 4 of the present invention is “(1) a microporous film made of a resin having a melting point of 100 ° C. to 180 ° C., a heat-resistant porous body, and an adhesive resin having a melting point lower than that of the resin constituting the microporous film. A preparation step of preparing an emulsion, (2) a charging step of charging the adhesive resin emulsion unipolarly, (3) an applying step of applying the charged adhesive resin emulsion to the microporous membrane and / or heat-resistant porous body, (4) A non-aqueous electrolyte secondary comprising: a laminating step of laminating an adhesive resin emulsion between the microporous membrane and the heat-resistant porous body; and (5) an adhering step of adhering by the action of the adhesive resin emulsion Manufacturing method of battery separator. "

  The invention according to claim 5 of the present invention is the “manufacturing of the separator for a non-aqueous electrolyte secondary battery according to claim 4, characterized in that, in the applying step, an adhesive resin emulsion is applied to the heat-resistant porous body. Method. "

  The invention according to claim 6 of the present invention is as follows. “Manufacturing of a separator for a non-aqueous electrolyte secondary battery according to claim 4 or 5, wherein an average primary particle diameter of the adhesive resin is 1 μm or less. Method. "

  The invention according to claim 7 of the present invention is “a nonaqueous electrolyte secondary battery including the separator for a nonaqueous electrolyte secondary battery according to any one of claims 1 to 3”.

  The invention according to claim 1 of the present invention is a nonaqueous electrolyte that is excellent in heat resistance and can improve the safety of a nonaqueous electrolyte secondary battery because a heat resistant porous body is bonded and integrated to a microporous membrane. It is a separator for secondary batteries (hereinafter, sometimes simply referred to as “separator”). In addition, an adhesive resin having a melting point lower than that of the microporous membrane is used, and the rate of decrease in the air permeability resistance is as low as 5% or less, and the adhesive is integrated without blocking the micropores of the microporous membrane. Therefore, the electrical resistance of the nonaqueous electrolyte secondary battery does not increase.

In the invention according to claim 2 of the present invention, the amount of the adhesive resin is a small amount of 0.01 to 4 g / m ² , so that the microporous membrane is tightly bonded and integrated without closing the micropores of the microporous membrane. is there.

  The invention according to claim 3 of the present invention is excellent in heat resistance with a heat shrinkage rate at 150 ° C. of 10% or less, and thus can improve the safety of the non-aqueous electrolyte secondary battery.

  In the invention according to claim 4 of the present invention, the adhesive resin emulsion can be interspersed by charging the adhesive resin emulsion to a single polarity and electrostatically repelling it, thereby closing the micropores of the microporous membrane. It is possible to bond and integrate without any problem. Therefore, it is possible to manufacture a separator that has excellent heat resistance and does not increase the electrical resistance of the nonaqueous electrolyte secondary battery.

  In the invention according to claim 5 of the present invention, since the adhesive resin emulsion is applied to the heat-resistant porous body, the adhesive resin emulsion concentrates on the heat-resistant porous body constituting material and is bonded and integrated. However, since a film is not formed, it is easy to manufacture a separator that does not block the micropores of the microporous membrane and does not increase the electrical resistance of the nonaqueous electrolyte secondary battery.

  In the invention according to claim 6 of the present invention, since the average primary particle diameter of the adhesive resin is 1 μm or less, it is more likely to be concentrated and scattered on the microporous film or the heat-resistant porous body, and an extremely small amount of the adhesive resin Therefore, it is easy to manufacture a separator that does not close the micropores of the microporous membrane and does not increase the electrical resistance of the nonaqueous electrolyte secondary battery.

  Since the invention according to claim 7 of the present invention includes the separator as described above, the safety is high and the electrical resistance is low.

  In the separator of the present invention, a microporous film made of a resin having a melting point of 100 to 180 ° C. is used so as to have a function (shutdown function) that prevents pores from flowing when abnormal heat is generated. If it is made of a resin having a melting point of less than 100 ° C., the shutdown function may be activated even in cases other than abnormal heat generation, and if it is made of a resin having a melting point exceeding 180 ° C., it becomes difficult to suppress abnormal heat generation. More preferably, a microporous film made of a resin having a melting point of 110 to 170 ° C. is used.

  The microporous membrane-constituting resin having such a melting point is not particularly limited as long as it has a melting point of 100 to 180 ° C. and does not dissolve in the electrolytic solution. For example, low density polyethylene, high density Examples thereof include polyethylene such as polyethylene, linear low-density polyethylene, and ultrahigh molecular weight polyethylene, and polyolefin resins such as polypropylene. The microporous membrane may be composed of two or more types of resins having a melting point of 100 to 180 ° C. instead of one type of resin.

  In the separator of the present invention, a microporous film is used so that it has excellent electrical insulation, as well as excellent ion permeability and low electrical resistance. "Means a porous membrane having an average flow pore size measured by the bubble point method of 3 µm or less, preferably 1 µm or less, more preferably 0.1 µm or less. The lower limit of the average flow pore size is not particularly limited as long as the pore size does not hinder the permeation of ions, but about 0.001 μm is appropriate. The “melting point” in the present invention refers to a temperature that gives a maximum value of a melting endothermic curve obtained by heating from room temperature at a temperature rising temperature of 10 ° C./min using a differential scanning calorimeter.

  In addition, the thickness of the “microporous membrane” used in the present invention is preferably 50 μm or less, more preferably 30 μm or less, in order to improve the volume energy density of the battery. The lower limit of the thickness only needs to be such that the electrode does not break through the separator when the battery is assembled, and about 3 μm is considered appropriate. The “thickness” in the present invention means a thickness measured with a micrometer (JIS B 7502 outer micrometer 0 to 25 mm electronic digital display) specified in JIS C 2318.

  In addition to the microporous membrane as described above, the separator of the present invention is excellent in heat resistance by including a heat-resistant porous material, prevents membrane breakage of the microporous membrane, and prevents contact between electrodes. It increases the safety of water electrolyte secondary batteries. The “heat-resistant porous body” in the present invention is composed of only a resin having a melting point higher than the melting point of the microporous membrane constituent resin or the melting point of the microporous membrane constituent resin so as to prevent shrinkage and breakage of the microporous membrane. It consists only of a resin having a higher softening point, or only a resin having a carbonization temperature higher than the melting point of the microporous film-constituting resin, or is composed of two or more kinds of these resins.

  The constituent resin of the heat-resistant porous body varies depending on the resin constituting the microporous membrane, and is not particularly limited. However, the resin constituting the heat-resistant porous body can be effectively prevented from breaking the microporous membrane. The melting point, softening point, or carbonization temperature is preferably 20 ° C. or more, more preferably 40 ° C. or more higher than the melting point of the resin having the highest melting point among the microporous membrane constituent resins. For example, the heat-resistant porous material can be composed of one or more types such as polypropylene, polyester, polyimide, polyethersulfone, polyacrylonitrile, polyvinyl alcohol, polyphenylene sulfide, aromatic polyamide, liquid crystal polyester, and the like. Among these, it is preferable to contain polyacrylonitrile which is excellent in oxidation resistance and excellent in affinity with the electrolytic solution.

  The “softening point” in the present invention refers to the starting point of the melting endotherm curve in the DSC curve obtained by heat flux differential running calorimetry (DSC, temperature rising temperature 10 ° C./min) specified in JIS K7121. The “carbonization temperature” refers to the mass decrease start temperature in the TG curve obtained by thermogravimetry specified in JIS K 7120.

  This heat-resistant porous body is a porous body that does not inhibit ion permeation and has a low electrical resistance, but its form is not limited. For example, it can be in the form of a porous film, non-woven fabric, woven fabric or the like. Among these, it is preferable that the non-woven fabric is excellent in electrolytic solution retention.

  The thickness of the heat-resistant porous material used in the present invention is not particularly limited, but is preferably 30 μm or less, more preferably 20 μm or less, and still more preferably for improving the volume energy density of the battery. 10 μm or less. The lower limit of the thickness of the heat-resistant porous body is not particularly limited, but about 3 μm is appropriate from the viewpoint of the handleability of the heat-resistant porous body.

  The pore size of the heat-resistant porous material used in the present invention is not particularly limited, but in order to suppress the generation of lithium dendrites, the average flow pore size measured by the bubble point method is preferably 10 μm or less, more preferably Is 5 μm or less, more preferably 1 μm or less. The lower limit of the pore diameter of the heat-resistant porous material is considered to be about 0.001 μm from the viewpoint of ion permeability.

  In the separator of the present invention, the microporous film and the heat-resistant porous body as described above are bonded by an adhesive resin having a melting point lower than that of the resin constituting the microporous film (hereinafter, sometimes referred to as “low melting point adhesive resin”). It is in an integrated state. In the separator of the present invention, since the low melting point adhesive resin is used, it can be in an integrated state without closing the micropores of the microporous membrane. This low melting point adhesive resin may have a melting point lower than that of the microporous film constituting resin (the resin having the lowest melting point in the case of two or more kinds of resins). It is preferably 10 ° C. or more, more preferably 20 ° C. or more. The low melting point adhesive resin varies depending on the resin constituting the microporous film, and is not particularly limited. For example, ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, ethylene-vinyl acetate copolymer , Ethylene copolymers such as ethylene-vinyl alcohol copolymer, polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinylidene fluoride-tetrafluoroethylene copolymer, polyvinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer Coalescence etc. can be used.

The separator of the present invention is in a state in which the microporous film and the heat-resistant porous body are bonded and integrated with the low melting point adhesive resin as described above. However, if the amount of the low melting point adhesive resin is large, the microporous film is formed with the low melting point adhesive resin. would have micropores are closed in, the electric resistance is high, a low melting point adhesive resin amount is preferably at 4g / m ² or less, more preferably at 2 g / m ² or less, 1 g / m ² or less More preferably. On the other hand, it is preferably 0.01 g / m ² or more, and more preferably 0.03 g / m ² or more so that the microporous membrane and the heat-resistant porous body are firmly bonded and integrated.

The separator of the present invention is in a state in which the microporous film and the heat-resistant porous body are bonded and integrated with a low melting point adhesive resin as described above, but the air resistance reduction rate (Gd) defined below is 5% or less. It is. As is clear from the following definition, the rate of decrease in the air permeability resistance is as low as 5% or less. This means that the state of the microporous film has not changed before and after the integration of the microporous film, that is, the microporous film. This means that the micropores are not blocked. Therefore, the rate of decrease in air permeability resistance of the separator of the present invention is preferably 3% or less, and more preferably 1% or less.
Gd = {(Ga−Gb) / Gb} × 100
Here, Gd is the air resistance reduction rate (%), Ga is the air permeability resistance (s) of the separator, and Gb is the air resistance of the microporous membrane obtained by removing the heat-resistant porous material and the adhesive resin from the separator ( s), respectively. The air resistance is measured five times using a Gurley tester (B-type) specified in JIS P 8117: 1998, and is an arithmetic average value of the air resistance. Further, in order to remove the heat-resistant porous material and the adhesive resin from the separator, the heat-resistant porous material is peeled off from the separator and then ultrasonically cleaned in a state immersed in ethyl alcohol.

The separator of the present invention is excellent in heat resistance, and it is preferable that the thermal shrinkage rate at 150 ° C. is 10% or less so that the electrodes do not short-circuit due to thermal contraction of the separator. More preferably, it is 7% or less, More preferably, it is 5% or less. In addition, the measurement of this thermal contraction rate is performed by the following procedure, and means a calculated value.
From the separator, a test piece having a length of 200 mm in the longitudinal direction (production direction) and 40 mm in the width direction (direction perpendicular to the longitudinal direction) was taken, and the test piece was obtained by two quartz glass plates (thickness: 5 mm). In a state of being sandwiched between, it is left in an oven heated to 150 ° C. After heating at the said temperature for 30 minutes, a test piece is taken out from the quartz glass plate, the length in the longitudinal direction of the test piece after heating is measured, and the thermal shrinkage rate is calculated by the following formula.
L = {(L0−L1) / L0} × 100
Here, L means the heat shrinkage rate (%), L0 means the initial length (= 200 mm) in the longitudinal direction of the test piece, and L1 means the length (mm) after the test piece is heated.

  In addition, the thickness of the separator of the present invention is preferably 50 μm or less, more preferably 30 μm or less so as not to reduce the volume energy density of the battery.

  Such a separator of the present invention includes, for example, (1) a microporous film made of a resin having a melting point of 100 ° C. to 180 ° C., a heat-resistant porous body, and an adhesive resin emulsion having a lower melting point than the resin constituting the microporous film. (2) Charging step for charging the adhesive resin emulsion to a single polarity, (3) Applying step for applying the charged adhesive resin emulsion to the microporous membrane and / or heat-resistant porous body, (4) Fine It can be manufactured by a laminating step of laminating an adhesive resin emulsion between the porous membrane and the heat-resistant porous body, and (5) an adhering step of adhering by the action of the adhesive resin emulsion. Since the adhesive resin emulsion can be scattered by charging the low melting point adhesive resin emulsion unipolarly and electrostatically repelling in this way, the air permeability resistance decreasing rate is 5% or less to some extent. Bonding and integration can be performed without blocking the micropores of the membrane.

  Hereinafter, description will be made based on FIG. 1 which is a schematic cross-sectional view of a manufacturing apparatus capable of manufacturing the separator of the present invention.

  Reference numeral 1 in FIG. 1 denotes an adhesive supply device that can supply a low-melting-point adhesive resin emulsion to a nozzle 2 described later. The low melting point adhesive resin constituting the low melting point adhesive resin emulsion can be composed of the low melting point adhesive resin described above. The dispersion medium used for the low melting point adhesive resin emulsion is not particularly limited as long as the low melting point adhesive resin can be uniformly dispersed. For example, acetone, methanol, ethanol, propanol, isopropanol Water or the like can be used, and these can be used alone or in combination of two or more.

  As the low melting point adhesive resin emulsion, it is preferable to prepare a low melting point adhesive resin having an average primary particle diameter of 1 μm or less. Easily concentrated and scattered on the microporous membrane or heat-resistant porous material, and can be bonded and integrated with a very small amount of low-melting-point adhesive resin. It is because it is excellent in property. More preferably, it is 0.1 μm or less. The lower limit is not particularly limited. The “average primary particle diameter” refers to a value obtained by measurement by a laser diffraction / scattering method.

  Reference numeral 2 in FIG. 1 denotes a nozzle capable of discharging the supplied low melting point adhesive resin emulsion. The diameter (inner diameter) of the nozzle 2 is not particularly limited, but is preferably 0.1 to 2 mm so that the low melting point adhesive resin emulsion can be finely applied without agglomeration. The nozzle 2 may be made of metal or non-metal. If the nozzle 2 is made of metal, the nozzle 2 can be used as one of the electrodes. If the nozzle 2 is made of non-metal, the discharged low melting point adhesive can be obtained by installing an electrode inside the nozzle 2. The resin emulsion can be charged unipolarly.

  In order to prevent the low-melting-point adhesive resin emulsion from dripping, it is preferable that the nozzle 2 is oriented so that the discharge direction from the nozzle 2 does not coincide with the action direction of gravity. In particular, the nozzle 2 is preferably oriented in a direction opposite to the direction of gravity or in a direction perpendicular to the direction of gravity.

  Reference numeral 3 in FIG. 1 denotes a voltage application device. The voltage application device 3 can apply a voltage to the nozzle 2 or the electrode in the nozzle 2. The voltage application device 3 is not particularly limited, but a direct current high voltage generator can be used, and a Van de Graf electromotive machine can also be used. The applied voltage is not particularly limited, but is preferably 5 to 50 KV. The polarity of the applied voltage may be either positive or negative, but the roll-shaped counter electrode 4 described later is grounded and the nozzle 2 side is applied positively so that corona discharge during voltage application can be easily suppressed. Thus, it is preferable that the nozzle 2 side has a positive potential.

In FIG. 1, 4 is a roll-shaped counter electrode. Since the roll-shaped counter electrode 4 is grounded, a potential difference is formed between the roll-shaped counter electrode 4 and the nozzle 2 described above, and the low melting point adhesive resin emulsion discharged from the nozzle 2 can be unipolarly charged. The roll-shaped counter electrode 4 is preferably made of a conductive material (for example, metal) having a volume resistance of 10 ⁹ Ω or less. In addition, even if the roll-shaped counter electrode 4 is a non-conductive material having a volume resistance exceeding 10 ⁹ Ω, the electrode may be provided inside or in contact with the roll surface. Moreover, although the counter electrode 4 in FIG. 1 is a roll shape, it does not need to be a roll shape and may be a flat plate or a belt shape.

  Reference numeral 5 in FIG. 1 denotes an unwinding roll A (5) capable of unwinding the heat-resistant porous body 5a. This unwinding roll A (5) supplies a heat-resistant porous body 5a onto the roll-like counter electrode 4 by a traction force such as nip rolls 7a and 7b, which will be described later, and has a low melting point charged unipolarly on the heat-resistant porous body 5a. An adhesive resin emulsion is applied.

  Reference numeral 6 in FIG. 1 denotes an unwinding roll B that can unwind the microporous film 6a. This unwinding roll B (6) supplies the microporous film 6a onto the heat-resistant porous body 5a to which the low melting point adhesive resin emulsion charged unipolarly is applied by the traction force of the nip rolls 7a and 7b described later, and laminated. Is done.

  Reference numerals 7a and 7b in FIG. 1 denote a pair of nip rolls that unwind the heat-resistant porous body 5a and the microporous film 6a from the unwinding rolls A and B (5, 6), and at the same time, heat-resistant porous body 5a and microporous film 6a. It has the effect | action which adheres.

  In FIG. 1, 8 is a heating device, which heats the laminate of the heat-resistant porous body 5a and the microporous film 6a to below the melting point of the low-melting adhesive resin emulsion, and removes the dispersion medium of the low-melting adhesive resin emulsion. Can be glued. The heating device 8 is not particularly limited. For example, an oven, a hot air generator, an electric furnace, a far infrared heater, a hot press using an endless belt, or a hot calender roll can be used.

  Reference numeral 9 in FIG. 1 denotes a separator that is difficult to delaminate and is bonded and integrated without closing the micropores of the microporous membrane 6a.

  Reference numeral 10 in FIG. 1 denotes a winding roll that can wind up the separator 9.

  When manufacturing the separator of the present invention using such a manufacturing apparatus, first, the microporous film, the heat-resistant porous body, and the low melting point adhesive resin emulsion as described above are prepared (preparation step). .

  Next, the low melting point adhesive resin emulsion is supplied from the adhesive supply device 1 to the nozzle 2, the low melting point adhesive resin emulsion is discharged from the nozzle 2, the nozzle 2 is applied by the voltage application device 3, and the roll-shaped counter electrode 4 is The low melting point adhesive resin emulsion is charged unipolarly by an electric field formed by being grounded (charging process). The electric field varies depending on the distance between the nozzle 2 and the roll-shaped counter electrode 4, the dispersion medium of the low-melting adhesive resin emulsion, the viscosity of the low-melting adhesive resin emulsion, and the like. It is preferably 5 kV / cm. As the electric field value increases, the low-melting point adhesive resin emulsion droplets tend to be finer. However, if it exceeds 5 kV / cm, air breakdown tends to occur. This is because the liquid droplets are difficult to form. In FIG. 1, a potential difference is provided by applying a voltage to the nozzle 2 and grounding the roll-shaped counter electrode 4, but applying a voltage to the roll-shaped counter electrode 4 and grounding the nozzle 2 causes a potential difference. Can also be provided. The charging polarity of the low melting point adhesive resin emulsion is not particularly limited. However, since the charging polarity affects the stability of application of the low melting point adhesive resin emulsion, the opposite of the roll shape is compared with a known charge train. It is preferable that the low-melting point adhesive resin constituting the low-melting point adhesive resin emulsion is charged with a polarity that is easily charged with respect to the material of the electrode 4.

  The thus-charged low melting point adhesive resin emulsion flies toward the roll-shaped counter electrode 4 by the action of an electric field, and is applied onto the heat-resistant porous body 5a supplied onto the roll-shaped counter electrode 4 (application process). . In this application step, since the low melting point adhesive resin emulsion is unipolarly charged, it can repel each other and be scattered. For this reason, in the application step, a scaly film as seen when a solution-type adhesive is used is not formed, so that a separator can be manufactured without closing the micropores of the microporous membrane. In addition, according to the manufacturing apparatus of FIG. 1, the low melting point adhesive resin emulsion is applied only to the heat resistant porous body 5a, but instead of or in addition to the heat resistant porous body 5a, the low melting point adhesive resin is applied to the microporous film 6a. An emulsion may be applied. However, when the low melting point adhesive resin emulsion is applied to the heat resistant porous material, the low melting point adhesive resin emulsion concentrates on the heat resistant porous material, and when the adhesive is integrated, the low melting point adhesive resin does not form a film. Since a separator can be produced without clogging the micropores of the membrane, it is preferable to apply a low-melting point adhesive resin emulsion to the heat-resistant porous body.

The amount of the low melting point adhesive resin emulsion to be applied is not particularly limited, but as described above, the adhesive strength between the microporous film 6a and the heat-resistant porous body 5a is excellent, and the microporous film 6a has fine pores. It is preferably 0.01 to 4 g / m ² (solid content) and more preferably 0.03 to 1 g / m ² (solid content) so as not to clog.

  Next, lamination is performed such that the low melting point adhesive resin emulsion is interposed between the heat-resistant porous body 5a and the microporous film 6a (lamination step). In addition, in the manufacturing apparatus of FIG. 1, although the lamination | stacking process is performed continuously after an application | coating process, after manufacturing the heat resistant porous body which provided the low melting-point adhesive resin emulsion once, it laminate | stacks with a microporous film. Also good. Further, even when the low melting point adhesive resin emulsion is applied to the microporous film 6a, the microporous film 6a is laminated so that the low melting point adhesive resin emulsion is interposed between the heat resistant porous body 5a and the microporous film 6a.

  The laminated body of the heat-resistant porous body 5a and the microporous film 6a is sent to the heating device 8, the dispersion medium of the low-melting point adhesive resin emulsion is removed, and the adhesive action of the low-melting point adhesive resin is manifested. The porous body 5a and the microporous film 6a are bonded and integrated to form the separator 9 (bonding process). In this heating device 8, it is possible to bond and integrate by heating below the melting point of the low melting point adhesive resin emulsion.

  A separator having a heat shrinkage rate of 10% or less at 150 ° C. can be manufactured by appropriately selecting a heat resistant porous material, a microporous film, and a low melting point adhesive resin.

The nonaqueous electrolyte secondary battery of the present invention can be exactly the same as a conventional nonaqueous electrolyte secondary battery except that the separator of the present invention as described above is used. For example, a positive electrode having a lithium-containing metal compound paste supported on a current collector is used, and a negative electrode is a lithium metal or lithium alloy, and a carbon material containing carbon or graphite capable of inserting and extracting lithium (for example, Non-water in which LiPF ₆ is dissolved in a mixed solvent of ethylene carbonate and diethyl carbonate as an electrolyte using a carbon material such as coke, natural graphite or artificial graphite), a composite tin oxide supported on a current collector, etc. An electrolyte or the like can be used. The cell structure of the non-aqueous electrolyte secondary battery is not particularly limited, and may be a laminated shape, a cylindrical shape, a square shape, a coin shape, or the like.

  Examples of the present invention will be described below, but the present invention is not limited to the following examples.

Example 1
45.7% ethanol aqueous solution was added to polyethylene-methyl methacrylate copolymer powder (Mitsui DuPont Polychemical Co., Ltd., average primary particle size: 0.02 μm, melting point: 90 ° C.), and the solid content concentration was 12.5 mass%. A low melting point adhesive resin emulsion (viscosity: 13.5 mPa · s) was prepared.

  In addition, a polytetrafluoroethylene tube was connected to the syringe, and a stainless steel nozzle 2 having an inner diameter of 0.6 mm was attached to the tip of the tube to obtain an adhesive supply device 1. Next, a high voltage power supply (voltage application device 3) was connected to the nozzle 2. Further, a stainless steel drum (ground, counter electrode 4) was installed at a position 10 cm away from the nozzle 2.

Next, a non-woven fabric (heat-resistant porous material, base material A (5a), basis weight: 10 g / m ² , thickness: 20 μm, average flow pore size: 0.5 μm) made of polyacrylonitrile fiber (softening point: 170 ° C.) While supplying to the stainless steel drum rotating at a constant speed (surface speed: 2 m / min), the low melting point adhesive resin emulsion is put into the syringe and discharged in a direction perpendicular to the direction of gravity using a microfeeder ( (Discharge amount: 0.5 g / hour), and a voltage of +20 kV is applied to the nozzle 2 from the high voltage power source, and the discharged low melting point adhesive resin emulsion is charged with a positive polarity and an electric field is applied to move toward the drum. Flyed and applied on the nonwoven fabric. The nozzle 2 was reciprocally swung at a constant speed (moving speed: 2 cm / min) in a direction perpendicular to the rotation direction of the drum. Moreover, the application amount of the low-melting-point adhesive resin emulsion in the nonwoven fabric was 0.5 g / m ² (solid content).

Subsequently, a polyethylene microporous film (base material B (6a), basis weight: 15 g / m ² , thickness: 24 μm, average so as to come into contact with the adhesive application surface of the nonwoven fabric provided with the low melting point adhesive resin emulsion. After supplying the flow pore size: 0.3 μm, melting point: 135 ° C., laminating the nonwoven fabric and the microporous membrane, they are bonded and integrated by heating for 5 seconds in an oven (heating device 8) set at a temperature of 87 ° C. Separator 9 (weight per unit area: 25.5 g / m ² , thickness: 44 μm) was produced. The physical properties of this separator 9 are as shown in Table 1.

(Example 2)
A separator 9 (weight per unit: 25.1 g / m ² , thickness: 44 μm) was obtained in the same manner as in Example 1 except that the application amount of the low melting point adhesive resin emulsion was 0.125 g / m ² (solid content). Manufactured. The physical properties of this separator 9 are as shown in Table 1.

(Comparative Example 1)
A separator (weight per unit: 30 g / m ² , thickness: 48 μm) was produced in the same manner as in Example 1 except that the application amount of the low melting point adhesive resin emulsion was 5 g / m ² (solid content). The physical properties of this separator were as shown in Table 1.

(Comparative Example 2)
After laminating the same polyacrylonitrile fiber non-woven fabric and polyethylene microporous membrane as in Example 1, it was partially heat-sealed with an embossed calendar set at a temperature of 135 ° C. (the surface of the total area of the fused portion was smooth) The separator was manufactured by making the percentage of the surface area considered to be 5%. The physical properties of this separator were as shown in Table 1.

(Comparative Example 3)
A polyethylene microporous membrane similar to that in Example 1 was used as a separator. The physical properties of this separator were as shown in Table 1.

(Measurement of rate of decrease in air resistance)
By the above-described method, the air resistance reduction rate of each separator was measured. The results are shown in Table 1.

(Measurement of interlayer adhesion)
In accordance with the delamination strength specified in JIS C-2111, the interlayer adhesive strength of the separators of Examples and Comparative Examples was measured. The results are shown in Table 1. If the interlayer adhesion is 5 N or more, the interlayer adhesion is excellent, and the separator can be handled without peeling at the time of battery group configuration.

(Measurement of heat shrinkage)
The thermal shrinkage rate of each separator was measured by the method described above. The results are shown in Table 1.

(Measurement of electrical resistance)
After impregnating the separator with an electrolytic solution ((ethylene carbonate) / (diethyl carbonate) volume ratio = 1/1, LiPF ₆ : 1 mol / L), the separator was sandwiched between copper foils and measured using an LCR high tester manufactured by Hioki Electric. The electrical resistance of the separator at 1 kHz was measured. The results are shown in Table 1.

１）比較例３のポリエチレン製微多孔膜を２枚重ねて測定した電気抵抗値（Ｍｍ）を１００とした場合の指数値、つまり、次の式から算出される値（Ｍｓはセパレータの電気抵抗値）
Ｒ＝（Ｍｓ／Ｍｍ）×１００

1) Index value when the electrical resistance value (Mm) measured by overlapping two polyethylene microporous membranes of Comparative Example 3 is 100, that is, a value calculated from the following formula (Ms is the electrical resistance of the separator) value)
R = (Ms / Mm) × 100

  As is apparent from the results in Table 1, the separator of the present invention has a low thermal contraction rate, can maintain the shape of the separator even after the micropores of the microporous membrane are closed by heat, and the short circuit between the electrodes during abnormal heat generation of the battery. In addition to being excellent in heat resistance, it is possible to produce a non-aqueous electrolyte secondary battery with low electrical resistance. Furthermore, according to the production method of the present invention, it is possible to produce a separator that can be integrated with a heat-resistant porous body without increasing the air permeability resistance of the microporous membrane, and that does not increase the internal resistance of the battery and has excellent heat resistance. all right.

Schematic cross-sectional view of separator manufacturing equipment

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Adhesive supply apparatus 2 Nozzle 3 Voltage application apparatus 4 Roll-shaped counter electrode 5 Unwinding roll A
5a Heat resistant porous body 6 Unwinding roll B
6a Microporous film 7a, 7b Nip roll 8 Heating device 9 Separator 10 Winding roll

Claims (7)

A separator for a non-aqueous electrolyte secondary battery in which a microporous film made of a resin having a melting point of 100 ° C. to 180 ° C. and a heat-resistant porous body are bonded and integrated with an adhesive resin having a melting point lower than that of the resin constituting the microporous film. A separator for a nonaqueous electrolyte secondary battery having a gas resistance reduction rate (Gd) defined below, which is 5% or less.
Gd = {(Ga−Gb) / Gb} × 100
Here, Gd is the air resistance reduction rate (%), Ga is the air resistance (s) of the nonaqueous electrolyte secondary battery separator, and Gb is the heat resistant porous material from the nonaqueous electrolyte secondary battery separator. The air resistance (s) of the microporous membrane from which the adhesive resin is removed, respectively. The separator for a nonaqueous electrolyte secondary battery according to claim 1, wherein the amount of the adhesive resin is 0.01 to 4 g / m ² . The separator for a nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein a heat shrinkage rate at 150 ° C is 10% or less. (1) A preparation step of preparing a microporous film made of a resin having a melting point of 100 ° C. to 180 ° C., a heat-resistant porous body, and an adhesive resin emulsion having a melting point lower than that of the microporous film-constituting resin,
(2) a charging step for charging the adhesive resin emulsion to a single polarity;
(3) An application step of applying a charged adhesive resin emulsion to the microporous membrane and / or heat-resistant porous body,
(4) a laminating step of laminating the adhesive resin emulsion between the microporous membrane and the heat-resistant porous body, and (5) an adhering step of adhering by the action of the adhesive resin emulsion,
A method for producing a separator for a non-aqueous electrolyte secondary battery. The method for producing a separator for a non-aqueous electrolyte secondary battery according to claim 4, wherein in the applying step, an adhesive resin emulsion is applied to the heat-resistant porous body. 6. The method for producing a separator for a non-aqueous electrolyte secondary battery according to claim 4, wherein the average primary particle diameter of the adhesive resin is 1 [mu] m or less. The nonaqueous electrolyte secondary battery provided with the separator for nonaqueous electrolyte secondary batteries of any one of Claims 1-3.

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