JP2015005420A - Cell separator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cell separator having a porous film layer formed by containing inorganic particles and a porous support, which is capable of improving battery characteristics by uniformly distributing fiber of a nonwoven cloth used as the porous support, and a method of manufacturing the same.SOLUTION: In this cell separator having the porous film layer formed by containing the inorganic particles and the porous support, the porous support is a polyester nonwoven cloth, and the polyester nonwoven cloth is manufactured by a wet papermaking method using fiber dispersion liquid containing at least aliphatic carboxylic acid metal salt and a nonionic surface active agent.

Description

  The present invention relates to a battery separator (hereinafter sometimes abbreviated as “separator”).

  Conventionally, as a separator for a lithium secondary battery, a polyolefin film having fine pores that have penetrated has been used. This battery separator suppresses heat generation by increasing the internal resistance of the battery by increasing the internal resistance of the battery when the battery generates heat due to abnormalities, and the internal resistance of the lithium cobalt oxide as an electrode agent It has been responsible for suppressing battery explosion due to thermal runaway.

  However, in applications that require charging and discharging with a large current, such as batteries for hybrid vehicles and uninterruptible power supplies, research on electrode composition has made it possible to suppress thermal runaway explosions, and conversely, rapid battery internal Due to the increase in temperature, in order to avoid electrode contact due to thermal contraction of the separator, there is an increasing demand for a separator having high heat resistance and low internal resistance.

  In response to this demand, Patent Document 1 proposes a separator made of a porous porous support having holes and a porous ceramic material that closes the holes. Polymer fibers are used for a flexible porous support, and zirconium, silica, and alumina are used for porous ceramics (inorganic particles). It is described that by using a low-density porous support and a porous ceramic in combination, the porosity in the separator and the heat resistance can be improved.

  In such a separator, a porous ceramic layer (porous membrane layer) is produced by coating a dispersion of a porous ceramic material on a flexible porous support. Examples of the porous support include nonwoven fabrics using polymer fibers. However, when the polymer fiber density of the porous support is low, there is a problem that the strength of the porous support decreases. In addition, the dispersion of the coated porous ceramic material is detached from the porous support, and a uniform porous ceramic layer cannot be obtained in the surface direction, resulting in a defective separator and an internal short circuit. Sometimes occurred. On the other hand, if the polymer fiber density is too high, there arises a problem that the thickness increases. In Patent Document 2, in order to impart an appropriate polymer fiber density and suppress an increase in thickness, a nonwoven fabric is manufactured using a wet papermaking method that is excellent in polymer fiber dispersibility. It is disclosed that a porous support having a balance between strength and thickness can be obtained while using ultrafine fibers.

  However, if the polymer density is further lowered to obtain a thin porous support, the density of the porous support is affected by the density of the porous support, which affects the density of the porous support, which allows the dispersibility of the fibers in water. It has been found that the dispersibility of the battery deteriorates and the battery characteristics are affected. In particular, Patent Document 2 uses different types of fibers, drawn fibers and undrawn fibers, and the fiber surface is basically hydrophobic. In this case, agglomeration is likely to occur between the same type of fibers during papermaking, and the fibers are not uniformly distributed between different types of fibers, affecting the density of the porous support and affecting the battery characteristics. was there.

Japanese Patent No. 4594098 JP 2009-230975 A

  The present invention relates to a battery separator having a porous membrane layer containing inorganic fine particles and a porous support, and a method for producing the same, by uniformly distributing the fibers of the nonwoven fabric used as the porous support, It is an object of the present invention to provide a battery separator capable of improving battery characteristics and a method for producing the same.

  As a result of intensive studies, it has been found that the above-described problems can be solved by the present invention described below.

[1] In a battery separator having a porous membrane layer containing inorganic fine particles and a porous support, the porous support is a polyester nonwoven fabric, and the polyester nonwoven fabric is at least an aliphatic carboxylic acid metal salt A battery separator characterized by being a polyester non-woven fabric produced by a wet papermaking method using a fiber dispersion containing a nonionic surfactant.
[2] The battery separator according to [1], wherein the nonionic surfactant is polypropylene glycol.
[3] A step of producing a polyester nonwoven fabric by a wet papermaking method using a fiber dispersion containing at least an aliphatic carboxylic acid metal salt and a nonionic surfactant, and using the polyester nonwoven fabric as a porous support, inorganic A method for producing a battery separator, comprising: coating a porous support with a coating liquid containing fine particles to form a porous membrane layer.

  The polyester fiber used in the wet papermaking method is obtained by cutting long fibers in water and shortening them. The reason for cutting in water is to prevent re-fusion of the fibers due to heat generated during cutting, but an oil agent is used so that the fibers are sufficiently immersed in water. This oil agent remains on the surface even when the short fiber is taken out from the water, and generally remains excessively on the surface of the short fiber. In addition, different types of polyester fibers often use different oil agents. Therefore, when polyester fibers are dispersed in water, the same type of polyester fibers are likely to aggregate together, and further, when an excess oil agent is used for redispersion. It is easy to embrace bubbles, and thereby the fiber aggregates are not dispersed in water but are present unevenly. In particular, when these fiber aggregates float in water, the fiber distribution becomes uneven in the wet papermaking process. The present invention is a polyester nonwoven fabric in which the porous support is produced by a wet papermaking method using a fiber dispersion containing at least an aliphatic carboxylic acid metal salt and a nonionic surfactant. By using a fiber dispersion containing at least an aliphatic carboxylic acid metal salt and a nonionic surfactant, the oil agent during the production of the polyester fiber can be re-dispersed to stabilize the surface state of different polyester fibers. And a porous support having a uniform fiber distribution can be obtained. In the porous membrane layer containing inorganic fine particles and the battery separator using the porous support, the battery characteristics of the battery can be improved.

The battery separator of the present invention is a battery separator having a porous membrane layer containing inorganic fine particles and a porous support, and the porous support is a polyester nonwoven fabric having a basis weight of 5 to 15 g / m ² . And the said polyester nonwoven fabric is a polyester nonwoven fabric manufactured by the wet papermaking method using the fiber dispersion liquid containing an aliphatic carboxylic acid metal salt and a nonionic surfactant at least.

  In this invention, the porous support body which is a polyester nonwoven fabric manufactured by the wet papermaking method (it may be described as "wet polyester nonwoven fabric" hereafter) is used as a component. The wet polyester nonwoven fabric contains stretched polyester fibers. The wet papermaking method is a method in which fibers are dispersed in water at a low concentration, a fiber web is made on a net, and strength is given to the fiber web by drying and / or heat treatment to obtain a nonwoven fabric. Polyester fibers are manufactured in the form of long fibers in advance by the hot-melt method or precipitation method, and then coated with an oil agent on the surface and cut to a predetermined length in water to prevent re-fusion by heat. Used as fiber. The fiber length of the stretched polyester fiber is preferably 1 to 30 mm, more preferably 3 to 15 mm. Moreover, since it becomes possible to improve uniformity while maintaining high porosity by using thin fibers, it is preferable to include stretched polyester fibers having a fineness of 1.0 dtex (dt) or less. Furthermore, when producing a thinner battery separator, it is more preferable to include a stretched polyester fiber of 0.6 dt or less.

  In order to maintain the strength of the polyester nonwoven fabric, unstretched polyester fibers can be combined. Since the unstretched polyester fiber has not been crystallized, when heated and pressurized at about 180 ° C. to 220 ° C., it is fused between the unstretched polyester fibers or between the stretched polyester fiber and the unstretched polyester, and the strength of the nonwoven fabric Can be significantly increased. Similarly to the stretched polyester fiber, the unstretched polyester fiber is produced in the form of a long fiber in advance, and then cut into a predetermined length in water while being coated with an oil, and used as a short fiber.

  Nonionic alkyl / polyoxyethylene ethers (alkyl groups are C12 to C24, polyoxyethylene units are 8 to 15), anionic alkyl / polyoxyethylene ether sulfate Salt, alkyl polyoxyethylene phosphate ester (alkyl group is C12 to C24, polyoxyethylene unit is 8 to 15, metal ions such as sodium and potassium as counter ions; ammonium ion, triethanolammonium ion, etc.) Etc. are used.

  In a general wet papermaking method, fibers are dispersed in water at a low concentration of about 0.01 to 0.2% by mass, and then made from water using a net such as a long net, a short net, or a circular net, Form a fiber web. At this time, if an excess oil agent is present in the polyester fiber originally having a hydrophobic surface, a fiber aggregate mainly including air bubbles is formed. Moreover, this fiber aggregate is often composed of the same type of fibers. That is, a fiber aggregate mainly containing stretched polyester fibers and a fiber aggregate mainly containing unstretched polyester fibers are formed. Since these fiber aggregates enclose bubbles, they tend to float in water and are difficult to disperse stably in water, and the fiber distribution becomes uneven in the wet papermaking process. Therefore, it is necessary to redisperse excess oil agent in water to make the fiber surface state uniform, to reduce the amount of bubbles to be embraced, and to disperse dissimilar polyester fibers stably in water. In the present invention, the fiber dispersion contains at least an aliphatic carboxylate and a nonionic surfactant.

  As an aliphatic carboxylate effective for the present invention, sodium salts such as capric acid, lauric acid, myristic acid and palmitic acid, potassium salts and the like can be used. However, in the case of sodium caprate, the penetrability into the hydrophobic part of the oil may be weak depending on the type of the oil. On the other hand, in the case of an aliphatic carboxylate having a carbon number equal to or greater than that of sodium myristate, the interaction between the aliphatic carboxylates is strengthened, and the permeability to the oil may be reduced. Therefore, the preferred aliphatic carboxylate is laurate, i.e. sodium laurate or potassium laurate.

The nonionic surfactant is used to stabilize the oil agent peeled off from the fiber surface into micelles in water. As such a material, since it is necessary to suppress the re-adsorption to the fiber surface, the solubility in water is high, but a part of the structure does not dissolve uniformly, and the hydrophobic part of the oil agent It needs to have some affinity. As a unit having a certain degree of affinity with the hydrophobic part of the oil agent and for micelleizing the oil agent, an alkylene oxide group is preferable, and a propylene oxide group is particularly excellent. Nonionic surfactants effective for the present invention include block polymers of ethylene oxide and propylene oxide, diol type and triol type propylene glycol, and the like. In particular, polypropylene glycol is a nonionic surfactant that is highly effective in micelleizing an oil agent and is preferable in terms of cost. Furthermore, polyalkylene oxides (for example, polyethylene oxide with ₁₀ units: EO ₁₀ , polyethylene oxide with 8 units and polypropylene oxide with 2 units: EO ₈ + PO ₂ ), lauryl ether, myristyl ether, stearyl ether, etc. Can be used in combination.

  The total addition amount of the aliphatic carboxylate and the nonionic surfactant to the polyester fiber is preferably 0.1 to 10.0 g per kg of the polyester fiber, more preferably 0, although it depends on the fiber diameter of the polyester fiber. .4 to 2.0 g. If the total addition amount is less than 0.1 g, the effect of improving the dispersibility of the polyester fiber may be difficult to be exhibited. On the other hand, if it exceeds 10.0 g, not only the effect of suppressing bubbles is decreased, but bubbles may be easily generated.

The porous support can be imparted with strength and thinned or made uniform by a treatment such as thermal calendering or calendering. The porous support preferably has a basis weight of 3 to 25 g / m ² , preferably a thickness of 5 to 50 μm, and a porosity of 30 to 80%. More preferably, the basis weight is 5 to 15 g / m ² , the thickness is 8 to 25 μm, and the porosity is 40 to 70%. In the porous support, in addition to polyester fibers such as stretched polyester fibers and unstretched polyester fibers, rayon, cellulose acetate, lyocell, pulp, acrylic, aramid, polyolefin and the like can be used in combination. In the present invention, the polyester nonwoven fabric refers to a nonwoven fabric having a polyester fiber content of 60% by mass or more.

  Examples of the inorganic fine particles constituting the porous membrane layer containing inorganic fine particles include aluminum hydroxide oxide such as boehmite; aluminum oxide, silicon oxide, zirconium oxide, aluminum silicate, magnesium silicate, titanium oxide, zinc oxide, etc. Metal oxides: Fine particles of sparingly soluble salts such as barium sulfate are used. An aluminum-based material such as boehmite or aluminum oxide is preferable. The particle diameter of the inorganic fine particles is preferably 10 nm to 10 μm, more preferably 0.1 μm to 5 μm. The particle size is obtained by sufficiently diluting the inorganic fine particles with water, and measuring this with a laser scattering type particle size measuring device (trade name: 3300EX2 manufactured by Microtrac Co., Ltd.). Was the particle diameter.

  After the inorganic fine particles are dispersed, a porous membrane layer is formed. If an organic solvent is used in the manufacturing process, restrictions on the manufacturing machine will increase, so inorganic fine particles are dispersed in water to prepare a coating solution, and this coating solution is applied to a porous support for battery use. It is preferred to produce a separator.

  The dispersion of the inorganic fine particles in water is performed by adjusting the viscosity by using a dispersion aid together. The inorganic fine particles are charged with anions or cations due to their surface properties and are stably dispersed in water. When the inorganic fine particle is an aluminum-based material, boehmite is a particularly preferable material from the viewpoint of dispersibility. As the dispersion aid, an anionic, cationic or nonionic surfactant, a water-soluble salt such as a phosphate is used.

  It is preferable to use a water-soluble cellulose derivative in consideration of adjustment of the viscosity of the coating liquid and setting of the coating liquid on a porous support. In particular, carboxymethyl cellulose (CMC) salts such as sodium carboxymethyl cellulose and carboxymethyl cellulose ammonium are effective materials for use in combination with an anionic surfactant. In addition, methyl cellulose, cationized cellulose, and the like can be used. The addition amount of these water-soluble cellulose derivatives is preferably 0.01 to 5.00% by mass, more preferably 0.10 to 2.00% by mass in terms of solid content.

  In order to impart film strength to the porous membrane layer, it is preferable to use an interparticle binder such as polyolefin, styrene butadiene, acrylic, polyester, etc. in addition to the water-soluble cellulose derivative. These interparticle binders are preferably used as latex. The use of the non-fibrous organic binder of the porous support as an interparticle binder is a more preferable method because the bonding property between the surface of the porous support and the inorganic fine particles can be improved. The interparticle binder is preferably 0.5 to 20.0% by mass, more preferably 1.0 to 10.0% by mass of the inorganic fine particles in terms of solid content.

  As an apparatus used for dispersion of inorganic fine particles, a normal stirrer with a rotation speed of 1000 rpm or less is sufficient when the concentration is low, but when the concentration exceeds 20% by mass, a homogenizer or the like of 2000 rpm or more is used. A strong stirrer with a rotational speed is preferred. In addition, a bead mill or the like can be used. As the order of dispersion, it is preferable to first dissolve the dispersion aid, add the inorganic fine particles, and finally add the water-soluble cellulose derivative solution.

The obtained dispersion liquid of inorganic fine particles is applied as a coating liquid on a porous support to form a porous membrane layer. As a coating method, a method using an air doctor coater, blade coater, knife coater, rod coater, squeeze coater, impregnation coater, gravure coater, kiss roll coater, die coater, reverse roll coater, transfer roll coater, spray coater, etc. Can be used. The coating amount of the porous membrane layer is preferably ¹ to 50 g / m ² by dry mass, more preferably ² to 30 g / m ² . After drying, it is also possible to adjust the thickness of the battery separator obtained by subjecting it to calendar treatment or thermal calendar treatment. The preferable thickness of the battery separator having a porous support is 10 to 30 μm, more preferably 12 to 25 μm.

  The obtained battery separator is cut and sandwiched between electrode materials for a lithium secondary battery, an electrolyte is injected, the battery is sealed, and a lithium secondary battery is obtained. The material constituting the positive electrode is mainly an active material and a conductive agent such as carbon black, a binder such as polyvinylidene fluoride and styrene butadiene rubber, and as the active material, lithium cobaltate, lithium nickelate, lithium manganate, A lithium manganese composite oxide such as lithium nickel manganese cobaltate (NMC) or lithium aluminum manganate (AMO), lithium iron phosphate, or the like is used. These are mixed and applied onto an aluminum foil as a current collector to form a positive electrode.

The material constituting the negative electrode is mainly an active material, a conductive agent, and a binder. As the active material, graphite, amorphous carbon material, silicon, lithium, lithium alloy, or the like is used. These are mixed and applied onto a copper foil as a current collector to form a negative electrode. In a lithium secondary battery, a battery separator is sandwiched between a positive electrode and a negative electrode, and an electrolytic solution is impregnated therein to provide ionic conductivity and conduct. In the lithium secondary battery, a non-aqueous electrolyte solution is used. Generally, this is composed of a solvent and a supporting electrolyte. As the solvent, for example, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC) and vinylene carbonate having an additive function, vinyl Carbonate system such as ethylene carbonate. Dimethoxyethane (DME) can also be used. As the supporting electrolyte, in addition to lithium hexafluorophosphate and lithium tetrafluoroborate, an organic lithium salt such as LiN (SO ₂ CF ₃ ) ₂ is also used. Ionic liquids can also be used.

  As the exterior body, a metal cylindrical can such as aluminum or stainless steel, a rectangular can, a sheet-type exterior body using a laminate film obtained by laminating aluminum foil with polypropylene, polyethylene, polyethylene terephthalate, polybutylene terephthalate, or the like can be used. Further, it can be used by stacking and stacking, or it can be used by rotating in a cylindrical shape.

  EXAMPLES Next, although an Example demonstrates this invention further in detail, this invention is not limited to these at all.

Example 1
[Preparation of porous support]
Fibers and adhesives were mixed at the following composition ratios to prepare fiber dispersions.

Stretched polyethylene terephthalate (PET) short fiber 70.0 parts by mass (fineness 0.3 dt, fiber length 3 mm)
30.0 parts by mass of unstretched polyethylene terephthalate short fiber (fineness 0.2 dt, fiber length 3 mm)
Sodium laurate 0.05 parts by mass Polypropylene glycol (triol type, molecular weight 3000) 0.05 parts by mass (Daiichi Kogyo Seiyaku, trade name: Cellogen (registered trademark) BSH-12) 0.20 parts by mass

Using this fiber dispersion, it was rolled up with a circular net and short net combination paper machine and dried at a Yankee temperature of 160 ° C. to prepare a web having a basis weight of 8.0 g / m ² . Next, strength was imparted with a hot-press roll at 190 ° C. to obtain a porous support (1) which is a wet polyester nonwoven fabric having a thickness of 15 μm.

[Preparation of boehmite coating solution]
The following materials were stirred for 2 hours with a homogenizer (Primics, TK HODISPER Model 2.5, rotation speed 2500 rpm) to prepare a boehmite dispersion.

Boehmite (trade name: C20, manufactured by Daimei Chemical Industry Co., Ltd.) 100 parts by mass Sodium metaphosphate 0.13 parts by mass Distilled water 100 parts by mass

  To the obtained boehmite dispersion, 100 parts by mass of a 0.9 mass% aqueous solution of sodium carboxymethylcellulose (manufactured by Nippon Paper Chemicals, trade name: MAC500LC) and acrylic latex (manufactured by JSR, trade name: TRD202A, concentration: 40.3% by weight) ) Was added in an amount of 7.5 parts by mass to prepare a coating liquid (1).

[Preparation of separator]
The porous support (1) was impregnated with the coating liquid (1) and dried at 85 ° C. to obtain a separator having a thickness of 24 μm.

(Example 2)
[Preparation of porous support]
Fibers and adhesives were mixed at the following composition ratios to prepare fiber dispersions.

Stretched PET staple fiber (fineness 0.3 dt, fiber length 3 mm) 70.0 parts by mass Unstretched PET staple fiber (fineness 0.2 dt, fiber length 3 mm) 30.0 parts by mass Sodium myristate 0.05 part by mass polypropylene glycol ( Diol type, molecular weight 400) 0.10 parts by mass (Daiichi Kogyo Seiyaku, trade name: Serogen (registered trademark) BSH-12) 0.20 parts by mass

Using this fiber dispersion, a fiber web having a weight per unit area of 8.0 g / m ² is produced by rolling up with a circular / short net combination paper machine, and after drying, strength is imparted by a hot press roll at 190 ° C. And the porous support body (2) which is a 15-micrometer-thick wet polyester nonwoven fabric was obtained. Next, the coating liquid (1) was impregnated and dried at 85 ° C. to obtain a separator having a thickness of 24 μm.

Example 3
[Preparation of porous support]
Fibers and adhesives were mixed at the following composition ratios to prepare fiber dispersions.

Stretched polyethylene terephthalate (PET) short fiber 70.0 parts by mass (fineness 0.3 dt, fiber length 3 mm)
30.0 parts by mass of unstretched polyethylene terephthalate short fiber (fineness 0.2 dt, fiber length 3 mm)
Sodium laurate 0.05 parts by mass Polypropylene glycol (triol type, molecular weight 3000) 0.04 parts by mass Polyalkylene oxide (ethylene oxide (EO) 8 + propylene oxide (PO) 2) lauryl ether 0.04 parts by mass (Daiichi Kogyo Seiyaku, trade name: Serogen (registered trademark) BSH-12) 0.20 parts by mass

Using this fiber dispersion, a fiber web having a basis weight of 8.5 g / m ² is produced by rolling up with a circular / short mesh combination paper machine, and after drying, strength is imparted by a hot press roll at 190 ° C. And the porous support body (3) which is a 15-micrometer-thick wet polyester nonwoven fabric was obtained. Next, the coating liquid (1) was impregnated and dried at 85 ° C. to obtain a separator having a thickness of 24 μm.

(Comparative Example 1)
[Preparation of porous support]
Fibers and adhesives were mixed at the following composition ratios to prepare fiber dispersions.

Stretched PET short fiber (fineness 0.3 dt, fiber length 3 mm) 70.0 parts by weight Unstretched PET short fiber (fineness 0.2 dt, fiber length 3 mm) 30.0 parts by weight Sodium laurate 0.10 parts by weight ( Daiichi Kogyo Seiyaku Co., Ltd., trade name: Serogen (registered trademark) BSH-12) 0.20 parts by mass

Using this fiber dispersion, a fiber web having a weight per unit area of 8.0 g / m ² is produced by rolling up with a circular / short net combination paper machine, and after drying, strength is imparted by a hot press roll at 190 ° C. And the porous support body (4) which is a 15-micrometer-thick wet polyester nonwoven fabric was obtained. Next, the coating liquid (1) was impregnated and dried at 85 ° C. to obtain a comparative separator having a thickness of 25 μm.

(Comparative Example 2)
Fibers and adhesives were mixed at the following composition ratios to prepare fiber dispersions.
Stretched PET short fibers (fineness 0.3 dt, fiber length 3 mm) 70.0 parts by mass Unstretched PET short fibers (fineness 0.2 dt, fiber length 3 mm) 30.0 parts by mass polypropylene glycol (triol type, molecular weight 3000) 0. 20 parts by mass (Daiichi Kogyo Seiyaku, trade name: Serogen (registered trademark) BSH-12) 0.20 parts by mass

Using this fiber dispersion, a fiber web having a weight per unit area of 8.0 g / m ² is produced by rolling up with a circular / short net combination paper machine, and after drying, strength is imparted by a hot press roll at 190 ° C. And the porous support body (5) which is a 15 micrometer-thick wet polyester nonwoven fabric was obtained. Next, the coating liquid (1) was impregnated and dried at 85 ° C. to obtain a comparative separator having a thickness of 25 μm.

(Comparative Example 3)
Fibers and adhesives were mixed at the following composition ratios to prepare fiber dispersions.
Stretched PET short fibers (fineness 0.3 dt, fiber length 3 mm) 70.0 parts by mass Unstretched PET short fibers (fineness 0.2 dt, fiber length 3 mm) 30.0 parts by mass Glyceryl laurate 0.05 parts by mass polypropylene glycol ( Triol type, molecular weight 3000) 0.05 part by mass (Daiichi Kogyo Seiyaku, trade name: Serogen (registered trademark) BSH-12) 0.20 part by mass

Using this fiber dispersion, a fiber web having a weight per unit area of 8.0 g / m ² is produced by rolling up with a circular / short net combination paper machine, and after drying, strength is imparted by a hot press roll at 190 ° C. And the porous support body (6) which is a 15-micrometer-thick wet polyester nonwoven fabric was obtained. Next, the coating liquid (1) was impregnated and dried at 85 ° C. to obtain a comparative separator having a thickness of 25 μm.

(Comparative Example 4)
Fibers and adhesives were mixed at the following composition ratios to prepare fiber dispersions.
Stretched PET staple fiber (fineness 0.3 dt, fiber length 3 mm) 70.0 parts by mass Unstretched PET staple fiber (fineness 0.2 dt, fiber length 3 mm) 30.0 parts by mass Glyceryl laurate 0.10 parts by mass Daiichi Kogyo Seiyaku Co., Ltd., trade name: Serogen (registered trademark) BSH-12) 0.20 parts by mass

Using this fiber dispersion, a fiber web having a weight per unit area of 8.0 g / m ² is produced by rolling up with a circular / short net combination paper machine, and after drying, strength is imparted by a hot press roll at 190 ° C. And the porous support body (7) which is a 15-micrometer-thick wet polyester nonwoven fabric was obtained. Next, the coating liquid (1) was impregnated and dried at 85 ° C. to obtain a comparative separator having a thickness of 25 μm.

[Measurement of average pore diameter]
The average pore diameter of the obtained separator was measured using Porous Materials Inc. Measured with a Capillary Flow Porometer CEP-1500A. The results are given in Table 1.

[Measurement of membrane resistance]
A separator impregnated with an electrolyte was sandwiched between cylindrical copper having a diameter of 3 cm and a diameter of 1.5 cm. The electrolyte is an electrolyte for a lithium secondary battery manufactured by Ube Industries (trade name: Purelite, solvent: EC / DEC / DME = 1/1/1 (volume ratio), supporting electrolyte: 1 mol of lithium hexafluorophosphate / L) was used. The resistance value between the electrodes was measured at a bias voltage of 20 kHz and 10 mV using Electrochemical Measurement Unit SI-1280B manufactured by Solatron using both coppers as electrodes. The results are given in Table 1.

[Evaluation of battery characteristics]
On the aluminum foil, lithium manganate, acetylene black, and polyvinylidene fluoride were applied at a mass ratio of 100/5/3 at a mass ratio of about 200 g / m ² , the solvent was dried, and further pressed to produce a positive electrode. On the other hand, spherical artificial graphite, acetylene black, and polyvinylidene fluoride were coated on a copper foil at a mass ratio of 85/15/5 in an amount of 100 g / m ² , dried and pressed to prepare a negative electrode.

  The separator obtained in the example was sandwiched between the obtained electrodes, and an electrolyte for a lithium secondary battery manufactured by Ube Industries (trade name: Purelite, solvent: EC / DEC / DME = 1/1/1 (volume Ratio), supporting electrolyte: lithium hexafluorophosphate 1 mol / l) was dropped, and sealed in an aluminum foil laminate film under reduced pressure to produce a lithium secondary battery. Next, the produced lithium secondary battery was charged to 4.2 V at 0.2 C, and then discharged at 0.2 C. At this time, the ratio of the discharge capacity initially performed under the condition of 0.2 C to the charge capacity was measured. Further, the internal resistance was measured with the voltage drop value taken as the voltage 30 minutes after the start of discharge under the condition of 0.2 C (discharge time of 300 minutes). The results are given in Table 1.

  From Table 1, the separator of Examples 1-3 which made the polyester nonwoven fabric manufactured by the wet papermaking method using the fiber dispersion liquid containing an aliphatic carboxylic acid metal salt and a nonionic surfactant at least as a porous support body Then, it can be seen that the average pore diameter is reduced by improving the dispersibility of the fibers, and as a result, the initial charge / discharge ratio (discharge capacity / charge capacity), which is battery characteristics, is improved.

  On the other hand, the separator of the comparative example 1 which made the polyester nonwoven fabric manufactured by the wet papermaking method using the fiber dispersion liquid containing an aliphatic carboxylic acid metal salt but not containing a nonionic surfactant as the porous support body. In Comparative Examples 2 and 3, the polyester nonwoven fabric produced by a wet papermaking method using a fiber dispersion containing a nonionic surfactant but not containing an aliphatic carboxylic acid metal salt was used as a porous support. In the separator, the average pore diameter was large, and the initial charge / discharge ratio (discharge capacity / charge capacity), which is battery characteristics, was lower than that of the separator of the example.

  The battery separator of the present invention can be used as a separator for a lithium secondary battery or a capacitor separator.

Claims (3)

  In a battery separator having a porous membrane layer containing inorganic fine particles and a porous support, the porous support is a polyester nonwoven fabric, and the polyester nonwoven fabric is at least an aliphatic carboxylic acid metal salt and nonionic A battery separator characterized by being a polyester nonwoven fabric produced by a wet papermaking method using a fiber dispersion containing a surfactant.   The battery separator according to claim 1, wherein the nonionic surfactant is polypropylene glycol.   A step of producing a polyester nonwoven fabric by a wet papermaking method using a fiber dispersion containing at least an aliphatic carboxylic acid metal salt and a nonionic surfactant, and containing inorganic fine particles using the polyester nonwoven fabric as a porous support A process for producing a separator for a battery comprising the steps of: coating a porous support on a porous support and forming a porous membrane layer.