JP5478733B2 - Nonaqueous electrolyte battery separator and nonaqueous electrolyte battery - Google Patents

Description

  The present invention relates to a non-aqueous electrolyte battery excellent in reliability at high temperatures and a separator that can constitute the non-aqueous electrolyte battery.

Lithium ion secondary batteries, which are a type of non-aqueous electrolyte battery, have a higher energy density than other batteries and do not have a memory effect, so power supplies for mobile devices such as mobile phones and notebook personal computers Is widely used. In recent years, as a measure to prevent global warming, a movement to promote CO ₂ reduction has been developed on a global scale. As a part of this, for example, in the automobile industry, as a battery for driving a motor of an electric vehicle or a hybrid electric vehicle. Development of lithium ion secondary batteries is underway.

  In current lithium ion secondary batteries, a polyolefin-based porous film having a thickness of, for example, about 15 to 30 μm is used as a separator interposed between a positive electrode and a negative electrode. In addition, as separator material, the constituent resin of the separator is melted below the thermal runaway temperature of the battery to close the pores, thereby increasing the internal resistance of the battery and improving the safety of the battery in the event of a short circuit. In order to ensure the so-called shutdown effect, polyethylene having a low melting point may be applied.

  As such a separator, for example, a uniaxially or biaxially stretched film is used to increase the porosity and improve the strength. Since such a separator is supplied as a single film, a certain strength is required in terms of workability and the like, and this is secured by the stretching. However, with such a stretched film, the degree of crystallinity has increased, and the shutdown temperature has increased to a temperature close to the thermal runaway temperature of the battery. Therefore, it can be said that the margin for ensuring the safety of the battery is sufficient. hard.

  In addition, the film is distorted by the stretching, and there is a problem that when it is exposed to a high temperature, shrinkage occurs due to residual stress. The shrinkage temperature is very close to the shutdown temperature. For this reason, when using a polyolefin-based porous film separator, if the battery temperature reaches the shutdown temperature, such as when there is a charging abnormality, the separator vacancies are sufficiently closed, and the current is immediately reduced to increase the battery temperature. Must be prevented. This is because if the separator holes are not sufficiently closed and the current cannot be reduced immediately, the battery temperature easily rises to the shrinkage temperature of the separator, and there is a risk of abnormal heat generation due to an internal short circuit. .

  As a technique for preventing such a short circuit due to thermal contraction of the separator and improving the reliability of the battery, for example, a multilayer in which a layer having high heat resistance is formed on the surface of a resin porous film (microporous film) serving as a base Structured separators have been proposed (for example, Patent Documents 1 to 5).

  In addition, in a lithium ion secondary battery, for example, foreign matter may be mixed in the manufacturing process. In such a case, a small hole is formed in the separator due to the pressure of the foreign matter, causing an internal short circuit, which causes heat generation of the battery. There is a fear. In particular, the polyolefin-based porous film separator is vulnerable to local heat generation, and the vicinity of the short-circuited portion of the separator is broken by heat generated by the short-circuit current, so that the internal short circuit is enlarged and the battery may be exposed to danger.

  Therefore, as a technique for solving these problems and improving the reliability of the battery, a battery (Patent Document 6) in which a thin film of carboxymethylcellulose is formed on the surface of the positive electrode, an insulator on the current collector, and this insulation There has been proposed a battery (Patent Document 7) using an electrode in which a region where an active material is provided and a region where no active material is provided on an object.

  In addition, a technique has been proposed in which a cross-linked polymer coating layer is formed on the surface of electrode active material particles to improve battery safety and suppress battery performance degradation (Patent Document 8).

  Furthermore, in order to secure shutdown characteristics and improve strength, a separator having a structure in which both sides of a blocking layer for securing shutdown characteristics are sandwiched between fine porous strength layers has been proposed (Patent Document 9). .

  According to the techniques of Patent Documents 1 to 9, it is possible to provide a battery having high reliability that hardly causes problems such as thermal runaway even when various abnormal situations are encountered.

JP 2006-351386 A JP 2007-273123 A JP 2007-273443 A JP 2007-280911 A International Publication No. 2009/44741 JP 2000-357505 A JP 2008-282799 A JP 2008-537293 A JP 11-329390 A

  By the way, especially in the case of the large capacity and high output type lithium ion secondary battery as described above, it is required to improve the reliability as compared with the conventional lithium ion secondary battery.

  For example, as described in Patent Document 5, the shape of the separator at a temperature of about 150 ° C. is provided by providing a heat-resistant layer containing heat-resistant fine particles on the surface of the porous resin film that acts as a shutdown function layer. It is possible to increase the stability and suppress the thermal shrinkage.

  However, on the other hand, it is not always easy to suppress the thermal shrinkage of the separator at a temperature higher than this (for example, about 200 ° C.) and to improve its shape stability. In terms of ensuring safety and reliability, the technique described in Patent Document 5 still leaves room for improvement.

  On the other hand, for example, it is conceivable to increase the shape stability of the separator at a high temperature by a method of forming a large number of functional layers as in Patent Document 9, but in that case, the manufacturing process of the separator increases. Thus, there is a problem that the manufacturing becomes complicated and the whole separator becomes thick, which causes a decrease in battery capacity.

  For these reasons, there is a need for the development of a technology that can further improve the reliability of the battery while suppressing an increase in the thickness of the separator by using a single functional layer for improving heat resistance.

  The present invention has been made in view of the above circumstances, and uses a separator for a nonaqueous electrolyte battery capable of ensuring excellent heat resistance while suppressing an increase in thickness, and uses the separator, and has high reliability. It is providing the nonaqueous electrolyte battery which has.

The separator for a non-aqueous electrolyte battery of the present invention is a separator for a non-aqueous electrolyte battery including a resin porous membrane and a heat-resistant porous layer disposed on the surface of the resin porous membrane, wherein the resin porous The membrane is formed from a resin whose main component is a polyolefin having a melting temperature of 80 to 180 ° C., and the heat-resistant porous layer includes swellable fine particles that swell by absorbing a non-aqueous electrolyte by heating, and heat-resistant fine particles And a binder, wherein the volume ratio of the swellable fine particles and the heat-resistant fine particles is 30:70 to 70:30 , and the binder contains an N-vinylacetamide-based polymer, When the total amount of the heat-resistant fine particles is 100 parts by mass, the content of the N-vinylacetamide-based polymer is 0.1 parts by mass or more, and the total volume of the constituent components of the separator is The ratio of all the resins is 50 to 99.9% by volume, and the heat-resistant porous layer has a thickness of 2 to 10 μm.

  The non-aqueous electrolyte battery of the present invention includes a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, and the separator is the separator for non-aqueous electrolyte batteries of the present invention.

  ADVANTAGE OF THE INVENTION According to this invention, the separator for nonaqueous electrolyte batteries which can ensure the outstanding heat resistance, suppressing the increase in thickness, and the nonaqueous electrolyte battery which uses this separator and has high reliability are provided. be able to.

FIG. 1 is a cross-sectional view showing an example of the lithium ion secondary battery of the present invention.

(Embodiment 1)
First, the non-aqueous electrolyte battery separator of the present invention (hereinafter simply referred to as “separator”) will be described. The separator of this invention is equipped with the resin porous membrane and the heat resistant porous layer arrange | positioned on the surface of the said resin porous membrane. That is, the separator of the present invention has a heat resistant porous layer on at least one surface of the resin porous membrane.

  In the separator of the present invention, the resin porous membrane is a layer having an original function of transmitting a separator while preventing a short circuit between the positive electrode and the negative electrode.

  As will be described in detail later, for example, a microporous membrane mainly composed of polyolefin is used for the resin porous membrane, similarly to a separator for a non-aqueous electrolyte battery such as a normal lithium ion secondary battery. However, as described above, such a porous resin membrane is likely to shrink under a high temperature environment and has poor shape stability under high temperature.

  The separator of the present invention is contained in a separator including a resin having poor shape stability at a high temperature as described above (including a resin contained in a resin porous membrane, a swellable fine particle contained in a heat resistant porous layer, and a binder). The ratio of (all resins) is 50 to 99.9% by volume in the total volume of the constituent components of the separator (in the total volume excluding the void portion; the same applies hereinafter), and the ratio is very large. By forming a thin heat-resistant porous layer containing specific swellable fine particles, heat-resistant fine particles, and a binder in a specific composition ratio on at least one surface of the membrane, for example, 200 ° C. while suppressing an increase in the overall thickness It is possible to provide a non-aqueous electrolyte battery (non-aqueous electrolyte battery of the present invention) that is more reliable and safer at high temperatures than ever before. It is said.

  The swellable fine particles contained in the heat-resistant porous layer according to the separator of the present invention usually do not absorb or absorb the non-aqueous electrolyte contained in the battery in the temperature range (approximately 70 ° C. or lower) in which the battery is used. Therefore, the degree of swelling is below a certain level, but when the inside of the battery is abnormally heated, it absorbs the non-aqueous electrolyte and swells greatly, and the degree of swelling increases as the temperature rises. Formed from resin. In the battery using the separator of the present invention, in a temperature range that is normally used, a flowable non-aqueous electrolyte that is not absorbed by the swellable fine particles exists in the pores of the separator. ) The ion conductivity is increased, and the battery has good characteristics. However, when heated above the temperature at which the degree of swelling increases as the temperature rises, the swellable fine particles contained in the heat-resistant porous layer absorb the nonaqueous electrolyte in the battery and swell. Since the flowable non-aqueous electrolyte present in the pores of the separator and the non-aqueous electrolyte at the interface between the separator and the positive electrode are reduced, the thermal runaway reaction between the positive electrode and the non-aqueous electrolyte can be satisfactorily suppressed.

  In the swellable fine particles, the temperature at which the degree of swelling increases with increasing temperature (hereinafter referred to as “thermal swellability”) is preferably 70 ° C. or higher, more preferably 75 ° C. or higher. preferable. If the temperature at which the swellable microparticles begin to exhibit thermal swellability is too low, the Li ion conductivity in the battery in the normal operating temperature range may become too low, which may hinder the use of the device. . Also, if the temperature at which the swellable microparticles begin to exhibit thermal swellability is too high, the temperature at which the effect of suppressing the thermal runaway reaction between the positive electrode and the non-aqueous electrolyte in the battery becomes too high, and the battery safety In addition, the reliability improvement effect may be reduced. Therefore, in the swellable fine particles, the temperature at which the thermal swellability starts to be exhibited is preferably 150 ° C. or less, and more preferably 145 ° C. or less.

  As the swellable fine particles contained in the heat-resistant porous layer, the liquid absorption amount of the nonaqueous electrolyte solution (nonaqueous electrolyte solution possessed by the battery) measured at 25 ° C. is 1.5 mL or less per 1 g of the swellable fine particles. Preferably, it is 1 mL or less.

  Although the details of the mechanism by which the swellable fine particles swell due to temperature rise are not clear, for example, in the case of cross-linked polymethyl methacrylate (cross-linked PMMA), which is an example of the swellable fine particles, the glass transition of the cross-linked PMMA that forms the main component of the particles Since the point (Tg) is in the vicinity of 100 ° C., a mechanism may be considered in which the cross-linked PMMA particles become flexible when the temperature reaches about 100 ° C., and more non-aqueous electrolyte solution is absorbed and swollen. Therefore, it is considered that the Tg of the swellable fine particles is preferably, for example, 50 ° C. or higher (more preferably 80 ° C. or higher) and 130 ° C. or lower. And as for swellable microparticles | fine-particles, it is preferable that the liquid absorption amount of the nonaqueous electrolyte solution (nonaqueous electrolyte solution which a battery has) measured at 130 degreeC is 2 mL or more per g of swellable microparticles | fine-particles.

  The “absorption amount of the non-aqueous electrolyte at 25 ° C. of the swellable fine particles” referred to in the present specification is a value determined as follows. Swellable fine particles (in the case of an aqueous dispersion, those dried for 1 day at room temperature) are sufficiently ground using a mortar and pestle to form a powder. 0.3 g of this powder is put in a glass container, 5 mL of a non-aqueous electrolyte (non-aqueous electrolyte used in a battery) is added thereto, and the powder is immersed in the non-aqueous electrolyte at 25 ° C. for 24 hours. Thereafter, the powder and the non-aqueous electrolyte are separated by filtration through a 25 μm metal mesh, the amount of the obtained non-aqueous electrolyte (the non-aqueous electrolyte not absorbed by the powder) is measured, and the glass container From the difference from the amount of the non-aqueous electrolyte solution put in, the absorption amount of the non-aqueous electrolyte solution at 25 ° C. of the swellable fine particles is obtained.

  Further, the “absorption amount of the non-aqueous electrolyte solution at 130 ° C. of the swellable fine particles” referred to in the present specification is a value obtained as follows. In a glass container, 0.3 g of a swellable fine particle powder obtained in the same manner as in the case of measuring the amount of absorption at 25 ° C. is added, and 5 mL of a non-aqueous electrolyte (non-aqueous electrolyte used in a battery) is added here. In addition, the powder is immersed in a non-aqueous electrolyte at 25 ° C. for 24 hours. Thereafter, the non-aqueous electrolyte in the glass container is heated to 130 ° C., and filtered with a 25 μm metal mesh while maintaining the temperature at 130 ° C. to separate the powder from the non-aqueous electrolyte, and the obtained non-aqueous electrolyte The amount of (non-aqueous electrolyte not absorbed by the powder) was measured, and from the difference from the amount of non-aqueous electrolyte placed in the glass container, the absorption of the non-aqueous electrolyte at 130 ° C. of the swellable fine particles Find the amount.

  In the absorption measurement at 25 ° C. and the absorption measurement at 130 ° C. by the above method, the loss of the non-aqueous electrolyte due to filtration and the loss due to the volatilization of the non-aqueous electrolyte solvent during heating (measurement of absorption at 130 ° C. Case) may occur. Therefore, each of the above absorption amounts is corrected using the loss amount measured by performing each of the above operations on only the non-aqueous electrolyte.

  The glass transition point (Tg) of the swellable fine particles referred to in the present specification is a value measured using a differential scanning calorimeter (DSC) in accordance with the provisions of Japanese Industrial Standard (JIS) K7121.

  The material constituting the swellable fine particles has heat resistance and electrical insulation, is stable to non-aqueous electrolyte, and is electrochemically stable that is not easily oxidized and reduced in the operating voltage range of the battery. A material is preferable, and examples of such a material include a crosslinked resin. More specifically, styrene resin [polystyrene (PS), etc.], styrene-butadiene rubber (SBR), acrylic resin (PMMA, etc.), polyalkylene oxide [polyethylene oxide (PEO), etc.], fluororesin (PVDF, etc.), And a crosslinked product of at least one resin selected from the group consisting of these and derivatives thereof; urea resin; polyurethane; and the like. In the swellable fine particles, the above-exemplified resins may be used alone or in combination of two or more. Further, the swellable fine particles may contain various known additives added to the resin, for example, an antioxidant, if necessary.

  Among the constituent materials of the swellable fine particles, crosslinked styrene resin, crosslinked acrylic resin, and crosslinked fluororesin are preferable, and crosslinked PMMA is particularly preferable.

  The average particle size of the swellable fine particles is preferably 0.05 μm or more, more preferably 0.1 μm or more, further preferably 0.2 μm or more, and preferably 3 μm or less. More preferably, it is 2 μm or less. As will be described in detail later, the heat-resistant porous layer is preferably formed using a heat-resistant porous layer forming composition in which the constituent components are dispersed or dissolved in a medium. In that case, if the average particle diameter of the swellable fine particles is too small, the surface area becomes large and the swellable fine particles are likely to aggregate with each other, which may make it difficult to disperse well in the medium of the heat-resistant porous layer forming composition. is there. In addition, if the average particle size of the swellable fine particles is too large, it is difficult to make the movement of lithium ions in the heat resistant porous layer uniform over the entire surface of the separator, which may cause a lithium ion migration barrier during battery charge / discharge. .

  The average particle size of the fine particles (swellable fine particles and heat-resistant fine particles described later) referred to in the present specification is obtained by, for example, dissolving the fine particles using a laser scattering particle size distribution meter (for example, “LA-920” manufactured by HORIBA). The particle size (D50) at 50% of the volume-based integrated fraction measured by dispersing the fine particles in a medium in which the fine particles do not swell can be defined.

  The heat-resistant porous layer contains heat-resistant fine particles together with the above-mentioned swellable fine particles, but “heat resistance” in the heat-resistant fine particles referred to in the present specification does not visually confirm a shape change such as deformation at least at 200 ° C. It means that. Further, the heat resistant temperature of the heat resistant fine particles is preferably 300 ° C. or higher. The “heat-resistant temperature” of the heat-resistant fine particles referred to in the present specification means a temperature at which no shape change such as deformation is visually confirmed.

  The heat-resistant fine particles have electrical insulating properties, are electrochemically stable, and are stable to a medium used for a non-aqueous electrolyte and a heat-resistant porous layer forming composition, which will be described later. There is no particular limitation as long as it does not dissolve in the non-aqueous electrolyte.

Specific examples of such heat-resistant fine particles include, for example, oxide fine particles such as iron oxide, SiO ₂ (silica), Al ₂ O ₃ (alumina), TiO ₂ , BaTiO ₃ , ZrO ₂ ; aluminum nitride, silicon nitride Nitride fine particles such as: Calcium fluoride, barium fluoride, barium sulfate and other poorly soluble ionic crystal fine particles; silicon, diamond and other covalently bonded crystal fine particles; talc, montmorillonite and other clay fine particles; boehmite, zeolite, apatite, Inorganic fine particles such as kaolin, mullite, spinel, olivine, sericite, bentonite and other mineral resource-derived substances or artificial products thereof. Further, the surface of the conductive fine particles such as metal fine particles; oxide fine particles such as SnO ₂ and tin-indium oxide (ITO); carbonaceous fine particles such as carbon black and graphite; It may be fine particles that have been made electrically insulating by surface treatment with the above-mentioned materials constituting the electrically insulating heat-resistant fine particles. These heat resistant fine particles may be used alone or in combination of two or more. As the heat-resistant fine particles, silica, alumina, and boehmite are more preferable, and boehmite is particularly preferable.

  The shape of the heat-resistant fine particle is not particularly limited, and may be any shape such as a spherical shape, a particle shape, or a plate shape.

  The average particle size of the heat-resistant fine particles (average particle size of primary particles) is preferably 0.05 μm or more, more preferably 0.1 μm or more, still more preferably 0.2 μm or more, It is preferably 3 μm or less, and more preferably 2 μm or less. If the average particle diameter of the heat-resistant fine particles is too small, the surface area becomes large and the heat-resistant fine particles are likely to aggregate with each other, which may make it difficult to disperse them well in the medium of the heat-resistant porous layer forming composition. In addition, if the average particle size of the heat-resistant fine particles is too large, it is difficult to make the movement of lithium ions in the heat-resistant porous layer uniform across the entire surface of the separator, which may cause a lithium ion migration barrier during battery charge / discharge. .

  The heat-resistant porous layer according to the separator of the present invention is a binder for increasing the adhesion between fine particles such as swellable fine particles and heat-resistant fine particles, and improving the adhesion between the heat-resistant porous layer and the resin porous membrane. Contains.

  For the binder, an N-vinylacetamide-based polymer is used. When an N-vinylacetamide-based polymer is used, the heat-resistant porous layer increases in strength because the heat-resistant fine particles and the swellable fine particles constituting the heat-resistant porous layer are densely packed. Even if the thickness of the separator is reduced or the amount of the binder in the heat resistant porous layer is particularly reduced, the heat resistance (shape stability at high temperature) of the separator can be maintained high. In addition, when the heat-resistant porous layer is formed using the heat-resistant porous layer forming composition, the N-vinylacetamide-based polymer functions as a thickener in the composition, and the heat resistance in the composition This can contribute to the suppression of sedimentation of fine particles and swellable fine particles. For this reason, the use of the N-vinylacetamide-based polymer makes it possible to form a heat-resistant porous layer that is more homogeneous and excellent in surface smoothness and is less likely to cause internal resistance spots in the battery.

The N-vinylacetamide-based polymer includes a homopolymer of N-vinylacetamide (poly N-vinylacetamide) and a copolymer of N-vinylacetamide.
Examples of the copolymer of N-vinylacetamide include a copolymer of N-vinylacetamide and an ethylenically unsaturated monomer other than N-vinylacetamide.

  Examples of ethylenically unsaturated monomers (ethylenically unsaturated monomers other than N-vinylacetamide) that can be used to form a copolymer of N-vinylacetamide include acrylic acid, methacrylic acid, methyl acrylate, ethyl acrylate, and propyl acrylate. , Butyl acrylate, octyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, octyl methacrylate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, acrylonitrile, methacrylonitrile, vinyl acetate, acrylamide , Methacrylamide, N-methylacrylamide, N, N-dimethylacrylamide, N-isopropylacrylic N-vinylformamide, N-methyl, N-vinylformamide, N-vinylpyrrolidone, N-vinyl-2-caprolactam, maleic acid, itaconic acid, 2-acrylamido-2-methyl-propanesulfonic acid, 2-acrylamide Ethanesulfonic acid, 2-methacrylamide amidoethanesulfonic acid, 3-methacrylamidopropanesulfonic acid, methyl acrylate sulfonic acid, methyl methacrylate sulfonic acid, acrylic acid-2-ethylsulfonic acid, methacrylic acid-2-ethylsulfonic acid, Acrylic acid-3-propylsulfonic acid, methacrylic acid-3-propylsulfonic acid, acrylic acid-2-methyl-3-propylsulfonic acid, methacrylic acid-2-methyl-3-propylsulfonic acid, acrylic acid-1,1 '-Dimethyl-2-ethylsulfonic acid, Examples include chloroic acid-1,1′-dimethyl-2-ethylsulfonic acid or salts thereof, methyl vinyl ketone, ethyl vinyl ketone, methyl vinyl ether, ethyl vinyl ether, fluorine-containing ethylene, styrene or derivatives thereof, and vinyl allylbenzene. Only one of these may be used, or two or more may be used in combination.

  The copolymerization ratio (mass ratio) of the copolymer of N-vinylacetamide and an ethylenically unsaturated monomer other than N-vinylacetamide is preferably 2 to 50% by mass of the latter ethylenically unsaturated monomer. .

  The molecular weight of the N-vinylacetamide polymer is a number average molecular weight (polystyrene conversion value) measured using gel permeation chromatography, preferably 1000 or more, more preferably 4000 or more, It is preferably 1000000 or less, more preferably 700000 or less, and further preferably 500000 or less.

  In addition to the N-vinylacetamide polymer, other binders can be used as the binder. Examples of such other binders include ethylene-vinyl acetate copolymers, acrylate copolymers, vinyl alcohol polymers, vinyl ether polymers, vinyl pyrrolidone polymers, and the like.

  In the heat-resistant porous layer, the composition ratio of the swellable fine particles, the heat-resistant fine particles and the binder is set as follows from the viewpoint of enhancing the shape stability of the separator at a high temperature. First, the volume ratio of swellable fine particles to heat-resistant fine particles is set to 10:90 to 95: 5, preferably 45:55 to 70:30. Further, when the total amount of the swellable fine particles and the heat-resistant fine particles is 100 parts by mass, the content of the N-vinylacetamide polymer is 0.1 parts by mass or more, preferably 0.15 parts by mass or more, more preferably Is 0.2 parts by mass or more, preferably 15 parts by mass or less, more preferably 5 parts by mass or less, still more preferably 3 parts by mass or less, and 1 part by mass or less. Is particularly preferred.

  Moreover, by preparing the composition for forming a heat resistant porous layer so that the content of the N-vinylacetamide-based polymer becomes the above value with respect to 100 parts by mass of the total amount of the swellable fine particles and the heat resistant fine particles. These fine particles can be satisfactorily coated with an N-vinylacetamide-based polymer, so that the precipitation of the fine particles in the composition can be better suppressed, and a heat-resistant porous layer having more uniform and excellent surface smoothness can be formed.

  In addition, the amount of pores in the heat-resistant porous layer is appropriately maintained. For example, from the viewpoint of improving the load characteristics of the battery, when the total amount of the swellable fine particles and the heat-resistant fine particles is 100 parts by mass, The amount (total amount of binder containing N-vinylacetamide-based polymer) is preferably 15 parts by mass or less, more preferably 5 parts by mass or less, still more preferably 3 parts by mass or less. It is particularly preferable that the amount is not more than parts. The binder content is 0.1 parts by mass or more, preferably 0.15 parts by mass or more, more preferably 0.2 parts by mass or more.

  The content of the swellable fine particles in the heat-resistant porous layer is preferably 10% by volume or more in the total volume of the constituent components of the heat-resistant porous layer (the total volume excluding the volume of the void portion; the same applies hereinafter), More preferably, it is 45 volume% or more. By setting the content of the swellable fine particles in the heat-resistant porous layer as described above, the thermal runaway reaction during battery heat generation can be satisfactorily suppressed.

  However, excessively containing swellable fine particles in the heat-resistant porous layer can be expected to improve the reliability and safety of the battery, but the amount of nonaqueous electrolyte absorbed in the temperature range where the battery is used increases. In addition, the smoothness of the surface of the heat-resistant porous layer may be reduced due to aggregation of the swellable fine particles, and the internal resistance may vary depending on the position of the separator, which may reduce the load characteristics of the battery. From such a viewpoint, the content of the swellable fine particles in the heat resistant porous layer is, for example, preferably 95% by volume or less, and 70% by volume or less in the total volume of the constituent components of the heat resistant porous layer. Is more preferable.

  In addition, the content of the heat-resistant fine particles in the heat-resistant porous layer enhances the shape stability of the separator at high temperatures, suppresses heat shrinkage when the inside of the battery becomes high temperature, and heat-resistant porous From the viewpoint of suppressing the aggregation of the swellable fine particles in the layer and enhancing the surface smoothness of the heat resistant porous layer, the total volume of the constituent components of the heat resistant porous layer is preferably 5% by volume or more, and 30 volumes. % Or more is more preferable.

  The separator of the present invention may have a heat-resistant porous layer only on one side of the resin porous membrane or on both sides. For example, from the viewpoint of increasing the productivity of the separator, It is preferable to have a heat-resistant porous layer only on one side of the membrane.

  The thickness of the heat resistant porous layer (when heat resistant porous layers are formed on both sides of the resin porous membrane, the total thickness of both heat resistant porous layers. The same applies to the thickness of the heat resistant porous layer). From the viewpoint of sufficiently ensuring the action of the heat-resistant porous layer that suppresses thermal shrinkage of the film, it is 2 μm or more, and preferably 3 μm or more. In addition, by setting the heat-resistant porous layer to such a thickness, heat generation due to an internal short circuit when conductive foreign matter is mixed in the battery can be well prevented. However, if the thickness of the heat-resistant porous layer is too thick, the total thickness of the separator increases, which may cause a reduction in battery load characteristics or make it difficult to improve battery capacity. Therefore, the thickness of the heat resistant porous layer is 10 μm or less, and preferably 5 μm or less. In the separator of the present invention, the shape stability at a high temperature of, for example, 200 ° C. can be enhanced only by forming one thin heat-resistant porous layer.

  The resin porous membrane according to the separator of the present invention has a melting temperature, that is, a melting temperature measured using a differential scanning calorimeter (DSC) of 80 ° C. or higher and 180 ° C. or lower in accordance with JIS K 7121. It is a resin porous membrane mainly composed of polyolefin. Examples of the polyolefin constituting the resin porous membrane include polyethylene (PE) such as low density polyethylene, high density polyethylene, and ultrahigh molecular weight polyethylene; polypropylene (PP); and the like, and only one of these is used. Or two or more of them may be used in combination. Examples of the resin porous membrane using two or more kinds of polyolefin include a polyolefin porous resin membrane having a three-layer structure in which PP layers are formed on both sides of the PE layer. Since the separator has a porous resin membrane composed of such a polyolefin, the so-called shutdown characteristic can be secured in which the polyolefin softens at 80 to 180 ° C. and the pores of the separator are blocked. it can. The melting temperature of the polyolefin constituting the resin porous membrane is more preferably 150 ° C. or lower.

  As the resin porous membrane, for example, an ion-permeable porous membrane having a large number of pores formed by a conventionally known solvent extraction method, dry type or wet drawing method (used widely as a battery separator) A microporous membrane) can be used.

  “Polyolefin is the main component” in the porous resin membrane means that the polyolefin is 50% by volume or more of the total volume of the components constituting the porous resin membrane. From the viewpoint of ensuring better characteristics, the polyolefin as the main component is preferably 70% by volume or more, more preferably 80% by volume or more, of the total volume of the components constituting the resin porous membrane. Preferred (100% by volume of polyolefin may be used).

  The porosity of the heat resistant porous layer is preferably 40 to 70%, and the volume of the polyolefin contained in the resin porous membrane is 50% or more of the pore volume of the heat resistant porous layer. preferable. Thereby, when shutdown occurs, the softened or melted polyolefin sufficiently closes the pores of the heat-resistant porous layer, and can block ionic conduction.

  The thickness of the resin porous membrane (when the separator has a plurality of resin porous membranes, the total thickness. The same applies to the thickness of the resin porous membrane), from the viewpoint of ensuring good battery shutdown characteristics. It is preferably 9 μm or more, and more preferably 12 μm or more. In addition, from the viewpoint of reducing the total thickness of the separator and further improving the capacity and output density of the battery, the thickness of the resin porous membrane is preferably 35 μm or less, and more preferably 21 μm or less.

  Further, in the separator of the present invention, from the viewpoint of ensuring good shutdown characteristics and elasticity, the resin (resin contained in the resin porous membrane, swellability contained in the heat resistant porous layer) is included in the total volume of the constituent components of the separator. All resins contained in the separator including the fine particles and the binder (the same applies hereinafter with respect to the ratio of the resin in the separator)) is preferably 50% by volume or more and preferably 80% by volume or more. However, if the ratio of the resin in the separator is too large, the ratio of the heat-resistant fine particles contained in the heat-resistant porous layer is reduced, and the shape stability of the separator at high temperatures is reduced. The ratio of all the resins in the inside is 99.9% by volume or less, and preferably 98% by volume or less.

  The total thickness of the separator is preferably 12 μm or more, and more preferably 21 μm or more, from the viewpoint of securing sufficient strength. However, if the separator is too thick, the effect of increasing the output of the battery may be reduced. Therefore, the total thickness of the separator is preferably 45 μm or less, and more preferably 35 μm or less.

  The porosity of the separator is preferably 30% or more and 40% or more in a dried state in order to ensure the amount of nonaqueous electrolyte retained and to improve ion permeability. Is more preferable. On the other hand, from the viewpoint of ensuring the strength of the separator and preventing internal short circuit, the porosity of the separator is preferably 70% or less, more preferably 60% or less, in a dry state. The porosity of the separator: P (%) can be calculated by obtaining the sum for each component i from the thickness of the separator, the mass per area, and the density of the constituent components using the following formula (1).

P = {1- (m / t) / (Σa _i · ρ _i )} × 100 (1)
Here, in the formula (1), a _i : the ratio of component i when the total mass is 1, ρ _i : density of component i (g / cm ³ ), m: mass per unit area of the separator (G / cm ² ), t: thickness of separator (cm).

Further, in the above formula (1), m is the mass per unit area (g / cm ² ) of the resin porous membrane, and t is the thickness (cm) of the resin porous membrane, whereby the formula (1) Can also be used to determine the porosity of the resin porous membrane: P (%). It is preferable that the porosity of the resin porous membrane calculated | required by this method is 30 to 70%.

In the formula (1), m is the mass per unit area (g / cm ² ) of the heat resistant porous layer, and t is the thickness (cm) of the heat resistant porous layer. Can also be used to determine the porosity of the heat-resistant porous layer: P (%). It is preferable that the porosity of the heat resistant porous layer calculated | required by this method is 30 to 75%.

  The thermal contraction rate of the separator of the present invention is preferably 5% or less, particularly preferably 0% when left in a 200 ° C. temperature atmosphere. If the thermal contraction rate of the separator is too large, the effect of suppressing the expansion of the internal short circuit due to the thermal contraction of the separator may be reduced when an internal short circuit occurs due to the mixing of conductive foreign substances. The thermal contraction rate of the separator can be ensured by configuring the separator as described above.

  The “thermal contraction rate of the separator when left in a 200 ° C. temperature atmosphere” as used herein is specifically measured by the method used in the examples described later.

  The separator of the present invention is, for example, a composition for forming a heat-resistant porous layer in the form of a slurry or paste by dispersing swellable fine particles, heat-resistant fine particles and a binder constituting the heat-resistant porous layer in a medium such as water or an organic solvent. It can be manufactured by preparing a product (the binder may be dissolved in a medium), applying it to the surface of the porous resin membrane, and drying it.

  In applying the heat-resistant porous layer forming composition, for example, a method of applying these compositions with a known coating apparatus can be employed. Examples of the coating apparatus that can be used when applying the heat-resistant porous layer forming composition include a gravure coater, a knife coater, a reverse roll coater, and a die coater.

  The medium used in the heat-resistant porous layer forming composition may be any medium that can uniformly disperse heat-resistant fine particles and swellable fine particles, and can uniformly dissolve or disperse the binder. Common organic solvents such as aromatic hydrocarbons, furans such as tetrahydrofuran, and ketones such as methyl ethyl ketone and methyl isobutyl ketone are preferably used. In order to control the interfacial tension, alcohols (ethylene glycol, propylene glycol, etc.) or various propylene oxide glycol ethers such as monomethyl acetate may be appropriately added to these media. When the binder is water-soluble or used as an emulsion, water may be used as described above, and alcohols (such as methyl alcohol, ethyl alcohol, isopropyl alcohol, and ethylene glycol) may be used as appropriate. In addition, the interfacial tension can be controlled.

  The heat-resistant porous layer forming composition preferably has a solid content of, for example, 10 to 80% by mass.

  The resin porous membrane can be subjected to surface modification in order to enhance the adhesion with the heat resistant porous layer. Surface modification is often effective because resin porous membranes composed mainly of polyolefins generally do not have high surface adhesion.

  Examples of the method for modifying the surface of the resin porous membrane include corona discharge treatment, plasma discharge treatment, and ultraviolet irradiation treatment. From the viewpoint of responding to environmental problems, for example, it is more desirable to use water as the medium for the heat-resistant porous layer forming composition. From this, the hydrophilicity of the surface of the resin porous membrane can be improved by surface modification. It is very preferable to raise it.

(Embodiment 2)
Next, the nonaqueous electrolyte battery of the present invention will be described. The non-aqueous electrolyte battery of the present invention includes a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, and the separator may be the separator of the present invention described in the first embodiment. There is no particular limitation, and various configurations and structures employed in conventionally known nonaqueous electrolyte batteries can be applied.

  The non-aqueous electrolyte battery of the present invention includes a primary battery and a secondary battery. The configuration of a secondary battery (lithium ion secondary battery) which is a particularly main aspect will be described in detail below. .

  Examples of the form of the nonaqueous electrolyte battery include a cylindrical shape (such as a rectangular tube shape or a cylindrical shape) using a steel can, an aluminum can, or the like as an outer can. Moreover, it can also be set as the soft package battery which used the laminated film which vapor-deposited the metal as an exterior body.

The positive electrode of the nonaqueous electrolyte battery of the present invention is not particularly limited as long as it is a positive electrode used in a conventionally known nonaqueous electrolyte secondary battery. For example, as an active material, a lithium-containing transition metal oxide represented by Li _{1 + x} MO ₂ (−0.1 <x <0.1, M: Co, Ni, Mn, etc.); LiMn ₂ O _4, etc. LiMn manganese oxide; LiMn _x M _(1-x) O _{2 in} which part of Mn of LiMn ₂ O ₄ is substituted with another element; olivine type LiMPO ₄ (M: Co, Ni, Mn, Fe); LiMn _0.5 Ni _0.5 O ₂ ; Li _{(1 + a)} Mn _x Ni _y Co _(1-xy) O ₂ (−0.1 <a <0.1, 0 <x <0.5, 0 <y <0.5) A positive electrode mixture in which a known conductive additive (carbon material such as carbon black) or a binder such as polyvinylidene fluoride (PVDF) is appropriately added to these positive electrode active materials. In addition, a product obtained by finishing a molded body using a current collector as a core material can be used.

  As the current collector of the positive electrode, a metal foil such as aluminum, a punching metal, a net, an expanded metal, or the like can be used. Usually, an aluminum foil having a thickness of 10 to 30 μm is preferably used.

  The lead portion on the positive electrode side is normally provided by leaving the exposed portion of the current collector without forming the positive electrode mixture layer on a part of the current collector and forming the lead portion at the time of producing the positive electrode. However, the lead portion is not necessarily integrated with the current collector from the beginning, and may be provided by connecting an aluminum foil or the like to the current collector later.

  The negative electrode of the nonaqueous electrolyte battery of the present invention is not particularly limited as long as it is a negative electrode used in a conventionally known nonaqueous electrolyte secondary battery. For example, carbon that can occlude and release lithium, such as graphite, pyrolytic carbons, cokes, glassy carbons, fired organic polymer compounds, mesocarbon microbeads (MCMB), and carbon fibers as active materials One type or a mixture of two or more types of system materials is used. Further, elements such as Si, Sn, Ge, Bi, Sb, In and alloys thereof, compounds that can be charged and discharged at a low voltage close to lithium metal such as lithium-containing nitrides or lithium-containing oxides, or lithium metal or lithium / aluminum An alloy can also be used as the negative electrode active material. In addition to these negative electrode active materials, a negative electrode mixture prepared by appropriately adding a conductive additive (carbon material such as carbon black) or a binder such as PVDF to a molded body using a current collector as a core is used. The above various alloys and lithium metal foils may be used alone, or the above various alloys and lithium metal may be laminated on a current collector.

  When a current collector is used for the negative electrode, a copper or nickel foil, a punching metal, a net, an expanded metal, or the like can be used as the current collector, but a copper foil is usually used. In the negative electrode current collector, when the thickness of the entire negative electrode is reduced in order to obtain a battery having a high energy density, the upper limit of the thickness is preferably 40 μm, and the lower limit is preferably 5 μm.

  Similarly to the lead portion on the positive electrode side, the negative electrode lead portion is usually exposed to the current collector without forming a negative electrode agent layer (a layer having a negative electrode active material) on a part of the current collector during negative electrode fabrication. It is provided by leaving a part and using it as a lead part. However, the lead portion on the negative electrode side is not necessarily integrated with the current collector from the beginning, and may be provided by connecting a copper foil or the like to the current collector later.

  The electrode can be used in the form of a laminated electrode body in which the positive electrode and the negative electrode are laminated via the separator of the present invention, or a wound electrode body in which this is wound. When laminating the positive electrode and the negative electrode via the separator of the present invention, it is preferable to contact the heat-resistant porous layer side of the separator of the present invention with the positive electrode. Thus, when the battery generates heat, the swellable fine particles contained in the heat-resistant porous layer absorb the non-aqueous electrolyte, and the non-aqueous electrolyte at the interface of the positive electrode decreases. The thermal runaway reaction can be suppressed well.

Examples of the nonaqueous electrolytic solution for the heat resistant porous layer include dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propionate, ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, ethylene glycol sulfite, 1,2- An organic solvent composed of only one kind such as dimethoxyethane, 1,3-dioxolane, tetrahydrofuran, 2-methyl-tetrahydrofuran, diethyl ether, or a mixed solvent of two or more kinds, for example, LiClO ₄ , LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiSbF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , Li ₂ C ₂ F ₄ (SO ₃ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiC _n F _{2n + 1 SO 3 (2 ≦ n ≦} 7), LiN (R f OS _{2) 2} [wherein, R _f represents a fluoroalkyl group. And the like prepared by dissolving at least one selected from lithium salts such as The concentration of the lithium salt in the non-aqueous electrolyte is preferably 0.5 to 1.5 mol / L, and more preferably 0.9 to 1.25 mol / L.

  Then, an example of the lithium ion secondary battery of this invention is demonstrated based on drawing. FIG. 1 is a cross-sectional view showing an example of the lithium ion secondary battery of the present invention. In FIG. 1, a lithium secondary battery of the present invention includes a positive electrode 1 having a positive electrode mixture layer containing the positive electrode active material described above, a negative electrode 2 having a negative electrode mixture layer containing a negative electrode active material, and A separator 3 and a non-aqueous electrolyte 4 are provided. The positive electrode 1 and the negative electrode 2 are spirally wound through a separator 3 and are housed in a cylindrical battery can 5 together with a nonaqueous electrolyte solution 4 as an electrode body having a wound structure.

  However, in FIG. 1, in order to avoid complication, the metal foil which is a current collector used for manufacturing the positive electrode 1 and the negative electrode 2 is not illustrated. Moreover, although the separator 3 shows the cut surface, it does not attach | subject the hatching which shows a cross section.

  The battery can 5 is made of, for example, iron and nickel-plated on the surface, and an insulator 6 made of, for example, polypropylene is disposed at the bottom of the battery can 5 prior to the insertion of the electrode body having the winding structure. The sealing plate 7 is made of, for example, aluminum and has a disk shape. A thin portion 7a is provided at the center of the sealing plate 7, and a pressure introduction port 7b for allowing the battery internal pressure to act on the explosion-proof valve 9 around the thin portion 7a. As a hole. And the protrusion part 9a of the explosion-proof valve 9 is welded to the upper surface of the thin part 7a, and the welding part 11 is comprised. The thin-walled portion 7a provided on the sealing plate 7 and the protruding portion 9a of the explosion-proof valve 9 are shown only on the cut surface for easy understanding on the drawing, and the contour line behind the cut surface is not shown. doing. In addition, the welded portion 11 between the thin-walled portion 7a of the sealing plate 7 and the protruding portion 9a of the explosion-proof valve 9 is also shown in an exaggerated state so as to facilitate understanding on the drawing.

  The terminal plate 8 is made of, for example, rolled steel, has a nickel-plated surface, and has a hat-like shape with a peripheral edge portion, and the terminal plate 8 is provided with a gas discharge port 8a. The explosion-proof valve 9 is made of, for example, aluminum and has a disk shape. A projection 9a having a tip portion is provided on the power generation element side (lower side in FIG. 1) at the center, and the thin-walled portion 9b As described above, the lower surface of the protruding portion 9a is welded to the upper surface of the thin-walled portion 7a of the sealing plate 7 to form the welded portion 11. The insulating packing 10 is made of, for example, polypropylene and has an annular shape. The insulating packing 10 is arranged at the upper part of the peripheral edge of the sealing plate 7, and the explosion-proof valve 9 is arranged at the upper part thereof, so that the sealing plate 7 and the explosion-proof valve 9 are insulated. At the same time, the gap between the two is sealed so that the electrolyte does not leak from between them. The annular gasket 12 is made of, for example, polypropylene. The lead body 13 is made of aluminum, for example, and connects the sealing plate 7 and the positive electrode 1. An insulator 14 is disposed on the upper part of the wound electrode body, and the negative electrode 2 and the bottom of the battery can 5 are connected to each other by a lead body 15 made of nickel, for example.

  In the battery of FIG. 1, the thin-walled portion 7a of the sealing plate 7 and the protruding portion 9a of the explosion-proof valve 9 are in contact with each other at the welded portion 11, and the peripheral portion of the explosion-proof valve 9 and the peripheral portion of the terminal plate 8 are in contact. 1 and the sealing plate 7 are connected by a lead body 13 on the positive electrode side. Therefore, in a normal state, the positive electrode 1 and the terminal plate 8 are connected to the lead body 13, the sealing plate 7, the explosion-proof valve 9 and their welded parts. The electrical connection is obtained by 11 and functions normally as an electric circuit.

  When an abnormal situation occurs in the battery, such as the battery is exposed to high temperature or generates heat due to overcharge, and gas is generated inside the battery and the internal pressure of the battery increases, the explosion-proof valve 9 The center part of the is deformed in the internal pressure direction (the upper direction in FIG. 1). Along with this, a shearing force is applied to the thin portion 7a of the sealing plate 7 integrated at the welded portion 11, and the thin portion 7a is broken, or the projection 9a of the explosion-proof valve 9 and the thin portion 7a of the sealing plate 7 are broken. After the welded portion 11 is peeled off, the thin-walled portion 9b provided in the explosion-proof valve 9 is cleaved to discharge the gas from the gas discharge port 8a of the terminal plate 8 to the outside of the battery, thereby preventing the battery from bursting. Designed to be able to.

  The non-aqueous electrolyte battery of the present invention is a conventionally known non-aqueous electrolyte battery (non-aqueous electrolyte primary battery, non-aqueous electrolyte solution, including automobile applications, power tools, and power supply applications for various electronic devices). The present invention can also be applied to the same uses as various uses in which secondary batteries are used.

  Hereinafter, the present invention will be described in detail based on examples. However, the following examples do not limit the present invention.

Example 1
<Preparation of separator>
In 600 g of water, 500 g of a polyhedral boehmite synthetic product (aspect ratio 1.4, D50 = 0.63 μm) as heat-resistant fine particles, and poly N-vinylacetamide (heat-resistant fine particles and swelling properties described later) as a binder 5 parts by mass with respect to a total of 100 parts by mass with fine particles) was dispersed by stirring for 1 hour using a three-one motor, and further an aqueous dispersion of crosslinked PMMA fine particles as swellable fine particles (D50 = 0). 0.5 μm, Tg = 105 ° C., solid content ratio 40 mass%) is added so that the ratio of the crosslinked PMMA fine particles to the boehmite synthetic product is 50:50 by volume, and uniformly dispersed to form a heat resistant porous layer A composition was prepared.

  The cross-linked PMMA fine particles have an absorption amount of non-aqueous electrolyte (non-aqueous electrolyte used in a battery described later) at 25 ° C. and 130 ° C. measured by the above-described method of 0 per 1 g of cross-linked PMMA fine particles. 0.7 mL and 2.0 mL.

  As a porous resin membrane for a separator, a three-layer PP / PE / PP microporous membrane having a thickness of 16 μm and a porosity of 40% and having a PP layer on both sides of the PE layer is prepared (melting of PP The temperature was 155 ° C., the melting temperature of PE was 135 ° C.), and both surfaces were subjected to corona discharge treatment. Then, the heat-resistant porous layer forming composition is uniformly applied to one side of the microporous membrane made of PP / PE / PP using a die coater so that the thickness after drying becomes 4.0 μm, and dried. A heat resistant porous layer was formed to obtain a separator.

In the heat-resistant porous layer according to the separator, the volume ratio of the swellable fine particles calculated by setting the specific gravity of boehmite to 3 g / cm ³ , the specific gravity of crosslinked PMMA to 1 g / cm ³ , and the specific gravity of the binder to 1 g / cm ³ is 45 volumes. %, And the volume ratio of the heat-resistant fine particles was 45% by volume. In addition to the specific gravity described above, the resin in the whole separator was calculated with a specific gravity of PE of 1 g / cm ³ and a specific gravity of PP of 1 g / cm ³ (in the polyolefin related to the resin porous membrane and the heat resistant porous layer). The volume ratio of the swellable fine particles and the binder) was 87% by volume.

<Preparation of positive electrode>
LiNi _0.6 Mn _0.2 Co _0.2 O _{2 as} positive electrode active material: 86.2 parts by mass, graphite as a conductive additive: 9.0 parts by mass, and acetylene black: 1.8 parts by mass, An N-methyl-2-pyrrolidone (NMP) solution containing 3 parts by mass of PVDF (binder) was added and kneaded well to prepare a positive electrode mixture-containing slurry. Next, the slurry is added in such an amount that the mass of the positive electrode mixture layer after drying is 11.6 mg / cm ^{2 on} one side of the positive electrode current collector on both surfaces of an aluminum foil having a thickness of 20 μm to be the positive electrode current collector. Was applied uniformly, then dried at 80 ° C., and further compression molded with a roll press to obtain a positive electrode. When applying the positive electrode mixture-containing slurry to the aluminum foil, a part of the aluminum foil was exposed. The thickness of the positive electrode mixture layer of the positive electrode was 26 μm per one side of the current collector (aluminum foil).

  The positive electrode is cut so that the size of the positive electrode mixture layer is 800 mm × 48 mm and includes the exposed portion of the aluminum foil, and an aluminum lead piece for taking out an electric current is formed on the exposed portion of the aluminum foil. Welded.

<Production of negative electrode>
Natural graphite as a negative electrode active material: 90 parts by mass and acetylene black as a conductive auxiliary agent: 4.7 parts by mass are mixed, and an NMP solution containing 5.3 parts by mass of PVDF (binder) is added thereto. The mixture was well kneaded to prepare a negative electrode mixture-containing slurry. Next, the weight of the negative electrode mixture layer after drying on both sides of a rolled copper foil having a thickness of 20 μm to be a negative electrode current collector is 5.0 mg / cm ² per side of the negative electrode current collector in the amount described above. The slurry was uniformly applied, then dried at 80 ° C., and further compression molded with a roll press to obtain a negative electrode. When applying the negative electrode mixture-containing slurry to the rolled copper foil, a part of the rolled copper foil was exposed. The thickness of the negative electrode mixture layer of the negative electrode was 21 μm per one side of the current collector (rolled copper foil).

  The negative electrode is cut so that the size of the negative electrode mixture layer is 850 mm × 52 mm and includes the exposed portion of the rolled copper foil, and a nickel lead piece for taking out the current is exposed to the rolled copper foil. Welded to the part.

<Battery assembly>
The positive electrode and the negative electrode were overlapped with the separator interposed so that the heat-resistant porous layer faced the positive electrode, and wound into a spiral shape to obtain a wound electrode body. This wound electrode body is inserted into a cylindrical outer casing (outer can) made of an aluminum alloy, and a non-aqueous electrolyte (ethylene carbonate, dimethyl carbonate and methyl ethyl carbonate are mixed at a volume ratio of 2: 4: 4). A solution in which LiPF ₆ is dissolved at a concentration of 1 mol / L) is injected into the exterior body, and the opening of the exterior body is heat-sealed to form a cylindrical winding having a length of 65 mm and a diameter of 18 mm. A non-aqueous electrolyte secondary battery (lithium ion secondary battery) having an electrode body therein was produced. The obtained battery had a rated capacity of 1150 mAh. The batteries of the following examples and comparative examples all have a rated capacity of 1150 mAh.

(Example 2)
A composition for forming a heat resistant porous layer was prepared in the same manner as in Example 1 except that the ratio of the crosslinked PMMA fine particles to the boehmite synthesized product was 30:70 by volume. A separator was prepared in the same manner as in Example 1 except that the composition for use was used. In the heat-resistant porous layer according to this separator, the volume ratio of swellable fine particles calculated in the same manner as in the separator of Example 1 is 27% by volume, and the volume ratio of heat-resistant fine particles is 63% by volume. The volume ratio of the resin in the whole separator calculated as described above was 82% by volume.

  And the nonaqueous electrolyte secondary battery was produced like Example 1 except having used this separator.

(Example 3)
A composition for forming a heat resistant porous layer was prepared in the same manner as in Example 1 except that the ratio of the crosslinked PMMA fine particles to the boehmite synthesized product was 70:30 in volume ratio. A separator was prepared in the same manner as in Example 1 except that the composition for use was used. In the heat resistant porous layer according to this separator, the volume ratio of the swellable fine particles calculated in the same manner as in the separator of Example 1 is 65% by volume, and the volume ratio of the heat resistant fine particles is 28% by volume. The volume ratio of the resin in the whole separator calculated as described above was 92% by volume.

  And the nonaqueous electrolyte secondary battery was produced like Example 1 except having used this separator.

Example 4
Formation of heat-resistant porous layer in the same manner as in Example 1 except that the amount of the N-vinylacetamide-based polymer was changed to 1 part by mass with respect to 100 parts by mass in total of the swellable fine particles and heat-resistant fine particles. A separator was prepared in the same manner as in Example 1 except that the composition for heat treatment was prepared and this heat-resistant porous layer forming composition was used. In the heat resistant porous layer according to this separator, the volume ratio of swellable fine particles calculated in the same manner as in the separator of Example 1 was 49% by volume, and the volume ratio of heat resistant fine particles was 49% by volume. The volume ratio of the resin in the whole separator calculated as described above was 86% by volume.

  And the nonaqueous electrolyte secondary battery was produced like Example 1 except having used this separator.

(Example 5)
The heat resistant porous layer was formed in the same manner as in Example 1 except that the amount of the N-vinylacetamide-based polymer was changed to 15 parts by mass with respect to 100 parts by mass in total of the swellable fine particles and the heat resistant fine particles. A separator was prepared in the same manner as in Example 1 except that the composition for heat treatment was prepared and this heat-resistant porous layer forming composition was used. In the heat-resistant porous layer according to this separator, the volume ratio of swellable fine particles calculated in the same manner as in the separator of Example 1 was 38% by volume, and the volume ratio of heat-resistant fine particles was 38% by volume. The volume ratio of the resin in the whole separator calculated as described above was 89% by volume.

  And the nonaqueous electrolyte secondary battery was produced like Example 1 except having used this separator.

(Comparative Example 1)
A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that a PE microporous film (thickness 20 μm, porosity 40%) was used as a separator without forming a heat-resistant porous layer. did.

(Comparative Example 2)
Without using crosslinked PMMA fine particles which are swellable fine particles, an acrylate copolymer (acrylic acid-butyl acrylate copolymer containing butyl acrylate as a main component as a monomer component) instead of an N-vinylacetamide polymer binder as a binder, A composition for forming a heat resistant porous layer was prepared in the same manner as in Example 1 except that the amount of the binder was changed to 5 parts by weight with respect to 100 parts by weight of the heat resistant fine particles, and this heat resistant porous layer forming composition was prepared. A separator was produced in the same manner as in Example 1 except that was used. In the heat-resistant porous layer according to this separator, the volume ratio of the heat-resistant fine particles calculated in the same manner as in the separator of Example 1 is 87% by volume, and the volume of the resin in the whole separator calculated in the same manner as in Example 1 The ratio was 74% by volume.

  And the nonaqueous electrolyte secondary battery was produced like Example 1 except having used this separator.

(Comparative Example 3)
Without using the heat-resistant fine particles, the same binder as used in Example 1 is added to 1000 g of the aqueous dispersion of the same crosslinked PMMA fine particles as used in Example 1, and 5 parts by mass with respect to 100 parts by mass of the swellable fine particles. The mixture was stirred and dispersed for 1 hour using a three-one motor to prepare a heat-resistant porous layer forming composition.

  A separator was prepared in the same manner as in Example 1 except that the heat-resistant porous layer forming composition was used. In the heat-resistant porous layer according to this separator, the volume ratio of the swellable fine particles calculated in the same manner as in the separator of Example 1 is 95% by volume, and the volume of the resin in the whole separator calculated in the same manner as in Example 1 The ratio was 100% by volume.

  And the nonaqueous electrolyte secondary battery was produced like Example 1 except having used this separator.

(Comparative Example 4)
The heat resistant porous material was the same as in Example 1 except that the amount of the N-vinylacetamide-based polymer was changed to an amount of 0.05 parts by mass with respect to 100 parts by mass in total of the swellable fine particles and the heat resistant fine particles. A separator was prepared in the same manner as in Example 1 except that a layer forming composition was prepared and this heat resistant porous layer forming composition was used. In the heat resistant porous layer according to this separator, the volume ratio of the swellable fine particles calculated in the same manner as in the separator of Example 1 was 49.95% by volume, and the volume ratio of the heat resistant fine particles was 49.95% by volume. The volume ratio of the resin in the whole separator calculated in the same manner as in Example 1 was 85% by volume.

  And the nonaqueous electrolyte secondary battery was produced like Example 1 except having used this separator.

  Next, the following evaluation was performed about the battery of Examples 1-5 and Comparative Examples 1-4, and the separator used for these batteries.

<Measurement of heat shrinkage of separator>
The separator was cut into a rectangular shape with a length of 5 cm and a width of 10 cm, and a cross line of 3 cm parallel to the vertical direction and 3 cm parallel to the horizontal direction was drawn with black ink. When the separator is cut into a rectangle, the longitudinal direction is set to the machine direction (MD) of the porous resin membrane constituting the separator, and the cross line is set so that the intersection is the center of the separator piece. . Thereafter, the separator piece was suspended in a thermostatic chamber whose interior was set to 200 ° C. And after taking out a separator piece from a thermostat after 1 hour and cooling to room temperature, length d (mm) of the shorter one of a crosshair was measured, and heat contraction rate (%) was computed by the following formula. .

  Thermal contraction rate = 100 × (30−d) / 30

<Measurement of load characteristics>
For each battery, after charging to 4.2 V at a current value of 1/2 C (575 mA) with respect to the rated capacity (1150 mAh), discharging to 3.0 V at a predetermined current value, and measuring the discharge capacity at each current value did. The discharge current values were 1 / 2C and 10C. The ratio of the discharge capacity at 10C to the discharge capacity at 1 / 2C was expressed as a percentage to obtain the capacity maintenance ratio. It can be said that the larger the capacity retention rate, the better the load characteristics of the battery.

<Internal short circuit test>
A thermocouple in the vicinity of the central side of each battery that has been charged with constant current to constant voltage up to the rated capacity [constant current: 1/3 C (383.3 mA), constant voltage: 4.2 V, charge end time: 4.5 hours]. Was wrapped with a glass wool with a thickness of 6 mm, and covered with a cylindrical aluminum laminate film with a diameter of 30 mm to heat-insulate the battery. In addition, the battery voltage and surface temperature during the test were monitored. Then, a stainless steel nail having a diameter of 3 mm was pierced at a speed of 1 mm / sec from the center of the charged battery at 20 ° C. Then, when a voltage drop due to a short circuit was observed, the descent of the nail was stopped and held, and the subsequent temperature rise on the battery surface was confirmed. Then, when the battery surface rises to 200 ° C. within 10 seconds from the stop of the nail, it is evaluated as “temperature rise (temperature rise)”, and when it does not fall under this, “temperature rise can be suppressed ( Temperature rise suppression) ”.

  The structure of the separator used for the battery of Examples 1-5 and Comparative Examples 1-4 is shown in Table 1, and each said evaluation result is shown in Table 2.

  The “amount of binder” of the heat-resistant porous layer in Table 1 means the amount (part by mass) relative to 100 parts by mass of the swellable fine particles and the heat-resistant fine particles, and “the ratio of the resin in the whole separator” is The volume ratio of all the resin in the whole volume of the component of a separator is shown.

  As shown in Table 2, Examples 1 to 1 comprising a heat-resistant porous layer containing swellable fine particles and heat-resistant fine particles in an appropriate volume ratio and containing an N-vinylacetamide-based polymer in an appropriate amount. In the separator No. 5, the heat shrinkage of the entire separator at 200 ° C. can be satisfactorily suppressed while the heat resistant porous layer is thinned to suppress an increase in the thickness of the entire separator. And the non-aqueous electrolyte secondary battery of Examples 1-5 using these separators has suppressed the temperature rise at the time of an internal short circuit test, and the reliability which is hard to produce thermal runaway even when abnormally overheating, and It can be confirmed that it is excellent in safety.

  In contrast, the separator of Comparative Example 1 in which no heat-resistant porous layer was formed, the separator of Comparative Example 2 in which a heat-resistant porous layer not containing swellable fine particles was formed, and the heat-resistant porous material containing no heat-resistant fine particles Both the separator of Comparative Example 3 in which the porous layer was formed and the separator of Comparative Example 4 in which the heat-resistant porous layer with a small amount of N-vinylacetamide polymer was formed had a large heat shrinkage rate at 200 ° C. The batteries of Comparative Examples 1 to 4 used have poor reliability during the internal short circuit test.

  In addition, the batteries of Examples 1 to 4 using the separator with the binder amount in the heat resistant porous layer being a suitable value are more loaded than the battery of Example 5 using the separator having a large amount of binder in the heat resistant porous layer. Good characteristics.

  The present invention can be implemented in other forms than the above without departing from the spirit of the present invention. The embodiments disclosed in the present application are merely examples, and the present invention is not limited thereto. The scope of the present invention is construed in preference to the description of the appended claims rather than the description of the above specification, and all modifications within the scope equivalent to the claims are construed in the scope of the claims. It is included.

DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Negative electrode 3 Separator 4 Non-aqueous electrolyte 5 Battery can 6 Insulator 7 Sealing board 7a Thin part 7b Pressure inlet 8 Terminal board 8a Gas exhaust 9 Explosion-proof valve 9a Protrusion part 9b Thin part 10 Insulation packing 11 Weld part 12 Annular gasket 13 Lead body 14 Insulator 15 Lead body

Claims (8)

A separator for a nonaqueous electrolyte battery comprising a resin porous membrane and a heat-resistant porous layer disposed on the surface of the resin porous membrane,
The resin porous membrane is formed from a resin whose main component is a polyolefin having a melting temperature of 80 to 180 ° C.,
The heat-resistant porous layer includes swellable fine particles that swell by absorbing a non-aqueous electrolyte by heating, heat-resistant fine particles, and a binder,
The volume ratio of the swellable fine particles and the heat-resistant fine particles is 30:70 to 70:30 ,
The binder includes an N-vinylacetamide-based polymer,
When the total amount of the swellable fine particles and the heat-resistant fine particles is 100 parts by mass, the content of the N-vinylacetamide polymer is 0.1 parts by mass or more,
The ratio of all the resins in the total volume of the constituent components of the separator is 50 to 99.9% by volume,
A separator for a non-aqueous electrolyte battery, wherein the heat-resistant porous layer has a thickness of 2 to 10 µm.   2. The nonaqueous electrolytic solution according to claim 1, wherein the content of the binder in the heat resistant porous layer is 15 parts by mass or less when the total amount of the swellable fine particles and the heat resistant fine particles is 100 parts by mass. Battery separator. The swellable fine particles are formed from a crosslinked acrylic resin,
The separator for a nonaqueous electrolyte battery according to claim 1, wherein the acrylic resin crosslinked body has a glass transition point of 50 to 130 ° C.   The separator for a non-aqueous electrolyte battery according to claim 1, wherein the swellable fine particles have an average particle diameter of 0.05 to 2 μm.   The separator for a nonaqueous electrolyte battery according to claim 1, wherein the heat resistant temperature of the heat resistant fine particles is 300 ° C. or higher.   The separator for a non-aqueous electrolyte battery according to claim 1, wherein the heat-resistant fine particles have an average particle diameter of 0.05 to 2 μm.   The separator for a non-aqueous electrolyte battery according to claim 1, wherein the thermal shrinkage rate when standing in a temperature atmosphere of 200 ° C. is 5% or less. Including positive electrode, negative electrode, separator and non-aqueous electrolyte,
The said separator is a separator for nonaqueous electrolyte batteries in any one of Claims 1-7, The nonaqueous electrolyte battery characterized by the above-mentioned.

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