JP2015028840A - Nonaqueous electrolyte battery separator and nonaqueous electrolyte battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a separator for a nonaqueous electrolyte battery which allows an excellent heat resistance to be ensured while suppressing the increase in thickness; and a nonaqueous electrolyte battery using such a separator, and having high reliability.SOLUTION: A nonaqueous electrolyte battery separator comprises: a resin porous film; and a heat-resistant porous layer on at least one side of the resin porous film. The percentage of the resin to the total volume of components forming the separator is 50-99.9 vol.%. The heat-resistant porous layer includes swelling microparticles, heat resistant microparticles, and a binder. The ratio of the volume of the swelling microparticles to that of the heat resistance microparticles is 10:90 to 95:5. Supposing that the total amount of the swelling microparticles and the heat resistance microparticles is 100 pts.mass, the amount of polymer, as the binder, having a group having a cyclic structure including an amide bond and a skeleton originating from a polymerizable double bond, and having a glass transition temperature of 130°C or higher and a weight-average molecular weight of 350,000 or more is 0.1 pt.mass or more. The heat-resistant porous layer has a thickness of 2-10 μm. A nonaqueous electrolyte battery comprises the separator.

Description

  The present invention relates to a lithium secondary battery having a high capacity and excellent safety.

Lithium ion secondary batteries, which are a type of non-aqueous electrolyte battery, have a higher energy density than other batteries and no memory effect, so they are widely used as power sources for mobile devices such as mobile phones and laptop computers. It's being 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 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 a polyolefin-based porous film separator is used, when the battery temperature reaches the shutdown temperature in the case of abnormal charging, the current must be immediately decreased to prevent the battery temperature from rising. This is because if the pores are not sufficiently closed and the current cannot be reduced immediately, the battery temperature easily rises to the contraction temperature of the separator, and there is a risk of ignition 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 pressure, causing an internal short circuit, which may cause battery heat generation. is there. 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 carboxymethyl cellulose 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.

  For example, as in Patent Document 9, 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. There is a problem that the battery capacity is reduced because the separator becomes complicated or the entire separator becomes thick.

  For these reasons, it is necessary to develop 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 the heat resistance.

  The present invention has been made in view of the above circumstances, and its purpose is to use a separator for a non-aqueous electrolyte battery that can ensure excellent heat resistance while suppressing an increase in thickness, and the separator. An object is to provide a non-aqueous electrolyte battery having high reliability.

  The separator for a non-aqueous electrolyte battery of the present invention that has achieved the above object has a heat-resistant porous layer on at least one surface of a porous resin film mainly composed of polyolefin having a melting temperature of 80 to 180 ° C. The ratio of the resin in the total volume of the constituent components of the separator is 50 to 99.9% by volume, and the heat-resistant porous layer increases the absorption amount of the non-aqueous electrolyte by heating in the non-aqueous electrolyte. Swellable fine particles that swell, heat-resistant fine particles, and a binder, and the volume ratio of the swellable fine particles and the heat-resistant fine particles is 10:90 to 95: 5, It has a group having a cyclic structure containing an amide bond and a skeleton derived from a polymerizable double bond, contains a polymer having a glass transition temperature of 130 ° C. or higher and a weight average molecular weight of 350,000 or higher. Before When the total amount of the swellable fine particles and the heat-resistant fine particles is 100 parts by mass, the amount of the polymer is 0.1 parts by mass or more, and the thickness of the heat-resistant porous layer is 2 to 10 μm. To do.

  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 non-aqueous electrolyte battery separator of the present invention. is there.

  According to the present invention, a separator for a non-aqueous electrolyte battery that can ensure excellent heat resistance while suppressing an increase in thickness, and a non-aqueous electrolyte battery having high reliability using the separator are provided. can do.

  The separator for nonaqueous electrolyte batteries of the present invention (hereinafter simply referred to as “separator”) 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 easily contracts under a high temperature environment, and has a poor shape stability under a high temperature.

  The separator of the present invention contains a resin having poor shape stability at a high temperature as described above (including the resin contained in the resin porous membrane, the swellable fine particles contained in the heat resistant porous layer, and the 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 related to the separator usually do not absorb the non-aqueous electrolyte contained in the battery or have a limited amount of absorption in the temperature range (approximately 70 ° C. or less) in which the battery is used. Therefore, although the degree of swelling is below a certain level, a resin having such a property that when the inside of the battery abnormally generates heat, it absorbs the non-aqueous electrolyte and swells greatly and the degree of swelling increases as the temperature rises is used. It is done. 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 functional 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 swell by absorbing the non-aqueous electrolyte in the battery. 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. . 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. It is preferably 1 ml or less.

  The details of the mechanism by which the swellable fine particles swell as the temperature rises are not clear, but, for example, crosslinked polymethyl methacrylate (PMMA), which is an example of the swellable fine particles, has a glass transition point ( Since 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 around 100 ° C., and swells by absorbing more non-aqueous electrolyte. Therefore, it is considered that the Tg of the swellable fine particles is preferably, for example, 70 ° 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 nonaqueous electrolyte (nonaqueous electrolyte used in a battery) is added thereto, and the powder is immersed in the nonaqueous electrolyte at 25 ° C. for 24 hours. Thereafter, it is filtered through a 25 μm metal mesh to separate the powder and the non-aqueous electrolyte, and the amount of the obtained non-aqueous electrolyte (the non-aqueous electrolyte not absorbed by the powder) is measured. From the difference from the amount of the nonaqueous electrolyte solution added, the absorption amount of the nonaqueous electrolyte solution at 25 ° C. of the swellable fine particles is determined.

  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. 0.3 g of the swellable fine particle powder obtained in the same manner as in the case of measuring the amount of absorption at 25 ° C. is placed in a glass container, and 5 ml of nonaqueous electrolyte (nonaqueous electrolyte used in the 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 addition, in the absorption measurement at 25 ° C. and the absorption measurement at 130 ° C. by the above method, loss of the non-aqueous electrolyte accompanying filtration and loss due to volatilization of the non-aqueous electrolyte solvent during heating (absorption at 130 ° C. Measurement case) can 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.

  Further, the Tg of the swellable fine particles and the binder (polymer used as a binder) described later in this specification is a value measured using a differential scanning calorimeter (DSC) in accordance with the provisions of JIS K7121. It is.

  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.), SBR, acrylic resin (PMMA, etc.), polyalkylene oxide (polyethylene oxide (PEO), etc.), fluororesin (PVDF, etc.), and derivatives thereof. Examples include a crosslinked product of at least one resin selected from the group; urea resin; polyurethane; 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 above-described constituent materials, crosslinked styrene resin, crosslinked acrylic resin, and crosslinked fluororesin are preferable, and crosslinked PMMA is particularly preferable.

  The swellable fine particles may have a homogeneous structure as a whole, or may have a core-shell structure in which the core part and the shell part are different. As the swellable fine particles having a core-shell structure, for example, the core part is composed of an acrylic resin crosslinked body (preferably crosslinked PMMA) having a Tg of 25 ° C. or less (preferably 0 ° C. or less), and the shell part has a Tg of 70 ° C. or more. Fine particles composed of a crosslinked acrylic resin (preferably 130 ° C. or less) (preferably crosslinked PMMA) can be used. When the swellable fine particles having such a core-shell structure are used, it is possible to suppress swelling at low temperatures with a high-Tg acrylic resin crosslinked body and to effectively swell with a low Tg acrylic resin crosslinked body. It becomes possible. In addition, when such swellable fine particles having a core-shell structure are used, it is possible to disperse the stress that the porous resin membrane of the separator tends to contract at high temperatures, and it is difficult to contract even when exposed to higher temperatures. A separator can be realized.

  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. On the other hand, if the average particle diameter 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 in the plane direction, which may become a lithium ion migration barrier during charge / discharge of the battery.

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 (D ₅₀ ) 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. The heat resistance (heat resistant temperature) of the heat resistant fine particles is more preferably 300 ° C. or higher.

  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. If it does not melt | dissolve in a non-aqueous electrolyte, there will be no restriction | limiting in particular.

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 conductive fine particles such as metal fine particles; oxide fine particles such as SnO ₂ and tin-indium oxide (ITO); carbon 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. Moreover, if the average particle diameter 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 in the plane direction, which may become a lithium ion migration barrier during charge / discharge of the battery.

  The heat-resistant porous layer related to the separator contains a binder in order to improve the adhesion between fine particles such as swellable fine particles and heat-resistant fine particles, and to improve the adhesion between the heat-resistant porous layer and the resin porous membrane. ing.

  The binder of the heat resistant porous layer has a group having a cyclic structure containing an amide bond and a skeleton derived from a polymerizable double bond, a glass transition temperature (Tg) of 130 ° C. or higher, and a weight average molecular weight of 350,000. The polymer (A) described above [hereinafter sometimes simply referred to as “polymer (A)”] is used.

  In a non-aqueous electrolyte battery, in order to increase the reliability at high temperatures, it is difficult for the separator interposed between the positive electrode and the negative electrode to shrink, and it is important to prevent direct contact between the positive electrode and the negative electrode. Become.

  If the Tg of the polymer (A) is 130 ° C. or higher, the heat-resistant fine particles related to the heat-resistant porous layer, or the heat-resistant porous layer and the resin porous membrane are firmly formed until the inside of the battery reaches 130 ° C. Can remain fixed. Therefore, since the shrinkage of the heat resistant porous layer itself and the resin porous membrane integrated with the heat resistant porous layer can be suppressed, a separator that can constitute a non-aqueous electrolyte battery excellent in reliability at high temperatures is provided. It becomes possible to form. The Tg of the polymer (A) is more preferably 150 ° C. or higher.

  The polymer (A) has a weight average molecular weight of 350,000 or more, preferably 400,000 or more, more preferably 1,000,000 or more, and further preferably 1,500,000 or more. In general, in a polymer having a skeleton derived from a polymerizable double bond, as the molecular weight thereof increases, Tg tends to increase and the adhesive strength tends to increase. Therefore, the weight average molecular weight should be the above value. Thus, the polymer (A) having a Tg of the above value can be easily obtained, and the peel strength between the heat-resistant porous layer and the resin porous film can be increased. Can be suppressed to a high degree. Further, since the decomposition of the polymer (A) in the battery can be suppressed by using the polymer (A) having a weight average molecular weight satisfying the above value as a binder, non-aqueous electrolysis having this heat-resistant porous layer is possible. The high temperature storage characteristics of the liquid battery can also be enhanced.

  The polymer (A) used as a binder has a cyclic structure containing an amide bond and a skeleton derived from a polymerizable double bond, and in addition to a large tensile strength and tensile modulus, Good adhesion to heat-resistant fine particles and swellable fine particles. Therefore, the use of the polymer (A) increases the strength of the heat-resistant porous layer because the heat-resistant fine particles and the swellable fine particles constituting the heat-resistant porous layer are densely filled. 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. When the heat-resistant porous layer is formed using the heat-resistant porous layer forming composition, the polymer (A) functions as a thickener in the composition, and the heat-resistant fine particles in the composition As a result, the use of the polymer (A) can form a heat-resistant porous layer that is more uniform and excellent in surface smoothness and is less likely to cause internal resistance spots in the battery. become.

  However, if the molecular weight of the polymer (A) is too large, the viscosity of the heat-resistant porous layer-forming composition may increase and the applicability may decrease. Therefore, the weight average molecular weight of the polymer (A) is preferably 20 million or less, more preferably 10 million or less, further preferably 4 million or less, and particularly preferably 3.5 million or less. preferable.

  The weight average molecular weight of the polymer (A) as used herein is a weight average molecular weight (polystyrene equivalent value) measured using gel permeation chromatography.

  The polymer (A) may have at least a part of a group having a cyclic structure containing an amide bond and a skeleton derived from a polymerizable double bond, and a group having a cyclic structure containing an amide bond; And a homopolymer or a copolymer obtained by polymerizing a monomer having a polymerizable double bond. The monomer for forming the polymer (A) may have only one or a plurality of groups having a cyclic structure containing an amide bond. The group having a cyclic structure containing an amide bond is more preferably a group represented by the following chemical formula (1).

  Specific examples of the polymer (A) include cyclic structures containing amide bonds such as poly (N-vinylcaprolactam) (a homopolymer of N-vinylcaprolactam) and polyvinylpyrrolidone (PVP: a homopolymer of vinylpyrrolidone). Homopolymer of a monomer having a group having a cyclic bond and a polymerizable double bond; two or more monomers having a cyclic structure containing an amide bond and a polymerizable double bond (N-vinylcaprolactam, vinylpyrrolidone, etc.) One or more monomers (N-vinylcaprolactam, vinylpyrrolidone, etc.) having a group having a cyclic structure containing an amide bond and a polymerizable double bond, and other polymerizable double bonds A monomer having a cyclic structure (a monomer other than a monomer having a cyclic structure containing an amide bond and a polymerizable double bond) or Copolymers of seed or greater; and the like.

  Having the other polymerizable double bond capable of constituting a copolymer of a monomer having a cyclic structure containing an amide bond and a polymerizable double bond and a monomer having another polymerizable double bond Examples of the monomer include vinyl acyclic amides, (meth) acrylic acid and esters thereof, (meth) acrylamide and derivatives thereof [“(meth) acrylamide” means acrylamide and methacrylamide. . ], Styrene and derivatives thereof, vinyl esters such as vinyl acetate, α-olefins, basic unsaturated compounds such as vinyl imidazole and vinyl pyridine and derivatives thereof, carboxyl group-containing unsaturated compounds and acid anhydrides thereof Vinyl sulfonic acid and its derivatives, vinyl ethylene carbonate and its derivatives, vinyl ethers, and the like.

  A group having a cyclic structure containing an amide bond and a group having a cyclic structure containing an amide bond in a copolymer of a monomer having a cyclic structure containing an amide bond and a polymerizable double bond and another monomer having a polymerizable double bond. The content of the unit derived from the monomer having a heavy bond is, for example, 40 mol out of 100 mol% of all the units derived from the monomer possessed by the vinyl pyrrolidone copolymer because it becomes easy to adjust Tg to the above value. % Or more, more preferably 60 mol% or more, and still more preferably 80 mol% or more.

  Moreover, another binder can also be used for a binder with a polymer (A). Examples of such other binders include ethylene-vinyl acetate copolymers, acrylate copolymers, water-soluble nylon, vinyl alcohol polymers, and vinyl ether polymers.

  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 amount of the polymer (A) 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.

  Moreover, by preparing the composition for forming a heat resistant porous layer such that the amount of the polymer (A) is 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 the polymer (A), and the precipitation of the fine particles in the composition can be suppressed more favorably, and a heat-resistant porous layer having more uniform and excellent surface smoothness can be formed.

  Further, from the viewpoint of maintaining the amount of pores in the heat-resistant porous layer appropriately, for example, from the viewpoint of improving the load characteristics of the battery, the amount of binder when the total amount of swellable fine particles and heat-resistant fine particles is 100 parts by mass [Total amount of binder containing polymer (A)] 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, and 1 part by mass or less. It is particularly preferable that

  The amount 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 pores; the same applies hereinafter) 45 More preferably, it is at least volume%. 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 amount 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. More preferred.

  In addition, the amount of heat-resistant fine particles in the heat-resistant porous layer enhances the shape stability of the separator at a high temperature, suppresses heat shrinkage when the inside of the battery becomes high temperature, and improves the heat-resistant porous layer. From the viewpoint of suppressing the aggregation of the swellable fine particles and improving 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% by volume. More preferably.

  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. Further, by setting the heat-resistant porous layer to such a thickness, it is possible to satisfactorily prevent ignition due to an internal short circuit when conductive foreign matter is mixed in the battery. 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.

  The “polyolefin is the main component” in the resin porous membrane means that the polyolefin is 50% by volume or more of the total volume of the components constituting the resin porous membrane. From the standpoint of ensuring better shutdown characteristics, the main component polyolefin is preferably 70% by volume or more, and 80% by volume or more of the total volume of the components constituting the resin porous membrane. Is more preferable (the polyolefin may be 100% by volume). Furthermore, the porosity of the heat resistant porous layer is preferably 40 to 70%, and the volume of the polyolefin is preferably 50% or more of the pore volume of the heat resistant porous layer.

  Thickness of the resin porous membrane [when the separator has a plurality of resin porous membranes, the total thickness thereof. The same applies to the thickness of the porous resin membrane. ] Is preferably 9 μm or more, and more preferably 12 μm or more, from the viewpoint of ensuring good shutdown characteristics of the battery. 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.

  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 porous membrane in the separator is too large, the amount of each component constituting the heat-resistant porous layer is reduced, and the shape stability of the separator at high temperatures is reduced. The ratio of the resin in the total volume is preferably 99.9% by volume or less, and more 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. Note that the porosity of the separator: P (%) can be calculated by calculating the sum of each component i from the thickness of the separator, the mass per area, and the density of the constituent components using the following equation (2).
P = {1- (m / t) / (Σa _i · ρ _i )} × 100 (2)
Here, in the formula (2), 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 (cm) of the separator.

Furthermore, in the formula (2), 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. 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 above formula (2), 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. When the thermal contraction rate of the separator is too large, there is a possibility that the effect of suppressing the occurrence of a problem at the time of occurrence of an internal short circuit due to mixing of conductive foreign matters may be reduced. 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. A product (a binder may be dissolved in a medium) is prepared, applied to the surface of the porous resin membrane, and dried.

  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 addition, for the purpose of controlling the interfacial tension, alcohol (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 addressing environmental problems, for example, it is more desirable to use water as the medium of the heat-resistant porous layer forming composition, and from this, the surface modification of the surface of the resin porous membrane can be achieved by surface modification. It is very preferable to increase the properties.

  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 only needs to be the separator of the present invention. Various configurations and structures employed in non-aqueous electrolyte batteries known from US Pat.

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

  Examples of the form of the non-aqueous electrolyte battery include a cylindrical shape (such as a rectangular tube shape or a cylindrical shape) using a steel can or an aluminum can 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 is not particularly limited as long as it is a positive electrode used in a conventionally known non-aqueous electrolyte secondary battery. For example, as an active material, lithium-containing transition metal oxide represented by Li _{1 + x} MO ₂ (−0.1 <x <0.1, M: Co, Ni, Mn, etc.); lithium manganese such as LiMn ₂ O ₄ 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); can be applied, and 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. The positive electrode mixture was finished into a molded body using the current collector as the core material. Or the like can be used for.

  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 is not particularly limited as long as it is a negative electrode used in a conventionally known non-aqueous 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. In addition, elements such as Si, Sn, Ge, Bi, Sb and In and alloys thereof, lithium-containing nitrides, oxides and other compounds that can be charged and discharged at a low voltage close to lithium metal, or lithium metals and lithium / aluminum alloys Can also be used as a negative electrode active material. A negative electrode mixture prepared by appropriately adding a conductive additive (carbon material such as carbon black) or a binder such as PVDF to these negative electrode active materials and using a current collector as a core material is used. In addition, the above-mentioned various alloys and lithium metal foils may be used alone or formed 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 laminate obtained by laminating the positive electrode and the negative electrode via the separator of the present invention, or a wound electrode body obtained by winding the laminate.

Nonaqueous electrolytes include, for example, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propionate, ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, ethylene glycol sulfite, 1,2-dimethoxyethane, 1, 3-dioxolane, tetrahydrofuran, 2-methyl - tetrahydrofuran, organic solvent consists of only one type, such as diethyl ether or in a mixture of two or more solvents, 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 (n ≧ 2), L What is prepared by dissolving at least one selected from lithium salts such as iN (RfOSO ₂ ) ₂ [where Rf is a fluoroalkyl group] is used. 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.

  The non-aqueous electrolyte may be used as a gel (gel electrolyte) by adding a known gelling agent such as a polymer.

  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. In addition, the average particle diameter of the heat resistant fine particles and the swellable fine particles used in this example is a value measured by the above method.

Example 1
<Preparation of separator>
In 600 g of water, 500 g of a polyhedral boehmite synthetic product (aspect ratio 1.4, D ₅₀ = 0.63 μm) as heat-resistant fine particles, PVP (heat-resistant fine particles and swellable fine particles described later) as a binder 5 parts by mass with respect to 100 parts by mass in total) was dispersed by stirring for 1 hour using a three-one motor, and further an aqueous dispersion of crosslinked PMMA fine particles, which are swellable fine particles (D ₅₀ = 0.5 μm). The solid portion ratio of the shell portion Tg = 105 ° C. and the core portion Tg = −40 ° C. is added so that the ratio of the crosslinked PMMA fine particles to the boehmite synthesized product is 50:50 by volume. A composition for forming a heat-resistant porous layer was prepared by dispersing in the above. The PVP used is “K-90 (trade name)” manufactured by ISP Japan, and has a weight average molecular weight of 1,600,000 and a Tg of 174 ° C.

  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 method per 1 g of swellable 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. and the PE melting temperature 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. Further, 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 (polyolefin related to the resin porous membrane, and 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% by mass, graphite as a conductive additive: 9.0% by mass, and acetylene black: 1.8% by mass Then, an NMP solution containing PVDF (binder) in an amount of 3% by mass in the positive electrode mixture composed of the positive electrode active material, the conductive auxiliary agent and the binder is added, and the mixture is well kneaded. An agent-containing slurry was prepared. Uniformly mix the slurry on both surfaces of an aluminum foil with a thickness of 20 μm to be a positive electrode current collector in such an amount that the mass of the positive electrode mixture layer after drying is 11.6 mg / cm ² per side of the positive electrode current collector. It was coated, 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% by mass and acetylene black as a conductive auxiliary agent: 4.7% by mass are mixed, and here, a negative electrode mixture comprising a negative electrode active material, a conductive auxiliary agent and a binder. An NMP solution containing PVDF (binder) in an amount of 5.3% by mass was added and kneaded well to prepare a negative electrode mixture-containing slurry. Uniformly mix the slurry on both sides of a rolled copper foil with a thickness of 20 μm serving as the negative electrode current collector in an amount such that the mass of the negative electrode mixture layer after drying is 5.0 mg / cm ² per side of the negative electrode current collector Then, it was 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 in 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 rated capacity of the obtained battery was 1150 mAh (the rated capacity of all the batteries of the following examples and comparative examples was 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
A composition for forming a heat resistant porous layer was prepared in the same manner as in Example 1 except that the amount of PVP 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 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
A composition for forming a heat resistant porous layer was prepared in the same manner as in Example 1, except that the amount of PVP was changed to 15 parts by mass with respect to 100 parts by mass of the swellable fine particles and heat resistant fine particles. A separator was prepared in the same manner as in Example 1 except that 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
Cross-linked PMMA fine particles that are swellable fine particles are not used, and the binder is replaced with PVP and an acrylate copolymer (commercially available acrylate copolymer mainly containing butyl acrylate as a monomer component; with respect to 100 parts by mass of heat-resistant fine particles The composition for forming a heat resistant porous layer was prepared in the same manner as in Example 1 except that the amount was 5 parts by mass), and the same procedure as in Example 1 was performed except that this composition for forming a heat resistant porous layer was used. A separator was produced. 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
The binder added to the boehmite dispersion was changed to an aqueous solution (concentration: 10% by mass) of PVP having a weight average molecular weight of 70,000 [“K-30 (trade name)” manufactured by ISP Japan, Tg: 163 ° C.]. A separator was prepared in the same manner as in Example 1 except that a heat-resistant porous layer forming composition was prepared in the same manner as in Example 1, 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 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 4
The same binder as used in Comparative Example 1 was added to 1000 g of an aqueous dispersion of the same crosslinked PMMA fine particles used in Example 1 in an amount of 5 parts by mass with respect to 100 parts by mass of the swellable fine particles. The composition for heat-resistant porous layer formation was prepared by stirring and dispersing for 1 hour.

  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 5
The composition for forming a heat-resistant porous layer is the same as in Example 1 except that the amount of PVP is changed to an amount that is 0.05 parts by mass with respect to 100 parts by mass of the swellable fine particles and heat-resistant fine particles. A separator was prepared in the same manner as in Example 1 except that 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.

  The following evaluation was performed about the battery of an Example and a comparative example, and the separator used for these batteries.

<Measurement of thermal contraction rate 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 thereof is set to the machine direction (MD) of the porous resin membrane constituting the separator, and the intersection of the cross lines is the center of the separator piece. I made it. Thereafter, the separator piece was suspended in a thermostatic chamber whose interior was set to 200 ° C. And after taking out the separator piece from the thermostat after 1 hour and cooling, the shorter length d (mm) of the crosshairs was measured, and the thermal contraction rate (%) was computed by the following formula.
Heat shrinkage rate = 100 × (30−d) / 30

<Load characteristic measurement>
Each battery was charged to 4.2 V at a current value of 1/2 C (1 mA) with respect to the rated capacity, then discharged to 3.0 V at a predetermined current value, and the discharge capacity at each current value was measured. The discharge current values were set to 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>
Each battery charged to the rated capacity was taped with a thermocouple in the vicinity of the center side surface, further wrapped with glass wool having a thickness of 6 mm, and packaged with a cylindrical laminate having a diameter of 30 mm to make the battery insulative. 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 ( The temperature rise was suppressed) ”.

  Table 1 shows the configuration of separators used in the batteries of Examples and Comparative Examples (Separators of Examples and Comparative Examples), and Table 2 shows the evaluation results.

  The “amount of binder” in 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 heat-resistant fine particles, and “the ratio of the resin in the whole separator” "Means the volume ratio of the resin in the total volume of the constituent components of the separator.

  As shown in Table 2, an embodiment comprising a heat-resistant porous layer containing swellable fine particles and heat-resistant fine particles in an appropriate volume ratio and containing a polymer (A) (PVP) in an appropriate amount. In the separators 1 to 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.

  On the other hand, the separator of Comparative Example 1 in which the heat resistant porous layer was not formed, the separator of Comparative Example 2 in which the heat resistant porous layer not containing swellable fine particles was formed, and the polymer (A) having a low weight average molecular weight The separator of Comparative Example 3 in which the heat-resistant porous layer containing C is formed, the separator of Comparative Example 4 in which the heat-resistant porous layer not containing the heat-resistant fine particles is formed, and the heat-resistant porous with a small amount of the polymer (A) All of the separators of Comparative Example 5 in which the layers were formed had a large heat shrinkage rate at 200 ° C., and the batteries of Comparative Examples 1 to 5 using these had poor reliability during the internal short circuit test.

  It should be noted that the batteries of Examples 1 to 4 using the separator with the binder amount in the heat-resistant porous layer as 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.

Claims (11)

A separator for a non-aqueous electrolyte battery having a heat-resistant porous layer on at least one surface of a porous resin membrane whose main component is a polyolefin having a melting temperature of 80 to 180 ° C,
The ratio of the resin in the total volume of the constituent components of the separator is 50 to 99.9% by volume,
The heat-resistant porous layer contains swellable fine particles that swell by increasing the amount of absorption of the non-aqueous electrolyte by heating in the non-aqueous electrolyte, heat-resistant fine particles, and a binder.
The volume ratio of the swellable fine particles and the heat-resistant fine particles is 10:90 to 95: 5,
As the binder, a polymer having a group having a cyclic structure containing an amide bond and a skeleton derived from a polymerizable double bond, a glass transition temperature of 130 ° C. or higher, and a weight average molecular weight of 350,000 or higher. Contains
When the total amount of the swellable fine particles and the heat-resistant fine particles is 100 parts by mass, the amount of the polymer is 0.1 parts by mass or more,
A separator for a non-aqueous electrolyte battery, wherein the heat-resistant porous layer has a thickness of 2 to 10 µm. The polymer having a cyclic structure containing an amide bond and a skeleton derived from a polymerizable double bond, the group having a cyclic structure containing an amide bond is a group represented by the following chemical formula (1), The separator for a nonaqueous electrolyte battery according to claim 1, wherein the glass transition temperature is 150 ° C or higher.

  The separator for a nonaqueous electrolyte battery according to claim 1 or 2, wherein the polymer having a group having a cyclic structure containing an amide bond and a skeleton derived from a polymerizable double bond is polyvinylpyrrolidone.   The nonaqueous electrolytic solution according to any one of claims 1 to 3, wherein the amount 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 contained in the heat-resistant porous layer are composed of a crosslinked acrylic resin and have a glass transition point of 70 to 130 ° C. 5. The nonaqueous electrolyte battery use according to any one of claims 1 to 4. Separator.   The swellable fine particles contained in the heat-resistant porous layer are composed of a core part composed of a crosslinked acrylic resin having a glass transition temperature of 25 ° C. or lower and a shell part composed of a crosslinked acrylic resin having a glass transition temperature of 70 ° C. or higher. The separator for nonaqueous electrolyte batteries according to claim 1, wherein the separator has a core-shell structure.   The swellable fine particles contained in the heat-resistant porous layer have an average particle diameter of 0.05 to 2 µm. The separator for a non-aqueous electrolyte battery according to any one of claims 1 to 6.   The non-aqueous electrolyte battery separator according to claim 1, wherein the heat-resistant fine particles contained in the heat-resistant porous layer have a heat-resistant temperature of 300 ° C. or higher.   The separator for a nonaqueous electrolyte battery according to any one of claims 1 to 8, wherein the heat-resistant fine particles contained in the heat-resistant porous layer have an average particle diameter of 0.05 to 2 µm.   The separator for a nonaqueous electrolyte battery according to any one of claims 1 to 9, which has a thermal shrinkage rate of 5% or less when left in a 200 ° C temperature atmosphere.   It has a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, The said separator is a separator for non-aqueous electrolyte batteries in any one of Claims 1-10, The non-aqueous electrolyte battery characterized by the above-mentioned.