WO2013080946A1 - Separator for non-aqueous electrolyte cell and non-aqueous electrolyte cell using same - Google Patents

Abstract

This separator for a non-aqueous electrolyte cell comprises a heat-resistant porous layer on at least one side of a resin porous membrane the primary component of which is a polyolefin having a melting temperature of 80 to 180ºC, and has the resin at the ratio of 50 to 99.9 vol% in the total volume of the structural components of the separator. The heat-resistant porous layer comprises heat-resistant microparticles, a binder, and expandable microparticles that expand in the nonaqueous electrolyte as a result of increased absorbtion of nonaqueous electrolyte when heated. The volume percentage of the expandable microparticles and heat-resistant microparticles is 10:90 to 95:5. The heat-resistant porous layer is characterized as follows: by containing a polymer, as the binder, which has groups having a cyclic structure comprising amide bonds and a skeleton derived from polymerizable double bonds, has a glass transition temperature of 130ºC or higher, and has a weight-average molecular weight of 350,000 or greater; in that the polymer content of the heat-resistant porous layer is 0.1 parts by mass or greater if the total amount of expandable microparticles and heat-resistant microparticles is 100 parts by mass; and in that the heat-resistant porous layer thickness is between 2 and 10 µm.

Description

Nonaqueous electrolyte battery separator and nonaqueous electrolyte battery using the same

The present invention relates to a separator for a non-aqueous electrolyte battery and a non-aqueous electrolyte battery using the same.

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. 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 stretched film or a biaxially stretched film is used for increasing the porosity and improving 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 when it is exposed to high temperature, there is a problem that 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 due to a charging abnormality or the like, the current must be immediately reduced 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 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, and in such a case, when pressure is applied to the separator, a small hole is formed in the separator due to the foreign matter, causing an internal short circuit, There is a risk of battery heat generation. 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 coating layer of a crosslinked polymer is formed on the surface of the electrode active material particles to improve battery safety and suppress deterioration in battery performance (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 highly reliable battery 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 Special table 2008-537293 JP 11-329390 A

By the way, particularly in the case of a high-capacity and high-power lithium ion secondary battery such as the motor driving battery, higher reliability is required than 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.

In addition, 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, in which case the manufacturing process of the separator increases, There is a problem in that the production becomes complicated and the entire separator becomes thick, resulting in a decrease in battery capacity.

Therefore, 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 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 according to the present invention is a separator for a non-aqueous electrolyte battery having a heat-resistant porous layer on at least one surface of a porous resin membrane 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 absorbs the non-aqueous electrolyte by heating in the non-aqueous electrolyte. The volume ratio of the swellable fine particles to the heat resistant fine particles is 10:90 to 95: 5, and includes the heat resistant porous material. The layer has, as the binder, 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. When the total amount of the swellable fine particles and the heat-resistant fine particles is 100 parts by mass, including the polymer, the polymer content is 0.1 parts by mass or more, and the heat-resistant porous layer has a thickness of It is characterized by being 2 to 10 μm.

The non-aqueous electrolyte battery of the present invention is a non-aqueous electrolyte battery including 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. It is characterized by.

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.

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

The nonaqueous electrolyte battery separator 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 porous resin membrane is a layer having the original function of permeating ions 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 voids, the same applies hereinafter), and the ratio is very high. 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 porous film, for example, 200 The shape stability at a high temperature such as ℃ is enhanced, thereby providing a non-aqueous electrolyte battery (non-aqueous electrolyte battery of the present invention) that is more reliable and safer at a higher temperature than ever before. Possible .

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. Resin is used. 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 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. 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 absorption amount of the non-aqueous electrolyte (non-aqueous electrolyte of the battery) measured at 25 ° C. is 1.5 mL or less per 1 g of the swellable fine particles. Is preferable, and it is more preferable that it is 1 mL or less.

The details of the mechanism by which the swellable fine particles swell when 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 of PMMA that forms the outer shape of the particles ( 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.

The swellable fine particles preferably have an absorption amount of a non-aqueous electrolyte (non-aqueous electrolyte of the battery) measured at 130 ° C. of 2 mL or more per gram of swellable fine particles.

The “absorption amount of the non-aqueous electrolyte solution at 25 ° C. of the swellable fine particles” as used herein is a value obtained 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, 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 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 the absorption amount 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.

Further, the Tg of the swellable fine particles and the binder (polymer used as a binder) to be described later is a differential scanning calorimeter (DSC) in accordance with the provisions of Japanese Industrial Standard (JIS) K7121. Is a measured value.

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 derivatives; 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 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 diameter 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-resistant temperature indicating the heat resistance of the heat-resistant fine particles is more preferably 300 ° C. or higher. The upper limit of the heat-resistant temperature is not particularly limited, but is usually about 1000 ° C.

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 their artificial products; Further, the surface of 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 particles 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 above polymerized product (A) [hereinafter sometimes simply referred to as “polymerized product (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. Although the upper limit of Tg of a polymer (A) is not specifically limited, Usually, it is about 400 degreeC.

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 coating properties 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) referred to in the present specification 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 amide bonds such as poly (N-vinylcaprolactam), which is a homopolymer of N-vinylcaprolactam, and polyvinylpyrrolidone (PVP), which is a homopolymer of vinylpyrrolidone. Monomers of monomers having a group having a structure and a polymerizable double bond; two types of monomers having a cyclic structure containing an amide bond and a polymerizable double bond (N-vinylcaprolactam, vinylpyrrolidone, etc.) One or more of the above copolymers; monomers having a cyclic structure containing an amide bond and a polymerizable double bond (N-vinylcaprolactam, vinylpyrrolidone, etc.) and other polymerizable doubles 1 of a monomer having a bond (a monomer other than a monomer having a cyclic structure containing an amide bond and a polymerizable double bond) Or a copolymer of two or more; 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 its derivatives, vinyl esters such as vinyl acetate, α-olefins, basic unsaturated compounds such as vinylimidazole and vinylpyridine 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, easy to adjust Tg to the above value, so that it is 40 mol% or more in 100 mol% of all the units derived from the monomer. Preferably, it is 60 mol% or more, more preferably 80 mol% or more.

Also, other binders can be used together with the polymer (A) as the binder. Examples of such other binders include ethylene-vinyl acetate copolymers, acrylate copolymers, water-soluble nylon, vinyl alcohol polymers, vinyl ether 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 improving 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 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.

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 including 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. The following is particularly preferable.

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, abnormal 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) in accordance with JIS K 7121, of 80 ° C. or higher and 180 ° C. or lower. 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 types 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 film made of such a polyolefin, it can secure a so-called shutdown characteristic in which the polyolefin softens at 80 to 180 ° C. and the pores of the separator are closed. 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). Further, 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.

Resin porous membrane thickness [when the separator has a plurality of porous resin membranes, the total thickness. 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 in the separator is too large, the amount of each component constituting the heat-resistant porous layer decreases, and the shape stability of the separator at high temperatures decreases. The resin ratio in the inside 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 ensuring 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 using the following equation (2) from the thickness of the separator, the mass per area, and the density of the constituent components.

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 (%). The porosity of the resin porous membrane obtained by this method is preferably 30 to 70%.

Further, 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 (%). The porosity of the heat resistant porous layer obtained by this method is preferably 30 to 75%.

The heat shrinkage 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.

As used herein, “the thermal contraction rate of the separator when left in a 200 ° C. temperature atmosphere” 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; 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.

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. 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 lithium ion secondary 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 lithium ion secondary battery. For example, as a positive electrode 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.); lithium such as LiMn ₂ O ₄ Manganese oxide: LiMn _(2-x) M _x O ₄ (0.01 <x <0.5, M: Co, Ni, etc.) obtained by substituting a part of Mn of LiMn ₂ O ₄ 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); and the like, and known conductive assistants (carbon materials such as carbon black) for these positive electrode active materials Etc.) or a binder such as polyvinylidene fluoride (PVDF) Was positive electrode mixture can be used such as those finished molded article a current collector as a core material.

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

The lead part on the positive electrode side is usually provided by leaving the exposed part of the current collector without forming the positive electrode mixture layer on a part of the current collector and forming the lead part 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 lithium ion secondary battery. For example, as a negative electrode active material, lithium, such as graphite, pyrolytic carbons, cokes, glassy carbons, fired organic polymer compounds, mesocarbon microbeads (MCMB), and carbon fibers, can be occluded and released. One type or a mixture of two or more types of carbon-based materials are 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-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 in which the positive electrode and the negative electrode are laminated via the separator of the present invention, or an electrode wound body in which this is wound.

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 (2 ≦ n ≦ 7 , LiN (RfOSO _{2) 2} [where, Rf is a fluoroalkyl group] which was prepared by dissolving at least one selected from lithium salts such as are 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.

Next, an example of the lithium ion secondary battery will be described with reference to the drawings. 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 ion 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 the present invention. The separator 3 and the non-aqueous electrolyte 4 are provided. The positive electrode 1 and the negative electrode 2 are spirally wound via a separator 3 and are housed in a cylindrical battery can 5 together with a nonaqueous electrolyte solution 4 as a wound electrode body.

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 on the bottom of the battery can 5 prior to the insertion of the wound electrode body. 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. is 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, 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 projecting portion 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 disposed at the upper part of the peripheral edge of the sealing plate 7, and the explosion-proof valve 9 is disposed at the upper portion 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 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. 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, crosslinked PMMA fine particles (D ₅₀ = 0.5 μm, shell parts) An aqueous dispersion (solid content ratio 40 mass%) of Tg = 105 ° C. and Tg = −40 ° C. of the core portion was added so that the ratio of the crosslinked PMMA fine particles to the boehmite synthesized product was 50:50 by volume. The composition for heat-resistant porous layer formation was prepared by uniformly dispersing. 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 crosslinked 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 of 0 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., 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. 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 parts by mass, graphite as a conductive additive: 9.0 parts by mass, and acetylene black: 1.8 parts by mass The mixture was mixed, and an NMP solution containing 3 parts by mass of PVDF (binder) was added thereto 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 the current is further exposed to the exposed portion of the aluminum foil. Welded to.

<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 with a thickness of 20 μm serving as the negative electrode current collector is 5.0 mg / cm ² per side of the negative electrode current collector. 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 was cut so that the size of the negative electrode mixture layer was 850 mm × 52 mm and the exposed portion of the rolled copper foil was included, and a nickel lead piece for taking out the current was further removed from the rolled copper foil. Welded to the exposed part.

<Battery assembly>
The positive electrode and the negative electrode were overlapped with the separator interposed so that the heat-resistant porous layer was opposed to the positive electrode, and wound into a spiral shape to obtain a wound electrode body. This wound electrode body was inserted into a cylindrical battery can made of an aluminum alloy, and a non-aqueous electrolyte (a solvent in which ethylene carbonate, dimethyl carbonate, and methyl ethyl carbonate were mixed at a volume ratio of 2: 4: 4, After injecting LiPF ₆ at a concentration of 1 mol / L into the outer package, the opening of the battery can is sealed, and a cylindrical wound electrode body with a length of 65 mm and a diameter of 18 mm is placed inside. A non-aqueous electrolyte secondary battery (lithium ion secondary battery) was prepared. 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, and this heat resistant porous layer was prepared. A separator was produced in the same manner as in Example 1 except that the 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 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.

Then, a nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that this separator was used.

(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 by volume, and this heat resistant porous layer was prepared. A separator was produced in the same manner as in Example 1 except that the 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 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.

Then, a nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that this separator was used.

(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.

Then, a nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that this separator was used.

(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.

Then, a nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that this separator was used.

(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.

Then, a nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that this separator was used.

(Comparative Example 3)
The binder added to the boehmite dispersion was changed to an aqueous solution (concentration of 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 swellable fine particles calculated in the same manner as in the separator of Example 1 is 45% by volume, and the volume ratio of the heat resistant fine particles is 45% by volume. The volume ratio of the resin in the whole separator calculated as described above was 87% by volume.

Then, a nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that this separator was used.

(Comparative Example 4)
The same binder as used in 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 produced 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.

Then, a nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that this separator was used.

(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.

Then, a nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that this separator was used.

The following evaluations were performed on the batteries of Examples and Comparative Examples and the separators used in 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 is the machine direction (MD direction) of the porous resin membrane constituting the separator, and the cross line is such that the intersection is the center of the separator piece. did. 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.

Thermal shrinkage = 100 × (30−d) / 30
<Load characteristic measurement>
Each battery was charged to 4.2 V at a current value of 1/2 C 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 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 central side surface, wrapped with glass wool having a thickness of 6 mm, and packaged with a cylindrical laminate film 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. And when the voltage drop by short circuit was observed, the progress of the nail was stopped and held, and the subsequent temperature rise of 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) ”.

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” 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 the resin in the total volume of the constituent components of the separator is meant.

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 the increase in the thickness of the entire separator. The non-aqueous electrolyte secondary batteries of Examples 1 to 5 using these separators are suppressed in temperature rise during the internal short circuit test, and are reliable and resistant to thermal runaway even when abnormally overheated. 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) The separators of Comparative Example 5 in which the layers were formed all had a large heat shrinkage rate at 200 ° C., and the batteries of Comparative Examples 1 to 5 using them had 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 having 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 forms other than those described 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 (11)

1. A separator for a nonaqueous electrolyte battery comprising a heat-resistant porous layer on at least one surface of a porous resin membrane 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,
   The heat-resistant porous layer includes 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,
   The heat-resistant porous layer has, as the binder, 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. Contains over 350,000 polymers,
   When the total amount of the swellable fine particles and the heat-resistant fine particles is 100 parts by mass, the content 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.
2. 2. The nonaqueous electrolyte battery according to claim 1, wherein the group having a cyclic structure including an amide bond is a group represented by the following chemical formula (1), and the glass transition temperature of the polymer is 150 ° C. or higher. Separator for use.
   

   
3. The separator for a non-aqueous electrolyte battery according to claim 1, wherein the polymer is polyvinylpyrrolidone.
4. 2. The nonaqueous electrolysis 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. Liquid battery separator.
5. The separator for a non-aqueous electrolyte battery according to claim 1, wherein the swellable fine particles are composed of a crosslinked acrylic resin and have a glass transition point of 70 to 130 ° C.
6. The swellable fine particles have a core-shell structure having 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.
7. The non-aqueous electrolyte battery separator according to claim 1, wherein the swellable fine particles have an average particle size of 0.05 to 3 µm.
8. The non-aqueous electrolyte battery separator according to claim 1, wherein the heat resistant temperature of the heat resistant fine particles is 300 ° C. or higher.
9. The non-aqueous electrolyte battery separator according to claim 1, wherein the heat-resistant fine particles have an average particle size of 0.05 to 3 µm.
10. The separator for a non-aqueous electrolyte battery according to claim 1, wherein the thermal shrinkage rate is 5% or less when left in a 200 ° C temperature atmosphere.
11. A non-aqueous electrolyte battery including a positive electrode, a negative electrode, a separator and a non-aqueous electrolyte,
    A nonaqueous electrolyte battery characterized in that the separator is a separator for a nonaqueous electrolyte battery according to any one of claims 1 to 10.
    

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