JPWO2013051079A1 - Heat-resistant porous membrane, non-aqueous battery separator and non-aqueous battery - Google Patents

Abstract

  A heat-resistant porous film formed on a porous substrate or an electrode, which contains at least fine particles having a heat-resistant temperature of 130 ° C. or more and an organic binder, and includes an amide bond as an organic binder. It has a structure having a structure 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, and is porous. A heat-resistant porous membrane having a 180 ° peel strength between the substrate and the electrode of 0.6 N / cm or more, and a separator for a nonaqueous battery having the heat-resistant porous membrane on the porous substrate; The problem is solved by a non-aqueous battery having the non-aqueous battery separator or an electrode integrated with the heat-resistant porous membrane. Provided are a non-aqueous battery having high safety and high-temperature storage characteristics, a heat-resistant porous membrane that can function as a separator between a positive electrode and a negative electrode and that can constitute the non-aqueous battery, and a separator that can constitute the non-aqueous battery. To do.

Description

  The present invention relates to a heat-resistant porous membrane suitable for application to a separator for partitioning a positive electrode and a negative electrode in a non-aqueous battery, a separator for a non-aqueous battery using the heat-resistant porous membrane, and the heat-resistant porous membrane. The present invention relates to a non-aqueous battery having a membrane or the non-aqueous battery separator and having excellent storage characteristics and safety.

  A lithium secondary battery, which is a kind of non-aqueous battery, is widely used as a power source for portable devices such as mobile phones and notebook personal computers because of its high energy density. Further, in recent years, taking advantage of the characteristic of high energy density, application as an in-vehicle power source such as an electric assist bicycle, an electric motorcycle, an electric vehicle, and a hybrid vehicle has been studied. Such a power source for in-vehicle use has a larger capacity than the power source of portable devices, and therefore it is important to ensure further safety.

  In current lithium secondary batteries, as a separator interposed between a positive electrode and a negative electrode, for example, a polyolefin-based microporous film (microporous film) having a thickness of about 20 to 30 μm is used. 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 secure the so-called shutdown effect, a material having a low melting point may be used among polyolefins such as polyethylene.

  By the way, 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 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 melting point, ie the shutdown temperature. For this reason, when a polyolefin-based microporous film separator is used, if the battery temperature reaches the shutdown temperature in the case of abnormal charging, 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 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, it has a porous substrate with good heat resistance, filler particles, and a resin component for ensuring a shutdown function It has been proposed to form an electrochemical element with a separator (Patent Documents 1 to 3).

  In addition, it has been proposed to increase heat resistance by forming a heat-resistant layer mainly composed of heat-resistant resin or inorganic fine particles on a polyolefin porous film (Patent Documents 4 to 6).

  According to the techniques disclosed in Patent Documents 1 to 6, it is possible to provide a battery having excellent safety that hardly causes thermal runaway even when abnormally overheated.

International Publication No. 2006/62153 JP 2005-536858 A International Publication No. 2009/44741 JP 2000-30686 A JP 2008-300362 A Special table 2008-524824

  By the way, when a lithium secondary battery is applied to, for example, a vehicle-mounted application, the usage environment is likely to become high temperature, and thus it is required to secure high temperature storage characteristics as well as safety.

  The present invention has been made in view of the above circumstances, and the purpose thereof is a non-aqueous battery having high safety and high-temperature storage characteristics, can function as a separator between a positive electrode and a negative electrode, and can constitute the non-aqueous battery. An object of the present invention is to provide a heat-resistant porous membrane and a separator that can constitute the nonaqueous battery.

  The heat-resistant porous membrane of the present invention that has achieved the above object is a heat-resistant porous film formed on a porous substrate for constituting a separator for a non-aqueous battery or an electrode used for a non-aqueous battery. The heat-resistant porous film includes at least a fine particle having a heat-resistant temperature of 130 ° C. or more and an organic binder, and the organic binder has a group having a cyclic structure including an amide bond, and polymerization A polymer having a glass transition temperature of 130 ° C. or higher and a weight average molecular weight of 350,000 or higher, and the porous substrate or the electrode The 180 ° peel strength between the layers is 0.6 N / cm or more.

  The separator for a nonaqueous battery of the present invention is characterized in that the porous substrate and the heat-resistant porous membrane of the present invention are integrated.

  Furthermore, the nonaqueous battery of the present invention has a positive electrode, a negative electrode, and a nonaqueous electrolyte, and the heat resistant porous membrane of the present invention is integrated with at least one of the positive electrode and the negative electrode. Or a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, wherein the separator is a separator for a non-aqueous battery according to the present invention.

  According to the present invention, a non-aqueous battery having high safety and high-temperature storage characteristics, a heat-resistant porous membrane that can function as a separator between a positive electrode and a negative electrode and can constitute the non-aqueous battery, and the non-aqueous battery are provided. A configurable separator can be provided.

It is a longitudinal section showing an example of the nonaqueous battery of the present invention typically.

  The heat-resistant porous film of the present invention contains at least a fine particle having a heat-resistant temperature of 130 ° C. or more and an organic binder, and is suitable as a separator for separating a positive electrode and a negative electrode in a nonaqueous battery. .

  That is, the heat-resistant porous membrane of the present invention acts as a separator that separates the positive electrode and the negative electrode in the non-aqueous battery, for example, by being integrated with at least one of the positive electrode and the negative electrode of the non-aqueous battery. Or a non-aqueous battery separator as an independent film by being integrated with a porous substrate.

  In the heat-resistant porous membrane of the present invention, fine particles having a heat-resistant temperature of 130 ° C. or more are mainly used, and the fine particles and electrodes integrated with the heat-resistant porous membrane, the porous substrate, and the heat-resistant porous membrane. The film is bonded by an organic binder.

  The heat-resistant porous membrane of the present invention has a 180 ° peel strength between an integrated porous substrate or non-aqueous battery electrode of 0.6 N / cm or more, preferably 1.0 N / cm or more. It is. When the peel strength between the heat resistant porous membrane and the porous substrate satisfies the above value, even if the porous substrate is made of a material that is easily contracted by heat, the heat resistant porous membrane The contraction can be suppressed by the action. Therefore, since the heat shrink of the whole separator (the separator for nonaqueous batteries of the present invention) having the heat resistant porous membrane and the porous base material is suppressed, in the battery using this (nonaqueous battery of the present invention) , Can improve the safety when abnormally overheating. In addition, even when the peel strength between the heat-resistant porous membrane and the electrode satisfies the above value, even if abnormal overheating of the battery occurs, the heat-resistant porous that functions as a separator between the positive electrode and the negative electrode Since contraction, breakage, and the like of the film are prevented, safety in abnormal overheating can be enhanced in a battery using the film (nonaqueous battery of the present invention).

  The peel strength as used herein is a value measured by the following method. A test piece having a length of 5 cm × 2 cm was cut out from an integrated product of the heat-resistant porous membrane and the porous substrate, or an integrated product of the heat-resistant porous membrane and the electrode, and the surface of the heat-resistant porous membrane was Adhesive tape is applied to a 2 cm × 2 cm area. The pressure-sensitive adhesive tape has a width of 2 cm and a length of about 5 cm, and is attached so that one end of the pressure-sensitive adhesive tape and one end of the heat-resistant porous membrane are aligned. Then, using a tensile tester, the end of the test piece opposite to the side where the adhesive tape was affixed and the end of the adhesive tape affixed to the test piece opposite the end affixed to the test piece Gripping and pulling at a pulling speed of 10 mm / min to measure the strength when the heat-resistant porous film is peeled off.

  A heat-resistant porous film having a 180 ° peel strength between the porous substrate or the electrodes and satisfying the above-described value can be obtained by adopting the configuration described below.

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

  In a non-aqueous battery, in order to increase safety 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.

  If the Tg of the polymer (A) is 130 ° C. or more, until the inside of the battery reaches 130 ° C., the heat-resistant porous membrane has a heat-resistant temperature of 130 ° C. or more, or between the heat-resistant porous membrane and the electrode Alternatively, the state in which the porous substrate is firmly fixed can be maintained. Therefore, since the shrinkage of the heat-resistant porous membrane itself or a porous base material integrated with the heat-resistant porous membrane (such as a microporous membrane made of polyolefin) can be suppressed, a non-aqueous battery with excellent safety can be obtained. It can be configured.

  The Tg of the polymer (A) in the present specification is a value measured using a differential scanning calorimeter (DSC) in accordance with JIS K 7121.

  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, it becomes easy to obtain a polymer (A) having a Tg of the above value, and the 180 ° peel strength between the heat-resistant porous film and the porous substrate or electrode is adjusted to the above value. It becomes easy to do. Moreover, 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 for the organic binder, the non-heat-resistant porous film having the heat resistant porous film is used. The high temperature storage characteristics of the water battery can also be enhanced.

  The heat-resistant porous film is preferably formed through a step of applying a heat-resistant porous film-forming composition (paint) prepared by dissolving an organic binder in a solvent, as will be described later. If the molecular weight of the polymer (A) is too large, the viscosity of the composition may increase and the coatability may be reduced. 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) used as the organic binder has a group having a cyclic structure containing an amide bond and a skeleton derived from a polymerizable double bond, and has a large tensile strength and tensile modulus. Adhesion with fine particles having a heat resistant temperature of 130 ° C. or higher is good. Therefore, by using the polymer (A) having such a structure and having the Tg and the weight average molecular weight, the heat resistance is excellent and the peel strength between the porous substrate is the above It is possible to form a heat-resistant porous film that satisfies the following value.

  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 poly (N-vinylcaprolactam) (a homopolymer of N-vinylcaprolactam), polyvinylpyrrolidone (PVP, a homopolymer of vinylpyrrolidone), and a cyclic structure containing an amide bond. Monomers of monomers having a group having a structure and a polymerizable double bond; two types of monomers (N-vinylcaprolactam, vinylpyrrolidone, etc.) having a group having a cyclic structure containing an amide bond and a polymerizable double bond One or more monomers having a cyclic structure containing an amide bond and a polymerizable double bond (N-vinylcaprolactam, vinylpyrrolidone, etc.) and other polymerizable doubles One type of monomer having a bond (a monomer other than a monomer having a cyclic structure including an amide bond and a polymerizable double bond) Copolymers of two or greater; 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 makes it easy to adjust the characteristics such as Tg and peel strength to the above values. Therefore, the total unit derived from the monomer of the vinylpyrrolidone copolymer is 100 mol. % Is preferably 40 mol% or more, more preferably 60 mol% or more, and still more preferably 80% or more.

  In addition to the polymer, the heat-resistant porous membrane of the present invention includes, for example, an ethylene-vinyl acetate copolymer (EVA, vinyl acetate-derived structural unit having 20 to 35 mol%), ( (Meth) acrylate polymer ["(Meth) acrylate" is meant to include acrylate and methacrylate. ], One or more of resins such as fluorine-based rubber, styrene-butadiene rubber (SBR), and polyurethane may be used in combination as an organic binder.

  The content of the organic binder in the heat-resistant porous film allows the organic binder to perform well, for example, the peel strength at 180 ° between the heat-resistant porous film and the porous substrate or electrode is From the viewpoint of facilitating the adjustment to the value, the total volume of the constituent components of the heat resistant porous membrane (the total volume excluding the void portion. The same applies hereinafter with respect to the content of each component of the heat resistant porous membrane. ), It is preferably 0.5% by volume or more. In the heat-resistant porous film of the present invention, since the polymer (A) is used for the organic binder, the porous group can be used even if the content of the organic binder in the heat-resistant porous film is reduced as described above. Adhesiveness with a material or an electrode can be improved, and the peel strength between them can be set to the above value.

  On the other hand, if the amount of the organic binder in the heat-resistant porous film is too large, the content of other components (such as fine particles having a heat-resistant temperature of 130 ° C. or higher) decreases, and the action of these other components decreases. There is. Therefore, the content of the organic binder in the heat-resistant porous film is preferably 20% by volume or less, more preferably 15% by volume or less, in the total volume of the constituent components of the heat-resistant porous film. More preferably, it is not more than volume%.

  The fine particles having a heat resistant temperature of 130 ° C. or more related to the heat resistant porous film are used as a main component of the heat resistant porous film or fill a void formed between fibrous materials to be described later. It has the effect | action which suppresses generation | occurrence | production of the resulting short circuit. The term “heat-resistant temperature is 130 ° C. or higher” in the fine particles having a heat-resistant temperature of 130 ° C. or higher in the present specification means that shape change such as deformation is not visually confirmed at least at 130 ° C. The heat resistance temperature of the fine particles is more preferably 150 ° C. or higher.

  The fine particles having a heat-resistant temperature of 130 ° C. or more have electrical insulation properties, are electrochemically stable, and further have a non-aqueous electrolyte (non-aqueous electrolyte) included in the battery or a composition for forming a heat-resistant porous film. If it is stable with respect to the solvent used for a thing (composition containing a solvent), there will be no restriction | limiting in particular. As used herein, “stable with respect to a non-aqueous electrolyte” means that no deformation or chemical composition change occurs in the non-aqueous electrolyte of a non-aqueous battery. In addition, the term “electrochemically stable” as used in the present specification means that no chemical change occurs during charging / discharging of the battery.

Specific examples of such fine particles having a heat-resistant temperature of 130 ° C. or higher include oxide fine particles such as iron oxide, SiO ₂ , Al ₂ O ₃ , TiO ₂ , BaTiO ₃ , ZrO ₂ ; aluminum nitride, silicon nitride, etc. Nitride fine particles; poorly soluble ionic crystal fine particles such as calcium fluoride, barium fluoride and barium sulfate; covalently bonded crystal fine particles such as silicon and diamond; clay fine particles such as talc and montmorillonite; boehmite, zeolite, apatite and kaolin Inorganic fine particles such as mullite, spinel, olivine, sericite, bentonite, hydrotalcite, 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 fine particles.

  Organic fine particles can also be used for the fine particles having a heat resistant temperature of 130 ° C. or higher. Specific examples of the organic fine particles include polyimide, melamine resin, phenol resin, crosslinked polymethyl methacrylate (crosslinked PMMA), crosslinked polystyrene (crosslinked PS), polydivinylbenzene (PDVB), benzoguanamine-formaldehyde condensate, etc. Molecular fine particles; heat-resistant polymer fine particles such as thermoplastic polyimide; The organic resin (polymer) constituting these organic fine particles is a mixture, modified body, derivative, copolymer (random copolymer, alternating copolymer, block copolymer, graft copolymer) of the materials exemplified above. ) Or a crosslinked product (in the case of the heat-resistant polymer).

  For the fine particles having a heat resistant temperature of 130 ° C. or higher, the various fine particles exemplified above may be used alone or in combination of two or more. The fine particles having a heat resistant temperature of 130 ° C. or higher may be particles containing two or more materials constituting the various fine particles exemplified above. Among the various exemplified fine particles, inorganic oxide fine particles are preferable, and alumina, silica, and boehmite are more preferable because, for example, the oxidation resistance of the heat-resistant porous film can be further improved.

The form of the fine particles having a heat resistant temperature of 130 ° C. or higher may be any form such as a spherical shape, a particle shape, or a plate shape, but a plate shape is preferable. Examples of the plate-like particles include various commercially available products, such as “Sun Lovely” (SiO ₂ ) manufactured by Asahi Glass S-Tech, pulverized product (TiO ₂ ) of “NST-B1” manufactured by Ishihara Sangyo Co., Ltd., Sakai Chemical Industry Co., Ltd. Plate-like barium sulfate “H series”, “HL series”, Hayashi Kasei “micron white” (talc), Hayashi Kasei “bengel” (bentonite), Kawai lime “BMM” and “BMT” (Boehmite), “Cerasure BMT-B” [Alumina (Al ₂ O ₃ )] manufactured by Kawai Lime Co., Ltd., “Seraph” (alumina) manufactured by Kinsei Matec Co., Ltd. ) Etc. are available. In addition, SiO ₂ , Al ₂ O ₃ , ZrO ₂ and CeO ₂ can be produced by the method disclosed in Japanese Patent Application Laid-Open No. 2003-206475.

  When the fine particles having a heat resistant temperature of 130 ° C. or higher are plate-like, the fine particles are oriented in the heat resistant porous film so that the flat plate surface is substantially parallel to the surface of the heat resistant porous film. The use of such a heat-resistant porous membrane can better suppress the occurrence of short circuits in the battery. This is because the fine particles having a heat-resistant temperature of 130 ° C. or more are oriented as described above so that the fine particles are arranged so as to overlap each other on a part of the flat plate surface, so that the heat-resistant porous film is directed from one side to the other side. It is considered that vacancies (through holes) are formed not in a straight line but in a bent shape (that is, the curvature is increased), thereby preventing lithium dendrite from penetrating through the heat-resistant porous film. Therefore, it is presumed that the occurrence of a short circuit is suppressed better.

  For example, the aspect ratio (the ratio of the maximum length in the plate-like particles to the thickness of the plate-like particles) is 5 or more as the form when the fine particles having a heat resistant temperature of 130 ° C. or higher are plate-like particles. Preferably, it is 10 or more, more preferably 100 or less, and even more preferably 50 or less. Further, the average value of the ratio of the major axis direction length to the minor axis direction length of the flat plate surface of the grains is preferably 0.3 or more, more preferably 0.5 or more (ie, the long length). The axial length and the minor axial length may be the same). When the fine particles having a heat resistant temperature of 130 ° C. or higher are plate-like particles having the aspect ratio and the average value of the ratio of the long axis direction length to the short axis direction of the flat plate surface, the above-mentioned short circuit prevention The effect is exhibited more effectively.

  The average value of the ratio of the length in the major axis direction to the length in the minor axis direction of the flat plate surface when the fine particles having a heat resistant temperature of 130 ° C. or higher are plate-like, for example, an image taken with a scanning electron microscope (SEM) Can be obtained by image analysis. Further, the aspect ratio when the fine particles having a heat resistant temperature of 130 ° C. or higher are plate-like can also be obtained by image analysis of an image taken by SEM.

  If the heat-resistant temperature is 130 ° C. or higher, the fine particles are too small, it may be difficult to adjust the peel strength at 180 ° between the heat-resistant porous membrane and the porous substrate or electrode to the above value. is there. Therefore, the average particle diameter of the fine particles having a heat resistant temperature of 130 ° C. or higher is preferably 0.01 μm or more, and more preferably 0.1 μm or more. However, if the fine particles having a heat-resistant temperature of 130 ° C. or higher are too large, the heat-resistant porous film becomes too thick and the energy density of a battery using this may be lowered. Therefore, the average particle size of the fine particles having a heat resistant temperature of 130 ° C. or higher is 15 μm or less, and preferably 5 μm or less.

  The average particle diameter of the fine particles having a heat resistant temperature of 130 ° C. or higher referred to in the present specification is, for example, a fine particle having a heat resistant temperature of 130 ° C. or higher using a laser scattering particle size distribution meter (for example, “LA-920” manufactured by HORIBA). It can be defined as the number average particle diameter measured by dispersing fine particles having a heat resistant temperature of 130 ° C. or higher in a medium in which the fine particles having a heat resistant temperature of 130 ° C. or higher do not swell.

The specific surface area of the fine particles having a heat resistant temperature of 130 ° C. or higher is preferably 100 m ² / g or less, more preferably 50 m ² / g or less, and further preferably 30 m ² / g or less. When the specific surface area of the fine particles having a heat-resistant temperature of 130 ° C. or higher is increased, generally, the amount of the organic binder required for favorably bonding the fine particles to each other and the fine particles to the base material and the electrode tends to increase. There is a possibility that the output characteristics when the battery is used may deteriorate. Moreover, when the specific surface area of the fine particles having a heat resistant temperature of 130 ° C. or higher is increased, the moisture adsorbed on the surface of the fine particles is increased, which may deteriorate the battery characteristics of the nonaqueous battery. On the other hand, the specific surface area of the fine particles having a heat resistant temperature of 130 ° C. or higher is preferably 1 m ² / g or higher. The specific surface area of the fine particles having a heat-resistant temperature of 130 ° C. or higher as used herein is a value measured by a BET method using nitrogen gas.

  In addition, since the heat-resistant porous film of the present invention uses fine particles having high heat resistance such as a heat-resistant temperature of 130 ° C. or higher, thermal shrinkage at high temperatures is suppressed by its action, and high dimensional stability is obtained. doing. Furthermore, when such a heat-resistant porous film having high heat resistance is integrated with the electrode (positive electrode and / or negative electrode), the overall dimensional stability of the heat-resistant porous film at high temperatures is further improved. On the other hand, the separator for a non-aqueous battery of the present invention in which the porous substrate and the heat-resistant porous membrane of the present invention are integrated is a porous substrate whose temperature is high, such as a polyolefin microporous membrane. Even if it is inferior in dimensional stability, it is integrated with a heat-resistant porous membrane having good dimensional stability at high temperatures by the action of fine particles having a heat-resistant temperature of 130 ° C. or higher. Thermal shrinkage is suppressed, and the dimensional stability of the entire separator at high temperatures is improved. Therefore, the non-aqueous battery having the heat-resistant porous membrane of the present invention integrated with the electrode and the non-aqueous battery having the non-aqueous battery separator of the present invention are composed of, for example, only a conventional polyethylene microporous membrane. Since the occurrence of a short circuit due to the thermal contraction of the separator that has occurred in the battery using the separator can be prevented, the reliability and safety when the inside of the battery is abnormally overheated can be further increased.

  Further, in the nonaqueous battery having the heat resistant porous membrane of the present invention (nonaqueous battery of the present invention), prevention of a short circuit due to the thermal contraction of the separator at a high temperature is achieved with a configuration other than increasing the thickness of the separator, for example. Therefore, it is possible to make the thickness of the separator (the heat-resistant porous membrane of the present invention or the separator for a non-aqueous battery of the present invention) that separates the positive electrode and the negative electrode relatively thin, thereby reducing the energy density. Can be suppressed as much as possible.

  The amount of the fine particles having a heat resistant temperature of 130 ° C. or higher in the heat resistant porous membrane is 10% of the total volume of the constituent components of the heat resistant porous membrane from the viewpoint of more effectively exerting the effect of using the fine particles. It is preferably at least volume%, more preferably at least 30 volume%, and even more preferably at least 40 volume%.

  When the heat-resistant porous film does not contain a fibrous material, which will be described later, and contains a heat-meltable fine particle or a swellable fine particle, which will be described later, and has a shutdown function, the heat resistance of the fine particles having a heat-resistant temperature of 130 ° C. or higher. The amount in the porous porous membrane is preferably 80% by volume or less in the total volume of the constituent components of the heat resistant porous membrane, for example. In addition, when the heat-resistant porous film does not contain a fibrous material described later and does not have a shutdown function, the amount of fine particles having a heat-resistant temperature of 130 ° C. or higher in the heat-resistant porous film is much larger. Specifically, there is no problem if it is 99.5% by volume or less in the total volume of the constituent components of the heat-resistant porous membrane.

  On the other hand, in the case of a heat-resistant porous film containing a fibrous material, which will be described later, and containing a heat-meltable fine particle and a swellable fine particle, which will be described later, and having a shutdown function, fine particles having a heat resistant temperature of 130 ° C. The amount in the heat resistant porous membrane is preferably, for example, 70% by volume or less in the total volume of the constituent components of the heat resistant porous membrane. In addition, when a heat-resistant porous film containing a fibrous material described later and having no shutdown function is used, the amount of fine particles having a heat-resistant temperature of 130 ° C. or higher in the heat-resistant porous film may be even larger. Specifically, there is no problem as long as it is 80% by volume or less in the total volume of the constituent components of the heat-resistant porous membrane.

  The heat resistant porous membrane may contain a fibrous material. By containing a fibrous material, the strength of the heat-resistant porous film can be increased. The “fibrous material” in the present specification means that having an aspect ratio [length in the longitudinal direction / width (diameter) in a direction perpendicular to the longitudinal direction] of 4 or more. The aspect ratio of the fibrous material is preferably 10 or more.

  The fibrous material preferably has a heat resistant temperature of 150 ° C. or higher. For example, a material that can be melted at a temperature of 140 ° C. or less to block the pores of the heat-resistant porous film and provide a function of blocking the movement of ions in the heat-resistant porous film (so-called shutdown function) When it is contained in the membrane (details will be described later), a fibrous material having a heat-resistant temperature of 150 ° C. or higher is also contained in the porous membrane, so that a shutdown occurs due to heat generation in the battery, and then 10 Even if the temperature of the separator rises by more than 0 ° C., the shape can be kept more stable. On the other hand, even when the shutdown function is not given, the heat resistant porous film using a fibrous material having a heat resistant temperature of 150 ° C. or higher, and further the separator using this heat resistant porous film, at a temperature of 150 ° C. However, the deformation can be substantially eliminated.

  As used herein, “a heat resistant temperature of 150 ° C. or higher” in a fibrous material having a heat resistant temperature of 150 ° C. or higher means that a shape change such as deformation is not visually confirmed at least at 150 ° C.

  The fibrous material preferably has a heat-resistant temperature of 150 ° C. or higher, and has an electrical insulating property, is electrochemically stable, and further has a non-aqueous electrolyte (non-aqueous electrolyte) included in a non-aqueous battery, If it is stable to the solvent used for the composition for heat resistant porous membrane formation, there will be no restriction | limiting in particular.

  Specific constituent materials of the fibrous material include, for example, cellulose, modified cellulose (such as carboxymethyl cellulose), polypropylene (PP), polyester [polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polybutylene terephthalate (PBT). And the like], resins such as polyacrylonitrile (PAN), aramid, polyamideimide, and polyimide; inorganic materials (inorganic oxides) such as glass, alumina, and silica; and the like. The fibrous material may contain one kind of these constituent materials, or may contain two or more kinds. In addition to the above-described constituent materials, the fibrous material may contain various known additives (for example, an antioxidant in the case of a resin) as necessary. Absent.

  The fibrous material may be subjected to a surface treatment such as a corona treatment or a surfactant treatment in order to enhance the adhesion with fine particles having a heat resistant temperature of 130 ° C. or higher.

  Although the diameter of a fibrous material should just be below the thickness of a heat resistant porous membrane, it is preferable that it is 0.01-5 micrometers, for example. If the diameter is too large, the entanglement between the fibrous materials will be insufficient, and for example, the effect of improving the strength of the heat-resistant porous membrane by using the fibrous materials may be reduced. On the other hand, if the diameter is too small, the pores of the heat-resistant porous membrane become too small, and the ion permeability tends to decrease, which may reduce the load characteristics of the battery.

  The state of the presence of the fibrous material in the heat resistant porous membrane is, for example, preferably that the angle of the long axis (long axis) with respect to the heat resistant porous membrane surface is 30 ° or less on average, 20 More preferably, it is not more than 0 °.

  In the case where the heat-resistant porous membrane contains the fibrous material, the content of the fibrous material in the heat-resistant porous membrane is from the viewpoint of more effectively exerting the action due to the use of the fibrous material. The total volume of the constituent components of the membrane is preferably 10% by volume or more, and more preferably 30% by volume or more. On the other hand, in the heat-resistant porous membrane containing the fibrous material, if the content of the fibrous material is too large, the content of other components (such as fine particles having a heat-resistant temperature of 130 ° C. or higher) decreases. Since the effect of these other components may be reduced, the content of the fibrous material is preferably 90% by volume or less, and 70% by volume or less in the total volume of the constituent components of the heat-resistant porous membrane. More preferably.

  A shutdown function can be imparted to the heat resistant porous membrane of the present invention. In order to obtain a heat-resistant porous film having a shutdown function, for example, heat-meltable fine particles that melt at 80 to 150 ° C., or a nonaqueous electrolyte solution that absorbs at a temperature of 80 to 150 ° C. increases and swells. A method of containing swellable fine particles can be employed. As used herein, “the amount of liquid absorbed by the nonaqueous electrolyte increases” means that the amount of liquid absorbed per 1 g of resin is 1.0 ml / g or more.

  In addition, the said shutdown function in a heat resistant porous membrane can be evaluated by the resistance rise by the temperature of a model cell, for example. That is, a model cell including a positive electrode, a negative electrode, a heat-resistant porous membrane (integrated with one of the positive electrode and the negative electrode), and a non-aqueous electrolyte is manufactured, and the model cell is placed in a thermostatic bath. Hold and measure the internal resistance value of the model cell while raising the temperature at a rate of 5 ° C./minute, and measure the temperature at which the measured internal resistance value is at least 5 times that before heating (resistance value measured at room temperature). By measuring, this temperature can be evaluated as the shutdown temperature of the heat resistant porous membrane.

  Heat-resistant fine particles that melt at 80 to 150 ° C., that is, those having a melting temperature of 80 to 150 ° C. measured using a differential scanning calorimeter (DSC) according to JIS K 7121 In the porous membrane, when exposed to 80 to 150 ° C. (or higher temperature), the heat-melting fine particles melt and the pores of the heat-resistant porous membrane are closed, so that the movement of Li ions Be inhibited. Therefore, in a non-aqueous battery using such a heat-resistant porous membrane as a separator between the positive electrode and the negative electrode, a rapid discharge reaction at a high temperature is suppressed. In this case, the shutdown temperature of the separator evaluated by the increase in internal resistance is not less than the melting point of the heat-meltable fine particles and not more than 150 ° C. The melting point (the melting temperature) of the heat-meltable fine particles is more preferably 140 ° C. or lower.

  Specific examples of the constituent material of the heat-meltable fine particles include polyethylene (PE), copolymerized polyolefin having a structural unit derived from ethylene of 85 mol% or more, PP, or a polyolefin derivative (chlorinated polyethylene, chlorinated polypropylene, etc.), polyolefin Examples thereof include wax, petroleum wax, carnauba wax and the like. Examples of the copolymer polyolefin include an ethylene-vinyl monomer copolymer, more specifically, an ethylene-vinyl acetate copolymer (EVA), an ethylene-methyl acrylate copolymer, or an ethylene-ethyl acrylate copolymer. it can. Moreover, polycycloolefin etc. can also be used. The heat-meltable fine particles may have only one kind of these constituent materials, or may have two or more kinds. Among these, PE, polyolefin wax, or EVA having a structural unit derived from ethylene of 85 mol% or more is preferable. Further, the heat-meltable fine particles may contain various known additives (for example, antioxidants) added to the resin as necessary, in addition to the above-described constituent materials. Absent.

  The particle diameter of the heat-meltable fine particles is a number average particle diameter measured by the same measurement method as that of the fine particles having a heat resistant temperature of 130 ° C. or higher, and is preferably 0.001 μm or more, for example, 0.1 μm or more. More preferably, it is preferably 15 μm or less, and more preferably 1 μm or less.

  In a heat-resistant porous membrane having swellable fine particles that swell due to an increase in the amount of absorption of the non-aqueous electrolyte at a temperature of 80 to 150 ° C., the swellable fine particles are non-aqueous when exposed to high temperatures in the battery. By increasing the amount of electrolyte absorbed, it expands greatly (hereinafter, the function of absorbing non-aqueous electrolyte and expanding greatly as the temperature rises in the swellable fine particles is referred to as “thermal swelling”). Since the conductivity of Li ions in the membrane is significantly reduced, the internal resistance of the battery is increased, and the shutdown function can be reliably ensured. The temperature at which the swellable fine particles start to exhibit the heat swellability is 80 ° C. or higher and 150 ° C. or lower, and more preferably 135 ° C. or lower.

  Examples of such swellable fine particles having thermal swellability include crosslinked polystyrene (PS), crosslinked acrylic resin [for example, crosslinked polymethyl methacrylate (PMMA)], and crosslinked fluororesin [for example, crosslinked polyvinylidene fluoride (PVDF). ] Is preferred, and cross-linked PMMA is particularly preferred.

  The particle size of the swellable fine particles is a number average particle size measured by dispersing the fine particles in a non-swelling medium (for example, water) using a laser scattering particle size distribution meter (for example, “LA-920” manufactured by HORIBA). It is preferable that it is 1-20 micrometers.

  Examples of commercially available swellable fine particles include cross-linked PMMA “Gantz Pearl (product name)” manufactured by Gantz Kasei Co., Ltd. and cross-linked PMMA “RSP1079 (product name)” manufactured by Toyo Ink Co., Ltd. are available.

  In order to give the heat-resistant porous membrane a shutdown function, it may contain only hot-melt fine particles, may contain only swellable fine particles, or contain both hot-melt fine particles and swellable fine particles. May be. Also, composite fine particles of a constituent material of a heat-fusible fine particle and a constituent material of a swellable fine particle such as a core-shell type fine particle having a swellable fine particle as a core and the surface thereof covered with the constituent material of a heat-fusible fine particle You may make it contain in a heat resistant porous membrane.

  When a heat-resistant porous film contains a heat-meltable fine particle or a swellable fine particle to provide a shutdown function, the heat-meltable fine particle or swelling in the heat-resistant porous film is required to ensure a good shutdown function. Content of heat-soluble fine particles (when the heat-resistant porous film contains both heat-meltable fine particles and swellable fine particles, it is the total amount thereof, and the constituent material of the heat-meltable fine particles and the constituent material of the swollen fine particles Is preferably 5 to 70% by volume in the total volume of the constituent components of the heat-resistant porous membrane. If the content of these fine particles is too small, the shutdown effect due to the inclusion of these may be small, and if too large, the heat resistant temperature in the heat-resistant porous film is 130 ° C. or higher, such as fine particles and fibrous materials Therefore, the effect secured by these may be reduced.

  Specific embodiments of the heat resistant porous membrane of the present invention include the following embodiments (a), (b) and (c).

(A) A sheet-like heat-resistant porous membrane formed by binding fine particles (and other fine particles if necessary) having an heat-resistant temperature of 130 ° C. or higher with an organic binder.

(B) Fine sheet having a heat resistance temperature of 130 ° C. or more and a fibrous material (further, if necessary, other fine particles) are uniformly dispersed, and these are heat-bonded in a sheet form formed by binding with an organic binder. Porous membrane.

(C) A material in which a large number of fibrous materials are aggregated to form a sheet-like material only, for example, a woven fabric or a nonwoven fabric (including paper) is used. A heat-resistant porous material comprising a single layer composed of fine particles having a temperature of 130 ° C. or higher and other fine particles as required, and binding the fibrous material related to the sheet-like material and various fine particles with an organic binder. film.

  Such a heat-resistant porous membrane is integrated with an electrode (positive electrode and / or negative electrode) used in a nonaqueous battery, and is used as a separator for partitioning the positive electrode and the negative electrode.

  Therefore, when the heat-resistant porous film of the present invention is formed and integrated with the electrode, for example, with respect to the heat-resistant porous film of the embodiments (a) and (b), the heat-resistant temperature is 130 ° C. or more. In addition, an organic binder and, if necessary, a fibrous material and other fine particles are dispersed in a solvent (including a dispersion medium; the same shall apply hereinafter) to prepare a heat-resistant porous film-forming composition. (The organic binder may be dissolved in a solvent), and this can be applied to the surface of the electrode and dried to directly form a heat-resistant porous film on the electrode surface.

  In addition, the heat-resistant porous film-forming composition is applied to a substrate such as a PET film or a metal plate, and dried to form the heat-resistant porous film of the aspect (a) or (b). After being peeled from the substrate, it may be superposed on the electrode and integrated with the electrode by a roll press or the like.

  In addition, in order to form the heat-resistant porous film of the aspect (c), a fibrous sheet-like material is impregnated with the heat-resistant porous film-forming composition, and an unnecessary composition is passed through a certain gap. After removing the matter, it can be dried to obtain an independent heat-resistant porous membrane. The heat-resistant porous film is then overlapped with the electrode and integrated with the electrode by a roll press or the like.

  Examples of the fibrous sheet used in the heat-resistant porous membrane of the aspect (c) include a woven fabric composed of at least one fibrous substance containing the above-mentioned exemplified materials as constituent components, and these Examples thereof include a porous sheet such as a nonwoven fabric having a structure in which fibrous materials are entangled with each other. More specifically, non-woven fabrics such as paper, PP non-woven fabric, polyester non-woven fabric (PET non-woven fabric, PEN non-woven fabric, PBT non-woven fabric, etc.) and PAN non-woven fabric can be exemplified.

  The solvent used in the composition for forming a heat-resistant porous film can uniformly disperse fine particles having a heat-resistant temperature of 130 ° C. or higher, heat-meltable fine particles, swellable fine particles, and can uniformly dissolve or disperse the organic binder. Any organic solvent may be used, for example, aromatic hydrocarbons such as toluene; furans such as tetrahydrofuran; ketones such as methyl ethyl ketone and methyl isobutyl ketone; In addition, for the purpose of controlling 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 solvents. In addition, when the binder is water-soluble or used as an emulsion, water may be used as a solvent. In this case, an alcohol (methyl alcohol, ethyl alcohol, isopropyl alcohol, ethylene glycol, etc.) is added as appropriate to the interface. The tension can also be controlled.

  In the composition for forming a heat resistant porous film, the solid content including fine particles having an heat resistant temperature of 130 ° C. or higher, an organic binder, hot melt fine particles, swellable fine particles, fibrous materials, etc., for example, 10 to 80 mass. % Is preferable.

  When plate-like particles are used as fine particles having a heat-resistant temperature of 130 ° C. or higher, in order to increase the orientation of the plate-like particles in the heat-resistant porous film, the composition for forming a heat-resistant porous film is applied to the electrode surface or other In the case of a coating film applied to the substrate surface (coating film before drying) or a sheet-like material impregnated with a heat-resistant porous film-forming composition, these compositions may be shared. For example, after impregnating the above-mentioned composition for forming a heat-resistant porous film as a method for allowing fine particles having a heat-resistant temperature of 130 ° C. or more to exist in the pores of the sheet-like material, a certain gap is passed through the sheet-like material. By the method, it is possible to apply a share to the composition for forming a heat-resistant porous film, whereby the orientation of the plate-like particles can be increased.

  Further, in order to further enhance the orientation of the plate-like fine particles having a heat-resistant temperature of 130 ° C. or higher in the heat-resistant porous film, a high solid content concentration (for example, 50 to 80) other than the method of applying the above-mentioned share. Mass%) heat-resistant porous film-forming composition; fine particles having a heat-resistant temperature of 130 ° C. or higher, various mixing / stirring devices such as dispersers, agitators, homogenizers, ball mills, attritors, jet mills, dispersions Heat-resistant porous material prepared by dispersing in an organic solvent using an apparatus and adding and mixing organic binders (further, if necessary, fibrous materials, heat-meltable fine particles, swellable fine particles, etc.). A method of using a composition for forming a membrane; using fine particles having a heat resistance of 130 ° C. or higher, which is modified by applying a dispersing agent such as oils and fats, surfactants, and silane coupling agents on the surface Method of using the prepared heat-resistant porous film-forming composition; using a heat-resistant porous film-forming composition prepared by using fine particles having a heat-resistant temperature of 130 ° C. or more different in shape, diameter, or aspect ratio Method: Method of controlling drying conditions after impregnating sheet-like composition with heat-resistant porous film forming composition or coating on substrate; Pressing heat-resistant porous film or pressurizing heat A method of impregnating a heat-resistant porous film-forming composition into a sheet-like material or applying it onto a substrate and then applying a magnetic field before drying can be employed. It may be carried out by a combination of two or more methods.

  The thickness of the heat-resistant porous membrane thus obtained is preferably 3 μm or more, for example, from the viewpoint of further enhancing the short-circuit prevention effect of the battery in which it is used and increasing the strength of the heat-resistant porous membrane. More preferably. On the other hand, from the viewpoint of further increasing the energy density of the battery, the thickness of the heat-resistant porous film is preferably 50 μm or less, and more preferably 30 μm or less.

In addition, the porosity of the heat resistant porous membrane is preferably 20% or more in a dry state in order to secure the liquid retention amount of the nonaqueous electrolyte and improve the ion permeability, and preferably 30% More preferably. On the other hand, from the viewpoint of securing the strength of the heat resistant porous membrane and preventing internal short circuit in the battery, the porosity of the heat resistant porous membrane is preferably 70% or less in a dry state, and is 60% or less. More preferably. The porosity of the heat-resistant porous membrane: P (%) is calculated from the thickness of the heat-resistant porous membrane, the mass per area, and the density of the constituent components for each component i using the following formula (2). It can be calculated by calculating the sum.
P = {1- (m / t) / (Σa _i · ρ _i )} × 100 (2)
Here, in the above formula, a _i : ratio of component i when the total mass is 1, ρ _i : density of component i (g / cm ³ ), m: per unit area of heat-resistant porous membrane Mass (g / cm ² ), t: thickness (cm) of heat-resistant porous membrane.

  Furthermore, the heat shrinkage rate at 150 ° C. of the heat-resistant porous membrane obtained by the method shown in the examples described later (heat shrinkage rate when integrated with the electrode) is preferably 5% or less.

  Further, the strength of the heat resistant porous membrane is desirably 50 g or more in terms of piercing strength using a needle having a diameter of 1 mm. If the piercing strength is too small, there is a possibility that a short circuit occurs due to the piercing of the heat-resistant porous film when lithium dendrite crystals are generated.

Further, the air permeability of the heat-resistant porous membrane is measured by a method according to JIS P 8117, and is a Gurley value indicated by the number of seconds that 100 ml of air permeates the membrane under a pressure of 0.879 g / mm ^2. It is desirable that it is 10 to 300 sec. If the air permeability is too high, the ion permeability is reduced, and if it is too low, the strength of the heat resistant porous membrane may be reduced.

  By setting it as the heat resistant porous membrane of the structure demonstrated so far, the said heat shrinkage rate, intensity | strength, and air permeability can be ensured.

  The separator for nonaqueous batteries of the present invention has a multilayer structure in which a porous substrate and the heat resistant porous membrane of the present invention are integrated.

  As the porous substrate for the separator, a resin nonwoven fabric, a woven fabric, a microporous membrane, or the like can be used.

  When providing the shutdown function to the separator of the present invention, it is preferable to use a thermoplastic resin having a melting point of 80 to 150 ° C. as the constituent resin of the porous substrate. Examples of the thermoplastic resin having a melting point of 80 to 150 ° C. include various thermoplastic resins exemplified above as the constituent resin of the thermomeltable fine particles. Among the porous substrates composed of such thermoplastic resins, microporous membranes made of polyolefin (PE, ethylene-propylene copolymer, etc.) are preferable.

  The shutdown function in the separator of the present invention can also be evaluated by the resistance increase due to the temperature of the model cell, similar to the shutdown function of the heat-resistant porous film. That is, a model cell including a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte is prepared, and the model cell is held in a thermostatic bath, and the internal resistance value of the model cell is set while increasing the temperature at a rate of 5 ° C./min. By measuring and measuring the temperature at which the measured internal resistance value is at least five times that before heating (resistance value measured at room temperature), this temperature can be evaluated as the shutdown temperature of the separator.

  On the other hand, when the heat resistance of the separator is emphasized and the shutdown function is not given, a porous substrate made of a heat resistant resin can also be used. As such a heat-resistant resin, any resin that has a heat-resistant temperature of 150 ° C. or more, is stable with respect to the nonaqueous electrolyte used in the battery, and is stable with respect to the oxidation-reduction reaction inside the battery. Good. More specifically, heat-resistant resins such as polyimide, polyamideimide, aramid, polytetrafluoroethylene, polysulfone, polyurethane, PAN, polyester (PET, PBT, PEN, etc.) can be mentioned.

As the microporous membrane used as the porous substrate, any of the above-described thermoplastic resin and the above-mentioned heat-resistant resin, manufactured by a conventionally known method, is used. be able to. For example, an ion-permeable porous film produced by a solvent extraction method, a dry or wet stretching (uniaxial or biaxial stretching) method, or the like can be used. In addition, a film microporous by a foaming method using a drug, supercritical CO ₂ or the like can also be used.

  In producing the separator of the present invention, the step of applying the heat-resistant porous film forming composition used in the formation of the heat-resistant porous film to the surface of the porous substrate and drying it is performed. Then, the method of forming the layer which consists of a heat resistant porous film on the surface of a porous base material is employable. Further, the heat-resistant porous film obtained by the method for forming the heat-resistant porous film of the independent film exemplified above and the porous base material may be stacked and integrated by a roll press or the like.

  In the case where plate-like particles are used for fine particles having a heat-resistant temperature of 130 ° C. or higher, the various methods exemplified above are used as methods for improving the orientation of plate-like particles in the heat-resistant porous film in order to improve the orientation. be able to.

  In the separator of the present invention, the heat-resistant porous film and the porous substrate do not need to be one each, and a plurality of sheets may constitute the separator. For example, it is good also as a structure which has arrange | positioned the porous base material on both surfaces of a heat resistant porous film, or the structure which has arrange | positioned the heat resistant porous film on both surfaces of a porous base material. However, if the total number of the heat-resistant porous membrane and the porous substrate is increased too much, it is not preferable because the thickness of the separator is increased, which may increase the internal resistance of the battery and decrease the energy density. The total number of the heat-resistant porous membrane and the porous substrate is preferably 5 or less.

  In the separator of the present invention thus obtained, the thickness is, for example, 5.5 μm or more from the viewpoint of further enhancing the short-circuit preventing effect of the battery, ensuring the strength of the separator, and improving its handleability. Preferably, the thickness is 10 μm or more. On the other hand, from the viewpoint of further increasing the energy density of the battery, the thickness of the separator is preferably 50 μm or less, and more preferably 30 μm or less.

  In the separator of the present invention, when the thickness of the heat-resistant porous film is X (μm) and the thickness of the porous substrate is Y (μm), the ratio Y / X of X to Y is 1-20. However, it is preferable that the thickness of the entire separator satisfies the preferable value. When Y / X is too large, the heat-resistant porous film becomes too thin, and, for example, when a porous substrate having poor dimensional stability at high temperatures is used, the effect of suppressing the thermal shrinkage becomes small. There is a fear. On the other hand, if Y / X is too small, the heat-resistant porous film becomes too thick, which increases the thickness of the entire separator and may cause a decrease in output characteristics, resulting in a decrease in battery characteristics. is there. When the separator has a plurality of heat-resistant porous films, the thickness X is the total thickness, and when the separator has a plurality of porous substrates, the thickness Y is the total thickness.

  In terms of specific values, the thickness of the porous substrate (when the separator has a plurality of porous substrates, the total thickness) is preferably 5 μm or more, and 30 μm or less. Is preferred. And the thickness of the heat resistant porous membrane (when the separator has a plurality of heat resistant porous membranes, the total thickness thereof) is preferably 0.5 μm or more, more preferably 1 μm or more, It is further preferably 2 μm or more, more preferably 10 μm or less, more preferably 5 μm or less, and even more preferably 3 μm or less.

Further, the porosity of the separator obtained by using the above equation (2), where m is the mass per unit area (g / cm ² ) of the separator and t is the thickness (cm) of the separator, is the retention of the non-aqueous electrolyte. In order to secure the liquid amount and improve the ion permeability, it is preferably 20% or more, more preferably 30% or more in the dried state. On the other hand, from the viewpoint of securing the strength of the separator and preventing internal short circuit, the porosity of the separator obtained by the above method is preferably 70% or less and more preferably 60% or less in a dry state. .

Furthermore, using the above formula (2), m is the mass per unit area (g / cm ² ) of the porous substrate, and t is the porous substrate according to the separator that is required as the thickness (cm) of the porous substrate. It is preferable that the porosity of the material is 30 to 70%. Further, the porosity of the heat-resistant porous film according to the separator obtained by (2) is 20% or more (more preferably 30% or more), as in the case of the heat-resistant porous film integrated with the electrode. ), 70% or less (more preferably 60% or less).

  It is preferable that the thermal shrinkage rate at 150 ° C. of the separator obtained by the method described in Examples below is 5% or less.

  The strength of the separator is desirably 50 g or more in terms of piercing strength using a needle having a diameter of 1 mm. If the piercing strength is too low, a short circuit may occur due to the piercing of the separator when lithium dendrite crystals are generated.

The air permeability of the separator is measured by a method according to JIS P 8117, and is 100 to 300 sec as a Gurley value indicated by the number of seconds that 100 ml of air passes through the membrane under a pressure of 0.879 g / mm ^2. Is desirable. If the air permeability is too high, the ion permeability is reduced, and if it is too low, the strength of the separator may be reduced.

Furthermore, it is preferable that the Gurley value of the separator satisfies the relationship of the following formula (3).
Gs ≦ max {Ga, Gb} +10 (3)
Here, Gs: Gurley value of the separator, Ga: Gurley value of the porous substrate, Gb: Gurley value of the heat-resistant porous film, and max {a, b}: whichever is greater of a and b. However, Gb is calculated | required using following (4) Formula.
Gb = Gs-Ga (4)

  By setting it as the separator of the structure demonstrated so far, the said heat shrinkage rate, intensity | strength, and air permeability can be ensured.

  The non-aqueous battery of the present invention has a positive electrode, a negative electrode, and a non-aqueous electrolyte, and the heat-resistant porous membrane of the present invention is integrated with at least one of the positive electrode and the negative electrode and used as a separator that separates the counter electrode. Or the separator of the present invention may be used as a separator for partitioning the positive electrode and the negative electrode, and there are no particular restrictions on the other configurations and structures, and conventionally known non-aqueous batteries (lithium primary batteries) Various configurations and structures employed in non-aqueous primary batteries such as non-aqueous secondary batteries such as lithium secondary batteries can be applied. Below, the lithium secondary battery which is especially a main form among the non-aqueous batteries of this invention is demonstrated in detail.

  Examples of the form of the lithium 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 secondary battery, that is, a positive electrode containing an active material capable of occluding and releasing Li ions. 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 is formed from a current collector as a core material (ie, And those finished positive electrode mixture layer), it can be used as a positive electrode.

  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 lithium secondary battery, that is, a negative electrode containing an active material capable of occluding and releasing Li ions. 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 obtained 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 a molded body (negative electrode mixture layer) using a current collector as a core material Those having a negative electrode agent layer such as those finished in the above, or those formed from the above-mentioned various alloys and lithium metal foils alone or formed on a current collector can be used as the negative electrode.

  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 30 μm, and the lower limit is preferably 5 μm.

  As with the lead portion on the negative electrode side, the negative electrode layer (including a layer having a negative electrode active material and a negative electrode mixture layer) is usually formed on a part of the current collector during the preparation of the negative electrode. Without leaving the exposed portion of the current collector, it is provided as a lead portion. 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 is formed by laminating the positive electrode and the negative electrode via the separator of the present invention, or integrating at least one of the positive electrode and the negative electrode with the heat-resistant porous membrane of the present invention, It can be used in the form of an electrode group having a laminated structure in which a positive electrode and a negative electrode are laminated so that this heat-resistant porous film is interposed, or an electrode group having a wound structure in which these are wound. In addition, when a battery is constituted by using at least one of the positive electrode and the negative electrode integrated with the heat-resistant porous film of the present invention, a separate separator (for example, a conventionally known lithium secondary battery) The microporous membrane separator made of polyolefin used in the battery of (1) may be used, but since the heat-resistant porous membrane of the present invention functions as a separator (that is, a separator) separating the positive electrode and the negative electrode, There is no need to use a separator.

As described above, a solution (nonaqueous electrolyte) in which a lithium salt is dissolved in an organic solvent is used as the nonaqueous electrolyte. The lithium salt is not particularly limited as long as it dissociates in a solvent to form Li ⁺ ions and does not cause a side reaction such as decomposition in a voltage range used as a battery. For example, inorganic lithium salts such as 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), LiN (R _f OSO ₂ ) ₂ [where R _f is a fluoroalkyl group], etc .; Can be used.

  The organic solvent used for the non-aqueous electrolyte is not particularly limited as long as it dissolves the lithium salt and does not cause a side reaction such as decomposition in a voltage range used as a battery. For example, cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and vinylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate; chain esters such as methyl propionate; cyclic esters such as γ-butyrolactone; Chain ethers such as ethane, diethyl ether, 1,3-dioxolane, diglyme, triglyme and tetraglyme; cyclic ethers such as dioxane, tetrahydrofuran and 2-methyltetrahydrofuran; nitriles such as acetonitrile, propionitrile and methoxypropionitrile; Sulfites such as ethylene glycol sulfite; and the like, and these may be used alone. , It may be used in combination of two or more thereof. In order to obtain a battery with better characteristics, it is desirable to use a combination that can obtain high conductivity, such as a mixed solvent of ethylene carbonate and chain carbonate. In addition, vinylene carbonates, 1,3-propane sultone, diphenyl disulfide, cyclohexylbenzene, biphenyl, and fluorobenzene are used for the purpose of improving safety, charge / discharge cycleability, and high-temperature storage properties of these non-aqueous electrolytes. An additive such as t-butylbenzene may be added as appropriate.

  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.

  Also, instead of the organic solvent, melting at room temperature such as ethyl-methylimidazolium trifluoromethylsulfonium imide, heptyl-trimethylammonium trifluoromethylsulfonium imide, pyridinium trifluoromethylsulfonium imide, guanidinium trifluoromethylsulfonium imide A salt can also be used.

  Further, a polymer material that contains the non-aqueous electrolyte and gels may be added, and the non-aqueous electrolyte may be gelled and used for a battery. Polymer materials for making the non-aqueous electrolyte into a gel include PVDF, vinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), PAN, polyethylene oxide, polypropylene oxide, ethylene oxide-propylene oxide copolymer And a known host polymer capable of forming a gel electrolyte, such as a crosslinked polymer having an ethylene oxide chain in the main chain or side chain, and a crosslinked poly (meth) acrylate.

  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 fine particles having a heat resistant temperature of 150 ° C., the swellable fine particles, and the heat-meltable fine particles used in this example is a value measured by the above method.

Example 1
<Production of electrode>
The positive electrode was produced as follows. First, 90 parts by mass of LiCoO ₂ (positive electrode active material), which is a lithium-containing composite oxide, was added and mixed with 5 parts by mass of carbon black as a conductive additive, and PVDF: 5 parts by mass was dissolved in NMP in this mixture. The solution was added and mixed to obtain a positive electrode mixture-containing slurry, which was passed through a 70-mesh net to remove large particles. After this positive electrode mixture-containing slurry is uniformly applied to both surfaces of a positive electrode current collector made of an aluminum foil having a thickness of 15 μm and dried, and then compression molded by a roll press machine to a total thickness of 105 μm This was cut and welded with an aluminum lead body to produce a strip-like positive electrode.

  Moreover, the negative electrode was produced as follows. Artificial graphite was used as the negative electrode active material, PVDF was used as the binder, these were mixed at a mass ratio of 95: 5, and NMP was added and mixed to obtain a negative electrode mixture-containing paste. This negative electrode mixture-containing paste was uniformly applied to both sides of a negative electrode current collector made of a copper foil having a thickness of 10 μm and dried, and then compression-molded with a roll press machine to a total thickness of 100 μm. It cut | disconnected and the lead body made from nickel was welded, and the strip | belt-shaped negative electrode was produced.

<Preparation of non-aqueous electrolyte>
In a solvent mixture of ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate having a volume ratio of 10:10:30, LiPF ₆ was dissolved at a concentration of 1.0 mol / l, and vinylene carbonate was added to the total mass of the non-aqueous electrolyte. The nonaqueous electrolytic solution was prepared by adding 2.5% by mass with respect to the aqueous solution.

<Preparation of separator>
4000 g boehmite powder (plate shape, average particle size 1 μm, aspect ratio 10, specific surface area 8 m ² / g) as fine particles having a heat resistance temperature of 130 ° C. or more was added to 4000 g of water in 4 portions, and 5 times at 2800 rpm with a disper. A uniform slurry was prepared by stirring for a period of time. To this dispersion was added 800 g of an aqueous solution (concentration: 10% by mass) of PVP [ISP Japan Ltd. “K-120 (trade name)”, Tg: 176 ° C.] having an organic binder weight average molecular weight of 3.5 million, and water. And stirred at room temperature until uniformly dispersed to prepare a slurry having a solid content ratio of 30% by mass (slurry for forming a heat resistant porous film).

  Three-layer polyolefin microporous membrane having a PP microporous membrane on both sides of a PE microporous membrane (thickness: 16 μm, porosity: 40%, thickness of each layer; PP layer: 5 μm / PE layer: 6 μm / PP layer: 5 μm, melting point of PE constituting the PE layer: 135 ° C.) was prepared, and corona discharge treatment was performed on one surface thereof. Then, the slurry is applied to the corona discharge treatment surface of the polyolefin microporous film having a three-layer structure by a microgravure coater and dried to form a heat-resistant porous film, whereby a separator having a thickness of 20 μm is formed. Obtained. The volume ratio of the organic binder in the total volume of the constituent components of the heat resistant porous membrane of this separator was 6% by volume, and the porosity of the heat resistant porous membrane was 53%.

<Battery assembly>
The separator obtained as described above is stacked while being interposed between the positive electrode and the negative electrode so that the heat-resistant porous membrane side faces the positive electrode side, and wound to form a spiral wound electrode group. did. The obtained wound electrode group is put into an iron outer can having a diameter of 18 mm and a height of 65 mm, and after sealing with a nonaqueous electrolyte, sealing is performed to produce a lithium secondary battery having the configuration shown in FIG. did. In this lithium secondary battery, when the battery is charged to 4.2 V (the positive electrode potential is 4.3 V based on Li), the design electric capacity is 1400 mAh (the lithium secondary batteries of the examples and comparative examples described later). The design battery capacities are all the same).

  Here, the battery shown in FIG. 1 will be described. In the lithium secondary battery shown in FIG. 1, the positive electrode 1 and the negative electrode 2 are spirally wound through the separator 3, and non-aqueous electrolysis is performed as an electrode group having a wound structure. It is accommodated in the outer can 5 together with the liquid 4. In FIG. 1, in order to avoid complication, a current collector used for manufacturing the positive electrode 1 and the negative electrode 2 is not shown.

  An insulator 6 made of PP is disposed at the bottom of the outer can 5 prior to the insertion of the electrode group having the winding structure. The sealing plate 7 is made of 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 this 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 behind the cut surface is The illustration is omitted. In addition, the welded portion 11 of the thin-walled portion 7a of the sealing plate 7 and the protruding portion 9a of the explosion-proof valve 9 is also illustrated in an exaggerated state so as to facilitate understanding on the drawing.

  The terminal plate 8 is made of rolled steel, has a nickel plating on the surface, and has a hat shape with a peripheral edge portion having a hook shape. The terminal plate 8 is provided with a gas discharge port 8a. The explosion-proof valve 9 is made of aluminum and has a disk shape, and a central portion is provided with a protruding portion 9a having a tip portion on the power generation element side (lower side in FIG. 1) and a thin portion 9b. As described above, the lower surface of the protruding portion 9a is welded to the upper surface of the thin portion 7a of the sealing plate 7 to constitute the welded portion 11. The insulating packing 10 is made of PP and has an annular shape. The insulating packing 10 is arranged at the upper part of the peripheral edge of the sealing plate 7. The explosion-proof valve 9 is arranged at the upper part of the insulating packing 10 and insulates the sealing plate 7 and the explosion-proof valve 9. The gap between the two is sealed so that the non-aqueous electrolyte does not leak between the two. The annular gasket 12 is made of PP, the lead body 13 is made of aluminum, the sealing plate 7 and the positive electrode 1 are connected to each other, an insulator 14 is disposed on the upper part of the wound electrode group, and the negative electrode 2 and the outer can The bottom of 5 is connected by a lead body 15 made of nickel.

  In this battery, 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, the peripheral portion of the explosion-proof valve 9 and the peripheral portion of the terminal plate 8 are in contact with each other. Since the positive electrode 1 and the terminal plate 8 are connected to the sealing plate 7 by the positive lead 13, the positive electrode 1 and the terminal plate 8 are electrically connected by the lead 13, the sealing plate 7, the explosion-proof valve 9, and their welded portions 11. Connection is obtained and functions normally as an electrical circuit.

  When the battery is exposed to a high temperature and an abnormal situation occurs, gas is generated inside the battery and the internal pressure of the battery rises, the internal pressure increases, so that the central portion of the explosion-proof valve 9 moves in the internal pressure direction ( In FIG. 2, the thin-walled portion 7 a is deformed in the upper direction), and accordingly, the thin-walled portion 7 a integrated with the welded portion 11 acts to break the thin-walled portion 7 a, or the protruding portion 9 a of the explosion-proof valve 9. After the welded portion 11 between the sealing plate 7 and the thin portion 7a of the sealing plate 7 is peeled off, the thin portion 9b provided on the explosion-proof valve 9 is cleaved and gas is discharged from the gas discharge port 8a of the terminal plate 8 to the outside of the battery. Designed to prevent battery rupture.

Example 2
4000 g of the same boehmite powder used in Example 1 was added to 4000 g of water in four portions, and the mixture was stirred with a disper at 2800 rpm for 5 hours to prepare a uniform dispersion. To this dispersion, 800 g of an aqueous solution (concentration: 10% by mass) of PVP [“K-90 (trade name)” manufactured by ISP Japan, Tg: 174 ° C.] having a weight average molecular weight of 1.6 million, which is an organic binder, is added. And stirred at room temperature until uniformly dispersed to prepare a slurry having a solid content ratio of 30% by mass. To this slurry, a fluorosurfactant (perfluoroalkylethylene oxide adduct) is added in an amount of 0.1 parts by mass with respect to 100 parts by mass of water, and stirred until uniform to form a heat resistant porous film. A slurry was obtained.

  The slurry is applied to one side of a polyolefin microporous membrane (not subjected to corona discharge treatment) having the same three-layer structure as used in Example 1, using a gravure coater, and then dried to form a heat-resistant porous film. By forming a membrane, a separator having a thickness of 20 μm was obtained. The volume ratio of the organic binder in the total volume of the constituent components of the heat resistant porous membrane of this separator was 6% by volume, and the porosity of the heat resistant porous membrane was 52%.

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

Example 3
The aqueous solution of the organic binder to be added to the boehmite dispersion is changed to an aqueous solution (concentration 10% by mass) of PVP having a weight average molecular weight of 400,000 [K-60 (trade name) manufactured by ISP Japan, Tg: 170 ° C.]. In the same manner as in Example 1, a heat-resistant porous forming slurry having a solid content ratio of 30% by mass was prepared, and a separator having a thickness of 20 μm was prepared in the same manner as in Example 1 except that this slurry was used. Was made. The volume ratio of the organic binder in the total volume of the constituent components of the heat resistant porous membrane of this separator was 6% by volume, and the porosity of the heat resistant porous membrane was 53%.

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

Example 4
4000 g of the same boehmite powder used in Example 1 was added to 4000 g of water in four portions, and the mixture was stirred with a disper at 2800 rpm for 5 hours to prepare a uniform dispersion. In this dispersion, 4000 g of an aqueous dispersion (solid content ratio: 40% by mass) of crosslinked PMMA fine particles (swellable fine particles, average particle size 0.4 μm) and PVP having a weight average molecular weight of 3.5 million (manufactured by ISP Japan, “ K-120 (trade name) ”, Tg: 176 ° C.] in an aqueous solution (concentration: 10% by mass), and further stirred at room temperature until uniformly dispersed by adding water, and the solid content ratio is 30% by mass. A heat-resistant porous forming slurry was prepared.

  By applying the slurry to the corona discharge treatment surface of the polyolefin microporous membrane having the same three-layer structure as used in Example 1 using a gravure coater, and drying to form a heat resistant porous membrane. A separator having a thickness of 20 μm was obtained. The volume ratio of the organic binder in the total volume of the constituent components of the heat-resistant porous film of this separator was 6% by volume, and the porosity of the heat-resistant porous film was 51%.

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

Example 5
Secondary particulate boehmite powder (average particle size 0.06 μm, specific surface area 100 m ² / g) with continuous primary particles was used as fine particles having a heat-resistant temperature of 130 ° C. or higher, and 4000 g of this boehmite powder was added to 4000 g of water four times. Separately added, the mixture was stirred with a disper at 2800 rpm for 5 hours to prepare a uniform dispersion. To this dispersion, 4000 g of an aqueous dispersion (solid content ratio 40%) of PE fine particles (heat-meltable fine particles, melting point 135 ° C., average particle size 1.0 μm) and PVP [ISP Japan Co., Ltd.] having a weight average molecular weight of 3.5 million “K-120 (trade name)”, Tg: 176 ° C.] (1200 g) in water (concentration: 10% by mass) was added and stirred at room temperature until water was uniformly dispersed and the solid content ratio was 30%. % Heat-resistant porous forming slurry was prepared.

A separator having a thickness of 20 μm is prepared by preparing a PET nonwoven fabric (weight per unit: 8 g / m ² , thickness: 16 μm) on the porous substrate, dipping the slurry on the porous substrate, and drying to form a heat resistant porous film. Got. The volume ratio of the organic binder in the total volume of the constituent components of the heat resistant porous film of this separator was 9% by volume, and the porosity of the heat resistant porous film was 51%.

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

Example 6
Alumina powder (average particle size 0.4 μm, specific surface area 7 m ² / g) is prepared as fine particles having a heat-resistant temperature of 130 ° C. or more, 4000 g of this alumina powder is added to 4000 g of water in four portions, and 2800 rpm is added by a disper at 2800 rpm. A uniform dispersion was prepared by stirring for 5 hours. To this dispersion, 4000 g of an aqueous dispersion (solid content ratio 40%) of PE fine particles (heat-meltable fine particles, melting point 135 ° C., average particle size 1.0 μm) and PVP [ISP Japan Co., Ltd.] having a weight average molecular weight of 3.5 million “K-120 (trade name)”, Tg: 176 ° C.] (1200 g) in water (concentration: 10% by mass) was added and stirred at room temperature until water was uniformly dispersed and the solid content ratio was 30%. % Heat-resistant porous forming slurry was prepared.

  On the negative electrode mixture layer of the same negative electrode as that prepared in Example 1, the slurry was applied using a gravure coater and then dried to form a heat-resistant porous film having a thickness of 20 μm. An integrated product with a porous membrane was obtained. The volume ratio of the organic binder in the total volume of the constituent components of the heat-resistant porous film was 15% by volume, and the porosity of the heat-resistant porous film was 46%.

  The integrated product of the negative electrode and the heat-resistant porous film and the same positive electrode as those prepared in Example 1 were superposed and wound in a spiral shape to produce a wound electrode group. And the lithium secondary battery was produced like Example 1 except having used this electrode group.

Example 7
The same slurry for forming a heat resistant porous film as that prepared in Example 6 was applied on the negative electrode mixture layer of the same negative electrode as that prepared in Example 1 using a gravure coater and then dried. Then, a heat-resistant porous film having a thickness of 10 μm was formed to obtain an integrated product of the negative electrode and the heat-resistant porous film.

  Moreover, after apply | coating the said slurry for heat resistant porous membrane formation same as what was prepared in Example 6 on the positive mix layer of the same positive electrode as what was produced in Example 1 using a gravure coater It dried and formed the heat-resistant porous membrane with a thickness of 10 micrometers, and obtained the integrated object of the positive electrode and the heat-resistant porous membrane.

  The heat-resistant porous membrane in the integrated product of the negative electrode and the heat-resistant porous membrane, and the heat-resistant porous membrane in the integrated product of the positive electrode and the heat-resistant porous membrane are organic in the total volume of the constituent components. The volume ratio of the binder was 15% by volume, and the porosity was 46%.

  The integrated product of the negative electrode and the heat-resistant porous membrane and the integrated product of the positive electrode and the heat-resistant porous membrane were superposed and wound in a spiral shape to produce a wound electrode group. And the lithium secondary battery was produced like Example 1 except having used this electrode group.

Comparative Example 1
The aqueous solution of the organic binder to be 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.). In the same manner as in Example 1, a heat-resistant porous forming slurry having a solid content ratio of 30% by mass was prepared, and a separator having a thickness of 20 μm was prepared in the same manner as in Example 1 except that this slurry was used. Was made. The volume ratio of the organic binder in the total volume of the constituent components of the heat resistant porous membrane of this separator was 6% by volume, and the porosity of the heat resistant porous membrane was 53%.

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

Comparative Example 2
A slurry for forming a heat resistant porous membrane was prepared in the same manner as in Example 1 except that the fine particles having a heat resistant temperature of 130 ° C. or higher were changed to boehmite powder having an average particle diameter of 0.005 μm and a specific surface area of 250 m ² / g. A separator having a heat-resistant porous film having a thickness of 20 μm was prepared in the same manner as in Example 1 except that this slurry was prepared. The volume ratio of the organic binder in the total volume of the constituent components of the heat resistant porous film of this separator was 6% by volume, and the porosity of the heat resistant porous film was 46%.

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

Comparative Example 3
4000 g of the same boehmite powder used in Example 1 was added to 4000 g of water in four portions, and the mixture was stirred with a disper at 2800 rpm for 5 hours to prepare a uniform dispersion. 200 g of an aqueous solution (concentration: 10% by mass) of PVP [ISP Japan Co., Ltd. “K-90 (trade name)”, Tg: 174 ° C.], which is an organic binder, is added to this dispersion as a weight average molecular weight of 1.6 million. And stirred at room temperature until uniformly dispersed to prepare a slurry for forming a heat resistant porous film.

  A separator having a heat-resistant porous film having a thickness of 20 μm was prepared in the same manner as in Example 1 except that the slurry was used. A secondary battery was produced. The volume ratio of the organic binder in the total volume of the constituent components of the heat resistant porous film of the separator was 1.5% by volume, and the porosity of the heat resistant porous film was 57%.

  The following evaluation was performed about the lithium secondary battery of an Example and a comparative example, and the separator or heat resistant porous membrane used for the battery of an Example and a comparative example.

<Heat shrinkage test of separator or heat-resistant porous membrane>
From the separator used in the batteries of Examples 1 to 5 and Comparative Examples 1 to 3, and the integrated product of the negative electrode and the heat-resistant porous film used in the batteries of Examples 6 and 7, the MD direction and the TD direction were each 5 cm. A strip-shaped sample piece of 10 cm was cut out. Here, the MD direction is the machine direction when producing an integrated product of the separator or negative electrode and the heat-resistant porous membrane, and the TD direction is a direction perpendicular to them.

  For each of the above samples, straight lines of 3 cm each in parallel with the long side direction and the short side direction are crossed with the oil pen so that the center in the long side direction (TD direction) and the center in the short piece direction (MD direction) intersect each other. Marked. The center of each straight line was the intersection of these straight lines. These samples are hung in a thermostatic bath, the temperature in the bath is increased at a rate of 5 ° C./min. After reaching 150 ° C., the temperature is maintained at 150 ° C. for 1 hour, and the stationary operation is performed at 150 ° C. for 1 hour from the start of the test. Measure the lengths of the marks in the long side direction and the short side direction at the time of execution, determine the difference from each length before temperature increase, and further determine the ratio between these differences and each length before temperature increase Thus, the thermal contraction rate in each direction was calculated. In addition, the heat shrinkage rate of each separator and the heat resistant porous film was set to the larger one of the heat shrinkage rate in the long side direction and the heat shrinkage rate in the short side direction.

<Charge / discharge characteristics evaluation>
About each battery of an Example and a comparative example, it charged on condition of the following, charge capacity and discharge capacity were calculated | required, respectively, and the ratio of discharge capacity with respect to charge capacity was evaluated as charging efficiency. The charging was constant current-constant voltage charging in which constant current charging was performed until the battery voltage reached 4.2 V at a current value of 0.2 C, and then constant voltage charging at 4.2 V was performed. The total charging time until the end of charging was 15 hours.

  When each battery after charging was discharged at a discharge current of 0.2 C until the battery voltage reached 3.0 V, the batteries of Examples 1 to 7 and Comparative Examples 1 to 3 had a charging efficiency of almost 100. %, Confirming that the battery operates well.

<High temperature storage characteristics evaluation>
About each battery of an Example and a comparative example, after charging on the same conditions as charging / discharging characteristic evaluation, it stored for 20 days in a 60 degreeC environment, and after each battery was returned to normal temperature, battery voltage is 3.0V. Discharge was performed until. And the value which remove | divided the discharge capacity obtained about each battery by the discharge capacity calculated | required at the time of charge / discharge characteristic evaluation was represented by percentage, and the capacity | capacitance maintenance factor after high temperature storage was calculated | required. That is, it can be said that the higher the capacity retention rate after high temperature storage, the better the high temperature storage characteristics.

<Heating test>
Each of the three batteries of the example and the comparative example was charged with a constant current up to 4.35 V at a current value of 0.5C. When charging, a battery having a surface temperature equal to the atmospheric temperature in an air atmosphere of 20.0 ° C. to 25 ° C. was used. The battery in a charged state was placed in a constant temperature bath, the temperature in the bath was increased at a rate of 5 ° C./min to reach 150 ° C., and the temperature was further maintained at 150 ° C. for 3 hours. The maximum temperature reached by the battery was measured by a thermocouple connected to the surface of the battery from the start of the temperature rise in the thermostat until the end of the constant value operation at 150 ° C. for 3 hours. And the average value of the ultimate temperature of three batteries was calculated | required about each of the Example and the comparative example.

  Each evaluation result is described in Table 1 (in Table 1, the thermal contraction rate of the separator or the heat-resistant porous film is simply described as “thermal contraction rate”). Table 1 also shows the weight-average molecular weight of the PVP used, the proportion of the organic binder (contained in the total volume of the constituent components of the heat-resistant porous film) for the heat-resistant porous films according to the batteries of the examples and comparative examples. Amount), and the peel strength at 180 ° between the heat resistant porous membrane and the porous substrate or the negative electrode (described as “peel strength” in Table 1).

  As shown in Table 1, PVP having a specific Tg and having a specific weight average molecular weight is used as an organic binder, and a heat resistant porous membrane satisfying a specific value in peel strength with a porous substrate or electrode The lithium secondary batteries of Examples 1 to 7 have capacity maintenance after high-temperature storage as compared to the lithium secondary battery of Comparative Example 1 having a heat-resistant porous film using PVP having a low weight average molecular weight as an organic binder. It has a high rate and has excellent high-temperature storage characteristics.

  Moreover, the separator or heat-resistant porous film which concerns on the lithium secondary battery of Examples 1-7 has a small thermal contraction rate in 150 degreeC. Therefore, the batteries of Examples 1 to 7 have high safety because the positive electrode and the negative electrode can be satisfactorily separated by the separator or the heat-resistant porous film that does not easily shrink even at high temperatures. It can be said that. Actually, in the batteries of Examples 1 to 7, the ultimate temperature at the time of the heating test is kept low, and it can be confirmed that the safety is good.

  On the other hand, in the batteries of Comparative Examples 1 to 3, the peel strength at 180 ° between the heat-resistant porous membrane of the separator used and the porous substrate was small, which caused the heat of the separator at 150 ° C. The shrinkage rate is large. Therefore, it can be said that the batteries of Comparative Examples 1 to 3 are inferior in safety to the batteries of the examples because the separator contracts when the temperature becomes high, and the positive electrode and the negative electrode come into contact with each other. Actually, it can be confirmed that the batteries of Comparative Examples 1 to 3 have a higher ultimate temperature during the heating test than the batteries of the examples and are inferior in safety.

  The present invention can be implemented in other forms without departing from the spirit of the present invention. The embodiments disclosed in the present application are examples, and the present invention is not limited to these embodiments. 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. included.

  The non-aqueous battery of the present invention can be applied to the same uses as various uses in which a non-aqueous battery such as a conventionally known lithium secondary battery is used.

1 Positive electrode 2 Negative electrode 3 Separator

Claims (10)

A heat-resistant porous film formed on a porous substrate for constituting a separator for a nonaqueous battery or an electrode used for a nonaqueous battery,
The heat-resistant porous film contains at least a fine particle having a heat-resistant temperature of 130 ° C. or higher and an organic binder,
The organic binder has a group having a cyclic structure containing an amide bond and a skeleton derived from a polymerizable double bond, has a glass transition temperature of 130 ° C. or higher, and a weight average molecular weight of 350,000 or higher. Contains polymer,
180.degree. Peel strength between the porous substrate or the electrodes is 0.6 N / cm or more. In a polymer having a group 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 heat resistant porous membrane according to claim 1, wherein the glass transition temperature is 150 ° C or higher.

  The heat-resistant porous membrane according to claim 1 or 2, wherein the polymer having a cyclic structure containing an amide bond and a skeleton derived from a polymerizable double bond is polyvinylpyrrolidone.   The heat-resistant porous membrane according to any one of claims 1 to 3, further comprising resin fine particles having a melting point of 80 to 150 ° C.   The heat-resistant porous membrane according to any one of claims 1 to 4, further comprising fine particles that swell due to an increase in the amount of absorption of the non-aqueous electrolyte at a temperature of 80 to 150 ° C in the non-aqueous electrolyte.   A separator for a non-aqueous battery, wherein the porous substrate and the heat-resistant porous membrane according to any one of claims 1 to 5 are integrated.   The separator for a nonaqueous battery according to claim 6, wherein the porous substrate is a polyolefin microporous membrane.   The separator for nonaqueous batteries according to claim 6 or 7, wherein the thermal shrinkage at 150 ° C is 5% or less.   It has a positive electrode, a negative electrode and a nonaqueous electrolyte, and the heat-resistant porous membrane according to any one of claims 1 to 5 is integrated with at least one of the positive electrode and the negative electrode. Non-aqueous battery. It has a positive electrode, a negative electrode, a separator, and a nonaqueous electrolyte, The said separator is a separator for nonaqueous batteries in any one of Claims 6-8, The nonaqueous battery characterized by the above-mentioned.

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