JP5603543B2 - Battery separator and non-aqueous electrolyte battery - Google Patents

Description

  The present invention relates to a battery separator capable of constituting a nonaqueous electrolyte battery excellent in load characteristics and safety, and a nonaqueous electrolyte battery having the separator.

  A lithium secondary battery, which is a type of non-aqueous electrolyte 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. For example, lithium secondary batteries tend to have higher capacities as mobile devices become more sophisticated, and ensuring safety is important.

  In current lithium secondary batteries, a polyolefin microporous film having a thickness of about 20 to 30 μm is used as a separator interposed between a positive electrode and a negative electrode. In addition, as separator material, the constituent resin of the separator is melted below the thermal runaway temperature of the battery to close the pores, thereby increasing the internal resistance of the battery and improving the safety of the battery in the event of a short circuit. In order to ensure the so-called shutdown effect, polyethylene having a low melting point may be applied.

  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, in such a stretched film, the degree of crystallinity of the constituent resin has increased, and the shutdown temperature has increased to a temperature close to the thermal runaway temperature of the battery, so there is a sufficient margin for ensuring the safety of the battery. It's hard to say.

  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 using a polyolefin-based microporous membrane separator, if the battery temperature reaches the shutdown temperature in the event 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 temperature of the battery easily rises to the shrinkage temperature of the separator, and there is a risk of an internal short circuit.

  As a technique for preventing such a short circuit due to thermal contraction of the separator and enhancing the reliability of the battery, for example, a separator having a multilayer structure including a layer having high heat resistance has been proposed (for example, Patent Documents 1 to 5). .

JP 2006-351386 A International Publication No. 2007/66768 JP 2007-273123 A JP 2007-273443 A JP 2007-280911 A

  By the way, the request | requirement with respect to the present non-aqueous electrolyte battery has further increased, and it is calculated | required to maintain an output characteristic at a high level, improving safety | security. The technology disclosed in the above-mentioned patent document has a certain effect in improving the safety of the nonaqueous electrolyte battery, but there is room for further improvement in response to such a request.

  This invention is made | formed in view of the said situation, The objective provides the separator which can comprise the nonaqueous electrolyte battery excellent in load characteristics and safety | security, and the nonaqueous electrolyte battery which has this separator. There is.

  The battery separator of the present invention that has solved the above problems is a battery comprising a multilayer porous film having at least a resin porous layer mainly composed of a thermoplastic resin and a heat resistant porous layer mainly composed of heat resistant fine particles. The heat-resistant fine particles have an average particle diameter of 0.2 to 1 μm, and a ratio of particles having a particle diameter larger than 2 μm is 10% by volume or less. .

  The battery of the present invention includes a positive electrode having an active material capable of occluding and releasing Li (lithium) ions, a negative electrode having an active material capable of occluding and releasing Li ions, an organic electrolyte, and a separator. The separator for a battery of the present invention is used as the separator.

  In addition, in the resin porous layer (I) in the present specification, “mainly composed of a thermoplastic resin” is a solid content ratio in the resin porous layer, and the thermoplastic resin is 50% by volume or more. I mean. Furthermore, “including heat-resistant fine particles as a main component” in the heat-resistant porous layer in the present specification means that the heat-resistant fine particles are 50% by volume or more in terms of the solid content ratio in the layer.

  ADVANTAGE OF THE INVENTION According to this invention, the separator which can comprise the nonaqueous electrolyte battery excellent in the load characteristic and safety | security, and the nonaqueous electrolyte battery which has this separator can be provided. That is, the non-aqueous electrolyte battery of the present invention is excellent in load characteristics and safety.

  The battery separator of the present invention (hereinafter sometimes simply referred to as “separator”) is a multilayer porous material having at least a resin porous layer mainly composed of a thermoplastic resin and a heat resistant porous layer mainly composed of heat resistant fine particles. It consists of a membrane. The resin porous layer is a layer having an original function of a separator that transmits ions while preventing a short circuit between the positive electrode and the negative electrode, and the heat resistant porous layer is a layer that plays a role of imparting heat resistance to the separator.

  In the heat-resistant porous layer, the heat-resistant fine particles are the main component and play a role of preventing thermal shrinkage and film breakage of the resin porous layer serving as the base material. In addition, when the inside of the battery generates heat abnormally and the resin porous layer melts, the positive electrode and the negative electrode are separated by the heat-resistant porous layer mainly containing heat-resistant fine particles, and the safety of the battery is ensured. .

  However, as described above, the heat-resistant porous layer can improve the heat resistance of the separator, but becomes an obstacle to the movement of Li ions that pass through the separator, and also causes a reduction in load characteristics of the battery. Therefore, in the present invention, the shape of the heat-resistant fine particles that are the main component of the heat-resistant porous layer is adjusted so that the heat-resistant porous layer can be made as thin as possible while suppressing the decrease in heat resistance. The influence on the movement of Li ions is reduced, and a battery having good load characteristics can be configured.

  The heat-resistant fine particles contained in the heat-resistant porous layer have an average particle diameter of 1 μm or less, preferably 0.8 μm or less. If the average particle size of the heat-resistant fine particles is too large, it becomes difficult to form a thin heat-resistant porous layer. In addition, the path length of the pores inside the heat-resistant porous layer becomes long, which becomes an obstacle when Li ions pass through the separator, and the load characteristics of the battery are likely to deteriorate. On the other hand, if the heat-resistant fine particles are too small, the surface area becomes large, so that the dispersibility of the heat-resistant fine particles in the heat-resistant porous layer is reduced or the amount of water adhering to the heat-resistant fine particles is increased. It becomes difficult to control the amount. If the amount of water in the battery increases, the battery characteristics may deteriorate. Therefore, the average particle diameter of the heat-resistant fine particles is preferably set to 0.2 μm or more from the viewpoint of suppressing the occurrence of such problems and configuring a battery with good characteristics.

  In addition, even if the heat-resistant fine particles contained in the heat-resistant porous layer satisfy the above average particle diameter, if a large amount of coarse particles are contained, it becomes difficult to make the heat-resistant porous layer thin, Problems such as lowering are likely to occur. Therefore, the ratio of particles having a particle diameter larger than 2 μm contained in all heat-resistant fine particles contained in the heat-resistant porous layer is 10% by volume or less, and preferably 7% by volume or less. On the other hand, from the viewpoint of optimizing the dispersibility of the heat-resistant fine particles and the moisture adhering to the heat-resistant fine particles, it is preferable that the proportion of particles having a particle diameter smaller than 0.2 μm is not more than a certain value. The ratio of the particles having a particle diameter smaller than 0.2 μm contained in the heat-resistant fine particles is more preferably 30% by volume or less, further preferably 20% by volume or less, and 10% by volume or less. It is particularly preferred.

  In addition, the average particle diameter of the heat-resistant fine particles referred to in this specification is a medium that does not swell or dissolve the fine particles using a laser scattering particle size distribution meter (for example, “LA-920” manufactured by HORIBA) (for example, water). The particle size (D50) at 50% of the volume-based integrated fraction measured by dispersing in a particle size. Further, the ratio of particles having a particle diameter larger than 2 μm and the ratio of particles having a particle diameter smaller than 0.2 μm in the heat-resistant fine particles can also be determined by the particle size distribution measurement when determining the average particle diameter. .

  The heat-resistant fine particles have electrical insulation properties, are electrochemically stable, and are stable in a solvent used for an organic electrolyte and a composition for forming a heat-resistant porous layer (a composition containing a solvent) described later. As long as it does not dissolve in the organic electrolyte at high temperature, there is no particular limitation. As used herein, “stable heat-resistant fine particles with respect to an organic electrolyte” refers to deformation and chemical composition in an organic electrolyte (an organic electrolyte used as an electrolyte in a non-aqueous electrolyte battery). It means heat-resistant fine particles that do not change. In addition, the “high temperature state” in the present specification specifically refers to a temperature of 150 ° C. or higher, and may be a stable particle that does not undergo deformation or chemical composition change in an organic electrolyte at such a temperature. That's fine. Further, “electrochemically stable” as used in the present specification means that no chemical change occurs during charging / discharging of the battery.

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

  Examples of the shape of the heat-resistant fine particles include various shapes such as a spherical shape, a particle shape, a plate shape, and a needle shape. From the viewpoint of better suppressing the thermal shrinkage of the separator, the aspect ratio is 1 or more and 3 or less. It is preferably a polyhedral shape or a substantially spherical shape (including a true spherical shape). The term “polyhedron-shaped particle” as used herein refers to a particle surrounded by a substantially polygonal surface (including a polygon), and has a substantially rhombohedral shape (including rhombohedral shape), a substantially hexagonal column shape (hexagonal column). And particles having a substantially cubic shape (including a cubic shape).

  The aspect ratio of a polyhedral particle is the distance Lf (μm) from the center (center of gravity) of the particle to the center of the farthest surface, and the distance Ln (μm) from the center of the particle to the nearest surface center. It means the value obtained by dividing, ie, “Lf / Ln”. The aspect ratio of the substantially spherical particles is a value obtained by dividing the major axis diameter (longest diameter) Ll (μm) of the sphere by the minor axis diameter (shortest diameter) Ls (μm) of the sphere, that is, It means “Ll / Ls”. From these definitions, the aspect ratio of the heat-resistant fine particles is 1 or more.

  When the heat-resistant fine particles have a polyhedral shape or a substantially spherical shape with an aspect ratio of 1 to 3, the separator is exposed to high temperature and the resin porous layer tends to shrink, so that the compressive stress is applied to the heat-resistant porous layer. Since the stress concentration can be controlled when applied, the resistance of the heat-resistant porous layer to the compressive stress can be further increased, and the thermal contraction of the separator can be suppressed more favorably. The reason for this will be described with reference to the drawings, taking polyhedral heat-resistant fine particles as an example.

  1 and 2 schematically show a cross-section of the main part of the heat-resistant porous layer according to the separator of the present invention (however, the back side of the cross-section is omitted), and the heat-resistant porous layer of FIG. The porous layer contains particles having an average particle diameter of 0.2 μm and an aspect ratio of 1.0 as the heat-resistant fine particles 1, and the heat-resistant porous layer in FIG. Contain 1.0 μm of plate-like particles having an aspect ratio of 5.0.

  In the heat resistant porous layer shown in FIG. 1, the directionality of the heat resistant fine particles 1 does not exist. On the other hand, in the heat resistant porous layer shown in FIG. 2, since the heat resistant fine particles 1 are plate-like particles, they are oriented in one direction [for example, the horizontal direction in the figure (direction parallel to the resin porous layer)]. There are some particles that do not face the direction parallel to the resin porous layer, such as the particles 1b, while showing a tendency to be easy. When the same compressive stress F (MPa) per unit area is applied to the heat resistant porous layer shown in FIGS. 1 and 2 as the resin porous layer contracts, the heat resistant porous layer of FIG. Compared with the particle 1b according to FIG. 2, a larger stress is applied to the particle 1b according to the heat resistant porous layer of FIG.

  Here, the particle 1b related to the heat resistant porous layer in FIG. 1 and the particle 1b related to the heat resistant porous layer in FIG. 2 have substantially the same adhesion area and the same adhesion force t (MPa) as the particles 1a and 1c, respectively. ). In this case, compared with the particle 1b related to the heat-resistant porous layer in FIG. 1, the particle 1b related to the heat-resistant porous layer in FIG. The stress may cause the particle 1b to be separated from the particle 1a or the particle 1c. That is, the heat resistant fine particle 1 having a small aspect ratio as shown in FIG. 1 is used in comparison with the heat resistant porous layer formed using the heat resistant fine particles 1 having a large aspect ratio as shown in FIG. In the heat resistant porous layer, it is considered that even if the compressive stress accompanying the thermal contraction of the resin porous layer is larger, the heat resistant porous layer is hardly broken. If the heat-resistant porous layer breaks along with the heat shrinkage of the resin porous layer, the entire separator shrinks. Therefore, by using heat-resistant fine particles having a smaller aspect ratio, specifically, heat-resistant fine particles having an aspect ratio of 1 or more and 3 or less, it is possible to destroy the heat-resistant porous layer caused by the heat shrinkage of the resin porous layer. Since it can suppress more highly, the thermal contraction of a separator can be suppressed more favorably. The aspect ratio of the heat-resistant fine particles is more preferably 2 or less from the viewpoint that such an effect becomes better.

  For the same reason as described above, when a large amount of coarse particles are contained in the heat-resistant fine particles, the heat-resistant porous layer is likely to be broken due to the compressive stress accompanying the thermal contraction of the resin porous layer. In particular, when the heat-resistant fine particles contain more than 10% by volume of particles having a particle diameter of more than 2 μm, the heat-resistant porous layer is more destroyed by the compressive stress accompanying the thermal contraction of the resin porous layer. The present inventors have confirmed that it tends to occur.

  For the heat resistant porous layer, it is preferable to use a resin binder for the purpose of adhering the heat resistant fine particles to each other or adhering the heat resistant fine particles and the resin porous layer. The resin binder is not particularly limited as long as the constituent components of the heat-resistant porous layer can be satisfactorily bonded to each other, are electrochemically stable, and are stable to the organic electrolyte. Specifically, for example, ethylene-vinyl acetate copolymer (EVA, structural unit derived from vinyl acetate is 20 to 35 mol%), acrylate copolymer, fluorine rubber, styrene butadiene rubber (SBR), polyvinyl Resins such as alcohol (PVA), polyvinyl butyral (PVB), polyvinyl pyrrolidone (PVP), polyurethane, and polyvinylidene fluoride (PVDF) are listed. Some of these resins prevent dissolution in organic electrolytes. In order to achieve this, those having a crosslinked structure introduced can also be used. These resin binders may be used alone or in combination of two or more. Among these, an acrylate copolymer having a crosslinked structure is particularly preferable.

  In addition to the resin binders described above, a known resin may be mixed with an amine compound or polyacrylic acid resin to increase flexibility, reduce the glass transition temperature (Tg), or use a known plasticizer (phthalate ester). Or the like) may be used, for example, to improve the elongation at break. Furthermore, the adhesiveness of the resin binder can be improved by introducing a carboxyl group. As a method for lowering the Tg of the resin, various known methods such as introduction of a crosslinked structure having a low crosslinking density and introduction of a long side chain can be employed.

  When the resin binder is used, it can be used in the form of an emulsion dissolved or dispersed in a medium (solvent) of a composition for forming a heat resistant porous layer described later.

  The amount of heat-resistant fine particles in the heat-resistant porous layer is preferably 70% by volume or more, more preferably 80% by volume or more, and 90% by volume or more in the total volume of the constituent components of the heat-resistant porous layer. More preferably it is. In the heat-resistant porous layer, the high content of heat-resistant fine particles as described above can better suppress the occurrence of short circuit due to direct contact between the positive electrode and the negative electrode when the battery becomes high temperature. Moreover, the thermal contraction of the whole separator can be suppressed more favorably.

  Further, as described above, the heat-resistant porous layer preferably contains a resin binder. From such a viewpoint, the amount of heat-resistant fine particles in the heat-resistant porous layer is, for example, the entire components of the heat-resistant porous layer. In the product, it is preferably 99% by volume or less. If the amount of the heat-resistant fine particles in the heat-resistant porous layer is less than 70% by volume, for example, it is necessary to increase the amount of the resin binder in the heat-resistant porous layer. May be easily filled with a resin binder, and the function as a separator may be reduced. In addition, when porous using a pore-opening agent or the like, the interval between the heat-resistant fine particles becomes too large and heat shrinkage occurs. There is a possibility that the effect of suppressing the decrease.

  In addition, the amount of the resin binder in the heat resistant porous layer ensures a better effect by using the resin binder, and from the viewpoint of suppressing exfoliation of the heat resistant porous layer from the resin porous layer and exfoliation of the heat resistant fine particles. It is preferable that it is 1 mass part or more with respect to 100 mass parts of conductive fine particles. However, if the amount of the resin binder is too large, pores in the heat resistant porous layer may be blocked and the effect of improving the load characteristics of the battery may be reduced. The amount is preferably 30 parts by mass or less with respect to 100 parts by mass of the fine particles.

  The thickness of the heat-resistant porous layer (when the separator has a plurality of heat-resistant porous layers, the total thickness. The same applies to the thickness of the heat-resistant porous layer hereinafter) more effectively suppresses heat shrinkage of the resin porous layer. In view of the above, the thickness is preferably 2 μm or more. In addition, it is particularly preferable that the heat-resistant porous layer has a thickness of 2.5 μm or more because the thermal contraction rate of the resin porous layer can be further suppressed. Furthermore, from the viewpoint of further improving the capacity and load characteristics of the battery by reducing the total thickness of the separator, the thickness of the heat-resistant porous layer is preferably 4 μm or less, and the load characteristics of the battery can be further enhanced. It is particularly preferable that the thickness is 6 μm or less.

  The resin porous layer according to the multilayer porous membrane constituting the separator of the present invention is mainly composed of a thermoplastic resin that is softened at 80 to 180 ° C. to close the pores and does not dissolve in the organic electrolyte solution of the battery. It is preferable. The thermoplastic resin softening at 80 to 180 ° C. is, for example, a thermoplastic resin having a melting temperature of 80 to 180 ° C. measured using a differential scanning calorimeter (DSC) according to JIS K 7121. Is mentioned. Specific examples of the thermoplastic resin include polyolefin and thermoplastic polyurethane. Examples of the polyolefin include polyethylene such as low density polyethylene, high density polyethylene, and ultrahigh molecular weight polyethylene; polypropylene; As the thermoplastic resin, those exemplified above may be used alone or in combination of two or more.

  The form of the resin porous layer may be any form as long as it has an ionic conductivity sufficient to obtain necessary battery characteristics, but more specifically, the porous layer, more specifically, a form in which fine particles are aggregated. Ion-permeable microporous film having a large number of pores formed by a conventional solvent extraction method, dry or wet stretching method, etc. (a microporous film widely used as a battery separator) The layer etc. which were comprised by can be illustrated.

  When the resin porous layer is formed, for example, by gathering thermoplastic resin fine particles, if necessary, the fine particles can be bound together, the resin porous layer and the heat resistant porous layer, In order to integrate the electrode, the resin porous layer may contain a resin binder. As a resin binder, the same thing as the various resin binder illustrated as what can be contained in a heat resistant porous layer can be used, These may be used individually by 1 type and may use 2 or more types together. When using a resin binder, as in the case of the heat resistant porous layer, it is dissolved or dispersed in a medium (solvent) of a composition for forming a resin porous layer described later. Can be used.

  The content of the thermoplastic resin in the resin porous layer is more effective in shutting down the thermoplastic resin constituting the resin porous layer when the inside of the battery becomes hot and plugging the pores of the separator. In order to facilitate, for example, the following is preferable. The volume of the thermoplastic resin in all the constituent components of the separator is preferably 10% by volume or more, and more preferably 20% by volume or more. Further, the volume of the thermoplastic resin is preferably 50% by volume or more, more preferably 70% by volume or more, and more preferably 80% by volume or more in all the constituent components of the resin porous layer. [The thermoplastic resin may be 100% by volume. ]. Furthermore, it is preferable that the porosity of the heat resistant porous layer calculated | required by the postscript method is 20 to 60%, and the volume of a thermoplastic resin is 50% or more of the void | hole volume of a heat resistant porous layer.

  The thickness of the resin porous layer (when the separator has a plurality of resin porous layers, the total thickness. The same applies to the thickness of the resin porous layer) is 8 μm or more from the viewpoint of ensuring good shutdown characteristics. Preferably, it is 10 μm or more. In addition, from the viewpoint of reducing the total thickness of the separator and further improving the capacity and load characteristics of the battery, the thickness of the resin porous layer is preferably 40 μm or less, more preferably 30 μm or less, and 16 μm. More preferably, it is more preferably 12 μm or less.

  Furthermore, the resin porous layer preferably has a pore size of 3 μm or less. If the resin porous layer has a small pore diameter as described above, even if small pieces are detached from the positive electrode or the negative electrode, it is possible to satisfactorily suppress the occurrence of a short circuit.

  The separator may have one resin porous layer and one heat resistant porous layer. For example, the separator has a plurality of heat resistant porous layers such as a heat resistant porous layer on both sides of the resin porous layer. Or a plurality of porous resin layers may be provided. However, increasing the number of layers may increase the thickness of the separator, leading to an increase in internal resistance and a decrease in energy density. Therefore, it is not preferable to increase the number of layers, and the layers constituting the separator (resin porous material) The total number of layers and heat-resistant porous layer) is preferably 5 layers or less, and more preferably 2 layers.

  The total thickness of the separator is preferably 10 μm or more from the viewpoint of more reliably separating the positive electrode and the negative electrode, and from the viewpoint of further improving the capacity and load characteristics of the battery, it is preferably 50 μm or less, and 20 μm or less. It is more preferable that it is 15 μm or less.

  In addition, the resin porous layer and the heat resistant porous layer may be integrated to form a separator, and the resin porous layer and the heat resistant porous layer are not integrated and exist as independent films. Alternatively, the resin porous layer or the heat resistant porous layer may be individually integrated with the electrode. In the case of a separator in which the resin porous layer and the heat resistant porous layer are not integrated, the separator is configured by superposing the resin porous layer and the heat resistant porous layer in the nonaqueous electrolyte battery. .

The porosity of the separator as a whole is preferably 30% or more in a dry state in order to ensure the amount of nonaqueous electrolyte retained and to improve ion permeability. On the other hand, from the viewpoint of securing separator strength and preventing internal short circuit, the separator porosity is preferably 70% or less in a dry state. The porosity of the separator: P (%) can be calculated by obtaining the sum of each component i from the thickness of the separator, the mass per area, and the density of the constituent components using the following equation (1).
P = 100− (Σa _i / ρ _i ) × (m / t) (1)
Here, in the above formula, a _i : ratio of component i expressed by mass%, ρ _i : density of component i (g / cm ³ ), m: mass per unit area of separator (g / cm ² ), t: The thickness (cm) of the separator.

Further, in the above formula (1), m is the mass per unit area (g / cm ² ) of the resin porous layer, and t is the thickness (cm) of the resin porous layer, thereby formula (1) Can also be used to determine the porosity of the resin porous layer: P (%). The porosity of the resin porous layer determined by this method is preferably 30% or more, more preferably 40% or more from the viewpoint of increasing the amount of nonaqueous electrolyte retained, and the physical properties of the resin porous layer From the viewpoint of increasing the mechanical strength and ensuring better shutdown characteristics, it is preferably 80% or less, more preferably 70% or less.

Furthermore, in the above formula (1), m is the mass per unit area (g / cm ² ) of the heat resistant porous layer, and t is the thickness (cm) of the heat resistant porous layer. Can also be used to determine the porosity of the heat-resistant porous layer: P (%). It is preferable that the porosity of the heat resistant porous layer calculated | required by this method is 20 to 60%.

  Further, the separator of the present invention has a thermal shrinkage rate when left in an atmosphere of 150 ° C., for example, in the MD direction (take-up direction during the production of the multilayer porous film constituting the separator) and the TD direction (MD direction). In any of the directions (perpendicular to each other), it is preferable that the resin does not easily shrink. Specifically, the thermal shrinkage rate is preferably 0 to 10%. If the separator has such characteristics, even when the inside of the battery reaches about 150 ° C., the separator hardly contracts, so that a short circuit due to contact between the positive and negative electrodes can be prevented more reliably, and the battery at high temperature The safety of the can be further increased. By making a separator into the above-mentioned composition, the above-mentioned heat shrinkage rate can be secured.

  When the resin porous layer and the heat-resistant porous layer are integrated, the heat shrinkage here refers to the overall shrinkage of the integrated separator (multilayer porous membrane). When the porous layers are independent of each other, the value of the smaller shrinkage rate is indicated. In addition, the resin porous layer and / or the heat resistant porous layer may be configured to be integrated with the electrode. In this case, the heat shrinkage rate measured in the state integrated with the electrode is indicated.

  In addition, the above-mentioned “thermal shrinkage rate when left in an atmosphere of 150 ° C.” is a value obtained by a measurement method employed in Examples described later.

  The separator (multilayer porous membrane for constituting the separator) of the present invention is, for example, a slurry or paste in which heat-resistant fine particles and resin binder constituting the heat-resistant porous layer are dispersed in a medium such as water or an organic solvent. A heat-resistant porous layer-forming composition (resin binder may be dissolved in a medium) is prepared, applied to the surface of the resin porous layer, and dried.

  In the case where the resin porous layer is composed of a microporous film made of a thermoplastic resin, a heat-resistant porous layer forming composition is applied to the surface of the microporous film with a known coating apparatus. Alternatively, the heat-resistant porous layer-forming composition can be applied to the surface of the resin porous layer by impregnating the microporous membrane into the heat-resistant porous layer-forming composition.

  On the other hand, when the resin porous layer is composed of aggregated thermoplastic resin fine particles, the thermoplastic resin fine particles constituting the resin porous layer, the resin binder used as necessary, etc. And a slurry-like or paste-like resin porous layer forming composition (resin binder may be dissolved in the medium) by dispersing in a medium such as organic solvent, and applying this to the substrate, After the resin porous layer is formed by drying, the heat-resistant porous layer forming composition is applied to the surface of the resin porous layer by the same method as in the case of the microporous membrane, and dried to form a separator (multilayer porous layer). Membrane) can be produced. On the other hand, the heat-resistant porous layer forming composition is applied to the substrate, dried to once form a heat-resistant porous layer, and the resin porous layer-forming composition is applied to the surface of the heat-resistant porous layer. And may be dried to produce a separator (multilayer porous membrane).

  Further, either one of the heat-resistant porous layer forming composition or the resin porous layer forming composition is applied to a base material, and the other composition is applied before these compositions are completely dried. Thus, the resin porous layer and the heat resistant porous layer can be formed simultaneously.

  The medium used for the resin porous layer forming composition and the heat resistant porous layer forming composition can uniformly disperse the thermoplastic resin fine particles and heat resistant fine particles, and can dissolve or disperse the resin binder uniformly. However, general organic solvents such as aromatic hydrocarbons such as toluene, furans such as tetrahydrofuran, and ketones such as methyl ethyl ketone and methyl isobutyl ketone are preferably used. In addition, for the purpose of controlling the interfacial tension, alcohol (ethylene glycol, propylene glycol, etc.) or various propylene oxide glycol ethers such as monomethyl acetate may be appropriately added to these media. Further, when the resin binder is water-soluble, when used as an emulsion, water may be used as described above, and alcohols (methyl alcohol, ethyl alcohol, isopropyl alcohol, ethylene glycol, etc.) may be used in this case as well. The interfacial tension can also be controlled by adding as appropriate.

  The resin porous layer forming composition and the heat resistant porous layer forming composition preferably have a solid content of, for example, 10 to 80% by mass.

  The resin porous layer can be subjected to surface modification in order to enhance the adhesiveness with the heat resistant porous layer. In particular, in the case of a porous resin layer made of polyolefin, surface adhesion is generally not high, so surface modification is often effective.

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

  The non-aqueous electrolyte battery of the present invention is not particularly limited as long as it has the separator of the present invention, and the configuration and structure adopted in conventionally known non-aqueous electrolyte batteries can be applied. The nonaqueous electrolyte battery of the present invention includes a primary battery and a secondary battery, and the configuration of a secondary battery, which is a main application, will be exemplified below.

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

The positive electrode is not particularly limited as long as it is a positive electrode used in a conventionally known non-aqueous electrolyte secondary battery, that is, a positive electrode containing an active material capable of occluding and releasing Li ions. For example, as an active material, a layered structure represented by a general formula of Li _{1 + x} MO ₂ (−0.1 <x <0.1, M: Co, Ni, Mn, Al, Mg, Zr, Ti, Sn, etc.) A lithium-containing transition metal oxide, LiMn ₂ O ₄ and a spinel-type lithium manganese oxide in which a part of the element is substituted with another element, LiMPO ₄ (M: Co, Ni, Mn, Fe, etc.) An olivine type compound or the like can be used. Specific examples of the lithium-containing transition metal oxide having a layered structure include LiCoO ₂ and LiNi _1-x Co _xy Al _y O ₂ (0.1 ≦ x ≦ 0.3, 0.01 ≦ y ≦ 0. 2) and other oxides containing at least Co, Ni and Mn (LiMn _1/3 Ni _1/3 Co _1/3 O ₂ , LiMn _5/12 Ni _5/12 Co _1/6 O ₂ , LiNi _{3 / 5} Mn _1/5 Co _1/5 O ₂ etc.).

  As the conductive aid, a carbon material such as carbon black is used, and as the binder, a fluorine resin such as PVDF is used, and the positive electrode mixture layer is formed by a positive electrode mixture in which these materials and an active material are mixed. For example, it is formed on the current collector surface.

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

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

The negative electrode is not particularly limited as long as it is a negative electrode used in a conventionally known non-aqueous electrolyte secondary battery, 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, compounds that can be charged and discharged at a low voltage close to lithium metal, such as elements such as Si, Sn, Ge, Bi, Sb, and In and alloys thereof, lithium-containing nitrides, or oxides such as Li ₄ Ti ₅ O ₁₂ Alternatively, lithium metal or a lithium / aluminum alloy can also be used as the negative electrode active material. A negative electrode mixture in which a conductive additive (carbon material such as carbon black) or a binder such as PVDF is appropriately added to these negative electrode active materials is finished into a molded body (negative electrode mixture layer) using the current collector as a core material. Or those obtained by laminating the above-mentioned various alloys or lithium metal foils alone or on the surface of the current collector.

  When a current collector is used for the negative electrode, a copper or nickel foil, a punching metal, a net, an expanded metal, or the like can be used as the current collector, but a copper foil is usually used. In the negative electrode current collector, when the thickness of the entire negative electrode is reduced in order to obtain a battery having a high energy density, the upper limit of the thickness is preferably 30 μm, and the lower limit is preferably 5 μm. Further, the lead portion on the negative electrode side may be formed in the same manner as the lead portion on the positive electrode side.

  The electrode can be used in the form of a laminated electrode body in which the positive electrode and the negative electrode are laminated via the separator of the present invention, or a wound electrode body in which this is wound.

As the organic electrolytic solution, a solution in which a lithium salt is dissolved in an organic solvent is used. The lithium salt is not particularly limited as long as it dissociates in a solvent to form Li ⁺ ions and hardly causes side reactions such as decomposition in a voltage range used as a battery. For example, LiClO ₄ , LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiSbF ₆ and other inorganic lithium salts, 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 (RfOSO ₂ ) ₂ [where Rf is a fluoroalkyl group] and the like can be used. .

  The organic solvent used in the organic electrolyte is not particularly limited as long as it dissolves the lithium salt and does not cause a side reaction such as decomposition in the voltage range used as a battery. For example, cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, 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 dimethoxyethane, 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; etc., and these should be used as a mixture of two or more. It can be. 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, cyclohexyl benzene, biphenyl, fluorobenzene, t are used for the purpose of improving safety, charge / discharge cycleability, and high-temperature storage properties of these electrolytes. -Additives such as butylbenzene can be added as appropriate.

  The concentration of the lithium salt in the organic 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, PVDF, vinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polyacrylonitrile (PAN), polyethylene oxide, polypropylene oxide, ethylene oxide-propylene oxide copolymer, main chain or An electrolyte gelled using a known host polymer capable of forming a gel electrolyte such as a crosslinked polymer containing an ethylene oxide chain in the side chain or a crosslinked poly (meth) acrylate ester can also be used.

  The non-aqueous electrolyte battery of the present invention can be applied to the same applications as those in which conventionally known non-aqueous electrolyte batteries are used, such as power supply applications for various electronic devices.

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

Example 1
(Create separator)
Water: 1000 g of polyhedral boehmite synthesized as heat-resistant fine particles (aspect ratio 1.4, average particle size: D50 = 0.63 μm, D10 = 0.31 μm, D90 = 0.92 μm, particle size 2 μm) Ratio of larger particles: 0.5% by volume): 1000 g and an acrylate copolymer as a resin binder (a commercially available acrylate copolymer having butyl acrylate as a main component as a monomer component; 100 parts by mass of heat-resistant fine particles) 3 parts by mass) was dispersed by stirring for 1 hour using a three-one motor to prepare a uniform slurry (heat-resistant porous layer forming composition).

As a microporous film for constituting the resin porous layer, a polyethylene microporous film (thickness 16 μm, porosity 40%) having a corona treatment on one side was prepared. A multilayer having the heat-resistant porous layer having a thickness of 2.5 μm on one side of the resin porous layer, by uniformly applying the slurry to the corona-treated surface of the microporous membrane using a die coater and drying the slurry. A porous membrane was obtained. The mass per unit area of the heat-resistant porous layer in this multilayer porous membrane was 0.34 mg / cm ² . Further, for the heat resistant porous layer according to the multilayer porous membrane, the volume ratio of the heat resistant fine particles calculated by setting the specific gravity of boehmite to 3 g / cm ³ and the specific gravity of the resin binder to 1 g / cm ³ is 91.7% by volume. Met. The multilayer porous membrane was slit to a width of 47 mm to obtain a separator.

(Preparation of negative electrode)
A negative electrode active material-containing paste was prepared by mixing 95 parts by mass of graphite as a negative electrode active material and 5 parts by mass of PVDF as a binder so as to be uniform using NMP as a solvent. This negative electrode mixture-containing paste is intermittently applied on both sides of a current collector made of copper foil with a thickness of 10 μm so that the coating length is 320 mm on the front side and 260 mm on the back side, dried, and then subjected to a calendar treatment. Then, the thickness of the negative electrode mixture layer was adjusted so that the total thickness was 142 μm, and the negative electrode mixture layer was cut to have a width of 45 mm to produce a negative electrode having a length of 330 mm and a width of 45 mm. Further, a tab was welded to the exposed portion of the copper foil of the negative electrode to form a lead portion.

(Preparation of positive electrode)
85 parts by mass of LiCoO _{2 as a} positive electrode active material, 10 parts by mass of acetylene black as a conductive auxiliary agent, and 5 parts by mass of PVDF as a binder are mixed so as to be uniform using NMP as a solvent. A mixture-containing paste was prepared. This positive electrode mixture-containing paste is intermittently applied on both sides of a current collector made of aluminum foil with a thickness of 15 μm so that the coating length is 320 mm on the front side and 260 mm on the back side, dried, and then subjected to calendar treatment. Then, the thickness of the positive electrode mixture layer was adjusted so that the total thickness was 150 μm, and the positive electrode mixture layer was cut to have a width of 43 mm to produce a positive electrode having a length of 330 mm and a width of 43 mm. Further, a tab was welded to the exposed portion of the aluminum foil of the positive electrode to form a lead portion.

(Battery assembly)
The positive electrode and the negative electrode obtained as described above were spirally wound through the separator to obtain a wound electrode body. The wound electrode body is crushed into a flat shape, placed in an aluminum outer can having a thickness of 6 mm, a height of 50 mm, and a width of 34 mm, and an organic electrolyte (ethylene carbonate and ethyl methyl carbonate mixed at a volume ratio of 1: 2). After injecting 2.4 ml of a solution in which LiPF ₆ was dissolved at a concentration of 1 mol / l in a solvent, sealing was performed to produce a nonaqueous electrolyte battery having the structure shown in FIG. 3 and the appearance shown in FIG. .

  Here, the battery shown in FIGS. 3 and 4 will be described. FIG. 1A is a plan view, and FIG. 1B is a partial cross-sectional view thereof. As shown in FIG. 3 is spirally wound through the separator 4 as described above, and then pressed so as to be flattened to form a flat wound body electrode group 6 in a rectangular tube-shaped outer can 5 together with the electrolyte. Contained. However, in order to avoid complication, in FIG. 1, the metal foil, electrolyte solution, etc. as a collector used in producing the positive electrode 2 and the negative electrode 3 are not shown. Further, the separator 4 does not distinguish between the resin porous layer and the heat resistant porous layer.

  The outer can 5 is made of an aluminum alloy and constitutes an outer casing of the battery. The outer can 5 also serves as a positive electrode terminal. And the insulator 16 which consists of a polyethylene sheet is arrange | positioned at the bottom part of the armored can 5, From the flat wound body electrode group 6 which consists of the positive electrode 2, the negative electrode 3, and the separator 4, at each end of the positive electrode 2 and the negative electrode 3, respectively. The connected positive electrode lead body 7 and negative electrode lead body 8 are drawn out. A stainless steel terminal 11 is attached to a sealing lid plate 9 made of aluminum alloy for sealing the opening of the outer can 5 via a polypropylene insulating packing 10, and an insulator 12 is attached to the terminal 11. A stainless steel lead plate 13 is attached.

  And this cover plate 9 is inserted in the opening part of the armored can 5, and the opening part of the armored can 5 is sealed by welding the junction part of both, and the inside of a battery is sealed. Further, in the battery of FIG. 3, the lid plate 9 is provided with a non-aqueous electrolyte inlet 14, and a sealing member is inserted into the non-aqueous electrolyte inlet 14, for example, laser welding or the like. (See FIG. 3 and FIG. 4, in practice, the non-aqueous electrolyte inlet 14 is actually sealed with the non-aqueous electrolyte inlet.) Although it is a member, for ease of explanation, it is shown as a non-aqueous electrolyte inlet 14). Further, the lid plate 9 is provided with a cleavage vent 15 as a mechanism for discharging the internal gas to the outside when the temperature of the battery rises.

  In the battery of this Example 1, the outer can 5 and the cover plate 9 function as a positive electrode terminal by directly welding the positive electrode lead body 7 to the lid plate 9, and the negative electrode lead body 8 is welded to the lead plate 13, The terminal 11 functions as a negative electrode terminal by conducting the negative electrode lead body 8 and the terminal 11 through the lead plate 13, but depending on the material of the outer can 5, the sign may be reversed. There is also.

  FIG. 4 is a perspective view schematically showing the external appearance of the battery shown in FIG. 3. FIG. 4 is shown for the purpose of showing that the battery is a square battery. FIG. 1 schematically shows a battery, and only specific members of the battery are shown. Also in FIG. 3, the inner peripheral portion of the electrode body is not cross-sectional.

Example 2
The heat-resistant fine particles used for forming the multilayer porous film are particles having an aspect ratio of 1.4, an average particle size: D50 = 0.86 μm, D10 = 0.47 μm, D90 = 1.18 μm, and a particle size larger than 2 μm. Ratio: 1.2% by volume, a polyhedron-shaped boehmite synthetic product was used, and a separator was prepared in the same manner as in Example 1 except that the heat-resistant porous layer had a thickness of 3.5 μm. A nonaqueous electrolyte battery was produced in the same manner as in Example 1 except that this separator was used. In addition, the mass per unit area of the heat resistant porous layer which concerns on the multilayer porous film which comprises a separator was 0.47 mg / cm < ² >.

Example 3
The heat-resistant fine particles used for the formation of the multilayer porous film are particles having an aspect ratio of 2.5, an average particle size: D50 = 0.40 μm, D10 = 0.28 μm, D90 = 0.79 μm, and a particle size larger than 2 μm. Proportion of: 1% by volume, changed to a polyhedron-shaped boehmite synthetic product, except that the thickness of the heat-resistant porous layer is 3.5 μm, to produce a separator in the same manner as in Example 1, A nonaqueous electrolyte battery was produced in the same manner as in Example 1 except that this separator was used. In addition, the mass per unit area of the heat resistant porous layer which concerns on the multilayer porous film which comprises a separator was 0.47 mg / cm < ² >.

Example 4
The heat-resistant fine particles used for the formation of the multilayer porous film are particles having an aspect ratio of 1.0, an average particle size: D50 = 0.66 μm, D10 = 0.49 μm, D90 = 0.87 μm, and a particle size larger than 2 μm. Proportion of: 2.5 volume%, changed to a spherical alumina synthetic product, and produced a separator in the same manner as in Example 1 except that the heat-resistant porous layer had a thickness of 3.5 μm. A nonaqueous electrolyte battery was produced in the same manner as in Example 1 except that this separator was used. For the heat-resistant porous layer related to the multilayer porous membrane constituting the separator, the volume ratio of the heat-resistant fine particles calculated with the specific gravity of alumina being 4 g / cm ³ and the specific gravity of the resin binder being 1 g / cm ³ was 89.3. The mass per unit area of the heat-resistant porous layer was 0.62 mg / cm ² .

Example 5
The heat-resistant fine particles used for forming the multilayer porous film are particles having an aspect ratio of 1.0, an average particle size: D50 = 0.99 μm, D10 = 0.64 μm, D90 = 1.55 μm, and a particle size larger than 2 μm. The separator was prepared in the same manner as in Example 1 except that the composition was changed to a spherical alumina synthetic product having a volume of 7.3% by volume and the thickness of the heat-resistant porous layer was 4 μm. A nonaqueous electrolyte battery was produced in the same manner as in Example 1 except that was used. In addition, the mass per unit area of the heat resistant porous layer which concerns on the multilayer porous film which comprises a separator was 0.74 mg / cm < ² >.

Example 6
The proportion of particles having an aspect ratio of 10, an average particle size: D50 = 0.95 μm, D10 = 0.43 μm, D90 = 1.78 μm, and a particle size larger than 2 μm is used for forming a multilayer porous membrane. : A separator was prepared in the same manner as in Example 1 except that the plate boehmite was changed to 5.5% by volume, and the thickness of the heat-resistant porous layer was 2.8 μm. A nonaqueous electrolyte battery was produced in the same manner as in Example 1 except that it was used. In addition, the mass per unit area of the heat resistant porous layer which concerns on the multilayer porous film which comprises a separator was 0.36 mg / cm < ² >.

Comparative Example 1
The heat-resistant fine particles used for forming the multilayer porous film are particles having an aspect ratio of 2.0, an average particle size: D50 = 1.26 μm, D10 = 0.78 μm, D90 = 1.95 μm, and a particle size larger than 2 μm. The separator was produced in the same manner as in Example 1 except that the boehmite was changed to 3.5 vol% and the thickness of the heat-resistant porous layer was 3.5 μm. A nonaqueous electrolyte battery was produced in the same manner as in Example 1 except that was used. In addition, the mass per unit area of the heat resistant porous layer which concerns on the multilayer porous film which comprises a separator was 0.45 mg / cm < ² >.

Comparative Example 2
The heat-resistant fine particles used for the formation of the multilayer porous membrane are particles having an aspect ratio of 2.0, an average particle size: D50 = 1.00 μm, D10 = 0.45 μm, D90 = 2.10 μm, and a particle size larger than 2 μm. The separator was prepared in the same manner as in Example 1 except that the boehmite was changed to 18.6% by volume and the thickness of the heat-resistant porous layer was 3.5 μm. A nonaqueous electrolyte battery was produced in the same manner as in Example 1 except that was used. In addition, the mass per unit area of the heat resistant porous layer which concerns on the multilayer porous film which comprises a separator was 0.45 mg / cm < ² >.

Comparative Example 3
In the same manner as in Example 1, except that the same polyethylene microporous film as that used for the resin porous layer related to the multilayer porous film in Example 1 was used for the separator without providing the heat-resistant porous layer. A water electrolyte battery was produced.

  The same separators as those used for assembling the nonaqueous electrolyte batteries of Examples 1 to 6 and Comparative Examples 1 to 3 (Separators of Examples 1 to 6 and Comparative Examples 1 to 3), and Examples 1 to 6 and Comparison The following evaluation was performed about the nonaqueous electrolyte battery of Examples 1-3. The evaluation results of the separator are shown in Table 1, and the evaluation results of the nonaqueous electrolyte battery are shown in Table 2.

<Heat shrinkage of separator>
A 10 cm × 5 cm strip-shaped sample piece was cut out from each separator (multilayer porous membrane). A straight line having a length of 3 cm was marked with an oil pen in parallel to the long side direction and the short side direction so that these sample pieces intersected the center in the long side direction and the center in the short side direction. The midpoint of the two straight lines was the intersection of both straight lines.

  Each said sample piece was suspended in the thermostat, the temperature in a tank was raised at the speed | rate of 5 degree-C / min, and after reaching | attaining 150 degreeC, it maintained at this temperature. From the length (3 cm) of the straight line before measuring the length of the straight line in the long side direction and the short side direction of each sample 3 hours after the temperature in the bath reached 150 ° C. The amount of change was determined, and the ratio of these changes to the length of the straight line before being suspended in the thermostat was expressed as a percentage, and the value with the larger ratio was defined as the thermal contraction rate of the sample. The heat shrinkage rate was measured three times for each example and comparative example, and the average value was obtained.

<Evaluation of load characteristics of non-aqueous electrolyte battery>
About each battery, the constant current charge was performed until the battery voltage became 4.2 V at a current value of 0.2 C, and then the constant current-constant voltage charge for performing the constant voltage charge at 4.2 V was performed. The total charging time until the end of charging was 15 hours. Each battery after charging was discharged at a discharge current of 0.2 C until the battery voltage reached 3.0 V, and the discharge capacity was measured (this discharge capacity is referred to as “0.2 C discharge capacity”). Next, after each battery was charged under the same conditions as described above, the battery was discharged at a discharge current of 2C until the battery voltage reached 3.0 V, and the discharge capacity was measured (this discharge capacity was determined as “2C discharge capacity”). "). The ratio of the 2C discharge capacity to the 0.2C discharge capacity of each battery was expressed as a percentage to evaluate the load characteristics. The above charging and discharging were all performed in a test chamber in which the temperature was controlled at 20 ° C.

<Battery heating test>
For each battery having a surface temperature equal to the atmospheric temperature at 20.0 to 25 ° C., constant current charging was performed until the battery voltage reached 4.35 V at a current value of 0.5 C. Each battery after charging was placed in a constant temperature bath, the temperature in the bath was increased at a rate of 5 ° C./min, and after reaching 150 ° C., this temperature was maintained for 3 hours. The surface temperature of each battery while being held at 150 ° C. for 3 hours was measured with a thermocouple connected to the battery surface, and the maximum temperature was determined. The maximum temperature was measured three times for each example and comparative example, and the average value was determined.

表２から明らかなように、実施例１〜６の非水電解液電池は、加熱試験時において、電池の温度上昇が殆ど見られず、安全性が良好であり、かつ負荷特性も優れている。

As is apparent from Table 2, the nonaqueous electrolyte batteries of Examples 1 to 6 show almost no increase in battery temperature during the heating test, have good safety, and have excellent load characteristics. .

It is a schematic diagram of the principal part cross section of the heat-resistant porous layer containing heat-resistant fine particles with a small aspect ratio. It is a schematic diagram of the principal part cross section of the heat-resistant porous layer containing heat-resistant fine particles with a large aspect ratio. It is a schematic diagram which shows an example of the nonaqueous electrolyte battery of this invention, (a) Top view, (b) Cross-sectional view. FIG. 4 is a perspective view of FIG. 3.

Explanation of symbols

1, 1a, 1b, 1c Heat-resistant fine particles 2 Positive electrode 3 Negative electrode 4 Separator

Claims (7)

A battery separator comprising a multilayer porous membrane having at least a resin porous layer mainly comprising a thermoplastic resin and a heat resistant porous layer mainly comprising heat-resistant fine particles and containing a resin binder,
The resin porous layer is composed of a polyolefin microporous film that thermally shrinks at 150 ° C.,
The resin porous layer and the heat resistant porous layer are integrated,
The heat-resistant fine particles have an average particle size of 0.40 to 1 μm, a proportion of particles having a particle size larger than 2 μm is 10% by volume or less, and an aspect ratio of 1 to 3 in a polyhedral shape or substantially A spherical shape,
The heat-resistant porous layer has a thickness of 2 to 4 μm, a porosity of 49.7 to 60%, and contains 1 to 10 parts by mass of a resin binder with respect to 100 parts by mass of the heat-resistant fine particles. And
A battery separator having a thermal shrinkage of 0 to 10% when left in an atmosphere of 150 ° C.   The battery separator according to claim 1, wherein the heat-resistant fine particles have a polyhedral shape with an aspect ratio of 1 to 3.   The battery separator according to claim 1 or 2, wherein a surface modification treatment selected from a corona discharge treatment, a plasma discharge treatment and an ultraviolet irradiation treatment is performed on the surface of the resin porous layer.   The battery separator according to claim 1, wherein the resin porous layer includes a polyethylene porous layer.   The battery separator according to any one of claims 1 to 4, wherein the heat-resistant fine particles have a particle size of 10% by volume or less with a particle diameter of less than 0.2 µm.   The battery separator according to any one of claims 1 to 5, wherein boehmite is contained as the heat-resistant fine particles.   A positive electrode having an active material capable of occluding and releasing Li ions, a negative electrode having an active material capable of occluding and releasing Li ions, an organic electrolyte, and a separator. A nonaqueous electrolyte battery comprising the battery separator according to any one of the above.

Images