JP2016181324A - Separator for electrochemical device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: an electrochemical device superior in safety; and a separator which enables the formation of the electrochemical device.SOLUTION: A separator for an electrochemical device according to the present invention comprises: a fine porous first separator layer 10 which has a multilayer structure, and performs a shutdown at each of melting points set in multiple stages; a thermally-resistant fine porous second separator layer 20 provided on one face of the first separator layer 10; and a fine porous third separator layer 30 which is provided on the other face of the first separator layer 10, or one face of the second separator layer 20, and performs a shutdown at lower temperatures than the temperatures when the first separator layer 10 does so.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a separator for an electrochemical element.

  Patent Document 1 proposes a separator having a first separator layer mainly including a resin having a melting point of 80 to 130 ° C. and a second separator layer mainly including a filler having a heat resistant temperature of 150 ° C. or higher. . In the separator described in Patent Document 1, a shutdown function is secured by the first separator layer, and resistance to thermal contraction and film breakage of the separator is secured by the second separator layer. Therefore, by using the separator described in Patent Document 1, it is possible to improve the safety of the lithium ion secondary battery.

  Patent Document 2 discloses a separator having two porous layers, a layer mainly composed of a thermoplastic resin having a melting point of 80 to 170 ° C. and a coating layer mainly composed of a thermoplastic resin having a lower melting point. A separator having a three-layered porous layer in which a layer in which a filler having a temperature of 150 ° C. or higher is mixed is proposed.

JP 2007-157723 A JP 2012-204243 A

  In a conventional lithium ion secondary battery, not only the separator but also the main member is provided with measures against thermal runaway, or a protection circuit for preventing thermal runaway is provided. However, even in a lithium ion secondary battery in which such safety measures are taken, a thermal runaway may occur due to some reaction, for example, heat generation due to overcharging. In this respect, there is still room for improvement.

  This invention is made | formed in view of the said situation, The objective is to provide the separator for electrochemical elements which can further improve the safety | security of an electrochemical element.

  The separator for an electrochemical element of the present invention that can achieve the above object is a microporous first separator layer having a multi-layered structure in which shutdown is performed at melting points set in multiple stages, and one surface of the first separator layer. The heat-resistant and microporous second separator layer provided on the first separator layer and the other side of the first separator layer or one side of the second separator layer are shut down at a lower temperature than the first separator layer. And a microporous third separator layer. In particular, the first separator layer is preferably composed of three or more resin layers.

  ADVANTAGE OF THE INVENTION According to this invention, the separator for electrochemical elements which can further improve the safety | security of an electrochemical element can be obtained. Problems, configurations, and effects other than those described above will be clarified by the following description of the embodiments.

Sectional drawing which shows an example of the typical structure of the separator in this Embodiment. Sectional drawing which shows another example of the typical structure of the separator in this Embodiment. Plot of resistance value versus separator temperature obtained in Example 1 Plot of resistance value versus separator temperature obtained in Comparative Example 1

  Electrochemical elements such as lithium ion secondary batteries are used in various applications such as mobile phones, notebook computers, electric vehicles, large storage batteries for power supplies, etc., due to the need for longer power supply time and increased output. There are demands for higher capacity, higher energy density, higher voltage, and the like. In addition, with lithium ion secondary batteries, the risk of thermal runaway, such as abnormal heat generation, increases with increasing energy density, and thus safety measures are also strongly required.

  For example, a lithium ion secondary battery has a positive electrode, a negative electrode, a separator and a non-aqueous electrolyte as main members, the separator is made of an insulating porous film, and is disposed between the positive electrode and the negative electrode. By separating them, the battery plays a role of allowing ions in the non-aqueous electrolyte to permeate through the through-hole while preventing an internal short circuit of the battery.

  Since most of the thermal runaway of lithium ion secondary batteries is triggered by internal short circuit of the battery, it can be said that the functioning to the separator occupies an important position in the safety measures of the lithium ion secondary battery. . In order to give a separator a function that takes into account the safety of lithium ion secondary batteries, when a battery generates heat until now, the separator melts at a temperature equal to or higher than the melting point of the thermoplastic resin such as polyolefin. It is common to provide a shutdown function that suppresses further heat generation of the battery by closing the through hole and cutting off the current.

  However, the polyolefin separator used in the lithium ion secondary battery has a problem that it shrinks and breaks when the temperature rises, and an internal short circuit easily occurs due to contact between the positive electrode and the negative electrode.

  The separator for an electrochemical element of the present invention (hereinafter simply referred to as “separator”) has been made in view of such a problem, and has a shutdown function at a plurality of shutdown temperatures, as well as breakage due to heat shrinkage or melting of a material. The film is given resistance to the film.

  The separator in the present embodiment includes a microporous first separator layer having a multi-layer structure that performs shutdown at melting points set in multiple stages, and a heat-resistant and microscopic material provided on one surface of the first separator layer. A porous second separator layer, and a microporous third separator layer that is provided on the other surface of the first separator layer or on one surface of the second separator layer and shuts down at a lower temperature than the first separator layer; have. For example, both the first separator layer and the third separator layer may be made of a plurality of materials, but the third separator layer is a component having a lower melting point than the material having the lowest melting point included in the first separator layer. Should be included.

<First separator layer>
The first separator layer serves as a base material for the separator. The positive electrode and the negative electrode of the electrochemical element are mainly separated by the first separator layer, and each of them is shut down at a melting point set in multiple stages. Do. The first separator has a plurality of pores communicating with one side and the other side, and the internal temperature of the electrochemical element using the separator is equal to or higher than the melting point of the thermoplastic resin constituting the first separator layer. When this happens, the thermoplastic resin melts and closes the pores of the first separator layer, causing a shutdown that suppresses the progress of the electrochemical reaction. This shutdown layer is a secondary shutdown layer (a primary shutdown layer (or a low temperature shutdown layer) will be described later).

  The thermoplastic resin constituting the first separator layer is electrically insulating, stable against non-aqueous electrolyte held in the electrochemical element, and redox within the operating voltage range of the electrochemical element. An electrochemically stable material is preferred. Specific examples of such thermoplastic resins include, for example, low density polyethylene (LDPE), high density polyethylene (HDPE), modified polyethylene, polypropylene (PP), paraffin, wax, copolymer polyolefin, polyolefin derivative (chlorinated polyethylene). Polyolefins such as fluororesins, polyimides, aramids, and the like. Examples of the copolymer polyolefin include ethylene-vinyl monomer copolymer (EVA), more specifically, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, ethylene-methyl acrylate copolymer, ethylene. -Acrylic acid copolymer, ethylene-methacrylic acid copolymer, etc. are mentioned. For the first separator layer, only one of the above-exemplified thermoplastic resins may be used, or two or more of them may be used in combination.

  Among the thermoplastic resins exemplified above, the melting point, that is, the melting temperature measured using a differential scanning calorimeter (DSC) in accordance with the provisions of JISK 7121 (the same applies to the melting point of each resin as used herein). ) Is preferably 80 ° C. or higher and 150 ° C. or lower. In this case, the shutdown in the separator appears under more preferable conditions.

  The first separator layer includes a thermoplastic resin having a melting point of 80 ° C. or higher and 150 ° C. or lower (hereinafter referred to as “resin (A)”) and a thermoplastic resin having a melting point higher than that of the resin (A) (hereinafter referred to as “ Resin (B) ”] is preferably used in combination. In the case of the first separator layer containing the resin (A) and the resin (B), after the shutdown occurs due to the melting of the resin (A), the first separator layer is reached until the melting point of the resin (B) is reached. The layer shape (separator shape) can be maintained. Therefore, even when the device temperature continues to rise after the occurrence of shutdown, the state where the positive electrode and the negative electrode are isolated can be maintained, and the safety of the electrochemical device can be further improved. Further, when the temperature in the electrochemical element exceeds the melting point of the resin (B), the resin (B) is also melted, and a thick layer formed of the resin (A) and the resin (B) after melting is formed. By being formed, the shutdown function is enhanced. Furthermore, the separator has a stable shape at a high temperature as compared with a single layer structure.

  In the first separator layer, when the resin (A) and the resin (B) are used in combination, for example, a two-layer structure of a layer composed of the resin (A) and a layer composed of the resin (B) A layer made of resin (B) on both sides of a layer made of resin (A), or a layer made of resin (A) on both sides of a layer made of resin (B) A multi-layer structure such as a three-layer structure may be considered. It is preferable that the first separator layer has a three-layer structure including two kinds of resins, that is, a resin constituting the outer layer and a resin constituting the inner layer. In the case of a two-layer structure in which two types of resins are laminated, the separator layer may be curved due to the difference in the physical properties of each resin. It is to become. In this case, the above-mentioned effect by using the resin (A) and the resin (B) in combination can be ensured more favorably.

  The melting point of the resin (B) may be higher than the melting point of the resin (A). For example, it is preferably higher by 10 ° C. than the melting point of the resin (A). Furthermore, the specific melting point of the resin (B) is preferably 130 ° C. or higher, and preferably 200 ° C. or lower.

  The content of the thermoplastic resin in the first separator layer [in the case of using the resin (A) and the resin (B) in combination, the total content thereof) is the total volume of components of the first separator layer ( The total volume excluding the void portion) is 50% by volume or more, preferably 70% by volume or more, and may be 100% by volume, that is, only thermoplastic resin.

  For the first separator layer, a microporous film made of a thermoplastic resin (such as a microporous film made of polyolefin) that is used as a separator in an electrochemical element such as a normal lithium ion secondary battery can be used. More specifically, a film or sheet formed of a thermoplastic resin as described above, for example, using a stretching method, that is, a thermoplastic resin mixed with an inorganic filler, is subjected to uniaxial or biaxial stretching. After forming fine voids, those produced by removing the inorganic filler as required can be used. In addition, a hole forming method using a solvent, that is, the above-described thermoplastic resin and other resin or paraffin are mixed to form a film or sheet, and then, in a solvent that dissolves only the other resin or paraffin, What is manufactured by immersing these films or sheets and dissolving only the other resin or paraffin to form pores can be used as the first separator layer. Furthermore, a microporous film made of a thermoplastic resin manufactured by a method combining the stretching method and the pore formation method using the solvent can also be used.

  Among such microporous membranes made of thermoplastic resin, specific examples of those in which the resin (A) and the resin (B) are used in combination include, for example, a layer containing PP on both sides of a layer containing PE. Examples thereof include a microporous membrane having a three-layer structure. In particular, the melting point of the resin constituting the outermost layer is preferably higher than the melting point of the resin constituting the inner layer.

<Second separator layer>
The second separator layer may be composed only of an inorganic filler of a heat resistant material, or may include an inorganic filler and an organic binder, and the inorganic filler may have a structure bound with an organic binder. Good.

  When the second separator layer contains an inorganic filler having high heat resistance, the first separator layer is activated by the action of the inorganic filler even when the temperature in the electrochemical element is such that the first separator layer contracts. Shrinkage and rupture can be suppressed. Even if the first separator layer breaks, the second separator layer containing the inorganic filler acts as a spacer for partitioning the positive electrode and the negative electrode, so that an effect of suppressing an internal short circuit of the electrochemical element can be expected. Therefore, in the case of a separator having a second separator layer that also contains an inorganic filler, the safety of the electrochemical element can be further enhanced.

  As the inorganic filler, those having a heat resistant temperature of 150 ° C. or more are preferable. The “heat-resistant temperature is 150 ° C. or higher” in the inorganic filler and the fibrous material described later in this specification means that shape change such as deformation is not visually confirmed at least at 150 ° C.

Specific examples of the constituent material of the inorganic filler having the heat-resistant temperature include inorganic materials such as iron oxide, magnesium oxide, SiO ₂ (silica), Al ₂ O ₃ (alumina), TiO ₂ , BaTiO ₂ , and ZrO _2. Oxides; inorganic hydroxides such as Al (OH) ₃ (aluminum hydroxide) and magnesium hydroxide; inorganic nitrides such as aluminum nitride and silicon nitride; poorly soluble substances such as calcium fluoride, barium fluoride and barium sulfate Examples include ionic crystals; covalent bonds such as silicon and diamond; and clays such as montmorillonite. Here, the inorganic oxide may be a material derived from mineral resources such as boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, mica, or these artificial products. In addition, the surface of a conductive material exemplified by a metal; a conductive oxide such as SnO ₂ or tin-indium oxide (ITO); a carbonaceous material such as carbon black or graphite; For example, the particles may be particles that have been electrically insulated by coating with the above-described inorganic oxide or the like. As the inorganic filler, only one kind of fine particles composed of the above exemplified materials may be used, or two or more kinds may be used in combination.

  Among the inorganic fillers composed of the above exemplified materials, alumina, silica, aluminum hydroxide, magnesium hydroxide, magnesium oxide, boehmite are more preferable, boehmite is more preferable, particle size and shape can be easily controlled, and an electrochemical element Synthetic boehmite that can reduce ionic impurities that adversely affect the characteristics is particularly preferred. There is no restriction | limiting in particular about the shape of an inorganic filler, Any shapes, such as substantially spherical shape (a spherical shape is included), an ellipsoid shape, and plate shape, may be sufficient. The particle size of the inorganic filler is an average particle size measured by a method described later, preferably 0.01 μm or more, more preferably 0.1 μm or more, and preferably 20 μm or less, More preferably, it is 5 μm or less.

  Specific examples of the organic binder include, for example, EVA (ethylene acetate-derived structural unit of 20 to 35 mol%), ethylene-acrylic acid copolymer (EEA) and other ethylene-acrylic acid copolymers, and fluorine-based ones. Rubber, styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), polyvinyl alcohol (PVA), polyvinyl butyral (PVB), polyvinyl pyrrolidone (PVP), polyethylene oxide (PEO), poly-N-vinyl Acetamide (PNVA), butyl acrylate-acrylic acid copolymer, cross-linked acrylic resin, polyurethane, epoxy resin and the like can be mentioned. In particular, a heat-resistant binder having a heat-resistant temperature of 150 ° C. or higher is preferably used. As the organic binder, those exemplified above may be used singly or in combination of two or more.

  Among the organic binders exemplified above, binders having high flexibility such as EVA, ethylene-acrylic acid copolymer, fluorine-based rubber, SBR, butyl acrylate-acrylic acid copolymer, PVP, CMC, and PNVA are preferable. Specific examples of such highly flexible organic binders include “Evaflex Series (EVA)” by Mitsui DuPont Polychemical Co., Ltd., EVA by Nippon Unicar Co., Ltd. -Acrylic acid copolymer) ", Nippon Unicar EEA, Daikin Industries" DAI-EL Latex Series (Fluororubber) ", JSR" TRD-2001 (SBR) ", Nippon Zeon" BM-400B " (SBR) ".

  When the organic binder is used, it may be used in the state of an emulsion dissolved or dispersed in a solvent of a composition for forming a second separator layer described later.

  The second separator layer may contain a fibrous material in order to ensure the shape stability and flexibility of the separator. The fibrous material preferably has a heat resistant temperature of 150 ° C. or higher.

  As the fibrous material, it has electrical insulation, is electrochemically stable, is stable to the non-aqueous electrolyte solution of the electrochemical element, and the solvent used in the production of the separator, preferably the above-mentioned The material is not particularly limited as long as it has a heat resistant temperature.

  Specific constituent materials of the fibrous material include, for example, cellulose and its modified products (carboxymethyl cellulose (CMC), hydroxypropyl cellulose (HPC), etc.), polyolefin (PP, propylene copolymer, etc.), polyester [polyethylene, etc. Resins such as terephthalate (PET), polyethylene naphthalate (PEN), polybutylene terephthalate (PBT), polyacrylonitrile (PAN), aramid, polyamideimide, polyimide; inorganic oxides such as glass, alumina, zirconia, silica; A fibrous material may be formed by using two or more of these constituent materials in combination. Further, the fibrous material may contain various additives, for example, an antioxidant when the fibrous material is a resin, as necessary.

  As the shape of the fibrous material, for example, the average diameter is preferably 0.01 to 20 μm, and the average length is preferably 0.1 to 50000 μm.

The average particle size of the fine particles (inorganic filler and low melting point material described later) referred to in the present specification is, for example, using an aqueous dispersion of fine particles and using a concentrated particle size analyzer “FPAR-1000” manufactured by Otsuka Electronics Co., Ltd. Then, it can be defined as D ₅₀ (particle diameter with a volume cumulative frequency of 50%) measured by dynamic light scattering.

  In the case where an organic binder is contained in the second separator layer, the content is 0.2% by volume or more in the total volume of the constituent components of the second separator layer, from the viewpoint of ensuring better effects of the organic binder. It is preferable that it is 0.5 volume% or more. However, if the amount of the organic binder in the second separator layer is too large, the amount of other components becomes too small, and there is a possibility that the effect of them cannot be sufficiently secured. The content of is preferably 20% by volume or less, and more preferably 10% by volume or less, in the total volume of the constituent components of the second separator layer.

  In the case where an inorganic filler is contained in the second separator layer, the content is 10% by volume or more in the total volume of the constituent components of the second separator layer, from the viewpoint of ensuring the above-mentioned effect by the inorganic filler more favorably. It is preferable that it is 40 volume% or more. However, if the amount of the inorganic filler in the second separator layer is too large, the amount of the other components becomes too small, and there is a possibility that the effect by them cannot be sufficiently secured. Therefore, the inorganic filler in the second separator layer The content of is preferably 99% by volume or less and more preferably 95% by volume or less in the total volume of the constituent components of the second separator layer.

  When the fibrous material is contained in the second separator layer, the content is 5 volumes in the total volume of the constituent components of the second separator layer, from the viewpoint of ensuring the above-mentioned effect by the fibrous material more favorably. % Or more, preferably 10% by volume or more. However, if the amount of the fibrous material in the second separator layer is too large, the amount of other components becomes too small, and there is a possibility that the effect by them cannot be sufficiently secured. The content of the shaped material is preferably 90% by volume or less, and more preferably 60% by volume or less, in the total volume of the constituent components of the second separator layer.

  The first separator layer may contain the inorganic filler, the organic binder, and the fibrous material.

<Third separator layer>
The thermoplastic resin constituting the third separator layer has a melting point lower than the melting point of the resin layer (secondary shutdown layer, for example, “resin (A)”) that causes shutdown by the thermoplastic resin constituting the first separator layer. It is a material (hereinafter referred to as “low melting point material”). The third separator layer is a primary shutdown layer (or a low-temperature shutdown layer), has electrical insulation, is stable with respect to the non-aqueous electrolyte held in the electrochemical element, and further has an operating voltage for the electrochemical element. An electrochemically stable material that is hardly oxidized and reduced in the range is preferable.

  Specific examples of such thermoplastic resins include, for example, low density polyethylene (LDPE), high density polyethylene (HDPE), modified polyethylene, polypropylene (PP), paraffin, wax, copolymer polyolefin, polyolefin derivative (chlorinated polyethylene). Polyolefins such as fluororesins, polyimides, aramids, and the like. Examples of the copolymer polyolefin include ethylene-vinyl monomer copolymer (EVA), more specifically, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, ethylene-methyl acrylate copolymer, ethylene. -Acrylic acid copolymer, ethylene-methacrylic acid copolymer, etc. are mentioned. In the third separator layer, only one kind of the above-exemplified thermoplastic resins may be used, or two or more kinds may be used in combination.

  Among the thermoplastic resins exemplified above, the melting point, that is, the melting temperature measured using a differential scanning calorimeter (DSC) in accordance with the provisions of JISK 7121 (the same applies to the melting point of each resin as used herein). ) Is preferably 80 to 150 ° C., particularly preferably 125 ° C. or less. In this case, the shutdown in the separator appears under more preferable conditions. Furthermore, there is no particular limitation on increasing the number of shutdown layers having different melting points such as the third and fourth shutdown layers.

  The content of the thermoplastic resin in the third separator layer is 50% by volume or more and preferably 70% by volume or more in the total volume (total volume excluding the voids) of the constituent components of the third separator layer. 100 volume%, that is, it may be composed of only a thermoplastic resin.

  The third separator layer may be composed of only a low melting point material, or may include a low melting point material and an organic binder, and the low melting point material may be bonded to each other with an organic binder. .

  The organic binder used for a 3rd separator layer is suitably used from the organic binders mentioned as an organic binder used for a 2nd separator layer. When an organic binder is used for the third separator layer, it may be used in the state of an emulsion dissolved or dispersed in a solvent for a composition for forming a third separator layer described later. The third separator layer may contain a fibrous material as in the second separator layer.

  In the case where an organic binder is contained in the third separator layer, the content is 0.2% by volume or more in the total volume of the constituent components of the third separator layer, from the viewpoint of ensuring a better effect of the organic binder. It is preferable that it is 0.5 volume% or more. However, if the amount of the organic binder in the third separator layer is too large, the amount of other components becomes too small, and there is a possibility that the effects of them cannot be sufficiently ensured. The content of is preferably 20% by volume or less, more preferably 10% by volume or less, in the total volume of the constituent components of the third separator layer.

<Separator>
From the viewpoint of further improving the short-circuit preventing effect in the electrochemical element, ensuring the strength of the separator and improving the handleability, the thickness of the separator of the present invention is preferably 3 μm or more, more preferably 5 μm or more. preferable. On the other hand, from the viewpoint of further increasing the energy density of the electrochemical element, the thickness of the separator of the present invention is preferably 45 μm or less, and more preferably 30 μm or less.

  The thickness of the first separator layer is preferably 2 μm or more, preferably 4 μm or more, preferably 30 μm or less, more preferably 20 μm or less. The thickness of the second separator layer is preferably 1 μm or more, more preferably 3 μm or more, preferably 15 μm or less, more preferably 10 μm or less. The thickness of the third separator layer is preferably 0.5 μm or more, more preferably 1 μm or more, preferably 15 μm or less, more preferably 10 μm or less.

  Further, the air resistance of the separator of the present invention is measured by a method according to JIS P 8117, and the Gurley value indicated by the number of seconds that 100 mL of air passes through the membrane is desirably 10 to 500 sec. . If the air permeability is too high, the ion permeability is reduced, whereas if it is too low, the strength of the separator may be reduced. By using the separator having the configuration described so far, such air permeability can be ensured.

  Further, 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 small, a short circuit may occur due to the piercing of the separator when lithium dendrite crystals are generated. For example, such a strength can be ensured by using a separator having a second separator layer that also contains an inorganic filler.

  The separator may have a configuration in which it is fixed and integrated with at least one of the positive electrode and the negative electrode.

<Manufacturing method of separator>
The separator is, for example, a second separator layer forming composition (slurry, paste, etc.) and a third separator layer forming composition (slurry, paste) on a microporous film made of a thermoplastic resin constituting the first separator layer. Etc.) and dried at a predetermined temperature to form the second separator layer and the third separator layer. If necessary, a surfactant may be used in the paint, or the first separator layer may be applied after surface treatment (corona treatment, ozone treatment, electron beam treatment, primer treatment, etc.).

  The composition for forming the second separator layer is prepared by dispersing an inorganic filler, a fibrous material or the like in a solvent, and dispersing or dissolving an organic binder used as necessary in the solvent.

  The composition for forming the third separator layer is prepared by dispersing or dissolving a low-melting-point material, a fibrous material or the like in a solvent, and dispersing or dissolving an organic binder used as necessary in the solvent. When the composition of the third separator layer forming composition is a dispersion or an emulsion, the shape of the fine particles is not particularly limited, and may be any shape such as a substantially spherical shape (including a true spherical shape), an elliptical shape, or a plate shape. There may be. The particle size of the third separator layer forming composition is an average particle size measured by the above method, preferably 0.01 μm or more, more preferably 0.1 μm or more, and 20 μm or less. Preferably, it is 5 μm or less.

  The solvent used in the composition for forming the second separator layer and the composition for forming the third separator layer can uniformly disperse the inorganic filler, the low melting point material, the fibrous material, and the like, and can dissolve or disperse the organic binder uniformly. However, 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 generally preferably used. 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 organic binder is water-soluble or used as an emulsion, water may be used as a solvent. In this case, alcohols (methyl alcohol, ethyl alcohol, isopropyl alcohol, ethylene glycol, etc.) are appropriately added. It is also possible to control the interfacial tension.

  The solid content (total content of all components excluding the solvent) in the second separator layer forming composition and the third separator layer forming composition is preferably 10 to 40% by mass, for example.

<Example of separator configuration>
FIG. 1 is a cross-sectional view showing an example of a typical configuration of a separator in the present embodiment.
In the separator 1, the second separator layer 20 is provided on one surface of the first separator layer 10, and the third separator layer 30 is provided on the other surface of the first separator layer 10. The first separator layer 10 has a three-layer structure having B layers 12 and 12 made of a resin (B) on both surfaces of an A layer 11 made of a resin (A). The A layer 11 uses, for example, PE having a melting point of 137 ° C. as the resin (A), the element temperature becomes equal to or higher than the melting point, and when it reaches the secondary shutdown temperature, it is shut down to close the micropores. . The B layer 12 uses, for example, PP having a melting point of 170 ° C. as the resin (B), and maintains the structure even after the shutdown of the A layer when the element temperature rises. Shut down. When the first separator layer uses a resin having three or more melting points, the melting point of the resin constituting the outermost layer is higher than the melting point of the resin constituting the inner layer in order to maintain the shape stabilizing function at high temperatures. preferable.

  The first separator layer 10 preferably has a layer structure of A / B / C or B / A / B using a plurality of types of resins (resins A to C). As a multilayer structure of A / B / C, a structure of low density polyethylene / high density polyethylene / polypropylene is exemplified, and each melting point is set to 80 ° C. to 125 ° C., 125 ° C. to 140 ° C., 160 ° C. to 170 ° C. adjust. Examples of the B / A / B multilayer structure include a combination of high-density polyethylene and polypropylene. In the case of high-density polyethylene, the temperature is preferably 125 ° C to 140 ° C, and in the case of polypropylene, the temperature is preferably 160 ° C to 170 ° C. In addition, it is preferable that a 1st separator layer is provided with the function which maintains the shape stabilization function at the time of high temperature. Therefore, it is preferable to use a material having a melting point of 140 ° C. or higher for at least one layer, and it is preferable to use polypropylene for any of the layers.

  The second separator layer 20 includes, for example, an inorganic filler 21 that is a heat resistant material, and the heat resistant temperature is set to 150 ° C. or higher. The third separator layer 30 includes a low melting point material having a melting point lower than the melting point of the resin (A) of the first separator layer 10, and for example, PE having a melting point of 100 ° C. to 110 ° C. is used.

  The third separator layer 30 is a primary shutdown layer (low temperature shutdown layer), and performs shutdown at a temperature lower than the shutdown temperature of the secondary shutdown layer that is the first separator layer 10. When the element temperature exceeds the melting point of the low-melting-point material and reaches the primary shutdown temperature, the low-melting-point material melts to shut down the micropores. Therefore, the shutdown can be performed at an earlier stage than the shutdown of the first separator, and the heat generation leading to the thermal runaway can be suppressed.

  Thereafter, when heat is generated for some reason such as an internal short circuit, the secondary shutdown layer of the first separator layer 10 is shut down, and heat generation can be suppressed in two stages. If further heat generation occurs after the first-stage shutdown, the low-melting-point material is dissolved, and the viscosity is further lowered due to the temperature rise. At this time, the low melting point material may flow out of the separator layer, and the sustained shutdown effect may be lost. Therefore, when there is no secondary shutdown layer in the first separator layer 10, the possibility of further heat generation is increased. Since the separator 1 has the secondary shutdown layer in the first separator layer 10, the melting temperature of the secondary shutdown layer in the first separator layer 10 is reached even if the sustained shutdown effect of the primary shutdown layer disappears. In this case, the shutdown can be performed again. Thus, the presence of a plurality of shutdown layers having different shutdown temperatures makes it possible to suppress heat generation in a wider temperature range, thereby contributing to an improvement in safety.

  The second separator layer 20 includes a heat resistant material and has a function of suppressing thermal shrinkage. By suppressing the heat shrinkage, an internal short circuit due to the film breakage of the separator can be suppressed. Therefore, the separator 1 of the present invention has a structure that combines a multi-stage shutdown by a plurality of thermoplastic resin layers having different melting points and a function of preventing film breakage by a heat-resistant material.

  The separator having the above structure can be manufactured by forming and bonding the separator layers, but it is preferable that the second and third separator layers are provided by coating. Since the slurry or paste-like composition binds to the first separator, which is a microporous film, with high adhesion, defects such as interfacial peeling are unlikely to occur. Further, since the third separator enters the vicinity of the opening, at the time of shutdown, the low melting point material of the melted third separator layer easily closes the opening portions of the first and second separators, and the shutdown performance can be expected to improve.

  In the separator 1, it is preferable that the third separator layer 30 is opposed to the negative electrode and the second separator layer 20 is opposed to the positive electrode. By such an arrangement, the safety of the electrochemical device is further improved. Can be increased. In the electrochemical device, dendrite is precipitated by long-term use and grows from the negative electrode toward the positive electrode. However, if the second separator layer 20 is disposed on the negative electrode side, the dendrite grows and the second separator is grown. There is a possibility of penetrating the layer 20 and having a tip protruding from the second separator layer 20 to the positive electrode side. In this state, if the first separator layer 10 and the third separator layer 30 melt and flow out due to heat generation, the tip of the dendrite may reach the positive electrode and cause a short circuit.

  On the other hand, in the separator 1 according to the present embodiment, the third separator layer 30 faces the negative electrode, and the second separator layer 20 faces the positive electrode. The first separator layer 10 and the third separator layer 30 are interposed therebetween. Therefore, even if the dendrite grows, it can be absorbed by the first separator layer 10 and the third separator layer 30 and does not penetrate through the second separator layer 20, but the first separator layer is increased due to the rise in element temperature. Even if 10 and the third separator layer 30 melt and flow out, the second separator layer 20 can prevent the dendrite from entering the positive electrode side, thereby preventing the occurrence of a short circuit.

  FIG. 2 is a cross-sectional view showing another example of a typical configuration of the separator in the present embodiment. In the separator 1, the second separator layer 20 is provided on one surface of the first separator layer 10, and the third separator layer 30 is provided on one surface of the second separator layer 20. The third separator layer 30 is disposed to face the negative electrode, and the first separator layer 10 is disposed to face the positive electrode. Even in this configuration, the same effects as the separator 1 shown in FIG. 1 can be obtained.

  The electrochemical device of the present invention has a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, and the separator only needs to be the separator of the present invention. Other configurations and structures are not particularly limited. Various configurations and structures employed in known electrochemical elements can be applied. The electrochemical device to which the separator of the present invention can be applied is not particularly limited as long as it uses a non-aqueous electrolyte. In addition to a lithium ion secondary battery, a lithium ion primary battery, a super capacitor, etc. Any application that requires safety can be preferably applied. That is, the electrochemical device of the present invention has a positive electrode, a negative electrode, a separator and a non-aqueous electrolyte, and the separator may be the separator of the present invention, and there is no particular limitation on the other configuration and structure, Various configurations and structures provided in various electrochemical elements (lithium ion secondary battery, lithium ion primary battery, supercapacitor, etc.) having a conventional non-aqueous electrolyte can be employed.

<Configuration example of electrochemical element>
Hereinafter, as an example of the electrochemical element of the present invention, application to a lithium ion secondary battery will be described in detail. Examples of the form of the lithium ion secondary battery include a cylindrical shape (such as a rectangular tube shape or a cylindrical shape) using a steel can or an aluminum can as an outer can. Moreover, it can also be set as the soft package battery which used the laminated film which vapor-deposited the metal as an exterior body.

  As a positive electrode, the thing of the structure which has the positive mix layer containing the lithium containing transition metal oxide which is a positive electrode active material, a binder, a conductive support agent, etc. on the single side | surface or both surfaces, for example can be used.

The positive electrode active material is not particularly limited as long as it is an active material used in a conventional lithium ion secondary battery, that is, an active material capable of occluding and releasing Li ions. Specifically, for example, a lithium-containing transition metal oxide having a layered structure represented by Li _{1 + x} MO ₂ (−0.1 <x <0.1, M: Co, Ni, Mn, Al, Mg, etc.), It is possible to use LiMn ₂ O ₄ , a spinel-structure lithium manganese oxide obtained by substituting some of its elements with other elements, or an olivine type compound represented by LiMPO ₄ (M: Co, Ni, Mn, Fe, etc.). Is possible. 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 , LiMn _{3 / 5} Ni _1/5 Co _1/5 O ₂ etc.).

  As the binder for the positive electrode, for example, a fluororesin such as polyvinylidene fluoride (PVDF) is used, and as the conductive additive for the positive electrode, for example, a carbon material such as carbon black is used.

  For the positive electrode, for example, a positive electrode mixture containing a positive electrode active material, a conductive additive and a binder is dispersed in a solvent such as N-methyl-2-pyrrolidone (NMP), and a positive electrode mixture-containing composition (slurry, paste, etc.) Can be produced by applying it to a current collector, drying it, and then subjecting it to press treatment such as calendering if necessary. However, the manufacturing method of a positive electrode is not necessarily limited to the said method, You may manufacture by another method.

  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 conventional lithium ion secondary battery, that is, a negative electrode containing an active material capable of occluding and releasing Li ions. For example, as a negative electrode active material, lithium, such as graphite, pyrolytic carbons, cokes, glassy carbons, fired organic polymer compounds, mesocarbon microbeads (MCMB), and carbon fibers, can be occluded and released. One type or a mixture of two or more types of carbon-based materials are used. In addition, elements such as Si, Sn, Ge, Bi, Sb, In and alloys thereof, lithium-containing nitrides, compounds that can be charged and discharged at a low voltage close to lithium metal such as lithium-containing oxides, or lithium metal or lithium / An aluminum alloy can also be used as the negative electrode active material. A negative electrode mixture in which a conductive auxiliary material (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. As the negative electrode, a single layer or a laminate of the above-mentioned various alloys and lithium metal foils alone or laminated on a current collector is used.

  In the case of a negative electrode having a negative electrode mixture layer, for example, a negative electrode mixture-containing composition obtained by dispersing a negative electrode active material and a binder, and further a negative electrode mixture containing a conductive auxiliary agent if necessary in a solvent such as NMP or water. An article (slurry, paste, etc.) is prepared, applied to a current collector, dried, and further subjected to a press treatment such as a calendar treatment as necessary. However, the manufacturing method of the negative electrode having the negative electrode mixture layer is not limited to the above method, and may be manufactured by other methods.

  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 positive electrode and the negative electrode can be used in the form of an electrode body such as a laminated body laminated via the separator of the present invention or a wound body obtained by winding the laminated body.

  In the electrode body, the separator may be integrated with at least one of the positive electrode and the negative electrode. In order to integrate the separator with the positive electrode, for example, a method of applying the positive electrode mixture-containing composition to a current collector to form a coating film, and stacking the separator on this coating film before drying is adopted. it can. Also, when the separator is integrated with the negative electrode, for example, a method of applying the negative electrode mixture-containing composition to a current collector to form a coating film, and stacking the separator on this coating film before drying Etc. can be adopted.

As the non-aqueous electrolyte, 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, 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 (2 ≦ n ≦ 5), LiN (RfOSO ₂ ) ₂ [where Rf is a fluoroalkyl group] or the like is used. Can do.

  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, 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, 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.

  The electrochemical device of the present invention can be applied to the same applications as conventionally known electrochemical devices.

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

(Preparation of negative electrode) Production Example 1
A negative electrode mixture-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 10 μm thick copper foil serving as a current collector to a coating length of 630 mm, dried, and calendered to a total thickness of 131 μm. The thickness of the negative electrode mixture layer was adjusted so that the width was 56 mm, and a negative electrode having a length of 650 mm and a width of 56 mm was produced. 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) Production Example 2
The positive electrode active material LiCoO ₂ : 85 parts by mass, the conductive auxiliary agent acetylene black: 10 parts by mass, and the binder PVDF: 5 parts by mass are mixed uniformly using NMP as a solvent. An agent-containing paste was prepared. This paste was applied to both sides of a 20 μm thick aluminum foil serving as a current collector, dried, and then subjected to calendering to adjust the thickness of the positive electrode mixture layer so that the total thickness was 125 μm. A positive electrode having a length of 610 mm and a width of 54 mm was produced by cutting to 54 mm. Further, a tab was welded to the exposed portion of the aluminum foil of the positive electrode to form a lead portion.

Example 1
Boehmite fine particles: 97 parts by mass, 3 parts by mass of an acrylate copolymer as a binder (a commercially available acrylate copolymer having butyl acrylate as a main component as a monomer component), water as a solvent is added and dispersed to obtain a solid content. A slurry for forming a second separator layer having a content of 30% by mass was prepared.

  This slurry is applied to one side of a microporous membrane (thickness 16 μm) of PP / high density PE / PP having a corona discharge treatment on both sides and dried, and the first separator layer has a thickness of 5 μm on one side. A separator r having a second separator layer was obtained.

  Modified polyethylene: 97 parts by mass, and 3 parts by mass of an acrylate copolymer as a binder were added and dispersed in water as a solvent to prepare a third separator layer forming slurry having a solid content of 30% by mass.

  The slurry was applied to a third separator layer having a thickness of 5 μm on the surface opposite to the second separator layer of the separator r having a second separator layer having a thickness of 5 μm on one side of the first separator layer, and dried. A separator P having second and third separator layers on both surfaces of one separator layer was obtained. The schematic diagram of the separator configuration is the same as in FIG. The melting point of each layer of PP / high density PE / PP was 170 ° C./128° C./170° C., and the melting point of the modified polyethylene-acrylate layer was 110 ° C.

(Example 2)
Boehmite fine particles: 97 parts by mass, 3 parts by mass of an acrylate copolymer as a binder (a commercially available acrylate copolymer having butyl acrylate as a main component as a monomer component), water as a solvent is added and dispersed to obtain a solid content. A slurry for forming a second separator layer having a content of 30% by mass was prepared.

  This slurry was applied to one side (corona discharge treatment surface) of a microporous film (thickness 16 μm) of PP / high density PE / PP having a corona discharge treatment on one side and dried, and the first separator layer A separator s having a second separator layer with a thickness of 5 μm on one side was obtained.

  Modified polyethylene: 97 parts by mass, and 3 parts by mass of an acrylate copolymer as a binder were added and dispersed in water as a solvent to prepare a third separator layer forming slurry having a solid content of 30% by mass.

  The slurry was applied to the upper surface of the second separator layer of the separator s having the second separator layer having a thickness of 5 μm on one side of the first separator layer, dried and applied to the first separator layer. A separator Q having a separator layer in which a second separator layer and a third separator layer were sequentially applied on one side of the separator layer was obtained. The outline of the configuration of the separator Q is the same as that in FIG.

(Comparative Example 1)
A separator R having only a first separator layer made of a microporous film (thickness: 16 μm) having a three-layer structure of PP / high density PE / PP was used in various experiments.

(Comparative Example 2)
A separator having only a first separator layer made of a single-layer microporous film (thickness: 16 μm) of high-density PE was used as a separator L and used in various experiments. The melting point of the high density PE layer is 135 ° C.

(Comparative Example 3)
Boehmite fine particles: 97 parts by mass, 3 parts by mass of an acrylate copolymer as a binder (a commercially available acrylate copolymer having butyl acrylate as a main component as a monomer component), water as a solvent is added and dispersed to obtain a solid content. A slurry for forming a second separator layer having a content of 30% by mass was prepared.

  This slurry was applied to one side (corona discharge treatment surface) of a microporous film (thickness 16 μm) of PP / high density PE / PP having a corona discharge treatment on one side and dried, and the first separator layer A separator S having a second separator layer having a thickness of 5 μm on one side was obtained.

(Comparative Example 4)
Boehmite fine particles: 97 parts by mass, 3 parts by mass of an acrylate copolymer as a binder (a commercially available acrylate copolymer having butyl acrylate as a main component as a monomer component), water as a solvent is added and dispersed to obtain a solid content. A slurry for forming a second separator layer having a content of 30% by mass was prepared.

  This slurry is applied to one side of a single-layer microporous membrane (thickness 16 μm) of high-density PE that has been subjected to corona discharge treatment on both sides and dried to form a second separator layer having a thickness of 5 μm on one side of the first separator layer. The separator T which has was obtained.

  Modified polyethylene: 97 parts by mass, and 3 parts by mass of an acrylate copolymer as a binder were added and dispersed in water as a solvent to prepare a third separator layer forming slurry having a solid content of 30% by mass.

  The slurry was applied to a third separator layer having a thickness of 5 μm on the surface opposite to the second separator layer of the separator T having a second separator layer having a thickness of 5 μm on one side of the first separator layer, and dried. A separator K having second and third separator layers on both surfaces of one separator layer was obtained. The melting point of the high-density PE layer is 135 ° C., and the melting point of the modified polyethylene-acrylate layer is 110 ° C.

  Measurements and tests were performed using the separators of Examples 1 and 2 and Comparative Examples 1 to 4. Specifically, (1) Examples 1 and 2 and Comparative Examples 1 to 4 were subjected to the following thermal shrinkage measurement. (2) About Example 1 and Comparative Examples 1-4, the air permeability resistance measurement was performed. (3) Using Example 1 and Comparative Example 1, the resistance change due to heating in the electrolytic solution of the separator sandwiched between the electrodes was measured. (4) Moreover, the overcharge test of the following lithium ion secondary battery was done about the lithium ion secondary battery using the separator of Example 1 and Comparative Examples 3 and 4. FIG.

(1) <Measurement of heat shrinkage rate of separator>
Each separator according to Examples 1 and 2 and Comparative Examples 1, 2, 3, and 4 was cut into a size of 10 cm × 5 cm to prepare a test piece. In the test piece, the direction (longitudinal direction) of 10 cm was made parallel to the longitudinal direction of the three-layer microporous film (the stretching direction during the production of the microporous film) according to the separator. Each said test piece was put in the thermostat adjusted to 150 degreeC, and it took out after 30 minutes, and measured the degree of heat shrink.
The results are shown in Table 1. Table 1 shows the thermal shrinkage measurement results of Examples 1 and 2 and Comparative Examples 1, 2, 3, and 4.

  As shown in Table 1, the separator R of Comparative Example 1 which is a microporous film having a three-layer structure contracted 40% in the longitudinal direction, and the separator L of Comparative Example 2 having a single-layer structure contracted 50% in the longitudinal direction. On the other hand, the separator P of Example 1 was within 3%, the separator Q of Example 2 was 25%, the separator S of Comparative Example 3 and the separator K of Comparative Example 4 were within 3%. The separators P and K having the first, second, and third separator layers have a heat-resistant material layer and a low-melting-point material layer, and can ensure good heat shrinkage due to the action of the inorganic filler related to the second separator layer. . In addition, it can be said that the separator Q can secure a certain heat shrinkability compared to the separators R and L. By using the separator having the first, second, and third separator layers, the occurrence of an internal short circuit can be suppressed in an electrochemical element such as a lithium ion secondary battery.

(2) <Measurement of air resistance of separator>
About the separator of Example 1 and Comparative Examples 1, 2, 3, and 4, the air resistance at non-heating and the air resistance at room temperature after heating at 110 ° C. for 30 minutes while being kept at room temperature Was measured. The results are shown in Table 2. Table 2 shows the air resistance measurement results of Example 1 and Comparative Examples 1, 2, 3, and 4.

  As shown in Table 2 above, in Example 1, it became impossible to measure in heating at 110 ° C. for 30 minutes, indicating that the separator was blocked (shut down). “Unmeasurable” means that even when the separator was set in the apparatus and measurement was started, the inner cylinder hardly moved and measurement was not started. This means that the separator membrane is blocked. On the other hand, in Comparative Examples 1, 2, and 3, it became 315.2, 325.2, and 342.8, respectively, and it turned out that the separator is not obstruct | occluded at 110 degreeC.

  Further, the separator K of Comparative Example 4 did not shrink as in Example 1, but sometimes the separator shape was not stable at high temperatures. Therefore, the first separator layer preferably has a plurality of layer structures.

(3) <Measurement of resistance change due to heating in the electrolyte of the separator sandwiched between electrodes>
(Test cell using separator)
The separator P produced in Example 1 was sandwiched between aluminum foil and copper foil as electrodes on both sides, placed in a pressure vessel (10 atm), and a non-aqueous electrolyte (ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate) was put on the separator portion. A solution prepared by dissolving LiPF ₆ at a concentration of 1.2 mol / L in a solvent mixed at a volume ratio of 2: 4: 4 was added and sealed. A terminal that connects to the internal electrode from the outside of the pressure vessel is provided, and it is configured to be able to measure the resistance between the electrodes, and at the same time, a thermometer is connected so that the tip of the thermocouple is placed at the separator did. The pressure vessel was placed in a thermostatic chamber, and the resistance and temperature of the separator P sandwiched between the electrodes were monitored at a rate of temperature increase of about 100 ° C. per hour.
Using the separator R described in Comparative Example 1, resistance and temperature were monitored in the same manner as the separator P.

(Monitoring results)
The measurement results of the resistance change of the test cells using Example 1 and Comparative Example 1 are shown in FIGS. 3 and 4, respectively. In the separator P of Example 1, the increase in the resistance value corresponding to the shutdown starts near 100 ° C. and reaches saturation near 110 ° C. In contrast, in the separator R of Comparative Example 1, the resistance saturation value is increased. The temperature shown is around 128 ° C., which is above the shutdown temperature of the separator P. The separator P having the first, second and third separator layers is shut down at around 110 ° C. by the modified polyethylene which is a low melting point material forming the third separator layer. On the other hand, the separator R formed only from the first separator layer is shut down at a high temperature due to melting of the high-density polyethylene. The separator P is considered to be a battery separator that can be shut down at a lower temperature than the separator R and has higher safety.

(4) <Overcharge test with secondary battery>
(Secondary battery using the separator of Example 1)
The negative electrode produced in Production Example 1 and the positive electrode produced in Production Example 2 were overlapped with the separator P produced in Example 1 interposed, and wound in a spiral shape to produce a wound electrode body. In this wound electrode body, the second separator layer of the separator was made to face the positive electrode. The wound electrode body was loaded into a battery container of 18650 specifications. Further, after injecting a non-aqueous electrolyte (a solution in which LiPF ₆ was dissolved at a concentration of 1 mol / L in a solvent in which ethylene carbonate and propylene carbonate were mixed at a volume ratio of 3: 7) into the battery container, sealing was performed. As a result, a lithium ion secondary battery p was obtained.

(Secondary battery using separator of comparative example)
Using the separator S produced in Comparative Example 3 and the separator K produced in Comparative Example 4, a lithium ion secondary battery s and a lithium ion secondary battery k were obtained in the same manner as the lithium ion secondary battery p.

  An overcharge test of lithium ion secondary batteries p, s, and k produced using the separators of Examples and Comparative Examples was performed. Each lithium ion secondary battery was fully charged and further overcharged at a charge rate of 2C. Table 3 shows the overcharge test results.

  By overcharging, the temperature rises gradually. In the lithium ion secondary battery p using the separator of Example 1 and the lithium ion secondary battery k using the separator of Comparative Example 4, the temperature is around 110 ° C. Shut down and peak temperature was 140 ° C. to suppress further exotherm. In the lithium ion secondary battery s using the separator of Comparative Example 3, the shutdown was performed at around 135 ° C., and the peak temperature was 160 ° C., thereby suppressing further heat generation. The separators P and K allow the lithium ion secondary battery to be shut down at a lower temperature than the separator S. Thus, the lithium ion secondary battery p having the separator P having the first, second, and third separator layers as members and the lithium ion secondary battery k having the separator K as members are lithium lithium separators having the separator S as members. By shutting down at a lower temperature than the ion secondary battery s, it can be said that the lithium ion secondary battery has higher safety.

  The low melting point material layer included in the third separator layer is preferably disposed at a position in contact with the negative electrode. When shutdown occurs at a low temperature, a coating can be formed on the negative electrode side to prevent reaction of the negative electrode.

  INDUSTRIAL APPLICABILITY The present invention can be applied to lithium secondary batteries for mobile phones, in-vehicle use, and industrial use that include a positive electrode and a negative electrode, and a separator and a water-insoluble electrolyte for maintaining electrical insulation between the positive electrode and the negative electrode.

DESCRIPTION OF SYMBOLS 1 Separator 10 1st separator layer 11 A layer 12 B layer 20 2nd separator layer 21 Inorganic filler 30 3rd separator layer

Claims (12)

An electrochemical element separator interposed between a positive electrode and a negative electrode of an electrochemical element,
A microporous first separator layer having a plurality of layer structures each performing shutdown at a melting point set in multiple stages;
A heat-resistant and microporous second separator layer provided on one surface of the first separator layer;
A microporous third separator layer that is provided on the other surface of the first separator layer, or one surface of the second separator layer, and shuts down at a lower temperature than the first separator layer;
The separator for electrochemical elements characterized by having.   2. The separator for an electrochemical element according to claim 1, wherein the third separator layer faces the negative electrode, and the second separator layer or the first separator layer faces the positive electrode. The first separator layer has a thermoplastic resin having a melting point of 125 ° C. or higher and 170 ° C. or lower,
3. The separator for an electrochemical element according to claim 1, wherein the third separator layer has a thermoplastic resin having a melting point in a range of 80 ° C. or more and 125 ° C. or less.   The first separator layer has a three-layer structure composed of two types of resins, a resin constituting an outer layer and a resin constituting an inner layer, and has a resin layer having a melting point of at least 140 ° C. The separator for an electrochemical element according to claim 1 or 2, wherein the melting point of the resin constituting the outer layer is higher than the melting point of the resin constituting the inner layer.   3. The separator for an electrochemical element according to claim 1, wherein the second separator layer and the third separator layer are applied layers applied to the first separator layer. 4.   The said 2nd separator layer contains the inorganic filler, The separator for electrochemical elements as described in any one of Claims 1-5 characterized by the above-mentioned.   The separator for an electrochemical element according to claim 6, wherein the inorganic filler is at least one selected from the group consisting of aluminum hydroxide, magnesium hydroxide, magnesium oxide, silica, boehmite, and alumina.   2. The thickness of the first separator layer is 4 to 20 μm, the thickness of the second separator layer is 3 to 10 μm, and the thickness of the third separator layer is 1 to 10 μm. The separator for electrochemical elements as described.   The third separator layer includes a thermoplastic resin and an organic binder, and the content of the thermoplastic resin is 70% by volume or more per total volume of the constituent components of the third separator layer, and the content of the organic binder 2. The separator for an electrochemical element according to claim 1, wherein the content is 0.5% by volume or more per total volume of components of the third separator layer.   The second separator layer includes an inorganic filler and an organic binder, and the content of the inorganic filler is 40% by volume or more and 95% by volume or less based on the total volume of the constituent components of the second separator layer. 2. The separator for an electrochemical element according to claim 1, wherein the content is 0.5 volume% or more and 10 volume% or less per total volume of the constituent components of the second separator layer. An electrochemical element having a positive electrode, a negative electrode, a separator and a non-aqueous electrolyte,
The said separator is a separator for electrochemical elements as described in any one of Claims 1-10, The electrochemical element characterized by the above-mentioned.   The electrochemical device according to claim 11, wherein the separator is fixed and integrated with at least one of a positive electrode and a negative electrode.

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