JP2014007089A - Separator for electrochemical element, and electrochemical element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrochemical element excellent in safety, and a separator capable of constituting the electrochemical element.SOLUTION: A separator for an electrochemical element of the present invention comprises: a first separator layer mainly consisting of a thermoplastic resin; and a second separator layer containing a fire extinguishing material. An electrochemical element of the present invention comprises: a positive electrode; a negative electrode; a separator; and a nonaqueous electrolyte, and the separator is the separator for an electrochemical element of the present invention.

Description

  The present invention relates to an electrochemical element excellent in safety and a separator that can constitute the electrochemical element.

  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 ignition and fire accidents increases with increasing energy density, so 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, and the separator is disposed between the positive electrode and the negative electrode, and the internal short circuit of the battery by separating them. This prevents the ions in the non-aqueous electrolyte from permeating through the through-holes. However, since most of the ignition accidents of lithium ion secondary batteries are triggered by the internal short circuit of the battery, the functional addition to the separator occupies an important position in the safety measures of the lithium ion secondary battery. It can be said.

  In order to provide a function to a separator considering the safety of a lithium ion secondary battery, until now, when the battery generates heat, the separator melts at the melting point of a thermoplastic resin such as polyolefin, which is a material of the separator. It is common to provide a shutdown function that suppresses further heat generation of the battery by closing and closing 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.

  For this reason, separators that have been provided with resistance to film breakage due to thermal shrinkage and melting of materials have been developed together with a shutdown function. For example, 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. ing. 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.

  Further, Patent Document 2 proposes a separator containing fine particles that can swell by absorbing a nonaqueous electrolytic solution and whose degree of swelling increases with an increase in temperature. The fine particles contained in the separator described in Patent Document 2 absorb the non-aqueous electrolyte when the temperature inside the battery becomes high, and cause liquid drainage. Function is expressed. In addition, the separator described in Patent Document 2 does not need to be manufactured through a stretching process, unlike the polyolefin microporous film employed in ordinary lithium ion secondary batteries, and the residual stress in the separator is reduced. Since it can be reduced, it is highly resistant to shrinkage and tearing at high temperatures.

  Therefore, by using the separators described in Patent Document 1 and Patent Document 2, it is possible to improve the safety of the lithium ion secondary battery.

International Publication No. 2007/066768 JP 2008-4441 A

  In a conventional lithium ion secondary battery, not only the separator but also the main member is provided with measures against ignition, or a protection circuit for preventing ignition 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, and there is still room for improvement in this respect.

  This invention is made | formed in view of the said situation, The objective is to provide the separator which can comprise the electrochemical element excellent in safety | security, and the said electrochemical element.

  The separator for an electrochemical element of the present invention that has achieved the above object is characterized by having a first separator layer mainly composed of a thermoplastic resin and a second separator layer containing a fire extinguishing material. is there.

  The electrochemical device of the present invention has a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, and the separator is the electrochemical device separator of the present invention.

  ADVANTAGE OF THE INVENTION According to this invention, the separator which can comprise the electrochemical element excellent in safety | security and the said electrochemical element can be provided.

  The separator for electrochemical devices of the present invention (hereinafter simply referred to as “separator”) has a first separator layer mainly composed of a thermoplastic resin and a second separator layer containing a fire extinguishing material.

  A 1st separator layer becomes a base material of the separator of this invention, and the positive electrode and negative electrode which an electrochemical element has are mainly isolated by the 1st separator layer. Further, when the internal temperature of the electrochemical element using the separator of the present invention is equal to or higher than the melting point of the thermoplastic resin constituting the first separator layer, the thermoplastic resin is melted to form pores of the separator. Shuts down and suppresses the progress of electrochemical reaction.

  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, polyolefins such as polyethylene (PE), polypropylene (PP), paraffin, wax, copolymer polyolefin, polyolefin derivatives (chlorinated polyethylene, fluororesin, etc.); polyimide; aramid Etc. 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 to 150 ° C. 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 to 150 ° C. [hereinafter referred to as “resin (A)”] and a thermoplastic resin having a higher melting point than this (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. Since the layer shape (separator shape) can be maintained, the positive electrode and the negative electrode can be maintained in an isolated state even when the device temperature continues to rise after the onset of shutdown. The safety of the element can be further increased. 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.

  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) It is preferable to have a multi-layered structure such as a three-layered structure, and in this case, the above-mentioned effect by using the resin (A) and the resin (B) in combination can be secured better. it can.

  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 using only the resin (A) include, for example, microporous membranes composed of a single layer containing PE, and resin (A ) And resin (B) in combination, for example, a microporous membrane having a two-layer structure having a layer containing PP on one side of a layer containing PE, and PP on both sides of the layer containing PE And a microporous film having a three-layer structure having a layer containing s.

  The second separator layer according to the separator of the present invention contains a fire extinguishing material.

  The fire extinguishing material referred to in this specification means a material having a function of suppressing combustion of a material separate from the fire extinguishing material. Even if the internal temperature of the electrochemical device having the separator of the present invention increases due to the fire extinguishing material contained in the second separator layer, the temperature rise and combustion of the members existing in the electrochemical device are suppressed. Therefore, the electrochemical device having the separator of the present invention (the electrochemical device of the present invention) has excellent safety.

  Fire extinguishing materials include those that have the action of stopping radical reactions (oxygen radicals, hydrogen radicals, etc.) that occur during combustion, those that absorb heat by vaporization or thermal decomposition, and those that are nonflammable by vaporization or thermal decomposition. Those having an action of generating gas, those having a char forming action, those having a suffocation action to suppress the supply of oxygen by the incombustible material itself, and the like are included. The fire-extinguishing material may be any material that can exhibit only one of the exemplified actions, but more preferably one that can exert two or more actions.

  When using a fire extinguishing material that has the action of stopping the radical reaction, it traps radicals generated by the heat generated in the electrochemical element and suppresses the progress of the reaction, thus suppressing further heat generation and combustion. Is done. Specific examples of the fire extinguishing material having an action of stopping the radical reaction include, for example, phosphorus compounds such as ammonium dihydrogen phosphate, sodium phosphate, phosphate ester, trimethyl phosphite, red phosphorus, phosphazene, etc .; sodium hydrogen carbonate And alkali metal compounds such as potassium hydrogen carbonate, sodium carbonate hydrate, potassium carbonate hydrate; ammonium sulfate; bromine compounds; halogenated compounds; halide-modified polymers such as perhalogenated alkyls;

  When a fire extinguishing material having an action of absorbing heat by vaporization or thermal decomposition is used, the temperature rise of the heat generating portion in the electrochemical element is suppressed. Among fire-extinguishing materials having an action of absorbing heat by vaporization or thermal decomposition, specific examples of inorganic compounds include, for example, alkali metal compounds such as sodium hydrogen carbonate, potassium hydrogen carbonate, sodium carbonate, potassium carbonate; dihydrogen phosphate And ammonium; urea; hydrates having crystal water such as potassium carbonate hydrate and sodium carbonate hydrate; hydroxides such as calcium hydroxide, magnesium hydroxide and aluminum hydroxide;

  Moreover, the organic compound generally used as a foaming agent generates gas by thermal decomposition, and an endothermic effect is obtained. Specific examples of the organic compound fire extinguishing material having an action of absorbing heat by vaporization or thermal decomposition include, for example, dinitropentamethylenetetramine, azodicarbonamide, p, p′-oxybisbenzenesulfonylhydrazide, hydrazodicarbonamide, Examples thereof include bistetrazole / diammonium, bistetrazole / piperazine, and 5-phenyltetrazole.

  When using a fire extinguishing material that has the effect of generating incombustible gas by vaporization or thermal decomposition, combustion is suppressed by the suffocation effect that the generated gas suppresses contact between the exothermic site in the electrochemical element and oxygen. It is done. In addition, an incombustible gas layer is formed inside the battery, preventing the movement of ions, thereby preventing current short-circuiting and preventing overcharging, thereby preventing internal short circuit and suppressing thermal runaway. . Among fire extinguishing materials that have the effect of generating nonflammable gases by vaporization or thermal decomposition, specific examples of inorganic compound systems include, for example, sodium hydrogen carbonate, potassium hydrogen carbonate, sodium carbonate, anhydrous sodium carbonate, potassium carbonate, etc. Compounds that generate carbon dioxide by thermal decomposition of benzene; compounds that generate ammonia gas by thermal decomposition, such as urea, ammonium dihydrogen phosphate, and ammonium chloride; ammonium hydrogen carbonate that generates carbon dioxide and ammonia gas; .

  Moreover, the organic compound generally used as a foaming agent generates gas by thermal decomposition. Along with the endothermic action by vaporization or thermal decomposition, it has a suffocation effect and can form a non-combustible gas layer inside the battery. Specific examples of organic compound-based fire-extinguishing materials that have a suffocating effect due to non-flammable gas, and also have an effect of forming a non-flammable gas layer inside the battery and blocking current, include, for example, dinitropentamethylenetetramine, azo Examples thereof include dicarbonamide, p, p′-oxybisbenzenesulfonyl hydrazide, hydrazodicarbonamide, bistetrazole / diammonium, bistetrazole / piperazine, and 5-phenyltetrazole.

  When using a fire extinguishing material with char-forming action, the heat conduction from the formed element suppresses heat conduction from the exothermic part to other parts, preventing further temperature rise inside the element. Moreover, combustion is suppressed by the suffocation action in which the contact between the heat generation site in the electrochemical element and oxygen is suppressed by the char. Specific examples of fire-extinguishing materials having a char-forming effect include, for example, phosphorus compounds such as ammonium dihydrogen phosphate, sodium phosphate, phosphate ester, trimethyl phosphite, red phosphorus, phosphazene; boron, borax, boron Examples thereof include acids, borates, zinc borates, boron compound-modified polymers; silicon compounds such as sodium silicate and silicon compounds; and the like.

  When a fire extinguishing material having a suffocating action is used, since it is a nonflammable material, supply of oxygen can be suppressed. Specific examples of the fire extinguishing material having a suffocating action include sodium chloride, antimony oxide, calcium carbonate, calcium chloride and the like.

  As the fire extinguishing material, only one of the various materials exemplified above may be used, or two or more of them may be used in combination. Moreover, powder fire extinguishing agents, such as ABC fire extinguishing agent, BC fire extinguishing agent, and PDK extinguishing agent which contain 1 or more types of the various materials of the said illustration, can also be used as a fire extinguishing material which concerns on a 2nd separator layer.

  When a particulate fire extinguishing material is used for the second separator layer, the particle size of the fire extinguishing material particles may be smaller than the thickness of the second separator layer, but is 1/100 to 1 of the thickness of the second separator layer. It is preferable to have an average particle size of about / 3. Specifically, the average particle diameter of the fire extinguishing material is preferably 0.01 μm or more, more preferably 0.1 μm or more, and preferably 20 μm or less, preferably 5 μm or less. Is more preferable. When the particle size of the fire-extinguishing material is too small, the gap between the particles becomes small, the ion conduction path becomes long, and the characteristics of the electrochemical device may deteriorate. Moreover, when the particle size of the fire extinguishing material is too large, the second separator layer becomes thick, which is not preferable because the energy density of the electrochemical element is lowered.

The average particle size of the fine particles (particulate fire extinguishing material and inorganic filler described later) referred to in the present specification is, for example, a fine particle aqueous dispersion prepared by a dense particle size analyzer “FPAR- use 1000 ", D ₅₀ as measured by dynamic light scattering can be defined as _(volume cumulative frequency particle diameter at 50%).

  The shape of the particulate fire extinguishing material is not particularly limited, and may be any shape such as a substantially spherical shape (including a true spherical shape), an ellipsoidal shape, and a plate shape.

  The second separator layer may be composed of only a fire extinguishing material, and includes a particulate fire extinguishing material and an organic binder, and has a structure in which the extinguishing materials are bound together by an organic binder. May be.

  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., “Evaflex-EEA Series (Ethylene) by Mitsui DuPont Polychemical 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 preferably further contains an inorganic filler. 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 the separator having the second separator layer containing the inorganic filler together with the fire extinguishing material, 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 oxides such as iron oxide, SiO ₂ (silica), Al ₂ O ₃ (alumina), TiO ₂ , BaTiO ₂ , and ZrO ₂ ; Inorganic hydroxides such as Al (OH) ₃ (aluminum hydroxide); Inorganic nitrides such as aluminum nitride and silicon nitride; Slightly soluble ionic crystals such as calcium fluoride, barium fluoride and barium sulfate; Silicon and diamond Covalent crystals of: 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 an artificial product thereof. 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 exemplified materials, alumina, silica, aluminum hydroxide, and boehmite are more preferable, boehmite is more preferable, the particle size and shape are easily controlled, and ions that adversely affect the characteristics of the electrochemical device Synthetic boehmite that can reduce volatile impurities 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 average particle size of the inorganic filler measured by the above method is 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.

  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 content rate of the fire extinguishing material in the second separator layer is the total volume of the constituent components of the second separator layer (the volume excluding the pores. The second separator) from the viewpoint of better securing the above-described effect of the fire extinguishing material. In the following description, the content of the constituent components of the layer is preferably 10% by volume or more, and more preferably 40% by volume or more. In addition, since the 2nd separator layer may be comprised only with the fire extinguishing material, the upper limit of the content rate of the fire extinguishing material in a 2nd separator layer is 100 in the whole volume of the structural component of a 2nd separator layer. As described above, the second separator layer preferably contains components other than the fire-extinguishing material. Therefore, when components other than the fire-extinguishing material are contained, the action of these components is effective. It is preferable to include an amount that can be sufficiently exerted, and it is desirable to limit the content of the fire extinguishing material accordingly.

  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 10% by volume or less and more preferably 5% 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 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.

  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.

  In addition, the 1st separator layer may contain the said fire extinguishing material, an inorganic filler, an organic binder, and a fibrous material.

  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. And the thickness of a 2nd separator layer becomes like this. Preferably it is 1 micrometer or more, More preferably, it is 3 micrometers or more, Preferably it is 15 micrometers or less, More preferably, it is 10 micrometers or less.

The separator of the present invention is performed by a method in accordance with JIS P 8117, and the Gurley value indicated by the number of seconds that 100 mL of air permeates through the membrane under a pressure of 0.879 g / mm ² is 10 to 400 sec. It is desirable to be. 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.

  In the separator of the present invention, for example, a composition for forming a second separator layer (slurry, paste, etc.) is applied to a microporous film made of a thermoplastic resin constituting the first separator layer, and dried at a predetermined temperature. Thus, the second separator layer can be formed.

  The composition for forming the second separator layer is a fire-extinguishing material, and inorganic fillers and fibrous materials used as necessary are dispersed in a solvent, and an organic binder used is dispersed in the solvent as needed. Or it is prepared by dissolving.

  The solvent used in the composition for forming the second separator layer may be any solvent that can uniformly disperse the fire-extinguishing material, the inorganic filler, the fibrous material, and the like, and can uniformly dissolve or disperse the organic binder. In 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. 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 is preferably 10 to 40% by mass, for example.

  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.

  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 prepared by appropriately adding a conductive additive (carbon material such as carbon black) or a binder such as PVDF to these negative electrode active materials is finished into a molded body (negative electrode mixture layer) using the current collector as the 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.

Production Example 1 (Preparation of negative electrode)
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 was intermittently applied on both sides of a 10 μm thick copper foil serving as a current collector so that the coating length was 320 mm on the front surface and 260 mm on the back surface. The thickness of the negative electrode mixture layer was adjusted so that the thickness was 142 μm, and was cut so as to have a width of 45 mm, thereby preparing 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.

Production Example 2 (Preparation of positive electrode)
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 is applied to both sides of a 15 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 becomes 130 μm. Cut to 43 mm, a positive electrode having a length of 330 mm and a width of 43 mm was produced. Further, a tab was welded to the exposed portion of the aluminum foil of the positive electrode to form a lead portion.

Production Example 3 (Preparation of negative electrode)
The negative electrode produced in Production Example 1 was punched out in a shape in which a 2 cm × 1 cm tab joint portion (exposed portion of the copper foil as a current collector) remained at the end of the 4 cm × 2.5 cm negative electrode mixture layer forming portion, A tab was welded to the exposed portion of the copper foil at the bonding site to form a lead portion.

Production Example 4 (Preparation of positive electrode)
The positive electrode produced in Production Example 2 was punched out in a shape in which a 2 cm × 1 cm tab joint portion (exposed portion of the aluminum foil as a current collector) remained at the end of the 4 cm × 2.5 cm positive electrode mixture layer forming portion. A tab was welded to the exposed portion of the copper foil at the bonding site to form a lead portion.

Example 1
Boehmite fine particles: 61 parts by mass, ammonium dihydrogen phosphate as a fire extinguishing material: 37 parts by mass, and PVP: 1 part by mass, and a dispersant and a surfactant added to 100 parts by mass. A certain water was added and dispersed to prepare a slurry for forming a second separator layer having a solid content of 30% by mass. This slurry is applied to one side of a three-layered microporous film (thickness 20 μm) of PP / PE / PP and dried to obtain a separator having a second separator layer having a thickness of 5 μm on one side of the first separator layer. It was.

The negative electrode produced in Production Example 1 and the positive electrode produced in Production Example 2 were overlapped with the separator interposed therebetween 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 negative electrode. The wound electrode body was crushed into a flat shape and loaded into a battery container. 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. A lithium ion secondary battery was obtained.

Example 2
Boehmite fine particles: 57 parts by mass, sodium hydrogen carbonate as a fire extinguishing material: 41 parts by mass, and PVP: 1 part by mass, and further adding a dispersant and a surfactant to make 100 parts by mass. Was added and dispersed to prepare a slurry for forming a second separator layer having a solid content of 29% by mass. This slurry is applied to one side of a microporous membrane (thickness 20 μm) having a three-layer structure of PP / PE / PP and dried to have a second separator layer having a thickness of 5 μm on one side of the first separator layer. A separator was obtained.

  And the lithium ion secondary battery was produced like Example 1 except having used the above-mentioned separator.

Example 3
Boehmite fine particles: 57 parts by mass, potassium hydrogen carbonate as a fire extinguishing material: 41 parts by mass, and PVP: 1 part by mass, and further adding a dispersant and a surfactant to make 100 parts by mass. Was added and dispersed to prepare a slurry for forming a second separator layer having a solid content of 29% by mass. This slurry is applied to one side of a microporous membrane (thickness 20 μm) having a three-layer structure of PP / PE / PP and dried to have a second separator layer having a thickness of 5 μm on one side of the first separator layer. A separator was obtained.

  And the lithium ion secondary battery was produced like Example 1 except having used the above-mentioned separator.

Example 4
The negative electrode produced in Production Example 3 and the positive electrode produced in Production Example 4 were stacked in the order of the negative electrode, the separator, the positive electrode, the separator, and the negative electrode while interposing the same separator as that produced in Example 3. Produced. In this electrode body, the second separator layer of the separator was made to face the negative electrode. This electrode body was loaded into an aluminum laminate pack, and 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) was added. After inject | pouring in the pack made from an aluminum laminate, sealing was performed and the lithium ion secondary battery was obtained.

Comparative Example 1
Without using a fire extinguishing material, a dispersant and a surfactant were further added to boehmite fine particles: 97 parts by mass and PVP: 2 parts by mass to make 100 parts by mass. A separator layer was prepared, and a separator was prepared in the same manner as in Example 1 except that this slurry was used. And the lithium ion secondary battery was produced like Example 1 except having used this separator.

Comparative Example 2
A lithium ion secondary battery was produced in the same manner as in Example 4 except that the separator produced in Comparative Example 1 was used and this separator was used.

  About the lithium ion secondary battery of Examples 1-3 and the comparative example 1, the 200 degreeC heating test of the following lithium ion secondary battery was done, and it used for the lithium ion secondary battery of Examples 1-3 and the comparative example 1. The following thermal shrinkage rate measurement was performed on the same separator as the above. Moreover, about the lithium ion secondary battery of Example 4 and Comparative Example 2, the shutdown test of the following lithium ion secondary battery was done.

<200 ° C heating test of lithium ion secondary battery>
The lithium ion secondary batteries of Examples 1 to 3 and Comparative Example 1 that were fully charged with a voltage of 4.2 V were placed in an electric furnace, and the change in the temperature of the battery surface was measured at a furnace temperature of 200 ° C. The speed of temperature rise was compared.

  As a result, the speed of the surface temperature rise of the lithium ion secondary batteries of Examples 1 to 3 was smaller than that of the lithium ion secondary battery of Comparative Example 1, and the fire extinguishing material contained in the second separator layer related to the separator As a result, the temperature rise could be suppressed. Therefore, it can be said that the lithium ion secondary batteries of Examples 1 to 3 are further improved in safety as compared with the battery of Comparative Example 1.

<Shutdown test of lithium ion secondary battery>
Changes in the temperature of the battery surface when the lithium ion secondary batteries of Example 4 and Comparative Example 2 that were fully charged with a voltage of 4.2 V were placed in a thermostatic bath and the bath temperature was increased at a constant rate. The battery resistance was measured simultaneously, and the shutdown temperature at which the resistance increased rapidly and the current was cut off was compared.

  As a result, the lithium ion secondary battery of Example 4 was shut down at 110 ° C., and the lithium ion secondary battery of Comparative Example 2 was shut down at 120 ° C. From this result, the digestible material contained in the separator according to the lithium ion secondary battery of Example 4 causes shutdown at a lower temperature, and prevents thermal runaway caused by overcharging at an earlier stage of heat generation. It can be said that it contributes to the improvement of safety.

<Measurement of thermal contraction rate of separator>
Each separator according to Examples 1 to 3 and Comparative Example 1 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 1 hour, and measured the degree of thermal contraction. In addition, about the microporous film of the same three-layer structure as what was used for manufacture of the separator which concerns on an Example and a comparative example, the thermal contraction rate measurement was performed by the same method as the above.

  As a result, the microporous film having a three-layer structure contracted by 40% in the longitudinal direction, whereas the contractions of the separators according to Examples 1 to 3 and Comparative Example 1 all remained at 5% in the longitudinal direction. Therefore, in these separators, good heat shrinkage can be ensured by the action of the inorganic filler related to the second separator layer, so in electrochemical elements such as lithium ion secondary batteries using these separators, Generation | occurrence | production of a short circuit can be suppressed and a temperature rise can be reduced.

Claims (10)

  A separator for an electrochemical element comprising a first separator layer mainly composed of a thermoplastic resin and a second separator layer containing a fire extinguishing material.   The separator for an electrochemical element according to claim 1, wherein the fire extinguishing material has an action of stopping a radical reaction and an action of char formation.   The separator for an electrochemical element according to claim 2, wherein the fire extinguishing material is ammonium dihydrogen phosphate.   The separator for an electrochemical element according to claim 1, wherein the fire extinguishing material has an action of stopping a radical reaction and an action of absorbing heat by vaporization or thermal decomposition.   The separator for an electrochemical element according to claim 4, wherein the fire extinguishing material is sodium hydrogen carbonate or potassium hydrogen carbonate.   The separator for an electrochemical element according to claim 1, wherein the fire extinguishing material has an action of stopping a radical reaction and an action of generating a nonflammable gas by thermal decomposition.   The separator for electrochemical devices according to any one of claims 1 to 6, wherein the second separator layer contains an inorganic filler.   The separator for electrochemical devices according to claim 7, wherein the inorganic filler contained in the second separator layer is at least one selected from the group consisting of aluminum hydroxide, boehmite and alumina. An electrochemical element having a positive electrode, a negative electrode, a separator and a non-aqueous electrolyte,
The said separator is an electrochemical element separator in any one of Claims 1-8, The electrochemical element characterized by the above-mentioned.   The electrochemical device according to claim 9, wherein the separator is integrated with the positive electrode and / or the negative electrode.