JP5408726B2 - Electrochemical element separator and electrochemical element - Google Patents

Description

  The present invention relates to an electrochemical element excellent in safety and an electrochemical element separator capable of constituting the electrochemical element.

  Electrochemical elements such as lithium secondary batteries are widely used as power sources for portable devices such as mobile phones and notebook personal computers because of their high energy density. For example, lithium secondary batteries tend to have higher capacities as mobile devices become more sophisticated, and ensuring safety is important.

  In current lithium secondary batteries, a polyolefin microporous film having a thickness of about 20 to 30 μm is used as a separator interposed between a positive electrode and a negative electrode. In addition, as separator material, the constituent resin of the separator is melted below the thermal runaway temperature of the battery to close the pores, thereby increasing the internal resistance of the battery and improving the safety of the battery in the event of a short circuit. In order to ensure the so-called shutdown effect, polyethylene having a low melting point may be applied. In addition, in order to keep the strength of the separator between the positive and negative electrodes when exposed to high temperatures, for example, the film breaking strength, ultra high molecular weight polyethylene, high molecular weight polyethylene and a plasticizer are kneaded, and this is used as a raw material to produce a separator. Sometimes.

  Furthermore, as such a separator, for example, a uniaxially stretched film or a biaxially stretched film is used for increasing the porosity and improving the strength. Since such a separator is supplied as a single film, a certain strength is required in terms of workability and the like, and this is secured by the stretching. And in order to suppress the heat shrink at high temperature, heat processing, such as heat fixation and heat relaxation, is also performed after the stretching.

  As described above, in the separator made of the conventional polyolefin microporous membrane, the shutdown characteristics at high temperatures, the improvement of the tear resistance, the suppression of thermal shrinkage, etc. are achieved. When the temperature becomes close to the melting point, the interval between the pores is narrowed, and finally, the constituent resin melts and closes the pores, so in practice, the thermal contraction and shutdown of the separator occur almost simultaneously. Therefore, if the current cannot be immediately reduced without sufficiently closing the separator holes, there is a risk of short circuit due to direct contact between the positive electrode and the negative electrode due to contraction of the separator.

  As a technique for preventing such a short circuit due to thermal contraction of the separator and improving the reliability of the battery, for example, a first separator layer mainly including a resin for ensuring a shutdown function, and a filler having a heat resistant temperature of 150 ° C. or more It has been proposed to form an electrochemical element by using a porous separator having a second separator layer containing mainly as a main component (Patent Document 1).

  According to the technique of Patent Document 1, it is possible to provide an electrochemical element such as a lithium secondary battery that is less likely to cause thermal runaway even when abnormally overheated and has excellent safety.

International Publication No. 2007/66768

  As described above, shutdown in an electrochemical device using a separator made of a normal polyolefin microporous membrane occurs when the separator resin shrinks and its constituent resin melts, thereby closing the pores of the separator. . Since the shrinkage of the separator gradually starts at a temperature lower than the melting point of the constituent resin of the separator, the shutdown start temperature is usually lower than the melting point of the constituent resin of the separator.

  On the other hand, in the electrochemical element described in Patent Document 1, since the shrinkage of the first separator layer for ensuring the shutdown function is highly suppressed by the action of the second separator layer, the shutdown is performed in the first separator. The melting point of the constituent resin of the layer becomes dominant, and shutdown is difficult to start at a temperature lower than this melting point.

  In the electrochemical element described in Patent Document 1, even when the inside becomes high temperature, the shrinkage of the entire separator is suppressed, and a high heat-resistant second separator layer that hardly shrinks is interposed between the positive electrode and the negative electrode. Because it exists, even if the shutdown start temperature becomes relatively high, the contact between the positive electrode and the negative electrode can be prevented in the meantime, so that thermal runaway can be suppressed well, and from the conventional polyolefin microporous film It has higher safety than an electrochemical device using a separator.

  However, in an electrochemical device, the higher the temperature, the lower the thermal stability of the positive electrode material and the negative electrode material, and the greater the heat generated in the device. In some circumstances, it is desirable that the temperature rise in the element is prevented early by inhibiting the movement of ions, and the technique described in Patent Document 1 still leaves room for improvement in this respect. Yes.

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

  The separator for an electrochemical element of the present invention that has achieved the above object mainly includes a porous layer (I) composed of a microporous film mainly composed of a thermoplastic resin, and a filler having a heat resistant temperature of 150 ° C. or higher. And a porous layer containing a polyolefin having a melting point at a temperature lower than the peak top temperature of the first stress peak in the TD direction of the microporous membrane constituting the porous layer (I) measured by thermomechanical analysis ( II).

  The electrochemical element of the present invention is an electrochemical element having a wound electrode body in which a positive electrode, a negative electrode, and a separator are wound in layers, and a non-aqueous electrolyte, and the separator is the electrochemical element of the present invention. It is an element separator.

  As used herein, “heat-resistant temperature is 150 ° C. or higher” means that deformation such as softening is not observed at least at 150 ° C.

  Further, in the porous layer (I) relating to the separator in the present specification, “mainly comprising a thermoplastic resin” means a solid content ratio in the porous layer (I), and the thermoplastic resin is 50% by volume or more. It means that. Further, in the porous layer (II) relating to the separator in the present specification, “mainly contains a filler having a heat-resistant temperature of 150 ° C. or higher” means a filler having a heat-resistant temperature of 150 ° C. or higher in a solid content ratio in the layer Is 50% by volume or more.

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

  The separator for an electrochemical element of the present invention (hereinafter sometimes simply referred to as “separator”) includes a porous layer (I) composed of a microporous film mainly composed of a thermoplastic resin, and a filler having a heat resistant temperature of 150 ° C. or more. And a porous layer (II) containing a polyolefin having a specific melting point.

  The separator of the present invention is short-circuited by direct contact between the positive electrode and the negative electrode even when the internal temperature of the element rises due to the action of the porous layer (II) mainly containing a filler having a heat resistant temperature of 150 ° C. or higher. It has a function to prevent. In other words, when the electrochemical device is at a high temperature, the positive and negative electrodes can be generated when the separator is thermally contracted by the porous layer (II) that is difficult to contract even if the porous layer (I) contracts. It is possible to prevent a short circuit due to direct contact. When the porous layer (I) and the porous layer (II) are integrated, the heat-resistant porous layer (II) acts as a separator skeleton, and the porous layer (I) The thermal contraction of the separator, that is, the thermal contraction of the entire separator is suppressed.

  On the other hand, in the separator of the present invention, the porous layer (I) is mainly for ensuring a shutdown function, and the internal temperature of the electrochemical device (the electrochemical device of the present invention) using this separator is increased. When this occurs, the thermoplastic resin constituting the porous layer (I) melts and closes the pores of the separator, thereby suppressing the progress of the electrochemical reaction.

  However, as described above, since the thermal contraction of the porous layer (I) is suppressed by the action of the porous layer (II), the shutdown due to the action of the porous layer (I) It begins when the thermoplastic resin that comprises) begins to melt.

  Therefore, in the separator for an electrochemical element of the present invention, the separator made of a conventional polyolefin microporous film is focused on the fact that the shutdown starts when it starts to shrink, and the microporous material constituting the porous layer (I) For the membrane, the peak top temperature of the first stress peak in the TD direction [direction perpendicular to the production direction (MD direction) of the microporous membrane constituting the porous layer (I)] measured by thermomechanical analysis (TMA) Based on the standard, polyolefin having a melting point lower than this temperature is contained in the porous layer (II), and the shutdown of the porous layer (II) is started by the polyolefin before the shutdown by the porous layer (I). Was able to start.

  In the electrochemical device of the present invention, the above-described actions in the separator of the present invention enhance the safety by preventing thermal runaway early even when the inside of the device is abnormally overheated.

  Further, as described above, in the separator of the present invention, the battery reaction can be suppressed before the shutdown starts at a lower temperature and reaches the temperature at which the thermal contraction of the porous layer (I) occurs. Therefore, even if the porous layer (II) is thinned and the function of suppressing the thermal contraction of the entire separator is somewhat reduced, the safety of the electrochemical element can be maintained well, so the thickness of the entire separator is reduced. Thus, the capacity of the electrochemical device can be increased.

  Furthermore, the porous layer (II) according to the separator of the present invention mainly contains a filler having a heat-resistant temperature of 150 ° C. or higher, thereby ensuring the mechanical strength of the layer. Compared to separators made of porous membranes, the range of options for polyolefins is wide. Therefore, various melting points can be used as long as the melting point is lower than the peak top temperature of the first stress peak in the TD direction measured by thermomechanical analysis (TMA) of the microporous film constituting the porous layer (I). Can be selected, whereby the shutdown start temperature of the separator can be set to a desired temperature.

  In determining the melting point of the polyolefin, the peak top temperature of the first stress peak of the microporous membrane constituting the porous layer (I) is obtained in the TD direction, and this is used as a reference for the following reason. . In electrochemical devices, a laminated electrode body in which a positive electrode and a negative electrode are overlapped with a separator interposed therebetween, and a wound electrode body obtained by further spirally winding the electrode body are used. In many respects, a wound electrode body is often used.

  The wound electrode body is formed by, for example, pulling out the positive electrode, the negative electrode, and the separator from the positive electrode roll wound with the belt-shaped positive electrode, the negative electrode roll wound with the belt-shaped negative electrode, and the separator roll wound with the belt-shaped separator, respectively. Combined and spirally manufactured. Therefore, the direction parallel to the winding direction in the wound electrode body is usually the MD direction of the separator, and the direction orthogonal to the winding direction (direction parallel to the winding axis) is usually the TD direction of the separator. is there.

  In the wound electrode body, for example, in order to prevent contact between the positive electrode and the negative electrode at both end faces, the length in the direction orthogonal to the winding direction of the separator is made longer than that of the positive electrode and the negative electrode. The separator protrudes from the positive electrode and the negative electrode at both end faces of the electrode. However, when the inside of the element becomes hot and the separator contracts, the positive electrode and the negative electrode are in direct contact with each other in the vicinity of both ends of the wound electrode body. May cause a short circuit.

  Thus, in an electrochemical device having a wound electrode body, the problem of short circuit at high temperature is largely related to the heat shrinkage characteristics in the direction perpendicular to the winding direction of the separator, that is, the TD direction of the separator. Therefore, in the separator of the present invention, the peak top temperature of the first stress peak measured by TMA [the heat in the TD direction of the porous layer (I) is measured in the TD direction of the microporous film constituting the porous layer (I). Corresponding to the temperature at which shrinkage occurs], the porous layer (II) contains a polyolefin that can be melted at a lower temperature so that the shutdown can be started at a lower temperature.

  The peak top temperature of the first stress peak measured by TMA of the microporous film constituting the porous layer (I) may be 150 ° C. or less because the shutdown start temperature may be too high. Preferably, the temperature is 120 ° C. or more from the viewpoint of suppressing the thermal strength from becoming too small.

The “peak top temperature of the first stress peak measured by TMA of the microporous membrane constituting the porous layer (I)” as used herein is a temperature measured by the following method. A measurement sample having a length (TD direction) of 10 mm and a width of 4 mm is cut out from the microporous membrane constituting the porous layer (I). Then, using a thermomechanical analyzer (for example, “EXSTAR7000” manufactured by SII), the measurement sample is attached to a tensile probe, and the initial load is 1 g, and the temperature is increased from room temperature to 200 ° C. at a temperature increase rate of 5 ° C./min. The temperature is measured up to ° C., and the temperature at the peak top is obtained from the first stress peak in the obtained temperature-stress curve. That is , the “peak top temperature” refers to a temperature at which the stress shows a maximum value in a stress peak that appears first when the temperature is raised from room temperature under the above conditions.

  By using a porous layer (I) (a microporous film constituting the same) having the following configuration, the above characteristics can be ensured.

  The thermoplastic resin that is the main component of the porous layer (I) of the separator has an electrical insulating property, is electrochemically stable, and further includes a non-aqueous electrolyte solution (hereinafter referred to as an electrochemical element described in detail later). , And may be abbreviated as “electrolyte”) or a thermoplastic resin that is stable to the solvent used in the production of the separator (details will be described later), but there is no particular limitation, but polyethylene (PE), polypropylene ( PP), polyolefins such as ethylene-propylene copolymer; polyesters such as polyethylene terephthalate and copolymerized polyesters;

  From the relationship with the shutdown temperature, the porous membrane (I) has a melting point, that is, a melting temperature measured using a differential scanning calorimeter (DSC) of 110 ° C. or higher in accordance with JIS K 7121. It is more preferable to use a thermoplastic resin at 170 ° C. as a constituent component, and it is a single-layer microporous film mainly composed of PE, or a laminated microporous film in which 2 to 5 layers of PE and PP are laminated ( A microporous film having a two-layer structure having a PE layer and a PP layer; a microporous film formed by sequentially stacking PE layers / PP layers / PE layers, and sequentially stacking PP layers / PE layers / PP layers It is preferable that the microporous membrane has a three-layer structure, and the like.

  When the porous layer (I) is composed of a thermoplastic resin having a melting point of 110 ° C. or more and 150 ° C. or less like PE and a thermoplastic resin having a melting point exceeding 150 ° C. like PP, for example, A microporous film formed by mixing PE and a resin having a higher melting point than PE such as PP is used as the porous layer (I), or a resin having a higher melting point than PE such as the PE layer and the PP layer. In the case where the laminated microporous membrane constituted by laminating the layers constituted by the above is used as the porous layer (I), the melting point is 110 ° C. or higher in the thermoplastic resin constituting the porous layer (I). The resin (for example, PE) at 150 ° C. or lower is preferably 30% by mass or more, and more preferably 50% by mass or more.

  As the microporous membrane as described above, for example, a microporous membrane composed of the above-described exemplified thermoplastic resin used in electrochemical elements such as lithium secondary batteries known in the past, that is, solvent extraction An ion-permeable microporous membrane produced by a method, a dry method or a wet stretching method (particularly a wet biaxial stretching method or a dry uniaxial stretching method) can be used.

  Further, the porous layer (I) may contain a filler or the like in order to improve the strength and the like within a range that does not impair the action of imparting the shutdown function to the separator. Examples of the filler that can be used for the porous layer (I) include the same fillers that can be used for the porous layer (II) described later (a filler having a heat resistant temperature of 150 ° C. or higher).

The particle size of the filler is an average particle size, for example, preferably 0.01 μm or more, more preferably 0.1 μm or more, preferably 10 μm or less, more preferably 1 μm or less. In addition, the average particle diameter as used in the present specification is a particle diameter (D _50% ) at a volume-based cumulative fraction of 50% measured by dispersing the filler in a medium (for example, water) that does not dissolve the filler [ The same applies to the filler and polyolefin particles related to the porous layer (II) described later. ].

  The content of the thermoplastic resin in the porous layer (I) is preferably as follows, for example, in order to make it easier to obtain the shutdown effect. The volume of the thermoplastic resin as a main component in all the constituent components of the porous layer (I) is 50% by volume or more, more preferably 70% by volume or more, and may be 100% by volume. Furthermore, the porosity of the porous layer (II) obtained by the method described later is 20 to 60%, and the volume of the thermoplastic resin is 50% or more of the pore volume of the porous layer (II). It is preferable.

  The filler having a heat resistant temperature of 150 ° C. or higher, which is mainly contained in the porous layer (II) of the separator, is stable with respect to the non-aqueous electrolyte of the electrochemical element, and is oxidized in the operating voltage range of the electrochemical element. Organic particles or inorganic particles may be used as long as they are difficult to be reduced and are electrochemically stable. However, fine particles are preferable from the viewpoint of dispersion, and inorganic fine particles are preferable from the viewpoint of stability (particularly oxidation resistance). More preferably used.

Specific examples of the constituent material of the inorganic particles include inorganic oxides such as iron oxide, Al ₂ O ₃ (alumina), SiO ₂ (silica), TiO ₂ , BaTiO ₃ , ZrO ₂ ; aluminum nitride, silicon nitride, etc. Inorganic nitrides of the above; poorly soluble ionic crystals such as calcium fluoride, barium fluoride and barium sulfate; covalent bonds such as silicon and diamond; clays such as montmorillonite; Here, the inorganic oxide may be boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, mica, or other mineral resource-derived substances or artificial products thereof. In addition, the surface of a conductive material exemplified by metal, SnO ₂ , conductive oxide such as tin-indium oxide (ITO), carbonaceous material such as carbon black, graphite, etc., is a material having electrical insulation ( For example, the particle | grains which gave the electrical insulation property by coat | covering with the said inorganic oxide etc. may be sufficient. As the inorganic particles, from the viewpoint of further improving the oxidation resistance of the porous layer (II), the above-mentioned inorganic oxide particles (fine particles) are preferable, and among these, alumina, silica, boehmite, and the like are more preferable.

  Organic particles (organic powder) include crosslinked polymethyl methacrylate, crosslinked polystyrene, crosslinked polydivinylbenzene, styrene-divinylbenzene copolymer crosslinked product, polyimide, melamine resin, phenol resin, benzoguanamine-formaldehyde condensate, etc. Examples thereof include various crosslinked polymer particles and heat-resistant polymer particles such as polysulfone, polyacrylonitrile (PAN), aramid, polyacetal, and thermoplastic polyimide. The organic resin (polymer) constituting these organic particles is a mixture, modified body, derivative, or copolymer (random copolymer, alternating copolymer, block copolymer, graft copolymer) of the materials exemplified above. Polymer) or a crosslinked product (in the case of the above-mentioned heat-resistant polymer).

  As the filler having a heat-resistant temperature of 150 ° C. or higher, only one kind of those exemplified above may be used, or two or more kinds may be used in combination.

  As a form of the filler having a heat resistant temperature of 150 ° C. or higher, for example, the filler may have a shape close to a sphere, or may have a plate shape, but is included in the porous layer (II). It is preferable that at least a part of the filler is plate-like particles. All of the fillers may be plate-like particles. When the porous layer (II) contains plate-like particles, it is possible to suppress the force that the porous film (A) contracts due to the collision between the plate-like particles. Further, the use of plate-like particles increases the path between the positive electrode and the negative electrode in the separator, that is, the so-called curvature. Therefore, even when dendrite is generated, it becomes difficult for the dendrite to reach the positive electrode from the negative electrode, and the reliability against a dendrite short can be improved.

Examples of the plate-like filler include various commercially available products, such as “Sun Lovely (trade name)” (SiO ₂ ) manufactured by Asahi Glass S-Tech, and “NST-B1 (trade name)” manufactured by Ishihara Sangyo Co., Ltd. (TiO ₂ ), Sakai Chemical Industry's plate-like barium sulfate “H series (trade name)”, “HL series (trade name)”, Hayashi Kasei Co., Ltd. “micron white (trade name)” (talc), “Bengel (trade name)” (bentonite) manufactured by Hayashi Kasei Co., Ltd. “BMM (trade name)” or “BMT (trade name)” (boehmite) manufactured by Kawai Lime Co., Ltd. Name) ”[Alumina (Al ₂ O ₃ )],“ Seraph (trade name) ”(alumina) manufactured by Kinsei Matec Co., Ltd.,“ Yodogawa Mica Z-20 (trade name) ”(sericite) manufactured by Yodogawa Mining Co., Ltd., etc. Is possible. In addition, SiO ₂ , Al ₂ O ₃ , ZrO ₂ , and CeO ₂ can be produced by the method disclosed in Japanese Patent Laid-Open No. 2003-206475.

  As a form in the case where the filler is a plate-like particle, the aspect ratio (ratio between the maximum length in the plate-like particle and the thickness of the plate-like particle) is preferably 5 or more, more preferably 10 or more, Is 100 or less, more preferably 50 or less. The aspect ratio of the plate-like particles referred to in the present specification is a value determined by image analysis of an image taken with a scanning electron microscope (SEM).

  Further, since the plate-like filler has a problem of being easily cracked by impact when it is thin, the average thickness is preferably 0.02 μm or more, and more preferably 0.05 μm or more. However, if the thickness of the plate-like filler is too large, the separator becomes thick, the discharge capacity is reduced, and the porous layer (B) is easily cracked during production of the electrochemical element, so the average thickness is , 0.7 μm or less is preferable, and 0.5 μm or less is more preferable.

  The average thickness of the plate-like filler is obtained as an average value (number average value) of 100 fillers by observing the cross section of the separator with an SEM.

Moreover, it is preferable that at least a part of the filler contained in the porous layer (II) is a fine particle having a secondary particle structure in which primary particles are aggregated. All of the filler may be fine particles having the secondary particle structure. When the porous layer (II) contains the filler having the secondary particle structure, it is possible to obtain the same heat shrinkage suppression effect and the dendrite short suppression effect as in the case of using the plate-like particles described above. Examples of the filler having the secondary particle structure include “Boehmite C06 (trade name)”, “Boehmite C20 (trade name)” (boehmite) manufactured by Daimei Chemical Co., Ltd., “ED-1 (trade name) manufactured by Yonesho Lime Industry Co., Ltd. ) ”(CaCO ₃ ), J. et al. M.M. Examples include “Zeolex 94HP (trade name)” (clay) manufactured by Huber.

  The average particle diameter of the filler relating to the porous layer (II) is, for example, preferably 0.01 μm or more, more preferably 0.1 μm or more, preferably 15 μm or less, more preferably 5 μm or less.

  The porous layer (II) includes a polyolefin having a melting point at a temperature lower than the peak top temperature of the first stress peak in the TD direction of the microporous film constituting the porous layer (I) measured by TMA. (Hereinafter referred to as “low melting point polyolefin”).

  As the low melting point polyolefin contained in the porous layer (II), those having a melting point, that is, a melting temperature measured by DSC of 90 ° C. or higher and 130 ° C. or lower in accordance with JIS K 7121 are preferable. Specific examples include low density polyethylene (LDPE), low molecular weight polyethylene, and ionomer.

  The low-melting-point polyolefin may be present in the porous layer (II) independently of the filler, for example, in a particulate form, and the porous layer (in a form covering a part or all of the surface of the filler ( II) may be present.

  When coating the filler with a low melting point polyolefin, melt the low melting point polyolefin or dissolve it in a solvent, add the filler to this, stir and mix, cool or remove the solvent, and then crush The method can be adopted.

  Alternatively, composite particles may be obtained by adsorbing or fixing low melting point polyolefin fine particles on the filler surface with high impact force, compression / shearing force, or the like. This composite particle formation may be performed dry or wet.

  When the low melting point polyolefin is used as the particles, the average particle diameter is preferably 1 μm or less, more preferably 0.5 μm or less, and preferably 0.1 μm or more.

  In the porous layer (II), the amount of the low melting point polyolefin is selected from the viewpoint of ensuring a good shutdown effect due to the use of the low melting point polyolefin in the entire volume of the constituent components of the porous layer (II) [porous layer (II The same applies to the content of each component of ] 5% by volume or more is preferable. However, if the amount of the low melting point polyolefin in the porous layer (II) is too large, the heat resistance strength of the porous layer (II) may be lowered. Therefore, the amount of the low melting point polyolefin in the porous layer (II) is preferably 30% by volume or less in the total volume of the constituent components of the porous layer (II).

  In the porous layer (II), the amount of the filler having a heat resistant temperature of 150 ° C. or higher is 50% by volume or more in the total volume of the constituent components of the porous layer (II), but 70% by volume or more. It is preferably 80% by volume or more, more preferably 90% by volume or more. By making the filler in the porous layer (II) high as described above, the occurrence of a short circuit due to direct contact between the positive electrode and the negative electrode when the electrochemical device becomes high temperature is further suppressed. Moreover, the thermal contraction of the whole separator can be suppressed satisfactorily. Moreover, it is preferable that the quantity of the filler whose heat-resistant temperature is 150 degreeC or more in porous layer (II) is 95 volume% or less in the whole volume of the structural component of porous layer (II).

  When plate-like particles are used as a filler having a heat-resistant temperature of 150 ° C. or higher, the presence form of the plate-like particles in the porous layer (II) is preferably such that the flat plate surface is substantially parallel to the separator surface, More specifically, the plate-like particles in the vicinity of the surface of the separator preferably have an average angle between the flat plate surface and the separator surface of 30 ° or less [most preferably, the average angle is 0 °, ie, the separator The plate-like flat surface in the vicinity of the surface is parallel to the separator surface]. Here, “near the surface” refers to a range of about 10% from the surface of the separator to the entire thickness. By increasing the orientation of the plate-like particles so that the existence form of the plate-like particles is in the state as described above, it becomes possible to exert the effect of suppressing the heat shrinkage of the porous layer (II) more strongly. In addition, internal short-circuiting that may be caused by lithium dendrite deposited on the electrode surface or protrusions of the active material on the electrode surface can be more effectively prevented. In addition, the presence form of the plate-like particles in the porous layer (II) can be grasped by observing the cross section of the separator with an SEM.

  The porous layer (II) preferably contains an organic binder in order to ensure the shape stability of the separator and to integrate the porous layer (II) and the porous layer (I). Examples of organic binders include ethylene-vinyl acetate copolymers (EVA, those having a structural unit derived from vinyl acetate of 20 to 35 mol%), ethylene-acrylic acid copolymers such as ethylene-ethyl acrylate copolymers, and fluorine-based binders. Rubber, styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), polyvinyl alcohol (PVA), polyvinyl butyral (PVB), polyvinyl pyrrolidone (PVP), cross-linked acrylic resin, polyurethane, epoxy resin, etc. 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, highly flexible binders such as EVA, ethylene-acrylic acid copolymer, fluorine-based rubber, and SBR are preferable. Specific examples of such highly flexible organic binders include “Evaflex Series (EVA)” from Mitsui DuPont Polychemical, EVA from Nihon Unicar, and “Evaflex-EEA Series (Ethylene) from Mitsui DuPont Polychemical. -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 for the porous layer (II), it can be used in the form of an emulsion dissolved or dispersed in the solvent for the composition for forming the porous layer (II) described later. Good.

  In the separator of the present invention, the thickness of the porous layer (II) [when the separator has a plurality of porous layers (II), the total thickness] is more effective for the above-described functions of the porous layer (II). From the viewpoint of increasing the capacity by suppressing the thickness of the entire separator while exhibiting it, it is preferably 10 to 35% of the thickness of the entire separator.

  In addition, the thickness of the entire separator of the present invention is preferably 10 μm or more from the viewpoint of more effectively exerting the original function of separating the separator between the positive electrode and the negative electrode, and the viewpoint of suppressing the thickness of the entire separator. Therefore, it is preferably 40 μm or less.

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

In the formula (1), m is the mass per unit area of the porous layer (I) (g / cm
² ) and t is the thickness (cm) of the porous layer (I), and the porosity (P) (%) of the porous layer (I) can also be obtained using the formula (1). . The porosity of the porous layer (I) determined by this method is preferably 30 to 70%.

Furthermore, in the formula (1), m is the mass per unit area (g / cm ² ) of the porous layer (II), and t is the thickness (cm) of the porous layer (II), The porosity: P (%) of the porous layer (II) can also be obtained using the formula (1). The porosity of the porous layer (II) obtained by this method is preferably 20 to 60%.

  The separator of the present invention includes, for example, a porous layer (II) -forming composition (such as a liquid composition such as a slurry) containing a filler having a heat resistant temperature of 150 ° C. or higher, a low-melting-point polyolefin, and the like. ) To form a porous layer (II) by applying to the surface of a microporous film for forming a porous layer (II) and drying to a predetermined temperature.

  The composition for forming the porous layer (II) contains an organic binder or the like, if necessary, in addition to a filler having a heat resistant temperature of 150 ° C. or higher and a low melting point polyolefin, and these include a solvent (including a dispersion medium. ). The organic binder can be dissolved in a solvent. The solvent used in the composition for forming the porous layer (II) is not particularly limited as long as it can uniformly disperse the filler and can uniformly dissolve or disperse the organic binder. Common organic solvents such as furans such as hydrogen and tetrahydrofuran, and ketones such as methyl ethyl ketone and methyl isobutyl ketone are preferably used. In addition, for the purpose of controlling the interfacial tension, 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 composition for forming the porous layer (II) preferably has a solid content containing, for example, a filler having a heat resistant temperature of 150 ° C. or higher, a low melting point polyolefin, an organic binder, and the like, for example, 10 to 80% by mass.

  In addition, the porous layer (II) forming composition is applied onto a substrate such as a film or a metal foil, dried at a predetermined temperature, and then peeled off from the substrate as necessary to form the porous layer (II). It is also possible to manufacture a separator by forming a porous film, and bonding the porous film and a microporous film for forming the porous layer (I) together. In this case, in order to integrate the microporous membrane for forming the porous layer (I) and the porous membrane to be the porous layer (II), for example, the porous layer (I) and the porous layer ( It is possible to use a method of superimposing II) and pasting them together using a roll press or the like.

  In the separator of the present invention, the porous layer (I) and the porous layer (II) do not have to be one each, and a plurality of layers may be present in the separator. For example, a configuration in which the porous layer (I) is disposed on both sides of the porous layer (II) or a configuration in which the porous layer (II) is disposed on both sides of the porous layer (I) may be employed. However, increasing the number of layers may increase the thickness of the separator and increase the internal resistance of the battery or decrease the energy density. Therefore, it is not preferable to increase the number of layers, and the porous layer in the separator is not preferable. The total number of layers (I) and porous layer (II) is preferably 5 or less.

  The electrochemical device of the present invention only needs to be provided with the separator of the present invention, and the same configuration and structure as those of conventionally known electrochemical devices can be applied to other configurations and structures.

  The electrochemical device of the present invention is not particularly limited, and includes lithium secondary batteries using non-aqueous electrolytes, lithium primary batteries, supercapacitors, etc., and particularly requires safety at high temperatures. If it is a use used, it can apply preferably. Hereinafter, the case where the electrochemical device of the present invention is a lithium secondary battery will be described in detail.

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

  The lithium secondary battery preferably has a mechanism for discharging the gas inside the battery to the outside when the temperature rises. As such a mechanism, a conventionally known mechanism can be used. In other words, in batteries that use metal cans such as steel cans and aluminum cans as outer cans, metal cleavage vents that crack at a certain pressure, resin vents that break at a certain pressure, and rubber that opens a lid at a certain pressure A vent made of metal or the like can be used, and among them, a metal cleavage vent is preferably used.

  On the other hand, in a soft package battery, since the sealing part is sealed by heat sealing of the resin, it is difficult to make a structure that can withstand such high temperature and high pressure when the temperature and internal pressure rise in the first place. Even if a mechanism is not provided, the gas inside the battery can be discharged to the outside when the temperature rises. That is, in the soft package battery, the sealing portion (heat fusion portion) of the outer package acts as a mechanism for discharging the gas inside the battery to the outside. In the case of a soft package battery, the gas inside the battery can be discharged to the outside when the temperature rises even by a method such as narrowing the width of the sealing portion only at a specific location (that is, The specific place acts as a mechanism for discharging the gas inside the battery to the outside).

  The negative electrode of the lithium secondary battery is not particularly limited as long as it is a negative electrode used in a conventionally known lithium secondary battery, that is, a negative electrode containing an active material capable of occluding and releasing Li (lithium) ions. Absent. For example, carbon that can occlude and release lithium, such as graphite, pyrolytic carbons, cokes, glassy carbons, fired organic polymer compounds, mesocarbon microbeads (MCMB), and carbon fibers as active materials One type or a mixture of two or more types of system materials is used. In addition, elements such as Si, Sn, Ge, Bi, Sb and In and alloys thereof, lithium-containing nitrides, oxides and other compounds that can be charged and discharged at a low voltage close to lithium metal, or lithium metals and lithium / aluminum alloys Can also be used as a negative electrode active material. A negative electrode mixture obtained by appropriately adding a conductive additive (carbon material such as carbon black) or a binder such as PVDF to these negative electrode active materials, and a molded body (negative electrode mixture layer) using a current collector as a core material And those having a negative electrode agent layer such as those obtained by using the above-mentioned various alloys and lithium metal foils alone or those obtained by forming the alloy or lithium metal layer on a current collector.

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

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

The positive electrode is not particularly limited as long as it is a positive electrode used in a conventionally known lithium secondary battery, that is, a positive electrode containing an active material capable of occluding and releasing Li ions. For example, as the active material, Li _{1 + x} MO ₂ (−0.1 <x <0.1, M: Co, Ni, Mn, Al, Mg, etc. Note that the element M is a metal element other than Li and is 10 atoms. A lithium-containing transition metal oxide having a layered structure represented by the following formula: LiMn ₂ O ₄ and a lithium manganese oxide having a spinel structure in which a part of the element is substituted with another element, LiMPO ₄ An olivine type compound represented by (M: Co, Ni, Mn, Fe, etc.) can be used. Specific examples of the lithium-containing transition metal oxide having a layered structure include LiCoO ₂ and LiNi _1-x Co _xy Al _y O ₂ (0.1 ≦ x ≦ 0.3, 0.01 ≦ y ≦ 0. 2) and other oxides containing at least Co, Ni and Mn (LiMn _1/3 Ni _1/3 Co _1/3 O ₂ , LiMn _5/12 Ni _5/12 Co _1/6 O ₂ , LiNi _{3 / 5} Mn _1/5 Co _1/5 O ₂ etc.). In particular, an active material containing 40% or more of Ni is preferable because the battery has a high capacity, and O (oxygen atom) may be substituted with 1 atom% of fluorine or sulfur atom.

  A carbon material such as carbon black is used as the conductive aid, and a fluororesin such as polyvinylidene fluoride (PVDF) is used as the binder. The positive electrode mixture is a mixture of these materials and an active material. The agent layer is formed, for example, on one side or both sides of the current collector.

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

  Similarly to the lead part of the negative electrode, the lead part on the positive electrode side usually leaves an exposed part of the current collector without forming a positive electrode mixture layer on a part of the current collector during the preparation of the positive electrode, To be provided. 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 electrode is used in the form of a wound electrode body in which the positive electrode and the negative electrode are laminated via the separator of the present invention and further wound.

  In forming the electrode body, it is preferable to arrange the separator so that the porous layer (I) faces the negative electrode. Although the detailed reason is unknown, in the case where the separator is arranged so that the porous layer (I) faces at least the negative electrode, in the case where the shutdown occurs than when the separator is arranged so as to face the positive electrode, Of the molten resin from the porous layer (I), the proportion absorbed by the electrode mixture layer (positive electrode mixture layer or negative electrode mixture layer) decreases, and the molten resin closes the pores of the separator. Since it is used more effectively, the effect of the shutdown becomes better.

  In addition, for example, when a lithium secondary battery has a mechanism that lowers the internal pressure of the battery by discharging the gas inside the battery to the outside when the internal pressure of the battery increases due to temperature rise, There is a possibility that the internal non-aqueous electrolyte volatilizes and the electrode is directly exposed to air. When the battery is in a charged state, when the negative electrode and air (oxygen or moisture) come into contact, Li ions occluded in the negative electrode, lithium deposited on the negative electrode surface, and air react to generate heat. And sometimes it catches fire. Moreover, the temperature of the battery rises due to this heat generation, causing a thermal runaway reaction of the positive electrode active material, and as a result, the battery may ignite.

  However, in the case of a battery configured such that the porous layer (I) mainly composed of a thermoplastic resin faces the negative electrode, the thermoplastic resin that is the main component of the porous layer (I) is melted at a high temperature and the negative electrode Since the surface is covered, the reaction between the negative electrode and air accompanying the operation of the mechanism for discharging the gas inside the battery to the outside can be suppressed. Therefore, there is no fear of heat generation due to the operation of the mechanism for discharging the gas inside the battery to the outside, and the battery can be kept safer.

  In addition, in lithium secondary batteries, various additives (eg, cyclohexylbenzene, vinylene carbonate, etc.) are used to ensure safety during overcharge and stable storage characteristics at high temperatures (mainly prevention of blistering of the exterior body). ) May be added to the non-aqueous electrolyte. Originally, these additives can be effective when exposed to an abnormal environment such as a high voltage or high temperature, but side reactions such as polymerization of the additive even under normal use environments. May occur. In particular, the above-mentioned side reaction often occurs on the positive electrode side that is often exposed to a high voltage. For example, when cyclohexylbenzene is polymerized on the positive electrode side, the separator is clogged and the impedance of the battery increases. Such a problem may occur. In particular, when the pore diameter of the separator is small, it is easily affected by such clogging.

  When the microporous membrane constituting the porous layer (I) related to the separator is porous by the stretch opening method (that is, manufactured by the dry uniaxial stretch method), the pore size control of the microporous membrane is It is difficult, and there is a limit in making it especially a large hole diameter. Therefore, when the battery is configured by arranging the separator so that the porous layer (I) is on the positive electrode side, when the non-aqueous electrolyte contains the additive, the pores of the separator due to the side reaction described above. The problem of clogging is noticeable. Therefore, in the lithium secondary battery of the present invention, particularly when a non-aqueous electrolyte containing the above-described additive is used, the separator is such that the relatively porous porous layer (II) is on the positive electrode side. It is more preferable to dispose the above, and thereby the clogging can be suppressed.

  Furthermore, since the porous layer (II) contains the filler as a main component, the oxidation resistance is superior to the porous layer (I). Therefore, by directing the porous layer (II) to the positive electrode side, Oxidation of the separator by the positive electrode can be suppressed more favorably, and a battery having further excellent storage characteristics at high temperatures and charge / discharge cycle characteristics can be obtained. For this reason, in the electrochemical device of the present invention, it is more preferable that the porous layer (II) is directed to the positive electrode side even when the non-aqueous electrolyte does not contain the additive.

  Therefore, in the case of a separator having a porous layer (I) mainly composed of a thermoplastic resin or a plurality of porous layers (II), the negative electrode side is the porous layer (I) and the positive electrode side is the porous layer (II). More preferably, the separator is configured as described above.

As the nonaqueous electrolytic solution according to the present invention, a solution in which a lithium salt is dissolved in an organic solvent is used. The lithium salt is not particularly limited as long as it dissociates in a solvent to form Li ⁺ ions and hardly causes side reactions such as decomposition in a voltage range used as a battery. For example, LiClO ₄ , LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiSbF ₆ and other inorganic lithium salts, LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , Li ₂ C ₂ F ₄ (SO ₃ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiC _n F _{2n + 1} SO ₃ (n ≧ 2), LiN (RfOSO ₂ ) ₂ [where Rf is a fluoroalkyl group] and the like can be used. .

  The organic solvent used 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, cyclohexyl benzene, biphenyl, fluorobenzene, t are used for the purpose of improving safety, charge / discharge cycleability, and high-temperature storage properties of these electrolytes. -Additives such as butylbenzene may be added as appropriate.

  The concentration of the lithium salt in the electrolytic solution is preferably 0.5 to 1.5 mol / l, and more preferably 0.9 to 1.25 mol / l.

  The electrochemical element of the present invention can be preferably used for the same applications as various applications to which electrochemical elements such as conventionally known lithium secondary batteries are applied.

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

Example 1
As a microporous film for constituting the porous layer (I), a microporous film for PE battery (thickness 12 μm, porosity 40%) was prepared. In addition, about this PE battery microporous film, the peak top temperature of the first stress peak in the TD direction measured by the said method was 131 degreeC.

  Emulsion of SBR as an organic binder (solid content ratio 40 mass%): 100 g and dispersion of ionomer fine particles as a low melting polyolefin (melting point 100 ° C., primary particle diameter 0.1 μm, solid content ratio 27 mass%): 100 g And 6000 g of water were placed in a container and stirred at room temperature until evenly dispersed.

  Boehmite powder (plate shape, average particle size 1 μm, aspect ratio 10): 2000 g, which is a filler having a heat resistance temperature of 150 ° C. or higher, was added to this dispersion in 4 portions, and the mixture was uniformly stirred at 2800 rpm for 5 hours with a disper. A slurry [a slurry for forming a porous layer (II), a solid content ratio of 25.3 mass%] was prepared. The slurry was applied to one side of the microporous membrane made of PE with a microgravure coater and dried to form a porous layer (II) having a thickness of 2.6 μm to obtain a separator.

Example 2
LDPE (melting point: 110 ° C., primary particle size: 6 μm) (600 g) was melted at 120 ° C., and boehmite powder (granular, average particle size: 0.6 μm) was added to 2000 g, mixed, cooled, and pre-ground by a stamp mill. This was further crushed by a wet bead mill to prepare a PE-coated filler having an average particle size of 1.1 μm.

  An organic binder SBR emulsion (solid content ratio 40% by mass): 100 g and water: 6000 g were placed in a container and stirred at room temperature until evenly dispersed. To this dispersion, the PE-coated filler: 2000 g was added in 4 portions, and stirred with a disper at 2800 rpm for 5 hours to obtain a uniform slurry [porous layer (II) forming slurry, solid content ratio of 25.3 mass%] Was prepared. The slurry is applied to one side of the same microporous membrane made of PE as used in Example 1 by a micro gravure coater and dried to form a porous layer (II) having a thickness of 3.6 μm, and a separator is formed. Obtained.

Comparative Example 1
A slurry for forming a porous layer (II) was prepared in the same manner as in Example 1 except that no dispersion of ionomer fine particles was used, and the thickness was 2 as in Example 1 except that this was used. A separator having a porous layer (II) of 6 μm was produced.

  The separators of Examples 1 and 2 and Comparative Example 1 were evaluated as follows. These results are shown in Table 1.

<Measurement of air permeability increase rate>
The separators of Examples 1 and 2 and Comparative Example 1 were each cut out to 10 × 10 cm and left in a thermostatic bath at 130 ° C. for 1 hour. After taking out from the thermostat, the air permeability (Gurley type air permeability meter based on JIS P 8117) was measured. The rate of increase in air permeability was calculated by the following formula from values before and after being left in a thermostatic bath.
Air permeability increase rate (%)
= 100 × (air permeability after leaving at 130 ° C. for 1 hour) / (air permeability before introduction into constant temperature bath)

<Measurement of thermal shrinkage>
The separators of Examples 1 and 2 and Comparative Example 1 were each cut into 10 × 10 cm, placed in a commercially available envelope, and left in a thermostat set at 130 ° C. for 1 hour. Then, each separator is taken out from the thermostat, and the dimension in the TD direction of the microporous membrane constituting the porous layer (I) is measured. From these values and the dimensions before being left in the thermostat, Shrinkage was calculated.
Thermal contraction rate (%) = 100 × (10−x) / 10
[In the above formula, x is the dimension (cm) in the TD direction of the microporous film constituting the porous layer (I) in the separator after being left in a thermostat set at 130 ° C. for 1 hour. ]

  As is apparent from Table 1, the rate of increase in air permeability after standing for 1 hour at 130 ° C. is 124% for the separator of Comparative Example 1, whereas it is significantly increased for the separators of Examples 1 and 2. Suggests that a good shutdown has occurred. The separators of Examples 1 and 2 and Comparative Example 1 all had a heat shrinkage rate of 1% or less after being left at 130 ° C. for 1 hour, and the heat of the entire separator due to the action of the porous layer (II). Shrinkage is well suppressed.

  That is, from the results of the heat shrinkage rate after standing at 130 ° C. for 1 hour, the separators of Examples 1 and 2 and Comparative Example 1 are all difficult to heat shrink and can constitute a highly safe electrochemical element. However, from the results of the rate of increase in air permeability, the separators of Examples 1 and 2 can start shutdown earlier than the separator of Comparative Example 1, and are more safe than the separator of Comparative Example 1. It can be confirmed that the separator can constitute a high electrochemical element.

Claims (8)

A porous layer comprising a microporous film mainly composed of a thermoplastic resin and having a MD direction and a TD direction, which is used for the separator of an electrochemical element having a wound electrode body in which a positive electrode, a negative electrode, and a separator are wound in layers. A separator for an electrochemical device having (I) and a porous layer (II) mainly comprising a filler having a heat resistant temperature of 150 ° C. or higher,
The separator for electrochemical elements is arranged so that its TD direction is a direction orthogonal to the winding direction of the wound electrode body,
The porous layer (II) is obtained from a temperature-stress curve obtained when the temperature is increased from room temperature to 200 ° C. at a temperature increase rate of 5 ° C./min as measured by thermomechanical analysis. A separator for an electrochemical element, comprising a polyolefin having a melting point at a temperature lower than the peak top temperature of the first stress peak in the TD direction of the microporous film constituting I).   The separator for an electrochemical element according to claim 1, wherein the content ratio of the polyolefin in the porous layer (II) is 5% by volume or more in the total volume of the constituent components of the porous layer (II).   The separator for an electrochemical element according to claim 1 or 2, wherein at least a part of the filler contained in the porous layer (II) is a plate-like particle.   The separator for an electrochemical element according to any one of claims 1 to 3, wherein at least a part of the filler contained in the porous layer (II) has a secondary particle structure in which primary particles are aggregated.   The separator for an electrochemical element according to any one of claims 1 to 4, wherein the filler contained in the porous layer (II) is at least one kind of particles selected from the group consisting of alumina, silica and boehmite.   The separator for an electrochemical element according to any one of claims 1 to 5, wherein the polyolefin contained in the porous layer (II) is in the form of particles.   The separator for an electrochemical element according to any one of claims 1 to 6, wherein a melting point of the thermoplastic resin contained in the porous layer (I) is 110 to 150 ° C. An electrochemical element having a wound electrode body in which a positive electrode, a negative electrode, and a separator are stacked and wound, and a non-aqueous electrolyte,
Said separator, Ri Oh in separator for an electrochemical device according to any one of claims 1 to 7, TD direction of the separator, arranged such that the direction orthogonal to the winding direction of the wound electrode body electrochemical device characterized Tei Rukoto.