JP2011146365A - Electrochemical element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrochemical element which exhibits excellent charge characteristics at low temperature, and good productivity. <P>SOLUTION: The electrochemical element includes a positive electrode, a negative electrode, a nonaqueous electrolyte, and a separator. The negative electrode includes a negative electrode mixture layer containing negative electrode active material on one surface or both surfaces of a collector. The separator includes a porous layer (I) formed of a fine porous film mainly containing thermoplastic resin, and a porous layer (II) mainly containing a filler of which a heat resistant temperature is 150°C or higher. The above problem is solved by the electrochemical element which is characterized in that a ratio Ra/Tb of an arithmetic average roughness Ra(μm) of a surface of the negative electrode mixture layer and a thickness Tb(μm) of the porous layer (II) is 0.10-0.27. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an electrochemical device excellent in production stability and charging characteristics at a low temperature.

  A lithium secondary battery, which is one type of electrochemical element, is widely used as a power source for portable devices such as mobile phones and notebook personal computers because of its high energy density. In addition, due to consideration of environmental issues, the importance of rechargeable secondary batteries is increasing, and in addition to portable devices, they can be applied to automobiles, electric tools, electric chairs, household and commercial power storage systems. Is being considered.

  As described above, there are a wide variety of characteristics required for batteries, and various measures are required depending on applications. For example, higher energy density for longer usage time, higher energy density when using at high current, and shorter charging time (ie, further improvement of input / output characteristics for adapting to high load equipment) ) Is required. Furthermore, considering that it is used under various temperature environments, it is required to have charging characteristics that do not hinder practical use even at low temperatures at which the reactivity of the electrochemical element decreases.

  Many electrode active materials have been proposed to meet such demands. For example, in the case of a negative electrode active material, alloy-based, oxide-based, nitride-based, and carbon materials include high graphite crystalline natural graphite and Artificial graphite and high aspect ratio carbon fibers are widely studied. In addition, composite materials having improved large current load characteristics by providing an amorphous or low crystal carbon coating layer on the surface of graphite particles have been proposed (see Patent Documents 1 to 4).

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

  For such a separator, for example, a uniaxially stretched film or a biaxially stretched film is used to increase the porosity and strength. Since such a separator is supplied as a single film, a certain strength is required in terms of workability and the like, and this is secured by the stretching. However, with such a stretched film, the degree of crystallinity has increased, and the shutdown temperature has increased to a temperature close to the thermal runaway temperature of the battery. Therefore, it can be said that the margin for ensuring the safety of the battery is sufficient. hard.

  In addition, the film is distorted by the stretching, and there is a problem that when it is exposed to a high temperature, shrinkage occurs due to residual stress. The shrinkage temperature is very close to the melting point, ie the shutdown temperature. For this reason, when using a polyolefin-based microporous membrane separator, if the battery temperature reaches the shutdown temperature in the event of abnormal charging, the current must be immediately reduced to prevent the battery temperature from rising. This is because if the pores are not sufficiently closed and the current cannot be reduced immediately, the temperature of the battery easily rises to the shrinkage temperature of the separator, and there is a risk of an internal short circuit.

  As a technique for preventing such a short circuit due to thermal contraction of the separator and 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 device by using a porous separator having a second separator layer containing mainly as a main component (Patent Document 5).

  If the separator described in Patent Document 5 is used and the carbon material described in Patent Documents 1 to 4 is used as a negative electrode active material, it is excellent in safety even during abnormal overheating, and further has high current load characteristics and low temperature characteristics. An excellent electrochemical device can be constructed.

JP-A-6-267531 Japanese Patent Laid-Open No. 10-162858 JP 2002-42887 A JP 2003-168429 A International Publication No. 2007/66768

  However, in the negative electrode configured using the carbon material described above, the surface of the negative electrode mixture layer may be rough and uneven. When a wound body is formed using such a negative electrode, a positive electrode, and a separator, when a polyolefin microporous membrane separator is used, the convex portion of the negative electrode is difficult to separate, and the distance between the positive electrode and the positive electrode is partially This may lead to a decrease in charge / discharge cycle characteristics or a problem in safety.

  In the case of the separator described in Patent Document 5, for example, the problem due to the convex portion of the negative electrode as described above due to the action of the filler related to the second separator layer formed on the surface of the first separator layer that can be configured with a microporous film. However, there is also a need for further improvement in battery reliability (including productivity in the inspection process, which is an indicator).

  This invention is made | formed in view of the said situation, The objective is to provide the electrochemical element which is excellent in the charge characteristic in low temperature, and favorable productivity.

  The electrochemical element of the present invention that has achieved the above object is an electrochemical element having a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator, wherein the negative electrode has a negative electrode active material on one or both sides of a current collector. The separator includes a porous layer (I) composed of a microporous film mainly composed of a thermoplastic resin, and a porous layer mainly composed of a filler having a heat resistant temperature of 150 ° C. or higher. (II), and the ratio Ra / Tb between the arithmetic average roughness Ra (μm) of the surface of the negative electrode mixture layer and the thickness Tb (μm) of the porous layer (II) is 0.8. It is characterized by being 10 to 0.27.

  Except for the porous substrate described later, “heat-resistant temperature is 150 ° C. or higher” in this specification means that deformation such as softening is not observed at least at 150 ° C.

  The term “mainly comprising a thermoplastic resin” in the porous layer (I) in the present specification is a solid content ratio in the porous layer (I), and the thermoplastic resin is 50% by volume or more. Means. Furthermore, in the porous layer (II) in the present specification, “mainly containing a filler having a heat resistant temperature of 150 ° C. or higher” means a solid content ratio in the layer (however, in the case of having a porous substrate described later) The solid content ratio excluding the porous substrate) means that the filler having a heat resistant temperature of 150 ° C. or higher is 50% by volume or higher.

  ADVANTAGE OF THE INVENTION According to this invention, the electrochemical element which is excellent in the charge characteristic in low temperature (for example, low temperature below 0 degreeC), and favorable productivity can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows typically an example of the electrochemical element (lithium secondary battery) of this invention, (a) is the top view, (b) is the fragmentary longitudinal cross-sectional view. It is a perspective view of the electrochemical element (lithium secondary battery) shown in FIG.

  The electrochemical device of the present invention includes a negative electrode having a negative electrode mixture layer containing a negative electrode active material on one or both sides of a current collector, and a porous layer (I) comprising a microporous film mainly composed of a thermoplastic resin, A separator having a porous layer (II) mainly containing a filler having a heat-resistant temperature of 150 ° C. or higher, an arithmetic average roughness Ra (μm) of the negative electrode mixture layer surface, and a porous layer ( The ratio Ra / Tb to the thickness Tb (μm) of II) is 0.10 or more and 0.27 or less.

  The arithmetic average roughness Ra of the negative electrode mixture layer surface of the negative electrode according to the present invention is the arithmetic average roughness specified in JIS B 0601. Specifically, a confocal laser microscope (manufactured by Lasertec Corporation, “ This is a numerical value obtained by measuring a 1 mm × 1 mm field of view with 512 × 512 pixels using an real-time scanning laser microscope 1LM-21D ”) and arithmetically averaging the absolute values from the average line of each point.

  Examples of the negative electrode active material that is a main component forming the negative electrode mixture layer of the negative electrode according to the present invention include metals such as lithium and alloys, metal oxides, metal nitrides, and carbonaceous materials such as graphite. Among these, high graphite crystalline natural graphite, artificial graphite, and high aspect ratio carbon fiber are preferable because of their high reversible capacity and high conductivity. However, in the natural graphite, artificial graphite, and high aspect ratio carbon fibers, many bulky materials are seen. When a negative electrode mixture layer is formed on the surface of the current collector by the method described later, the surface is May be rough. Furthermore, the carbon material provided with an amorphous or low crystalline carbon coating layer on the surface of the graphite particles has characteristics such as high load characteristics and particularly excellent charging characteristics at low temperatures, but the surface tends to be hard. When the negative electrode mixture layer is formed using such a material, the arithmetic average roughness Ra of the surface is often roughened to, for example, about 0.3 to 1.2 μm.

  When the negative electrode having the surface property as described above is used and a spirally wound electrode body is produced by overlapping with the positive electrode and the separator, a convex portion on the negative electrode surface is formed particularly when a polyolefin-based microporous membrane separator is used. The separator may be difficult to insert, and the distance between the positive electrode and the electrode may be partially reduced, which may cause deterioration of charge / discharge cycle characteristics of the battery and may cause a problem in safety.

  As a result of intensive studies, the present inventors have determined that a porous layer (I) composed of a microporous film mainly composed of a thermoplastic resin and a porous layer (II) mainly composed of a filler having a heat resistant temperature of 150 ° C. or higher. Ra / Tb which is the ratio of the thickness Tb (μm) of the porous layer (II) and the arithmetic average roughness Ra (μm) of the negative electrode mixture layer surface is within the above range. By adjusting, it discovered that a high electrochemical characteristic and safety | security could be ensured, and came to complete this invention.

Among the negative electrode active materials according to the battery of the present invention, the above-described amorphous or low-crystalline carbon coating layer is provided on the surface of the graphite particles as a material capable of particularly improving charging characteristics at a low temperature (0 ° C. or lower). and carbon materials are preferred, as such carbon materials, R value is the peak intensity ratio of 1360 cm ^-1 to the peak intensity of 1580 cm ^-1 in the argon ion laser Raman spectrum _(I 1360 _/ I ₁₅₈₀₎ of 0.1 For example, graphite having a surface spacing d _{002 of} 002 plane of 0.338 nm or less is 0.5 or less.

  The R value can be obtained from a Raman spectrum obtained using an argon laser having a wavelength of 514.5 nm [for example, “T-5400” (Laser power: 1 mW) manufactured by Ramanaor Inc.].

The graphite whose R value and d ₀₀₂ satisfy the above values has an average particle diameter D50% (particle diameter at a volume-based cumulative fraction of 50%. The same as in the case of measuring the average particle diameter of the filler according to the separator described later. It is preferably 10 μm or more, and preferably 30 μm or less. Further, the specific surface area of the graphite (according to the BET method. An example of the apparatus is “Bell Soap Mini” manufactured by Nippon Bell Co., Ltd.) is preferably 1.0 m ² / g or more, and 5.0 m ² / g. The following is preferable.

The graphite satisfying the R value and d ₀₀₂ satisfies the above values, for example, a natural graphite having d ₀₀₂ of 0.338 nm or less or graphite obtained by spherically shaping artificial graphite, and the surface thereof is coated with an organic compound. And after baking at 800-1500 degreeC, it can grind | pulverize and it can obtain by sizing through a sieve. The organic compound covering the base material includes aromatic hydrocarbons; tars or pitches obtained by polycondensation of aromatic hydrocarbons under heat and pressure; tars mainly composed of a mixture of aromatic hydrocarbons. , Pitch or asphalt; In order to coat the base material with the organic compound, a method of impregnating and kneading the base material into the organic compound can be employed. Also, the R value and d ₀₀₂ satisfy the above values by a vapor phase method in which hydrocarbon gas such as propane or acetylene is carbonized by pyrolysis and deposited on the surface of graphite having d ₀₀₂ of 0.338 nm or less. Graphite can be produced.

R value is the peak intensity ratio of 1360 cm ^-1 to the peak intensity of 1580 cm ^-1 in the argon ion laser Raman spectrum _(I 1360 _/ I ₁₅₈₀₎ is 0.1 or more and 0.5 or less, the surface of 002 plane spacing _{d 002} In the case of using graphite having a thickness of 0.338 nm or less, from the viewpoint of further improving the low temperature characteristics of the battery, it is preferable to use such graphite in a proportion of 30% by mass or more in the total amount of the negative electrode active material, 80% by mass It is more preferable to use it in the above proportion (100% by mass, that is, only the graphite may be used for the negative electrode active material).

  When other negative electrode active materials are used together with the graphite, examples of such negative electrode active materials include graphite having an R value of less than 0.1 (graphite having high surface crystallinity), pyrolytic carbons, coke, and the like. Carbon materials that can occlude and release Li ions, such as carbonaceous materials, glassy carbons, fired bodies of organic polymer compounds, mesocarbon microbeads (MCMB), and carbon fibers.

In order to improve the low-temperature charging characteristics of the electrochemical element, it is preferable to use propylene carbonate as a solvent for the non-aqueous electrolyte. However, among the carbon materials used as the negative electrode active material, the crystallinity is higher. At low values, the resistance to propylene carbonate is high. Therefore, for example, when a carbon material having low crystallinity and higher resistance to propylene carbonate is used as compared with natural graphite or artificial graphite having an R value of less than 0.1, it relates to the electrochemical element together with the negative electrode. Since the non-aqueous electrolyte can also be configured to enhance the charging characteristics at a lower temperature, a further improvement effect of the charging characteristics at a low temperature can be expected. Have low crystallinity, the higher the carbon material resistant to propylene carbonate, carbon fibers having a high aspect ratio, R value and d ₀₀₂ and the graphite can be mentioned that satisfy the values of defined, R value and d ₀₀₂ is the The graphite satisfying the following value is particularly preferable. In addition, as an aspect-ratio (ratio of length and diameter) which concerns on the high aspect-ratio carbon fiber, 3-20 are preferable, for example.

  In addition to the negative electrode active material, the negative electrode mixture layer includes a binder such as polyvinylidene fluoride, and a conductive additive used as necessary (for example, a carbon material such as carbon black). Depending on the agent, it can be formed on one or both sides of the negative electrode current collector. The thickness of the negative electrode mixture layer is preferably 10 to 100 μm per one side of the current collector.

  As the negative electrode current collector, a copper or nickel foil, a punching metal, a net, an expanded metal, or the like can be used, but a copper foil is usually used. In the negative electrode current collector, when the thickness of the whole negative electrode is reduced in order to obtain an electrochemical element 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 separator used in the electrochemical device of the present invention includes a porous layer (I) composed of a microporous film mainly composed of a thermoplastic resin, and a porous porous layer mainly composed of a filler having a heat resistant temperature of 150 ° C. or higher. (II).

  The porous layer (I) related to the separator is mainly for ensuring a shutdown function. When the temperature of the electrochemical element of the present invention reaches or exceeds the melting point of a thermoplastic resin [hereinafter referred to as resin (A)], which is a main component of the porous layer (I), the porous layer (I) The resin (A) melts and closes the pores of the separator, thereby causing a shutdown that suppresses the progress of the electrochemical reaction.

  In addition, the porous layer (II) according to the separator has a function of preventing a short circuit due to direct contact between the positive electrode and the negative electrode even when the internal temperature of the electrochemical element rises, and has a heat resistant temperature of 150. Its function is ensured by a plate-like filler having a temperature of ℃ or higher. That is, when the electrochemical device is at a high temperature, the positive and negative electrodes that 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. In the case where the porous layer (I) and the porous layer (II) are integrated as described later, the heat-resistant porous layer (II) acts as a skeleton of the separator, The thermal contraction of the layer (I), that is, the thermal contraction of the entire separator is suppressed.

  The resin (A) relating to the porous layer (I) of the separator has an electrical insulation property, is electrochemically stable, and further has a non-aqueous electrolyte (hereinafter referred to as “electrochemical solution”) included in an electrochemical element described in detail later. There is no particular limitation as long as it is a thermoplastic resin that is stable to a solvent used in the manufacture of the separator (details will be described later), but polyethylene (PE), polypropylene (PP ), Polyolefins such as ethylene-propylene copolymers; polyesters such as polyethylene terephthalate and copolymerized polyesters;

  In addition, it is preferable that a separator has the property (namely, shutdown function) which the hole obstruct | occludes in 80 degreeC or more and 150 degrees C or less (more preferably 100 degreeC or more). Therefore, the porous film (I) has a melting point, that is, a melting temperature measured using a differential scanning calorimeter (DSC) in accordance with JIS K 7121, preferably 80 ° C. or higher and 150 ° C. or lower (more preferably (100 ° C. or higher) thermoplastic resin having a constituent component thereof is more preferable, and it is a single layer microporous film mainly composed of PE or laminated microporous film in which 2 to 5 layers of PE and PP are laminated. A film or the like is preferable.

When the porous layer (I) is composed of a thermoplastic resin having a melting point of 80 ° 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 membrane composed of a mixture of 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. When the laminated microporous membrane constituted by laminating the layers constituted by the above is used as the porous layer (I), the melting point of the resin (A) constituting the porous layer (I) is 80 ° C. The resin (for example, PE) having a temperature of 150 ° C. or less is preferably 30% by mass or more, and more preferably 50% by mass or more.

  Examples of the microporous membrane as described above include a microporous membrane composed of the above-described exemplary thermoplastic resin used in, for example, a conventionally known lithium secondary battery, that is, a solvent extraction method, a dry or wet stretching method. An ion-permeable microporous membrane produced by the above 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 not impairing the action of imparting a 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 (plate-like filler having a heat-resistant temperature of 150 ° C. or higher, and fillers having other shapes). Things.

  The particle diameter of the filler is an average particle diameter, 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. The average particle diameter of the filler referred to in the present specification is measured by, for example, using a laser scattering particle size distribution meter (for example, “LA-920” manufactured by HORIBA), dispersing these fine particles in a medium in which the filler is not dissolved. The same applies to the filler according to the porous layer (II) described later. ].

  By including the porous layer (I) having the above-described structure, it becomes easy to provide a shutdown function to the separator, and it is possible to easily achieve safety when the internal temperature of the electrochemical element rises. Become.

  The content of the resin (A) in the porous layer (I) is preferably, for example, as follows in order to make it easier to obtain the shutdown effect. The volume of the resin (A) 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 resin (A) is 50% or more of the pore volume of the porous layer (II). Preferably there is.

  The filler related to the porous layer (II) has a heat-resistant temperature of 150 ° C. or higher, is stable with respect to the electrolyte solution of the electrochemical device, and is electrochemically resistant to oxidation and reduction in the operating voltage range of the electrochemical device. Organic particles or inorganic particles may be used as long as they are stable, but fine particles are preferable from the viewpoint of dispersion and the like, and inorganic fine particles are more preferably used from the viewpoint of stability (particularly oxidation resistance).

  The filler is preferably plate-shaped. The porous layer (II) contains a plate-like filler, so that even when the negative electrode mixture layer is combined with a negative electrode having a rough surface, the productivity of the electrochemical element can be more effectively suppressed, and the porous layer ( Even when II) is integrated with the porous layer (I), the force that the porous membrane (I) contracts due to the collision between the plate-like fillers can be more favorably suppressed. Further, the use of the plate-like filler 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 Co., Ltd. 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. Among these, boehmite, alumina, and silica (SiO ₂ ) are preferable.

  As the form of the plate-like filler, the aspect ratio (ratio between the maximum length in the plate-like filler and the thickness of the plate-like filler) is preferably 5 or more, more preferably 10 or more, and preferably 100 or less. More preferably, it is 50 or less. The aspect ratio of the plate-like filler can be obtained by, for example, image analysis of an image taken with a scanning electron microscope (SEM).

  In addition, since the plate-like filler has a problem of being easily cracked by impact when the plate thickness 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 thickness of the separator is increased, the discharge capacity is reduced, and the porous layer (II) is liable to break during the production of the electrochemical element. The thickness is preferably 0.7 μm or less, and more preferably 0.5 μm or less.

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

  The porous layer (II) may contain a filler other than a plate shape (for example, a filler such as a sphere or a substantially sphere) together with the plate filler. The filler having a shape other than the plate shape preferably has a heat resistant temperature of 150 ° C. or higher as in the case of the plate filler, and examples thereof include inorganic particles or organic particles having such heat resistant temperature.

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 inorganic particles, when the electrochemical element is configured so that the porous layer (II) faces the positive electrode, its high temperature storage and charge / discharge cycle characteristics can be improved (details will be described later). The inorganic oxide particles (fine particles) are preferable, and alumina, silica, and boehmite are particularly preferably used.

  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, 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).

The porous layer (II) may contain fine particles having a secondary particle structure in which primary particles are aggregated together with the plate-like filler. The filler having the secondary particle structure also has the same heat shrinkage suppressing action as that of the plate-like filler and the action of suppressing dendrite shorts. 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.

  In addition, when the porous layer (II) also contains a filler having a shape other than a plate shape together with the plate-like filler, from the viewpoint of better securing the above-described effect due to the use of the plate-like filler. In the total amount of filler contained in the porous layer (II), the plate-like filler is preferably 80% by volume or more, and more preferably 90% by volume or more.

  If the average particle diameter of the filler having a heat resistant temperature of 150 ° C. or higher (the average particle diameter of the plate-like filler and other-shaped fillers; the same applies hereinafter) of the porous layer (II) is too small, the ion permeability decreases. Therefore, it is preferably 0.3 μm or more, more preferably 0.5 μm or more. Moreover, since an electrical characteristic will deteriorate easily when too large, the average particle diameter of the filler whose heat-resistant temperature is 150 degreeC or more becomes like this. Preferably it is 5 micrometers or less, More preferably, it is 2 micrometers or less.

  Amount of filler having a heat resistant temperature of 150 ° C. or higher in the porous layer (II) [when a filler having a shape other than a plate is used together with a plate filler, the total amount thereof. The same applies hereinafter for the amount of filler having a heat resistant temperature of 150 ° C. or higher in the porous layer (II). ] In the total volume of the constituent components of the porous layer (II) [However, in the case of using the porous substrate described later, in the total volume of the constituent components excluding the porous substrate. The same applies to the content of each component of the porous layer (II). ], 50% by volume or more, preferably 70% by volume or more, more preferably 80% by volume or more, and still more preferably 90% by volume or more. By making the content of 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 is at a high temperature is better suppressed. In particular, in the case of a separator having a configuration in which the porous layer (I) and the porous layer (II) are integrated, the thermal contraction of the entire separator can be satisfactorily suppressed.

  Moreover, the porous layer (II) binds fillers having a heat resistant temperature of 150 ° C. or higher, or binds the porous layer (I) and the porous layer (II) as necessary. For this reason, it is preferable to contain an organic binder. From such a viewpoint, the suitable upper limit of the filler amount having a heat resistant temperature of 150 ° C. or higher in the porous layer (II) is, for example, a constituent component of the porous layer (II). Is 99.5% by volume. If the amount of the filler having a heat resistant temperature of 150 ° C. or higher in the porous layer (II) is less than 70% by volume, for example, it is necessary to increase the amount of the organic binder in the porous layer (II). In the porous layer (II), the pores of the porous layer (II) are easily filled with an organic binder, and the function as a separator may be deteriorated. There is a possibility that the effect of suppressing the heat shrinkage may be reduced due to the excessively large interval.

  In the porous layer (II), the above plate-like fillers are laminated on their plate-like surfaces (if they are laminated in the thickness direction on a wide surface forming a flat plate, the horizontal positions of the upper and lower fillers are shifted from each other. The number of laminated plate-like fillers is preferably 5 or more, and more preferably 10 or more. In the porous layer (II) relating to the separator, the presence of the plate-like filler as described above can further increase the strength of the separator (for example, penetration strength measured by a measurement method described later). . However, if the number of laminated layers of the plate-like filler in the porous layer (II) is too large, the thickness of the porous layer (II) and thus the thickness of the separator is increased, and the energy density of the electrochemical device is decreased. There is a fear. Therefore, the number of laminated plate-like fillers in the porous layer (II) is preferably 50 or less, and more preferably 20 or less.

  The number of laminated plate-like fillers in the porous layer (II) is determined by the cross section polisher method, by cutting the separator with an argon ion laser beam under a reduced pressure atmosphere, and observing the cross section with an SEM. It is obtained by measuring. The place where the measurement is performed is arbitrary, but in the separator according to the present invention, the porous layer (II) when cut perpendicularly to the laminated surface of the porous layer (I) and the porous layer (II). In any of these locations, it is preferable to disperse the plate filler so that the number of laminated layers is 5 or more.

  Further, the presence form of the plate-like particles in the porous layer (II) of the plate-like filler is preferably such that the flat plate surface is substantially parallel to the surface of the separator. The plate-like filler in the vicinity of the surface preferably has an average angle between the flat plate surface and the separator surface of 30 ° or less [most preferably, the average angle is 0 °, that is, a plate shape in the vicinity of the separator surface. The flat plate 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 filler so that the form of the plate-like filler is in the state as described above, it becomes possible to exert the heat shrinkage suppressing action 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 said plate-shaped filler in porous layer (II) can be grasped | ascertained by observing the cross section of a separator by 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 Mitsui DuPont Polychemical's “Evaflex Series (EVA)”, Nihon Unicar's EVA, Mitsui DuPont Polychemical's “Evaflex-EAA Series (Ethylene). -Acrylic acid copolymer) ", Nippon Unicar EEA, Daikin Industries" DAI-EL Latex Series (Fluororubber) ", JSR" TRD-2001 (SBR) ", Nippon Zeon" BM-400B " (SBR) ".

  In addition, when using the said organic binder for porous layer (II), if it uses in the form of the emulsion dissolved or disperse | distributed to the solvent of the composition for porous layer (II) formation mentioned later. Good.

  In order to ensure the shape stability and flexibility of the separator, a fibrous material or the like may be mixed with the filler in the porous layer (II). The fibrous material has a heat-resistant temperature of 150 ° C. or higher, has an electrical insulation property, is electrochemically stable, and further uses an electrolyte solution described in detail below and a solvent used in manufacturing a separator. If it is stable, the material is not particularly limited. The “fibrous material” in the present specification means an aspect ratio [length in the longitudinal direction / width in the direction perpendicular to the longitudinal direction (diameter)] of 4 or more. The ratio is preferably 10 or more.

  Specific examples of the constituent material of the fibrous material include, for example, cellulose and modified products thereof [carboxymethylcellulose (CMC), hydroxypropylcellulose (HPC), etc.], polyolefin [polypropylene (PP), propylene copolymer, etc.], Polyester [polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polybutylene terephthalate (PBT), etc.], polyacrylonitrile (PAN), polyaramid, polyamideimide, polyimide, and other resins; glass, alumina, zirconia, silica, and other inorganic materials An oxide; etc. can be mentioned, and two or more of these constituent materials may be used in combination to form a fibrous material. The fibrous material may contain various known additives (for example, an antioxidant in the case of a resin) as necessary.

  In addition, the separator according to the present invention improves the handleability particularly when the porous layer (II) is used as an independent film without integrating the porous layer (I) and the porous layer (II). Therefore, a porous substrate can be used for the porous layer (II). The porous substrate has a heat resistant temperature of 150 ° C. or more formed by forming a sheet-like material such as a woven fabric or a nonwoven fabric (including paper), and a commercially available nonwoven fabric or the like is used as the substrate. Can do. In the separator of this aspect, the filler having a heat resistant temperature of 150 ° C. or higher is preferably contained in the voids of the porous substrate, but the organic binder is used to bind the porous substrate and the filler. You can also

  The “heat resistance” of the porous substrate means that a substantial dimensional change due to softening or the like does not occur, and the change in the length of the object, that is, the porous substrate with respect to the length at room temperature. The heat resistance is evaluated based on whether or not the upper limit temperature (heat resistance temperature) at which the shrinkage ratio (shrinkage ratio) can be maintained at 5% or less is sufficiently higher than the shutdown temperature of the separator. In order to increase the safety of the electrochemical device after shutdown, the porous substrate preferably has a heat resistant temperature that is 20 ° C. or more higher than the shutdown temperature. More specifically, the heat resistant temperature of the porous substrate is 150 ° C. It is preferable that the temperature is higher than or equal to ° C, and more preferably higher than or equal to 180 ° C.

  When the porous layer (II) is formed using a porous substrate, it is preferable that all or a part of the filler having a heat resistant temperature of 150 ° C. or higher exists in the voids of the porous substrate. By setting it as such a form, the effect | action of the said filler can be exhibited more effectively.

  The diameter of the fibrous material (including the fibrous material constituting the porous substrate and other fibrous materials) may be equal to or less than the thickness of the porous layer (II), and is, for example, 0.01 to 5 μm. It is preferable. If the diameter of the fibrous material is too large, the entanglement between the fibrous materials is insufficient. For example, when a porous substrate is formed by forming a sheet-like material, the strength becomes small and handling becomes difficult. There is. On the other hand, when the diameter of the fibrous material is too small, the pores of the separator become too small and the ion permeability tends to be lowered, and the load characteristics of the electrochemical device may be lowered.

  When the fibrous material is used for the porous layer (II) (including the case where the fibrous material is used as the porous substrate), the content thereof is, for example, in all the constituent components of the porous layer (II). , Preferably it is 10 volume% or more, More preferably, it is 20 volume% or more, Preferably it is 90 volume% or less, More preferably, it is 80 volume% or less. The state of the fibrous material in the porous layer (II) is, for example, preferably that the angle of the long axis (long axis) with respect to the separator surface is 30 ° or less on average, and 20 ° or less. More preferably.

  In the separator according to the present invention, the thickness of the porous layer (II) [when the separator has a plurality of porous layers (II), the total thickness] From the viewpoint of exhibiting effectively, it is preferably 3 μm or more. However, if the porous layer (II) is too thick, the energy density of the electrochemical device may be lowered. Therefore, the thickness of the porous layer (II) is preferably 8 μm or less.

  Further, the thickness of the porous layer (I) [when the separator has a plurality of porous layers (I), the total thickness thereof. same as below. ] Is preferably 6 μm or more, more preferably 10 μm or more, from the viewpoint of more effectively exerting the above-described action (particularly the shutdown action) due to the use of the porous layer (I). However, if the porous layer (I) is too thick, in addition to the possibility of causing a decrease in the energy density of the electrochemical element, the force that the porous layer (I) tends to shrink by heat increases. In the configuration in which the porous layer (I) and the porous layer (II) are integrated, the effect of suppressing the thermal contraction of the entire separator may be reduced. Therefore, the thickness of the porous layer (I) is preferably 25 μm or less, more preferably 20 μm or less, and still more preferably 14 μm or less.

  When the thickness of the porous layer (I) constituting the separator is A (μm) and the thickness of the porous layer (II) is B (μm), the ratio A / B between A and B is 10 or less. Preferably, it is 5 or less, more preferably 1 or more, and more preferably 2 or more. In the separator according to the present invention, even when the thickness ratio of the porous layer (I) is increased and the porous layer (II) is thinned, the occurrence of a short circuit due to thermal contraction of the separator is ensured while ensuring a good shutdown function. Can be suppressed. In the separator, when there are a plurality of porous layers (I), the thickness A is the total thickness, and when there are a plurality of porous layers (II), the thickness B is the total thickness. .

  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. In addition, the porosity of the separator: P (%) can be calculated from the thickness of the separator, the mass per area, and the true density of the constituent components using the following equation (1).

P = {1-m / (ρ × t)} × 100 (1)
Here, m: mass per unit area of the separator (g / cm ² ), ρ: average density (g / cm ³ ) of each component contained in the porous layers (I) and (II), t: separator Thickness (cm). Note that ρ can be calculated using the following equation (2).
ρ = {(t−t _m ) × (Σa _i ρ _i ) + t _m × ρ _m } / t (2)
In the above formula, t _m : thickness of porous layer (I) (cm), a _i : ratio of component i expressed in mass%, ρ _i : density of component i (g / cm ³ ), ρ _m : It is the density (g / cm ³ ) of the porous layer (I). In any of the above formulas, the mass m per unit area of the separator is calculated by measuring the mass of a separator cut out in a 20 cm square with an electronic balance and calculating the mass per 1 cm ^2. The thickness tm of the porous layer (I) is obtained by measuring the thicknesses of 10 measurement points randomly with a micrometer and averaging them.

In the formula (1), m is the mass per unit area (g / cm ² ) of the porous layer (I), and t is the thickness (cm) of the porous layer (I). 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 according to the present invention is measured by a method according to JIS P 8117, and has a Gurley value of 10 to 300 sec indicated by the number of seconds that 100 ml of air passes through the membrane under a pressure of 0.879 g / mm ^2. It is desirable that 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 employ | adopting the said structure, it can be set as the separator which has the said air permeability.

  Furthermore, the separator according to the present invention preferably has a penetration strength required by the following method of 3.0 N or more. If it is a separator which has such penetration strength, the fall of productivity by comprising an electrochemical element in combination with the negative electrode with a rough surface as mentioned above can be suppressed more favorably. In addition, it can be set as the separator which has the said penetration strength by employ | adopting the said structure.

  The penetration strength of the separator is determined by the following method. The separator is fixed on a plate having a hole with a diameter of 2 inches so as not to be wrinkled or bent, and a semicircular metal pin having a tip diameter of 1.0 mm is lowered to the separator at a speed of 120 mm / min. Measure the force when the separator is perforated 5 times. And an average value is calculated | required about the measurement of 3 times except the maximum value and the minimum value among the said 5 times of measured values, and this is made into the penetration strength of a separator.

  The average pore size of the separator is preferably 0.01 μm or more, more preferably 0.05 μm or more, preferably 1 μm or less, more preferably 0.5 μm or less. The average pore size of the porous layer (I) is preferably 0.01 to 0.5 μm, and the average pore size of the porous layer (II) is preferably 0.05 to 1 μm.

  The shutdown characteristic of the electrochemical device of the present invention having the separator having the above-described configuration can be obtained, for example, by the temperature change of the internal resistance of the electrochemical device. Specifically, it can be measured by placing the electrochemical element in a thermostat, increasing the temperature from room temperature at a rate of 1 ° C. per minute, and determining the temperature at which the internal resistance of the electrochemical element increases. is there. In this case, the internal resistance of the electrochemical element at 150 ° C. is preferably 5 times or more of room temperature, more preferably 10 times or more. By using the separator having the above structure, such characteristics can be obtained. Can be secured.

  The separator according to the present invention preferably has a heat shrinkage rate at 150 ° C. of 5% or less. If the separator has such a characteristic, even when the inside of the electrochemical device reaches about 150 ° C., the separator hardly contracts, so that a short circuit due to contact between the positive and negative electrodes can be prevented more reliably, and at a high temperature. The safety of the electrochemical device can be further increased. By employ | adopting the said structure, it can be set as the separator which has the above thermal contraction rates.

  When the porous layer (I) and the porous layer (II) are integrated, the heat shrinkage referred to here indicates the shrinkage rate of the whole separator, and the porous layer (I) and the porous layer (I) are porous. When the layer (II) is independent, the value of the smaller shrinkage rate is indicated. As will be described later, the porous layer (I) and / or the porous layer (II) can be integrated with the electrode. In that case, the measurement was performed in an integrated state with the electrode. Refers to heat shrinkage.

  The “150 ° C. thermal shrinkage rate” means that the separator or the porous layer (I) and the porous layer (II) (when integrated with the electrode, in an integrated state with the electrode) , The temperature is raised to 150 ° C., left for 3 hours, then taken out, and the dimensions required by comparing with the dimensions of the separator or porous layer (I) and porous layer (II) before being put in the thermostatic bath The percentage of decrease is expressed as a percentage.

  As a method for producing the separator, for example, the following method (a) or (b) can be employed. In the production method (a), the porous substrate contains a filler having a heat resistant temperature of 150 ° C. or higher (a plate-like filler and a filler having another shape used as necessary. The same applies to the production method of the separator). The porous layer (II) forming composition (liquid composition such as slurry) is applied, and then dried at a predetermined temperature to form the porous layer (II). In this method, the separator is superposed on the microporous film for forming the porous layer (I). In this case, the porous layer (I) and the porous layer (II) may be integrated with each other, and each of them is an independent film and is superposed in the electrochemical element by assembling the electrochemical element. It may function as an integrated separator in the state.

  In order to integrate the porous layer (I) and the porous layer (II), for example, a method in which the porous layer (I) and the porous layer (II) are overlapped and bonded together by a roll press or the like. Can be adopted.

  As the porous substrate in the above case, specifically, a woven fabric composed of at least one kind of fibrous material containing each of the exemplified materials as a constituent component, or a structure in which these fibrous materials are entangled with each other. Examples thereof include porous sheets such as non-woven fabrics. More specifically, non-woven fabrics such as paper, PP non-woven fabric, polyester non-woven fabric (PET non-woven fabric, PEN non-woven fabric, PBT non-woven fabric, etc.) and PAN non-woven fabric can be exemplified.

  The 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 these are dispersed in a solvent (including a dispersion medium; the same applies hereinafter). It is a thing. 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 hydrocarbons, furans such as tetrahydrofuran, and ketones such as methyl ethyl ketone and methyl isobutyl ketone are preferably used. In addition, for the purpose of controlling the interfacial tension, 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 including a filler having an heat resistant temperature of 150 ° C. or higher and an organic binder, for example, 10 to 80% by mass.

  When the opening diameter of the pores of the porous substrate is relatively large, for example, 5 μm or more, this tends to cause a short circuit of the electrochemical element. Therefore, in this case, as described above, it is preferable to have a structure in which all or part of the filler having a heat resistant temperature of 150 ° C. or higher exists in the voids of the porous substrate. In order to make the filler or the like exist in the voids of the porous substrate, for example, after applying the porous layer (II) -forming composition containing these to the porous substrate, the excess composition is passed through a certain gap. A process such as drying may be used after removing.

  Moreover, in the porous layer (II), as described above, in order to increase the orientation of the plate-like filler, after applying and impregnating the porous layer (II) forming composition on the porous substrate, A method of applying a shear or a magnetic field to the composition may be used. For example, as described above, after the composition for forming the porous layer (II) is applied to the porous substrate, the composition can be shared by passing through a certain gap.

  Further, in order to more effectively exert the actions of the filler and other components constituting the porous layer (II), these components are unevenly distributed so that the components are parallel or substantially parallel to the surface of the separator. It is good also as a form gathered in layers.

  In the separator production method (b), the composition for forming the porous layer (II) is further made to contain a fibrous material as necessary, and this is applied onto a substrate such as a film or a metal foil, and a predetermined temperature is applied. After drying, the method is peeled off from the substrate as necessary. Thereby, the porous membrane used as porous layer (II) can be formed.

  In the production method (b), as in the production method (a), the porous layer (I) composed of a microporous film mainly composed of the resin (A) and the porous layer (II) mainly composed of a filler are Each may be an independent configuration or may be an integrated configuration. In order to integrate the porous layer (I) and the porous layer (II), in addition to the method of laminating the individually formed porous layer (II) and porous layer (I) by a roll press or the like, The porous layer (II) -forming composition is applied on the surface of the porous layer (I), dried, and directly dried on the surface of the porous layer (I). ) May be employed.

  Moreover, it is good also as a structure which formed the porous layer (II) on the surface of the electrode which comprises an electrochemical element by a manufacturing method (b), and the separator and the electrode were integrated.

  In the case of employing any of the production methods (a) and (b), the porous layer (I) may be integrated with at least one of the positive electrode and the negative electrode. In order to integrate the porous layer (I) with the electrode, for example, a method of roll pressing the microporous film to be the porous layer (I) and the electrode can be employed. Further, by the production method (b), the porous layer (II) may be formed on the surface of the positive electrode, and the microporous film that becomes the porous layer (I) may be attached to the surface of the negative electrode to be integrated. Even if the separator in which the porous layer (I) and the porous layer (II) produced by the method (a) or (b) are integrated is attached to one of the surfaces of the positive electrode and the negative electrode, they are integrated. Good. In order to attach and integrate the separator in which the porous layer (I) and the porous layer (II) are integrated on the surface of the electrode, for example, a method of roll pressing the separator and the electrode can be employed. .

  Note that 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, the porous layer (I) may be arranged on both sides of the porous layer (II), or the porous layer (II) may be arranged on both sides of the porous layer (I). However, increasing the number of layers may increase the thickness of the separator, leading to an increase in the internal resistance of the electrochemical device and a decrease in energy density. Therefore, it is not preferable to increase the number of layers. The total number of layers of the porous layer (I) and the porous layer (II) is preferably 5 or less.

  In addition, as described above, the porous layer (I) and the porous layer (II) are independent constituent elements in addition to integrating the separator as an independent film, and the electrochemical element is assembled. Thus, they can be superposed in the electrochemical element and function as a separator interposed between the positive electrode and the negative electrode. Furthermore, the porous layer (I) and the porous layer (II) do not need to be in contact with each other, and another layer, for example, a fibrous layer constituting the porous substrate is interposed between them. May be.

  The electrochemical device of the present invention is not particularly limited, and includes lithium secondary batteries using a non-aqueous electrolyte, lithium primary batteries, supercapacitors, etc., and safety at high temperatures is particularly required. If it is a use, it can apply preferably.

  Moreover, the electrochemical device of the present invention includes the separator and the negative electrode, and as long as the separator and the negative electrode are arranged as will be described in detail later, there are no particular restrictions on the other configurations and structures, Various configurations and structures employed in various electrochemical elements (lithium secondary batteries, lithium primary batteries, supercapacitors, etc.) having conventionally known non-aqueous electrolytes can be applied.

  Hereinafter, as an example, application to a lithium secondary battery will be mainly described. 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.

  An electrochemical element such as a lithium secondary battery preferably has a mechanism for discharging gas inside the battery (electrochemical element) to the outside when the temperature rises. As such a mechanism, a conventionally known mechanism can be used. That is, in batteries (electrochemical elements) that use metal cans such as steel cans and aluminum cans (electrochemical elements), metal cleavage vents that crack at constant pressure, resin vents that break at constant pressure, constant pressure For example, a rubber vent that opens the lid can be used, and a metal cleavage vent is preferably used.

  On the other hand, in a soft package battery (electrochemical element), the sealing part is sealed by heat sealing of the resin. Therefore, when the temperature and internal pressure rise in the first place, the structure should be able to withstand such high temperature and high pressure. However, when the temperature rises without providing a special mechanism, the gas inside the battery (electrochemical element) can be discharged to the outside. That is, in the soft package battery (electrochemical element), the sealing part (heat fusion part) of the outer package acts as a mechanism for discharging the gas inside the battery (electrochemical element) to the outside. In the case of a soft package battery (electrochemical element), the gas inside the battery (electrochemical element) is exhausted to the outside when the temperature rises even if the width of the sealing part is narrowed to a specific location. [In other words, the specific location acts as a mechanism for exhausting the gas inside the battery (electrochemical element) to the outside].

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 can be used in the form of a laminated electrode body in which the negative electrode and the positive electrode are laminated via the separator, or a wound electrode body in which the electrode is wound. In the electrochemical device of the present invention, the porous layer (I) related to the separator preferably faces at least the negative electrode, and the electrode body as described above has the porous layer (I) of the separator as the negative electrode. It is recommended that it be formed to face.

  Although the detailed reason is unknown, when the separator is disposed so that the porous layer (I) faces at least the negative electrode, the porous layer is more likely to be shut down than when disposed on the positive electrode side. Since the ratio of the resin (A) melted from (I) to be absorbed by the electrode mixture layer is reduced and the melted resin (A) is used more effectively to close the pores of the separator, The effect of shutdown is better.

  For example, when the electrochemical element has a mechanism for reducing the internal pressure of the electrochemical element by discharging the gas inside the electrochemical element to the outside when the internal pressure of the electrochemical element rises due to a temperature rise, When is operated, the internal non-aqueous electrolyte may volatilize and the electrode may be directly exposed to air. When the electrochemical device is in a charged state, when the negative electrode and air (oxygen or moisture) come into contact, Li ions occluded in the negative electrode or lithium deposited on the negative electrode surface react with air. It generates heat and sometimes ignites. In addition, the temperature of the electrochemical element rises due to this heat generation, causing a thermal runaway reaction of the positive electrode active material, and as a result, the electrochemical element may ignite.

  However, in the case of an electrochemical device configured such that the porous layer (I) mainly composed of the resin (A) faces the negative electrode, the resin (A) that is the main component of the porous layer (I) at a high temperature is used. Since it melts and covers the surface of the negative electrode, the reaction between the negative electrode and air accompanying the operation of the mechanism for discharging the gas inside the electrochemical element 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 electrochemical element to the outside, and the electrochemical element can be kept safer.

  Further, when a material having excellent oxidation resistance (for example, an inorganic oxide) is used as the filler having a heat resistant temperature of 150 ° C. or higher used for the porous layer (II), the porous layer (II) is directed to the positive electrode side. Therefore, it becomes possible to suppress the oxidation of the separator by the positive electrode, and an electrochemical device having excellent storage characteristics and charge / discharge cycle characteristics at high temperatures can be obtained, so the porous layer (II) is directed to the positive electrode side. It is more preferable to adopt a configuration. For example, in the case of a separator having a porous layer (I) mainly composed of resin (A) and 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 so that

  The positive electrode having the positive electrode mixture layer and the negative electrode having the negative electrode mixture layer as described above are, for example, a positive electrode mixture obtained by dispersing the positive electrode mixture in a solvent such as N-methyl-2-pyrrolidone (NMP). The composition for forming the agent layer (slurry, etc.) or the composition for forming the negative electrode mixture layer (slurry, etc.) obtained by dispersing the negative electrode mixture in a solvent such as NMP or water is applied to the surface of the current collector and dried. It is produced by this. In this case, for example, a positive electrode and a porous layer prepared by applying a composition for forming a positive electrode mixture layer to the surface of a current collector and applying the composition for forming a porous layer (II) before the composition is dried. Prepared by applying an integrated material with the layer (II) or a composition for forming a negative electrode mixture layer to the surface of the current collector, and applying the composition for forming the porous layer (II) before the composition is dried A lithium secondary battery (electrochemical element) can also be configured using an integrated product of the negative electrode and the porous layer (II).

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

  The organic solvent used in the electrolytic solution is not particularly limited as long as it dissolves the lithium salt and does not cause side reactions such as decomposition in the voltage range used as a battery. For example, cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, chain carbonates such as dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate; chain esters such as methyl propionate; cyclic esters such as γ-butyrolactone; Chain ethers such as dimethoxyethane, diethyl ether, 1,3-dioxolane, diglyme, triglyme and tetraglyme; cyclic ethers such as dioxane, tetrahydrofuran and 2-methyltetrahydrofuran; nitriles such as acetonitrile, propionitrile and methoxypropionitrile Sulfites such as ethylene glycol sulfite; etc., and these should be used as a mixture of two or more. It can be. In order to obtain a battery with better characteristics, it is desirable to use a combination that can obtain high conductivity, such as a mixed solvent of ethylene carbonate and chain carbonate. In addition, for the purpose of improving safety such as improvement of charge / discharge cycle characteristics, high-temperature storage property and prevention of overcharge, these electrolytic solutions have acid anhydrides, sulfonic acid esters, dinitriles, vinylene carbonates, 1,3-propanesulphate. Ton, diphenyl disulfide, cyclohexylbenzene, biphenyl, fluorobenzene, t-butylbenzene and other additives (including these derivatives) can also 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.

  Since the electrochemical device of the present invention has excellent charging characteristics at low temperatures, taking advantage of these characteristics, it is possible to use electric power such as conventionally well-known lithium secondary batteries, particularly for power supply of equipment used at low temperatures. It can be preferably used for the same uses as various uses to which chemical elements 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
<Production of negative electrode>
The average particle diameter D50% is 18 [mu] _{m, d 002} is at 0.338 nm, a R value is 0.18, and the graphite A specific surface area by BET method is 3.2 m ² / g, an average particle diameter D50% is 16μm , D ₀₀₂ of 0.336 nm, R value of 0.05, and graphite B mixed at a mass ratio of 85:15: 98 parts by mass, viscosity adjusted to a range of 1500 to 5000 mPa · s CMC aqueous solution having a concentration of mass%: 1.0 part by mass and SBR: 1.0 part by mass using ion-exchanged water having a specific conductivity of 2.0 × 10 ⁵ Ω / cm or more as a solvent, A negative electrode mixture-containing paste was prepared.

  The negative electrode mixture-containing paste is intermittently applied to both sides of a 10 μm-thick current collector made of copper foil, dried, and then calendered to give a total thickness of 142 μm. Was adjusted to obtain a negative electrode. The arithmetic average roughness Ra of the negative electrode mixture layer surface of this negative electrode was measured using a confocal laser microscope. The negative electrode was cut to a width of 45 mm, and a tab was welded to the exposed portion of the copper foil to form a lead portion.

<Preparation of positive electrode>
LiCoO _{2 as a} positive electrode active material: 70 parts by mass and LiNi _0.8 Co _0.2 O ₂ : 15 parts by mass, acetylene black as a conductive auxiliary agent: 10 parts by mass, and PVDF as a binder: 5 parts by mass, NMP was mixed uniformly as a solvent to prepare a positive electrode mixture-containing paste. This paste is intermittently applied to both sides of a 15 μm-thick aluminum foil serving as a current collector, dried, and then calendered to adjust the thickness of the positive electrode mixture layer so that the total thickness becomes 150 μm. Then, the positive electrode was fabricated by cutting to a width of 43 mm. Further, a tab was welded to the exposed portion of the aluminum foil of the positive electrode to form a lead portion.

<Preparation of separator>
Add 5 kg of ion-exchanged water and 0.5 kg of a dispersant (aqueous polycarboxylic acid ammonium salt, solid content concentration 40%) to 5 kg of secondary aggregate boehmite. A dispersion was prepared by crushing treatment. The treated dispersion was vacuum-dried at 120 ° C. and observed by SEM. As a result, the shape of boehmite was almost plate-like. Moreover, when the average particle diameter (D50%) of boehmite was measured as refractive index 1.65 using the laser scattering particle size distribution analyzer ("LA-920" by HORIBA), it was 1.0 micrometer.

  To 500 g of the above dispersion, 0.5 g of xanthan gum as a thickener and 17 g of a resin binder dispersion (modified polybutyl acrylate, solid content 45% by mass) as a binder are added and stirred with a three-one motor for 3 hours to form a uniform slurry. [Slurry a for forming porous layer (II), solid content ratio 50 mass%] was prepared.

PE microporous separator for lithium secondary batteries [porous layer (I): thickness 12 μm, porosity 40%, average pore diameter 0.02 μm, PE melting point 135 ° C.] on one side corona discharge treatment (discharge amount 40 W) Min / m ² ) was applied, and the slurry a for forming the porous layer (II) was applied to the treated surface by a micro gravure coater and dried to form the porous layer (II) to obtain a separator. The thickness (Tb) of the porous layer (II) was adjusted to the thickness shown in Table 1 by adjusting the groove depth of the gravure roll, the slurry supply rate, and the coating rate.

The porous layer (II) in the obtained separator had a mass per unit area of 3.4 g / m ² . Further, the penetration strength of the separator measured by the above-described method (the penetration strength of the separator was also measured by the same method in each of Examples and Comparative Examples described later) was 3.9 N, and the volume content of the filler was 88. The porosity of the porous layer (II) was 55%. Furthermore, the number of laminated plate-like boehmite in the porous layer (II) determined by the above method was 6 to 8 (the number of laminated plate-like fillers was also the same in the examples and comparative examples described later). Was measured).

<Battery assembly>
The positive electrode, the negative electrode, and the separator obtained as described above were overlapped with the porous layer (I) facing the negative electrode, and wound in a spiral shape to produce a wound electrode body. The obtained wound electrode body is crushed into a flat shape, put into an aluminum outer can having a thickness of 6 mm, a height of 50 mm, and a width of 34 mm, and an electrolytic solution (ethylene carbonate and ethyl methyl carbonate are mixed at a volume ratio of 1: 2). In the solvent, LiPF ₆ was dissolved at a concentration of 1.2 mol / l and further 3% by weight of vinylene carbonate was added) and sealed, and the structure shown in FIG. 1 had the appearance shown in FIG. A lithium secondary battery was produced. This battery is provided with a cleavage vent for lowering the pressure when the internal pressure rises at the top of the can.

  Here, the battery shown in FIGS. 1 and 2 will be described. FIG. 1A is a plan view, and FIG. 1B is a partial cross-sectional view thereof. As shown in FIG. 2 is spirally wound through the separator 3 as described above, and then pressed so as to be flattened and accommodated in a rectangular tube-shaped outer can 4 together with the electrolyte as a flat wound electrode body 6 Has been. However, in FIG. 1, in order to avoid complication, a metal foil, an electrolytic solution, and the like as a current collector used for manufacturing the positive electrode 1 and the negative electrode 2 are not illustrated. Also, the separator layers are not shown separately.

  The outer can 6 is made of an aluminum alloy and constitutes an outer casing of the battery. The outer can 4 also serves as a positive electrode terminal. And the insulator 5 which consists of PE sheets is arrange | positioned at the bottom part of the armored can 4, and it connects to each one end of the positive electrode 1 and the negative electrode 2 from the flat wound electrode body 6 which consists of the positive electrode 1, the negative electrode 2, and the separator 3. The positive electrode lead body 7 and the negative electrode lead body 8 thus drawn are drawn out. A stainless steel terminal 11 is attached to a sealing lid plate 9 made of aluminum alloy for sealing the opening of the outer can 4 through a PP insulating packing 10, and an insulator 12 is attached to the terminal 11. A stainless steel lead plate 13 is attached.

  And this cover plate 9 is inserted in the opening part of the armored can 4, and the opening part of the armored can 4 is sealed by welding the junction part of both, and the inside of a battery is sealed. Further, in the battery of FIG. 1, a non-aqueous electrolyte inlet 14 is provided in the cover plate 9, and a sealing member is inserted into the non-aqueous electrolyte inlet 14, for example, laser welding or the like. (See FIG. 1 and FIG. 2, in practice, the non-aqueous electrolyte inlet 14 is actually sealed with the non-aqueous electrolyte inlet.) Although it is a member, for ease of explanation, it is shown as a non-aqueous electrolyte inlet 14). Further, the lid plate 9 is provided with a cleavage vent 15 as a mechanism for discharging the internal gas to the outside when the temperature of the battery rises.

  In the battery of this Example 1, the outer can 5 and the cover plate 9 function as a positive electrode terminal by directly welding the positive electrode lead body 7 to the lid plate 9, and the negative electrode lead body 8 is welded to the lead plate 13, The terminal 11 functions as a negative electrode terminal by conducting the negative electrode lead body 8 and the terminal 11 through the lead plate 13, but depending on the material of the outer can 4, the sign may be reversed. There is also.

  FIG. 2 is a perspective view schematically showing the external appearance of the battery shown in FIG. 1. FIG. 2 is shown for the purpose of showing that the battery is a square battery. FIG. 1 schematically shows a battery, and only specific members of the battery are shown. Also in FIG. 1, the inner peripheral portion of the electrode group is not cross-sectional.

Example 2
By changing the groove depth of the gravure roll, the supply speed of the slurry, and the application speed when applying the porous layer (II) forming slurry a to the corona discharge treatment surface of the PE microporous membrane separator, the porous layer A separator was prepared in the same manner as in Example 1 except that the thickness Tb of (II) was changed as shown in Table 1, and a lithium secondary battery was prepared in the same manner as in Example 1 except that this separator was used. Produced.

Example 3
A negative electrode was produced in the same manner as in Example 1 except that the mixing ratio of graphite A and graphite B was 90:10 by mass ratio, and the arithmetic average roughness on the surface of the negative electrode mixture layer was the same as in Example 1. Ra was measured.

  In addition, by changing the groove depth of the gravure roll, the supply speed of the slurry, and the application speed when applying the porous layer (II) forming slurry a to the corona discharge treatment surface of the PE microporous membrane separator, A separator was produced in the same manner as in Example 1 except that the thickness Tb of the quality layer (II) was changed as shown in Table 1.

  And the lithium secondary battery was produced like Example 1 except having used the said negative electrode and the said separator.

Example 4
A negative electrode was produced in the same manner as in Example 1 except that only the negative electrode active material was graphite A, and the arithmetic average roughness Ra of the negative electrode mixture layer surface was measured in the same manner as in Example 1. And the lithium secondary battery was produced like Example 3 except having used this negative electrode.

Example 5
By changing the groove depth of the gravure roll, the supply speed of the slurry, and the application speed when applying the porous layer (II) forming slurry a to the corona discharge treatment surface of the PE microporous membrane separator, the porous layer A separator was prepared in the same manner as in Example 1 except that the thickness Tb of (II) was changed as shown in Table 1, and a lithium secondary battery was prepared in the same manner as in Example 4 except that this separator was used. Produced.

Example 6
A negative electrode was produced in the same manner as in Example 1 except that the mixing ratio of graphite A and graphite B was set to 70:30 by mass ratio, and the arithmetic average roughness on the surface of the negative electrode mixture layer was obtained in the same manner as in Example 1. Ra was measured. And the lithium secondary battery was produced like Example 1 except having used this negative electrode.

Example 7
A negative electrode was produced in the same manner as in Example 1 except that the mixing ratio of graphite A and graphite B was 50:50 by mass ratio, and the arithmetic average roughness on the surface of the negative electrode mixture layer was the same as in Example 1. Ra was measured. And the lithium secondary battery was produced like Example 1 except having used this negative electrode.

Example 8
A negative electrode was produced in the same manner as in Example 1 except that the mixing ratio of graphite A and graphite B was set to 30:70 by mass ratio, and the arithmetic average roughness on the surface of the negative electrode mixture layer was obtained in the same manner as in Example 1. Ra was measured. And the lithium secondary battery was produced like Example 1 except having used this negative electrode.

Example 9
A porous layer (II) forming slurry b was prepared in the same manner as the porous layer (II) forming slurry a except that secondary aggregate alumina was used instead of the secondary aggregate boehmite. In addition, when the SEM observation was performed similarly to Example 1 about the alumina dispersion liquid formed in the middle of preparation of the slurry b for porous layer (II) formation, the shape of the alumina was plate shape. Further, with respect to the alumina dispersion, the average particle diameter D50% of alumina measured in the same manner as in Example 1 was 0.6 μm.

  A separator provided with a porous layer (II) having a thickness Tb shown in Table 1 was prepared in the same manner as in Example 1 except that the slurry b was used, and Example 1 except that this separator was used. In the same manner, a lithium secondary battery was produced.

Example 10
A porous layer (II) forming slurry c was prepared in the same manner as the porous layer (II) forming slurry a except that secondary aggregate silica was used instead of the secondary aggregate boehmite. The silica dispersion formed during the preparation of the porous layer (II) forming slurry c was subjected to SEM observation in the same manner as in Example 1. As a result, the shape of the silica was plate-like. Further, with respect to the silica dispersion, the average particle diameter D50% of silica measured in the same manner as in Example 1 was 2.0 μm.

  A separator provided with a porous layer (II) having a thickness Tb shown in Table 1 was prepared in the same manner as in Example 1 except that the slurry c was used, and Example 1 except that this separator was used. In the same manner, a lithium secondary battery was produced.

Example 11
Instead of graphite A and graphite B, a carbon fiber having an average diameter of 4 μm and an aspect ratio (ratio of length to diameter) of 5 (d ₀₀₂ is 0.336 nm, R value is 0.07. A negative electrode is produced in the same manner as in Example 1 except that “fiber A” is used as the negative electrode active material, and the arithmetic average roughness Ra of the negative electrode mixture layer surface is measured in the same manner as in Example 1. did. And the lithium secondary battery was produced like Example 1 except having used this negative electrode.

Example 12
A negative electrode was produced in the same manner as in Example 1 except that the mixing ratio of graphite A and graphite B was 20:80 in terms of mass ratio, and the arithmetic average roughness of the negative electrode mixture layer surface was the same as in Example 1. Ra was measured. Furthermore, it was the same as in Example 9 except that the thickness Tb of the porous layer (II) was changed as shown in Table 1 by changing the groove depth of the gravure roll, the supply rate of the slurry, and the coating rate. A separator was produced. And the lithium secondary battery was produced like Example 1 except having used this negative electrode and the separator.

Example 13
A negative electrode was produced in the same manner as in Example 1 except that the mixing ratio of graphite A and graphite B was 90:10 by mass ratio, and the arithmetic average roughness on the surface of the negative electrode mixture layer was the same as in Example 1. Ra was measured. Furthermore, it was the same as in Example 10 except that the thickness Tb of the porous layer (II) was changed as shown in Table 1 by changing the groove depth of the gravure roll, the supply speed of the slurry, and the coating speed. A separator was produced. And the lithium secondary battery was produced like Example 1 except having used this negative electrode and the separator.

Example 14
Instead of the graphite A and graphite B, average particle diameter D50% is 25 [mu] _{m, d 002} is at 0.336 nm, a R value of 0.08, graphite specific surface area by BET method is 0.6 m ² / g C Was used in the same manner as in Example 1 except that was used as the negative electrode active material, and the arithmetic average roughness Ra of the negative electrode mixture layer surface was measured in the same manner as in Example 1. And the lithium secondary battery was produced like Example 2 except having used this negative electrode.

Example 15
Graphite C used in Example 14 and carbon fiber having an average diameter of 0.1 μm and an aspect ratio of 100 (d ₀₀₂ is 0.340 nm, R value is 0.19, hereinafter referred to as “carbon fiber B”) Is prepared in the same manner as in Example 1 except that a mixture obtained by mixing at a mass ratio of 85:15 is used as the negative electrode active material, and the negative electrode mixture layer surface is prepared in the same manner as in Example 1. The arithmetic average roughness Ra was measured. And the lithium secondary battery was produced like Example 2 except having used this negative electrode.

Comparative Example 1
A lithium secondary battery was produced in the same manner as in Example 1 except that the same PE microporous membrane separator as used in Example 1 was used as the separator without forming the porous layer (II).

Comparative Example 2
By changing the groove depth of the gravure roll, the supply speed of the slurry, and the application speed when applying the porous layer (II) forming slurry a to the corona discharge treatment surface of the PE microporous membrane separator, the porous layer A separator was prepared in the same manner as in Example 1 except that the thickness Tb of (II) was changed as shown in Table 2, and a lithium secondary battery was prepared in the same manner as in Example 1 except that this separator was used. Produced.

Comparative Example 3
By changing the groove depth of the gravure roll, the supply speed of the slurry, and the application speed when applying the porous layer (II) forming slurry a to the corona discharge treatment surface of the PE microporous membrane separator, the porous layer A separator was prepared in the same manner as in Example 1 except that the thickness Tb of (II) was changed as shown in Table 2, and a lithium secondary battery was prepared in the same manner as in Example 4 except that this separator was used. Produced.

Comparative Example 4
By changing the groove depth of the gravure roll, the supply speed of the slurry, and the application speed when applying the porous layer (II) forming slurry a to the corona discharge treatment surface of the PE microporous membrane separator, the porous layer A separator was prepared in the same manner as in Example 1 except that the thickness Tb of (II) was changed as shown in Table 2, and a lithium secondary battery was prepared in the same manner as in Example 6 except that this separator was used. Produced.

Comparative Example 5
A negative electrode was produced in the same manner as in Example 1 except that the mixing ratio of graphite A and graphite B was 20:80 in terms of mass ratio, and the arithmetic average roughness of the negative electrode mixture layer surface was the same as in Example 1. Ra was measured. And the lithium secondary battery was produced like Example 1 except having used this negative electrode.

Comparative Example 6
A negative electrode was prepared in the same manner as in Example 1 except that only the negative electrode active material was graphite B, and the arithmetic average roughness Ra on the surface of the negative electrode mixture layer was measured in the same manner as in Example 1. And the lithium secondary battery was produced like Example 1 except having used this negative electrode.

  The configurations of the negative electrode and the separator in the lithium secondary batteries of Examples 1 to 15 and Comparative Examples 1 to 6 are shown in Tables 1 and 2.

  The lithium secondary batteries of Examples 1 to 15 and Comparative Examples 1 to 6 were subjected to the following charging current measurement, withstand voltage experiment, and heating test at −5 ° C. and 10% charging depth. These results are shown in Table 3.

<Measurement of charge current at -5 ° C and 10% charge>
The lithium secondary batteries of Examples 1 to 15 and Comparative Examples 1 to 6 were allowed to stand in a thermostatic bath at −5 ° C. for 5 hours, and then, for each battery, a constant current of 1200 mA (1.0 C) to 4.2 V. After reaching 4.2V, constant voltage charging was performed at 4.2V, and the current value was measured when the charging depth (the ratio of the actually charged capacity to the standard capacity) reached 10%. . In Table 3, the charging current of each battery is shown as a relative value when the value of the battery of Comparative Example 6 is set to 100.

<Withstand voltage experiment>
A voltage of 500 V (AC 60 Hz) was applied to each of the 100 lithium secondary batteries of Examples 1 to 15 and Comparative Examples 1 to 6 before injection of the non-aqueous electrolyte, and a battery in which a current of 7 mA or more flowed was defective. And the number of occurrences was examined.

  In order to know how much charge / discharge cycle reliability can be ensured in the withstand voltage experiment, the distance between the electrodes becomes small even without short-circuiting, and in extreme cases, the capacity is likely to decrease with the charge / discharge cycle. It is a test means. If the dielectric breakdown does not occur for a certain withstand voltage, it means that the distance between the electrodes is maintained above the reference. In order to clarify the difference here, a higher value is tested. That is, in this withstand voltage test, the fact that the number of defects generated is small means that the ratio of defects generated during the production of a battery (electrochemical element) is small, and the battery (electrochemical element) is excellent in productivity. Can be evaluated.

  The test voltage of the withstand voltage may be 1V if it is a positive voltage as long as it is a normal short circuit check, but it is preferably 50V or more, more preferably 100V or more, and particularly preferably 300V or more in order to further improve the reliability. Moreover, although the test voltage has never exceeded a high level, 2000V or lower is desirable because of excessive quality. Furthermore, since the current as a capacitor flows, the determination current is preferably 2 G (mA) or more, and preferably 4 G (mA) or more, where G is the value when the 0.2 C discharge capacity of the battery is expressed as an Ah value. More desirable. In addition, since the detection rate decreases if the determination current is set too high, it is preferably 20 G (mA) or less, and more preferably 10 G (mA) or less. It is desirable to perform this withstand voltage test in combination in the battery manufacturing process because the reliability of the manufactured battery is further increased. Since the discharge capacity of 0.2 C of the batteries of Examples 1 to 15 and Comparative Examples 1 to 6 is 1.2 Ah, G = 1.2, and 7 mA is 4 G or more and 10 G or less.

<Heating test>
About the lithium secondary battery (each 10 pieces) of Examples 1-15 and Comparative Examples 1-6, constant current charge was performed until the battery voltage became 4.25V at a current value of 1.0C, and then 4.25V. The constant current-constant voltage charge which performs constant voltage charge in was performed. The total charging time until the end of charging was 2.5 hours. Each battery charged under the above conditions was placed in a thermostat, heated from 30 ° C. to 150 ° C. at a rate of 5 ° C. per minute, and then allowed to stand at 150 ° C. for 3 hours to measure the surface temperature of the battery. Table 3 lists the number of batteries (overheated temperature number) in which the battery surface temperature rose to 160 ° C. or higher.

  As shown in Table 3, when Ra / Tb is large as in the batteries of Comparative Example 2 and Comparative Example 3, Tb is too small with respect to Ra, and the number of withstand voltage failures is slightly increased. Further, even in the battery of Comparative Example 1 using a separator in which the porous layer (II) is not formed, the number of defective withstand voltages is slightly large.

  On the other hand, when Ra / Tb is small as in the batteries of Comparative Examples 4 to 6, Tb is too large for Ra, so the charging characteristics at low temperatures were lower than those of the battery of the example. In particular, the battery of Comparative Example 6 in which graphite having a suitable R value was not used for the negative electrode was significantly different from the battery of the example.

  The batteries of Examples 1 to 15 in which Ra / Tb is appropriate with respect to the battery of such a comparative example have good charging characteristics at low temperatures, and have no withstand voltage failure or temperature increase during a heating test. .

1 Positive electrode 2 Negative electrode 3 Separator

Claims (7)

An electrochemical device having a positive electrode, a negative electrode, a non-aqueous electrolyte and a separator,
The negative electrode has a negative electrode mixture layer containing a negative electrode active material on one side or both sides of a current collector,
The separator has a porous layer (I) composed of a microporous film mainly composed of a thermoplastic resin, and a porous layer (II) mainly composed of a filler having a heat resistant temperature of 150 ° C. or higher.
The ratio Ra / Tb between the arithmetic average roughness Ra (μm) of the negative electrode mixture layer surface and the thickness Tb (μm) of the porous layer (II) is 0.10 to 0.27. An electrochemical element.   2. The electrochemical device according to claim 1, wherein the arithmetic average roughness Ra of the surface of the negative electrode mixture layer is 0.3 to 1.2 μm.   The electrochemical element according to claim 1 or 2, wherein the thickness Tb of the porous layer (II) in the separator is 3 to 8 µm.   The electrochemical element according to any one of claims 1 to 3, wherein the filler contained in the porous layer (II) in the separator is at least one plate-like particle selected from the group consisting of alumina, silica and boehmite.   The electrochemical element according to any one of claims 1 to 4, wherein the porous layer (I) in the separator contains a polyolefin having a melting point of 100 to 150 ° C.   The electrochemical device according to claim 1, wherein the negative electrode mixture layer contains a carbon material as a negative electrode active material.   The negative electrode mixture layer has an R value, which is a peak intensity ratio of 1360 cm −1 to a peak intensity of 1580 cm −1 in an argon ion laser Raman spectrum, of 0.1 to 0.5, and an interplanar spacing d002 of 0.338 nm. The electrochemical element according to claim 6, wherein the following graphite is contained as a negative electrode active material, and a ratio of the graphite in all negative electrode active materials is 30% by mass or more.

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