JP2012033268A - Electrochemical element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrochemical element excellent in safety at the time of overcharge and charging performance at low temperature.SOLUTION: In an electrochemical element having a positive electrode, a negative electrode, a nonaqueous electrolyte and a separator, the separator has a porous layer (I) comprising a fine porous film mainly composed of a thermoplastic resin and a porous layer (II) including a filler with a heatproof temperature of 150°C or more as a main body, and at least the porous layer (II) faces the positive electrode. The negative electrode includes graphite having the ratio of the peak intensity of 1360 cmto the peak intensity of 1580 cmin argon ion laser raman spectrum, a R value (I/I) of 0.1-0.5 and a surface interval in a 002 surface (d) of 0.338 nm or less as a negative electrode active material. The nonaqueous electrolyte includes a compound with an alkyl group combined with a benzene ring.

Description

  The present invention relates to an electrochemical device that is excellent in safety during overcharging and charging characteristics at low temperatures.

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

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

  By the way, as such a separator, for example, a uniaxially stretched film or a biaxially stretched film is used for increasing the porosity and improving the strength. Since such a separator is supplied as a single film, a certain strength is required in terms of workability and the like, and this is secured by the stretching. However, 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 element by using a porous separator having a second separator layer containing mainly as a main component (Patent Document 1).

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

  In addition, for electrochemical elements such as lithium secondary batteries, various improvements in characteristics other than safety as described above have been studied. For example, in Patent Documents 2 and 3, the capacity can be increased by using a negative electrode active material whose surface is coated with a carbon material having low crystallinity, and the irreversible capacity during the initial charge / discharge cycle is reduced. Thus, it is disclosed that the capacity maintenance rate of the charge / discharge cycle can be increased and the rapid charge / discharge characteristics can be greatly improved.

International Publication No. 2007/66768 JP 2000-223120 A JP 2000-340232 A

  By the way, in recent electrochemical devices such as lithium secondary batteries, there is a tendency to increase the capacity, for example, as the performance of applied devices increases, but at the same time, the safety against overcharge is also higher. It is required that it can be secured by Although the electrochemical device disclosed in Patent Document 1 has good safety against overcharging, it is expected that a technology that exceeds this will be required in the future.

  Further, considering that the electrochemical element is used in various temperature environments, it is also required to have charging characteristics that do not hinder practical use even in a low temperature environment where the reactivity of the electrochemical element is reduced.

  This invention is made | formed in view of the said situation, The objective is to provide the electrochemical element excellent in the safety | security at the time of an overcharge, and the charge characteristic in low temperature.

The electrochemical element of the present invention that has solved the above problems is an electrochemical element having a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator, and the separator is made of a microporous film mainly composed of a thermoplastic resin. It has a porous layer (I) and a porous layer (II) mainly comprising a filler having a heat-resistant temperature of 150 ° C. or higher, the porous layer (II) faces at least the positive electrode, and the negative electrode , 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 to 0.5, spacing of 002 plane _{d 002} Graphite containing 0.338 nm or less as a negative electrode active material, the proportion of the graphite in the negative electrode active material is 70% by mass or more, and the non-aqueous electrolyte is attached to the benzene ring. And it is characterized in that it contains a compound kill group is bonded.

  In the electrochemical device of the present invention, when overcharged, a compound in which an alkyl group is bonded to the benzene ring in the non-aqueous electrolyte is polymerized to form a conductive path in the pores of the separator, thereby causing a soft short. An increase in temperature of the electrochemical element due to overcharging can be suppressed.

  However, especially when the electrochemical device is overcharged, the separator is easily oxidized by the positive electrode. If the separator deteriorates, the soft short circuit cannot be caused stably, and the safety during overcharge is ensured. There is a possibility that it cannot be done. Therefore, in the electrochemical device of the present invention, the separator is disposed so that the porous layer (II) having a heat resistance temperature of 150 ° C. or more as a main component and having better oxidation resistance faces at least the positive electrode. Further, it is possible to suppress the oxidative deterioration of the separator during overcharge and to cause the soft short circuit more stably.

In the electrochemical device of the present invention, the negative electrode active material contains 70 mass% of graphite having the R value of 0.1 to 0.5 and d ₀₀₂ of 0.338 nm or less in the total amount of the negative electrode active material. By using a negative electrode formed with a ratio of at least%, the charging characteristics at a low temperature (for example, a low temperature of 0 ° C. or lower) at which the reactivity of the electrochemical device is reduced are enhanced.

  In the electrochemical device of the present invention, the above-described actions improve the characteristics at low temperatures (especially, low temperatures of 0 ° C. or lower) while improving safety during overcharging.

  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.

  In the present specification, the term “mainly comprising a thermoplastic resin” in the porous layer (I) means a solid content ratio in the porous layer (I), and the resin (A) that is a thermoplastic resin is 50. It means that it is more than volume%. 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 the 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 excellent in the safety | security at the time of an overcharge and the discharge characteristic in low temperature (especially low temperature below 0 degreeC) can be provided.

  The separator according to the electrochemical element 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 the 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 device rises, and has a heat resistant temperature of 150. Its function is ensured by fillers of over ℃. In other words, when the electrochemical device is at a high temperature, the positive and negative electrodes can be generated when the separator is thermally contracted by the porous layer (II) that is difficult to contract even if the porous layer (I) contracts. It is possible to prevent a short circuit due to direct contact. In the case where the porous layer (I) and the porous layer (II) are integrated as will be described later, the heat-resistant porous layer (II) acts as a skeleton of the separator, and is porous. The thermal contraction of the layer (I), that is, the thermal contraction of the entire separator is suppressed.

  The resin (A) related to the porous layer (I) has electrical insulation, is electrochemically stable, and is used for non-aqueous electrolytes of electrochemical elements, which will be described in detail later, and separator manufacturing. There is no particular limitation as long as it is a thermoplastic resin that is stable in the solvent used (described later in detail), but polyolefins such as polyethylene (PE), polypropylene (PP), and ethylene-propylene copolymer; polyethylene terephthalate and copolymer Polyester such as polymerized polyester;

  In addition, it is preferable that the separator of this invention 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 membrane (I) has a melting point, that is, a melting temperature measured using a differential scanning calorimeter (DSC) in accordance with the provisions of JIS K 7121 of 80 ° C. or higher and 150 ° C. (more preferably 100 ° C. More preferably, it is a single layer microporous film having PE as a main component, or a laminated microporous film in which 2 to 5 layers of PE and PP are laminated. And the like.

  When the porous layer (I) is constituted by using 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 film formed by mixing PE and a resin having a higher melting point than PE such as PP is used as the porous layer (I), or a resin having a higher melting point than PE such as the PE layer and the PP layer. 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 that does not impair the action of imparting the shutdown function to the separator. Examples of the filler that can be used for the porous layer (I) include the same fillers that can be used for the porous layer (II) described later (a filler having a heat resistant temperature of 150 ° C. or higher).

  The particle size of the filler is an average particle size, for example, preferably 0.01 μm or more, more preferably 0.1 μm or more, preferably 10 μm or less, more preferably 1 μm or less. In addition, the average particle diameter as used in this specification is the number measured by dispersing these fine particles in a medium in which the filler is not dissolved using, for example, a laser scattering particle size distribution meter (for example, “LA-920” manufactured by HORIBA). It can be defined as an average particle diameter [the same applies to the filler according to the porous layer (II) described later. ].

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

  The content of the resin (A) in the porous layer (I) is preferably as follows, for example, in order to more easily 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 an 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).

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

  Organic particles (organic powder) include crosslinked polymethyl methacrylate, crosslinked polystyrene, crosslinked polydivinylbenzene, crosslinked styrene-divinylbenzene copolymer, 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, polyaramid, polyacetal, and thermoplastic polyimide. The organic resin (polymer) constituting these organic particles is a mixture, modified body, derivative, or copolymer (random copolymer, alternating copolymer, block copolymer, graft copolymer) of the materials exemplified above. Polymer) or a crosslinked product (in the case of the above-mentioned heat-resistant polymer).

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

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

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

  Further, since the plate-like filler has a problem of being easily cracked by impact when the thickness is small, 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.

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

  The average particle diameter of the filler relating to the porous layer (II) (the average particle diameter determined by the above-described measurement method for the filler having a secondary particle structure) is, for example, preferably 0.01 μm or more, more preferably 0. .1 μm or more, preferably 15 μm or less, more preferably 5 μm or less.

  The amount of filler having a heat resistant temperature of 150 ° C. or higher in the porous layer (II) is the total volume of the constituent components of the porous layer (II) [However, when using the porous substrate described later, the porous substrate During the entire volume of components excluding. 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 filler in the porous layer (II) high as described above, the occurrence of a short circuit due to direct contact between the positive electrode and the negative electrode when the electrochemical device becomes high temperature is further suppressed. 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 more, or binds the porous layer (I) and the porous layer (II) as necessary. Therefore, it is preferable to contain an organic binder. From such a viewpoint, the preferred 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). The pores of the porous layer (II) are easily filled with an organic binder, and the function as a separator may be reduced. There is a possibility that the effect of suppressing the heat shrinkage may be reduced due to the excessively large interval.

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

  Also, when plate-like particles are used as a filler having a heat-resistant temperature of 150 ° C. or higher, in the porous layer (II), they are laminated on those 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 may be deviated from each other), and the number of stacked fillers is preferably 5 or more, and more preferably 10 or more. In the porous layer (II) related to the separator, the presence of the plate-like filler in this manner can 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. In addition, the number of laminated plate-like fillers in the porous layer (II) can be measured by the method employed in Examples described later.

  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's EEA, Daikin Industries'" Daiel Latex Series (Fluororubber) ", JSR's" TRD-2001 (SBR) ", Nippon Zeon's" EM-400B " (SBR) ".

  When the organic binder is used for the porous layer (II), it can be used in the form of an emulsion dissolved or dispersed in the solvent for the composition for forming the porous layer (II) described later. Good.

  In 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.

  The separator used in the electrochemical device of the present invention is handled particularly when the porous layer (II) is used as an independent film without integrating the porous layer (I) and the porous layer (II). A porous substrate can be used for the porous layer (II) in order to enhance the properties. 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 is present 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 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.

  The separator according to the electrochemical device of the present invention has a pore diameter of preferably 0.025 μm or more, and more preferably 0.03 μm or more, from the viewpoint of improving electrical characteristics. Moreover, since there exists a possibility that the intensity | strength of a separator may fall when the pore diameter of a separator is too large, the pore diameter is 0.07 micrometer or less, and it is preferable that it is 0.04 micrometer or less. In addition, the pore diameter of the separator as used in this specification uses the bubble point value P (Pa) measured by the method prescribed | regulated to JISK3832, for example using "CFE-1500AEX palm porosimeter" by PMI. The pore diameter (maximum pore diameter) calculated by the following formula.

d = (K4γcos θ) / P
In the above formula, d: bubble point pore diameter (μm), γ: surface tension (mN / m), θ: contact angle (°), K: capillary constant.

  In the separator according to the present invention, in order to adjust the pore diameter as described above, a method of heat-treating the separator at a temperature close to the melting point of the material while adjusting the temperature and the holding force of the separator is adopted. Thus, the pore diameter of the separator can be adjusted to an appropriate value.

  The thickness of the separator according to the present invention is preferably 6 μm or more, and more preferably 10 μm or more, from the viewpoint of more reliably separating the positive electrode and the negative electrode. On the other hand, if the separator is too thick, the energy density of the electrochemical device may be lowered. Therefore, the thickness is preferably 50 μm or less, and more preferably 30 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 the 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. .

  In terms of specific values, the thickness of the porous layer (I) [when the separator has a plurality of porous layers (I), the total thickness] is preferably 5 μm or more, It is preferable that it is 30 micrometers or less. The thickness of the porous layer (II) [when the separator has a plurality of porous layers (II), the total thickness] is preferably 1 μm or more, more preferably 2 μm or more, and 4 μm. More preferably, it is 20 μm or less, more preferably 10 μm or less, and even more preferably 6 μm or less. If the porous layer (I) is too thin, the shutdown function may be weakened. If it is too thick, the energy density of the electrochemical device may be lowered, and in addition, the force for heat shrinking is large. Thus, for example, in the configuration in which the porous layer (I) and the porous layer (II) are integrated, there is a possibility that the effect of suppressing the thermal contraction of the entire separator is reduced. Further, if the porous layer (II) is too thin, the effect of suppressing the occurrence of a short circuit due to thermal contraction of the separator may be reduced, and if it is too thick, the thickness of the entire separator is increased.

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

In the formula (1), m is the mass per unit area (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 equation (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. Further, the strength of the separator is desirably 50 g or more in terms of piercing strength using a needle having a diameter of 1 mm. If the piercing strength is too small, a short circuit may occur due to the piercing of the separator when lithium dendrite crystals are generated. By employ | adopting the said structure, it can be set as the separator which has the said air permeability and piercing strength.

  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.

  In addition, the separator according to the electrochemical element of the present invention preferably has a thermal 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 here refers to the shrinkage rate of the integrated separator as a whole, and the porous layer (I) and the porous layer (I) 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. heat 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. and 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 a separator according to the electrochemical device of the present invention, for example, the following method (a) or (b) can be employed. In the production method (a), a porous layer (II) forming composition containing a filler having a heat resistant temperature of 150 ° C. or higher (such as a liquid composition such as a slurry) is applied to a porous substrate, and then a predetermined temperature is applied. To form a porous layer (II), which is superposed on the microporous film for forming the porous layer (I) produced by the above method to form one separator. is there. 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. It may function as an integral separator.

  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) may be any solvent as long as it can uniformly disperse the filler and the like, 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.

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

  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 porous layer (II) -forming composition further contains 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 film used as the 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 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, Instead of using the substrate, the composition for forming the porous layer (II) is applied to the surface of the porous layer (I), dried, and the porous layer (II) is directly applied to 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 manufacturing 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 serving as 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, a configuration in which the porous layer (I) is disposed on both sides of the porous layer (II) or a configuration in which the porous layer (II) is disposed on both sides of the porous layer (I) may be employed. However, increasing the number of layers may increase the thickness of the separator, 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 material layer constituting the porous substrate is interposed therebetween. 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., especially at the time of overcharge and safety at high temperatures. Can be preferably applied to applications that require.

  In addition, as the nonaqueous electrolytic solution according to the electrochemical device of the present invention, a solution in which a lithium salt is dissolved in an organic solvent is used. The nonaqueous electrolytic solution further includes a compound in which an alkyl group is bonded to a benzene ring. It must be contained. The compound contained in the non-aqueous electrolyte is for polymerizing to form a conductive path in the pores of the separator and causing a soft short when the electrochemical element is overcharged.

  Examples of the compound having an alkyl group bonded to the benzene ring include cyclohexylbenzene, t-butylbenzene, t-amylbenzene, octylbenzene and the like.

  The content (blending amount) of the compound in which the alkyl group is bonded to the benzene ring in the nonaqueous electrolytic solution used for the electrochemical element is 0.5% by mass or more from the viewpoint of more effectively ensuring the effect of the use of the compound. It is preferable that it is 1.0% by mass or more. However, if the amount of the compound in which the alkyl group is bonded to the benzene ring is too large, the electrical characteristics tend to be reduced. Therefore, the content (blending amount) of the compound in the non-aqueous electrolyte used in the electrochemical element is: It is preferably 10% by mass or less, more preferably 5% by mass or less, and particularly preferably 4% by mass or less.

The lithium salt used in the non-aqueous electrolyte 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 the voltage range used as a battery. For example, LiClO ₄ , LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiSbF ₆ and other inorganic lithium salts, LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , Li ₂ C ₂ F ₄ (SO ₃ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiC _n F _{2n + 1} SO ₃ (n ≧ 2), LiN (RfOSO ₂ ) ₂ [where Rf is a fluoroalkyl group] and the like can be used. .

  The organic solvent used for the non-aqueous electrolyte is not particularly limited as long as it dissolves the lithium salt and does not cause a side reaction such as decomposition in a voltage range used as an electrochemical element. 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, these non-aqueous electrolytes include vinylene carbonates, 1,3-propane sultone, diphenyl disulfide, biphenyl, fluorobenzene and the like for the purpose of improving safety, charge / discharge cycleability, and high-temperature storage properties. These additives may be added as appropriate.

  The concentration of the lithium salt in the non-aqueous electrolyte is preferably 0.5 to 1.5 mol / l, and more preferably 0.9 to 1.25 mol / l.

In the electrochemical device of the present invention, as the negative electrode active material, 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 or more 0 A negative electrode containing graphite having a surface spacing d _{002 of} 002 plane of 0.338 nm or less at a ratio of 70% by mass or more in the total amount of the negative electrode active material is used. By using a negative electrode containing such a negative electrode active material, a non-aqueous electrolyte containing an additive that easily reduces the reactivity of an electrochemical element at low temperatures, such as a compound in which an alkyl group is bonded to a benzene ring Even when is used, excellent charging characteristics at a low temperature can be maintained.

Examples of the graphite whose R value and d ₀₀₂ satisfy the above values include graphite whose surface is coated with a low crystalline carbon material. Such graphite is obtained by using natural graphite or artificial graphite having a d ₀₀₂ of 0.338 nm or less in a spherical shape as a base material, covering the surface with an organic compound, and firing at 800 to 1500 ° C. It can be obtained by crushing and 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.

Graphite whose R value and d ₀₀₂ satisfy the above values preferably has an average particle diameter D50 (which can be measured by the same apparatus as in the measurement of the number average particle diameter of the filler according to the separator) of 10 μm or more. Moreover, it is preferable that it is 30 micrometers or less. Furthermore, the specific surface area of the graphite is preferably 1.0 m ² / g or more, and preferably 5.0 m ² / g or less.

In addition, as the negative electrode active material, only graphite whose R value and d ₀₀₂ satisfy the above values may be used, but other negative electrode active materials can be used in combination with the graphite. As such a negative electrode active material, for example, graphite having an R value of less than 0.1 (graphite with high surface crystallinity), pyrolytic carbons, cokes, glassy carbons, and fired bodies of organic polymer compounds And carbon-based materials capable of occluding and releasing Li ions, such as mesocarbon microbeads (MCMB) and carbon fibers. When these carbon-based materials are used in combination, as described above, the ratio of graphite in which the R value and d ₀₀₂ satisfy the above values in the total amount of the negative electrode active material related to the negative electrode is 70% by mass or more. It is good and it is more preferable to set it as 80 mass% or more.

  For the negative electrode, for example, one having a structure in which a negative electrode mixture layer composed of the negative electrode active material, a binder and, if necessary, a negative electrode mixture containing a conductive auxiliary agent is formed on one side or both sides of a current collector is used. be able to. Such a negative electrode is, for example, coated with a slurry-like paste-like negative electrode mixture-containing composition in which the negative electrode mixture is dispersed in a solvent, dried on one or both sides of the current collector, and then dried as necessary. Can be manufactured through a step of adjusting the thickness of the negative electrode mixture layer by applying a press treatment. In addition, you may produce the negative electrode which concerns on this invention by methods other than the above. The thickness of the negative electrode mixture layer is preferably 10 to 100 μm per one surface of the current collector, for example.

  As the binder for the negative electrode, fluorine resin such as polyvinylidene fluoride (PVDF), SBR, CMC, or the like can be used. Moreover, carbon materials, such as carbon black, etc. can be used for the conductive support agent of a negative electrode.

  As the current collector for the negative electrode, a foil made of copper or nickel, 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 entire negative electrode is reduced in order to obtain a battery having a high energy density, the upper limit of the thickness is preferably 30 μm, and the lower limit is preferably 5 μm.

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

  In the negative electrode according to the present invention, the arithmetic average roughness (Ra) of the surface of the negative electrode mixture layer becomes relatively rough as 0.7 to 1.2 μm due to the use of the negative electrode active material. Then, as described above, since the separator of the present invention having high strength is used, it is possible to prevent the occurrence of a micro short-circuit due to the convex portion on the negative electrode surface penetrating the separator, and to increase the productivity.

  In addition, the arithmetic average roughness (Ra) of the negative electrode mixture layer surface of the negative electrode referred to in this specification is the arithmetic average roughness specified in JIS B 0601. Specifically, a confocal laser microscope (Lasertech Corporation) It is a numerical value obtained by measuring a visual field of 1 mm × 1 mm with 512 × 512 pixels using an “Real-time scanning laser microscope 1LM-21D” manufactured by the company, and arithmetically averaging the absolute values from the average line of each point. .

  As long as the electrochemical device of the present invention includes the separator, the negative electrode, and the nonaqueous electrolytic solution, there are no particular restrictions on the other configurations and structures, and various electrochemical devices having conventionally known nonaqueous electrolytic solutions ( Various configurations and structures employed in lithium secondary batteries, lithium primary batteries, supercapacitors, and the like 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 among them, 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.

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

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

  The electrode can be used in the form of a laminated electrode body in which the positive electrode and the negative electrode are laminated via the separator, or a wound electrode body in which the electrode is wound. In addition, in the electrochemical device of the present invention, as described above, in order to suppress oxidative deterioration of the separator particularly during overcharge, the porous layer (II) related to the separator needs to face at least the positive electrode, The electrode body as described above is required to be formed so that the porous layer (II) of the separator faces the negative electrode.

  In the electrochemical device of the present invention, it is more preferable to dispose the separator so that the porous layer (I) faces the negative electrode. 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 separator holes, The effect of shutdown is better.

  Further, 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 increases due to a temperature rise, this mechanism 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 element configured such that the porous layer (I) mainly composed of the resin (A) faces the negative electrode, the resin (A) that is the main body of the porous layer (I) is formed at a high temperature. 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.

  Thus, for example, in the case of a separator having a porous layer (I) mainly composed of resin (A) or a plurality of porous layers (II), the positive electrode side becomes the porous layer (II) and the negative electrode side becomes the porous layer ( More preferably, the separator is configured so as to satisfy (I).

  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). By applying a composition for forming an agent layer (slurry, etc.) or a composition for forming a negative electrode mixture layer (slurry, etc.) in which the negative electrode mixture is dispersed in a solvent such as NMP onto a current collector and drying it. Produced. In this case, for example, the positive electrode mixture layer-forming composition is applied to the current collector surface, and the porous layer (II) -forming composition is applied before the composition is dried. The porous layer (II) -forming composition is applied to the surface of the current collector, and the porous layer (II) -forming composition is applied 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) produced in this manner.

  The electrochemical device of the present invention has the same application as various applications to which a conventionally known electrochemical device such as a lithium secondary battery is applied (for example, a power supply for a portable electronic device such as a mobile phone or a notebook personal computer). Can be preferably used.

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

Example 1
Graphite having an average particle diameter D ₅₀ of 18 μm, d ₀₀₂ of 0.338 nm, an R value of 0.18, a specific surface area of 3.2 m ² / g, an average particle diameter D ₅₀ of 16 μm, and d ₀₀₂ of A mixture of graphite having an R value of 0.05 at 0.336 nm and a mass ratio of 85:15: 95 parts by mass and PVDF as a binder: 5 parts by mass are made uniform using NMP as a solvent. To prepare a negative electrode mixture-containing paste. This 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 reduce the total thickness of the negative electrode mixture layer to 142 μm. It was adjusted. The arithmetic mean roughness (Ra) of the negative electrode mixture layer surface of the negative electrode obtained using a confocal laser microscope was 0.75 μm.

  Then, it cut | disconnected so that it might become 45 mm in width, and the negative electrode was obtained. Further, a tab was welded to the exposed portion of the copper foil of the negative electrode to form a lead portion.

<Preparation of positive electrode>
LiCoO _{2 as a} positive electrode active material: 70 parts by mass, LiNi _0.8 Co _0.2 O ₂ : 15 parts by mass, acetylene black as a conductive additive: 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>
An organic binder SBR emulsion (solid content ratio 40% by mass): 100 g and water: 6000 g were placed in a container and stirred at room temperature until evenly dispersed. Boehmite powder (plate shape, average particle size 1 μm, aspect ratio 10): 2000 g, which is a filler having a heat resistance temperature of 150 ° C. or higher, was added to this dispersion in 4 portions, and the mixture was uniformly stirred at 2800 rpm for 5 hours with a disper. A slurry [a slurry for forming a porous layer (II), a solid content ratio of 25.3 mass%] was prepared. The slurry was applied on a microporous membrane made of PE [porous layer (I): thickness 12 μm, porosity 40%, pore diameter 0.033 μm, melting point 135 ° C.] with a microgravure coater and dried to obtain a thickness of A 2.6 μm porous layer (II) was formed to obtain a separator.

The porous layer (II) in the obtained separator had a mass per unit area of 3.4 g / m ² . Further, the puncture strength of the separator in the porous layer (II) was 3.9 N, the volume content of the plate boehmite was 88% by volume, and the porosity of the porous layer (II) was 55%. . Furthermore, the pore diameter (bubble point pore diameter) of the separator measured by the above method was 0.033 μm.

  Further, the number of laminated plate boehmite in the porous layer (II) obtained by cutting the separator with an argon ion laser beam under a reduced pressure atmosphere by a cross section polisher method and observing the cross section with an SEM was 6 to The number was 8 (the number of laminated plate-like fillers was also measured in the same manner in each example described later).

<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 ethylmethyl carbonate are mixed at a volume ratio of 1: 2). 1 was dissolved in LiPF ₆ at a concentration of 1.2 mol / l, 3% by weight of vinylene carbonate was added, and 4% by weight of cyclohexylbenzene was added). A lithium secondary battery having the structure shown in FIG. 2 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 a polyethylene sheet is arrange | positioned at the bottom part of the armored can 4, From the flat wound electrode body 6 which consists of the positive electrode 1, the negative electrode 2, and the separator 3, it connects to each one end of the positive electrode 1 and the negative electrode 2 The positive electrode lead body 7 and the negative electrode lead body 8 thus drawn are drawn out. Further, 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 polypropylene insulating packing 10, and an insulator 12 is attached to the terminal 11. A stainless steel lead plate 13 is attached.

  And this cover plate 9 is inserted in the opening part of the armored can 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
On the microporous membrane [porous layer (I)] made of polyethylene (PE) in the same manner as in Example 1 except that the gap of the microgravure coater was adjusted and the thickness after drying was 4.3 μm. A porous layer (II) was formed to produce a separator.

The porous layer (II) in the obtained separator had a mass per unit area of 6.0 g / m ² . Further, the puncture strength of the separator in the porous layer (II) was 3.9 N, the volume content of the plate boehmite was 86% by volume, and the porosity of the porous layer (II) was 55%. . Furthermore, the pore diameter (bubble point pore diameter) of the separator measured by the above method was 0.033 μm. The number of laminated plate boehmite in the porous layer (II) was 12-16.

  A lithium secondary battery was produced in the same manner as in Example 1 except that the separator was used.

Example 3
On the microporous film [porous layer (I)] made of polyethylene (PE) in the same manner as in Example 1 except that the gap of the microgravure coater and the pump discharge amount were adjusted and the thickness after drying was 7.5 μm. A porous layer (II) was formed on to prepare a separator.

The porous layer (II) in the obtained separator had a mass per unit area of 9.8 g / m ² . Further, the puncture strength of the separator in the porous layer (II) was 4.0 N, the volume content of the plate boehmite was 88% by volume, and the porosity of the porous layer (II) was 53%. . Furthermore, the pore diameter (bubble point pore diameter) of the separator measured by the above method was 0.033 μm. The number of laminated plate boehmite in the porous layer (II) was 22 to 28.

  A lithium secondary battery was produced in the same manner as in Example 1 except that the separator was used.

Example 4
A negative electrode was produced in the same manner as in Example 1 except that the mass ratio of the graphite having an R value of 0.18 to the graphite having an R value of 0.05 in the negative electrode active material was 90:10. The obtained negative electrode had a total thickness of 144 μm after calendar treatment, and the arithmetic average roughness (Ra) of the surface of the negative electrode mixture layer determined using a confocal laser microscope was 0.9 μm.

  A lithium secondary battery was produced in the same manner as in Example 1 except that the negative electrode was used.

Example 5
A lithium secondary battery was produced in the same manner as in Example 1 except that the same negative electrode as produced in Example 4 and the same separator as produced in Example 2 were used.

Example 6
A lithium secondary battery was produced in the same manner as in Example 1 except that the same negative electrode as produced in Example 4 and the same separator as produced in Example 3 were used.

Example 7
A negative electrode was produced in the same manner as in Example 1 except that only graphite having the same R value of 0.18 as used in Example 1 was used as the negative electrode active material. The obtained negative electrode had a total thickness of 145 μm after calendering, and the arithmetic average roughness (Ra) of the negative electrode mixture layer surface of the negative electrode determined using a confocal laser microscope was 1.1 μm. .

  A lithium secondary battery was produced in the same manner as in Example 1 except that the negative electrode was used.

Example 8
A lithium secondary battery was produced in the same manner as in Example 1 except that the same negative electrode as produced in Example 7 and the same separator as produced in Example 2 were used.

Example 9
A lithium secondary battery was produced in the same manner as in Example 1, except that the same negative electrode as produced in Example 7 and the same separator as produced in Example 3 were used.

Example 10
A nonaqueous electrolytic solution was prepared in the same manner as in Example 1 except that t-butylbenzene was used instead of cyclohexylbenzene, and lithium dihydrogen was prepared in the same manner as in Example 1 except that this nonaqueous electrolytic solution was used. A secondary battery was produced.

Example 11
A lithium secondary battery was produced in the same manner as in Example 1 except that only LiCoO ₂ was used as the positive electrode active material.

Comparative Example 1
A negative electrode was prepared in the same manner as in Example 1 except that only the graphite having the same R value of 0.05 as that used in Example 1 was used as the negative electrode active material, and the negative electrode was used. In the same manner as in Example 1, a lithium secondary battery was produced.

Comparative Example 2
Using the same negative electrode as that produced in Example 1, and using the same PE microporous membrane as that used in the production of the separator in Example 1 as a separator without forming the porous layer (II), Further, a lithium secondary battery was produced in the same manner as in Example 1 except that the nonaqueous electrolytic solution prepared in the same manner as in Example 1 was used except that cyclohexylbenzene was not added. The separator had a puncture strength of 3.7 N, and the pore diameter (bubble point pore diameter) measured by the above method was 0.033 μm.

Comparative Example 3
A lithium secondary battery was produced in the same manner as in Comparative Example 1 except that the same negative electrode as that produced in Example 7 was used.

Comparative Example 4
Except for using the negative electrode produced in the same manner as in Example 1 except that the mass ratio of the graphite having an R value of 0.18 to the graphite having an R value of 0.05 in the negative electrode active material was 50:50. A lithium secondary battery was produced in the same manner as in Comparative Example 2.

Comparative Example 5
A lithium secondary battery was produced in the same manner as in Comparative Example 1 except that the thickness of the PE microporous membrane used for the separator was changed to 16 μm. The puncture strength of the separator was 4.9N.

Comparative Example 6
A lithium secondary battery was produced in the same manner as in Example 1 except that the separator was disposed so that the porous layer (II) was directed to the negative electrode side when producing the wound electrode body.

Comparative Example 7
A negative electrode using only the graphite having an R value of 0.18 in the Raman spectrum, a polyethylene (PE) fine material having no porous layer (II) formed on the surface, and the separator used in Example 1 A lithium secondary battery was produced in the same manner as in Example 1 except that the porous film was used as a separator without forming the porous layer (II).

  For the lithium secondary batteries of Examples 1 to 11 and Comparative Examples 1 to 7, the following room temperature discharge capacity measurement, charge current measurement at −5 ° C. and 10% charge depth, withstand voltage experiment, and high temperature storage test of the battery went. These results are shown in Tables 1 and 2.

<Room temperature discharge capacity measurement>
For the lithium secondary batteries of Examples 1 to 11 and Comparative Examples 1 to 7, constant current discharge was performed at room temperature (25 ° C.) until the battery voltage became 3.0 V at a constant current of 240 mA (0.2 C). Subsequently, after charging at a constant current of 240 mA (0.2 C) up to 4.2 V, a constant voltage charge is performed at 4.2 V until the total charging time is 8 hours, followed by a constant current of 240 mA (0.2 C). Constant current discharge was performed until the battery voltage reached 3.0 V, and the discharge capacity was measured. In Tables 1 and 2, the room temperature discharge capacity of each battery is shown as a relative value when the value of the battery of Comparative Example 1 is 100.

<Measurement of charge current at -5 ° C and 10% charge>
The lithium secondary batteries of Examples 1 to 11 and Comparative Examples 1 to 7 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 Tables 1 and 2, the charging current of each battery is shown as a relative value when the value of the battery of Comparative Example 1 is 100.

<Withstand voltage experiment>
A voltage of 500 V (AC 60 Hz) was applied to each of the 20 lithium secondary batteries of Examples 1 to 11 and Comparative Examples 1 to 7 before injection of the non-aqueous electrolyte, and a battery in which a current of 5 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 secured, the distance between the electrodes is reduced even in the absence of a short circuit, and in extreme cases, the capacity tends to decrease with charge / discharge cycles. 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.

  The test voltage of the withstand voltage may be 1V if it is a positive voltage if only a normal short-circuit check is performed, but 50V or more is desirable, 100V or more is more desirable, and 300V or more is particularly desirable 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 value is preferably 2G (mA) or more when the discharge capacity of the battery at 0.2 C when expressed by the Ah value is G (Ah). The above is more desirable. In addition, since the detection rate decreases if the determination current value is set too high, it is preferably 20 G (mA) or less, and more preferably 10 G (mA) or less. Since the discharge capacity G of the batteries of this example and the comparative example is 1.2 (Ah), 5 mA is 4 G (mA) or more and 10 G (mA) or less. By incorporating this withstand voltage test into the battery manufacturing process, the reliability of the manufactured battery is further increased, which is desirable.

  The effect of improving the reliability by the withstand voltage experiment becomes apparent when the thickness of the porous layer (I) of the separator is 20 μm or less.

<Overcharge test>
For the lithium secondary batteries of Examples 1 to 11 and Comparative Examples 1 to 7, after discharging the battery to 3.0 V at 1 C (1200 mA), the upper limit voltage was set to 15 V in an environment of 23 ° C. and 0.5 C ( 600 mA) was charged, the surface temperature of each battery at that time was measured, and the maximum temperature was determined.

<High temperature storage test>
For the lithium secondary batteries of Examples 1 to 11 and Comparative Examples 1 to 7, constant current charging was performed at a current value of 1.0 C until the battery voltage reached 4.25 V, and then constant voltage charging at 4.25 V A constant current-constant voltage charge 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. In Tables 1 and 2, the battery surface temperature increased to 160 ° C. or higher was indicated as “x”, and the case where such temperature increase was not observed was indicated as “◯”.

As shown in Tables 1 and 2, by placing the separator porous layer (II) on the positive electrode side as in the examples, overcharge of an additive having an alkyl group bonded to a benzene ring such as cyclohexylbenzene. A unique effect to enhance the safety improvement effect was observed. On the other hand, since the maximum temperature at the time of overcharge in Example 1 is lower than that in Comparative Example 6, the effect of disposing the separator porous layer (II) on the positive electrode side and the non-aqueous electrolyte The action of the additive having an alkyl group bonded to the benzene ring functions synergistically on the positive electrode side. On the other hand, when the separator porous layer (II) is disposed on the negative electrode side, the maximum temperature during overcharge tends to increase. In addition, the use of graphite coated with low-crystal carbon as the negative electrode active material (graphite whose R value and d ₀₀₂ satisfy the above values) improves the charging characteristics at low temperatures of the battery. In general, when a battery is formed using a thin polyolefin separator of 14 μm or less, the yield in the production process tends to deteriorate, but the electrochemical device of the present invention (lithium secondary battery) Then, the productivity will also become favorable by using the separator in which the porous layer (II) was formed.

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.

Explanation of symbols

1 Positive electrode 2 Negative electrode 3 Separator

Claims (9)

An electrochemical device having a positive electrode, a negative electrode, a non-aqueous electrolyte and a separator,
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. Layer (II) faces at least the positive electrode,
The negative electrode is a R value of 0.1 to 0.5 is the peak intensity ratio of 1360 cm ^-1 to the peak intensity of 1580 cm ^-1 in the argon ion laser Raman spectrum, the surface spacing _{d 002} of the 002 plane is 0.338nm It contains the following graphite as a negative electrode active material,
The ratio of the graphite in the negative electrode active material is 70% by mass or more,
The non-aqueous electrolyte contains a compound in which an alkyl group is bonded to a benzene ring.   The electrochemical element according to claim 1, wherein the negative electrode further contains graphite having an R value of less than 0.1 as a negative electrode active material.   The electrochemical element according to claim 1 or 2, wherein the separator has a pore diameter of 0.025 to 0.07 µm.   The electrochemical element according to any one of claims 1 to 3, wherein at least a part of the filler contained in the porous layer (II) is a plate-like particle.   The electrochemical element according to any one of claims 1 to 4, wherein at least a part of the filler contained in the porous layer (II) has a secondary particle structure in which primary particles are aggregated.   The electrochemical element according to any one of claims 1 to 5, wherein the filler contained in the porous layer (II) is at least one particle selected from the group consisting of alumina, silica and boehmite.   The electrochemical element according to any one of claims 1 to 6, wherein the porous layer (I) contains a polyolefin having a melting point of 80 to 150 ° C.   The electrochemical element according to any one of claims 1 to 7, wherein a nonaqueous electrolytic solution having a content of a compound in which an alkyl group is bonded to a benzene ring is 0.5 to 5% by mass.   The electrochemical element according to any one of claims 1 to 8, wherein the compound having an alkyl group bonded to a benzene ring is cyclohexylbenzene.

Images