JP2011054503A - Separator for electrochemical element, electrochemical element and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrochemical element that is superior in high-temperature storage characteristics and charge-discharge cycle characteristics and has superior safety at temperature rise, and a manufacturing method thereof, and a separator with which the electrochemical element can be constructed. <P>SOLUTION: A separator has a porous resin layer (I), including primary components of a resin (A) whose melting point is 80-180°C, and a heat-resistant porous layer (II) formed with a filler (B), having a heatproof temperature of 150°C or higher being coupled therewith by an organic binder (C), wherein the heat-resistant porous layer (II) contains an adhesive resin (D) that develops adhesiveness by heating the resin at a temperature lower than the melting point of the resin (A). An electrochemical element has such a separator which is integrated with an electrode. An electrochemical element is manufactured by a manufacturing method including a step of hot-pressing a group of electrodes comprising the separator and an electrode. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an electrochemical element excellent in high-temperature storage characteristics and charge / discharge cycle characteristics, and excellent in safety at abnormal temperature rise, a method for producing the same, and a separator for an electrochemical element that can constitute the electrochemical element It is about.

  A lithium secondary battery, which is a kind of electrochemical element, is widely used as a power source for portable devices such as mobile phones and notebook personal computers because of its high energy density.

  In a current lithium secondary battery, for example, a polyolefin-based porous film (microporous film) having a thickness of about 15 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 shutdown temperature. For this reason, when a polyolefin-based porous film separator is used, when the battery temperature reaches the shutdown temperature in the case of abnormal charging, the current must be immediately decreased 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 battery temperature easily rises to the contraction temperature of the separator, and there is a risk of ignition due to 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 multilayer in which a layer having high heat resistance is formed on the surface of a resin porous film (microporous film) serving as a base Structured separators have been proposed (for example, Patent Documents 1 to 5). By using these separators, for example, thermal runaway hardly occurs even when abnormal overheating occurs, and a battery having excellent reliability can be configured.

  In addition, in lithium secondary batteries, various battery characteristics are required to be improved along with improvements in the functions of applied devices. For example, in order to improve energy density, in general, use in a high temperature environment or for a long time is required. Deterioration is severe due to the use of the battery, resulting in a problem of battery durability. In addition, the increase in energy density makes it difficult to ensure safety that suppresses the occurrence of abnormalities such as battery smoke and fire.

  Degradation factors of such lithium secondary batteries include the process of repeated storage and charge / discharge in a high temperature environment, where the nonaqueous electrolyte decomposes and gas is generated in the battery, and the electrodes in the battery themselves expand and contract. For example, the distance between the positive electrode and the negative electrode may vary, and the uniformity of the charge / discharge reaction may be lost.

  On the other hand, as one means for solving such a problem, a method of arranging an adhesive layer between the separator and the electrode and integrating the separator and the electrode via the adhesive layer has been developed. It has been proposed to use polyvinylidene fluoride (PVDF) or the like as the constituent resin of the layer (Patent Documents 6 to 10).

  Also proposed is a technology in which a polymer having a polymerizable functional group is supported on a separator and polymerization is started by a non-aqueous electrolyte in the battery to form a crosslinked structure, whereby the electrode and the separator are bonded and integrated. (Patent Documents 11 to 13).

JP 2006-351386 A JP 2007-273123 A JP 2007-273443 A JP 2007-280911 A JP 2008-123996 A Japanese Patent Laid-Open No. 10-255849 Japanese Patent Laid-Open No. 2003-77545 JP-A-10-172606 JP-A-10-177865 Japanese Patent Laid-Open No. 10-189054 JP 2005-100951 A JP 2007-157469 A JP 2007-157570 A

  However, since the technique described in Patent Document 6 uses a PVDF porous film as a separator, it becomes difficult for the separator to maintain the film shape, for example, when the temperature inside the battery is equal to or higher than the melting point of PVDF. There is a risk that a short circuit may occur easily.

  In the technique described in Patent Document 7, a porous layer such as PVDF is formed on the surface of a microporous film made of, for example, polyethylene (PE), thereby preventing a short circuit due to melting of PVDF or the like. However, the microporous membrane made of PE is weak against heat, and further shrinks when heated, so that it is difficult to sufficiently prevent a short circuit between the positive and negative electrodes when the temperature in the battery rises.

  Furthermore, in the techniques described in Patent Documents 8 to 10, for example, an adhesive resin layer is formed on the surface of a microporous film made of polypropylene (PP), and PP is superior in heat resistance to PE, but made of PP This microporous membrane is similar to the microporous membrane made of PE in that it shrinks when heated, and it is difficult to say that these can sufficiently prevent a short circuit between the positive and negative electrodes when the temperature in the battery rises.

  Further, Patent Documents 11 to 13 can exhibit an effect of suppressing thermal contraction of the PE microporous membrane by forming a reactive adhesive resin layer on the surface of the PE microporous membrane and integrating it with the electrode. Although it is described, the short circuit resistance when the inside of the battery becomes high temperature is not particularly considered, and since the PE microporous film is used, the short circuit in such a case can be sufficiently suppressed. It is hard to be.

  For this reason, in electrochemical devices such as lithium secondary batteries, the deterioration of characteristics due to the occurrence of variations in the distance between the positive electrode and the negative electrode due to repeated storage and charging / discharging in a high temperature environment is suppressed. On the other hand, the development of technology that can improve safety during abnormal temperature rise is required.

  The present invention has been made in view of the above circumstances, and its purpose is an electrochemical element excellent in high-temperature storage characteristics and charge / discharge cycle characteristics, and excellent in safety at abnormal temperature rise, and a method for producing the same And a separator capable of constituting the electrochemical device.

  The separator for an electrochemical element of the present invention capable of achieving the above object is a separator used for an electrochemical element having a positive electrode, a negative electrode, a nonaqueous electrolyte and a separator, and has a melting point of 80 to 180 ° C. A porous resin layer (I) comprising A) as a main component and a heat resistant porous layer (II) formed by binding a filler (B) having a heat resistant temperature of 150 ° C. or higher with an organic binder (C). The heat-resistant porous layer (II) contains an adhesive resin (D) that exhibits adhesiveness when heated to a temperature lower than the melting point of the resin (A). It is a feature.

  The electrochemical element of the present invention is an electrochemical element having a positive electrode, a negative electrode, a non-aqueous electrolyte and a separator, wherein the separator is a separator for an electrochemical element of the present invention, and the separator is a positive electrode and a negative electrode It is characterized by being integrated with at least one of the above.

  Furthermore, the method for producing an electrochemical element of the present invention is a method for producing an electrochemical element having a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator, and the separator for an electrochemical element of the present invention is used. A process of forming an electrode group by winding and laminating between the positive electrode and the negative electrode, or by laminating and laminating the separator between the positive electrode and the negative electrode, and heating pressing the electrode group And a step of integrating at least one of the positive electrode and the negative electrode with the separator.

  According to the present invention, an electrochemical element excellent in high-temperature storage characteristics and charge / discharge cycle characteristics and excellent in safety at abnormal temperature rise, a method for producing the same, and a separator that can constitute the electrochemical element are provided. be able to.

It is an external appearance perspective view which shows an example of the electrochemical element (lithium secondary battery) of this invention. It is the II sectional view taken on the line of FIG.

  The separator for an electrochemical device of the present invention comprises a resin porous layer (I) mainly composed of a resin (A) having a melting point of 80 to 180 ° C. and a filler (B) having a heat resistant temperature of 150 ° C. or higher as an organic binder ( C) and the heat-resistant porous layer (II) formed by binding. The resin porous layer (I) is a layer having an original function of transmitting a separator while preventing a short circuit between the positive electrode and the negative electrode in an electrochemical device using the separator of the present invention. II) is a layer that plays a role of imparting heat resistance to the separator.

  The heat-resistant porous layer (II) contains an adhesive resin (D) that exhibits adhesiveness when heated, separately from the organic binder (C). The separator of the present invention can be bonded and integrated with the positive electrode and / or the negative electrode constituting the electrochemical element by the action of the adhesive resin (D). Therefore, in the electrochemical device using the electrode group in which the separator of the present invention is used and integrated with the positive electrode and / or the negative electrode, between the positive electrode and the negative electrode even during high-temperature storage and under repeated charge / discharge conditions. The distance is less likely to vary, and the deterioration of the charge / discharge characteristics is suppressed.

  The resin porous layer (I) has a melting point of 80 ° C. or higher (preferably 100 ° C. or higher) and 180 ° C. or lower, that is, melting measured using a differential scanning calorimeter (DSC) in accordance with JIS K 7121. The main component is a resin (A) having a temperature of 80 ° C. or higher (preferably 100 ° C. or higher) and 180 ° C. or lower. By using a separator having such a resin porous layer (I) containing the resin (A) as a main component, the thermoplastic resin melts when the inside of the electrochemical device using the separator becomes high temperature. Thus, a so-called shutdown function for closing the hole of the separator can be ensured.

  The resin (A) as the main component of the resin porous layer (I) has a melting point of 80 ° C. or higher and 180 ° C. or lower, has an electrical insulating property, is electrochemically stable, and will be described in detail later. There is no particular limitation as long as it is a thermoplastic resin that is stable to the medium used in the composition for forming the non-aqueous electrolyte solution or the heat-resistant porous layer (II) of the electrochemical element, but low density polyethylene, high density polyethylene, Examples thereof include polyolefins such as polyethylene (PE) such as ultrahigh molecular weight polyethylene and polypropylene (PP); thermoplastic polyurethanes, etc., and only one of these may be used, or two or more may be used in combination. .

  For the resin porous layer (I), for example, a polyolefin microporous film used in electrochemical elements such as conventionally known lithium secondary batteries, that is, a polyolefin mixed with an inorganic filler or the like is used. A film or sheet formed by uniaxial or biaxial stretching to form fine pores can be used. Also, the resin (A) and another resin are mixed to form a film or sheet, and then the film or sheet is immersed in a solvent that dissolves only the other resin, so that only the other resin is mixed. What melt | dissolved and formed the void | hole can also be used as a resin porous layer (I).

  The resin porous layer (I) may contain a filler for the purpose of improving the strength. Examples of such a filler include various fillers described later as specific examples of the filler (B) used in the heat resistant porous layer (II).

  The “resin (A) as a main component” in the resin porous layer (I) includes 70% by volume or more of the resin (A) in the total volume of the constituent components of the resin porous layer (I). It means that. The amount of the resin (A) in the resin porous layer (I) is preferably 80% by volume or more and more preferably 90% by volume or more in the total volume of the constituent components of the resin porous layer (I). preferable.

  The pore diameter of the resin porous layer (I) is preferably 3.0 μm or less from the viewpoint of satisfactorily suppressing the occurrence of a short circuit even when small pieces are peeled off from the positive electrode or the negative electrode.

In addition, the porosity of the resin porous layer (I) is 30% or more in a dry state in order to secure a liquid retention amount of the non-aqueous electrolyte included in the electrochemical element and to improve ion permeability. It is preferable that it is 40% or more. On the other hand, the porosity of the resin porous layer (I) is preferably 80% or less and 70% or less in the dry state from the viewpoint of ensuring strength and ensuring the shutdown function satisfactorily. Is more preferable. In addition, the porosity: P (%) is obtained from the thickness of the resin porous layer (I), the mass per area, and the density of the constituent components by using the following formula (1) to obtain the sum for each component i. Can be calculated by
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 resin porous layer (I) ( g / cm ² ), t: thickness (cm) of the porous resin layer (I).

  Moreover, the thickness of the resin porous layer (I) [when the separator has a plurality of resin porous layers (I), the total thickness thereof. The same applies to the thickness of the resin porous layer (I). ] Is preferably 8 μm or more and more preferably 10 μm or more from the viewpoint of ensuring a good shutdown function. However, if the resin porous layer (I) is too thick, the volume ratio occupied by the separator in the electrochemical element becomes too large, which may cause a decrease in capacity of the electrochemical element, for example, and the thickness is 40 μm or less. It is preferable that it is and it is more preferable that it is 30 micrometers or less.

  The heat resistant porous layer (II) according to the separator of the present invention contains a filler (B) having a heat resistant temperature of 150 ° C. or higher, and the filler (B) has a heat resistant temperature of 150 ° C. or higher and is electrochemical. There is no particular limitation as long as it is electrochemically stable in the device and stable with respect to the non-aqueous electrolyte in the electrochemical device. In the present specification, the “heat-resistant temperature is 150 ° C. or higher” in the filler (B) means that shape change such as deformation is not visually confirmed at least at 150 ° C. The heat-resistant temperature of the filler (B) is preferably 200 ° C. or higher, more preferably 300 ° C. or higher, and further preferably 500 ° C. or higher.

The filler (B) is preferably an inorganic fine particle having electrical insulation, and specifically, iron oxide, silica (SiO ₂ ), alumina (Al ₂ O ₃ ), TiO ₂ , BaTiO ₃ , ZrO _{2 and the} like. Inorganic oxide fine particles; inorganic nitride fine particles such as aluminum nitride and silicon nitride; poorly soluble ionic crystal fine particles such as calcium fluoride, barium fluoride and barium sulfate; covalently bonded crystal fine particles such as silicon and diamond; talc, And clay fine particles such as montmorillonite. Here, the inorganic oxide fine particles may be fine particles such as boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite and the like, or artificial products thereof. In addition, the inorganic compound constituting these inorganic fine particles may be element-substituted or solid solution, if necessary, and the inorganic fine particles may be surface-treated. In addition, the inorganic fine particles electrically insulate the surface of a conductive material exemplified by metals, SnO ₂ , conductive oxides such as tin-indium oxide (ITO), carbonaceous materials such as carbon black and graphite. It is also possible to use particles that are made electrically insulating by coating with a material having the above (for example, the above-mentioned inorganic oxide).

  Organic fine particles can also be used for the filler (B). Specific examples of the organic fine particles include polyimide, melamine resin, phenol resin, crosslinked polymethyl methacrylate (crosslinked PMMA), crosslinked polystyrene (crosslinked PS), polydivinylbenzene (PDVB), benzoguanamine-formaldehyde condensate, etc. Molecular fine particles; heat-resistant polymer fine particles such as thermoplastic polyimide; The organic resin (polymer) constituting these organic fine particles is a mixture, modified body, derivative, copolymer (random copolymer, alternating copolymer, block copolymer, graft copolymer) of the materials exemplified above. ) Or a crosslinked product (in the case of the heat-resistant polymer).

  As the filler (B), those exemplified above may be used singly or in combination of two or more. Among the various fillers exemplified above, inorganic oxide fine particles are preferable, more specifically. Is more preferably at least one selected from alumina, silica and boehmite.

  The particle size of the filler (B) is an average particle size, preferably 0.001 μm or more, more preferably 0.1 μm or more, preferably 15 μm or less, more preferably 1 μm or less. The average particle size of the filler (B) is, for example, a volume standard measured by dispersing the filler (B) in a medium that does not dissolve, using a laser scattering particle size distribution meter (for example, “LA-920” manufactured by HORIBA). Is the particle size (D50) at 50% of the cumulative fraction.

The shape of the filler (B) may be, for example, a shape close to a sphere or a plate shape, but is preferably a plate-like particle from the viewpoint of preventing a short circuit. Typical examples of the plate-like particles include plate-like Al ₂ O ₃ and plate-like boehmite.

  In the case where the filler (B) is a plate-like particle, the aspect ratio is preferably 5 or more, more preferably 10 or more, and preferably 100 or less, and 50 or less. More preferably. Furthermore, the average value of the ratio of the length in the major axis direction to the length in the minor axis direction (length in the major axis direction / length in the minor axis direction) of the flat plate surface of the grains is preferably 3 or less, and preferably 2 or less. Is more preferable, and a value close to 1 is particularly preferable.

  In addition, the average value of the ratio of the length in the major axis direction to the length in the minor axis direction of the flat plate surface in the plate-like filler (B) is, for example, image analysis of an image taken with a scanning electron microscope (SEM). It can ask for. Further, the aspect ratio of the plate-like particles can be obtained by image analysis of an image taken by SEM.

  The presence form of the plate-like filler (B) in the separator is preferably such that the flat plate surface is substantially parallel to the surface of the separator, and more specifically, the plate-like filler (B) in the vicinity of the separator surface. The average angle between the flat plate surface and the separator surface is preferably 30 ° or less [most preferably, the average angle is 0 °, that is, the plate-like flat plate surface in the vicinity of the separator surface is Parallel to the surface]. Here, “near the surface” refers to a range of about 10% from the surface of the separator to the entire thickness. When the presence of the plate-like filler (B) is as described above, the resin porous layer (I) can be more effectively prevented from thermal shrinkage, and as a whole, a separator having a particularly low thermal shrinkage rate is formed. can do.

  In the electrochemical device using the separator of the present invention, when a high output characteristic is required, it is preferable to use a filler having a secondary particle structure in which primary particles are aggregated as the filler (B). By using the filler having the above structure, it is possible to enlarge the voids of the heat resistant porous layer (II), and it is possible to form an electrochemical element having high output characteristics.

  In order to construct an electrochemical device with higher output characteristics, the filler (B) used for the heat resistant porous layer (II) has an aspect ratio of 1.0 to 1.0 as in the case of the plate shape. 3.0 polyhedron shape [meaning a shape surrounded by a substantially polygonal (including polygonal) surface, specifically, a substantially rhombohedral shape (including rhombohedral shape), a substantially hexagonal prism shape ( It is preferable to use a shape such as a hexagonal column shape), a substantially cubic shape (including a cube shape), or a spherical shape (true and substantially spherical).

  As the organic binder (C) used for the heat resistant porous layer (II), the filler (B) and the heat resistant porous layer (II) and the resin porous layer (I) can be satisfactorily bonded, and electrochemically. There is no particular limitation as long as it is stable and stable with respect to the non-aqueous electrolyte for electrochemical devices. Specifically, fluororesin [polyvinylidene fluoride (PVDF), etc.], fluoro rubber, styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), polyvinyl alcohol (PVA), polyvinyl butyral (PVB) ), Polyvinylpyrrolidone (PVP), poly N-vinylacetamide, cross-linked acrylic resin, polyurethane, epoxy resin and the like. These organic binders may be used alone or in combination of two or more.

  Among the organic binders exemplified above, a heat-resistant resin having a heat resistance of 150 ° C. or higher, for example, a melting point (melting temperature) measured in the same manner as the resin (A) is 150 ° C. or higher or does not show a melting point. Resins are preferable, and in particular, highly flexible materials such as fluorine-based rubber and SBR are more preferable. Specific examples thereof include “DAIEL Latex Series (fluorine rubber, trade name)” manufactured by Daikin Industries, Ltd., “TRD-2001 (SBR, trade name)” manufactured by JSR Corporation, and “EM- 400B (SBR, trade name) ". A cross-linked acrylic resin (self-crosslinking acrylic resin) having a low glass transition temperature and having a structure in which butyl acrylate is a main component and is cross-linked is also preferable.

  In using these organic binders, they may be used in the form of an emulsion dissolved or dispersed in a medium of a composition (slurry or the like) for forming a heat resistant porous layer (II) described later.

  The adhesive resin (D) contained in the heat resistant porous layer (II) has a function of developing adhesiveness by heating, but the minimum temperature at which the adhesive resin (D) exhibits adhesiveness is the separator. The temperature must be lower than the melting point of the resin (A) (details will be described later), which is the main component of the resin porous layer (I), and specifically, it should be 60 ° C. or higher and 120 ° C. or lower. preferable. By using such an adhesive resin (D), it is possible to satisfactorily suppress the deterioration of the resin porous layer (I) when the separator and the positive electrode and / or the negative electrode are integrated by heating and pressing. it can.

  There is almost no adhesiveness (stickiness) at room temperature (for example, 25 ° C.), and the performance that develops adhesiveness by thermocompression bonding is called delayed tackiness, but the separator of the present invention has the presence of adhesive resin (D). Therefore, it is preferable to have such a delayed tack property. More specifically, for example, the peel strength obtained when a peel test at 180 ° between the electrode (for example, positive electrode) constituting the electrochemical element and the separator is performed is preferably in the state before the hot press. Is less than 0.05 N / 20 mm, particularly preferably 0 N / 20 mm (a state having no adhesive force), and a delayed tack property of 0.05 N / 20 mm or more in a state after being hot-pressed at a temperature of 60 to 120 ° C. It is preferable to have.

  However, if the peel strength is too strong, the electrode mixture layer (the positive electrode mixture layer and the negative electrode mixture layer) may peel from the current collector of the electrode, and the conductivity may be lowered. The peel strength by the peel test at ° is preferably 10 N / 20 mm or less after being hot-pressed at a temperature of 60 to 120 ° C.

  In addition, the peel strength at 180 ° between the electrode and the separator in the present specification is a value measured by the following method. The separator and the electrode are each cut into a size of 5 cm in length and 2 cm in width, and the cut-out separator and the electrode are overlapped. When obtaining the peel strength in the state after being hot-pressed, a test piece is prepared by hot-pressing a 2 cm × 2 cm region from one end. The end of the test piece on the side where the separator and the electrode are not heated and pressed is opened, and the separator and the electrode are bent so that these angles are 180 °. Thereafter, using a tensile tester, both the one end side of the separator opened at 180 ° of the test piece and the one end side of the electrode are gripped and pulled at a pulling speed of 10 mm / min. Measure the strength when peeled off. In addition, the peel strength of the separator and the electrode before heating press was determined by preparing a test piece in the same manner as above except that the separator and electrode cut out as described above were stacked and pressed without heating. The peel test is performed in the same manner as described above.

  Therefore, the adhesive resin (D) used in the separator of the present invention has almost no adhesiveness (tackiness) at room temperature (for example, 25 ° C.), and the lowest temperature at which adhesiveness is developed is lower than the melting point of the resin (A). Preferably, those having a delayed tack property of 60 ° C. or higher and 120 ° C. or lower are desirable. The temperature of the heating press when integrating the separator and the electrode is more preferably 80 ° C. or higher and 100 ° C. or lower so that the thermal contraction of the resin porous layer (I) constituting the separator does not occur so significantly. The minimum temperature at which the adhesiveness of the adhesive resin (D) is manifested is more preferably 80 ° C. or higher and 100 ° C. or lower.

  As the adhesive resin (D) having a delayed tack property, a resin that has almost no fluidity at room temperature, exhibits fluidity when heated, and has a property of being in close contact with a press is preferable. Further, a resin of a type that is solid at room temperature, melts by heating, and exhibits adhesiveness by a chemical reaction can be used as the adhesive resin (D).

  The adhesive resin (D) preferably has a softening point in the range of 60 ° C. or higher and 120 ° C. or lower with the melting point, glass transition point and the like as indices. The melting point and glass transition point of the adhesive resin (D) are determined by, for example, the method specified in JIS K 7121, and the softening point of the adhesive resin (D) is determined by, for example, the method specified in JIS K 7206. Can be measured.

  Specific examples of such adhesive resin (D) include, for example, low density polyethylene (LDPE), poly-α-olefin [PP, polybutene-1, etc.], polyacrylate ester, polyvinyl acetate, and these resins. [Ethylene-vinyl acetate copolymer (EVA), ethylene-methyl acrylate copolymer (EMA), ethylene-ethyl acrylate copolymer (EEA), ethylene-butyl acrylate copolymer] Polymer (EBA), ethylene-methyl methacrylate copolymer (EMMA), ionomer resin, etc.].

  Each resin, or a resin having adhesiveness at room temperature such as SBR, nitrile rubber (NBR), fluorine rubber, or ethylene-propylene rubber is used as a core, and the melting point and softening point are within a range of 60 ° C to 120 ° C. A resin having a core-shell structure with a resin as a shell can be used as the adhesive resin (D). In this case, various acrylic resins and polyurethane can be used for the shell. Furthermore, as the adhesive resin (D), one-pack type polyurethane, epoxy resin, or the like that exhibits adhesiveness in the range of 60 ° C. or higher and 120 ° C. or lower can be used.

  In the adhesive resin (D), the above-exemplified resins may be used alone or in combination of two or more.

  Commercial products of the adhesive resin (D) having the delayed tack as described above include “Morescommelt Excel Peel (PE, trade name)” manufactured by Matsumura Oil Research Laboratory, “Aqua-Tex (EVA) manufactured by Chuo Rika Kogyo Co., Ltd. , Product name) ", EVA manufactured by Nihon Unicar," Heat Magic (EVA, product name) "manufactured by Toyo Ink, and" Evaflex-EEA series (ethylene-acrylic acid copolymer) manufactured by Mitsui DuPont Polychemical Co., Ltd. " , “Trade name” ”,“ Aron Tac TT-1214 (acrylic ester, trade name) ”manufactured by Toa Gosei Co., Ltd.,“ High Milan (ethylene ionomer resin, trade name) ”manufactured by Mitsui DuPont Polychemical Co., Ltd., and the like.

  In the heat resistant porous layer (II), the amount of the organic binder (C) improves the binding between the fillers (B) and the adhesion between the heat resistant porous layer (II) and the resin porous layer (I). From a viewpoint, it is preferable that it is 1 mass part or more with respect to 100 mass parts of fillers (B), and it is more preferable that it is 2 mass parts or more. However, if the amount of the organic binder (C) in the heat-resistant porous layer (II) is too large, the pores of the heat-resistant porous layer (II) are blocked, and various characteristics of electrochemical devices represented by load characteristics in particular are May decrease. Therefore, the amount of the organic binder (C) in the heat resistant porous layer (II) is preferably 30 parts by mass or less and more preferably 20 parts by mass or less with respect to 100 parts by mass of the filler (B). .

  In addition, in the heat resistant porous layer (II), the amount of the adhesive resin (D) improves the adhesion between the separator and the electrode, and improves the high temperature storage characteristics and charge / discharge cycle characteristics of the electrochemical device. From a viewpoint of ensuring favorable, it is preferable that it is 1 mass part or more with respect to 100 mass parts of filler (B), and it is more preferable that it is 10 mass parts or more. However, if the amount of the adhesive resin (D) in the heat-resistant porous layer (II) is too large, the pores of the heat-resistant porous layer (II) are blocked, and various characteristics of electrochemical devices represented by load characteristics in particular. May decrease. Therefore, the amount of the adhesive resin (D) in the heat resistant porous layer (II) is preferably 50 parts by mass or less and more preferably 40 parts by mass or less with respect to 100 parts by mass of the filler (B). preferable.

  Furthermore, the amount of the filler (B) in the heat resistant porous layer (II) is the composition of the heat resistant porous layer (II) from the viewpoint of satisfactorily suppressing the heat shrinkage of the entire separator and imparting high heat resistance to the separator. The total volume of the components is preferably 50% by volume or more, and more preferably 60% by volume or more. Therefore, in the formation of the heat resistant porous layer (II), the amount of the organic binder (C) and the adhesive resin (D) is set to the above-described preferable value while the amount of the filler (B) is set to the above-described preferable value. It is preferable to adjust the composition ratio of each component so that

The porosity of the heat-resistant porous layer (II) is 30% or more in a dry state in order to secure the amount of the nonaqueous electrolyte solution possessed by the electrochemical element and improve the ion permeability. It is preferable that it is 50% or more. On the other hand, from the viewpoint of securing strength and preventing internal short circuit, the porosity of the heat resistant porous layer (II) is preferably 80% or less and more preferably 70% or less in a dry state. . The porosity of the heat-resistant porous layer (II): P (%) is obtained by using the formula (1), and m is the mass per unit area (g / cm ² ) of the heat-resistant porous layer (II). , T can be determined as the thickness (cm) of the heat resistant porous layer (II).

  The separator of the present invention may have one resin porous layer (I) and one heat resistant porous layer (II), and the heat resistant porous layer (II) is disposed on at least one side of the separator. If it is, you may have two or more of either one layer or both layers. Specifically, the heat-resistant porous layer (II) is disposed only on one surface of the resin porous layer (I) to form a separator. For example, the heat-resistant porous layer (II) is formed on both surfaces of the resin porous layer (I). ) May be arranged as a separator. However, if the separator has too many layers, it is not preferable because the thickness of the separator is increased, which may increase the internal resistance of the electrochemical device and decrease the energy density. The number of layers in the separator is 5 or less. It is preferable that

  The thickness of the entire separator is preferably 10 μm or more and 50 μm or less.

  The separator of the present invention is, for example, a composition for forming a heat resistant porous layer (II) containing a filler (B), an organic binder (C), an adhesive resin (D) and the like in the resin porous layer (I) ( It can be manufactured by a method of forming a heat resistant porous layer (II) by applying a liquid composition such as a slurry and drying at a predetermined temperature.

  The heat-resistant porous layer (II) forming composition contains a filler (B), an organic binder (C), an adhesive resin (D), and the like, and these are dispersed in a solvent (including a dispersion medium; the same applies hereinafter). It has been made. The organic binder (C) and the adhesive resin (D) can also be dissolved in a solvent. The solvent used in the heat-resistant porous layer (II) forming composition can uniformly disperse the filler (B) and the like, and can dissolve or disperse the organic binder (C) and the adhesive resin (D) uniformly. For example, organic solvents such as aromatic hydrocarbons such as toluene, furans such as tetrahydrofuran, ketones such as methyl ethyl ketone and methyl isobutyl ketone are generally 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 heat resistant porous layer (II) preferably has a solid content including the filler (B), the organic binder (C) and the adhesive resin (D), for example, 10 to 80% by mass.

  In order to increase the adhesive strength between the resin porous layer (I) and the heat resistant porous layer (II), the resin porous layer (I) [resin porous layer] is formed before the heat resistant porous layer (II) is formed. Surface modification of the resin (A) for forming (I) and the like as a main component]. In particular, when the resin (A) constituting the resin porous layer (I) is a polyolefin, its surface adhesion is generally not high, and surface modification is often effective.

  Examples of the method for modifying the surface of the resin porous layer (I) before forming the heat resistant porous layer (II) include methods such as corona discharge treatment, plasma discharge treatment, and ultraviolet irradiation treatment. From the viewpoint of environmental problems in recent years, it is more preferable to use water as the solvent for the composition for forming the heat resistant porous layer (II). Also from this point, the resin porous layer can be obtained by surface modification. (I) It is very preferable to increase the hydrophilicity of the surface.

  In addition, for using plate-like particles as filler (B) and enhancing the orientation of such plate-like particles to make their functions more effective, the heat-resistant porous layer (II) containing plate-like particles is formed. After applying the composition to the resin porous layer (I), a method of applying a shear or a magnetic field to the composition may be used. For example, after applying a heat-resistant porous layer (II) -forming composition containing a plate-like filler (B) to the resin porous layer (I), a share is given to the composition by passing through a certain gap. You can hang it.

  Further, in order to more effectively exert the functions of the constituents such as the filler (B), the constituents are unevenly distributed, and the constituents are gathered in layers in parallel or substantially parallel to the separator film surface. It is good.

  In addition, the manufacturing method of the separator of this invention is not necessarily limited to the said method, You may manufacture by another method. For example, the heat-resistant porous layer (II) forming composition is applied to a substrate surface such as a liner and dried to form the heat-resistant porous layer (II), and then peeled off from the substrate. The heat-resistant porous layer (II) can be laminated with a microporous film or the like to be the resin porous layer (I) and integrated by hot pressing or the like to produce a separator.

  The separator of the present invention has a heat shrinkage rate measured when it is allowed to stand in a temperature atmosphere of 150 ° C., specifically, a heat shrinkage rate measured by the method described in Examples described later in a range of 0 to 10% or less. Preferably there is. If the thermal contraction rate of the separator is too large, the separator contracts during abnormal heat generation of the electrochemical element, thereby increasing the possibility of occurrence of a short circuit between the positive and negative electrodes. The thermal contraction rate of the separator can be ensured by configuring the separator as described above.

  The electrochemical device to which the separator of the present invention can be applied is not particularly limited as long as it uses a non-aqueous electrolyte, and in addition to a lithium secondary battery, a lithium primary battery, a super capacitor, etc. It can be preferably applied if it is a use that requires high performance. That is, as long as the electrochemical device of the present invention includes the separator of the present invention, other configurations and structures are not particularly limited, and various electrochemical devices having a conventionally known non-aqueous electrolyte ( Various configurations and structures included in a lithium secondary battery, a lithium primary battery, a super capacitor, and the like can be employed.

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

The positive electrode used for the lithium secondary battery conventionally known can be used for the positive electrode which concerns on a lithium secondary battery. For example, the positive electrode active material is not particularly limited as long as it is an active material used in a conventionally known lithium secondary battery, that is, an active material capable of occluding and releasing Li ions. For example, a lithium-containing transition metal oxide having a layered structure represented by Li _{1 + x} MO ₂ (−0.1 <x <0.1, M: Co, Ni, Mn, Al, Mg, etc.), LiMn ₂ O ₄ , It is possible to use a spinel structure lithium manganese oxide in which a part of the element is substituted with another element, an olivine type compound represented by LiMPO ₄ (M: Co, Ni, Mn, Fe, etc.), or the like.

Specific examples of the lithium-containing transition metal oxide having a layered structure include LiCoO ₂ and LiNi _1-x Co _xy Al _y O ₂ (0.1 ≦ x ≦ 0.3, 0.01 ≦ y ≦ 0. 2) and other oxides containing at least Co, Ni and Mn (LiMn _1/3 Ni _1/3 Co _1/3 O ₂ , LiMn _5/12 Ni _5/12 Co _1/6 O ₂ , LiMn _{3 / 5} Ni _1/5 Co _1/5 O ₂ etc.).

  Examples of the positive electrode conductive assistant include carbon materials such as carbon black, and examples of the positive electrode binder include fluorine resins such as polyvinylidene fluoride (PVDF). For the positive electrode, it is possible to use a positive electrode mixture layer formed of a positive electrode mixture containing the positive electrode active material, a conductive additive and a binder on one or both sides of the current collector. .

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

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

The negative electrode is a negative electrode used in a conventionally known lithium secondary battery, that is, at least one selected from a carbon material that can occlude and release Li ions, a lithium alloy, a metal that can be alloyed with lithium, and a lithium metal. There is no particular limitation as long as it is a negative electrode using a seed as an active material. More specifically, the active material occludes lithium, such as graphite, pyrolytic carbons, cokes, glassy carbons, fired organic polymer compounds, mesocarbon microbeads (MCMB), and carbon fibers. , One or a mixture of two or more releasable carbon-based materials is used. In addition, elements such as Si, Sn, Ge, Bi, Sb, In and alloys thereof, or lithium-containing oxides such as lithium metal, lithium / aluminum alloy, Li ₄ Ti ₅ O ₁₂ , and Li ₂ Ti ₃ O ₇ are also used as negative electrode actives. It can be used as a substance. A negative electrode mixture in which a conductive additive (carbon material such as carbon black) or a binder such as PVDF is appropriately added to these negative electrode active materials is finished into a molded body (negative electrode mixture layer) using the current collector as a core material. The above-mentioned various alloys or lithium metal foils or those laminated on the surface of the current collector can be used as the negative electrode.

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

  The positive electrode 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 to the surface of the current collector and drying it. Produced.

  The electrode can be used in the form of a laminate electrode group in which the positive electrode and the negative electrode are laminated via the separator of the present invention, or a wound electrode group in which this is wound.

As the non-aqueous electrolyte, a solution in which a lithium salt is dissolved in an organic solvent is used. The lithium salt is not particularly limited as long as it dissociates in a solvent to form Li ⁺ ions and hardly causes side reactions such as decomposition in a voltage range used as a battery. For example, 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 (R _f OSO ₂ ) ₂ [where Rf is a fluoroalkyl group], or the like is used. Can do.

  The organic solvent used for the non-aqueous electrolyte is not particularly limited as long as it dissolves the lithium salt and does not cause a side reaction such as decomposition in a voltage range used as a battery. For example, cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, chain carbonates such as dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate, chain esters such as methyl propionate, cyclic esters such as γ-butyrolactone, Chain ethers such as dimethoxyethane, diethyl ether, 1,3-dioxolane, diglyme, triglyme and tetraglyme, cyclic ethers such as dioxane, tetrahydrofuran and 2-methyltetrahydrofuran, nitriles such as acetonitrile, propionitrile and methoxypropionitrile And sulfites such as ethylene glycol sulfite. These may be used as a mixture of two or more. Kill. In order to obtain a battery with better characteristics, it is desirable to use a combination that can obtain high conductivity, such as a mixed solvent of ethylene carbonate and chain carbonate. In addition, vinylene carbonates, 1,3-propane sultone, diphenyl disulfide, cyclohexylbenzene, biphenyl, and fluorobenzene are used for the purpose of improving safety, charge / discharge cycle characteristics, and high-temperature storage characteristics of these non-aqueous electrolytes. An additive such as t-butylbenzene may be added as appropriate.

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

  Also, instead of the organic solvent, melting at room temperature such as ethyl-methylimidazolium trifluoromethylsulfonium imide, heptyl-trimethylammonium trifluoromethylsulfonium imide, pyridinium trifluoromethylsulfonium imide, guanidinium trifluoromethylsulfonium imide A salt can also be used.

  Furthermore, PVDF, vinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polyacrylonitrile (PAN), polyethylene oxide, polypropylene oxide, ethylene oxide-propylene oxide copolymer, main chain or An electrolyte gelled using a known host polymer capable of forming a gel electrolyte such as a crosslinked polymer containing an ethylene oxide chain in the side chain or a crosslinked poly (meth) acrylate ester can also be used.

  An example of the lithium secondary battery will be described with reference to the drawings. The lithium secondary battery shown in the drawings is merely an example of the present invention, and the electrochemical element of the present invention is not limited to those illustrated in these drawings. FIG. 1 is an external perspective view showing an example of a lithium secondary battery, and FIG. 2 is a cross-sectional view taken along the line II of FIG.

  A lithium secondary battery 1 shown in FIGS. 1 and 2 is an example of a battery in which a wound body electrode group 9 is accommodated in a rectangular outer can 2. That is, the lithium secondary battery 1 includes a rectangular outer can 2 and a cover plate 3. As described above, the outer can 2 also serves as a positive electrode terminal. The cover plate 3 is made of a metal such as an aluminum alloy and seals the opening of the outer can 2. The lid 3 is provided with a terminal 5 made of a metal such as stainless steel through an insulating packing 4 made of a synthetic resin such as PP.

  As shown in FIG. 2, the lithium secondary battery 1 includes a positive electrode 6, a negative electrode 7, and a separator 8, and the separator 8 and at least one of the positive electrode 6 and the negative electrode 7 are made of an adhesive resin (D). An integrated flat wound electrode group 9 is housed in the outer can 2 together with a non-aqueous electrolyte. However, in FIG. 2, in order to avoid complication, the collector which concerns on the positive electrode 6 and the negative electrode 7, the nonaqueous electrolyte solution, etc. are not shown in figure. Further, each layer of the separator 8 is not shown separately, and the inner peripheral side portion of the wound body electrode group 9 is not shown in cross section.

  Further, an insulator 10 formed of a synthetic resin sheet such as a polytetrafluoroethylene sheet is disposed at the bottom of the outer can 2, and is connected to one end of each of the positive electrode 6 and the negative electrode 7 from the wound body electrode group 9. The positive electrode lead body 11 and the negative electrode lead body 12 are drawn out. The positive electrode lead body 11 and the negative electrode lead body 12 are made of a metal such as nickel. A lead plate 14 made of a metal such as stainless steel is attached to the terminal 5 via an insulator 13 made of a synthetic resin such as PP.

  The cover plate 3 is inserted into the opening of the outer can 2, and the joint of the two is welded to seal the opening of the outer can 2, thereby sealing the inside of the battery.

  In FIG. 2, by directly welding the positive electrode lead body 11 to the lid plate 3, the outer can 2 and the lid plate 3 function as a positive electrode terminal, and the negative electrode lead body 12 is welded to the lead plate 14. The terminal 5 functions as a negative electrode terminal by conducting the negative electrode lead body 12 and the terminal 5 through 14, but depending on the material of the outer can 2, the sign may be reversed. is there.

  The electrochemical device of the present invention includes, for example, a step of forming the laminate electrode group or the wound electrode group using the separator of the present invention, and a heating press to the electrode group, Can be produced by the method of the present invention comprising a step of integrating at least one of the separator and the separator.

  The temperature of the heating press applied to the electrode group may be a temperature lower than the melting point of the resin (A) constituting the resin porous layer (I) related to the separator, but as described above, it is 60 ° C. or higher and 120 ° C. or lower. It is more preferable that the heat shrinkage of the resin porous layer (I) is 80 ° C. or more and 100 ° C. or less so that the heat shrinkage does not occur so significantly. Further, the pressure during the hot pressing is preferably 0.1 Pa or more, but is not particularly limited. The heating press time is not particularly limited, but is preferably 30 seconds or longer.

  The electrode group in which the separator and the positive electrode and / or the negative electrode are integrated by the heating press is inserted into the outer package (battery case) according to a conventional method, and then injected with a non-aqueous electrolyte, sealed and electrically It can be a chemical element.

  In addition, when the electrode group is subjected to a heat press, in addition to directly heating the electrode group, for example, the electrode group is inserted into an exterior body made of a metal laminate film such as an aluminum laminate film, and non-aqueous electrolysis is performed. After injecting the liquid and sealing the outer package, the entire outer package may be subjected to a heat press. In this case, preferable heating temperature, pressing pressure, and pressing time are the same as those described above.

  The electrochemical device of the present invention can be applied to the same applications as those in which conventionally known electrochemical devices are used.

  Hereinafter, the present invention will be described in detail based on examples. However, the following examples do not limit the present invention. In addition, the average particle diameter (D50) and aspect ratio of the filler (B) shown below are values measured by the above method. Also, D10 and D90 of the filler (B) are particle sizes at 10% and 90% in the volume-based integrated fraction measured by the same method as D50.

Example 1
<Preparation of separator>
1000 g of water, a polyhedron-shaped boehmite synthetic product (filler (B) (aspect ratio 1.4, D50 = 0.63 μm, D10 = 0.31 μm, D90 = 0.92 μm), acrylate co-polymer (C)) Polymer [commercially available acrylate copolymer mainly containing butyl acrylate as a monomer component; 3 parts by mass with respect to 100 parts by mass of filler (B)], and EVA emulsion [filler (D) (adhesive resin (D)) B) 30 parts by mass of EVA with respect to 100 parts by mass] was stirred for 3 hours with a three-one motor to obtain a uniform slurry. A microporous membrane made of PE having a corona discharge treatment on one side [resin porous layer (I): thickness 16 μm, porosity 40%, PE melting point 135 ° C.] and the above slurry on a die coater And dried to form a heat-resistant porous layer (II) having a thickness of 3.5 μm to obtain a separator. In this separator, the basis weight of the heat-resistant porous layer (II) is 0.34 mg / cm ² , the volume content of the filler (B) in the heat-resistant porous layer (II) [the component of the heat-resistant porous layer (II) Volume content in the total volume. The same applies to the volume content of the filler (B). ] Was 83% by volume, and the porosity of the heat resistant porous layer (II) was 44%.

<Production of negative electrode>
A negative electrode mixture-containing paste was prepared by uniformly mixing 95 parts by mass of graphite as a negative electrode active material and 5 parts by mass of PVDF as a binder using NMP as a solvent. This negative electrode mixture-containing paste was intermittently applied on both sides of a negative electrode current collector made of a copper foil having a thickness of 10 μm so that the coating length was 320 mm on the front surface and 260 mm on the back surface, dried, and then subjected to calendar treatment. The thickness of the negative electrode mixture layer was adjusted so that the total thickness was 142 μm, and the negative electrode mixture layer was cut to a width of 45 mm to obtain a negative electrode having a length of 330 mm and a width of 45 mm. Further, a tab was welded to the exposed surface of the negative electrode current collector to form a lead portion.

<Preparation of positive electrode>
A positive electrode mixture-containing paste was prepared by uniformly mixing 85 parts by mass of LiCoO _{2 as a} positive electrode active material, 10 parts by mass of acetylene black as a conductive additive and 5 parts by mass of PVDF as a binder using NMP as a solvent. This positive electrode mixture-containing paste was intermittently applied on both sides of a positive electrode current collector made of an aluminum foil having a thickness of 15 μm so that the coating length was 320 mm on the front surface and 259 mm on the back surface. The thickness of the positive electrode mixture layer was adjusted so that the total thickness was 150 μm, and the positive electrode mixture layer was cut to a width of 43 mm to obtain a positive electrode having a length of 330 mm and a width of 43 mm. Further, a tab was welded to the exposed surface of the positive electrode current collector to form a lead portion.

<Battery assembly>
The negative electrode and the positive electrode, and the separator slit to a width of 47 mm between them are arranged so that the heat-resistant porous layer (II) faces the positive electrode, and wound in a spiral shape to form a wound body. An electrode group was prepared. The obtained wound body electrode group was crushed into a flat shape, and after applying a heat press at a pressure of 0.5 Pa at 80 ° C. for 1 minute using a hydraulic heat press machine, the thickness was 6 mm, the height was 50 mm, Place in an aluminum outer can with a width of 34 mm, place a lid on the upper opening end of the outer can, and laser weld it. From the electrolyte inlet of the lid, a non-aqueous electrolyte (ethylene carbonate and ethyl methyl carbonate 1 : A solution prepared by dissolving LiPF ₆ at a concentration of 1 mol / l in a solvent mixed at a volume ratio of 2) After injecting 2.4 ml, the electrolyte inlet was sealed, and the appearance shown in FIG. A lithium secondary battery having the structure shown in 2 was produced.

Example 2
The filler (B) is changed to a boehmite synthetic product having a polyhedral shape and an aspect ratio of 1.4, D50 = 0.86 μm, D10 = 0.47 μm, D90 = 1.18 μm, and the thickness of the heat resistant porous layer (II) A separator was prepared in the same manner as in Example 1 except that the thickness was 3.8 μm, and a lithium secondary battery was prepared in the same manner as in Example 1 except that this separator was used.

In the separator of Example 2, the basis weight of the heat-resistant porous layer (II) was 0.52 mg / cm ² , and the volume content of the filler (B) in the heat-resistant porous layer (II) was 83% by volume. The porosity of layer (II) was 45%.

Example 3
A separator was obtained in the same manner as in Example 1 except that the filler (B) was changed to a plate-like boehmite composite having an aspect ratio of 10, D50 = 0.93 μm, D10 = 0.43 μm, and D90 = 1.78 μm. A lithium secondary battery was produced in the same manner as in Example 1 except that this separator was used.

In the separator of Example 3, the basis weight of the heat resistant porous layer (II) was 0.47 mg / cm ² , and the volume content of the filler (B) in the heat resistant porous layer (II) was 82% by volume. The porosity of layer (II) was 43%.

Example 4
The separator was the same as in Example 1 except that the filler (B) was changed to a spherical alumina composite product with an aspect ratio of 1.0, D50 = 0.66 μm, D10 = 0.49 μm, and D90 = 0.87 μm. A lithium secondary battery was produced in the same manner as in Example 1 except that this separator was used.

In the separator of Example 4, the basis weight of the heat resistant porous layer (II) was 0.62 mg / cm ² , and the volume content of the filler (B) in the heat resistant porous layer (II) was 83% by volume. The porosity of layer (II) was 46%.

Example 5
A separator was prepared in the same manner as in Example 1 except that an emulsion containing PP as the adhesive resin (D) was used instead of the EVA emulsion, and the same as in Example 1 except that this separator was used. Thus, a lithium secondary battery was produced.

In the separator of Example 5, the basis weight of the heat resistant porous layer (II) was 0.47 mg / cm ² , and the volume content of the filler (B) in the heat resistant porous layer (II) was 82% by volume. The porosity of layer (II) was 44%.

Comparative Example 1
A separator was prepared in the same manner as in Example 3 except that the adhesive resin (D) was not used, and this separator was used as in Example 1 except that the wound electrode group was not heated and pressed. Thus, a lithium secondary battery was produced.

In the separator of Comparative Example 1, the basis weight of the heat resistant porous layer (II) is 0.47 mg / cm ² , and the volume content of the filler (B) in the heat resistant porous layer (II) is 88% by volume, The porosity of layer (II) was 48%.

Comparative Example 2
The same PE microporous membrane as that used in the manufacture of the separator of Example 1 was used for the separator as it was without forming the heat-resistant porous layer (II), and the wound electrode group was not heated and pressed. A lithium secondary battery was produced in the same manner as in Example 1 except that.

Comparative Example 3
The same PE microporous membrane as that used in the production of the separator of Example 1 was used for the separator as it was without forming the heat-resistant porous layer (II), and the temperature during the hot pressing of the wound body electrode group A lithium secondary battery was produced in the same manner as in Example 1 except that the temperature was 140 ° C. In addition, in the battery of Comparative Example 3, the temperature at the time of hot pressing of the wound body electrode group was set to 140 ° C. The separator according to the battery of Comparative Example 3 does not contain the adhesive resin (D). Therefore, the separator and the electrode are integrated by performing a heat press at a temperature at which PE as a constituent resin of the separator can be melted.

  In Table 1, the structure of the separator of Examples 1-5 and Comparative Examples 1-3 and the heat press temperature of a wound body electrode group are shown. Moreover, each evaluation below was performed about the separator of Examples 1-5 and Comparative Examples 1-3, and the lithium secondary battery of Examples 1-5 and Comparative Examples 1-3. These results are shown in Tables 2 and 3.

<Heat shrinkage test>
A strip-shaped test piece in which the MD direction and the TD direction of each separator were 5 cm and 10 cm, respectively, was cut out. In addition, MD direction is a machine direction at the time of manufacture of the microporous film used for the resin porous layer (I) of the separator, and TD direction is a direction perpendicular to the MD direction. In the test piece, a straight line of 3 cm in parallel with each of the MD direction and the TD direction was marked with an oily magic so as to intersect at the centers of the MD direction and the TD direction. The center of these straight lines is the intersection of these straight lines.

Each test piece is hung in a thermostat, the temperature in the bath is increased to 150 ° C. at a rate of 5 ° C./min, and then kept at 150 ° C. for 1 hour, and then the test piece is taken out of the thermostat and MD direction and TD The length of the mark in the direction was measured, and the thermal contraction rate was calculated by the following formula.
Thermal contraction rate (%) = 100 × (3-x) / 3
[In the above formula, x is the dimension (cm) in the MD or TD direction of the separator after being left for 1 hour in a thermostat set at 150 ° C. ]

  The thermal contraction rate was measured for each of the Examples and Comparative Examples by preparing three test pieces in both the MD direction and the TD direction, and calculating the average value of each. In addition, in Table 2, although both the MD direction and TD direction of a separator are shown about the said heat shrinkage rate, the one where a larger value is evaluated as the heat shrinkage rate of each separator.

<180 ° peel test>
The same positive electrode used for each separator and lithium secondary battery was cut into a size of 5 cm in length and 2 cm in width, and each separator and the positive electrode were combined with the heat resistant porous layer (II) of the separator and the positive electrode mixture. The test piece was produced by superposing the layers so as to be in contact with each other and heating and pressing a 2 cm × 2 cm region from one end at 80 ° C. for 1 minute at a pressure of 0.5 Pa. The ends of these test pieces on the side where the separator and the positive electrode were not heated and pressed were opened, and the separator and the positive electrode were bent so that the angle between them was 180 °. Thereafter, using a tensile tester, the one end side of the separator opened at 180 ° of the test piece and the one end side of the positive electrode are gripped and pulled at a tensile speed of 10 mm / min. The strength at the time of peeling was measured. Further, the peel strength between the separator and the positive electrode before hot pressing was measured in the same manner as described above except that the separator and the positive electrode cut out as described above were stacked and pressed without heating. In addition, about the separator of the comparative example 3, the temperature at the time of a hot press was 140 degreeC, and the said peeling test was implemented.

<Load characteristics>
For each of the batteries of Examples 1 to 5 and Comparative Examples 1 to 3, constant current charging was performed until the current value of 0.2C reached 4.20 V, and then constant voltage charging at 4.20 V was performed. Voltage charging was performed. The total charging time until the end of charging was 15 hours. Next, discharging was performed at a current value of 0.2 C until the battery voltage reached 3 V, and discharge capacities were obtained (these capacities are referred to as “0.2 C discharging capacities”).

  Next, for each battery, after performing constant current-constant voltage charging under the same conditions as described above, discharging was performed at a current value of 2C until the battery voltage reached 3 V, and discharge capacity was obtained (the capacity of these batteries was determined). "2C discharge capacity").

  For each battery, the 2C discharge capacity was divided by the 0.2C discharge capacity and expressed as a percentage to evaluate the load characteristics. The above charging and discharging were all performed in a test chamber in which the temperature was controlled at 20 ° C.

<Heating test>
For each of the batteries of Examples 1 to 5 and Comparative Examples 1 to 3, a current value of 0.5 C was obtained in an air atmosphere of 20.0 to 25 ° C. with the surface temperature being the same as the air atmosphere temperature. The constant current charging was performed until 4.35V. The battery in a charged state was placed in a thermostatic bath, the bath temperature was increased to 150 ° C. at a rate of 5 ° C./min, and then kept at 150 ° C. for 3 hours. The maximum temperature reached by the battery was measured by a thermocouple connected to the battery surface from the start of the test to the end of the 150 ° C. constant value operation. In addition, this heating test was conducted for each of the three examples and the comparative example, and the average value of the maximum temperatures was obtained.

<High temperature storage characteristics>
The batteries of Examples 1 to 5 and Comparative Examples 1 to 3 (batteries not subjected to the above heating test) were charged at 20 ° C. to 4.2 V at 395 mA (0.5 C), and then 4.2 V. The battery was fully charged by charging at a constant voltage of 2.5 hours, and the thickness of the battery at this time was measured. Then, it discharged to 3V with the electric current value of 1C in 20 degreeC, and measured the discharge capacity before storage.

  Next, each battery was charged in the same manner as described above, and then stored in a constant temperature bath at 80 ° C. for 5 days. Each battery after storage was naturally cooled to 20 ° C., the thickness was measured, and the swelling of the battery after high-temperature storage was determined from comparison with the thickness of the battery before storage. Thereafter, each battery was discharged under the same conditions as before storage, and the discharge capacity after high-temperature storage was measured. The percentage of the discharge capacity before storage was expressed as a percentage, and the capacity retention rate (%) after high-temperature storage was determined. .

<Charge / discharge cycle characteristics>
About each battery of Examples 1-5 and Comparative Examples 1 to 3 (batteries not subjected to the high temperature storage characteristic test), the battery was charged at 45 ° C. until reaching 4.2 V at 0.5 C, and further 4.2 V The battery was charged at a constant voltage for 2.5 hours to be fully charged, and then a charge / discharge cycle of discharging to 1 V at 1 C was repeated 300 times, and the discharge capacity at the first cycle and the discharge capacity at the 300th cycle were measured. Subsequently, using the discharge capacity at the first cycle and the discharge capacity at the 300th cycle, the capacity retention rate was calculated by the following formula, and the charge / discharge cycle characteristics were evaluated.
Capacity maintenance rate (%)
= (Discharge capacity at 300th cycle / Discharge capacity at 1st cycle) × 100

  As is clear from Table 2, the separators of Examples 1 to 5 have a small thermal shrinkage, and the peel strength from the positive electrode at 180 ° is 0.01 N / 20 mm at the maximum at room temperature, that is, before heating press. However, after heating and pressing at 80 ° C., both are 0.5 N / 20 mm or more, and the separator and the positive electrode are firmly integrated.

  Further, as is apparent from Table 3, the lithium secondary battery of Comparative Example 1 in which the heat resistant porous layer (II) does not contain the adhesive resin (D) and the separator and the positive electrode are not integrated, and The lithium secondary battery of Comparative Example 2 in which the heat-resistant porous layer (II) is not formed and the separator and the positive electrode are not integrated has a large battery swelling after high-temperature storage and poor high-temperature storage characteristics. The capacity retention rate after the charge / discharge cycle is low, and the charge / discharge cycle characteristics are inferior.

  On the other hand, the lithium secondary batteries of Examples 1 to 5 have a small battery swelling after high-temperature storage, a good capacity maintenance ratio, and a high capacity maintenance ratio after the charge / discharge cycle and an excellent charge / discharge cycle. It has characteristics. These effects in the batteries of Examples 1 to 5 are that the electrode and the separator are integrated by the adhesive resin (D) of the heat-resistant porous layer (II) according to the separator, so that the battery can be stored in a charged state. This is considered to be obtained by increasing the internal resistance of the battery based on the increase in the distance between the electrodes due to gas generation and expansion / contraction of the electrode in the charge / discharge cycle process, and reducing the generation of lithium dendrite due to current concentration.

  Moreover, since the lithium secondary battery of Examples 1-5 uses the separator with high heat resistance, the temperature rise of the battery is suppressed also in the heating test, and it has high safety.

  In the battery of Comparative Example 3 using a wound electrode group in which a PE microporous membrane not formed with the heat-resistant porous layer (II) was used as a separator and heated and pressed at 140 ° C., normal charging was performed. The battery could not be discharged and the battery characteristics could not be evaluated. This is presumably because PE wound on the separator was melted and the pores of the separator were blocked by heating and pressing the wound body electrode group at 140 ° C.

1 Electrochemical element (lithium secondary battery)
2 exterior can 3 lid plate 4 insulation packing 5 terminal 6 positive electrode 7 negative electrode 8 separator 9 wound body electrode group 10 insulator 11 positive electrode lead body 12 negative electrode lead body 13 insulator 14 lead plate

Claims (8)

A separator used for an electrochemical device having a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator,
A porous resin layer (I) mainly composed of a resin (A) having a melting point of 80 to 180 ° C. and a filler (B) having a heat resistant temperature of 150 ° C. or higher are bound by an organic binder (C). Heat resistant porous layer (II),
The heat-resistant porous layer (II) contains an adhesive resin (D) that exhibits adhesiveness when heated to a temperature lower than the melting point of the resin (A). Element separator.   The separator for an electrochemical element according to claim 1, wherein the lowest temperature at which the adhesiveness of the adhesive resin (D) is exhibited is 60 to 120 ° C.   The electrochemistry according to claim 1 or 2, wherein the adhesive resin (D) is at least one selected from the group consisting of poly-α-olefins, polyacrylic acid esters, polyvinyl acetate, and copolymers thereof. Element separator.   The separator for an electrochemical element according to any one of claims 1 to 3, wherein the resin (A) is a polyolefin.   The separator for electrochemical elements according to any one of claims 1 to 4, wherein the filler (B) is at least one selected from the group consisting of alumina, silica and boehmite.   The separator for an electrochemical element according to any one of claims 1 to 5, which has a thermal shrinkage rate of 0 to 10% when left in a temperature atmosphere of 150 ° C.   An electrochemical element having a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator, wherein the separator is the separator for an electrochemical element according to any one of claims 1 to 6, and the separator is at least a positive electrode and a negative electrode. An electrochemical element characterized by being integrated with one side. A method for producing an electrochemical device having a positive electrode, a negative electrode, a non-aqueous electrolyte and a separator,
The separator for an electrochemical element according to any one of claims 1 to 6, wherein the separator is disposed between a positive electrode and a negative electrode and laminated, or the separator is disposed between a positive electrode and a negative electrode. A step of forming a group of electrodes by winding the stacked layers, and a step of applying a heat press to the group of electrodes to integrate at least one of a positive electrode and a negative electrode with a separator. A method for producing an electrochemical element.

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