JP6738339B2 - Electrochemical element separator, method for producing the same, and method for producing the electrochemical element - Google Patents

Description

The present invention relates to an electrochemical element separator capable of ensuring high adhesion strength with an electrode of an electrochemical element, a method for producing the same, and a method for producing an electrochemical element using the electrochemical element separator. is there.

In recent years, as mobile devices (portable devices) such as mobile phones, PDAs, and notebook computers have become more important, the batteries installed therein have become more important. Particularly, due to environmental considerations, the importance of rechargeable secondary batteries is increasing. Such secondary batteries are currently used not only for power supply of small devices such as the above-mentioned mobile devices but also for large devices such as automobiles, electric bicycles, household power storage systems, and commercial power storage systems. Application is also being considered.

In applying the secondary battery to the above-mentioned applications, it is required to improve various battery characteristics. For example, when the energy density is improved, generally, use in a high temperature environment or long-term use is required. Causes severe deterioration and causes a problem of battery durability. Further, due to the increase in energy density, it becomes difficult to secure safety that suppresses the occurrence of abnormalities such as battery smoke and ignition.

For this reason, for example, by using a laminate having a layer containing fine particles having excellent heat resistance as a separator on the surface of a polyolefin microporous film that is used as a separator for a normal secondary battery, a secondary battery Has been developed (Patent Document 1 and the like).

In addition, as a cause of deterioration of the secondary battery, the non-aqueous electrolyte decomposes to generate gas in the battery or the electrode itself in the battery expands and contracts during the process of repeated storage and charging/discharging in a high temperature environment. In some cases, the distance between the positive electrode and the negative electrode varies due to these, and the uniformity of the charge/discharge reaction is lost.

On the other hand, techniques for suppressing the occurrence of such problems are being developed. In Patent Document 2, a porous diaphragm (separator) disposed between a positive electrode and a negative electrode and a positive electrode or a negative electrode are adhered with a polymer powder such as polyvinylidene fluoride, so that after a charge/discharge cycle has elapsed. There has been proposed a battery that can improve the capacity retention rate of the battery.

Further, in Patent Document 3, a resin porous layer (I) containing a resin having a melting point of 100 to 170° C. as a main component, and a heat resistant porous layer containing a filler having a heat resistant temperature of 150° C. or more as a main component (II ), and a separator and an electrode are integrated by using a separator on which at least one surface has an adhesive resin that exhibits adhesiveness when heated at a temperature lower than the melting point of the resin. Of lithium secondary batteries, etc., which suppresses the variation in the distance between the positive electrode and the negative electrode during high temperature storage and repeated charging/discharging and suppresses deterioration of high temperature storage characteristics and charge/discharge cycle characteristics. Elements have been proposed.

International Publication No. 2007/066768 JP 2001-6744 A JP, 2011-23186, A

By the way, when the separator and the electrode are integrated with an adhesive resin (polymer), if the adhesion strength between them is attempted to be increased, the load characteristics of the battery are usually deteriorated. Therefore, in order to increase the adhesion strength between the separator and the electrode and further improve the battery characteristics as described above, it is necessary to develop a technique capable of suppressing the deterioration of the load characteristics.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a separator for an electrochemical element capable of ensuring a high adhesion strength with an electrode of an electrochemical element, a method for producing the same, and the electric An object of the present invention is to provide a method of manufacturing an electrochemical device using a separator for a chemical device.

The separator for an electrochemical device of the present invention which can achieve the above-mentioned object has a resin porous layer (I) containing a heat-meltable resin (A) as a main component and having a melting point of 100 to 170° C., and a heat-resistant porous layer. (II), which has a layer of an adhesive resin (C) on at least one surface thereof, and the adhesive resin (C) is polyvinylidene fluoride or fluorine. A copolymer of vinylidene chloride and a polymerizable vinyl monomer containing fluorine, which is composed of a mixture of a crystalline resin (C1) and an amorphous resin (C2). (C1) has a melting point of 80 to 170° C., the amorphous resin (C2) has no melting point or has a melting point of 70° C. or less, and the amorphous resin (C2) in the mixture is The ratio of the resin (C2) is 10% by mass or more and 50% by mass or less, and the basis weight of the layer of the adhesive resin (C) on the surface where the layer of the adhesive resin (C) is present is 0. It is characterized by being 1 to 1.5 g/m ² .

The separator for an electrochemical device of the present invention comprises a coating liquid in which the crystalline resin (C1) and the amorphous resin (C2) are dispersed in the resin porous layer (I) or the heat resistant porous layer. Coating the surface of the resin layer (II) to form a coating film, and drying the coating film at a temperature at which the amorphous resin (C2) flows to obtain the adhesive resin (C). It can be manufactured by the manufacturing method of the present invention including the step of forming a layer.

Further, the method for producing an electrochemical device of the present invention is a method for producing an electrochemical device having a positive electrode, a negative electrode, a non-aqueous electrolyte and a separator for an electrochemical device of the present invention, wherein the positive electrode and the negative electrode are: A step of forming an electrode body by laminating via the electrochemical device separator, and pressing the electrode body while heating to bond the electrochemical device separator to the positive electrode and/or the negative electrode. And a step of integrating them.

According to the present invention, there are provided a separator for an electrochemical element capable of ensuring high adhesion strength with an electrode of an electrochemical element, a method for producing the same, and a method for producing an electrochemical element using the separator for an electrochemical element. Can be provided.

It is an appearance perspective view showing typically an example of the electrochemical device (lithium secondary battery) concerning the present invention. It is the II sectional view taken on the line of FIG. FIG. 1 is a vertical cross-sectional view that schematically shows an example of the electrochemical device separator of the present invention.

The electrochemical device separator of the present invention (hereinafter, simply referred to as “separator”) has an adhesive resin (C) layer on at least one surface thereof. The separator of the present invention can be bonded and integrated with the positive electrode and/or the negative electrode forming the electrochemical element by the action of the adhesive resin (C). Therefore, in the electrochemical device using the electrode body in which the separator of the present invention is used and which is integrated with the positive electrode and/or the negative electrode, the positive electrode and the negative electrode can be used even during high-temperature storage and under repeated charging/discharging conditions. Is less likely to vary, and deterioration of charge/discharge characteristics is suppressed.

In addition, since the electrode and the separator are integrated, it is possible to suppress the winding deviation in the wound electrode body and the positional deviation of each component in the laminated electrode body during the assembly of the electrochemical element. The productivity of the device can also be increased.

However, the adhesive resin (C) adheres to the surface of the electrode to inhibit the movement of ions between the positive electrode and the negative electrode due to the charge/discharge reaction of the electrochemical element. When the electrochemical device is charged and discharged with a light load, the influence of the adhesive resin (C) on the battery characteristics due to the inhibition of ion migration does not pose a problem, but the charging and discharging is performed with a larger current value. Then, the influence thereof becomes large, and the load characteristics may be deteriorated.

Therefore, in the present invention, the layer of the adhesive resin (C) is made of a mixture of a specific crystalline resin (C1) and a specific amorphous resin (C2). As a result, the layer of the adhesive resin (C) in the state where the electrode and the separator are integrated by the layer of the adhesive resin (C) can have a structure in which ions can move well in the layer, and The adhesion strength with the separator can also be increased. Therefore, in the electrochemical device constituted by using the separator of the present invention, it is possible to improve the high temperature storage characteristics and the charge/discharge cycle characteristics while maintaining good load characteristics.

Further, in the separator of the present invention, when the temperature inside the electrochemical device is abnormally increased due to the shutdown function of the resin porous layer (I) and the action of increasing the heat resistance of the entire separator by the heat resistant porous layer (II). It can also increase the safety of. That is, when the temperature of the battery becomes high, the resin porous layer (I) tries to shrink in the battery, but the heat-resistant porous layer (II) keeps the shape stable even at high temperature makes the entire separator Thermal contraction is suppressed, and even if the resin porous layer (I) melts and shuts down, the heat-resistant porous layer (II) maintains the insulation between the positive electrode and the negative electrode.

The layer of the adhesive resin (C) is composed of a mixture of the crystalline resin (C1) and the amorphous resin (C2), and the crystalline resin (C1) and the amorphous resin (C2) For this, polyvinylidene fluoride (PVDF) or a copolymer of vinylidene fluoride and a polymerizable vinyl monomer containing fluorine is used. By forming a layer from a mixture of a plurality of resins (C1) and (C2) having different crystallinity, the layer can be made porous while enhancing the adhesive strength with the electrode, and the migration of ions within the layer can be achieved. Can be smooth. Therefore, by using a separator having such a layer of the adhesive resin (C), it is possible to obtain an electrochemical element having a high adhesion strength with an electrode and good load characteristics.

As a copolymer of vinylidene fluoride and a polymerizable vinyl monomer containing fluorine, for example, vinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), vinylidene fluoride-chlorotrifluoroethylene copolymer ( PVDF-CTFE), vinylidene fluoride-tetrafluoroethylene copolymer (PVDF-TFE), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer (PVDF-HFP-TFE) and the like.

The crystalline resin (C1) has higher crystallinity than the amorphous resin (C2), and therefore has a melting point, that is, a differential scanning calorific value in accordance with JIS (Japanese Industrial Standard) K 7121. The melting temperature measured using a meter (DSC) is higher than that of the amorphous resin (C2). Specifically, the crystalline resin (C1) has a melting point of 80° C. or higher and 170° C. or lower.

On the other hand, the amorphous resin (C2) has no melting point (that is, no melting behavior is confirmed by the above method using DSC) or a melting point (melting temperature measured by the above method using DSC). , Which is lower than that of the crystalline resin (C1). Specifically, when the melting point of the amorphous resin (C2) can be observed, the melting point is 70° C. or lower.

The fact that the resin (C1) is crystalline can be confirmed by the melting point being 80° C. or higher and 170° C. or lower, and the fact that the resin (C2) is amorphous means that the melting point is not observed or the melting point is 70° C. It can be confirmed by the following, but other methods, for example, in the X-ray diffraction intensity curve of the resin (C1), the presence of a peak derived from the crystal of the resin (C1) and the X of the resin (C2) It can also be confirmed by the absence of a peak derived from the resin (C2) crystal in the line diffraction intensity curve.

In the layer of the adhesive resin (C), the crystalline resin (C1) is preferably present in the form of particles. The crystalline resin (C1) is in the form of particles and scattered in the layer, and the amorphous resin (C2) is present around it to form a layer. The gap formed with the high quality resin (C2) becomes large, and it becomes easy to make the layer porous.

When the crystalline resin (C1) is in the form of particles, if the particle size is small to a certain extent, more of the particles can be dispersed evenly in the layer of the adhesive resin (C), and the porosity of the layer can be improved. Quality improvement becomes easier. Therefore, when the crystalline resin (C1) is in the form of particles, the average particle size is preferably 0.5 μm or less, more preferably 0.4 μm or less. Since the resin (C1) having a too small particle diameter is difficult to manufacture and handle, the average particle diameter of the crystalline resin (C1) is preferably 0.01 μm or more, and 0.1 μm or more. Is more preferable.

The average particle size of the crystalline resin (C1) as used herein is a number average particle size measured using a laser scattering particle size distribution meter (for example, "LA-920" manufactured by Horiba Ltd.).

In the layer of the adhesive resin (C), the ratio of the amorphous resin (C2) in the total amount of the crystalline resin (C1) and the amorphous resin (C2) is 10% by mass or more, It is preferably 20% by mass or more, more preferably 30% by mass or more, and 50% by mass or less, preferably 40% by mass or less. In other words, the proportion of the crystalline resin (C1) in the total amount of the crystalline resin (C1) and the amorphous resin (C2) is 50% by mass or more, preferably 60% by mass or more. 90 mass% or less, preferably 80 mass% or less, more preferably 70 mass% or less. In the case where the mixture of the crystalline resin (C1) and the amorphous resin (C2) contains both of them in the above proportions, and thus the layer of the adhesive resin (C) is formed, Further, the effect of increasing the adhesion strength with the electrode and the effect of maintaining the load characteristics of the electrochemical element at a high level are exhibited more favorably.

When the separator is integrated with only one of the positive electrode and the negative electrode, the layer of the adhesive resin (C) is allowed to exist only on the surface of the separator surface which is in contact with the electrode to be integrated. However, when the separator is integrated with both the positive electrode and the negative electrode, they are present on both sides of the separator.

On the surface where the adhesive resin (C) layer is present in the separator, the basis weight of the adhesive resin (C) layer is 0.1 g/m ² or more from the viewpoint of good adhesion to the electrode, and It is preferably ² g/m ² or more, and more preferably 0.4 g/m ² or more. However, if the weight of the layer of the adhesive resin (C) is too large on the surface where the layer of the adhesive resin (C) in the separator is present, the thickness of the entire separator becomes too large, or the adhesive resin (C) becomes too thick. There is a high possibility that the holes of the electrochemical device will be blocked, and the movement of ions inside the electrochemical device may be hindered. Therefore, the basis weight of the adhesive resin (C) on the surface where the layer of the adhesive resin (C) in the separator is present is 1.5 g/m ² or less, preferably 1 g/m ² or less, and It is more preferably 9 g/m ² or less.

When forming a layer of the adhesive resin (C) on both surfaces of the separator, it is desirable that the basis weight of both layers be within the above range.

In the separator of the present invention, by adopting the above-mentioned constitution with respect to the adhesive resin (C), for example, it is obtained when a peeling test at 180° between the electrode constituting the electrochemical element and the separator is carried out. The peel strength before heating and pressing can be less than 0.05 N/20 mm, preferably 0.03 N/20 mm or less, more preferably 0 N/20 mm (no adhesive force at all), and 50 In the state after hot pressing at a temperature of -100°C, it can be 0.1 N/20 mm or more, preferably 0.2 N/20 mm or more.

The peel strength at 180° between the electrode and the separator as used herein is a value measured by the following method. Each of the separator and the electrode is cut into a size of 5 cm in length and 2 cm in width, and the cut separator and the electrode are stacked. To obtain the peel strength in the state after hot pressing, a test piece is prepared by hot pressing a region of 2 cm×2 cm 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 negative electrode are bent so that their angles are 180°. Then, using a tensile tester, one end side of the separator and one end side of the electrode opened at 180° of the test piece were grasped and pulled at a pulling speed of 10 mm/min, and the separator and the electrode were both heated and pressed in the area. The strength when peeled off is measured. Further, the peeling strength of the separator and the electrode in the state before the heating and pressing is performed in the same manner as the above except that the separator and the electrode cut out as described above are stacked and pressed without heating. A peeling test is performed in the same manner as described above.

The separator of the present invention comprises a resin porous layer (I) mainly composed of a heat-meltable resin (A) having a melting point of 100 to 170° C., and a heat-resistant porous material that suppresses thermal contraction of the resin porous layer (I). And a quality layer (II). The resin porous layer (I) is a layer having an original function of a separator that allows ions to pass while preventing a short circuit between the positive electrode and the negative electrode in the electrochemical device using the separator of the present invention, and the heat resistant porous layer (II) is a layer that plays a role of imparting heat resistance to the separator.

The resin porous layer (I) has a melting point of 100° C. or higher and 170° C. or lower, that is, a melting temperature measured by DSC in accordance with JIS K 7121 is 100° C. or higher and 170° C. or lower. The resin (A) is the main component. By using the separator having the resin porous layer (I) containing such a heat-meltable resin (A) as a main component, the heat-meltable resin can be used when the temperature inside the electrochemical device using the separator becomes high. It is possible to secure a so-called shutdown function in which (A) melts and blocks the holes of the separator.

The heat-meltable resin (A), which is the main component of the resin porous layer (I), has a melting point of 100° C. or higher and 170° C. or lower, has electrical insulation properties, is electrochemically stable, and is later There is no particular limitation as long as it is a stable thermoplastic resin for the medium used for the nonaqueous electrolytic solution contained in the electrochemical device to be described in detail or the composition for forming the heat resistant porous layer (II), but polyethylene (PE), Polypropylene (PP), polyolefin such as ethylene-propylene copolymer, and the like are preferable, and the melting point is higher than the temperature at which the adhesiveness of the adhesive resin (C) to be used among these thermofusible resins (A) develops. It is preferable to select the higher one.

For the resin porous layer (I), for example, a microporous film made of polyolefin used in a conventionally known electrochemical element such as a lithium secondary battery, that is, a polyolefin mixed with an inorganic filler is used. The film or sheet thus formed may be uniaxially or biaxially stretched to form fine pores. Further, the above-mentioned heat-meltable resin (A) is mixed with another resin to form a film or sheet, and thereafter, the film or sheet is immersed in a solvent that dissolves only the other resin, and the other A resin porous layer (I) can also be obtained by dissolving only the resin of (1) to form pores. Furthermore, a non-woven fabric made of the heat-fusible resin (A) can be used as the resin porous layer (I). Further, a resin porous layer (I) may be formed by laminating a plurality of the resin-made microporous membranes and nonwoven fabrics described above, or laminating a plurality of microporous membranes or nonwoven fabrics.

The resin porous layer (I) may contain a filler for the purpose of improving strength. Examples of such a filler include various fillers described later as specific examples of the filler (electrically insulating filler having a heat resistant temperature of 150° C. or higher) used in the heat resistant porous layer (II).

In the resin porous layer (I), "having the heat-melting resin (A) as a main component" means that the heat-melting resin (A) is the total volume (voids) of the components of the resin porous layer (I). The total volume excluding a portion. The same applies hereinafter.), which means that 70% by volume or more is contained. The amount of the heat-fusible resin (A) in the resin porous layer (I) is preferably 80% by volume or more and 90% by volume or more in the total volume of the constituent components of the resin porous layer (I). More preferably, it may be 100% by volume.

The heat resistant porous layer (II) can be configured to have, for example, a heat resistant temperature of 150° C. or higher and an electrically insulating filler as a main component. The filler has a heat-resistant temperature of 150° C. or higher, has electrical insulation, is electrochemically stable in the electrochemical device, and stable to the non-aqueous electrolyte in the electrochemical device. There is no particular limitation. The “heat resistant temperature of 150° C. or higher” in the filler as used herein means that no shape change such as deformation is visually confirmed at least at 150° C. The heat resistant temperature of the filler is preferably 200° C. or higher, more preferably 300° C. or higher, and further preferably 500° C. or higher.

The electrically insulating filler having a heat resistant temperature of 150° C. or higher is preferably inorganic fine particles having electrically insulating properties, and specifically, iron oxide, silica (SiO ₂ ), alumina (Al ₂ O ₃ ), titania Inorganic oxide particles such as (TiO ₂ ) and barium titanate (BaTiO ₃ ); inorganic nitride particles such as aluminum nitride and silicon nitride; sparingly soluble ionic crystal particles such as calcium fluoride, barium fluoride and barium sulfate; Examples thereof include covalent bond crystal particles such as silicon and diamond; clay particles such as montmorillonite. Here, the fine particles of the inorganic oxide may be fine particles such as substances derived from mineral resources such as boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, mica, or artificial materials thereof. Further, the inorganic compounds constituting these inorganic fine particles may be element-substituted or may be solid-solved, if necessary, and the inorganic fine particles may be surface-treated. In addition, the inorganic fine particles are formed on the surface of a conductive material such as a metal, SnO ₂ , a conductive oxide such as tin-indium oxide (ITO), a carbonaceous material such as carbon black or graphite, and an electrically insulating material. The particles may be electrically insulating by being coated with a material having (for example, the above-mentioned inorganic oxide).

Organic fine particles can be used as the electrically insulating filler having a heat resistant temperature of 150° C. or higher. Specific examples of the organic fine particles include polyimide, melamine resin, phenol resin, crosslinked polymethylmethacrylate (crosslinked PMMA), crosslinked polystyrene (crosslinked PS), polydivinylbenzene (PDVB), benzoguanamine-formaldehyde condensate and the like. Examples thereof include fine particles of molecules; fine particles of heat-resistant polymer such as thermoplastic polyimide. The organic resin (polymer) constituting these organic fine particles is a mixture of the materials exemplified above, a modified product, a derivative, a copolymer (random copolymer, alternating copolymer, block copolymer, graft copolymer). ), and a crosslinked body (in the case of the above-mentioned heat-resistant polymer).

As the electrically insulating filler having a heat resistant temperature of 150° C. or higher, one of the above-mentioned examples may be used alone, or two or more thereof may be used in combination. Fine particles are preferable, and more specifically, at least one selected from alumina, silica, and boehmite is more preferable.

The average particle size of the electrically insulating filler having a heat resistant temperature of 150° C. or higher is preferably 0.01 μm or more, more preferably 0.1 μm or more, and 0.3 μm or more. Is most preferable, 5 μm or less is preferable, 2 μm or less is more preferable, and 1 μm or less is most preferable. The average particle size of the electrically insulating filler having a heat resistant temperature of 150° C. or higher is obtained by dispersing the filler in a medium that does not dissolve, using a laser scattering particle size distribution meter (for example, “LA-920” manufactured by HORIBA). It can be defined as the measured number average particle diameter (the average particle diameter of the filler in the examples described later is the value measured by this method).

The shape of the electrically insulating filler having a heat resistant temperature of 150° C. or higher may be, for example, a shape close to a sphere or a plate shape, but from the viewpoint of short circuit prevention, a plate-like particle is used. It is preferable to have. Typical plate-like particles include plate-like Al ₂ O ₃ and plate-like boehmite.

When the filler is plate-like particles, the aspect ratio is preferably 5 or more, more preferably 10 or more, and preferably 100 or less, and 50 or less. Is more preferable. Further, the average value of the ratio of the major axis direction length to the minor axis direction length (long axis direction length/minor axis direction length) of the flat plate surface of the particles is preferably 3 or less, and 2 or less. Is more preferable, and a value close to 1 is particularly preferable.

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 is determined by, for example, performing image analysis on an image taken by a scanning electron microscope (SEM). be able to. Furthermore, the aspect ratio of the plate-like particles can also be obtained by image analysis of an image taken by SEM.

The existence form of the filler in the separator is preferably a plate surface is substantially parallel to the surface of the separator, more specifically, for the plate-like filler in the vicinity of the surface of the separator, the plate surface and The average angle with the separator surface is preferably 30° or less [most preferably, the average angle is 0°, that is, the plate-shaped flat plate surface near the surface of the separator is parallel to the surface of the separator. ]. The term “vicinity of the surface” as used herein refers to a range from the surface of the separator to approximately 10% of the total thickness. In the case where the plate-like filler is present as described above, it is possible to more effectively prevent heat shrinkage of the resin porous layer (I), and to form a separator having a particularly small heat shrinkage rate as a whole. You can

Further, in the electrochemical device using the separator of the present invention, when high output characteristics are required, it is preferable to use a filler having a secondary particle structure in which primary particles are aggregated, as the filler. By using such a filler, the voids of the heat resistant porous layer (II) can be enlarged, and an electrochemical device having high output characteristics can be formed.

When the heat-resistant porous layer (II) has a heat-resistant temperature of 150° C. or higher as the main component and an electrically insulating filler as a main component, the phrase “containing the heat-resistant temperature of 150° C. or higher as an electrically insulating filler as the main component” It means that the filler is contained in an amount of 70% by volume or more in the total volume of the constituent components of the heat-resistant porous layer (II) (total volume excluding pores. The same applies hereinafter). The amount of the filler in the heat resistant porous layer (II) 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 heat resistant porous layer (II). By setting the content of the filler in the heat-resistant porous layer (II) to be high as described above, heat shrinkage of the entire separator can be suppressed well, and high heat resistance can be imparted.

When the heat-resistant porous layer (II) has a heat-resistant temperature of 150° C. or higher as a main component and contains an electrically insulating filler, the fillers are bound to each other or the heat-resistant porous layer (II) and the resin porous layer are combined. It is desirable to contain a binder resin (B) for binding the quality layer (I). Therefore, the suitable upper limit of the amount of the filler in the heat resistant porous layer (II) is, for example, 99% by volume in the total volume of the constituent components of the heat resistant porous layer (II). When the amount of the filler in the heat resistant porous layer (II) is less than 70% by volume, for example, it is necessary to increase the amount of the binder resin (B) in the heat resistant porous layer (II). In this case, the pores of the heat resistant porous layer (II) are filled with the binder resin (B), and there is a possibility that the function as a separator may be lost.

As the binder resin (B) used for the heat resistant porous layer (II), the fillers can be favorably adhered to each other and the heat resistant porous layer (II) and the resin porous layer (I) can be favorably adhered, and electrochemically stable, There is no particular limitation as long as it is stable with respect to the non-aqueous electrolyte solution for electrochemical device. Specifically, fluororesin (PVDF etc.), fluorocarbon rubber, styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), polyvinyl alcohol (PVA), polyvinyl butyral (PVB), polyvinyl pyrrolidone ( PVP), poly N-vinyl acetamide, crosslinked acrylic resin, polyurethane, epoxy resin and the like. These binder resins (B) may be used alone or in combination of two or more.

Among the binder resins (B) exemplified above, a heat-resistant resin having a heat resistance of 150° C. or higher is preferable, and a highly flexible material such as fluororubber or SBR is particularly 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, and "EM- manufactured by Zeon Corporation". 400B (SBR, trade name)" and the like. Further, a low glass transition temperature crosslinked acrylic resin (self-crosslinking acrylic resin) having a structure in which butyl acrylate is the main component and which is crosslinked is also preferable.

When these binder resins (B) are used, they may be dissolved or dispersed in a medium of a composition (slurry or the like) for forming a heat resistant porous layer (II) described later or used in the form of an emulsion. Good.

The heat-resistant porous layer (II) is a resin having high heat resistance, for example, a resin having a melting temperature of 180° C. or higher measured by DSC according to JIS K 7121, or a thermosetting resin. It is also possible to use a resin having a thermal decomposition temperature of 200° C. or higher. Specifically, polyimide, polyamideimide, polyamide, cellulose, crosslinked polymethylmethacrylate, crosslinked polystyrene, crosslinked polydivinylbenzene, styrene-divinylbenzene copolymer crosslinked product, polyimide, melamine resin, phenol resin, benzoguanamine-formaldehyde condensation And polysulfone, polyether sulfone, polyphenylene sulfide, polytetrafluoroethylene, polyacrylonitrile, polyacetal, and the like, and polyimide, polyamideimide, wholly aromatic polyamide (aramid), and cellulose are preferably used.

The porosity of the heat-resistant porous layer (II) is 40% or more in a dry state in order to secure a holding amount of the non-aqueous electrolytic solution contained in the electrochemical element and improve ion permeability. It is preferably 50% or more, and more preferably 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. .. In addition, the porosity: P (%) is obtained by calculating the sum of each component i from the thickness of the heat resistant porous layer (II), the mass per area, and the density of the constituents by using the following formula (1). Can be calculated by

P=100−(Σa _i /ρ _i )×(m/t) (1)

Here, in the formula (1), a _i : ratio of the component i expressed in mass%, ρ _i : density of the component i (g/cm ³ ), m: per unit area of the heat resistant porous layer (II) (G/cm ² ) and t: 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), or may have two or more layers. Specifically, the heat-resistant porous layer (II) is arranged only on one side of the resin porous layer (I) to form a separator. For example, the heat-resistant porous layer (II) is formed on both sides of the resin porous layer (I). ) May be arranged to serve as a separator. However, if the number of layers that the separator has is too large, the thickness of the separator may increase, which may lead to an increase in the internal resistance of the electrochemical element and a decrease in the energy density, which is not preferable, and the number of layers in the separator is 5 or less. Is preferred.

The separator of the present invention is, for example, a composition for forming a heat-resistant porous layer (II) in which the resin porous layer (I) contains an electrically insulating filler having a heat-resistant temperature of 150° C. or higher and a binder resin (B). After coating (slurry or the like), the coating liquid is dried at a predetermined temperature and then the adhesive resin (C) is dispersed therein [a dispersion liquid containing a crystalline resin (C1) and an amorphous resin (C2). ] To form a coating film, the coating film is dried, and a layer of the adhesive resin (C) is formed on the surface of the separator having the resin porous layer (I) and the heat resistant porous layer (II). It can be manufactured by the forming method.

When the heat-resistant porous layer (II) has a heat-resistant temperature of 150° C. or more as a main component and contains an electrically insulating filler, the heat-resistant porous layer (II)-forming composition is, for example, the filler and the binder resin. It contains (B) and the like and is dispersed in a solvent (including a dispersion medium; the same applies hereinafter). The binder resin (B) can be dissolved in a solvent. The solvent used in the composition for forming the heat resistant porous layer (II) may be any solvent as long as it can uniformly disperse the filler and the like and can also uniformly dissolve or disperse the binder resin (B). For example, toluene In general, organic solvents such as aromatic hydrocarbons such as, furans such as tetrahydrofuran, ketones such as methyl ethyl ketone and methyl isobutyl ketone are preferably used. For the purpose of controlling the interfacial tension, alcohols (ethylene glycol, propylene glycol, etc.), various propylene oxide-based glycol ethers such as monomethyl acetate, etc. may be appropriately added to these solvents. Further, when the binder resin (B) is water-soluble, or when it is used as an emulsion, water may be used as a solvent, and alcohols (methyl alcohol, ethyl alcohol, isopropyl alcohol, ethylene glycol, etc.) may be used at this time as well. The interfacial tension can be controlled by appropriately adding it.

The composition for forming the heat resistant porous layer (II) preferably has a solid content of, for example, 10 to 80% by mass containing the filler and the binder resin (B).

In addition, using plate-like particles as the filler, in order to enhance the orientation of such plate-like particles and make their functions work more effectively, a composition for forming a heat-resistant porous layer (II) containing plate-like particles is used. May be applied to the resin porous layer (I), and then a shear or magnetic field may be applied to the composition. For example, after applying a heat-resistant porous layer (II)-forming composition containing the plate-shaped filler to the resin porous layer (I), a certain gap is passed to share the composition. You can

Further, when the heat resistant porous layer (II) is formed from the resin having high heat resistance, a method in which a coating solution obtained by dissolving the resin in a solvent is applied to the surface of the resin porous layer (I) and dried A method in which a coating solution obtained by dissolving the resin in a solvent is applied to the surface of the resin porous layer (I) and phase separation is performed with a poor solvent; It is also possible to use a method of forming a coating film of a coating solution in which a resin is dissolved in a solvent and then transferring the coating film onto the surface of the resin porous layer (I).

In addition, in order to adjust the porosity and the pore diameter of the heat resistant porous layer (II), an electrically insulating filler having a heat resistant temperature of 150° C. or higher, such as alumina, silica, or titania, is applied to the resin containing the resin. It can also be mixed with a liquid.

A coating liquid in which the adhesive resin (C) is dispersed is applied to the laminate of the resin porous layer (I) and the heat resistant porous layer (II) formed as described above to obtain the adhesive resin (C The separator of the present invention can be produced by forming the layer (1). In this case, as described above, the heat resistant porous layer (II) can be formed on one side or both sides of the resin porous layer (I), and the layer of the adhesive resin (C) is a resin porous layer. It can be formed on one side or both sides of a laminate of the layer (I) and the heat resistant porous layer (II).

Further, in order to more effectively exert the action of the constituents such as the filler, the constituents are unevenly distributed, and the constituents are gathered in layers in parallel or substantially parallel to the membrane surface of the separator. Good.

The temperature at which the coating film formed by applying the coating liquid in which the adhesive resin (C) is dispersed is dried is the temperature at which the amorphous resin (C2) flows. When the amorphous resin (C2) has a melting point, the "temperature at which the amorphous resin (C2) flows" is a temperature equal to or higher than the melting point and has a melting point. If not, the temperature is equal to or higher than the glass transition temperature (Tg) determined by DSC by the method specified in JIS K 7121, or is equal to or higher than the softening point determined by the method specified in JIS K 7206. Means the temperature of.

By drying at such a temperature, the amorphous resin (C2) flows to form a layer. The drying temperature of the coating film is preferably set to a temperature lower than the melting point of the crystalline resin (C1), whereby the particles of the crystalline resin (C1) remain in their original shape, Further, the amorphous resin (C2) flows while forming a gap to form a layer, so that the layer is made more porous.

The manufacturing method of the separator of the present invention is not limited to the above-mentioned method and may be manufactured by other methods. For example, the composition for forming the heat resistant porous layer (II) is applied to the surface of a substrate such as a liner, dried to form the heat resistant porous layer (II), and then peeled from the substrate. The heat resistant porous layer (II) is overlaid with a microporous membrane or the like to be the resin porous layer (I) by heat pressing or the like to form a laminate, and then one or both sides of this laminate are treated in the same manner as above. The separator can also be manufactured by a method of forming a layer of the adhesive resin (C).

The thickness of the separator manufactured in this manner is preferably 6 μm or more, and more preferably 10 μm or more, from the viewpoint of more surely separating the positive electrode and the negative electrode because the separator is used for the electrochemical device separator. preferable. On the other hand, if the separator is too thick, the energy density when used as an electrochemical element may decrease, so the thickness is preferably 50 μm or less, and more preferably 30 μm or less.

Further, when the thickness of the resin porous layer (I) constituting the separator is X (μm) and the thickness of the heat resistant porous layer (II) is Y (μm), the ratio X/Y of X and Y is It is preferably 10 or less, more preferably 7 or less, most preferably 5 or less, more preferably 1 or more, more preferably 2 or more, and 3 or more. Is most preferred. In the separator of the present invention, even if the thickness ratio of the resin porous layer (I) is increased and the heat-resistant porous layer (II) is thinned, it is possible to suppress the thermal contraction of the entire separator. It is possible to highly suppress the occurrence of a short circuit due to thermal contraction of the separator in the above. In the separator, when there are a plurality of resin porous layers (I), the thickness X is the total thickness thereof, and when there are a plurality of heat resistant porous layers (II), the thickness Y is the total thickness thereof. Is.

Expressed in a concrete value, the thickness of the resin porous layer (I) [when there are a plurality of resin porous layers (I), the total thickness thereof. ] Is preferably 5 μm or more and 30 μm or less. Then, the thickness of the heat resistant porous layer (II) [when there are a plurality of heat resistant porous layers (II), the total thickness thereof. ] Is preferably 1 μm or more, more preferably 2 μm or more, further preferably 4 μm or more, preferably 20 μm or less, more preferably 10 μm or less, and 6 μm or less Is more preferable. If the resin porous layer (I) is too thin, the shutdown characteristics may be weakened, and if it is too thick, the energy density of the electrochemical element may be lowered, and in addition, the force for thermal contraction may be reduced. There is a possibility that the effect becomes large and the effect of suppressing the thermal contraction of the entire separator becomes small. Further, if the heat resistant porous layer (II) is too thin, the effect of suppressing the heat shrinkage of the entire separator may be reduced, and if it is too thick, the thickness of the entire separator may be increased.

The porosity of the entire separator is preferably 30% or more in a dry state from the viewpoint of ensuring a liquid holding amount of the non-aqueous electrolyte and improving ion permeability. On the other hand, the porosity of the separator is preferably 70% or less in a dry state from the viewpoint of securing the strength of the separator and preventing an internal short circuit. The porosity of the separator: P (%) can be calculated by setting m to be the mass per unit area of the separator (g/cm ² ) and t to be the thickness (cm) of the separator in the formula (1). , Can be obtained using the above equation (1).

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

Further, the separator of the present invention is performed by a method according to JIS P 8117, and a Gurley value indicated by the number of seconds in which 100 ml of air permeates the membrane under a pressure of 0.879 g/mm ² is 10 to 500 sec. Is desirable. If the air permeability is too high, the ion permeability will be low, while if it is too low, the strength of the separator may be low. Further, the strength of the separator is preferably 50 g or more as the puncture strength using a needle having a diameter of 1 mm. When the puncture strength is too low, when a dendrite crystal of lithium is generated, a short circuit may occur due to breakage of the separator. By adopting the above configuration, a separator having the air permeability and the puncture strength can be obtained.

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 electrolytic solution, and other than a lithium secondary battery, a lithium primary battery, a supercapacitor, etc. It can be preferably applied if it is required to be used. That is, the electrochemical device to which the separator of the present invention can be applied is not particularly limited as to the configuration and structure other than the separator, and various electrochemical devices having a conventionally known non-aqueous electrolytic solution (lithium secondary battery, Various configurations and structures provided in the lithium primary battery, supercapacitor, etc. can be adopted.

Hereinafter, as an example, the application to a lithium secondary battery will be described in detail. Examples of the form of the lithium secondary battery include a tubular shape (square tubular shape or cylindrical shape) using a steel can, an aluminum can, or the like as an outer can. It is also possible to use a soft package battery having a laminated film formed by vapor-depositing a metal as an exterior body.

As the positive electrode of the lithium secondary battery, the positive electrode used in conventionally known lithium secondary batteries can be used. For example, the positive electrode active material is not particularly limited as long as it is an active material used in conventionally known lithium secondary batteries, 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, or It is possible to use a lithium manganese oxide having a spinel structure in which a part of the element is replaced with another element, an olivine type compound represented by LiMPO ₄ (M:Co, Ni, Mn, Fe, etc.).

Specific examples of the lithium-containing transition metal oxide of the layer structure, LiCoO ₂ and _{LiNi 1-x Co x-y} Al y O 2 (0.1 ≦ x ≦ 0.3,0.01 ≦ y ≦ 0. 2) and the like, 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 ) and the like.

Examples of the conductive additive for the positive electrode include a carbon material such as carbon black, and examples of the binder for the positive electrode include a fluororesin such as polyvinylidene fluoride (PVDF). Then, as the positive electrode, a positive electrode mixture layer formed of the positive electrode mixture containing the positive electrode active material, the conductive additive and the binder can be used on one side or both sides of the current collector. ..

As the current collector of the positive electrode, a foil of metal such as aluminum, punching metal, net, 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 usually provided by leaving the exposed portion of the current collector as a lead portion without forming the positive electrode mixture layer on a part of the current collector during the production of the positive electrode. However, the lead portion is not necessarily required to be 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.

As the negative electrode, at least one selected from negative electrodes used in conventionally known lithium secondary batteries, that is, a carbon material capable of inserting and extracting Li ions, a lithium alloy, a metal alloyable 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. As the active material, more specifically, lithium, such as graphite, pyrolytic carbons, cokes, glassy carbons, sintered bodies of organic polymer compounds, mesocarbon microbeads (MCMB), carbon fibers, etc., is occluded. , One or a mixture of two or more types of releasable carbon-based materials is used. Further, elements such as Si, Sn, Ge, Bi, Sb, and In and alloys thereof, or lithium-containing oxides such as lithium metal and lithium/aluminum alloys, and Li ₄ Ti ₅ O ₁₂ and Li ₂ Ti ₃ O ₇ are also negative electrode active materials. It can be used as a substance. A negative electrode mixture obtained by appropriately adding a conductive auxiliary agent (carbon material such as carbon black) or a binder such as PVDF to these negative electrode active materials is finished into a molded body (negative electrode mixture layer) using the current collector as a core material. It is possible to use, as the negative electrode, a metal foil, a foil of the above-mentioned various alloys or a lithium metal, or a foil laminated on the surface of the current collector.

When a current collector is used for the negative electrode, a copper or nickel foil, a punching metal, a net, an expanded metal or the like can be used as the current collector, but a copper foil is usually used. When the thickness of the entire negative electrode is reduced in order to obtain a battery having a high energy density, this negative electrode current collector preferably has an upper limit of thickness of 30 μm and a lower limit of 5 μm. 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 or the negative electrode having the negative electrode mixture layer as described above is, 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 or the like) or a composition for forming a negative electrode mixture layer (slurry or the like) obtained by dispersing a negative electrode mixture in a solvent such as NMP on the surface of a current collector and drying. Created.

The electrode is an electrode body such as a laminated body (laminated electrode body) in which the positive electrode and the negative electrode are laminated via the separator of the present invention, or a wound body (rolled electrode body) in which the positive electrode and the negative electrode are wound. It can be used in any form.

As the non-aqueous electrolytic solution, a solution in which a lithium salt is dissolved in an organic solvent is used. The lithium salt is not particularly limited as long as it dissociates in a solvent to form Li ⁺ ions and hardly causes a side reaction such as decomposition in the voltage range used as a battery. For example, inorganic lithium salts such as LiClO ₄ , LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiSbF ₆ ; LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , Li ₂ C ₂ F ₄ (SO ₃ ) ₂ , LiN(CF ₃ SO ₂ ) ₂ , LiC(CF ₃ SO ₂ ) ₃ , LiC _n F _2n+1 SO ₃ (n≧2), LiN(R _f OSO ₂ ) ₂ [where Rf is a fluoroalkyl group]; or the like; be able to.

The organic solvent used for the non-aqueous electrolyte is not particularly limited as long as it dissolves the above-mentioned lithium salt and does not cause a side reaction such as decomposition in the voltage range used for the battery. For example, cyclic carbonates such as ethylene carbonate (EC), propylene carbonate, butylene carbonate and vinylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate (DEC) and methyl ethyl carbonate (MEC); chain esters such as methyl propionate Cyclic ester such as γ-butyrolactone; chain ether such as dimethoxyethane, diethyl ether, 1,3-dioxolane, diglyme, triglyme, tetraglyme; cyclic ether such as dioxane, tetrahydrofuran, 2-methyltetrahydrofuran; acetonitrile, propio Examples thereof include nitriles such as nitrile and methoxypropionitrile; sulfite esters such as ethylene glycol sulfite; and the like, and two or more kinds of them can be mixed and used. In addition, in order to obtain a battery having better characteristics, it is desirable to use a combination solvent such as a mixed solvent of ethylene carbonate and chain carbonate that can obtain high conductivity. In addition, for the purpose of improving the characteristics such as safety, charge/discharge cycle characteristics, and high temperature storage characteristics of these non-aqueous electrolytes, vinylene carbonates, 1,3-propanesultone, diphenyl disulfide, cyclohexylbenzene, biphenyl, fluorobenzene. , T-butylbenzene and the like can be added as appropriate.

The concentration of this 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.

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

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

As shown in FIG. 2, the lithium secondary battery 1 has 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 (C). The flat wound electrode body 9 integrated with layers is housed in the outer can 2 together with the non-aqueous electrolyte. However, in FIG. 2, in order to avoid complication, the current collectors related to the positive electrode 6 and the negative electrode 7, the nonaqueous electrolytic solution, and the like are not shown. Further, the layers of the separator 8 are not shown separately, and further, the inner peripheral side portion of the spirally wound electrode body 9 is not shown in cross section.

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

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

In FIG. 2, by directly welding the positive electrode lead body 11 to the cover plate 3, the outer can 2 and the cover plate 3 function as a positive electrode terminal, the negative electrode lead body 12 is welded to the lead plate 14, and the lead plate is formed. The terminal 5 functions as a negative electrode terminal by electrically connecting the negative electrode lead body 12 and the terminal 5 via 14; however, depending on the material of the outer can 2, the positive and negative may be reversed. is there.

An electrochemical device using the separator of the present invention has a step of winding or laminating a positive electrode and a negative electrode via the separator of the present invention to form an electrode body, and applying pressure while heating the electrode body ( That is, it can be produced by the method of the present invention, which comprises the steps of hot pressing) and adhering and integrating the separator and the positive electrode and/or the negative electrode.

The heating temperature for hot pressing the electrode body is lower than the melting point of the crystalline resin (C1), and the melting point of the heat-meltable resin (A) constituting the resin porous layer (I) of the separator. The temperature is preferably lower than 50°C, more preferably 50°C or higher and 95°C or lower. The pressure during hot pressing is not particularly limited, but is preferably 0.1 Pa or more. Further, the time of hot pressing is not particularly limited, but 30 s or more is preferable.

The electrode body in which the separator and the positive electrode and/or the negative electrode are integrated through the process of heating and pressing the electrode body is inserted into the outer casing (battery case) according to a conventional method, and then the non-aqueous electrolyte is injected and sealed. It can be turned to an electrochemical device.

When the electrode body is pressed while being heated, the electrode body is directly subjected to a heat press, or the electrode body is inserted into an exterior body made of a metal laminate film such as an aluminum laminate film, and the non-aqueous electrolyte solution is used. After injecting and sealing the exterior body, the whole exterior body can be heated and pressed. In this case, preferable heating temperature, pressing pressure and pressing time are the same as those in the above case.

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

Example 1
<Production of positive electrode>
LiCo _0.995 Mg _0.005 O ₂ (positive electrode active material) which is a lithium-containing composite oxide: 94 parts by mass, carbon black: 3 parts by mass as a conductive additive was added and mixed, and PVDF: 3 was added to this mixture. A solution prepared by dissolving parts by mass in NMP was added and mixed to form a positive electrode mixture-containing slurry, which was passed through a net of 70 mesh to remove one having a large particle size. This positive electrode mixture-containing slurry was evenly applied to both surfaces of a positive electrode current collector made of aluminum foil having a thickness of 15 μm and dried, and then compression-molded by a roll press machine to a total thickness of 136 μm. Then, the aluminum-made lead body was cut and welded to produce a strip-shaped positive electrode.

<Production of negative electrode>
As the negative electrode active material, artificial graphite having a d ₀₀₂ measured by X-ray diffractometry of 0.336 nm was used, SBR was used as a binder, CMC was used as a thickener, and these were mixed at a mass ratio of 98:1:1. And mixed with water to obtain a negative electrode mixture-containing paste. This negative electrode mixture-containing paste was uniformly applied to both surfaces of a negative electrode current collector made of copper foil having a thickness of 10 μm, dried, and then compression-molded by a roll press machine to a total thickness of 138 μm, It cut|disconnected and the lead body made from nickel was welded, and the strip|belt-shaped negative electrode was produced.

<Preparation of non-aqueous electrolyte>
1. LiPF ₆ was dissolved in a mixed solvent of EC, MEC, and DEC in a volume ratio of 10:10:30 at a concentration of 1.0 mol/l, and vinylene carbonate was added to the total mass of the nonaqueous electrolytic solution. A nonaqueous electrolytic solution was prepared by adding 5% by mass.

<Production of separator>
300 g of an aqueous dispersion of SBR (solid content ratio 40% by mass), which is the binder resin (B), and 4000 g of water were placed in a container and stirred at room temperature until uniformly dispersed. To this dispersion, 4000 g of boehmite powder (plate-like, average particle size 1 μm, aspect ratio 10), which is an electrically insulating filler having a heat resistant temperature of 150° C. or higher, was added in four portions, and stirred at 2800 rpm for 5 hours with a disper To prepare a uniform slurry. A microporous membrane in which PP layer/PE layer/PP layer are laminated in this order (thickness: 16 μm, porosity: 40%, average pore diameter: 0.02 μm, thickness of both PP layers as surface layers: 5 μm for each, PE (Thickness of layer: 6 μm, melting point of PE constituting PE layer: 135° C., melting point of PP constituting PP layer: 166° C.), and the thickness after drying the slurry with a microgravure coater on one side. Each layer having a thickness of 23 μm is formed by applying each of the coatings to a thickness of 3.5 μm and drying to form the heat-resistant porous layer (II) [resin porous layer (I) and heat-resistant porous layer (II)]. A laminate] was obtained. The volume content of the filler in the heat resistant porous layer (II) of this laminate was 92% by volume, and the porosity of the heat resistant porous layer (II) was 48%.

Next, an aqueous dispersion of PVDF which is a crystalline resin (C1) (concentration of PVDF: 25% by mass, melting point of PVDF is 100° C.) and an aqueous dispersion of PVDF which is an amorphous resin (C2) ( The concentration of PVDF: 25% by mass, no melting point of PVDF) was mixed at 70:30 (mass ratio) to prepare a coating liquid for forming a layer of the adhesive resin (C). This coating solution was applied on the heat-resistant porous layers (II) on both sides of the laminate of the resin porous layer (I) and the heat-resistant porous layer (II), respectively, and dried at 80° C. to obtain an adhesive resin ( By forming the layer C), a separator having a layer structure shown in FIG. 3 and a thickness of 24 μm was obtained. That is, the separator 8 has a laminate having the heat resistant porous layers (II) 82, 82 on both sides of the resin porous layer (I) 81, and the adhesive resin (C ) Layers 83, 83. The basis weight of the adhesive resin (C) relating to this separator was 0.6 g/m ^{2 on} both sides. The average particle size of the crystalline resin (C1) was 0.2 μm.

That is, the separator 8 has heat-resistant porous layers (II) 82, 82 on both sides of the resin porous layer (I) 81, and the surface of each heat-resistant porous layer (II) 82, 82 [resin The surface opposite to the surface in contact with the porous layer (I)] has layers 83, 83 of adhesive resin (C).

<Assembly of lithium secondary battery>
The separator obtained as described above was superposed while being interposed between the positive electrode and the negative electrode, and spirally wound to produce a wound electrode body. The wound electrode body thus obtained was crushed into a flat shape, and heated and pressed at 80° C. for 1 minute under a pressure of 0.5 Pa. The wound electrode body was placed in an aluminum outer can having a thickness of 6 mm, a height of 50 mm and a width of 34 mm, a lid plate was placed on the upper open end of the outer can, and laser welding was performed. After injecting the non-aqueous electrolyte solution from the inlet, the battery was charged under the following conditions in a dry room with a dew point of −30° C. First, the battery was charged with a constant current of 0.25 CmA (197.5 mA) for 1 hour so that the charged amount was 25% (197.5 mAh) of the designed electric capacity of the battery, and the gas generated in the outer can was dissolved in the electrolytic solution. It was naturally released from the inlet. Then, the electrolyte solution inlet was sealed, and the battery case formed of the outer can and the lid plate was sealed to obtain a lithium secondary battery having the appearance shown in FIG. 1 and the structure shown in FIG.

Although not shown in FIGS. 1 and 2, the lithium secondary battery of Example 1 is provided with a cleavage vent on the top of the outer can 2 for releasing the pressure when the internal pressure rises, and the lid 3 has a lid. It has an electrolytic solution injection port, and this electrolytic solution injection port is sealed with a sealing material (the same applies to each Example and Comparative Example described later).

Example 2
A lithium secondary battery was obtained in the same manner as in Example 1 except that the weight of the adhesive resin (C) relating to the separator of Example 1 was set to 1.5 g/m ^{2 on} both sides and the thickness was 25 μm. It was

Example 3
A lithium secondary battery was obtained in the same manner as in Example 1 except that the weight of the adhesive resin (C) relating to the separator of Example 1 was 0.1 g/m ^{2 on} both sides and the thickness was 23 μm. It was

Comparative Example 1
A lithium secondary battery was obtained in the same manner as in Example 1 except that the weight of the adhesive resin (C) relating to the separator of Example 1 was 2.0 g/m ^{2 on} both sides and the thickness was 26 μm. It was

Each of the produced lithium secondary batteries of Examples 1 to 3 and Comparative Example 1 was subjected to chemical conversion treatment under the following conditions. The designed electric capacities when the batteries were charged to 4.2 V were 790 mAh in all cases.

The battery was charged at 0.3 CmA (237 mA) to 4.1 V and then stored at 60° C. for 12 hours, and the stored battery was charged at 0.3 CmA (237 mA) to 4.2 V. Then, it was further charged at a constant voltage of 4.2 V for 2.5 hours, and then discharged to 3 V at 1 CmA (790 mA) to obtain a lithium secondary battery for evaluation.

The following evaluations were performed on the separators used in the lithium secondary batteries of Examples 1 to 3 and Comparative Example 1 and the lithium secondary batteries of Examples 1 to 3 and Comparative Example 1.

<180° peel test>
The same electrode (positive electrode or negative electrode) as that 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 was overlapped with the electrode to form an area of 2 cm × 2 cm from one end. Was hot-pressed at 80° C. for 1 minute at a pressure of 0.5 Pa to prepare a test piece. The end of the test piece on the side where the separator and the electrode were not heated and pressed was opened, and the separator and the electrode were bent so that the angle between them was 180°. Then, using a tensile tester, one end side of the separator and one end side of the electrode opened at 180° of the test piece were grasped and pulled at a pulling speed of 10 mm/min, and the separator and the electrode were both heated and pressed in the area. The strength at the time of peeling was measured. Further, the peeling strength of the separator and the electrode before the hot pressing was measured in the same manner as above except that the separator and the electrode cut out as described above were stacked and pressed without heating.

<Heat shrinkage test>
Strip-shaped test pieces having the MD and TD directions of Examples 1 to 3 and Comparative Example 1 in the MD and TD directions of 5 cm and 10 cm were cut out. The MD direction is the machine direction during the production of the microporous membrane used for the resin porous layer (I) of the separator, and the TD direction is the direction perpendicular to the MD direction. In the above-mentioned test piece, a 3 cm straight line was marked with an oil-based marker parallel to each of the MD direction and the TD direction so as to intersect at the centers of the MD direction and the TD direction. The center of these straight lines was the intersection of these straight lines.

Each of the above test pieces is hung in a thermostatic chamber, the temperature inside the chamber is raised to 150°C at a rate of 5°C/minute, and then the temperature is maintained at 150°C for 1 hour. Was measured and the heat shrinkage rate was calculated by the following formula.
Heat shrinkage rate (%) = 100 x (3-x)/3
[In the above formula, x is a dimension (cm) in the MD direction of the separator after left for 1 hour in a constant temperature bath set at 150°C. ]

<Load characteristic evaluation>
For each of the lithium secondary batteries of Examples 1 to 3 and Comparative Example 1, constant current charging was performed at a current value of 0.2 C until 4.20 V, and then constant current charging at 4.20 V was performed. Constant current charging was carried out. The total charging time until the end of charging was 15 hours. Next, each battery after charging was discharged at a current value of 0.2 C until the battery voltage became 3 V, and the discharge capacity was obtained (these capacities are referred to as “0.2 C discharge capacity”).

Next, each battery was subjected to constant current-constant voltage charging under the same conditions as described above, and then discharged at a current value of 2 C until the battery voltage became 3 V to obtain discharge capacities (these capacities were It is called "2C discharge capacity".)

Then, for each battery, the 2C discharge capacity was divided by the 0.2C discharge capacity, and this was expressed as a percentage to obtain the capacity retention rate. The above charging and discharging were all carried out in a test room where the temperature was controlled at 20°C.

<High temperature storage characteristics>
Each of the lithium secondary batteries of Examples 1 to 3 and Comparative Example 1 (batteries not evaluated otherwise) was charged at 395 mA (0.5 C) at 20° C. to 4.2 V, and further, 4. The battery was fully charged by charging at a constant voltage of 2 V for 2.5 hours, and the thickness of the battery at this time was measured. After that, the battery was discharged at 1° C. to 3 V at 20° C., and the discharge capacity before storage was measured.

Next, each battery was charged in the same manner as 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 by comparison with the thickness of the battery before storage. Then, each battery was discharged under the same conditions as before storage and the discharge capacity after high temperature storage was measured. Then, the discharge capacity after high temperature storage was divided by the discharge capacity before storage and this value was expressed as a percentage to calculate the capacity retention rate after high temperature storage.

<Charge/discharge cycle characteristics>
Each of the lithium secondary batteries of Examples 1 to 3 and Comparative Example 1 (batteries not subjected to other evaluations) was charged at 45C at 0.5C to 4.2V, and further charged to 4.2V. The battery was charged at a constant voltage for 2.5 hours to be fully charged, and then a charging/discharging cycle of discharging to 3V at 1C was repeated 300 times, and the discharge capacity at the first cycle and the discharge capacity at the 300th cycle were measured. Subsequently, the discharge capacity at the 300th cycle was divided by the discharge capacity at the first cycle, and this value was expressed as a percentage to calculate the capacity retention rate.

<150°C heating test>
For each of the lithium secondary batteries of Examples 1 to 3 and Comparative Example 1 (batteries for which other evaluations were not performed), constant current-constant voltage charging was performed under the same conditions as when measuring the 0.2 C discharge capacity. Each battery after charging was placed in a constant temperature bath, the temperature inside the bath was increased at a rate of 5° C./min, and after reaching 150° C., the temperature was maintained for 3 hours. The surface temperature of each battery during holding at 150° C. for 3 hours was measured by a thermocouple connected to the battery surface, and the maximum temperature was obtained. The maximum temperature was measured three times in each Example and Comparative Example, and the average value was calculated.

The constitutions of the separators used in the lithium secondary batteries of Examples 1 to 3 and Comparative Example 1 are shown in Table 1, and the evaluation results are shown in Tables 2 and 3. In the column of "Type and ratio" of the adhesive resin (C) shown in Table 1, "crystalline" in the lower row is crystalline resin (C1), and "amorphous" is amorphous resin (C2). ) Respectively, and each numerical value means the ratio (mass ratio) of each resin in the mixture. The particle size of the adhesive resin (C) shown in Table 1 is the average particle size of the crystalline resin (C1). Further, the basis weight of the adhesive resin (C) shown in Table 1 is the basis weight per one side of the separator, and the thickness of the heat resistant porous layer (II) is also the thickness per one side of the separator.

As is clear from Table 1 and Table 2, a layer of the adhesive resin (C) composed of a mixture containing the crystalline resin (C1) and the amorphous resin (C2) in proper proportions, The separators used for the lithium secondary batteries of Examples 1 to 3, which were formed on the surface of the resin porous layer (I) with an appropriate basis weight, could have a low heat shrinkage rate at 150°C. Further, the above-mentioned separator has a small peel strength at 180° from the electrode of 0.02 N/20 mm at maximum at room temperature, that is, before hot pressing, and shows almost no adhesiveness, but after hot pressing, any of them is used. It was 0.20 N/20 mm or more, and sufficient adhesive strength with the electrode could be secured.

On the other hand, in the separator used for the lithium secondary battery of Comparative Example 1 in which the basis weight of the layer of the adhesive resin (C) is too large, the heat shrinkage at 150° C. is slightly higher than that of the separator of the above Example. Became.

Note that, although an actual example in which the basis weight of the adhesive resin (C) layer is too small is not shown, when the basis weight of the adhesive resin (C) layer is less than 0.1 g/m ² , heating press is performed. The peel strength afterwards decreases, and it becomes impossible to secure sufficient adhesive strength with the electrode.

In addition, as shown in Table 2, in the lithium secondary batteries of Examples 1 to 3, an adhesive composed of a mixture containing a crystalline resin (C1) and an amorphous resin (C2) in an appropriate ratio. Since a separator formed by forming a layer of a conductive resin (C) on the surface of a resin porous layer (I) with an appropriate basis weight and integrating the separator and the electrode by the adhesive resin (C), Even after the integration, it is considered that the non-aqueous electrolyte can satisfactorily flow through the layer of the adhesive resin (C), the capacity retention rate at the time of load characteristic evaluation is high, and the load characteristic is excellent. Was there.

Furthermore, as shown in Table 3, the lithium secondary batteries of Examples 1 to 3 have a small swollen amount after high-temperature storage, a good capacity retention rate, and excellent high-temperature storage characteristics. It also had excellent charge-discharge cycle characteristics with a high capacity retention rate.

On the other hand, in the battery of Comparative Example 1 using the separator in which the adhesive resin (C) layer had a too large basis weight, the flow of the non-aqueous electrolyte in the adhesive resin (C) layer was hindered, so that the load The capacity retention rate during characteristic evaluation, the capacity retention rate during high temperature storage test, and the capacity retention rate during charge/discharge cycle characteristic evaluation were low, and the load characteristics, high temperature storage characteristics and charge/discharge cycle characteristics were inferior.

Although no actual example is shown, when a separator having a basis weight of the adhesive resin (C) of less than 0.1 g/m ² is used, high-temperature storage characteristics and charge/discharge cycle characteristics are inferior.

Comparative example 2
A coating liquid for forming a layer of the adhesive resin (C) with the mass ratio of the water dispersion of the crystalline resin (C1) and the water dispersion of the amorphous resin (C2) being 100:0. A lithium secondary battery was obtained in the same manner as in Example 1 except that was prepared.

Comparative Example 3
A coating liquid for forming a layer of the adhesive resin (C) with the mass ratio of the water dispersion of the crystalline resin (C1) and the water dispersion of the amorphous resin (C2) being 40:60. A lithium secondary battery was obtained in the same manner as in Example 1 except that was prepared.

With respect to the separators used in the lithium secondary batteries of Comparative Examples 2 and 3, the 180° peel test and the heat shrink test were performed in the same manner as described above. Further, for each of the lithium secondary batteries of Comparative Examples 2 and 3, after performing the chemical conversion treatment in the same manner as described above, in the same manner as described above, load characteristic evaluation, high temperature storage characteristic evaluation, charge/discharge cycle characteristic evaluation, and 150° C. A heating test was conducted. The evaluation results are shown in Tables 4 and 5 together with the results of Example 1.

As is clear from Table 4, the separator used in the lithium secondary battery of Comparative Example 2 in which the layer of the adhesive resin (C) was composed only of the crystalline resin (C1), and the amorphous resin (C2) In the separators used in the lithium secondary battery of Comparative Example 3 in which the ratio was too large, the heat shrinkage rate at 150° C. was slightly higher than that of the separator of Example 1. Further, in the separator of Comparative Example 3, even before hot pressing, the peel strength at 180° from the electrode was larger than 0.1 N/20 mm, and the separator had a certain degree of adhesiveness. It has been found that there may be inconvenience during the process depending on the conditions such as the laminating process and the winding process.

Further, as shown in Table 5, the battery of Comparative Example 2 has a larger swollen amount after high temperature storage and is inferior in high temperature storage characteristics as compared with the battery of Example 1, and the maximum temperature of the battery in the 150° C. heating test is Became higher and the safety decreased. In addition, the battery of Comparative Example 3 has a low capacity retention rate during load characteristic evaluation, a capacity retention rate during high temperature storage test, and a low capacity retention rate during charge/discharge cycle characteristic evaluation. The cycle characteristics were poor, and the maximum temperature of the battery in the 150° C. heating test was high, and the safety was low.

Example 4
With respect to the same separator and electrode used in Example 1, the temperature of the hot press was set to each temperature shown in Table 6, and the 180° peeling test was performed in the same manner as above, and after the hot press at each temperature. Peel strength was measured.

In addition, the same wound electrode body as that used in Example 1 was crushed into a flat shape and subjected to a heat press at a temperature of 0.5 Pa for 1 minute at each temperature shown in Table 6 to obtain each wound electrode body. A lithium secondary battery was assembled in the same manner as in Example 1. Each assembled battery was subjected to chemical conversion treatment in the same manner as described above, and then subjected to load characteristic evaluation, high temperature storage characteristic evaluation, and charge/discharge cycle characteristic evaluation. Table 6 shows the measurement results of the peel strength and the evaluation results of the batteries.

In the wound electrode body pressed at room temperature (without heating), the adhesive strength of the separator does not develop, so the battery swells after storage at high temperature and the charge/discharge cycle characteristics were poor. In the spirally wound electrode body, a sufficient adhesive force was developed in the separator, the swelling of the battery after high temperature storage was reduced, and the charge/discharge cycle characteristics were improved. On the other hand, in the wound electrode body heated and pressed at a temperature equal to or higher than the melting point (100° C.) of the crystalline resin (C1), the load characteristics, the capacity retention rate at high temperature storage, and the charge/discharge cycle characteristics were lowered.

The present invention can be implemented in other forms than the above without departing from the spirit of the present invention. The embodiments disclosed in the present application are examples, and the present invention is not limited to these embodiments. The scope of the present invention is interpreted by giving priority to the description of the appended claims rather than the description of the above-mentioned specification, and all modifications within the scope equivalent to the scope of the claims are defined in the claims. included.

The electrochemical device having the separator of the present invention is excellent in high-temperature storage characteristics and charge/discharge cycle characteristics because the separator and the positive electrode and/or the negative electrode are integrated by the adhesive resin (C), and the load is high. It has good characteristics and productivity. Therefore, the electrochemical device having the separator of the present invention makes use of such characteristics, such as the use as a driving power source for mobile information devices such as mobile phones and notebook computers, and the conventionally known lithium secondary batteries and the like. It can be widely applied to the same uses as various uses in which the electrochemical device is used.

1 Electrochemical device (lithium secondary battery)
2 outer can 3 cover plate 4 insulating packing 5 terminal 6 positive electrode 7 negative electrode 8 separator 9 wound electrode body 10 insulator 11 positive electrode lead body 12 negative electrode lead body 13 insulator 14 lead plate 81 resin porous layer (I)
82 Heat-resistant porous layer (II)
83 Layer of adhesive resin (C)

Claims (8)

A separator for an electrochemical element, comprising a resin porous layer (I) containing a heat-meltable resin (A) having a melting point of 100 to 170° C. as a main component, and a heat resistant porous layer (II),
At least one surface has an adhesive resin (C) layer,
The adhesive resin (C) is polyvinylidene fluoride or a copolymer of vinylidene fluoride and a polymerizable vinyl monomer containing fluorine, and is made of a crystalline resin (C1) and an amorphous resin (C2). ) And a mixture of
The crystalline resin (C1) has a melting point of 80 to 170° C.,
The amorphous resin (C2) has no melting point or has a melting point of 70° C. or lower,
The ratio of the amorphous resin (C2) in the mixture is 10% by mass or more and 50% by mass or less,
For the electrochemical element, the basis weight of the layer of the adhesive resin (C) on the surface on which the layer of the adhesive resin (C) is present is 0.1 to 1.5 g/m ² . Separator. The separator for an electrochemical element according to claim 1, wherein the crystalline resin (C1) is present in a particulate form in the mixture. The separator for an electrochemical element according to claim 2, wherein the crystalline resin (C1) has an average particle size of 0.01 to 0.5 μm. The heat-resistant porous layer (II) is formed by using an electrically insulating filler as a main component having a heat-resistant temperature of 150° C. or more, and binding the filler with a binder resin (B). The separator for an electrochemical element according to any one of 1. It is a manufacturing method of the separator for electrochemical elements in any one of Claims 1-4, Comprising:
A coating liquid in which the crystalline resin (C1) and the amorphous resin (C2) are dispersed is applied to the surface of the resin porous layer (I) or the heat resistant porous layer (II). To form a coating film,
And a step of forming the layer of the adhesive resin (C) by drying the coating film at a temperature at which the amorphous resin (C2) flows. Production method. The method for producing a separator for an electrochemical element according to claim 5, wherein the temperature for drying the coating film is set to a temperature lower than the melting point of the crystalline resin (C1). A method for producing an electrochemical device having a positive electrode, a negative electrode, a non-aqueous electrolytic solution, and the electrochemical device separator according to claim 1.
A step of forming the electrode body by laminating the positive electrode and the negative electrode with the electrochemical device separator interposed therebetween;
A step of applying pressure to the electrode body while heating it to a temperature lower than the melting point of the crystalline resin (C1) to bond the electrochemical element separator and the positive electrode and/or the negative electrode to be integrated. And a method for manufacturing an electrochemical device. The method for producing an electrochemical element according to claim 7, wherein a heating temperature when pressurizing the electrode body while heating is 50 to 95°C.

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