JP2014022051A - Separator for electrochemical element and electrochemical element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrochemical element exhibiting excellent stability and storage characteristics at high temperatures, and to provide a separator which can constitute the electrochemical element while ensuring high productivity.SOLUTION: The separator for electrochemical element for use in an electrochemical element having a nonaqueous electrolyte contains a material which adsorbs transition metal ions eluted into the nonaqueous electrolyte, and a filler having a heatproof temperature of 150°C or higher. A sodium salt of ethylenediamine tetra-acetic acid is used as the material adsorbing transition metal ions eluted into the nonaqueous electrolyte. The electrochemical element includes a positive electrode using a lithium-containing transition metal oxide as an active material, a negative electrode, a nonaqueous electrolyte, and a separator, and the separator is the inventive separator for electrochemical element.

Description

  The present invention relates to an electrochemical element excellent in safety and storage characteristics at high temperatures, and a separator capable of constituting the electrochemical element and having good productivity.

  Electrochemical elements such as lithium ion secondary batteries are widely used as power sources for portable electronic devices, in-vehicle power sources, and the like because of their high energy density. For example, lithium ion secondary batteries for electronic devices tend to have higher capacities with higher performance, and ensuring the safety of electrochemical elements is important. Further, in a medium-sized and large-sized lithium ion secondary battery such as a vehicle-mounted power supply, further safety must be ensured.

  In current lithium ion secondary batteries, a separator is interposed between a positive electrode and a negative electrode, and a polyolefin microporous film having a thickness of, for example, about 20 to 30 μm is used as the separator. In addition, the separator material 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. I am letting.

  As such a separator, for example, a uniaxially stretched or biaxially stretched film is used in order to improve the strength that can be achieved by crystallization by porosity and molecular orientation. 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 using a microporous membrane separator made of polyolefin, if the battery temperature reaches the shutdown temperature in the case of abnormal charging, the current must be immediately reduced to prevent the battery temperature from rising. This is because if the pores are not sufficiently closed and the current cannot be reduced immediately, the temperature of the battery easily rises to the shrinkage temperature of the separator, and there is a risk of an internal short circuit. If the exothermic reaction continues in such a state, it shifts to a so-called meltdown state in which the separator itself melts, and the positive electrode and the negative electrode are directly short-circuited. It is important to examine the isolation and insulation properties.

On the other hand, paying attention to the positive electrode active material, from the viewpoint of improving the safety of the lithium ion secondary battery, for example, the use of LiFePO ₄ or LiMn ₂ O ₄ having high safety has been conventionally studied. _In the case of ₂ O ₄ , it is known that when a charged battery is stored at a high temperature, Mn ions are eluted in the non-aqueous electrolyte solution and deposited on the negative electrode, which causes a reduction in battery capacity. It has been. Such problems due to elution of transition metal ions in the positive electrode active material can also occur in lithium-containing transition metal oxides other than LiMn ₂ O ₄ , although to a different extent.

  A technique for solving both of the problems related to the safety of the battery caused by the separator and the problems related to the storage characteristics of the battery caused by the positive electrode active material has been studied. Patent Document 1 proposes a nonaqueous electrolyte battery using a separator containing fine particles containing a polyamine group having a specific structure and having a specific average particle diameter. The fine particles have both the function of trapping transition metal ions eluted by polyamine groups and the function of suppressing the thermal contraction of the separator, thereby improving safety when the temperature inside the battery becomes excessively high. In addition, it is possible to suppress a decrease in capacity during battery storage due to transition metal ions eluted from the positive electrode active material.

  On the other hand, in the case of the technique described in Patent Document 1, since a certain amount of steps are required to manufacture the fine particles constituting the separator, the productivity is inferior to, for example, a conventional lithium ion secondary battery separator.

JP 2012-14994 A

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an electrochemical element excellent in safety and storage characteristics at high temperatures and a separator that can constitute the electrochemical element and has good productivity. It is to provide.

  The separator for an electrochemical element of the present invention that has achieved the above object is a separator used for an electrochemical element having a non-aqueous electrolyte, and adsorbs transition metal ions eluted in the non-aqueous electrolyte. And a filler having a heat resistant temperature of 150 ° C. or higher, and using a sodium salt of ethylenediaminetetraacetic acid as a material for adsorbing transition metal ions eluted in the non-aqueous electrolyte It is.

  The electrochemical device of the present invention is an electrochemical device comprising a positive electrode using a lithium-containing transition metal oxide as an active material, a negative electrode, a non-aqueous electrolyte, and a separator. It is the separator for electrochemical elements of the invention.

  ADVANTAGE OF THE INVENTION According to this invention, the separator which can comprise the electrochemical element excellent in the safety | security at high temperature and a storage characteristic, and the said electrochemical element, and favorable productivity can be provided.

It is a top view which represents typically an example of the electrochemical element (lithium ion secondary battery) of this invention. It is the sectional view on the AA line of FIG.

  The separator for an electrochemical element of the present invention (hereinafter simply referred to as “separator”) has a material that adsorbs transition metal ions eluted in the non-aqueous electrolyte (hereinafter referred to as “adsorbent material”) and a heat-resistant temperature of 150 ° C. It contains the above filler. In the electrochemical device having the separator of the present invention (the electrochemical device of the present invention), even if the transition metal ions are eluted from the lithium-containing transition metal oxide, which is the positive electrode active material, into the non-aqueous electrolyte, the separator is contained. Since it is trapped by the adsorbing material, precipitation of the transition metal on the negative electrode is suppressed. Therefore, the electrochemical device has good storage characteristics at high temperatures.

  In the separator of the present invention, ethylenediaminetetraacetic acid sodium salt (EDTA / Na salt) is used as the adsorbing material. Since the EDTA / Na salt traps transition metal ions by a mechanism in which Na ions are desorbed and take in transition metal ions, it has an excellent function of trapping eluted transition metal ions in the non-aqueous electrolyte. In addition, EDTA / Na salt can be contained in the separator without being supported on or chemically bonded to other materials constituting the separator, for example, thereby suppressing an increase in the number of manufacturing steps of the separator. can do. Therefore, according to the present invention, it is possible to provide a separator that has a high trapping ability for the eluted transition metal ions in the nonaqueous electrolytic solution and has a high productivity.

  As the EDTA · Na salt that can be used in the separator of the present invention, ethylenediaminetetraacetic acid disodium (two of the four carboxyl groups of ethylenediaminetetraacetic acid are Na salts. EDTA · 2Na), Examples thereof include sodium ethylenediaminetetraacetate (one in which all four carboxyl groups of ethylenediaminetetraacetic acid are Na salts).

  Moreover, the separator of this invention contains the filler whose heat-resistant temperature is 150 degreeC or more. For example, even if the separator is thinned, the positive electrode and the negative electrode can be satisfactorily separated by the filler having a heat resistant temperature of 150 ° C. or higher, so that a decrease in the energy density of the electrochemical element is suppressed as much as possible to prevent occurrence of a short circuit. can do. Furthermore, since the heat shrinkage of the separator can be suppressed by a filler having a heat-resistant temperature of 150 ° C. or higher, the electrochemical element having the separator of the present invention has a positive electrode and a negative electrode due to the heat shrinkage of the separator even when abnormally heated. Contact is unlikely to occur and the safety is excellent.

  As used herein, “heat-resistant temperature is 150 ° C. or higher” in a filler having a heat-resistant temperature of 150 ° C. or higher means that shape change such as deformation is not visually confirmed at least at 150 ° C.

  As a filler having a heat-resistant temperature of 150 ° C. or higher, it has an electrical insulating property, is electrochemically stable, and is a composition used for forming a non-aqueous electrolyte solution or separator having an electrochemical element. If it is stable with respect to the solvent used for (composition containing a solvent), there will be no restriction | limiting in particular. As used herein, “stable with respect to a non-aqueous electrolyte” means that deformation and chemical composition change do not occur in a non-aqueous electrolyte related to an electrochemical element. In addition, “electrochemically stable” as used in the present specification means that no chemical change occurs during charging / discharging of the electrochemical element.

Specific examples of such a filler having a heat resistant temperature of 150 ° C. or higher include fine oxide particles such as iron oxide, silica (SiO ₂ ), alumina (Al ₂ O ₃ ), TiO ₂ , BaTiO ₃ , and ZrO ₂ ; Nitride fine particles such as aluminum nitride and silicon nitride; refractory ion crystal fine particles such as calcium fluoride, barium fluoride and barium sulfate; covalently bonded crystal fine particles such as silicon and diamond; clay fine particles such as talc and montmorillonite; boehmite And inorganic fine particles such as zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, hydrotalcite and the like, or artificial materials thereof. Further, the surface of conductive fine particles such as metal fine particles; oxide fine particles such as SnO ₂ and tin-indium oxide (ITO); carbon fine particles such as carbon black and graphite; It may be fine particles that have been made electrically insulating by surface treatment with the above-mentioned materials constituting the electrically insulating fine particles.

  Moreover, organic fine particles can also be used for the filler having a heat resistant temperature of 150 ° C. or higher. Specific examples of organic fine particles include polyimides, melamine resins, phenol resins, crosslinked polymethyl methacrylate (crosslinked PMMA), crosslinked polystyrene (crosslinked PS), polydivinylbenzene (PDVB), and high crosslinking amounts such as benzoguanamine-formaldehyde condensates. 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).

  For the filler having a heat resistant temperature of 150 ° C. or higher, the various fine particles exemplified above may be used alone or in combination of two or more. Further, the filler having a heat resistant temperature of 150 ° C. or higher may be a particle containing two or more materials constituting the various exemplified fine particles. Among the various exemplified fine particles, inorganic oxide fine particles are preferable, and alumina, silica, and boehmite are more preferable because, for example, the oxidation resistance of the heat-resistant porous film can be further improved.

  If the average particle size of the filler having a heat resistant temperature of 150 ° C. or higher is too small, the above-described effect due to the filler may not be sufficiently ensured. Therefore, the average particle size is preferably 0.01 μm or more, preferably 0.1 μm or more. It is more preferable that However, if the average particle size of the filler having a heat resistant temperature of 150 ° C. or higher is too large, for example, the separator becomes too thick, and the energy density of an electrochemical device using the separator may decrease. Therefore, the average particle diameter of the filler having a heat resistant temperature of 150 ° C. or higher is preferably 15 μm or less, and more preferably 5 μm or less.

  The average particle diameter of each fine particle (filler having a heat-resistant temperature of 150 ° C. or more, and heat-fusible fine particles and heat-swellable fine particles described later) in the present specification is, for example, a laser scattering particle size distribution meter (for example, “HORIBA” LA-920 ") can be defined as the number average particle size measured by dispersing the fine particles in a medium in which the fine particles do not dissolve or swell.

  The separator of the present invention only needs to contain the adsorbing material and a filler having a heat resistant temperature of 150 ° C. or higher. For example, the adsorbing material is contained in a porous film formed by binding the filler with a binder. The separator of this invention can be comprised by making it contain.

  As a binder for binding fillers having a heat-resistant temperature of 150 ° C. or more, ethylene-vinyl acetate copolymer (EVA, vinyl acetate-derived structural unit is 20 to 35 mol%), ethylene-ethyl acrylate copolymer Ethylene-acrylic acid copolymers such as polymers, fluorine-based rubber, styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), polyvinyl alcohol (PVA), polyvinyl butyral (PVB), polyvinyl pyrrolidone ( PVP), cross-linked acrylic resin, polyurethane, epoxy resin and the like can be mentioned, and in particular, a heat-resistant binder having a heat-resistant temperature of 150 ° C. or higher is preferably used. As the binder, those exemplified above may be used alone or in combination of two or more.

  Among the binders exemplified above, highly flexible binders such as EVA, ethylene-acrylic acid copolymer, fluorine-based rubber, and SBR are preferable. Specific examples of such highly flexible binders include “Evaflex Series (EVA)” by Mitsui DuPont Polychemical Co., Ltd., EVA by Nippon Unicar Co., Ltd., “Evaflex-EEA Series (Ethylene- Acrylic acid copolymer) ”, Nippon Unicar's EEA, Daikin Industries’ “Dai-L Latex Series” (fluorinated rubber), JSR ’s “TRD-2001 (SBR)”, Nippon Zeon ’s “BM-400B” SBR) "and the like.

  The content of the filler having a heat resistant temperature of 150 ° C. or higher in the separator is the total volume of the constituent components of the separator (the total volume excluding the void portion. In the following, the content of each component is the same.), Preferably 60% by volume or more, and more preferably 90% by volume or more.

  The upper limit value of the content of the filler having a heat resistant temperature of 150 ° C. or higher in the separator is not particularly limited. For example, as described above, the separator of the present invention includes only the adsorbing material, the filler and the binder having a heat resistant temperature of 150 ° C. or higher. Therefore, the entire amount excluding the adsorbing material and the binder can be a filler having a heat resistant temperature of 150 ° C. or higher. The suitable upper limit of the content rate of the filler whose heat-resistant temperature is 150 degreeC or more in the case of the separator of such an aspect is 99 volume% in the whole volume of the component of a separator, for example.

  Further, in the separator of the present invention, the amount of the adsorbing material is such that the amount of the EDTA / Na salt used for forming the separator is, based on the volume, a heat resistant temperature of 150 from the viewpoint of ensuring the above-mentioned effect due to its use. The amount is preferably 10 parts or more, more preferably 50 parts or more with respect to 100 parts of filler at 100C or higher. However, if the amount of the adsorbing material in the separator is too large, the effect of improving the dimensional stability of the separator at high temperatures due to the filler may be reduced, so the amount of EDTA / Na salt used for forming the separator is As a standard, it is preferably 50 parts or less and more preferably 40 parts or less with respect to 100 parts of filler having a heat resistant temperature of 150 ° C. or more.

  In the separator manufacturing method described later, when water is used as the solvent of the composition used for forming the separator, for example, EDTA / Na salt added to the composition is used in the separator after formation. The number of carboxyl groups in the Na salt may change (for example, when EDTA · 2Na is used, the number of Na contained in one molecule is not 2 in the separator). However, even in such a case, the separator of the present invention can trap trapped transition metal ions in the non-aqueous electrolyte well.

  In addition, the separator of the present invention closes the vacancies when the temperature of the electrochemical element rises, as is generally used in electrochemical elements such as lithium ion secondary batteries, and allows ion permeability. It is also possible to provide a so-called shutdown function that secures the safety of the device by reducing the above.

  Specific examples of the separator having a shutdown function include a porous layer (I) mainly composed of polyolefin having a shutdown function (such as a microporous membrane made of polyolefin) and a porous body mainly including a filler having a heat resistant temperature of 150 ° C. or more. A separator having a porous layer (II), more specifically, a separator having the porous layer (II) formed on the surface of the porous layer (I), and the like. In this case, the adsorbing material may be contained in the porous layer (II), for example.

  In the case of providing a shutdown function by using a separator having a porous layer (I) composed of a polyolefin microporous membrane, the polyolefin microporous membrane is made of an electrochemical element such as a normal lithium ion secondary battery. The separator currently used can be used. Specifically, a microporous film composed of a copolymer polyolefin such as polyethylene (PE), polypropylene (PP), and ethylene-propylene copolymer can be used.

  The microporous membrane made of polyolefin is composed of the polyolefin as described above. For example, a film or sheet formed by a stretching method, that is, a polyolefin mixed with an inorganic filler is uniaxially or biaxially stretched to form a fine film. After forming the pores, those produced by removing the inorganic filler as required can be used. In addition, the pore formation method using a solvent, that is, the polyolefin illustrated above and another resin or paraffin are mixed to form a film or sheet, and then, in a solvent that dissolves only the other resin or paraffin, What is manufactured by immersing a film or sheet and dissolving only the other resin or paraffin to form pores can be used as a polyolefin microporous film. Furthermore, a polyolefin microporous membrane produced by a method combining the stretching method and the pore formation method using the solvent can also be used.

  Further, the polyolefin microporous membrane may have a single layer structure or a laminated structure having a plurality of layers. That is, for example, a microporous membrane composed of a single layer containing PE, a microporous membrane having a two-layer structure having a layer containing PP on one side of a layer containing PE, and PP on both sides of a layer containing PE It may be a microporous film having a three-layer structure having a layer to be contained.

  Since the temperature at which the shutdown function in the separator is manifested is too low, the pores of the separator may be blocked during normal use of the electrochemical element, and the performance of the electrochemical element may be deteriorated quickly. More preferably, the temperature is 100 ° C. or higher. In addition, if the temperature at which the shutdown function is manifested in the separator is too high, there is a risk that the internal temperature of the electrochemical element will rise before the shutdown function works, leading to thermal runaway. More preferably, it is 130 ° C. or lower.

  Therefore, at least a part of the polyolefin constituting the porous layer (I) has a melting point [measured using a differential scanning calorimeter (DSC) in accordance with the provisions of JIS K 7121] within the temperature range where the shutdown function is exhibited. Melting temperature to be done. The same applies to the “melting point” described in the present specification. It is preferable that what has] is used.

  When the separator of the present invention has a porous layer (I) mainly composed of polyolefin and a porous layer (II) mainly composed of a filler having a heat resistant temperature of 150 ° C. or higher, the porous layer (I) and the porous layer Each layer (II) may be a single layer, or one or both may be two or more layers. For example, you may have porous layer (II) on both surfaces of porous layer (I).

  In addition, since the polyolefin content in the porous layer (I) mainly composed of polyolefin such as a microporous membrane made of polyolefin is mainly composed of polyolefin, the total volume of constituents of the porous layer (I) (voids) The total volume excluding the portion) is 50% by volume or more, preferably 70% by volume or more, and may be 100% by volume, that is, it may be composed of only polyolefin.

  Further, the content of the filler having a heat resistant temperature of 150 ° C. or higher in the porous layer (II) mainly including a filler having a heat resistant temperature of 150 ° C. or higher mainly includes a filler having a heat resistant temperature of 150 ° C. or higher. In the total volume of the constituent components of the porous layer (II) (total volume excluding the void portion), it is 50% by volume or more, preferably 70% by volume or more, and preferably 99% by volume or less. .

  As described above, the porous layer (II) preferably contains the adsorbing material in addition to the filler having a heat-resistant temperature of 150 ° C. or higher, and, for example, in order to bind the filler, An exemplary binder may be contained.

  In the separator having the porous layer (I) mainly composed of polyolefin, the shutdown function works when the temperature rises, but when this porous layer (I) is composed of a polyolefin microporous film, As usual, it is stretched to obtain a microporous structure. However, when the separator of the present invention has a porous layer (I), an electrochemical element using this separator is caused by the action of a filler having a heat resistant temperature of 150 ° C. or higher contained mainly in the porous layer (II). Even if the inside becomes high temperature, shrinkage of the entire separator can be suppressed.

  In order to give the separator of the present invention a shutdown function, in addition to the above method, the separator contains resin fine particles having a melting point in the preferred temperature range in which the shutdown function is exhibited (hereinafter referred to as “heat-meltable fine particles”). Can be adopted.

  As the constituent resin of the heat-meltable fine particles, the melting point is within the above-mentioned temperature range, it is stable to the electrolyte solution of the electrochemical element, and the electrochemical element is not easily oxidized and reduced in the operating voltage range of the electrochemical element. And stable resins are preferred. Specific examples include PE, copolymerized polyolefin, polyolefin derivatives (such as chlorinated polyethylene), polyolefin wax, petroleum wax, and carnauba wax. Examples of the copolymer polyolefin include ethylene-vinyl monomer copolymers, more specifically ethylene-acrylic copolymers such as ethylene-propylene copolymers, EVA, ethylene-methyl acrylate copolymers, and ethylene-ethyl acrylate copolymers. An acid copolymer can be illustrated. The structural unit derived from ethylene in the copolymerized polyolefin is desirably 85 mol% or more. Moreover, polycycloolefin etc. can also be used. As the heat-meltable fine particles, one of the above exemplified resins may be used alone, or two or more of them may be used.

  Among the materials exemplified above, PE, polyolefin wax, or EVA having a structural unit derived from ethylene of 85 mol% or more is preferably used as the heat-meltable fine particles. Moreover, the heat-meltable fine particles may contain various known additives (for example, antioxidants) added to the resin as necessary.

  The separator of the present invention can also be shut down by containing fine particles that swell when heated by absorbing the non-aqueous electrolyte and whose degree of swelling increases as the temperature rises (hereinafter referred to as “thermally swellable fine particles”). Functions can be added.

  As the heat-swellable fine particles, in the temperature range (approximately 70 ° C. or lower) in which the electrochemical element is usually used, the electrolytic solution is not absorbed or the amount of absorption is limited, and thus the degree of swelling is below a certain level. However, when heated to the required temperature (Tc), fine particles composed of a resin having such properties that it absorbs the non-aqueous electrolyte and swells greatly and the degree of swelling increases as the temperature rises are used. . In an electrochemical device using a separator containing heat-swellable fine particles, a flowable non-aqueous electrolyte that is not absorbed by the heat-swellable fine particles exists in the pores of the separator at a temperature lower than Tc. The temperature at which the property of increasing the degree of swelling with increasing temperature (hereinafter sometimes referred to as “thermal swellability”) appears, although the Li ion conductivity becomes high and becomes an electrochemical device having good load characteristics. When heated above, the heat-swellable fine particles absorb the non-aqueous electrolyte in the electrochemical element and swell greatly, and the swollen heat-swellable fine particles close the pores of the separator and are non-flowable. By reducing the amount of water electrolyte and causing the electrochemical element to wither, the reactivity between the non-aqueous electrolyte and the active material is suppressed, and the safety of the electrochemical element is ensured. Moreover, when the temperature is higher than Tc, the liquid withering further proceeds due to the thermal swellability, and the reaction of the device is further suppressed, so that safety at high temperatures can be further improved.

  The temperature at which the heat-swellable fine particles start to show heat-swellability is preferably 75 ° C. or higher. By setting the temperature at which the heat-swellable fine particles start to exhibit heat-swellability to 75 ° C. or higher, the temperature (Tc) at which the internal resistance of the electrochemical device is increased by significantly reducing the Li ion conductivity is approximately 80 ° C. or higher. It is because it can set to. On the other hand, since the Tc of the separator increases as the lower limit of the temperature exhibiting thermal swellability increases, the temperature at which the thermal swellable fine particles begin to exhibit thermal swellability is set to 125 ° C in order to set Tc to approximately 130 ° C or lower. It is preferable to set it as follows, and it is more preferable to set it as 115 degrees C or less. If the temperature showing the heat swellability is too high, the thermal runaway reaction of the active material in the electrochemical element cannot be sufficiently suppressed, and the safety improvement effect of the electrochemical element by using the heat swellable fine particles cannot be sufficiently ensured. In addition, if the temperature exhibiting thermal swellability is too low, the conductivity of Li ions may be too low in the temperature range of use of a normal electrochemical device (approximately 70 ° C. or less).

  Further, at a temperature lower than the temperature exhibiting the heat swellability, it is desirable that the heat swellable fine particles do not absorb the non-aqueous electrolyte as much as possible and have less swelling. This is because, in the use temperature region of the electrochemical element, for example, room temperature, the non-aqueous electrolyte is more likely to be held in a state where it can flow into the pores of the separator than to be taken into the heat-swellable fine particles. This is because the load characteristics and the like of the above are improved.

  The heat-swellable fine particles have heat resistance and electrical insulation, are stable to non-aqueous electrolytes, and are electrochemically stable that are not easily oxidized and reduced in the operating voltage range of the electrochemical element. It is preferably composed of a material, specifically, more preferably composed of a styrene resin crosslinked body, an acrylic resin crosslinked body, a fluororesin crosslinked body, etc., and particularly composed of crosslinked PMMA. Preferably used.

  The mechanism by which these resin crosslinked bodies absorb and swell the non-aqueous electrolyte as the temperature rises is not clear, but a correlation with the glass transition point (Tg) is conceivable. That is, since the resin generally becomes flexible when heated to its Tg, it is estimated that the resin as described above can absorb a large amount of non-aqueous electrolyte and swell at temperatures above Tg. The Therefore, as the heat-swellable fine particles, it is desirable to use a crosslinked resin having a Tg of about 75 to 125 ° C. in consideration of the fact that the temperature at which the shutdown action actually occurs is somewhat higher than the temperature at which the heat-swellability begins to be exhibited. it is conceivable that. The Tg of the resin crosslinked body which is a heat-swellable fine particle referred to in the present specification is a value measured using DSC in accordance with the provisions of JIS K7121.

  In the so-called dry state before containing the non-aqueous electrolyte, the resin cross-linked body is reversible to some extent to the volume change accompanying the temperature change, such as expansion due to temperature rise and contraction again by lowering the temperature. In addition, since it has a heat-resistant temperature that is considerably higher than the temperature that exhibits thermal swellability, it can be heated to 200 ° C or higher even if the lower limit of the temperature that exhibits thermal swellability is about 100 ° C. The material can be selected. Therefore, even when heating is performed in a separator manufacturing process or the like, the resin is not dissolved or the thermal swellability of the resin is not impaired, and handling in a manufacturing process including a general heating process becomes easy.

  The heat-meltable fine particles and the heat-swellable fine particles may be used by being contained in the separator. When the separator has a porous layer (I) and a porous layer (II), the porous layer (II ) Is preferably contained. Thereby, it can be set as the separator which has a shutdown function.

  The heat-meltable fine particles and the heat-swellable fine particles may have an average particle size that is 1/100 to 1/3 of the thickness of the separator, although their particle size at the time of drying may be smaller than the thickness of the separator. Specifically, the average particle size of the heat-meltable fine particles and heat-swellable fine particles is preferably 0.1 to 20 μm. When the particle size of the heat-meltable fine particles or the heat-swellable fine particles is too small, the gap between the particles becomes small, the ion conduction path becomes long, and the characteristics of the electrochemical device may deteriorate. On the other hand, if the particle size is too large, the separator becomes thick, which may cause a decrease in the energy density of the electrochemical element.

  The shape of the filler having a heat-resistant temperature of 150 ° C. or higher, the heat-meltable fine particles and the heat-swellable fine particles is not particularly limited, but on the surface of the porous layer (I) mainly composed of polyolefin such as a polyolefin microporous film. In the case where the porous layer (II) is provided, from the viewpoint of further enhancing the effect of suppressing the thermal contraction of the entire separator in the porous layer (II), in the form of secondary particles in which plate-like particles or primary particles are connected. Preferably there is.

  In addition, as described later, when the separator of the present invention is directly formed on the surface of the electrode of the electrochemical element, or when the separator is formed using a porous substrate such as a nonwoven fabric, the electrochemical element by dendrite Since the short circuit can be effectively suppressed, the filler having a heat resistant temperature of 150 ° C. or higher is preferably a plate-like particle. When a separator is formed by orienting plate-like particles as will be described later, it is possible to lengthen the path related to ion conduction, and thus it is possible to more effectively prevent an internal short circuit of an electrochemical element due to dendrites. Become.

  As the form of the plate-like particles, it is desirable that the aspect ratio is 5 or more, more preferably 10 or more, and 100 or less, more preferably 50 or less. Further, 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 grain is 3 or less, more preferably 2 or less and close to 1. It is desirable to be a value.

  In addition, the average value of the ratio of the long axis direction length and the short axis direction length of the flat plate surface in the plate-like particle can be obtained by image analysis of an image taken with a scanning electron microscope (SEM), for example. it can. Further, the aspect ratio of the plate-like particles can be obtained by image analysis of an image taken by SEM.

  When the filler having a heat-resistant temperature of 150 ° C. or higher is a plate-like particle, the average particle diameter is preferably 0.01 μm or more, more preferably 0.1 μm or more, as in the case of other shapes. Moreover, it is preferable that it is 15 micrometers or less, and it is more preferable that it is 5 micrometers or less. The larger the average particle size of the plate-like particles, the greater the effect of suppressing the thermal contraction of the entire separator. However, if this is too large, the thickness of the entire separator will increase and the energy density of the electrochemical device will decrease. There is a risk of causing it.

  The form of the plate-like particles in the separator is preferably such that the flat plate surface is substantially parallel to the surface of the separator. More specifically, the plate-like particle in the porous layer (II) has its flat plate surface. The average angle between the separator 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 separator porous layer (II) is the surface of the separator. It is parallel to].

  In addition, when the filler having a heat resistant temperature of 150 ° C. or higher is in the form of secondary particles in which primary particles are continuous (hereinafter simply referred to as “secondary particles”), the secondary particles in the porous layer (II) Since it exists in the state which mutually intertwined, compared with the case where it is a primary particle, it becomes possible to suppress the thermal contraction of the whole separator more effectively. Moreover, since the filler having a heat-resistant temperature of 150 ° C. or higher is a secondary particle, it becomes possible to effectively secure a gap between the particles, and the movement of ions in the electrochemical element becomes easier. In particular, it is possible to configure an electrochemical element suitable for use in applications such as automobiles and power tools that require high output.

  The average particle size of the secondary particles is a number average particle size measured by the same method as the number average particle size of the fine particles, and is preferably 0.1 μm or more, more preferably 0.2 μm or more. Moreover, it is preferable that it is 15 micrometers or less, and it is more preferable that it is 5 micrometers or less. If the average particle diameter of the secondary particles is too large, the thickness of the entire separator may be too large. Moreover, when the average particle diameter of the secondary particles is too small, there is a possibility that the effect of suppressing the thermal contraction of the entire separator is reduced.

  The average particle diameter of the primary particles constituting the secondary particles is preferably 0.01 μm or more, and more preferably 1 μm or less. If the average particle size of the primary particles is too small, the pore size formed by the voids between the particles becomes too small, which may hinder ion migration and reduce the output of the electrochemical device. In addition, if the average particle diameter of the primary particles is too large, the number of primary particles forming the secondary particles decreases, the entanglement between the particles decreases, and the heat shrinkage of the entire separator due to the use of the secondary particles. There is a possibility that the suppression effect is reduced.

  In addition, the separator of the present invention is used for filling fillers and other fine particles (heat-fusible fine particles and heat-swellable fine particles for improving safety) having a heat resistant temperature of 150 ° C. or higher, for example, in pores of a porous substrate such as a nonwoven fabric. Or a layer containing a filler or other fine particles having a heat-resistant temperature of 150 ° C. or higher may be formed on the surface of the porous substrate.

  Examples of the constituent material of the porous substrate such as nonwoven fabric include cellulose and its modified products [CMC, hydroxypropyl cellulose (HPC), etc.], polyolefin [polypropylene (PP), propylene copolymer, etc.], polyester [PET , Polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), etc.], resins such as polyacrylonitrile (PAN), aramid, polyamideimide, polyimide; inorganic oxides such as glass, alumina, zirconia, silica; A porous substrate such as a nonwoven fabric may be formed by using two or more of these constituent materials in combination. Moreover, the porous base material, such as a nonwoven fabric, may contain various known additives (for example, an antioxidant in the case of a resin) as necessary.

  The porosity of the separator of the present invention is preferably 30% or more and preferably 70% or less when the separator is in a dry state. If the porosity of the separator is too small, the movement of ions in the separator may be hindered. If it is too large, the strength of the separator may be reduced. The porosity of the separator: P (%) can be calculated by obtaining the sum for each component i from the thickness of the separator, the mass per area, and the density of the constituent components using the following equation (1).

P = {1- (m / t) / (Σa _i · ρ _i )} × 100 (1)
Here, in the above formula, a _i : ratio of component i when the total mass is 1, ρ _i : density of component i (g / cm ³ ), m: mass per unit area of the separator (g / cm ² ), t: thickness of separator (cm).

In the case of a separator having a porous layer (I) and a porous layer (II), in the formula (1), m is the mass per unit area (g / cm ² ) of the porous layer (I). , the thickness (cm) of the porous layer to t (I), by the ratio of component i when set to 1 the entire mass porous layer a _i (I), using the equation (1) Thus, the porosity of the porous layer (I): P (%) can also be obtained. The porosity of the porous layer (I) determined by this method is preferably 30 to 70%.

Further, in the case of the multilayer separator, in the formula (1), m is the mass per unit area (g / cm ² ) of the porous layer (II), and t is the thickness of the porous layer (II) ( cm), and a _i is the ratio of the component i when the mass of the entire porous layer (II) is 1, so that the porosity of the porous layer (II) using the formula (1): P (%) can also be obtained. The porosity of the porous layer (II) obtained by this method is preferably 20 to 60%.

  The thickness of the separator is preferably 5 μm or more, and more preferably 10 μm or more, from the viewpoint of securing the strength of the separator and better suppressing, for example, the occurrence of an internal short circuit. However, if the separator is too thick, it is likely to cause a decrease in the energy density of the electrochemical element and increase in internal resistance. Therefore, the thickness of the separator is preferably 40 μm or less, more preferably 30 μm or less. preferable.

  In addition, when the separator has a porous layer (I) and a porous layer (II), the thickness of the porous layer (I) [when the separator has a plurality of porous layers (I) The total thickness] is 10-30 μm, the thickness of the porous layer (II) [when the separator has a plurality of porous layers (II), the total thickness] is 1-10 μm, And it is preferable to adjust so that the thickness of the whole separator may become the said suitable value.

  The separator of the present invention can be produced, for example, by the following methods (I), (II) and (III).

  In the production method (I), a filler and an EDTA / Na salt having a heat-resistant temperature of 150 ° C. or more and, if necessary, a binder, heat-meltable fine particles, heat-swellable fine particles, etc. are dispersed in water or an appropriate solvent. A porous layer integrated with the electrode by applying the composition (slurry, paste, etc.) on the surface of the electrode (positive electrode and / or negative electrode) used in the electrochemical device and drying to remove the solvent As a method of forming a separator.

  The separator-forming composition used in the production method (I) includes a filler having a heat-resistant temperature of 150 ° C. or higher, the adsorbing material, and a binder, a heat-meltable fine particle, a heat-swellable fine particle, if necessary. These are dispersed in a solvent (including a dispersion medium; the same applies hereinafter) (the binder may be dissolved). The solvent used in the composition for forming the separator can uniformly disperse fillers, heat-melting fine particles, and heat-swellable fine particles having a heat-resistant temperature of 150 ° C. or more, and can uniformly dissolve or disperse EDTA / Na salt and binder. An organic solvent such as an aromatic hydrocarbon such as toluene; a furan such as tetrahydrofuran; a ketone such as methyl ethyl ketone and methyl isobutyl ketone; 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 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.) and various surfactants are used. The interfacial tension can also be controlled by appropriately adding. In addition, since EDTA / Na salt can be dissolved in water, it is more preferable to use water as a solvent of the separator-forming composition. In this case, in the separator (or the layer containing the adsorbent material related to the separator) Thus, the adsorbing material can be more uniformly distributed.

  In the composition for forming a separator, the solid content including a filler having a heat resistant temperature of 150 ° C. or higher, an EDTA / Na salt, a binder, a heat-meltable fine particle, a heat-swellable fine particle, and the like is, for example, 10 to 40% by mass. Preferably there is.

  As a method for applying the separator-forming composition to the electrode surface, for example, a coating method using a known coating apparatus such as a blade coater, a roll coater, a die coater, a spray coater, or a gravure coater can be employed. In addition, when using plate-like particles for a filler having a heat resistant temperature of 150 ° C. or higher, it is preferable to apply a share to the applied composition for forming a separator from the viewpoint of increasing the orientation of the plate-like particles in the separator. . Therefore, when using plate-like particles for a filler having a heat-resistant temperature of 150 ° C. or higher, among the above-mentioned coating apparatuses, such as a blade coater or a die coater, a coating that can share the composition for forming a separator at the time of coating. It is preferred to use an apparatus.

  The separator manufacturing method (II) is the same composition for forming a separator as that used in the manufacturing method (I) for a porous film mainly made of polyolefin (such as a microporous film made of polyolefin) or a porous substrate such as a nonwoven fabric. This is a manufacturing method in which an object is applied or impregnated and then dried at a predetermined temperature.

  In addition, when the porous substrate is a non-woven fabric and the opening diameter of the pores is relatively large (for example, when the opening diameter of the pores is 5 μm or more), this tends to cause a short circuit of the electrochemical element. . Therefore, in this case, it is preferable to have a structure in which all or part of the filler, heat-meltable fine particles, heat-swellable fine particles having a heat resistant temperature of 150 ° C. or higher are present in the pores of the nonwoven fabric. By adopting such a structure, it becomes possible to lengthen or complicate the ion conduction path, and to effectively prevent short circuit of the electrochemical element due to dendrites. In order to allow fillers, heat-meltable fine particles, heat-swellable fine particles, etc. having a heat resistant temperature of 150 ° C. or more to exist in the pores of the non-woven fabric, for example, a non-woven fabric is coated or impregnated with a separator-forming composition containing these Then, a process such as drying after removing a surplus composition through a certain gap may be used.

  Further, when plate-like particles are used for a filler having a heat-resistant temperature of 150 ° C. or higher, it is preferable to apply a share to the separator-forming composition as described above in order to increase the orientation of the plate-like particles in the separator. However, a share can be applied to the composition for forming a separator by applying a certain gap after applying or impregnating the composition for forming a separator to a nonwoven fabric.

  The separator manufacturing method (III) is the same as the separator forming method used in the manufacturing method (I) or manufacturing method (II), applied to the surface of a suitable substrate such as PET, dried and porous. In this method, a film is formed, and the film is peeled off from the substrate to form an independent film separator.

  In addition, the separator of this invention should just contain the said adsorption material and the filler whose heat resistant temperature is 150 degreeC or more, and is not necessarily limited to the thing of each structure demonstrated so far.

  The electrochemical device of the present invention includes a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator, the positive electrode uses a lithium-containing transition metal oxide as an active material, and the separator is the separator of the present invention. Other configurations and structures are not particularly limited, and various configurations and structures that are conventionally used in electrochemical elements such as lithium ion secondary batteries can be applied.

  The electrochemical device of the present invention includes non-aqueous electrolyte secondary batteries (non-aqueous electrolyte secondary batteries) such as lithium ion secondary batteries, non-aqueous electrolyte primary batteries (non-aqueous electrolyte primary batteries), and supercapacitors. Etc. are included.

  As a positive electrode, the thing of the structure which has the positive mix layer containing the lithium containing transition metal oxide which is a positive electrode active material, a binder, a conductive support agent, etc. on the single side | surface or both surfaces, for example can be used.

Specific examples of the lithium-containing transition metal oxide that is the positive electrode active material include, for example, LiM _x Mn _{2 -x} O ₄ (where M is Li, B, Mg, Ca, Sr, Ba, Ti, V, Cr). , Fe, Co, Ni, Cu, Al, Sn, Sb, In, Nb, Mo, W, Y, Ru, and Rh, at least one element selected from 0.01 ≦ x ≦ 0 .5) Spinel-type lithium manganese composite oxide, Li _x Mn _(1-yx) Ni _y M _z O _(2-k) F _l (where M is Co, Mg, Al, B) , Ti, V, Cr, Fe, Cu, Zn, Zr, Mo, Sn, Ca, Sr and W, at least one element selected from 0.8 ≦ x ≦ 1.2, 0 <Y <0.5, 0 ≦ z ≦ 0.5, k + l <1, −0.1 ≦ k ≦ 0.2 0 ≦ l ≦ 0.1) lamellar compound represented _{by, LiCo 1-x M x O} 2 ( however, M is, Al, Mg, Ti, Zr , Fe, Ni, Cu, Zn, Ga, Ge, Nb , Mo, Sn, Sb and Ba, a lithium cobalt composite oxide represented by 0 ≦ x ≦ 0.5), LiNi _1-x M _x O ₂ ( Where M is at least one element selected from the group consisting of Al, Mg, Ti, Zr, Fe, Co, Cu, Zn, Ga, Ge, Nb, Mo, Sn, Sb and Ba, and 0 Lithium nickel composite oxide represented by ≦ x ≦ 0.5), LiM _1-x N _x O ₂ (where M is at least one element selected from the group consisting of Fe, Mn and Co, N is Al, Mg, Ti, Zr, Ni, C Olivine type complex oxide represented by 0 ≦ x ≦ 0.5) which is at least one element selected from the group consisting of Zn, Ga, Ge, Nb, Mo, Sn, Sb and Ba 1 type of these may be used and 2 or more types may be used together.

  The electrochemical device of the present invention effectively traps transition metal ions that are eluted from the positive electrode and deposited on the negative electrode, thereby degrading the characteristics and causing a short circuit, by the action of the adsorbing material contained in the separator. Can do. Therefore, in the electrochemical device of the present invention, when the spinel-type lithium-manganese composite oxide, in which Mn is easily eluted, is used as the positive electrode active material, the effect is particularly remarkable.

  As the binder for the positive electrode, for example, a fluororesin such as polyvinylidene fluoride (PVDF) is used, and as the conductive additive for the positive electrode, for example, a carbon material such as carbon black is used.

  For the positive electrode, for example, a positive electrode mixture containing a positive electrode active material, a conductive additive and a binder is dispersed in a solvent such as N-methyl-2-pyrrolidone (NMP), and a positive electrode mixture-containing composition (slurry, paste, etc.) Can be manufactured by passing through a current collector, drying it, and applying a press treatment such as a calender treatment if necessary. However, the manufacturing method of a positive electrode is not necessarily limited to the said method, You may manufacture by another method.

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

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

The negative electrode is not particularly limited as long as it is a negative electrode used in a conventionally known electrochemical element such as a lithium ion secondary battery, that is, a negative electrode containing an active material capable of occluding and releasing Li ions. For example, carbon that can occlude and release lithium, such as graphite, pyrolytic carbons, cokes, glassy carbons, fired organic polymer compounds, mesocarbon microbeads (MCMB), and carbon fibers as active materials One type or a mixture of two or more types of system materials is used. In addition, simple compounds containing elements such as Si, Sn, Ge, Bi, Sb, and In, compounds and alloys thereof, lithium-containing nitrides, oxides and other compounds that can be charged and discharged at a low voltage close to lithium metal, or lithium metal Alternatively, a lithium / aluminum alloy, or a Ti oxide represented by Li ₄ Ti ₅ O ₁₂ can also be used as the negative electrode active material. A negative electrode mixture obtained by appropriately adding a conductive additive (carbon material such as carbon black) or a binder such as PVDF to these negative electrode active materials is collected by the same method as that described above for forming the positive electrode mixture layer, for example. A finished product (a negative electrode mixture layer) using an electric current body as a core material, or a laminate of the above-mentioned various alloys or lithium metal foils alone or laminated on a current collector as a negative electrode material layer, or the like is used.

  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 whole negative electrode is reduced in order to obtain an electrochemical element having a high energy density, the upper limit of the thickness is preferably 30 μm, and the lower limit is preferably 5 μm. 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 and the negative electrode can be used in the form of a laminated body laminated via the separator of the present invention or a wound electrode body obtained by winding the laminated body. When the separator of the present invention is integrated with the electrode, the surface of either the positive electrode or the negative electrode (the positive electrode mixture layer surface of the positive electrode, the negative electrode mixture layer surface or the negative electrode layer surface of the negative electrode) And may be formed on the surfaces of both the positive electrode and the negative electrode.

Moreover, the electrochemical element of this invention can use the solution which melt | dissolved lithium salt in the organic solvent as a non-aqueous electrolyte. 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 a voltage range used as an electrochemical element. 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 R _f is a fluoroalkyl group], etc .; Can be used.

  The organic solvent used for the non-aqueous electrolyte is not particularly limited as long as it dissolves the lithium salt and does not cause a side reaction such as decomposition in a voltage range used as an electrochemical element. For example, cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate; chain esters such as methyl propionate; cyclic esters such as γ-butyrolactone; Chain ethers such as dimethoxyethane, diethyl ether, 1,3-dioxolane, diglyme, triglyme and tetraglyme; cyclic ethers such as dioxane, tetrahydrofuran and 2-methyltetrahydrofuran; nitriles such as acetonitrile, propionitrile and methoxypropionitrile Sulfites such as ethylene glycol sulfite; etc., and these should be used as a mixture of two or more. It can be.

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

  Further, as the non-aqueous electrolyte, a gelled gel (gel electrolyte) can be used by adding a gelling agent such as a known polymer.

  Examples of the form of the electrochemical device of the present invention 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 element which used the laminated film which vapor-deposited the metal as an exterior body.

  The electrochemical device of the present invention can be applied to the same uses as various uses in which electrochemical devices such as conventionally known lithium ion secondary batteries are used.

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

Example 1
<Preparation of positive electrode>
The positive electrode active material LiMn ₂ O ₄ , the binder PVDF NMP solution, and the conductive auxiliary agent Denka Black were sufficiently kneaded with a planetary mixer to prepare a positive electrode mixture-containing slurry. In this positive electrode mixture-containing slurry, the ratio of the positive electrode active material, the binder, and the conductive additive was set to 92: 4: 4 by mass ratio. The positive electrode mixture-containing slurry is applied to one side of a current collector made of an aluminum foil having a thickness of 15 μm, dried at 100 ° C. for 9 hours, calendered with a 2t press, and further vacuum dried at 120 ° C. for 12 hours. Thus, a positive electrode having a width of 35 mm and a length of 25 mm was obtained. A lead body for extracting current was attached to the positive electrode.

<Production of negative electrode>
Graphite, CMC, and SBR were mixed in water and sufficiently kneaded to prepare a negative electrode mixture-containing slurry. In this negative electrode mixture-containing slurry, the ratio of graphite, CMC, and SBR was set to 98: 1: 1 by mass ratio. The negative electrode mixture-containing slurry is applied to one side of a current collector made of a copper foil having a thickness of 10 μm, dried at 100 ° C. for 9 hours, calendered with a 2t press, and further vacuum dried at 120 ° C. for 12 hours. Thus, a negative electrode having a width of 35 mm and a length of 30 mm was obtained. A lead body for current extraction was attached to this negative electrode.

<Preparation of separator>
Boehmite with an average particle size of 1 μm, an aqueous solution of ammonium polyacrylate (concentration 40% by mass) as a dispersant, a resin binder dispersion (modified polybutyl acrylate, solid content 45% by mass) as a binder, an interface The boehmite dispersion solution was prepared by mixing the active agent with water. In this boehmite dispersion solution, the ratio of boehmite, dispersant, and binder was 70:10:20 by mass ratio, and the surfactant concentration was 0.1 mass%. The boehmite dispersion solution and a separately prepared aqueous solution of EDTA · 2Na were mixed so that the ratio of boehmite and EDTA · 2Na was 1: 1 by volume, and the mixture was sufficiently stirred to obtain a porous layer (II ) A forming composition was prepared.

  For porous layer (I), a microporous membrane (thickness: 20 μm, porosity: 40%, thickness of each layer; PP layer: PP layer and PE layer in the order of PP / PE / PP) 7 μm / PE layer: 6 μm / PP layer: 7 μm), and the porous layer (II) -forming composition was applied to one surface of the porous layer (II) with a bar coater and dried at room temperature to obtain a porous layer (I A separator having a porous layer (II) having a thickness of 5 μm on one side was obtained. This separator was cut into a size of 5 cm × 5 cm.

<Battery assembly>
The positive electrode and the negative electrode were overlapped via the separator to obtain a laminated electrode body. In this laminated electrode body, the porous layer (II) of the separator was opposed to the negative electrode. Then, the laminated electrode body is sandwiched between two laminate films, and the three sides of both laminate films are heat sealed, and a non-aqueous electrolyte (ethylene carbonate and diethyl carbonate is added from the remaining one side of both laminate films. A solution prepared by dissolving LiPF ₆ at a concentration of 1.5 mol / l was injected into a solvent mixed at a volume ratio of 3: 7. Thereafter, the remaining one side of both laminated films was vacuum heat sealed to produce a lithium ion secondary battery having the cross-sectional structure shown in FIG. 2 with the appearance shown in FIG.

  Here, FIG. 1 and FIG. 2 will be described. FIG. 1 is a plan view schematically showing a lithium ion secondary battery, and FIG. 2 is a cross-sectional view taken along line AA of FIG. The lithium ion secondary battery 1 includes a laminated electrode body formed by laminating a positive electrode 5 and a negative electrode 6 with a separator 7 in a laminated film outer package 2 constituted by two laminated films, and a non-aqueous electrolyte. (Not shown) is accommodated, and the laminate film outer package 2 is sealed by heat-sealing the upper and lower laminate films at the outer peripheral portion thereof. In FIG. 2, each layer constituting the laminate film outer package 2, each layer of the positive electrode 5 and the negative electrode 6, and each layer of the separator 7 are not shown separately in order to prevent the drawing from becoming complicated.

  The positive electrode 5 is connected to the positive electrode external terminal 3 in the battery 1 through a lead body. Although not shown, the negative electrode 6 is also connected to the negative electrode external terminal 4 in the battery 1 through a lead body. doing. The positive electrode external terminal 3 and the negative electrode external terminal 4 are drawn out to the outside of the laminate film exterior body 2 so that they can be connected to an external device or the like.

Example 2
A laminated electrode body was produced in the same manner as in Example 1 except that the porous layer (II) of the separator was opposed to the positive electrode, and lithium ions were produced in the same manner as in Example 1 except that this laminated electrode body was used. A secondary battery was produced.

Example 3
A separator was produced in the same manner as in Example 1 except that boehmite was changed to alumina, and a lithium ion secondary battery was produced in the same manner as in Example 1 except that this separator was used.

Example 4
A laminated electrode body was produced in the same manner as in Example 3 except that the separator porous layer (II) was opposed to the positive electrode, and lithium ions were produced in the same manner as in Example 3 except that this laminated electrode body was used. A secondary battery was produced.

Example 5
A separator was produced in the same manner as in Example 1 except that boehmite was changed to silica, and a lithium ion secondary battery was produced in the same manner as in Example 1 except that this separator was used.

Example 6
A laminated electrode body was produced in the same manner as in Example 5 except that the separator porous layer (II) was opposed to the positive electrode, and lithium ions were produced in the same manner as in Example 5 except that this laminated electrode body was used. A secondary battery was produced.

Comparative Example 1
A separator was prepared in the same manner as in Example 1 except that no aqueous solution of EDTA · 2Na was used. A lithium ion secondary battery was prepared in the same manner as in Example 1 except that this separator was used.

Comparative Example 2
A laminated electrode body was produced in the same manner as in Comparative Example 1 except that the separator porous layer (II) was opposed to the positive electrode, and lithium ions were produced in the same manner as in Comparative Example 1 except that this laminated electrode body was used. A secondary battery was produced.

Comparative Example 3
A separator was produced in the same manner as in Comparative Example 1 except that boehmite was changed to alumina, and a lithium ion secondary battery was produced in the same manner as in Comparative Example 1 except that this separator was used.

Comparative Example 4
A laminated electrode body was prepared in the same manner as in Comparative Example 3 except that the separator porous layer (II) was opposed to the positive electrode, and lithium ions were produced in the same manner as in Comparative Example 3 except that this laminated electrode body was used. A secondary battery was produced.

Comparative Example 5
A separator was produced in the same manner as in Comparative Example 1 except that boehmite was changed to silica, and a lithium ion secondary battery was produced in the same manner as in Comparative Example 1 except that this separator was used.

Comparative Example 6
A laminated electrode body was produced in the same manner as in Comparative Example 5 except that the separator porous layer (II) was opposed to the positive electrode, and lithium ions were produced in the same manner as in Comparative Example 5 except that this laminated electrode body was used. A secondary battery was produced.

Comparative Example 7
The same procedure as in Example 1 was conducted except that the microporous membrane having a three-layer structure used as the separator porous layer (I) in Example 1 was used as the separator without forming the porous layer (II). A laminated electrode body was produced, and a lithium ion secondary battery was produced in the same manner as in Example 1 except that this laminated electrode body was used.

  The storage characteristic evaluation of the lithium ion secondary batteries of the examples and comparative examples and the thermal contraction rate measurement of the same separators used for the lithium ion secondary batteries of the examples and comparative examples were performed by the following methods, respectively. . These results are shown in Table 1.

<Storage characteristics evaluation>
About each battery of an Example and a comparative example, after carrying out constant current charge until it became 4.2V with a current value of 4.5mA, it carried out constant voltage charge until the current value became 0.45mA with a voltage of 4.2V, Thereafter, a series of operations for discharging to 3 V at a current value of 4.5 mA was taken as one cycle, and charging and discharging were performed for two cycles, and a discharge capacity (capacity before storage) of the second cycle was determined. Subsequently, each battery was subjected to constant current charging and constant voltage charging under the same conditions as described above, and each battery after charging was stored in a thermostat at 80 ° C. for 24 hours. Each battery after storage is taken out from the thermostatic chamber, discharged to 3 V at a current value of 4.5 mA, and then charged and discharged as before storage for each battery, and the discharge capacity at the second cycle (capacity after storage) Asked. And the value which remove | divided the capacity | capacitance after storage of each battery by the capacity | capacitance before storage was represented by the percentage, and capacity | capacitance recovery rate (%) was calculated | required. It can be said that the higher the capacity recovery rate, the better the storage characteristics (high temperature storage characteristics) of the battery.

<Measurement of thermal contraction rate of separator>
Each separator was cut into a size of 10 cm in the longitudinal direction (longitudinal direction of the microporous membrane having a three-layer structure according to the separator) × 5 cm in the width direction (width direction of the microporous membrane having the three-layer structure according to the separator). A 3 cm line was drawn in parallel with the longitudinal direction and the width direction of these test pieces with an oil pen so that the intersection of both lines was at the center of each line. Then, each test piece was preserve | saved for 1 hour in a 150 degreeC thermostat. Each test piece after storage is taken out from the thermostat, and the length X (cm) of the longitudinal line and the transverse line is measured, and the thermal contraction rate in the longitudinal direction and the transverse direction of the separator based on the following formula ( %).
Thermal contraction rate (%) = 100 × (3-X) / 3

  As shown in Table 1, the lithium ion secondary batteries of Examples 1 to 6 using the separator to which EDTA / Na salt was added were the lithium ion secondary batteries of Comparative Examples 1 to 6 using the separator to which this was not added. Compared to the battery and the lithium ion secondary battery of Comparative Example 7 using a normal polyolefin microporous membrane separator, the capacity recovery rate after high-temperature storage is about 10% higher and the storage characteristics are good.

  In addition, the separators according to the lithium ion secondary batteries of Examples 1 to 6 have a smaller thermal shrinkage rate due to heating at 150 ° C. for 1 hour than that of a normal polyolefin microporous membrane separator. The lithium ion secondary batteries of Examples 1 to 6 were estimated to be less likely to cause a short circuit between the positive electrode and the negative electrode due to the shrinkage of the separator even when the temperature inside the lithium ion secondary battery was high. In addition, the thermal contraction rate of the separator which concerns on the lithium ion secondary battery of Examples 1-6 is equivalent to the separator which concerns on the lithium ion secondary battery of Comparative Examples 1-6, and by adding EDTA * Na salt, separator It was also found that the heat resistance of was not impaired.

1 Electrochemical element (lithium ion secondary battery)
2 Laminate film exterior 5 Positive electrode 6 Negative electrode 7 Separator

Claims (7)

A separator used for an electrochemical element having a non-aqueous electrolyte,
Containing a material that adsorbs transition metal ions eluted in the non-aqueous electrolyte and a filler having a heat-resistant temperature of 150 ° C. or higher,
A separator for an electrochemical element, wherein a sodium salt of ethylenediaminetetraacetic acid is used as a material that adsorbs transition metal ions eluted in the non-aqueous electrolyte.   The separator for an electrochemical element according to claim 1, wherein the filler having a heat resistant temperature of 150 ° C or higher is at least one selected from the group consisting of boehmite, alumina, and silica.   The separator for an electrochemical element according to claim 1 or 2, comprising a porous layer (I) mainly comprising polyolefin and a porous layer (II) mainly comprising a filler having a heat resistant temperature of 150 ° C or higher. .   The separator for an electrochemical element according to claim 3, wherein the porous layer (II) contains a material that adsorbs transition metal ions eluted in the nonaqueous electrolytic solution.   The separator for an electrochemical element according to any one of claims 1 to 4, which has a thermal shrinkage rate of 0 to 10% when left in an atmosphere of 150 ° C. An electrochemical device comprising a positive electrode using a lithium-containing transition metal oxide as an active material, a negative electrode, a non-aqueous electrolyte, and a separator,
The said separator is an electrochemical element separator in any one of Claims 1-5, The electrochemical element characterized by the above-mentioned.   The electrochemical device according to claim 6, wherein the separator is integrated with the positive electrode and / or the negative electrode.

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