JP2010050076A - Separator for electrochemical element, lithium battery or lithium ion battery using this, and manufacturing method of separator for electrochemical element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a new separator for an electrochemical element capable of constituting the electrochemical element capable of suppressing heat generation of the battery at the time of internal or external short circuit and suppressing internal resistance, and a lithium ion battery using the same. <P>SOLUTION: The separator 1 contains filler particles 3 for giving thermal resistance and strength to the separator 1 and a binder 5 which disperses the filler particles and a template agent and forms a heat insulating layer, and is made of a heat resistant porous layer 2' having a gap 4. The gap is formed by the template agent. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electrochemical element separator, a lithium battery or a lithium ion battery using the same, and a method for producing an electrochemical element separator.

  In recent years, a secondary battery having a high voltage and a high energy density has been demanded as a power source for mobile terminals such as notebook computers and mobile phones. At present, in order to satisfy the capabilities required for these applications, a lithium ion secondary battery using a non-aqueous electrolyte is drawing attention.

  A non-aqueous electrolyte secondary battery typified by a lithium ion secondary battery has a high battery voltage and high energy, so that a large current flows when the battery is internally short-circuited or externally short-circuited. Therefore, at the time of short circuit, there is a problem of battery heat generation due to Joule heat generation, and a problem of battery swelling and characteristic deterioration due to gas generation due to melting and decomposition of the electrolyte and separator.

  In order to solve these problems, a non-aqueous electrolyte battery using a separator made of a synthetic resin film having fine pores made of polypropylene or polyethylene has been proposed (for example, see Patent Document 1). Patent Document 1 describes that heat generated at the time of a short circuit clogs the micropores of the separator with a melt, prevents the movement of ions, prevents current from flowing, and suppresses excessive heat generation and ignition of the battery. ing.

  Currently, as the use of nonaqueous electrolyte secondary batteries expands, batteries with higher safety are required. In particular, there is a demand for improvement in safety when an internal short circuit occurs.

  When an internal short circuit occurs, it is considered that the temperature may be 600 ° C. or higher in the short circuit part due to local heat generation. For this reason, in the conventional separator which consists of polyolefin resin, the separator of the short circuit part may shrink | contract by the heat | fever at the time of a short circuit, and the contact area (short circuit area) of a positive electrode and a negative electrode may increase.

Therefore, a battery using a separator with improved heat resistance by forming a layer containing a filler such as a metal oxide on the surface of a porous substrate has been proposed (see, for example, Patent Documents 2 and 3). However, in the separator having the heat-resistant layer including the filler proposed in Patent Documents 2 and 3, since the metal oxide is contained in a large amount, the diffusion of lithium ions in the separator is inhibited, and the internal resistance of the battery is increased. There was a problem.
Japanese Patent Laid-Open No. 60-023954 JP 2005-038793 A JP 2006-164661 A

  In view of such circumstances, the present invention provides a novel separator for an electrochemical element that can suppress the heat generation of the battery at the time of internal or external short circuit and can constitute an electrochemical element with reduced internal resistance, and lithium using the same. An object of the present invention is to provide a battery or a lithium ion battery.

  As a result of various studies to solve the above problems, the present inventors have completed the present invention.

  The present invention is (1) a separator comprising a heat-resistant porous layer containing filler particles and a binder and having voids, wherein the voids are produced by a template agent. The present invention relates to an element separator.

The present invention also provides (2) a separator for an electrochemical device having a porous substrate and a heat-resistant porous layer provided on the surface of the porous substrate, wherein the heat-resistant porous layer comprises filler particles and The present invention relates to a separator for an electrochemical element, characterized in that it is a layer containing a binder and having voids, and the voids are made of a template agent.

  In the present invention, (3) wherein the void is produced by removing the template agent from the heat-resistant layer containing filler particles, a binder, and the template agent. It is related with the separator for electrochemical elements as described in (2).

  The present invention is also characterized in that (4) the void is produced by dissolving a template agent in an electrolytic solution from a heat-resistant layer containing filler particles, a binder and a template agent. It is related with the separator for electrochemical elements as described in any one of (1)-(3).

  The present invention also relates to (5) the separator for an electrochemical element according to any one of (1) to (4), wherein the template agent is soluble in an electrolytic solution.

  In the present invention, (6) the template agent is a metal oxide, metal carbonate, metal nitrate, metal citrate, metal ammonium salt, metal acetate, ionic liquid, polymer and lithium. It is related with the separator for electrochemical elements as described in any one of said (1)-(5) containing at least 1 type chosen from salt.

  Moreover, this invention functions as an overcharge prevention agent, when the said template agent melt | dissolves in the electrolyte solution in a battery (7) Any one of said (1)-(5) characterized by the above-mentioned. It is related with the separator for electrochemical elements of description.

  The present invention also relates to (8) the separator for electrochemical devices according to (7), wherein the template agent contains at least one selected from alkyl-substituted benzene compounds, aryl-substituted benzene compounds, diaryl ether compounds and halogen-substituted anisole compounds. .

  In addition, according to any one of the above (1) to (5), the present invention (9) functions as a flame retardant for the electrolytic solution when the template agent is dissolved in the electrolytic solution in the battery. The separator for an electrochemical element according to one item.

  Moreover, this invention is (10) The separator for electrochemical devices of the said (9) description in which the said template agent contains at least 1 type chosen from a phosphate ester compound and a phosphazene compound.

  Further, the present invention provides (11) any one of the above (1) to (5), wherein the template agent functions as a corrosion inhibitor for the positive electrode current collector when dissolved in the electrolyte solution in the battery. It is related with the separator for electrochemical elements as described in any one.

  The present invention also relates to (12) the separator for electrochemical elements according to (11), wherein the template agent is a lithium salt having an OB bond.

The invention also relates to (13) wherein the filler _{particles, Al 2 O 3, SiO 2} , said containing montmorillonite, mica, _ZnO, at least one selected from TiO _2, BaTiO _3, ZrO 2 and glass (1) - It relates to the separator for electrochemical elements as described in any one of (12).

The present invention also relates to (14) the separator for an electrochemical element according to any one of (1) to (13), wherein the filler particles contain at least Al ₂ O ₃ .

  Moreover, this invention relates to the separator for electrochemical elements as described in any one of said (1)-(14) whose average particle diameter of the secondary particle of the said filler particle is 5 nm-5 micrometers (15).

  The present invention also relates to (16) the separator for an electrochemical element according to any one of (1) to (15), wherein the binder is a thermosetting resin or a thermoplastic resin.

  The present invention also relates to (17) the separator for an electrochemical element according to any one of (2) to (16), wherein the porous substrate contains polyolefin.

  Moreover, this invention relates to the lithium battery or lithium ion battery which has the separator for electrochemical elements as described in any one of (18) said (1)-(17).

  The present invention also includes (19) a step of heating a composition containing filler particles, a template agent and a binder to form a heat-resistant layer containing the filler particles, the binder and the template agent, and then heat resistance. It is related with the manufacturing method of the separator for electrochemical elements including the process of producing a space | gap in a heat resistant layer by removing a template agent from a layer, and forming a heat resistant porous layer.

  The present invention also relates to (20) the method for producing a separator for an electrochemical element according to (19), wherein the template agent is removed by dissolving in an electrolytic solution.

  The separator for electrochemical elements of the present invention can suppress heat generation of the battery at the time of internal or external short circuit, and can suppress internal resistance. Moreover, the lithium battery or lithium ion battery of the present invention is a battery having improved internal safety and low internal resistance.

  The best mode for carrying out the invention will be described below.

  The separator 1 for an electrochemical element of the present invention is a separator comprising a heat-resistant porous layer 2 containing filler particles 3 and a binder 5 and having voids 4 as shown in FIG. It is produced by an agent.

  Moreover, the separator 1 for electrochemical elements of this invention is the separator for electrochemical elements which has the porous base | substrate 6 and the heat resistant porous layer 2 'provided in the surface of the said porous base | substrate 6, as shown in FIG. The heat-resistant porous layer 2 ′ contains filler particles 3 and a binder 5 and has voids 4, and the voids 4 are made of a template agent. In this case, the heat-resistant porous layer 2 ′ may be disposed only on one side of the porous substrate 6 (see FIG. 2) or may be disposed on both sides (not shown).

  Thus, in the present invention, a composition containing filler particles, a template agent, and a binder is formed, for example, in a layered form (hereinafter, formed using a composition containing filler particles, a template agent, and a binder). Layer is simply referred to as “heat-resistant layer”), and voids are produced (hereinafter, a layer in which voids are formed in the “heat-resistant layer” is simply referred to as “heat-resistant porous layer”), and it is left as it is (see FIG. 1) or in combination with a porous substrate conventionally used for a separator (see FIGS. 2 to 4), it can be used as a separator for an electrochemical element. By using it in combination with a porous substrate, it becomes easy to impart flexibility to the separator for electrochemical devices. When combined with the porous substrate, the heat resistant porous layer 2 ′ is provided on the surface of the porous substrate 6 as described above (see FIG. 2), and the heat resistance is contained in the pores 7 of the porous substrate 6. The form (refer FIG. 3) which provided the porous layer may be sufficient.

  Since the separator for an electrochemical element of the present invention has a void, an ion conduction path is secured, so that the resistance can be reduced. The voids may be continuous holes or non-continuous holes, but are preferably continuous holes from the viewpoint of reducing resistance. The size of the void is not particularly limited as long as lithium ions can pass through, but the average void diameter is preferably 5 nm to 5 μm from the viewpoint of the mechanical strength of the heat-resistant porous layer, preferably 0.01 μm to More preferably, it is 1 μm. Moreover, it is preferable that the volume ratio which the space | gap in the separator for electrochemical elements occupies is 5-80 volume% from a viewpoint of the mechanical strength of a heat resistant porous layer. The voids are preferably formed uniformly or substantially uniformly.

  The thickness of the heat-resistant porous layer in the present invention is not particularly limited, but is preferably 0.5 μm to 50 μm, more preferably 0.5 μm to 30 μm. When the thickness of the heat-resistant porous layer is less than 0.5 μm, the heat resistance of the separator for electrochemical elements becomes insufficient, and it may be difficult to provide a highly safe battery. When the thickness exceeds 50 μm This may be disadvantageous in terms of the energy density of an electrochemical device using the same.

Hereafter, each component which comprises the separator for electrochemical elements of this invention is demonstrated.
(Filler particles)
In the present invention, the filler particles are used for the purpose of imparting heat resistance and strength to the separator for electrochemical devices. The filler particles used are preferably particles having a melting point of 120 ° C. or higher, and more preferably 150 ° C. or higher. Moreover, although the upper limit of melting | fusing point does not have a restriction | limiting in particular, It is preferable that it is 4000 degrees C or less, and it is more preferable that it is 3000 degrees C or less. When the melting point is less than 120 ° C., it is difficult to impart heat resistance.

The shape of the filler particles is not particularly limited and may be any of an amorphous filler, a plate-like filler, a needle-like filler, and a spherical filler, but the filler particles may be uniformly dispersed in the heat-resistant layer. In view of this, spherical fillers are preferred from this point. When the dispersion of the filler particles is uneven, the heat resistance of the portion where the filler particles are not present or the portion where the filler particles are small is lowered, and when used as a battery, a hole may be formed in the portion when abnormal heat is generated. Therefore, it is desirable that the filler particles be uniformly dispersed.
The particle diameter of the filler particles is not particularly limited, but the average particle diameter of the secondary particles is preferably 5 nm to 5 μm, and more preferably 0.01 μm to 1 μm. When the average particle size exceeds 5 μm, the strength of the separator for electrochemical devices decreases, that is, becomes brittle, and the smoothness of the surface tends to decrease. When the average particle size is less than 5 nm, the dispersibility decreases. However, it tends to be difficult to produce a separator in which is uniformly dispersed. The average particle diameter of the secondary particles can be measured using a laser diffraction scattering method.

  The content of the filler particles is preferably 5% by weight or more and 95% by weight or less, more preferably 10% by weight or more and 75% by weight or less of the total weight of the filler particles, the template agent and the binder. . If the content of the filler particles is less than 5% by weight, sufficient heat resistance may not be obtained, and if it exceeds 95% by weight, the separator for an electrochemical element may become brittle and difficult to handle. .

Examples of filler particles used in the present invention include particles made of electrically insulating metal oxides, metal nitrides, metal carbides, and the like, and polymer particles. These particles may be used alone or in combination of two or more. Specific examples of the filler particles include particles made of metal oxides such as Al ₂ O ₃ , SiO ₂ , montmorillonite, mica, ZnO, TiO ₂ , BaTiO ₃ , ZrO ₂ , glass; silicon nitride, gallium nitride, titanium nitride, Particles made of metal nitride such as lithium nitride; from metal carbides such as WC, W ₂ C, CuC, CoC, VC, MnC, ZrC, NbC, CrC, MoC, W _0.3 Co _0.2 C _0.5, etc. And particles such as crosslinked acrylic polymer such as crosslinked polymethyl methacrylate (crosslinked PMMA), polymer particles such as polytetrafluoroethylene, crosslinked polyurethane, crosslinked polystyrene, benzoguanamine polymer, melamine polymer, polyolefin polymer, and the like. In the present invention, a metal oxide is preferably used, and among these, Al ₂ O ₃ particles can be suitably used.

(Binder)
The binder used in the present invention is not particularly limited as long as the filler particles and the template agent can be dispersed and a heat-resistant layer can be formed. For example, a thermosetting resin or a thermoplastic resin can be suitably used.

  Examples of the thermosetting resin include an aramid resin, a phenol resin, an epoxy resin, a urethane resin, and an epoxy resin. In the step of heating the liquid composition containing the filler particles, the template agent and the binder in the method for producing the separator for electrochemical elements described later, the thermosetting resin which is the binder component can be simultaneously cured. Thermoplastic resins include polyethylene (high density polyethylene, medium density polyethylene, low density polyethylene), polypropylene, polyvinyl chloride, polyvinylidene chloride, polyvinylidene fluoride, polystyrene, polyvinyl acetate, polytetrafluoroethylene, polyhexafluoropropylene. , ABS resin (acrylonitrile butadiene styrene resin), acrylic resin and the like. Moreover, these copolymers can also be used.

  The content of the binder is preferably 5% by weight or more and 90% by weight or less, and more preferably 10% by weight or more and 50% by weight or less of the total weight of the filler particles, the template agent, and the binder. When the content of the binder is less than 5% by weight, the function as a binder for connecting the filler particles, the template agent, and the porous substrate may be insufficient. When the content exceeds 90% by weight, the filler particles In addition, the content of the template agent may be insufficient, and it may be difficult to obtain an effect of heat resistance or low resistance.

(Template agent)
In the present invention, the template agent is used for producing voids in the heat-resistant porous layer. The template agent is not particularly limited as long as it is dispersed or dissolved in the heat-resistant layer containing the filler particles and the binder and can be removed from the heat-resistant layer, and is soluble in the electrolyte solution. preferable.

  Examples of the template agent include inorganic substances such as metal oxides, metal carbonates, metal nitrates, metal citrates, metal ammonium salts, metal acetates, and the like. Sodium, calcium, magnesium, aluminum, zirconium, silicon, titanium, etc. are mentioned.

Moreover, organic substances, such as an ionic liquid, a polymer | macromolecule, and lithium salt, can also be used as a template agent. As the ionic liquid, a salt having a melting point of room temperature (25 ° C.) or less and a liquid appearance at room temperature is preferable. However, even if the salt has a melting point higher than room temperature, the filler particles and the binder are dissolved in the solvent. It can be mixed with an agent and dispersed in the heat-resistant layer. The composition of the ionic liquid is not particularly limited, and any composition that can be uniformly dispersed or dissolved in the heat-resistant layer can be suitably used. Examples of the cation include ammonium, pyridinium, pyrrolidinium, pyrrolium, oxazolium, oxazolinium, imidazolium, phosphonium, and sulfonium. As anions, N (SO ₂ F) ₂ ⁻ , N (SO ₂ CF ₃ ) ₂ ⁻ , N (SO ₂ C ₂ F ₅ ) ₂ ⁻ , BF ₄ ⁻ , PF ₆ ⁻ , CF ₃ SO ₃ ^{− are used.} or CF ₃ CO ₂ ^- and the like, can be used an ionic liquid which is a combination of these cations and anions. The said ionic liquid may be used independently and can also be used in mixture of 2 or more types. Among these anions, particularly hydrophobic anions such as N (SO ₂ F) ₂ ⁻ , N (SO ₂ CF ₃ ) ₂ ⁻ , N (SO ₂ C ₂ F ₅ ) ₂ ⁻ , CF ₃ SO ₃ ⁻ or CF ₃ CO ₂ ^— is preferably used. By using a hydrophobic anion, the handling property of the ionic liquid constituted thereby, particularly the handling property in an air atmosphere, becomes easy. There is no restriction | limiting in particular as a polymer | macromolecule, If it can disperse | distribute or melt | dissolve uniformly in a heat resistant layer, it can use suitably, For example, polyvinyl alcohol, polyvinyl acetate, etc. are mentioned.

The lithium salt is preferably one which is soluble in the electrolyte solution, for _{example, 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 (RfOSO ₂ ) ₂ [where Rf is a fluoroalkyl group] Etc.

  In the present invention, it is preferable to use a template agent that functions as an overcharge preventing agent when dissolved in the electrolyte in the battery. Such an overcharge inhibitor preferably has a low oxidative decomposition voltage and a large oxidative decomposition current in order to enhance the overcharge preventing action. However, when the oxidative decomposition voltage is too low, the battery is used, particularly at high temperature storage. As a result, oxidative electrolysis of the overcharge inhibitor may occur, and the battery characteristics may deteriorate. A compound that forms a high-resistance film on the active material surface in an overcharged state is preferred. Among these, a compound that undergoes an oxidation reaction at a battery voltage higher than the maximum operating voltage of the battery, particularly a compound having an oxidation voltage measured by a cyclic voltammetry method of 4.3 V or more and 4.9 V or less is preferable. If the oxidation voltage exceeds 4.9V, the effect of preventing overcharge is reduced, and if it is less than 4.3V, battery characteristics may be deteriorated. The upper limit of the oxidation potential is 4.8 V or less, particularly 4.7 V or less. The lower limit of the oxidation potential is 4.4V or higher, and particularly preferably 4.5V or higher.

  The overcharge inhibitor is preferably one containing at least one selected from alkyl-substituted benzene compounds, aryl-substituted benzene compounds, diaryl ether compounds, and halogen-substituted anisole compounds. Specific examples include the following compounds. it can. For example, the alkyl-substituted benzene compound is a benzene substituted with an alkyl group having 1 to 10 carbon atoms, such as toluene, ethylbenzene, n-propylbenzene, n-butylbenzene, cumene, t-butylbenzene, 4 Examples include -t-butyltoluene, tetralin, cyclohexylbenzene, diphenylmethane, and the like, or fluorine-substituted products thereof. The aryl-substituted benzene compound represents benzene substituted with an aryl group having 6 to 12 carbon atoms, such as biphenyl, naphthalene, o-terphenyl, m-terphenyl, p-terphenyl, o-cyclohexylbiphenyl, etc. And fluorine-substituted compounds such as 2-fluorobiphenyl and 4-fluorobiphenyl. Examples of diaryl ethers include ethers composed of aryl groups having 6 to 12 carbon atoms, such as diphenyl ether, ditoluyl ether, diphenoxybenzene, diphenylene oxide, and fluorine-substituted compounds such as 4-fluorodiphenyl ether. Is done. Or these fluorine substitution products etc. are illustrated. Halogen-substituted anisole represents anisole in which hydrogen in a benzene ring or methoxy group is substituted with fluorine, and includes 2,4-difluoroanisole, 2,3-difluoroanisole, 2,5-difluoroanisole, 2-fluoro-4- Examples include chloroanisole, 2-chloro-4-fluoroanisole, 2-fluoroanisole, 3-fluoroanisole, 4-fluoroanisole and the like.

  Among these, toluene, ethylbenzene, cyclohexylbenzene, 4-t-butyltoluene, biphenyl, 4-phenyl, 4-methylbenzene, cyclohexylbenzene, 4-tert-butyltoluene, biphenyl, 4-phenyl Fluorobibiphenyl, 2-fluorobiphenyl, o-terphenyl, 4-fluorodiphenyl ether, diphenyl ether, 2,4-difluoroanisole, 2-fluoroanisole or 4-fluoroanisole are preferred, toluene, ethylbenzene, cyclohexylbenzene, o-terphenyl , Biphenyl, 4-fluorodiphenyl ether, 2-fluoroanisole and 4-fluoroanisole are more preferable, and biphenyl is particularly preferable. Such an overcharge inhibitor can be appropriately selected, and may be used as a single compound or a mixture of a plurality of compounds. When mixing a plurality of compounds, it is most desirable to combine biphenyl and toluene, biphenyl and ethylbenzene, cyclohexylbenzene and toluene, or cyclohexylbenzene and ethylbenzene.

  In the present invention, it is preferable to use a template agent that functions as a flame retardant for the electrolytic solution when dissolved in the electrolytic solution in the battery. As a flame retardant for an electrolyte solution, among compounds used as a flame retardant for engineering plastics, any compound can be used without particular limitation as long as it can exist relatively stably in a battery. For example, phosphate ester It is preferable that it contains at least one selected from a compound or a phosphazene compound.

As a phosphoric acid ester compound, the phosphoric acid ester compound shown by General formula (1) can be mentioned, for example.

(In formula, R1-R3 is a C1-C7 hydrocarbon group, and may be same or different. Moreover, the hydrogen atom of R1-R3 may be substituted by the fluorine atom. )
The hydrocarbon group having 1 to 7 carbon atoms in the general formula (1) is an alkyl group such as a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, or an octyl group; An aryl group; and the like. Moreover, the hydrogen atom of these hydrocarbon groups may be substituted with a fluorine atom, which facilitates enhancing chemical stability. Among these, a methyl group or a phenyl group is preferable, and specifically, trimethyl phosphate or triphenyl phosphate is more preferable.

As a phosphazene compound, the phosphazene compound represented by General formula (2) can be mentioned, for example.

(Wherein R1 to R6 are organic groups having 1 to 10 carbon atoms and may be the same or different. The hydrogen atoms of R1 to R3 may be substituted with fluorine atoms.)
The organic group having 1 to 10 carbon atoms in the general formula (2) is an alkyl group such as a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, and a decyl group; Alkoxy groups such as methoxy group, ethoxy group, propoxy group, butoxy group, pentoxy group, hexyloxy group, heptyloxy group, octyloxy group; methoxymethyl group, ethoxymethyl group, propoxymethyl group, butoxymethyl group, methoxyethyl group Alkoxy group such as ethoxyethyl group, propoxyethyl group, methoxypropyl group, ethoxypropyl group, propoxypropyl group; vinyl group, 1-propenyl group, 2-propenyl group, 1-butenyl group, 1-pentenyl group, 3 -Butenyl group, 3-pentenyl group, 2-fluoroethenyl group, 2 2-difluoroethenyl group, 1,2,2-trifluoroethenyl group, 4,4-difluoro-3-butenyl group, 3,3-difluoro-2-propenyl group, 5,5-difluoro-4-pentenyl group Alkenyl groups such as phenyl groups; aryl groups such as phenyl groups; aryloxy groups such as phenoxy groups; By substituting a hydrogen atom of an organic group with a fluorine atom, chemical stability can be easily improved. Among these, a methyl group, an ethyl group, and a 1,2,2-trifluoroethenyl group are preferable.
Moreover, in this invention, it is preferable to use what functions as a corrosion inhibitor of a positive electrode electrical power collector, when it melt | dissolves in the electrolyte solution in a battery as a template agent. As such a corrosion inhibitor, a lithium salt having an O (oxygen) -B (bromine) bond is preferably used, and specific examples include lithium bis (oxalate) borate and lithium oxalyldifluoroborate. By using a lithium salt having an OB bond as a template agent, the template agent elutes into the electrolyte solution, and the OB bond dissociates when the battery is charged and discharged. It is thought to form a stable passive film.

By preventing corrosion of the positive electrode current collector using such a template agent, lithium bis (fluoroalkylsulfonyl) that could not be used as an electrolyte salt of a lithium battery so far as it corrodes the positive electrode, for example, aluminum. Imido LiN (SO ₂ Rf) ₂ (Rf represents a fluorinated alkyl C _n F _{2n + 1} group), for example lithium bis (trifluoromethanesulfonyl) imide LiN (SO ₂ CF ₃ ) ₂ or lithium bis (hexafluoroethanesulfonyl) ) Imido LiN (SO ₂ C ₂ F ₅ ) ₂ can be used. In addition, an ionic liquid composed of bis (fluoroalkylsulfonyl) imide anion N (SO ₂ Rf) ₂ ^— can be used as an electrolyte solvent. The ionic liquid referred to here is a salt having a melting point of room temperature (25 ° C.) or lower and a liquid appearance at room temperature (25 ° C.).

Compared with lithium hexafluorophosphate LiPF ₆ and LiBF ₄ that have been used in conventional lithium ion secondary batteries, the lithium bis (fluoroalkylsulfonyl) imide has a high degree of dissociation when dissolved in an electrolyte, There is an advantage that an electrolytic solution exhibiting high ionic conductivity can be prepared, and there is an advantage that it exhibits high thermal stability, and since the ionic liquid is hardly volatile, a lithium ion battery using this as an electrolytic solution solvent And lithium batteries are more secure. Therefore, the added value as a battery improves by enabling these use.

  In the present invention, the compounding amount of the template agent is preferably 10/90 to 90/10, more preferably 30/70 to 70/30, as the weight ratio of the template agent / binder. When the weight ratio of the template agent is less than 10, the voids formed in the heat-resistant porous layer are reduced, so that the ion conduction path is insufficient and the internal resistance is difficult to suppress. It becomes difficult to form a heat-resistant layer in which the agent is dispersed.

  In the separator for electrochemical elements of the present invention, the voids are preferably formed uniformly or substantially uniformly, and for this purpose, the template agent may be uniformly or substantially uniformly dispersed or dissolved in the binder. preferable. Examples of a method of dispersing or dissolving the template agent uniformly or substantially uniformly in the binder include, for example, a method of dispersing or dissolving in the binder using a template agent that dissolves in the binder solvent, and a template agent. When not dissolving in the binder solvent, a slurry composed of the template agent, filler particles, binder, and binder solvent may be mechanically mixed.

  In the method for producing a separator for an electrochemical device according to the present invention, a composition containing filler particles, a template agent and a binder is mechanically mixed and dispersed uniformly, and then heated to produce filler particles, a binder and A step (I) of forming a heat-resistant layer containing a template agent, and then a step (II) of forming a heat-resistant porous layer by creating voids in the heat-resistant layer by removing the template agent from the heat-resistant layer. Is included.

  In the step (I), the composition containing the filler particles, the template agent and the binder is mechanically mixed and dispersed uniformly, and then heated to contain the filler particles, the binder and the template agent. Forming a conductive layer. As a method for producing the composition, for example, filler particles and a solution in which a binder is dissolved or dispersed in a solvent are mixed, then a template agent is mixed, then mechanically mixed, and then applied to a substrate. The method of drying a solvent by heating is mentioned. In addition to the filler particles, template agent, binder, and binder solvent, other substances may be added. As a mechanical mixing method, a known stirrer, disperser, pulverizer, or the like can be used.

  The solvent for dissolving or dispersing the binder is not particularly limited as long as the binder can be dissolved or dispersed. For example, carbonate compounds such as ethylene carbonate and propylene carbonate; 3-methyl-2-oxazolidinone, N-methylpyrrolidone and the like Heterocyclic compounds; cyclic ethers such as dioxane and tetrahydrofuran; chain ethers such as diethyl ether, ethylene glycol dialkyl ether, propylene glycol dialkyl ether, polyethylene glycol dialkyl ether, polypropylene glycol dialkyl ether; methanol, ethanol, isopropanol, ethylene glycol Monoalkyl ether, propylene glycol monoalkyl ether, polyethylene glycol monoalkyl ether, polypropylene glycol Alcohols such as rumonoalkyl ether, ethylene glycol, propylene glycol, polyethylene glycol, polypropylene glycol, glycerin; nitrile compounds such as acetonitrile, glutarodinitrile, methoxyacetonitrile, propionitrile, benzonitrile; carboxylic acid ester, phosphoric acid ester, Esters such as phosphonic acid esters; aprotic polar substances such as dimethyl sulfoxide, sulfolane, dimethylformamide, dimethylacetamide; nonpolar solvents such as toluene and xylene; chlorinated solvents such as methylene chloride and ethylene chloride; water; be able to.

  Although the usage-amount of the said solvent is not specifically limited, It is preferable that it is 5-50 mass% with respect to a binder. If it is less than 5% by mass, the viscosity of the slurry composed of filler particles, template agent, binder, and binder solvent tends to be high, and it tends to be difficult to prepare a uniform slurry. The viscosity of the slurry composed of the filler particles, the template agent, the binder, and the solvent of the binder is lowered, and the workability during application tends to be deteriorated.

  Next, the composition is heated to form a heat-resistant layer containing filler particles, a binder and a template agent. Since the composition containing the filler particles, the template agent, the binder, and the binder solvent is a slurry composition in which the filler particles and the template agent are dispersed, the slurry composition can be used as a film or a metal foil. A heat-resistant layer can be formed by heating on a predetermined temperature after coating on a substrate or coating or impregnation on a porous substrate.

  Heating is appropriately selected according to the composition of the composition, the thickness of the heat-resistant layer, and the like, but is usually performed at 50 to 200 ° C. for 1 to 60 minutes. Moreover, you may heat on vacuum conditions as needed.

  As the substrate, a plastic film such as polyethylene terephthalate or polyimide, a metal foil such as glass, copper, or aluminum can be used. The thickness of the substrate is not particularly limited, but is usually 5 to 50 μm.

  As the porous substrate, a polyolefin microporous film such as polyethylene or polypropylene, an electrically insulating organic or inorganic fiber, a porous fabric made of pulp, a nonwoven fabric, paper, or the like can be used. Examples of electrically insulating organic fibers include fibers made of thermoplastic polymers such as polyolefin, rayon, vinylon, polyester, acrylic, polystyrene, nylon (trade name), and natural fibers such as manila hemp. Examples of the electrically insulating inorganic fiber include glass fiber and alumina fiber. The thickness of the porous substrate is not particularly limited, but is preferably a thickness having an appropriate mechanical strength and suitable for lowering resistance, and about 10 to 30 μm is preferable. As the porous substrate, those generally marketed for electrochemical devices can be used. As an example, a polyethylene microporous membrane “Hypore N8416” manufactured by Asahi Kasei Chemicals Corporation can be mentioned.

  The heat-resistant layer is composed of at least filler particles, a binder, and a template agent, but may further contain other substances as long as the effects of the present invention are obtained. Although the thickness of a heat resistant layer is not specifically limited, 0.5 micrometers-5 micrometers are preferable. If the thickness of the heat-resistant layer is less than 0.5 μm, the mechanical strength of the separator for electrochemical elements is inferior, and the heat resistance becomes insufficient, and it may be difficult to provide a highly safe battery. When the thickness exceeds 5 μm, there is a tendency to be disadvantageous in terms of the energy density of an electrochemical element using the thickness.

Next, in step (II), the template agent is removed from the heat resistant layer to produce voids in the heat resistant layer to form a heat resistant porous layer. In the heat-resistant layer formed in the step (I), the template agent is dispersed or dissolved, and in the step (II), a solvent that dissolves the template agent and does not dissolve the binder and filler. It is sufficient to dissolve the template agent and remove it from the heat resistant layer. The method for removing the template agent in step (II) is not particularly limited, but it is preferable to remove the template agent that is soluble in the electrolytic solution by dissolving it in the electrolytic solution, so that the heat-resistant layer is immersed in the electrolytic solution in the battery. It is more preferable to stack and remove the template agent by dissolving it in the electrolytic solution. The template agent is soluble in the electrolyte solution is not particularly limited as long as it does not deteriorate the characteristics of the battery in a voltage range to be used as a _{battery, 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 (RfOSO ₂ ) ₂ [where Rf is a fluoroalkyl group] and other lithium salts, ionic liquids, and the like that function as an overcharge inhibitor when dissolved in the electrolyte in the battery. By using a material that functions as a flame retardant, a material that functions as a corrosion inhibitor for the positive electrode current collector, etc., each function is exhibited and the characteristics of the battery It is possible to improve.

  When the template agent is not removed in the battery, the template agent may be dissolved and removed from the heat-resistant layer using a solvent in which the template agent is soluble and the binder and filler particles are insoluble. For example, when the template agent is soluble in the electrolytic solution, the heat-resistant layer may be immersed in the electrolytic solution for a predetermined time to dissolve and remove the template agent in the electrolytic solution. By repeating washing with an electrolytic solution as necessary and drying, a separator comprising a heat-resistant porous layer containing filler particles and a binder and having voids can be obtained.

  The base material used in the step (I) is peeled off before or after the template agent is removed in the step (II), and the obtained heat-resistant porous layer is left as it is or in combination with a porous substrate. It can be used as a separator for an element.

The separator for an electrochemical element of the present invention thus obtained is produced by using a template agent to make the gap more open compared to the case where no template agent is used, and when used in a battery. The internal resistance can be further reduced.
An electrochemical element such as a lithium battery or a lithium ion battery can be produced using the electrochemical element separator of the present invention. The basic structure of an electrochemical element is that a positive electrode and a negative electrode are arranged opposite to each other with a separator for electrochemical elements, and this is impregnated with a non-aqueous electrolyte.

In the case of a lithium battery and a lithium ion battery, the positive electrode active material contained in the positive electrode is a composite oxide of lithium and a transition metal such as LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ ; MnO ₂ , V ₂ O Transition metal oxides such as ₅ ; transition metal sulfides such as MoS ₂ and TiS; conductive polymer compounds such as polyacetylene, polyacene, polyaniline, polypyrrole, polythiophene; poly (2,5-dimercapto-1,3,4 Disulfide compounds such as thiadiazole); As the current collector of the positive electrode, a metal foil such as aluminum; punching metal, net, expanded metal, or the like is used, but usually an aluminum foil having a thickness of 10 to 30 μm is preferably used.

  As the negative electrode active material contained in the negative electrode, lithium alloys such as lithium metal and lithium aluminum alloy, carbonaceous materials capable of occluding and releasing lithium, cokes such as graphite, phenolic resin, and furan resin, carbon fiber, glassy carbon, Pyrolytic carbon, activated carbon, etc. are 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 is used as the current collector. Usually, a copper foil is used. In the case of reducing the thickness of the whole negative electrode in order to obtain a battery having a high energy density, the upper limit of the thickness is preferably 30 μm, and the lower limit is preferably 5 μm.

  Examples of the conductive aid used when producing an electrode using an electrode active material include carbon black such as acetylene black and ketjen black, metal fibers such as aluminum and nickel, natural graphite, thermally expanded graphite, and carbon fiber. Ruthenium oxide, titanium oxide, etc. are used. Among these, acetylene black and ketjen black that can ensure desired conductivity with a small amount of blend are preferable. In addition, about 0.5-20 mass% is normally mix | blended with a conductive support agent with respect to an electrode active material, However, It is more preferable to mix | blend 1-10 mass%.

  As the binder used together with the conductive assistant, various known binders can be used. For example, polytetrafluoroethylene, polyvinylidene fluoride, carboxymethyl cellulose, fluoroolefin copolymer crosslinked polymer, styrene-butadiene copolymer, poly Examples include acrylonitrile, polyvinyl alcohol, polyacrylic acid, polyimide, petroleum pitch, coal pitch, and phenol resin.

The electrolytic solution has a property of dissolving the template agent, and 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 does not cause a side reaction such as decomposition in a 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 (RfOSO ₂ ) ₂ [where Rf is a fluoroalkyl group] and the like can be used. . The concentration of the lithium salt in the electrolytic solution is preferably 0.5 to 2 mol / L, and more preferably 0.9 to 1.5 mol / L.

  The organic solvent used in the electrolytic solution is not particularly limited as long as it dissolves the above lithium salt and does not cause a side reaction such as decomposition in the voltage range used as a battery. For example, cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate; chain esters such as methyl propionate; cyclic such as γ-butyrolactone Esters; chain ethers such as dimethoxyethane, diethyl ether, 1,3-dioxolane, diglyme, triglyme and tetraglyme; cyclic ethers such as dioxane, tetrahydrofuran and 2-methyltetrahydrofuran; acetonitrile, propionitrile, methoxypro Nitriles such as pionitrile; sulfites such as ethylene glycol sulfite; ionic liquids; and the like. It may have, may be used in combination of two or more thereof. In order to obtain a battery with better characteristics, it is desirable to use a combination that can obtain high conductivity, such as a mixed solvent of ethylene carbonate and chain carbonate.

  In addition, vinylene carbonates, 1,3-propane sultone, diphenyl disulfide, cyclohexane, biphenyl, fluorobenzene, t- for the purpose of improving safety, charge / discharge cycleability, and high-temperature storage properties of these electrolytes. Additives such as butylbenzene can also be added as appropriate.

  Examples of the form of the lithium battery or lithium ion battery of the present invention include a cylindrical shape such as a rectangular tube shape or a cylindrical shape using a steel can, an aluminum can, or the like as an exterior body (outer can). Moreover, it can also be set as the soft package battery which used the laminated film which vapor-deposited the metal as an exterior body.

  The separator for an electrochemical device of the present invention is a polarizable electrode used in an electric double layer capacitor, one of positive and negative electrodes, and the other is a substance capable of inserting / extracting lithium ions used in a lithium ion battery. The present invention can also be applied to a hybrid type electricity storage device as an electrode as an active material.

  The lithium battery or lithium ion battery of the present invention can be applied to the same applications as those in which conventionally known lithium batteries or lithium ion batteries are used.

  Hereinafter, the present invention will be described in detail by way of examples. However, the following examples do not limit the present invention.

Example 1
<Preparation of separator for electrochemical device>
As filler particles, 1 g of Al ₂ O ₃ (“nanopowder Al ₂ O ₃ ”, spherical filler, melting point 2020 ° C., manufactured by Aldrich) was weighed and placed in an agate mortar. Next, an N-methylpyrrolidone (NMP) solution of polyvinylidene fluoride (PVDF) (“PVDF # 1120” manufactured by Kureha Co., Ltd., concentration of 12% by weight of PVDF) is used as the solution containing the binder, and the solid content of PVDF is 0. Then, 1 g of lithium bis (trifluoromethanesulfonyl) imide was added as a template agent, and 1 g of NMP was further added to prepare slurry (a).

This slurry (a) is applied on a glass substrate with a gap of 100 μm using an applicator, dried at 80 ° C. for 2 hours, and composed of Al ₂ O ₃ filler particles, a template agent, and a PVDF binder. A heat resistant layer was prepared. It was 25 micrometers when the thickness of the heat-resistant layer peeled off from the glass substrate was measured with the micrometer.

  Next, the heat-resistant layer peeled from the glass substrate was mixed with ethylene carbonate (made by Kishida Co., Ltd.), diethyl carbonate (made by Kishida Co., Ltd.) and dimethyl carbonate (made by Kishida Co., Ltd.) (1: 1: 1 volume ratio). It was immersed in the solution for 1 hour, and the template agent was dissolved and removed in the mixed solution. Then, after repeatedly washing with dimethyl carbonate (manufactured by Kishida Co., Ltd.), it was vacuum-dried at 80 ° C. for 3 hours to obtain an electrochemical element separator (A) comprising only a heat-resistant porous layer. It was 25 micrometers when the thickness of the separator (A) for electrochemical elements which consists only of a heat resistant porous layer was measured with the micrometer.

Moreover, the photograph which image | photographed the surface of the separator (A) for electrochemical elements by 50,000 times using the electron microscope (Hitachi High-Technologies Corporation "SU-70") is shown in FIG.
When the average particle diameter of the Al ₂ O ₃ used was measured by a laser diffraction method (manufactured by Shimadzu Corporation, laser diffraction particle size measuring device “SALD3000J”), the average particle diameter (50) was 0.07 μm.

The thermogravimetric change of the heat-resistant layer before and after the dimethyl carbonate cleaning was measured with a thermogravimetric analyzer (“SII EXSTAR6000 / TGDTA6300” manufactured by Seiko Instruments Inc.). _Since it was the same as the measurement result of the thermogravimetric change of the heat-resistant layer (Al ₂ O ₃ / PVDF = 2/1 (weight ratio)) of only the ₂ O ₃ filler particles and the PVDF binder, 99 wt. It was confirmed that the template agent exceeding the ratio was removed.

<Evaluation of heat-resistant dimensional stability>
The electrochemical device separator (A) of Example 1 was cut to obtain a 2 cm × 2 cm square test piece. Next, the test piece was sandwiched between two glass plates having a length of 7.5 cm, a width of 7.5 cm, and a thickness of 5 mm, and then placed horizontally on a stainless steel vat. Then, it left to stand in 120 degreeC oven for 1 hour, and measured the area.

The area maintenance factor was evaluated as (area after standing / area before standing: 4 cm ² ) × 100 (%), and used as an index of heat-resistant dimensional stability. The results are shown in Table 1. In addition, it is excellent in heat-resistant dimensional stability, so that an area maintenance factor is large.

<Preparation of positive electrode for lithium secondary battery>
Lithium cobaltate as a positive electrode active material (manufactured by Nippon Chemical Industry Co., Ltd., “Cellseed 10N”), conductive carbon (manufactured by Denki Kagaku Kogyo Co., Ltd., “Denka Black”), and polyvinylidene fluoride (manufactured by Kureha Corporation, “PVDF # 1120”) and N-methylpyrrolidone (hereinafter referred to as NMP) as a coating solvent, in a ratio of positive electrode active material: conductive carbon: binder resin: NMP = 94: 3: 3: 28 (weight ratio) After mixing and making a paste, applying it to an aluminum current collector foil (“20CB”, manufactured by Nippon Electric Power Industry Co., Ltd.), drying at 80 ° C. for 3 hours, rolling, punching out into a 9 mm diameter circle, A positive electrode for a secondary battery was obtained.

<Production of lithium secondary battery>
The electrochemical element separator (A) of Example 1 was cut using circular metallic lithium having a thickness of 1 mm and a diameter of 15 mm as a counter electrode and the positive electrode for a lithium secondary battery obtained above as a working electrode. The counter electrode and the working electrode were made to face each other through a circular separator having a diameter of 16 mm and a polyethylene microporous membrane (manufactured by Asahi Kasei Chemicals Corporation, “Hypore N8416”, film thickness 25 μm). The polyethylene microporous membrane was arranged on the positive electrode side, and the separator for electrochemical elements (A) was arranged on the negative electrode side. Further, a secondary lithium secondary solution is prepared by a conventional method using a nonaqueous electrolytic solution in which 1% by weight of vinylene carbonate is added to a mixed solution (1: 1: 1 volume ratio) of 1.0M LiPF ₆ / ethylene carbonate, diethyl carbonate and dimethyl carbonate. A battery was produced.

<Evaluation of electrode characteristics>
The counter electrode (lithium electrode) was charged to 4.2 V with a current corresponding to 0.05C. Discharge was performed up to 3.0 V with a current corresponding to 0.1 C with respect to the lithium electrode, and the initial (initial) discharge capacity (x) was measured. Next, after charging to 4.2 V with a current corresponding to 0.1 C, the battery was discharged to 3.0 V with a current corresponding to 2.0 C, the discharge capacity (y) was measured, and the discharge capacity maintenance rate was calculated according to the following formula: (%) Was calculated.

Discharge capacity retention rate (%) = discharge capacity (y) / discharge capacity (x) × 100
Example 2
<Synthesis of ionic liquid>
Diethyl sulfide (manufactured by Tokyo Chemical Industry Co., Ltd.) 9.02 g (0.1 mol) and acetonitrile (manufactured by Wako Pure Chemical Industries, Ltd.) 20 g were stirred in a flask, and further, iodomethane 14.2 (0.1 mol) was added. It was. This was stirred at 25 ° C. under reflux and reacted for 10 hours. After the reaction, the crystals obtained by concentration were washed with 500 ml of ethyl acetate (manufactured by Wako Pure Chemical Industries, Ltd.) and dried in vacuo at 70 ° C. for 3 hours. 2.71 g (0.01 mol) of this crystal was dissolved in 50 ml of purified water, 2.87 g (0.01 mol) of lithium bis (trifluoromethanesulfonyl) imide (manufactured by Kishida Chemical Co., Ltd.) was added, and the mixture was stirred at 25 ° C. for 10 hours. did. To this was added 50 ml of methylene chloride (manufactured by Wako Pure Chemical Industries, Ltd.), and then the organic phase was extracted and washed with 500 ml of purified water. After the methylene chloride was removed by concentrating the organic phase, vacuum drying was performed at 160 ° C. for 3 hours, molecular sieves 4A (manufactured by Wako Pure Chemical Industries, Ltd.) was added, and the mixture was allowed to stand for 1 day. 2.5 g of ionic liquid (b) represented by (I) was obtained.

  The melting point of the ionic liquid (b) represented by the general formula (I) was less than 25 ° C., and the NMR spectrum was measured at 400 MHz by “AV400M” manufactured by BRUKER. The results are as follows.

¹ H-NMR [ppm] [d ₆ -dimethyl sulfoxide, δ 1.34 (t), δ 2.84 (s), δ 3.30 (m)]
<Preparation of separator for electrochemical element and lithium secondary battery>
An electrochemical process having a thickness of 25 μm was performed through the same steps as in Example 1 except that 1 g of the ionic liquid obtained above was used instead of 1 g of lithium bis (trifluoromethanesulfonyl) imide used in Example 1. An element separator (B) and a lithium secondary battery were prepared and evaluated in the same manner.

Example 3
Instead of 1 g of lithium bis (trifluoromethanesulfonyl) imide used in Example 1, 1 g of magnesium oxide (manufactured by Wako Pure Chemical Industries, Ltd., average particle size 50 nm) was used, and ethylene carbonate, diethyl carbonate and dimethyl carbonate were used. A 27 μm-thick separator for electrochemical devices (C) and a lithium battery were processed in the same manner as in Example 1 except that 20 wt% hydrochloric acid aqueous solution was used instead of the mixed solvent to dissolve and remove magnesium oxide. Were prepared and evaluated in the same manner.

Example 4
The slurry (a) prepared in Example 1 was applied on a polyethylene microporous membrane (manufactured by Asahi Kasei Chemicals Corporation, “Hypore N8416”, film thickness 25 μm) placed on a glass substrate, and then vacuum-dried at 30 ° C. did. Subsequently, it was immersed in the mixed solution (1: 1: 1 volume ratio) of ethylene carbonate, diethyl carbonate, and dimethyl carbonate for 1 hour, and the template agent was dissolved and removed in the mixed solution. Then, after repeatedly washing with dimethyl carbonate, it was vacuum-dried at 80 ° C. for 3 hours to obtain an electrochemical element separator (D) in which a heat-resistant porous layer was disposed on a polyethylene microporous film. It was 27 micrometers when the thickness of the separator (D) for electrochemical elements which has arrange | positioned the heat resistant porous layer on the polyethylene microporous film with the micrometer was measured.

  Using the electrochemical device separator (D), the same operation as in Example 1 was performed to produce a lithium secondary battery, which was similarly evaluated. That is, the evaluation of the heat-resistant dimensional stability was performed using an electrochemical element separator (D) in which a heat-resistant porous layer was disposed on a polyethylene microporous film instead of the electrochemical element separator (A) of Example 1. For the evaluation of electrode characteristics, an electrochemical element separator (D) in which a heat-resistant porous layer was disposed on a polyethylene microporous film was used instead of the electrochemical element separator (A) and the polyethylene microporous film.

Comparative Example 1
Electrochemical element separator (E) by stacking two polyethylene microporous membranes (“Hypore N8416”, 25 μm thickness, manufactured by Asahi Kasei Chemicals Corporation) widely used as separators for conventional lithium ion secondary batteries Was made. Using the electrochemical device separator (E), the same operation as in Example 1 was performed to produce a lithium secondary battery, which was similarly evaluated. That is, the heat resistant dimensional stability was evaluated by using one polyethylene microporous membrane instead of the electrochemical element separator (A) of Example 1, and the electrode characteristics were evaluated by the electrochemical element separator (A) and the polyethylene fine film. Instead of the porous membrane, an electrochemical device separator (E) in which two polyethylene microporous membranes were stacked was used.

Comparative Example 2
The separator for electrochemical devices (F) was produced in the same manner as in Example 1 except that lithium bis (trifluoromethanesulfonyl) imide was not used. It was 24 micrometers when the thickness of the separator (F) for electrochemical elements was measured with the micrometer.

Moreover, the photograph which image | photographed the surface of the separator for electrochemical elements (F) by 50,000 times using the electron microscope (Hitachi High-Technologies Corporation "SU-70") is shown in FIG.
Using the electrochemical device separator (F), the same operation as in Example 1 was performed to produce a lithium secondary battery, which was similarly evaluated.

Comparative Example 3
Except not using lithium bis (trifluoromethanesulfonyl) imide, operation was performed in the same manner as in Example 4 to prepare an electrochemical device separator (G) in which a heat-resistant porous layer was disposed on a polyethylene microporous membrane. . It was 27 micrometers when the thickness of the separator (G) for electrochemical elements which has arrange | positioned the heat resistant porous layer on the polyethylene microporous film with the micrometer was measured.

Using the electrochemical device separator (G), the same operation as in Example 1 was performed to produce a lithium secondary battery, which was similarly evaluated. That is, evaluation of heat-resistant dimensional stability was performed using an electrochemical element separator (G) in which a heat-resistant porous layer was disposed on a polyethylene microporous membrane instead of the electrochemical element separator (A) of Example 1. For the evaluation of the electrode characteristics, an electrochemical element separator (G) in which a heat-resistant porous layer was disposed on a polyethylene microporous film was used instead of the electrochemical element separator (A) and the polyethylene microporous film.

  For Examples 1 to 3 and Comparative Example 2, the “area maintenance ratio” is the area maintenance ratio of the heat resistant porous layer alone, and the “discharge capacity maintenance ratio” is the heat resistant porous layer and porous substrate as a separator. It is the discharge capacity maintenance rate of the cell for evaluation used repeatedly.

  For Example 4 and Comparative Example 3, the “area maintenance ratio” is the area maintenance ratio of the porous substrate provided with the heat resistant porous layer on the surface, and the “discharge capacity maintenance ratio” is the heat resistance on the surface as a separator. It is the discharge capacity maintenance rate of an evaluation cell using a porous substrate provided with a porous layer alone.

  In Comparative Example 1, the “area maintenance ratio” is the area maintenance ratio of one layer of the porous substrate, and the “discharge capacity maintenance ratio” is the discharge capacity of the evaluation cell using two layers of the porous substrate as a separator. It is a maintenance rate.

  As shown in Table 1, the separators for electrochemical elements of Examples 1 to 4 can suppress the heat generation of the battery at the time of short circuit because the area retention rate is high and the heat resistant dimensional stability is excellent. Since the lithium secondary battery used has a high discharge capacity maintenance rate, it is clear that internal resistance can be suppressed, and both safety and high performance can be achieved. In contrast, the separator for an electrochemical element of Comparative Example 1 made of a polyethylene microporous film does not contain filler particles, and therefore has a low area maintenance ratio and poor heat-resistant dimensional stability, and Comparative Examples 2 and 3 using no template agent. The lithium secondary battery using the electrochemical element separator had a low discharge capacity retention rate.

Example 5
<Preparation of separator for electrochemical device>
1 g of Al ₂ O ₃ (“AEROXIDE AluC” manufactured by Evonik, melting point 2020 ° C.) as filler particles and 0.5 g of distilled biphenyl (manufactured by Wako Pure Chemical Industries, Ltd.) as a template agent were weighed and placed in an agate mortar. Next, after adding 1 g of polyvinylidene fluoride (PVDF) (“PVDF # 1100” manufactured by Kureha Co., Ltd.) as a binder, 2 g of cyclohexane (manufactured by Wako Pure Chemical Industries, Ltd.) is added to prepare a slurry (c). did.

This slurry (c) is applied on a glass substrate with a gap of 100 μm using an applicator, dried at 40 ° C. for 2 hours, and composed of Al ₂ O ₃ filler particles, a template agent, and a PVDF binder. A heat resistant layer (h) was produced. It was 25 micrometers when the thickness of the heat-resistant layer (h) peeled from the glass substrate was measured with the micrometer. When the average particle diameter of the Al ₂ O ₃ used was measured by a laser diffraction method (manufactured by Shimadzu Corporation, laser diffraction particle size measuring instrument “SALD3000J”), the average particle diameter (D50) was 0.1 μm.

<Evaluation of heat-resistant dimensional stability>
The heat-resistant layer (h) of Example 5 was peeled from the glass substrate, and a mixed solution (1: 1) of ethylene carbonate (manufactured by Kishida Co., Ltd.), diethyl carbonate (manufactured by Kishida Co., Ltd.) and dimethyl carbonate (manufactured by Kishida Co., Ltd.). : 1 volume ratio) It was immersed in the solution for 1 hour, and the template agent was dissolved in the mixed solution and removed. Then, after repeatedly washing with dimethyl carbonate (manufactured by Kishida Co., Ltd.), it was vacuum-dried at 80 ° C. for 3 hours to obtain an electrochemical element separator (H) consisting only of a heat-resistant porous layer. It was 25 micrometers when the thickness of the separator (H) for electrochemical elements was measured with the micrometer.

The thermogravimetric change of the heat-resistant layer before and after the dimethyl carbonate cleaning was measured with a thermogravimetric analyzer (“SII EXSTAR6000 / TGDTA6300” manufactured by Seiko Instruments Inc.). _Since it was the same as the measurement result of the thermogravimetric change of the heat-resistant layer (Al ₂ O ₃ / PVDF = 2/1 (weight ratio)) of only the ₂ O ₃ filler particles and the PVDF binder, the template agent was washed. Was confirmed to be removed.

  The electrochemical element separator (H) was cut to obtain a 2 cm × 2 cm square test piece. Next, the test piece was sandwiched between two glass plates of length 7.5 cm × width 7.5 cm × thickness 5 mm, and then placed horizontally on a stainless steel bat. And it was left to stand in 120 degreeC oven for 1 hour, and the area was measured.

The area maintenance rate was evaluated as (area after standing / area before standing: 4 cm ² ) × 100 (%) and used as an index of heat-resistant dimensional stability. The results are shown in Table 2. In addition, it is excellent in heat-resistant dimensional stability, so that an area maintenance factor is large.

<Preparation of positive electrode for lithium ion secondary battery>
Lithium cobalt oxide (“CELLSEED 10N” manufactured by Nippon Chemical Industry Co., Ltd.) as the positive electrode active material, conductive carbon (“DENKA BLACK” manufactured by Denki Kagaku Kogyo Co., Ltd.), and polyvinylidene fluoride (Kureha Co., Ltd.) as the binder resin “PVDF # 1120”) and N-methylpyrrolidone (hereinafter referred to as “NMP”) as a coating solvent, positive electrode active material: conductive carbon: binder resin: NMP = 94: 3: 3: 28 (weight ratio) The mixture was made into a paste form at a ratio of, applied to an aluminum current collector foil (manufactured by Nippon Electric Power Industry Co., Ltd., “20CB”), dried at 80 ° C. for 3 hours, rolled, and punched into a circle having a diameter of 14 mm. The positive electrode for lithium ion secondary batteries was obtained.

<Production of lithium secondary battery>
Circular metal lithium having a diameter of 16 mm obtained by cutting the heat-resistant layer (h) of Example 5 using circular metallic lithium having a thickness of 1 mm and a diameter of 15 mm as the counter electrode and the positive electrode obtained above as the working electrode. The counter electrode and the working electrode were made to face each other through a heat-resistant layer (h) and a polyethylene microporous membrane (manufactured by Asahi Kasei Chemicals Corporation, “Hypore N8416”, film thickness 25 μm). The polyethylene microporous membrane was disposed on the positive electrode side, and the heat-resistant layer (h) was disposed on the negative electrode side. Further, by using a nonaqueous electrolytic solution in which 1% by weight of vinylene carbonate is added to a mixed solution (1: 1: 1 volume ratio) of 1.0M LiPF ₆ / ethylene carbonate, diethyl carbonate and dimethyl carbonate, a secondary lithium secondary solution is obtained. A battery was produced.

<Evaluation of battery characteristics>
The counter electrode (lithium electrode) was charged to 4.2 V with a current corresponding to 0.05C. Discharge was performed up to 3.0 V with a current corresponding to 0.1 C with respect to the lithium electrode, and the initial (initial) discharge capacity (x) was measured. Next, after charging to 4.2 V with a current corresponding to 0.1 C, the battery was discharged to 3.0 V with a current corresponding to 2.0 C, the discharge capacity (y) was measured, and the discharge capacity maintenance rate was calculated according to the following formula: (%) Was calculated.

Discharge capacity retention rate (%) = discharge capacity (y) / discharge capacity (x) × 100
<Overcharge prevention characteristics>
1 part by weight of vinylene carbonate and 2 parts by weight of biphenyl were dissolved in 100 parts by weight of a mixed solution (1: 1: 1 volume ratio) of 1M LiPF ₆ / ethylene carbonate, diethyl carbonate and dimethyl carbonate to prepare an electrolytic solution. . In addition, a three-electrode electrolytic cell using glassy carbon as a working electrode and metallic lithium as a reference electrode and a counter electrode was produced. 10 ml of the electrolytic solution was put into this electrolytic cell and heated to 80 ° C., and then the oxidative decomposition starting voltage and oxidative decomposition current of the overcharge inhibitor were measured as indicators of the overcharge prevention characteristics. The oxidative decomposition starting voltage and the oxidative decomposition current were measured by a cyclic voltammetry method, with a sweep rate of 10 mV / sec and a voltage sweep range of 3.0 V to 5.0 V. The oxidative decomposition starting voltage was a voltage at which an oxidative decomposition current of 0.5 mA / cm ² flowed, and the oxidative decomposition current was an oxidation current value of 4.7V. The decomposition voltage of biphenyl was 4.48 V, and the oxidation current value at 4.7 V was 18 mA / cm ⁻² .

Example 6
The slurry (c) prepared in Example 5 was applied on a polyethylene microporous membrane (manufactured by Asahi Kasei Chemicals Corporation, “Hypore N8416”, film thickness 25 μm) placed on a glass substrate, and then vacuum dried at 30 ° C. The heat resistant layer (i) was produced. It was 27 micrometers when the thickness of the polyethylene microporous film | membrane which has arrange | positioned the heat resistant layer (i) was measured with the micrometer.

  Using the heat resistant layer (i), the same operation as in Example 5 was performed to produce a lithium secondary battery and evaluated in the same manner. That is, evaluation of the heat-resistant dimensional stability was performed using the electrochemical element separator (I) in which the heat-resistant layer (i) was disposed on the polyethylene microporous film instead of the electrochemical element separator (H) of Example 5. In the evaluation of the electrode characteristics, a polyethylene microporous membrane in which the heat-resistant layer (i) is arranged is used in place of the heat-resistant layer (h) and the polyethylene microporous membrane.

Comparative Example 4
Two layers of polyethylene microporous membranes ("Hypore N8416" manufactured by Asahi Kasei Chemicals Co., Ltd., 25 μm thick), widely used as separators for conventional lithium ion secondary batteries, are stacked on top of each other to form an electrochemical device separator (J). Produced. Using the electrochemical device separator (J), a lithium secondary battery was produced in the same manner as in Example 5 and evaluated in the same manner. That is, the heat resistant dimensional stability was evaluated using one polyethylene microporous film in place of the electrochemical element separator (H) of Example 5, and the electrode characteristics were evaluated using a heat resistant layer (h) and a polyethylene microporous film. Instead of the separator, an electrochemical device separator (J) in which two polyethylene microporous membranes were stacked was used.

A three-electrode electrolytic cell using glassy carbon as a working electrode and metallic lithium as a reference electrode and a counter electrode was produced. 10 ml of a solution obtained by adding 1 part by weight of vinylene carbonate to 100 parts by weight of a mixed solution (1: 1: 1 volume ratio) of 1M LiPF ₆ / ethylene carbonate, diethyl carbonate and dimethyl carbonate as an electrolytic solution was placed in this electrolytic cell at 80 ° C. After heating, the oxidative decomposition onset voltage and oxidative decomposition current of the overcharge inhibitor were measured as indicators of overcharge prevention characteristics. The measurement of the oxidative decomposition starting voltage and the oxidative decomposition current was performed by a cyclic voltammetry method, and the overcharge prevention characteristics were evaluated at a sweep rate of 10 mV / sec and a voltage sweep range of 3.0 V to 5.0 V. No degradation was observed during

Comparative Example 5
A heat resistant layer (k) was produced in the same manner as in Example 5 except that biphenyl was not used. It was 24 micrometers when the thickness of the heat resistant layer was measured with the micrometer.

  Using the heat-resistant layer (k), the same operation as in Example 5 was performed to produce a lithium secondary battery and evaluated in the same manner.

Comparative Example 6
A heat resistant layer (l) was prepared in the same manner as in Example 6 except that biphenyl was not used. It was 27 micrometers when the thickness of the polyethylene microporous film which has arrange | positioned the heat resistant layer (l) was measured with the micrometer.

Using the heat-resistant layer (l), the same operation as in Example 5 was performed to produce a lithium secondary battery and evaluated in the same manner. That is, the evaluation of the heat-resistant dimensional stability was performed using the electrochemical element separator (L) in which the heat-resistant layer (l) was disposed on the polyethylene microporous film instead of the electrochemical element separator (H) of Example 5. In the evaluation of the electrode characteristics, a polyethylene microporous membrane in which the heat-resistant layer (l) is arranged is used in place of the heat-resistant layer (h) and the polyethylene microporous membrane.

  For Example 5 and Comparative Example 5, the “area maintenance ratio” is the area maintenance ratio of the heat resistant layer alone, and the “discharge capacity maintenance ratio” is used by overlapping the heat resistant layer and the porous substrate as a separator. It is the discharge capacity maintenance rate of the cell for evaluation.

  Further, for Example 6 and Comparative Example 6, “area maintenance ratio” is the area maintenance ratio of the porous substrate provided with the heat resistant layer on the surface, and “discharge capacity maintenance ratio” is the surface of the heat resistant layer as a separator. It is the discharge capacity maintenance rate of the cell for evaluation which used the provided porous substrate independently.

  For Comparative Example 4, the “area maintenance ratio” is the area maintenance ratio of one layer of the porous substrate, and the “discharge capacity maintenance ratio” is the discharge capacity of the evaluation cell using two layers of the porous substrate as a separator. It is a maintenance rate.

  As shown in Table 2, the separators for electrochemical elements of Examples 5 and 6 have a high area retention rate and excellent heat-resistant dimensional stability, and thus can suppress the heat generation of the battery at the time of a short circuit. The lithium secondary battery used has a high discharge sustaining capacity and excellent cycle characteristics, and the results of the overcharge prevention characteristics indicate that the safety in the overcharged state can be improved. On the other hand, the separator for an electrochemical element of Comparative Example 4 made of a polyethylene microporous film does not contain filler particles, and therefore has a low area maintenance rate and poor heat-resistant dimensional stability, and Comparative Examples 5 and 6 using no template agent. The lithium secondary battery using the electrochemical element separator had a low discharge capacity retention rate.

Example 7
<Preparation of separator for electrochemical device>
1 g of Al ₂ O ₃ (“AEROXIDE AluC” manufactured by Evonik, melting point 2020 ° C.) as filler particles and 1 g of trimethyl phosphate (manufactured by Kishida Chemical Co., Ltd.) as a template agent were weighed and placed in an agate mortar. Next, after adding 1 g of polyvinylidene fluoride (PVDF) (manufactured by Kureha Co., Ltd., “PVDF # 1100”) as a binder, 2 g of cyclohexane (manufactured by Wako Pure Chemical Industries, Ltd.) is added, and the slurry (d) is added. Produced. This slurry (d) is applied to a glass substrate with a gap of 100 μm using an applicator, dried at 40 ° C. for 2 hours, and composed of Al ₂ O ₃ filler particles, a template agent, and a PVDF binder. A heat-resistant layer (m) was produced. It was 25 micrometers when the thickness of the heat-resistant layer (m) peeled from the glass substrate was measured with the micrometer. When the average particle diameter of the Al ₂ O ₃ used was measured by a laser diffraction method (manufactured by Shimadzu Corporation, laser diffraction particle size measuring instrument “SALD3000J”), the average particle diameter (D50) was 0.1 μm.

<Evaluation of heat-resistant dimensional stability>
The heat-resistant layer (m) of Example 7 was peeled from the glass substrate, and a mixed solution (1: 1) of ethylene carbonate (manufactured by Kishida Co., Ltd.), diethyl carbonate (manufactured by Kishida Co., Ltd.) and dimethyl carbonate (manufactured by Kishida Co., Ltd.). : 1 volume ratio) It was immersed in the solution for 1 hour, and the template agent was dissolved in the mixed solution and removed. Then, after repeatedly washing with dimethyl carbonate (manufactured by Kishida Co., Ltd.), it was vacuum-dried at 80 ° C. for 3 hours to obtain an electrochemical element separator (M) comprising only a heat-resistant porous layer. It was 25 micrometers when the thickness of the separator (M) for electrochemical elements was measured with the micrometer.

When the thermogravimetric change of the heat-resistant layer before and after the dimethyl carbonate washing was measured with a thermogravimetric analyzer (manufactured by Seiko Instruments Inc., “SII EXSTAR6000 / TGDTA6300”), the measurement result after dimethyl carbonate washing was Since it was the same as the measurement result of the thermogravimetric change of the Al ₂ O ₃ filler particles and the PVDF binder-only heat-resistant layer (Al ₂ O ₃ / PVDF = 2/1 (weight ratio)), the template was washed. It was confirmed that the agent was removed.

  The electrochemical element separator (M) was cut to obtain a square test piece of 2 cm × 2 cm. Next, the test piece was sandwiched between two glass plates of length 7.5 cm × width 7.5 cm × thickness 5 mm, and then placed horizontally on a stainless steel bat. And it was left to stand in 120 degreeC oven for 1 hour, and the area was measured.

The area maintenance rate was evaluated as (area after standing / area before standing: 4 cm ² ) × 100 (%) and used as an index of heat-resistant dimensional stability. The results are shown in Table 3. In addition, it is excellent in heat-resistant dimensional stability, so that an area maintenance factor is large.

<Preparation of positive electrode for lithium secondary battery>
Lithium cobalt oxide (“CELLSEED 10N” manufactured by Nippon Chemical Industry Co., Ltd.) as the positive electrode active material, conductive carbon (“DENKA BLACK” manufactured by Denki Kagaku Kogyo Co., Ltd.), and polyvinylidene fluoride (Kureha Co., Ltd.) as the binder resin “PVDF # 1120”) and N-methylpyrrolidone (hereinafter referred to as “NMP”) as a coating solvent, positive electrode active material: conductive carbon: binder resin: NMP = 94: 3: 3: 28 (weight ratio) The mixture was made into a paste form at a ratio of, applied to an aluminum current collector foil (manufactured by Nippon Electric Power Industry Co., Ltd., “20CB”), dried at 80 ° C. for 3 hours, rolled, and punched into a circle having a diameter of 14 mm. The positive electrode for lithium ion secondary batteries was obtained.

<Production of lithium secondary battery>
Circular metal lithium having a diameter of 16 mm obtained by cutting the heat-resistant layer (m) of Example 7 using circular metallic lithium having a thickness of 1 mm and a diameter of 15 mm as the counter electrode and the positive electrode obtained above as the working electrode. The counter electrode and the working electrode were made to face each other through a heat-resistant layer (m) and a polyethylene microporous membrane (manufactured by Asahi Kasei Chemicals Corporation, “Hypore N8416”, film thickness 25 μm). The polyethylene microporous film was disposed on the positive electrode side, and the heat-resistant layer (m) was disposed on the negative electrode side. Further, by using a nonaqueous electrolytic solution in which 1% by weight of vinylene carbonate is added to a mixed solution (1: 1: 1 volume ratio) of 1.0M LiPF ₆ / ethylene carbonate, diethyl carbonate and dimethyl carbonate, a secondary lithium secondary solution is obtained. A battery was produced.

<Evaluation of battery characteristics>
The counter electrode (lithium electrode) was charged to 4.2 V with a current corresponding to 0.05C. Discharge was performed up to 3.0 V with a current corresponding to 0.1 C with respect to the lithium electrode, and the initial (initial) discharge capacity (x) was measured. Next, after charging to 4.2 V with a current corresponding to 0.1 C, the battery was discharged to 3.0 V with a current corresponding to 2.0 C, the discharge capacity (y) was measured, and the discharge capacity maintenance rate was calculated according to the following formula: (%) Was calculated.

Discharge capacity retention rate (%) = discharge capacity (y) / discharge capacity (x) × 100
<Heating test>
The lithium secondary battery produced above was installed in a heating tank, and the heating tank was raised to 140 ° C. at a temperature rising rate of 5 ° C./min, and left in that state for 10 minutes. Thereafter, the temperature of the battery was monitored, and the maximum temperature reached by the battery temperature was measured.

Example 8
A heat-resistant layer (n) was produced in the same manner as in Example 7 except that 1 g of triphenyl phosphate (manufactured by Kishida Chemical Co., Ltd.) was used instead of 1 g of trimethyl phosphate. It was 25 micrometers when the thickness of the heat resistant layer was measured with the micrometer.

  Using the heat-resistant layer (n), the same operation as in Example 7 was performed to produce a lithium secondary battery and evaluated in the same manner.

Example 9
The slurry (d) produced in Example 7 was applied on a polyethylene microporous membrane (manufactured by Asahi Kasei Chemicals Corporation, “Hypore N8416”, film thickness 25 μm) placed on a glass substrate, and then vacuum-dried at 30 ° C. Thus, a heat resistant layer (o) was produced. It was 27 micrometers when the thickness of the polyethylene microporous film which has arrange | positioned the heat resistant layer (o) was measured with the micrometer.

  Using the heat-resistant layer (o), the same operation as in Example 7 was performed to produce a lithium secondary battery and evaluated in the same manner. That is, evaluation of heat-resistant dimensional stability was performed using a separator for electrochemical elements (O) in which a heat-resistant layer (o) was disposed on a polyethylene microporous membrane instead of the separator for electrochemical elements (M) of Example 7. In the evaluation of the electrode characteristics, a polyethylene microporous membrane in which the heat-resistant layer (o) is arranged is used in place of the heat-resistant layer (m) and the polyethylene microporous membrane.

Comparative Example 7
Two layers of polyethylene microporous membranes ("Hypore N8416" manufactured by Asahi Kasei Chemicals Co., Ltd., 25 μm thick) widely used as separators for conventional lithium ion secondary batteries are stacked to form a separator for electrochemical devices (P). Produced. Using the electrochemical device separator (P), a lithium secondary battery was produced in the same manner as in Example 7 and evaluated in the same manner. That is, the heat resistant dimensional stability was evaluated by using one polyethylene microporous film instead of the electrochemical element separator (M) of Example 7, and the electrode characteristics were evaluated by the heat resistant layer (m) and the polyethylene microporous film. Instead of the separator, an electrochemical device separator (P) in which two polyethylene microporous films were stacked was used.

Comparative Example 8
A heat resistant layer (q) was produced in the same manner as in Example 7 except that trimethyl phosphate was not used. It was 24 micrometers when the thickness of the heat resistant layer was measured with the micrometer.

  The same operation as in Example 7 was performed using the heat-resistant layer (q), and a lithium secondary battery was produced and evaluated in the same manner.

Comparative Example 9
A heat resistant layer (r) was produced in the same manner as in Example 9 except that trimethyl phosphate was not used. It was 27 micrometers when the thickness of the polyethylene microporous film which has arrange | positioned the heat resistant layer (r) was measured with the micrometer.

Using the heat-resistant layer (r), the same operation as in Example 7 was performed to produce a lithium secondary battery and evaluated in the same manner. That is, evaluation of heat-resistant dimensional stability was performed using an electrochemical element separator (R) in which a heat-resistant layer (r) was disposed on a polyethylene microporous membrane instead of the electrochemical element separator (M) of Example 7. In the evaluation of the electrode characteristics, a polyethylene microporous membrane having a heat-resistant layer (r) disposed therein was used in place of the heat-resistant layer (m) and the polyethylene microporous membrane.

  For Examples 7 and 8 and Comparative Example 8, “area maintenance ratio” is the area maintenance ratio of the heat resistant layer alone, and “discharge capacity maintenance ratio” and “maximum temperature” are the heat resistant layer and porous as a separator. It is the discharge capacity maintenance rate and the maximum temperature of the evaluation cell that is used by overlapping the substrate.

  For Example 9 and Comparative Example 9, “area maintenance ratio” is the area maintenance ratio of the porous substrate having a heat-resistant layer provided on the surface, and “discharge capacity maintenance ratio” and “maximum temperature” are the surface as a separator. The discharge capacity retention rate and the maximum temperature of the evaluation cell using a porous substrate provided with a heat resistant layer alone.

  In Comparative Example 7, “area maintenance ratio” is the area maintenance ratio of one layer of the porous substrate, and “discharge capacity maintenance ratio” and “maximum temperature” are evaluations using two layers of porous substrates as separators. Cell discharge capacity maintenance rate and maximum temperature.

  As shown in Table 3, the separators for electrochemical elements of Examples 7 to 8 can suppress the heat generation of the battery at the time of short circuit because the area retention rate is high and the heat resistant dimensional stability is excellent. It can be seen that the lithium secondary battery used has a high discharge sustaining capacity and excellent cycle characteristics, and the maximum temperature in the heating test is low and the temperature rise can be suppressed, so that both safety and high performance can be achieved. On the other hand, the separator for an electrochemical element of Comparative Example 7 composed of a polyethylene microporous membrane does not contain filler particles, has a low area maintenance rate, is inferior in heat resistant dimensional stability, cannot suppress a temperature rise, and uses a template agent. In the lithium secondary batteries using the separators for electrochemical elements of Comparative Examples 8 and 9, the discharge capacity retention rate was lowered and the temperature rise could not be suppressed.

Example 10
<Synthesis of lithium bis (oxalate) borate>
Lithium bis (oxalate) borate was synthesized according to the description in “BT Yu, WH Qiu, FS Li and GX Xu, Electrochemical and Solid State Letters, 9 (2006), A1”. did.

<Preparation of separator for electrochemical device>
1 g of Al ₂ O ₃ (“AEROXIDE AluC” manufactured by Evonik, melting point 2020 ° C.) as filler particles and 1 g of lithium bis (oxalate) borate as a template agent were weighed and placed in an agate mortar. Next, after adding 1 g of polyvinylidene fluoride (PVDF) (manufactured by Kureha Co., Ltd., “PVDF # 1100”) as a binder, 2 g of N-methylpyrrolidone (NMP) (manufactured by Wako Pure Chemical Industries, Ltd.) is added. Thus, slurry (e) was prepared. This slurry (e) is applied on a glass substrate with a gap of 100 μm using an applicator, dried at 40 ° C. for 2 hours, and composed of Al ₂ O ₃ filler particles, a template agent, and a PVDF binder. A heat-resistant layer (s) was produced. It was 25 micrometers when the thickness of the heat-resistant layer (s) peeled from the glass substrate was measured with the micrometer. A separator consisting only of the composition layer was produced. It was 25 micrometers when the thickness of the separator was measured with the micrometer. When the average particle diameter of the Al ₂ O ₃ used was measured by a laser diffraction method (manufactured by Shimadzu Corporation, laser diffraction particle size measuring instrument “SALD3000J”), the average particle diameter (D50) was 0.1 μm.

<Evaluation of heat-resistant dimensional stability>
The heat-resistant layer (s) of Example 10 was peeled from the glass substrate, and a mixed solution (1: 1) of ethylene carbonate (manufactured by Kishida Co., Ltd.), diethyl carbonate (manufactured by Kishida Co., Ltd.) and dimethyl carbonate (manufactured by Kishida Co., Ltd.). : 1 volume ratio) It was immersed in the solution for 1 hour, and the template agent was dissolved in the mixed solution and removed. Then, after repeatedly washing with dimethyl carbonate (manufactured by Kishida Co., Ltd.), it was vacuum-dried at 80 ° C. for 3 hours to obtain a separator for electrochemical devices (S) consisting only of a heat-resistant porous layer. It was 25 micrometers when the thickness of the separator (S) for electrochemical elements was measured with the micrometer.

When the thermogravimetric change of the heat-resistant layer before and after the dimethyl carbonate washing was measured with a thermogravimetric analyzer (manufactured by Seiko Instruments Inc., “SII EXSTAR6000 / TGDTA6300”), the measurement result after dimethyl carbonate washing was Since it was the same as the measurement result of the thermogravimetric change of the Al ₂ O ₃ filler particles and the PVDF binder-only heat-resistant layer (Al ₂ O ₃ / PVDF = 2/1 (weight ratio)), the template was washed. It was confirmed that the agent was removed.

  The electrochemical device separator (S) was cut to obtain a 2 cm × 2 cm square test piece. Next, the test piece was sandwiched between two glass plates of length 7.5 cm × width 7.5 cm × thickness 5 mm, and then placed horizontally on a stainless steel bat. And it was left to stand in 120 degreeC oven for 1 hour, and the area was measured.

The area maintenance rate was evaluated as (area after standing / area before standing: 4 cm ² ) × 100 (%) and used as an index of heat-resistant dimensional stability. The results are shown in Table 4. In addition, it is excellent in heat-resistant dimensional stability, so that an area maintenance factor is large.

<Preparation of positive electrode for lithium ion secondary battery>
Lithium cobalt oxide (“CELLSEED 10N” manufactured by Nippon Chemical Industry Co., Ltd.) as the positive electrode active material, conductive carbon (“DENKA BLACK” manufactured by Denki Kagaku Kogyo Co., Ltd.), and polyvinylidene fluoride (Kureha Co., Ltd.) as the binder resin “PVDF # 1120”) and N-methylpyrrolidone (hereinafter referred to as “NMP”) as a coating solvent, positive electrode active material: conductive carbon: binder resin: NMP = 94: 3: 3: 28 (weight ratio) The mixture was made into a paste form at a ratio of, applied to an aluminum current collector foil (manufactured by Nippon Electric Power Industry Co., Ltd., “20CB”), dried at 80 ° C. for 3 hours, rolled, and punched into a circle having a diameter of 14 mm. The positive electrode for lithium ion secondary batteries was obtained.

<Production of lithium secondary battery>
Circular metal lithium having a diameter of 16 mm obtained by cutting the heat-resistant layer (s) of Example 10 using circular metal lithium having a thickness of 1 mm and a diameter of 15 mm as a counter electrode and the positive electrode obtained above as a working electrode. The counter electrode and the working electrode were made to face each other through the heat-resistant layer (s) and a polyethylene microporous membrane (manufactured by Asahi Kasei Chemicals Corporation, “Hypore N8416”, film thickness 25 μm). The polyethylene microporous membrane was disposed on the positive electrode side, and the heat-resistant layer (s) was disposed on the negative electrode side. Further, by using a nonaqueous electrolytic solution in which 1% by weight of vinylene carbonate is added to a mixed solution (1: 1: 1 volume ratio) of 1.0M LiPF ₆ / ethylene carbonate, diethyl carbonate and dimethyl carbonate, a secondary lithium secondary solution is obtained. A battery was produced.

<Evaluation of battery characteristics>
The counter electrode (lithium electrode) was charged to 4.2 V with a current corresponding to 0.1 C. Discharge was performed at a current corresponding to 0.1 C up to 3.0 V, and an initial (initial) discharge capacity (x) was measured. Subsequently, 29 cycles of repeating charge-discharge in the same manner at a current corresponding to 1.0 C were performed, the 30th discharge capacity (y) was measured, and the discharge capacity retention rate (%) was calculated by the following formula.

Discharge capacity retention rate (%) = discharge capacity (y) / discharge capacity (x) × 100
Example 11
The slurry (e) prepared in Example 10 was applied on a polyethylene microporous membrane (manufactured by Asahi Kasei Chemicals Corporation, “Hypore N8416”, film thickness 25 μm) placed on a glass substrate, and then vacuum-dried at 30 ° C. Thus, a heat resistant layer (t) was produced. It was 27 micrometers when the thickness of the polyethylene microporous film | membrane which has arrange | positioned the heat resistant layer (t) was measured with the micrometer.

  Using the heat-resistant layer (t), the same operation as in Example 10 was performed to produce a lithium secondary battery and evaluated in the same manner. That is, evaluation of the heat-resistant dimensional stability was performed using an electrochemical element separator (T) in which a heat-resistant layer (t) was disposed on a polyethylene microporous film instead of the electrochemical element separator (S) of Example 10. In the evaluation of the electrode characteristics, a polyethylene microporous membrane having a heat-resistant layer (t) disposed therein was used instead of the heat-resistant layer (s) and the polyethylene microporous membrane.

Comparative Example 10
Two layers of polyethylene microporous membranes ("Hypore N8416", manufactured by Asahi Kasei Chemicals Co., Ltd., 25 μm thick) widely used as separators for conventional lithium ion secondary batteries are stacked to form an electrochemical element separator (U). Produced. Using the electrochemical device separator (U), the same operation as in Example 10 was performed to produce a lithium secondary battery and evaluated in the same manner. That is, the evaluation of heat-resistant dimensional stability was performed using one polyethylene microporous membrane instead of the electrochemical device separator (S) of Example 10, and the evaluation of electrode characteristics was performed using a heat-resistant layer (s) and a polyethylene microporous membrane. Instead of the separator, an electrochemical element separator (U) in which two polyethylene microporous films were stacked was used.

Comparative Example 11
A heat resistant layer (v) was produced in the same manner as in Example 10 except that lithium bis (oxalate) borate was not used. It was 24 micrometers when the thickness of the heat resistant layer was measured with the micrometer.

  Using the heat-resistant layer (v), the same operation as in Example 10 was performed to produce a lithium secondary battery and evaluated in the same manner.

(Comparative Example 12)
A heat resistant layer (w) was produced in the same manner as in Example 11 except that lithium bis (oxalate) borate was not used. It was 27 micrometers when the thickness of the polyethylene microporous film which has arrange | positioned the heat resistant layer (w) was measured with the micrometer.

Using the heat-resistant layer (w), the same operation as in Example 10 was performed to produce a lithium secondary battery and evaluated in the same manner. That is, evaluation of heat-resistant dimensional stability was performed using a separator for electrochemical elements (W) in which a heat-resistant layer (w) was disposed on a polyethylene microporous membrane instead of the separator for electrochemical elements (S) of Example 10. In the evaluation of the electrode characteristics, a polyethylene microporous membrane having a heat-resistant layer (w) disposed therein was used instead of the heat-resistant layer (s) and the polyethylene microporous membrane.

  In addition, for Example 10 and Comparative Example 11, the “area maintenance ratio” is the area maintenance ratio of the heat resistant layer alone, and the “discharge capacity maintenance ratio” is used by overlapping the heat resistant layer and the porous substrate as a separator. It is the discharge capacity maintenance rate of the cell for evaluation.

  Further, for Example 11 and Comparative Example 12, “area maintenance ratio” is the area maintenance ratio of the porous substrate provided with the heat resistant layer on the surface, and “discharge capacity maintenance ratio” is the surface of the heat resistant layer as a separator. It is the discharge capacity maintenance rate of the cell for evaluation which used the provided porous substrate independently.

  For Comparative Example 10, the “area maintenance ratio” is the area maintenance ratio of one layer of the porous substrate, and the “discharge capacity maintenance ratio” is the discharge capacity of the evaluation cell using two layers of the porous substrate as a separator. It is a maintenance rate.

  As can be seen from Table 4, the separators for electrochemical devices of Examples 10 and 11 have a high area retention rate and excellent heat-resistant dimensional stability, and thus can suppress the heat generation of the battery at the time of short circuit, and lithium bis ( It can be seen that despite the use of (trifluoromethanesulfonyl) imide, the discharge sustaining capacity is high and the cycle characteristics are excellent. On the other hand, the separator for an electrochemical element of Comparative Example 10 made of a polyethylene microporous film has low area maintenance ratio and poor heat-resistant dimensional stability because it does not contain filler particles, and Comparative Examples 11 and 12 using no template agent. The lithium secondary battery using the electrochemical element separator had a low discharge capacity retention rate.

It is a schematic sectional drawing which shows the separator which consists only of a heat resistant porous layer which is an example of the separator for electrochemical elements of this invention. It is a schematic sectional drawing which shows the separator which consists of a porous base | substrate which provided the heat resistant porous layer (composition layer) on the surface which is an example of the separator for electrochemical elements of this invention. It is the schematic which shows the separator which consists of a porous base | substrate which contains the heat resistant porous layer inside as an example of the separator for electrochemical elements of this invention. It is the schematic which shows the separator which is an example of the separator for electrochemical elements of this invention, and combines a heat resistant porous layer and a porous base | substrate. 2 is a photograph showing the surface of an electrochemical element separator produced in Example 1. FIG. 5 is a photograph showing the surface of an electrochemical element separator produced in Comparative Example 2. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Separator for electrochemical elements 2 Heat resistant porous layer 2 'Heat resistant porous layer 3 Filler particle 4 Void 5 Binder 6 Porous substrate 7 Pore

Claims (20)

  A separator for an electrochemical device, comprising a heat-resistant porous layer containing filler particles and a binder and having voids, wherein the voids are made of a template agent.   A separator for an electrochemical device having a porous substrate and a heat-resistant porous layer provided on the surface of the porous substrate, the heat-resistant porous layer containing filler particles and a binder and having voids A separator for an electrochemical element, wherein the separator is a layer and the void is made of a template agent.   3. The separator for an electrochemical element according to claim 1, wherein the void is formed by removing the template agent from the heat-resistant layer containing filler particles, a binder, and the template agent. 4.   The said space | gap is produced by dissolving a template agent in electrolyte solution from the heat resistant layer containing a filler particle, a binder, and a template agent. The separator for electrochemical elements as described in 2.   The separator for an electrochemical element according to any one of claims 1 to 4, wherein the template agent is soluble in an electrolytic solution.   The template agent comprises at least one selected from metal oxides, metal carbonates, metal nitrates, metal citrates, metal ammonium salts, metal acetates, ionic liquids, polymers and lithium salts. Item 6. The separator for an electrochemical element according to any one of Items 1 to 5.   The separator for an electrochemical element according to any one of claims 1 to 5, which functions as an overcharge preventing agent when the template agent is dissolved in an electrolyte in a battery.   The separator for an electrochemical element according to claim 7, wherein the template agent contains at least one selected from alkyl-substituted benzene compounds, aryl-substituted benzene compounds, diaryl ether compounds, and halogen-substituted anisole compounds.   The separator for an electrochemical element according to any one of claims 1 to 5, wherein when the template agent is dissolved in an electrolyte solution in a battery, the template agent functions as a flame retardant for the electrolyte solution.   The separator for an electrochemical element according to claim 9, wherein the template agent contains at least one selected from a phosphate ester compound and a phosphazene compound.   The separator for an electrochemical element according to any one of claims 1 to 5, which functions as a corrosion inhibitor for a positive electrode current collector when the template agent is dissolved in an electrolytic solution in a battery.   The separator for an electrochemical element according to claim 11, wherein the template agent is a lithium salt having an OB bond. The filler _{particles, Al 2 O 3, SiO 2} , montmorillonite, mica, _ZnO, TiO 2, BaTiO _3, electric according to any one of claims 1 to 12 comprising at least one selected from ZrO ₂ and glass Chemical element separator. The filler particles, separator for an electrochemical device according to any one of claims 1 to 13 comprising at least Al ₂ O _3.   The separator for an electrochemical element according to any one of claims 1 to 14, wherein an average particle diameter of secondary particles of the filler particles is 5 nm to 5 µm.   The separator for an electrochemical element according to any one of claims 1 to 15, wherein the binder is a thermosetting resin or a thermoplastic resin.   The separator for an electrochemical element according to any one of claims 2 to 16, wherein the porous substrate contains a polyolefin.   The lithium battery or lithium ion battery which has the separator for electrochemical elements as described in any one of Claims 1-17.   By heating the composition containing the filler particles, the template agent and the binder to form a heat resistant layer containing the filler particles, the binder and the template agent, and then removing the template agent from the heat resistant layer The manufacturing method of the separator for electrochemical elements including the process of producing a space | gap in a heat resistant layer and forming a heat resistant porous layer.   The method for producing a separator for an electrochemical element according to claim 19, wherein the template agent is removed by dissolving in an electrolytic solution.