JP2012169160A - Electrode for sodium secondary battery and sodium secondary battery - Google Patents

Abstract

Although there is an expectation for higher output of a sodium secondary battery, in order to improve discharge load characteristics in an electrode including a carbon material that can be doped and dedoped with sodium ions as an electrode active material. However, the technology for improving the discharge load characteristics has not yet been clarified.
An electrode in which an electrode mixture containing a carbon material that can be doped and dedoped with sodium ions as a main component is supported on a current collector, the porosity of the electrode mixture being 25% or more and 50% or less. An electrode for a sodium secondary battery.
[Selection figure] None

Description

  The present invention relates to an electrode for a sodium secondary battery and a sodium secondary battery.

  A sodium secondary battery is suitable as a high energy density battery because it can generate a higher voltage than a battery of an aqueous electrolyte. Moreover, since sodium is an abundant and inexpensive material, it is expected that large-scale power can be supplied in large quantities by putting it into practical use.

  A sodium secondary battery usually includes a positive electrode including a positive electrode active material capable of doping and dedoping sodium ions, a negative electrode including a negative electrode active material capable of doping and dedoping sodium ions, and an electrolyte. .

  The electrode includes a current collector and an electrode mixture formed on the current collector. The electrode mixture includes an electrode active material such as a positive electrode active material and a negative electrode active material, and a binder. A carbon material is used as the negative electrode active material, and an electrode using polyvinylidene fluoride (hereinafter sometimes referred to as PVdF) as the binder. Has been proposed (Patent Document 1). If an excellent discharge load characteristic can be obtained using the above materials, it can be applied to a power tool or a power source for driving an electric vehicle that requires high output.

JP-A-11-40156

  However, although there is an expectation for higher output of a sodium secondary battery, there has been no study on improvement of discharge load characteristics in an electrode including a carbon material that can be doped and dedoped with sodium ions as an electrode active material. However, the technology for improving the discharge load characteristics has not yet been clarified.

  The inventors of the present invention have intensively studied to solve the above problems, and have reached the present invention. That is, the present invention provides the following inventions.

  An electrode in which an electrode mixture containing a carbon material that can be doped and dedoped with sodium ions as a main component is supported on a current collector, and the porosity of the electrode mixture is 25% or more and 50% or less. Battery electrode.

  If the electrode for sodium secondary batteries of this invention is used, the discharge load characteristic of a battery can be improved and the secondary battery which shows the outstanding output characteristic can be manufactured.

<Electrode for sodium secondary battery of the present invention>
An electrode for a sodium secondary battery of the present invention is an electrode in which a current collector carries an electrode mixture containing a carbon material that can be doped and dedoped with sodium ions as a main component, and the porosity of the electrode mixture is It is 25% or more and 50% or less.

  The porosity of the electrode mixture is preferably 30% or more and 45% or less.

The density of the electrode mixture is preferably 0.80 g / cm ³ or more and 1.25 g / cm ³ or less, more preferably 0.90 g / cm ³ or more and 1.15 g / cm ³ or less.

  The porosity of the electrode mixture indicates the volume ratio occupied by the voids in the electrode mixture, and is calculated by Equation 1.

空隙率の測定方法として、アルキメデス法を用いる。具体的には電極合剤体積を測定し、該電極合剤に対し適当な液体を空隙内に含浸させ、その含浸量より算出する。ここで適当な液体としては、温度に対する密度が既知の液体を示し、例えば水が挙げられる。分解した電池から得られた電極合剤の場合、電極合剤が電解液で濡れているため、電解液を構成する溶媒で残留電解質等を十分に洗浄除去、乾燥した後、上記操作を行い、空隙率を測定する。

The Archimedes method is used as a method for measuring the porosity. Specifically, the volume of the electrode mixture is measured, and an appropriate liquid is impregnated into the gap with respect to the electrode mixture, and the amount is calculated from the impregnation amount. Here, as the appropriate liquid, a liquid having a known density with respect to temperature is exemplified, and water is an example. In the case of the electrode mixture obtained from the decomposed battery, since the electrode mixture is wet with the electrolyte solution, the residual electrolyte etc. are sufficiently washed away with the solvent constituting the electrolyte solution, dried, and then the above operation is performed. Measure porosity.

  The thickness of the electrode mixture is preferably 25 μm or more and 130 μm or less, and more preferably 40 μm or more and 100 μm or less.

・ <Electrode active material>
In the present invention, the electrode active material is mainly composed of a carbon material, and can be doped and dedoped with sodium ions.

Examples of the carbon material include carbon black, pyrolytic carbons, carbon fiber, and a fired organic material. The carbon material is preferably a non-graphitized carbon material (also referred to as “hard carbon”). Among these, carbon microbeads made of a non-graphitized carbon material can be mentioned, and specifically, ICB (trade name: Nika beads) manufactured by Nippon Carbon Co., Ltd. can be mentioned.
Examples of the shape of the particles constituting the carbon material include a flake shape such as natural graphite, a spherical shape such as mesocarbon microbeads, a fibrous shape such as graphitized carbon fiber, and an aggregate shape of fine particles. When the shape of the particles constituting the carbon material is spherical, the average particle diameter is preferably 0.01 μm or more and 30 μm or less, more preferably 0.1 μm or more and 20 μm or less.

In the sodium secondary battery of the present invention, in order to smoothly dope and dedope sodium ions, the carbon material as the electrode active material is preferably a carbon material that has not been activated. Non-activated carbon materials are preferred. The non-activated carbon material is a carbon material that has been subjected to a deactivation treatment for the carbon material.
“Inactivation treatment” means treatment for removing the surface functional groups of the carbon material, and a specific treatment method is 600 ° C. or more and 2000 ° C. or less (preferably 800 ° C. in an inert gas atmosphere). The method of heat-processing at the temperature of 1800 degrees C or less) is mentioned.
When an activated carbon material is used as an electrode active material, sodium ions are not doped and undoped smoothly, and the irreversible capacity may increase.

As the organic material fired body, among carbon materials obtained by carbonization (firing) of various organic materials, a carbon material that can be doped with sodium ions and can be dedoped may be used. A non-graphitized carbon material, which is a suitable carbon material, can be obtained by firing an organic material that is unlikely to have a graphite crystal structure.
Organic materials used as raw materials for the organic material fired body include natural mineral resources such as petroleum and coal, various synthetic resins synthesized from these resources (thermosetting resin, thermoplastic resin, etc.), petroleum pitch, and coal pitch. And various plant residue oils such as spinning pitch, plant-derived organic materials such as wood, etc., and these can be used alone or in combination of two or more.

  As the synthetic resin, phenol resin, resorcinol resin, furan resin, epoxy resin, urethane resin, unsaturated polyester resin, melamine resin, urea resin, aniline resin, bismaleimide resin, benzoxazine resin, polyacrylonitrile resin, polystyrene resin, Polyamide resins, cyanate resins, ketone resins, and the like can be given, and these can be used alone or in combination of two or more. These resins may contain a curing agent and an additive. Examples of the curing method include a thermosetting method, a thermal oxidation method, an epoxy curing method, and an isocyanate curing method when a phenol resin is used. In the case of using an epoxy resin, a phenol resin curing method, an acid anhydride curing method, an amine curing method, and the like can be given.

  The organic material is preferably an organic material having an aromatic ring. By using the organic material, a carbon material that can be doped with sodium ions and can be dedope can be obtained with high yield. Thereby, the environmental load is small, the manufacturing cost can be reduced, and the industrial utility value is higher.

  Examples of the organic material having an aromatic ring include, among the above synthetic resins, phenol resins (such as novolac type phenol resins and resol type phenol resins), epoxy resins (such as bisphenol type epoxy resins and novolac type epoxy resins), and aniline resins. , Bismaleimide resins and benzoxazine resins, and these can be used alone or in combination of two or more. These resins may contain a curing agent and an additive.

  The organic material having an aromatic ring is preferably an organic material produced by polymerizing phenol or a derivative thereof and an aldehyde compound. Since the organic material is inexpensive among organic materials having an aromatic ring and has a large industrial production amount, a carbon material obtained by carbonizing the organic material is a preferable carbon material.

  Examples of the organic material obtained by polymerizing phenol or a derivative thereof and an aldehyde compound include phenol resins. Phenolic resins are inexpensive and have a large industrial production amount, which is preferable as a raw material for carbon materials. When the carbon material obtained by carbonizing the phenol resin is used as the electrode active material of the sodium secondary battery of the present invention, the charge / discharge capacity of the sodium secondary battery is particularly large when the charge / discharge is repeated. A carbon material obtained by carbonizing a phenol resin is preferable. Phenol resin has a structure in which three-dimensional crosslinking is developed, and the carbon material obtained by carbonizing the resin is also a carbon material having a structure in which unique three-dimensional crosslinking is derived from the structure. It is estimated to be. Thereby, it is considered that the discharge capacity is particularly increased.

  Examples of phenol or derivatives thereof include phenol, o-cresol, m-cresol, p-cresol, catechol, resorcinol, hydroquinone, xylenol, pyrogallol, bisphenol A, bisphenol F, p-phenylphenol, p-tert-butylphenol, p-tert-octylphenol, α-naphthol, β-naphthol and the like can be mentioned, and these can be used alone or in combination of two or more.

  Examples of the aldehyde compound include formaldehyde, paraformaldehyde, trioxane, acetaldehyde, propionaldehyde, polyoxymethylene, chloral, furfural, glyoxal, n-butyraldehyde, caproaldehyde, allylaldehyde, benzaldehyde, crotonaldehyde, acrolein, tetraoxymethylene, Examples thereof include phenylacetaldehyde, o-tolualdehyde, salicylaldehyde, and the like, and these can be used alone or in combination of two or more.

  Examples of the phenol resin include a resol type phenol resin and a novolac type phenol resin. The resol type phenol resin can be obtained by polymerizing phenol or a derivative thereof and an aldehyde compound in the presence of a basic catalyst. The novolac type phenol resin can be obtained by polymerizing phenol or a derivative thereof and an aldehyde compound in the presence of an acidic catalyst.

  When a self-hardening resol type phenol resin is used, an acid or a curing agent may be added to the resol type phenol resin, or a novolac type phenol resin may be added to reduce the degree of curing. These may be combined and added to the resol type phenol resin.

  As the novolak type phenol resin, a type called a random novolak having the same methylene group bonding position at the ortho-position and the para-position (this type comprises a known organic acid and phenol or a derivative thereof and an aldehyde compound). And / or a method of removing water and unreacted monomers from the resulting condensate by carrying out a condensation reaction at 100 ° C. for several hours using an inorganic acid catalyst) and a methylene group bond at the ortho position. Type called high ortho novolac (this type is an addition condensation of phenol or its derivative and aldehyde compound under weak acidity using metal salt catalyst such as zinc acetate, lead acetate, zinc naphthenate, etc. A method of reacting, adding a direct or acid catalyst, conducting a condensation reaction while further dehydrating, and removing unreacted materials as necessary More is obtained.) It is known.

  Various other organic materials can be used as the organic material having an aromatic ring in the molecular structure.

  The synthetic resin is generally a polymer in which monomers are polymerized. As the organic material having an aromatic ring, an organic material in which several to several tens of monomers are polymerized can be used.

  When phenol or a derivative thereof and an aldehyde compound are polymerized, a by-product may be generated or an unpolymerized product may remain. These by-products and unpolymerized materials can also be used as organic materials, and by reducing waste, the environmental impact can be reduced, and carbon materials can be obtained at low cost, resulting in more industrial utility value. high.

  Wood etc. can be mentioned as a plant-derived organic material. Charcoal obtained by carbonizing these is preferable as a carbon material used for the electrode active material. As the timber, waste timber, waste timber generated in a wood processing process such as sawdust, forest thinned timber, and the like can also be used. As the constituent components of wood, three types of cellulose, hemicellulose and lignin are generally mentioned as the main components, and lignin is an organic material having an aromatic ring and is preferable.

  Wood includes cycads, ginkgo, conifers (cedar, cypress, red pine, etc.), maize, etc., broadleaf trees (Mizunara, beech, poplar, haruni, oak, etc.), herbaceous plants, palms, bamboo Angiosperms and the like such as

  Among the above-mentioned wood, cedar is widely used as a building material, and cedar sawdust is generated in the processing process. Cedar sawdust is a preferable organic material, and can reduce the environmental load and obtain a carbon material at a low cost. Bincho charcoal obtained by carbonizing oak is also preferable as the carbon material used for the electrode active material.

  By using a carbon material obtained by carbonization (firing) of plant residue oil as the carbon material used for the electrode active material, resources can be effectively used and industrial utility value is higher.

  Examples of plant residual oil include various residual oils generated during the manufacture of various petrochemical products such as ethylene. More specifically, there can be mentioned petroleum heavy oil composed of distillation residue oil, fluid catalytic cracking residue oil, hydrodesulfurized oil thereof, or mixed oil thereof. Among these, a residual oil generated during the production of a petrochemical product having an aromatic ring is preferable, and specific examples of the residual oil include a residual oil generated during the production of resorcinol.

The carbon material used for the electrode active material can be obtained by carbonizing (baking) one or more organic materials among the above-described various organic materials. The carbonization temperature is preferably 800 ° C. or higher and 2500 ° C. or lower. Carbonization is preferably performed in an inert gas atmosphere. The organic material may be carbonized as it is, or a heated product obtained by heating the organic material in the presence of an oxidizing gas of 400 ° C. or lower may be carbonized in an inert gas atmosphere. Examples of the inert gas include nitrogen and argon, and examples of the oxidizing gas include air, H ₂ O, CO ₂ , and O ₂ . Carbonization may be performed under reduced pressure. These heating and carbonization may be performed using equipment such as a rotary kiln, a roller hearth kiln, a pusher kiln, a multistage furnace, and a fluidized furnace. A rotary kiln is a general-purpose facility.

  The carbon material obtained by carbonization (firing) may be pulverized as necessary. The pulverization is, for example, an impact friction pulverizer, a centrifugal pulverizer, a ball mill (tube mill, compound mill, conical ball mill, rod mill), vibration mill, colloid mill, friction disk mill, or jet mill. Can be used. A ball mill is a pulverizer generally used. At the time of pulverization, in order to suppress the mixing of the metal powder into the carbon material, the contact portion with the carbon material in these pulverizers may be made of a non-metallic material such as alumina or agate. By the pulverization, the carbon material is pulverized so that the average particle size of the particles constituting the carbon material is usually 50 μm or less, preferably 30 μm or less, particularly preferably 10 μm or less.

・ <Binder>
Examples of the binder include a polymer of a fluorine compound. Examples of the fluorine compound include fluorinated alkyl (C1-18) (meth) acrylate, perfluoroalkyl (meth) acrylate [for example, perfluorododecyl (meth) acrylate, perfluoro n-octyl (meth) acrylate, Perfluoro n-butyl (meth) acrylate], perfluoroalkyl-substituted alkyl (meth) acrylate [for example, perfluorohexylethyl (meth) acrylate, perfluorooctylethyl (meth) acrylate], perfluorooxyalkyl (meth) acrylate [ For example, perfluorododecyloxyethyl (meth) acrylate and perfluorodecyloxyethyl (meth) acrylate, etc.], fluorinated alkyl (C1-C18) crotonate, fluorinated alkyl (carbon Number 1-18) Malate and fumarate, fluorinated alkyl (carbon number 1-18) itaconate, fluorinated alkyl-substituted olefin (about 2-10 carbon atoms, about 1-17 fluorine atoms) such as perfluorohexylethylene, carbon Examples include fluorinated olefins, tetrafluoroethylene, trifluoroethylene, vinylidene fluoride, hexafluoropropylene, and the like in which fluorine atoms are bonded to double bond carbons of about 2 to 10 and about 1 to 20 fluorine atoms. Examples of the binder include a copolymer of a fluorine compound and a monomer containing an ethylenic double bond that does not contain a fluorine atom, which will be described later.

  Other examples of the binder include non-fluorinated polymers. The non-fluorine polymer is a polymer that does not contain fluorine. The electrode in the present invention preferably has a non-fluorinated heavy body, and can reduce the initial irreversible capacity of the sodium secondary battery. Examples of non-fluorine polymers include monomer addition polymers containing ethylenic double bonds that do not contain fluorine atoms. Examples of such monomers include (cyclo) alkyl (C1-22) (meth) acrylate [for example, methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, iso-butyl (Meth) acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, isodecyl (meth) acrylate, lauryl (meth) acrylate, octadecyl (meth) acrylate, etc.]; aromatic ring-containing (meth) acrylate [for example, benzyl (Meth) acrylate, phenylethyl (meth) acrylate, etc.]; mono (meth) acrylate of alkylene glycol or dialkylene glycol (alkylene group having 2 to 4 carbon atoms) [for example, 2-hydroxyethyl (meth) acrylate, 2- Hi Roxypropyl (meth) acrylate, diethylene glycol mono (meth) acrylate]; (poly) glycerin (degree of polymerization 1 to 4) mono (meth) acrylate; polyfunctional (meth) acrylate [for example, (poly) ethylene glycol (degree of polymerization 1) ~ 100) di (meth) acrylate, (poly) propylene glycol (degree of polymerization 1-100) di (meth) acrylate, 2,2-bis (4-hydroxyethylphenyl) propane di (meth) acrylate, trimethylolpropane tri ( (Meth) acrylate monomers such as (meth) acrylate]; (meth) acrylamide (meth) acrylamide, (meth) acrylamide derivatives [eg, N-methylol (meth) acrylamide, diacetone acrylamide, etc.] Acrylamide monomer; ) Cyano group-containing monomers such as acrylonitrile, 2-cyanoethyl (meth) acrylate, 2-cyanoethylacrylamide; styrene and styrene derivatives having 7 to 18 carbon atoms [for example, α-methylstyrene, vinyltoluene, p-hydroxystyrene and Styrene monomers such as divinylbenzene] Diene monomers such as alkadienes having 4 to 12 carbon atoms [for example, butadiene, isoprene, chloroprene, etc.]; Carboxylic acid (2 to 12 carbon atoms) vinyl esters [for example, , Vinyl acetate, vinyl propionate, vinyl butyrate and vinyl octoate, etc.], carboxylic acid (2 to 12 carbon atoms) (meth) allyl ester [for example, (meth) allyl acetate, (meth) allyl propionate and octanoic acid ( Alkenyl ester monomers such as (meth) allyl etc.]; Epoxy group-containing monomers such as cidyl (meth) acrylate and (meth) allyl glycidyl ether; monoolefins having 2 to 12 carbon atoms [for example, ethylene, propylene, 1-butene, 1-octene and 1-dodecene, etc.] Monoolefins; chlorine, bromine or iodine atom-containing monomers, halogen atom-containing monomers other than fluorine such as vinyl chloride and vinylidene chloride; (meth) acrylic acid such as acrylic acid and methacrylic acid and alkali salts thereof; butadiene And conjugated double bond-containing monomers such as isoprene. The addition polymer may be a copolymer such as an ethylene / vinyl acetate copolymer, a styrene / butadiene copolymer, or an ethylene / propylene copolymer. The carboxylic acid vinyl ester polymer may be partially or completely saponified, such as polyvinyl alcohol.

  Other examples of the binder include, for example, polysaccharides such as starch, methylcellulose, carboxymethylcellulose, hydroxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, carboxymethylhydroxyethylcellulose, nitrocellulose, and derivatives thereof; phenol resin; melamine resin; polyurethane resin A urea resin; a polyamide resin; a polyimide resin; a polyamideimide resin; a petroleum pitch; and a coal pitch. A plurality of types of binders may be used as the binder.

  The blending ratio of the binder in the electrode of the present invention is usually about 0.5 to 30 parts by weight, preferably about 2 to 20 parts by weight with respect to 100 parts by weight of the carbon material.

<Method for producing electrode>
The electrode of the present invention will be described. The electrode of the present invention is, for example, an electrode mixture containing a carbon material that can be doped and dedoped with sodium ions, a binder and, if necessary, a conductive material, etc. carried on a current collector, It is in the form of a sheet. Examples of the method for producing the electrode of the present invention include a method in which an electrode mixture paste formed by adding a solvent to a carbon material, a binder, a conductive material, and the like is applied to a current collector or dipped in a current collector and then dried. be able to. By drying, the solvent in the electrode mixture paste is removed, and the electrode mixture is bound to the current collector to obtain an electrode.

  As the solvent used in the electrode mixture paste, for example, an organic solvent can be used. As polar solvents, amides such as N-methyl-2-pyrrolidone, N, N-dimethylacetamide, dimethylformamide; isopropyl alcohol, ethyl Examples include alcohols such as alcohol and methyl alcohol; ethers such as propylene glycol dimethyl ether; ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone. Examples of the nonpolar solvent include hexane and toluene. Moreover, water can also be used as a solvent, and it is more preferable to use water in order to suppress electrode manufacturing cost.

  Examples of the material for the current collector of the electrode of the present invention include metals such as nickel, aluminum, titanium, copper, gold, silver, platinum, aluminum alloy, and stainless steel, such as carbon materials, activated carbon fibers, nickel, aluminum, and zinc. Copper, tin, lead or alloys thereof are formed by plasma spraying or arc spraying, for example, rubber or resin such as styrene-ethylene-butylene-styrene copolymer (SEBS) is dispersed in a conductive material. Examples include conductive films. Examples of the shape of the current collector include a foil shape, a flat plate shape, a mesh shape, a net shape, a lath shape, a punching shape, an embossed shape, and a combination thereof (for example, a mesh-like flat plate). It is done. Concavities and convexities may be formed on the surface of the current collector by etching.

  The method for applying the electrode mixture paste of the present invention to a current collector is not particularly limited. Examples thereof include a doctor blade method, a slit die coating method, a screen coating method, a curtain coating method, a knife coating method, a gravure coating method, and an electrostatic spray method. Moreover, as drying performed after application | coating, you may carry out by heat processing, and you may carry out by ventilation drying, vacuum drying, etc. When drying is performed by heat treatment, the temperature is usually about 50 to 150 ° C. Moreover, you may press after drying. Examples of the pressing method include a mold press and a roll press. By the method mentioned above, the electrode of the present invention can be manufactured. Moreover, the thickness of an electrode is about 5-500 micrometers normally.

<Sodium secondary battery of the present invention>
A sodium secondary battery has a first electrode and a second electrode, and usually further includes an electrolyte and a separator. In the sodium secondary battery of the present invention, the first electrode is the electrode for the sodium secondary battery of the present invention. When the second electrode has sodium metal or a sodium alloy, the first electrode acts as a positive electrode, and when the second electrode has a sodium-containing transition metal compound that can be doped and dedoped with sodium ions, The electrode acts as a negative electrode.

  A sodium secondary battery usually has an electrode group obtained by laminating and winding a negative electrode, a separator, and a positive electrode. The electrode group is housed in a battery can, and an electrolyte solution composed of an organic solvent containing an electrolyte is used. It can be manufactured by impregnating the electrode group.

  Here, as the shape of the electrode group, for example, a cross section when the electrode group is cut in a direction perpendicular to the winding axis is a circle, an ellipse, a rectangle, a rectangle with rounded corners, or the like. The shape can be mentioned. In addition, examples of the shape of the battery include a paper shape, a coin shape, a cylindrical shape, and a square shape.

<Sodium secondary battery of the present invention-positive electrode>
In the sodium secondary battery of the present invention, when the second electrode has a sodium-containing transition metal compound that can be doped and dedoped with sodium ions, the sodium secondary battery electrode of the present invention acts as a negative electrode, The second electrode acts as a positive electrode. As the positive electrode, an electrode in which a positive electrode mixture containing a sodium-containing transition metal compound capable of doping and dedoping sodium ions is supported on a positive electrode current collector can be used.

Examples of the sodium-containing transition metal compound include the following compounds.
That, NaFeO _2, NaMnO _2, NaNiO ₂ and NaCoO oxide represented by NaM ¹ _a1 O _2, such as _2, oxide represented by ^{_{Na 0.44 Mn 1-a2 M 1}} a2 O 2, Na 0.7 Mn 1- an oxide represented by _a2 M ¹ _a2 O _2.05 (M ¹ is one or more transition metal elements, 0 <a1 <1, 0 ≦ a2 <1);
Oxides represented by Na _b M ² _c Si ₁₂ O ₃₀ such as Na ₆ Fe ₂ Si ₁₂ O ₃₀ and Na ₂ Fe ₅ Si ₁₂ O ₃₀ (M ² is one or more transition metal elements, 2 ≦ b ≦ 6, 2 ≦ c ≦ 5);
Na ₂ Fe ₂ Si ₆ O ₁₈ and _{Na 2 MnFeSi 6 O 18 Na d} M 3 e Si 6 O 18 oxide represented by such (M ³ is one or more transition metal elements, 2 ≦ d ≦ 6, 1 ≦ e ≦ 2);
^{_{Na 2 FeSiO Na f M 4 g}} Si oxide represented by ₂ O _6, such as ₆ (M ⁴ is at least one element selected from the group consisting of transition metal elements, Mg and Al, 1 ≦ f ≦ 2, 1 ≦ g ≦ 2)
Phosphates such as NaFePO ₄ , NaMnPO ₄ , Na ₃ Fe ₂ (PO ₄ ) ₃ ;
Fluorophosphates such as Na ₂ FePO ₄ F, Na ₂ VPO ₄ F, Na ₂ MnPO ₄ F, Na ₂ CoPO ₄ F, Na ₂ NiPO ₄ F;
Fluorosulfates such as NaFeSO ₄ F, NaMnSO ₄ F, NaCoSO ₄ F, NaFeSO ₄ F;
Borates such as NaFeBO ₄ and Na ₃ Fe ₂ (BO ₄ ) ₃ ;
Na ₃ FeF _6, Na ₂ fluorides represented by Na _h M ⁵ F ₆ of MnF ₆ such (M ⁵ is one or more transition metal elements, 2 ≦ h ≦ 3); and the like, which is 1 Species or a mixture of two or more can be used.

Among these, an oxide represented by NaM ¹ O ₂ (M ¹ represents one or more transition metal elements) is preferable. Preferable specific examples thereof include NaMnO ₂ , NaNiO ₂ , NaCoO _2, and NaFe ₁ -pq Mn _p Ni _q O ₂ having a α-NaFeO ₂ type structure (p and q are values satisfying the following relationship). And oxides such as 0 ≦ p + q ≦ 1, 0 ≦ p ≦ 1, 0 ≦ q ≦ 1).

  In the sodium transition metal compound, a part of the transition metal element may be substituted with a metal element other than the transition metal element as long as the effects of the invention are not impaired. By substitution, the characteristics of the battery of the present invention may be improved. Examples of metals other than the transition metal elements include Li, K, Ag, Mg, Ca, Sr, Ba, Al, Ga, In, Zn, Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, and Tb. , Ho, Er, Tm, Yb and Lu.

  The positive electrode current collector is not particularly limited as long as it has high conductivity and can be easily processed into a thin film, and metals such as Al, Ni, stainless steel, and Cu can be used. Examples of the shape of the positive electrode current collector include a foil shape, a flat plate shape, a mesh shape, a net shape, a lath shape, a punching metal shape, an embossed shape, and a combination thereof (for example, a mesh flat plate). Is mentioned.

  The positive electrode mixture may contain a conductive material, and a carbon material can be used as the conductive material. Examples of the carbon material include fibrous carbon materials such as graphite powder, carbon black, and carbon nanotubes. Usually, the ratio of the conductive material in the electrode mixture is 5 to 20 parts by weight with respect to 100 parts by weight of the electrode active material. In the case where the fine carbon material or the fibrous carbon material as described above is used as the conductive material, this ratio can be lowered.

  Examples of the binder used for the positive electrode include the same binders as those used for the electrode of the present invention.

  The positive electrode is manufactured by supporting a positive electrode mixture containing a positive electrode active material capable of doping and dedoping sodium ions on a positive electrode current collector. As a method for supporting the positive electrode mixture on the positive electrode current collector, for example, a positive electrode mixture paste comprising a positive electrode active material, a conductive material, a binder and a solvent is prepared and kneaded. The method of apply | coating to a body and drying is mentioned. The method for applying the positive electrode mixture paste to the current collector is not particularly limited. Examples thereof include a slit die coating method, a screen coating method, a curtain coating method, a knife coating method, a gravure coating method, and an electrostatic spray method. Moreover, as drying performed after application | coating, you may carry out by heat processing, and you may carry out by ventilation drying, vacuum drying, etc. When drying is performed by heat treatment, the temperature is usually about 50 to 150 ° C. Moreover, you may press after drying. Examples of the pressing method include a mold press and a roll press. By the method mentioned above, the electrode of the present invention can be manufactured. The thickness of the electrode mixture is usually about 5 to 500 μm.

<Sodium Secondary Battery-Separator of the Present Invention>
Examples of the separator that can be used in the sodium secondary battery of the present invention include porous films, nonwoven fabrics, woven fabrics, and the like made of materials such as polyolefin resins such as polyethylene and polypropylene, fluororesins, and nitrogen-containing aromatic polymers. A material having a form can be used. Moreover, it is good also as a single layer or laminated separator which used 2 or more types of these materials. Examples of the separator include separators described in JP 2000-30686 A, JP 10-324758 A, and the like. The thickness of the separator is preferably as thin as possible as long as the mechanical strength is maintained in that the volume energy density of the battery is increased and the internal resistance is reduced. In general, the thickness of the separator is preferably about 5 to 200 μm, more preferably about 5 to 40 μm.

  The separator preferably has a porous film containing a thermoplastic resin. In a secondary battery, normally, when an abnormal current flows in the battery due to a short circuit between the positive electrode and the negative electrode, the current is interrupted to prevent an excessive current from flowing (shut down). is important. Therefore, the separator shuts down at the lowest possible temperature when the normal use temperature is exceeded (when the separator has a porous film containing a thermoplastic resin, the micropores of the porous film are blocked). Even after the shutdown, even if the temperature in the battery rises to a certain high temperature, it is required to maintain the shutdown state without breaking the film due to the temperature, in other words, to have high heat resistance. By using a separator having a laminated porous film in which a heat resistant porous layer containing a heat resistant resin and a porous film containing a thermoplastic resin are laminated as a separator, the thermal breakage of the secondary battery of the present invention It becomes possible to prevent more. Here, the heat-resistant porous layer may be laminated on both surfaces of the porous film.

<Sodium secondary battery-separator-laminated porous film separator of the present invention>
Hereinafter, a separator composed of a laminated porous film in which a heat resistant porous layer containing a heat resistant resin and a porous film containing a thermoplastic resin are laminated will be described. Here, the thickness of this separator is usually 40 μm or less, preferably 20 μm or less. Moreover, when the thickness of the heat resistant porous layer is A (μm) and the thickness of the porous film is B (μm), the value of A / B is preferably 0.1-1. Furthermore, from the viewpoint of ion permeability, this separator preferably has an air permeability of 50 to 300 seconds / 100 cc, more preferably 50 to 200 seconds / 100 cc in terms of air permeability by the Gurley method. . The porosity of this separator is usually 30 to 80% by volume, preferably 40 to 70% by volume.

(Heat resistant porous layer)
In the laminated porous film, the heat resistant porous layer contains a heat resistant resin. In order to further improve the ion permeability, the heat-resistant porous layer is preferably a thin heat-resistant porous layer having a thickness of 1 to 10 μm, more preferably 1 to 5 μm, and particularly 1 to 4 μm. The heat-resistant porous layer has fine pores, and the size (diameter) of the pores is usually 3 μm or less, preferably 1 μm or less. Furthermore, the heat resistant porous layer can also contain a filler described later.

  Examples of the heat resistant resin contained in the heat resistant porous layer include polyamide, polyimide, polyamideimide, polycarbonate, polyacetal, polysulfone, polyphenylene sulfide, polyetheretherketone, aromatic polyester, polyethersulfone and polyetherimide. In order to further improve the heat resistance, polyamide, polyimide, polyamideimide, polyethersulfone and polyetherimide are preferable, and polyamide, polyimide and polyamideimide are more preferable. Even more preferably, the heat-resistant resin is a nitrogen-containing aromatic polymer such as aromatic polyamide (para-oriented aromatic polyamide, meta-oriented aromatic polyamide), aromatic polyimide, aromatic polyamideimide, and particularly preferably aromatic. Polyamide, particularly preferably para-oriented aromatic polyamide (hereinafter sometimes referred to as para-aramid). Examples of the heat resistant resin include poly-4-methylpentene-1 and cyclic olefin polymers. By using these heat resistant resins, the heat resistance can be increased, that is, the thermal film breaking temperature can be increased.

  The thermal film breaking temperature depends on the kind of the heat-resistant resin, but the thermal film breaking temperature is usually 160 ° C. or higher. By using the nitrogen-containing aromatic polymer as the heat-resistant resin, the thermal film breaking temperature can be increased to about 400 ° C. at the maximum. Further, when poly-4-methylpentene-1 is used, the thermal film breaking temperature can be increased up to about 250 ° C., and when a cyclic olefin-based polymer is used up to about 300 ° C., respectively.

  The para-aramid is obtained by condensation polymerization of a para-oriented aromatic diamine and a para-oriented aromatic dicarboxylic acid halide, and the amide bond is in the para position of the aromatic ring or an oriented position equivalent thereto (for example, 4,4 ′ -Substantially consisting of repeating units bonded in the opposite direction, such as biphenylene, 1,5-naphthalene, 2,6-naphthalene, etc., in an orientation extending coaxially or in parallel. As para-aramid, para-aramid having a para-orientation type or a structure according to para-orientation type, specifically, poly (paraphenylene terephthalamide), poly (parabenzamide), poly (4,4′-benzanilide terephthalamide) , Poly (paraphenylene-4,4′-biphenylenedicarboxylic amide), poly (paraphenylene-2,6-naphthalenedicarboxylic acid amide), poly (2-chloro-paraphenylene terephthalamide), paraphenylene terephthalamide / 2 An example is a 1,6-dichloroparaphenylene terephthalamide copolymer.

  The aromatic polyimide is preferably a wholly aromatic polyimide produced by condensation polymerization of an aromatic dianhydride and a diamine. Specific examples of the dianhydride include pyromellitic dianhydride, 3,3 ′, 4,4′-diphenylsulfone tetracarboxylic dianhydride, 3,3 ′, 4,4′-benzophenone tetracarboxylic acid Examples include dianhydrides, 2,2′-bis (3,4-dicarboxyphenyl) hexafluoropropane and 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride. Examples of the diamine include oxydianiline, paraphenylenediamine, benzophenonediamine, 3,3′-methylenedianiline, 3,3′-diaminobenzophenone, 3,3′-diaminodiphenylsulfone, and 1,5-naphthalenediamine. Can be mentioned. Moreover, a polyimide soluble in a solvent can be preferably used. Examples of such a polyimide include a polycondensate polyimide of 3,3 ′, 4,4′-diphenylsulfonetetracarboxylic dianhydride and an aromatic diamine.

  Examples of the aromatic polyamideimide include those obtained from condensation polymerization using aromatic dicarboxylic acid and aromatic diisocyanate, and those obtained from condensation polymerization using aromatic diacid anhydride and aromatic diisocyanate. Can be mentioned. Specific examples of the aromatic dicarboxylic acid include isophthalic acid and terephthalic acid. Specific examples of the aromatic dianhydride include trimellitic anhydride. Specific examples of the aromatic diisocyanate include 4,4'-diphenylmethane diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, orthotolylene diisocyanate, and m-xylene diisocyanate.

  The filler that may be contained in the heat-resistant porous layer may be selected from any of organic powder, inorganic powder, or a mixture thereof. The average particle diameter of the particles constituting the filler is preferably 0.01 to 1 μm. Examples of the shape of the filler include a substantially spherical shape, a plate shape, a columnar shape, a needle shape, a whisker shape, and a fibrous shape, and any particle can be used. Preferably there is.

  Examples of the organic powder as the filler include, for example, styrene, vinyl ketone, acrylonitrile, methyl methacrylate, ethyl methacrylate, glycidyl methacrylate, glycidyl acrylate, methyl acrylate and the like alone or in combination of two or more types; polytetrafluoroethylene, Fluororesin such as tetrafluoroethylene-6 fluorinated propylene copolymer, tetrafluoroethylene-ethylene copolymer, polyvinylidene fluoride, etc .; melamine resin; urea resin; polyolefin; powder made of organic matter such as polymethacrylate Can be mentioned. An organic powder may be used independently and can also be used in mixture of 2 or more types. Among these organic powders, polytetrafluoroethylene powder is preferable from the viewpoint of chemical stability.

  Examples of inorganic powders as fillers include powders made of inorganic substances such as metal oxides, metal nitrides, metal carbides, metal hydroxides, carbonates, sulfates, and specific examples include alumina and silica. , Titanium dioxide, or calcium carbonate powder. An inorganic powder may be used independently and can also be used in mixture of 2 or more types. Among these inorganic powders, alumina powder is preferable from the viewpoint of chemical stability. It is more preferable that all of the particles constituting the filler are alumina particles, and it is even more preferable that all of the particles constituting the filler are alumina particles, and part or all of them are substantially spherical alumina particles.

  The filler content in the heat-resistant porous layer depends on the specific gravity of the filler material. For example, when all of the particles constituting the filler are alumina particles, the total weight of the heat-resistant porous layer is 100, The weight of the filler is usually 20 to 95 parts by weight, preferably 30 to 90 parts by weight. These ranges can be appropriately set depending on the specific gravity of the filler material.

(Porous film)
In the laminated porous film, the porous film contains a thermoplastic resin. The thickness of this porous film is usually 3 to 30 μm, more preferably 3 to 20 μm. Similar to the heat resistant porous layer, the porous film has fine pores, and the pore size is usually 3 μm or less, preferably 1 μm or less. The porosity of the porous film is usually 30 to 80% by volume, preferably 40 to 70% by volume. In the nonaqueous electrolyte secondary battery, when the normal use temperature is exceeded, the porous film plays a role of closing the fine pores by softening the thermoplastic resin constituting the porous film.

  Examples of the thermoplastic resin contained in the porous film include those that soften at 80 to 180 ° C., and those that do not dissolve in the electrolyte solution in the nonaqueous electrolyte secondary battery may be selected. Specifically, examples of the thermoplastic resin include polyolefins such as polyethylene and polypropylene, and thermoplastic polyurethane, and a mixture of two or more of these may be used. In order to soften and shut down at a lower temperature, polyethylene is preferable as the thermoplastic resin. Specific examples of the polyethylene include polyethylene such as low density polyethylene, high density polyethylene, and linear polyethylene, and also include ultrahigh molecular weight polyethylene. In order to further increase the puncture strength of the porous film, the thermoplastic resin preferably contains at least ultra high molecular weight polyethylene. In addition, in terms of production of the porous film, the thermoplastic resin may preferably contain a wax made of polyolefin having a low molecular weight (weight average molecular weight of 10,000 or less).

<Sodium secondary battery of the present invention-electrolyte or solid electrolyte>
In the electrolyte solution that can be used in the sodium secondary battery of the present invention, electrolytes include NaClO ₄ , NaPF ₆ , NaAsF ₆ , NaSbF ₆ , NaBF ₄ , NaCF ₃ SO ₃ , NaN (SO ₂ CF ₃ ) ₂ , lower Examples thereof include aliphatic carboxylic acid sodium salt and NaAlCl _4, and a mixture of two or more of these may be used. Among these, it is preferable to use those containing at least one selected from the group consisting of NaPF ₆ , NaAsF ₆ , NaSbF ₆ , NaBF ₄ , NaCF ₃ SO ₃ and NaN (SO ₂ CF ₃ ) ₂ containing fluorine. Moreover, in this invention, it is preferable to use electrolyte as the state (liquid state) melt | dissolved in the organic solvent, ie, a non-aqueous electrolyte.

  In the electrolyte solution that can be used in the sodium secondary battery of the present invention, examples of the organic solvent include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, isopropyl methyl carbonate, vinylene carbonate, 4-trifluoromethyl. Carbonates such as -1,3-dioxolan-2-one and 1,2-di (methoxycarbonyloxy) ethane; 1,2-dimethoxyethane, 1,3-dimethoxypropane, pentafluoropropyl methyl ether, 2,2 , 3,3-tetrafluoropropyldifluoromethyl ether, ethers such as tetrahydrofuran and 2-methyltetrahydrofuran; esters such as methyl formate, methyl acetate and γ-butyrolactone; Nitriles such as tolyl and butyronitrile; amides such as N, N-dimethylformamide and N, N-dimethylacetamide; carbamates such as 3-methyl-2-oxazolidone; sulfolane, dimethyl sulfoxide and 1,3-propane sultone Sulfur-containing compounds such as those described above; or those obtained by further introducing a fluorine substituent into the above organic solvent can be used. Two or more of these may be mixed and used as the organic solvent.

  The concentration of the electrolyte in the nonaqueous electrolytic solution is usually about 0.1 to 2 mol / L, preferably about 0.3 to 1.5 mol / L.

A solid electrolyte may be used instead of the above electrolytic solution. As the solid electrolyte, for example, a polymer electrolyte such as a polyethylene oxide polymer compound, a polymer compound including at least one of a polyorganosiloxane chain or a polyoxyalkylene chain can be used. Moreover, what is called a gel type which hold | maintained the nonaqueous electrolyte solution in the polymer | macromolecule can also be used. Further, sulfide electrolytes such as Na ₂ S—SiS ₂ , Na ₂ S—GeS ₂ , Na ₂ S—P ₂ S ₅ , Na ₂ S—B ₂ S ₃ , or Na ₂ S—SiS ₂ —Na ₃ PO _4. When using an inorganic compound electrolyte containing sulfide such as Na ₂ S—SiS ₂ —Na ₂ SO ₄ and a NASICON type electrolyte such as NaZr ₂ (PO ₄ ) ₃ , safety may be further improved. In the nonaqueous electrolyte secondary battery of the present invention, when a solid electrolyte is used, the solid electrolyte may serve as a separator, and in that case, the separator may not be required.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to a following example, unless the summary is changed.

<Production Example 1> (Production of Electrode Active Material C ¹ )
Example of production of tetraphenylcalix [4] resorcinarenes (compound (1): PCRA) In a four-necked flask, 200 g of resorcinol, 1.5 L of methyl alcohol and 194 g of benzaldehyde were placed in a nitrogen stream and cooled with ice. 36.8 g of hydrochloric acid was added dropwise. After completion of dropping, the temperature was raised to 65 ° C., and then kept at that temperature for 5 hours. 1 L of water was added to the obtained reaction mixture, and the precipitate was collected by filtration, washed with water until the filtrate became neutral, and dried to obtain 294 g of tetraphenylcalix [4] resorcinarenes (PCRA). The obtained PCRA was heated in an atmosphere of air in a rotary kiln at 300 ° C. for 1 hour (pretreatment step), and then the rotary kiln was replaced with an argon atmosphere and heated at 1000 ° C. for 4 hours. Then ground in a ball mill (agate balls, 28 rpm, 5 minutes), to obtain an electrode active material ^{C 1.}

<Example 1> (Production of Sodium Secondary battery electrode ^{E 1)}
As an electrode active material, was prepared ^{C 1,} sodium polyacrylate as binders in Production Example 1 (Wako Ltd., polymerization degree 22,000～70,000), the electrode mixture paste using water as a solvent. A binder liquid in which the binder is dissolved in water is prepared, and weighed to have a composition of electrode active material C ¹ : binder: water = 97: 3: 150 (weight ratio), and a disperse mat (manufactured by VMA-GETZMANN) ) Was used to stir and mix to obtain an electrode mixture paste. The rotation conditions of the rotating blades were 2,000 rpm for 5 minutes. The obtained electrode mixture paste was applied to a copper foil using a doctor blade, dried at 60 ° C. for 2 hours, and then cut into a 4 cm width using a roll press, and then the roll press (SA-602, using tester Sangyo Co., Ltd.), to obtain an electrode E ¹ for sodium secondary batteries by rolling at 0.5 MPa.

<Example 2> (Production of Sodium Secondary battery electrode ^{E 2)}
As an electrode active material, commercially available carbonaceous material powder (Nippon Carbon Co., Ltd., trade name: NICABEADS ICB-0510) except for using the obtained by the same procedure as in Example 1, a sodium secondary battery electrode E ² It was.

<Example 3> (Production of Sodium Secondary battery electrode ^{E 3)}
As an electrode active material, a commercially available carbon material powder (trade name: Nikabeads ICB-0510, manufactured by Nippon Carbon Co., Ltd.) was used, and the electrode E for sodium secondary battery was operated in the same manner as in Example 1 except that it was not pressed. ² was obtained.

<Example 4> (preparation of sodium secondary battery electrode ^{E 4)}
As an electrode active material, a commercially available carbon material powder (manufactured by Nippon Carbon Co., Ltd., trade name: Nikabeads ICB-0510) was used, and an electrode cut into a 4 cm width was used using a roll press (SA-602, manufactured by Tester Sangyo Co., Ltd.). Te, except that the 0.26MPa is in the same operation as in example 1 to obtain a electrode ^{E 4} sodium secondary battery.

<Example 5> (Production of Sodium Secondary battery electrode ^{E 5)}
As an electrode active material, a commercially available carbon material powder (manufactured by Nippon Carbon Co., Ltd., trade name: Nikabeads ICB-0510), PVdF # 1300 (manufactured by Kureha) as a binder, and NMP (lithium battery grade, manufactured by Kishida Chemical Co., Ltd.) as a solvent ) Was used. A binder solution in which the binder is dissolved in NMP is prepared, and weighed so that the composition of carbon material: binder: NMP = 90: 10: 100 (weight ratio) is obtained. K. An electrode mixture paste was obtained by stirring and mixing using a film mix 30-25 type (manufactured by PRIMIX Corporation). The rotation condition of the rotating wheel was 5,000 rpm for 3 minutes. The obtained electrode mixture paste was applied to a copper foil using a doctor blade, dried at 60 ° C. for 2 hours, and then cut to a width of 2.5 cm, and a roll press (SA-602, Tester Sangyo Co., Ltd.). Ltd.) was used to obtain an electrode E ⁵ for sodium secondary batteries by rolling 4 times with 0.5 MPa.

<Example 6> (Production of Sodium Secondary battery electrode ^{E 6)}
The sodium secondary battery was operated in the same manner as in Example 5 except that the composition was carbon material: binder: NMP = 80: 20: 100 (weight ratio) and the press pressure was 0.025 MPa. to obtain a use electrodes ^{E 6.}

<Comparative Example 1> (Production of Sodium Secondary battery electrode ^{D 1)}
Carbon material: binder: NMP = 80: 20: 100 except that weighed so as to have the composition (weight ratio), in the same operation as in Example 5, to obtain a sodium secondary battery electrode ^{D 1.}

Production of battery: Coin cells were used for battery evaluation of the electrodes. An electrode is placed in a depression of the lower part of a coin cell (manufactured by Hosen Co., Ltd.) with the copper foil facing downward, and 1M NaPF ₆ / propylene carbonate as an electrolytic solution, polypropylene porous film as a separator (thickness 20 μm) ) And metallic sodium (manufactured by Aldrich) as a negative electrode were combined to produce a battery. The battery was assembled in a glove box in an argon atmosphere.

Evaluation and charging / discharging conditions of sodium secondary battery: Discharge is CC-CV (constant current-constant voltage: constant current-constant voltage) at 0.05C rate (rate of complete discharge in 20 hours) from rest potential to 0.005V Discharge was performed. Charging was performed at a rate of 0.05 C (speed of complete charging in 20 hours), and CC (constant current: constant current) charging was performed, and the voltage was cut off at 1.5 V. After one cycle of the above charging / discharging, as a test of the discharge load characteristics, CC (constant current) discharge at a 0.1 C rate up to 0.005 V, and CC (constant current) charging at a 5 C rate up to 1.5 V are performed. went. Table 1 Sodium secondary battery electrodes E ^{1 to} E ⁶ , D ¹ porosity, electrode density (← Describe detailed measurement method), electrode mixture thickness, sodium prepared using each electrode The discharge load characteristic of a secondary battery is shown. The electrode density was calculated by measuring the weight, area, and thickness of the obtained electrode mixture and dividing the weight of the electrode mixture by the volume (area × thickness) of the electrode mixture. In the present invention, the discharge load characteristic indicates the dedoping characteristic of sodium ions from the carbon material. In Examples 1 to 6 and Comparative Example 1, the charge capacity at the time of 5C rate charging is simply 0.05C rate. It was calculated by dividing by the charge capacity at the time of charging.

  From Table 1, it was found that the discharge load characteristics of the sodium secondary battery can be improved by using the sodium secondary battery electrode of the present invention.

Production Example 2 (Production of laminated porous film)
(1) Manufacture of coating solution for heat-resistant porous layer After 272.7 g of calcium chloride was dissolved in 4200 g of NMP, 132.9 g of paraphenylenediamine was added and completely dissolved. To the obtained solution, 243.3 g of terephthalic acid dichloride was gradually added and polymerized to obtain para-aramid, which was further diluted with NMP to obtain a para-aramid solution having a concentration of 2.0% by weight. To 100 g of the obtained para-aramid solution, 2 g of first alumina powder (Nippon Aerosil Co., Ltd., alumina C, average particle size 0.02 μm) and 2 g of second alumina powder (Sumitomo Chemical Co., Ltd. Sumiko Random, AA03, average particles) 4 g in total as a filler is added and mixed, treated three times with a nanomizer, filtered through a 1000 mesh wire net, degassed under reduced pressure, and a slurry-like coating liquid for heat-resistant porous layer is obtained. Manufactured. The weight of the alumina powder (filler) with respect to the total weight of the para-aramid and the alumina powder was 67% by weight.

(2) Production and Evaluation of Laminated Porous Film As the porous film, a polyethylene porous film (film thickness 12 μm, air permeability 140 seconds / 100 cc, average pore diameter 0.1 μm, porosity 50%) was used. . The polyethylene porous film was fixed on a PET film having a thickness of 100 μm, and the slurry-like coating liquid for heat-resistant porous layer was applied onto the porous film by a bar coater manufactured by Tester Sangyo Co., Ltd. While the coated porous film on the PET film is integrated, it is immersed in a poor solvent of water to deposit a para-aramid porous film (heat-resistant porous layer), and then the solvent is dried to obtain a PET film. And a laminated porous film in which the heat resistant porous layer and the porous film were laminated was obtained. The thickness of the laminated porous film was 16 μm, and the thickness of the para-aramid porous film (heat resistant porous layer) was 4 μm. The laminated porous film had an air permeability of 180 seconds / 100 cc and a porosity of 50%. When the cross section of the heat-resistant porous layer in the laminated porous film was observed with a scanning electron microscope (SEM), a relatively small fine hole of about 0.03 to 0.06 μm and a relatively large fine of about 0.1 to 1 μm. It was found to have pores. In addition, evaluation of the laminated porous film was performed as follows (A)-(C).

(A) Thickness measurement The thickness of the laminated porous film and the thickness of the porous film were measured in accordance with JIS standards (K7130-1992). Moreover, as the thickness of the heat resistant porous layer, a value obtained by subtracting the thickness of the porous film from the thickness of the laminated porous film was used.
(B) Measurement of air permeability by Gurley method The air permeability of the laminated porous film was measured with a digital timer type Gurley type densometer manufactured by Yasuda Seiki Seisakusho, based on JIS P8117.
(C) Porosity A sample of the obtained laminated porous film was cut into a square having a side length of 10 cm, and the weight W (g) and the thickness D (cm) were measured. The weight of each layer in the sample (Wi; i is an integer from 1 to n) is determined, and the volume of each layer is determined from Wi and the true specific gravity (g / cm ³ ) of the material of each layer. The porosity (volume%) was obtained from the following formula.
Porosity (volume%) = 100 × {1− (W1 / true specific gravity 1 + W2 / true specific gravity 2 + ·· + Wn / true specific gravity n) / (10 × 10 × D)}

  In the said Example, if the laminated porous film as obtained by the manufacture example is used as a separator, the sodium secondary battery which can prevent a thermal membrane breakage can be obtained.

Claims (6)

  An electrode in which an electrode mixture containing a carbon material that can be doped and dedoped with sodium ions as a main component is supported on a current collector, and the porosity of the electrode mixture is 25% or more and 50% or less. Battery electrode. 2. The electrode for a sodium secondary battery according to claim 1, wherein a density of the electrode mixture is 0.80 g / cm ³ or more and 1.25 g / cm ³ or less.   The electrode for a sodium secondary battery according to claim 1 or 2, wherein the electrode mixture has a thickness of 25 µm to 130 µm.   A first electrode, a second electrode, and a nonaqueous electrolytic solution are provided, the first electrode is the electrode according to any one of claims 1 to 3, and the second electrode can be doped and dedoped with sodium ions. A sodium secondary battery which is an electrode having an electrode active material having sodium.   The sodium secondary battery according to claim 4, wherein the sodium-containing electrode active material is a sodium-containing transition metal compound.   The sodium secondary battery according to claim 4 or 5, further comprising a separator between the first electrode and the second electrode.