JP2009209038A - Composite metal oxide and sodium secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sodium secondary battery that can reduce the amount of lithium used and has a higher discharge capacity retention upon repetition of charge and discharge than the conventional one and a composite metal oxide usable as a positive electrode active material for the sodium secondary battery. <P>SOLUTION: The composite metal oxide comprises Na and M<SP>1</SP>(wherein M<SP>1</SP>represents three or more elements selected from the group consisting of Mn, Fe, Co and Ni) and has a Na:M<SP>1</SP>molar ratio of a:1 (wherein a is a value in a range of more than 0.5 and less than 1). The composite metal oxide is represented by formula (1): Na<SB>a</SB>M<SP>1</SP>O<SB>2</SB>(wherein M<SP>1</SP>and a are same as above, respectively). The positive electrode active material for the sodium secondary battery comprises the composite metal oxide. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a composite metal oxide and a sodium secondary battery.

  Composite metal oxides are used as positive electrode active materials for secondary batteries. Among secondary batteries, lithium secondary batteries have already been put into practical use as small power sources for mobile phones and notebook computers, and furthermore, large power sources such as electric power sources for electric vehicles and hybrid vehicles, and power sources for distributed power storage. Since it can be used as a product, the demand is increasing. However, in the lithium secondary battery, the raw material of the positive electrode active material contains a large amount of rare metal elements such as lithium, and there is concern about the supply of the raw material to meet the increase in demand for large-scale power supplies. .

  On the other hand, a sodium secondary battery has been studied as a secondary battery that can solve the above supply concerns. Sodium secondary batteries can be made of abundant and inexpensive materials, and it is expected that large-scale power supplies can be supplied in large quantities by putting them into practical use.

  As a positive electrode active material for a sodium secondary battery, Patent Document 1 discloses a raw material having a composition ratio of Na, Mn and Co (Na: Mn: Co) of 0.7: 0.5: 0.5. A positive electrode active material obtained by firing is specifically described.

JP 2007-287661 A (Example 1)

  However, although the amount of lithium used can be reduced by using the positive electrode active material described above, in a sodium secondary battery using the positive electrode active material, the discharge capacity maintenance rate upon repeated charge and discharge is sufficient. Absent. An object of the present invention is to use a sodium secondary battery that can reduce the amount of lithium used and has a large discharge capacity retention rate when charging and discharging are repeated, and a positive electrode active material thereof. An object of the present invention is to provide a composite metal oxide that can be used.

The inventors of the present invention have intensively studied to solve the above-mentioned problems and have arrived at the present invention. That is, the present invention provides the following inventions.
<1> Including Na and M ¹ (wherein M ¹ represents three or more elements selected from the group consisting of Mn, Fe, Co and Ni), and the molar ratio of Na: M ¹ is a: 1 (where a is a value in the range of more than 0.5 and less than 1).
<2> A composite metal oxide represented by the following formula (1).
Na _a M ¹ O ₂ (1)
(Here, each of M ¹ and a has the same meaning as described above.)
<3> The composite metal oxide according to <1> or <2>, wherein M ¹ contains at least Mn.
<4> The molar ratio of M ¹ : Mn is 1: b (where M ¹ has the same meaning as described above, and b is a value of 0.2 or more and less than 1). > The composite metal oxide described.
<5> The composite metal oxide according to any one of <1> to <4>, wherein M ¹ represents Mn, Fe, and Ni.
The composite metal oxide according to any one of <1> to <5>, wherein <6> a is a value in the range of 0.6 to 0.9.
<7> A positive electrode active material for a sodium secondary battery, comprising the composite metal oxide according to any one of <1> to <6>.
<8> A positive electrode for a sodium secondary battery, comprising the positive electrode active material according to <7>.
<9> A sodium secondary battery having the positive electrode according to <8>.
<10> The sodium secondary battery according to <9>, further including a separator.
<11> The sodium secondary battery according to <10>, wherein the separator is 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.

  According to the present invention, the amount of lithium used can be reduced, and compared with the conventional case, the sodium secondary battery has a large discharge capacity maintenance rate when charging and discharging are repeated, and used as a positive electrode active material thereof The present invention is extremely useful industrially.

The powder X-ray-diffraction figure of complex metal oxide C1. The powder X-ray diffraction pattern of complex metal oxide E1. The powder X-ray-diffraction figure of complex metal oxide E2. The powder X-ray-diffraction figure of complex metal oxide E3.

<Composite metal oxide of the present invention>
The composite metal oxide of the present invention contains Na and M ¹ (wherein M ¹ represents three or more elements selected from the group consisting of Mn, Fe, Co and Ni), and Na: M ¹ The molar ratio is a: 1 (where a is a value in the range of more than 0.5 and less than 1).

Examples of the composite metal oxide of the present invention include those represented by the following formula (1).
Na _a M ¹ O ₂ (1)
(Here, each of M ¹ and a has the same meaning as described above.)

In the mixed metal oxide of the present invention, in one embodiment, M ¹ includes at least Mn. At this time, the molar ratio of M ¹ : Mn is preferably 1: b (where M ¹ has the same meaning as described above, and b is a value of 0.2 or more and less than 1). . Further, when M ¹ contains at least Mn and Ni, it is more preferable from the viewpoint of increasing the average discharge voltage of the obtained sodium secondary battery and increasing the energy density of the battery. Even when M ¹ represents Mn, Fe and Ni, that is, when Co which is a rare metal element is not included, the excellent effect of the present invention can be obtained, and it is even more preferable. When M ¹ represents Mn, Fe and Ni, the preferred Mn: Fe: Ni composition (molar ratio) is 1: (0.3-3) :( 0.01-2), more preferably 1: (0.5-2) :( 0.1-1.2).

  In order to further enhance the effect of the present invention, a is preferably a value in the range of 0.6 to 0.9, more preferably a value in the range of 0.7 to 0.9. Even more preferably, it is about 0.8, that is, a value in the range of 0.75 to 0.84.

Mixed metal oxide of the present invention, a part of M ^1, may be substituted with a metal element other than M ^1. The battery characteristics of the sodium secondary battery may be improved by substitution.

<Method for producing composite metal oxide of the present invention>
The composite metal oxide of the present invention can be produced by firing a mixture of metal-containing compounds having a composition capable of becoming the composite metal oxide of the present invention by firing. Specifically, the metal-containing compound containing the corresponding metal element can be produced by weighing and mixing so as to have a predetermined composition, and then firing the resulting mixture. For example, a complex metal oxide having a metal element ratio represented by Na: Mn: Fe: Ni = 0.7: 0.333: 0.333: 0.333, which is one of the preferred metal element ratios, is Na ₂ CO ₃ , MnO ₂ and Fe ₃ O ₄ were weighed so that the molar ratio of Na: Mn: Fe: Ni would be 0.7: 0.333: 0.333: 0.333, and And the resulting mixture is fired.

Metal-containing compounds that can be used to produce the composite metal oxides of the present invention include oxides and compounds that can become oxides when decomposed and / or oxidized at high temperatures, such as hydroxides and carbonates. , Nitrates, halides, and oxalates can be used. As the sodium compound, Na ₂ CO ₃ , NaHCO ₃ , and Na ₂ O ₂ are preferable, and Na ₂ CO ₃ is more preferable from the viewpoint of handleability. The manganese compound is preferably MnO ₂ , the iron compound is preferably Fe ₃ O ₄ , the nickel compound is preferably NiO, and the cobalt compound is preferably Co ₃ O ₄ . These metal-containing compounds may be hydrates.

  For the mixing of the metal-containing compound, an apparatus usually used industrially, such as a ball mill, a V-type mixer, or a stirrer, can be used. The mixing at this time may be either dry mixing or wet mixing. Further, a mixture of metal-containing compounds having a predetermined composition may be obtained by a crystallization method.

  By firing the mixture of the above metal-containing compounds, for example, by holding and firing in the temperature range of 600 ° C. to 1600 ° C. for 0.5 to 100 hours, the composite metal oxide of the present invention is obtained. . For example, a preferable firing temperature range is a temperature range of 600 ° C to 900 ° C, and more preferably a temperature range of 650 ° C to 850 ° C. When a compound that can be decomposed and / or oxidized at a high temperature, such as a hydroxide, carbonate, nitrate, halide, or oxalate, is used as a mixture of metal-containing compounds, it is maintained at a temperature range of 400 to 1600 ° C. It is also possible to carry out the above-mentioned calcination after calcination to form an oxide or removal of crystal water. The atmosphere in which the calcination is performed may be any of an inert gas atmosphere, an oxidizing atmosphere, or a reducing atmosphere. Moreover, it can also grind | pulverize after calcination.

  Examples of the atmosphere during firing include an inert atmosphere such as nitrogen and argon; an oxidizing atmosphere such as air, oxygen, oxygen-containing nitrogen, and oxygen-containing argon; and hydrogen containing 0.1% to 10% by volume of hydrogen. Any of reducing atmospheres, such as nitrogen containing hydrogen and hydrogen containing argon containing 0.1 volume%-10 volume%, may be sufficient. In order to fire in a strong reducing atmosphere, an appropriate amount of carbon may be contained in a mixture of metal-containing compounds and fired. Baking is preferably performed in an oxidizing atmosphere such as air.

By using an appropriate amount of a halide such as fluoride or chloride as the metal-containing compound, the crystallinity of the produced composite metal oxide and the average particle size of the particles constituting the composite metal oxide can be controlled. In this case, the halide may play a role as a reaction accelerator (flux). Examples of the flux include NaF, MnF ₃ , FeF ₂ , NiF ₂ , CoF ₂ , NaCl, MnCl ₂ , FeCl ₂ , FeCl ₃ , NiCl ₂ , CoCl ₂ , Na ₂ CO ₃ , NaHCO ₃ , NH ₄ Cl, NH _4. I, B ₂ O ₃ , H ₃ BO _{3 and the} like can be mentioned, and these can be used as a raw material of the mixture (metal-containing compound) or by adding an appropriate amount to the mixture. These fluxes may be hydrates.

  When the composite metal oxide of the present invention is used as a positive electrode active material for a sodium secondary battery, the composite metal oxide obtained as described above is optionally subjected to pulverization, washing, classification, etc. using a ball mill or a jet mill. It may be preferable to go and adjust the particle size. Moreover, you may perform baking twice or more. Further, a surface treatment such as coating the particle surface of the composite metal oxide with an inorganic substance containing Si, Al, Ti, Y or the like may be performed. The composite metal oxide of the present invention preferably has a crystal structure that is not a tunnel structure.

  The composite metal oxide of the present invention can be used alone or as a positive electrode active material for a sodium secondary battery by performing a surface treatment such as coating. The positive electrode active material contains the composite metal oxide of the present invention. When the composite metal oxide of the present invention is used in a sodium secondary battery, the obtained sodium secondary battery has a higher discharge capacity retention rate when charging and discharging are repeated than in the conventional case. In addition, according to the present invention, the internal resistance of the sodium secondary battery obtained can be reduced, and the overvoltage during charging and discharging can also be reduced. If the overvoltage at the time of charging / discharging can be made small, the large current discharge characteristic of a secondary battery can be improved more. Moreover, the stability of the battery when the secondary battery is overcharged can be improved.

<Positive electrode for sodium secondary battery of the present invention and method for producing the same>
The positive electrode for sodium secondary batteries of the present invention contains the positive electrode active material of the present invention. The positive electrode for a sodium secondary battery of the present invention can be produced by supporting a positive electrode mixture containing the positive electrode active material of the present invention, a conductive material and a binder on a positive electrode current collector.

  Examples of the conductive material include carbon materials such as natural graphite, artificial graphite, cokes, and carbon black. Examples of the binder include thermoplastic resins, and specifically, polyvinylidene fluoride (hereinafter also referred to as “PVDF”), polytetrafluoroethylene, tetrafluoroethylene, hexafluoropropylene, and fluoride. Fluorine resins such as vinylidene copolymers, propylene hexafluoride / vinylidene fluoride copolymers, tetrafluoroethylene / perfluorovinyl ether copolymers; and polyolefin resins such as polyethylene and polypropylene . As the positive electrode current collector, Al, Ni, stainless steel, or the like can be used.

  As a method of supporting the positive electrode mixture on the positive electrode current collector, it is fixed by press molding or pasting using an organic solvent, coating on the positive electrode current collector, drying and pressing. A method is mentioned. In the case of forming a paste, a slurry composed of a positive electrode active material, a conductive material, a binder, and an organic solvent is prepared. Examples of organic solvents include amines such as N, N-dimethylaminopropylamine and diethyltriamine; ethers such as ethylene oxide and tetrahydrofuran; ketones such as methyl ethyl ketone; esters such as methyl acetate; dimethylacetamide and N-methyl- Examples include aprotic polar solvents such as 2-pyrrolidone. Examples of the method for coating the positive electrode mixture on the positive electrode current collector 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.

<Sodium secondary battery of the present invention>
The sodium secondary battery of this invention has the positive electrode for sodium secondary batteries of this invention. The sodium secondary battery of the present invention includes, for example, a positive electrode for the sodium secondary battery of the present invention, a separator, and a negative electrode in which a negative electrode mixture is supported on a negative electrode current collector, and an electrode group is formed by stacking and winding in this order. The electrode group can be accommodated in a battery can and manufactured by impregnating the electrode group with an electrolytic solution composed of an organic solvent containing an electrolyte.

  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, an ellipse, a rectangle, a rectangle with rounded corners, or the like. 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-negative electrode>
As a negative electrode that can be used in the sodium secondary battery of the present invention, a negative electrode mixture containing a negative electrode active material is supported on a negative electrode current collector, and sodium ions such as sodium metal or sodium alloy can be occluded / desorbed. An electrode can be used. Examples of the negative electrode active material include carbon materials such as natural graphite, artificial graphite, coke, carbon black, pyrolytic carbon, carbon fiber, and organic polymer compound fired body capable of absorbing and desorbing sodium ions. . The shape of the carbon material may be any of a flake shape such as natural graphite, a spherical shape such as mesocarbon microbeads, a fibrous shape such as graphitized carbon fiber, or an aggregate of fine powder. Here, the carbon material may play a role as a conductive material.

  Further, as the negative electrode active material, chalcogen compounds such as oxides and sulfides that can occlude and desorb sodium ions at a lower potential than the positive electrode can also be used.

  The negative electrode mixture may contain a binder and a conductive material as necessary. Therefore, the negative electrode of the sodium secondary battery of the present invention may contain a mixture of a negative electrode active material and a binder. Examples of the binder include a thermoplastic resin, and specific examples include PVDF, thermoplastic polyimide, carboxymethyl cellulose, polyethylene, and polypropylene.

  Examples of the negative electrode current collector include Cu, Ni, and stainless steel, and Cu is preferable because it is difficult to form an alloy with sodium and it can be easily processed into a thin film. The method of supporting the negative electrode mixture on the negative electrode current collector is the same as in the case of the positive electrode. The method of pressure molding, pasting with a solvent, etc., coating on the negative electrode current collector, and pressing after drying For example, a method of fixing by, for example.

<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, the separator is placed between the positive electrode and the negative electrode, and 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 and an excessive current flows. It preferably plays the role of blocking (shuts down). Here, the shutdown is performed by closing the micropores of the porous film in the separator when the normal use temperature is exceeded. After the shutdown, even if the temperature in the battery rises to a certain high temperature, it is preferable to maintain the shutdown state without breaking the film due to the temperature, in other words, high heat resistance. As such a separator, a porous film having a heat resistant material such as a laminated porous film in which a heat resistant porous layer and a porous film are laminated, preferably a heat resistant porous layer containing a heat resistant resin and a porous material containing a thermoplastic resin. A laminated porous film obtained by laminating a porous film can be used, and by using a porous film having such a heat-resistant material as a separator, it is possible to further prevent thermal breakage of the secondary battery of the present invention. It becomes possible. 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 made of a laminated porous film in which a heat resistant porous layer and a porous film are laminated will be described. Here, the thickness of this separator is usually 5 μm or more and 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 or more and 1 or less. 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 preferably contains a heat resistant resin. In order to further enhance the ion permeability, the heat-resistant porous layer is preferably a thin heat-resistant porous layer having a thickness of 1 μm to 10 μm, further 1 μm to 5 μm, particularly 1 μm 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. Moreover, the heat resistant porous layer may be formed from an inorganic powder.

  Examples of the heat resistant resin contained in the heat resistant porous layer include polyamide, polyimide, polyamideimide, polycarbonate, polyacetal, polysulfone, polyphenylene sulfide, polyether ketone, aromatic polyester, polyether sulfone, and polyetherimide. From the viewpoint of further improving 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”). Further, 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 type of heat-resistant resin, and is selected and used according to the use scene and purpose of use. Usually, the thermal film breaking temperature is 160 ° C. or higher. When the nitrogen-containing aromatic polymer is used as the heat-resistant resin, the temperature is about 400 ° C., when poly-4-methylpentene-1 is used, about 250 ° C., and when the cyclic olefin polymer is used, 300 is used. The thermal film breaking temperature can be controlled to about 0 ° C., respectively. In addition, when the heat resistant porous layer is made of an inorganic powder, the thermal film breaking temperature can be controlled to, for example, 500 ° C. or higher.

  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′- It consists essentially of repeating units bonded at opposite orientations, such as biphenylene, 1,5-naphthalene, 2,6-naphthalene, etc., oriented in the opposite direction 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 , 6-dichloroparaphenylene terephthalamide copolymer and the like.

  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 And dianhydrides, 2,2′-bis (3,4-dicarboxyphenyl) hexafluoropropane, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, and the like. Examples of diamines include oxydianiline, paraphenylenediamine, benzophenonediamine, 3,3′-methylenedianiline, 3,3′-diaminobenzophenone, 3,3′-diaminodiphenylsulfone, 1,5′-naphthalenediamine Etc. Moreover, a polyimide soluble in a solvent can be preferably used. An example of such a polyimide is 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, orthotolylane diisocyanate, m-xylene diisocyanate, and the like.

  When the heat resistant porous layer contains a heat resistant resin, the heat resistant porous layer may contain one or more fillers. 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 particles constituting the filler preferably have an average particle size of 0.01 μm or more and 1 μm or less. 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 fiber shape, and any particle can be used. It is preferable that Examples of the substantially spherical particles include particles having a particle aspect ratio (particle major axis / particle minor axis) in the range of 1 to 1.5. The aspect ratio of the particles can be measured by an electron micrograph.

  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, or two or more kinds of copolymers; 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 the inorganic powder as the filler include powders made of inorganic materials such as metal oxides, metal nitrides, metal carbides, metal hydroxides, carbonates, sulfates, etc. Among these, inorganic materials having low conductivity The powder consisting of is preferably used. Specific examples include powders made of alumina, silica, titanium dioxide, barium sulfate, calcium carbonate, or the like. 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. Incidentally, when the heat-resistant porous layer is formed from an inorganic powder, the inorganic powder exemplified above may be used, and may be mixed with a binder as necessary.

  When the heat-resistant porous layer contains a heat-resistant resin, the filler content depends on the specific gravity of the filler material. For example, when all of the particles constituting the filler are alumina particles, the total amount of the heat-resistant porous layer is When the weight is 100, the weight of the filler is usually 5 or more and 95 or less, preferably 20 or more and 95 or less, more preferably 30 or more and 90 or less. 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 preferably has micropores and is preferably shut down. In this case, the porous film contains a thermoplastic resin. The thickness of this porous film is usually 3 to 30 μm, more preferably 3 to 25 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 can close the micropores 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 polyolefin resins such as polyethylene and polypropylene, and thermoplastic polyurethane resins, and a mixture of two or more of these may be used. In order to soften and shut down at a lower temperature, the thermoplastic resin preferably contains polyethylene. Specific examples of polyethylene include polyethylene such as low density polyethylene, high density polyethylene, and linear polyethylene, and ultra high molecular weight polyethylene having a molecular weight of 1,000,000 or more. 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).

  In addition, as a porous film having a heat resistant material different from the above laminated porous film, a porous film made of a heat resistant resin and / or an inorganic powder, or a heat resistant resin and / or an inorganic powder is a polyolefin resin or a thermoplastic polyurethane resin. Examples thereof include a porous film dispersed in a thermoplastic resin film. Here, the above-mentioned thing can be mentioned as a heat resistant resin and inorganic powder.

<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.

  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. Usually, two or more of these are mixed and used as the organic solvent.

Moreover, you may use a solid electrolyte instead of the said electrolyte solution. As the solid electrolyte, for example, an organic solid electrolyte such as a polyethylene oxide polymer compound, a polymer compound containing 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 high molecular compound can also be used. Na ₂ S—SiS ₂ , Na ₂ S—GeS ₂ , NaTi ₂ (PO ₄ ) ₃ , NaFe ₂ (PO ₄ ) ₃ , Na ₂ (SO ₄ ) ₃ , Fe ₂ (SO ₄ ) ₂ (PO ₄ ) Inorganic solid electrolytes such as Fe ₂ (MoO ₄ ) ₃ may be used. Using these solid electrolytes, safety may be further improved. In the sodium 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 at all by these. Unless otherwise specified, the electrode and secondary battery fabrication method for charge / discharge test and the powder X-ray diffraction measurement method are as follows.

(1) Production of electrode (positive electrode) A composite metal oxide as a positive electrode active material, acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductive material, and PVDF (manufactured by Kureha Co., Ltd., PolyVinyllineDiFluoridePolyfloon) as a binder Each was weighed so as to have a composition of active material: conductive material: binder = 85: 10: 5 (weight ratio). After that, first, the mixed metal oxide and acetylene black are sufficiently mixed in an agate mortar, and an appropriate amount of N-methyl-2-pyrrolidone (NMP: manufactured by Tokyo Chemical Industry Co., Ltd.) is added to this mixture, and then PVDF is further added. The mixture was mixed to make a uniform slurry. The obtained slurry is applied to an aluminum foil having a thickness of 40 μm, which is a current collector, with a thickness of 100 μm using an applicator, and this is put into a dryer and sufficiently dried while removing NMP. As a result, an electrode sheet was obtained. This electrode sheet was punched out to a diameter of 1.5 cm with an electrode punching machine, and then sufficiently pressed with a hand press to obtain a positive electrode.

(2) Battery production In the lower part of the coin cell (made by Hosen Co., Ltd.), a positive electrode is placed with the aluminum foil facing downward, and 1M NaClO ₄ / propylene carbonate as electrolyte and polypropylene as separator. A battery was fabricated by combining a porous film (thickness 20 μm) and metallic sodium (manufactured by Aldrich) as a negative electrode. The battery was assembled in a glove box in an argon atmosphere.

(3) Powder X-ray diffraction measurement The measurement was performed under the following conditions using a powder X-ray diffraction measurement apparatus RINT2500TTR manufactured by Rigaku Corporation.
X-ray: CuKα
Voltage-current: 40 kV-140 mA
Measurement angle range: 2θ = 10-60 °
Step: 0.02 °
Scan speed: 4 ° / min

Comparative Example 1 (Na: Mn: Co = 0.7: 0.50: 0.50)
(1) Manufacture of complex metal oxide Sodium carbonate (Na ₂ CO ₃ : Wako Pure Chemical Industries, Ltd .: purity 99.8%), manganese oxide (IV) (MnO ₂ : Taka Co., Ltd.) as metal-containing compounds Purity Chemical Laboratory: Purity 99.9%), and cobalt trioxide (Co ₃ O ₄ : Shodo Chemical Industry Co., Ltd .: purity 99%), Na: Mn: Co molar ratio is 0.7. : 0.50: 0.50 and mixed for 4 hours by a dry ball mill to obtain a mixture of metal-containing compounds. The obtained metal-containing compound mixture was filled in an alumina boat, heated in an air atmosphere using an electric furnace, and held at 800 ° C. for 2 hours to obtain a composite metal oxide C1 of Comparative Example 1. . The powder X-ray diffraction pattern of the composite metal oxide C1 of Comparative Example 1 is shown in FIG.

(2) Evaluation of charge / discharge performance as a positive electrode active material of a sodium secondary battery Using the composite metal oxide C1 of Comparative Example 1 as a positive electrode active material for a sodium secondary battery, a battery was prepared and determined under the following conditions. A current charge / discharge test was conducted.

Charging / discharging conditions:
Charging was performed by CC (Constant Current: constant current) at a rate of 0.1 C up to 4.0 V (speed of complete charging in 10 hours). For discharging, CC discharging was performed at the same speed as the charging speed, and cut off at a voltage of 1.5V. Charging and discharging after the next cycle were performed at the same rate as the charging rate, and cut off at a charging voltage of 4.0 V and a discharging voltage of 1.5 V as in the first cycle.

  With respect to this battery, when the charge / discharge cycle was repeated 10 times, the discharge capacity retention rate at the 10th cycle relative to the discharge capacity at the 1st cycle was 76%.

Example 1 (Na: Mn: Co: Ni = 0.7: 0.495: 0.495: 0.01, in formula (1), M ¹ is Mn, Co and Ni, and a is 0 And b is 0.495.)
(1) Manufacture of complex metal oxide Sodium carbonate (Na ₂ CO ₃ : Wako Pure Chemical Industries, Ltd .: purity 99.8%), manganese oxide (IV) (MnO ₂ : Taka Co., Ltd.) as metal-containing compounds Purity Chemical Laboratory: Purity 99.9%), Cobalt tetraoxide (Co ₃ O ₄ : Shodo Chemical Industry Co., Ltd .: Purity 99%), and Nickel (II) oxide (NiO: High Purity Chemical Co., Ltd.) Laboratories: 99% purity) was weighed so that the molar ratio of Na: Mn: Co: Ni was 0.7: 0.495: 0.495: 0.01 and mixed for 4 hours in a dry ball mill. Thus, a mixture of metal-containing compounds was obtained. The obtained metal-containing compound mixture was filled in an alumina boat, heated in an air atmosphere using an electric furnace, and held at 800 ° C. for 2 hours to obtain a composite metal oxide E1 of Example 1. . The powder X-ray diffraction pattern of the composite metal oxide E1 of Example 1 is shown in FIG.

(2) Evaluation of charge / discharge performance as positive electrode active material of sodium secondary battery Using the composite metal oxide E1 of Example 1 as the positive electrode active material for sodium secondary battery, a battery was produced. The constant current charge / discharge test was carried out under the same conditions as above. With respect to this battery, when the charge / discharge cycle was repeated 10 times, the discharge capacity retention rate at the 10th cycle relative to the discharge capacity at the 1st cycle was 109%.

Example 2 (Na: Mn: Co: Ni = 0.7: 0.45: 0.45: 0.10, in formula (1), M ¹ is Mn, Co and Ni, and a is 0. .7 and b is 0.45.)
(1) Production of composite metal oxide Examples except that the metal-containing compound was used in such an amount that the molar ratio of Na: Mn: Co: Ni was 0.7: 0.45: 0.45: 0.10. In the same manner as in Example 1, a composite metal oxide E2 of Example 2 was obtained. The powder X-ray diffraction pattern of the mixed metal oxide E2 of Example 2 is shown in FIG.

(2) Evaluation of charge / discharge performance as a positive electrode active material of a sodium secondary battery Using the composite metal oxide E2 of Example 2 as a positive electrode active material for a sodium secondary battery, a battery was produced. The constant current charge / discharge test was carried out under the same conditions as above. With respect to this battery, when the charge / discharge cycle was repeated 10 times, the discharge capacity retention rate at the 10th cycle relative to the discharge capacity at the 1st cycle was 89%.

Example 3 (Na: Mn: Co: Ni = 0.7: 0.333: 0.333: 0.333, in formula (1), M ¹ is Mn, Co and Ni, and a is 0 .7 and b is 0.333.)
(1) Production of composite metal oxide Examples except that the metal-containing compound was used in such an amount that the molar ratio of Na: Mn: Co: Ni was 0.7: 0.333: 0.333: 0.333. In the same manner as in Example 1, a composite metal oxide E3 of Example 3 was obtained. The powder X-ray diffraction pattern of the mixed metal oxide E3 of Example 3 is shown in FIG.

(2) Charging / discharging performance evaluation as a positive electrode active material of a sodium secondary battery Using the composite metal oxide E3 of Example 3 as a positive electrode active material for a sodium secondary battery, a battery was produced. A constant current charge / discharge test was performed under the same conditions as in FIG. With respect to this battery, when the charge / discharge cycle was repeated 10 times, the discharge capacity retention rate at the 10th cycle relative to the discharge capacity at the 1st cycle was 90%.

Example 4 (Na: Mn: Fe: Ni = 0.7: 0.333: 0.333: 0.333, in formula (1), M ¹ is Mn, Fe and Ni, and a is 0 .7 and b is 0.333.)
(1) Manufacture of complex metal oxide Sodium carbonate (Na ₂ CO ₃ : Wako Pure Chemical Industries, Ltd .: purity 99.8%), manganese oxide (IV) (MnO ₂ : Taka Co., Ltd.) as metal-containing compounds Purity Chemical Laboratory: Purity 99.9%), Iron Oxide (II, III) (Fe ₃ O ₄ : High Purity Chemical Laboratory, Inc .: Purity 99%), and Nickel (II) Oxide (NiO: Stock) Company high purity chemical laboratory: 99% purity) was weighed so that the molar ratio of Na: Mn: Fe: Ni would be 0.7: 0.333: 0.333: 0.333, and dried using a dry ball mill. Mixing for 4 hours gave a mixture of metal-containing compounds. The obtained metal-containing compound mixture was filled in an alumina boat, heated in an air atmosphere using an electric furnace, and held at 800 ° C. for 2 hours to obtain a composite metal oxide E4 of Example 4. .

(2) Charging / discharging performance evaluation as a positive electrode active material of a sodium secondary battery Using the composite metal oxide E4 of Example 4 as a positive electrode active material for a sodium secondary battery, a battery was produced. The constant current charge / discharge test was carried out under the same conditions as above. With respect to this battery, when the charge / discharge cycle was repeated 10 times, the discharge capacity retention rate at the 10th cycle relative to the discharge capacity at the 1st cycle was 83%.

Example 5 (Na: Mn: Fe: Co = 0.7: 0.333: 0.333: 0.333, M ¹ in formula (1) is Mn, Fe and Co, and a is 0 .7 and b is 0.333.)
(1) Manufacture of complex metal oxide Sodium carbonate (Na ₂ CO ₃ : Wako Pure Chemical Industries, Ltd .: purity 99.8%), manganese oxide (IV) (MnO ₂ : Taka Co., Ltd.) as metal-containing compounds Purity Chemical Laboratory: Purity 99.9%), Iron Oxide (II, III) (Fe ₃ O ₄ : High Purity Chemical Laboratory, Inc .: Purity 99%), and Cobalt Tetroxide (Co ₃ O ₄ : Seido Chemical Industry Co., Ltd .: Purity 99%) was measured so that the molar ratio of Na: Mn: Fe: Co would be 0.7: 0.333: 0.333: 0.333, and a dry ball mill For 4 hours to obtain a mixture of metal-containing compounds. The obtained metal-containing compound mixture was filled in an alumina boat, heated in an air atmosphere using an electric furnace, and held at 800 ° C. for 2 hours to obtain a composite metal oxide E5 of Example 5. .

(2) Evaluation of charge / discharge performance as positive electrode active material of sodium secondary battery Using the composite metal oxide E5 of Example 5 as the positive electrode active material for sodium secondary battery, a battery was produced. The constant current charge / discharge test was carried out under the same conditions as above. With respect to this battery, when the charge / discharge cycle was repeated 10 times, the discharge capacity retention rate at the 10th cycle relative to the discharge capacity at the 1st cycle was 78%.

Example 6 (Na: Mn: Fe: Co: Ni = 0.7: 0.25: 0.25: 0.25: 0.25) In formula (1), M ¹ is Mn, Fe, Co And Ni, a is 0.7, and b is 0.25.)
(1) Manufacture of complex metal oxide Sodium carbonate (Na ₂ CO ₃ : Wako Pure Chemical Industries, Ltd .: purity 99.8%), manganese oxide (IV) (MnO ₂ : Taka Co., Ltd.) as metal-containing compounds Purity chemical laboratory product: purity 99.9%), iron oxide (II, III) (Fe ₃ O ₄ : high purity chemical laboratory product: purity 99%), cobalt tetraoxide (Co ₃ O ₄ : Shodo Chemical Industry Co., Ltd .: purity 99%) and nickel oxide (II) (NiO: high purity chemical laboratory Co., Ltd .: purity 99%), Na: Mn: Fe: Co: Ni molar ratio 0.7: 0.25: 0.25: 0.25: 0.25 was weighed and mixed for 4 hours with a dry ball mill to obtain a mixture of metal-containing compounds. The obtained metal-containing compound mixture was filled in an alumina boat, heated in an air atmosphere using an electric furnace, and held at 800 ° C. for 2 hours to obtain a composite metal oxide E6 of Example 6. .

(2) Charging / discharging performance evaluation as a positive electrode active material of a sodium secondary battery Using the composite metal oxide E6 of Example 6 as a positive electrode active material for a sodium secondary battery, a battery was produced. The constant current charge / discharge test was carried out under the same conditions as above. With respect to this battery, when the charge / discharge cycle was repeated 10 times, the discharge capacity retention rate at the 10th cycle relative to the discharge capacity at the 1st cycle was 88%.

Example 7 (Na: Mn: Fe: Ni = 0.8: 0.333: 0.333: 0.333, in formula (1), M ¹ is Mn, Fe and Ni, and a is 0 .8, and b is 0.333.)
(1) Manufacture of complex metal oxide Sodium carbonate (Na ₂ CO ₃ : Wako Pure Chemical Industries, Ltd .: purity 99.8%), manganese oxide (IV) (MnO ₂ : Taka Co., Ltd.) as metal-containing compounds Purity Chemical Laboratory: Purity 99.9%), Iron Oxide (II, III) (Fe ₃ O ₄ : High Purity Chemical Laboratory, Inc .: Purity 99%), and Nickel (II) Oxide (NiO: Stock) Company high purity chemical research laboratory: purity 99%) was measured so that the molar ratio of Na: Mn: Fe: Ni was 0.8: 0.333: 0.333: 0.333. Mixing for 4 hours gave a mixture of metal-containing compounds. The obtained metal-containing compound mixture was filled in an alumina boat, heated in an air atmosphere using an electric furnace, and held at 800 ° C. for 2 hours to obtain a composite metal oxide E7 of Example 7. .

(2) Charging / discharging performance evaluation as a positive electrode active material of a sodium secondary battery Using the composite metal oxide E7 of Example 7 as a positive electrode active material for a sodium secondary battery, a battery was produced. The constant current charge / discharge test was carried out under the same conditions as above. With respect to this battery, when the charge / discharge cycle was repeated 10 times, the discharge capacity retention rate at the 10th cycle relative to the discharge capacity at the 1st cycle was 93%.

Example 8 (Na: Mn: Fe: Ni = 0.9: 0.333: 0.333: 0.333, in formula (1), M ¹ is Mn, Fe and Ni, and a is 0 .9, and b is 0.333.)
(1) Manufacture of complex metal oxide Sodium carbonate (Na ₂ CO ₃ : Wako Pure Chemical Industries, Ltd .: purity 99.8%), manganese oxide (IV) (MnO ₂ : Taka Co., Ltd.) as metal-containing compounds Purity Chemical Laboratory: Purity 99.9%), Iron Oxide (II, III) (Fe ₃ O ₄ : High Purity Chemical Laboratory, Inc .: Purity 99%), and Nickel (II) Oxide (NiO: Stock) Company high purity chemical laboratory: 99% purity) was weighed so that the molar ratio of Na: Mn: Fe: Ni was 0.9: 0.333: 0.333: 0.333, Mixing for 4 hours gave a mixture of metal-containing compounds. The obtained metal-containing compound mixture was filled in an alumina boat, heated in an air atmosphere using an electric furnace, and held at 800 ° C. for 2 hours to obtain a composite metal oxide E8 of Example 8. .

(2) Charging / Discharging Performance Evaluation as Positive Electrode Active Material of Sodium Secondary Battery A battery was produced using the composite metal oxide E8 of Example 8 as a positive electrode active material for sodium secondary battery. The constant current charge / discharge test was carried out under the same conditions as above. With respect to this battery, when the charge / discharge cycle was repeated 10 times, the discharge capacity retention rate at the 10th cycle relative to the discharge capacity at the 1st cycle was 88%.

Example 9 (Na: Mn: Fe: Ni = 0.7: 0.38: 0.38: 0.24, in formula (1), M ¹ is Mn, Fe and Ni, and a is 0 .7, and b is 0.38.)
(1) Manufacture of complex metal oxide Sodium carbonate (Na ₂ CO ₃ : Wako Pure Chemical Industries, Ltd .: purity 99.8%), manganese oxide (IV) (MnO ₂ : Taka Co., Ltd.) as metal-containing compounds Purity Chemical Laboratory: Purity 99.9%), Iron Oxide (II, III) (Fe ₃ O ₄ : High Purity Chemical Laboratory, Inc .: Purity 99%), and Nickel (II) Oxide (NiO: Stock) Company high purity chemical research laboratory: purity 99%), the Na: Mn: Fe: Ni molar ratio is 0.7: 0.38: 0.38: 0.24, weighed in a dry ball mill Mixing for 4 hours gave a mixture of metal-containing compounds. The obtained metal-containing compound mixture was filled in an alumina boat, heated in an air atmosphere using an electric furnace, and held at 800 ° C. for 2 hours to obtain a composite metal oxide E9 of Example 9. .

(2) Charging / discharging performance evaluation as a positive electrode active material of a sodium secondary battery Using the composite metal oxide E9 of Example 9 as a positive electrode active material for a sodium secondary battery, a battery was produced. The constant current charge / discharge test was carried out under the same conditions as above. With respect to this battery, when the charge / discharge cycle was repeated 10 times, the discharge capacity retention rate at the 10th cycle relative to the discharge capacity at the 1st cycle was 93%.

Example 10 (Na: Mn: Fe: Ni = 0.7: 0.42: 0.42: 0.16, M ¹ in the formula (1) is Mn, Fe and Ni, and a is 0 .7 and b is 0.42.)
(1) Manufacture of complex metal oxide Sodium carbonate (Na ₂ CO ₃ : Wako Pure Chemical Industries, Ltd .: purity 99.8%), manganese oxide (IV) (MnO ₂ : Taka Co., Ltd.) as metal-containing compounds Purity Chemical Laboratory: Purity 99.9%), Iron Oxide (II, III) (Fe ₃ O ₄ : High Purity Chemical Laboratory, Inc .: Purity 99%), and Nickel (II) Oxide (NiO: Stock) Company high-purity chemical research laboratory: purity 99%) was measured so that the molar ratio of Na: Mn: Fe: Ni was 0.7: 0.42: 0.42: 0.16. Mixing for 4 hours gave a mixture of metal-containing compounds. The obtained metal-containing compound mixture was filled in an alumina boat, heated in an air atmosphere using an electric furnace, and held at 800 ° C. for 2 hours to obtain a composite metal oxide E10 of Example 10. .

(2) Charging / discharging performance evaluation as a positive electrode active material of a sodium secondary battery Using the composite metal oxide E10 of Example 10 as a positive electrode active material for a sodium secondary battery, a battery was produced. The constant current charge / discharge test was carried out under the same conditions as above. With respect to this battery, when the charge / discharge cycle was repeated 10 times, the discharge capacity retention rate at the 10th cycle relative to the discharge capacity at the 1st cycle was 84%.

Example 11 (Na: Mn: Fe: Ni = 0.7: 0.46: 0.46: 0.08, in formula (1), M ¹ is Mn, Fe and Ni, and a is 0 .7 and b is 0.46.)
(1) Manufacture of complex metal oxide Sodium carbonate (Na ₂ CO ₃ : Wako Pure Chemical Industries, Ltd .: purity 99.8%), manganese oxide (IV) (MnO ₂ : Taka Co., Ltd.) as metal-containing compounds Purity Chemical Laboratory: Purity 99.9%), Iron Oxide (II, III) (Fe ₃ O ₄ : High Purity Chemical Laboratory, Inc .: Purity 99%), and Nickel (II) Oxide (NiO: Stock) Company high purity chemical laboratory: 99% purity) was weighed so that the molar ratio of Na: Mn: Fe: Ni was 0.7: 0.46: 0.46: 0.08. Mixing for 4 hours gave a mixture of metal-containing compounds. The obtained metal-containing compound mixture was filled in an alumina boat, heated in an air atmosphere using an electric furnace, and held at 800 ° C. for 2 hours to obtain a composite metal oxide E11 of Example 11. .

(2) Evaluation of charge / discharge performance as a positive electrode active material of a sodium secondary battery A battery was prepared using the composite metal oxide E11 of Example 11 as a positive electrode active material for a sodium secondary battery. The constant current charge / discharge test was carried out under the same conditions as above. With respect to this battery, when the charge / discharge cycle was repeated 10 times, the discharge capacity retention rate at the 10th cycle relative to the discharge capacity at the 1st cycle was 90%.

Production example (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 the first alumina powder (Nippon Aerosil Co., Ltd., Alumina C, average particle size 0.02 μm) and 2 g of the second alumina powder (Sumitomo Chemical Co., 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 alumina powder (filler) with respect to the total weight of para-aramid and alumina powder is 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 water which is a poor solvent 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), relatively small pores of about 0.03 μm to 0.06 μm and relatively large fines of about 0.1 μm to 1 μm were observed. 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. Obtain the weight (Wi (g)) of each layer in the sample, and obtain the volume of each layer from Wi and the true specific gravity (true specific gravity i (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 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 (11)

Na and M ¹ (wherein M ¹ represents three or more elements selected from the group consisting of Mn, Fe, Co and Ni), and the molar ratio of Na: M ¹ is a: 1 (here And a is a value in the range of more than 0.5 and less than 1.). A composite metal oxide represented by the following formula (1).
Na _a M ¹ O ₂ (1)
(Here, each of M ¹ and a has the same meaning as described above.) The mixed metal oxide according to claim 1 or 2, wherein M ¹ contains at least Mn. The composite according to claim 3, wherein the molar ratio of M ¹ : Mn is 1: b (where M ¹ has the same meaning as described above, and b is a value of 0.2 or more and less than 1). Metal oxide. The mixed metal oxide according to any one of claims 1 to 4, wherein M ¹ represents Mn, Fe and Ni.   The composite metal oxide according to claim 1, wherein a is a value in the range of 0.6 to 0.9.   The positive electrode active material for sodium secondary batteries containing the complex metal oxide in any one of Claims 1-6.   The positive electrode for sodium secondary batteries containing the positive electrode active material of Claim 7.   A sodium secondary battery having the positive electrode according to claim 8.   The sodium secondary battery according to claim 9, further comprising a separator.   The sodium secondary battery according to claim 10, wherein the separator is 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.

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