WO2014157125A1 - Sodium secondary battery - Google Patents

Abstract

A sodium secondary battery which comprises: a layer that contains a positive electrode active material that can be doped and undoped with sodium ions; a layer that contains a negative electrode active material that can be doped and undoped with sodium ions; an electrolyte that is capable of conducting sodium ions; and a collector. This sodium secondary battery comprises at least one collector that has such a structure wherein the layer that contains a positive electrode active material is laminated on one surface of the collector and the layer that contains a negative electrode active material is laminated on the other surface. In this sodium secondary battery, the electrolyte is composed of a solid electrolyte. Consequently, this sodium secondary battery has a simple battery structure.

Description

Sodium secondary battery

The present invention relates to a sodium secondary battery.

In recent years, research and development of secondary batteries have been actively conducted, and sodium secondary batteries using sodium ions, which are inexpensive materials, as conductive ions have attracted attention.

A conventional sodium secondary battery has a structural unit in which a layer containing a positive electrode active material is laminated on both sides of a current collector, and a layer containing a negative electrode active material on both sides of a current collector. It was a sodium secondary battery having a structure in which a separator was laminated between structural units (Japanese Patent Laid-Open No. 2010-225525).

However, the above-mentioned sodium secondary battery has a complicated battery structure because all current collectors require current collecting terminals for extracting current to the outside.

The present invention has been made in view of such circumstances, and an object thereof is to provide a sodium secondary battery having a simple battery structure.

The inventor has conducted extensive studies to solve the above-described problems, and has reached the present invention.

That is, the present invention includes a layer containing a positive electrode active material that can be doped and dedoped with sodium ions, a layer containing a negative electrode active material that can be doped and dedoped with sodium ions, an electrolyte capable of conducting sodium ions, and a current collector. A layer containing the positive electrode active material on one surface of the current collector, and a layer containing the negative electrode active material on the other surface. Provided is a sodium secondary battery having at least one current collector, wherein the electrolyte is a solid electrolyte.

According to the present invention, a sodium secondary battery having a simple battery structure can be provided. A sodium secondary battery is extremely useful industrially because it can be made of an inexpensive material.

It is a schematic diagram which shows an example of the sodium secondary battery of this embodiment. It is a schematic diagram which shows the bipolar electrode sheet of a sodium secondary battery manufacturing process in an Example. It is a schematic diagram which shows the sodium secondary battery obtained in an Example.

The sodium secondary battery of this embodiment includes a layer containing a positive electrode active material that can be doped and dedoped with sodium ions, a layer containing a negative electrode active material that can be doped and dedoped with sodium ions, an electrolyte capable of conducting sodium ions, A sodium secondary battery having a current collector, wherein a layer containing the positive electrode active material is laminated on one surface of the current collector, and a layer containing the negative electrode active material on the other surface At least one of the current collectors laminated, and the electrolyte is a solid electrolyte.

A structure in which a layer containing the positive electrode active material is laminated on one surface of a current collector and a layer containing the negative electrode active material is laminated on the other surface is called a bipolar electrode.
Hereinafter, it demonstrates in order.

<Solid electrolyte>
The electrolyte of the sodium secondary battery of this embodiment is an electrolyte that is solid at room temperature and can conduct sodium ions. Conventionally, in a lithium secondary battery, the solid electrolyte has too low ionic conductivity and it has been difficult to use as a real battery. However, in a sodium secondary battery, sufficient ionic conductivity is obtained. When such a solid electrolyte is used, an ionic short circuit does not occur on the back and front of the current collector, so that the insulating portions on the back and front of the current collector are not necessary. In addition, since the solid electrolyte has higher flame retardancy than a liquid electrolyte at room temperature, a sodium secondary battery with higher safety can be provided.

The solid electrolyte may be an organic solid electrolyte, an inorganic solid electrolyte, or a mixture thereof. From the viewpoint of improving the interfacial bonding between the positive electrode active material and the solid electrolyte and the interfacial bonding between the negative electrode active material and the solid electrolyte, the organic solid electrolyte is preferable. The organic solid electrolyte is more preferably a polymer containing sodium ions.

<Organic solid electrolyte>
The organic solid electrolyte is obtained, for example, by mixing a polymerizable monomer, a sodium salt, and, if necessary, a polymerization initiator and polymerizing the mixture. Alternatively, a polymerizable monomer and, if necessary, a polymerization initiator may be mixed and polymerized, and then the obtained polymer and sodium salt may be dissolved in a solvent. Examples of the polymerization method include polymerization methods such as thermal polymerization, photopolymerization, and radiation polymerization.

<Polymerizable monomer>
As the polymerizable monomer, a monomer containing one or more structural units selected from the group consisting of a structural unit represented by the following formula (1) and a structural unit represented by the following formula (2) can be used. .
—CH ₂ —CH ₂ —O— (1)
—CH ₂ —CHCH ₃ —O— (2)

Examples of the monomer containing one or more structural units selected from the group consisting of the structural unit represented by the above formula (1) and the structural unit represented by the above formula (2) include NK ester A manufactured by Shin-Nakamura Chemical Co., Ltd. -200, A-400, A-600, APG-100, APG-200, APG-400, APG-700, A-GLY-9E, A-GLY-20E, A-TMMT, AD-TMP, ATM-35E , A-TMMT, A9550, A-DPH.

<Sodium salt>
Examples of the sodium salt include NaPF ₆ , NaBF ₄ , NaClO ₄ , NaCF ₃ CONSO ₂ CF ₃ , NaN (SO ₂ C ₂ F ₅ ) ₂ , NaN (SO ₂ CF ₃ ) ₂ , NaCF ₃ SO ₃ , NaC ( CF ₃ SO _{2) 3} and the like.

<Polymerization initiator>
Examples of the polymerization initiator include azo polymerization initiators and peroxide polymerization initiators.

Examples of the azo polymerization initiator include 2,2′-azobis-isobutyronitrile, 2,2′-azobis-2-methylbutyronitrile, and 2,2′-azobis-2,4-dimethylvaleronitrile. It is done.

As peroxide-based polymerization initiators, isobutyl peroxide, lauroyl peroxide, benzoyl peroxide, m-toluoyl peroxide, t-butylperoxy-2-ethylhexanoate, t-butylperoxybivalate- Butyloxyneodecanate, diisopropylperoxydicarbonate, diethoxyperoxydicarbonate, bis- (4-tert-butylcyclohexyl) peroxydicarbonate, dimethoxyisopropylperoxydicarbonate, dicyclohexylperoxydicarbonate and 3,3 , 5-trimethylhexanoyl peroxide.

<Inorganic solid electrolyte>
A commercially available product can be used as the inorganic solid electrolyte, and examples thereof include a NASICON type solid electrolyte and a sulfide type solid electrolyte.
The composition of the NASICON solid electrolyte preferably contains Na _{1 + x} Zr ₂ Si _x O ₁₂ (x is 0 or more and 3 or less).
The composition of the sulfide-based solid electrolyte preferably includes, for example, Na ₂ S and P ₂ S ₅ .

<Layer containing positive electrode active material>
As the positive electrode active material of the sodium secondary battery of this embodiment, a material capable of doping and dedoping sodium can be used.

Examples of the positive electrode active material include sodium metal, a sodium alloy, and a sodium inorganic compound that can be doped and dedoped with sodium ions. The layer containing the positive electrode active material is, for example, one in which an electrode mixture containing a Na compound, a binder, a conductive agent and the like is supported on a current collector, and is preferably in a sheet form.

As a method for producing a positive electrode active material using a Na compound,
(1) A method in which an electrode mixture formed by adding a solvent to a Na compound, a binder, a conductive agent and the like is applied to a current collector by a doctor blade method or the like, or dipped and dried,
(2) A sheet obtained by adding a solvent to the Na compound, binder, conductive agent, etc., kneading, shaping, and drying is bonded to the current collector surface via a conductive adhesive, and then pressed and heat-treated. Method,
(3) After forming a mixture of Na compound, binder, conductive agent and liquid lubricant on the current collector, the liquid lubricant is removed, and then the obtained sheet-like molded product is uniaxial or multiaxial. And a method of stretching in the direction. When the layer containing the positive electrode active material is in the form of a sheet, the thickness is preferably about 5 to 500 μm.

As Na compound,
NaFeO _2, NaMnO _2, NaNiO ₂ and NaCoO oxide represented by ^NaM ₁ a _{O 2,} such as _2, oxide represented by ^{_{Na 0.44 Mn 1-a M 1}} a O 2, Na 0.7 Mn _1-a M ¹ _a O _2.05 oxide (M ¹ is one or more transition metal elements, 0 ≦ a <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, 3 ≦ 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);
Phosphate salts such as NaFePO ₄ and Na ₃ Fe ₂ (PO ₄ ) ₃ ; Borate salts such as NaFeBO ₄ and Na ₃ Fe ₂ (BO ₄ ) ₃ ;
Na ₃ FeF ₆ and _Na 2 MnF ₆ fluorides represented by _Na h ^M 5 _{F 6} etc. ^{(M 5} is one or more transition metal elements, 2 ≦ h ≦ 3);
Etc.

In the layer containing the positive electrode active material, among the Na compounds, a compound containing Fe can be preferably used. The use of a compound containing Fe is very important from the viewpoint of constituting a secondary battery with abundant and inexpensive materials.

It is preferable that a buffer layer further exists on the surface of the positive electrode active material. By having the buffer layer, it is possible to have a potential gradient and smooth charge and discharge.

Examples of the conductive agent used in the layer containing the positive electrode active material include various carbon materials such as natural graphite, artificial graphite, cokes, and carbon black. Moreover, you may use the carbon material used for a negative electrode active material as a electrically conductive agent in the layer containing a positive electrode active material.

As a current collector carrying a layer containing a positive electrode active material,
Metals such as nickel, aluminum, titanium, copper, gold, silver, platinum, aluminum alloys or stainless steel;
Formed by plasma spraying or arc spraying of carbon material, activated carbon fiber, nickel, aluminum, zinc, copper, tin, lead or alloys thereof;
Examples thereof include a conductive film in which a conductive agent is dispersed in a resin such as rubber or styrene-ethylene-butylene-styrene copolymer (SEBS).
Among these, aluminum, an aluminum alloy, nickel, stainless steel and the like are preferable, and aluminum and an aluminum alloy are preferable from the viewpoint of being easily processed into a thin film and being inexpensive.

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 or a punching metal shape, or a combination thereof (for example, a mesh flat plate). . Moreover, you may form the unevenness | corrugation by an etching process or embossing on the surface of a collector.

In the layer containing the positive electrode active material, the same binder and solvent as those used in the layer containing the negative electrode active material described later can be used. In the above, the conductive adhesive means a mixture of a conductive agent and a binder.

The amount of the binder in the layer containing the positive electrode active material is preferably about 0.5 to 30 parts by mass, more preferably 2 to 30 parts per 100 parts by mass of the Na compound when a Na compound is used as the positive electrode active material. The compounding amount of the conductive agent is preferably about 1 to 50 parts by mass, more preferably about 1 to 30 parts by mass with respect to 100 parts by mass of the Na compound. The amount is preferably about 50 to 500 parts by mass, more preferably about 100 to 200 parts by mass with respect to 100 parts by mass.

<Separator>
In the present invention, since a solid electrolyte is used, it is not necessary to use a separator. However, when a polymerizable monomer is used as a raw material for the solid electrolyte, the distance between the layer containing the positive electrode active material and the layer containing the negative electrode active material is constant. A separator may be used for the purpose. In addition, a separator may be used for the purpose of preventing a short circuit between a layer containing a positive electrode active material such as a pinhole of a solid electrolyte and a layer containing a negative electrode active material.

As the separator, for example, a material such as a porous film, a nonwoven fabric, a woven fabric, or the like made of a polyolefin resin such as polyethylene or polypropylene, a fluororesin, or a nitrogen-containing aromatic polymer can be used. Further, two or more of the above materials may be used as a separator, or the above materials may be laminated. Examples of the separator include those described in JP 2000-30686 A, JP 10-324758 A, and the like.

The pore diameter of the separator is preferably about 0.01 to 10 μm. The thickness of the separator should be as thin as possible so that the mechanical strength is maintained in that the volume energy density of the battery is increased and the internal resistance is reduced, preferably about 1 to 300 μm, more preferably 5 to 40 μm. Degree.

From the viewpoint of ion permeability, the 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.

Further, the porosity of the separator is preferably 30 to 80% by volume, more preferably 40 to 70% by volume. The separator may be a laminate of separators having different porosity.

In the sodium secondary battery, when an abnormal current flows in the battery due to a short circuit between the layer containing the positive electrode active material and the layer containing the negative electrode active material, the current at the short circuit point is interrupted, It is preferable to have a function of preventing (shutdown) an excessive current from flowing.

When the separator has a porous film containing a thermoplastic resin, the shutdown is performed when the separator at the short-circuited portion is overheated due to a short circuit and exceeds a presumed (normal) use temperature. Is made by softening or melting to close the micropores. And even if the temperature in a battery rises to a certain high temperature after shutting down, it is preferable that heat resistance is high enough to maintain the shutdown state without breaking the film due to the temperature.

Examples of such a separator include a porous film having a heat-resistant material, and a laminated film in which a heat-resistant porous layer and a porous film are laminated. By using the film as a separator, the sodium of this embodiment can be used. It becomes possible to further improve the heat resistance of the secondary battery.

Next, the laminated film in which the heat resistant porous layer and the porous film are laminated will be described more specifically.
In the laminated film, the heat resistant porous layer is a layer having higher heat resistance than the porous film, and the heat resistant porous layer may be formed from an inorganic powder described later or may contain a heat resistant resin. Good. When the heat resistant porous layer contains a heat resistant resin, the heat resistant porous layer can be formed by an easy technique such as coating.

Examples of the heat resistant resin include polyamide, polyimide, polyamideimide, polycarbonate, polyacetal, polysulfone, polyphenylene sulfide, polyetherketone, aromatic polyester, polyethersulfone, 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 preferred are nitrogen-containing aromatic polymers such as aromatic polyamides (para-oriented aromatic polyamides, meta-oriented aromatic polyamides), aromatic polyimides, aromatic polyamideimides, and particularly preferred are aromatic polyamides and production surfaces. Particularly preferred is para-oriented aromatic polyamide (hereinafter sometimes referred to as “para-aramid”).

Moreover, poly-4-methylpentene-1 and a cyclic olefin polymer can also be mentioned as a heat resistant resin. By using these heat resistant resins, the heat resistance can be increased, that is, the thermal film breaking temperature can be increased.

The above-mentioned 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. 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 ° C. To some extent, the thermal film breaking temperature can be controlled. 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 para-oriented aromatic diamine and para-oriented aromatic dicarboxylic acid halide. For example, even on different aromatic rings such as 4,4′-biphenylene, 1,5-naphthalene, 2,6-naphthalene and the like, from a repeating unit having an amide bond in an orientation position corresponding to the para position. The aramid is also included in the para-aramid. Specifically, poly (paraphenylene terephthalamide), poly (parabenzamide), poly (4,4′-benzanilide terephthalamide), poly (paraphenylene-4,4′-biphenylenedicarboxylic acid amide), poly ( Examples thereof include para-aramid such as paraphenylene-2,6-naphthalenedicarboxylic acid amide), poly (2-chloro-paraphenylene terephthalamide), and paraphenylene terephthalamide / 2,6-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 Examples thereof include acid dianhydride, 2,2′-bis (3,4-dicarboxyphenyl) hexafluoropropane, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, and the like. Specific examples of the diamine include oxydianiline, paraphenylenediamine, benzophenonediamine, 3,3′-methylenedianiline, 3,3′-diaminobenzophenone, 3,3′-diaminodiphenylsulfone, 1,5 '-Naphthalenediamine and the like. 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 of aromatic dicarboxylic acid and aromatic diisocyanate, and those obtained from condensation polymerization of aromatic diacid anhydride and aromatic diisocyanate. 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.

In the present embodiment, the thickness of the heat resistant porous layer is preferably 1 μm or more and 10 μm or less, more preferably 1 μm or more and 5 μm or less, and particularly preferably 1 μm or more and 4 μm or less in order to further increase sodium ion permeability. The heat-resistant porous layer has fine pores, and the size (diameter) of the pores is preferably 3 μm or less, more preferably 1 μm or less.

Further, when the heat resistant porous layer contains a heat resistant resin, it can further contain a filler. The filler is selected from organic powder, inorganic powder, or a mixture thereof as the material 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 organic powder include styrene, vinyl ketone, acrylonitrile, methyl methacrylate, ethyl methacrylate, glycidyl methacrylate, glycidyl acrylate, and methyl acrylate, or a copolymer of two or more kinds, polytetrafluoroethylene, 4 fluorine. Fluorine resins such as fluorinated ethylene-6fluoropropylene copolymer, tetrafluoroethylene-ethylene copolymer, polyvinylidene fluoride, etc .; melamine resin; urea resin; polyolefin; powder made of organic matter such as polymethacrylate . The organic powder may be used alone or in combination of two or more. Among these organic powders, polytetrafluoroethylene powder is preferable from the viewpoint of chemical stability.

Examples of the inorganic powder include powders made of inorganic substances such as metal oxides, metal nitrides, metal carbides, metal hydroxides, carbonates, sulfates, etc. Among these, they are made of inorganic substances having low conductivity. Powder is preferably used. Specific examples include powders made of alumina, silica, titanium dioxide, calcium carbonate, or the like. The inorganic powder may be used alone or in combination of two or more. Among these inorganic powders, alumina powder is preferable from the viewpoint of chemical stability. Here, 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. It is embodiment which is. 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 the total mass of the heat resistant porous layer is 100, the filler mass is preferably It is 5 or more and 95 or less, More preferably, it is 20 or more and 95 or less, More preferably, it is 30 or more and 90 or less. These ranges are particularly suitable when all of the particles constituting the filler are alumina particles.

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. 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.

As described above, the heat-resistant porous layer can also contain two or more fillers. In this case, when the average value of the particles constituting each of the two or more fillers is measured, the first largest value is D ₁ , and the second largest value is D ₂ , it is preferable the value of D ₂ / _{D 1} is 0.15 or less. Thereby, in the micropores of the heat-resistant porous layer of the laminated film, micropores having a relatively small size and micropores having a relatively large size are generated in a well-balanced manner. In the sodium secondary battery obtained, the heat resistance of the separator made of the laminated film can be increased by the structure of the micropores having a relatively small size, and the sodium ion permeability is improved by the structure of the micropores having a relatively large size. Can provide a high output at a high current rate, that is, excellent rate characteristics and a suitable separator.

The average particle diameter may be a value measured from an electron micrograph. That is, the particles (filler particles) photographed in the scanning electron micrograph of the surface or cross section of the heat-resistant porous layer in the laminated film are classified by size, and the first among the average particle diameter values in each classification When the large value is D ₁ and the second largest value is D ₂ , the value of D ₂ / D ₁ may be 0.15 or less. For the average particle size, 25 particles are arbitrarily extracted in each of the above classifications, the particle size (diameter) is measured for each, and the average value of the 25 particle sizes is defined as the average particle size. In addition, the particle | grains which comprise said filler mean the primary particle | grains which comprise a filler.

In the laminated film, the porous film preferably has fine pores and has a shutdown function. The size (diameter) of the micropores in the porous film is preferably 3 μm or less, more preferably 1 μm or less. The porosity of the porous film is preferably 30 to 80% by volume, more preferably 40 to 70% by volume. In a sodium secondary battery, when the normal use temperature is exceeded, the micropores can be closed by the deformation and softening of the porous film by the shutdown function.

In this embodiment, specific examples of the resin constituting the porous film 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 terms of softening and shutting down at a lower temperature, the porous film preferably contains a polyolefin resin, and more preferably contains polyethylene. Specific examples of polyethylene include polyethylene such as low density polyethylene, high density polyethylene, and linear polyethylene, and ultrahigh molecular weight polyethylene can also be used. In the sense of further increasing the puncture strength of the porous film, the resin constituting it preferably contains at least ultra high molecular weight polyethylene. Moreover, it may be preferable to contain the wax which consists of polyolefin of a low molecular weight (weight average molecular weight 10,000 or less) in the manufacture surface of a porous film.

The thickness of the porous film is preferably 3 to 30 μm, more preferably 3 to 20 μm. Moreover, as thickness of a laminated film, Preferably it is 40 micrometers or less, More preferably, it is 20 micrometers 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.

Next, an example of manufacturing a laminated film will be described.
First, the manufacturing method of a porous film is demonstrated. The production of the porous film is not particularly limited. For example, as described in JP-A-7-29563, a plasticizer is added to a thermoplastic resin to form a film, and then the plasticizer is mixed with an appropriate solvent. As described in JP-A-7-304110, a film made of a thermoplastic resin produced by a known method is used, and a structurally weak amorphous portion of the film is selectively stretched. Thus, there is a method for forming fine holes.

For example, when the porous film is formed from a polyolefin resin containing ultra-high molecular weight polyethylene and a low molecular weight polyolefin having a weight average molecular weight of 10,000 or less, the following production method is preferable from the viewpoint of production cost. .

That is, as a 1st manufacturing method of a porous film,
(1) A step of kneading 100 parts by mass of ultrahigh molecular weight polyethylene, 5 to 200 parts by mass of a low molecular weight polyolefin having a weight average molecular weight of 10,000 or less, and 100 to 400 parts by mass of an inorganic filler to obtain a polyolefin resin composition ( 2) Step of forming a sheet using the polyolefin resin composition (3) Step of removing inorganic filler described later from the sheet obtained in step (2) (4) Sheet obtained in step (3) And a method including a step of obtaining a porous film by stretching.

Moreover, as a 2nd manufacturing method of a porous film,
(1) A step of kneading 100 parts by mass of ultrahigh molecular weight polyethylene, 5 to 200 parts by mass of a low molecular weight polyolefin having a weight average molecular weight of 10,000 or less, and 100 to 400 parts by mass of an inorganic filler to obtain a polyolefin resin composition ( 2) Step of forming a sheet using the polyolefin resin composition (3) Step of stretching the sheet obtained in step (2) (4) From the stretched sheet obtained in step (3), an inorganic filler And a method including a step of obtaining a porous film by removing.

From the viewpoint of the strength and ion permeability of the porous film, the inorganic filler used preferably has an average particle diameter (diameter) of 0.5 μm or less, and more preferably 0.2 μm or less. Here, the value measured from an electron micrograph is used for the average particle diameter. Specifically, 50 particles are arbitrarily extracted from the inorganic filler particles photographed in the photograph, each particle diameter is measured, and the average value is used.

Examples of the inorganic filler include calcium carbonate, magnesium carbonate, barium carbonate, zinc oxide, calcium oxide, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, calcium sulfate, silicic acid, zinc oxide, calcium chloride, sodium chloride, magnesium sulfate. Etc. These inorganic fillers can be removed from the sheet or film with an acid or alkaline solution. Calcium carbonate is preferably used from the viewpoints of particle size controllability and selective solubility in acid.

The method for producing the polyolefin resin composition is not particularly limited, but a mixing device, such as a roll, a Banbury mixer, a single screw extruder, a twin screw extruder, or the like, is used to mix materials constituting the polyolefin resin composition such as polyolefin resin and inorganic filler. And mixed to obtain a polyolefin resin composition. When mixing the materials, additives such as fatty acid esters, stabilizers, antioxidants, ultraviolet absorbers and flame retardants may be added as necessary.

The method for producing a sheet comprising the polyolefin resin composition is not particularly limited, and can be produced by a sheet forming method such as inflation processing, calendar processing, T-die extrusion processing, Skyf method. Since a sheet with higher film thickness accuracy can be obtained, it is preferable to produce the sheet by the following method.

A preferred method for producing a sheet comprising a polyolefin resin composition is a method of rolling a polyolefin resin composition using a pair of rotational molding tools adjusted to a surface temperature higher than the melting point of the polyolefin resin contained in the polyolefin resin composition. It is a method to do. The surface temperature of the rotary forming tool is preferably (melting point + 5) ° C. or higher. The upper limit of the surface temperature is preferably (melting point + 30) ° C. or less, and more preferably (melting point + 20) ° C. or less. Examples of the pair of rotary forming tools include a roll and a belt. The peripheral speeds of the two rotary forming tools do not necessarily have to be exactly the same peripheral speed, and the difference between them may be about ± 5% or less. By producing a porous film using a sheet obtained by such a method, a porous film excellent in strength, ion permeation, air permeability and the like can be obtained. Moreover, you may use what laminated | stacked the sheet | seat of the single layer obtained by the above methods for manufacture of a porous film.

When the polyolefin resin composition is roll-formed with a pair of rotary molding tools, the polyolefin resin composition discharged in a strand form from an extruder may be directly introduced between the pair of rotary molding tools, and once pelletized polyolefin A resin composition may be used.

When stretching a sheet made of a polyolefin resin composition or a sheet from which the inorganic filler has been removed, a tenter, a roll, an autograph or the like can be used. In view of air permeability, the draw ratio is preferably 2 to 12 times, more preferably 4 to 10 times. The stretching temperature is preferably performed at a temperature not lower than the softening point and not higher than the melting point of the polyolefin resin, and more preferably 80 to 115 ° C. If the stretching temperature is too low, film breakage tends to occur during stretching, and if it is too high, the air permeability and ion permeability of the resulting film may be lowered. Moreover, it is preferable to heat set after extending | stretching. The heat set temperature is preferably a temperature below the melting point of the polyolefin resin.

In this embodiment, a porous film containing a thermoplastic resin obtained by the method as described above and a heat-resistant porous layer are laminated to obtain a laminated film. The heat resistant porous layer may be provided on one side of the porous film or may be provided on both sides.

As a method of laminating a porous film and a heat-resistant porous layer, a method of separately producing a heat-resistant porous layer and a porous film and laminating each of them, and containing a heat-resistant resin and a filler on at least one surface of the porous film Examples of the method include forming a heat resistant porous layer by applying a coating liquid to be applied. In this embodiment, when the heat resistant porous layer is relatively thin, the latter method is preferable from the viewpoint of productivity.

Specific examples of a method for forming a heat resistant resin layer by applying a coating solution containing a heat resistant resin and a filler to at least one surface of the porous film include the following steps.
(A) In a polar organic solvent solution containing 100 parts by mass of a heat resistant resin, a slurry-like coating liquid is prepared by dispersing 1 to 1500 parts by mass of a filler with respect to 100 parts by mass of the heat resistant resin.
(B) The coating solution is applied to at least one surface of the porous film to form a coating film.
(C) The heat resistant resin is deposited from the coating film by means of humidification, solvent removal, or immersion in a solvent that does not dissolve the heat resistant resin, and then dried as necessary.

The coating liquid is preferably applied continuously by a coating apparatus described in JP-A-2001-316006 and a method described in JP-A-2001-23602.

In the polar organic solvent solution, when the heat-resistant resin is para-aramid, a polar amide solvent or a polar urea solvent can be used as the polar organic solvent, specifically, N, N-dimethyl. Examples include, but are not limited to, formamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone (NMP), tetramethylurea and the like.

When para-aramid is used as the heat-resistant resin, it is preferable to add an alkali metal or alkaline earth metal chloride during the para-aramid polymerization for the purpose of improving the solubility of para-aramid in a solvent. Specific examples include lithium chloride or calcium chloride, but are not limited thereto. The amount of the chloride added to the polymerization system is preferably in the range of 0.5 to 6.0 mol, more preferably in the range of 1.0 to 4.0 mol, per 1.0 mol of the amide group formed by condensation polymerization. . If the chloride is less than 0.5 mol, the solubility of the resulting para-aramid may be insufficient, and if it exceeds 6.0 mol, the solubility of the chloride in the solvent may be substantially exceeded, which may be undesirable. . Generally, if the alkali metal or alkaline earth metal chloride is less than 2% by mass, the solubility of para-aramid may be insufficient. If it exceeds 10% by mass, the alkali metal or alkaline earth metal chloride may be insufficient. May not dissolve in polar organic solvents such as polar amide solvents or polar urea solvents.

When the heat-resistant resin is an aromatic polyimide, the polar organic solvent for dissolving the aromatic polyimide includes those exemplified as the solvent for dissolving aramid, dimethyl sulfoxide, cresol, and o-chlorophenol. It can be used suitably.

As a method of dispersing the filler to obtain a slurry-like coating liquid, a pressure disperser (Gorin homogenizer, nanomizer) or the like may be used as the apparatus.

Examples of the method of applying the slurry-like coating liquid include a coating method such as a knife, blade, bar, gravure, die, etc., and coating of a bar, knife, etc. is simple, but industrially, Die coating having a structure in which the solution does not come into contact with outside air is preferable. Moreover, coating may be performed twice or more. In this case, it is usual to carry out after depositing the heat-resistant resin in the step (c).

In the case where the heat-resistant porous layer and the porous film are separately manufactured and laminated, it is preferable to fix them by a method using an adhesive, a method using thermal fusion, or the like.

<Layer containing negative electrode active material>
As the negative electrode active material of the sodium secondary battery of the present embodiment, a known electrode active material that can be doped and dedoped with sodium can be used. Among these, a carbon material is preferable, and the carbon material is more preferably non-graphitizable carbon or graphitizable carbon.

Here, “non-graphitizable carbon” is a carbon material that does not easily become graphite even when heated in an inert atmosphere, and is also a material called hard carbon. It has minute graphite crystals irregularly and has pores with a size of several nanometers between the crystals.

“Easily graphitized carbon” is a carbon material in which a graphite structure having a three-dimensional stacking regularity is easily formed by heat treatment at a high temperature of 2500 ° C. or more (prone to become graphite). It is called a material.

For both “non-graphitizable carbon” and “graphitizable carbon”, the value of the lattice spacing on the 002 plane, which can be examined by X-ray diffraction measurement of the carbon material powder, is the value of the lattice spacing on the 002 plane of graphite. It is larger than 3.3Å (0.33 nm) to 3.4Å (0.34 nm). That is, “non-graphitizable carbon” and “graphitizable carbon” both have layers having a graphene structure, but the distance between each layer is larger than 3.4 mm (0.34 nm). Yes. By having such a structure, sodium can be doped (inserted) or dedoped (desorbed) into the gap between the layers.

The spacing between layers is wider for non-graphitizable carbon than for graphitizable carbon. For this reason, non-graphitizable carbon is more preferable than graphitizable carbon because the layer having a graphene structure is rearranged by heating and the reaction of generating graphite is less likely to occur, and as a result, capacity reduction is less likely to occur in a high-temperature environment. .

In the X-ray diffraction measurement, when a Cu-Kα ray is used as a target, a 002 diffraction line is obtained when 2θ is around 23 ° to 27 °, and the lattice spacing of the 002 plane can be measured.

Furthermore, the carbon material is non-graphitizable carbon, and preferably satisfies one or more requirements selected from the group consisting of the following conditions 1, 2, 3, and 4.

[Condition 1]
Condition 1 is that Raman spectroscopy measurement is performed using a laser having a wavelength of 532 nm, and the obtained Raman spectrum has one peak in each of a wavelength range of 1300 to 1400 cm ^{−1 and} a range of 1570 to 1620 cm ⁻¹ , A fitting function is obtained by performing fitting using two Lorentz functions and one baseline function in a wavelength range of 600 to 1740 cm ⁻¹ of the Raman spectrum, and then subtracts the baseline function after fitting from the fitting function. R obtained by dividing ID by IG, where ID is the maximum value of the scattering intensity in the wavelength range of 1300 to 1400 cm ⁻¹ and IG is the maximum value in the wavelength range of 1570 to 1620 cm ^−1. 1.07 or more and 3 or less. That's it. When such a carbon material is used as a negative electrode active material, sodium ions can be efficiently doped and dedoped in a sodium secondary battery. Further, when a sodium secondary battery using such a carbon material as a negative electrode active material is charged and discharged, the discharge capacity is unlikely to decrease even if charging and discharging are repeated.

In the present embodiment, the Raman spectrum is obtained by using a microscopic Raman spectroscope (manufactured by JASCO Corporation, model number NRS-1000), as a laser beam having a wavelength of 532 nm, an output of 5 mW, a single spectrometer, and an electronically cooled CCD detector. It can be obtained by measuring with an irradiation time of 15 seconds and an integration count of 10 times. In the obtained Raman spectrum, the vertical axis represents the scattered light intensity in arbitrary units, and the horizontal axis represents the wave number of Raman shift (unit: cm ⁻¹ ).

Note that in the Raman spectroscopic measurement, the carbon material which is the negative electrode active material can be measured as it is, or the layer containing the negative electrode active material having a carbon material may be measured. In this case, as a production condition of the layer containing the negative electrode active material, the carbon material and polyvinylidene fluoride are weighed so that the mass ratio is 85:15, and these are converted into N-methyl-2-pyrrolidone (NMP). It is recommended to disperse and apply 0.1 mm of the resulting slurry on a copper foil and vacuum dry at 150 ° C. In addition, when Raman spectroscopic measurement is performed on a layer containing a negative electrode active material, a laser is irradiated onto the surface coated with the carbon material that is the negative electrode active material.

R is obtained by the following (1) to (4).

(1) Using two Lorentz functions and one baseline function, the following equation (a) is obtained.
y = [A ₁ / {(x−x ₁ ) ² + B ₁ ² }] + [A ₂ / {(x−x ₂ ) ² + B ₂ ² }] + [C ₁ x ³ + C ₂ x ² + C ₃ x + C ₄ ] ... (a)

The first term on the right side is a Lorentz function which is a response function indicating a Raman spectrum in the wave number range of 1300 to 1400 cm ⁻¹ , A ₁ is the maximum scattering intensity of the peak in this range, and B ₁ is the half-width at half maximum of the peak. (Unit: cm ⁻¹ ), x ₁ is the wave number (unit: cm ⁻¹ ) at the maximum value of the scattering intensity of the peak.
The second term on the right side is a Lorentz function which is a response function indicating a Raman spectrum in the wave number range of 1570 to 1620 cm ⁻¹ , A ₂ is the maximum scattering intensity of the peak in this range, and B ₂ is the half-width at half maximum (unit) : Cm ⁻¹ ), x ₂ is the wave number (unit: cm ⁻¹ ) at the maximum value of the scattering intensity of the peak.
The third term on the right side is a baseline function using a cubic polynomial.
In the above formula (a), A ₁ , B ₁ , x ₁ , A ₂ , B ₂ , x ₂ , C ₁ , C ₂ , C ₃ and C ₄ are unknowns.

(2) On the other hand, the above A ₁ , B ₁ , x ₁ , A _{2 are} obtained by the least square method using 1000 or more data points (x, y) in the wave number range of 600 to 1740 cm ⁻¹ of the measured Raman spectrum. , B ₂ , x ₂ , C ₁ , C ₂ , C _3, and C ₄ are obtained, and the above equation (a) is fitted. Thus, a fitting function is obtained by substituting the optimum values of A ₁ , B ₁ , x ₁ , A ₂ , B ₂ , x ₂ , C ₁ , C ₂ , C ₃ and C ₄ into the above formula (a).

(3) Subtract the third term (baseline function) on the right side from the fitting function to obtain a fitting spectrum. The fitting spectrum is represented by the following formula (b).
y = [A ₁ / {(x−x ₁ ) ² + B ₁ ² }] + [A ₂ / {(x−x ₂ ) ² + B ₂ ² }] (b)

(4) In the fitting spectrum, the maximum value of the scattered light intensity in the wave number range of 1300 to 1400 cm ⁻¹ is ID, the maximum value of the scattered light intensity in the wave number range of 1570 to 1620 cm ⁻¹ is IG, and ID is divided by IG. (ID / IG) to obtain R. Note that the value of R matches the value of A ₁ / A ₂ .

In the above fitting spectrum, A ₁ / B ₁ obtained by dividing the maximum scattering intensity of the peak in the wave number range of 1300 to 1400 cm ⁻¹ by the half width of the peak indicating the maximum intensity, and the wave number of 1570 to 1620 cm ⁻¹ . A ₂ / B ₂ obtained by dividing the maximum intensity of the peak of the range by the half width of the peak indicating the maximum intensity is obtained, and (A ₁ / B ₁ ) is divided by (A ₂ / B ₂ ) ( (A ₁ × B ₂ ) / (B ₁ × A ₂ )), an NR value is obtained.

In the present embodiment, the fitting is performed using software “Igor Pro (name), manufactured by Wave Metrics”.

R is preferably 1.10 or more and 3 or less, more preferably 1.3 or more and 3 or less, in the sense of further increasing the charge / discharge capacity of the sodium secondary battery of the present embodiment.

B ₁ represents, in the sense of enhancing the charge-discharge capacity of a sodium secondary battery of the present embodiment is preferably in the range of 25 cm ^-1 or more 100 cm ^-1 or less.

NR is preferably 0.62 or more in order to further increase the charge / discharge capacity of the sodium secondary battery of the present embodiment.

[Condition 2]
Next, Condition 2 will be described among the conditions to be satisfied by the carbon material used as the negative electrode active material of the sodium secondary battery of the present embodiment.

Condition 2 is the X-ray small angle scattering spectrum obtained by X-ray small angle scattering measurement, the slope of the approximate straight line obtained by linear approximation by the least square method for 0.6 nm ^-1 or 1.8 nm ^-1 or less wave number range A, where the standard deviation of _A is σ _A , the A is −0.5 or more and 0 or less, and the σ _A is 0 or more and 0.010 or less.
When such a carbon material is used as the negative electrode active material, a sodium secondary battery having excellent charge / discharge characteristics can be obtained.

In this embodiment, X-ray small angle scattering measurement is performed using an X-ray small angle scattering device (NanoSTAR, manufactured by Bruker AXS Co., Ltd.) equipped with a two-dimensional detector.

Hereinafter, specific examples of measurement will be described.
A carbon material to be measured is filled in a quartz capillary with an inner diameter of 1 mm, and a rotating X-ray generator of a Cu target with a Cu target is used to irradiate X-rays generated at an output of 50 kV and 100 mA. In the measurement using the X-ray small-angle scattering apparatus, the X-ray is an X-ray consisting of a cross-coupled Gobel mirror and three pinhole slits (the diameters of the slits are 500 μmφ, 150 μmφ, and 500 μmφ from the X-ray generator side). The carbon material is irradiated through the optical system and further through the quartz capillary.

X-rays scattered by the carbon material are detected using a two-dimensional detector (two-dimensional Multi Wire detector, Hi-STAR). The camera length from the sample to the detector is 106 cm, and the size of the direct beam stopper is 2 mmφ. The degree of vacuum in the apparatus is 40 Pa or less. The calibration of the scattering angle 2θ and the direct beam position is performed using the primary (2θ = 1.513 °) and secondary (2θ = 3.027 °) peaks of silver behenate. In this case, the range of the scattering angle 2θ that can be measured is 0.08 to 3 °.

The detected two-dimensional scattered image is analyzed according to a conventional method using analysis software (SAXS Ver. 4.1.29, manufactured by Bruker AXS), and an X-ray small angle scattering spectrum is obtained. In the obtained X-ray small angle scattering spectrum, the horizontal axis is wave number q (nm ⁻¹ ), and the vertical axis is S (common logarithm of scattering intensity I: log (I)).

Also, only a quartz capillary containing no carbon material is measured in the same manner as described above to obtain a blank X-ray small angle scattering spectrum (hereinafter sometimes referred to as “blank”). If the value of S at the time of q = 0.6 nm ^-1 in the X-ray small angle scattering spectrum of the carbon material is not less than 10 times the value of q = 0.6 nm ^-1 in the blank, the X-ray small angle scattering of the carbon material The spectrum shall be reliable.

Moreover, the 0.6 nm ^-1 or 1.8 nm ^-1 or less in the wavenumber range of small-angle X-ray scattering spectrum, determine the approximate straight line linearly approximated by the least square method, the standard deviation of the slope A and A of the approximate line sigma _A Ask for. For the calculation of A and σ _A , software “Igor Pro (name), manufactured by Wave Metrics” is used. Linear approximation is performed by partitioning the 100 points at equal intervals in the 0.6 nm ^-1 or 1.8 nm ^-1 or less in the wavenumber range.

[Condition 3]
Next, Condition 3 will be described among the conditions to be satisfied by the carbon material used as the negative electrode active material of the sodium secondary battery of the present embodiment.

Condition 3 is that for an electrode having an electrode mixture obtained by mixing 85 parts by mass of a carbon material and 15 parts by mass of polyvinylidene fluoride, the carbon material in the electrode after sodium ion doping and dedoping is 10 nm. The above pores are substantially absent.
When such a carbon material is used as the negative electrode active material, a sodium secondary battery having excellent charge / discharge characteristics can be obtained.

Specifically, first, an electrode having an electrode mixture obtained by mixing 85 parts by mass of a carbon material and 15 parts by mass of polyvinylidene fluoride is used as a negative electrode, sodium metal is used as a counter electrode, and a sodium secondary battery is manufactured. The current is made to flow from the negative electrode to the counter electrode. Thereby, the negative electrode is doped with sodium ions. Sodium ion doping is performed at a constant current until 0.005 V is reached at a current of 10 mA per 1 g of the carbon material.

Next, with respect to the sodium secondary battery having a negative electrode doped with sodium ions by the above operation, a current is passed from the counter electrode to the negative electrode. As a result, sodium ions are dedoped from the negative electrode. Sodium ion dedoping is performed at a constant current until 1.5 V is reached at a current of 10 mA per 1 g of the carbon material.

After de-doping sodium ions from the negative electrode, the battery is decomposed in an inert atmosphere such as dry Ar or nitrogen, the negative electrode is taken out, washed with dimethyl carbonate (hereinafter sometimes referred to as DMC), and in vacuum After drying, the electrode mixture is recovered.

In this embodiment, the fact that pores having a diameter of 10 nm or more are not substantially present in the carbon material is confirmed by image observation of a bright field image using a transmission electron microscope (TEM).

Specifically, for the collected electrode mixture, a focused ion beam processing apparatus is used to produce a slice having a thickness of about 100 nm to 200 nm for the carbon material particles contained in the collected electrode mixture. The obtained slice is observed at an acceleration voltage of 200 kV to confirm that pores having a diameter of 10 nm or more are not substantially present in the carbon material in the image field.

In this embodiment, the diameter of the pore is determined as the area equivalent diameter for the pore image obtained by image observation by the above method.

Note that sample transfer between each operation is performed in an inert atmosphere.

In this embodiment, the pores of the carbon material may be pores inside the carbon material or may be on the surface. In any case, it is determined by the above image observation.

[Condition 4]
Next, Condition 4 among the conditions to be satisfied by the carbon material used as the negative electrode active material of the sodium secondary battery of the present embodiment will be described.

Condition 4 is that for an electrode having an electrode mixture obtained by mixing 85 parts by mass of a carbon material and 15 parts by mass of polyvinylidene fluoride, 1 mg of the electrode mixture in the electrode after sodium ion doping and non-aqueous electrolysis 8 mg of a liquid (concentration 1M NaClO ₄ / propylene carbonate) is put in a sealed container, α-Al ₂ O ₃ is used as a reference, a heating rate is 10 ° C./min, and a differential thermal analysis is performed in a range of 40 ° C. to 410 ° C. The total calorific value (Q ₁ value) per 1 g of the electrode mixture and non-aqueous electrolyte in the range of 100 ° C. or more and 400 ° C. or less, which is obtained by measurement, is 800 joules / g or less. .
When such a carbon material is used as the negative electrode active material, a sodium secondary battery having excellent charge / discharge characteristics can be obtained.

In this embodiment, the differential thermal analysis measurement is performed using a differential thermal analysis measurement apparatus (DSC200, manufactured by Seiko Instruments Inc.).

Specifically, first, for an electrode having an electrode mixture obtained by mixing 85 parts by mass of a carbon material and 15 parts by mass of polyvinylidene fluoride, the electrode is used as a negative electrode and a counter electrode is used, for example, sodium metal. Then, a battery is prepared, and a current is passed from the negative electrode to the counter electrode, so that the negative electrode is doped with sodium ions. At this time, it is carried out with a constant current until it becomes 0.005 V at a current of 10 mA per 1 g of the carbon material.

After doping, the battery is decomposed in an inert atmosphere such as dry Ar, the negative electrode is taken out, washed with dimethyl carbonate (hereinafter sometimes referred to as DMC), dried in vacuum, and then electrode mixture Recover. The electrode mixture is doped with sodium ions.

Next, in an inert atmosphere such as in dry Ar, 1 mg of the electrode mixture after recovery and 8 mg of non-aqueous electrolyte (NaClO ₄ / propylene carbonate at a concentration of 1 M) (volume: 2 μL) were sealed in a sealed container for differential thermal analysis measurement. The sample was put in, sealed with caulking, and differential thermal analysis measurement was performed in the range of 40 ° C. or higher and 410 ° C. or lower, with α-Al ₂ O _{3 as the} reference and a heating rate of 10 ° C./min. A total calorific value (Q ₁ value) per 1 g of the electrode mixture and the nonaqueous electrolytic solution in the range of from 0 ° C. to 400 ° C. is obtained.

Here, the Q ₁ value can be obtained by using an endothermic spectrum obtained by differential thermal analysis measurement (the horizontal axis is the heat flow (unit: mW), and the vertical axis is the temperature (unit: ° C.)). .

The Q ₁ value is 800 joules / g or less. In order to further enhance the effect of the sodium secondary battery of the present embodiment, the total calorific value per 1 g of the electrode mixture and the non-aqueous electrolyte in the range of 100 ° C. to 200 ° C. in the differential thermal analysis measurement (Q ₂ Value) is preferably 50 joules / g or less.

Furthermore, the total endothermic value (Q ₃ value) per 1 g of the electrode mixture and non-aqueous electrolyte in the range of 90 ° C. or more and 100 ° C. or less in the differential thermal analysis measurement is 0.5 joule / g or less. preferably, the more preferred _{Q 3} value is below 0.2 joules / g.

In this way, precipitation of sodium metal in the carbon material can be further suppressed.

Here, the Q ₂ value and Q ₃ value are obtained by using an endothermic spectrum obtained by differential thermal analysis measurement (the horizontal axis is the heat flow (unit: mW), and the vertical axis is the temperature (unit: ° C.)). Obtainable.

In the present embodiment, the carbon material satisfies any one of the above conditions 1 to 4, but preferably satisfies the condition 1, and satisfies the conditions 1, 2, or 1, 3 or 1, 4 It is more preferable that the conditions 1, 2, 3 or the conditions 1, 2, 4 are satisfied, and it is more preferable that all of the above conditions 1 to 4 are satisfied.

In the present embodiment, the carbon material may be a powder. If the BET specific surface area at that time is 1 m ² / g or more, the wettability of the electrolytic solution is good, the time required for pouring the liquid at the time of battery production is shortened, and the advantages in battery production are great. Moreover, it is preferable that the BET specific surface area of a carbon material is 700 m < ² > / g or less.

The BET specific surface area can be measured from a value calculated from a nitrogen adsorption isotherm at liquid nitrogen temperature. In the present embodiment, AUTOSORB manufactured by Yuasa Ionics is used as the measuring device.

In the present embodiment, the carbon material is in a powder form, and the average particle size of the constituent particles is preferably 50 μm or less, more preferably 30 μm or less, and even more preferably 10 μm or less. When the carbon material is fine, the packing density of the electrode is improved and the internal resistance is reduced.

Here, the average particle diameter is a volume average particle diameter measured using a laser diffraction particle size distribution measuring device (for example, SALD2000J (registered trademark, manufactured by Shimadzu Corporation)) by dispersing a carbon material in a neutral detergent-containing aqueous solution. means.

In order to further increase the charge / discharge capacity of the sodium secondary battery of the present embodiment, the carbon material preferably has an atomic ratio (H / C) of hydrogen to carbon of 0.2 or less.

Further, as a carbon material suitable for the present embodiment, carbon microbeads can be mentioned, and specifically, an ICB (trade name: Nika beads) manufactured by Nippon Carbon Co., Ltd. can be mentioned.

Hereinafter, a method for producing a carbon material that can be used in the sodium secondary battery of the present embodiment will be described.

The carbon material in the present embodiment is a carbon material that satisfies the above conditions, such as a carbon material obtained by carbonization of various organic materials, such as a material having an R value of 1.07 or more and 3 or less (condition 1). Use it. Organic materials include natural mineral resources such as petroleum and coal, and various synthetic resins (thermosetting resin, thermoplastic resin, etc.) synthesized from these resources as well as petroleum pitch, coal pitch, spinning pitch, etc. Various plant residue oils, plant-derived organic materials such as wood, and the like can be used, and these organic materials may 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 synthetic resins may be used alone or in combination of two or more. Moreover, you may add a hardening | curing agent and an additive. The curing method is not particularly limited. For example, when a phenol resin is used, examples thereof include thermal curing, thermal oxidation, epoxy curing, and isocyanate curing. In the case of using an epoxy resin, phenol resin curing, acid anhydride curing, amine curing, and the like can be given.

Among organic materials, organic materials having an aromatic ring are preferable. By using the organic material, the carbon material can be obtained with high yield, the environmental load is small, the production 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, which may be used alone or in combination of two or more. Moreover, you may add the hardening | curing agent and the additive.

As the organic material having an aromatic ring, an organic material obtained by polymerizing phenol or a derivative thereof and an aldehyde compound is preferable. 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 preferable as the carbon material in the present embodiment.

As an organic material obtained by polymerizing phenol or a derivative thereof and an aldehyde compound, a phenol resin can be exemplified. Phenolic resins are inexpensive and have a large industrial production amount, which is preferable as a raw material for carbon materials. When a carbon material obtained by carbonizing a phenol resin is used as an active material of a sodium secondary battery, particularly as a negative electrode active material, the charge / discharge capacity of the secondary battery, particularly the discharge capacity after repeated charge / discharge is large. The phenolic resin is characterized by a structure with developed three-dimensional crosslinking, and the carbon material obtained by carbonizing the resin is also a carbon material having a developed structure with unique three-dimensional crosslinking derived from the characteristics. Estimated. It is estimated that this structure contributes to the large discharge capacity.

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 may 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 may be used alone or in combination of two or more.

The phenol resin is not particularly limited, and examples thereof 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, and the novolac type phenol resin can be obtained by using phenol or a derivative thereof and an aldehyde compound as an acidic catalyst. It can be obtained by polymerizing in the presence.

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. Moreover, you may add combining them.

The novolak type phenol resin is a method in which phenol or a derivative thereof and an aldehyde compound are subjected to a condensation reaction at a normal pressure of 100 ° C. for several hours using a known organic acid and / or inorganic acid as a catalyst, followed by dehydration and unreacted monomer removal. A random novolak type in which the position of the methylene group is the same as the ortho-position and the para-position, and phenol or a derivative thereof and an aldehyde compound, such as zinc acetate, lead acetate, zinc naphthenate, etc. After the addition condensation reaction with a catalyst under weak acidity, the condensation reaction proceeds directly or with further addition of an acid catalyst while dehydrating, and if necessary, the step of removing unreacted substances. Many high ortho novolaks are known.

As the phenol resin, commercially available products can be used, for example,
Powdered phenol resin (manufactured by Gunei Chemical Co., Ltd., trade names: Resitop, PGA-4528, PGA-2473, PGA-4704, PGA-4504, manufactured by Sumitomo Bakelite Co., Ltd., trade names: Sumilite Resin PR-UFC-504, PR -EPN, PR-ACS-100, PR-ACS-150, PR-12687, PR-13355, PR-16382, PR-217, PR-310, PR-311, PR-50064, PR-50099, PR-50102 , PR-50252, PR-50395, PR-50590, PR-50590B, PR-50699, PR-50869, PR-51316, PR-51326B, PR-51350B, PR-51510, PR-51541B, PR-51794, PR -51820, PR-51939, P -53153, PR-53364, PR-53497, PR-53724, PR-53769, PR-53804, PR-54364, PR-54458A, PR-54545, PR-55170, PR-8000, PR-FTZ-1, PR -FTZ-15);
Liquid phenolic resin (PR-51947A, PR-53123, PR-53338, PR-53717, PR-54135, PR54313, PR54562), flaky phenolic resin (manufactured by Sumitomo Bakelite Co., Ltd., trade name: Sumilite Resin PR-12686R, PR -13349, PR-50235A, PR-51363F, PR-51494G, PR-51618G, PR-53194, PR-53195, PR-54869, PR-F-110, PR-F-143, PR-F-151F, PR -F-85G, PR-HF-3, PR-HF-6);
Liquid phenolic resin (manufactured by Sumitomo Bakelite Co., Ltd., trade names: Sumilite Resin PR-50087, PR-50607B, PR-50702, PR-50781, PR-51138C, PR-51206, PR-51663, PR-51947A, PR-53123 , PR-53338, PR-53365, PR-53717, PR-54135, PR-54313, PR-54562, PR-55345, PR-940, PR-9400, PR-967);
Novolak-type liquid phenolic resin (manufactured by Sumitomo Bakelite Co., Ltd., trade names: Sumilite Resin PR-51629, PR-53093, PR-53473, PR-53522, PR-53546, PR-53800, PR-54438, PR-54540C, PR -55438);
Resole type liquid phenol resin (manufactured by Gunei Chemical Co., Ltd., trade names: Resitop PL-4826, PL-2390, PL-4690, PL-3630, PL-4222, PL-4246, PL-2211, PL-3224, PL- 4329, manufactured by Sumitomo Bakelite Co., Ltd., trade names: Sumilite Resin PR-50273, PR-51206, PR-51781, PR-53056, PR-53311, PR-53416, PR-53570, PR-54387),
Fine particulate phenol resin (trade name: Belpearl, R800, R700, R600, R200, R100, S830, S870, S890, S895, S290, S190, manufactured by Air Water);
True spherical phenol resin (manufactured by Gunei Chemical Co., Ltd., trade names: Marilyn GU-200, FM-010, FM-150, HF-008, HF-015, HF-075, HF-300, HF-500, HF-1500 );
Solid phenolic resin (manufactured by Gunei Chemical Co., Ltd., trade names: Residtop PS-2601, PS-2607, PS-2655, PS-2768, PS-2608, PS-4609, PSM-2222, PSK-2320, PS-6132)
Etc. are exemplified.

A wide variety of other organic materials can be used as the organic material having an aromatic ring in the molecular structure. It is not necessary to be a synthetic resin as described above, and any organic material that can become a carbon material by carbonization may be used.

The synthetic resin is generally characterized by polymerizing monomers to form a polymer, but as the organic material having an aromatic ring in the present embodiment, an organic material in which several to several tens of monomers are polymerized is used. You can also.

In the polymerization of phenol or a derivative thereof and an aldehyde compound, a by-product may be generated or an unpolymerized product may remain. In the present embodiment, these by-products and an unpolymerized product are removed. It can also be used as an organic material, can reduce the environmental burden in terms of reducing waste, and can obtain a carbon material at a low cost, which has a higher industrial utility value.

Moreover, in this embodiment, by using a carbon material obtained by carbonizing a plant-derived organic material as the carbon material, the environmental load can be reduced, and the industrial utility value is higher.

Wood can be used as an organic material derived from plants, and charcoal obtained by carbonizing this is a preferred embodiment as a carbon material in the present embodiment. In addition, as the timber, waste timber, waste timber generated in a wood processing process such as sawdust, forest thinned timber, and the like can be used. As the constituent components of wood, three types of cellulose, hemicellulose and lignin are generally listed as the main components, and lignin is also an organic material having an aromatic ring and is preferable.

Wood includes cycads, ginkgo biloba, conifers (cedar, cypress, Japanese red pine, etc.), maize, etc. And angiosperms such as mosquitoes.

Among the above-mentioned timber, cedar is widely used as a building material, and cedar sawdust generated in the processing process is preferable because it can reduce the environmental burden and obtain a carbon material at low cost. Bincho charcoal obtained by carbonizing oak is also a preferred embodiment as a carbon material in the present embodiment.

Further, in this embodiment, by using a carbon material obtained by carbonization of plant residue oil as the carbon material, resources can be effectively used, and industrial utility value is higher.

As the plant residual oil, various residual oils at the time of manufacturing various petrochemical products such as ethylene can be exemplified. More specifically, petroleum heavy oil composed of distillation residue oil, fluid catalytic cracking residue oil, hydrodesulfurized oil thereof, or mixed oil thereof can be exemplified. Among them, it is preferable to use a residual oil at the time of producing a petrochemical product having an aromatic ring, and specifically, a residual oil at the time of producing resorcinol can be mentioned.

Residual oil at the time of resorcinol production can be obtained, for example, as follows. A liquid composition containing an alkyl aromatic hydrocarbon is oxidized to a liquid composition containing an aromatic hydroperoxide, and the liquid composition is contacted with an aqueous alkali solution to extract the aromatic hydroperoxide into an oil phase. To do. The resulting oil phase and acid are brought into contact with each other, the aromatic hydroperoxides are acid-decomposed and converted into an oil phase containing resorcinol, and the light-boiling component containing an organic solvent and resorcinol and tar are separated to produce tar. Get. This tar can be used as a residual oil during the production of resorcinol, and a carbon material obtained by carbonizing this tar is a preferred carbon material in the present embodiment.

The carbon material in the present embodiment can be obtained by carbonizing the above-mentioned various organic materials singly or in combination of two or more. The carbonization temperature is preferably 800 ° C. or higher and 2500 ° C. or lower, and carbonization is preferably performed in an inert gas atmosphere. Further, the organic material may be carbonized as it is, or a fired 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. For these heating and carbonization, for example, equipment such as a rotary kiln, roller hearth kiln, pusher kiln, multi-stage furnace, fluidized furnace or the like may be used. Rotary giraffes are versatile.

In addition, the carbon material obtained by the carbonization may be activated. In the present embodiment, the carbon material is preferably an unactivated carbon material, that is, an unactivated carbon material. Here, the activation means that a carbon material obtained by carbonization is further fired at a temperature of 200 ° C. or higher and 1500 ° C. or lower in the presence of an oxidizing gas.

Further, the carbon material obtained by carbonization may be pulverized as necessary. For pulverization, for example, impact friction pulverizer, centrifugal pulverizer, ball mill (tube mill, compound mill, conical ball mill). , Rod mills), vibration mills, colloid mills, friction disk mills, jet mills, and the like are preferably used, and grinding by a ball mill is generally used. During the pulverization, it is better to avoid mixing metal powder, and it is better to use a non-metallic material such as alumina or agate for the contact portion of the carbon material in these pulverizers.

It is preferable that a buffer layer is further provided on the surface of the negative electrode active material. The presence of the buffer layer makes it possible to have a potential gradient and smooth charge and discharge.

In the present embodiment, the layer containing the negative electrode active material is, for example, an electrode mixture containing a carbon material, a binder (binder), and, if necessary, a conductive agent in the present embodiment supported on a current collector. It is a thing, Preferably it is a sheet form.

In this case, as a manufacturing method of the layer containing the negative electrode active material, for example,
(1) A method in which an electrode mixture formed by adding a solvent to a carbon material, a binder, a conductive agent, etc., is applied to a current collector by a doctor blade method, or dipped and dried (2) a carbon material, a binder (3) a carbon material, which is obtained by adding a solvent to a conductive agent, kneading, shaping, drying, and bonding a sheet obtained by drying to a current collector surface via a conductive adhesive or the like, followed by pressing and heat treatment drying. A method of forming a mixture comprising a binder, a conductive agent and a liquid lubricant on a current collector, removing the liquid lubricant, and then stretching the resulting sheet-like molded product in a uniaxial or multiaxial direction. Etc.
When the electrode is in the form of a sheet, the thickness is preferably about 5 to 500 μm.

As a material of the current collector carrying the layer containing the negative electrode active material,
Metals such as nickel, aluminum, titanium, copper, gold, silver, platinum, aluminum alloys or stainless steel;
Formed by plasma spraying or arc spraying of carbon material, activated carbon fiber, nickel, aluminum, zinc, copper, tin, lead or alloys thereof;
A conductive film in which a conductive agent is dispersed in a resin such as rubber or styrene-ethylene-butylene-styrene copolymer (SEBS);
Etc. Among these, aluminum, an aluminum alloy, nickel, and stainless steel are preferable, and aluminum and an aluminum alloy are more preferable from the viewpoint of being easily processed into a thin film and being inexpensive.

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, or a punching metal shape, or a combination thereof (for example, a mesh flat plate). Moreover, you may form the unevenness | corrugation by an etching process or embossing on the surface of a collector.

Examples of the binder include a monomer addition polymer (fluorine compound) containing a fluorine atom and an ethylenic double bond.
As such a monomer, for example,
(Meth) acrylate having a fluorinated alkyl group having 1 to 18 carbon atoms;
(Meth) acrylates having a C 1-18 perfluoroalkyl group such as perfluorododecyl (meth) acrylate, perfluoro n-octyl (meth) acrylate, perfluoro n-butyl (meth) acrylate;
(Meth) acrylates having an alkyl group substituted with a perfluoroalkyl group, such as perfluorohexylethyl (meth) acrylate, and perfluorooctylethyl (meth) acrylate;
(Meth) acrylates having an alkyl group substituted with a perfluorooxy group such as perfluorododecyloxyethyl (meth) acrylate and perfluorodecyloxyethyl (meth) acrylate;
A crotonate having a fluorinated alkyl group of 1 to 18 carbon atoms;
A malate having a fluorinated alkyl group having 1 to 18 carbon atoms;
A fumarate having a fluorinated alkyl group having 1 to 18 carbon atoms;
Itaconate having a fluorinated alkyl group of 1 to 18 carbon atoms;
Examples thereof include fluorinated olefins having 2 to 10 carbon atoms and 1 to 17 fluorine atoms, such as perfluorohexylethylene, tetrafluoroethylene, trifluoroethylene, vinylidene fluoride and hexafluoropropylene.

Further, as the binder, a copolymer of the above-described fluorine compound and a monomer containing an ethylenic double bond that does not contain a fluorine atom described later can be given.

Examples of the binder include monomer addition polymers (non-fluorine polymers) containing an ethylenic double bond that does not contain a fluorine atom. In the present embodiment, the layer containing the negative electrode active material preferably has a non-fluorine polymer, and can reduce the initial irreversible capacity of the sodium secondary battery.

As a monomer constituting the non-fluorine polymer, 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 ( (Cyclo) alkyl (meth) acrylates having 1 to 22 carbon atoms such as (meth) acrylate and octadecyl (meth) acrylate;
Aromatic ring-containing (meth) acrylates such as benzyl (meth) acrylate and phenylethyl (meth) acrylate;
Alkylene glycol having 2 to 4 carbon atoms of alkylene group such as 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, and diethylene glycol mono (meth) acrylate or dialkyl having 2 to 4 carbon atoms of alkylene group Mono (meth) acrylates of alkylene glycols;
(Poly) glycerin mono (meth) acrylate having a degree of polymerization of 1 to 4;
(Poly) ethylene glycol di (meth) acrylate having a polymerization degree of 1 to 100, (poly) propylene glycol di (meth) acrylate having a polymerization degree of 1 to 100, and 2,2-bis (4-hydroxyethylphenyl) propanedi ( (Meth) acrylates and (meth) acrylate monomers such as polyfunctional (meth) acrylates such as trimethylolpropane tri (meth) acrylate;
(Meth) acrylamide monomers such as N-methylol (meth) acrylamide and (meth) acrylamides such as diacetone acrylamide and (meth) acrylamide derivatives;
Cyano group-containing monomers such as (meth) acrylonitrile, 2-cyanoethyl (meth) acrylate, and 2-cyanoethylacrylamide;
Styrene and styrenic monomers such as α-methylstyrene, vinyltoluene, p-hydroxystyrene, and styrene derivatives having 7 to 18 carbon atoms such as divinylbenzene;
Diene monomers such as butadiene, isoprene and alkadienes having 4 to 12 carbon atoms such as chloroprene;
Such as vinyl acetate, vinyl propionate, vinyl butyrate, and vinyl octoate such as carboxylic acid vinyl esters of 2 to 12 carbon atoms, (meth) allyl acetate, (meth) allyl propionate, and (meth) allyl octanoate Alkenyl ester monomers such as carboxylic acid (meth) allyl esters having 2 to 12 carbon atoms;
Epoxy group-containing monomers such as glycidyl (meth) acrylate and (meth) allyl glycidyl ether;
Monoolefins having 2 to 12 carbon atoms, such as ethylene, propylene, 1-butene, 1-octene, and 1-dodecene;
Monomers containing halogen atoms other than fluorine, such as chlorine, bromine or iodine atom-containing monomers, vinyl chloride and vinylidene chloride;
(Meth) acrylic acid such as acrylic acid and methacrylic acid;
Etc.

The addition polymer may be a copolymer such as an ethylene / vinyl acetate copolymer, a styrene / butadiene copolymer, or an ethylene / propylene copolymer. Moreover, the carboxylic acid vinyl ester polymer may be partially or completely saponified, such as polyvinyl alcohol.

In addition, examples of the compound that can be used as a binder include polysaccharides such as starch, methylcellulose, carboxymethylcellulose, hydroxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, carboxymethylhydroxyethylcellulose, and nitrocellulose and derivatives thereof;
Synthetic resins such as phenolic resin, melamine resin, polyurethane resin, urea resin, polyamide resin, polyimide resin, polyamideimide resin;
Pitches such as oil pitch and coal pitch;
Can be given. Two or more binders may be used simultaneously.

Also, the above-mentioned binder may act as a thickener in the electrode mixture.

Regarding the blending amount of the constituent material in the layer containing the negative electrode active material, the blending amount of the binder is preferably about 0.5 to 30 parts by mass, more preferably about 2 to 20 parts by mass with respect to 100 parts by mass of the carbon material. is there.

Examples of the solvent include aprotic polar solvents such as N-methylpyrrolidone, alcohols such as isopropyl alcohol, ethyl alcohol or methyl alcohol, ethers such as propylene glycol dimethyl ether, and ketones such as acetone, methyl ethyl ketone or methyl isobutyl ketone. Etc. When the binder is thickened, a plasticizer may be used to facilitate application to the current collector.

Examples of the conductive agent include various carbon materials such as natural graphite, artificial graphite, cokes, and carbon black. Moreover, you may use the non-graphitizable carbon and graphitizable carbon mentioned above as a electrically conductive agent.

<Bipolar electrode>
A bipolar electrode can be manufactured by laminating a layer containing the positive electrode active material on one surface of the current collector and laminating a layer containing the negative electrode active material on the other surface.

Examples of the method for forming the layer containing the negative electrode active material on one surface of the current collector include the same method as the method for producing the layer containing the negative electrode active material.

As a material of the current collector contained in the bipolar electrode,
Metals such as nickel, aluminum, titanium, copper, gold, silver, platinum, aluminum alloys or stainless steel;
Formed by plasma spraying or arc spraying of carbon material, activated carbon fiber, nickel, aluminum, zinc, copper, tin, lead or alloys thereof;
A conductive film in which a conductive agent is dispersed in a resin such as rubber or styrene-ethylene-butylene-styrene copolymer (SEBS);
Etc. Among these, aluminum, an aluminum alloy, nickel, or stainless steel is preferable, and aluminum and an aluminum alloy are more preferable from the viewpoint of being easily processed into a thin film and being inexpensive.

The shape of the current collector included in the bipolar electrode is preferably a current collector that does not transmit sodium ions, for example, a foil or a plate. As the current collector included in one bipolar electrode, a current collector in which a plurality of current collectors of different types or the same type may be used. However, in order to simplify the battery structure, a plurality of current collectors are stacked. It is preferable to use a single current collector.

As a production method for forming the layer containing the positive electrode active material on the other surface of the current collector, the same method as the method for producing the layer containing the positive electrode active material can be mentioned.

<Sodium secondary battery>
One of the outermost layers of the battery is a negative electrode and the other is a positive electrode. In the negative electrode, a layer containing the negative electrode active material is formed only on one surface of the current collector. In the positive electrode, a layer containing the positive electrode active material is formed only on one surface of the current collector. One or more bipolar electrodes are interposed between the negative electrode and the positive electrode. The layer containing the negative electrode active material of the negative electrode and the layer containing the positive electrode active material of the bipolar electrode are arranged so as to face each other, and the layer containing the positive electrode active material of the positive electrode and the layer containing the negative electrode active material of the bipolar electrode face each other To place. When a plurality of bipolar electrodes are used, they are arranged so that the layer containing the negative electrode active material of one bipolar electrode faces the layer containing the positive electrode active material of the other bipolar electrode. A separator containing a solid electrolyte may be interposed between the negative electrode and the bipolar electrode and between the positive electrode and the bipolar electrode. Of course, when using a plurality of bipolar electrodes, a separator containing a solid electrolyte may be interposed between the bipolar electrodes.

<Solid electrolyte forming electrode>
A solid electrolyte-forming electrode can be obtained by applying a polymerizable monomer solution in which sodium salt is dissolved to the surfaces of the negative electrode, bipolar electrode and positive electrode by the doctor blade method or the like and then polymerizing the polymerizable monomer after immersion. .

<Laminated electrode>
The above-described solid electrolyte-forming negative electrode, solid electrolyte-forming bipolar electrode, and solid electrolyte-forming positive electrode are stacked, and the negative electrode, bipolar electrode, and positive electrode of FIG. 1 are integrally connected with the solid electrolyte by hot pressing with a uniaxial press. An electrode can be obtained.

The sodium secondary battery of the present invention can be manufactured by connecting lead wires to the outermost negative electrode current collector and positive electrode current collector of the multilayer electrode and storing the multilayer electrode in a container.

1: current collector, 2: layer containing positive electrode active material, 3: layer containing negative electrode active material, 4: solid electrolyte, 5: separator (solid electrolyte), 11: bipolar electrode, 12: positive electrode, 13: negative electrode, 21: Bipolar electrolyte sheet

[Preparation of monomer solution]
90% by mass of a commercially available polyethylene glycol diacrylate (A-400 (trade name), Shin-Nakamura Chemical Co., Ltd.) as a polymerizable monomer, 10% by mass of NaPF ₆ as a sodium salt, and 2,2′-azobis as a polymerization initiator -0.45 mass% (0.5 mass% with respect to the polymerizable monomer) of isobutyronitrile was mixed, and the monomer solution 1 was adjusted.

[Adjustment of electrolyte 1]
As the electrolytic solution 1, a 10% by mass NaPF ₆ propylene carbonate solution (hereinafter, 1M NaPF ₆ PC) manufactured by Kishida Chemical was used as it was.

[Adjustment of carbon material 1]
As carbon material 1, commercially available hard carbon (Carbotron P (trade name, registered trademark), manufactured by Kureha Battery Materials Japan Co., Ltd.), 0.001 MPa (gauge pressure display when atmospheric pressure is 0) The pressure was reduced to -0.1 MPa) at 200 ° C. for 12 hours and dried.

[Adjustment of binder solution]
A binder solution was prepared by dissolving 2% by mass of sodium polyacrylate (product number: 196-02955, degree of polymerization: 22,000 to 70,000) as a binder in 98% by mass of pure water.

[Preparation of negative electrode sheet]
The carbon material 1 and the binder solution are weighed and kneaded so that the dried carbon material 1 is 97% by mass and the binder is 3% by mass. After defoaming, a 15 μm thick aluminum foil is used with a doctor blade. After coating so that the amount of the active material after drying was 2.2 mAh / cm ² , it was dried under reduced pressure at 130 ° C. for 24 hours.

[Thickening of negative electrode sheet 1]
After cutting the negative electrode sheet described above to 50 mm × 50 mm, the negative electrode sheet 1 was produced by thickening with a biaxial roll press. The roll press was performed by adjusting the linear pressure between 10 and 500 kN / m so that the porosity of the electrode mixture (a mixture of carbon material and binder) was between 40 and 60%. The porosity of the electrode mixture can be determined according to a generally known method.

[Preparation of negative electrode electrolyte sheet 1]
The above-mentioned monomer solution 1 is applied to the negative electrode material coated surface of the negative electrode sheet 1 and impregnated in the active material layer, and then sandwiched between two 100 mm × 100 mm 50 μm-thick PET sheets and oxygen is blocked. The negative electrode electrolyte sheet 1 which makes [polymer / negative electrode] 1 unit is produced by heating and curing at 5 ° C. for 5 minutes and removing the PET sheet.

[Production of composite metal oxide and positive electrode]
In a polypropylene beaker, 44.88 g of potassium hydroxide was completely dissolved in 300 ml of distilled water to prepare a potassium hydroxide aqueous solution.
Further, in another polypropylene beaker, 21.21 g of iron (II) chloride tetrahydrate, 19.02 g of nickel (II) chloride hexahydrate, and manganese (II) chloride tetrahydrate were added to 300 ml of distilled water. 15.83 g was dissolved to prepare an iron-nickel-manganese-containing aqueous solution.
While stirring the potassium hydroxide aqueous solution, the iron-nickel-manganese-containing aqueous solution was added dropwise toward the potassium hydroxide aqueous solution, whereby a precipitate was generated to obtain a slurry.

The obtained slurry was filtered to separate a solid, washed with distilled water, and then dried at 100 ° C. to obtain a precipitate. The obtained precipitate, sodium carbonate and calcium hydroxide were weighed so that the molar ratio was Fe: Na: Ca = 0.4: 0.99: 0.01, and then dried using an agate mortar. Mix to obtain a mixture.

The obtained mixture was put into an alumina firing vessel, fired by holding it in an air atmosphere at 900 ° C. for 6 hours using an electric furnace, and cooled to room temperature to obtain a composite metal oxide.

When powder X-ray diffraction analysis of the composite metal oxide was performed, it was assigned to the α-NaFeO ₂ type crystal structure. Further, when the composition of the composite metal oxide is analyzed by ICP-AES, the molar ratio of Na: Ca: Fe: Ni: Mn is 0.99: 0.01: 0.4: 0.3: 0.3. there were.

The obtained composite metal oxide, acetylene black (HS100, manufactured by Denki Kogyo Co., Ltd.), VT471 (binder solution, 5% by weight, manufactured by Daikin Industries, Ltd.), and N-methylpyrrolidone (NMP, Kishida Chemical Co., Ltd.) Co., Ltd.) was weighed so that the mass ratio was composite metal oxide: conductive material: binder: NMP = 90: 5: 5: 100. These were stirred for 5 minutes at 2000 rpm using a disperser (disper mat, manufactured by VMA-GETZMANN) to obtain a positive electrode mixture paste.

[Preparation of Positive Electrode Sheet 1]
The obtained positive electrode mixture paste was applied to a 15 μm thick aluminum foil using a doctor blade so that the amount of active material after drying was 2.0 mAh / cm ^2, and dried at 60 ° C. for 2 hours. After cutting to 50 mm × 50 mm, the positive electrode sheet 1 of the positive electrode was produced by thickening with a biaxial roll press (positive electrode sheet). The roll press conditions are the same as those of the negative electrode sheet 1 described above.

[Preparation of positive electrode electrolyte sheet 1]
The above-mentioned monomer solution 1 is applied to the positive electrode material coated surface of the above-described positive electrode sheet 1 and impregnated in the active material layer, and then sandwiched by two 100 mm × 100 mm 50 μm-thick PET sheets while blocking oxygen. The positive electrode electrolyte sheet 1 which makes [polymer / positive electrode] 1 unit is produced by heating and curing at 5 ° C. for 5 minutes and removing the PET sheet.

[Manufacture of bipolar electrode 1]
In the same manner as the preparation of the positive electrode sheet 1, the positive electrode mixture paste was applied to the surface of the negative electrode sheet before being densified, dried at 60 ° C. for 2 hours, cut to 55 mm × 55 mm, and then biaxial A bipolar electrode (negative electrode / positive electrode) is prepared by densifying with a roll press. The roll press conditions are the same as those of the negative electrode sheet 1 described above. This electrode is hereinafter abbreviated as bipolar electrode sheet 1.

[Bipolar sheet with separator 1]
The above-mentioned bipolar sheet 1 is inserted into a bag made of a polyethylene separator. Hereinafter, the bipolar sheet 1 with a separator is abbreviated.

[Preparation of Bipolar Electrolyte Sheet 1]
After the monomer solution 1 is applied to the bipolar sheet with a separator 1 described above and impregnated in the active material layer and the separator, it is sandwiched between two 100 mm × 100 mm 50 μm thick PET sheets and oxygen is blocked at 90 ° C. Heat for minutes to cure and remove the PET sheet. Subsequently, by cutting to 50 mm × 50 mm, a bipolar electrolyte sheet 1 having [polymer / negative electrode / positive electrode / polymer] that is not ionically connected on the back and front as one unit is produced (FIG. 2).

[Electrode electrolyte laminate 1]
The above-described positive electrode electrolyte sheet 1 ([positive electrode / polymer]), bipolar electrolyte sheet 1 ([polymer / negative electrode / positive electrode / polymer]), and negative electrode electrolyte sheet 1 ([polymer / negative electrode]) are stacked to form an electrode electrolyte laminate 1. Make it.

[Laminated continuum 1]
The above-described electrode electrolyte laminate 1 is hot-pressed at 100 ° C. to produce a laminated continuum 1 in which the polymer layers of the positive electrolyte sheet 1, the bipolar electrolyte sheet 1, and the negative electrode electrolyte sheet 1 are integrated (FIG. 3). .

[Polymer bipolar battery 1]
A lead for current extraction is attached to the positive electrode and negative electrode current collectors on both sides of the above-described laminated continuous body, and the polymer bipolar battery 1 (rated 50 mAh, average discharge voltage 6.2 V) is prepared by housing in an aluminum laminate case. .

[Electrode laminate 1]
The positive electrode sheet 1, the separator-equipped bipolar sheet 1, and the negative electrode electrolyte sheet 1 are stacked to produce the electrode laminate 1.

[Electrolyte Bipolar Battery 1]
A lead for current extraction is attached to the positive electrode and negative electrode current collectors on both sides of the above-described laminated continuous body, and the lead is accommodated in an aluminum laminate case, and the electrolytic solution 1 is injected into the electrolytic bipolar battery 1 (rated 50 mAh, An average discharge voltage of 6.2 V) is produced.

[Example 1]
[Charge / discharge test]
A constant current charge / discharge test is performed using the bipolar battery 1 under the following conditions.
Charging / discharging conditions: First, charging is performed at 5.0 mA with CC (constant current: constant current) from the rest potential to 8.0 V (the side on which the negative electrode is doped with Na). Next, discharging is performed at CC (side where Na is dedoped from the negative electrode sheet), and cut off at a voltage of 4.0V. This operation is repeated five times to confirm that the bipolar battery 1 can be charged / discharged.

[Recharge storage test]
After the bipolar battery 1 is recharged to 8 V, it is removed from the charge / discharge tester, and the battery voltage after storage for 1 week at room temperature is measured.

[Comparative Example 1]
Except that the bipolar battery 1 of Example 1 is changed to the electrolyte bipolar battery 1, charging and discharging are performed in the same manner as in Example 1, and a recharge storage test is performed.

[result]
The polymer bipolar battery 1 of the present invention has a voltage of 6 V or more even after one week, while the electrolyte bipolar battery 1 has a voltage of 4 V or less.

The polymer bipolar battery 1 of the present invention has a separator for comparison, but operates as a battery without having a separator.

Claims (4)

Sodium secondary battery having a layer containing a positive electrode active material that can be doped and dedoped with sodium ions, a layer containing a negative electrode active material that can be doped and dedoped with sodium ions, an electrolyte capable of conducting sodium ions, and a current collector Because
At least one current collector having a structure in which a layer containing the positive electrode active material is laminated on one surface of the current collector and a layer containing the negative electrode active material is laminated on the other surface; A sodium secondary battery, wherein the electrolyte is a solid electrolyte. The sodium secondary battery according to claim 1, wherein the current collector is a current collector containing one or more selected from the group consisting of aluminum and aluminum alloys. The sodium secondary battery according to claim 1 or 2, wherein the solid electrolyte is a polymer containing sodium ions. 4. The polymer according to claim 1, wherein the solid electrolyte is a polymer containing one or more structural units selected from the group consisting of a structural unit represented by the following formula (1) and a structural unit represented by the following formula (2). The sodium secondary battery in any one.
—CH ₂ —CH ₂ —O— (1)
—CH ₂ —CHCH ₃ —O— (2)

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