JP5924645B2 - Negative electrode material for sodium secondary battery, electrode for sodium secondary battery, and sodium secondary battery - Google Patents

Description

  The present invention relates to a negative electrode material for a sodium secondary battery, an electrode for a sodium secondary battery using the negative electrode material, and a sodium secondary battery using the electrode.

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

  A sodium secondary battery usually includes a positive electrode including a positive electrode active material that can be doped and dedoped with sodium ions, a negative electrode including a negative electrode active material that can be doped and dedoped with sodium ions, and an electrolyte.

  As a negative electrode active material, what consists of a carbon material and an alloy material is proposed until now, and what consists of a carbon material is anticipated from a viewpoint of the lifetime of a battery, The sodium secondary battery provided with such a negative electrode Is disclosed (see Patent Document 1).

JP 2009-129742 A

However, the sodium secondary battery described in Patent Document 1 has a problem that charge / discharge capacity is insufficient.
The present invention has been made in view of the above circumstances, and has a high charge / discharge capacity sodium secondary battery, a sodium secondary battery electrode suitable for the secondary battery, and a sodium secondary battery suitable for the electrode. It is an object to provide a negative electrode material for a battery.

To solve the above problem,
The present invention relates to a negative electrode material for a sodium secondary battery containing an amorphous carbon material that can be doped and dedoped with sodium ions, and the amorphous carbon material has a differential heat at a measurement temperature range of 400 ° C. or higher. -In the thermogravimetric simultaneous measurement, one of the first peak showing the maximum calorific value and the second peak showing the calorific value next thereto is in the measurement temperature zone 400 to 615 ° C, and the other is The amorphous carbon material has a maximum calorific value in the measurement temperature zone of 400 to 615 ° C. in the simultaneous measurement of the differential thermo-thermogravimetry at the measurement temperature zone of 400 ° C. or higher. A negative electrode material for a sodium secondary battery, comprising: an amorphous carbon material (A) having a peak; and an amorphous carbon material (B) having a peak showing a maximum calorific value in a measurement temperature range of 620 to 800 ° C. Is the amorphous carbon material (A) Fine amorphous carbon material (B), the amorphous carbon material (A): 99.5 at a weight ratio of amorphous carbon material (B): 0.5~90: contains in the range of 10, the An amorphous carbon material (A) is a non-graphitized carbon material, and the amorphous carbon material (B) is acetylene black. A negative electrode material for a sodium secondary battery is provided.

The negative electrode material for a sodium secondary battery of the present invention preferably has a weight change of 0.1 to 10% at a measurement temperature zone of 620 to 800 ° C. in simultaneous differential thermal-thermogravimetric measurement.
The negative electrode material for a sodium secondary battery of the present invention is preferably in the form of a powder having a BET specific surface area of 1 to 200 m ² / g .

Moreover, this invention provides the electrode for sodium secondary batteries characterized by including the negative electrode material for sodium secondary batteries of the said invention.
The present invention also provides an electrode for a sodium secondary battery in which an electrode mixture layer containing as a main component an amorphous carbon material that can be doped and dedoped with sodium ions is formed on a current collector, An amorphous carbon material (A) having a peak showing a maximum calorific value in a measurement temperature zone of 400 to 615 ° C. in simultaneous measurement of differential heat and thermogravimetry at a measurement temperature zone of 400 ° C. or higher; And an amorphous carbon material (B) having a peak showing the maximum calorific value in a measurement temperature zone of 620 to 800 ° C., and the electrode mixture layer has a differential heat-thermogravimetric weight at a measurement temperature zone of 400 ° C. or higher. In the simultaneous measurement, a peak indicating the maximum calorific value is present in the measurement temperature range 400 to 615 ° C., and a peak indicating the subsequent calorific value is present in the measurement temperature range 620 to 800 ° C. The weight change at 0.1 to 10 The electrode mixture layer comprises the amorphous carbon material (A) and the amorphous carbon material (B) in a mass ratio of amorphous carbon material (A): amorphous carbon material (B). in 99.5: 0.5 to 90: contains in the range of 10, the amorphous carbon material (a) is a non-graphitizable carbon material, the amorphous carbon material (B) is acetylene black An electrode for a sodium secondary battery is provided.

The present invention also provides a sodium secondary battery comprising the sodium secondary battery electrode of the present invention as a negative electrode.
The sodium secondary battery of the present invention preferably further comprises a separator.

  ADVANTAGE OF THE INVENTION According to this invention, the sodium secondary battery with a high charging / discharging capacity | capacitance, the electrode for sodium secondary batteries suitable for this secondary battery, and the negative electrode material for sodium secondary batteries suitable for this electrode are provided.

<Anode material for sodium secondary battery>
A negative electrode material for a sodium secondary battery according to the present invention (hereinafter also referred to as “negative electrode material”) is a negative electrode material containing an amorphous carbon material that can be doped and dedoped with sodium ions, The amorphous carbon material has a first peak indicating the maximum calorific value and a second peak indicating the subsequent calorific value in the differential thermal-thermogravimetric simultaneous measurement at a measurement temperature range of 400 ° C. or higher. One of them has a measurement temperature zone of 400 to 615 ° C, and the other has a measurement temperature zone of 620 to 800 ° C. Such a negative electrode material can form a sodium secondary battery having a high charge / discharge capacity by containing an amorphous carbon material having a specific heat generation pattern as described above in simultaneous differential heat-thermogravimetric measurement.
In the present specification, “simultaneous measurement of differential heat and thermogravimetry” means what is performed in air unless otherwise specified.

  The amorphous carbon material is an electrode active material (negative electrode active material), and in the differential thermal-thermogravimetric simultaneous measurement at a measurement temperature zone of 400 ° C. or higher, the first peak showing the maximum calorific value, And a second peak indicating the next calorific value. And an amorphous carbon material has either one of said 1st and 2nd peak in measurement temperature zone 400-615 degreeC, and has the other in measurement temperature zone 620-800 degreeC. Here, “having a peak in the measurement temperature range of 400 to 615 ° C.” means having a peak in at least one of the measurement temperature ranges of 400 to 615 ° C. Similarly, “having a peak in the measurement temperature zone of 620 to 800 ° C.” means having a peak in at least one of the measurement temperature zones of 620 to 800 ° C.

  In addition to the first peak and the second peak, the amorphous carbon material may or may not have an exothermic peak indicating a calorific value smaller than these in a measurement temperature range of 400 ° C. or higher. It does not have to be. In addition, the amorphous carbon material may or may not have an exothermic peak separately in a measurement temperature range of less than 400 ° C., but if it has an exothermic peak, the exotherm indicated by that peak The amount is preferably at least smaller than the calorific value indicated by the first peak.

  The amorphous carbon material may be made of one kind of material or may be made of two or more kinds of materials. For example, as the amorphous carbon material, an amorphous carbon material having both the first and second peaks may be used alone, or the amorphous carbon material having the first peak, May be used together one by one with amorphous carbon materials having different second peaks.

  As an example of a preferable amorphous carbon material, an amorphous carbon material having a peak showing a maximum calorific value in a measurement temperature range of 400 to 615 ° C. in simultaneous measurement of differential heat and thermogravimetry at a measurement temperature range of 400 ° C. or more (A) and the amorphous carbon material (B) which has the peak which shows the maximum calorific value in the measurement temperature zone 620-800 degreeC are mentioned, The said amorphous carbon material (A) and (B Is more preferable.

  The amorphous carbon material has a total content of the amorphous carbon materials (A) and (B) of preferably 90% by mass or more, more preferably 95% by mass or more, and 100% by mass. Also good.

Examples of the amorphous carbon material (A) include non-graphitized carbon material (hard carbon), carbon black, pyrolytic carbon, carbon fiber, and fired organic material. Here, “pyrolytic carbon” means hydrocarbons such as acetylene and methane, and carbon obtained by vapor phase pyrolysis of carbon monoxide (CO).
Among these, the amorphous carbon material (A) is preferably a non-graphitized carbon material.

Examples of the shape of the amorphous carbon material (A) include flakes such as natural graphite, spheres such as mesocarbon microbeads, fibers such as graphitized carbon fibers, and aggregates of fine particles.
When the amorphous carbon material (A) is spherical, the average particle size is preferably 0.01 to 30 μm, more preferably 0.1 to 20 μm.

  The amorphous carbon material (A) is preferably carbon microbeads made of a non-graphitized carbon material, and as a commercially available product, “ICB (trade name: Nika beads)” manufactured by Nippon Carbon Co., Ltd. can be mentioned.

  The amorphous carbon material (A) preferably has a peak at 450 to 615 ° C. indicating the maximum calorific value in the differential thermal-thermogravimetric simultaneous measurement at a measurement temperature range of 400 ° C. or higher. The amorphous carbon material (A) may or may not have an exothermic peak in addition to the peak showing the maximum calorific value in a measurement temperature range of 400 ° C. or higher. Good. Further, the amorphous carbon material (A) may or may not have an exothermic peak separately in a measurement temperature range of less than 400 ° C.

The amorphous carbon material (A) is preferably a non-activated carbon material that has been subjected to an inactivation treatment because it is more smoothly doped and dedoped with sodium ions. It is more preferable that Here, the “inactivation treatment” means a treatment for removing the surface functional group of the carbon material, and a specific treatment method is preferably an inert gas atmosphere, preferably 600 to 2000 ° C. A method of heat treating the carbon material at a temperature of preferably 800 to 1800 ° C. can be exemplified.
When the activated carbon material that has been activated is used as an electrode active material, sodium ions may not be doped and dedoped smoothly, and the irreversible capacity may increase.

  Examples of the organic material fired body include those capable of doping and dedoping sodium ions among the fired materials obtained by carbonization (firing) of various organic materials. For example, the non-graphitized carbon material, which is a suitable carbon material, can be obtained by firing an organic material that is unlikely to have a graphite crystal structure, as shown below.

Examples of the organic material used as a raw material of the organic material fired body include natural mineral resources such as petroleum and coal; synthetic resins such as thermosetting resins and thermoplastic resins synthesized using these mineral resources as raw materials; Examples include plant residue oils such as coal pitch and spinning pitch; organic materials derived from plants such as wood.
The said organic material may be used individually by 1 type, and may use 2 or more types together.

Examples of the synthetic resin include 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. Examples thereof include resins, polyamide resins, cyanate resins, and ketone resins.
The synthetic resin may be obtained by a known curing method. For example, examples of the curing method of the phenol resin include a thermal curing method, a thermal oxidation method, an epoxy curing method, an isocyanate curing method, and the like. Examples of the curing method include a phenol resin curing method, an acid anhydride curing method, and an amine curing method.
The synthetic resin may contain a curing agent and an additive.
The said synthetic resin may be used individually by 1 type, and may use 2 or more types together.

  The organic material is preferably an organic material having an aromatic ring. By using such an organic material, the amorphous carbon material (A) can be obtained with a high yield, so that the environmental burden and the manufacturing cost can be reduced, and the industrial utility value becomes higher.

Examples of organic materials having an aromatic ring include, among the synthetic resins, phenol resins (novolak type phenol resins, resol type phenol resins, etc.), epoxy resins (bisphenol type epoxy resins, novolac type epoxy resins, etc.), aniline resins, Examples thereof include bismaleimide resins and benzoxazine resins. These synthetic resins may contain a curing agent and an additive.
The organic material having an aromatic ring is preferably an organic material obtained by polymerizing phenol and / or a derivative thereof and an aldehyde compound. Such an organic material is inexpensive among organic materials having an aromatic ring and has a large industrial production.
The organic material which has an aromatic ring may be used individually by 1 type, and may use 2 or more types together.

  An example of the organic material obtained by polymerizing the above phenol and / or its derivative and an aldehyde compound is a phenol resin. When the amorphous carbon material (A) obtained by carbonizing the phenol resin is used, the charge / discharge capacity of the sodium secondary battery and the discharge capacity when the charge / discharge is repeated are particularly large. Since the phenolic resin has a structure in which three-dimensional crosslinking is developed, the amorphous carbon material (A) obtained by carbonizing the phenol resin also has a structure in which unique three-dimensional crosslinking derived from the structure is developed. Therefore, it is estimated that the discharge capacity becomes particularly large.

Examples of the phenol derivatives include o-cresol, m-cresol, p-cresol, catechol, resorcinol, hydroquinone, xylenol, pyrogallol, bisphenol A, bisphenol F, p-phenylphenol, p-tert-butylphenol, p-tert. -Octylphenol, 1-naphthol, 2-naphthol, etc. are mentioned.
As said phenol and / or its derivative (s), 1 type may be used independently and 2 or more types may be used together.

Examples of the aldehyde compound include formaldehyde, paraformaldehyde, trioxane, acetaldehyde, propionaldehyde, polyoxymethylene, chloral, furfural, glyoxal, n-butyraldehyde, caproaldehyde, allylaldehyde, benzaldehyde, crotonaldehyde, acrolein, tetra Examples include oxymethylene, phenylacetaldehyde, o-tolualdehyde, and salicylaldehyde.
The said aldehyde compound may be used individually by 1 type, and may use 2 or more types together.

  Among the phenol resins, the resol type phenol resin is obtained by polymerizing phenol and / or a derivative thereof and an aldehyde compound in the presence of a basic catalyst. The novolak type phenol resin can be obtained by polymerizing phenol and / or a derivative thereof and an aldehyde compound in the presence of an acidic catalyst.

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

  As a novolac type phenol resin, a type called a random novolak having the same methylene group bonding position at the ortho-position and the para-position (this type includes, for example, phenol and / or a derivative thereof and an aldehyde compound with a known organic compound). Obtained by a condensation reaction at 100 ° C. for several hours under normal pressure using an acid and / or an inorganic acid catalyst, and removing water and unreacted monomers from the resulting condensate). A type called high ortho novolac with many methylene group bonds (this type is weakly acidic using, for example, phenol and / or its derivatives and aldehyde compounds using a metal salt catalyst such as zinc acetate, lead acetate, zinc naphthenate, etc. Addition condensation reaction under the conditions, add the acid catalyst directly or add the condensation reaction while dehydrating, if necessary Obtained by a method for removing unreacted reactants Te.) It is known.

  As the organic material having an aromatic ring, a wide variety of materials other than those described above can be used.

  The synthetic resin is generally a polymer in which monomers are polymerized. And what organically polymerized several to several dozen monomers can also be used as an organic material which has an aromatic ring.

  When phenol and / or a derivative thereof and an aldehyde compound are polymerized, a by-product may be generated or an unpolymerized product may remain. These by-products and unpolymerized materials can also be used as organic materials. In such a case, the environmental burden can be reduced by reducing waste, and the amorphous carbon material (A) can be obtained at a low cost. And the industrial utility value becomes higher.

Preferable examples of the plant-derived organic material include charcoal obtained by carbonizing wood and the like.
Examples of the wood include cycads, ginkgo biloba, conifers (cedar, cypress, red pine, etc.), maize, etc .; Examples include angiosperms such as bamboo.

  As the wood, waste wood, waste wood generated in a wood processing process such as sawdust, forest thinned wood, or the like can be used. The main constituent components of wood generally include three types of cellulose, hemicellulose, and lignin. Among these, lignin is an organic material having an aromatic ring, and thus is preferable.

  Among the wood, cedar is widely used as a building material, and cedar sawdust is generated in the processing process. Cedar sawdust is a preferred organic material, which can reduce the environmental burden and can provide the amorphous carbon material (A) at low cost. Bincho charcoal obtained by carbonizing oak is also preferable as the amorphous carbon material (A).

  When an amorphous carbon material (A) obtained by carbonization (firing) of the above-mentioned plant residue oil is used, resources can be effectively used and industrial utility value is higher.

  Examples of the plant residue oil include various residue oils generated during the production of various petrochemical products such as ethylene, and more specifically, distillation residue oil, fluid catalytic cracking residue oil, and hydrodesulfurized oils thereof. And petroleum heavy oils composed of these mixed oils. Among these, the plant residue oil is preferably a residue oil generated during the production of a petrochemical product having an aromatic ring. Examples thereof include a residue oil generated during the production of resorcinol.

The organic material fired body is obtained by carbonizing (firing) one or more organic materials.
The carbonization temperature is preferably 800 to 2500 ° C.
Carbonization is preferably performed in an inert gas atmosphere. Then, the organic material may be carbonized consistently under an inert gas atmosphere, or a heated product obtained by heating the organic material in the presence of an oxidizing gas of 400 ° C. or lower is obtained under an inert gas atmosphere. May be carbonized.
Examples of the inert gas include nitrogen and argon. Examples of the oxidizing gas include air, water vapor (H ₂ O), carbon dioxide (CO ₂ ), oxygen (O ₂ ) and the like. It is done.
Carbonization may be performed under reduced pressure.
The heating and carbonization may be performed using equipment such as a rotary kiln, a roller hearth kiln, a pusher kiln, a multistage furnace, and a fluidized furnace. Of these, the rotary kiln is a commonly used facility.

The organic material fired body obtained by carbonization (firing) may be pulverized and used as necessary.
For pulverization, for example, impact pulverizer, centrifugal pulverizer, ball mill (tube mill, compound mill, conical ball mill, rod mill), vibration mill, colloid mill, friction disk mill, jet mill, etc. Can be used. Among these, a ball mill is a pulverizer generally used. At the time of pulverization, in order to suppress mixing of metal powder into the organic material fired body, the contact portion with the organic material fired body in the pulverizer may be made of a non-metallic material such as alumina or agate. .
The average particle size of the particles of the fired organic material obtained by pulverization is preferably 50 μm or less, more preferably 30 μm or less, and even more preferably 10 μm or less.

  The amorphous carbon material (A) other than the organic material fired body is also appropriately obtained by a known method.

  Examples of the amorphous carbon material (B) include non-graphite powders that do not correspond to the amorphous carbon material (A), such as carbon black and acetylene black, and acetylene black is preferable.

  The amorphous carbon material (B) preferably has a peak at 650 to 750 ° C. that indicates the maximum calorific value in the differential thermal-thermogravimetric simultaneous measurement at a measurement temperature range of 400 ° C. or higher. The amorphous carbon material (B) may or may not have an exothermic peak in addition to the peak showing the maximum calorific value in a measurement temperature range of 400 ° C. or higher. Good.

  When the amorphous carbon material (B) is spherical, the average particle size is preferably smaller than the average particle size of the amorphous carbon material (A), preferably 1 to 500 nm, more preferably 5 to 5 nm. 100 nm.

  Mass ratio of amorphous carbon material (A) and amorphous carbon material (B) contained in the negative electrode material (mass of amorphous carbon material (A): mass of amorphous carbon material (B) ) Is preferably 99.5: 0.5 to 90:10, more preferably 99: 1 to 95: 5. By setting it as such a range, the sodium secondary battery mentioned later becomes higher charge / discharge capacity.

The negative electrode material may contain other components in addition to the amorphous carbon material as long as the effects of the present invention are not impaired. As said other component, arbitrary things can be selected according to the objective.
The content of the amorphous carbon material in the negative electrode material is preferably 90% by mass or more, more preferably 95% by mass or more, and may be 100% by mass.

  The negative electrode material preferably has a weight change of 0.1 to 10% in a measurement temperature zone of 620 to 800 ° C. in a differential thermal-thermogravimetric simultaneous measurement (TG / DTA), and is 0.5 to 7%. More preferably. This weight change is accompanied by thermal decomposition of the component having the first peak or the second peak, and is observed with the occurrence of these peaks. As such a component, the amorphous carbon material (B) It can be illustrated. When the weight change is in such a range, a sodium secondary battery with higher charge / discharge capacity can be configured.

  In differential thermal-thermogravimetric simultaneous measurement, for example, the sample to be measured is raised from room temperature (for example, 25 ° C.) to a desired temperature (for example, 800 ° C. or more) at a temperature rising rate of 0.5 to 2 ° C./min. What is necessary is just to make it warm and to measure.

The negative electrode material is preferably in the form of powder, and preferably has a BET specific surface area of 1 to 200 m ² / g. When the BET specific surface area is in such a range, a sodium secondary battery having a higher charge / discharge capacity can be configured.

<Electrode for sodium secondary battery>
An electrode for a sodium secondary battery according to the present invention (hereinafter sometimes referred to as “electrode”) includes the negative electrode material according to the present invention, and is suitable for use as a negative electrode. Such an electrode can have the same configuration as a conventional electrode except that the negative electrode material is used.

  As an example of the electrode, a layer (electrode mixture layer) made of an electrode mixture containing the negative electrode material, a binder, and, if necessary, other components such as a conductive material (electrode mixture layer) is formed on a current collector. Is mentioned. Here, when the electrode is a negative electrode, the “current collector” means a “negative electrode current collector” as distinguished from a “positive electrode current collector” of a positive electrode described later. Similarly, when the electrode is a negative electrode, the “electrode mixture” means a “negative electrode mixture” as distinguished from a “positive electrode mixture” of the positive electrode described later.

  The shape of the electrode is not particularly limited, but is preferably a sheet from the viewpoint of ease of handling.

  The electrode can be manufactured in the same manner as a conventional electrode except that the negative electrode material is used. For example, an electrode mixture paste is prepared by blending the negative electrode material, a binder, other components such as a conductive material used as necessary, and a solvent, and a layer made of the paste is prepared by a technique such as coating or dipping. It can be manufactured by forming on the current collector and removing the solvent in the paste to form an electrode mixture layer. In the electrode mixture layer, the electrode mixture is bound by removing the solvent. The solvent may be removed by a normal drying method.

Examples of the binder include a polymer of a fluorine compound.
Examples of the fluorine compound include partially fluorinated alkyl (C1 to C18) (meth) acrylate, perfluoroalkyl (meth) acrylate [for example, perfluorododecyl (meth) acrylate, perfluoro n-octyl (meth) Acrylate, perfluoro n-butyl (meth) acrylate], perfluoroalkyl-substituted alkyl (meth) acrylate [for example, perfluorohexylethyl (meth) acrylate, perfluorooctylethyl (meth) acrylate], perfluoroalkyloxyalkyl ( Meth) acrylate [e.g. perfluorododecyloxyethyl (meth) acrylate, perfluorodecyloxyethyl (meth) acrylate], fluorinated alkyl (C1-18) crotonate, fluorinated al (C1-C18) malate and fumarate, fluorinated alkyl (C1-C18) itaconate, fluorinated alkyl-substituted olefin (C2-C10, C1-C17) [e.g. perfluorohexylethylene] And fluorinated olefins having 2 to 10 carbon atoms and 1 to 20 fluorine atoms [for example, tetrafluoroethylene, trifluoroethylene, vinylidene fluoride, hexafluoropropylene] and the like. . In the present specification, “(meth) acrylate” means both acrylate and methacrylate. Further, for example, “fluorinated alkyl (C 1-18)” means fluorinated alkyl having 1-18 carbon atoms.

Other examples of the binder include a non-fluorine polymer that is a polymer having no fluorine atom.
Examples of the non-fluorine polymer include addition polymers of monomers having an ethylenic double bond having no fluorine atom.
Examples of the monomer include (cyclo) alkyl (C1-22) (meth) acrylate [for example, methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) ) Acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, isodecyl (meth) acrylate, lauryl (meth) acrylate, octadecyl (meth) acrylate, etc.], aromatic ring-containing (meth) acrylate [for example, benzyl (meth) ) Acrylate, phenylethyl (meth) acrylate, etc.], alkylene glycol or dialkylene glycol (alkylene group having 2 to 4 carbon atoms) mono (meth) acrylate [for example, 2-hydroxyethyl (meth) acrylate, 2-hydroxy Propyl (meth) acrylate, diethylene glycol mono (meth) acrylate], (poly) glycerin (degree of polymerization 1 to 4) mono (meth) acrylate, polyfunctional (meth) acrylate [for example, (poly) ethylene glycol (degree of polymerization 1 to 100) di (meth) acrylate, (poly) propylene glycol (degree of polymerization 1 to 100) di (meth) acrylate, 2,2-bis (4-hydroxyethylphenyl) propane di (meth) acrylate, trimethylolpropane tri (meta) (Meth) acrylic acid ester monomers (monomers having a (meth) acrylic acid ester skeleton); (meth) acrylamides, (meth) acrylamide derivatives [for example, N-methylol (meth) ) Acrylamide, diacetone acrylamide, etc.] etc. (Meth) acrylamide monomers (monomers having a (meth) acrylamide skeleton); cyano group-containing monomers such as (meth) acrylonitrile, 2-cyanoethyl (meth) acrylate, 2-cyanoethylacrylamide; styrene, carbon Styrenic monomers (monomers having a styrene skeleton) such as styrene derivatives [for example, α-methylstyrene, vinyltoluene, p-hydroxystyrene, divinylbenzene, etc.] having 7 to 18 carbon atoms; 4 to 12 carbon atoms Diene monomers such as alkadienes [for example, butadiene, isoprene, chloroprene, etc.]; carboxylic acid (2 to 12 carbon atoms) vinyl esters [for example, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl octoate, etc.], carboxylic acids (C2-C12) (meth) allyl ester [for example, acetic acid (meth) ali , Alkenyl ester monomers (monomers having an alkenyl ester skeleton) such as propionic acid (meth) allyl, octanoic acid (meth) allyl, etc.]; glycidyl (meth) acrylate, epoxy such as (meth) allyl glycidyl ether Group-containing monomer; monoolefin such as monoolefin having 2 to 12 carbon atoms [for example, ethylene, propylene, 1-butene, 1-octene, 1-dodecene, etc.]; monomer having chlorine, bromine or iodine atom [For example, monomers having halogen atoms other than fluorine atoms such as vinyl chloride and vinylidene chloride]; (meth) acrylic acid and alkali salts thereof; monomers having conjugated double bonds such as butadiene and isoprene It is done. Examples of the addition polymer include copolymers such as ethylene / vinyl acetate copolymer, styrene / butadiene copolymer (SBR), and ethylene / propylene copolymer. Further, the carboxylic acid vinyl ester polymer may be partially or completely saponified, such as polyvinyl alcohol. In the present specification, “(cyclo) alkyl” means linear, branched and cyclic alkyl. “(Meth) acryl” means both acrylic and methacrylic.
The binder preferably contains the non-fluorinated polymer, and by doing so, the initial irreversible capacity of a sodium secondary battery described later can be further reduced.

  Examples of the binder include a copolymer of the above-described fluorine compound and a monomer having an ethylenic double bond having no fluorine atom.

  Other examples of the binder include polysaccharides such as starch, methylcellulose, carboxymethylcellulose (CMC), hydroxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, carboxymethylhydroxyethylcellulose, nitrocellulose, and derivatives thereof (one of the polysaccharides). Polysaccharides in which the hydrogen atom of the hydroxyl group is substituted with one or more groups selected from the group consisting of alkyl groups, carboxyalkyl groups, hydroxyalkyl groups and nitro groups); phenol resins; melamine resins; polyurethane resins; urea Resin; Polyamide resin; Polyimide resin; Polyamideimide resin; Petroleum pitch; Coal pitch and the like.

  The said binder may be used individually by 1 type, and may use 2 or more types together.

  The blending amount of the binder in the electrode mixture paste is preferably 0.5 to 30 parts by mass, more preferably 1 to 20 parts by mass with respect to 100 parts by mass of the negative electrode material which is a main component. By setting the lower limit value or more, the electrode mixture is more strongly bound, and by setting the upper limit value or less, a sodium secondary battery having a higher charge / discharge capacity can be configured.

Examples of the solvent used for preparing the electrode mixture paste include an organic solvent and water.
Examples of the organic solvent include polar solvents such as N-methyl-2-pyrrolidone, N, N-dimethylacetamide, N, N-dimethylformamide and other amides (compounds having an amide bond); isopropyl alcohol, Alcohols such as ethyl alcohol and methyl alcohol (aliphatic compounds having a hydroxyl group); Ethers such as propylene glycol dimethyl ether (compounds having an ether bond); Ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone (two hydrocarbon groups) And a compound having a skeleton bonded to a carbonyl group. Moreover, if it is a nonpolar solvent, hexane, toluene, etc. will be mentioned.
The said solvent may be used individually by 1 type, and may use 2 or more types together.
As said solvent, it is preferable to use water from the point which can manufacture an electrode at low cost.

  The blending amount of the solvent in the electrode mixture paste may be appropriately adjusted so that the paste has appropriate fluidity, and is not particularly limited, but is preferably 20 to 80% by mass.

  In the electrode mixture paste, the total amount of the negative electrode material and the binder in all the compounding components other than the solvent (that is, the total amount of the negative electrode material and the binder in the electrode mixture layer) is preferably 90 masses. % Or more, more preferably 95% by mass or more, and may be 100% by mass.

  Examples of the material of the current collector include simple metals such as nickel, aluminum, titanium, copper, gold, silver, and platinum; alloys such as aluminum alloys and stainless steels; carbon materials, activated carbon fibers, nickel, aluminum, zinc, and copper. Formed by plasma spraying or arc spraying of tin, lead or an alloy of these single metals; conductive material in which conductive material is dispersed in resin such as rubber or styrene-ethylene-butylene-styrene copolymer (SEBS) For example.

  Examples of the shape of the current collector include a foil shape, a flat plate shape, a mesh shape, a net shape, a lath shape, a punching shape, an embossed shape, and a shape obtained by combining one or more of these (for example, a mesh-like flat plate). Can be mentioned. Further, the surface of the current collector may be made uneven by an etching process.

  The method of coating the electrode mixture paste on the current collector is not particularly limited, and is a doctor blade method, slit die coating method, screen coating method, curtain coating method, knife coating method, gravure coating method, electrostatic spraying. The law etc. can be illustrated.

When the solvent in the electrode mixture paste is removed by a drying method, for example, any one of heating, air blowing, and reduced pressure may be used alone or in combination of two or more.
The heating temperature is preferably 50 to 150 ° C.

An electrode is obtained by forming an electrode mixture layer by removing the solvent.
After removing the solvent, the formed electrode mixture layer may be pressed to form an electrode.
Examples of the pressing method include a mold pressing method and a roll pressing method.
The thickness of the electrode (the total thickness of the current collector and the electrode mixture layer) is preferably 5 to 500 μm.

  Reflecting that the electrode mixture layer contains the amorphous carbon material (B), in the differential thermal-thermogravimetric simultaneous measurement (TG / DTA), the weight change in the measurement temperature zone of 620 to 800 ° C. It is preferable that it is 0.1 to 10%, and it is more preferable that it is 0.5 to 7%.

<Sodium secondary battery>
The sodium secondary battery according to the present invention is characterized in that the electrode according to the present invention is provided as a negative electrode, and can have the same configuration as a conventional sodium secondary battery except that the electrode is used. . The sodium secondary battery according to the present invention preferably includes a separator.

  A sodium secondary battery, for example, a negative electrode, a separator, and a positive electrode are laminated in this order to form a laminated body, and an electrode group formed by winding the laminated body is housed in a battery can, and the electrode group is impregnated with an electrolyte solution Can be manufactured. The electrolytic solution is preferably made of an organic solvent containing an electrolyte. Further, instead of the electrolytic solution, a solid electrolyte or a gel electrolyte may be used.

  Examples of the shape of the electrode group include those in which a cross section in a direction perpendicular to the winding axis has a shape such as a circle, an ellipse, a rectangle, or a rectangle with corners cut off. Examples of the shape of the sodium secondary battery include a paper type, a coin type, a cylindrical type, and a square type.

  Examples of the positive electrode include a positive electrode active material that can be doped and dedoped with sodium ions, a binder, and a layer composed of a positive electrode mixture including other components such as a conductive material as necessary (positive electrode mixture layer), What was formed on the positive electrode electrical power collector is mentioned.

  The shape of the positive electrode is not particularly limited, but is preferably a sheet from the viewpoint of ease of handling.

  For example, the positive electrode is prepared by mixing a positive electrode active material, a binder, other components such as a conductive material used as necessary, and a solvent to prepare a positive electrode mixture paste. It can be manufactured by forming a layer made of a paste on a positive electrode current collector and removing the solvent in the paste to form a positive electrode mixture layer. That is, it can be produced by the same method as in the case of the electrode (negative electrode) except that the blending components for forming the mixture are different.

Examples of the positive electrode active material include sodium-containing transition metal compounds.
Examples of the sodium-containing transition metal compound include
NaFeO _2, NaMnO _2, NaNiO ₂ and NaCoO oxide represented by NaM ¹ _a1 O _2, such as _2, oxide represented by ^{_{Na 0.44 Mn 1-a2 M 1}} a2 O 2, Na 0.7 Mn 1-a2 M ¹ _a2 O _2.05 oxide (M ¹ represents one or more transition metal elements, 0 <a1 ≦ 1, 0 ≦ a2 <1);
Oxides represented by Na _b M ² _c Si ₁₂ O ₃₀ such as Na ₆ Fe ₂ Si ₁₂ O ₃₀ and Na ₂ Fe ₅ Si ₁₂ O ₃₀ (M ² represents one or more transition metal elements and 2 ≦ b ≦ 6, 2 ≦ c ≦ 5);
Na ₂ Fe ₂ Si ₆ O ₁₈ and Na ₂ MnFeSi ₆ oxide represented by O in ₁₈ such ^{_{Na d M 3 e Si 6 O}} 18 (M 3 represents one or more transition metal elements, 2 ≦ d ≦ 6 1 ≦ e ≦ 2);
^{_{Na 2 FeSiO Na f M 4 g}} Si oxide represented by ₂ O _6, such as ₆ (M ⁴ is a transition metal element, showing one or more elements selected from the group consisting of Mg and Al, 1 ≦ f ≦ 2 1 ≦ g ≦ 2);
NaFePO ₄ , NaMnPO ₄ , Na ₃ Fe ₂ (PO ₄ ) ₃ , Na ₃ Ti ₂ (PO ₄ ) ₃ , Na ₂ FePO ₄ F, Na ₂ VPO ₄ F, Na ₂ MnPO ₄ F, Na ₂ CoPO ₄ F, _{Na 2 NiPO 4 F, Na 3} V 2 (PO 4) 2 F 3 Na h M 5 i (PO 4) such as _j F _k phosphate and fluorophosphate represented by (M ⁵ is one or more 1 ≦ h ≦ 3, 1 ≦ i ≦ 3, 1 ≦ j ≦ 3, 0 ≦ k ≦ 3);
Fluorosulfates such as NaFeSO ₄ F, NaMnSO ₄ F, NaCoSO ₄ F, NaFeSO ₄ F;
Borates such as NaFeBO ₄ and Na ₃ Fe ₂ (BO ₄ ) ₃ ;
Na ₃ FeF _6, Na ₂ MnF fluoride represented by Na _h M ⁵ F ₆ etc. ₆ (M ⁵ represents one or more transition metal elements, a 2 ≦ h ≦ 3.);
Etc.
The said sodium containing transition metal compound may be used individually by 1 type, and may use 2 or more types together.

Among these, the sodium-containing transition metal compound is preferably an oxide represented by NaM ¹ O ₂ (M ¹ represents one or more transition metal elements). Preferred specific examples thereof include α NaMnO _2, NaNiO ₂ having the structure -NaFeO ₂ type, NaCoO ₂ and _{naFe 1-pq Mn p Ni q} O 2 (p, q is a value that satisfies the following relationship .0 ≦ p + q ≦ 1,0 ≦ p And oxides such as ≦ 1, 0 ≦ q ≦ 1).

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

The binder contained in the positive electrode mixture is the same as the binder used in combination with the negative electrode material.
The solvent used for preparing the positive electrode mixture paste is the same as the solvent used for preparing the electrode (negative electrode) mixture paste.

The blending amounts of the binder and the solvent in the positive electrode mixture paste are the same as those in the electrode (negative electrode) mixture paste.
That is, the blending amount of the binder in the positive electrode mixture paste is preferably 0.5 to 30 parts by mass, more preferably 1 to 20 parts by mass with respect to 100 parts by mass of the positive electrode active material which is the main component. . Moreover, what is necessary is just to adjust suitably the compounding quantity of the said solvent in positive mix paste so that a paste may have appropriate fluidity | liquidity, Although it does not specifically limit, It is preferable that it is 20-80 mass%.
In the positive electrode mixture paste, the total amount of the positive electrode active material and the binder in all the components other than the solvent is preferably 90% by mass or more, more preferably 95% by mass or more, and 100% by mass. There may be.

Examples of the conductive material contained in the positive electrode mixture include carbon materials.
Examples of the carbon material include particulate carbon materials such as graphite powder and carbon black; and fibrous carbon materials such as carbon nanotubes.
The content of the conductive material in the positive electrode mixture is preferably 5 to 20 parts by mass with respect to 100 parts by mass of the positive electrode active material. In the case of using the fine particulate carbon material or the fibrous carbon material as described above as the conductive material, this ratio can be lowered.

  The material of the positive electrode current collector may be any material as long as it has high conductivity and can be easily processed into a thin film. Examples thereof include simple metals such as Al, Ni, and Cu; alloys such as stainless steel.

  Examples of the shape of the positive electrode current collector include a foil shape, a flat plate shape, a mesh shape, a net shape, a lath shape, a punching shape, an embossed shape, a shape obtained by combining one or more of these (for example, a mesh-like flat plate), etc. Is mentioned. Further, the surface of the current collector may be made uneven by an etching process.

  The method for applying the positive electrode mixture paste onto the positive electrode current collector, the method for removing the solvent in the positive electrode mixture paste, and the method for forming the positive electrode mixture layer may be the same as those for the electrode (negative electrode). For example, the positive electrode mixture layer after removal of the solvent may be pressed, and the pressing method may be the same as in the case of the electrode (negative electrode).

  The thickness of the positive electrode (total thickness of the positive electrode current collector and the positive electrode mixture layer) is preferably 5 to 500 μm.

  Examples of the separator include those having a structure such as a porous film, a nonwoven fabric, a woven fabric made of a material such as a polyolefin resin such as polyethylene or polypropylene; a fluororesin; a nitrogen-containing aromatic polymer.

  The separator may be either a single layer structure or a multilayer structure. In the case of a multilayer structure, the number of layers is not particularly limited, and all layers may be the same or all layers may be different from each other. Only the layers may be the same. Here, “the layers are different from each other” means that at least one of the material and the structure of the layers is different from each other.

  Examples of preferable separators include separators described in "JP 2000-30686 A", "JP 10-324758 A", and the like.

  The thickness of the separator is preferably as thin as possible as long as the mechanical strength is maintained from the viewpoint that the volume energy density of the battery is improved and the internal resistance is reduced, and is preferably 5 to 200 μm, more preferably 5 to 40 μm. .

  The separator preferably has a porous film made of a thermoplastic resin. In a sodium secondary battery, normally, when an abnormal current flows in the battery due to a short circuit between the positive electrode and the negative electrode, the current is interrupted to prevent the excessive current from flowing (shut down). is important. Therefore, when the separator exceeds the normal use temperature, the flow of excessive current is shut down as low as possible (if the separator has a porous film made of thermoplastic resin, the pores of the porous film are And shuts down without breaking (thermal breakage) even if the temperature in the battery rises to a certain high temperature after shutdown, in other words, it has high heat resistance. Is required. By using a separator having a laminated porous film in which a heat resistant porous layer made of a heat resistant resin and a porous film made of a thermoplastic resin are laminated as a separator, an excessive current is prevented while preventing thermal breakage of the separator. The better effect of shutting down the flow is obtained. Here, the said heat resistant porous layer may be laminated | stacked only on the single side | surface of the porous film, and may be laminated | stacked on both surfaces.

Hereinafter, the separator having the above laminated porous film will be described.
The thickness of such a separator is preferably 40 μm or less, more preferably 20 μm or less. Further, when the thickness of the heat resistant porous layer is a (μm) and the thickness of the porous film is b (μm), the value of a / b is preferably 0.1-1.
Furthermore, this separator preferably has an air permeability of 50 to 300 seconds / 100 cc, more preferably 50 to 200 seconds / 100 cc, from the viewpoint of ion permeability.
And the porosity of this separator becomes like this. Preferably it is 30-80 volume%, More preferably, it is 40-70 volume%.

The heat resistant porous layer is made of a heat resistant resin. And in order to improve ion permeability more, the thickness of a heat-resistant porous layer becomes like this. Preferably it is 1-10 micrometers, More preferably, it is 1-5 micrometers, More preferably, it is 1-4 micrometers.
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. Furthermore, the heat resistant porous layer may contain a filler to be described later.

  Examples of the material of the heat resistant resin constituting the heat resistant porous layer include polyamide, polyimide, polyamideimide, polycarbonate, polyacetal, polysulfone, polyphenylene sulfide, polyetheretherketone, aromatic polyester, polyethersulfone, polyetherimide. In order to further improve the heat resistance, polyamide, polyimide, polyamideimide, polyethersulfone, and polyetherimide are preferable, and polyamide, polyimide, and polyamideimide are more preferable. Among these, 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 poly A bromide, particularly preferably para-oriented aromatic polyamide (hereinafter sometimes referred to as "para-aramid".). Examples of the material for the heat resistant resin include poly-4-methylpentene-1 and cyclic olefin polymers (polymers obtained by polymerizing monomers having a cyclic olefin skeleton). By using these heat-resistant resins, the heat resistance, that is, the thermal film breaking temperature can be further increased.

  The thermal film breaking temperature depends on the kind of the heat-resistant resin, but is preferably 160 ° C. or higher. For example, the thermal film breaking temperature can be increased to about 400 ° C. at the maximum by using the heat-resistant resin made of the nitrogen-containing aromatic polymer. In addition, by using poly-4-methylpentene-1 as a heat-resistant resin, up to about 250 ° C., and by using the cyclic olefin polymer, up to about 300 ° C. The temperature can be increased.

  The para-aramid is obtained by condensation polymerization of a para-oriented aromatic diamine and a para-oriented aromatic dicarboxylic acid halide, and the amide bond is in the para position of the aromatic ring or an oriented position equivalent thereto (for example, 4,4 ′ -Substantially consisting of repeating units bonded in the opposite direction, such as biphenylene, 1,5-naphthalene, 2,6-naphthalene, etc., oriented in the opposite direction coaxially or in parallel. That is, the para-aramid has a para-orientation type or a structure according to the para-orientation type, and examples thereof include poly (paraphenylene terephthalamide), poly (parabenzamide), poly (4,4′-benzanilide terephthalate). Amide), poly (paraphenylene-4,4′-biphenylenedicarboxylic acid amide), poly (paraphenylene-2,6-naphthalenedicarboxylic acid amide), poly (2-chloro-paraphenylene terephthalamide), 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.
Examples of the dianhydride include pyromellitic dianhydride, 3,3 ′, 4,4′-diphenylsulfone tetracarboxylic dianhydride, 3,3 ′, 4,4′-benzophenone tetracarboxylic acid And dianhydride, 2,2′-bis (3,4-dicarboxyphenyl) hexafluoropropane, and 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride.
Examples of the diamine include oxydianiline, paraphenylenediamine, benzophenonediamine, 3,3′-methylenedianiline, 3,3′-diaminobenzophenone, 3,3′-diaminodiphenylsulfone, 1,5- Naphthalenediamine is mentioned.
As the aromatic polyimide, those soluble in a solvent are preferable, and examples thereof include a condensation polymerization product of 3,3 ′, 4,4′-diphenylsulfonetetracarboxylic dianhydride and an aromatic diamine. It is done.

Examples of the aromatic polyamide imide include those obtained by condensation polymerization using aromatic dicarboxylic acid and aromatic diisocyanate, and those obtained by condensation polymerization using aromatic diacid anhydride and aromatic diisocyanate. Are listed.
Examples of the aromatic dicarboxylic acid include isophthalic acid and terephthalic acid.
An example of the aromatic dianhydride includes trimellitic anhydride.
Examples of the aromatic diisocyanate include 4,4′-diphenylmethane diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, orthotolylene diisocyanate, and m-xylene diisocyanate.

  The filler that the heat-resistant porous layer may contain may be selected from any of organic powder, inorganic powder, or a mixture thereof. The particles constituting the filler preferably have an average particle diameter of 0.01 to 1 μm. Examples of the shape of the filler include a substantially spherical shape, a plate shape, a columnar shape, a needle shape, a whisker shape, and a fiber shape, and any of these may be used, but since it is easy to form a uniform hole, it may be a substantially spherical shape. preferable.

In the filler, examples of the material of the organic powder include one or more selected from the group consisting of styrene, vinyl ketone, acrylonitrile, methyl methacrylate, ethyl methacrylate, glycidyl methacrylate, glycidyl acrylate, and methyl acrylate. Polymers of monomers (homopolymers, copolymers): Fluorine series such as polytetrafluoroethylene, tetrafluoroethylene-6-fluoropropylene copolymer, tetrafluoroethylene-ethylene copolymer, polyvinylidene fluoride Examples include resins (resins containing fluorine atoms); melamine resins; urea resins; polyolefins; polymethacrylates and the like. Among these, polytetrafluoroethylene is preferable from the viewpoint of chemical stability.
The said organic powder may be used individually by 1 type, and may use 2 or more types together.

  In the filler, examples of the material of the inorganic powder include metal oxide, metal nitride, metal carbide, metal hydroxide, carbonate, sulfate, etc., preferably alumina, silica, titanium dioxide, carbonic acid. From the viewpoint of chemical stability, calcium is more preferable. In the filler, it is preferable that all particles constituting the filler are alumina particles, all particles constituting the filler are alumina particles, and a part or all of them are substantially spherical alumina particles. Is more preferable.

  The filler content in the heat-resistant porous layer may be appropriately set according to the specific gravity of the filler material. For example, when all particles constituting the filler are alumina particles, 100 parts by mass of the heat-resistant porous layer The amount is preferably 20 to 95 parts by mass, more preferably 30 to 90 parts by mass.

In the laminated porous film, the porous film is made of a thermoplastic resin.
The thickness of the porous film is preferably 3 to 30 μm, more preferably 3 to 20 μm.
Like the heat resistant porous layer, the porous film has micropores, and the size (diameter) of the pores 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 the nonaqueous electrolyte secondary battery, the porous film plays a role of closing fine pores by softening the thermoplastic resin constituting the film when the temperature of the separator exceeds the normal use temperature.

As a thermoplastic resin which comprises a porous film, what softens at 80-180 degreeC is mentioned, What is necessary is just to select what does not melt | dissolve in the electrolyte solution in a nonaqueous electrolyte secondary battery. Examples of the thermoplastic resin include polyolefins such as polyethylene and polypropylene; thermoplastic polyurethanes, and among these, polyethylene is preferable because it can be softened at a lower temperature to shut down the flow of excessive current.
The said thermoplastic resin may be used individually by 1 type, and may use 2 or more types together.

  Examples of the polyethylene include low density polyethylene, high density polyethylene, linear polyethylene, and ultrahigh molecular weight polyethylene. In order to further increase the puncture strength of the porous film, it is preferable to use at least ultrahigh molecular weight polyethylene as the thermoplastic resin. Moreover, it may be preferable from the manufacture surface of a porous film that a thermoplastic resin contains the wax which consists of polyolefin of a low molecular weight (weight average molecular weight 10,000 or less).

Examples of the electrolyte in the electrolyte include NaClO ₄ , NaPF ₆ , NaAsF ₆ , NaSbF ₆ , NaBF ₄ , NaCF ₃ SO ₃ , NaN (SO ₂ CF ₃ ) ₂ , lower aliphatic carboxylic acid sodium salt, NaAlCl ₄ Among them, among these, at least one selected from the group consisting of NaPF ₆ , NaAsF ₆ , NaSbF ₆ , NaBF ₄ , NaCF ₃ SO ₃ and NaN (SO ₂ CF ₃ ) ₂ containing fluorine atoms is included. Those are preferred. Here, the “lower aliphatic carboxylic acid” means an aliphatic carboxylic acid having 1 to 5 carbon atoms.
The said electrolyte may be used individually by 1 type, and may use 2 or more types together.
The electrolyte is preferably used in a state (liquid) dissolved in an organic solvent, that is, as a non-aqueous electrolyte.

Examples of the organic solvent in the electrolytic solution include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, isopropyl methyl carbonate, vinylene carbonate, 4-trifluoromethyl-1,3-dioxolan-2-one, Carbonates such as 1,2-di (methoxycarbonyloxy) ethane (compound having a carbonate skeleton); 1,2-dimethoxyethane, 1,3-dimethoxypropane, pentafluoropropylmethyl ether, 2,2,3, Ethers such as 3-tetrafluoropropyldifluoromethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran (compound having an ether bond); Esters such as methyl formate, methyl acetate, γ-butyrolactone (Compounds having an ester bond); nitriles such as acetonitrile and butyronitrile (compounds in which a cyano group is directly bonded to a carbon atom of a hydrocarbon group); amides such as N, N-dimethylformamide and N, N-dimethylacetamide (Compound having an amide bond); carbamates such as 3-methyl-2-oxazolidone (compound having a carbamate skeleton); sulfur-containing compounds such as sulfolane, dimethyl sulfoxide, 1,3-propane sultone; these organic solvents (compounds) And a fluorine-containing organic solvent (compound) in which at least one hydrogen atom constituting) is substituted with a fluorine atom.
Examples of the fluorine-containing organic solvent include 4-fluoro-1,3-dioxolan-2-one (hereinafter sometimes referred to as “FEC” or “fluoroethylene carbonate”), difluoroethylene carbonate (DFEC: trans or Cis-4,5-difluoro-1,3-dioxolan-2-one) and the like.
The said organic solvent may be used individually by 1 type, and may use 2 or more types together.

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

In order to improve the wettability with the separator, one or two surfactants such as trioctyl phosphate, polyoxyethylene ether having a perfluoroalkyl group, and perfluorooctane sulfonate ester are used in the electrolytic solution. You may add more.
The addition amount of the surfactant is preferably 3% by mass or less, more preferably 0.01 to 1% by mass with respect to the total amount (mass) of the electrolytic solution.

  In the sodium secondary battery, a solid electrolyte or a gel electrolyte may be used instead of the electrolytic solution.

Examples of the solid electrolyte include polymer electrolytes such as a polymer compound having a polyoxyalkylene chain such as polyethylene oxide, and a polymer compound having at least one polyorganosiloxane chain and / or a polyoxyalkylene chain. When a solid electrolyte is used, the solid electrolyte may serve as a separator. In that case, it is not necessary to separately provide a separator in the sodium secondary battery.
The gel electrolyte is obtained by holding a non-aqueous electrolyte in a polymer.
In the sodium secondary battery, sulfide electrolytes such as Na ₂ S—SiS ₂ , Na ₂ S—GeS ₂ , Na ₂ S—P ₂ S ₅ , Na ₂ S—B ₂ S ₃ ; Na ₂ S—SiS _{2 -Na 3 PO 4, Na 2} S-SiS 2 -Na inorganic compound electrolytes containing sulfides such as _{2 SO 4; NaZr 2 (PO} 4) can also be used NASICON type electrolyte such as _3, the use of these , May be able to increase safety.

  Since the sodium secondary battery according to the present invention includes the electrode including the negative electrode material according to the present invention, the sodium secondary battery has high charge / discharge capacity and excellent battery performance.

Hereinafter, the present invention will be described in more detail with reference to specific examples. However, the present invention is not limited to the following examples. In the following, the concentration unit “M” means “mol / L”.
In this example, the differential heat-thermogravimetric simultaneous measurement of the negative electrode material and the electrode mixture layer and the measurement of the BET specific surface area of the negative electrode material were performed by the following methods, respectively.

(Method of simultaneous differential heat-thermogravimetric measurement of negative electrode material and electrode mixture layer)
Using “TG / DTA6300” manufactured by SII Technology, the temperature was measured in a temperature range of 25 to 800 ° C. at a temperature rising rate of 1 ° C./min in air. And the weight change (%) in 620-800 degreeC of the negative electrode material and electrode mixture layer at this time was calculated | required.

(Method for measuring BET specific surface area of negative electrode material)
After 1 g of the negative electrode material was dried at 150 ° C. for 15 minutes in a nitrogen gas atmosphere, measurement was performed using “Macsorb HM-1201 / 1208” manufactured by Mountec.

<Manufacture of negative electrode material>
[Example 1]
98 parts by mass of non-graphitized carbon material (“ICB0510” (trade name: Nikabeads, average particle size 6 μm) manufactured by Nippon Carbon Co., Ltd.) as the amorphous carbon material (A), and acetylene black as the amorphous carbon material (B) 2 parts by mass (average particle size: 50 nm) was mixed to obtain a powdered negative electrode material (C1). The negative electrode material (C1) had a BET specific surface area of 180 m ² / g. Table 1 shows the weight change (%) at 620 to 800 ° C. in the simultaneous differential thermal-thermogravimetric measurement of the negative electrode material (C1).
The amorphous carbon material (A) had a peak showing the maximum calorific value at 564 ° C. in the differential thermal-thermogravimetric simultaneous measurement at a measurement temperature range of 400 ° C. or higher. Further, the amorphous carbon material (B) had a peak showing the maximum calorific value at 707 ° C. in the differential thermal-thermogravimetric simultaneous measurement at a measurement temperature range of 400 ° C. or higher. Of these peaks, the peak at 564 ° C. was the first peak having a larger calorific value than the peak at 707 ° C.

[Example 2]
Except that the amount of amorphous carbon material (A) used was 97 parts by mass instead of 98 parts by mass, and the amount of amorphous carbon material (B) used was 3 parts by mass instead of 2 parts by mass. In the same manner as in Example 1, a negative electrode material (C2) was obtained. The negative electrode material (C2) had a BET specific surface area of 179 m ² / g. Table 1 shows the weight change (%) at 620 to 800 ° C. in the simultaneous differential thermal-thermogravimetric measurement of the negative electrode material (C2).

[Example 3]
The amount of the amorphous carbon material (A) used is 96 parts by mass instead of 98 parts by mass, and the amount of the amorphous carbon material (B) used is 4 parts by mass instead of 2 parts by mass. A negative electrode material (C3) was obtained in the same manner as in Example 1. The BET specific surface area of the negative electrode material (C3) was 177 m ² / g. Table 1 shows the weight change (%) at 620 to 800 ° C. in the simultaneous differential thermal-thermogravimetric measurement of the negative electrode material (C3).

<Manufacture of electrodes>
[Example 4]
A binder liquid is prepared by dissolving styrene-butadiene copolymer (SBR) (“AL-1002” manufactured by Japan A & L) and carboxymethylcellulose (CMC) (“Serogen 4H” manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) as water as a binder. And this was mixed with the negative electrode material (C1) which is an electrode active material, and the electrode mixture paste was prepared. The compounding ratio (mass ratio) of each component at this time was electrode active material: binder: water = 97: 3: 150. The blending ratio (mass ratio) of SBR and CMC was SBR: CMC = 1: 2. Mixing of the binder liquid and the electrode active material was performed by using a dispermat (manufactured by VMA-GETZMANN), stirring the rotating blades at 2000 rpm, and stirring them for 5 minutes.
Then, using a doctor blade, the obtained electrode mixture paste was applied onto a copper foil having a thickness of 13 μm, dried at 60 ° C. for 2 hours to form an electrode mixture layer, and then cut into a 4 cm width. Then, this cut piece was rolled at 0.25 MPa using a roll press (“SA-602” manufactured by Tester Sangyo Co., Ltd.) to obtain an electrode (E1) having an electrode mixture layer thickness of 50 μm.

[Example 5]
An electrode (E2) having an electrode mixture layer thickness of 50 μm is obtained in the same manner as in Example 4 except that the negative electrode material (C2) is used instead of the negative electrode material (C1) as the electrode active material. It was.

[Example 6]
An electrode (E3) having an electrode mixture layer thickness of 50 μm was obtained in the same manner as in Example 4 except that the negative electrode material (C3) was used instead of the negative electrode material (C1) as the electrode active material. It was.

[Comparative Example 1]
The same as Example 4 except that the amorphous carbon material (A) (hereinafter sometimes referred to as “negative electrode material (D1)”) was used as the electrode active material instead of the negative electrode material (C1). By the method, an electrode (F1) having an electrode mixture layer thickness of 50 μm was obtained. Table 1 shows the weight change (%) at 620 to 800 ° C. in the differential thermal-thermogravimetric simultaneous measurement of the negative electrode material (D1).

  In addition, in the said Example and comparative example, the weight change (%) in 620-800 degreeC in the differential thermal-thermogravimetric simultaneous measurement of an electrode mixture layer was the same as the case of the negative electrode material used, respectively.

<Manufacture of secondary batteries>
Using the obtained electrodes (E1) to (E3) and (F1), secondary batteries were produced by the following procedure.
That is, any one of the electrodes (E1) to (E3) and (F1) is placed in the depression of the lower part of the coin cell (made by Hosen Co., Ltd.) with the copper foil facing down, and the concentration is 1M as the electrolytic solution. A sodium secondary battery was prepared by combining a propylene carbonate solution of NaPF ₆ , a polyethylene porous film having a thickness of 20 μm as a separator, and metallic sodium (manufactured by Aldrich) as a negative electrode. The secondary battery was manufactured in an argon atmosphere in a glove box.
Here, in order to eliminate as much as possible the influence of elements other than the amorphous carbon material constituting the negative electrode material on the secondary battery, the electrodes (E1) to (E3) and (F1) are not positive electrodes but positive electrodes. The functioning secondary battery was configured.

<Measurement of charge / discharge capacity of secondary battery>
The charge / discharge capacity of the obtained secondary battery was measured. Specifically, it is as follows.
For each secondary battery, CC-CV (constant current-constant voltage: constant current-constant voltage) discharge was performed at a 0.05 C rate (rate of complete charge in 20 hours) to 0.005 V, and this discharge rate The first cycle charge / discharge was performed by performing CC (constant current) charge at the same speed and cutting off at a voltage of 1.5V. Charging / discharging after the second cycle was performed at the same rate as the above-described charging rate, and cut off at a charging voltage of 4.0 V and a discharging voltage of 1.5 V as in the first cycle.

  A secondary battery manufactured using the electrodes (E1) to (E3) of Examples 1 to 3 with the initial charge and initial discharge capacities of the secondary battery manufactured using the electrode (F1) of Comparative Example 1 being 100, respectively. The capacity | capacitance of the initial charge and initial discharge of the battery was calculated | required as a relative capacity | capacitance with respect to this. The results are shown in Table 1.

  As is apparent from the above results, it was confirmed that the charge / discharge capacity of the sodium secondary battery was increased by using the negative electrode material according to the present invention.

  The present invention can be used in the energy field.

Claims (7)

A negative electrode material for a sodium secondary battery containing an amorphous carbon material that can be doped and dedoped with sodium ions,
The amorphous carbon material has a first peak showing the maximum calorific value and a second peak showing the next calorific value in the differential thermal-thermogravimetric simultaneous measurement at a measurement temperature range of 400 ° C. or higher. , One of them has a measurement temperature zone of 400 to 615 ° C, the other has a measurement temperature zone of 620 to 800 ° C,
The amorphous carbon material has an amorphous carbon material (A) having a peak showing a maximum calorific value in a measurement temperature zone of 400 to 615 ° C. in simultaneous differential heat-thermogravimetric measurement at a measurement temperature zone of 400 ° C. or higher. And an amorphous carbon material (B) having a peak showing a maximum calorific value in a measurement temperature zone of 620 to 800 ° C,
The negative electrode material for a sodium secondary battery includes the amorphous carbon material (A) and the amorphous carbon material (B) in a mass ratio of amorphous carbon material (A): amorphous carbon material (B). in 99.5: 0.5 to 90: contain in the range of 10,
The amorphous carbon material (A) is a non-graphitized carbon material,
The negative electrode material for a sodium secondary battery, wherein the amorphous carbon material (B) is acetylene black.   2. The negative electrode material for a sodium secondary battery according to claim 1, wherein a change in weight in a measurement temperature zone of 620 to 800 ° C. is 0.1 to 10% in simultaneous differential heat-thermogravimetric measurement. 3. The negative electrode material for a sodium secondary battery according to claim 1, wherein the negative electrode material has a BET specific surface area of 1 to 200 m ² / g in a powder form.   A sodium secondary battery electrode comprising the negative electrode material for a sodium secondary battery according to any one of claims 1 to 3. A sodium secondary battery electrode in which an electrode mixture layer containing an amorphous carbon material that can be doped and dedoped with sodium ions as a main component is formed on a current collector,
Amorphous carbon material (A) in which the amorphous carbon material has a peak showing a maximum calorific value in a measurement temperature zone of 400 to 615 ° C. in simultaneous differential heat-thermogravimetry at a measurement temperature zone of 400 ° C. or higher. And an amorphous carbon material (B) having a peak showing a maximum calorific value in a measurement temperature zone of 620 to 800 ° C,
The electrode mixture layer has a peak showing the maximum calorific value in the measurement temperature zone of 400 to 615 ° C. in the differential thermal-thermogravimetric simultaneous measurement at a measurement temperature zone of 400 ° C. or higher, and shows the next calorific value. It has a peak in the measurement temperature zone 620-800 ° C, the weight change in the measurement temperature zone 620-800 ° C is 0.1-10%,
The electrode mixture layer comprises the amorphous carbon material (A) and the amorphous carbon material (B) in a mass ratio of 99.99% by mass of the amorphous carbon material (A): the amorphous carbon material (B). 5: 0.5 to 90: in the range of 10 ,
The amorphous carbon material (A) is a non-graphitized carbon material,
The said amorphous carbon material (B) is acetylene black, The electrode for sodium secondary batteries characterized by the above-mentioned.   A sodium secondary battery comprising the sodium secondary battery electrode according to claim 4 as a negative electrode.   The sodium secondary battery according to claim 6, further comprising a separator.