JP2010272491A - Method of manufacturing sodium secondary battery, and sodium secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a sodium secondary battery having a high capacity and excellent cycle characteristics. <P>SOLUTION: A group of electrodes obtained by laminating a positive electrode capable of doping/dedoping of sodium ions, a negative electrode capable of doping/dedoping of the sodium ions, and a separator or by laminating or winding them, and an electrolyte are housed in a battery case, and the sodium ions are doped on the negative electrode, and after that the battery case is sealed. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a sodium secondary battery.

A so-called lithium secondary battery that uses an oxide such as LiMO ₂ (M is a transition metal such as Co, Mn, or Ni) for the positive electrode and a carbon material or a low potential compound of lithium for the negative electrode is used as a power source for portable devices. Widely used. On the other hand, since lithium secondary batteries use a lot of expensive and rare lithium, they are difficult to spread as large batteries.

  On the other hand, development of a sodium secondary battery using sodium as an electrode active material is underway (see, for example, Patent Document 1). Since the sodium secondary battery uses inexpensive sodium instead of expensive lithium, the material cost can be reduced as compared with the lithium secondary battery.

JP 2005-317511 A

  Conventional sodium secondary batteries do not have practical secondary battery performance like lithium secondary batteries, and there is still room for improvement. An object of the present invention is to provide a method for producing a sodium secondary battery capable of exhibiting a high discharge capacity and good cycle characteristics as compared with the prior art.

In view of the above problems, the present inventors have made various studies and reached the present invention.
That is, the present invention relates to the following inventions.
<1> A positive electrode that can be doped / undoped with sodium ions, a negative electrode that can be doped / dedoped with sodium ions, and a separator, or an electrode group obtained by stacking and winding, and an electrolyte. A method for producing a sodium secondary battery, which is housed in a battery case and the negative electrode is doped with sodium ions and then the battery case is sealed.
<2> The method for producing a sodium secondary battery according to <1>, wherein the anode is doped with sodium ions and then aged at 30 to 70 ° C. for 10 minutes or more before sealing.
<3> The method for producing a sodium secondary battery according to <1> or <2>, wherein the step of doping the negative electrode with sodium ions and further repeating the step of dedoping sodium ions from the negative electrode one or more times is performed after sealing. .
<4> The method for producing a sodium secondary battery according to <3>, wherein doping and dedoping of sodium ions in the negative electrode is performed at 30 to 70 ° C.
<5> The method for producing a sodium secondary battery according to any one of <1> to <4>, wherein the atmospheric gas is pressurized and / or decompressed before sealing.
<6> The method for producing a sodium secondary battery according to any one of <1> to <5>, wherein an electrolyte dissolved in an organic solvent is used as the electrolyte.
<7> A sodium secondary battery produced by the production method according to any one of <1> to <6>.

  According to the present invention, it is possible to obtain a practical sodium secondary battery that has a significantly improved discharge capacity and cycle characteristics as compared with the prior art. Moreover, the present invention can be applied to a large battery, and the present invention is extremely practical.

The present invention includes a positive electrode capable of doping / de-doping sodium ions, a negative electrode capable of doping / de-doping sodium ions and a separator, or an electrode group obtained by stacking or winding, an electrolyte, Is contained in a battery case, and the negative electrode is doped with sodium ions, and then the battery case is sealed.
In the present invention, after the negative electrode is doped with sodium ions, the negative electrode holds sodium in an ionic or metallic state.

  One of the features of the method for producing a sodium secondary battery of the present invention is that the battery case is sealed after the negative electrode is doped with sodium ions. Although the detailed reason is unknown at present, the discharge capacity and cycle characteristics can be improved by sealing the battery case after activating the negative electrode by doping sodium ions into the negative electrode.

  Hereinafter, a positive electrode, a negative electrode, an electrolyte, a separator, and a battery case according to the method for producing a sodium secondary battery of the present invention will be described.

(1) Positive electrode The positive electrode is a sheet in which a positive electrode mixture containing a positive electrode active material, a binder, a conductive agent and the like is supported on a positive electrode current collector, and is usually in a sheet form. More specifically, a positive electrode mixture formed by adding a solvent to a positive electrode active material, a binder, a conductive agent, and the like, is applied to a positive electrode current collector by a doctor blade method or the like, and is dried. A method in which a sheet obtained by adding a solvent to a positive electrode active material, a binder, a conductive agent, etc., kneading, forming, and drying is bonded to the surface of the positive electrode current collector via a conductive adhesive, and then pressed and dried. A mixture of a positive electrode active material, a binder, a conductive agent, a liquid lubricant, and the like is formed on the positive electrode current collector, then the liquid lubricant is removed, and then a uniaxial or multiaxial direction is stretched. Can be mentioned. When the positive electrode has a sheet shape, the thickness is usually about 5 to 500 μm.

As the positive electrode active material, a positive electrode material that can be doped / undoped with sodium ions can be used. From the viewpoint of the cycleability of the obtained sodium secondary battery, it is preferable to use a sodium inorganic compound as the material. Examples of the sodium inorganic compound include the following compounds. That, 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 oxide represented by M ¹ _a O _2.05 (M ¹ is one or more transition metal elements, 0 ≦ a <1); Na ₆ Fe ₂ Si ₁₂ O ₃₀ and Na ₂ Fe ₅ Si ₁₂ O ₃₀ Oxides represented by Na _b M ² _c 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 Na _d M ³ _e Si ₆ oxide represented by O _18, such as ₂ MnFeSi ₆ O ₁₈ (M ³ is one or more transition metal elements, 3 ≦ d ≦ 6,1 ≦ e ≦ 2); Na 2 FeSiO Na _f M ⁴ _g Si ₂ oxide represented by O ₆ (M ⁴ is at least one element selected from the group consisting of transition metal elements, Mg and Al, such as _6, 1 ≦ f ≦ 2, 1 ≦ g ≦ 2); phosphate represented by NaM ⁶ _a PO ₄ such as NaFePO ₄ , NaMnPO ₄ , NaNiPO ₄ (M ⁶ is one or more transition metal elements); Na ₃ Fe ₂ Phosphate such as (PO ₄ ) ₃ ; Borate such as NaFeBO ₄ and Na ₃ Fe ₂ (BO ₄ ) ₃ ; Represented by Na _h M ⁵ F ₆ such as Na ₃ FeF ₆ and Na ₂ MnF ₆ Fluoride (M ⁵ is one or more transition metal elements, 2 ≦ h ≦ 3);

In addition, a chalcogen compound such as sulfide can be used as the positive electrode material. As sulfides, compounds represented by M ⁶ S ₂ such as TiS ₂ , ZrS ₂ , VS ₂ , V ₂ S ₅ , TaS ₂ , FeS ₂ and NiS ₂ (M ⁶ is one or more transition metal elements), etc. Is mentioned. In this case, for example, sodium metal or sodium alloy may be used as the negative electrode.

  Among the above-mentioned sodium inorganic 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.

  Examples of the conductive agent used for the positive electrode include natural graphite, artificial graphite, cokes, carbon materials such as carbon black, and the like.

  Examples of the binder used for the positive electrode include a polymer of a fluorine compound. Examples of the fluorine compound include fluorinated alkyl (C1-18) (meth) acrylate, perfluoroalkyl (meth) acrylate [for example, perfluorododecyl (meth) acrylate, perfluoro n-octyl (meth) acrylate, Perfluoro n-butyl (meth) acrylate], perfluoroalkyl-substituted alkyl (meth) acrylate [for example, perfluorohexylethyl (meth) acrylate, perfluorooctylethyl (meth) acrylate], perfluorooxyalkyl (meth) acrylate [ For example, perfluorododecyloxyethyl (meth) acrylate and perfluorodecyloxyethyl (meth) acrylate, etc.], fluorinated alkyl (C1-18) crotonate, fluorinated alkyl ( Prime numbers 1 to 18) Malate and fumarate, fluorinated alkyl (1 to 18 carbon atoms) itaconate, fluorinated alkyl-substituted olefins (about 2 to 10 carbon atoms, about 1 to 17 fluorine atoms) such as perfluorohexylethylene, carbon Examples include fluorinated olefins, tetrafluoroethylene, trifluoroethylene, vinylidene fluoride, hexafluoropropylene, and the like in which fluorine atoms are bonded to double bond carbons of about 2 to 10 and about 1 to 20 fluorine atoms.

  Other examples of the binder include monomer addition polymers containing an ethylenic double bond that does not contain a fluorine atom. Examples of such monomers include (cyclo) alkyl (C1-22) (meth) acrylate [for example, methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, iso-butyl (Meth) acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, isodecyl (meth) acrylate, lauryl (meth) acrylate, octadecyl (meth) acrylate, etc.]; aromatic ring-containing (meth) acrylate [for example, benzyl (Meth) acrylate, phenylethyl (meth) acrylate, etc.]; mono (meth) acrylate of alkylene glycol or dialkylene glycol (alkylene group having 2 to 4 carbon atoms) [for example, 2-hydroxyethyl (meth) acrylate, 2- Hi Roxypropyl (meth) acrylate, diethylene glycol mono (meth) acrylate]; (poly) glycerin (degree of polymerization 1 to 4) mono (meth) acrylate; polyfunctional (meth) acrylate [for example, (poly) ethylene glycol (degree of polymerization 1) ~ 100) di (meth) acrylate, (poly) propylene glycol (degree of polymerization 1-100) di (meth) acrylate, 2,2-bis (4-hydroxyethylphenyl) propane di (meth) acrylate, trimethylolpropane tri ( (Meth) acrylate monomers such as (meth) acrylate]; (meth) acrylamide (meth) acrylamide, (meth) acrylamide derivatives [eg, N-methylol (meth) acrylamide, diacetone acrylamide, etc.] Acrylamide monomer; ) Cyano group-containing monomers such as acrylonitrile, 2-cyanoethyl (meth) acrylate, 2-cyanoethylacrylamide; styrene and styrene derivatives having 7 to 18 carbon atoms [for example, α-methylstyrene, vinyltoluene, p-hydroxystyrene and Styrene monomers such as divinylbenzene]; Diene monomers such as alkadienes having 4 to 12 carbon atoms [for example, butadiene, isoprene, chloroprene, etc.]; Carboxylic acid (2 to 12 carbon atoms) vinyl esters [for example, , Vinyl acetate, vinyl propionate, vinyl butyrate and vinyl octoate, etc.], carboxylic acid (2 to 12 carbon atoms) (meth) allyl ester [for example, (meth) allyl acetate, (meth) allyl propionate and octanoic acid ( Alkenyl ester based monomers such as (meth) allyl etc.] An epoxy group-containing monomer such as glycidyl (meth) acrylate and (meth) allyl glycidyl ether; a monoolefin having 2 to 12 carbon atoms [e.g., ethylene, propylene, 1-butene, 1-octene and 1-dodecene, etc.] Monoolefins of the following: Monomers containing chlorine, bromine or iodine atoms, monomers containing halogen atoms other than fluorine such as vinyl chloride and vinylidene chloride; (meth) acrylic acids such as acrylic acid and methacrylic acid; butadiene, isoprene, etc. And conjugated double bond-containing monomers.

  The addition polymer may be a copolymer such as an ethylene / vinyl acetate copolymer, a styrene / butadiene copolymer, or an ethylene / propylene copolymer. The carboxylic acid vinyl ester polymer may be partially or completely saponified, such as polyvinyl alcohol. The binder may be a copolymer of a fluorine compound and a monomer containing an ethylenic double bond not containing a fluorine atom.

  Other examples of the binder further include, for example, polysaccharides and derivatives thereof such as starch, methylcellulose, carboxymethylcellulose, hydroxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, carboxymethylhydroxyethylcellulose, nitrocellulose; phenol resin; melamine resin Polyurethane resin, urea resin, polyamide resin, polyimide resin, polyamideimide resin, petroleum pitch, coal pitch, and the like.

  Examples of the solvent used for the positive electrode include aprotic polar solvents such as N-methyl-2-pyrrolidone, alcohols such as isopropyl alcohol, ethyl alcohol or methyl alcohol, ethers such as propylene glycol dimethyl ether, acetone, Examples thereof include ketones such as methyl ethyl ketone and methyl isobutyl ketone.

  A conductive adhesive is a mixture of a conductive agent and a binder. In particular, the mixture of carbon black and polyvinyl alcohol does not require the use of a solvent, is easy to prepare, and is excellent in storage stability. Is preferred.

  Further, in the positive electrode mixture, the amount of the constituent material may be set as appropriate, but the amount of the binder is usually about 0.5 to 30 parts by weight with respect to 100 parts by weight of the positive electrode active material. The amount of the conductive agent is usually about 1 to 50 parts by weight, preferably about 1 to 30 parts by weight with respect to 100 parts by weight of the positive electrode active material. The blending amount is usually about 50 to 500 parts by weight, preferably about 100 to 200 parts by weight with respect to 100 parts by weight of the positive electrode active material.

  Examples of the positive electrode current collector used for the positive electrode include metals such as nickel, aluminum, titanium, copper, gold, silver, platinum, aluminum alloys, and stainless steel, such as carbon materials, activated carbon fibers, nickel, aluminum, and zinc. A conductive agent is dispersed in a resin formed by plasma spraying or arc spraying of copper, tin, lead or an alloy thereof, for example, rubber or a resin such as styrene-ethylene-butylene-styrene copolymer (SEBS). Examples include conductive films. In particular, aluminum, nickel, stainless steel, and the like are preferable. In particular, aluminum is preferable because it can be easily processed into a thin film and is inexpensive. Examples of the shape of the positive electrode current collector include a foil shape, a flat plate shape, a mesh shape, a net shape, a lath shape, a punching metal shape, an embossed shape, or a combination thereof (for example, a mesh flat plate). Is mentioned. Concavities and convexities by etching treatment may be formed on the surface of the positive electrode current collector.

(2) Negative Electrode Next, the negative electrode will be described. Examples of the negative electrode include those in which a negative electrode mixture containing a negative electrode active material, a binder and, if necessary, a conductive agent is supported on a negative electrode current collector, sodium metal or a sodium alloy. Is. More specifically, a negative electrode mixture formed by adding a solvent to a negative electrode active material and a binder, or the like, is applied to a negative electrode current collector by a doctor blade method or the like, and is dried to dry the negative electrode active material and A method in which a sheet obtained by adding a solvent to a bond or the like is kneaded, molded, and dried and bonded to the surface of the negative electrode current collector via a conductive adhesive or the like, followed by pressing and heat treatment drying, a negative electrode active material, a binder And a mixture of a liquid lubricant and the like formed on the negative electrode current collector, then the liquid lubricant is removed, and then the obtained sheet-like molded product is stretched in a uniaxial or multiaxial direction. It is done. When the negative electrode has a sheet shape, the thickness is usually about 5 to 500 μm.

  As the negative electrode active material, a negative electrode material that can be doped / undoped with sodium ions can be used. As the material, a carbon material such as carbon black, pyrolytic carbon, carbon fiber, non-graphitizable carbon material, and fired organic material, which can be doped / undoped with sodium ions can be used. The shape of the carbon material may be any of a flake shape such as natural graphite, a spherical shape such as mesocarbon microbeads, a fibrous shape such as graphitized carbon fiber, or an aggregate of fine powder.

  Moreover, as a suitable carbon material that can be used as the negative electrode active material, carbon microbeads can be cited, and specifically, ICB (trade name: Nika beads) manufactured by Nippon Carbon Co., Ltd. can be exemplified.

  As a fired organic material that can be doped / undoped with sodium ions, a carbon material that can be doped / undoped with sodium ions is used among carbon materials obtained by carbonization (firing) of various organic materials. That's fine. 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. Examples include various plant residue oils, organic materials derived from plants such as wood, and the like, and these can be used alone or in combination of two or more.

  As the synthetic resin, phenol resin, resorcinol resin, furan resin, epoxy resin, urethane resin, unsaturated polyester resin, melamine resin, urea resin, aniline resin, bismaleimide resin, benzoxazine resin, polyacrylonitrile resin, polystyrene resin, Polyamide resin, cyanate resin, ketone resin, and the like can be given, and these can be used alone or in combination of two or more. Moreover, you may use it by making it contain a hardening | curing agent and an additive. Although the curing method is not particularly limited, for example, when a phenol resin is used, thermal curing, thermal oxidation, epoxy curing, isocyanate curing and the like can be mentioned. Moreover, when an epoxy resin is used, phenol resin curing, acid anhydride curing, amine curing, and the like can be given.

  Among organic materials, an organic material having an aromatic ring is 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, and these can be used alone or in combination of two or more. Moreover, you may contain the hardening | curing agent and the additive.

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

  An example of an organic material obtained by polymerizing phenol or a derivative thereof and an aldehyde compound is a phenol resin. 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 a negative electrode active material for a sodium secondary battery, the charge / discharge capacity of the secondary battery and the discharge capacity after repeated charge / discharge are particularly large. A phenolic resin is characterized by a structure with developed three-dimensional crosslinking, and a 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. It is considered that this estimation contributes particularly to the 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, Examples thereof include p-tert-octylphenol, α-naphthol, β-naphthol and the like, and these can be used alone or in combination of two or more.

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

  Although it does not specifically limit as a phenol resin, A resol type phenol resin, a novolak type phenol resin, etc. can be used. 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 removal of unreacted monomers. A metal salt such as zinc acetate, lead acetate, zinc naphthenate, and the like, which is obtained by a random novolak type in which the methylene group bonding positions are the same in the ortho and para positions, and phenol or a derivative thereof and an aldehyde compound. 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.

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

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

  During polymerization of phenol or its derivatives and aldehyde compounds, by-products may be generated or unpolymerized products may remain, but these by-products and unpolymerized products can be used as organic materials. In addition, the environmental load can be reduced in terms of reducing waste, and a carbon material can be obtained at a low cost, resulting in higher industrial utility value.

  Further, by using a carbon material obtained by carbonization (firing) of a plant-derived organic material as the carbon material used for the negative electrode active material, the environmental load can be reduced, and the industrial utility value is higher.

  Wood and the like can be exemplified as the plant-derived organic material, and charcoal obtained by carbonizing this is a preferred embodiment as a carbon material used for the negative electrode active material. 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 mentioned as 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. Angiosperms, etc. can be mentioned.

  Among the timbers, 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 can obtain a carbon material at low cost. Bincho charcoal obtained by carbonizing oak is also a preferred embodiment as a carbon material used for the negative electrode active material.

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

  Examples of plant residue oils include various residue oils during the production of various petrochemical products such as ethylene. More specifically, there can be mentioned petroleum heavy oil composed of distillation residue oil, fluid catalytic cracking residue oil, hydrodesulfurized oil thereof, or mixed oil thereof. Among 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.

The carbon material used for the negative electrode active material can be obtained by carbonizing (sintering) 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 heated product obtained by heating the organic material in the presence of an oxidizing gas of 400 ° C. or lower may be carbonized in an inert gas atmosphere. Examples of the inert gas include nitrogen and argon, and examples of the oxidizing gas include air, H ₂ O, CO ₂ , and O ₂ . Carbonization may be performed under reduced pressure. These heating and carbonization may be performed using equipment such as a rotary kiln, a roller hearth kiln, a pusher kiln, a multi-stage furnace, and a fluidized furnace. Rotary giraffes are versatile.

  The carbon material obtained by carbonization (firing) may be pulverized as necessary. For pulverization, for example, impact friction pulverizer, centrifugal pulverizer, ball mill (tube mill, compound mill, A pulverizer for fine pulverization such as a conical ball mill, a rod mill), a vibration mill, a colloid mill, a friction disk mill or a jet mill is preferably used, and pulverization 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.

  The same binder and conductive agent as those used in the positive electrode can be used. In the negative electrode, a carbon material that can be doped / undoped with sodium ions may serve as a conductive agent.

Further, when the positive electrode active material in the positive electrode is the above-described sodium inorganic compound, a chalcogen compound such as a sulfide that can be doped / dedoped with sodium ions at a lower potential than the positive electrode can also be used. Here, as sulfides, TiS ₂ , ZrS ₂ , VS ₂ , V ₂ S ₅ , TaS ₂ , FeS ₂ , NiS ₂ , and M ⁶ S ₂ (where M ⁶ is one or more transition metal elements). ) And the like.

  Examples of the negative electrode current collector include Cu, Ni, and stainless steel, and Cu is preferable because it is difficult to form an alloy with sodium and it can be easily processed into a thin film. Examples of the shape of the negative electrode current collector include a foil shape, a flat plate shape, a mesh shape, a net shape, a lath shape, a punching metal shape, an embossed shape, or a combination thereof (for example, a mesh flat plate). Is mentioned. Concavities and convexities by etching treatment may be formed on the surface of the negative electrode current collector.

(3) Electrolyte Next, the electrolyte will be described. Examples of 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, and the} like. A mixture of two or more kinds may be used. Among these, it is preferable to use those containing at least one selected from the group consisting of NaPF ₆ , NaAsF ₆ , NaSbF ₆ , NaBF ₄ , NaCF ₃ SO ₃ and NaN (SO ₂ CF ₃ ) ₂ containing fluorine. Moreover, in this invention, it is preferable to use electrolyte as the state (liquid state) melt | dissolved in the organic solvent, ie, a non-aqueous electrolyte.

  Examples of the organic solvent in the non-aqueous electrolyte 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; 1,2-dimethoxyethane, 1,3-dimethoxypropane, pentafluoropropyl methyl ether, 2,2,3,3-tetrafluoropropyl difluoromethyl ether , Ethers such as tetrahydrofuran and 2-methyltetrahydrofuran; esters such as methyl formate, methyl acetate and γ-butyrolactone; nitriles such as acetonitrile and butyronitrile; N Amides such as N-dimethylformamide and N, N-dimethylacetamide; Carbamates such as 3-methyl-2-oxazolidone; Sulfur-containing compounds such as sulfolane, dimethyl sulfoxide and 1,3-propane sultone; What further introduce | transduced the fluorine substituent into the solvent can be used. Two or more of these may be mixed and used as the organic solvent.

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

In the present invention, the electrolyte can be used in a state where the non-aqueous electrolyte is held in a polymer compound, that is, as a gel electrolyte, or as a solid, that is, as a solid electrolyte. As the solid electrolyte, for example, an organic solid electrolyte in which the electrolyte is held in a polymer compound containing at least one of a polyethylene oxide polymer compound, a polyorganosiloxane chain or a polyoxyalkylene chain can be used. . Na ₂ S—SiS ₂ , Na ₂ S—GeS ₂ , NaTi ₂ (PO ₄ ) ₃ , NaFe ₂ (PO ₄ ) ₃ , Na ₂ (SO ₄ ) ₃ , Fe ₂ (SO ₄ ) ₂ (PO ₄ ) ), Fe ₂ (MoO ₄ ) ₃ , β-alumina, β ″ -alumina, NASICON, etc. Inorganic solid electrolytes such as NASICON may be used. The safety of the battery can be further enhanced by using these solid electrolytes. is there.

(4) Separator As the separator, for example, a material having a form of 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 is used. it can. Moreover, it is good also as a single layer or laminated separator which used 2 or more types of these materials. Examples of the separator include separators described in JP 2000-30686 A, JP 10-324758 A, and the like. The thickness of the separator is preferably as thin as possible as long as the mechanical strength is maintained in that the volume energy density of the battery is increased and the internal resistance is reduced. In general, the thickness of the separator is preferably about 5 to 200 μm, more preferably about 5 to 40 μm.

  The separator preferably has a porous film containing a thermoplastic resin. In the secondary battery, the separator is disposed between the positive electrode and the negative electrode. In addition, when an abnormal current flows in the battery due to a short circuit between the positive electrode and the negative electrode, it is preferable to play a role of blocking (shutting down) an excessive current by blocking the current. Here, the shutdown is performed by closing the micropores of the porous film in the separator when the normal use temperature is exceeded. After the shutdown, even if the temperature in the battery rises to a certain high temperature, it is preferable to maintain the shutdown state without breaking the film due to the temperature, in other words, high heat resistance. As such a separator, a porous film having a heat resistant material such as a laminated film in which a heat resistant porous layer and a porous film are laminated, preferably a heat resistant porous layer containing a heat resistant resin and a porous film containing a thermoplastic resin Can be mentioned, and by using a porous film having such a heat-resistant material as a separator, it is possible to further prevent thermal breakage of the secondary battery. Here, the heat-resistant porous layer may be laminated on both surfaces of the porous film.

  Hereinafter, a laminated film in which a heat resistant porous layer and a porous film preferable as a separator are laminated will be described. Here, the thickness of this separator is usually 5 μm or more and 40 μm or less, preferably 20 μm or less. Moreover, when the thickness of the heat resistant porous layer is A (μm) and the thickness of the porous film is B (μm), the value of A / B is preferably 0.1 or more and 1 or less. Furthermore, 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. . The porosity of this separator is usually 30 to 80% by volume, preferably 40 to 70% by volume.

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

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

  The thermal film breaking temperature depends on the type of heat-resistant resin, and is selected and used according to the use scene and purpose of use. Usually, the thermal film breaking temperature is 160 ° C. or higher. When the nitrogen-containing aromatic polymer is used as the heat-resistant resin, the temperature is about 400 ° C., when poly-4-methylpentene-1 is used, about 250 ° C., and when the cyclic olefin polymer is used, 300 is used. The thermal film breaking temperature can be controlled to about 0 ° C., respectively. Moreover, when the heat resistant porous layer is made of an inorganic powder, the thermal film breaking temperature can be controlled to, for example, 500 ° C. or higher.

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

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

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

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

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

  Examples of the inorganic powder as the filler include powders made of inorganic materials such as metal oxides, metal nitrides, metal carbides, metal hydroxides, carbonates, sulfates, etc. Among these, inorganic materials having low conductivity The powder consisting of is preferably used. Specific examples include powders made of alumina, silica, titanium dioxide, barium sulfate, calcium carbonate, or the like. An inorganic powder may be used independently and can also be used in mixture of 2 or more types. Among these inorganic powders, alumina powder is preferable from the viewpoint of chemical stability. It is more preferable that all of the particles constituting the filler are alumina particles, and it is even more preferable that all of the particles constituting the filler are alumina particles, and part or all of them are substantially spherical alumina particles. Incidentally, when the heat-resistant porous layer is formed from an inorganic powder, the inorganic powder exemplified above may be used, and may be mixed with a binder as necessary.

  When the heat-resistant porous layer contains a heat-resistant resin, the filler content depends on the specific gravity of the filler material. For example, when all of the particles constituting the filler are alumina particles, the total amount of the heat-resistant porous layer is When the weight is 100, the weight of the filler is usually 5 or more and 95 or less, preferably 20 or more and 95 or less, more preferably 30 or more and 90 or less. These ranges can be appropriately set depending on the specific gravity of the filler material.

  In the laminated film, the porous film preferably has micropores and is preferably shut down. In this case, the porous film contains a thermoplastic resin. The thickness of this porous film is usually 3 to 30 μm, more preferably 3 to 25 μm. Similar to the heat resistant porous layer, the porous film has fine pores, and the pore size is usually 3 μm or less, preferably 1 μm or less. The porosity of the porous film is usually 30 to 80% by volume, preferably 40 to 70% by volume. In the sodium secondary battery, when the normal use temperature is exceeded, the porous film can close the micropores by softening the thermoplastic resin constituting the porous film.

  Examples of the thermoplastic resin contained in the porous film include those that soften at 80 to 180 ° C. When a non-aqueous electrolyte is used, a resin that does not dissolve therein may be selected. Specifically, examples of the thermoplastic resin include polyolefin resins such as polyethylene and polypropylene, and thermoplastic polyurethane resins, and a mixture of two or more of these may be used. In order to soften and shut down at a lower temperature, the thermoplastic resin preferably contains polyethylene. Specific examples of polyethylene include polyethylene such as low density polyethylene, high density polyethylene, and linear polyethylene, and ultra high molecular weight polyethylene having a molecular weight of 1,000,000 or more. In order to further increase the puncture strength of the porous film, the thermoplastic resin preferably contains at least ultra high molecular weight polyethylene. In addition, in terms of production of the porous film, the thermoplastic resin may preferably contain a wax made of polyolefin having a low molecular weight (weight average molecular weight of 10,000 or less).

  The porous film having a heat resistant material different from the laminated film includes a porous film made of a heat resistant resin and / or an inorganic powder, and a heat resistant resin and / or an inorganic powder such as a polyolefin resin or a thermoplastic polyurethane resin. A porous film dispersed in a thermoplastic resin film can also be exemplified. Here, the above-mentioned thing can be mentioned as a heat resistant resin and inorganic powder.

(5) Battery Case The battery case may be any conventionally known battery case, and is determined according to the intended use in consideration of necessary mechanical strength and weight. For example, an outer can type such as a bottomed cylindrical shape or a bottomed rectangular tube shaped steel can or an aluminum can, or a film case type formed of a metal laminated resin film can be used.

  In addition, the metal layer in the metal laminate resin film used in the film case type battery case may be any one that can impart airtightness to the film by suppressing the permeation of outside air, such as aluminum, titanium, and the like. An alloy containing, for example, is used as the material, and aluminum is particularly preferable. The resin layer of the film is not particularly limited as long as it has appropriate flexibility and strength, and a thermoplastic resin such as polyethylene, polypropylene, and polyethylene terephthalate can be suitably used. Further, the metal layer and the resin layer of the metal laminated resin film may be one layer or multiple layers.

  Next, the specific procedure in the manufacturing method of the sodium secondary battery of this invention is demonstrated.

  As a procedure for assembling the sodium secondary battery, an electrode group obtained by laminating the positive electrode, the negative electrode, and the separator described above or an electrode group obtained by laminating and winding the electrode group is housed in a battery case, and then the electrolyte is used. The method of accommodating is mentioned.

  As the shape of the electrode group, the cross section of the electrode group (in the case of lamination and winding, the cross section when cut in the direction perpendicular to the winding axis) is, for example, a circle, an ellipse, a rectangle, or a corner. Examples of such a shape can be a rectangle. In addition, examples of the shape of the battery include a paper shape, a coin shape, a cylindrical shape, and a square shape.

The method of doping sodium ions into the negative electrode before sealing in the present invention is relatively easy because a large amount of sodium ions can be doped into the negative electrode, so that an external voltage is applied between the positive and negative electrodes (hereinafter referred to as “charging”). Is preferably selected.
Particularly, the negative electrode is doped with sodium ions by charging, and when the sodium ion dope amount, that is, the initial charge amount is 10% or more of the full charge capacity, the discharge capacity and the cycle characteristics tend to be further improved. This is preferable. In this case, the negative electrode may be one in which a negative electrode active material, a binder, and, if necessary, a negative electrode mixture containing a conductive agent or the like are supported on the negative electrode current collector. Here, the “full charge capacity” can be obtained by preparing a spare battery described later.

In the production method of the present invention, from the viewpoint of promoting electrolyte penetration into the negative electrode and stabilizing the negative electrode film, the negative electrode is doped with sodium ions and then held at an appropriate temperature and time (sealing) before sealing. It is desirable to seal it after
A preferable aging temperature and time are 10 to 30 minutes at 30 to 70 ° C. By making such a range, gas generation is suppressed and sufficient aging can be performed.

Moreover, in the manufacturing method of this invention, it is desirable to do sealing after repeating the process which dopes sodium ion to a negative electrode, and also performs the dedope of sodium ion from a negative electrode 1 time or more. After the first dope of sodium ions to the negative electrode, the initial reaction that occurs in the negative electrode is almost completed by performing dedope, and then sealing is performed to reduce the battery characteristics that sodium is considered to be involved in. Can be suppressed.
In this case, when the doping and dedoping of sodium ions in the negative electrode is performed at 30 to 70 ° C., it is possible to further suppress the deterioration of battery characteristics and to be more effective.

In the present invention, it is desirable to perform atmospheric gas pressurization and / or decompression after the electrode group and the electrolyte are accommodated in the battery case and before sealing. This atmospheric gas pressurization and / or decompression has the effect of removing the initial product that inhibits the charge / discharge reaction, which is extremely effective for suppressing the deterioration of the battery characteristics particularly in the sodium secondary battery.
Further, by reducing the pressure, gas contained in fine gaps and pores of the positive electrode, the negative electrode, and the separator can be removed, and penetration of the electrolyte into the gaps and pores can be promoted. On the other hand, the penetration of the electrolyte into fine gaps and pores of the positive electrode, the negative electrode, and the separator can also be promoted by pressurizing the atmospheric gas. In particular, by alternately performing atmospheric gas pressurization and pressure reduction, the electrolyte can be more uniformly penetrated into fine gaps and pores, and the electrolyte dispersibility in the battery can be improved, which is more effective.
Specifically, the atmospheric gas can be pressurized and / or decompressed by placing the assembled battery in a pressure-resistant container, replacing the inside of the container with the atmospheric gas, and then depressurizing with a vacuum pump. The method of introducing and pressurizing gas is mentioned.
As the atmospheric gas, inert gases such as nitrogen, helium, and argon are usually used.

  The sodium secondary battery manufactured by the manufacturing method of the present invention described above is a sodium secondary battery having a large discharge capacity and excellent cycle characteristics.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these.

The production of the sodium secondary battery was performed by the following method.
(1-1) Production of Positive Electrode Active Material In a glove box in an argon atmosphere, Na ₂ O ₂ (manufactured by Fluka Chemie AG) and Fe ₃ O ₄ (manufactured by Aldrich Chemical Company, Inc.) were mixed with NaFe and NaFeO ₂ . After weighing to a stoichiometric ratio, the mixture was mixed well in an agate mortar. The obtained mixture was put in an alumina crucible, and the atmosphere was evacuated with a vacuum pump in advance, and then placed in an electric furnace where argon was introduced and replaced. Immediately before reaching 100 ° C., the electric furnace was opened to the air, and thereafter heated in an air atmosphere, held at 650 ° C. for 12 hours, and taken out to obtain a sodium inorganic compound (MC1) as a positive electrode active material. .

(1-2) Preparation of positive electrode MC1 as a positive electrode active material, acetylene black, and polyvinylidene fluoride were mixed at a ratio of 85: 10: 5, and an appropriate amount of N-methylpyrrolidone was further added and mixed. A slurry was obtained. A masking tape was applied to a part of an aluminum foil having a thickness of 20 μm, and the slurry was applied to the surface with a doctor blade, followed by drying to form a coating film. Next, after a coating film was similarly formed on the opposite surface, a roll press was applied to produce an electrode (positive electrode) having a width of about 50 mm, a length of about 300 mm, and a thickness of about 180 μm. Subsequently, an aluminum lead plate having a thickness of 50 μm and a width of 5 mm for the current collector was connected to one end of the electrode (positive electrode) from which the masking tape was peeled off by ultrasonic welding.

(2-1) Preparation of negative electrode active material Phenol resin (powdered phenol resin, trade name, Sumilite resin, PR-217) powder was placed on an alumina boat, placed in an annular furnace, and 1000 ° C. in an argon gas atmosphere. And the phenolic resin powder was carbonized. In the furnace, the argon gas flow rate was 0.1 L / min per 1 g of the phenol resin powder, the temperature rising rate from room temperature to 1000 ° C. was about 5 ° C./min, and the holding time at 1000 ° C. was 1 hour. After carbonization, the carbon material (MA1) which is a negative electrode active material was obtained by pulverizing with a ball mill (agate ball, 28 rpm, 5 minutes). The average particle size was 50 μm or less. The average particle size was measured as a volume average particle size measured using a laser diffraction particle size distribution analyzer SALD2000J (registered trademark, manufactured by Shimadzu Corporation) after dispersing the carbon material with a neutral detergent-containing aqueous solution.

(2-2) Preparation of negative electrode An appropriate amount of N-methylpyrrolidone was added to a mixture of (MA1) as the negative electrode active material and polyvinylidene fluoride in a ratio of 95: 5 and mixed to obtain a paint-like slurry. . A masking tape was applied to a part of a copper foil having a thickness of 10 μm, and the slurry was applied to the surface with a doctor blade, followed by drying to form a coating film. Next, after forming a coating film on the opposite surface in the same manner, a roll press was applied to produce an electrode having a width of about 55 mm, a length of about 330 mm, and a thickness of about 230 μm, which was used as a negative electrode. Subsequently, a nickel lead plate having a thickness of 30 μm and a width of 5 mm for the current collector was connected to one end of the electrode (negative electrode) from which the masking tape was peeled off by resistance welding.

(3) Production of battery (Example)
In the dry box, the positive electrode and the negative electrode dried at 110 ° C. with a vacuum dryer, and a polyolefin microporous membrane separator having a width of about 60 mm and a thickness of about 20 μm that had been dried at 60 ° C. were prepared.
Next, the separator is laminated between the positive electrode and the negative electrode so that both ends in the width direction of the separator protrude almost evenly from the electrode end so that no short circuit occurs between the positive electrode and the negative electrode. Using a rotating machine, the wound section was wound into an oval shape to obtain an electrode group having a height of about 60 mm, a width of about 55 mm, and a thickness of about 3 mm.
Next, two 90 mm square laminate films with polyolefin films bonded on both sides of the aluminum foil were prepared and stacked, and heat-sealed with a modified polyethylene sheet on the three sides, and formed into a bag shape to form a battery case. A laminate container was obtained. Next, the laminate container was dried at 60 ° C. in a vacuum dryer, and after drying, the laminate container was moved to the dry box, and the electrode group was inserted into the laminate container.
Next, 10 ml of a 1 mol / L non-aqueous electrolyte obtained by dissolving sodium perchlorate (electrolyte) in a propylene carbonate solvent as an organic solvent was poured into a laminate container. After confirming that the non-aqueous electrolyte was absorbed by the electrode group, the opening was temporarily secured with a clip, and subsequent operations such as charge and discharge described in detail in Examples 1 to 6 below were performed.
After the necessary work was completed, sealing was performed by thermally welding the opening in a vacuum chamber to obtain the battery of the example.

(4) Battery fabrication (comparative example)
A battery of a comparative example was obtained in the same manner as the battery fabrication method of the example except that sealing was performed immediately without performing temporary fixing.

(5) Preparation of spare battery Moreover, the spare battery was produced as follows and the full charge capacity was calculated | required. Use the same negative electrode, non-aqueous electrolyte and separator as above, and prepare sodium metal as the counter electrode, place the separator between the counter electrode and the negative electrode, and store it in the battery case. A spare battery was prepared by housing. A lead wire is connected to each of the negative electrode and the counter electrode. In addition, a power source is prepared, and the lead wire connected to the negative electrode of the reserve battery is connected to the negative electrode of the power source, the lead wire connected to the counter electrode is connected to the positive electrode of the power source, and a current of 5 mA is voltageed by the power source. Was made to flow to 0 V, the current was cut off, and the time until that was measured to obtain the current capacity (mAh). After cutting off the current, it was allowed to stand for 10 minutes, and the time when the voltage was 0.2 V or less was taken as the end point of charging. Here, when the voltage exceeds 0.2 V, the same operation as described above, that is, a current of 5 mA is passed until the voltage becomes 0 V, the current is cut off, and the time until that time is measured. The operation for obtaining the current capacity (mAh) was performed. The total current capacity required until the end of charging was defined as the full charge capacity.

Example 1
Using the temporarily secured battery, initial charging was performed up to 3.0 V by constant current charging at an initial charging current of 5 mA. Thereafter, the clip temporarily holding the opening was removed, and it was confirmed that there was sufficient non-aqueous electrolyte in the container, and then the opening was sealed by heat welding. Next, the battery was charged to 4.0 V by constant current charging at 20 mA. Subsequently, discharge was performed at a constant current of up to 2.0 V at 20 mA, and the results of evaluating the discharge capacity are shown in Table 1-1. The test was performed at 25 ° C. and 10 ° C. In Examples, a significant increase in discharge capacity was observed compared to Comparative Examples.
Next, a charge / discharge cycle test was performed under the same charge / discharge conditions (charging up to 4.0 V by constant current charging at 20 mA, constant current discharging up to 2.0 V at 20 mA). The test was conducted at 25 ° C. Table 1-2 shows the discharge capacity retention rate in 100 cycles. Note that the discharge capacity maintenance ratio (hereinafter sometimes referred to as “capacity maintenance ratio”) is defined by the following equation.

Discharge capacity retention ratio = (discharge capacity at the 100th cycle) / (discharge capacity at the first cycle)

(Example 2)
A plurality of the temporarily-attached batteries are prepared, the full charge capacity is 100%, and the battery charge is 2%, 5%, 8%, 10%, 30%, 50%, 80% of the full charge capacity. % And 100% (hereinafter, abbreviated as initial charge amount%), the initial charge was performed at a charge current of 5 mA.
Then, after removing the clip and confirming the amount of the non-aqueous electrolyte, sealing was performed in the same manner as in Example 1. Note that there was no shortage of non-aqueous electrolyte in any of the batteries. Moreover, about the battery whose battery voltage is higher than 3.0V, after discharging until it became 3.0V with discharge current 5mA, it sealed, and the sodium secondary battery was manufactured.
The results of confirming the discharge capacity under the same charge / discharge conditions as in Example 1 for each battery are shown in Table 2-1. The test was performed at 25 ° C. and 10 ° C.
The discharge capacity of the battery having an initial charge amount of 10% or more was 90% or more of the battery sealed after 100% charge (full charge). Moreover, the low temperature characteristic (10 degreeC) was also favorable.

  Next, a charge / discharge cycle test was performed under the same charge / discharge conditions as in Example 1 (charging to 4.0 V by constant current charging at 20 mA, constant current discharging to 2.0 V at 20 mA). The test was conducted at 25 ° C. Table 2-2 shows the discharge capacity retention ratio in 100 cycles. A battery having an initial charge amount of 10% or more had a discharge capacity retention rate of 90% or more after 100 cycles.

(Example 3)
A plurality of temporarily secured batteries were prepared, and the initial charge was performed in the same manner as in Example 2 so that the initial charge amount was 5%, 8%, and 10% under the charging condition (constant current 5 mA). Next, the battery after initial charge was aged at 10 ° C., 20 ° C., 30 ° C., 50 ° C., 70 ° C., and 90 ° C. for 30 minutes, and then sealed in the same manner as in Example 1. In addition, there was no shortage of any non-aqueous electrolyte. For these batteries, the discharge capacity was measured under the same current and voltage conditions as in Example 2. The results are shown in Table 3-1. The test was conducted at 25 ° C.
The battery aged at 30% to 70 ° C. with an initial charge of 10% had a large discharge capacity. Although a large capacity can be obtained at 90 ° C., it does not change from 70 ° C. and its usefulness for raising the temperature to a temperature exceeding 70 ° C. is poor.

Next, a charge / discharge cycle test was performed under the same charge / discharge conditions as in Example 2 for the batteries having an initial charge amount of 8% and 10%. Table 3-2 shows the discharge capacity retention ratio in 100 cycles. The test was conducted at 25 ° C.
In particular, a battery having an initial charge amount of 10% and an aging temperature of 30 ° C. or higher showed a better discharge capacity maintenance rate exceeding 90% in 100 cycles. In addition, the discharge capacity retention rate of each of the batteries having an initial charge amount of 8% and 10% improved as the aging temperature increased.

Further, a plurality of temporarily secured batteries were prepared, and the initial charge was performed by unifying the initial charge amount to 10% under the same charging conditions (constant current 5 mA) as in Example 2. Next, the battery after the initial charge was combined with any temperature of 20 ° C., 30 ° C., 70 ° C., or 80 ° C. and any time of 10 minutes, 1 hour, 4 hours, 12 hours, or 24 hours. Aging was performed under conditions. About the battery sealed by the method similar to Example 1 after aging, the discharge capacity was measured on the same current and voltage conditions as Example 2. None of the non-aqueous electrolytes were deficient. The results are shown in Table 3-3. The test was conducted at 25 ° C.
The discharge capacity depends on the aging temperature, and in a battery aged at 30 ° C. or higher, a better characteristic exceeding 150 mAh was obtained. Even when aged for 10 minutes, good characteristics of 150 mAh were obtained at a temperature of 30 ° C. or higher. Since 80 ° C. is the same as 70 ° C., the usefulness of raising the temperature to a temperature exceeding 70 ° C. is poor.

Example 4
A plurality of temporarily secured batteries were prepared, and the initial charge was performed by changing the initial charge amount from 2% to 50%. Next, after the battery was charged for the first time after charging and discharging at a charging current of 5 mA, a discharge current of 5 mA and up to 3 V), the discharge capacity of the sealed battery was measured. None of the non-aqueous electrolytes were deficient. The discharge capacity was measured at 25 ° C. for all the charge / discharge cycles, and the measurement at 10 ° C. was also performed for those with 3 charge / discharge cycles. The results are shown in Table 4-1.
In all the batteries, an increase in the discharge capacity was observed with an increase in the number of charge / discharge repetitions, but the discharge capacity was not sufficient in the case of a battery having an initial charge amount of 8% or less. On the other hand, in the case of a battery having an initial charge amount of 10% or more, better characteristics were obtained in which the number of charge / discharge repetitions exceeded 150 mAh. In addition, although evaluation was performed at an aging temperature of 30 ° C., a capacity of 160 mAh or more was obtained in both the charge / discharge repetition times 2, 3, and 5.

(Example 5)
A plurality of temporarily secured batteries were prepared, and the batteries with initial charge amounts of 5%, 8%, 10%, 50%, and 100% were charged and discharged once under the same charging conditions and discharging conditions as in Example 4. It was.
During this charge / discharge, the ambient temperature was 20 ° C., 30 ° C., 50 ° C., 70 ° C., and 80 ° C. Each battery after charging and discharging was sealed in the same manner as in Example 1.
Thereafter, the discharge capacity of each battery was measured under the same current and voltage conditions as in Example 2 (constant current 20 mA, up to 2.0 V). The results are shown in Table 5-1. There was no shortage of any non-aqueous electrolyte.
Moreover, about the battery whose initial charge amount is 50%, after charging / discharging 3 times at each temperature, it sealed by the method similar to Example 1. FIG. Thereafter, the discharge capacity was measured under the same current and voltage conditions as in Example 1 (constant current 20 mA, up to 2.0 V). The results are shown in Table 5-1.

(Example 6)
A plurality of temporarily secured batteries were prepared, and initial charging was performed with initial charging amounts of 8%, 10%, 30%, 50%, and 100%. Next, before performing sealing, atmospheric gas pressurization or pressure reduction was performed under the following conditions. Argon was used as the atmospheric gas.

Depressurization condition: 50 kPa
Pressure condition: 300kPa

About each battery which sealed by the method similar to Example 1 after pressurization or pressure reduction, the discharge capacity was measured by the same current and voltage as Example 2. The results are shown in Table 6-1. There was no shortage of any non-aqueous electrolyte. In the case of a battery with an initial charge of 5%, the effects of pressure reduction and pressurization are not significant, and an increase in discharge capacity is observed when the charge is 10% or more.

Next, the effect of pressurization, depressurization, pressurization and depressurization after injection of the non-aqueous electrolyte was confirmed.
At that time, the initial charge amount was 5%, 10%, and 50%. Before sealing, it was fixed to pressurization and decompression. The results are shown in Table 6-2. An increase in capacity is observed when the initial charge amount is 10% or more.

  Furthermore, about the combination of pressure increase / decrease after injection and pressure increase / decrease before sealing. The effect was confirmed when the initial charge amount was 50%. The results are shown in Table 6-3.

  In addition, the pressure was reduced after injection, 10% charged, aged at 30 ° C. for 30 minutes, subjected to pressure and pressure reduction, and sealed (battery), and pressure reduction after injection. After performing charge and discharge of 10% at 30 ° C. and applying pressure and pressure reduction, the same capacity check as in Example 1 was performed on the sealed battery (battery). The results are shown in Table 6-4.

  It was confirmed that even if aging at 30 ° C. or charging / discharging cycle was performed after applying pressure increase / decrease, further improvement in characteristics of the obtained battery could be realized by further combining pressure increasing / decreasing.

  As is clear from the above examples, according to the present invention, although the details of the reason are not clear, each step in the battery assembly acts to eliminate various factors that may cause a decrease in battery performance, and the battery characteristics are improved. Significant improvements can be achieved.

  According to the present invention, it is possible to obtain a sodium secondary battery capable of greatly improving a high discharge capacity and cycle characteristics at a low cost. Therefore, not only a small power source such as a mobile phone or a laptop computer, but also an automobile application and power storage. It can be applied to large power sources for applications and the like, and is extremely useful industrially.

Claims (7)

  A battery case comprising an electrode group obtained by laminating or laminating or winding a positive electrode capable of doping and dedoping sodium ions, a negative electrode capable of doping and dedoping sodium ions, and a separator, and an electrolyte. A method for producing a sodium secondary battery, comprising housing and sealing a battery case after doping the negative electrode with sodium ions.   The method for producing a sodium secondary battery according to claim 1, wherein the anode is doped with sodium ions and then aged at 30 to 70 ° C for 10 minutes or more before sealing.   The method for producing a sodium secondary battery according to claim 1 or 2, wherein the step of doping the sodium ion into the negative electrode and further de-doping the sodium ion from the negative electrode is repeated after one or more times.   The method for producing a sodium secondary battery according to claim 3, wherein doping and dedoping of sodium ions in the negative electrode is performed at 30 to 70 ° C. 5.   The method for producing a sodium secondary battery according to claim 1, wherein atmospheric gas pressurization and / or decompression is performed before sealing.   The method for manufacturing a sodium secondary battery according to claim 1, wherein an electrolyte dissolved in an organic solvent is used as the electrolyte.   The sodium secondary battery manufactured with the manufacturing method in any one of Claim 1 to 6.