JP2010272492A - Sodium secondary battery manufacturing method and sodium secondary battery - Google Patents

Abstract

A method for producing a sodium secondary battery having high capacity and excellent cycle characteristics is provided.
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 electrolytic solution Is stored in the battery case, and then the battery case is sealed, and the electrolytic solution injection is divided into two or more times.
[Selection figure] None

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.

  As a result of intensive studies to optimize the battery assembly process of the sodium secondary battery in order to solve the above-mentioned problems, the inventors have greatly improved the discharge capacity and cycle characteristics of the battery by the electrolyte injection method. As a result, the present invention has been found.

That is, the present invention relates to the following inventions.
<1> 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 solution Is a method for manufacturing a sodium secondary battery in which the battery case is sealed after the battery is sealed in the battery case, and the injection of the electrolyte is divided into two or more times.
<2> The method for producing a sodium secondary battery according to <1>, wherein the viscosity of the electrolyte used for the first injection is lower than the viscosity of the electrolyte used for the second and subsequent injections.
<3> The method for producing a sodium secondary battery according to <1>, wherein the electrolyte concentration of the electrolyte solution used for the first injection is lower than the electrolyte concentration of the electrolyte solution used for the second and subsequent injections.
<4> The method for producing a sodium secondary battery according to <1>, wherein the electrolytic solution used for at least the first injection includes a component that forms a film on the electrode surface by charging.
<5> Any one of <1> to <4>, wherein at least one of the positive electrode and the negative electrode is electrically connected to sodium metal and pre-doped with sodium ions. The manufacturing method of the sodium secondary battery of description.
<6> The method for producing a sodium secondary battery according to any one of <1> to <5>, wherein the first injection is performed on the electrode and / or the separator before assembly of the electrode group.
<7> The first injection is performed by immersing at least one electrode before assembling the electrode group in an electrolytic solution, the at least one electrode is electrically connected to sodium metal, and sodium metal is used as a counter electrode. The method for producing a sodium secondary battery according to <6>, wherein by applying voltage, the electrode is doped with sodium ions, the electrode group is assembled, and the liquid is injected for the second time and thereafter after being accommodated in the battery case. .
<8> The method for producing a sodium secondary battery according to any one of <1> to <7>, wherein charging is performed between the injections.
<9> The method for producing a sodium secondary battery according to any one of <1> to <8>, wherein aging is performed at 30 to 70 ° C. after any of the injections.
<10> The method for producing a sodium secondary battery according to <8>, wherein discharging is performed at least once after charging.
<11> After the electrode group is accommodated in the battery case, before the battery case is sealed, the atmosphere gas is pressurized and / or decompressed at least once. The manufacturing method of the sodium secondary battery of description.
<12> A sodium secondary battery produced by the production method according to any one of <1> to <11>.

  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 relates to 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 electrolytic solution. Is a method for manufacturing a sodium secondary battery in which a battery case is sealed after the battery is sealed in the battery case, and the electrolytic solution injection is divided into two or more times. It is.

  Hereinafter, the positive electrode, the negative electrode, the electrolytic solution, the separator, and the battery case according to the battery manufacturing method 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) Electrolytic Solution Next, the electrolytic solution will be described. In the present invention, the electrolytic solution is usually used as a non-aqueous electrolytic solution in which an electrolyte is dissolved in an organic solvent. Moreover, electrolyte solution can also become a gel form after injection. 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.

  Examples of the organic solvent in the non-aqueous electrolyte include propylene carbonate (viscosity 2.5 mPa · s (25 ° C.)), ethylene carbonate (viscosity 1.9 mPa · s (40 ° C.)), and dimethyl carbonate (viscosity 0.59 mPa · s). (25 ° C.)), diethyl carbonate (viscosity 0.75 mPa · s (25 ° C.)), ethyl methyl carbonate (viscosity 0.65 mPa · s (25 ° C.)), isopropyl methyl carbonate, vinylene carbonate, 4-trifluoromethyl- Carbonates such as 1,3-dioxolan-2-one and 1,2-di (methoxycarbonyloxy) ethane; 1,2-dimethoxyethane, 1,3-dimethoxypropane, pentafluoropropyl methyl ether, 2,2, 3,3-tetrafluoropropyl difluoromethyl ether, Ethers such as trahydrofuran and 2-methyltetrahydrofuran; Esters such as methyl formate, methyl acetate and γ-butyrolactone; Nitriles such as acetonitrile and butyronitrile; N, N-dimethylformamide, N, N-dimethylacetamide and the like Amides; carbamates such as 3-methyl-2-oxazolidone; sulfur-containing compounds such as sulfolane, dimethyl sulfoxide and 1,3-propane sultone; or those obtained by further introducing a fluorine substituent into the above organic solvent Can do. Two or more of these may be mixed and used as the organic solvent. It is also possible to control the viscosity of the nonaqueous electrolytic solution by using a plurality of organic solvents and changing the mixing ratio thereof.

  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.

(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 electrode group, a method of laminating the above-described positive electrode, negative electrode, and separator, or a method of laminating and winding are mentioned. As the shape of the electrode group, the cross section of the electrode group (in the case of stacking 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 the shape include a rectangle.

  The obtained electrode group is housed in a battery case, and after the electrolyte solution is injected, the battery case is sealed to manufacture a sodium secondary battery. The shape of the battery is not particularly limited, and examples thereof include a paper shape, a coin shape, a cylindrical shape, and a square shape.

  One of the features of the production method of the present invention is that the electrolytic solution is divided into two or more times. Although the detailed reason is unknown at present, the discharge capacity and the cycle characteristics can be improved by dividing the electrolyte solution into two or more times instead of once.

The “electrolyte injection” is performed not only after the electrode group is accommodated in the battery case, but also on the components of the electrode group (positive electrode, negative electrode, and separator) before assembly of the electrode group. May be. However, the liquid injection is performed at least once after the electrode group is accommodated in the battery case.
Examples of the method for injecting the components of the electrode group before assembling the electrode group include, for example, a method of impregnating the components of each electrode group in the electrolyte solution, and an electrolyte solution for the components of the electrode group The method of dropping by using a dropper or the like.
Here, by injecting the electrode and / or the separator before assembling the electrode group, (1) Even when injecting an electrolyte containing a high-viscosity electrolyte component, it is diluted with an appropriate solvent. Then, the process of volatilizing the solvent after injecting can be adopted, and it is easy to increase the electrolyte concentration in the electrolyte. (2) It is possible to select and inject a preferable electrolyte in each electrode. There is an advantage that it can be used in combination with another process such as pre-doping or surface treatment of the electrode in advance.

In the production method of the present invention, it is desirable that the viscosity of the electrolyte used for the first injection is lower than the viscosity of the electrolyte used for the second and subsequent injections.
By doing so, it is easy to replace the electrolyte solution with air or the like in the pores of the electrode, and the electrolyte solution can be sufficiently distributed in the pores, and the time required for that is shortened. In addition, there is an advantage that the occurrence of charge / discharge inhibition factors due to some action can be eliminated in advance in the obtained battery.

  The electrolyte solution suitable for the first injection is preferably one containing a relatively low viscosity electrolyte component among the components constituting the electrolyte solution, and preferably one having a lower electrolyte concentration.

In the production method of the present invention, it is desirable that the electrolyte concentration of the electrolyte solution used for the first injection is lower than the electrolyte concentration of the electrolyte solution used for the second and subsequent injections.
By doing so, the electrolyte tends to penetrate into the pores of the electrode, and in the obtained battery, the uniformity of the electrochemical reaction tends to be ensured over the entire electrode, and some complex action is caused. Even if a charging / discharging inhibiting factor occurs due to this, it may help to alleviate this.
The electrolyte is not particularly limited, and any of the above-described electrolytes may be used.
As the concentration of the electrolyte in the electrolytic solution, when the electrolytic concentration of the first electrolytic solution is 1, the electrolytic concentration of the second and subsequent electrolytic solutions is preferably about 1.1 or more and 3 or less.

Moreover, in the manufacturing method of this invention, you may charge, after accommodating an electrode group and electrolyte solution in a battery case.
If the electrolyte used for at least the first injection contains a component that forms a film on the electrode surface by charging, a protective film is formed on the electrode surface, thereby suppressing the decomposition of the electrolyte solution, and some complex action This is preferable because the occurrence of charging / discharging inhibiting factors due to the above can be suppressed, and the storage and cycle deterioration characteristics are improved. Examples of the component that forms the film include ethylene carbonate, sulfonium compound, vinylene carbonate, sultone, and the like. For example, an electrolytic solution containing at least 10% by weight of one or more of these can be used.

  Moreover, it is preferable that at least one of the positive electrode and the negative electrode is electrically connected to sodium metal and pre-doped with sodium ions. When the electrode is electrically connected to sodium metal and sodium ions are pre-doped, the sodium component corresponding to the irreversible capacity is replenished, the effective sodium component contributing to the charge / discharge reaction is increased, and the obtained sodium This is preferable because the capacity of the secondary battery can be increased. Also, sodium metal usually disappears from sodium metal as sodium ions are pre-doped on the electrode. The electrode pre-doped with sodium ions holds sodium in an ionic or metallic state.

  In addition, at least one electrode (preferably a negative electrode) before assembly of the electrode group is immersed in an electrolytic solution to perform an initial injection, and the at least one electrode (preferably a negative electrode) and sodium metal are electrically connected. By connecting externally with sodium metal as a counter electrode, doping the electrodes with sodium ions, assembling the electrode group and storing it in the battery case, the second and subsequent injections may be performed. desirable.

  In addition, charging is performed between injections, or aging is performed at 30 to 70 ° C. after any of the injections, so that the electrolyte and the electrode are mixed together. It is possible to stabilize the contact interface and suppress the occurrence of charge / discharge inhibiting factors due to some complex action.

  Furthermore, it is effective to perform at least one discharge after charging. By performing the discharge, it is possible to suppress the occurrence of charge / discharge inhibition factors due to some complex action.

In addition, after the electrode group is accommodated in the battery case, it is preferable to perform atmospheric gas pressurization and / or pressure reduction at least once before the battery case is sealed. Alternatively, the reduced pressure has an effect of removing an initial product that inhibits the charge / discharge reaction, which is extremely effective for suppressing deterioration of battery characteristics particularly in a 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 electrolytic solution into the gaps and pores can be promoted. On the other hand, also by pressurizing the atmospheric gas, it is possible to promote the penetration of the electrolytic solution into the fine gaps and pores of the positive electrode, the negative electrode, and the separator. In particular, by alternately performing atmospheric gas pressurization and pressure reduction, the electrolyte solution 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 Examples.

(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) Production of negative electrode An appropriate amount of N-methylpyrrolidone was added to and mixed with MA1 as a negative electrode active material and polyvinylidene fluoride mixed at a ratio of 95: 5 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) Battery Production Here, a basic battery production procedure for a sodium secondary battery is shown (hereinafter referred to as production procedures [1] to [10]).
[1] The positive electrode and the negative electrode dried at 110 ° C. in a vacuum dryer were prepared in a dry box.
[2] A polyolefin microporous membrane separator having a width of about 60 mm and a thickness of about 20 μm, which was dried in a dry box at 60 ° C. in a dry box, was prepared.
[3] In the dry box, the separator is sandwiched between the positive and negative electrodes 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. Then, using a winding machine, the wound cross 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.
[4] Next, two 90 mm square laminate films with polyolefin films bonded on both sides of an aluminum foil were prepared, stacked and heat-sealed with a modified polyethylene sheet on three sides, and formed into a bag shape. A container was obtained and dried at 60 ° C. in a vacuum dryer.
[5] After drying, the laminate container was moved to the dry box, and the electrode group was inserted into the laminate container.
[6] Next, sodium perchlorate (electrolyte) was dissolved in a propylene carbonate solvent as an organic solvent to obtain a 1 mol / L nonaqueous electrolytic solution.
[7] A part of the electrolytic solution was poured into the laminate container, and it was confirmed that the electrolytic solution was absorbed by the electrode group.
[8] The opening was temporarily fixed with a clip.
[9] The temporary fixing was removed, and after the electrolyte solution was poured into the laminate container, the temporary fixing was performed.
[10] The temporary fixing was removed, and the opening was thermally welded in a vacuum chamber to perform sealing, thereby obtaining a battery.

Example 1
In the production procedure [7], 5 ml of the electrolytic solution was injected, and then the production procedure [8] was performed. After standing for 6 hours, 5 ml of the electrolytic solution was injected in the production procedure [9]. [10] was performed to obtain the battery of Example 1.

(Comparative Example 1)
In the production procedure [7], 10 ml of the electrolytic solution was injected, the production procedure [9] was not performed, and [10] was performed to obtain a battery of Comparative Example 1.

About the battery of Example 1 and the battery of Comparative Example 1, after charging to 4.0 V at a charging current of 5 mA as the initial charge, discharging was performed at a constant current of up to 2.0 V at 20 mA to confirm the discharge capacity. The test was performed at 25 ° C and 10 ° C. In addition, about Comparative Example 1, after leaving still for 6 hours after sealing, it used for the test. The results are shown in Table 1-1. In the example, a significant increase in capacity was observed compared to the comparative example.
Next, a charge / discharge cycle test was performed under the same charge / discharge conditions except that only the charge current was changed to 20 mA. Table 1-2 shows the discharge capacity retention rate in 100 cycles. Compared with the comparative example, the example confirmed a significant improvement in cycle characteristics. 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)
In the production procedure [6], the solvent was changed from propylene carbonate (PC) to a mixed solvent consisting of PC and ethyl methyl carbonate (EMC) (solvent composition PC: EMC = 40: 60), and the production procedure was prepared. In [7], 5 ml of the electrolyte solution was injected, and then the preparation procedure [8] was performed, and after standing for 6 hours, in the preparation procedure [9], the solvent composition was changed to PC: EMC = 40: 60. A battery of Example 2 was obtained by injecting 5 ml of an electrolytic solution with PC: EMC = 60: 40 and performing the production procedure [10]. In addition, the viscosity of the non-aqueous electrolyte of PC: EMC = 40: 60 is lower than the viscosity of the non-aqueous electrolyte of PC: EMC = 60: 40.

(Comparative Example 2)
In the preparation procedure [6], the solvent is changed from propylene carbonate (PC) to a mixed solvent composed of PC and ethyl methyl carbonate (EMC) (solvent composition PC: EMC = 50: 50), and the above preparation is made. In the procedure [7], 10 ml of the electrolyte solution was injected, and the battery of Comparative Example 2 was obtained by performing [10] without performing the production procedure [9].

Regarding the battery of Example 2 and the battery of Comparative Example 2, as the initial charge, after charging to 4.0 V at a charging current of 5 mA, the battery was discharged to 2.0 V at a constant current of 20 mA, and the discharge capacity was confirmed. The test was performed at 25 ° C and 10 ° C. The results are shown in Table 2-1. In the example, a significant increase in capacity was observed compared to the comparative example.
Next, a charge / discharge cycle test was performed under the same charge / discharge conditions except that only the charge current was changed to 20 mA. Table 2-2 shows the discharge capacity retention ratio in 100 cycles.

(Example 3)
In the production procedure [6], an electrolyte solution in which only the electrolyte concentration was changed to 0.7 mol / L was prepared, and in the production procedure [7], 5 ml of the electrolyte solution having an electrolyte concentration of 0.7 mol / L was injected, Next, after performing the preparation procedure [8] and allowing to stand for 6 hours, in the preparation procedure [9], the electrolyte concentration was changed from 0.7 mol / L to 1.3 mol / L. The battery was used, and the production procedure [10] was performed to obtain the battery of Example 3.

The battery of Example 3 was charged to 4.0 V at a charging current of 5 mA as an initial charge, and then discharged to 2.0 V at a constant current of 20 mA to confirm the discharge capacity. The test was performed at 25 ° C and 10 ° C. Table 3-1 shows the results of Example 3 together with the results of Comparative Example 1. In the example, a significant increase in capacity was observed compared to the comparative example.
Next, a charge / discharge cycle test was performed under the same charge / discharge conditions except that only the charge current was changed to 20 mA. Table 3-2 shows the discharge capacity retention ratio in 100 cycles.

Example 4
In preparation procedure [6], five types of electrolyte solutions were prepared in the same manner except that vinylene carbonate (VC) was added at 1%, 2%, 6%, 10%, and 16%, respectively. In preparation procedure [7] Then, 5 ml of each of these electrolytes was injected, and 5 pieces prepared according to the preparation procedure [8] were prepared and allowed to stand for 6 hours. Then, in the preparation procedure [9], vinylene carbonate was added to each of them. 5 ml of a non-electrolytic solution was injected, and the production procedure [10] was performed to produce five batteries. These batteries were charged to 4.0 V with a charging current of 5 mA, then discharged to 2.0 V with a 20 mA constant current, and the discharge capacity was confirmed. The test was performed at 25 ° C and 10 ° C. The results are shown in Table 4-1 together with the results of Comparative Example 1. In the example, a significant increase in capacity was observed compared to the comparative example. The result of VC 16% was equivalent to the result of 10%.
Next, a charge / discharge cycle test was performed under the same charge / discharge conditions except that only the charge current was changed to 20 mA. Table 4-2 shows the discharge capacity retention ratio in 100 cycles.

(Example 5)
The positive electrode, the negative electrode, and the separator prepared in Preparation Procedures [1] and [2] were put in a sealed container with a lid filled with the electrolyte solution according to Preparation Procedure [6] in advance and immersed in the electrolyte solution. After immersion, the positive electrode, the negative electrode, and the separator were taken out, and the production procedure [3] and subsequent steps were performed quickly. At that time, the production procedure [7] is omitted, the production procedure [8] is performed as necessary, and the production procedure [9] [in this case, injection until the electrolytic group is immersed in the electrolytic solution], the production procedure [10 The following battery A-1, battery A-2, battery A-3, battery B, battery C, and battery D were obtained. In addition, about battery A-1, A-2, A-3, B, and C, after leaving still for 6 hours after sealing, it used for the test. In the production procedure, the batteries A-1, A-2, A-3, and B to D are produced in the following manner.
-Battery A-1, A-2, A-3:
The same electrolytic solution as in Example 1 was used. A-1 was only the positive electrode, A-2 was the negative electrode only, A-3 was the positive electrode, the negative electrode, and the separator immersed in the electrolytic solution. The production procedure [8] was not performed.
Battery B:
Using the electrolytic solution having the same composition as that of Example 2, the positive electrode, the negative electrode, and the separator were immersed using the electrolytic solution having the composition first injected in Example 2. The production procedure [8] was not performed.
-Battery C:
Using the electrolytic solution having the same composition as in Example 3, the positive electrode, the negative electrode, and the separator were immersed using the electrolytic solution having the composition first injected in Example 3. The production procedure [8] was not performed.
-Battery D:
The electrolyte solution of VC 10% in Example 4 was immersed in the positive electrode, the negative electrode, and the separator using immersion. Through the production procedure [8], the same electrolytic solution as in Example 4 was used in the production procedure [9].

The batteries of Example 5 were charged to 4.0 V at a charging current of 5 mA, and then discharged at a constant current of 20 mA to 2.0 V to confirm the discharge capacity. The test was performed at 25 ° C and 10 ° C. The results are shown in Table 5-1 together with the results of Comparative Example 1. In the example, a significant increase in capacity was observed compared to the comparative example.
Next, a charge / discharge cycle test was performed under the same charge / discharge conditions except that only the charge current was changed to 20 mA. Table 5-2 shows the discharge capacity retention ratio in 100 cycles. Compared with the comparative example, the example confirmed a significant improvement in cycle characteristics.

(Example 6)
Of the positive electrode, negative electrode, and separator prepared in Preparation Procedures [1] and [2], only the negative electrode was immersed in advance in an electrolytic solution prepared in Preparation Procedure [6] in a sealed container with a lid, and sodium was used as the counter electrode. Then, energization was performed up to 0.3 V at a current of 20 mA, and the negative electrode was pre-doped with sodium ions. In this energization, the positive electrode of the power source was connected to sodium metal, and the negative electrode of the power source was connected to the negative electrode. After the energization was completed, the negative electrode was taken out and the procedure [3] and subsequent steps were performed quickly. At that time, the manufacturing procedures [7] and [8] are omitted, and the battery is manufactured by performing the manufacturing procedure [9] [in this case, injection until the electrode group is immersed in the electrolytic solution] and the manufacturing procedure [10]. did. These batteries were charged to 4.0 V with a charging current of 5 mA and then discharged at a constant current of 20 mA to 2.0 V to confirm the discharge capacity. The test was performed at 25 ° C and 10 ° C. The results are shown in Table 6-1 together with the results of Comparative Example 1. In the example, a significant increase in capacity was observed compared to the comparative example.
Next, a charge / discharge cycle test was performed under the same charge / discharge conditions except that only the charge current was changed to 20 mA. Table 6-2 shows the discharge capacity retention ratio in 100 cycles.

(Example 7)
A battery was fabricated according to the fabrication procedure except that metal sodium cut into a width of 5 mm, a length of 20 mm, and a thickness of 200 μm was crimped to one end of the negative electrode current collector prepared in the fabrication procedure [1]. In preparation procedure [7], 5 ml of electrolyte solution was injected, then preparation procedure [8] was performed, and after standing for 6 hours, 5 ml injection was performed in preparation procedure [9], and preparation procedure [10] was performed. By doing so, a battery was produced. About this battery, as a first charge, after charging to 4.0 V at a charging current of 5 mA, discharging was performed at a constant current of up to 2.0 V at 20 mA, and the discharge capacity was confirmed. The test was performed at 25 ° C and 10 ° C. The results are shown in Table 7-1 together with the results of Comparative Example 1. In the example, a significant increase in capacity was observed compared to the comparative example.
Next, a charge / discharge cycle test was performed under the same charge / discharge conditions except that only the charge current was changed to 20 mA. Table 7-2 shows the discharge capacity retention ratio in 100 cycles. Compared with the comparative example, the example confirmed a significant improvement in cycle characteristics.

  Next, the same as Example 2, 3, 4, 5 (the battery of A-1 for Example 5) except that the electrode having the same sodium metal pressure bonding as that described above was used for the negative electrode only. Battery b, battery c, battery d, and battery e were produced in the process. These batteries were tested in the same manner as described above. The results are shown in Tables 7-3 and 7-4 together with the results of Comparative Example 1. In the example, a significant increase in capacity and a significant improvement in cycle characteristics were recognized as compared with the comparative example.

(Example 8)
In Examples 1, 3, 4, and 5 (A-3 for Example 5), after the production procedure [8], charging was performed at 5 mA for 5 hours, and otherwise, the battery 8-A and the battery were similarly manufactured. Each of 8-C, Battery 8-D, and Battery 8-E was obtained. In addition, about the battery 8-E, in preparation procedure [7], it injected until an electrode group hits electrolyte solution, and preparation procedure [8] is performed.
Further, instead of the negative electrode in Example 6, the positive electrode was previously immersed in a sealed container with a lid filled with the electrolytic solution according to the production procedure [6], and discharged to 1.5 V at a current of 20 mA using sodium as a counter electrode. And pre-doping was performed. Here, the positive electrode of the power source was connected to sodium metal, and the negative electrode of the power source was connected to the positive electrode. Thereafter, the production steps [4] and [5] are performed, and the same electrolytic solution as that used for the immersion is used, and the production procedure [7] [in this case, injection until the electrode group is immersed in the electrolytic solution] After performing the procedure [8], after charging for 5 hours at 5 mA, the production procedure [9] [in this case, injection until the electrode group is immersed in the electrolyte solution] and [10] are performed to obtain a battery 8-F. It was.
Further, in Example 7, after the production procedure [8], the battery 8-G was obtained in the same manner except that it was left to stand for 6 hours and charged at 5 mA for 5 hours.

About these batteries, after charging to 4.0V by charge current 5mA as initial charge, it discharged by 20 mA, constant current to 2.0V, and confirmed discharge capacity. The test was performed at 25 ° C and 10 ° C. The results are shown in Table 8-1 together with the results of Comparative Example 1. In the example, a significant increase in capacity was observed compared to the comparative example.
Next, a charge / discharge cycle test was performed under the same charge / discharge conditions except that only the charge current was changed to 20 mA. The discharge capacity maintenance rate in 100 cycles is shown in Table 8-2. In addition, about the comparative example, after sealing, after leaving still for 6 hours, it used for the test.

Example 9
In Examples 1, 2, and 3, after the production procedure [8], aging was performed at 20 ° C., 30 ° C., 40 ° C., 50 ° C., 60 ° C., 70 ° C., and 80 ° C. Got. The batteries were 9-A, 9-B, and 9-C in the order of the numbers in the examples. For these batteries, as the first charge, after charging to 4.0 V at a charging current of 5 mA, discharging was performed at a constant current of up to 2.0 V at 20 mA to confirm the discharge capacity. The test was conducted at 25 ° C. The results are shown in Table 9-1.
Moreover, in the process of manufacturing the battery 8-D, the battery 8-E, the battery 8-F, and the battery 8-G of Example 8, the operation of charging at 5 mA for 5 hours after the manufacturing procedure [8] is performed at 50 ° C. A battery was obtained in the same manner as above. These batteries were designated as Battery 9-D, Battery 9-E, Battery 9-F, and Battery 9-G in order of the battery numbers in Example 8. For these batteries, as the first charge, after charging to 4.0 V at a charging current of 5 mA, discharging was performed at a constant current of up to 2.0 V at 20 mA to confirm the discharge capacity. The test was performed at 25 ° C and 10 ° C. The results are shown in Table 9-2 together with the results of Comparative Example 1.
Next, a charge / discharge cycle test was performed under the same charge / discharge conditions except that only the charge current was changed to 20 mA. The discharge capacity retention ratio in 100 cycles is shown in Table 9-3 together with the result of Comparative Example 1. In any of the examples, a significant performance improvement was seen over the comparative example.

(Example 10)
In the production procedure of the battery 8-A, the battery 8-C, the battery 8-D, the battery 8-E, the battery 8-F, and the battery 8-G in Example 8, the battery was charged at 5 mA for 5 hours after the production procedure [8]. Thereafter, the battery was continuously charged for 10 hours and further discharged at 20 mA to 2 V to obtain a battery. About these batteries, they were named Battery 10-A, Battery 10-C, Battery 10-D, Battery 10-E, Battery 10-F, and Battery 10-G in the order of the battery numbers.
Further, in the production procedure of the battery 9-D, the battery 9-E, the battery 9-F, and the battery 9-G in Example 9, after the production procedure [8], the battery was charged at 5 mA at 50 mA for 5 hours, and then A battery was obtained in the same manner except that the battery was charged at 50 ° C. for 10 hours and further discharged at 20 mA to 2.0 V. About these batteries, it was set as battery 10T-D, battery 10T-E, battery 10T-F, and battery 10T-G in the order of the battery numbers. For these batteries, as the first charge, after charging to 4.0 V at a charging current of 5 mA, discharging was performed at a constant current of up to 2.0 V at 20 mA to confirm the discharge capacity. The test was performed at 25 ° C and 10 ° C. The results are shown in Table 10-1 together with the results of Comparative Example 1.
Next, a charge / discharge cycle test was performed under the same charge / discharge conditions except that only the charge current was changed to 20 mA. Table 10-2 shows the discharge capacity retention ratio in 100 cycles. In the example, both the discharge capacity and the cycle characteristic were significantly improved as compared with the comparative example.

(Example 11)
In the manufacturing procedure of the battery 10-A, the battery 10-C, the battery 10-D, the battery 10-E, the battery 10-F, and the battery 10-G in Example 10, before the temporary fixing of the manufacturing procedure [8], Under the following conditions, “reduced pressure”, “atmospheric gas pressurization” or “atmospheric gas pressurization after depressurization” was performed, and the battery was obtained in the same manner except that. About these batteries, it was set as the battery 11-A, the battery 11-C, the battery 11-D, the battery 11-E, the battery 11-F, and the battery 11-G in the order of the battery numbers. Argon was used as the atmospheric gas.

Depressurization condition: 50 kPa
Pressure condition: 300kPa

  Further, in addition to the atmospheric gas pressurization / depressurization operation performed in the manufacturing procedure of the battery 11-A, the battery 11-C, the battery 11-D, the battery 11-E, the battery 11-F, and the battery 11-G, the sealing is performed. The pressure was further reduced under the above-described pressure reduction conditions before, and in the same manner, the batteries 11-A2, 11-C2, 11-D2, 11-E2, 11-F2, and 11-G2 were obtained. .

  For these batteries, as the first charge, after charging to 4.0 V at a charging current of 5 mA, discharging was performed at a constant current of up to 2.0 V at 20 mA to confirm the discharge capacity. The test was conducted at 25 ° C. The results are shown in Table 11-1 and Table 11-2 together with the result of Comparative Example 1.

  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 (12)

A battery case comprising 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 laminating or winding, and an electrolyte solution A sodium secondary battery manufacturing method for sealing a battery case after being housed in
A method for producing a sodium secondary battery, wherein the injection of the electrolyte is divided into two or more times.   The method for producing a sodium secondary battery according to claim 1, wherein the viscosity of the electrolyte used for the first injection is lower than the viscosity of the electrolyte used for the second and subsequent injections.   The method for producing a sodium secondary battery according to claim 1, wherein the electrolyte concentration of the electrolyte solution used for the first injection is lower than the electrolyte concentration of the electrolyte solution used for the second and subsequent injections.   The method for producing a sodium secondary battery according to claim 1, wherein the electrolyte used for at least the first injection contains a component that forms a film on the electrode surface by charging.   5. The sodium secondary battery according to claim 1, wherein at least one of the positive electrode and the negative electrode is electrically connected to sodium metal and pre-doped with sodium ions. 6. Manufacturing method.   The method for producing a sodium secondary battery according to any one of claims 1 to 5, wherein the first liquid injection is performed on the electrode and / or separator before assembly of the electrode group. Perform the initial injection by immersing at least one electrode in the electrolyte before assembling the electrode group,
By electrically connecting the at least one electrode and sodium metal and applying an external voltage with sodium metal as a counter electrode, the electrode is doped with sodium ions,
The method for manufacturing a sodium secondary battery according to claim 6, wherein the second and subsequent injections are performed after the electrode group is assembled and accommodated in the battery case.   The method for producing a sodium secondary battery according to any one of claims 1 to 7, wherein charging is performed between the liquid injection and the liquid injection.   The method for producing a sodium secondary battery according to any one of claims 1 to 8, wherein aging is performed at 30 to 70 ° C after any of the injections.   The method for producing a sodium secondary battery according to claim 8, wherein at least one discharge is performed after charging.   The sodium secondary battery according to any one of claims 1 to 10, wherein after the electrode group is accommodated in the battery case, the atmosphere gas is pressurized and / or decompressed at least once before the battery case is sealed. Manufacturing method.   The sodium secondary battery manufactured with the manufacturing method in any one of Claim 1 to 11.