WO2011037250A1

WO2011037250A1 - Sodium-ion-type power storage device

Info

Publication number: WO2011037250A1
Application number: PCT/JP2010/066798
Authority: WO
Inventors: 滋和大森; 智久世
Original assignee: 住友化学株式会社
Priority date: 2009-09-28
Filing date: 2010-09-28
Publication date: 2011-03-31

Abstract

Disclosed is a high-capacity power storage device produced using sodium which is an element contained in a great deal of resources. Specifically disclosed is a sodium-ion-type power storage device, which comprises a positive electrode, a negative electrode, and an electrolytic solution containing a sodium ion and an anion, wherein the positive electrode can adsorb and detach an anion or, alternatively, can be doped and dedoped with an anion, and the negative electrode can be doped and dedoped with a sodium ion and has been doped with a sodium ion previously.

Description

Sodium ion storage device

The present invention relates to a power storage device. In particular, the present invention relates to an electricity storage device capable of storing and discharging by movement of sodium ions.

Currently, in the field of late-night power storage and the like, a power storage device capable of storing a large amount of electric energy is required. In the field of transportation equipment such as electric vehicles and hybrid cars, and in the field of portable equipment such as mobile personal computers, mobile phones, and portable audio equipment, power storage devices that can operate for a long time, specifically, per unit volume There is a need for power storage devices that store large amounts of electrical energy.

As such an electricity storage device, a hybrid capacitor is considered promising, and a lithium ion capacitor is known as the capacitor. A lithium ion capacitor has a positive electrode, a negative electrode, a separator, and an electrolyte, and graphite is used for the negative electrode. At the time of charging, lithium ions are inserted between graphite layers in the negative electrode, and anions in the electrolytic solution are adsorbed on the electrode surface in the positive electrode, so that an electric double layer is formed, thereby storing the lithium ion capacitor. A lithium ion capacitor is promising as an electricity storage device in the above field because it has both the high output characteristics of an electric double layer capacitor and the large capacity characteristics of a lithium ion secondary battery. Such a lithium ion capacitor is specifically described in Patent Document 1, for example.

JP 2008-47853 A

Since lithium ion capacitors are manufactured using a lot of expensive and rare lithium, there is room for improvement. An object of the present invention is to provide a large-capacity electricity storage device that uses resource-rich sodium.

The present inventors produced an electricity storage device in the same manner as the lithium ion capacitor except that the lithium salt contained in the electrolytic solution was changed to a sodium salt. When a charge / discharge test of the electricity storage device was performed, it was found that the electricity storage device was difficult to discharge and could not be used as an electricity storage device. The inventors of the present invention have made various studies in order to solve the above problems, and have reached the present invention. The present invention provides the following means.
<1> A positive electrode, a negative electrode, and an electrolytic solution containing sodium ions and anions,
The positive electrode can adsorb and desorb anions, can be doped with anions and can be undoped;
The negative electrode can be doped and dedoped with sodium ions, and the negative electrode is an electrode pre-doped with sodium ions,
Sodium ion storage device.
<2> The sodium ion type electricity storage device according to <1>, wherein the negative electrode has a negative electrode active material, and the negative electrode active material is a carbon material that can be doped with sodium ions and dedoped.
<3> The sodium ion type electricity storage device according to <2>, wherein the carbon material is a non-graphitized carbon material.
<4> The sodium ion type electricity storage device according to <2> or <3>, wherein the carbon material is a non-activated carbon material.
<5>
The negative electrode is preliminarily doped with sodium ions to a certain extent that the redox potential difference between the negative electrode and sodium metal preliminarily doped with sodium ions is 1.00 V or less. The sodium ion type electrical storage device according to any one of the above.
<6> The sodium ion storage battery device according to any one of <1> to <5>, further including a separator disposed between the positive electrode and the negative electrode.

According to the present invention, it is possible to provide a large-capacity electricity storage device that uses abundant sodium and has a large electrical energy stored per unit volume.

These show an example (schematic diagram) of a coin-type sodium ion-type electricity storage device used in Examples and Comparative Examples of the present invention. These show an example (schematic diagram) of a wound sodium ion storage device. These show an example (schematic diagram) of a stacked sodium ion type electricity storage device. These show an example (schematic diagram) of a stacked sodium ion type electricity storage device different from FIG. These show an example (schematic diagram) of a laminated film type sodium ion type electricity storage device.

The sodium ion type electricity storage device of the present invention has a positive electrode, a negative electrode, and an electrolytic solution containing sodium ions and anions. The positive electrode can adsorb and desorb anions, or can be doped with anions and dedoped, and the negative electrode can be doped with sodium ions and dedoped. The negative electrode is an electrode that can be doped and is pre-doped with sodium ions. According to the present invention, an irreversible capacity of an electrode can be reduced, and an electric storage device having a large capacity and extremely excellent cycle characteristics can be realized. Since sodium that is abundant in resources is used, an inexpensive electricity storage device can be realized. In the present invention, the sodium ion storage device can also be called a sodium ion capacitor.

Hereinafter, the positive electrode, the negative electrode, the electrolytic solution, the separator, and the shape of the device according to the sodium ion type electricity storage device of the present invention will be described.

(Positive electrode)
The positive electrode in the present invention can adsorb and desorb anions, or can be doped with anions and dedoped. Specific examples of the positive electrode include polarizable electrodes. In the polarizable electrode, the same number of anions as sodium ions occluded in the negative electrode during charging form an electric double layer on the surface of the positive electrode, and the electric charge is held by the electrostatic capacity of the electric double layer. This charge is dissipated during discharge. The polarizable electrode is not limited as long as it is an electrochemically inactive electrode. The polarizable electrode is preferably an electrode having a large specific surface area, which increases the amount of electricity that can be retained. As a suitable example of the material constituting the positive electrode exhibiting such polarizability, activated carbon (also referred to as activated carbon material) can be given.

As the activated carbon, activated carbon obtained by carbonizing organic airgel is preferable from the viewpoint of having a high specific surface area. Since activated carbon has a large anion adsorptivity and a large specific surface area, the electrostatic capacity of the obtained electricity storage device is increased. Examples of the activation method include a method using an oxidizing gas, and specifically, a method of exposing a raw material or an intermediate during the production of activated carbon or activated carbon to the oxidizing gas at a high temperature for a certain time. Examples of the oxidizing gas include H ₂ O, CO ₂ and O ₂ . Another example of activation is a method of treating activated carbon, raw materials or intermediates during the production of activated carbon, zinc chloride, phosphoric acid, potassium sulfide, potassium hydroxide, etc., and then treating the resulting mixture at a high temperature. It is done. The method using the oxidizing gas is preferable because it can suppress the mixing of metal impurities. As the oxidizing gas, H ₂ O and CO ₂ are preferable.

The activated carbon is preferably activated carbon activated at an activation temperature of 200 ° C. or higher, and the pore volume tends to be improved. The activated carbon is preferably activated carbon activated at an activation temperature of 1100 ° C. or lower, and the yield of activated carbon tends to be improved. The activated carbon is preferably activated carbon activated with an activation time of 1 minute or longer, and the pore volume tends to be improved. The activated carbon is preferably activated carbon activated with an activation time of 24 hours or less, and the yield of activated carbon tends to be improved.

As a method of using activated carbon for an electrode, for example, a method of using activated carbon in a carbonized state for an electrode, a method of using a crushed activated carbon for an electrode, a granulated shape, a granule shape, a fiber of crushed activated carbon For example, a method of forming into various shapes such as a shape, a felt shape, a fine shape, or a sheet shape and using the electrode. The activated carbon used in the forming method has an average particle size of particles constituting the activated carbon of usually 50 μm or less, preferably 30 μm or less, particularly preferably 10 μm or less. In this case, it is preferable to use the activated carbon after pulverization. By using finely pulverized activated carbon for the electrode, the bulk density of the electrode can be improved and the internal resistance of the electrode can be reduced.

As a material constituting the positive electrode, a chalcogen compound such as sulfide can also be used. Examples of the sulfide are represented by M ¹ S ₂ (M ¹ is one or more transition metal elements) such as TiS ₂ , ZrS ₂ , VS ₂ , V ₂ S ₅ , TaS ₂ , FeS _2, and NiS _2. Compounds and the like. These compounds can be used for electrodes as well as activated carbon. These compounds, like activated carbon, have an average particle size of usually 50 μm or less, preferably 30 μm or less, particularly preferably 10 μm or less. In this case, it is preferable to use these compounds after pulverization. . By using these finely pulverized compounds for the electrode, the bulk density of the electrode can be improved and the internal resistance of the electrode can be reduced.

For the pulverization, for example, impact friction pulverizer, centrifugal pulverizer, ball mill (tube mill, compound mill, conical ball mill, rod mill), vibration mill, colloid mill, friction disk mill, jet mill, etc. The pulverizer is preferably used. When a ball mill is used, it is preferable that the balls and the pulverization container are made of non-metal such as alumina, zirconia, agate, etc., in order to avoid mixing of metal powder.

When a powdery material (eg, powdered activated carbon, powdered compound, etc.) is used as the material constituting the positive electrode, the positive electrode constituting material, the binder, and the conductive agent are usually placed on the current collector. A positive electrode is produced by forming a positive electrode active material layer on the current collector by adhering a mixture containing the like. As a specific method, for example, (1) a mixed slurry obtained by adding a solvent to a mixture containing a positive electrode constituent material, a binder and a conductive agent is applied to a current collector by a doctor blade method or the like, A method of drying this, (2) a method of immersing the current collector in the mixed slurry and drying it, and (3) adding a solvent to a mixture containing a positive electrode constituent material, a binder and a conductive agent, and kneading. Molding and drying the kneaded product obtained in this way to obtain a sheet, joining the sheet and a current collector with a conductive adhesive or the like to obtain a joined body, and pressing the joined body and thermally drying the method, (4) A mixture containing a positive electrode constituent material, a binder, a conductive agent and a liquid lubricant is applied on a current collector to obtain a coated current collector, and the liquid lubricant is removed from the coated current collector. Examples thereof include a method of stretching the obtained sheet-like molded product in a uniaxial or multiaxial direction. When the positive electrode is formed into a sheet shape, the thickness is usually about 5 to 500 μm.

As a material of the current collector constituting the positive electrode, for example, nickel, aluminum, titanium, copper, gold, silver, platinum, aluminum alloy, stainless steel and other metal materials such as carbon material, activated carbon fiber, nickel, aluminum, Conductive agent for materials obtained by plasma spraying or arc spraying zinc, copper, tin, lead or alloys thereof, or resin such as rubber, styrene-ethylene-butylene-styrene copolymer (SEBS) For example, a conductive resin material in which is dispersed. Particularly preferred is aluminum which is lightweight, excellent in electrical conductivity and electrochemically more stable.
Examples of the shape of the current collector include a foil shape, a flat plate shape, a mesh shape, a net shape, a lath shape, a punching metal shape, an embossed shape, or a combination thereof (for example, a mesh-like flat plate). It is done. Irregularities may be formed on the current collector surface by etching treatment.

Examples of the conductive agent include conductive carbon such as graphite, carbon black, acetylene black, and ketjen black; graphite-based conductive agents such as natural graphite, thermally expanded graphite, scaly graphite, and expanded graphite; vapor grown carbon fiber, and the like Carbon fiber; Metal fine particles or metal fiber such as aluminum, nickel, copper, silver, gold, platinum; Conductive metal oxide such as ruthenium oxide or titanium oxide; Conductive polymer such as polyaniline, polypyrrole, polythiophene, polyacetylene, polyacene Is mentioned. Carbon black, acetylene black, and ketjen black are particularly preferable from the viewpoint of effectively improving conductivity in a small amount. The blending ratio of the conductive agent in the electrode is usually about 5 to 50 parts by weight, preferably about 10 to 30 parts by weight with respect to 100 parts by weight of the activated carbon of the present invention.

Examples of the binder include a polymer of a fluorine compound. Examples of the fluorine compound include fluorinated alkyl (having 1 to 18 carbon atoms) (meth) acrylate, perfluoroalkyl (meth) acrylate [for example, perfluorododecyl (meth) acrylate, perfluoro n-octyl (meth) acrylate, Perfluoro n-butyl (meth) acrylate, etc.], perfluoroalkyl-substituted alkyl (meth) acrylate [eg, perfluorohexylethyl (meth) acrylate, perfluorooctylethyl (meth) acrylate, etc.], perfluorooxyalkyl (meth) Acrylate [for example, perfluorododecyloxyethyl (meth) acrylate and perfluorodecyloxyethyl (meth) acrylate, etc.], fluorinated alkyl (C1-18) crotonate, fluorinated amine Kill (carbon number 1 to 18) malate and fumarate, fluorinated alkyl (carbon number 1 to 18) itaconate, fluorinated alkyl-substituted olefin (about 2 to 10 carbon atoms, about 1 to 17 fluorine atoms) [for example perfluorohexyl Fluorinated olefin, tetrafluoroethylene, trifluoroethylene, vinylidene fluoride, hexafluoropropylene, etc. in which fluorine atoms are bonded to ethylene, a double bond carbon having about 2 to 10 carbon atoms, and about 1 to 20 fluorine atoms] Is mentioned.

The binder may be a monomer addition polymer containing an ethylenic double bond not containing a fluorine atom. Examples of such monomers include (cyclo) alkyl (C1-22) (meth) acrylate [eg, 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 To 100) di (meth) acrylate, (poly) propylene glycol (degree of polymerization 1 to 100) di (meth) acrylate, 2,2-bis (4-hydroxyethylphenyl) propane di (meth) acrylate, trimethylolpropane tri ( (Meth) acrylate monomers such as (meth) acrylate]; (meth) acrylamides such as (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 [eg, ethylene, propylene, 1-butene, 1-octene, 1-dodecene, etc.] Monoolefins of: chlorine, bromine or iodine atom-containing monomers, for example, halogen atom-containing monomers other than fluorine such as vinyl chloride and vinylidene chloride; (meth) acrylic acid such as acrylic acid and methacrylic acid; butadiene, isoprene And conjugated double bond-containing monomers. The addition polymer may be a copolymer such as an ethylene-vinyl acetate copolymer, a styrene-butadiene copolymer, and 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 binders include polysaccharides such as starch, methylcellulose, carboxymethylcellulose, hydroxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, carboxymethylhydroxyethylcellulose, nitrocellulose, and derivatives thereof; phenol resins; melamine resins; polyurethane resins; Examples include urea resin: polyimide resin; polyamideimide resin; petroleum pitch; coal pitch.

Among these, as the binder, a polymer of a fluorine compound is preferable, and polytetrafluoroethylene which is a polymer of tetrafluoroethylene is particularly preferable.

As the binder, a plurality of types of binders may be used. The mixing ratio of the binder in the electrode is usually about 0.5 to 30 parts by weight, preferably about 2 to 30 parts by weight with respect to 100 parts by weight of the activated carbon. Examples of the solvent used for the binder include isopropyl alcohol (also referred to as IPA), alcohols such as ethanol and methanol, ethers, and ketones. If the binder thickens, a plasticizer may be used to easily apply the binder to the current collector.

The conductive adhesive is usually a mixture of the conductive agent and the binder, and preferably, a mixture of carbon black and polyvinyl alcohol. This mixture does not require an organic solvent and is prepared. Is easy and storage stability is excellent.

(Negative electrode)
The negative electrode in the sodium ion type electricity storage device of the present invention can be doped with sodium ions that are cations and can be undoped. The negative electrode usually has a negative electrode active material. As an example of the negative electrode, a negative electrode mixture containing a negative electrode active material, a binder, and a conductive agent as required can be doped with sodium ions and dedoped, and attached to the negative electrode current collector. In other words, a negative electrode active material layer formed on a current collector can be used. The negative electrode is usually in the form of a sheet. As a specific method for producing a negative electrode, (1) a negative electrode mixture slurry obtained by adding a solvent to a negative electrode mixture containing a negative electrode active material and a binder is used as a negative electrode current collector by a doctor blade method or the like. (2) A method of immersing the current collector in the negative electrode mixture and drying it, (3) A solvent is added to the negative electrode mixture containing the negative electrode active material and a binder The kneaded product obtained by kneading is molded and dried to obtain a sheet, the sheet and the negative electrode current collector are joined with a conductive adhesive or the like to obtain a joined body, and the joined body is pressed and heated. (4) A mixture containing a negative electrode active material, a binder, and a liquid lubricant is applied onto the negative electrode current collector to obtain a coated current collector, and the liquid lubricant is removed from the coated current collector. And a method of stretching the sheet-like molded product obtained in the uniaxial or multiaxial direction. When the negative electrode is in the form of a sheet, the thickness is usually about 5 to 500 μm.

The negative electrode active material is not particularly limited as long as it is a material that can be doped with sodium ions and can be undoped, but preferably can be doped with sodium ions and be undoped. It is a carbon material that can be used. The carbon material may be selected from carbon black, pyrolytic carbons, carbon fibers, organic material fired bodies, and the like. The carbon material is preferably a non-graphitized carbon material (also referred to as “hard carbon”). Among these, carbon microbeads made of a non-graphitized carbon material can be mentioned, and specifically, ICB (trade name: Nika beads) manufactured by Nippon Carbon Co., Ltd. can be mentioned.
Examples of the shape of the particles constituting the carbon material include a flake shape such as natural graphite, a spherical shape such as mesocarbon microbeads, a fibrous shape such as graphitized carbon fiber, and an aggregate shape of fine particles. When the shape of the particles constituting the carbon material is spherical, the average particle diameter is preferably 0.01 μm or more and 30 μm or less, more preferably 0.1 μm or more and 20 μm or less.

In the electricity storage device of the present invention, in order to smoothly dope and dedope sodium ions, the carbon material as the negative electrode active material is preferably a carbon material that has not been subjected to activation treatment, particularly preferably. It is a non-activated carbon material. The non-activated carbon material is a carbon material that has been subjected to a deactivation treatment for the carbon material.
“Inactivation treatment” means treatment for removing the surface functional groups of the carbon material, and a specific treatment method is 600 ° C. or more and 2000 ° C. or less (preferably 800 ° C. in an inert gas atmosphere). The method of heat-processing at the temperature of 1800 degrees C or less) is mentioned.
When the activated carbon material is used as the negative electrode active material, sodium ions are not doped and dedoped smoothly, and the irreversible capacity may increase.

The organic material fired body used for the negative electrode active material in the electricity storage device of the present invention can be doped with sodium ions and dedoped among carbon materials obtained by carbonization (firing) of various organic materials. A carbon material that can be used may be used. A non-graphitized carbon material, which is a suitable carbon material, can be obtained by firing an organic material that is unlikely to have a graphite crystal structure.
Organic materials used as raw materials for the organic material fired body include natural mineral resources such as petroleum and coal, various synthetic resins synthesized from these resources (thermosetting resin, thermoplastic resin, etc.), petroleum pitch, and coal pitch. And various plant residue oils such as spinning pitch, plant-derived organic materials such as wood, etc., 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. These resins may contain a curing agent and an additive. The curing method is not particularly limited. For example, when a phenol resin is used, a thermal curing method, a thermal oxidation method, an epoxy curing method, an isocyanate curing method, and the like can be given. In the case of using an epoxy resin, a phenol resin curing method, an acid anhydride curing method, an amine curing method, and the like can be given.

The organic material is preferably an organic material having an aromatic ring. By using the organic material, a carbon material that can be doped with sodium ions and can be dedope can be obtained with high yield. Thereby, the environmental load is small, the manufacturing 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. These resins may contain a curing agent and an additive.

The organic material having an aromatic ring is preferably an organic material produced by polymerizing phenol or a derivative thereof and an aldehyde compound. Since 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 the carbon material obtained by carbonizing the phenol resin is used as the negative electrode active material of the sodium ion type electricity storage device of the present invention, the charge / discharge capacity of the electricity storage device is particularly large when the charge / discharge is repeated, A carbon material obtained by carbonizing a phenol resin is preferable. Phenol resin has a structure in which three-dimensional crosslinking is developed, and the carbon material obtained by carbonizing the resin is also a carbon material having a structure in which unique three-dimensional crosslinking is derived from the structure. It is estimated to be. Thereby, it is considered that the discharge capacity is particularly increased.

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 aldehyde compounds 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 of two or more.

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

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

As a novolak type phenol resin, a type called a random novolak having a methylene group bonding position at the same ortho-position and para-position (this type is obtained by combining a phenol or its derivative and an aldehyde compound with a known organic acid and / or Alternatively, it can be obtained by a condensation reaction at a normal pressure of 100 ° C. for several hours using an inorganic acid catalyst, and water and unreacted monomers are removed from the resulting condensate), and there are many methylene group bonds at the ortho position. A type called high ortho novolac (this type is an addition condensation reaction between phenol or its derivative and an aldehyde compound using a metal salt catalyst such as zinc acetate, lead acetate or zinc naphthenate under weak acidity. , Directly or by adding an acid catalyst, conducting a condensation reaction while further dehydrating, and removing unreacted materials as necessary Ri obtained) is known.

A wide variety of other organic materials can be used as the organic material having an aromatic ring in the molecular structure.

The synthetic resin is generally a polymer in which monomers are polymerized. As the organic material having an aromatic ring, an organic material in which several to several tens of monomers are polymerized can be used.

When the phenol or its derivative and the aldehyde compound are polymerized, a by-product may be generated or an unpolymerized product may remain. These by-products and unpolymerized materials can also be used as organic materials, and by reducing waste, the environmental impact can be reduced, and carbon materials can be obtained at low cost, resulting in more industrial utility value. high.

Examples of plant-derived organic materials include wood. Charcoal obtained by carbonizing these is preferable as a carbon material used for the negative electrode active material. As the timber, waste timber, waste timber generated in a wood processing process such as sawdust, forest thinned timber, and the like can also be used. As the constituent components of wood, three types of cellulose, hemicellulose and lignin are generally mentioned as the main components, and lignin is an organic material having an aromatic ring and is preferable.

Wood includes cycads, ginkgo, conifers (cedar, cypress, red pine, etc.), maize, etc., broadleaf trees (Mizunara, beech, poplar, harunire, oak, etc.), herbaceous plants, palms, bamboo Angiosperms and the like such as

Among the above wood, cedar is widely used as a building material, and cedar sawdust is generated in the processing process. Cedar sawdust is a preferable organic material, and can reduce the environmental load and obtain a carbon material at a low cost. Bincho charcoal obtained by carbonizing oak is also preferable as a carbon material used for the negative electrode active material.

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

Examples of plant residual oil include various residual oils generated during the manufacture 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 these, a residual oil generated during the production of a petrochemical product having an aromatic ring is preferable, and specific examples of the residual oil include a residual oil generated during the production of resorcinol.

The carbon material used for the negative electrode active material can be obtained by carbonizing (baking) one or more organic materials among the above-described various organic materials. The carbonization temperature is preferably 800 ° C. or higher and 2500 ° C. or lower. Carbonization is preferably performed in an inert gas atmosphere. 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 multistage furnace, and a fluidized furnace. A rotary kiln is a general-purpose facility.

Carbon material obtained by carbonization (firing) may be pulverized as necessary. The pulverization is, for example, an impact friction pulverizer, a centrifugal pulverizer, a ball mill (tube mill, compound mill, conical ball mill, rod mill), vibration mill, colloid mill, friction disk mill, or jet mill. Can be used. A ball mill is a pulverizer generally used. At the time of pulverization, in order to suppress the mixing of the metal powder into the carbon material, the contact portion with the carbon material in these pulverizers may be made of a non-metallic material such as alumina or agate. By the pulverization, the carbon material is pulverized so that the average particle size of the particles constituting the carbon material is usually 50 μm or less, preferably 30 μm or less, particularly preferably 10 μm or less.

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

Examples of the negative electrode current collector include Cu, Ni, and stainless steel. Cu is preferable because it is difficult to form an alloy with sodium and it is easy to process 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-like flat plate). It is done. Concavities and convexities by etching treatment may be formed on the surface of the negative electrode current collector.

In the sodium ion type electricity storage device of the present invention, the negative electrode constituting the electricity storage device is an electrode pre-doped with sodium ions. Thereby, the irreversible capacity | capacitance of an electrode can be reduced. An electricity storage device having a large discharge capacity and excellent cycle characteristics can be obtained. A sodium ion type electricity storage device that can be sufficiently used as an electricity storage device can be obtained. In the present invention, the electrode pre-doped with sodium ions holds sodium in an ionic or metallic state.

Next, in the present invention, a specific method for pre-doping sodium ions into the negative electrode will be described.

As a suitable method for preliminarily doping the negative electrode with sodium ions, for example, a method using sodium metal may be mentioned. Specifically, this method is a method of electrically connecting the negative electrode and sodium metal. In this method, a potential difference is generated between the sodium metal and the electrode (the negative electrode in the electricity storage device of the present invention) to form a local battery that is electrically shorted, and the sodium ions are eluted from the sodium metal. Then, the eluted sodium ions move to the electrode having a high potential. In this way, the electrode (the negative electrode in the electricity storage device of the present invention) is pre-doped with sodium ions.

A more preferred method is a method of applying an external voltage between the negative electrode and sodium metal, that is, a method of electrolysis. In this method, the positive pole of the power source is connected to sodium metal, and the negative pole of the power source is connected to a negative electrode that is pre-doped. Sodium ions are eluted from sodium metal by electrolysis, and the eluted sodium ions are taken into the negative electrode. The amount of sodium ions doped in the negative electrode is large, and the doping rate of sodium ions is fast.

As a suitable method for pre-doping sodium ions into the negative electrode, a method in which a liquid in which sodium metal is melted is brought into contact with the negative electrode can be mentioned. In this method, the chemical reaction between the liquid in which sodium metal is melted and the negative electrode is promoted, and the negative electrode is pre-doped with sodium ions.

As a preferred method for pre-doping sodium ions into the negative electrode, there is a method in which the negative electrode is placed in a sodium vapor atmosphere obtained using sodium metal. In this method, the chemical reaction between sodium vapor and the negative electrode is promoted, and the negative electrode is pre-doped with sodium ions. In the present invention, even when sodium metal is deposited on the negative electrode surface, the negative electrode is regarded as being doped with sodium ions.

The amount of sodium ions preliminarily doped into the negative electrode (preliminary dope amount) is appropriately designed according to the material constituting the negative electrode. The pre-doping amount is preferably 5% or more of the full charge capacity. In addition, the amount of pre-doping is such that the redox potential difference between the negative electrode preliminarily doped with sodium ions and sodium metal is 1.00 V or less, 0.50 V or less, 0.30 V or less, 0.10 V or less, or 0. It is preferable that the amount be 05 V or less. When the negative electrode is preliminarily doped with sodium ions in this way, the discharge capacity and cycle characteristics of the obtained electricity storage device tend to be further improved. In this case, as the negative electrode, an electrode in which a negative electrode active material, a binder, and, if necessary, a negative electrode mixture containing a conductive agent and the like are supported on the negative electrode current collector can be used.

(Electrolyte)
In the sodium ion type electricity storage device of the present invention, the electrolytic solution contains sodium ions and anions. The electrolytic solution is usually an electrolyte dissolved in an organic solvent. The electrolytic solution is also referred to as a nonaqueous electrolytic solution. The electrolyte dissolved in the organic solvent is decomposed into sodium ions (cations) and anions. Examples of the electrolyte include NaClO ₄ , NaPF ₆ , NaBF ₄ , NaCF ₃ SO ₃ , NaN (CF ₃ SO ₂ ) ₂ , NaN (C ₂ F ₅ SO ₂ ) ₂ , NaC (CF ₃ SO ₂ ) ₃ , Na _{_{_{3 BO 3, NaF, NaAsF 6}}} , NaSbF 6, NaTaF 6, NaNbF 6, Na 2 SiF 6, NaCN, include sodium salts, such as NaAlF _{_4,} NaAlCl _4.

In the electrolytic solution, the concentration of the electrolyte may be appropriately set in consideration of the solubility of the electrolyte in the electrolytic solution, and is usually about 0.2 to 5 mol (electrolyte) / L (electrolytic solution), preferably 0.3. About 3 to 3 mol (electrolyte) / L (electrolytic solution), particularly preferably about 0.8 to 1.5 mol / L mol (electrolyte) / L (electrolytic solution). When the concentration is 0.2 mol / L or more, the ionic conductivity of the electrolytic solution is increased, and the internal resistance of the obtained electricity storage device can be decreased. When the concentration is 5 mol / L or less, the viscosity of the electrolytic solution is reduced. As a result, the internal resistance can be reduced.

An organic polar solvent is used as the organic solvent for dissolving the electrolyte. The water content in the electrolytic solution containing the organic polar solvent is usually 200 ppm by weight or less, preferably 50 ppm by weight or less, more preferably 20 ppm by weight or less. By suppressing the water content, it is possible to suppress the influence on the electrode due to the electrolysis of water, particularly the decrease in withstand voltage.

Specific examples of the organic polar solvent include the following compounds (ether, fluorinated dioxolane, amide, nitrile, carboxylic acid ester, lactone, carbonate, sulfoxide, sulfone, nitro compound, other heterocyclic compounds, hydrocarbons, And silicon compounds).

Examples of ethers include
Monoethers (for example, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, ethylene glycol monophenyl ether, tetrahydrofuran, 3-methyltetrahydrofuran, etc.), diethers (for example, ethylene glycol dimethyl ether, ethylene glycol) Diethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethyl ether, methyl isopropyl ether, etc.), triethylene glycol dimethyl ether, ethylene glycol monomethyl ether acetate, cyclic ether [cyclic ether having 2 to 4 carbon atoms (for example, tetrahydrofuran, 2-methylteto Hydrofuran, 1,3-dioxolane, 1,4-dioxane, 2-methyl-1,3-dioxolane, etc.), 4-butyl-dioxolane, and the like crown ether] of 5 to 18 carbon atoms.

Examples of fluorinated dioxolanes include
2,2-di (trifluoromethyl) -1,3-dioxolane, 2,2-di (trifluoromethyl) -4,5-difluoro-1,3-dioxolane, 2,2-di (trifluoromethyl) -4,4,5,5-tetrafluoro-1,3-dioxolane, 2,2-dimethyl-4,4,5,5-tetrafluoro-1,3-dioxolane or 2,2-dimethyl-4,5 -Difluoro-1,3-dioxolane and the like.

Examples of amides include
Formamides (eg, N-methylformamide, N, N-dimethylformamide, N-ethylformamide, N, N-diethylformamide, etc.), acetamides (eg, N-methylacetamide, N, N-dimethylacetamide, N- Ethylacetamide, N, N-diethylacetamide, etc.), propionamides (eg, N, N-dimethylpropionamide, etc.), hexamethylphosphorylamide, oxazolidinones (eg, N-methyl-2-oxazolidinone, 3,5- Dimethyl-2-oxazolidinone), 1,3-dimethyl-2-imidazolidinone, N-methylpyrrolidone and the like.

Examples of nitriles include
Acetonitrile, glutaronitrile, adiponitrile, methoxyacetonitrile, 3-methoxypropionitrile, acrylonitrile, fluorine-containing propionitrile (one obtained by substituting one or more hydrogen atoms of propionitrile with a fluorine atom) and the like.

Examples of carboxylic acid esters include
Examples include methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, methyl butyrate, methyl valerate, ethyl propionate, dimethyl malonate, diethyl malonate, maleic anhydride, and derivatives thereof.

Examples of lactones include
γ-butyrolactone, 3-methyl-γ-butyrolactone, 2-methyl-γ-butyrolactone, α-acetyl-γ-butyrolactone, β-butyrolactone, γ-valerolactone, 3-methyl-γ-valerolactone, δ-valerolactone Etc.

Examples of carbonates include
Ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, dimethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, diethyl carbonate, 4-allyloxymethyl-1,3-dioxolan-2-one, 4- (1 '-Propenyloxymethyl) -1,3-dioxolan-2-one, 4-allyloxymethyl-5-vinyl-1,3-dioxolan-2-one, 4- (1'-propenyloxymethyl) -5- Vinyl-1,3-dioxolan-2-one, 4-acryloyloxymethyl-1,3-dioxolan-2-one, 4-methacryloyloxymethyl-1,3-dioxolan-2-one, 4-methacryloyloxymethyl- 5-vinyl-1 3-dioxolan-2-one, 4-methoxycarbonyloxymethyl-1,3-dioxolan-2-one, 4-allyloxycarbonyloxymethyl-1,3-dioxolan-2-one, 4- (1′-propenyl) Oxycarbonyloxymethyl) -1,3-dioxolane-2-one, 4-vinylethylene carbonate, 4,5-divinylethylene carbonate, 4,4,5,5-tetramethyl-1,3-dioxolan-2-one 4,4,5,5-tetraethyl-1,3-dioxolan-2-one, vinylene carbonate, 4-methyl vinylene carbonate, 4,5-dimethyl vinylene carbonate, 5,5-dimethyl-1,3-dioxane- 2-one and 5,5-diethyl-1,3-dioxane-2-one, dipropyl carbonate, methyl butyl carbonate, ethyl butyl carbonate, ethyl propyl carbonate, butyl ester Pills carbonate, and compounds obtained by substituting a hydrogen atom 1 or more fluorine atoms of the carbonate.

Examples of sulfoxides include
Dimethyl sulfoxide, sulfolane, 3-methylsulfolane, 2,4-dimethylsulfolane, fluorine-containing sulfolane (substitution of one or more hydrogen atoms of sulfolane with fluorine atoms), 1,3-propane sultone, 1,4-butane sultone, Examples include compounds in which one or more hydrogen atoms of these compounds are substituted with fluorine atoms.

Examples of sulfones are:
Examples thereof include dimethyl sulfone, diethyl sulfone, di-n-propyl sulfone, diisopropyl sulfone, di-n-butyl sulfone, di-sec-butyl sulfone, and di-tert-butyl sulfone.

Examples of nitro compounds include
Examples include nitromethane and nitroethane.

Examples of other heterocyclic compounds include
N-methyl-2-oxazolidinone, 3,5-dimethyl-2-oxazolidinone, 1,3-dimethyl-2-imidazolidinone, N-methylpyrrolidinone and the like can be mentioned.

Examples of hydrocarbons include
Aromatic solvents (for example, toluene, xylene, ethylfluorobenzene, fluorobenzene in which 1 to 6 hydrogen atoms of benzene are substituted with fluorine atoms), paraffinic solvents (for example, normal paraffin, isoparaffin, etc.) It is done.

Examples of silicon compounds include
Compounds having a silicon atom in the molecule, such as oxazolidinone compounds (eg 3-trimethylsilyl-2-oxazolidinone, 3-trimethylsilyl-4-trifluoromethyl-2-oxazolidinone, 3-triethylsilyl-2-oxazolidinone), imidazole compounds (For example, N-trimethylsilylimidazole, N-trimethylsilyl-4-methyl-imidazole, N-triethylsilylimidazole, etc.), phosphate compounds (for example, tris (trimethylsilyl) phosphate, tris (triethylsilyl) phosphate, trimethylsilyldimethylphosphate, trimethylsilyldiallyl Phosphates, etc.), cyclic carbonate compounds (eg 4-trimethylsilyl-1,3-dioxolan-2-one, 4-trimethyl) Ryl-5-vinyl-1,3-dioxolan-2-one, 4-trimethylsilylmethyl-1,3-dioxolan-2-one, etc.), phenyl compounds (eg, phenyltrimethylsilane, phenyltriethylsilane, phenyltrimethoxysilane) , Phenylthiotrimethylsilane, phenylthiotriethylsilane, etc.), carbamate compounds (eg, methyl-N-trimethylsilyl carbamate, methyl-N, N-bistrimethylsilyl carbamate, ethyl-N-trimethylsilyl carbamate, methyl-N-triethylsilyl carbamate, Vinyl-N-trimethylsilylcarbamate), carbonate compounds (eg, methyltrimethylsilylcarbonate, allyltrimethylsilylcarbonate, ethyltrimethylsilylcarbonate) Etc.), methoxytrimethylsilane, hexamethyldisiloxane, pentamethyldisiloxane, methoxymethyltrimethylsilane, trimethylchlorosilane, butyldiphenylchlorosilane, trifluoromethyltrimethylsilane, acetyltrimethylsilane, 3-trimethylsilylcyclopentene, allyltrimethylsilane, vinyltrimethyl Examples thereof include silane and hexamethyldisilazane.

The organic polar solvent may be a mixture of two or more different solvents (mixed solvent).
The organic polar solvent contained in the electrolytic solution is preferably a solvent mainly composed of ester solvents such as carbonates and lactones, and particularly preferably propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, It is an ester solvent mainly composed of at least one selected from the group consisting of isopropyl methyl carbonate, vinylene carbonate and diethyl carbonate. Here, “main component” means that the ester solvent occupies 50% by weight or more, preferably 70% by weight or more of the mixed solvent. When the ester solvent is contained in the electrolytic solution, the electrolytic solution is excellent in oxidation resistance, so that the positive electrode potential during operation of the electricity storage device is increased. Thereby, the charge / discharge capacity (energy density) per unit volume as the electricity storage device can be further increased. The effect which suppresses rapid decomposition | disassembly of electrolyte solution is also acquired. A mixed solvent composed of a combination of ethylene carbonate and dimethyl carbonate is preferred as the organic polar solvent contained in the electrolytic solution.

If necessary, various additives are added to the electrolytic solution. Specifically, phosphoric acid esters (for example, trimethyl phosphate, triethyl phosphate, triallyl phosphate, etc.) and phosphonic acids for suppressing gas generation and improving withstand voltage, fluorine containing for high capacity and high output Examples include organosilicon compounds. The fluorine-containing organosilicon compound is represented by the following formula.
CF ₃ CH ₂ CH ₂ Si (CH ₃ ) ₃
(CH ₃ ) ₃ Si—O—Si (CH ₃ ) (CF ₃ CH ₂ CH ₂ ) —Si (CH ₃ )

The addition ratio of phosphoric acid esters and phosphonic acids is usually about 10% by weight or less with respect to the weight of the electrolyte from the viewpoint of the electrical conductivity of the electrolyte and the solubility in organic solvents, and the addition ratio of the fluorine-containing organosilicon compound Is usually about 0.1 to 5% by weight based on the weight of the electrolytic solution.

As additives, benzoic acids [for example, benzoic acid alkyl esters such as methyl benzoate, ethyl benzoate, propyl benzoate, benzoic acid, etc.] may be used. An effect of preventing metal elution from the current collector can be obtained. When benzoic acids are used as additives, the addition ratio is usually about 0.001 to 10.0% by weight, preferably 0.005 to 5% by weight, particularly preferably 0.1 to 0.1% by weight based on the weight of the electrolyte. 1% by weight. Benzoic acids can also be used as organic polar solvents.

(Separator)
The sodium ion type electricity storage device of the present invention may further have a separator. The separator is disposed between the positive electrode and the negative electrode. The separator suppresses a short circuit between both electrodes by separating the positive electrode and the negative electrode. The separator may play a role of holding the electrolytic solution. The separator is preferably an insulating film having a large ion permeability and a predetermined mechanical strength.
Examples of the separator include paper made of viscose rayon, natural cellulose, kraft paper, manila paper, mixed paper obtained by making fibers such as cellulose or polyester, polyethylene nonwoven fabric, polypropylene nonwoven fabric, polyester nonwoven fabric, polybutylene terephthalate nonwoven fabric. , Non-woven fabric such as glass fiber non-woven fabric, aramid fiber non-woven fabric, polyethylene, polypropylene, polyester, aramid (para-type wholly aromatic polyamide, etc.), vinylidene fluoride, tetrafluoroethylene, copolymer of vinylidene fluoride and propylene hexafluoride And a porous film composed of a material such as fluorine-containing resin such as fluororubber.
The separator may be a molded product made of ceramic powder particles such as silica and the binder described above. The molded product is usually molded integrally with the positive electrode and the negative electrode. A separator made of a material such as polyethylene or polypropylene may contain a surfactant or silica particles in order to improve the affinity with a polar solvent. The separator may contain an organic solvent such as acetone and a plasticizer such as dibutyl phthalate (DBP).

The separator may contain a proton conducting polymer.
The separator is more preferably a viscose rayon or natural cellulose paper, kraft paper, manila paper, a mixed paper obtained by making a cellulose or polyester fiber, a polyethylene nonwoven fabric, a polypropylene nonwoven fabric, a polyester nonwoven fabric or a glass fiber nonwoven fabric. .
The pore diameter of the separator is usually about 0.01 to 10 μm. The thickness of the separator is usually about 1 to 300 μm, preferably about 5 to 30 μm.

(Electric storage device)
Examples of the shape of the sodium ion type electricity storage device include a coin type, a wound type, a laminated type, a bellows type, and a laminated pack type.
As shown in FIG. 1, a coin type manufacturing method includes a current collector (1-2), an electrode active material layer (1-3) on the inner bottom of a metal container (1-1) such as stainless steel. The separator (1-4), the electrode active material layer (1-3), and the current collector (1-2) are sequentially laminated, and after injecting the electrolyte, the metal lid (1-5) and gasket (1- 6) and the like.
As an example of winding type production, as shown in FIG. 2, a mixed slurry containing a conductive carbon material is applied to a current collector (2-2) and dried to form an electrode active material layer (2-3). An electrode group obtained by preparing the formed laminated sheet and winding the two laminated sheets through the separator (2-4) is placed in a cylindrical metal container (2-1) such as aluminum or stainless steel. For example, a method of sealing with an electrode sealing plate (2-5) after inserting and injecting an electrolytic solution can be used. The current collector is provided with a lead in advance, the lead (2-6) of one laminated sheet acts as a positive electrode, and the lead (2-6) of the other laminated sheet acts as a negative electrode. Charge and discharge.
As shown in FIG. 3, a laminate type manufacturing method includes alternately laminating sheets of current collectors (3-2) and electrode active material layers (3-3) and separators (3-4). Method of inserting the obtained electrode group into a metal container (3-1) such as aluminum or stainless steel, injecting an electrolyte, and alternately connecting the current collector to the lead (3-5) and sealing As shown in FIG. 4, the laminated sheet of the current collector (4-2) and the electrode active material layer (4-3) and the separator (4-4) are alternately pressed, and the outer layer is sealed with a rubber material or the like. For example, a method of sealing after filling with an electrolytic solution may be used. As a bipolar structure including the gasket (4-6) as appropriate, a structure in which the working voltage can be arbitrarily set may be used.
As shown in FIG. 5, a laminate pack type manufacturing method is a resin sheet in which an electrode group obtained by alternately laminating a laminate sheet of electrodes (5-2) and a separator (5-3) is vapor-deposited on aluminum. For example, a method may be used in which the electrode is inserted into a laminate pack (5-1), an electrolyte solution is injected, and the electrodes (5-2) are alternately connected to the leads (5-4) for sealing.
The bellows type (not shown) can be prepared in the same manner as the multilayer type using an electrode group obtained by laminating two sheets of electrodes while folding them in a bellows shape with a separator interposed therebetween.

Hereinafter, the present invention will be described in more detail with reference to examples. The present invention is not limited to these examples.

(Preparation of positive electrode)
Activated carbon (manufactured by Kuraray Co., Ltd., RP20) as a positive electrode active material and polyvinylidene fluoride (PVDF: Kureha Co., Ltd., PolyvinylideneDiFluoride) mixed at a ratio of 95: 5, and further N-methylpyrrolidone (NMP: An appropriate amount of Tokyo Chemical Industry Co., Ltd.) was added and mixed to obtain a slurry. The obtained slurry is applied to an aluminum foil having a thickness of 40 μm, which is a current collector, with a thickness of 100 μm using an applicator, and this is put into a dryer and sufficiently dried while removing NMP. As a result, an electrode sheet was obtained. This electrode sheet was punched out to a diameter of 1.5 cm with an electrode punching machine, and then sufficiently pressed with a hand press to obtain a positive electrode.

(Preparation of negative electrode)
Add a suitable amount of N-methylpyrrolidone (NMP) to a mixture of non-graphitized carbon material (Nippon Carbon: ICB0510) as a negative electrode active material and polyvinylidene fluoride (PVDF) in a ratio of 95: 5. A slurry was obtained. Apply the obtained slurry onto a copper foil with a thickness of 10 μm, which is a current collector, with a thickness of 100 μm using an applicator, put it in a dryer, and dry it thoroughly while removing NMP. Thus, a negative electrode sheet was obtained.
This negative electrode sheet was punched to a diameter of 1.5 cm using an electrode punching machine, and then sufficiently pressed by a hand press to obtain a negative electrode.

(Pre-doping of sodium ions into the negative electrode)
A spare cell was prepared as follows and sodium ions were pre-doped into the negative electrode. The negative electrode, 1M NaClO ₄ / propylene carbonate (PC) as a non-aqueous electrolyte, and a separator were used. Sodium metal was prepared as a counter electrode, a separator was disposed between the counter electrode and the negative electrode, accommodated in a coin cell, and a non-aqueous electrolyte was injected to prepare a spare cell. The spare cell was assembled in a glove box with an argon atmosphere.

Prepare a power supply, and configure a circuit that connects the positive electrode of the power supply to the sodium metal side, and connects the negative electrode of the power supply to the negative electrode side to be pre-doped, and a CC (constant of 0.007 mA until the potential difference becomes 0.005V. A negative electrode preliminarily doped with sodium ions was obtained by discharging (current: constant current).

Example 1
(Production of electricity storage device)
A negative electrode pre-doped with sodium ions, 1M NaClO ₄ / PC as a non-aqueous electrolyte, a polypropylene porous membrane (film thickness 20 μm) as a separator, and the positive electrode are prepared. Then, a separator was disposed between the positive electrode and the negative electrode, accommodated in a coin cell, and a non-aqueous electrolyte was injected to produce the electricity storage device 1. The electrical storage device 1 was assembled in a glove box in an argon atmosphere.

Prepare a power supply, configure a circuit that connects the positive electrode of the power supply to the positive electrode side of the electricity storage device 1, and connects the negative electrode of the power supply to the pre-doped negative electrode side of the electricity storage device 1, and performs constant current charge / discharge under the following conditions The test was conducted.
Charging / discharging conditions:
Charging was performed by CC (constant current: constant current) charging at 0.004 mA up to 4.0 V. Discharge was performed by CC discharge at the same rate as the charge rate, and was cut off at a voltage of 1.5V. Charging and discharging after the next cycle were performed at the same rate as the charging rate, and cut off at a charging voltage of 4.0 V and a discharging voltage of 1.5 V as in the first cycle.

As a result of conducting a constant current charge / discharge test on the electricity storage device 1, the discharge capacity at the second cycle is 107 mAh / g as a value normalized by the weight of the negative electrode active material, which exceeds the value of the lithium ion capacitor. In addition, a large-capacity electricity storage device with a large electrical energy stored per unit volume was obtained. The ratio of the discharge capacity at the 20th cycle to the discharge capacity at the 2nd cycle (discharge capacity retention ratio) was 89%, and the cycle characteristics were also good.

Example 2
A mixed solvent in which ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed at a ratio of 1: 1 (weight ratio) to the nonaqueous electrolytic solution was used. An electricity storage device 2 was produced in the same manner as in Example 1 except that 1M NaClO ₄ / (EC + DMC) was used as the non-aqueous electrolyte.

For the electricity storage device 2, the same circuit as in Example 1 was constructed and tested under the same charge / discharge conditions. The discharge capacity at the second cycle was 200 mAh / g as a value normalized by the weight of the negative electrode active material. Thus, an extremely large capacity electricity storage device having an extremely large value exceeding the value of the lithium ion capacitor and a large electric energy stored per unit volume was obtained. The ratio of the discharge capacity at the 20th cycle to the discharge capacity at the 2nd cycle (discharge capacity retention ratio) was 97%, and the cycle characteristics were also very good.

Comparative Example 1
An electricity storage device 3 was produced in the same manner as in Example 1 except that the negative electrode pre-doped with sodium ions was used instead of the negative electrode pre-doped with sodium ions.

Regarding the electricity storage device 3, a circuit similar to that in Example 1 was constructed and tested under the same charge / discharge conditions, but no effective charge current and discharge current were observed, and the device did not operate.

Comparative Example 2
An electricity storage device 4 was produced in the same manner as in Example 2 except that the negative electrode pre-doped with sodium ions was used instead of the negative electrode pre-doped with sodium ions.

For the electricity storage device 4, a circuit similar to that of Example 2 was configured and tested under the same charge / discharge conditions. However, no effective charge current and discharge current were observed, and the device did not operate.

Example 3
A nonaqueous electrolytic solution was prepared using sodium hexafluorophosphate (NaPF ₆ ) as an electrolyte and propylene carbonate (PC) as a solvent. An electricity storage device 5 was produced in the same manner as in Example 1 except that 1M NaPF ₆ / PC was used as the non-aqueous electrolyte.

Regarding the electricity storage device 5, the same circuit as in Example 1 was configured and the test was performed under the same charge / discharge conditions. As a result, the discharge capacity at the second cycle was 140 mAh / min as a value normalized by the weight of the negative electrode active material. g, an extremely large value that surpasses the value of the lithium ion capacitor, and an extremely large-capacity electricity storage device with a large electrical energy stored per unit volume was obtained. The ratio of the discharge capacity at the 20th cycle to the discharge capacity at the 2nd cycle (discharge capacity retention rate) was 91%, and the cycle characteristics were also very good.

Comparative Example 3
An electricity storage device 6 was produced in the same manner as in Example 3 except that the negative electrode pre-doped with sodium ions was used instead of the negative electrode pre-doped with sodium ions.

Regarding the electricity storage device 6, a circuit similar to that in Example 3 was configured and a test was performed under the same charge / discharge conditions. However, no effective charging current and discharging current were observed, and the device did not operate as an electricity storage device.

The electricity storage device of the present invention is a device that uses abundant sodium in terms of resources, has an excellent capacitance per unit volume, and can be used for storing electrical energy. In particular, because of its excellent characteristics, it can be suitably used for energy storage in the field of portable equipment and transportation equipment.

1-1 Metal container 1-2 Current collector in electrode (positive electrode or negative electrode) 1-3 Active material layer in electrode (positive electrode or negative electrode) 1-4 Separator 1-5 Metal lid
1-6 Gasket 2-1 Metal container 2-2 Current collector in electrode (positive electrode or negative electrode) 2-3 Active material layer in electrode (positive electrode or negative electrode) 2-4 Separator 2-5 Electrode sealing plate 2-6 Lead 3-1 Metal container 3-2 Current collector in electrode (positive electrode or negative electrode) 3-3 Active material layer in electrode (positive electrode or negative electrode) 3-4 Separator 3-5 Lead 3-6 Terminal 3-7 Safety valve 4- 1 Pressure plate and terminal 4-2 Current collector in electrode (positive electrode or negative electrode) 4-3 Active material layer in electrode (positive electrode or negative electrode) 4-4 Separator 4-6 Gasket 5-1 Laminate pack 5-2 Electrode (positive electrode) Or negative electrode)
5-3 Separator 5-4 Lead

Claims

A positive electrode, a negative electrode, and an electrolytic solution containing sodium ions and anions,
The positive electrode can adsorb and desorb anions, can be doped with anions and can be undoped;
The negative electrode can be doped and dedoped with sodium ions, and the negative electrode is an electrode pre-doped with sodium ions,
Sodium ion storage device.
The sodium ion-type electricity storage device according to claim 1, wherein the negative electrode has a negative electrode active material, and the negative electrode active material is a carbon material that can be doped with sodium ions and dedoped.
3. The sodium ion type electricity storage device according to claim 2, wherein the carbon material is a non-graphitized carbon material.
4. The sodium ion type electricity storage device according to claim 2, wherein the carbon material is a non-activated carbon material.
The negative electrode is preliminarily doped with sodium ions to a certain extent that the redox potential difference between the negative electrode and sodium metal preliminarily doped with sodium ions is 1.00 V or less. The sodium ion type electrical storage device according to any one of the above.
The sodium ion type electricity storage device according to any one of claims 1 to 5, further comprising a separator disposed between the positive electrode and the negative electrode.