Battery Materials

Abstract

Provided is a battery material characterized by containing a carbon nanostructure which emits light when excited at a certain wavelength in a wavelength range of 300-800 nm.

Description

[Technical Field]

[0001] The present invention relates to battery materials comprising carbon nanostructures. [Background technology]

[0002] In recent years, electronic devices have become smaller and lighter, and this has led to a demand for smaller and lighter batteries as their power sources. Non-aqueous electrolyte secondary batteries such as lithium-ion batteries have been put to practical use as small, lightweight, high-capacity, rechargeable batteries, and are used in portable electronic devices and communication devices such as small video cameras, mobile phones, and laptop computers.

[0003] Lithium-ion secondary batteries have excellent advantages, such as high energy density, higher capacity, and higher operating voltage than other batteries. However, due to their high energy density, they are at risk of overheating and fire depending on the conditions of use, so high safety standards are required. In particular, hybrid vehicles, which have recently been attracting attention, require higher energy density and output characteristics, making even higher safety standards necessary.

[0004] Generally, lithium-ion secondary batteries are composed of a positive electrode, a negative electrode, and an electrolyte. During charging, lithium ions escape from the positive electrode active material into the electrolyte and are inserted into the negative electrode active material, such as carbon particles. During discharging, lithium ions escape from the negative electrode active material into the electrolyte and are inserted into the positive electrode active material, allowing current to be extracted to an external circuit. In this way, charging and discharging occur within the lithium-ion secondary battery as lithium ions move back and forth between the positive and negative electrodes via the electrolyte.

[0005] Meanwhile, as the performance of portable electronic devices improves, higher-capacity batteries are required. Sn and Si, which have much higher capacities per unit weight than conventional carbon, are being actively researched as negative electrode active materials. However, when Si or Si alloys are used as negative electrode active materials, there is a problem of large volume expansion, which leads to poor cycle characteristics. To solve this problem, graphite is mixed into the battery, but if the graphite is unevenly distributed during mixing, the cycle characteristics (lifespan) may be reduced.

[0006] In recent years, further improvements in rate characteristics are being demanded as lithium-ion secondary batteries are increasingly used in a variety of applications, such as as high-output power sources for plug-in hybrid vehicles, hybrid vehicles, power tools, etc. Batteries used as these high-output power sources are required to be able to charge and discharge at high speeds.

[0007] The theoretical capacity of currently available positive electrode active materials is significantly lower than that of negative electrode active materials. Therefore, to achieve high capacity and high power output in lithium-ion batteries, it is necessary to impart high electrical and ionic conductivity to the positive electrode. To improve the electronic conductivity of the positive electrode, a method of adding a carbon material to the electrode as a conductive additive has been used. Examples of such carbon materials include graphite, acetylene black, and ketjen black. Recently, the use of carbon nanotubes and graphene has been reported. However, increasing the amount of such conductive additive reduces the amount of active material in the electrode, resulting in a decrease in battery capacity.

[0008] Furthermore, in order to enhance the electronic conductivity of an electrode material, an electrode material has been proposed in which the particle surface of an electrode active material is coated with an organic compound that serves as a carbon source, and then the organic compound is carbonized to form a carbonaceous coating on the surface of the electrode active material, with the carbon in this carbonaceous coating acting as an electronic conductive material (e.g., Patent Document 1). However, the carbonization process requires a long-term heat treatment at a high temperature of 500°C or higher in an inert gas atmosphere, which reduces the capacity of the electrode. Furthermore, since the carbonization process involves heating at a high temperature of 500 to 800°C in a reducing or inert atmosphere, there is a possibility that the positive electrode active material itself may be reduced. Therefore, usable positive electrode active materials have been limited to lithium iron phosphate, lithium nickel phosphate, lithium cobalt phosphate, lithium manganese phosphate, etc. For other positive electrode active materials, the carbon source has been limited to conductive polymer materials. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-15111 Summary of the Invention [Problem to be solved by the invention]

[0010] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a battery material that can be suitably used as a material for forming batteries such as lithium ion secondary batteries and that can improve the rate characteristics of the batteries. [Means for solving the problem]

[0011] As a result of extensive research to achieve the above-mentioned object, the inventors discovered that batteries manufactured using battery materials containing luminescent carbon nanostructures have excellent rate characteristics, and thus completed the present invention.

[0012] That is, the present invention provides the following battery material. 1. A battery material comprising a carbon nanostructure, characterized in that the carbon nanostructure emits light when excited by a wavelength of 300 to 800 nm. 2. The battery material of 1, wherein the absolute quantum yield of the carbon nanostructure is 10% or more. 3. The battery material of 2, wherein the absolute quantum yield of the carbon nanostructure is 30% or more. 4. The battery material according to any one of 1 to 3, wherein the carbon nanostructure is a carbon quantum dot. 5. The battery material according to any one of 1 to 4, wherein the carbon nanostructure is non-conductive and contains nitrogen. 6. The battery material of 5, wherein the nitrogen is derived from an amine. 7. The battery material according to any one of 1 to 6, wherein the carbon contained in the carbon nanostructure is derived from a polycarboxylic acid or a sugar. 8. The battery material according to any one of 1 to 7, further comprising an active material, conductive carbon, and a binder. 9. The battery material of 8, wherein the active material is selected from the group consisting of metals, semi-metals, metal alloys, metal oxides, semi-metal oxides, metal phosphates, metal sulfides, and metal nitrides. 10. The active material is FeS2, TiS2, MoS2, LiFePO4, V2O6, V6O 13 , MnO2, LiCoO2, LiMnO2, LiMn2O4, LiMo2O4, LiV3O8, LiNiO2, Li z Ni y M 1-y O2 (wherein M represents at least one metal element selected from Co, Mn, Ti, Cr, V, Al, Sn, Pb, and Zn, and 0.05≦z≦1.10, 0.5≦y≦1.0), Li(Ni a Co b Mn c )O2(However, 0 <a<1、0<b<1、0<c<1、a+b+c=1)、Li4Ti5O 12 , Si, SiO x , AlO x , SnO x , SbO x , BiO x , GeO x, AsO x , PbO x , ZnO x , CdO x , InO x , TiO x and GaO x (However, at least one selected from 0 < x ≦ 2) is a battery material of 9. 11. Any of the battery materials of 8 to 10 for electrode formation. 12. An electrode having an active material layer made of the battery material of 11. 13. A secondary battery provided with the electrode of 12. 14. A method for manufacturing a battery material according to any one of the battery materials of 1 to 11, including a step of synthesizing a carbon nanostructure by mixing a polyvalent carboxylic acid or a saccharide, amines, and a solvent and heating them. 15. The method for manufacturing a battery material of 14, in which the above synthesis is performed by solvothermal synthesis. 16. The method for manufacturing a battery material of 15, in which the above synthesis is performed by hydrothermal synthesis. 17. The method for manufacturing a battery material of 16, including a step of replacing the solvent of the carbon nanostructure aqueous solution obtained by hydrothermal synthesis with an organic solvent. 18. The method for manufacturing a battery material according to any one of claims 8 to 10, After preparing a solution or dispersion liquid containing an active material and a carbon nanostructure, a step of removing the solvent to produce a composite of the active material - carbon nanostructure is included.

Effect of the Invention

[0013] By using the battery material of the present invention, a battery with excellent rate characteristics can be provided.

Brief Description of the Drawings

[0014] [Figure 1] It is a figure showing the fluorescence spectrum of the aqueous solution A1 obtained in Example 1 - 1. [Figure 2] It is a figure showing the fluorescence spectrum of the aqueous solution A2 obtained in Example 1 - 2. [Figure 3]FIG. 1 is a diagram showing the fluorescence spectrum of aqueous solution A3 obtained in Example 1-3. [Figure 4] FIG. 1 shows the fluorescence spectrum of aqueous solution A4 obtained in Example 1-4. [Figure 5] FIG. 1 is a diagram showing the fluorescence spectrum of aqueous solution A5 obtained in Comparative Example 1-1. [Figure 6] FIG. 1 is a diagram showing the fluorescence spectrum of aqueous solution A6 obtained in Comparative Example 1-2. DETAILED DESCRIPTION OF THE INVENTION

[0015] The battery material of the present invention contains carbon nanostructures, which emit light when excited at a wavelength between 300 and 800 nm. In the present invention, the use of carbon nanostructures with such properties allows for the production of batteries with excellent rate and cycle characteristics. The luminescence of the carbon nanostructures can be confirmed using known measuring devices. In the present invention, for example, the luminescence can be confirmed by measuring the obtained carbon nanostructure aqueous solution with a spectrofluorometer F-7000 manufactured by Hitachi High-Tech Science Corporation, with the excitation wavelength fixed at a wavelength between 300 and 800 nm. The excitation wavelength can be determined from the maximum absorption wavelength in absorption spectrum measurement.

[0016] Carbon nanostructures are generally structures composed primarily of carbon atoms, with at least one of the three dimensions of the structure being in the nanometer range, for example, on the order of several nm to several hundred nm.

[0017] The absolute quantum yield of the carbon nanostructures is preferably 10% or more, more preferably 30% or more, and even more preferably 50% or more, from the viewpoint of further improving the discharge capacity of the resulting battery. The upper limit of the absolute quantum yield is not particularly limited, but is usually 90% or less. The absolute quantum yield can be confirmed using a known measuring device. In the present invention, for example, the absolute quantum yield can be confirmed by measuring the maximum absorption wavelength in absorption spectroscopy using an absolute PL quantum yield meter manufactured by Hamamatsu Photonics K.K. for the resulting aqueous carbon nanostructure solution, using the maximum absorption wavelength as the excitation wavelength.

[0018] Examples of carbon nanostructures include carbon quantum dots, graphene quantum dots, and carbon materials containing a fused ring structure, which is a partial structure of fibrous π-conjugated polymers and graphene, which have the above-mentioned light-emitting properties. Among these, carbon quantum dots, which are carbon materials with an average particle size of 20 nm or less, are preferred. The above average particle size is a value measured by a transmission electron microscope (TEM).

[0019] In addition, the carbon nanostructure is preferably non-conductive from the viewpoint of further improving the discharge capacity of the resulting battery. In the present invention, "non-conductive" means that the conductivity of the obtained powder of carbon nanostructure measured with a low resistance meter Loresta-GP manufactured by Mitsubishi Chemical Analytech Corporation is below the detection limit (resistance value 10 7 Ω).

[0020] The carbon nanostructure preferably contains nitrogen. The nitrogen content of the carbon nanostructure is not particularly limited as long as it contains nitrogen, but in consideration of further improving the discharge capacity of the resulting battery, the nitrogen content is preferably 5 to 30 mass%, more preferably 10 to 25 mass%, and even more preferably 10 to 20 mass%.

[0021] The carbon nanostructures can be produced by known methods, for example, by using a carbon source consisting of a polycarboxylic acid or a sugar and a nitrogen source consisting of an amine as raw materials, mixing these with a solvent, and heating the mixture.

[0022] The polycarboxylic acid is not particularly limited as long as it is a carboxylic acid having two or more carboxy groups. Specific examples thereof include: Citric acid, succinic acid, oxalic acid, Examples of the polycarboxylic acid include quinic acid, galactaric acid, glyceric acid, gluconic acid, glucuronic acid, ascorbic acid, and gallic acid. Among these, citric acid, succinic acid, and oxalic acid are preferred, and citric acid is more preferred. The polycarboxylic acids may be used alone or in combination of two or more.

[0023] The sugars include monosaccharides, disaccharides, and polysaccharides. These sugars may be used singly or in combination of two or more.

[0024] Preferred monosaccharides are those having 3 to 9 carbon atoms, and particularly 5 to 6 carbon atoms. Specific examples include pentoses such as xylose; hexoses such as glucose, mannose, and galactose; deoxyhexoses such as fucose; hexosamines such as glucosamine and galactosamine; hexosamine derivatives such as N-acetylglucosamine and N-acetylgalactosamine; sialic acids such as neuraminic acid, N-acetylneuraminic acid, and N-glycolylneuraminic acid; and uronic acids such as glucuronic acid and iduronic acid. Of these, hexoses are preferred, and glucose is more preferred. The above monosaccharides may be used alone or in combination of two or more.

[0025] Examples of disaccharides include sucrose, lactulose, lactose, maltose, trehalose, cellobiose, etc. The above disaccharides may be used singly or in combination of two or more.

[0026] Examples of polysaccharides include starch, amylose, amylopectin, glycogen, cellulose, chitin, agarose, carrageenan, heparin, hyaluronic acid, pectin, xyloglucan, glucomannan, etc. Among these, those that are soluble in water are preferred from the viewpoint of synthesis. The above polysaccharides may be used alone or in combination of two or more.

[0027] Examples of amines include aliphatic amines, aromatic amines, hydroxyamines, polyamines, heterocyclic amines, amino acids, and amino group-containing polyalkylene glycols. Among these, aliphatic amines, aromatic amines, and amino acids are preferred. The above amines may be used alone or in combination of two or more.

[0028] Examples of aliphatic amines include methylamine, ethylamine, n-propylamine, isopropylamine, n-butylamine, isobutylamine, s-butylamine, t-butylamine, n-pentylamine, 1-methyl-n-butylamine, 2-methyl-n-butylamine, 3-methyl-n-butylamine, 1,1-dimethyl-n-propylamine, 1,2-dimethyl-n-propylamine, 2,2-dimethyl-n-propylamine, 1-ethyl-n-propylamine, n-hexylamine, 1-methyl-n-pentylamine, 2-methyl-n-pentylamine, 3-methyl-n-pentylamine, 4-methyl-n-pentyl ...1-dimethyl-n-propylamine, 1,2-dimethyl-n-propylamine, 2,2-dimethyl-n-propylamine, 1,1-dimethyl-n-propylamine, 1,1-dimethyl-n-propylamine, 1,1-dimethyl-n-propylamine, 1,1-dimethyl-n-propylamine, 1,1-dimethyl-n-propylamine, 1,1-dimethyl-n-propylamine, 1,1-dimethyl-n-propylamine, 1,1- monoamines such as 1-ethyl-n-butylamine, 1,2-dimethyl-n-butylamine, 1,3-dimethyl-n-butylamine, 2,2-dimethyl-n-butylamine, 2,3-dimethyl-n-butylamine, 3,3-dimethyl-n-butylamine, 1-ethyl-n-butylamine, 2-ethyl-n-butylamine, 1,1,2-trimethyl-n-propylamine, 1,2,2-trimethyl-n-propylamine, 1-ethyl-1-methyl-n-propylamine, 1-ethyl-2-methyl-n-propylamine, 2-ethylhexylamine, 2-aminoethanol, 1-amino-2-propanol, 2-amino-1-propanol, and 2-aminoethanethiol;Ethylenediamine, N,N-dimethylethylenediamine, N,N'-dimethylethylenediamine, N,N-diethylethylenediamine, N,N'-diethylethylenediamine, N-ethylethylenediamine, diethylenetriamine, 1,2-diaminopropane, 1,3-diaminopropane, 2-(2-aminoethylamino)ethanol, N-isopropylethylenediamine, N-isopropyl-1,3-diaminopropane, triethylenetetramine, N,N'-bis(2-hydroxyethyl)ethylenediamine, 2,2-dimethyl-1,3-propanediamine, 2-methyl-2,3-propanediamine, 1,2-diamino-2-methylpropane, 3,3'-diamino-N-methyldipropylamine, 2,3-dimethyl-2,3-butanediamine, 3,3'-diaminodipropylamine, N,N-bis(2-aminoethyl)-1,3-propanediamine, triethylenetetramine Examples of diamines include tetramethylenediamine, 2,2'-oxybis(ethylamine), tetramethylenediamine, 1,4-diaminobutane, 2,2'-thiobis(ethylamine), 1,5-diaminopentane, 2-methyl-1,5-diaminopentane, 1,6-diaminoheptane, 1,7-diaminopentane, 1,10-diaminodecane, 1,11-diaminoundecane, 1,12-diaminododecane, N,N'-bis(3-aminopropyl)ethylenediamine, diethylene glycol bis(3-aminopropyl)ether, 1,14-diamino-3,6,9,12-tetraoxatetradecane, bis(aminomethyl)cyclohexane, 1,2-cyclohexanediamine, 1,3-cyclohexanediamine, 1,4-cyclohexanediamine, bis(aminomethyl)norbornane, 1,4-bis(aminomethyl)cyclohexane, and 1,2-bis(2-aminoethoxy)ethane. Among these, compounds having two or more amino groups are preferred, and diamines having two carbon atoms between the amino groups are more preferred.

[0029] Examples of aromatic amines include aralkyl monoamines such as benzylamine, p-methoxycarbonylbenzylamine, p-ethoxycarbonylphenylbenzyl, p-methylbenzylamine, m-methylbenzylamine, and o-methoxybenzylamine, aniline, p-methoxycarbonylaniline, p-ethoxycarbonylaniline, p-methoxyaniline, 1-naphthylamine, 2-naphthylamine, anthranilamine, 1-aminopyrene, 4-biphenylylamine, o-phenylaniline, and 4-amino-p-terphenylamine. aryl monoamines such as fluorene, 2-aminofluorene, etc.; 1,2-phenylenediamine, 1,3-phenylenediamine, 1,4-phenylenediamine, 3-nitro-1,2-phenylenediamine, 4-nitro-1,2-phenylenediamine, 3-methyl-1,2-phenylenediamine, 4-methyl-1,2-phenylenediamine, 1,2,4-benzenetriamine, 3,4-dimethyl-1,2-phenylenediamine, 4,5-dimethyl-1,2-phenylenediamine, 3-fluoro-1,2-phenylenediamine, 4-fluoro-1,2 -phenylenediamine, 3,4-difluoro-1,2-phenylenediamine, 3,5-difluoro-1,2-phenylenediamine, 4,5-difluoro-1,2-phenylenediamine, 3-chloro-1,2-phenylenediamine, 4-chloro-1,2-phenylenediamine, 3,4-dichloro-1,2-phenylenediamine, 3,5-dichloro-1,2-phenylenediamine, 4,5-dichloro-1,2-phenylenediamine, 3-bromo-1,2-phenylenediamine, 4-bromo-1,2-phenylenediamine, 3,4-dibromo-1,2-phenylenediamine Examples of aryldiamines include aryldiamines such as bromo-1,2-phenylenediamine, 3,5-dibromo-1,2-phenylenediamine, 4,5-dibromo-1,2-phenylenediamine, 2,3-naphthalenediamine, benzidine, 3,3'-diaminobenzidine, 3,4-diaminobenzoic acid, methyl 3,4-diaminobenzoate, ethyl 3,4-diaminobenzoate, 4-(4-aminophenoxy)-1,2-benzenediamine, 3,4-diaminobenzophenone, and 5,6-diamino-1,3-dihydro-2H-benzimidazol-2-one.

[0030] Examples of heterocyclic amines include barbituric acid, aziridine, azetidine, pyrrolidine, piperidine, piperazine, azepane, pyridine, pyridazine, pyrimidine, pyrazine, imidazole, benzimidazole, pyrazole, oxazole, isoxazole, benzoxazole, thiazole, isothiazole, benzothiazole, triazine, azepine, diazepine, benzodiazepine, pyrrole, imidazoline, morpholine, thiazine, indole, isoindole, purine, quinoline, isoquinoline, quinoxaline, pteridine, acridine, carbazole, cinnoline, benzo-C-cinnoline, porphyrin, chlorine, choline, triaminotriazine, trichlorotriazine, and derivatives thereof.

[0031] Examples of amino acids include cysteine, glycine, alanine, valine, phenylalanine, threonine, lysine, asparagine, tryptophan, serine, glutamic acid, aspartic acid, ornithine, thyroxine, cystine, leucine, isoleucine, proline, tyrosine, asparagine, glutamine, histidine, methionine, and threonine. Examples of amino group-containing polyalkylene glycols include amino group-containing polyethylene glycols and amino group-containing polypropylene glycols. When the amino acids have optical isomers, the amino acids may be D- or L-isomers, or may be racemic.

[0032] The amount of the amines used is preferably 10 to 300 parts by mass, more preferably 20 to 150 parts by mass, per 100 parts by mass of the carbon source, from the viewpoint of nitrogen introduction efficiency.

[0033] As the raw material, organic compounds other than the above carbon sources and nitrogen sources may also be used. Such organic compounds are not particularly limited as long as they do not impair the effects of the present invention.

[0034] The solvent is not particularly limited as long as it can dissolve the raw materials used. Examples of such solvents include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone (NMP), hexamethylphosphoric triamide, acetonitrile, acetone, alcohols (methanol, ethanol, 1-propanol, 2-propanol, etc.), glycols (ethylene glycol, triethylene glycol, etc.), cellosolves (ethyl cellosolve, methyl cellosolve, etc.), polyhydric alcohols (glycerin, pentaerythritol, etc.), tetrahydrofuran, toluene, ethyl acetate, butyl acetate, benzene, toluene, xylene, pentane, hexane, heptane, chlorobenzene, dichlorobenzene, trichlorobenzene, hexadecane, benzyl alcohol, and oleylamine. In the present invention, water is preferred among these. The above solvents may be used alone or in combination of two or more.

[0035] The amount of solvent used is preferably 100 to 10,000 parts by mass, more preferably 400 to 2,500 parts by mass, per 100 parts by mass of the raw material, in order to obtain carbon nanostructures with uniform particle sizes.

[0036] When synthesizing the carbon nanostructure, an acid catalyst or a surfactant may be further included, if necessary.

[0037] The acid catalyst may be either a homogeneous or heterogeneous acid catalyst, but heterogeneous acid catalysts are preferred from the viewpoint of improving quantum yield. Examples of homogeneous acid catalysts include inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid, and organic acids such as sulfonic acid and p-toluenesulfonic acid. On the other hand, heterogeneous acid catalysts are preferably solid acid catalysts, such as cationic ion exchange resins, cationic ion exchange membranes, and the solid acid catalysts described in Nature 438, p. 178 (2005). Commercially available solid acid catalysts can be used, such as ion exchange resins manufactured by Rohm and Haas, such as AMBERLYST® 15, 16, 31, and 35, and AMBERLITE® IR120B, IR124, 200CT, and 252; ion exchange membranes manufactured by DuPont, such as NAFION®; and inorganic solid acid catalysts such as zeolite and polyphosphoric acid. The acid catalysts may be used alone or in combination of two or more.

[0038] When a homogeneous acid catalyst is used, it is usually added in an amount of 0.01 to 10 parts by mass, more preferably 0.1 to 5 parts by mass, and even more preferably 0.5 to 1 part by mass, per 100 parts by mass of the raw material.

[0039] The heterogeneous acid catalyst is preferably a porous material having pores capable of containing the generated carbon nanostructures. The particle or disk diameter of the generated carbon nanostructures can be controlled by the size of the pores. In general, it is preferable to produce carbon quantum dots with particle diameters (disk diameters) of up to 20 nm using a porous solid acid catalyst with pore diameters of up to 20 nm.

[0040] When a heterogeneous acid catalyst is used, it is preferably added in an amount of about 0.1 to 100 parts by mass, more preferably 1.0 to 50 parts by mass, and even more preferably 5.0 to 10 parts by mass, per 100 parts by mass of the raw material.

[0041] The surfactant may be a cationic surfactant, an anionic surfactant, or a nonionic surfactant.

[0042] Examples of cationic surfactants include cetyltrimethylammonium bromide and cetyltrimethylammonium chloride. Examples of anionic surfactants include sodium dodecyl sulfate and sodium dodecylbenzenesulfonate. Examples of nonionic surfactants include polyethylene glycol and polypropylene glycol. These surfactants may be used alone or in combination of two or more.

[0043] The amount of surfactant used is preferably 10 to 2,000 parts by mass, more preferably 50 to 500 parts by mass, per 100 parts by mass of raw materials, in terms of dispersibility of the raw materials and the critical micelle concentration under synthesis conditions.

[0044] When synthesizing the carbon nanostructures, the components may be mixed in any order. The synthesis may be carried out either continuously or batchwise. In the present invention, a continuous synthesis is preferred because it allows for the continuous and efficient mass production of carbon nanostructures with uniform particle sizes.

[0045] As a continuous system, for example, a flow reactor (flow reactor) can be suitably employed. As the flow reactor, a known device can be used, and an example thereof is the Phoenix Flow Reactor, a high-temperature flow reaction system manufactured by Thales Nanotechnology Inc. By using a flow reactor, reactions (solvothermal synthesis, hydrothermal synthesis) can be carried out continuously and efficiently under high temperature and pressure.

[0046] The reaction temperature can be adjusted appropriately depending on conditions such as the type of solvent used in the raw material solution, and is not particularly limited, but from the viewpoint of carrying out the reaction efficiently, it is preferably about 100 to 450° C., more preferably 150 to 400° C., and even more preferably 250 to 350° C. If the reaction temperature is too high, a carbide that is insoluble in the reaction solvent may be produced. The reaction time (residence time) is preferably 1 to 30 minutes, more preferably 1.5 to 20 minutes, and more preferably 2 to 16 minutes, from the viewpoint of allowing the reaction to proceed completely and suppressing the production of carbonized products insoluble in the reaction solvent.

[0047] When a batch system is employed, heating may be carried out under normal pressure (atmospheric pressure) or under pressure (solvothermal synthesis, hydrothermal synthesis).

[0048] When the reaction is carried out under normal pressure, the reaction temperature varies depending on the boiling point of the solvent used, but is usually preferably about 40 to 250°C, more preferably 60 to 200°C, and even more preferably 100 to 150°C. Heating is usually carried out in a water bath or oil bath, but heating with microwaves is also possible. This allows the product to be obtained in a shorter time when water is used as the solvent, compared to heating in a water bath or oil bath.

[0049] When the reaction is carried out under normal pressure, the reaction time is preferably about 1 minute to 240 hours, more preferably about 10 minutes to 48 hours, and even more preferably about 12 to 30 hours.

[0050] When pressurization is performed, for example, an autoclave can be suitably used. By using an autoclave, the reaction temperature can be raised to above the boiling point at normal pressure. For example, even when water is used as a solvent, a reaction temperature of about 200°C can be easily achieved by using an autoclave for the reaction.

[0051] The reaction temperature, similar to the case of reaction under normal pressure, depends on the boiling point of the solvent used, but is usually preferably about 100 to 450° C., more preferably 150 to 400° C., and even more preferably 250 to 350° C. The reaction time is preferably about 30 seconds to 24 hours, more preferably about 1 minute to 1 hour, and even more preferably about 2 to 10 minutes.

[0052] The pressure is not particularly limited as long as it can achieve the desired reaction temperature, but is preferably about 200 kPa to 20.0 MPa, and more preferably about 500 kPa to 15.0 MPa.

[0053] Furthermore, when a solid acid catalyst is used in a batchwise reaction, it is preferable to carry out the reaction with stirring, and good results can be obtained by increasing the stirring speed within a range that does not crush the solid catalyst. The stirring speed is preferably about 10 to 500 rpm, and more preferably about 50 to 300 rpm.

[0054] The average particle size of the carbon nanostructures obtained by each of the above methods is preferably 20 nm or less, more preferably 15 nm or less, and even more preferably 10 nm or less. The lower limit of the particle size is not particularly limited, but is usually 1 nm or more. When the particle size is within the above range, the carbon nanostructures do not aggregate in a solvent, and no aggregates are formed during preparation or application of an electrode-forming composition (such as an electrode slurry). Furthermore, the particle size of the carbon nanostructures is sufficiently small compared to the size of the active material, providing excellent coating properties on the active material.

[0055] The obtained product can be purified by removing low-molecular-weight impurities by dialysis, ultrafiltration, etc., and then removing high-molecular-weight impurities by centrifugation, etc. The pore size of the dialysis membrane or ultrafiltration membrane and the centrifugal force during centrifugation may be appropriately set according to the molecular weight of the substance to be removed.

[0056] To further purify the sample to a higher purity, column purification may be performed. In this case, the column packing material may be normal phase or reverse phase. As normal phase packing materials, silica particles, alumina particles, etc. may be used. On the other hand, as reverse phase packing materials, silica particles surface-modified with long-chain alkyl groups may be used. Furthermore, pressure may be applied during column purification to shorten the time required.

[0057] When preparing a battery material using the carbon nanostructure, the material may be used in the form of a solution after the reaction, or may be isolated by removing the solvent. When a solvent different from that used in synthesizing the carbon nanostructure is used in preparing the battery material, the desired solvent system may be prepared by solvent substitution.

[0058] The battery material of the present invention can be used for forming an undercoat layer and an active material layer of an electrode, for producing an electrolyte, etc., and is particularly suitable for use as a material for forming an active material layer of an electrode.

[0059] When the above battery material is used as a material for forming an active material layer, it is preferable to combine the above carbon nanostructure with the following active material, conductive additive, binder, and, if necessary, solvent (dispersion medium).

[0060] The amount of carbon nanostructures in the battery material varies depending on the required electrical and thermal properties, the viscosity of the material, production costs, etc., but is preferably 0.01 to 1.0 mass% of the solid content, more preferably 0.01 to 0.75 mass%, and even more preferably 0.05 to 0.5 mass%. By keeping the amount of carbon nanostructures in the above range, a battery with excellent rate characteristics and cycle characteristics can be obtained. The solid content here means the components other than the solvent contained in the battery material of the present invention.

[0061] As the active material, various active materials that have conventionally been used in electrodes for energy storage devices such as secondary batteries can be used, and examples thereof include metals, semi-metals, metal alloys, metal oxides, semi-metal oxides, metal phosphates, metal sulfides, and metal nitrides.

[0062] Specific examples of the active material include the following. Examples of metal active materials include Al, Sn, and Zn. Examples of semimetallic active materials include Si, Ge, and As. Examples of metal alloy active materials include Li-Al based alloys, Li-Mg based alloys, Li-Al-Ni based alloys, Na-Hg based alloys, and Na-Zn based alloys. Metal oxide active materials include AlO x , SnO x , SbO x , BiO x , PbOx , ZnO x , CdO x , InO x , TiO x and GaO x (where 0 < x ≦ 2), V2O6, V6O 13 , MnO2, LiCoO2, LiMnO2, LiMn2O4, LiMo2O4, LiV3O8, LiNiO2, Li z Ni y M 1-y O2 (where M represents at least one metal element selected from Co, Mn, Ti, Cr, V, Al, Sn, Pb, and Zn, 0.05 ≦ z ≦ 1.10, 0.5 ≦ y ≦ 1.0), ternary active material (Li(Ni a Co b Mn c )O2 (where 0 < a < 1, 0 < b < 1, 0 < c < 1, a + b + c = 1)), tin silicate (SnSiO3), lithium bismuth oxide (Li3BiO4), lithium zinc oxide (Li2ZnO2), and lithium titanium oxide (Li4Ti5O 12 ) etc. can be mentioned. As the active material of the half - metal oxide, SiO x , GeO​​​​​​​​​​​​​​​​​​​​​​13 , MnO2, LiCoO2, LiMnO2, LiMn2O4, LiMo2O4, LiV3O8, LiNiO2, Li z Ni y M 1-y O2 (where M represents at least one metal element selected from Co, Mn, Ti, Cr, V, Al, Sn, Pb, and Zn, 0.05 ≦ z ≦ 1.10, 0.5 ≦ y ≦ 1.0), Li(Ni a Co b Mn c )O2 (where 0 < a < 1, 0 < b < 1, 0 < c < 1, a + b + c = 1), Li4Ti5O 12 , Si, SiO x , AlO x , SnO x , SbO x , BiO x , GeO x , AsO x , PbO x , ZnO x , CdO x , InO<L x , TiO x and GaO x (where 0 < x ≦ 2) is preferred, and TiO x (where 0 < x ≦ 2) is more preferred.

[0064] <00003"64> Further, for Li(Ni a Co b Mn c )O2, those satisfying 1 / 3 ≦ a < 1, 0 < b ≦ 1 / 3, 0 < c ≦ 1 / 3, a + b + c = 1 are even more preferred. Note that for the above Li(Ni a Co b Mn c)O2 can also be obtained as a commercially available product, and examples of such commercially available products include NCM111 (manufactured by Beijing Easping Material Technology, manufactured by Toshima Manufacturing Co., Ltd., a=1 / 3, b=1 / 3, c=1 / 3), NCM523 (manufactured by Beijing Easping Material Technology, manufactured by JIANGSU Easping Material Technology, a=0.5, b=0.2, c=0.3), NCM622 (manufactured by Beijing Easping Material Technology, a=0.6, b=0.2, c=0.2), and NCM811 (manufactured by Beijing Easping Material Technology, a=0.8, b=0.1, c=0.1).

[0065] The amount of active material to be added varies depending on the required electrical and thermal properties, the viscosity of the composition, production costs, etc., but is preferably 80 to 99.8 mass % of the solid content, more preferably 85 to 98.5 mass %, and even more preferably 90 to 98 mass %.

[0066] Examples of the conductive additive include carbon materials such as graphite, carbon black, acetylene black, vapor-grown carbon fiber, carbon nanotubes, carbon nanohorns, and graphene, and conductive polymers such as polyaniline, polypyrrole, polythiophene, polyacetylene, and polyacene.The conductive additives may be used alone or in combination of two or more.

[0067] The amount of the conductive additive is not particularly limited, but is preferably 0.05 to 9 mass % of the solid content, more preferably 0.1 to 6 mass %, and even more preferably 0.2 to 3 mass %. By keeping the amount of the conductive additive within the above range, good electrical conductivity can be obtained.

[0068] The binder can be appropriately selected from known materials and is not particularly limited, but examples of binders that can be used in the present invention include polyvinylidene fluoride (PVdF), polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, polyvinyl alcohol, polyimide, ethylene-propylene-diene terpolymer, styrene-butadiene rubber, carboxymethyl cellulose, polyacrylic acid, polyaniline, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, and polypropylene. These can be used alone or in combination of two or more.

[0069] The amount of the binder is not particularly limited, but is preferably 0.14 to 10 mass % of the solid content, more preferably 0.5 to 7 mass %, and even more preferably 1 to 5 mass %. By setting the amount of the binder within the above range, good adhesion to the current collecting substrate can be obtained without reducing the capacity.

[0070] If necessary, the binder may be dissolved in a suitable solvent, which will be described later, before mixing.

[0071] The solvent is not particularly limited as long as it can disperse or dissolve the raw materials used. Examples of such solvents include those similar to those exemplified in the description of the carbon nanostructures, but more preferred examples include water, NMP, dimethyl sulfoxide, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, γ-butyrolactone, tetrahydrofuran, dioxolane, sulfolane, dimethylformamide, and dimethylacetamide. These solvents may be selected appropriately depending on the raw materials used, but NMP is preferred when using a water-insoluble binder such as PVdF. The above solvents may be used alone or in combination of two or more.

[0072] When preparing the battery material for forming the active material, the preparation method is not particularly limited, and the respective components may be mixed in any order. In addition, when the solvent used in the synthesis of the carbon nanostructures is the same as the solvents exemplified above or a solvent miscible with them, the resulting reaction solution may be used as is. On the other hand, when the solvent used in the synthesis of the carbon nanostructures is a solvent immiscible with the solvents exemplified above, it is preferable to use a solution obtained by removing the solvent from the resulting reaction solution and isolating it, or to use a solution obtained by solvent substitution with an appropriate solvent. In particular, when water is used as the solvent in the synthesis of the carbon nanostructures, it is preferable to substitute the solvent with the organic solvent.

[0073] Furthermore, in the present invention, a solution or dispersion containing the active material and the carbon nanostructures can be prepared before mixing the above components, and then the solvent can be removed to produce a composite of the active material and the carbon nanostructures. By using this composite as the battery material of the present invention, a battery with excellent rate characteristics and cycle characteristics can be obtained.

[0074] The electrode of the present invention has an active material layer (thin film) made of the battery material described above on a substrate that is a current collector, or the battery material alone is formed into a thin film. When the active material layer is formed on a substrate, examples of the method for forming the active material layer include a method in which an electrode-forming composition prepared without using a solvent is pressure-molded onto a substrate (dry method), or a method in which an electrode-forming composition is prepared using a solvent, and then coated on a current collector and dried (wet method). These methods are not particularly limited, and various conventionally known methods can be used. For example, wet methods include various printing methods such as offset printing and screen printing, doctor blade methods, dip coating methods, spin coating methods, bar coating methods, slit coating methods, and inkjet methods.

[0075] Examples of substrates used for the electrodes include metal substrates such as platinum, gold, iron, stainless steel, copper, aluminum, and lithium; alloy substrates made of any combination of these metals; oxide substrates such as indium tin oxide (ITO), indium zinc oxide (IZO), and antimony tin oxide (ATO); and carbon substrates such as glassy carbon, pyrolytic graphite, and carbon felt.

[0076] When the above battery material is formed into a thin film by itself, the thin film may be formed on a substrate that can be peeled off after the thin film is formed, using the above-mentioned wet method or dry method as appropriate, or a method of spreading the battery material thinly on the substrate using a glass rod, etc. As the substrate, a substrate that does not have adhesiveness to the thin film, such as a glass plate, can be used, and even a substrate that has adhesiveness to the thin film can be used as long as its surface has been treated to enable peeling of the thin film (such as by attaching a release paper or forming a release layer).

[0077] The thickness of the active material layer (thin film) is not particularly limited, but is preferably about 0.01 to 1,000 μm, more preferably about 1 to 100 μm. When the thin film is used alone as an electrode, the thickness is preferably 10 μm or more.

[0078] In order to further suppress the elution of the active material contained in the electrode, the active material layer (thin film) may further contain a polyalkylene oxide and an ion-conductive salt, or the electrode may be covered with a protective film, which preferably contains a polyalkylene oxide and an ion-conductive salt. The polyalkylene oxide is not particularly limited, but polyethylene oxide, polypropylene oxide, etc. are preferred. The number average molecular weight of the polyalkylene oxide is preferably 300,000 to 900,000, and more preferably 500,000 to 700,000. The number average molecular weight is a value measured in terms of polystyrene by gel permeation chromatography (GPC) using tetrahydrofuran as a solvent.

[0079] Examples of the ion-conductive salt include lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(pentafluoroethanesulfonyl)imide (LiBETI), lithium trifluoromethanesulfonate (LiCF3SO3), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), lithium hexafluorophosphate (LiPF6), etc. The ion-conductive salt is preferably contained in an amount of 5 to 50 parts by mass per 100 parts by mass of the polyalkylene oxide.

[0080] The protective film can be formed, for example, by applying a composition containing polyalkylene oxide, an ion-conductive salt, and a solvent onto the substrate on which the active material layer (thin film) has been formed by a dipping method or the like, and then drying the composition at 40 to 60°C for 30 to 120 minutes. The solvent is preferably acetonitrile, dichloromethane, or the like. The thickness of the protective film is not particularly limited, but is preferably about 10 to 1,000 μm, and more preferably about 50 to 500 μm.

[0081] The secondary battery of the present invention is provided with the above-described electrodes, and more specifically, is provided with at least one pair of positive and negative electrodes, a separator interposed between the electrodes, and an electrolyte, at least one of the positive and negative electrodes being the above-described electrode. Other constituent members of the battery element may be appropriately selected from conventionally known components.

[0082] Examples of materials used for the separator include porous polyolefin, polyamide, and polyester.

[0083] As the electrolyte, an electrolytic solution composed of an electrolyte salt, which is the main body of ion conduction, a solvent, etc. can be suitably used from the viewpoint of easily achieving practically sufficient performance.

[0084] Examples of the electrolyte salt include lithium salts such as LiPF, LiBF, LiN(C2F5SO2), LiAsF, LiSbF, LiAlF, LiGaF, LiInF, LiClO, LiN(CF3SO2), LiCF3SO, LiSiF, and LiN(CF3SO2)(C4F9SO2), metal iodides such as LiI, NaI, KI, CsI, and CaI2, iodide salts of quaternary imidazolium compounds, iodide salts and perchlorates of tetraalkylammonium compounds, and metal bromides such as LiBr, NaBr, KBr, CsBr, and CaBr2. These electrolyte salts can be used alone or in combination.

[0085] The solvent is not particularly limited as long as it does not corrode or decompose the materials constituting the battery, thereby deteriorating performance, and dissolves the electrolyte salt. For example, non-aqueous solvents include cyclic esters such as ethylene carbonate, propylene carbonate, butylene carbonate, and γ-butyrolactone; ethers such as tetrahydrofuran and dimethoxyethane; and chain esters such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. These solvents can be used alone or in combination.

[0086] The electrode may be pressed as necessary. In this case, the pressing pressure is preferably 1 kN / cm or more. A commonly used pressing method can be used, but mold pressing and roll pressing are particularly preferred. The pressing pressure is not particularly limited, but is preferably 2 kN / cm or more, more preferably 3 kN / cm or more. The upper limit of the pressing pressure is preferably about 40 kN / cm, more preferably about 30 kN / cm.

[0087] A battery produced using the battery material of the present invention has superior rate characteristics and cycle characteristics compared to general secondary batteries.

[0088] The type of secondary battery and the type of electrolyte are not particularly limited, and any type of battery such as a lithium ion battery, nickel-metal hydride battery, manganese battery, or air battery may be used, but a lithium ion battery is preferred. The lamination method and production method are also not particularly limited.

[0089] The shape of the cell is not particularly limited, and various conventionally known cell shapes such as a cylindrical shape, a flat wound rectangular shape, a laminated rectangular shape, a coin shape, a flat wound laminate shape, and a laminated laminate shape can be used. When applied to a coin-shaped cell, the electrode of the present invention described above may be punched into a predetermined disk shape and used. For example, a lithium ion secondary battery can be produced by placing one electrode on a lid of a coin cell to which a washer and spacer are welded, placing a separator of the same shape impregnated with an electrolyte solution on top of that, and then placing the electrode of the present invention on top of that with the active material layer facing downwards, placing a case and a gasket on top, and sealing the battery with a coin cell crimping machine. [Example]

[0090] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples. The measuring devices used in the examples are as follows. [Flow reactor] Equipment: Phoenix Flow Reactor, a high-temperature flow reaction system manufactured by Thales Nanotechnology Inc. [Fluorescence spectrum measurement] Equipment: Hitachi High-Tech Science Corporation, F-7000 spectrofluorometer [Absolute quantum yield analysis] Equipment: Hamamatsu Photonics, absolute PL quantum yield meter [Conductivity measurement] Equipment: Mitsubishi Chemical Analytech Co., Ltd., low resistance meter Loresta-GP [Elemental analysis] Equipment: Perkin-Elmer fully automated elemental analyzer CHNS / O Analyzer 2400 The resulting solution was placed in an aluminum cup container and dried on a hot plate at 150°C, and the resulting powder was analyzed. [Transmission electron microscope (TEM)] Equipment: Hitachi, Ltd., H-8000 A TEM substrate was immersed in the obtained solution and dried, and then observed at an acceleration voltage of 200 kV and a magnification of 20,000 times. The diameters of 10 particles were measured to determine the number-average particle size. [Rotation and revolution mixer] Equipment: Thinky Corporation, Awatori Rentaro ARE-310 [Roll press machine] Equipment: Pressure / heat roll press SA-602 manufactured by Takumi Giken Co., Ltd. [Coin cell crimping machine] Equipment: HOUSEHEN Co., Ltd., manual coin crimping machine CR2032 [micrometer] Equipment: Mitutoyo Corporation, IR54 [Charge / discharge measuring device] Equipment: Toyo Systems Co., Ltd., TOSCAT 3100

[0091] [1] Production of carbon nanostructures (carbon quantum dots) (1) Preparation of aqueous solution of carbon nanostructures [Example 1-1] Using 20.0 g (0.1 mol) of citric acid (Fujifilm Wako Pure Chemical Industries, Ltd.) as a carbon source and 12.5 g (0.2 mol) of ethylenediamine (Tokyo Chemical Industry Co., Ltd.) as a nitrogen source, an aqueous solution with a raw material concentration of 10 mass% was prepared by dissolving the aqueous solution in 292 g of water. This aqueous solution was continuously synthesized using a flow reactor at a flow rate of 4 mL / min (residence time of 2 minutes) and a temperature of 300°C, to obtain aqueous solution A1 of carbon nanostructures. Elemental analysis revealed that the carbon content was 38.8 mass %, hydrogen content was 7.1 mass %, and nitrogen content was 17.0 mass %, and the particle size was 5 nm. Water was distilled off from the resulting aqueous solution A1 under reduced pressure to obtain a brown solid D1. Solid D1 was placed in a high resistance probe unit for powders, and the conductivity was measured using a low resistance meter Loresta GP at a pressure of 20 kN, which was below the detection limit.

[0092] [Example 1-2] An aqueous solution A2 was prepared in the same manner as in Example 1-1, except that the reaction temperature was changed to 340°C. Elemental analysis revealed that the carbon content was 46.0 mass %, hydrogen content was 7.9 mass %, and nitrogen content was 17.6 mass %, and the particle size was 5 nm. In the same manner as in Example 1-1, water was distilled off under reduced pressure from the resulting aqueous solution A2 to obtain a brown solid D2, and the electrical conductivity of the obtained solid D2 was measured, and was found to be below the detection limit.

[0093] [Examples 1-3] An aqueous solution A3 was prepared in the same manner as in Example 1-1, except that the raw material ethylenediamine was changed to N-ethylethylenediamine. Elemental analysis revealed that the carbon content was 57.5 mass %, hydrogen content was 7.6 mass %, and nitrogen content was 16.7 mass %, and the particle size was 14 nm. In the same manner as in Example 1-1, water was distilled off under reduced pressure from the resulting aqueous solution A3 to obtain a brown solid D3, and the electrical conductivity of the obtained solid D3 was measured, and was found to be below the detection limit.

[0094] [Examples 1-4] An aqueous solution A4 was prepared in the same manner as in Example 1-1, except that the raw material ethylenediamine was changed to 2-(2-aminoethylamino)ethanol. Elemental analysis revealed that the carbon content was 53.3 mass %, hydrogen content was 7.0 mass %, and nitrogen content was 16.0 mass %, and the particle size was 7 nm. In the same manner as in Example 1-1, water was distilled off under reduced pressure from the resulting aqueous solution A4 to obtain a brown solid D4, and the electrical conductivity of the obtained solid was measured, and was found to be below the detection limit.

[0095] [Comparative Example 1-1] An aqueous solution A5 was prepared in the same manner as in Example 1-1, except that the raw material was changed to citric acid only. Elemental analysis revealed that the carbon content was 44.5 mass %, hydrogen content was 4.5 mass %, and nitrogen content was 0.0 mass %, and the particle size was 10 nm. In the same manner as in Example 1-1, water was distilled off under reduced pressure from the resulting aqueous solution A5 to give a brown solid D5, and the electrical conductivity of the resulting solid was measured, finding it to be below the detection limit. In the same manner as in Example 1-1, water was distilled off under reduced pressure from the resulting aqueous solution A3 to obtain a brown solid D3, and the electrical conductivity of the obtained solid D3 was measured, and was found to be below the detection limit.

[0096] [Comparative Example 1-2] An aqueous solution A6 was prepared in the same manner as in Example 1-1, except that the raw material was glucose alone and the reaction temperature was changed to 250°C. Elemental analysis revealed that the carbon content was 41.9 mass %, hydrogen content was 6.6 mass %, and nitrogen content was 0.0 mass %, and the particle size was 200 nm. In the same manner as in Example 1-1, water was distilled off under reduced pressure from the resulting aqueous solution A6 to give a brown solid D6, and the electrical conductivity of the solid was measured, finding it to be below the detection limit.

[0097] (2) Measurement of fluorescence spectrum and quantum yield Aqueous solutions A1 to A6 obtained in Examples 1-1 to 1-4 and Comparative Examples 1-1 and 1-2 were each diluted 1,000 times with water, and the fluorescence spectra and absolute quantum yields were measured. The excitation wavelength was fixed at 360 nm during the measurements. The results are shown in Table 1. The fluorescence spectra obtained by the measurements are shown in Figures 1 to 6.

[0098] [Table 1] *The maximum fluorescence wavelengths in the table are values ​​automatically detected by the measuring device.

[0099] The carbon nanostructures (carbon quantum dots) synthesized in Examples 1-1 to 1-4 had a maximum fluorescence wavelength around 440 nm, and the quantum yield was also higher than that of the comparative examples.

[0100] (3) Solvent substitution [Example 2-1] An appropriate amount of NMP was added to the aqueous solution A1 obtained in Example 1-1, and water was removed by distillation under reduced pressure using a rotary evaporator. The resulting solution was passed through a 1.0 μm filter to remove aggregates, yielding an NMP solution B1. The solid content was measured as the dry residue after drying at 150° C. for 2 hours, and was found to be 6.9% by mass.

[0101] [Example 2-2] An NMP solution B2 was obtained in the same manner as in Example 2-1, except that the aqueous solution A2 obtained in Example 1-2 was used instead of the aqueous solution A1. The solid content was 6.2 mass %.

[0102] [Example 2-3] An NMP solution B3 was obtained in the same manner as in Example 2-1, except that the aqueous solution A3 obtained in Example 1-3 was used instead of the aqueous solution A1. The solid content was 6.2 mass %.

[0103] [Example 2-4] An NMP solution B4 was obtained in the same manner as in Example 2-1, except that the aqueous solution A4 obtained in Example 1-4 was used instead of the aqueous solution A1. The solid content was 6.2 mass %.

[0104] [Comparative Example 2-1] An NMP solution B5 was obtained in the same manner as in Example 2-1, except that the aqueous solution A5 obtained in Comparative Example 1-1 was used instead of the aqueous solution A1. The solid content was 5.4 mass %.

[0105] [Comparative Example 2-2] An NMP solution B6 was obtained in the same manner as in Example 2-1, except that the aqueous solution A6 obtained in Comparative Example 1-2 was used instead of the aqueous solution A1. The solid content was 12.6 mass %.

[0106] [2] Manufacturing and evaluation of lithium-ion batteries (1) Electrode manufacturing [Example 3-1] Ternary cathode active material Li(Ni 0.5 Co 0.2 Mn0.3 2.781 g of 2-O2 (NCM523-5Y, manufactured by Beijing Easping Material Technology Co., Ltd.), 0.052 g of acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductive additive, 0.042 g of Solution B1 prepared in Example 2-1, and 1.28 g of an NMP solution (solids concentration 5% by mass) of PVdF (manufactured by Kureha Corporation, #7300) as a binder were mixed (solids mass ratio 95.9:1.8:0.1:2.2), and 0.859 g of NMP was further added to bring the total solids concentration to 58% by mass. This mixture was mixed in a planetary centrifugal mixer (2,000 rpm, 10 minutes, three times) to prepare a slurry for forming an electrode. This was spread uniformly on aluminum foil (1085, manufactured by UACJ Corporation, substrate thickness 15 μm) using a doctor blade method (wet film thickness 100 μm), and then dried at 80°C for 30 minutes and then at 120°C for 30 minutes to form an active material layer. This was then pressed using a roll press to produce electrode C1 (film thickness 40 μm).

[0107] [Example 3-2] Ternary cathode active material Li(Ni 0.5 Co 0.2 Mn 0.3 2.770 g of 2-O2 (NCM523-5Y, manufactured by Beijing Easping Material Technology Co., Ltd.), 0.052 g of acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductive additive, 0.210 g of Solution B1 prepared in Example 2-1, and 1.28 g of an NMP solution (solids concentration 5% by mass) of PVdF (manufactured by Kureha Corporation, #7300) as a binder were mixed (solids mass ratio 95.5:1.8:0.5:2.2), and 0.692 g of NMP was further added to bring the total solids concentration to 58% by mass. This mixture was mixed in a planetary centrifugal mixer (2,000 rpm, 10 minutes, three times) to prepare a slurry for forming an electrode. This was spread uniformly on aluminum foil (1085, manufactured by UACJ Corporation, substrate thickness 15 μm) using a doctor blade method (wet film thickness 100 μm), and then dried at 80°C for 30 minutes and then at 120°C for 30 minutes to form an active material layer. This was then pressed using a roll press to produce electrode C2 (film thickness 40 μm).

[0108] [Example 3-3] Ternary cathode active material Li(Ni 0.5 Co 0.2 Mn 0.3 2.770 g of PO2 (NCM523-5Y, manufactured by Beijing Easping Material Technology Co., Ltd.), 0.052 g of acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductive additive, 0.233 g of Solution B2 prepared in Example 2-2, and 1.28 g of an NMP solution (solids concentration 5% by mass) of PVdF (manufactured by Kureha Corporation, #7300) as a binder were mixed (solids mass ratio 95.5:1.8:0.5:2.2), and 0.669 g of NMP was further added to bring the total solids concentration to 58% by mass. This mixture was mixed in a planetary centrifugal mixer (2,000 rpm, 10 minutes, three times) to prepare a slurry for forming an electrode. This was spread uniformly on aluminum foil (1085, manufactured by UACJ Corporation, substrate thickness 15 μm) using a doctor blade method (wet film thickness 100 μm), and then dried at 80°C for 30 minutes and then at 120°C for 30 minutes to form an active material layer. This was then pressed using a roll press to produce electrode C3 (film thickness 37 μm).

[0109] [Example 3-4] Ternary cathode active material Li(Ni 0.5 Co 0.2 Mn 0.32.770 g of PVDF (NCM523-5Y, manufactured by Beijing Easping Material Technology Co., Ltd.), 0.052 g of acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductive additive, 0.065 g of Solution B3 prepared in Example 2-3, and 1.28 g of an NMP solution (solids concentration 5% by mass) of PVdF (manufactured by Kureha Corporation, #7300) as a binder were mixed (solids mass ratio 95.5:1.8:0.5:2.2), and 0.826 g of NMP was further added to bring the total solids concentration to 58% by mass. This mixture was mixed in a planetary centrifugal mixer (2,000 rpm, 10 minutes, three times) to prepare a slurry for forming an electrode. This was spread uniformly on aluminum foil (1085, manufactured by UACJ Corporation, substrate thickness 15 μm) using a doctor blade method (wet film thickness 100 μm), and then dried at 80°C for 30 minutes and then at 120°C for 30 minutes to form an active material layer. This was then pressed using a roll press to produce electrode C4 (film thickness 42 μm).

[0110] [Examples 3-5] Ternary cathode active material Li(Ni 0.5 Co 0.2 Mn 0.3 2.770 g of PVDF (NCM523-5Y, manufactured by Beijing Easping Material Technology Co., Ltd.), 0.052 g of acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductive additive, 0.054 g of Solution B4 prepared in Example 2-4, and 1.28 g of an NMP solution (solids concentration 5% by mass) of PVdF (manufactured by Kureha Corporation, #7300) as a binder were mixed (solids mass ratio 95.5:1.8:0.5:2.2), and 0.837 g of NMP was further added to bring the total solids concentration to 58% by mass. This mixture was mixed in a planetary centrifugal mixer (2,000 rpm, 10 minutes, three times) to prepare a slurry for forming an electrode. This was spread uniformly on aluminum foil (1085, manufactured by UACJ Corporation, substrate thickness 15 μm) using a doctor blade method (wet film thickness 100 μm), and then dried at 80°C for 30 minutes and then at 120°C for 30 minutes to form an active material layer. This was then pressed using a roll press to produce electrode C5 (film thickness 42 μm).

[0111] [Comparative Example 3-1] Ternary cathode active material Li(Ni 0.5 Co 0.2 Mn 0.3 2.784 g of 2.784 g of 2-hydroxybenzophenone (NCM523-5Y, manufactured by Beijing Easping Material Technology Co., Ltd.), 0.052 g of acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductive additive, and 1.28 g of an NMP solution (solids concentration: 5% by mass) of PVdF (manufactured by Kureha Corporation, #7300) as a binder were mixed (solids mass ratio: 96:1.8:2.2), and then 0.888 g of NMP was added to achieve a total solids concentration of 58% by mass. This mixture was mixed in a planetary mixer (2,000 rpm, 10 minutes, three times) to prepare a slurry for forming an electrode. This slurry was uniformly spread on aluminum foil (1085, manufactured by UACJ Corporation, substrate thickness: 15 μm) using a doctor blade (wet film thickness: 100 μm), and then dried at 80°C for 30 minutes and then at 120°C for 30 minutes to form an active material layer. This was pressed with a roll press to produce electrode C6 (film thickness 40 μm).

[0112] [Comparative Example 3-2] Ternary cathode active material Li(Ni 0.5 Co 0.2 Mn 0.32.770 g of 2-O2 (NCM523-5Y, manufactured by Beijing Easping Material Technology Co., Ltd.), 0.052 g of acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductive additive, 0.271 g of Solution B3 prepared in Comparative Example 2-1, and 1.28 g of an NMP solution (solids concentration 5% by mass) of PVdF (manufactured by Kureha Corporation, #7300) as a binder were mixed (solids mass ratio 95.5:1.8:0.5:2.2), and 0.635 g of NMP was further added to bring the total solids concentration to 58% by mass. This mixture was mixed in a planetary centrifugal mixer (2,000 rpm, 10 minutes, three times) to prepare a slurry for forming an electrode. This was spread uniformly on aluminum foil (1085, manufactured by UACJ Corporation, substrate thickness 15 μm) using a doctor blade method (wet film thickness 100 μm), and then dried at 80°C for 30 minutes and then at 120°C for 30 minutes to form an active material layer. This was then pressed using a roll press to produce electrode C7 (film thickness 40 μm).

[0113] [Comparative Example 3-3] Ternary cathode active material Li(Ni 0.5 Co 0.2 Mn 0.3 2.770 g of 2-O2 (NCM523-5Y, manufactured by Beijing Easping Material Technology Co., Ltd.), 0.052 g of acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductive additive, 0.115 g of Solution B4 prepared in Comparative Example 2-2, and 1.28 g of an NMP solution (solids concentration 5% by mass) of PVdF (manufactured by Kureha Corporation, #7300) as a binder were mixed (solids mass ratio 95.5:1.8:0.5:2.2), and 0.787 g of NMP was further added to bring the total solids concentration to 58% by mass. This mixture was mixed in a planetary centrifugal mixer (2,000 rpm, 10 minutes, three times) to prepare a slurry for forming an electrode. This was spread uniformly on aluminum foil (1085, manufactured by UACJ Corporation, substrate thickness 15 μm) using a doctor blade method (wet film thickness 100 μm), and then dried at 80°C for 30 minutes and then at 120°C for 30 minutes to form an active material layer. This was then pressed using a roll press to produce electrode C8 (film thickness 41 μm).

[0114] [Comparative Example 3-4] Ternary cathode active material Li(Ni 0.5 Co 0.2 Mn 0.3 2.770 g of 02 (NCM523-5Y, manufactured by Beijing Easping Material Technology Co., Ltd.), 0.052 g of acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductive additive, 0.290 g of an NMP solution (solids concentration 5% by mass) of polyvinylpyrrolidone (K15, manufactured by Tokyo Chemical Industry Co., Ltd., molecular weight 10,000) and 1.28 g of an NMP solution (solids concentration 5% by mass) of PVdF (#7300, manufactured by Kureha Corporation) as a binder were mixed (solids mass ratio 95.5:1.8:0.5:2.2), and 0.612 g of NMP was added to bring the total solids concentration to 58% by mass. This mixture was mixed in a planetary centrifugal mixer (2,000 rpm, 10 min, 3 times) to prepare a slurry for forming an electrode. This was spread uniformly on aluminum foil (1085, manufactured by UACJ Corporation, substrate thickness 15 μm) using a doctor blade method (wet film thickness 100 μm), and then dried at 80°C for 30 minutes and then at 120°C for 30 minutes to form an active material layer. This was then pressed using a roll press to produce electrode C9 (film thickness 44 μm).

[0115] (2) Lithium-ion battery manufacturing [Example 4-1] The electrode C1 produced in Example 3-1 was punched out into a disk shape with a diameter of 10 mm, and after measuring its mass, it was dried in vacuum at 120° C. for 12 hours and transferred to a glove box filled with argon. Six sheets of lithium foil (Honjo Chemical Co., Ltd., 0.17 mm thick) punched to a diameter of 14 mm were placed on the lid of a 2032-type coin cell (Hosen Co., Ltd.) with a washer and spacer welded to the lid. A separator (Celgard Co., Ltd., 2400) punched to a diameter of 16 mm and soaked in electrolyte (Kishida Chemical Co., Ltd., ethylene carbonate:diethyl carbonate = 1:1 (volume ratio), containing 1 mol / L of lithium hexafluorophosphate (LiPF6) electrolyte) for at least 24 hours was placed on top of the foil. Electrode C1 was then placed on top of the separator, with the active material-coated side facing down. After adding a drop of electrolyte, a case and gasket were placed on top, and the coin cell was sealed using a coin cell crimping machine. The cell was then left to stand for 24 hours to prepare a test secondary battery.

[0116] [Examples 4-2 to 4-5] Test secondary batteries were fabricated in the same manner as in Example 4-1, except that electrodes C2 to C5 fabricated in Examples 3-2 to 3-5, respectively, were used instead of electrode C1.

[0117] [Comparative Examples 4-1 to 4-4] Test secondary batteries were fabricated in the same manner as in Example 4-1, except that electrodes C6 to C9 fabricated in Comparative Examples 3-1 to 3-4, respectively, were used instead of electrode C1.

[0118] The lithium ion secondary batteries produced in Examples 4-1 to 4-5 and Comparative Examples 4-1 to 4-4 were evaluated for electrode properties using a charge / discharge measuring device under the following conditions. Table 2 shows the discharge capacity of each secondary battery at discharge rates of 0.2 C and 10 C, as a ratio based on the discharge capacity of Comparative Example 4-1. [Measurement conditions] Rate characteristics: Current: 0.2C constant current charge, 0.2C, 0.5C, 3C, 5C, 10C constant current discharge (Li(Ni 0.5 Co 0.2 Mn 0.3 The O2 capacity was set to 160mAh / g, and the discharge rate was increased every two cycles, and finally the discharge rate was set to 0.5C. Cutoff voltage: 4.20V-3.00V ·Temperature: Room temperature

[0119] [Table 2] *In the table, CA stands for citric acid, EDA stands for ethylenediamine, EEDA stands for N-ethylethylenediamine, AEAE stands for 2-(2-aminoethylamino)ethanol, and AB stands for acetylene black.

[0120] The lithium ion secondary batteries produced in Examples 4-1, 4-4, and 4-5 and Comparative Example 4-1 were evaluated for electrode properties using a charge / discharge measuring device under the following conditions. Table 2 shows the charge capacities of each secondary battery at charge rates of 0.2 C and 10 C, relative to the charge capacity of Comparative Example 4-1. [Measurement conditions] Rate characteristics: Current: 0.2C, 0.5C, 3C, 5C, 10C constant current charging, 0.2C constant current discharging (Li(Ni 0.5 Co 0.2 Mn 0.3 ) The O2 capacity was set to 160mAh / g, and the charge rate was increased every two cycles, and finally the charge rate was set to 0.5C. Cutoff voltage: 4.20V-3.00V ·Temperature: Room temperature

[0121] [Table 3] *In the table, CA stands for citric acid, EDA stands for ethylenediamine, EEDA stands for N-ethylethylenediamine, and AEAE stands for 2-(2-aminoethylamino)ethanol.

[0122] The results in Tables 1 and 2 confirm that the use of battery materials containing the carbon nanostructures defined in the present invention makes it possible to obtain batteries with excellent rate characteristics. It was also confirmed that the effects are present in both charging (input) and discharging (output).

Claims

1. A secondary battery material comprising a carbon nanostructure, an active material, conductive carbon, and a binder, wherein the carbon nanostructure is a non-conductive carbon quantum dot containing nitrogen, the nitrogen being derived from an aliphatic amine, and emitting light when excited by a wavelength of 300 to 800 nm, and the secondary battery material has an absolute quantum yield of 10% or more.

2. 2. The secondary battery material according to claim 1, wherein the carbon nanostructure has an absolute quantum yield of 30% or more.

3. 3. The secondary battery material according to claim 2, wherein the carbon nanostructure has an absolute quantum yield of 50% or more.

4. The nitrogen is ethylenediamine, N,N-dimethylethylenediamine, N,N'-dimethylethylenediamine, N,N-diethylethylenediamine, N,N'-diethylethylenediamine, N-ethylethylenediamine, diethylenetriamine, 1,2-diaminopropane, 1,3-diaminopropane, 2-(2-aminoethylamino)ethanol, N-isopropylethylenediamine, N-isopropyl-1,3-diaminopropane, triethylenetetramine , N,N'-bis(2-hydroxyethyl)ethylenediamine, 2,2-dimethyl-1,3-propanediamine, 2-methyl-2,3-propanediamine, 1,2-diamino-2-methylpropane, 3,3'-diamino-N-methyldipropylamine, 2,3-dimethyl-2,3-butanediamine, 3,3'-diaminodipropylamine, N,N-bis(2-aminoethyl)-1,3-propanediamine, triethylenetetramine, 2,2'-oxybis(ethoxy) amine), tetramethylenediamine, 1,4-diaminobutane, 2,2'-thiobis(ethylamine), 1,5-diaminopentane, 2-methyl-1,5-diaminopentane, 1,6-diaminoheptane, 1,7-diaminopentane, 1,10-diaminodecane, 1,11-diaminoundecane, 1,12-diaminododecane, N,N'-bis(3-aminopropyl)ethylenediamine, diethylene glycol bis(3-aminopropyl)ether, 1,14 4. The secondary battery material according to claim 1, which is derived from at least one diamine selected from the group consisting of 1,2-diamino-3,6,9,12-tetraoxatetradecane, bis(aminomethyl)cyclohexane, 1,2-cyclohexanediamine, 1,3-cyclohexanediamine, 1,4-cyclohexanediamine, bis(aminomethyl)norbornane, 1,4-bis(aminomethyl)cyclohexane, and 1,2-bis(2-aminoethoxy)ethane.

5. 5. The secondary battery material according to claim 1, wherein the carbon contained in the carbon nanostructure is derived from a polycarboxylic acid or a sugar.

6. 6. The secondary battery material according to claim 1, wherein the active material is selected from the group consisting of metals, semi-metals, metal alloys, metal oxides, semi-metal oxides, metal phosphates, metal sulfides, and metal nitrides.

7. The active material is FeS 2 , TiS 2 , MoS 2 , LiFePO 4 , V 2 O 6 , V 6 O 13 , MnO 2 , LiCoO 2 , LiMnO 2 , LiMn 2 O 4 , LiMo 2 O 4 , LiV 3 O 8 , LiNiO 2 , Li z Ni y M 1-y O 2 (wherein M represents at least one metal element selected from Co, Mn, Ti, Cr, V, Al, Sn, Pb, and Zn, and 0.05≦z≦1.10, 0.5≦y≦1.0), Li (Ni a Co b Mn c ) O 2 (where 0<a<1, 0<b<1, 0<c<1, a+b+c=1), Li 4 Ti 5 O 12 , Si, SiO x , AlO x , SnO x , SbO x , Bio x , GeO x , AsO x , PbO x , ZnO x , CdO x , InO x , TiO x and GaO x 7. The secondary battery material according to claim 6, wherein x is at least one selected from the group consisting of 0<x≦2.

8. 8. The secondary battery material according to claim 1, wherein the amount of the carbon nanostructure is 0.01 to 1.0 mass % of the solid content.

9. The secondary battery material according to any one of claims 1 to 8, which is used for forming an electrode.

10. An electrode having an active material layer made of the secondary battery material according to claim 9.

11. A secondary battery comprising the electrode according to claim 10.

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