Carbonaceous material suitable for the negative electrode active material of an energy storage device, negative electrode for an energy storage device, energy storage device

Abstract

The present invention provides a carbonaceous material which is suitable for a negative electrode active material of a power storage device (such as a lithium-ion secondary battery, sodium-ion secondary battery, lithium sulfur battery, lithium air battery, all solid state battery, or capacitor) having high discharge capacity and high cycle durability. The present invention also provides a negative electrode which contains the carbonaceous material and a power storage device which includes the negative electrode.　Disclosed is a carbonaceous material in which the nitrogen content obtained by element analysis is 1.0-4.0 mass%, the oxygen content obtained by element analysis is 1.1-2.1 mass%, and a carbon face spacing (d002) observed by X-ray diffraction measurement is not less than 3.70 Å.

Description

Technical Field

[0001] This patent application claims priority under the Paris Convention with respect to Japanese Patent Application No. 2020-154229 (filing date: September 15, 2020), and the entire content thereof is hereby incorporated herein by reference in its entirety. The present invention relates to a carbonaceous material suitable for a negative electrode active material of a power storage device, a negative electrode for a power storage device including the carbonaceous material, and a power storage device having the negative electrode.

Background Art

[0002] Non-aqueous electrolyte secondary batteries such as lithium-ion secondary batteries are widely used in small portable devices such as mobile phones and notebook computers because they have a high energy density and excellent output characteristics. As a negative electrode material for lithium-ion secondary batteries, nitrogen-containing graphitizable carbon capable of doping (charging) and de-doping (discharging) an amount of lithium exceeding the theoretical capacity of graphite of 372 mAh / g has been disclosed (for example, Patent Document 1, Patent Document 2, Patent Document 3).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0004] In recent years, with the consideration of applying lithium-ion secondary batteries to in-vehicle applications and the like, in addition to the above high-capacity characteristics, there is also an emerging demand for cycle durability. For example, in-vehicle lithium-ion secondary batteries are large and expensive, making it difficult to replace them during use. Therefore, at least the same level of durability as that of automobiles is required for lithium-ion secondary batteries, and in particular, high cycle durability is required, where the discharge capacity does not easily decrease even when charge and discharge are repeated.

[0005] On the other hand, the nitrogen element contained in the carbon materials described in Patent Documents 1 to 3 can serve as a lithium-ion storage site and improve the discharge capacity, but it can also become a reaction point with lithium ions, so there is a possibility that cycle durability cannot be ensured, and it has been difficult to achieve both high discharge capacity and high cycle durability.

[0006] Therefore, an object of the present invention is to provide a carbonaceous material suitable for a negative electrode active material of an electricity storage device (for example, a lithium-ion secondary battery, a sodium-ion secondary battery, a lithium-sulfur battery, a lithium-air battery, a all-solid-state battery, a capacitor, etc.) having a high discharge capacity and high cycle durability, a negative electrode for an electricity storage device containing the carbonaceous material, and an electricity storage device having the negative electrode.

Means for Solving the Problems

[0007] As a result of intensive studies by the present inventors, it has been found that the above problems can be solved by using a negative electrode made of a specific carbonaceous material, leading to the present invention. That is, the present invention includes the following preferred embodiments. 〔1〕A carbonaceous material having a nitrogen element content of 1.0 mass% or more and 4.0 mass% or less, an oxygen element content of 1.1 mass% or more and 2.1 mass% or less, determined by elemental analysis, and a carbon interplanar spacing (d 002 ) of 3.70 Å or more observed by X-ray diffraction measurement. 〔2〕The carbonaceous material according to the above 〔1〕, having an oxygen element content of 1.2 mass% or more and 2.0 mass% or less determined by elemental analysis. [(3)] The carbonaceous material according to the above (1) or (2), wherein the ratio (R O / N ) of the oxygen content to the nitrogen content determined by elemental analysis is 0.30 or more and 1.0 or less. [(4)] The carbonaceous material according to any one of the above (1) to (3), wherein the value of the full width at half maximum of the peak near 1360 cm -1 in the Raman spectrum observed by laser Raman spectroscopy is 250 cm -1 or more. [(5)] The carbonaceous material according to any one of the above (1) to (4), wherein the value of the full width at half maximum of the peak near 1650 cm -1 in the Raman spectrum observed by laser Raman spectroscopy is 98 cm -1 or more. [(6)] The carbonaceous material according to any one of the above (1) to (5), wherein the average particle diameter D 50 is 30 μm or less. [(7)] The carbonaceous material according to any one of the above (1) to (6), wherein the carbonaceous material is derived from saccharides. [(8)] The carbonaceous material according to any one of the above (1) to (7), which is used as a negative electrode active material of an electric storage device. [(9)] A negative electrode for an electric storage device containing the carbonaceous material according to the above (8). [(10)] An electric storage device having the negative electrode for an electric storage device according to the above (9). [Advantages of the Invention]

[0008] An electric storage device using the negative electrode containing the carbonaceous material of the present invention has a high discharge capacity and high cycle durability. Here, the cycle durability in this specification refers to the capacity retention rate (cycle capacity retention rate) when the battery is repeatedly charged and discharged and used. [Modes for Carrying Out the Invention]

[0009] Hereinafter, embodiments of the present invention will be described in detail. The scope of the present invention is not limited to the embodiments described here, and various modifications can be made without departing from the spirit of the present invention. In the following description, an example applied to a lithium-ion battery as an electric storage device will be used for explanation.

[0010] In the carbonaceous material of the present invention, the nitrogen element content determined by elemental analysis is 1.0% by mass or more. When the nitrogen element content in the carbonaceous material is less than 1.0% by mass, the number of sites for adsorbing and desorbing lithium ions during charge and discharge decreases, and the discharge capacity tends to decrease. In order to obtain such a high discharge capacity, the nitrogen element content in the carbonaceous material of the present invention needs to be 1.0% by mass or more, preferably 1.5% by mass or more, more preferably 1.75% by mass or more, and still more preferably 2.0% by mass or more.

[0011] Further, in the carbonaceous material of the present invention, the nitrogen element content determined by elemental analysis is 4.0% by mass or less. When the nitrogen element content in the carbonaceous material is more than 4.0% by mass, the charge-discharge efficiency decreases. This is presumably because nitrogen that has not been incorporated into the carbon skeleton exists as a surface functional group such as an —NH2 group, and when the abundance of such surface functional groups increases, irreversible side reactions that can occur during charge and discharge cannot be suppressed. In addition to this, it has been found that when the nitrogen element content in the carbonaceous material is 4.0% by mass or less, surprisingly, the discharge capacity hardly decreases even when charge and discharge are repeated, that is, there is a tendency to obtain high cycle durability. The reason for this is not clear, but the following reasons are conceivable. That is, when the carbonaceous material contains a large amount of nitrogen element, a decrease in discharge capacity due to irreversible side reactions occurring during repeated charge and discharge, a decrease in discharge capacity due to expansion and contraction of the electrode during charge and discharge, and a decrease in discharge capacity due to structural changes around the nitrogen element that becomes particularly distorted in the carbonaceous material during repeated charge and discharge are considered to occur in combination. It is considered that the factors deteriorating the cycle durability are eliminated by the nitrogen element content being 4.0% by mass or less. In order to obtain such high cycle durability, the nitrogen element content in the carbonaceous material needs to be 4.0 mass% or less, in certain embodiments 3.8 mass% or less, preferably 3.5 mass% or less, more preferably 3.3 mass% or less, and even more preferably 3.0 mass% or less.

[0012] Note that the details of the measurement of the nitrogen element content are as described below and are measured by an elemental analysis method (inert gas fusion method). The method for adjusting the nitrogen element content to the above range is not limited at all, but if the inert gas flow rate is made too large or the heating rate is made too small, the nitrogen element in the carbonaceous material is likely to desorb, and the amount of nitrogen element in the obtained carbonaceous material will decrease. Therefore, it is advisable to adjust the inert gas flow rate, the heating rate, and the heat treatment temperature.

[0013] In the carbonaceous material of the present invention, the oxygen element content determined by elemental analysis is 1.1 mass% or more and 2.1 mass% or less. The oxygen element in the carbonaceous material, like the nitrogen element, becomes a site for adsorbing and desorbing lithium ions during charge and discharge. Therefore, when the oxygen element content is large, the discharge capacity tends to increase. For this reason, the oxygen element content determined by elemental analysis needs to be 1.0 mass% or more, in certain embodiments 1.1 mass% or more, preferably 1.2 mass% or more, more preferably 1.4 mass% or more, even more preferably 1.5 mass% or more (1.5 mass% or more than 1.5 mass%), and still more preferably 1.6 mass% or more. On the other hand, when the oxygen element content is large, like the above-mentioned nitrogen element, it may cause deterioration of cycle durability. For this reason, in the carbonaceous material of the present invention, the oxygen element content is 2.0 mass% or less in certain embodiments, preferably 1.9 mass% or less, and even more preferably 1.8 mass% or less. The details of the measurement of the oxygen element content are as described in the examples and are measured by the elemental analysis method (inert gas fusion method) described below.

[0014] In the carbonaceous material of the present invention, in order to obtain high discharge capacity and high cycle durability, the ratio R of the nitrogen element content to the hydrogen element content N / H(Nitrogen element content / Hydrogen element content) is preferably 6 or more and 37 or less, more preferably 8 or more and 25 or less, still more preferably 10 or more and 20 or less, and even more preferably 12 or more and 15 or less. Further, in the carbonaceous material of the present invention, in order to obtain a high discharge capacity and high cycle durability, the ratio R of the oxygen element content to the nitrogen element content O / N (Oxygen element content / Nitrogen element content) is preferably 0.30 or more and 1.0 or less. This is considered to be due to the following reasons. That is, when both the oxygen element content and the nitrogen element content are increased, the discharge capacity increases while the cycle durability deteriorates. Also, if either the oxygen element content or the nitrogen element content is too much or too little, the oxygen and nitrogen present as surface functional groups such as —OH groups and —NH2 groups in the carbon structure increase, resulting in a decrease in discharge capacity and a decrease in cycle durability. In order to obtain a high discharge capacity and high cycle durability, the lower limit of R O / N is preferably 0.30 or more, more preferably 0.35 or more, and still more preferably 0.40 or more. Also, the upper limit of R O / N is preferably 1.0 or less, more preferably 0.90 or less, and still more preferably 0.80 or less. The ratio R of the nitrogen element content to the hydrogen element content N / H is calculated from the nitrogen element content and the hydrogen element content measured as described above by the formula R N / H = Nitrogen element content / Hydrogen element content, and the ratio R of the oxygen element content to the nitrogen element content O / N is calculated from the oxygen element content and the nitrogen element content measured as described above by the formula R O / N = Oxygen element content / Nitrogen element content.

[0015] In the carbonaceous material of the present invention, from the viewpoint that the smaller the content of hydrogen element in the carbonaceous material, the fewer the edge portions of carbon, the wider the carbon plane, and the easier the electron movement, it is preferable. From this viewpoint, the content of hydrogen element determined by elemental analysis in the carbonaceous material is preferably 0.50% by mass or less, more preferably 0.40% by mass or less, and even more preferably 0.35% by mass or less. Further, the larger the content of hydrogen element in the carbonaceous material, the easier the adsorption and desorption of lithium ions, which is preferable. From this viewpoint, the content of hydrogen element in the carbonaceous material is preferably 0.10% by mass or more, more preferably 0.15% by mass or more. The details of the measurement of the hydrogen element content are as described later and are measured by an elemental analysis method (inert gas fusion method).

[0016] In the carbonaceous material of the present invention, the carbon interlayer spacing (d 002 ) calculated by Bragg's equation from the peak position (diffraction angle 2θ) observed by powder X-ray diffraction method 002 is 3.70 Å or more. d 002 is about 3.35 to 3.40 Å when the carbon planes are closest, such as in the case of graphite. However, when d 002 is larger than that in the case of graphite, lithium ions can move efficiently, and high discharge capacity can be obtained by forming micropores that can occlude a large amount of clustered lithium. From this viewpoint, it is necessary that d 002 is 3.70 Å or more, preferably 3.74 Å or more, and more preferably 3.76 Å or more. On the other hand, if d 002 is too large, the volume of the carbonaceous material may increase, and the specific capacity per volume may decrease. From this viewpoint, it is preferable that d

[0017] In the carbonaceous material of the present invention, the value of the full width at half maximum of the peak near 1360 cm -1 in the Raman spectrum observed by laser Raman spectroscopy is preferably 250 cm -1 or more. Here, 1360 cm -1The nearby peak is a Raman peak generally referred to as the D band, which is a peak caused by the disorder and defects of the graphite structure. 1360 cm -1 The peak near is usually 1345 cm -1 ~1375 cm -1 , preferably 1350 cm -1 ~1370 cm -1 is observed in the range of. The full width at half maximum (FWHM) of the peak of the D band is related to the amount of disorder and defects of the graphite structure contained in the carbonaceous material. Such structural disorder can be caused by the introduction of nitrogen elements into the carbon skeleton. When the FWHM of the Raman peak in the D band is less than 250 cm -1 , the structural development progresses too much, and due to the development of the graphite structure, lithium ions tend to be unable to efficiently enter and exit. Therefore, from the perspective of facilitating resistance reduction, the FWHM of the peak near 1360 cm -1 is preferably 250 cm -1 or more, more preferably 260 c m -1 or more, still more preferably 270 cm -1 or more. Also, when the FWHM is greater than 300 cm -1 , it becomes difficult to maintain the graphite structure contained in the carbonaceous material, the amount of amorphous increases, and the sites capable of occluding lithium tend to decrease. Therefore, the amount of lithium ions occluded decreases, and the discharge capacity may decrease. From such a perspective, the FWHM of the peak near 1360 cm -1 is preferably 300 cm -1 or less.

[0018] Also, in the carbonaceous material of the present invention, the value of the FWHM of the peak near 1650 cm -1 in the Raman spectrum observed by laser Raman spectroscopy is preferably 98 cm -1 or more. Here, the peak near 1650 cm -1 is a Raman peak generally referred to as the G band, which is a peak caused by the graphite structure. When the FWHM of the Raman peak in the G band is 98 cm -1If it is in the range less than, the structural development progresses too much, and due to the development of the graphite structure, lithium ions cannot efficiently enter and exit, and the resistance tends to increase. Therefore, from the viewpoint of making it easy to reduce the resistance, the half-value width of the peak near 1650 cm -1 is preferably 98 cm -1 or more, more preferably 100 cm -1 or more, and still more preferably 102 cm -1 or more. Also, there is no particular limitation on the upper limit of the half-value width of the peak near 1650 cm -1 , but it is usually 115 cm -1 or less, preferably 110 cm -1 or less, and more preferably 107 cm -1 or less.

[0019] The measurement of the Raman spectrum is performed using a Raman spectrometer (for example, Raman spectrometer "LabRAM ARAMIS (VIS)" manufactured by Horiba, Ltd.). Specifically, for example, the measurement target particles are set on the observation stage, the magnification of the objective lens is set to 100 times, the focus is adjusted, and while irradiating the measurement cell with 532 nm argon ion laser light, the exposure time is 1 second, the integration number is 100 times, and the measurement range is 50 - 2000 cm -1 is measured.

[0020] The average particle diameter D 50 of the carbonaceous material of the present invention is 30 μm or less, which not only improves the coatability during electrode fabrication, but also reduces the diffusion free path of lithium ions within the particles of the carbonaceous material, making rapid charge and discharge easier to obtain, which is preferable. Furthermore, in a lithium ion secondary battery, it is important to increase the electrode area in order to improve the input / output characteristics. For this purpose, it is necessary to reduce the coating thickness of the active material on the current collector during electrode preparation. From these viewpoints, the average particle diameter D 50The smaller it is, the more preferable it is, preferably 30 μm or less, more preferably 25 μm or less, even more preferably 20 μm or less, particularly preferably 18 μm or less, and most preferably 15 μm or less. When the average particle diameter of the carbonaceous material serving as the active material is equal to or less than the above upper limit, it is easy to reduce the coating thickness during electrode preparation. Further, the average particle diameter D of the carbonaceous material of the present invention 50 is 2 μm or more, which suppresses an increase in specific surface area due to fine powder in the carbonaceous material and an increase in reactivity with the electrolytic solution, and makes it easy to suppress an increase in irreversible capacity, which is preferable. Further, when manufacturing a negative electrode using the carbonaceous material, it is easy to secure voids formed between the carbonaceous materials, it is difficult to suppress the movement of lithium ions in the electrolytic solution, and it is easy to reduce the resistance of the power storage device. From these viewpoints, the average particle diameter D 50 is preferably 2 μm or more, more preferably 3 μm or more, even more preferably 4 μm or more, and particularly preferably 5 μm or more. The average particle diameter D 50 is the particle diameter at which the cumulative volume becomes 50%, and can be obtained, for example, by measuring the particle size distribution by the laser scattering method using a particle diameter and particle size distribution measuring device (「Microtrac MT3300EXII」 manufactured by Microtrac Bell Corporation).

[0021] The carbonaceous material of the present invention (1) A step of mixing a raw material with a nitrogen-containing compound (hereinafter, also referred to as a "nitrogen-containing compound"), (2) A step of heating the obtained mixture to a first predetermined temperature between 500 and 1200 °C at a heating rate of 100 °C / hour or more in an inert gas atmosphere, (3) A step of performing heat treatment at a temperature of 500 to 1200 °C, preferably the first predetermined temperature, preferably in an inert gas atmosphere to obtain a carbide, and (4) A step of heating the obtained carbide to a second predetermined temperature between the first predetermined temperature and 1400 °C at a heating rate of 100 °C / hour or more in an inert gas atmosphere, and (5) A step of performing heat treatment with an inert gas at a temperature of 800 to 1400 °C, preferably the second predetermined temperature It can be produced by a method including the following. In this specification, the above step (2) and / or (3) may be referred to as a low-temperature firing (step), and the above step (4) and / or (5) may be referred to as a high-temperature firing (step), respectively. The carbonaceous material can be obtained by a normal method, such as pulverizing a carbide with a ball mill or a jet mill, etc. The pulverization may be performed after step (3) and / or after step (5).

[0022] There is no limitation on the raw material of the carbonaceous material of the present invention, and known carbon raw materials with poor graphitization properties such as petroleum pitch, coal pitch, and coconut shells can be applied. However, as a raw material that easily obtains the carbonaceous material of the present invention having the above characteristics and is easy to modify the structure such as a cross-linked structure, it is preferable to apply saccharides. By using saccharides as a raw material, a carbonaceous material derived from saccharides, more specifically, a substance having a saccharide skeleton can be obtained.

[0023] When saccharides are used as a raw material, there is no particular limitation on their type. For example, monosaccharides such as glucose, galactose, mannose, fructose, ribose, and glucosamine, disaccharides such as sucrose, trehalose, maltose, cellobiose, maltitol, lactobionic acid, and lactosamine, and polysaccharides such as starch, glycogen, agarose, pectin, cellulose, chitin, and chitosan can be exemplified. These saccharides can be used alone or in combination of two or more. Among these saccharides, starch is preferable because it is easily available in large quantities. By using such saccharides as a raw material, a carbonaceous material derived from saccharides can be obtained.

[0024] The nitrogen-containing compound is not particularly limited. For example, inorganic ammonium salts such as ammonium chloride, ammonium sulfate, ammonium carbonate, and ammonium nitrate, organic ammonium salts such as ammonium formate, ammonium acetate, ammonium oxalate, and diammonium hydrogen citrate, aromatic amine hydrochlorides such as aniline hydrochloride and aminonaphthalene hydrochloride, and nitrogen-containing organic compounds such as melamine, pyrimidine, pyridine, pyrrole, imidazole, indole, and urea can be exemplified. Among these nitrogen-containing compounds, melamine and urea with a high nitrogen content in the molecule are preferred from the viewpoint that the nitrogen element is easily incorporated into the carbonaceous material.

[0025] In addition to the above nitrogen-containing compound, an acid catalyst may be added. The acid catalyst to be added is not particularly limited, and for example, an organic acid can be mentioned. The organic acid is not particularly limited, and for example, aliphatic carboxylic acids such as formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, undecanoic acid, palmitic acid, stearic acid, succinic acid, linoleic acid, oleic acid, and adipic acid; aromatic carboxylic acids such as benzoic acid, salicylic acid, phthalic acid, and terephthalic acid; hydroxycarboxylic acids such as lactic acid, tartaric acid, citric acid, and malic acid; carboxylic acids such as ethylenediaminetetraacetic acid, and sulfonic acids such as p-toluenesulfonic acid and methanesulfonic acid can be mentioned. By adding an acid catalyst, the reaction between the saccharide and the nitrogen-containing compound is promoted, and a carbonaceous material with a large nitrogen content tends to be obtained.

[0026] The mixing method of the raw material and the nitrogen-containing compound, or the raw material, the nitrogen-containing compound, and the acid catalyst is not particularly limited, but dry or wet mixing can be used.

[0027] In the case of dry mixing, these mixtures can be obtained by adding a nitrogen-containing compound, or a nitrogen-containing compound and an acid catalyst, to the raw materials. In this case, from the viewpoint of uniformly mixing the nitrogen-containing compound, or the nitrogen-containing compound and the acid catalyst, with the raw materials, for example, it is preferable to grind the nitrogen-containing compound, or the nitrogen-containing compound and the acid catalyst, and the raw materials in a mortar or to make them powdery by pulverizing them with a ball mill while mixing.

[0028] In the case of wet mixing, for example, the raw material can be dissolved in a solvent to prepare a solution, and then the nitrogen-containing compound, or the nitrogen-containing compound and an acid catalyst, can be added to this solution for mixing. Further, the solution may be mixed by spraying (such as spray spraying) it onto the nitrogen-containing compound. Also, mixing may be carried out by adding the raw material to a solution prepared by dissolving the nitrogen-containing compound, or the nitrogen-containing compound and an acid catalyst, in a solvent. After mixing, the solvent may be evaporated if necessary. By such treatment, a mixture of the raw material and the nitrogen-containing compound, or the nitrogen-containing compound and an acid catalyst, can be obtained. The solvent to be used is not particularly limited, and examples thereof include water, alcohol solvents (ethanol, methanol, ethylene glycol, isopropyl alcohol, etc.), ester solvents (ethyl acetate, butyl acetate, ethyl lactate, etc.), ether solvents (tetrahydrofuran, dimethoxyethane, 1,4-dioxane, etc.), ketone solvents (acetone, 2-butanone, cyclopentanone, cyclohexanone, etc.), aliphatic hydrocarbon solvents (pentane, hexane, heptane, etc.), aromatic hydrocarbon solvents (toluene, xylene, mesitylene, etc.), nitrile solvents (acetonitrile, etc.), and chlorinated hydrocarbon solvents (dichloromethane, chloroform, chlorobenzene, etc.), as well as mixtures thereof. In order to uniformly mix the raw material and the nitrogen-containing compound, or the raw material and the nitrogen-containing compound and an acid catalyst, it is effective that both are easily soluble in the solvent. Therefore, water, alcohol solvents, and mixtures thereof are preferred as the solvent. The method for evaporating the solvent is not particularly limited, and examples thereof include heat treatment and reduced-pressure treatment, as well as methods combining these. The temperature of the heat treatment may be a temperature at which thermal decomposition of the nitrogen-containing compound hardly occurs, or a temperature at which thermal decomposition of the saccharide hardly occurs, and it varies depending on the type of the solvent, but is preferably 40 to 150 °C, more preferably 50 to 120 °C, and even more preferably 60 to 100 °C.

[0029] The nitrogen content of the nitrogen-containing compound to be mixed with the raw material is preferably 0.1 molar equivalent or more, more preferably 0.2 molar equivalent or more, still more preferably 0.3 molar equivalent or more, and preferably 2.0 molar equivalents or less, more preferably 1.0 molar equivalent or less, still more preferably 0.8 molar equivalent or less, based on the mass of the resulting mixture. When the amount of the nitrogen-containing compound to be mixed is equal to or greater than the above lower limit, nitrogen element is efficiently incorporated into the resulting carbonaceous material, which is preferable. When the amount of the nitrogen-containing compound to be mixed is equal to or less than the above upper limit, excessive incorporation of nitrogen element can be suppressed, and excessive disruption of the carbon structure does not occur. Therefore, a power storage device including the resulting carbonaceous material exhibits a high discharge capacity and is more likely to exhibit high cycle durability.

[0030] In the production method of the present invention, the mixture obtained from step (1) in which the raw material is mixed with a nitrogen-containing compound or a nitrogen-containing compound and an acid catalyst is heated to perform a first firing, and further, a second firing is performed on the obtained carbide. In the first firing, preferably, the mixture obtained from step (1) is heated, and heat treatment is performed at a temperature between 500 and 1200 °C, preferably 600 and 1150 °C, more preferably 700 and 1100 °C, still more preferably 800 and 1100 °C, preferably at the first predetermined temperature described below, in an inert gas, preferably in an inert gas atmosphere, to obtain a carbide [step (3)]. Examples of the inert gas include nitrogen gas. The temperature at which the heat treatment is performed with the inert gas is preferably the first predetermined temperature described below, but is not particularly limited as long as it is within the above range. Also, the temperature at which the heat treatment is performed with the inert gas may be a constant temperature, but is not particularly limited as long as it is within the above range.

[0031] At this time, the mixture obtained from step (1) in which the raw material is mixed with a nitrogen-containing compound or a nitrogen-containing compound and an acid catalyst is preferably heated in an inert gas atmosphere such as nitrogen gas at a heating rate of 100 °C / hour or more, preferably 100 to 600 °C / hour, to a first predetermined temperature between 500 and 1200 °C, preferably 600 to 1150 °C, more preferably 700 to 1130 °C, still more preferably 800 to 1100 °C [step (2)]. The heating in step (2) is carried out in an inert gas atmosphere, but heat treatment may be carried out under an inert gas supply.

[0032] In the production method of the present invention, next, the carbide obtained by the first firing is subjected to a second firing. In the second firing, preferably, the carbide obtained from step (3) is heated, and heat treatment is carried out at a temperature between 800 and 1400 °C, preferably 1050 to 1380 °C, more preferably 1100 to 1370 °C, still more preferably 1150 to 1360 °C, particularly preferably 1200 to 1350 °C, preferably at a second predetermined temperature described below, in an inert gas such as nitrogen gas, preferably in an inert gas atmosphere [step (5)]. The temperature at which heat treatment is carried out with an inert gas is preferably the second predetermined temperature described below, but is not particularly limited as long as it is within the above range. Also, the temperature at which heat treatment is carried out with an inert gas may be a constant temperature, but is not particularly limited as long as it is within the above range.

[0033] At this time, volatile organic substances may be added to the carbide obtained from step (3) and subjected to step (4). Volatile organic substances refer to organic compounds that hardly (e.g., 80% or more, preferably 90% or more) carbonize and volatilize (vaporize or thermally decompose into gas) when heat-treated with an inert gas such as nitrogen (e.g., at 500°C or higher). Although not particularly limited, examples of volatile organic substances include thermoplastic resins and low-molecular-weight organic compounds. Specifically, examples of thermoplastic resins include polystyrene, polyethylene, polypropylene, poly(meth)acrylic acid, poly(meth)acrylate esters, etc. In this specification, (meth)acrylic refers to the general term for methacrylic and acrylic. Examples of low-molecular-weight organic compounds include toluene, xylene, mesitylene, styrene, naphthalene, phenanthrene, anthracene, pyrene, etc. Since it is preferable that the surface of the carbon precursor is not oxidized and activated when volatilized and thermally decomposed at the firing temperature, polystyrene, polyethylene, and polypropylene are preferable as thermoplastic resins. From the viewpoint of safety, it is preferable that low-molecular-weight organic compounds have low volatility at room temperature (e.g., 20°C), and naphthalene, phenanthrene, anthracene, pyrene, etc. are preferable. Adding such volatile organic substances is preferable in that the specific surface area can be made smaller while maintaining the characteristic structure of the carbonaceous material of the present invention.

[0034] At this time, the carbide obtained from step (3) is preferably heated in an inert gas atmosphere such as nitrogen gas at a heating rate of 100°C / hour or more, preferably 100 to 600°C / hour, to a second predetermined temperature in the range of the first predetermined temperature to 1400°C [step (4)]. The heating in step (4) is carried out in an inert gas atmosphere, but heat treatment may be performed under the supply of an inert gas.

[0035] The second firing is usually carried out at a temperature equal to or higher than the temperature of the first firing, preferably at a temperature higher than the temperature of the first firing. Therefore, in this specification, the first firing and the second firing may be referred to as low-temperature firing and high-temperature firing, respectively. The temperature of the second firing, that is, the second predetermined temperature in step (4), is preferably a temperature equal to or higher than the temperature of the first firing, that is, the first predetermined temperature in step (2), in terms of obtaining a carbonaceous material that gives a high discharge capacity and charge-discharge efficiency when used for an electrode. The second predetermined temperature is more preferably a temperature 50 to 700 °C higher than the first predetermined temperature, still more preferably a temperature 100 to 500 °C higher than the first predetermined temperature, even more preferably a temperature 150 to 400 °C higher than the first predetermined temperature, and particularly preferably a temperature 200 to 300 °C higher than the first predetermined temperature. Further, the second predetermined temperature is preferably 1400 °C or lower, more preferably 1380 °C or lower, still more preferably 1360 °C or lower, and particularly preferably 1350 °C or lower.

[0036] The carbonaceous material of the present invention can be suitably used as a negative electrode active material of an electric storage device. The present invention also provides a negative electrode for an electric storage device including the carbonaceous material of the present invention.

[0037] Hereinafter, a method for manufacturing a negative electrode for an electric storage device of the present invention will be specifically described. The negative electrode of the present invention can be manufactured by adding a binder to the carbonaceous material of the present invention, adding an appropriate amount of an appropriate solvent and kneading to obtain an electrode mixture, applying the electrode mixture to a current collector made of a metal plate or the like, drying, and then performing pressure molding.

[0038] Further, for the purpose of reducing the irreversible capacity of the obtained negative electrode, lithium pre-doping can also be performed by a known method.

[0039] By using the carbonaceous material of the present invention, it is possible to manufacture an electrode (negative electrode) having high conductivity without adding a conductive assistant. However, for the purpose of imparting even higher conductivity, a conductive assistant can be added as necessary during the preparation of the electrode mixture. As the conductive assistant, conductive carbon black, vapor-grown carbon fiber (VGCF), nanotubes, etc. can be used. The addition amount of the conductive assistant varies depending on the type of conductive assistant used. However, if the added amount is too small, the expected conductivity may not be obtained, and if it is too large, the dispersion in the electrode mixture may deteriorate. From such a viewpoint, the preferable ratio of the conductive assistant to be added is 0.5 to 10% by mass (where the amount of the active material (carbonaceous material) + the amount of the binder + the amount of the conductive assistant = 100% by mass), more preferably 0.5 to 7% by mass, and particularly preferably 0.5 to 5% by mass. As the binder, those that do not react with the electrolyte, such as PVDF (polyvinylidene fluoride), polytetrafluoroethylene, and a mixture of SBR (styrene-butadiene rubber) and CMC (carboxymethyl cellulose), are not particularly limited. Among them, PVDF is preferable because the PVDF adhering to the surface of the active material rarely inhibits lithium ion movement and good input / output characteristics can be obtained. To dissolve PVDF and form a slurry, a polar solvent such as N-methylpyrrolidone (NMP) is preferably used, but an aqueous emulsion such as SBR or CMC dissolved in water can also be used. If the addition amount of the binder is too large, the resistance of the obtained electrode becomes large, so the internal resistance of the battery may increase and the battery characteristics may deteriorate. Also, if the addition amount of the binder is too small, the bonding between the particles of the negative electrode material and the current collector may become insufficient. The preferable addition amount of the binder varies depending on the type of binder used. For example, in the case of a PVDF-based binder, it is preferably 3 to 13% by mass, more preferably 3 to 10% by mass. On the other hand, in the case of a binder that uses water as the solvent, a plurality of binders such as a mixture of SBR and CMC are often used in combination, and the total amount of all binders used is preferably 0.5 to 5% by mass, more preferably 1 to 4% by mass. Further, the carbonaceous material of the present invention in the electrode mixture is preferably 80% by mass or more, more preferably 90% by mass or more. Further, the content of the carbonaceous material of the present invention in the electrode mixture is preferably 100% by mass or less, more preferably 97% by mass or less.

[0040] The electrode active material layer is basically formed on both sides of the current collector, but may be formed on one side if necessary. The thicker the electrode active material layer, the more preferable it is for increasing the capacity. However, since a wider electrode area facing the counter electrode is advantageous for improving the input / output characteristics, if the electrode active material layer is too thick, the input / output characteristics may deteriorate. From the viewpoint of achieving both high capacity and good input / output characteristics, the thickness of the active material layer (per side) is preferably 10 to 80 μm, more preferably 20 to 75 μm, and even more preferably 30 to 75 μm.

[0041] The power storage device of the present invention includes the negative electrode for a power storage device of the present invention. A power storage device having a negative electrode for a power storage device containing the carbonaceous material of the present invention has a high discharge capacity and high cycle durability.

[0042] When forming a negative electrode for a power storage device using the carbonaceous material of the present invention, other materials constituting the battery such as the positive electrode material, separator, and electrolyte are not particularly limited, and various materials conventionally used or proposed as non-aqueous solvent secondary batteries can be used.

[0043] For example, as the positive electrode material, layered oxide-based (represented by LiMO2, where M is a metal: for example, LiCoO2, LiNiO2, LiMnO2, or LiNi x Co y Mo z O2 (where x, y, and z represent the composition ratio)), olivine-based (represented by LiMPO4, where M is a metal: for example, LiFePO4, etc.), spinel-based (represented by LiM2O4, where M is a metal: for example, LiMn2O4, etc.) composite metal chalcogen compounds are preferred, and these chalcogen compounds may be mixed and used as necessary. These positive electrode materials are molded together with a suitable binder and a carbon material for imparting conductivity to the electrode, and a positive electrode is formed by forming a layer on a conductive current collector.

[0044] The non-aqueous solvent type electrolyte used in combination with these positive and negative electrodes is generally formed by dissolving an electrolyte in a non-aqueous solvent. As the non-aqueous solvent, for example, organic solvents such as propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, dimethoxyethane, diethoxyethane, γ-butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, sulfolane, or 1,3-dioxolane can be used alone or in combination of two or more. As the electrolyte, LiClO4, LiPF6, LiBF4, LiCF3SO3, LiAsF6, LiCl, LiBr, LiB(C6H5)4, or LiN(SO3CF3)2, etc. are used.

[0045] The power storage device is generally formed by opposing the positive and negative electrodes formed as described above through a liquid-permeable separator as needed and immersing them in the electrolyte. As such a separator, a permeable or liquid-permeable separator made of a non-woven fabric or other porous material commonly used in secondary batteries can be used. Alternatively, instead of the separator or together with the separator, a solid electrolyte made of a polymer gel impregnated with the electrolyte can also be used.

[0046] The carbonaceous material of the present invention is suitable as a carbonaceous material for a battery (typically a power storage device for vehicle driving) mounted on a vehicle such as an automobile. In the present invention, the vehicle can generally be targeted without particular limitation, such as those known as electric vehicles, hybrid vehicles with a fuel cell or internal combustion engine, etc., but at least includes a power supply device equipped with the above battery, an electric drive mechanism driven by power supply from the power supply device, and a control device for controlling this. The vehicle may further be equipped with a regenerative brake or a regenerative brake, and a mechanism for converting the energy generated by braking into electricity and charging the power storage device.

Examples

[0047] Hereinafter, the present invention will be specifically described by way of examples, but these do not limit the scope of the present invention. In addition, the method for measuring the physical property values of the carbonaceous material is described below. The physical property values described in this specification, including the examples, are based on the values obtained by the following methods.

[0048] (Elemental analysis) Elemental analysis was performed based on the inert gas dissolution method using an oxygen, nitrogen, and hydrogen analyzer EMGA-930 manufactured by Horiba, Ltd. The detection method of the apparatus is Oxygen: Inert gas fusion-non-dispersive infrared absorption method (NDIR), Nitrogen: Inert gas fusion-thermal conductivity method (TCD), Hydrogen: Inert gas fusion-non-dispersive infrared absorption method (NDIR) Calibration was performed using (oxygen and nitrogen) Ni capsules, TiH2 (H standard sample), and SS-3 (N, O standard sample). 20 mg of the sample whose moisture content was measured at 250 °C for about 10 minutes as a pretreatment was placed in a Ni capsule, degassed in the elemental analyzer for 30 seconds, and then measured. The test was analyzed with 3 specimens, and the average value was taken as the analysis value.

[0049] (X-ray diffraction) The carbonaceous material powder was filled in a sample holder, and X-ray diffraction measurement was performed using MiniFlexII manufactured by Rigaku Corporation. CuKα (λ = 1.5418 Å) was used as the radiation source, and the scanning range was 10° < 2θ < 35°.

[0050] (Raman spectrum) Using a Raman spectrometer ("LabRAM ARAMIS (VIS)" manufactured by Horiba, Ltd.), the measurement target particles, which are carbonaceous materials, were set on the observation stage of the microscope. The magnification of the objective lens was set to 100 times, focused, and measured while irradiating with argon ion laser light. The details of the measurement conditions are as follows. Wavelength of argon ion laser light: 532 nm Laser power on the sample: 15 mW Resolution: 5 - 7 cm -1 Measurement range: 50 - 2000 cm-1 Exposure time: 1 second Number of integrations: 100 times Peak intensity measurement: Automatic correction with baseline correction, Polynom - 3rd order Peak search & fitting process: GaussLoren

[0051] (Average particle size D by laser scattering method 50 ) The average particle size (particle size distribution) of the carbonaceous material was measured by the following method. The sample was put into an aqueous solution containing 5 mass% of a surfactant ("Toriton X100" manufactured by Wako Pure Chemical Industries, Ltd.), treated with an ultrasonic cleaner for 10 minutes or more, and dispersed in the aqueous solution. The particle size distribution was measured using this dispersion. The particle size distribution measurement was performed using a particle size and particle size distribution measuring device ("Microtrac MT3300EXII" manufactured by Microtrac Bell Co., Ltd.). D 50 is the particle size at which the cumulative volume is 50%, and this value was used as the average particle size.

[0052] (Example 1) 10 g of starch, 0.29 g of melamine (0.037 mol per 1 mol of starch monosaccharide unit), and 0.76 g of adipic acid (0.084 mol per 1 mol of starch monosaccharide unit) were placed in a 100 - ml container and mixed by shaking at 2 Hz for 5 minutes. The obtained mixture was heated to 600°C in a nitrogen gas atmosphere. At this time, the heating rate up to 600°C was 600°C / hour (10°C / min). Next, carbonization treatment was carried out by heat - treating at 600°C for 60 minutes (low - temperature firing treatment) under a nitrogen gas stream to obtain a carbide (first firing). At this time, the supply amount of nitrogen gas was 1 L / min per 10 g of starch. Then, the obtained carbide was pulverized with a ball mill to obtain a pulverized carbide. Next, the pulverized carbide was heated to 1000°C and heat - treated at 1000°C for 60 minutes to perform high - temperature firing treatment to obtain a carbonaceous material (second firing). At this time, the heating rate up to 1000°C was 600°C / hour (10°C / min). The above heating and heat - treatment were carried out under a nitrogen gas stream. The supply amount of nitrogen gas was 3 L / min per 5 g of pulverized carbide.

[0053] (Example 2) A carbonaceous material was obtained by performing the same treatment as in Example 1, except that 0.045 mol of melamine and 0.025 mol of adipic acid were used per 1 mol of starch monosaccharide unit.

[0054] (Example 3) A carbonaceous material was obtained by performing the same treatment as in Example 1, except that 0.075 mol of melamine and 0.042 mol of adipic acid were used per 1 mol of starch monosaccharide unit, and the second firing temperature was 1100 °C.

[0055] (Example 4) A carbonaceous material was obtained by performing the same treatment as in Example 1, except that 0.15 mol of melamine was used per 1 mol of starch monosaccharide unit, and the second firing temperature was 1100 °C.

[0056] (Example 5 :Reference Example ) A carbonaceous material was obtained by performing the same treatment as in Example 1, except that 0.045 mol of melamine and 0.042 mol of adipic acid were used per 1 mol of starch monosaccharide unit.

[0057] (Comparative Example 1) A carbonaceous material was obtained by performing the same treatment as in Example 1, except that 0.15 mol of melamine was used per 1 mol of starch monosaccharide unit.

[0058] (Comparative Example 2) A carbonaceous material was obtained by performing the same treatment as in Comparative Example 1, except that the second firing temperature was 1200 °C.

[0059] (Comparative Example 3) A carbonaceous material was obtained by performing the same treatment as in Comparative Example 1, except that the second firing temperature was 800 °C.

[0060] (Comparative Example 4) The mixture of Example 1 was used as starch, and the treatment was carried out in the same manner as in Example 1 to obtain a carbonaceous material.

[0061] (Comparative Example 5) Glucose and ammonium chloride (1.1 mol with respect to 1 mol of glucose) were mixed in a mortar. The obtained mixture was heated to 1000 °C in a nitrogen gas atmosphere. At this time, the heating rate up to 1000 °C was 240 °C / hour (4 °C / min). Next, carbonization treatment was carried out by heat-treating at 1000 °C for 60 minutes under a nitrogen gas stream to obtain a carbide (first firing). At this time, the supply amount of nitrogen gas was 1 L / min per 5 g of glucose. Thereafter, the obtained carbide was pulverized with a ball mill to obtain a pulverized carbide. Next, the pulverized carbide was heated to 1200 °C and heat-treated at 1200 °C for 60 minutes to perform a high-temperature firing treatment to obtain a carbonaceous material (second firing). At this time, the heating rate up to 1200 °C was 600 °C / hour (10 °C / min). The above heating and heat treatment were carried out under a nitrogen gas stream. The supply amount of nitrogen gas was 3 L / min per 5 g of the pulverized carbide.

[0062] (Comparative Example 6) Melamine was 0.015 mol with respect to 1 mol of starch monosaccharide units, and the treatment was carried out in the same manner as in Example 1 except that the second firing temperature was 800 °C to obtain a carbonaceous material.

[0063] (Fabrication of electrode) Using the carbonaceous materials obtained in each example and each comparative example, a negative electrode was fabricated according to the following procedure. 95 parts by mass of a carbonaceous material, 2 parts by mass of conductive carbon black (“Super-P (registered trademark)” manufactured by TIMICAL), 1 part by mass of CMC, 2 parts by mass of SBR, and 90 parts by mass of water were mixed to obtain a slurry. The obtained slurry was applied to a copper foil with a thickness of 18 μm, dried, and pressed to obtain an electrode with a thickness of 45 μm.

[0064] (Initial battery capacity and charge-discharge efficiency) The electrode fabricated above was used as the working electrode, and metallic lithium was used as the counter electrode and the reference electrode. As the solvent, propylene carbonate and ethylene glycol dimethyl ether were mixed at a volume ratio of 1:1 and used. LiClO4 was dissolved in this solvent at 1 mol / L and used as the electrolyte. A polypropylene membrane was used as the separator. A coin cell was fabricated in a glove box under an argon atmosphere. Regarding the lithium secondary battery having the above configuration, after measuring the DC resistance value before the initial charge using a charge-discharge test apparatus (manufactured by Toyo System Co., Ltd., "TOSCAT"), a charge-discharge test was conducted. Lithium doping was performed at a rate of 70 mA / g with respect to the mass of the active material and doped until the lithium potential reached 1 mV. Further, a constant voltage of 1 mV with respect to the lithium potential was applied for 8 hours to complete the doping. The capacity (mAh / g) at this time was defined as the charge capacity (initial charge capacity) (evaluation of the initial charge). Next, delithiation was performed at a rate of 70 mA / g with respect to the mass of the active material until the lithium potential reached 1.5 V, and the capacity discharged at this time was defined as the discharge capacity (initial discharge capacity) (evaluation of the initial discharge). The percentage of the discharge capacity / charge capacity was defined as the charge-discharge efficiency (initial charge-discharge efficiency) and used as an index for the utilization efficiency of lithium ions in the battery.

[0065] 〈Cycle capacity retention rate〉 After repeating the above initial charge-discharge evaluation conditions 10 times, the discharge capacity obtained was defined as the discharge capacity at the 10th cycle. Further, the 10-cycle capacity retention rate was calculated by the following formula. 10-cycle capacity retention rate (%) = Discharge capacity at the 10th cycle (mAh / g) / Initial discharge capacity (mAh / g) × 100

[0066] The production conditions of the carbonaceous materials, the evaluation results of the physical properties of the obtained carbonaceous materials, and the evaluation results of the battery characteristics in each example and each comparative example are shown in the following respective tables. The batteries fabricated using the carbonaceous materials of the respective examples exhibited a high discharge capacity and a high cycle capacity retention rate. On the other hand, in the batteries fabricated using the carbonaceous materials of the respective comparative examples that did not have a predetermined nitrogen element content or oxygen element content, neither the discharge capacity nor the cycle capacity retention rate was sufficiently high.

[0067]

Table 1

[0068]

Table 2

[0069]

Table 3

[0070]

Table 4

Claims

1. A carbonaceous material determined by elemental analysis to have a nitrogen element content of 1.0% by mass or more and 3.49% by mass or less, an oxygen element content of 1.1% by mass or more and 2.1% by mass or less, a hydrogen element content of more than 0.10% by mass and 0.50% by mass or less, the ratio RN / H (nitrogen element content / hydrogen element content) of the nitrogen element content to the hydrogen element content is 6 or more and 37 or less, and the carbon interplanar spacing (d ００２ ) is 3.70 Å or more.

2. The carbonaceous material according to claim 1, wherein the oxygen element content determined by elemental analysis is 1.2% by mass or more and 2.0% by mass or less.

3. The ratio of the oxygen content to the nitrogen content (R Ｏ／Ｎ 3. The carbonaceous material according to claim 1, wherein the σ is 0.30 or more and 1.0 or less.

4. The value of the full width at half maximum of the peak near 1360 cm of the Raman spectrum observed by laser Raman spectroscopy is 250 cm －１ or more. The carbonaceous material according to any one of claims 1 to 3 －１ ​

5. 1650 cm of the Raman spectrum observed by laser Raman spectroscopy －１ The half-width value of the peak in the vicinity is 98 cm －１ The carbonaceous material according to any one of claims 1 to 4.

6. Average particle diameter D ５０ The carbonaceous material according to any one of claims 1 to 5, wherein ５０ is 30 μm or less.

7. The carbonaceous material according to any one of claims 1 to 6, wherein the carbonaceous material is derived from saccharides.

8. The carbonaceous material according to any one of claims 1 to 7, which is used as a negative electrode active material of an electricity storage device.

9. A negative electrode for an electricity storage device, comprising the carbonaceous material according to claim 8.

10. An electricity storage device having the negative electrode for an electricity storage device according to claim 9.

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