Carbonaceous material with controlled true density, negative electrode for power storage device, and power storage device

Abstract

The present invention pertains to a carbonaceous material in which: the half-width value of a peak near 1360 cm-1 of a Raman spectrum observed by laser Raman spectroscopy is 200-280 cm-1; the true density obtained by a helium method is 1.30-1.95 g / cc; and the nitrogen element content determined by elemental analysis is 0.5-4.6 mass%.

Description

Carbonaceous material with controlled true density, negative electrode for power storage device, and power storage device

[0001] The present invention relates to a carbonaceous material having a specific true density, a negative electrode for an electricity storage device including the carbonaceous material, and an electricity storage device including the negative electrode for an electricity storage device.

[0002] Electricity storage devices, such as secondary batteries and capacitors, are widely used and utilize electrochemical phenomena. For example, lithium-ion secondary batteries, which are one type of electricity storage device, are widely used in small portable devices such as mobile phones and laptops.

[0003] For example, Patent Document 1 discloses a negative electrode material for non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries, in which the nitrogen element content is 1.0 mass % or more and the oxygen content is 1.5 mass % or less, as determined by elemental analysis, and the ratio of the nitrogen element content to the hydrogen element content (R Ｎ／Ｈ ) is 6 or more and 100 or less, and the ratio of the oxygen content to the nitrogen content (R Ｏ／Ｎ ) is 0.1 or more and 1.0 or less, and the carbon interplanar spacing (d ００２ The document also proposes a carbonaceous material having a peak at 1360 cm in the Raman spectrum observed by laser Raman spectroscopy of the carbonaceous material, and describes that this carbonaceous material is suitable for use as a negative electrode active material for a non-aqueous electrolyte secondary battery having a high charge / discharge capacity, preferably a high charge / discharge efficiency, and a low resistance. －１ The half-width value of the peak in the vicinity is preferably 190 cm －１ It is also described that this is preferable because it tends to increase the number of sites for occluding lithium ions.

[0004] International Publication No. 2019 / 009333

[0005] However, there is a constant demand for the development of carbonaceous materials that can provide electricity storage devices with excellent electrical properties. An object of the present invention is to provide a carbonaceous material that, when applied to a negative electrode, can provide an electricity storage device having high charge and discharge capacities per mass, high current efficiency, and high energy density. Another object of the present invention is to provide an electricity storage device negative electrode containing such a carbonaceous material, and an electricity storage device containing such an electricity storage device negative electrode.

[0006] As a result of extensive research, the present inventors have found that the above-mentioned problems can be solved by making the carbonaceous material have a specific Raman spectrum peak half width, a specific true density, and a specific nitrogen element content. That is, the present invention encompasses the following preferred embodiments: [1] A carbonaceous material having a specific Raman spectrum peak half width at 1360 cm as observed by laser Raman spectroscopy. －１ The half-width value of the peak in the vicinity is 200 to 280 cm －１ [2] The carbonaceous material according to [1], wherein the total content of alkali metal elements and alkaline earth metal elements determined by ICP atomic emission spectroscopy is 0.70 to 2.0 mass%. [3] The carbonaceous material according to [1], wherein the total content of alkali metal elements and alkaline earth metal elements determined by X-ray diffraction measurement is 0.70 to 2.0 mass%. ００２ ) is 3.65 to 4.00 Å. [4] The carbonaceous material according to any one of [1] to [3], which is a carbonaceous material for a negative electrode of an electricity storage device. [5] A negative electrode for an electricity storage device, comprising the carbonaceous material according to [4]. [6] A power storage device, comprising the negative electrode for an electricity storage device according to [5].

[0007] According to the present invention, it is possible to provide a carbonaceous material that, when applied to a negative electrode, can provide an electricity storage device having high charge capacity and discharge capacity per mass, high current efficiency, and high energy density.

[0008] FIG. 4 is a diagram illustrating the relationship between the discharge capacity and the voltage when the electricity storage device is discharged.

[0009] Hereinafter, embodiments of the present invention will be described in detail, but it is not intended that the present invention be limited to the following embodiments.

[0010] In this specification, the term "electricity storage device" refers to a general device that includes a negative electrode containing a carbonaceous material and utilizes an electrochemical phenomenon. Specifically, the electricity storage device includes, for example, secondary batteries such as lithium-ion secondary batteries, nickel-metal hydride secondary batteries, and nickel-cadmium secondary batteries, which can be repeatedly used by charging, and capacitors such as electric double layer capacitors. Among these, the electricity storage device may be a secondary battery, particularly a nonaqueous electrolyte secondary battery (e.g., a lithium-ion secondary battery, a sodium-ion battery, a lithium-sulfur battery, a lithium-air battery, an all-solid-state battery, an organic radical battery, etc.), and particularly may be a lithium-ion secondary battery.

[0011] <Carbonaceous Material> The carbonaceous material of the present invention has a Raman spectrum observed by laser Raman spectroscopy at 1360 cm －１ The half-width value of the peak in the vicinity is 200 to 280 cm －１ The carbonaceous material is characterized by having a true density of 1.30 to 1.95 g / cc as determined by the helium method and a nitrogen element content of 0.5 to 4.6 mass% as determined by elemental analysis. The inventors have discovered that because the carbonaceous material has these characteristics, when used as a carbonaceous material for the negative electrode of an electricity storage device, it is possible to achieve high charge capacity, high discharge capacity, high current efficiency, and high energy density. Although the reason for this is unclear, the following mechanism of action is presumed as a non-limiting mechanism of action.

[0012] An energy storage device is required to have a large amount of electricity (i.e., energy density) that can be extracted from the device. Generally, the higher the energy density of an energy storage device, the greater the discharge capacity of the device. However, as can be seen from the relationship between discharge capacity and voltage during discharge of an energy storage device ( FIG. 1 ), even if the discharge capacity is the same, a larger CV (Constant Voltage) discharge capacity results in a higher energy density. This will be explained in more detail using FIG. 1 . For ease of viewing the drawing, the scale ratios of the vertical and horizontal axes in FIG. 1 are appropriately changed. The left side of FIG. 1 shows the relationship between discharge capacity and voltage when a certain energy storage device is discharged via CC (Constant Current). The capacity below 0.1 V is designated as the CV discharge capacity (shown by the solid line), and the capacity above 0.1 V is designated as the CC discharge capacity (shown by the dashed line). To facilitate understanding, in the left diagram of FIG. 1, the CV discharge capacity is set to 250 mAh / g and the CC discharge capacity is set to 290 mAh / g (= 540 - 250). The discharge capacity of this electricity storage device is 540 mAh / g, which is the sum of the CV discharge capacity and the CC discharge capacity. The energy density of this electricity storage device is calculated by dividing the area S of the shaded area by the １ The right side of FIG. 1 also shows the relationship between discharge capacity and voltage when CC discharge is performed on another electricity storage device. To facilitate understanding, the CV discharge capacity of this electricity storage device is set to 300 mAh / g, and the discharge capacity is set to 540 mAh / g, the same as the electricity storage device in the left side of FIG. 1. The energy density of this electricity storage device is calculated by dividing the area S of the shaded area by the １ and S ２ Since it corresponds to the sum of S ２The energy density of the power storage device in the diagram on the right side of Figure 1 is higher by this amount. That is, even if the discharge capacity is the same (540 mAh / g), the larger the CV discharge capacity, the higher the energy density. Furthermore, when the CV discharge capacity is divided by the CC discharge capacity to obtain the CV / CC ratio, the larger this value, the higher the energy density tends to be. Higher energy density also tends to be achieved by increasing the charge / discharge efficiency of the negative electrode when fabricating an actual battery with a certain capacity. Increasing the charge / discharge efficiency of the negative electrode can be achieved, for example, by reducing the volume (coating amount) of the negative electrode. Higher energy density can also be achieved by increasing the value obtained by multiplying the charge / discharge efficiency by the CV / CC ratio. This is because a high value tends to result in favorable values ​​for both charge / discharge efficiency and discharge voltage. When a carbonaceous material is used as a carbonaceous material for the negative electrode of a lithium ion secondary battery, it is believed that, due to the structure of the carbonaceous material, the CC discharge capacity is mainly related to the release of lithium ions trapped between the carbon surfaces of the carbonaceous material, while the CV discharge capacity is mainly related to the release of lithium ion clusters occluded in the carbonaceous material. The fact that the carbonaceous material of the present invention has the above-mentioned specific half-width value is related to the disordered spacing of the carbon surfaces of the carbonaceous material, and as a result, it is believed that lithium ions are easily trapped between the carbon surfaces of the carbonaceous material, allowing more lithium ions to be released, i.e., high charge / discharge capacity and high CC discharge capacity can be achieved.

[0013] The carbonaceous material of the present invention also has a true density (hereinafter referred to as "true density ρ Ｈｅ "), but the true density ρ ＨｅA small ρ means that there are many pores that cannot accommodate helium. The presence of many such pores results in an increase in intercrystalline voids in the hard carbon, which allows electrolyte ions (lithium ions in the case of lithium-ion secondary batteries) to be occluded in the form of clusters. As a result, more electrolyte ions are occluded in the carbonaceous material, allowing more electrolyte ions to be released. This is thought to achieve high charge / discharge capacity, high CV discharge capacity, high current efficiency, and high energy density. The carbonaceous material of the present invention also has a nitrogen element content within a specific range. The inventors have found that porous carbon having many pores that cannot accommodate helium can be produced by carbonizing and heat-treating a mixture of a carbon source compound and a nitrogen-containing compound under appropriate conditions. The carbonaceous material produced by this production method usually has a nitrogen element content within a specific range. Having a nitrogen element content within a specific range means that the carbonaceous material has a true density ρ that is equal to or less than a specific value or within a specific range. Ｈｅ Therefore, it is believed that when the carbonaceous material has a nitrogen element content within a specific range, it can achieve high charge / discharge capacity, high CV discharge capacity, high current efficiency, and high energy density.

[0014] The half width value of the carbonaceous material in the present invention is 200 cm －１ If the half width is smaller than 280 cm, the carbon structure will have fewer disorder and defects, and the number of storage sites for electrolyte ions will be reduced, which tends to make it difficult to achieve a high charge / discharge capacity and a high CC discharge capacity of an electrode made using the carbonaceous material. －１ If the value is larger, the number of sites for irreversibly occluding electrolyte ions in the carbon structure increases, which tends to make it difficult to achieve high charge / discharge efficiency. －１ , preferably 205 to 280 cm －１ , more preferably 210 to 280 cm －１ , more preferably 220 to 280 cm －１ , particularly preferably 230 to 275 cm －１ , more particularly preferably 240 to 270 cm －１When the half width is equal to or greater than the lower limit, a higher charge / discharge capacity and a higher CC discharge capacity can be achieved for an electrode made using the carbonaceous material. When the half width is equal to or less than the upper limit, a suitable charge / discharge efficiency can be achieved for an electricity storage device including an electrode made using the carbonaceous material. －１ The peak around 1360 cm is a Raman peak generally called the D band, which is a peak caused by disorder and defects in the graphite structure. －１ The peak around 1345 cm －１ ~1375cm －１ , preferably 1350 cm －１ ~1370cm －１ The Raman spectrum is observed in the range of . The Raman spectrum is measured using a Raman spectrometer, for example, under the conditions described in the Examples. The value of the half width can be adjusted to fall within the above range, for example, by adjusting the amount of the nitrogen-containing compound or activator used in producing the carbonaceous material and / or by adjusting the temperature or time of the heat treatment.

[0015] The true density ρ of the carbonaceous material of the present invention Ｈｅ If the true density ρ of the carbonaceous material is greater than 1.95 g / cc, it is difficult for the carbonaceous material to occlude a sufficient amount of electrolyte ion clusters. Ｈｅ The lower limit of the true density ρ is usually 1.30 g / cc or more. Ｈｅ is 1.30 to 1.95 g / cc, preferably 1.35 to 1.94 g / cc, more preferably 1.40 to 1.93 g / cc, even more preferably 1.45 to 1.92 g / cc, particularly preferably 1.50 to 1.91 g / cc, and even more particularly preferably 1.55 to 1.90 g / cc. Ｈｅ can be measured by a gas pycnometer method, for example, by the method described in the Examples below. Ｈｅ can be adjusted within the above range, for example, by adjusting the amount of nitrogen-containing compound used in producing the carbonaceous material and / or adjusting the temperature or time of the heat treatment.

[0016] The true density ρ of a carbonaceous material is less than or within a specific range. ＨｅIn addition, by having a nitrogen element content determined by elemental analysis within a specific range, high charge / discharge capacity, high CV discharge capacity, high current efficiency, and high energy density can be achieved. The nitrogen element content is 0.5 to 4.6 mass%, preferably 0.6 to 4.5 mass%, more preferably 0.65 to 4.4 mass%, even more preferably 0.7 to 4.3 mass%, still more preferably 0.8 to 4.2 mass%, particularly preferably 0.9 to 4.0 mass%, even more particularly preferably 1.0 to 3.5 mass%, and even more particularly preferably 1.0 to 3.0 mass%. When the nitrogen element content is above the lower limit, the spacing of the carbon planes of the carbonaceous material is disrupted, ensuring sites for adsorption and desorption of electrolyte ions during charge / discharge. Furthermore, the carbonaceous material can occlude electrolyte ion clusters, resulting in high charge / discharge capacity, high CV discharge capacity, high current efficiency, and high energy density. On the other hand, when the nitrogen element content is below the upper limit, the decrease in discharge capacity during repeated charge / discharge can be suppressed, and current efficiency can be improved. The nitrogen element content is an analytical value obtained by elemental analysis of the carbonaceous material, and can be measured, for example, by the method described in the Examples below. The nitrogen element content can be adjusted to within the above range, for example, by adjusting the amount of a nitrogen-containing compound used in producing the carbonaceous material and / or by adjusting the temperature or time of heat treatment.

[0017] The oxygen element content determined by elemental analysis of the carbonaceous material is preferably 3.0 mass% or less from the viewpoint of current efficiency, particularly from the viewpoint of suppressing a decrease in discharge capacity and improving current efficiency during repeated charge and discharge. The lower the better, the better, with the lower limit being 0 mass% or more. The oxygen element content is more preferably 0 to 3.0 mass%, even more preferably 0 to 2.5 mass%, even more preferably 0 to 2.4 mass%, particularly preferably 0 to 2.3 mass%, even more particularly preferably 0 to 2.2 mass%, and even more particularly preferably 0 to 2.1 mass%. The oxygen element content determined by elemental analysis represents the amount of oxygen element contained in the entire carbonaceous material. A low oxygen element content determined by elemental analysis reduces the number of sites available for new reaction with the electrolyte, electrolyte, or electrolyte ions during repeated charge and discharge, thereby suppressing a decrease in discharge capacity, particularly during repeated charge and discharge. The oxygen element content determined by elemental analysis of the carbonaceous material can be reduced by increasing the amount of nitrogen-containing compound used in producing the carbonaceous material. It can also be adjusted to be below the upper limit or within the above range by adjusting the temperature or time of heat treatment, for example.

[0018] The total content of alkali metal elements and alkaline earth metal elements in the carbonaceous material determined by ICP atomic emission spectroscopy is preferably 0.70 to 2.0 mass% (e.g., 0.75 to 2.0 mass%, 0.80 to 2.0 mass%, 0.85 to 2.0 mass%, 0.90 to 2.0 mass%), more preferably 0.70 to 1.8 mass%, even more preferably 0.70 to 1.6 mass%, still more preferably 0.70 to 1.4 mass%, particularly preferably 0.70 to 1.2 mass%, and more particularly preferably 0.70 to 1.1 mass% (e.g., 0.75 to 1.0 mass%, 0.75 to 0.90 mass%). The total content of alkali metal elements and alkaline earth metal elements determined by ICP atomic emission spectroscopy represents the total content of alkali metal elements and alkaline earth metal elements contained in the entire carbonaceous material. When the total content of alkali metal elements and alkaline earth metal elements determined by ICP atomic emission spectroscopy is equal to or greater than the lower limit, many pores capable of absorbing lithium ions as clusters can be formed during the process of obtaining the carbonaceous material, thereby improving the CV discharge capacity. On the other hand, when the total content of alkali metal elements and alkaline earth metal elements is equal to or less than the upper limit, pores capable of absorbing lithium ions as clusters can be formed during the process of obtaining the carbonaceous material, while erosion of the crystal structure in the carbon surface direction can progress. As a result, the CV discharge capacity can be improved, but the CC discharge capacity cannot be improved as much as the CV discharge capacity. As a result, the CV / CC ratio obtained by dividing the CV discharge capacity by the CC discharge capacity is increased, and the energy density of the power storage device can be increased. The total content of alkali metal elements and alkaline earth metal elements in the carbonaceous material can be adjusted within the above range by selecting a compound containing an alkali metal element and / or an alkaline earth metal element as an activator during the production of the carbonaceous material, or by adjusting the temperature or time of heat treatment in addition to the selection. The total content of alkali metal elements and alkaline earth metal elements in the carbonaceous material is determined by ICP emission spectrometry, and a more specific example of the measurement method is described in the Examples below.

[0019] The carbon interplanar spacing (d００２ The carbon interplanar spacing (d) is preferably 3.65 to 4.00 Å, more preferably 3.68 to 3.95 Å, even more preferably 3.70 to 3.90 Å, particularly preferably 3.71 to 3.85 Å, and even more particularly preferably 3.73 to 3.85 Å. ００２ When the carbon interplanar spacing (d) is equal to or greater than the lower limit, the spacing between carbon planes increases, allowing electrolyte ions to migrate efficiently. Furthermore, the micropores are sufficiently developed, which increases the number of storage sites for clustered electrolyte ions, resulting in higher discharge capacity and current efficiency. ００２ When the carbon interplanar spacing (d) is equal to or less than the upper limit, the volume of the carbonaceous material can be appropriately reduced to increase the effective capacity per volume, and the discharge capacity per volume can be increased. ００２ The carbon interplanar spacing (d) is measured by X-ray diffraction measurement using the Bragg equation, specifically by the method described in the Examples. ００２ ) can be adjusted within the above range, for example, by adjusting the amount of the nitrogen-containing compound used in producing the carbonaceous material and / or by adjusting the temperature or time of the heat treatment.

[0020] <Method for Producing Carbonaceous Material> The method for producing a carbonaceous material of the present invention is not particularly limited as long as it can produce a carbonaceous material having the above-described properties. For example, a method may be used in which a compound serving as a carbon source is mixed with a nitrogen-containing compound, or a nitrogen-containing compound serving as a carbon source is prepared, the resulting mixture or the prepared nitrogen-containing compound is heat-treated in an inert gas atmosphere at 500 to 900°C, and then pulverized and / or classified, and the resulting pulverized and / or classified carbonized product is further heat-treated at 800 to 1300°C, the method including a mixing step with an activator before the heat treatment at 800 to 1300°C. Here, the "nitrogen-containing compound serving as a carbon source" described above is different from the "compound (nitrogen-containing compound) containing nitrogen other than sugars" described below. The carbon source compound or nitrogen-containing compound used as a raw material is not particularly limited as long as a carbonaceous material satisfying the above-mentioned properties can be obtained. However, from the viewpoint of being able to adjust the above-mentioned properties of the carbonaceous material to a preferred range, a compound having a saccharide skeleton (hereinafter sometimes abbreviated as "saccharide compound"; furthermore, throughout this specification, saccharide compounds include nitrogen-free saccharide compounds and nitrogen-containing saccharide compounds, which will be described later) or a nitrogen-containing compound having a saccharide skeleton is preferred. Therefore, the carbonaceous material of the present invention is preferably a carbonaceous material derived from a sugar or a nitrogen-containing sugar. Below, a production method using a saccharide compound or a nitrogen-containing saccharide compound as a carbon source will be described.

[0021] In a preferred embodiment of the present invention, the method for producing a carbonaceous material of the present invention comprises the following steps (1) to (4): (1) a step of mixing a nitrogen-free saccharide compound (hereinafter also referred to as a "nitrogen-free saccharide compound") with a nitrogen-containing saccharide compound, or a step of mixing a nitrogen-free saccharide compound and / or a nitrogen-containing saccharide compound with a nitrogen-containing compound other than a saccharide (referred to as a "nitrogen-containing compound" throughout this specification), or a step of preparing a nitrogen-containing saccharide compound, (2) a step of heat-treating the mixture obtained in step (1) or the nitrogen-containing saccharide compound prepared in step (1) at 500 to 900°C under an inert gas atmosphere to obtain a charcoal, (3) a step of pulverizing and / or classifying the charcoal, and (4) a step of heat-treating the pulverized and / or classified charcoal at 800 to 1300°C under an inert gas atmosphere to obtain a carbonaceous material, and the method further comprises the following step (a): (a) a step of also mixing an activator before the heat treatment in step (4). Includes.

[0022] Examples of nitrogen-free saccharide compounds that can be used in step (1) include, but are not limited to, monosaccharides such as glucose, galactose, mannose, fructose, and ribose; disaccharides such as sucrose, trehalose, maltose, cellobiose, maltitol, lactobionic acid, and lactosamine; and polysaccharides such as starch, glycogen, agarose, pectin, cellulose, oligosaccharides, and xylitol. As the nitrogen-free saccharide compound, one of these compounds may be used alone, or two or more may be used in combination. Among these nitrogen-free saccharide compounds, starch is preferred because it is easily available in large quantities. Examples of starch include corn starch, potato starch, wheat starch, rice starch, tapioca starch, sago starch, sweet potato starch, mylostarch, kudzu starch, bracken starch, lotus root starch, mung bean starch, and potato chestnut starch. These starches may be physically, enzymatically, or chemically processed, and may be starches processed into pregelatinized starch, phosphate cross-linked starch, starch acetate, hydroxypropyl starch, oxidized starch, dextrin, etc. Corn starch and wheat starch, as well as pregelatinized starches thereof, are preferred as starches because of their availability and low cost.

[0023] Examples of nitrogen-containing saccharide compounds that can be used in step (1) include, but are not limited to, glucosamine, chitin, chitosan, and quaternary nitrogen-modified polysaccharides (cationically modified hydroxyethyl cellulose, cationically modified starch, cationically modified tamarind gum, cationically modified locust bean gum, cationically modified tara gum, cationically modified fenugreek gum, etc.). As the nitrogen-containing saccharide compound, one of these compounds may be used, or two or more may be used in combination. In this specification, "nitrogen-free saccharide compounds" refers to saccharide compounds having a nitrogen element content of less than 500 ppm, and "nitrogen-containing saccharide compounds" refers to saccharide compounds having a nitrogen element content of 500 ppm or more.

[0024] In a preferred embodiment, from the viewpoint of increasing the density of an electrode obtained from the carbonaceous material, the saccharide compound is a saccharide compound having a cross-sectional area of ​​3 μm in an image obtained by observing the cross section of a particle of the compound with a secondary electron microscope. ２ 100 μm or more ２ When 20 particles below are randomly selected, ２ It is preferable to use a compound in which the number of particles having the above voids is preferably 3 or less, more preferably 2 or less, and even more preferably 1 or less. When producing a carbide using such a compound with few voids as a raw material, additional treatment such as step (b) described below is usually not required.

[0025] The nitrogen-containing compound that can be used in step (1) is not particularly limited as long as it has a nitrogen atom in its molecule and does not correspond to a sugar. Examples of such compounds include 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, dicyandiamide, pyrimidine, pyridine, pyrrole, imidazole, indole, urea, cyanuric acid, and benzoguanamine. As the nitrogen-containing compound, one of these nitrogen-containing compounds may be used alone, or two or more may be used in combination. Among these nitrogen-containing compounds, nitrogen-containing compounds with a high intramolecular nitrogen content are preferred, from the viewpoint of incorporating a large amount of nitrogen element into the carbonaceous material. For example, melamine, dicyandiamide, and urea are preferred. From the viewpoint of reaction with sugar compounds during the heat treatment process, the nitrogen-containing compound is preferably a compound having a volatilization temperature of preferably 100°C or higher, more preferably 150°C or higher.

[0026] In the mixing step (1), the mixing ratio of the nitrogen-free saccharide compound to the nitrogen-containing saccharide compound, the mixing ratio of the nitrogen-free saccharide compound to the nitrogen-containing compound, the mixing ratio of the nitrogen-containing saccharide compound to the nitrogen-containing compound, or the mixing ratio of the nitrogen-free saccharide compound to the nitrogen-containing saccharide compound and the nitrogen-containing compound is not particularly limited and may be adjusted as appropriate to obtain a carbonaceous material having desired properties. For example, increasing the amount of the nitrogen-containing compound tends to increase the nitrogen element content in the carbonaceous material. From the viewpoint of adjusting the above-mentioned properties of the carbonaceous material to a preferred range, it is preferable to adjust the mixing ratio so that the nitrogen element content in the mixture is 1.0 to 20.0 mass% based on the total mass of the mixture. The nitrogen element content in the mixture is preferably 3.0 to 15.0 mass%, more preferably 5.0 to 10.0 mass%. When the nitrogen element content in the nitrogen-containing saccharide compound is within the above-mentioned range of the nitrogen element content in the mixture, such a nitrogen-containing saccharide compound may be prepared in step (1) instead of mixing the raw material compounds. The nitrogen-containing saccharide compound that may be prepared may be one kind of nitrogen-containing saccharide compound alone or a combination of two or more kinds. The amount of nitrogen element in the saccharide compound can be measured, for example, using an oxygen / nitrogen / hydrogen analyzer.

[0027] In a preferred embodiment of the present invention, the amount of the saccharide compound contained in the mixture obtained by mixing in step (1) is preferably 50 to 99% by mass, more preferably 80 to 95% by mass, based on the total mass of the saccharide compound and the nitrogen-containing compound. The amount of the nitrogen-containing compound contained in the mixture is preferably 1 to 30% by mass, more preferably 2 to 28% by mass, even more preferably 3 to 26% by mass, even more preferably 4 to 24% by mass, and particularly preferably 5 to 22% by mass, based on the total mass of the saccharide compound and the nitrogen-containing compound. The amount of the nitrogen-containing compound mixed in step (1) is preferably 0.013 to 0.56 mol, more preferably 0.026 to 0.50 mol, even more preferably 0.040 to 0.45 mol, even more preferably 0.054 to 0.41 mol, and particularly preferably 0.069 to 0.36 mol, based on 1 mol of starch monosaccharide units in the saccharide compound.

[0028] In step (1), when mixing the raw materials or preparing the nitrogen-containing saccharide compound, at least one carbon source selected from the group consisting of coconut shells, walnut shells, rice husks, buckwheat husks, coffee grounds, wood, pulp, bamboo, and paper may be further mixed, as long as the effects of the present invention are not impaired. These additional carbon sources may be of a grade commonly used in the art. When an additional carbon source is mixed, the amount thereof is preferably 50 mass% or less, more preferably 40 mass% or less, based on the total mass of the saccharide compound, the nitrogen-containing compound if contained in the mixture, and the additional carbon source. In one embodiment of the present invention, the carbonaceous material in the present invention does not include carbonaceous materials derived from coconut shells, walnut shells, rice husks, buckwheat husks, coffee grounds, wood, pulp, bamboo, or paper.

[0029] In step (1), at least one crosslinking agent may be further mixed when mixing the raw materials or preparing the nitrogen-containing saccharide compound. The crosslinking agent is a compound capable of crosslinking saccharide compounds. It acts as a catalyst to promote the interchain bond formation reaction of saccharide compounds and / or the reaction between saccharide compounds and nitrogen-containing compounds, which proceeds in parallel with the hydrolysis reaction or dehydration reaction of the saccharide compounds, or it itself crosslinks the saccharide compounds and / or nitrogen-containing compounds. In the heat treatment process, saccharide compounds often melt, fuse, foam, etc., and as a result, the resulting carbonaceous material often has a flat shape rather than a spherical shape. When a crosslinking agent is used in heat treatment, fusion or foaming between the raw materials can be suppressed, thereby increasing the density of the electrode obtained using the resulting carbonaceous material.

[0030] When a crosslinking agent is used, the type thereof is not particularly limited. Examples of such acids include aliphatic monocarboxylic 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, lauric acid, myristic acid, palmitic acid, stearic acid, linoleic acid, and oleic acid; aromatic monocarboxylic acids such as benzoic acid, salicylic acid, and toluic acid; polycarboxylic acids such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, fumaric acid, maleic 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; sulfonic acids such as p-toluenesulfonic acid and methanesulfonic acid; amino acids such as glycine, alanine, valine, leucine, isoleucine, serine, threonine, cysteine, methionine, asparagine, glutamine, proline, phenylalanine, tyrosine, and tryptophan; and hydrochloric acid and sulfuric acid. When a crosslinking agent is used, one of these crosslinking agents may be used alone or two or more may be used in combination. Among these crosslinking agents, polycarboxylic acids and hydroxycarboxylic acids are preferred from the viewpoint of suppressing melting and foaming of the raw materials in the step of obtaining a carbonized product by heat treatment, and among these, succinic acid, adipic acid, and citric acid are more preferred.

[0031] When a crosslinking agent is used, the amount thereof is preferably 1 to 30 mass %, more preferably 3 to 10 mass %, based on the total mass of the saccharide compound, the activator, the nitrogen-containing compound if present in the mixture, and the crosslinking agent. When a crosslinking agent is used, increasing the amount of the crosslinking agent increases the true density ρ of the carbonaceous material. Ｈｅ tends to be higher.

[0032] The heat treatment temperature in step (2) is preferably 550 to 850°C, more preferably 600 to 800°C. The heating rate until the heat treatment temperature (ultimate temperature) is reached is preferably 50°C / hour or more, more preferably 50°C / hour to 200°C / hour. The heat treatment time is typically a holding time at the ultimate temperature of 5 minutes or more, preferably 5 minutes to 2 hours, more preferably 10 minutes to 1 hour, and even more preferably 30 minutes to 1 hour. If the heat treatment temperature and time are within the above ranges, the carbonization of the saccharide compound can be controlled, and the above characteristic values ​​of the carbonaceous material can be adjusted to the desired ranges. The heat treatment temperature may be a constant temperature, or may vary within the above range.

[0033] Step (2) is carried out in an inert gas atmosphere. As long as the step is carried out in an inert gas atmosphere, the inert gas may or may not be actively supplied. Examples of the inert gas include argon gas, helium gas, and nitrogen gas, and nitrogen gas is preferred. This heat treatment step produces a carbide, which is a precursor for producing a carbonaceous material.

[0034] In step (3), the obtained carbide is pulverized and / or classified. The pulverization and classification methods are not particularly limited, and may be performed by conventional methods, such as methods using a ball mill or a jet mill. By pulverizing and / or classifying the carbide, it is possible to break down or remove agglomerates formed by the heat treatment in step (2). The average particle size of the carbonaceous material obtained in step (3) is preferably 0.1 μm to 20 μm, more preferably 0.5 μm to 19 μm, even more preferably 1.0 μm to 18 μm, and particularly preferably 1.5 μm to 17 μm, from the viewpoints of the electrode density and volumetric efficiency of an electrode produced using the carbonaceous material, and the charge / discharge efficiency of a battery produced using the electrode. The average particle size is measured by a laser diffraction scattering method throughout this specification.

[0035] In step (4), the pulverized and / or classified carbide is heat-treated at 800 to 1300°C under an inert gas atmosphere to obtain the carbonaceous material of the present invention. The heat treatment temperature in step (4) is preferably 1000 to 1250°C, more preferably 1050 to 1200°C, and even more preferably 1100 to 1150°C. In this specification, heat treatment at 800 to 1300°C means maintaining a temperature of 800 to 1300°C for 1 minute or more. The heating rate until the heat treatment temperature (ultimate temperature) is reached is preferably 50°C / hour or more, more preferably 50°C / hour to 200°C / hour. Furthermore, the heat treatment time is typically maintained at the ultimate temperature for 1 minute or more, preferably 5 minutes to 2 hours, more preferably 10 minutes to 1 hour, even more preferably 10 minutes to 45 minutes, and particularly preferably 10 minutes to 30 minutes. If the heat treatment temperature and time are within the above ranges, the above-mentioned characteristic values ​​of the final carbonaceous material can be adjusted to the desired values. Here, the heat treatment temperature may be a constant temperature, but may also vary within the above range.

[0036] In a preferred embodiment, step (4) is carried out in the presence of a volatile organic substance, or step (4) is carried out in the absence of a volatile organic substance, followed by a further heat treatment in an inert gas atmosphere in the presence of a volatile organic substance (step (5)). When step (4) is carried out in the presence of a volatile organic substance or when step (5) is carried out, the heat treatment temperature is set so that volatile substances derived from the volatile organic substance generated by the heat treatment are present in the atmosphere in which the heat treatment is carried out.

[0037] The amount of the volatile organic substance in step (4) or step (5) is preferably 1 to 30 parts by mass, more preferably 2 to 20 parts by mass, and even more preferably 3 to 15 parts by mass, relative to 100 parts by mass of the pulverized and / or classified carbonized material obtained in step (3) or 100 parts by mass of the carbonaceous material obtained in step (4), respectively.

[0038] When step (4) is performed in the presence of a volatile organic compound, the pulverized and / or classified carbonized material obtained in step (3) may be mixed with the volatile organic compound, and the resulting mixture may be subjected to step (4). Volatile organic compounds refer to organic compounds that volatilize (become gasified or thermally decomposed into gas) without carbonizing (e.g., 80% by mass or more, preferably 90% by mass or more) during heat treatment (e.g., at 500°C or higher) under an inert gas atmosphere. Examples of volatile organic compounds include, but are not limited to, thermoplastic resins and low-molecular-weight organic compounds. Specific examples of thermoplastic resins include polystyrene, polyethylene, polypropylene, poly(meth)acrylic acid, poly(meth)acrylic acid esters, etc. In this specification, (meth)acrylic is a general term for methacrylic and acrylic. The volatile organic compound may also be a resin partially containing a thermoplastic resin, such as a copolymer. Examples of such resins include acrylonitrile-chlorinated polyethylene-styrene copolymer (ACS resin), acrylonitrile-acrylic acid ester-styrene copolymer (AAS resin), acrylonitrile-ethylene-styrene copolymer (AES resin), styrene-ethylene-propylene-styrene block copolymer (SEPS resin), styrene-ethylene-butylene-styrene block copolymer (SEBS resin), styrene-isoprene-styrene block copolymer (SIS resin), styrene-butadiene-styrene block copolymer (SBS resin), acrylonitrile-styrene copolymer (AS resin), acrylonitrile-butadiene-styrene copolymer (ABS resin), etc. Specific examples of low molecular weight organic compounds include ethylene, propane, hexane, toluene, xylene, mesitylene, styrene, naphthalene, phenanthrene, anthracene, pyrene, etc. Since it is preferable that the thermoplastic resin is one that volatilizes at the heat treatment temperature and does not oxidize and activate the surface of the carbon source when thermally decomposed, polystyrene, polyethylene, polypropylene, and poly(meth)acrylic acid are preferred.Furthermore, from the viewpoint of safety, it is preferable that the low-molecular-weight organic compound is one that has low volatility at room temperature (e.g., 20°C), and naphthalene, phenanthrene, anthracene, pyrene, etc. are preferred.The volatile organic compounds can be used alone or in combination of two or more. The use of such volatile organic compounds is preferred in that the oxygen element content can be reduced while maintaining the characteristic structure of the present invention.

[0039] Alternatively, the volatile organic compound may be gasified and mixed with an inert gas, and then supplied to step (4). The volatile organic compound is not particularly limited, but examples thereof include low-molecular-weight organic compounds. Examples of low-molecular-weight organic compounds include ethylene, propane, hexane, toluene, xylene, mesitylene, styrene, naphthalene, phenanthrene, anthracene, and pyrene. Among these, compounds with high volatility are preferred from the viewpoint of miscibility with the inert gas, and ethylene, propane, hexane, and toluene are preferred. The volatile organic compounds may be used alone or in combination of two or more. The use of such volatile organic compounds is preferred in that the oxygen element content can be further reduced while maintaining the characteristic structure of the present invention.

[0040] When a volatile organic substance is used in step (4), it is believed that the volatile organic substance deactivates radical active sites, etc., on the surface of the carbide particles. Such radical active sites typically react with oxygen in the air, increasing the oxygen element content of the carbonaceous material. In a preferred embodiment of the present invention, when the oxygen element content of the carbonaceous material, particularly the oxygen element content measured by elemental analysis, is low, it is believed that there are fewer radical reaction sites, etc., on the surface of the carbonaceous material, making it less susceptible to oxidation, and that the number of sites that can become reaction sites during repeated charge and discharge is reduced. As a result, it is believed that when the radical active sites, etc., of the carbide are deactivated by a volatile organic substance, a higher discharge capacity can be maintained even after repeated charge and discharge.

[0041] When step (4) is performed in the absence of volatile organic compounds, followed by a further heat treatment (step (5)) in an inert gas atmosphere in the presence of volatile organic compounds, it is believed that the radical active sites on the surface of the carbonaceous material particles can be reduced while maintaining the carbon structure obtained in step (4). The heat treatment temperature in step (5) is preferably less than 1200°C, more preferably 700 to less than 1200°C, even more preferably 750 to 1100°C, and particularly preferably 800 to 1000°C. From the viewpoints of maintaining the carbon structure obtained in step (4) and achieving a high discharge capacity, the heat treatment temperature in step (5) is preferably equal to or lower than the upper limit. Furthermore, from the viewpoints of sufficient decomposition of volatile organic compounds and deactivation of the radical active sites of the carbonaceous material, the heat treatment temperature in step (5) is preferably equal to or higher than the lower limit. The heat treatment time in step (5) is preferably 1 minute to 1 hour, more preferably 10 to 40 minutes, at the temperature reached. When the heat treatment temperature and time in the presence of a volatile organic substance are within the above ranges, it is believed that the radical active sites of the carbonaceous material can be reduced, and as a result, a higher discharge capacity can be maintained even after repeated charge and discharge. Examples of volatile organic substances that can be used in step (5) include the same volatile organic substances as those exemplified as volatile organic substances that can be used when step (4) is performed in the presence of a volatile organic substance.

[0042] The production method includes step (a) of mixing an activator prior to the heat treatment in step (4). By producing a carbonaceous material by the production method including step (a), pores can be formed in the carbonaceous material. The carbonaceous material having such pores has a true density ρ of not more than a specific value or within a specific range. Ｈｅ and has a Raman spectrum of 1360 cm within a specific range. －１ By having a half-width value of the peak in the vicinity of the above range and having a nitrogen element content determined by elemental analysis within a specific range, it is possible to provide a carbonaceous material suitable for an electricity storage device that can achieve a high energy density in addition to a high charge capacity, a high discharge capacity, and a high current efficiency.

[0043] Step (a) may be, for example, one or more of the following steps: - a step of mixing a saccharide compound and / or a nitrogen-containing compound with an activator before the mixing in step (1); - a step of also mixing an activator during the mixing in step (1); - a step of mixing the mixture obtained in step (1) or the nitrogen-containing saccharide compound prepared in step (1) with an activator; - a step of mixing the carbonized material obtained in step (2) with an activator; and - a step of mixing the pulverized and / or classified carbonized material obtained in step (3) with an activator.

[0044] Examples of activators that can be used in step (a) include compounds containing alkali metal elements (lithium, sodium, potassium, rubidium, cesium, etc.) or alkaline earth metal elements (beryllium, magnesium, calcium, strontium, barium, radium, etc.), including halides (fluorides, chlorides, bromides, etc.), hydroxides, cyanides, carbonates, hydrogencarbonates, sulfates, nitrates, phosphates, silicates, and metal acid salts of alkali metal elements. Specific examples of compounds containing an alkali metal element include lithium chloride, sodium chloride, potassium chloride, rubidium chloride, cesium chloride, lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide, cesium hydroxide, lithium cyanide, sodium cyanide, potassium cyanide, rubidium cyanide, cesium cyanide, lithium carbonate, sodium carbonate, potassium carbonate, rubidium carbonate, cesium carbonate, sodium bicarbonate, potassium bicarbonate, rubidium bicarbonate, cesium bicarbonate, lithium sulfate, sodium sulfate, potassium sulfate, rubidium sulfate, cesium sulfate, lithium nitrate, sodium nitrate, potassium nitrate, rubidium nitrate, cesium nitrate, lithium phosphate, sodium phosphate, potassium phosphate, rubidium phosphate, cesium phosphate, lithium silicate, sodium silicate , potassium silicate, rubidium silicate, cesium silicate, lithium citrate, sodium citrate, potassium citrate, rubidium citrate, cesium citrate, lithium aluminate, sodium aluminate, potassium aluminate, rubidium aluminate, cesium aluminate, lithium antimonate, sodium antimonate, potassium antimonate, rubidium antimonate, cesium antimonate, lithium molybdate, sodium molybdate, potassium molybdate, rubidium molybdate, cesium molybdate, lithium chromate, sodium chromate, potassium chromate, rubidium chromate, cesium chromate, lithium vanadate, sodium vanadate, potassium vanadate, rubidium vanadate, cesium vanadate, and hydrates thereof. Among these, from the viewpoints of pore-forming ability and safety, the compound containing an alkali metal element is preferably a compound containing sodium or potassium.One type of activator may be used, or two or more types may be used in combination.

[0045] The method for mixing the activator in step (a) is not particularly limited. When the activator is solid, the solid activator may be mixed with a saccharide compound or the like. When the activator is water-soluble, an aqueous solution of the activator may be mixed with a saccharide compound or the like.

[0046] The total amount of activators mixed in step (a) is set to a value that ultimately results in a true density ρ that is equal to or less than the upper limit or within the range. Ｈｅ There are no particular limitations as long as a carbonaceous material having the above properties can be obtained. For example, the amount is preferably 0.5 to 10 mass%, more preferably 0.6 to 8 mass%, relative to the total mass of the saccharide compound and the nitrogen-containing compound, or the mass of the nitrogen-containing saccharide compound when no nitrogen-containing compound is used, or relative to the mass of the carbonized product obtained in step (2). The total amount of activator mixed in step (a) is preferably 0.001 to 0.15 mol, more preferably 0.005 to 0.10 mol, and even more preferably 0.01 to 0.05 mol, relative to 1 mol of starch monosaccharide units in the saccharide compound.

[0047] A phosphorus-containing compound may also be mixed prior to the heat treatment in step (4). When a phosphorus-containing compound is also mixed, it can be mixed in, for example, one or more of the following steps: a step of mixing a saccharide compound and / or a nitrogen-containing compound with a phosphorus-containing compound prior to the mixing in step (1); a step of also mixing a phosphorus-containing compound in the mixing in step (1); a step of mixing the mixture obtained in step (1) or the nitrogen-containing saccharide compound and the phosphorus-containing compound prepared in step (1); a step of mixing the carbonized material obtained in step (2) with a phosphorus-containing compound; and a step of mixing the pulverized and / or classified carbonized material obtained in step (3) with a phosphorus-containing compound. When a phosphorus-containing compound is also mixed, the phosphorus-containing compound may be mixed simultaneously with or at a different time from the mixing of the activator.

[0048] The phosphorus-containing compound is not particularly limited as long as it is a compound having a phosphorus atom in the molecule. For example, inorganic phosphoric acid, organic phosphoric acid, and salts thereof, organic phosphorus, phosphonium salts, etc. can be used. As the phosphorus-containing compound, one type of phosphorus-containing compound may be used, or two or more types may be used in combination.

[0049] Examples of inorganic phosphoric acids include phosphoric acid, dihydrogen phosphate, ammonium dihydrogen phosphate, primary phosphate, secondary phosphate, tertiary phosphate, pyrophosphoric acid, pyrophosphate, tripolyphosphoric acid, tripolyphosphate, phosphorous acid, phosphite, hypophosphorous acid, hypophosphite, diphosphorous acid, and phosphorus pentoxide. Examples of organic phosphoric acids include phosphonic acid (phosphonic acid compounds), and examples of phosphonic acids include nitrilotrismethylenephosphonic acid, phosphonobutanetricarboxylic acid, methyldiphosphonic acid, methylenephosphonic acid, ethylidenediphosphonic acid, and triphenyl phosphate. When these phosphoric acids are in the form of a salt, the salt may be, for example, an alkali metal salt and / or an alkaline earth metal salt, or an ammonium salt. Examples of organic phosphoric acids include triphenylphosphine, triphenylphosphine oxide, tricyclohexylphosphine, tricyclohexylphosphine oxide, trialkylphosphine, and trialkylphosphine oxide. Examples of phosphonium salts include tetraalkylphosphonium salts and tetraphenylphosphonium salts. These salts may be, for example, halides, sulfates, phosphates, or acetates. Among these phosphorus-containing compounds, phosphoric acid and ammonium dihydrogen phosphate, which have a high intramolecular phosphorus content, are preferred from the viewpoint of incorporating a large amount of phosphorus element into the carbonaceous material. As the phosphorus-containing compound, a compound having a volatilization temperature of preferably 100°C or higher, more preferably 150°C or higher, is preferred from the viewpoint of reaction with a saccharide compound during the heat treatment process.

[0050] The method for mixing the phosphorus-containing compound is not particularly limited. When the phosphorus-containing compound is solid, the solid phosphorus-containing compound may be mixed with a saccharide compound or the like. When the phosphorus-containing compound is water-soluble, an aqueous solution of the phosphorus-containing compound may be mixed with a saccharide compound or the like.

[0051] When a phosphorus-containing compound is also mixed, the total amount thereof is preferably 0.5 to 10 mass%, more preferably 0.6 to 8 mass%, based on the total mass of the saccharide compound and the nitrogen-containing compound, or the mass of the nitrogen-containing saccharide compound when no nitrogen-containing compound is used, or based on the mass of the carbonized product obtained in step (2). When a phosphorus-containing compound is also mixed, the total amount thereof is preferably 0.001 to 0.20 mol, more preferably 0.005 to 0.15 mol, and even more preferably 0.01 to 0.10 mol, based on 1 mol of starch monosaccharide unit in the saccharide compound.

[0052] In addition to steps (1) to (4) or steps (1) to (5), the production method may further include step (b) of gelatinizing the saccharide compound before, simultaneously with, or after step (1). When step (b) is further carried out, cavities present in the saccharide compound disappear, and as a result, the density of the electrode formed from the finally obtained carbonaceous material can be increased, and the discharge capacity per volume can be increased.

[0053] When step (b) is performed, the gelatinization method is not particularly limited. Examples include a method of heating a saccharide compound alone or in any mixture with a nitrogen-containing compound or the like in the presence of water, and a method of subjecting a saccharide compound alone or in any mixture with a nitrogen-containing compound or the like to mechanical treatment with impact, crushing, friction, and / or shear. The application of such heat or external force can cause cavities in the saccharide compound to be blocked and disappear. The gelatinization in step (b) can be carried out, for example, by observing the cross-section of a particle of the gelatinized saccharide compound with a secondary electron microscope, and then forming a cavities with a cross-sectional area of ​​3 μm or less. ２ 100 μm or more ２ When 20 particles below are randomly selected, ２It is preferable to continue the measurement until the number of particles having the above voids is reduced to a predetermined amount or less, preferably 3 or less, more preferably 2 or less, and even more preferably 1 or less. The above-mentioned microscopic observation may be performed after removing aggregates contained in the compound or mixture after gelatinization by pulverization or classification. When step (b) is performed, the mixture obtained through step (1) and optional step (b) as described above is heat-treated in step (2). Therefore, when step (b) is performed, step (b) is a step performed before step (2).

[0054] In a preferred embodiment of the present invention, the production method may include one or more of the following steps as step (b): - step (b1) before step (1), mixing a saccharide compound with 5 to 50% by mass of water relative to the mass of the compound, and heating at a temperature of 50 to 200°C for 1 minute to 5 hours; - step (b2) before step (1), subjecting the saccharide compound to a mechanical treatment having an action of impact, crushing, friction, and / or shear; - step (b3) simultaneously with the mixing in step (1) or after the mixing or preparation in step (1), mixing a mixture containing a saccharide compound or a prepared nitrogen-containing saccharide compound with 5 to 50% by mass of water relative to the mass of the saccharide compound contained in the mixture or the prepared nitrogen-containing saccharide compound, and heating at a temperature of 50 to 200°C for 1 minute to 5 hours; - A step (b4) of subjecting the mixture containing the saccharide compound or the prepared nitrogen-containing saccharide compound to a mechanical treatment having the effects of impact, crushing, friction, and / or shear, either simultaneously with the mixing in step (1) or after the mixing or preparation in step (1).

[0055] Although a certain amount of water is required in step (b1), a smaller amount is preferable from the viewpoint of suppressing the energy required to distill off the mixed water in the process of producing a carbonaceous material. Therefore, the amount of water is 5 to 50 mass% relative to the mass of the nitrogen-containing saccharide compound when no saccharide compound or nitrogen-containing compound is used, preferably 10 to 50 mass%, more preferably 10 to 30 mass%. The heating temperature is 50 to 200°C, preferably 60 to 180°C, more preferably 80 to 180°C, and the heating time is 1 minute to 5 hours, preferably 3 minutes to 1 hour, more preferably 10 minutes to 30 minutes.

[0056] In step (b2), examples of the equipment used for the mechanical treatment having impact, crushing, friction, and / or shearing action include a pulverizer, extruder, flour mill, grinder, and kneader. The treatment conditions, such as the treatment time, are not particularly limited. For example, when a ball vibration mill is used, treatment conditions of 20 Hz and 10 minutes can be adopted.

[0057] The preferred amount of water, heating temperature and heating time in step (b3) are the same as those described for step (b1).

[0058] The preferred apparatus and treatment conditions in step (b4) are the same as those described for step (b2).

[0059] <Negative electrode for electricity storage device> The carbonaceous material of the present invention or the carbonaceous material produced by the production method can be suitably used as a carbonaceous material for the negative electrode of an electricity storage device, more specifically, as an active material for the negative electrode of an electricity storage device. By using the carbonaceous material, it is possible to produce a negative electrode for an electricity storage device that provides high charge capacity and discharge capacity per mass, high current efficiency, and high energy density. Therefore, the present invention also covers a negative electrode for an electricity storage device that includes the carbonaceous material.

[0060] The negative electrode can be manufactured by a method commonly used in the art. For example, a carbonaceous material is first mixed with a binder, and then further mixed with an appropriate amount of a suitable solvent to prepare a slurry electrode mixture. The resulting electrode mixture is applied to a current collector plate such as a metal plate, dried, and then pressure-molded. This allows the manufacture of a negative electrode for an electricity storage device, such as a non-aqueous electrolyte secondary battery, such as a lithium-ion secondary battery, a sodium-ion battery, a lithium-sulfur battery, or a lithium-air battery.

[0061] The amount of the carbonaceous material in the electrode mixture is preferably 80 to 100% by mass, and more preferably 90 to 97% by mass, when the total amount of the active material (carbonaceous material) + the amount of the binder + the amount of any optional components (for example, the conductive assistant described below) used is taken as 100% by mass.

[0062] The binder is not particularly limited as long as it does not react with the electrolyte. Examples include PVDF (polyvinylidene fluoride), polytetrafluoroethylene, and a mixture of SBR (styrene butadiene rubber) and CMC (carboxymethyl cellulose). A mixture of SBR and CMC is particularly preferred because the SBR and CMC attached to the active material surface do not significantly inhibit the movement of electrolyte ions, resulting in good input / output characteristics. If the amount of binder is too large, the resistance of the resulting electrode increases, which can increase the internal resistance of the energy storage device and degrade its electrical characteristics. Furthermore, if the amount of binder is too small, the bonding between the particles of the negative electrode material and with the current collector may be insufficient. The preferred amount of binder varies depending on the type of binder used. For example, when a binder uses water as a solvent, it is often used by mixing multiple binders, such as a mixture of SBR and CMC, and the total mass of these binders is preferably 0.5 to 5 mass%, more preferably 1 to 4 mass%, when the total mass of the active material, binder, and optional components, if used, is taken as 100 mass%.On the other hand, when a PVDF-based binder is used, it is preferably 3 to 13 mass%, more preferably 3 to 10 mass%, when the total mass of the active material, binder, and optional components, if used, is taken as 100 mass%.

[0063] A polar solvent such as water is preferably used as the solvent to form an aqueous emulsion of SBR or the like or an aqueous solution of CMC. A polar solvent such as N-methylpyrrolidone is preferably used to dissolve PVDF to form a slurry. The amount of solvent is preferably 10 to 200 parts by mass, more preferably 50 to 150 parts by mass, assuming that the amount of active material + the amount of binder + the amount of optional components, if used, is 100 parts by mass.

[0064] If it is desired to impart higher conductivity to the negative electrode, a conductive additive may be further mixed into the electrode mixture as needed. Examples of conductive additives include conductive carbon black, vapor-grown carbon fiber (VGCF), nanotubes, etc. The amount of conductive additive varies depending on the type of conductive additive used; however, if the amount is too small, the desired conductivity may not be achieved, while if the amount is too large, dispersion in the electrode mixture may be poor. From this perspective, when a conductive additive is used, its amount is preferably 0.5 to 10% by mass, more preferably 0.5 to 7% by mass, and even more preferably 0.5 to 5% by mass, assuming that the amount of active material + amount of binder + amount of conductive additive = 100% by mass.

[0065] The active material layer is generally formed on both sides of the current collector plate, but may be formed on one side if necessary. A thicker active material layer is preferable for achieving higher capacity, since fewer current collector plates or separators are required. However, since a larger electrode area facing the counter electrode is advantageous for improving input / output characteristics, if the active material layer is too thick, the input / output characteristics may deteriorate. From the viewpoint of output during discharge of the electricity storage device, 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.

[0066] <Electricity storage device> An electricity storage device using the carbonaceous material in the negative electrode can have a high energy density as well as a high charge capacity and discharge capacity per mass and a high current efficiency. The present invention also covers such an electricity storage device, i.e., an electricity storage device including the negative electrode for an electricity storage device of the present invention. When manufacturing the electricity storage device of the present invention, other materials constituting the electricity storage device, such as the positive electrode material, separator, and electrolyte, are not particularly limited. Various materials that have been conventionally used or proposed for electricity storage devices can be used.

[0067] The positive electrode material is a layered oxide [LiMO ２ where M represents a metal, for example, LiCoO ２ , LiNiO ２ , LiMnO ２ , or LiNi ｘ Co ｙ Moｚ O ２ (where x, y, and z represent the composition ratio)], olivine-based (LiMPO ４ where M represents a metal, for example, LiFePO ４ etc.), spinel-based (LiM ２ O ４ where M represents a metal, for example, LiMn ２ O ４ A composite metal chalcogen compound such as a fluorine-containing compound (e.g., fluorine-containing ...

[0068] For example, when the electricity storage device is a non-aqueous electrolyte secondary battery, the non-aqueous solvent-type electrolyte solution is generally prepared by dissolving an electrolyte in a non-aqueous solvent. Examples of non-aqueous solvents include organic solvents such as propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dimethoxyethane, diethoxyethane, γ-butyl lactone, tetrahydrofuran, 2-methyltetrahydrofuran, sulfolane, and 1,3-dioxolane, and these can be used alone or in combination of two or more. In addition, the electrolyte can be LiClO ４ , LiPF ６ , LiBF ４ , LiCF ３ SO ３ , LiAsF ６ , LiCl, LiBr, LiB(C ６ H ５ ) ４ , or LiN(SO ３ CF ３ ) ２ etc. are used.

[0069] When the power storage device is a nonaqueous electrolyte secondary battery, the nonaqueous electrolyte secondary battery is generally produced by arranging the positive electrode and negative electrode formed as described above facing each other, with a liquid-permeable separator interposed between them as needed, and immersing them in an electrolyte solution. Such a separator can be a nonwoven fabric or other permeable or liquid-permeable separator made of a porous material commonly used in secondary batteries. Alternatively, a solid electrolyte made of a polymer gel impregnated with an electrolyte solution can be used instead of or together with the separator.

[0070] The present invention will be described in detail below with reference to examples, but the scope of the present invention is not limited to these examples. Hereinafter, methods for measuring the physical properties of carbonaceous materials and negative electrodes using the same will be described. The physical properties and measurements (or physical property values ​​and measured values) described in this specification, including the examples, are based on values ​​determined by the following methods.

[0071] <Raman Spectrum> A Raman spectrometer ("Laser Raman Microscope Ramanforce" manufactured by Nanophoton Inc.) was used. The carbonaceous material to be measured was set on the observation stage, the magnification of the objective lens was set to 20 times, the material was focused, and measurements were taken while irradiating it with argon ion laser light. The details of the measurement conditions are as follows. From the obtained Raman spectrum, a peak at 1360 cm －１ The half-width of the peak around the wavelength of the argon ion laser beam was determined. The laser power on the sample was 100-300 W / cm. ２ Resolution: 5-7cm －１ Measurement range: 150-4000 cm －１ Measurement mode: XY Averaging Exposure time: 20 seconds Number of integrations: 2 Peak intensity measurement: Baseline correction Polynom-3rd order automatic correction Peak search & fitting processing Gauss Lorentz

[0072] <True density determined by helium method> True density ρ of carbonaceous material Ｈｅwas determined using a fully automatic pycnometer (Quantachrome Instruments' "UltraPyc1200e"). The measurement conditions were as follows: Cell size: Large Gas used: Helium Sample amount: 1.0 g Equilibration time: Automatic Flow purge: 10 min Maximum number of measurements: 30 Required deviation: 0.0500%

[0073] <Hydrogen, oxygen, and nitrogen elemental content> 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 methods used by this device were oxygen: inert gas fusion-non-dispersive infrared absorption (NDIR), nitrogen: inert gas fusion-thermal conduction (TCD), and hydrogen: inert gas fusion-non-dispersive infrared absorption (NDIR), and calibration was performed using a Sn capsule (oxygen / nitrogen), TiH ２ (H standard sample), SS-3 (O standard sample), and SiN (N standard sample). Five mg of the sample, which had been pretreated at 250°C for approximately 10 minutes and had its moisture content measured, was placed in a Sn capsule and degassed for 30 seconds in an analyzer, after which elemental analysis was performed. Three samples were analyzed for each carbonaceous material, and the average of the measured contents of each element was taken as the content of each element in the carbonaceous material.

[0074] <Content of alkali metal elements and alkaline earth metal elements> The content of alkali metal elements and alkaline earth metal elements was measured by the following method. First, a calibration curve for the content of each alkali metal element and alkaline earth metal element was created from a standard solution of known concentration. Next, the pulverized measurement sample was dried at 115 ° C. for 3 hours. 0.1 g of the dried measurement sample was introduced into a decomposition vessel, 10 mL of nitric acid was added and mixed, and then the sample was dissolved using a microwave sample pretreatment device ("MARS6" manufactured by CEM Japan Co., Ltd.). The solution was removed and diluted to 25 mL to prepare a measurement solution, which was then analyzed using an ICP optical emission spectrometer ("ICPE-9820" manufactured by Shimadzu Corporation). The concentration of each alkali metal element and alkaline earth metal element was determined from the obtained value and the previously created calibration curve, and the content of each alkali metal element and alkaline earth metal element was calculated using the following formula. The total content of alkali metal elements and alkaline earth metal elements was calculated by adding the content of alkali metal elements and the content of alkaline earth metal elements. In Examples 1 to 8 and Comparative Examples 1, 2, and 4, the total content was calculated as the content of sodium element.

[0075] <Carbon interplanar spacing d by X-ray diffraction measurement ００２ The carbonaceous material to be measured was loaded into a sample holder of a "MiniFlex II" manufactured by Rigaku Corporation, and an X-ray diffraction pattern was obtained using CuKα radiation monochromatized by a Ni filter as the radiation source. The peak positions of the X-ray diffraction pattern were determined by the centroid method (a method in which the centroid position of the diffraction line is determined and the peak position is determined using the corresponding 2θ value), and correction was performed using the diffraction peak of the (111) plane of high-purity silicon powder for standard material. The wavelength λ of CuKα radiation was set to 0.15418 nm, and d was calculated using the Bragg formula shown below. ００２ was calculated.

[0076] Example 1: 10.0 g of starch (corn starch), 0.16 g of trisodium citrate dihydrate (0.010 mol per mol of starch monosaccharide units), and 100 mL of pure water were added to a beaker and stirred at 100 rpm for 1 hour using a stirrer. The mixture was then dried at 50°C for 8 hours using a dryer (Tokyo Rikakikai Co., Ltd., "WFO-520") to obtain a dried product. The resulting dried product was pulverized using an agate mortar. The pulverized dried product, 1.16 g of melamine (0.15 mol per mol of starch monosaccharide units), and 0.76 g of adipic acid (0.085 mol per mol of starch monosaccharide units) were introduced into a sample bottle and shaken to obtain a mixture (steps (1) and (a)). The resulting mixture was heated to 600°C at a heating rate of 10°C / min (60°C / hr) while supplying nitrogen gas. Next, the mixture was heat-treated at 600°C for 30 minutes while supplying nitrogen gas to obtain a carbonized product (step (2)). The amount of nitrogen gas supplied during the temperature increase and heat treatment was 0.5 L / min per 10.0 g of starch. The obtained carbonized product was pulverized in a ball mill to obtain D ５０A pulverized carbide having a particle size of 5 μm was obtained (step (3)). The pulverized carbide and polystyrene (manufactured by Sekisui Plastics Co., Ltd., average particle size 400 μm, residual carbon content 1.2 mass%) were introduced into a 100 mL container at a mass ratio of 1:0.1 and mixed by shaking at 2 Hz for 5 minutes. The resulting mixture was heated to 1150°C at a heating rate of 10°C / min while supplying nitrogen gas. Next, a carbonaceous material was obtained by heat-treating the mixture at 1150°C for 10 minutes while supplying nitrogen gas (step (4)). The nitrogen gas supply rate during heating and heat treatment was 3 L / min per 5.0 g of pulverized carbide. The resulting carbonaceous material was analyzed.

[0077] Example 2 A carbonaceous material was obtained in the same manner as in Example 1, except that the amount of trisodium citrate dihydrate used as an activator was changed from 0.16 g (0.010 mol per mol of starch monosaccharide units) to 0.32 g (0.020 mol per mol of starch monosaccharide units), and the obtained carbonaceous material was analyzed.

[0078] Example 3 A carbonaceous material was obtained in the same manner as in Example 1, except that the amount of melamine as the nitrogen-containing compound was changed from 1.16 g (0.15 mol per mol of starch monosaccharide units) to 2.00 g (0.26 mol per mol of starch monosaccharide units), and the obtained carbonaceous material was analyzed.

[0079] Example 4 A carbonaceous material was obtained in the same manner as in Example 1, except that 10.0 g of glucose was used instead of 10.0 g of starch as the saccharide compound, and the obtained carbonaceous material was analyzed.

[0080] Example 5 A carbonaceous material was obtained in the same manner as in Example 1, except that 1.16 g of dicyandiamide (0.23 mol per mol of starch monosaccharide units) was used as the nitrogen-containing compound instead of 1.16 g of melamine (0.15 mol per mol of starch monosaccharide units), and the obtained carbonaceous material was analyzed.

[0081] Example 6 A carbonaceous material was obtained in the same manner as in Example 1, except that the amount of trisodium citrate dihydrate used as an activator was changed from 0.16 g (0.010 mol per mol of starch monosaccharide units) to 0.80 g (0.050 mol per mol of starch monosaccharide units), and the obtained carbonaceous material was analyzed.

[0082] Example 7 A carbonaceous material was obtained in the same manner as in Example 1, except that 0.20 g of disodium molybdate dihydrate (0.013 mol per mol of starch monosaccharide units) was used as the activator instead of 0.16 g of trisodium citrate dihydrate (0.010 mol per mol of starch monosaccharide units), and the obtained carbonaceous material was analyzed.

[0083] Example 8 A carbonaceous material was obtained in the same manner as in Example 7, except that 0.4 g of ammonium dihydrogen phosphate (0.057 mol per 1 mol of starch monosaccharide unit) as a phosphorus-containing compound was also introduced into the sample bottle in step (1) and step (a), and the obtained carbonaceous material was analyzed.

[0084] Comparative Example 1 Step (a) was not performed, and in step (1), 10.0 g of starch (corn starch), 1.16 g of melamine (0.15 mol per mol of starch monosaccharide units), and 0.76 g of adipic acid (0.085 mol per mol of starch monosaccharide units) were introduced into a sample bottle and shaken to obtain a mixture. Step (2) and subsequent steps were carried out in the same manner as in Example 1 to obtain a carbonaceous material, which was then analyzed.

[0085] Comparative Example 2 A carbonaceous material was obtained in the same manner as in Example 1, except that in step (4), instead of increasing the temperature to 1150°C and performing heat treatment at 1150°C for 10 minutes, the temperature was increased to 1350°C and heat treatment at 1350°C for 60 minutes, and the obtained carbonaceous material was analyzed.

[0086] Comparative Example 3: Coconut shells were crushed and dry-distilled at 500°C to obtain coconut shell char with a particle size of 2.360 to 0.850 mm (containing 98% by mass of particles with a particle size of 2.360 to 0.850 mm). 100 g of this coconut shell char was subjected to a vapor-phase demineralization treatment at 870°C for 50 minutes while supplying nitrogen gas containing 1% by volume of hydrogen chloride gas at a flow rate of 10 L / min. Next, the supply of hydrogen chloride gas was stopped, and a vapor-phase deoxidation treatment was further performed at 870°C for 30 minutes while supplying nitrogen gas at a flow rate of 10 L / min to obtain a carbon precursor. The obtained carbon precursor was coarsely pulverized to an average particle size of 10 μm using a ball mill, and then pulverized and classified using a compact jet mill (Seishin Enterprise Co., Ltd., "Cojet System α-mkIII") to obtain a carbon precursor with an average particle size of 9.6 μm. 9.1 g of this carbon precursor was mixed with 0.9 g of polystyrene (manufactured by Sekisui Plastics Co., Ltd., average particle size 400 μm, residual carbon content 1.2%). 10 g of this mixture was introduced into a graphite sheath (length 100 mm, width 100 mm, height 50 mm) and heated to 1250°C at a heating rate of 60°C / min in a nitrogen flow rate of 5 L / min in a Motoyama Co., Ltd. high-speed heating furnace. The temperature was then maintained for 11 minutes and allowed to cool naturally. After confirming that the temperature inside the furnace had dropped to 200°C or below, the carbonaceous material was removed from the furnace. The resulting carbonaceous material was analyzed.

[0087] Comparative Example 4 A carbonaceous material was obtained in the same manner as in Comparative Example 1, except that in step (4), instead of increasing the temperature to 1150°C and performing heat treatment at 1150°C for 10 minutes, the temperature was increased to 1000°C and heat treatment at 1000°C for 60 minutes, and the obtained carbonaceous material was analyzed.

[0088] <Electrode Fabrication> Using the carbonaceous materials obtained in each Example and Comparative Example, negative electrodes were fabricated according to the following procedure. 95 parts by mass of the carbonaceous material, 2 parts by mass of conductive carbon black ("Super-P (registered trademark)" manufactured by TIMCAL), 1 part by mass of carboxymethyl cellulose (CMC), 2 parts by mass of styrene-butadiene rubber (SBR), and 90 parts by mass of water were mixed to obtain a slurry. The obtained slurry was applied to one side of a 15 μm thick copper foil, dried, pressed, and punched out to a diameter of 14 mm to obtain a 45 μm thick electrode.

[0089] <Charge capacity and discharge capacity per mass, and current efficiency> The electrode prepared above was used as the working electrode, and metallic lithium was used as the counter electrode and reference electrode. Ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate were mixed in a volume ratio of 1:1:1 and used as the solvent. LiPF ６ The electrolyte solution was prepared using a polypropylene membrane as the separator. Coin cells were fabricated in a glove box under an argon atmosphere. A charge-discharge test was performed on the lithium secondary battery with the above configuration using a charge-discharge tester ("TOSCAT" manufactured by Toyo Systems Co., Ltd.). Lithium doping was performed at a rate of 70 mA / g relative to the active material mass until the doping reached 1 mV relative to the lithium potential. A constant voltage of 1 mV relative to the lithium potential was further applied, and doping was terminated when the doping rate reached 2 mA / g relative to the active material mass. The capacity at this time was designated the initial charge capacity (mAh). Next, undoping (CC discharge) was performed at a rate of 70 mA / g relative to the active material mass until the doping reached 1.5 V relative to the lithium potential, and the discharged capacity at this time was designated the initial discharge capacity (mAh). The initial charge capacity and discharge capacity were divided by the mass of the negative electrode to obtain the charge capacity per mass (mAh / g) and discharge capacity per mass (mAh / g) (evaluation of initial charge / discharge). The initial discharge capacity was divided by the initial charge capacity, and the percentage of the obtained value was used as the current efficiency (%).

[0090] <CC Discharge Capacity, CV Discharge Capacity, and CV / CC Ratio> The capacity per mass at 0.1 V or less when CC discharge was performed was defined as the CV discharge capacity (mAh / g), and the capacity per mass at 0.1 V or more was defined as the CC discharge capacity (mAh / g). The CV discharge capacity was divided by the CC discharge capacity, and the resulting value was defined as the CV / CC ratio.

[0091]

[0092]

[0093] When the carbonaceous material of the present invention is applied to a negative electrode, it is possible to provide an electricity storage device having high charge capacity and discharge capacity per mass, high current efficiency, and high energy density. Therefore, the carbonaceous material of the present invention can be suitably used as a carbonaceous material for the negative electrode of an electricity storage device.

Claims

1. 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 200 to 280 cm －１ and the true density determined by the helium method is 1.30 to 1.95 g / cc, and the nitrogen element content determined by elemental analysis is 0.5 to 4.6 mass%, a carbonaceous material. －１ ​ 2. The carbonaceous material according to claim 1, wherein the total content of alkali metal elements and alkaline earth metal elements determined by ICP emission spectrometry is 0.70 to 2.0% by mass.

3. The carbon interlayer spacing (d ００２ ) determined by X-ray diffraction measurement is 3.65 to 4.00 Å, and the carbonaceous material according to claim 1.

4. The carbonaceous material according to any one of claims 1 to 3, which is a carbonaceous material for a negative electrode of an energy storage device.

5. A negative electrode for an energy storage device, comprising the carbonaceous material according to claim 4.

6. An energy storage device, comprising the negative electrode for an energy storage device according to claim 5.

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