CN118055902A - Carbonaceous material, negative electrode for electricity storage device, and method for producing carbonaceous material - Google Patents

Abstract

The present invention relates to a carbonaceous material having a nitrogen element content of 1.0 mass% or more based on elemental analysis and a phosphorus element content of 0.5 mass% or more based on fluorescent X-ray analysis.

Description

Carbonaceous material, negative electrode for electricity storage device, and method for producing carbonaceous material

Technical Field

The present invention relates to a carbonaceous material, a negative electrode for an electric storage device, and a method for producing a carbonaceous material.

Background

The power storage device is a device such as a secondary battery and a capacitor that uses an electrochemical phenomenon, and is widely used. For example, a lithium ion secondary battery as one of the electric storage devices is widely used in small portable devices such as a mobile phone and a notebook computer. As a negative electrode material of a lithium ion secondary battery, hardly graphitizable carbon capable of doping (charging) and dedoping (discharging) lithium in an amount exceeding 372mAh/g of theoretical capacity has been developed and used gradually (for example, patent document 1).

The hardly graphitizable carbon may be obtained by using, for example, petroleum pitch, coal pitch, phenol resin, or plant as a carbon source. Among these carbon sources, particularly, a plant-derived raw material such as a sugar compound is a raw material that can be continuously and stably supplied by cultivation, and can be obtained at low cost, and thus, attention has been paid. Further, since a carbonaceous material obtained by calcining a plant-derived carbon raw material has a plurality of pores, a good charge-discharge capacity can be expected (for example, patent document 1 and patent document 2).

As a carbonaceous material that can be used as a negative electrode of a lithium ion secondary battery or the like, a carbonaceous material in which the content of various elements other than carbon element is adjusted to a specific amount is known (patent document 3).

Prior art literature

Patent literature

Patent document 1: international publication No. 2019/009332

Patent document 2: international publication No. 2019/009333

Patent document 3: japanese patent laid-open No. 2009-200014

Disclosure of Invention

Problems to be solved by the invention

Although carbonaceous materials used as negative electrode materials are known, demands for a high capacity of a negative electrode and an improvement in current efficiency still remain in various applications of an electric storage device. Accordingly, an object of the present invention is to provide a carbonaceous material for an electrical storage device having a high discharge capacity per unit weight and a high current efficiency when used as a negative electrode layer. Another object of the present invention is to provide a negative electrode for an electric storage device comprising such a carbonaceous material, and an electric storage device comprising such a negative electrode for an electric storage device.

Means for solving the problems

The inventors have conducted intensive studies and as a result, they have found that: by setting the nitrogen element content and the phosphorus element content in the carbonaceous material within the prescribed ranges, a carbonaceous material suitable for an electric storage device having a high discharge capacity per unit weight and excellent current efficiency is obtained.

That is, the present invention includes the following suitable modes.

The carbonaceous material has a nitrogen element content of 1.0 mass% or more based on elemental analysis and a phosphorus element content of 0.5 mass% or more based on fluorescent X-ray analysis.

[ 2 ] The carbonaceous material according to [ 1 ], wherein the carbon-to-surface spacing (d ₀₀₂) as measured by X-ray diffraction isThe above.

[ 3 ] The carbonaceous material according to [1 ] or [ 2 ], wherein the content of oxygen element based on elemental analysis is less than 1.5% by mass.

The carbonaceous material according to any one of [1 ] to [ 3], wherein a half-value width of a peak in the vicinity of 1360cm ^-1 in a Raman spectrum observed by a laser Raman spectroscopy is 230cm ^-1 or more.

The carbonaceous material according to any one of [ 1] to [ 4 ], wherein a half-value width of a peak around 1650cm ^-1 in a Raman spectrum observed by a laser Raman spectroscopy is 98cm ^-1 or more.

The carbonaceous material according to any one of [1 ] to [ 5 ], which is a carbonaceous material for a negative electrode of an electric storage device.

The negative electrode for an electric storage device according to [ 7 ], which comprises the carbonaceous material according to any one of [ 1] to [ 6 ].

[ 8 ] An electrical storage device comprising the negative electrode for electrical storage device of [ 7 ].

The method for producing a carbonaceous material according to any one of [ 9 ] [1] to [ 6], comprising at least the steps of:

(1) A step of mixing a compound having a saccharide skeleton with a nitrogen-containing compound to obtain a mixture;

(2) A step of heat-treating the mixture at 500-900 ℃ in an inert gas atmosphere to obtain carbide;

(3) A step of pulverizing and/or classifying the carbide; and

(4) A step of heat-treating the crushed and/or classified carbide at 800-1600 ℃ in an inert gas atmosphere to obtain a carbonaceous material,

The method for producing the carbonaceous material comprises the steps of:

(a) And (3) a step of mixing a compound having a saccharide skeleton, a mixture containing the compound, or a carbide of the mixture with a phosphorus-containing compound before the heat treatment in the step (4).

Effects of the invention

According to the present invention, a carbonaceous material suitable for an electrical storage device having a high discharge capacity per unit weight and excellent current efficiency can be provided.

Detailed Description

Hereinafter, embodiments of the present invention will be described in detail. The present invention is not limited to the following embodiments.

In the present specification, the power storage device refers to all devices including a negative electrode containing a carbonaceous material and utilizing an electrochemical phenomenon. Specifically, the power storage device includes, for example, a lithium ion secondary battery, a nickel hydrogen secondary battery, a nickel cadmium secondary battery, and other secondary batteries that can be repeatedly used by charging, and a capacitor, and the like, such as an electric double layer capacitor. Among these, the power 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, or the like), among which may be a lithium ion secondary battery.

The carbonaceous material of the present invention is a carbonaceous material suitable for providing an electrical storage device having a high discharge capacity per unit weight and excellent current efficiency, and has a nitrogen element content of 1.0 mass% or more based on elemental analysis and a phosphorus element content of 0.5 mass% or more based on fluorescent X-ray analysis.

The carbonaceous material of the present invention has a phosphorus element content of 0.5 mass% or more based on fluorescent X-ray analysis. The phosphorus content is an analysis value obtained by performing fluorescent X-ray analysis on a carbonaceous material. When the phosphorus content is less than 0.5 mass%, sites for adsorbing and desorbing lithium ions during charge and discharge become small, and therefore the discharge capacity and current efficiency per unit weight cannot be sufficiently improved. The phosphorus element content is preferably 0.6 mass% or more, more preferably 0.7 mass% or more, still more preferably 0.9 mass% or more, and still more preferably 1.2 mass% or more, from the viewpoint of easier improvement of discharge capacity and current efficiency. The phosphorus element content may be 1.4 mass% or more, 1.6 mass% or more, 1.7 mass% or more, or the like from the viewpoint of facilitating further improvement of discharge capacity. The upper limit of the content of the phosphorus element is preferably 4.0 mass% or less, more preferably 3.0 mass% or less, further preferably 2.7 mass% or less, further more preferably 2.5 mass% or less, particularly preferably 2.3 mass% or less, and particularly preferably 2.0 mass% or less, from the viewpoint of easily suppressing the occurrence of irreversible adsorption of lithium ions and easily improving the current efficiency. The phosphorus content of the carbonaceous material based on the fluorescent X-ray analysis can be adjusted to the above range by adjusting the addition amount of the phosphorus-containing compound that can be added at the time of producing the carbonaceous material, adjusting the temperature at which the heat treatment is performed, the time, and the like.

The carbonaceous material of the present invention has a nitrogen element content of 1.0 mass% or more based on elemental analysis. The nitrogen element content is an analysis value obtained by elemental analysis of a carbonaceous material. The discovery is as follows: by containing 1.0 mass% or more of nitrogen element in the carbonaceous material, the discharge capacity and current efficiency can be further improved as compared with a carbonaceous material containing only phosphorus element. Carbonaceous materials containing only phosphorus tend to have an increased oxygen atom content because phosphorus is easily oxidized, and thus current efficiency tends to be lowered. On the other hand, although the reason is not clear, it is considered that: the carbonaceous material containing both the nitrogen element and the phosphorus element tends to reduce the phosphorus element and reduce the oxygen element content, and thus the current efficiency can be improved. Further, when the nitrogen element content is less than 1.0 mass%, sites for adsorbing and desorbing lithium ions at the time of charge and discharge become small due to the proximity of carbon surfaces, and therefore, the discharge capacity per unit weight cannot be sufficiently improved in this point as well. The nitrogen element content is preferably 1.2 mass% or more, more preferably 1.5 mass% or more, still more preferably 1.9 mass% or more, still more preferably 2.0 mass% or more, and particularly preferably 2.2 mass% or more, from the viewpoint of easier improvement of discharge capacity and current efficiency. The upper limit of the nitrogen element content is preferably 8.0 mass% or less, more preferably 6.0 mass% or less, further preferably 5.0 mass% or less, and still further preferably 4.0 mass% or less, from the viewpoint of suppressing a decrease in discharge capacity upon repeated charge and discharge. The nitrogen element content of the carbonaceous material based on elemental analysis can be adjusted to the above range by adjusting the addition amount of the nitrogen-containing compound that can be added at the time of producing the carbonaceous material, adjusting the temperature at which the heat treatment is performed, the time, and the like.

The carbon-to-carbon spacing (d ₀₀₂) of the carbonaceous material of the invention based on X-ray diffraction measurement is preferably from the viewpoints of easy widening of the carbon-to-carbon spacing, effective movement of lithium ions, sufficiently developed micropores, increased absorption and storage sites of clustered lithium, and easy improvement of discharge capacity and current efficiency per unit weightAbove, more preferably/>The above is more preferably/>The above is more preferably/>The above is particularly preferred/>The above. In addition, from the viewpoints of appropriately reducing the volume of the carbonaceous material by appropriately reducing d ₀₀₂, increasing the practical capacity per unit volume, and easily increasing the discharge capacity per unit volume, the upper limit of the carbon-surface spacing (d ₀₀₂) is preferably/>Hereinafter, more preferable areHereinafter, it is more preferable that/>Hereinafter, it is more preferable that/>The following is given. The carbon surface spacing (d ₀₀₂) was measured by X-ray diffraction and using Bragg formula, specifically, by the method described in examples. The carbon surface spacing (d ₀₀₂) can be adjusted to the above range by adjusting the amount of the nitrogen-containing compound that can be added when producing the carbonaceous material, adjusting the temperature and time at which the heat treatment is performed, and the like.

In a preferred embodiment of the present invention, the value of the half-value width of the peak around 1360cm ^-1 in the raman spectrum of the carbonaceous material of the present invention, which is observed by the laser raman spectroscopy, is preferably 230cm ^-1 or more, more preferably 240cm ^-1 or more, still more preferably 250cm ^-1 or more, still more preferably 260cm ^-1 or more, from the viewpoint of easier improvement of the discharge capacity of the electrode produced using the carbonaceous material. Here, the peak around 1360cm ^-1 means a raman peak, which is generally called D-band, which is a peak caused by disturbance/defect of graphite structure. The peak around 1360cm ^-1 is usually observed in the range 1345cm ^-1～1375cm^-1, preferably 1350cm ^-1～1370cm^-1. The raman spectrum is measured using a raman spectrometer under the conditions described in examples. The half width of the peak around 1360cm ^-1 can be adjusted to the above range by adjusting the amount of the nitrogen-containing compound that can be added at the time of producing the carbonaceous material, adjusting the temperature and time at which the heat treatment is performed, and the like.

In a preferred embodiment of the present invention, the value of the half-value width of the peak around 1650cm ^-1 in the raman spectrum of the carbonaceous material of the present invention, which is observed by the laser raman spectroscopy, is preferably 98cm ^-1 or more, more preferably 100cm ^-1 or more, still more preferably 101cm ^-1 or more, still more preferably 102cm ^-1 or more, from the viewpoint of more easily improving the discharge capacity per unit weight of the electrode produced using the carbonaceous material. Here, the peak around 1650cm ^-1 means a raman peak, which is generally called G band, and is a peak caused by disorder/defect of graphite structure. A peak around 1650cm ^-1 is generally observed in the range of 90cm ^-1～120cm^-1, preferably in the range of 100cm ^-1～110cm^-1. The raman spectrum is measured using a raman spectrometer under the conditions described in examples. The half width of the peak around 1650cm ^-1 can be adjusted within the above range by adjusting the amount of the nitrogen-containing compound that can be added at the time of producing the carbonaceous material, adjusting the temperature and time at which the heat treatment is performed, and the like.

The oxygen element content of the carbonaceous material according to the present invention based on elemental analysis is preferably less than 1.5 mass%, more preferably 1.3 mass% or less, further preferably 1.2 mass% or less, and still further preferably 1.1 mass% or less, from the viewpoint of easier improvement of current efficiency. The lower limit of the oxygen element content is preferably 0 mass% or more. The oxygen element content of the carbonaceous material based on elemental analysis can be reduced by increasing the addition amount of the nitrogen-containing compound and the phosphorus-containing compound that can be added in the production of the carbonaceous material, and can be adjusted to the above range by adjusting the temperature, time, and the like at which the heat treatment is performed.

In the carbonaceous material of the invention, the true density of the carbonaceous material by the butanol impregnation method is preferably 1.50g/cc or more, more preferably 1.51g/cc or more, still more preferably 1.52g/cc or more, still more preferably 1.55g/cc or more, and preferably 1.65g/cc or less, more preferably 1.64g/cc or less, still more preferably 1.62g/cc or less, still more preferably 1.60g/cc or less, from the viewpoint of easily increasing the electrode density of the negative electrode obtained by using the carbonaceous material, and consequently, the discharge capacity per unit volume is also easily increased in addition to the discharge capacity per unit weight.

In the carbonaceous material of the invention, the tap bulk density of the carbonaceous material is preferably 0.70g/cc or more, more preferably 0.72g/cc or more, still more preferably 0.75g/cc or more, still more preferably 0.78g/cc or more, and particularly preferably 0.80g/cc or more, from the viewpoint of easiness in increasing the electrode density. In addition, from the viewpoint of liquid absorption of the electrolyte at the time of manufacturing the electrode, the tap volume density is preferably 1.0g/cc or less, more preferably 0.97g/cc or less, still more preferably 0.95g/cc or less, still more preferably 0.93g/cc or less, and particularly preferably 0.91g/cc or less. The tap bulk density of the carbonaceous material is determined as follows: a cylindrical glass container having a diameter of 1.8cm and filled with carbonaceous material through a sieve having a mesh size of 300 μm was allowed to freely fall from a height of 5cm, and the procedure was repeated 100 times, with 1 set, until the rate of change in density obtained from the volume and mass of the carbonaceous material was 2% or less before and after the 1 set operation.

In the carbonaceous material of the invention, the ratio D ₈₀/D₂₀ of D ₈₀ to D ₂₀ in the volume-based particle size distribution of the carbonaceous material by the laser diffraction scattering particle size distribution measurement method is preferably 3.5 or more, more preferably 4.0 or more, still more preferably 4.5 or more, still more preferably 5.0 or more, particularly preferably 5.5 or more, particularly preferably 6.0 or more, from the viewpoint of easiness in increasing the electrode density, and from the same viewpoint, it is preferably 18 or less, more preferably 16 or less, and still more preferably 15 or less. The volume-based particle size distribution by the laser diffraction scattering particle size distribution measurement method of D ₈₀/D₂₀ may be measured using a particle size/particle size distribution measuring apparatus with the dispersion of the carbonaceous material as a measurement sample, and the particle size at which the cumulative volume in the particle size distribution is 80% is designated as D ₈₀, and the particle size at which the cumulative volume is 20% is designated as D ₂₀.

In the carbonaceous material of the invention, from the viewpoint of easiness in increasing the electrode density, the circularity measured for particles having a diameter of 5 μm or more in a circle corresponding to the projected area of the flow type particle image analyzer is preferably 0.70 or more, more preferably 0.71 or more, still more preferably 0.72 or more, still more preferably 0.73 or more, and from the same viewpoint, it is preferably 0.99 or less, still more preferably 0.98 or less, still more preferably 0.96 or less. The circularity is the following value: using a flow type particle image analyzer, a projection image of particles was obtained using a carbonaceous material dispersion as a measurement sample, the diameter of an equivalent circle having the same projection area was D μm for 1 particle in the projection image, and the length at which the distance between two parallel lines sandwiching the particle image was the maximum was M μm, using the following formula: the circularity= (D/M) ² is calculated as the circularity of the unit particle, and an average value of circularities obtained by measuring the circularities of the unit particle for 5000 or more, preferably 1 ten thousand or more particles having D of 5 μm or more, for example.

The method for producing a carbonaceous material according to the present invention is not particularly limited as long as a carbonaceous material having the above-described characteristics can be obtained, and the following methods are exemplified: mixing a compound which is a carbon source with a nitrogen-containing compound, subjecting the resulting mixture to heat treatment in an inert gas atmosphere at 500 ℃ or more and 900 ℃ or less, thereafter pulverizing and/or classifying, and further subjecting the resulting carbide to heat treatment at 800 to 1600 ℃, the method comprising: and mixing with a phosphorus-containing compound before heat treatment at 800-1600 ℃. The compound to be used as the raw material is not particularly limited as long as it can obtain a carbonaceous material satisfying the above characteristics, and is preferably a compound having a saccharide skeleton from the viewpoint of easily adjusting the above characteristics of the carbonaceous material to a preferable range. Thus, the carbonaceous material of the invention is preferably a carbonaceous material of sugar origin. Hereinafter, a method for producing a compound having a saccharide skeleton is described. In the present specification, a compound having a saccharide skeleton is also referred to as a saccharide compound.

In a preferred embodiment of the present invention, the method for producing a carbonaceous material according to the present invention comprises at least the steps of:

(1) A step of mixing a compound having a saccharide skeleton with a nitrogen-containing compound to obtain a mixture;

(2) A step of heat-treating the mixture at 500-900 ℃ in an inert gas atmosphere to obtain carbide;

(3) A step of pulverizing and/or classifying the carbide; and

(4) A step of heat-treating the crushed and/or classified carbide at 800-1600 ℃ in an inert gas atmosphere to obtain a carbonaceous material,

The method for producing the carbonaceous material comprises the steps of:

(a) And (3) a step of mixing a compound having a saccharide skeleton, a mixture containing the compound, or a carbide of the mixture with a phosphorus-containing compound before the heat treatment in the step (4).

The invention also provides a manufacturing method of the carbonaceous material.

The step (1) is a step of mixing a compound having a saccharide skeleton with a nitrogen-containing compound to obtain a mixture. Examples of the compound having a saccharide skeleton which can be used as a raw material include monosaccharides such as glucose, galactose, mannose, fructose, ribose, and glucosamine; disaccharides such as sucrose, trehalose, maltose, cellobiose, maltitol, lactobionic acid, and lactosamine; polysaccharides such as starch, glycogen, agarose, pectin, cellulose, chitin, chitosan, oligosaccharide, and xylitol. As the compound having a saccharide skeleton, 1 kind of compound among these may be used, or 2 or more kinds may be used in combination. Among these compounds having a saccharide skeleton, starch is preferred because it is easy to obtain a large amount. Examples of starches include corn starch, potato starch, wheat starch, rice starch, tapioca starch, sago starch, sweet potato starch, millet starch, vines starch, fern starch, lotus root starch, mung bean starch, and arrowhead starch. These starches may be subjected to physical processing, enzymatic processing or chemical processing, and may be alpha-starch, phosphoric acid cross-linked starch, acetic acid starch, hydroxypropyl starch, oxidized starch, starch processed into dextrins, and the like. From the viewpoint of low cost in terms of availability, preferred starches are corn starch and wheat starch, and their alpha-starch.

In a preferred embodiment of the production method of the present invention, from the viewpoint of easiness in increasing the density of an electrode made of a carbonaceous material, a compound having a saccharide skeleton is preferably used, and from the viewpoint of easiness in increasing the density of an electrode made of a carbonaceous material, it is preferable to use a compound having a void of 1 μm ² or more, preferably 3 or less, more preferably 2 or less, and even more preferably 1 or less, when 20 particles having a cross-sectional area of 3 μm ² or more and 100 μm ² or less are arbitrarily selected from images obtained by secondary electron microscopic observation of the cross-section of particles of the compound. When a carbide is produced using such a compound having a small void as a raw material, an additional treatment such as the step (b) described later is not generally required.

The nitrogen-containing compound that can be used in the step (1) is not particularly limited as long as it has a nitrogen atom in the molecule, and examples thereof 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, diammonium hydrogen citrate, and the like; aromatic amine hydrochlorides such as aniline hydrochloride and aminonaphthalene hydrochloride; nitrogen-containing organic compounds such as melamine, pyrimidine, pyridine, pyrrole, imidazole, indole, urea, cyanuric acid, benzoguanamine, and the like. As the nitrogen-containing compound, 1 kind of nitrogen-containing compound among them may be used, or 2 or more kinds may be used in combination. Among these nitrogen-containing compounds, melamine and urea having a high nitrogen content in the molecule are preferable from the viewpoint of easy incorporation of nitrogen into the carbonaceous material in a large amount. From the viewpoint of the reaction with the saccharide compound during the heat treatment, the nitrogen-containing compound preferably has a volatilization temperature of 100 ℃ or higher, more preferably 150 ℃ or higher.

The mixing ratio of the compound having a saccharide skeleton and the nitrogen-containing compound is not particularly limited, and may be appropriately adjusted so that a carbonaceous material having desired properties can be obtained. For example, if the amount of the nitrogen-containing compound is increased, the nitrogen element content contained in the carbonaceous material tends to increase.

In a preferred embodiment of the present invention, the amount of the compound having a saccharide skeleton contained in the mixture obtained in the step (1) is preferably 50 to 99% by mass, more preferably 80 to 95% by mass, based on the total amount of the compound having a saccharide skeleton 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 3 to 15% by mass, based on the total amount of the compound having a saccharide skeleton and the nitrogen-containing compound. The amount of the nitrogen-containing compound to be mixed in the step (1) is preferably 0.03 to 0.30 mol, more preferably 0.05 to 0.20 mol, and still more preferably 0.07 to 0.15 mol, based on 1 mol of the starch monosaccharide unit in the compound having a saccharide skeleton used as a raw material.

In the step (1), when the carbon precursor is mixed with the nitrogen-containing compound to obtain a mixture, at least 1 kind of crosslinking agent may be further mixed. The crosslinking agent is a compound capable of crosslinking a compound having a saccharide skeleton used as a raw material, and functions as a catalyst for promoting an inter-chain bond formation reaction of a saccharide compound and/or a reaction of a saccharide compound and a nitrogen-containing compound, which is carried out together with a hydrolysis reaction and a dehydration reaction of a saccharide compound, or crosslinks a saccharide compound and/or a nitrogen-containing compound by itself. As a result, the obtained carbonaceous material is often not spherical but has a flat shape. When the carbonaceous material is calcined using a crosslinking agent, fusion and foaming of raw materials are easily suppressed, and as a result, the density of an electrode obtained using the carbonaceous material is easily increased.

When a crosslinking agent is used, the type thereof is not particularly limited, and examples thereof include aliphatic monocarboxylic acids such as formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, undecanoic acid, lauric acid, myristic acid, palmitic acid, stearic acid, linoleic acid, oleic acid, and the like; 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 ethylenediamine tetraacetic 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; hydrochloric acid, sulfuric acid, and the like. When a crosslinking agent is used, 1 kind of the crosslinking agent may be used, or 2 or more kinds may be used in combination. Among these crosslinking agents, polycarboxylic acids and hydroxycarboxylic acids are preferable from the viewpoint of suppressing melting and foaming of the raw materials in the step of obtaining the carbide by heat treatment, and succinic acid, adipic acid and citric acid are more preferable.

When the crosslinking agent is further used, the amount thereof is preferably 1 to 30% by mass, more preferably 3 to 10% by mass, based on the total amount of the compound having a saccharide skeleton, the nitrogen-containing compound and the crosslinking agent contained in the mixture. When the amount of the crosslinking agent is increased when the crosslinking agent is added, the true density of the carbonaceous material tends to be high.

Next, in the step (2), the mixture obtained in the step (1) is heat-treated at 500 to 900 ℃ under an inert gas atmosphere to obtain carbide. The heat treatment temperature in the step (2) is preferably 550 to 850 ℃, more preferably 600 to 800 ℃. The temperature rise rate until the heat treatment temperature (reaching temperature) is 50 ℃/hr or more, preferably 50 ℃/hr to 200 ℃/hr. The holding time of the heat treatment time at the reaching temperature is usually 5 minutes or more, preferably 5 minutes to 2 hours, more preferably 10 minutes to 1 hour, and still more preferably 30 minutes to 1 hour. If the heat treatment temperature and time are within the above ranges, carbonization of the compound having a saccharide skeleton is easily controlled, and the above characteristic values of the carbonaceous material are easily adjusted to desired ranges. The heat treatment temperature may be a constant temperature, and is not particularly limited as long as it is within the above range.

The step (2) is performed under an inert gas atmosphere. The step may be performed in an inert gas atmosphere, and the inert gas may be positively supplied or may not be supplied. Examples of the inert gas include argon, helium, and nitrogen is preferable. By such a heat treatment step, carbide, which is a precursor for providing a carbonaceous material, can be obtained.

In the step (3), the obtained carbide is crushed and/or classified. The method of pulverizing and classifying is not particularly limited, and may be carried out by a usual method, for example, a method using a ball mill, a jet mill, or the like. By pulverizing and/or classifying the carbide, the aggregates generated by the heat treatment in the step (2) can be broken up or removed.

In the step (4), the crushed and/or classified carbide is subjected to a heat treatment at 800 to 1600 ℃ in an inert gas atmosphere, whereby the carbonaceous material of the invention can be obtained. The heat treatment temperature in the step (4) is preferably 900 to 1400 ℃, more preferably 1000 to 1400 ℃, and even more preferably 1100 to 1200 ℃. The temperature rise rate until the heat treatment temperature (reaching temperature) is 50 ℃/hr or more, preferably 50 ℃/hr to 200 ℃/hr. The holding time of the heat treatment time at the reaching temperature is usually 1 minute or more, preferably 5 minutes to 2 hours, more preferably 10 minutes to 1 hour, and still more preferably 10 minutes to 30 minutes. If the heat treatment temperature and time are within the above ranges, it is easy to adjust the above characteristic values of the finally obtained carbonaceous material to be within desired ranges. The heat treatment temperature may be a constant temperature, and is not particularly limited as long as it is within the above range.

The production method of the present invention includes the following step (a): the method comprises mixing a compound having a saccharide skeleton, a mixture containing the compound or a carbide of the mixture with a phosphorus-containing compound before heat treatment at 800-1600 ℃ in step (4). The carbonaceous material is produced by a production method including the step (a), whereby phosphorus element can be contained in the carbonaceous material. Although the reason is not clear, by the presence of prescribed amounts of nitrogen element and phosphorus element in the carbonaceous material, a carbonaceous material suitable for an electric storage device having a high discharge capacity per unit weight and excellent current efficiency can be provided.

The step (a) may be performed by mixing the compound having a saccharide skeleton used in the step (1) with a phosphorus-containing compound, or may be performed by mixing the phosphorus-containing compound together when the compound having a saccharide skeleton and the nitrogen-containing compound are mixed in the step (1) to obtain a mixture, or may be performed by mixing the mixture obtained in the step (1) with a phosphorus-containing compound, or may be performed by mixing the carbide obtained in the step (2) with a phosphorus-containing compound, or may be performed by mixing the crushed and/or classified carbide obtained in the step (3) with a phosphorus-containing compound.

The phosphorus-containing compound that can be used in the step (a) is not particularly limited as long as it has a phosphorus atom in the molecule, and for example, inorganic phosphoric acid, organic phosphoric acid, salts thereof, organic phosphorus, phosphonium salts, and the like can be used. As the phosphorus-containing compound, 1 kind of phosphorus-containing compound may be used, or 2 or more kinds may be used in combination.

Examples of the inorganic phosphoric acid include phosphoric acid, dihydrogen phosphate, ammonium dihydrogen phosphate, single phosphate, double phosphate, triple phosphate, pyrophosphoric acid, tripolyphosphoric acid, phosphorous acid, hypophosphorous acid, and phosphorus pentoxide. Examples of the organic phosphoric acid include phosphonic acids (phosphonic acid compounds), and examples of the phosphonic acids include nitrilotrimethylene phosphonic acid, phosphonobutane tricarboxylic acid, methyl diphosphonic acid, methylene phosphonic acid, ethylene diphosphonic acid, and triphenyl phosphate. When these phosphoric acids are salts, the salts may be, for example, alkali metal salts and/or alkaline earth metal salts, or ammonium salts. Examples of the organic phosphorus include triphenylphosphine, triphenylphosphine oxide, 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, and acetates. Among these phosphorus-containing compounds, phosphoric acid and monoammonium phosphate having a high phosphorus content in the molecule are preferable from the viewpoint that phosphorus easily enters the carbonaceous material in a large amount. As the phosphorus-containing compound, from the viewpoint of the reaction with the saccharide compound during the heat treatment, it is preferable that: the volatilization temperature is preferably 100℃or higher, more preferably 150℃or higher.

The method of mixing the phosphorus-containing compound in the step (a) is not particularly limited, and when the phosphorus-containing compound is a solid, the phosphorus-containing compound in a solid state may be mixed with a compound having a saccharide skeleton or the like. In addition, when the phosphorus-containing compound is water-soluble, for example, an aqueous solution of the phosphorus-containing compound may be mixed with a compound having a saccharide skeleton or the like.

The amount of the phosphorus-containing compound to be mixed in the step (a) is not particularly limited as long as the carbonaceous material having the phosphorus element content in the above range can be finally obtained, and is preferably 0.5 to 10% by mass, more preferably 0.6 to 8% by mass, based on the total amount of the compound having a saccharide skeleton and the nitrogen-containing compound or the amount of the carbide obtained in the step (2). The amount of the phosphorus-containing compound to be mixed in the step (a) is preferably 0.001 to 0.20 mol, more preferably 0.005 to 0.15 mol, and still more preferably 0.01 to 0.10 mol, based on 1 mol of the starch monosaccharide unit in the compound having a saccharide skeleton used as a raw material.

In the step (4), a volatile organic compound may be added to the crushed and/or classified carbide obtained in the step (3) and supplied to the step (4). The volatile organic compound is an organic compound that is substantially (for example, 80% or more, preferably 90% or more) free from carbonization and volatilizes (gasifies or thermally decomposes to form a gas) when heat-treated with an inert gas such as nitrogen gas (for example, 500 ℃ or more). The volatile organic compound is not particularly limited, and examples thereof include thermoplastic resins and low-molecular organic compounds. Specifically, examples of the thermoplastic resin include polystyrene, polyethylene, polypropylene, poly (meth) acrylic acid, and poly (meth) acrylate. In this specification, (meth) acrylic refers to a generic term of methacrylic acid and acrylic acid. Examples of the low-molecular organic compound include ethylene, propane, hexane, toluene, xylene, mesitylene, styrene, naphthalene, phenanthrene, anthracene, pyrene, and the like. The thermoplastic resin is preferably polystyrene, polyethylene or polypropylene, since it is preferably volatilized at the calcination temperature and does not oxidize and activate the surface of the carbon precursor when thermally decomposed. The low-molecular organic compound is preferably low in volatility at ordinary temperature (for example, 20 ℃) from the viewpoint of safety, and is preferably naphthalene, phenanthrene, anthracene, pyrene, or the like. The addition of such a volatile organic compound is preferable from the viewpoint of being able to further reduce the content of oxygen element and the specific surface area while maintaining the characteristic structure of the present invention.

The volatile organic compound may be gasified and mixed with an inert gas such as nitrogen gas, and supplied to the step (4). The volatile organic compound is not particularly limited, and low-molecular organic compounds may be mentioned. Examples of the low-molecular organic compound include ethylene, propane, hexane, toluene, xylene, mesitylene, styrene, naphthalene, phenanthrene, anthracene, pyrene, and the like. The low-molecular-weight organic compound is preferably highly volatile from the viewpoint of mixing with an inert gas such as nitrogen, and is preferably ethylene, propane, hexane, toluene, or the like. The addition of such a volatile organic compound is preferable from the viewpoint of being able to further reduce the content of oxygen element and the specific surface area while maintaining the characteristic structure of the present invention.

In the case of producing a carbonaceous material by the above-described production method, the production method may further include the following step (b) in addition to the steps (1) to (4): before step (1), simultaneously with step (1), or after step (1), the compound having a saccharide skeleton is gelatinized. When the step (b) is further performed, the voids contained in the compound having a saccharide skeleton used as a raw material are blocked, and as a result, the density of the electrode formed of the finally obtained carbonaceous material is easily increased, and the discharge capacity per unit volume is easily increased.

In the step (b), the gelatinization method is not particularly limited, and examples thereof include: a method in which a compound having a saccharide skeleton is heated alone or in any mixture with a nitrogen-containing compound or the like in the presence of water; a method of mechanically treating a compound having a saccharide skeleton, alone or in any mixture with a nitrogen-containing compound or the like, with impact, crushing, friction and/or shearing. By applying such heat and external force, the voids contained in the compound having the saccharide skeleton are blocked. The gelatinization in the step (b) is preferably performed until particles having a void of 1 μm ² or more are a predetermined amount or less, preferably 3 or less, more preferably 2 or less, and even more preferably 1 or less, when 20 particles having a cross-sectional area of 3 μm ² or more and 100 μm ² or less are arbitrarily selected from images obtained by secondary electron microscopic observation of the cross-section of the particles of the gelatinized compound having a saccharide skeleton. The microscopic observation may be performed after removing aggregates contained in the gelatinized compound by pulverization or classification. When step (b) is performed, in step (2), the mixture obtained through step (1) and any step (b) described above is subjected to heat treatment. Therefore, in the case of performing the step (b), the step (b) is performed before the step (2).

In a preferred embodiment of the present invention, the production method of the present invention may include the following steps as step (b):

a step (b 1) of mixing 5 to 50 mass% of water with respect to the mass of the compound having a saccharide skeleton and heating the mixture at a temperature of 50 to 200 ℃ for 1 minute to 5 hours before the step (1);

A step (c 1) of subjecting the compound having a saccharide skeleton to a mechanical treatment having an impact, crushing, friction and/or shearing action before the step (1);

A step (b 2) of mixing 5 to 50 mass% of water relative to the mass of the compound having a saccharide skeleton with the mixture containing the compound having a saccharide skeleton, and heating the mixture at a temperature of 50 to 200 ℃ for 1 minute to 5 hours, simultaneously with the step (1) or after the step (1); and/or

And (c 2) simultaneously with the step (1) or after the step (1), subjecting the mixture containing the compound having a saccharide skeleton to a mechanical treatment having an impact, crushing, friction and/or shearing action.

The step (b 1) is a step of mixing 5 to 50 mass% of water with respect to the mass of the compound having a saccharide skeleton and heating the mixture at a temperature of 50 to 200 ℃ for 1 minute to 5 hours before the step (1). The amount of water to be mixed with the compound having a saccharide skeleton is required to be a predetermined amount or more, and from the viewpoint of suppressing the energy required for distilling off the mixed water in the process of producing a carbonaceous material, the amount is preferably 5 to 50% by mass, preferably 10 to 50% by mass, more preferably 10 to 30% by mass, based on the mass of the compound. The heating temperature is 50 to 200 ℃, preferably 60 to 180 ℃, more preferably 80 to 180 ℃. Further, the heating time is 1 minute to 5 hours, preferably 3 minutes to 1 hour, more preferably 10 minutes to 30 minutes.

The step (c 1) is a step of subjecting the compound having a saccharide skeleton to mechanical treatment having impact, crushing, friction and/or shearing action before the step (1). Examples of the device used for mechanical treatment having impact, crushing, friction and/or shearing action include a pulverizer, an extruder, a pulverizer, a grinding mill, and a kneading device. The treatment conditions such as the treatment time are not particularly limited, and for example, in the case of using a ball vibration mill, treatment conditions of 20Hz and 10 minutes are exemplified.

The step (b 2) is a step of mixing 5 to 50 mass% of water based on the mass of the compound having a saccharide skeleton with the mixture containing the compound having a saccharide skeleton at the same time as the step (1) or after the step (1), and heating the mixture at a temperature of 50 to 200 ℃ for 1 minute to 5 hours, and the same applies to the preferred embodiments and the like described in the step (b 1).

The step (c 2) is a step of subjecting the mixture containing the compound having a saccharide skeleton to mechanical treatment having impact, crushing, friction and/or shearing action at the same time as the step (1) or after the step (1), and the same applies to the description of the preferred embodiment and the like described in the step (c 1).

The carbonaceous material of the invention or the carbonaceous material obtained by the production method of the invention can be suitably used as an active material for a negative electrode of an electric storage device.

Hereinafter, a method for producing a negative electrode for an electric storage device using the carbonaceous material of the invention will be specifically described. The negative electrode is prepared, for example, by adding a binder (binder) to a carbonaceous material and adding an appropriate amount of an appropriate solvent thereto, and then kneading them. The obtained electrode mixture is applied to a collector plate including a metal plate or the like, dried, and then subjected to compression molding, whereby a negative electrode for a power storage device, for example, a negative electrode for a nonaqueous electrolyte secondary battery such as a lithium ion secondary battery, a sodium ion battery, a lithium sulfur battery, or a lithium air battery can be produced.

By using the carbonaceous material of the invention, an electrode (negative electrode) having a high discharge capacity per unit weight and excellent current efficiency can be produced. In the case where it is desired to impart high conductivity to the electrode, a conductive additive may be added when preparing an electrode mixture, if necessary. As the conductive auxiliary agent, conductive carbon black, vapor Grown Carbon Fiber (VGCF), nanotubes, and the like can be used. The amount of the conductive additive to be added may vary depending on the type of the conductive additive to be used, and if the amount is too small, the desired conductivity may not be obtained, and if the amount is too large, the dispersion in the electrode mixture may be deteriorated. From this viewpoint, in the case of adding the conductive auxiliary agent, the amount thereof is preferably 0.5 to 10 mass%, more preferably 0.5 to 7 mass%, still more preferably 0.5 to 5 mass% when the amount of the active material (carbonaceous material), the amount of the binder (binder), and the amount of the conductive auxiliary agent=100 mass%. The binder is not particularly limited as long as it does not react with the electrolyte, and examples thereof include PVDF (polyvinylidene fluoride), polytetrafluoroethylene, and a mixture of SBR (styrene-butadiene-rubber) and CMC (carboxymethyl cellulose). Among them, a mixture of SBR and CMC is preferable because SBR and CMC attached to the surface of the active material do not inhibit lithium ion migration and can obtain good input/output characteristics. For dissolving an aqueous emulsion such as SBR and CMC to form a slurry, a polar solvent such as water is preferably used, or a solvent emulsion such as PVDF may be dissolved in N-methylpyrrolidone or the like to use. If the amount of the binder added is too large, the resistance of the obtained electrode increases, and therefore, the internal resistance of the battery may increase, and the battery characteristics may be degraded. If the amount of the binder added is too small, the particles of the negative electrode material may be insufficiently bonded to each other and to the current collector. The preferable amount of binder to be added varies depending on the kind of binder to be used, and for example, a solvent is usually used by mixing a plurality of binders such as a mixture of SBR and CMC with a water binder, and is preferably 0.5 to 5% by mass, more preferably 1 to 4% by mass, based on the total amount of all binders to be used. On the other hand, the PVDF-based binder is preferably 3 to 13 mass%, more preferably 3 to 10 mass%. The amount of carbonaceous material in the electrode mixture is preferably 80 mass% or more, and more preferably 90 mass% or more. The amount of carbonaceous material in the electrode mixture is preferably 100 mass% or less, and more preferably 97 mass% or less.

The electrode active material layer is formed substantially on both sides of the current collector plate, and may be formed on one side as needed. In the case of the electrode active material layer thickness, the current collector, separator, and the like are required to be small, and therefore, it is preferable to increase the capacity. However, when the electrode area opposed to the counter electrode is large, it is advantageous to improve the input/output characteristics, and therefore, if the electrode active material layer is too thick, the input/output characteristics may be degraded. From the viewpoint of output at the time of discharging the battery, the thickness (one side each) of the active material layer is preferably 10 to 80 μm, more preferably 20 to 75 μm, still more preferably 30 to 75 μm.

The electric storage device obtained using the carbonaceous material of the invention has a high discharge capacity per unit weight and excellent current efficiency. When the carbonaceous material of the invention is used to form a negative electrode for an electric storage device, other materials constituting a battery, such as a positive electrode material, a separator, and an electrolyte solution, are not particularly limited, and various materials conventionally used or proposed as electric storage devices may be used.

For example, as the positive electrode material, a layered oxide compound (represented by LiMO ₂, M is a metal such as LiCoO ₂、LiNiO₂、LiMnO₂ or LiNi _xCo_yMo_zO₂ (where x, y, and z represent a composition ratio)), an olivine compound (represented by LiMPO ₄, M is a metal such as LiFePO ₄, or the like), a spinel compound (represented by LiM ₂O₄, M is a metal such as LiMn ₂O₄, or the like), and these chalcogen compounds may be mixed and used as necessary are preferable. These positive electrode materials are formed into a layer on a conductive current collector by molding together with an appropriate binder and a carbon material for imparting conductivity to the electrode.

For example, in the case where the power storage device is a nonaqueous electrolyte secondary battery, the nonaqueous solvent type electrolyte is generally formed by dissolving an electrolyte in a nonaqueous solvent. As the nonaqueous solvent, for example, one or a combination of two or more organic solvents such as propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, dimethoxyethane, diethoxyethane, γ -butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, sulfolane, or 1, 3-dioxolane may be used. As the electrolyte, LiClO₄、LiPF₆、LiBF₄、LiCF₃SO₃、LiAsF₆、LiCl、LiBr、LiB(C₆H₅)₄ or LiN (SO ₃CF₃)₂, etc. can be used.

In addition, when the power storage device is a nonaqueous electrolyte secondary battery, the nonaqueous electrolyte secondary battery is generally formed by facing the positive electrode and the negative electrode formed by the above operation through a liquid-permeable separator as needed, and immersing the positive electrode and the negative electrode in an electrolyte. As such a separator, a separator of permeability or liquid permeability formed of nonwoven fabric or other porous material, which is commonly used in secondary batteries, may be used. Alternatively, a solid electrolyte formed of a polymer gel impregnated with an electrolyte may be used instead of or together with the separator.

The carbonaceous material of the present invention is suitable as a carbonaceous material for an electric storage device (typically, a nonaqueous electrolyte secondary battery for driving a vehicle) mounted in a vehicle such as an automobile. In the present invention, a vehicle generally refers to a vehicle known as an electric vehicle, a hybrid vehicle used with a fuel cell or an internal combustion engine, or the like, and may be provided with at least: the battery power supply device includes the battery, an electric drive mechanism driven by power supplied from the power supply device, and a control device for controlling the electric drive mechanism. The vehicle may further include a power generation brake and a secondary brake, and a mechanism for converting braking energy into electricity and charging the nonaqueous electrolyte secondary battery may be provided.

Examples

Hereinafter, the present invention will be specifically described by way of examples, which should not be construed as limiting the scope of the present invention. The following describes a method for measuring physical properties of a carbonaceous material and a negative electrode obtained using the carbonaceous material, and the physical properties and measurements (or physical property values and measured values) described in the present specification are based on values obtained by the following method, including examples.

(Oxygen and Nitrogen element content)

Elemental analysis was performed by an inert gas dissolution method using oxygen/nitrogen/hydrogen analyzers EMGA-930 manufactured by horiba, ltd.

The detection method of the device comprises the following steps of: inert gas melting-non-dispersive infrared absorption (NDIR), nitrogen: inert gas fusion-Thermal Conductivity (TCD), hydrogen: the inert gas melting-non-dispersive infrared absorption method (NDIR) was performed by using (oxygen/nitrogen) Ni capsules, tiH ₂ (H standard sample), SS-3 (O standard sample), and SiN (N standard sample) as the pretreatment, and 20mg of the sample after measuring the moisture content at 250 ℃ for about 10 minutes was placed in the Ni capsules, and the samples were degassed in the elemental analyzer for 30 seconds, and then measured. The test was performed using 3 samples, and the average value was used as an analysis value. The oxygen and nitrogen element contents in the sample were obtained in the above-described manner.

(Phosphorus element content)

The analysis was performed by a fluorescent X-ray analysis method using ZSX Primus- μmanufactured by the Cocky corporation.

The specimen measurement area was set to be within a circumference of 30mm in diameter using a holder for the top irradiation system. 2.0g of the sample to be measured and 2.0g of a polymer binder (spectra Blend 44. Mu. Powder, manufactured by Chemplex Co.) were mixed in a mortar, and put into a molding machine. A15 ton load was applied to the molding machine for 1 minute to prepare pellets having a diameter of 40 mm. The produced pellets were wrapped with a polypropylene film, and placed on a sample holder for measurement. The X-ray source was set at 30kV and 100mA. Since the phosphorus element content was obtained from the intensity of phosphorus kα rays, the spectroscopic crystal used Ge (111), the detector used a gas flow type scale factor tube, and the measurement was performed at a scanning speed of 4 °/minute for a range of 137 to 144 ° 2θ.

(Determination of average out-of-plane distance d ₀₀₂ based on X-ray diffraction and Using Bragg formula)

Using MiniFlexII manufactured by "phylogenetic company", powder of the carbonaceous materials prepared in examples and comparative examples described below was filled into the sample holder, and cukα rays obtained by monochromatizing the powder using a Ni filter were used as a line source to obtain an X-ray diffraction pattern. The peak position of the diffraction pattern was determined by a gravity center method (a method of determining the gravity center position of the diffraction line and determining the peak position by using a2θ value corresponding thereto), and the diffraction peak on the (111) plane of the high-purity silicon powder for the standard substance was used for correction. The wavelength λ of cukα ray was set to 0.15418nm, and d ₀₀₂ was calculated by using the Bragg formula described below.

[ Mathematics 1]

(Particle size distribution based on laser Scattering method)

The average particle diameter (particle size distribution) of the carbide was measured by the following method. 5mg of the sample was put into 2mL of an aqueous solution containing 5% by mass of a surfactant (and "Toriton X100" manufactured by Wako pure chemical industries, ltd.) and treated with an ultrasonic cleaner for 10 minutes or more, and dispersed in the aqueous solution. The particle size distribution was determined using the dispersion. Particle size distribution measurement was performed using a particle size/particle size distribution measuring apparatus (Microtrac MT3300EXII manufactured by Microtrac BEL Co.). D ₅₀ is a particle size at which the cumulative volume becomes 50%, and this value is used as the average particle size.

(Raman Spectroscopy)

The particles to be measured, which are carbonaceous materials, were placed on a base of an observation table using a raman spectrometer (a "laser raman microscope Ramanforce" manufactured by Nanophoton corporation), and the objective lens was focused at a magnification of 20 times, and then measured while being irradiated with an argon ion laser. The details of the measurement conditions are shown below.

Wavelength of argon ion laser: 532nm

Laser power on sample: 100-300W/cm ²

Resolution ratio: 5-7cm ^-1

Measurement range: 150-4000cm ^-1

Measurement mode: XY Averaging

Exposure time: 20 seconds

Cumulative number of times: 2 times

Peak intensity determination: automatic correction was performed using Polynom-3 times for baseline correction

Peak search & fitting Process GaussLoren

Example 1

10G of starch (corn starch), 0.54g of melamine (0.07 mol based on 1 mol of starch monosaccharide unit), 0.38g of adipic acid (0.04 mol based on 1 mol of starch monosaccharide unit) and 0.2g of monoammonium phosphate (0.03 mol based on 1 mol of starch monosaccharide unit) were put into a sample bottle and mixed with shaking, thereby obtaining a mixture (step 1 and step a). The resulting mixture was warmed to 600 ℃ under a nitrogen atmosphere. At this time, the temperature rise rate to 600℃was 600℃per hour (10℃per minute). Then, a carbonization treatment was performed for 30 minutes at 600 ℃ under a nitrogen gas stream to obtain carbide (step 2). At this time, the supply amount of nitrogen was 0.5L/min with respect to 10g of starch. Thereafter, the obtained carbide was pulverized by a ball mill, whereby a pulverized carbide having a D ₅₀ of 5.5 μm was obtained (step 3). The obtained crushed carbide was heated to 1200 ℃ and subjected to high-temperature calcination treatment for 60 minutes at 1200 ℃ to thereby obtain a carbonaceous material (step 4). At this time, the temperature rise rate to 1200℃was 600℃per hour (10℃per minute). The above-mentioned temperature rising and heat treatment were performed under a nitrogen flow. The amount of nitrogen gas supplied was 3L/min with respect to 5g of the crushed carbide.

Example 2

10G of starch (corn starch), 1.16g of melamine (0.15 mol based on 1 mol of starch monosaccharide unit), 0.76g of adipic acid (0.08 mol based on 1 mol of starch monosaccharide unit), and 0.4g of monoammonium phosphate (0.06 mol based on 1 mol of starch monosaccharide unit) were put into a sample bottle, and mixed with shaking, to obtain a mixture (step 1 and step a). Thereafter, the same treatments as those of step 2, step 3 and step 4 of example 1 were performed to obtain a carbonaceous material.

Example 3

The same treatments as in step 1, step a, step 2 and step 3 of example 2 were performed to obtain a pulverized char. The obtained crushed carbide was heated to 1100 ℃, and subjected to high-temperature calcination treatment for 60 minutes at 1100 ℃ to obtain a carbonaceous material (step 4). At this time, the temperature rise rate to 1100℃was 600℃per hour (10℃per minute). The above-mentioned temperature rising and heat treatment were performed under a nitrogen flow. The amount of nitrogen gas supplied was 3L/min with respect to 5g of the carbide after pulverization.

Example 4

10G of starch (corn starch), 1.16g of melamine (0.15 mol based on 1 mol of starch monosaccharide unit), 0.76g of adipic acid (0.08 mol based on 1 mol of starch monosaccharide unit), and 0.2g of monoammonium phosphate (0.03 mol based on 1 mol of starch monosaccharide unit) were put into a sample bottle, and mixed with shaking, to obtain a mixture (step 1 and step a). Thereafter, the same treatments as those of step 2, step 3 and step 4 of example 3 were performed to obtain a carbonaceous material.

Example 5

10G of starch (corn starch), 1.16g of melamine (0.15 mol based on 1 mol of starch monosaccharide unit), 0.76g of adipic acid (0.08 mol based on 1 mol of starch monosaccharide unit), and 0.1g of monoammonium phosphate (0.01 mol based on 1 mol of starch monosaccharide unit) were put into a sample bottle, and mixed with shaking, to obtain a mixture (step 1 and step a). Thereafter, the same treatments as those of step 2, step 3 and step 4 of example 3 were performed to obtain a carbonaceous material.

Example 6

10G of starch (corn starch), 1.16g of melamine (0.15 mol based on 1 mol of starch monosaccharide unit), 0.76g of adipic acid (0.08 mol based on 1 mol of starch monosaccharide unit), and 0.6g of monoammonium phosphate (0.08 mol based on 1 mol of starch monosaccharide unit) were put into a sample bottle, and mixed with shaking, to obtain a mixture (step 1 and step a). Thereafter, the same treatments as those of step 2, step 3 and step 4 of example 3 were performed to obtain a carbonaceous material.

Example 7

10G of starch (corn starch), 1.16g of melamine (0.15 mol based on 1 mol of starch monosaccharide unit), and 0.76g of adipic acid (0.08 mol based on 1 mol of starch monosaccharide unit) were put into a sample bottle, and mixed with shaking to obtain a mixture (step 1). The resulting mixture was warmed to 600 ℃ under a nitrogen atmosphere. At this time, the temperature rise rate to 600℃was 600℃per hour (10℃per minute). Then, a carbonization treatment was performed by performing a heat treatment at 600 ℃ for 30 minutes under a nitrogen gas stream, thereby obtaining carbide (step 2). At this time, the supply amount of nitrogen was 0.5L/min with respect to 10g of starch. Thereafter, the obtained carbide was pulverized by a ball mill, whereby a pulverized carbide having a D ₅₀ of 5.5 μm was obtained (step 3). To 5g of the obtained pulverized carbonized product, 0.5g of an 85 mass% phosphoric acid aqueous solution was added and mixed in a mortar to obtain a mixed carbonized product of a phosphorus-containing compound (step a). The carbide obtained was heated to 1100 ℃, and subjected to high-temperature calcination treatment for 60 minutes at 1100 ℃ to obtain a carbonaceous material (step 4). At this time, the temperature rise rate to 1100℃was 600℃per hour (10℃per minute). The above-mentioned temperature rising and heat treatment were performed under a nitrogen flow. The amount of nitrogen gas supplied was 3L/min with respect to 5g of the carbide after pulverization.

Comparative example 1

10G of starch (maize starch) are warmed to 600℃under a nitrogen atmosphere. At this time, the temperature rise rate to 600℃was 600℃per hour (10℃per minute). Then, carbonization treatment was performed by heat treatment at 600 ℃ for 60 minutes under a nitrogen gas stream, thereby obtaining carbide. At this time, the amount of nitrogen supplied was 1L/min relative to 10g of starch. Thereafter, the obtained carbide was pulverized by a ball mill, whereby a pulverized carbide having a D ₅₀ of 5.5 μm was obtained. The carbide obtained after pulverization and mixing was heated to 1200 ℃, and the carbide was subjected to high-temperature calcination treatment at 1200 ℃ for 60 minutes to obtain a carbonaceous material. At this time, the temperature rise rate to 1200℃was 600℃per hour (10℃per minute). The above-mentioned temperature rising and heat treatment were performed under a nitrogen flow. The amount of nitrogen gas supplied was 3L/min with respect to 5g of the carbide after pulverization.

Comparative example 2

10G of starch (corn starch) and 0.2g of 85 mass% phosphoric acid aqueous solution were added and mixed in a mortar to obtain a mixture. The resulting mixture was warmed to 600 ℃ under a nitrogen atmosphere. At this time, the temperature rise rate to 600℃was 600℃per hour (10℃per minute). Then, carbonization treatment was performed by heat treatment at 600 ℃ for 30 minutes under a nitrogen gas flow, thereby obtaining carbide. At this time, the supply amount of nitrogen was 0.5L/min with respect to 10g of starch. Thereafter, the obtained carbide was pulverized by a ball mill, whereby a pulverized carbide having a D ₅₀ of 5.5 μm was obtained. The carbide obtained after pulverization and mixing was heated to 1200 ℃, and the carbide was subjected to high-temperature calcination treatment at 1200 ℃ for 60 minutes to obtain a carbonaceous material. At this time, the temperature rise rate to 1200℃was 600℃per hour (10℃per minute). The above-mentioned temperature rising and heat treatment were performed under a nitrogen flow. The amount of nitrogen gas supplied was 3L/min with respect to 5g of the carbide after pulverization.

Comparative example 3

10G of starch (corn starch), 0.58g of melamine (0.08 mol based on 1 mol of starch monosaccharide units), and 0.38g of adipic acid (0.04 mol based on 1 mol of starch monosaccharide units) were put into a sample bottle, and mixed with shaking, to obtain a mixture. The resulting mixture was warmed to 600 ℃ under a nitrogen atmosphere. At this time, the temperature rise rate to 600℃was 600℃per hour (10℃per minute). Then, carbonization treatment was performed by heat treatment at 600 ℃ for 30 minutes under a nitrogen gas flow, thereby obtaining carbide. At this time, the supply amount of nitrogen was 0.5L/min with respect to 10g of starch. Thereafter, the obtained carbide was pulverized by a ball mill, whereby a pulverized carbide having a D ₅₀ of 5.5 μm was obtained. The carbide obtained after pulverization and mixing was heated to 1200 ℃, and the carbide was subjected to high-temperature calcination treatment at 1200 ℃ for 60 minutes to obtain a carbonaceous material. At this time, the temperature rise rate to 1200℃was 600℃per hour (10℃per minute). The above-mentioned temperature rising and heat treatment were performed under a nitrogen flow. The amount of nitrogen gas supplied was 3L/min with respect to 5g of the carbide after pulverization.

Comparative example 4

10G of starch (corn starch), 0.2g of melamine (0.026 mol based on 1 mol of starch monosaccharide unit), 0.76g of adipic acid (0.08 mol based on 1 mol of starch monosaccharide unit) and 0.4g of monoammonium phosphate (0.06 mol based on 1 mol of starch monosaccharide unit) were put into a sample bottle and mixed with shaking, thereby obtaining a mixture (step 1 and step a). The resulting mixture was warmed to 600 ℃ under a nitrogen atmosphere. At this time, the temperature rise rate to 600℃was 600℃per hour (10℃per minute). Then, a carbonization treatment was performed for 30 minutes at 600 ℃ under a nitrogen gas stream to obtain carbide (step 2). At this time, the supply amount of nitrogen was 0.5L/min with respect to 10g of starch. Thereafter, the obtained carbide was pulverized by a ball mill to obtain a pulverized carbide having a D ₅₀ of 5.5. Mu.m (step 3). The obtained crushed carbide was heated to 1200 ℃ and subjected to high-temperature calcination treatment for 60 minutes at 1200 ℃ to thereby obtain a carbonaceous material (step 4). At this time, the temperature rise rate to 1200℃was 600℃per hour (10℃per minute). The above-mentioned temperature rising and heat treatment were performed under a nitrogen flow. The amount of nitrogen gas supplied was 3L/min with respect to 5g of the crushed carbide.

Comparative example 5

10G of starch (corn starch), 1.16g of melamine (0.15 mol based on 1 mol of starch monosaccharide unit), and 0.76g of adipic acid (0.08 mol based on 1 mol of starch monosaccharide unit) were put into a sample bottle, and mixed with shaking, to obtain a mixture. The resulting mixture was warmed to 600 ℃ under a nitrogen atmosphere. At this time, the temperature rise rate to 600℃was 600℃per hour (10℃per minute). Then, carbonization treatment was performed by heat treatment at 600 ℃ for 30 minutes under a nitrogen gas flow, thereby obtaining carbide. At this time, the supply amount of nitrogen was 0.5L/min with respect to 10g of starch. Thereafter, the obtained carbide was pulverized by a ball mill, whereby a pulverized carbide having a D ₅₀ of 5.5 μm was obtained. The carbide obtained after pulverization and mixing was heated to 1100 ℃, and the carbonaceous material was obtained by performing high-temperature calcination treatment for 60 minutes at 1100 ℃. At this time, the temperature rise rate to 1100℃was 600℃per hour (10℃per minute). The above-mentioned temperature rising and heat treatment were performed under a nitrogen flow. The amount of nitrogen gas supplied was 3L/min with respect to 5g of the carbide after pulverization.

(Fabrication of electrode)

Using the carbonaceous materials obtained in each example and each comparative example, a negative electrode was produced in the following manner.

95 Parts by mass of carbonaceous material, 2 parts by mass of conductive carbon black (Super-P (registered trademark) manufactured by TIMCAL corporation), 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 a copper foil having a thickness of 15. Mu.m, dried, pressed, and punched with a diameter of 14mm to obtain an electrode having a thickness of 45. Mu.m.

(Discharge capacity per unit weight)

The electrode produced as described above was used as a working electrode, and metallic lithium was used as a counter electrode and a reference electrode. As the solvent, ethylene carbonate and dimethyl carbonate were mixed with carbonic acid in such a manner that the volume ratio was 1:1:1. 1mol/L LiPF ₆ was dissolved in the solvent and used as an electrolyte. The separator uses a polypropylene film. Coin cells were fabricated in a glove box under an argon atmosphere.

The lithium secondary battery having the above-described structure was subjected to a charge/discharge test using a charge/discharge test apparatus (manufactured by eastern systems, inc., "TOSCAT"). The doping of lithium was carried out at a rate of 70mA/g with respect to the mass of the active material until the doping reached 1mV with respect to the lithium potential. Further, a constant voltage of 1mV with respect to the lithium potential was applied, and doping was terminated at a stage where the rate reached 2mA/g with respect to the mass of the active material. The capacity at this time was set as the charging capacity. Next, the undoped material was doped at a rate of 70mA/g with respect to the mass of the active material until the lithium potential reached 1.5V, the charged capacity at this time was set to a charge capacity (mAh), and the discharged capacity was set to a discharge capacity (mAh). The obtained charge capacity and discharge capacity were divided by the weight of the negative electrode, respectively, and the obtained values were set as a charge capacity per unit weight (mAh/g) and a discharge capacity per unit weight (mAh/g). The discharge capacity was divided by the charge capacity, and the percentage of the obtained value was set as the current efficiency (%).

The carbonaceous materials obtained in examples and comparative examples were measured for the nitrogen element content, the phosphorus element content, the carbon surface spacing (d ₀₀₂), the oxygen element content, the half-value width of the peak around 1360cm ^-1 and the half-value width of the peak around 1650cm ^-1 by the above-described measurement methods, and the results are shown in table 1. The discharge capacity and current efficiency per unit weight measured for the obtained battery are also shown in table 1.

The battery fabricated using the carbonaceous material of each example had a high discharge capacity per unit weight and exhibited excellent current efficiency. On the other hand, in the battery fabricated using the carbonaceous material of each comparative example having no prescribed nitrogen element content and phosphorus element content, the discharge capacity per unit weight was not sufficiently high or the current efficiency was not sufficiently high.

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Claims (9)

1. A carbonaceous material having a nitrogen element content of 1.0 mass% or more based on elemental analysis and a phosphorus element content of 0.5 mass% or more based on fluorescent X-ray analysis.

2. The carbonaceous material according to claim 1, which has a carbon-to-surface spacing (d ₀₀₂) as determined by X-ray diffraction ofThe above.

3. The carbonaceous material according to claim 1 or 2, having an oxygen element content of less than 1.5 mass% based on elemental analysis.

4. The carbonaceous material according to any one of claim 1 to 3, wherein,

In the Raman spectrum observed by the laser Raman spectroscopy, a half-value width of a peak around 1360cm ^-1 is 230cm ^-1 or more.

5. The carbonaceous material according to any one of claim 1 to 4, wherein,

In the Raman spectrum observed by the laser Raman spectroscopy, a half-value width of a peak around 1650cm ^-1 is 98cm ^-1 or more.

6. The carbonaceous material according to any one of claims 1 to 5, which is a carbonaceous material for a negative electrode of an electrical storage device.

7. A negative electrode for an electrical storage device, comprising the carbonaceous material according to any one of claims 1 to 6.

8. An electric storage device comprising the negative electrode for an electric storage device according to claim 7.

9. The method for producing a carbonaceous material according to any one of claims 1 to 6, comprising at least the steps of:

(1) A step of mixing a compound having a saccharide skeleton with a nitrogen-containing compound to obtain a mixture;

(2) Performing heat treatment on the mixture at 500-900 ℃ in an inert gas atmosphere to obtain carbide;

(3) A step of pulverizing and/or classifying the carbide; and

(4) A step of heat-treating the crushed and/or classified carbide at 800-1600 ℃ in an inert gas atmosphere to obtain a carbonaceous material,

The method for producing the carbonaceous material comprises the steps of:

(a) And (3) a step of mixing a compound having a saccharide skeleton, a mixture containing the compound, or a carbide of the mixture with a phosphorus-containing compound before the heat treatment in the step (4).