Carbonaceous material, method for producing carbonaceous material, negative electrode for nonaqueous electrolyte battery, and nonaqueous electrolyte battery

Abstract

The present invention pertains to a carbonaceous material which has a silicon element content of 5 mass% or more, and in which the distance Lc in a graphite lamination direction and the distance La in a graphite surface direction in an X-ray crystal analysis of the carbonaceous material satisfy 1<Lc / La.

Description

Carbonaceous material, method for producing carbonaceous material, negative electrode for non-aqueous electrolyte battery, and non-aqueous electrolyte battery

[0001] The present invention relates to a carbonaceous material, a method for producing a carbonaceous material, a negative electrode for a nonaqueous electrolyte battery, and a nonaqueous electrolyte battery.

[0002] Non-aqueous electrolyte secondary batteries, such as lithium-ion secondary batteries, have high energy density and excellent output characteristics, and are therefore widely used in small portable devices such as mobile phones and laptop computers. In recent years, their application to automotive applications, such as hybrid vehicles and electric vehicles, has also been promoted. As a negative electrode material for lithium-ion secondary batteries, non-graphitizable carbons capable of doping (charging) and dedoping (discharging) lithium in amounts exceeding the theoretical capacity of graphite, 372 mAh / g, have been developed and used (see, for example, Patent Documents 1 and 2, and Non-Patent Document 1).

[0003] However, as further improvements in capacity are currently required, the battery capacity of graphite is insufficient, and proposals have been made to achieve higher battery capacity by coexisting metals with high lithium absorption capabilities. While silicon and tin are being investigated due to their high absorption capacity as metals alone, the short battery life caused by expansion due to Li absorption and contraction upon release has become a problem. One solution to this problem is to combine graphite with carbon.

[0004] Methods for effectively utilizing silicon contained in plants have been investigated for composites with carbon materials (Patent Document 2, Non-Patent Document 2).

[0005] JP 2017-107856 A JP 2017-91822 A

[0006] Journal of The Electrochemical Society, 2016, Vol. 163, No. 7, A1295-A1299Scientifc Reports (2022) 12:975

[0007] In recent years, the application of lithium-ion secondary batteries to automotive applications has been considered, and there is a demand for even higher capacity lithium-ion secondary batteries. However, conventional carbonaceous materials often have insufficient discharge capacity and low lithium ion utilization efficiency.

[0008] Therefore, an object of the present invention is to provide a carbonaceous material suitable as a negative electrode active material that provides a nonaqueous electrolyte secondary battery (e.g., a lithium ion secondary battery, a sodium ion secondary battery, a lithium-sulfur battery, or a lithium-air battery) with high charge / discharge capacity and charge / discharge efficiency; a negative electrode containing the carbonaceous material; a nonaqueous electrolyte secondary battery having the negative electrode; and a method for producing the carbonaceous material.

[0009] The present inventors have found that the above object can be achieved by the carbonaceous material for a non-aqueous electrolyte secondary battery of the present invention, which will be described below. That is, the present invention encompasses the following preferred embodiments: [1] A carbonaceous material having a silicon content of 5 mass % or more, wherein the distance L in the graphite stacking direction in X-ray crystallography of the carbonaceous material is ｃ and the distance L in the graphite plane direction ａ is 1<L ｃ / L ａ [2] The distance L in the graphite plane direction is ａ [3] The carbonaceous material according to [1], wherein the distance L in the graphite stacking direction is 4 to 12 Å. ｃ and the distance L in the graphite plane direction ａ is 1<L ｃ / L ａ The carbonaceous material according to [1] or [2] satisfies <3. [4] The carbonaceous material according to any one of [1] to [3], having a potassium content of 0.2 mass % or less. [5] The carbonaceous material according to [1] or [2], having a carbon interplanar spacing d calculated using the Bragg equation by wide-angle X-ray diffraction. ００２The carbonaceous material according to any one of [1] to [4], wherein the surface roughness is 3.75 Å or greater. [6] The carbonaceous material according to any one of [1] to [5], which is derived from a grass plant. [7] A method for producing a carbonaceous material, comprising: (1) heating a carbide precursor having a silicon content of 3 mass% or greater at 300 to 900°C in an inert gas atmosphere, followed by cooling to 200°C or less to obtain a carbide; (2) heating the carbide obtained in step (1) at 500 to 1000°C in an inert gas atmosphere, followed by cooling to 200°C or less to obtain a carbide; and (3) heating the carbide obtained in step (2) at 800 to 1500°C in an inert gas atmosphere, followed by cooling to 200°C or less to obtain a carbonaceous material. [8] The production method according to [7], further comprising, between steps (1) and (2), a step of crushing the carbide obtained in step (1) and a step of washing with an acid. [9] The carbonaceous material has a silicon content of 5 mass% or more, and the distance L in the graphite stacking direction in X-ray crystallography of the carbonaceous material ｃ and the distance L in the graphite plane direction ａ is 1<L ｃ / L ａ

[10] A negative electrode for a non-aqueous electrolyte battery using the carbonaceous material according to any one of [1] to [5].

[11] A non-aqueous electrolyte battery using the negative electrode according to

[10] .

[0010] According to the present invention, it is possible to provide a carbonaceous material suitable as a negative electrode active material, which provides a nonaqueous electrolyte secondary battery having high charge / discharge capacity and charge / discharge efficiency, a negative electrode containing the carbonaceous material, a nonaqueous electrolyte secondary battery having the negative electrode, and a method for producing the carbonaceous material.

[0011] Hereinafter, embodiments of the present invention will be described in detail. Note that the scope of the present invention is not limited to the embodiments described here, and various modifications can be made without departing from the spirit of the present invention.

[0012] The carbonaceous material of the present invention has a silicon content of 5% by mass or more. If the silicon content in the carbonaceous material is less than 5% by mass, the number of sites for absorbing and desorbing lithium ions during charge and discharge is reduced, and sufficient charge and discharge capacity cannot be obtained. From the viewpoint of improving charge and discharge capacity, the silicon content in the carbonaceous material of the present invention is preferably 6% by mass or more, more preferably 8% by mass or more, even more preferably 10% by mass or more, still more preferably 12% by mass or more, and particularly preferably 13% by mass or more. Furthermore, the silicon content in the carbonaceous material is preferably 50% by mass or less, more preferably 45% by mass or less, and even more preferably 40% by mass or less. When the silicon atom content in the carbonaceous material is equal to or less than the above upper limit, this is preferable from the viewpoint of preventing distortion of the carbonaceous material's structure due to expansion of silicon upon Li adsorption and maintaining a stable structure. By preventing distortion of the carbonaceous material's structure, sites for absorbing and desorbing lithium ions are maintained, and a conductive path structure is maintained, thereby increasing the charge and discharge capacity. The content of silicon element in the carbonaceous material of the present invention is preferably 5 to 50 mass%, more preferably 6 to 50 mass%, even more preferably 8 to 45 mass%, even more preferably 10 to 45 mass%, particularly preferably 12 to 40 mass%, and especially preferably 13 to 40 mass%. Suitable embodiments of the silicon element content in the carbonaceous material include, for example, a range of 5 to 30 mass% or 6 to 25 mass%. In this specification, the silicon element content is the content measured by X-ray fluorescence analysis, and may be measured, for example, by the method described in the Examples.

[0013] The method for adjusting the silicon element content to fall within the above range is not particularly limited as long as it can produce a carbonaceous material having a silicon element content within the above range. For example, a method for producing a carbonaceous material using a plant-derived raw material containing a large amount of silicon as a carbon source, as described below, can be mentioned.

[0014] The peak with a half-width of 2° or less detected at 20 to 30° (2θ) obtained by X-ray crystal diffraction measurement is derived from crystalline silica, which is a non-electron conductor and does not intercalate Li ions. Therefore, it is a resistive component and is electrochemically inactive. If crystalline silica is mixed into a carbon material in an amount that allows this peak to be detected, the number of sites for lithium ion occlusion in the carbon material decreases, resulting in a decrease in charge / discharge capacity. Therefore, it is preferable that a peak with a half-width of 2° or less is not detected at 20 to 30° (2θ) obtained by X-ray crystal diffraction measurement. To prevent this peak from being detected, it is preferable to avoid using a carbon precursor containing crystalline silica as a raw material when producing a carbonaceous material.

[0015] The carbonaceous material of the present invention has a length L in the graphite stacking direction in X-ray crystallography of the carbonaceous material. ｃ and the distance L in the graphite plane direction ａ However, 1<L ｃ / L ａ Here, the distance L in the graphite plane direction ａ Distance L in the graphite stacking direction ｃ L is the ratio of ｃ / L ａ When L is greater than 1, the carbonaceous material has randomly mixed crystals, and the crystal growth relationship is as described above, so the crystal density of the particles increases, and as a result, the electrode density tends to increase, resulting in a larger volumetric capacity as an electrode. In addition, it is believed that the charge / discharge efficiency can be improved because the number of fine amorphous carbon end faces (total amount of end faces) decreases. ｃ / L ａ is the L of the crystal plane ａ From the viewpoint of not excessively suppressing the growth in the direction, the ratio is preferably less than 3, more preferably 1.1 to 2.5, even more preferably 1.2 to 2.4, and even more preferably 1.3 to 2.3.

[0016] In the carbonaceous material of the present invention, the distance L in the graphite stacking direction in X-ray crystallography of the carbonaceous material ｃ is the L of the crystal plane ｃFrom the viewpoint of promoting directional growth and improving carbon density, the thickness is preferably 6 to 15 Å, more preferably 7 to 14 Å, even more preferably 8 to 13 Å, and even more preferably 9 to 12 Å.

[0017] In the carbonaceous material of the present invention, the distance L in the graphite plane direction in X-ray crystallography of the carbonaceous material ａ is the L of the crystal plane ａ If the growth in the direction is too suppressed, there is a concern that the efficiency at the carbon terminal will decrease, so the thickness is preferably 4 to 12 Å, more preferably 4.5 to 11 Å, even more preferably 5 to 10 Å, and even more preferably 5.5 to 9 Å.

[0018] The potassium element content in the carbonaceous material of the present invention is preferably 0.2% by mass or less, more preferably 0.15% by mass or less, and even more preferably 0.1% by mass or less, from the viewpoint of improving charge / discharge capacity and charge / discharge efficiency. When the potassium element content in the carbonaceous material is equal to or less than the above upper limit, a non-aqueous electrolyte secondary battery using this carbonaceous material tends to have a large undoped capacity and a small undoped capacity. Furthermore, when the potassium element content in the carbonaceous material is equal to or less than the above upper limit, the occurrence of a short circuit due to the elution and reprecipitation of these metal elements in the electrolyte is suppressed, thereby ensuring the safety of the non-aqueous electrolyte secondary battery. It is particularly preferable that the carbonaceous material does not substantially contain potassium element. The potassium element content in the carbonaceous material is typically 0% by mass or more. The potassium element content is measured by X-ray fluorescence analysis. For example, the measurement may be performed by the method described in the Examples.

[0019] The carbonaceous material of the present invention has a carbon interplanar spacing d calculated using the Bragg equation by wide-angle X-ray diffraction. ００２ is preferably 3.75 Å or more, more preferably 3.78 Å or more, even more preferably 3.79 Å or more, still more preferably 3.80 Å or more, and is preferably 4.10 Å or less, more preferably 4.00 Å or less. ００２ When the carbon interplanar spacing d is equal to or greater than the lower limit and equal to or less than the upper limit, it is easy to obtain a carbonaceous material that provides a battery with an excellent battery capacity retention rate at low temperatures. ００２By adjusting the carbon spacing d to within the above range, not only is the battery capacity improved by the inclusion of silicon element, but also an improvement in battery capacity due to the carbon skeleton is brought about. Furthermore, since a carbonaceous material having a carbon spacing within the above range also has excellent characteristics at low temperatures, it is possible to alleviate the phenomenon that the Li insertion / desorption reaction is relatively sensitive to temperature, which is said to occur in silicon-containing carbonaceous materials. ００２ can be adjusted to within the above range by, for example, adjusting the heating temperature (for example, the temperature of the first carbonization step or the temperature of the second carbonization step). In addition, a carbonaceous material having the above carbon interplanar spacing has excellent properties at low temperatures, and therefore can mitigate the temperature sensitivity of the Li insertion / desorption reaction. ００２ can be determined by X-ray crystallography, and can be measured, for example, by the method described in the Examples.

[0020] The specific surface area of ​​the carbonaceous material of the present invention measured by the nitrogen adsorption BET method is preferably 300 m ２ / g or less, more preferably 200m ２ / g or less, more preferably 150m ２ / g or less, and even more preferably 100m ２ / g or less, particularly preferably 80m ２ / g or less, particularly preferably 60m ２ / g or less, most preferably 40m ２ / g or less. When the specific surface area is equal to or less than the above upper limit, the hygroscopicity of the carbonaceous material is likely to be reduced, and the amount of moisture present in the carbonaceous material is likely to be reduced. As a result, hydrolysis of the electrolyte solution due to moisture and electrolysis of water are suppressed, and the generation of acid and gas associated therewith is likely to be suppressed. Furthermore, when the specific surface area is equal to or less than the above upper limit, the contact area between air and the carbonaceous material is likely to be reduced, and the oxidation of the carbonaceous material itself is likely to be suppressed. There are no particular restrictions on the lower limit of the specific surface area of ​​the carbonaceous material measured by the nitrogen adsorption BET method, but from the viewpoint of increasing the contact area with the electrolyte and easily reducing the resistance of the battery, it is preferably 5 m ２ / g or more, more preferably 9m ２ / g or more, more preferably 9.5m ２In this specification, the specific surface area measured by the BET method means the specific surface area determined by the nitrogen adsorption BET multipoint method. Specifically, it can be measured by the method described below.

[0021] Although there are no particular limitations on the method for adjusting the BET specific surface area within the above range, for example, in the method for producing a carbonaceous material described below, lowering the temperature or shortening the heating time in the step of obtaining a carbon precursor and / or the step of obtaining a carbide tends to increase the BET specific surface area of ​​the finally obtained carbonaceous material due to suppression of thermal structural contraction, etc. Therefore, in order to obtain a carbonaceous material having a BET specific surface area within the desired range, the firing temperature and firing time may be adjusted.

[0022] The average particle diameter D of the carbonaceous material of the present invention ５０ is preferably 30 μm or less, more preferably 25 μm or less, even more preferably 20 μm or less, even more preferably 18 μm or less, particularly preferably 16 μm or less, and most preferably 15 μm or less. When the average particle size is below the above upper limit, not only is the coating property during electrode preparation good, but the free diffusion path of lithium ions within the carbonaceous material particles is reduced, making it easier to achieve rapid charge and discharge. Furthermore, in lithium ion secondary batteries, it is important to increase the electrode area to improve input / output characteristics, and to achieve this, it is necessary to reduce the coating thickness of the active material on the current collector plate during electrode preparation. When the average particle size of the carbonaceous material to be used as the active material is below the above upper limit, it is easy to reduce the coating thickness during electrode preparation. In addition, the average particle size D of the carbonaceous material of the present invention is ５０ is preferably 2 μm or more, more preferably 3 μm or more, even more preferably 4 μm or more, and even more preferably 5 μm or more. ５０ When the average particle diameter D is equal to or greater than the above lower limit, an increase in the specific surface area due to fine powder in the carbonaceous material and an increase in reactivity with the electrolyte are suppressed, and an increase in irreversible capacity is easily suppressed. Furthermore, when a negative electrode is produced using the carbonaceous material, voids formed between the carbonaceous material are easily secured, and the migration of lithium ions in the electrolyte is not easily suppressed, which makes it easy to reduce the resistance of the nonaqueous electrolyte secondary battery. ５０is the particle size at which the cumulative volume becomes 50%, and can be determined by measuring the particle size distribution by a laser scattering method using, for example, a particle size / particle size distribution measuring device ("Microtrac MT3300EXII" manufactured by Microtrac Bell Co., Ltd.).

[0023] 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-mentioned properties. From the viewpoint of increasing the silicon element content, it is preferable to produce the carbonaceous material using a carbide precursor that contains a relatively large amount of silicon.

[0024] Examples of carbide precursors containing relatively large amounts of silicon include plant-derived materials, such as bamboo, rice straw, wheat straw, barley straw, rice straw, buckwheat straw, soybean straw, bran, rice husks, wheat husks, buckwheat husks, corn stalks, sugarcane tops, peanut husks, red cedar sawdust, larch bark, and fallen ginkgo leaves. From the viewpoint of increasing the silicon content in the final carbonaceous material, bamboo, rice straw, wheat straw, barley straw, rice straw, buckwheat straw, bran, rice husks, wheat husks, buckwheat husks, and peanut husks are preferred as carbide precursors. Considering the generation scale, accumulation, availability, and stability of the plant raw materials, such as decay, the carbonaceous material is preferably derived from a grass family plant, and more preferably from rice husks. Note that "a carbonaceous material derived from a grass family plant" means that the carbon source of the carbonaceous material is derived from a grass family plant.

[0025] The method for producing the carbonaceous material of the present invention is not particularly limited as long as it can produce the carbonaceous material of the present invention having the above-described properties. For example, the carbonaceous material can be produced using a carbonaceous material production method that includes at least the steps described below.

[0026] The present invention also provides a method for producing a carbonaceous material that has high charge / discharge capacity and charge / discharge efficiency and is suitable as a negative electrode active material or conductive material for nonaqueous electrolyte secondary batteries (e.g., lithium ion secondary batteries, sodium ion batteries, lithium-sulfur batteries, and lithium-air batteries).

[0027] In one embodiment of the present invention, the method for producing a carbonaceous material of the present invention includes at least the following steps: (1) heating a carbide precursor having a silicon content of 3% by mass or more at 300 to 900°C in an inert gas atmosphere, followed by cooling to 200°C or lower to obtain a carbide; (2) heating the carbide obtained in step (1) at 500 to 1000°C in an inert gas atmosphere, followed by cooling to 200°C or lower to obtain a carbide; and (3) heating the carbide obtained in step (2) at 800 to 1500°C in an inert gas atmosphere, followed by cooling to 200°C or lower to obtain a carbonaceous material. The present invention also provides a method for producing the above carbonaceous material. The above production method is not particularly limited as long as it includes each of steps (1) to (3). It may include only steps (1) to (3), or it may include additional steps before or after each of the above steps. The carbide to be heat-treated in step (2) may be the carbide obtained in step (1) as is, or may be the carbide that has been further treated. The carbide to be heat-treated in step (3) may be the carbide obtained in step (2) as is, or may be the carbide that has been further treated.

[0028] First, the method for producing a carbonaceous material of the present invention, which includes steps (1), (2), and (3), will be described.

[0029] Step (1) involves heating a raw material, a carbide precursor having a silicon content of 3% by mass or more, at 300 to 900°C in an inert gas atmosphere and then cooling to 200°C or below to obtain a carbide. Examples of carbide precursors having a silicon content of 3% by mass or more include the carbide precursors described above that contain relatively high amounts of silicon and carbide precursors obtained by calcining such carbide precursors. The inert gas is not particularly limited as long as it is a gas that does not contain oxygen, and examples include nitrogen gas, argon gas, helium gas, carbon dioxide gas, and water vapor. The inert gas may be one of the above gases or a mixture of two or more of the above gases. In the present invention, the inert gas refers to a gas that does not oxidize and erode carbon at the heat treatment temperature. From the viewpoint of reducing production costs, nitrogen gas, superheated steam, or carbon dioxide gas is preferred, and from the viewpoint of operability, nitrogen gas is preferred. Step (1) is preferably performed under an inert gas supply. When step (1) is carried out under supply of an inert gas, the supply amount of the inert gas is preferably 0.01 to 20 L / min, more preferably 0.02 to 15 L / min, and even more preferably 0.03 to 10 L / min, per 10 g of the carbide precursor, from the viewpoint of the removal of volatile components.

[0030] The heating temperature in step (1) is 300 to 900°C, preferably 310 to 850°C, more preferably 320 to 800°C, and even more preferably 330 to 750°C. The heating temperature may be constant or may vary within the above range. The heat treatment time is preferably 0.2 to 8 hours, more preferably 0.5 to 4 hours, and even more preferably 0.5 to 2 hours. It is believed that the heat treatment at the above heating temperature in step (1) dries the physically adsorbed water contained in the carbide precursor, and a dehydration reaction occurs at the molecular level in the carbide precursor, thereby promoting carbonization. By performing this heat treatment in an inert gas atmosphere, preferably while supplying an inert gas, it is believed that structural loss due to carbon oxidation does not occur when water is removed from the carbide precursor by drying and dehydration, and a carbide that maintains a fine structure can be obtained. The above heating conditions are believed to facilitate efficient and sufficient removal of water from the carbon precursor raw material by drying and dehydration, and also facilitate the final production of a carbonaceous material having the above characteristics. After the heat treatment, the charcoal can be obtained by cooling to 200° C. or less. The cooling temperature may be 200° C. or less, but it is preferable to cool to 150° C. or less, more preferably 100° C. or less, even more preferably 50° C. or less, and even more preferably room temperature (25° C.) or less to obtain the charcoal.

[0031] Step (2) is a step of heating the carbide obtained in step (1) at 500 to 1000°C in an inert gas atmosphere and then cooling to 200°C or less to obtain a carbide. Examples of inert gases include argon gas, helium gas, and nitrogen gas, and nitrogen gas is preferred. Step (2) is preferably carried out under an inert gas supply. When step (2) is carried out under an inert gas supply, the supply amount of the inert gas is preferably 0.01 to 20 L / min, more preferably 0.02 to 15 L / min, and even more preferably 0.03 to 10 L / min per 10 g of carbide, from the viewpoint of the ability to remove volatile components.

[0032] The heating temperature in step (2) is 500 to 1000°C, preferably 600 to 1000°C, more preferably 700 to 950°C, and even more preferably 800 to 950°C. The heating temperature may be constant or may be set to a temperature that varies within the above range. The heat treatment time is preferably 0.2 to 8 hours, more preferably 0.3 to 4 hours, and even more preferably 0.4 to 3 hours. After the heat treatment, the mixture is cooled to 200°C or less to obtain a carbide. The cooling temperature may be 200°C or less, but is preferably 150°C or less, more preferably 100°C or less, even more preferably 50°C or less, and even more preferably room temperature (25°C) or less to obtain a carbide.

[0033] The subsequent step (3) is a step in which the carbide obtained in step (2) is heated to 800 to 1500°C in an inert gas atmosphere and then cooled to 200°C to obtain the target carbonaceous material. Examples of inert gases include argon gas, helium gas, and nitrogen gas, and nitrogen gas is preferred. Step (3) is preferably carried out under the supply of an inert gas. When step (3) is carried out under the supply of an inert gas, the supply amount of the inert gas is L ｃ and L ａ From the viewpoint of keeping the flow rate within a predetermined range, the flow rate is preferably 0.01 to 20 L / min, more preferably 0.02 to 15 L / min, and even more preferably 0.03 to 10 L / min per 10 g of carbonized material.

[0034] The heating temperature in step (3) is 800 to 1500°C, preferably 850 to 1450°C, more preferably 900 to 1400°C, and even more preferably 900 to 1350°C. If the heating temperature is within the above range, it is easy to finally obtain a carbonaceous material having the above characteristics. The heating temperature may be constant or may be set to a temperature that varies within the above range. Examples of inert gases include argon gas, helium gas, and nitrogen gas, and nitrogen gas is preferred. The heat treatment time is preferably 0.2 to 8 hours, more preferably 0.3 to 4 hours, and even more preferably 0.4 to 3 hours. After the above heat treatment, the carbonaceous material can be obtained by cooling to 200°C or below. The cooling temperature may be 200°C or below, but is preferably 150°C or below, more preferably 100°C or below, even more preferably 50°C or below, and even more preferably room temperature (25°C) or below to obtain the carbonaceous material.

[0035] The manufacturing method of the present invention includes steps (1) to (3), which allows for sufficient removal of decomposition products volatilized during each step, suppressing the generation of amorphous carbon portions due to the decomposition products, and preventing the deactivation of Li ions in the carbon portions, which is believed to be the effect of the present invention. For example, step (2) is a step of removing volatiles at high temperature, so that the L of the crystal plane is not easily degraded. ａ Growth in the graphite surface direction is suppressed, increasing the number of carbon ends, and there is concern that Li ions may be deactivated at these ends, resulting in a decrease in Li ion efficiency. On the other hand, by performing steps (1) to (3) separately, volatilized decomposition products can be sufficiently removed, reducing the amount of fine amorphous carbon (total amount of end faces) formed when decomposition products remain. Li ions may be deactivated at carbon ends or amorphous end faces, resulting in a decrease in charge / discharge efficiency. However, the suppression of deactivation due to the reduction in amorphous end faces is thought to outweigh the deactivation that may occur at the crystalline end, thereby improving charge / discharge efficiency. In nonaqueous electrolyte secondary batteries such as Li-ion batteries, a decrease in this efficiency often leads to Li deficiency on the positive electrode side, resulting in unstable battery operation, which is undesirable. Therefore, not only high battery capacity but also high initial Li ion efficiency contributes significantly to battery performance.

[0036] In addition, L ａ Large in the direction, L ｃ In the case of crystals that are small in the direction (sometimes referred to as tabular), aggregation is likely to occur, which may result in voids and a decrease in carbon density. ｃ / L ａ In the case of the carbonaceous material of the present invention that satisfies the above condition, such aggregation can be suppressed and the carbon density can be increased.

[0037] Furthermore, if the heat treatment in step (3) is performed continuously after the heat treatment in step (2) without cooling the carbide to 200°C or below, volatile substances such as decomposition products generated in step (2) may coat the materials in the structure construction process, inhibiting the construction of the crystal structure. Furthermore, the carbide obtained in step (3) may be coated, suppressing the desorption of volatile substances generated in step (3). Furthermore, if a decomposable organic substance is added in step (3), it may become difficult to control the coating with this substance. On the other hand, according to the production method of the present invention, the reaction between the hydrogen generated in step (3) and the volatile substances generated in step (2) can be suppressed, thereby improving safety during industrial production. In particular, by introducing a sufficient amount of inert gas and cooling to 200°C or below to obtain the carbide in step (2), the volatile substances can be sufficiently removed.

[0038] The method for producing a carbonaceous material of the present invention may further include a step of adding at least one volatile organic substance to the carbonized material obtained in step (2) before subjecting the carbonized material to step (3), which involves calcining the carbonized material at a high temperature. This step allows the organic substance volatilized during the calcination of the carbonized material to adhere to the surface of the carbonized material, making it easier to produce a carbonaceous material with a lower specific surface area. Such a carbonaceous material can maintain high charge / discharge capacity and charge / discharge efficiency while reducing hygroscopicity and suppressing hydrolysis of the electrolyte solution due to moisture and electrolysis of water.

[0039] Volatile organic compounds are organic compounds that are hardly carbonized (e.g., preferably 80% or more, more preferably 90% or more of the substance is not carbonized) and volatilize (vaporize or pyrolyze into gas) when heat-treated in an inert gas atmosphere such as nitrogen at a temperature of, for example, 500°C or higher. Examples of volatile organic compounds include, but are not limited to, thermoplastic resins and low-molecular-weight organic compounds. Examples of thermoplastic resins include polystyrene, polyethylene, polypropylene, poly(meth)acrylic acid, and poly(meth)acrylic acid esters. In this specification, (meth)acrylic is a general term for methacrylic and acrylic. Examples of low-molecular-weight organic compounds include toluene, xylene, mesitylene, styrene, naphthalene, phenanthrene, anthracene, and pyrene. Since thermoplastic resins that volatilize at firing temperatures and do not oxidize and activate the surface of the carbon precursor when thermally decomposed are preferred, polystyrene, polyethylene, and polypropylene are preferred. From the viewpoint of safety, the low molecular weight organic compound is more preferably a compound that is less volatile at room temperature (for example, 20° C.), and naphthalene, phenanthrene, anthracene, pyrene, etc. are particularly preferred.

[0040] The amount of the volatile organic compound added is not particularly limited, but is usually in the range of 1 to 30 parts by mass per 100 parts by mass of the carbonized material obtained in step (2). The step of adding the volatile organic compound may be performed in step (3) immediately after the addition, or may be performed after heat treatment in an inert gas at a temperature lower than that in step (3).

[0041] The production method of the present invention preferably further includes a step of removing metal components and the like that may be contained in a carbide precursor (e.g., a plant-derived carbide precursor) having a silicon content of 3 mass% or more. Examples of the metal components and the like to be removed include potassium, sodium, calcium, and the like. The step of removing metal components and the like may be carried out either before or after step (1). The method for removing metal components and the like may be any method, such as washing with an acid or washing with an alkali, or a combination of both. However, the method of washing with an acid is preferred because it does not destroy the structure of the carbide precursor and also because it reduces the difficulty of treating metal-removed wastewater by dissolving the organic matter that constitutes the carbide precursor in water.

[0042] The acid used may be any of mineral acids such as hydrochloric acid, sulfuric acid, and nitric acid, or water-soluble organic acids such as formic acid, acetic acid, butyric acid, and citric acid. They may be used alone or in combination. Considering the metal removal efficiency and residual properties, hydrochloric acid is preferred. The concentration of the acidic water used is not particularly limited, but when using hydrochloric acid, it is preferable to use acidic water in the range of 0.01N to 2N, more preferably 0.05N to 1.8N, and even more preferably 0.1N to 1.5N.

[0043] The temperature of the acid washing is not particularly limited and is naturally complementary to the washing time, but it is usually carried out at a temperature ranging from room temperature to 80° C. for a period ranging from 0.5 to 6 hours, more preferably from 1 to 5 hours. This operation may be carried out once, or may be carried out multiple times by repeating the dewatering, as long as the metal content can be reduced to the target level.

[0044] After acid washing, the carbonized material may be washed with ion-exchanged water or the like to deoxidize it.

[0045] In the present invention, it is preferable to pulverize the carbonized product obtained in step (1) and adjust the particle size of the carbonized product to the final target particle size before step (2). By pulverizing the carbonized product in advance, volatiles remaining and formed during the carbonization in step (1) can be effectively removed.

[0046] The average particle diameter D of the carbide to be subjected to step (2)５０ is preferably 2 μm or more, more preferably 3 μm or more, even more preferably 4 μm or more, and even more preferably 5 μm or more. ５０ is preferably 30 μm or less, more preferably 25 μm or less, even more preferably 22 μm or less, and particularly preferably 20 μm or less. ５０ When the average particle diameter D ５０ is easily adjusted to the range described above for the carbonaceous material, and the charge / discharge capacity and charge / discharge efficiency of the non-aqueous electrolyte secondary battery are easily increased. ５０ can be measured in the same manner as described for the carbonaceous material.

[0047] In a preferred embodiment, the production method of the present invention further includes, between steps (1) and (2), a step of crushing the carbide obtained in step (1) and a step of washing with acid. The order of the acid washing step and the crushing step is not particularly limited. The acid washing step may be performed after the crushing step, or the acid washing step may be performed after the crushing step. However, it is more preferable to perform the acid washing step after the crushing step. This embodiment is not particularly limited as long as the crushing step and the washing step are each performed at least once between steps (1) and (2). The crushing step and the washing step may each be performed once or twice or more times between steps (1) and (2). The crushing step and / or the washing step may also be performed at a step other than between steps (1) and (2).

[0048] The method for producing the carbonaceous material of the present invention is not limited to the above-described production method of the present invention, and any production method may be used as long as the carbonaceous material satisfies the above characteristics. In the production method of the present invention, the carbide or carbon precursor is cooled to 200°C or less in each of steps (1) to (3) before the next step, with the intention of sufficiently removing volatile matter generated in steps (1) and (2), particularly step (2), before final heating in step (3). However, it is also possible to perform the heat treatments of steps (2) and (3) consecutively without cooling to 200°C or less, for example, particularly in step (2), when a step of sufficiently removing volatile matter generated by the heat treatment is performed by injecting a large amount of inert gas.

[0049] The carbonaceous material of the present invention or the carbonaceous material obtained by the production method of the present invention can be suitably used as a negative electrode active material for a non-aqueous electrolyte secondary battery. The present invention also provides a negative electrode for a non-aqueous electrolyte secondary battery containing the carbonaceous material of the present invention, and a non-aqueous electrolyte secondary battery having the negative electrode.

[0050] The method for producing the negative electrode for a non-aqueous electrolyte secondary battery of the present invention will be specifically described below. The negative electrode of the present invention can be produced, for example, by adding a binder to the carbonaceous material of the present invention, adding an appropriate amount of a suitable solvent, kneading them to prepare an electrode mixture, applying the obtained electrode mixture to a current collector plate made of a metal plate or the like, drying it, and then pressure-molding it.

[0051] By using the carbonaceous material of the present invention, an electrode (negative electrode) having high conductivity can be produced without adding a conductive additive. To further enhance conductivity, a conductive additive can be added as needed during the preparation of the electrode mixture. Examples of conductive additives that can be used include conductive carbon black, vapor-grown carbon fiber (VGCF), and nanotubes. The amount of conductive additive added varies depending on the type of conductive additive used. Adding too little may result in the desired conductivity not being achieved, while adding too much may result in poor dispersion in the electrode mixture. From this perspective, the preferred proportion of conductive additive added is 0.5 to 10% by mass (where the amount of active material (carbonaceous material) + the amount of binder + the amount of conductive additive = 100% by mass), more preferably 0.5 to 7% by mass, and particularly preferably 0.5 to 5% by mass. The binder is not particularly limited as long as it does not react with the electrolyte, such as PVDF (polyvinylidene fluoride), polytetrafluoroethylene, or 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 lithium ion migration, resulting in good input / output characteristics. A polar solvent such as water is preferably used to dissolve an aqueous emulsion of SBR or CMC to form a slurry, but a solvent-based emulsion of PVDF or the like can also be dissolved in N-methylpyrrolidone or the like. Adding too much binder increases the resistance of the resulting electrode, which can increase the internal resistance of the battery and degrade battery performance. Adding too little binder can result in insufficient bonding between the particles of the negative electrode material and with the current collector. The preferred amount of binder to be added varies depending on the type of binder used, but for example, in binders that use water as a solvent, a mixture of multiple binders, such as a mixture of SBR and CMC, is often used, and the total amount of all binders used is preferably 0.5 to 5 mass %, more preferably 1 to 4 mass %. On the other hand, in the case of PVDF-based binders, the amount is preferably 3 to 13 mass %, more preferably 3 to 10 mass %.The amount of the carbonaceous material of the present invention in the electrode mixture is preferably 80% by mass or more, more preferably 90% by mass or more, and is preferably 100% by mass or less, more preferably 97% by mass or less.

[0052] The electrode 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 electrode active material layer is preferable for achieving higher capacity because fewer current collector plates, separators, etc. are required. However, since a larger electrode area facing the counter electrode is advantageous for improving input / output characteristics, if the electrode active material layer is too thick, the input / output characteristics may deteriorate. From the viewpoint of output during battery discharge, 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.

[0053] The nonaqueous electrolyte secondary battery of the present invention includes the negative electrode for a nonaqueous electrolyte secondary battery of the present invention. A nonaqueous electrolyte secondary battery having a negative electrode for a nonaqueous electrolyte secondary battery containing the carbonaceous material of the present invention has high charge / discharge capacity and charge / discharge efficiency.

[0054] When the carbonaceous material of the present invention is used to form a negative electrode for a non-aqueous electrolyte secondary battery, other materials constituting the battery, such as a positive electrode material, a separator, and an electrolyte solution, are not particularly limited, and various materials that have been conventionally used or proposed for non-aqueous solvent secondary batteries can be used.

[0055] For example, the positive electrode material is a layered oxide (LiMO ２ where M is a metal, for example, LiCoO ２ , LiNiO ２ , LiMnO ２ , or LiNi ｘ Co ｙ Mo ｚ O ２ (where x, y, and z represent the composition ratio), olivine-based (LiMPO ４ where M is a metal, for example LiFePO ４ etc.), spinel type (LiM ２ O ４ where M is a metal, for example LiMn ２ O ４These positive electrode materials are preferably composite metal chalcogen compounds such as those described above, and these chalcogen compounds may be mixed and used as needed. The positive electrode is formed by molding these positive electrode materials together with a suitable binder and a carbon material for imparting conductivity to the electrode, and forming a layer on a conductive current collector.

[0056] The non-aqueous electrolyte used in combination with these positive and negative electrodes is generally formed by dissolving an electrolyte in a non-aqueous solvent. As the non-aqueous solvent, for example, organic solvents such as propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, dimethoxyethane, diethoxyethane, γ-butyllactone, tetrahydrofuran, 2-methyltetrahydrofuran, sulfolane, or 1,3-dioxolane can be used singly or in combination. In addition, as the electrolyte, 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.

[0057] A nonaqueous electrolyte secondary battery is generally formed by arranging the positive electrode and negative electrode formed as described above facing each other, optionally with a liquid-permeable separator interposed therebetween, and immersing them in an electrolyte solution. Such separators can be nonwoven fabrics commonly used in secondary batteries or other permeable or liquid-permeable separators made of porous materials. Alternatively, a solid electrolyte made of a polymer gel impregnated with an electrolyte solution can be used instead of or together with the separator.

[0058] The carbonaceous material of the present invention is suitable as a carbonaceous material for batteries (typically, non-aqueous electrolyte secondary batteries for driving vehicles) mounted on vehicles such as automobiles. The vehicle referred to in the present invention is not particularly limited to those generally known as electric vehicles, hybrid vehicles with fuel cells or internal combustion engines, and the like, and is equipped with at least a power supply device including the battery, an electric drive mechanism driven by power supplied from the power supply device, and a control device for controlling the same. The vehicle may further be equipped with a dynamic brake or a regenerative brake, and may be equipped with a mechanism for converting braking energy into electricity and charging the non-aqueous electrolyte secondary battery.

[0059] The carbonaceous material of the present invention preferably has low resistance, and therefore can also be used, for example, as an additive that imparts conductivity to battery electrode materials. The type of battery is not particularly limited, but nonaqueous electrolyte secondary batteries and lead-acid batteries are preferred. Adding the carbonaceous material to such battery electrode materials can form a conductive network, increasing the conductivity and suppressing irreversible reactions, thereby extending the battery's lifespan.

[0060] The present invention will be described in detail below with reference to examples, but these examples are not intended to limit the scope of the present invention. Measurement methods for the physical properties of carbonaceous materials are described below, but the physical properties described in this specification, including the examples, are based on values ​​determined by the following methods.

[0061] (Elemental Analysis) (Silicon and Potassium Contents) The silicon and potassium contents were measured, for example, by the following method. A carbon sample containing predetermined silicon and potassium elements was prepared in advance, and a calibration curve was created using an X-ray fluorescence analyzer to show the relationship between the silicon Kα ray intensity and the silicon content, and the relationship between the potassium Kα ray intensity and the potassium content. Next, the silicon Kα ray and potassium Kα ray intensities were measured for the sample in X-ray fluorescence analysis, and the silicon and potassium contents were determined from the previously prepared calibration curves. X-ray fluorescence analysis was performed using a "ZSX Primus II" manufactured by Rigaku Corporation under the following conditions. 5.0 g of the sample to be measured was weighed onto a nylon filter sheet, the measurement surface was wrapped in polypropylene film, and the sheet was placed in a sample holder for measurement. The X-ray source was set to 30 kV and 100 mA for silicon element measurement and 40 kV and 75 mA for potassium element measurement, and measurements were performed.

[0062] (Specific Surface Area by Nitrogen Adsorption BET Method) An approximate formula derived from the BET formula is shown below.

[0063] Using the above approximation formula, a specific relative pressure (p / p) is calculated by the multipoint method using nitrogen adsorption at liquid nitrogen temperature. ０ ) and substitute the measured adsorption amount (v) to obtain v ｍ The specific surface area (SSA: unit is m ２ g －１ ) was calculated.

[0064]

[0065] In the above formula, v ｍ is the amount of adsorption required to form a monolayer on the sample surface (cm ３ / g), v is the measured adsorption amount (cm ３ / g), p ０ is the saturated vapor pressure, p is the absolute pressure, c is a constant (reflecting the heat of adsorption), and N is Avogadro's number 6.022 × 10 ２３ , a (nm ２ ) is the area occupied by the adsorbate molecule on the sample surface (molecular occupied cross-sectional area).

[0066] Specifically, the amount of nitrogen adsorbed to a carbonaceous material at liquid nitrogen temperature was measured using a "BELL Sorb Mini" manufactured by Nippon BELL Co., Ltd., as follows. The measurement sample was filled into a sample tube, and the sample tube was cooled to -196°C. The pressure was then reduced once, and nitrogen (purity 99.999%) was then adsorbed onto the measurement sample at a desired relative pressure. The amount of nitrogen adsorbed onto the sample when equilibrium pressure was reached at each desired relative pressure was defined as the amount of adsorbed gas v.

[0067] (Average particle diameter D by laser scattering method ５０ ) The average particle size (particle size distribution) of the carbonaceous material or carbide was measured by the following method. The sample was placed in an aqueous solution containing 5 mass% of a surfactant ("Toriton X100" manufactured by Wako Pure Chemical Industries, Ltd.), treated with an ultrasonic cleaner for 10 minutes or more, and dispersed in the aqueous solution. The particle size distribution was measured using this dispersion. The particle size distribution measurement was performed using a particle size / particle size distribution measuring device ("Microtrac MT3300EXII" manufactured by Microtrac Bell Co., Ltd.). D ５０ is the particle size at which the cumulative volume becomes 50%, and this value was used as the average particle size.

[0068] (X-ray diffraction) Powder of a carbonaceous material or carbide was filled into a sample holder, and X-ray diffraction measurement was performed using "MiniFlex II" manufactured by Rigaku Corporation. Based on the obtained data, X-ray crystallography was performed to determine the L ａ and L ｃ The radiation source was CuKα (λ=1.5418 Å), and the scanning range was 10°<2θ<90°.

[0069] (Carbon interplanar spacing d using the Bragg equation obtained by X-ray diffraction measurement) ００２ Using a "MiniFlex II" manufactured by Rigaku Corporation, powders of the carbonaceous materials prepared in the examples and comparative examples described below were filled into a sample holder, and CuKα rays monochromated by a Ni filter were used as the radiation source to obtain an X-ray diffraction pattern. The peak positions of the diffraction pattern were determined by the centroid method (a method in which the centroid position of the diffraction lines is determined and the peak position is determined using the corresponding 2θ value), and correction was made using the diffraction peak of the (111) plane of high-purity silicon powder for standard material. The wavelength λ of CuKα rays was set to 1.5418 Å, and d was calculated using the Bragg formula shown below. ００２was calculated.

[0070]

[0071] (Example 1) Step 1: 8,000 g of rice husks were heated in a batch-type atmosphere furnace to a first temperature of 700°C under a nitrogen atmosphere. At this time, the heating rate up to 700°C was 200°C / hour (3.3°C / min). Next, the husks were carbonized by heat treatment at a low firing temperature of 700°C for 60 minutes under a nitrogen gas flow, to obtain a charcoal. At this time, the nitrogen gas supply rate was 200 L / min. The charcoal was cooled to 50°C under a nitrogen atmosphere to obtain the target charcoal. Pulverization: Next, the obtained charcoal was pulverized in a ball mill to obtain particles with an average particle size D ５０ A pulverized carbide with a particle size of 7 μm was obtained. Acid washing: A 3 L three-neck flask was equipped with a condenser, a thermometer, and a stirrer, and 0.6 L of 1N hydrochloric acid was added to 100 g of the obtained pulverized carbide. Acid washing was performed twice at 80°C for 2 hours. After cooling to room temperature, the liquid was removed using a Nutsche funnel, and then deoxidization washing was performed with 2 L of ion-exchanged water. The obtained pulverized carbide was then dried for 3 hours in a hot air dryer at 100°C.

[0072] Step 2: 15 g of the pulverized carbide was heated to 900°C in a tubular furnace. The heating rate up to 900°C was 600°C / hour (10°C / min). Next, a high-temperature firing treatment was performed by heat treatment at a high-temperature firing temperature of 900°C for 30 minutes to obtain a carbide. The temperature-raising step of heating to a predetermined temperature and the high-temperature firing treatment of heat treatment at 900°C for 30 minutes were performed under a nitrogen gas flow. The nitrogen gas supply rate was 0.1 L / min. The desired carbide was obtained by cooling to room temperature under a nitrogen atmosphere.

[0073] Step 3: 10 g of the carbide obtained in Step 2 was heated to 1300°C in a tubular furnace. The heating rate to 1300°C was 240°C / hour (4°C / min). Next, a high-temperature firing treatment was performed by heat-treating the material at a high-temperature firing temperature of 1300°C for 30 minutes, and then the material was cooled to room temperature in a nitrogen atmosphere to obtain the target carbonaceous material. The temperature-raising step of heating to a predetermined temperature and the high-temperature firing treatment of heat-treating the material at 1300°C for 30 minutes were performed in a nitrogen gas flow. The nitrogen gas supply rate was 2 L / min.

[0074] Example 2 3 g of polystyrene was added to 10 g of the carbide obtained in step 2 of Example 1, and the mixture was further heated to 900°C in a tubular furnace. The heating rate up to 900°C was 600°C / hour (10°C / min). A high-temperature firing treatment was then performed by heat-treating the mixture at a high-temperature firing temperature of 900°C for 30 minutes, thereby obtaining a carbide. The temperature-raising step of heating to a predetermined temperature and the high-temperature firing treatment of heat-treating the mixture at 900°C for 30 minutes were performed under a nitrogen gas flow. The nitrogen gas supply rate was 0.1 L / min. The mixture was cooled to room temperature under a nitrogen atmosphere, thereby obtaining the target carbide. Step 3 was performed in the same manner as in Example 1, except that the carbide obtained as described above was used, to obtain a carbonaceous material.

[0075] The carbide obtained in step 1 of Example 1 was heated at 1300°C in a nitrogen atmosphere, and the resulting carbonaceous material was pulverized to obtain the target product. The heating step at 1300°C in a nitrogen atmosphere was carried out under the same conditions as in step 3 of Example 1.

[0076] Comparative Example 2 The carbide obtained in step 1 of Example 1 was pulverized and acid-washed to obtain a pulverized carbide in the same manner as in Example 1. The pulverized carbide obtained was then heated at 1,300°C in a nitrogen atmosphere to obtain the target product. The heating step at 1,300°C in a nitrogen atmosphere was carried out under the same conditions as in step 3 of Example 1.

[0077] Comparative Example 3 A carbon material was obtained in the same manner as in Example 1, except that in the acid washing in step 1, 0.6 L of a 1 N aqueous solution of sodium hydroxide was used instead of 0.6 L of 1 N hydrochloric acid, and dealkalization washing was performed with 2 L of ion-exchanged water.

[0078] (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 CMC, 2 parts by mass of SBR, and 90 parts by mass of water were mixed to obtain a slurry. The obtained slurry was applied to a copper foil with a thickness of 18 μm, dried, and pressed to obtain an electrode with a thickness of 45 μm. The density of the obtained electrode was as shown in Table 2.

[0079] (Battery Initial Capacity and Charge / Discharge 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 was dissolved at 1 mol / L and used as the electrolyte. A polypropylene membrane was used as the separator. A coin cell was fabricated in a glove box under an argon atmosphere.

[0080] For the lithium secondary battery having the above configuration, a charge / discharge test was performed using a charge / discharge tester ("TOSCAT" manufactured by Toyo Systems Co., Ltd.) to measure the DC resistance before initial charging, followed by a charge / discharge test. 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 applied for 8 hours to terminate the doping. The capacity (mAh / g) at this time was taken as the charge capacity. Next, undoping was performed at a rate of 70 mA / g relative to the active material mass until the doping reached 2.5 V relative to the lithium potential, and the capacity at this time was taken as the discharge capacity. The percentage of the discharge capacity / charge capacity was taken as the charge / discharge efficiency (initial charge / discharge efficiency) and was used as an index of the utilization efficiency of lithium ions in the battery.

[0081] The firing conditions in each example and comparative example, and the evaluation results of the physical properties of the obtained carbonaceous materials are shown in Table 1. Furthermore, the evaluation results of the battery characteristics are shown in Table 2. Furthermore, when the carbonaceous materials obtained in Examples 1 and 2 were subjected to X-ray crystal diffraction measurement, no peaks with a half-value width of 2° or less were detected between 20° and 30° (2θ).

[0082]

[0083]

[0084] It was confirmed that the carbonaceous materials of the present examples had high discharge capacity and high efficiency. In contrast, the carbonaceous materials of Comparative Examples 1 and 2 had high charge capacity but very low charge / discharge efficiency. Carbonaceous materials with low charge / discharge efficiency such as those shown in Comparative Examples 1 and 2 may have insufficient durability or problems with battery stability when used, for example, as electrodes. Furthermore, in order to achieve a high discharge capacity, it is thought that the initial charge capacity must also be high, but this is inefficient in that it requires the supply of excess Li ions to compensate for the consumption. Furthermore, the carbonaceous material of Comparative Example 3 had high charge / discharge efficiency but very low charge / discharge capacity.

Claims

1. A carbonaceous material having a silicon content of 5% by mass or more, wherein the distance L in the graphite stacking direction in X-ray crystallography of the carbonaceous material ｃ and the distance L in the graphite plane direction ａ is 1<L ｃ / L ａ Meet the carbonaceous material.

2. Distance L in the graphite surface direction ａ The carbonaceous material according to claim 1, wherein the surface roughness is 4 to 12 Å.

3. Distance L in the graphite stacking direction ｃ and the distance L in the graphite plane direction ａ is 1<L ｃ / L ａ The carbonaceous material according to claim 1 or 2, which satisfies <3.

4. The carbonaceous material according to any one of claims 1 to 3, having a potassium content of 0.2 mass% or less.

5. Carbon interplanar spacing d calculated using the Bragg equation by wide-angle X-ray diffraction ００２ The carbonaceous material according to any one of claims 1 to 4, wherein the surface roughness is 3.75 Å or more.

6. The carbonaceous material according to any one of claims 1 to 5, which is derived from a grass family plant.

7. A method for producing a carbonaceous material, comprising: (1) heating a carbide precursor having a silicon content of 3% by mass or more at 300-900°C in an inert gas atmosphere, and then cooling it to 200°C or less to obtain a carbide; (2) heating the carbide obtained in step (1) at 500-1000°C in an inert gas atmosphere, and then cooling it to 200°C or less to obtain a carbide; and (3) heating the carbide obtained in step (2) at 800-1500°C in an inert gas atmosphere, and then cooling it to 200°C or less to obtain a carbonaceous material.

8. The method according to claim 7, further comprising the steps of crushing the carbide obtained in step (1) and washing it with an acid between steps (1) and (2).

9. The carbonaceous material has a silicon content of 5 mass% or more, and the distance L in the graphite stacking direction in X-ray crystallography of the carbonaceous material ｃ and the distance L in the graphite plane direction ａ is 1<L ｃ / L ａ The method according to claim 7 or 8, wherein the above formula (1) is satisfied.

10. A negative electrode for a non-aqueous electrolyte battery, which uses the carbonaceous material according to any one of claims 1 to 5.

11. A non-aqueous electrolyte battery using the negative electrode according to claim 10.

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