JP7638137B2 - Carbonaceous material, its manufacturing method and electrochemical device - Google Patents

Description

The present invention relates to a carbonaceous material, its manufacturing method, and an electrochemical device.

Carbonaceous materials are used in electrochemical devices such as lithium ion secondary batteries, nonaqueous electrolyte batteries such as sodium ion batteries, and lithium ion capacitors, and carbonaceous materials with properties suited to the application are required. For example, in small portable device applications such as mobile phones and laptops, battery capacity per volume is important, so there is a demand for high discharge capacity. In addition, lithium ion secondary batteries for vehicles are large and expensive, making them difficult to replace midway through use, so they must have at least the same durability as an automobile, and are required to have high cycle durability, with discharge capacity unlikely to decrease even after repeated charging and discharging.

As one method for increasing the discharge capacity of a battery, the use of a pre-doped carbonaceous material has been proposed. Patent Document 1 describes a pre-doped electricity storage device that contains a carbonaceous material with a specific range of mesopore and macropore specific surface area.

Patent No. 5302646

However, the carbonaceous material described in Patent Document 1 does not necessarily have sufficiently high durability and initial efficiency, and there has been a demand for a carbonaceous material that can be pre-doped and simultaneously satisfy the requirements of high capacity, high durability, and high initial efficiency.

The present invention therefore aims to provide a carbonaceous material that can be pre-doped at high speed and simultaneously satisfies high capacity, high initial efficiency, and high cycle durability, and a method for producing the same.

As a result of extensive research into solving the above problems, the inventors discovered that by setting the pore volume, the ratio of the desorption amount to the adsorption amount, and the mesopore volume of the carbonaceous material within appropriate ranges, it is possible to obtain a carbonaceous material that allows for rapid pre-doping and achieves high capacity, high initial efficiency, and high cycle durability, all of which have been difficult to satisfy simultaneously until now, and thus completed the present invention.

That is, the present invention includes the following preferred embodiments.
[1] A carbonaceous material, in which the pore volume determined by performing a Grand Canonical Monte Carlo simulation on the carbon dioxide adsorption/desorption isotherm is 0.05 cm ³ /g or more and 0.20 cm ³ /g or less, the ratio of the desorption amount to the adsorption amount at a relative pressure of 0.01 in the adsorption/desorption isotherm is 1.05 or more, and the mesopore volume determined by the BJH method is 3.7 mm ³ /g or more and 41 mm ³ /g or less.
[2] The carbonaceous material according to [1], having an average particle size (D ₅₀ ) of 1.3 μm or more and 9.5 μm or less.
[3] The carbonaceous material according to [1] or [2], which has a specific surface area of 3 m ² /g or more and 60 m ² /g or less, as determined by a BET method using a nitrogen adsorption method.
[4] The carbonaceous material according to any one of [1] to [3], wherein the average interplanar spacing d ₀₀₂ of the (002) plane calculated using the Bragg equation by wide-angle X-ray diffraction is 0.36 nm or more and 0.42 nm or less.
[5] The carbonaceous material according to any one of [1] to [4], which is for use in an electrochemical device.
[6] The carbonaceous material according to [5], which is pre-doped with metal ions.
[7] An electrochemical device comprising the carbonaceous material according to any one of [1] to [6].
[8] The method for producing a carbonaceous material according to any one of [1] to [6], comprising a temperature increasing step of increasing the temperature of a carbon precursor from a temperature of 600° C. or lower to 900° C., and a heat treatment step of heat treating the carbon precursor at a temperature of 900° C. or higher and 1260° C. or lower.
[9] The method according to [8], wherein the temperature increasing step is carried out in the presence of a volatile organic substance and/or a volatile substance derived from a volatile organic substance.
[10] The manufacturing method according to [8], wherein the temperature increasing step is carried out in the absence of volatile organic substances and volatile substances derived from volatile organic substances, and the heat treatment step is carried out at a temperature of more than 1100°C.
[11] The method according to any one of [8] to [10], further comprising a pulverization step of pulverizing the carbon precursor and/or the carbon precursor after the heat treatment.
[12] The manufacturing method according to any one of [8] to [11], wherein in the temperature increasing step, the temperature increasing rate from 600° C. to 900° C. is 60° C./min or less.

The present invention provides a carbonaceous material and a method for producing the same that allows for rapid pre-doping and simultaneously satisfies high capacity, high initial efficiency, and high cycle durability.

The following describes in detail an embodiment of the present invention. Note that the following is an explanation of an embodiment of the present invention, and is not intended to limit the present invention to the following embodiment.

<Carbonaceous materials>
In the carbonaceous material of the present invention, the pore volume (hereinafter sometimes simply referred to as "pore volume") determined by performing a grand canonical Monte Carlo simulation on the carbon dioxide adsorption/desorption isotherm is 0.05 cm ³ /g or more and 0.20 cm ³ /g or less, the ratio of the desorption amount to the adsorption amount (hereinafter sometimes simply referred to as "ratio of desorption amount to adsorption amount") at a relative pressure of 0.01 in the adsorption/desorption isotherm is 1.05 or more, and the mesopore volume (hereinafter sometimes simply referred to as "mesopore volume") determined by the BJH method is 3.7 mm ³ /g or more and 41 mm ³ /g or less.

[Pore volume]
In the present invention, the pore volume obtained by performing a grand canonical Monte Carlo simulation on the adsorption and desorption isotherm of carbon dioxide is 0.05 cm ³ /g or more and 0.20 cm ³ /g or less. When the pore volume is 0.05 cm ³ /g or more and 0.20 cm ³ /g or less, the carbonaceous material can be pre-doped at a high speed and simultaneously satisfies high capacity, high initial efficiency, and high cycle durability. When the pore volume is less than 0.05 cm ³ /g, it is considered that the pores are excessively blocked by thermal contraction, and the discharge capacity is likely to decrease. When the pore volume exceeds 0.20 cm ³ /g, the active sites that are the starting points of side reactions are likely to increase, and therefore the cycle durability and initial efficiency are likely to decrease. The pore volume is preferably 0.07 cm ³ /g or more, more preferably 0.13 cm ³ /g or more, and preferably 0.19 cm ³ /g or less, more preferably 0.17 cm ³ /g or less. When the pore volume is within the above range, pre-doping is possible at high speed, and high capacity, high initial efficiency, and high cycle durability are more likely to be satisfied at the same time. The pore volume of the carbonaceous material of the present invention can be adjusted within the above range by appropriately adjusting the type of carbon precursor in the method for producing a carbonaceous material of the present invention described later; the heating rate in the heating step; the temperature and/or time in the heat treatment step; the type and/or amount of the volatile organic substance, etc. By performing a grand canonical Monte Carlo simulation on the adsorption and desorption isotherm of carbon dioxide, for example, the pore volume at a pore diameter of 0.35 to 1.47 nm can be obtained. The pore volume can be measured using a gas adsorption apparatus, and can be obtained, for example, by the method described in the Examples.

Here, the pore volume obtained by performing a Grand Canonical Monte Carlo simulation on the carbon dioxide adsorption/desorption isotherm in the present invention will be described. Usually, the pore volume of mesopores (pores with a pore diameter of about 2 nm to about 50 nm) or micropores (pores with a pore diameter of less than about 2 nm) can be obtained by applying an analysis method called the BJH method or the MP method to the nitrogen adsorption/desorption isotherm at 77 K. However, in the present invention, the carbon dioxide adsorption/desorption isotherm at 273 K is used. This method uses carbon dioxide with a smaller molecular size than nitrogen, and since the measurement is performed at a higher temperature, the molecules do not form clusters, so it was found that it is possible to evaluate the pore structure in more detail. As a result, it was found that it is possible to more precisely evaluate the pores that are the starting point of side reactions that affect cycle durability, which are difficult to evaluate using normal measurement methods, and to more precisely measure the discrepancy (hysteresis) between the adsorption curve and the desorption curve that is thought to be due to the ink bottle-shaped pores described later.

[Ratio of carbon dioxide desorption amount to adsorption amount]
In the present invention, the ratio of the desorption amount to the adsorption amount at a relative pressure of 0.01 in the adsorption and desorption isotherm of carbon dioxide is 1.05 or more. When the ratio of the desorption amount to the adsorption amount is 1.05 or more, the carbonaceous material can be pre-doped at a high speed and simultaneously satisfies high capacity, high initial efficiency, and high cycle durability, and particularly improves cycle durability. When the ratio of the desorption amount to the adsorption amount is less than 1.05, side reactions are likely to occur, leading to a decrease in cycle durability. The ratio of the desorption amount to the adsorption amount is preferably 1.08 or more, more preferably 1.1 or more, even more preferably 1.2 or more, and even more preferably 1.4 or more. The upper limit of the ratio of the desorption amount to the adsorption amount is not particularly limited, but is usually 10.0 or less. When the ratio of the desorption amount to the adsorption amount is within the above range, the cycle durability tends to be further improved. In the present invention, the ratio of the desorption amount to the adsorption amount refers to the value obtained by dividing the desorption amount by the adsorption amount, that is, the value of the desorption amount/adsorption amount. In the present invention, the ratio of the desorption amount to the adsorption amount can be adjusted to be equal to or higher than the lower limit by appropriately adjusting the temperature rise rate in the temperature rise step, the temperature and/or time in the heat treatment step, the type and/or amount of the volatile organic substance, etc. in the production method of the carbonaceous material of the present invention described below. The desorption amount and adsorption amount of carbon dioxide can be measured using a gas adsorption apparatus, and can be determined, for example, by the method described in the Examples.

Here, we will explain the ratio of the amount of desorption and the amount of adsorption (amount of desorption/amount of adsorption) at a relative pressure of 0.01 in the adsorption/desorption isotherm of carbon dioxide. If we assume a cylindrical pore with one end closed, the adsorption curve and the desorption curve should theoretically match. However, depending on the structure of the pore, a mismatch between the adsorption curve and the desorption curve (hysteresis) may occur. There are various theories about the cause of this phenomenon, but one theory that hysteresis occurs in the case of ink bottle-shaped pores has been proposed. In other words, since the ink bottle type has a neck (the radius of the neck is shorter than the radius of the bottom), it has a different saturated vapor pressure. If the relative pressure is changed in the direction of decreasing, the adsorption layer in the neck does not evaporate until it reaches the saturated vapor pressure corresponding to the radius of the neck. In other words, even if evaporation is attempted from the adsorption layer at the bottom, it is difficult to evaporate because it is held down by the condensation layer at the inlet, and it is suddenly desorbed when the saturated vapor pressure corresponding to the radius of the neck is reached. In this way, a discrepancy between the amount of adsorption and the amount of desorption is likely to occur, and the amount of desorption is likely to be greater than the amount of adsorption. Therefore, if the ratio of the amount of desorption to the amount of adsorption at a relative pressure of 0.01 in the adsorption/desorption isotherm is in the above range, this indicates the possibility of the presence of ink bottle-shaped pores.

[Mesopore volume]
The mesopore volume of the carbonaceous material of the present invention determined by the BJH method is 3.7 mm ³ /g or more and 41 mm ³ /g or less. When the mesopore volume is 3.7 mm ³ /g or more and 41 mm ³ /g or less, the carbonaceous material can be pre-doped at a high speed and simultaneously satisfies high capacity, high initial efficiency and high cycle durability, and particularly high-speed pre-doping is possible. When the mesopore volume is less than 3.7 mm ³ /g, the diffusion rate of ions from the electrolyte to the carbonaceous material tends to decrease, so the pre-doping rate is likely to be slow. When the mesopore volume exceeds 41 mm ³ /g, the active sites that are the starting points of side reactions are likely to increase, so the initial efficiency and cycle durability are likely to decrease. The mesopore volume is preferably 4.0 mm ³ /g or more, more preferably 8.0 mm ³ /g or more, and even more preferably 10.5 mm ³ /g or more, and preferably 35 mm ³ /g or less, more preferably 22 mm ³ /g or less. When the mesopore volume is within the above range, high-speed pre-doping is possible, and high capacity, high initial efficiency, and high cycle durability are more easily satisfied at the same time, and particularly high-speed pre-doping is easily achieved. Here, the "mesopore volume" generally refers to the volume of pores having a pore diameter of about 2 nm or more and about 50 nm or less, but in the present invention, it may refer to pores having a diameter of 2.5 nm or more and 33 nm or less, particularly from the viewpoint of evaluating the active sites that are the starting points of side reactions and the diffusibility of the electrolyte. The mesopore volume can be adjusted within the above range, for example, by appropriately adjusting the type and particle size of the carbon precursor in the method for producing the carbonaceous material of the present invention described later; the temperature and/or time of the heat treatment step; the type and/or amount of the volatile organic substance, etc. The mesopore volume can be measured using a gas adsorption apparatus, and can be determined, for example, by the method described in the Examples.

[Average particle diameter (D ₅₀ )]
In the present invention, the average particle diameter (D ₅₀ ) of the carbonaceous material is preferably 1.3 μm or more, more preferably 2.2 μm or more, even more preferably 2.6 μm or more, and preferably 9.5 μm or less, more preferably 8.0 μm or less, even more preferably 5.5 μm or less, even more preferably 4.9 μm or less, and particularly preferably 4.7 μm or less. When the average particle diameter (D ₅₀ ) of the carbonaceous material is the lower limit or more, active sites that are the starting points of side reactions are unlikely to be generated, so that cycle durability and initial efficiency are likely to be improved. When the average particle diameter (D ₅₀ ) is the upper limit or less, it is easy to increase the electrode density and improve the ion diffusion rate, so that high-speed pre-doping tends to be possible. In addition, it is easy to adjust the mesopore volume to the above-mentioned range. Here, the average particle diameter (D ₅₀ ) in the present invention refers to the volume average particle diameter at which the cumulative volume from the fine particle side is 50% in the particle size distribution measured by the laser scattering method. The average particle size ( _D50 ) can be adjusted to within the above range, for example, by appropriately adjusting the particle size of the carbon precursor in the production method for a carbonaceous material of the present invention described below, the conditions of the grinding step, the temperature and/or time of the heat treatment step, the mixing ratio of carbonaceous materials having different particle sizes, etc. In particular, in order to obtain a carbonaceous material having a desired average particle size, the average particle size may be adjusted to within the above range by mixing two or more carbonaceous materials having different average particle sizes.

[BET specific surface area by nitrogen adsorption method]
The BET specific surface area (hereinafter also simply referred to as "specific surface area") of the carbonaceous material of the present invention measured by the nitrogen adsorption method is preferably 3 m ² /g or more, more preferably 9 m ² /g or more, even more preferably 13 m ² /g or more, even more preferably 16 m ² /g or more, particularly preferably 22 m ² /g or more, and is preferably 60 m ² /g or less, more preferably 40 m ² /g or less, and even more preferably 35 m ² /g or less. When the specific surface area is within the above range, the number of active sites that are the starting points of side reactions is likely to be reduced, and a suitable reaction area with the electrolyte can be secured, so that pre-doping can be performed at a high speed, and high capacity, high initial efficiency, and high cycle durability can be easily satisfied at the same time. The specific surface area of the carbonaceous material of the present invention can be adjusted within the above range by appropriately adjusting the type and/or particle size of the carbon precursor in the method for producing the carbonaceous material of the present invention described later; the temperature and/or time of the heat treatment step; the conditions of the pulverization step; the type and/or amount of the volatile organic substance, and the like. The specific surface area of the carbonaceous material of the present invention can be measured using a gas adsorption apparatus, and can be determined, for example, by the method described in the Examples.

[Average interplanar spacing of (002) plane d ₀₀₂ ]
The average interplanar spacing d ₀₀₂ of the (002) plane of the carbonaceous material of the present invention, calculated from the wide-angle X-ray diffraction method using the Bragg formula, is preferably 0.36 nm or more, more preferably 0.38 nm or more, and preferably 0.42 nm or less, more preferably 0.40 nm or less. When the average interplanar spacing d ₀₀₂ of the (002) plane is within the above range, the capacity retention rate at low temperatures tends to be excellent. In addition, since ions are easily introduced, the carbonaceous material is likely to be suitable for various electrochemical devices. The average interplanar spacing d ₀₀₂ of the (002) plane of the carbonaceous material of the present invention can be adjusted within the above range, for example, by appropriately adjusting the heating rate of the heating step; the temperature and/or time of the heat treatment step, etc. in the manufacturing method of the carbonaceous material of the present invention described later. The average interplanar spacing d ₀₀₂ of the (002) plane can be measured by X-ray diffraction, and can be determined, for example, by the method described in the Examples.

<Method of producing carbonaceous material>
The carbonaceous material of the present invention is, for example,
The carbon precursor can be produced by a method including a temperature increasing step of increasing the temperature of the carbon precursor from a temperature of 600° C. or less to 900° C., and a heat treatment step of heat treating the carbon precursor at a temperature of 900° C. or more and 1260° C. or less.

[Carbon Precursor]
In the present invention, the raw material of the carbon precursor is not particularly limited as long as it forms a carbonaceous material, and can be widely selected from carbon precursors derived from plants, carbon precursors derived from minerals, carbon precursors derived from natural materials, carbon precursors derived from synthetic materials, etc. From the viewpoint of environmental protection and commercial viewpoints, it is preferable that the carbonaceous material of the present invention is based on a carbon precursor derived from plants, in other words, it is preferable that the carbon precursor that becomes the carbonaceous material of the present invention is derived from plants.

Carbon precursors derived from minerals include, for example, petroleum-based and coal-based pitches and coke. Carbon precursors derived from natural materials include, for example, natural fibers such as cotton and hemp, regenerated fibers such as rayon and viscose rayon, and semi-synthetic fibers such as acetate and triacetate. Carbon precursors derived from synthetic materials include, for example, polyamides such as nylon, polyvinyl alcohols such as vinylon, polyacrylonitriles such as acrylic, polyolefins such as polyethylene and polypropylene, polyurethanes, phenolic resins, and polyvinyl chloride resins.

There is no particular limitation on the plant that is the raw material for the plant-derived carbon precursor (hereinafter sometimes referred to as "plant-derived char"). Examples include coconut shells, coffee beans, tea leaves, sugar cane, fruits (e.g., mandarin oranges, bananas), straw, rice husks, broad-leaved trees, coniferous trees, and bamboo. These examples include waste after their original use (e.g., used tea leaves) or parts of the raw plant (e.g., mandarin oranges, banana peels). These plants can be used alone or in combination of two or more kinds. Among these plants, coconut shells, which are easily available in large quantities, are preferred.
In addition, char generally refers to a powdered solid rich in carbon that does not melt or soften and is obtained when coal is heated, but here it also refers to a powdered solid rich in carbon that does not melt or soften and is obtained by heating organic matter.

There is no particular limitation on the type of coconut shell, but examples include coconut shells from palm trees (oil palm), coconut palm, salak palm, and mulberry palm. These coconut shells can be used alone or in combination. Coconut and palm shells are particularly preferred, as they are used as food, detergent raw materials, biodiesel oil raw materials, etc., and are biomass waste generated in large quantities.

There is no particular limitation on the method for producing char from coconut shells, and char can be produced using methods known in the art. For example, coconut shells can be heat-treated (hereinafter sometimes referred to as "pre-calcination") at a temperature of about 300 to 1000°C in an atmosphere of an inert gas such as nitrogen, carbon dioxide, helium, argon, carbon monoxide, or fuel exhaust gas, a mixture of these inert gases, or a mixture of these inert gases with other gases that mainly contain these inert gases (for example, a mixture of nitrogen and a halogen gas).

It can also be obtained in the form of char (e.g., coconut shell char).

Carbonaceous materials produced from plant-derived char can be doped with large amounts of active material, and are therefore fundamentally suitable as carbonaceous materials for electrochemical devices such as nonaqueous electrolyte secondary batteries. However, plant-derived char generally contains large amounts of metal elements (especially potassium, iron, etc.) that were contained in the plant raw material, and using electrodes containing carbonaceous materials with a high content of such metal elements in electrochemical devices can have undesirable effects on electrochemical properties and safety. Therefore, it is preferable to reduce the content of potassium, iron, etc. contained in the carbonaceous material as much as possible.

In addition to potassium and iron, plant-derived char often contains alkali metals (e.g., sodium), alkaline earth metals (e.g., magnesium or calcium), transition metals (e.g., copper), and other elements (hereinafter, these are also collectively referred to as "ash"). When an electrode containing a carbonaceous material containing these metal elements is used as the negative electrode of a nonaqueous electrolyte secondary battery such as a lithium ion secondary battery, impurities may dissolve into the electrolyte during dedoping from the negative electrode, adversely affecting battery performance and impairing the reliability of the nonaqueous electrolyte secondary battery, so it is preferable to reduce the content of these metals.

Therefore, it is preferable to reduce the ash content (alkali metal elements, alkaline earth metal elements, transition metal elements, and other elements) in the plant raw material or plant-derived char before heating and heat-treating the carbon precursor to obtain a carbonaceous material. Hereinafter, reducing the ash content in the char of the plant raw material or plant-derived raw material is also referred to as "decalcification". There are no particular limitations on the decalcification method, and it is possible to use, for example, a method of extracting and decalcifying metals using an acidic solution containing a mineral acid such as hydrochloric acid or sulfuric acid, or an organic acid such as acetic acid or formic acid (liquid-phase decalcification), or a method of decalcifying by exposure to a high-temperature gas phase containing a halogen compound such as hydrogen chloride (gas-phase decalcification).

Liquid-phase demineralization may be performed in the form of either plant raw materials or plant-derived char. Liquid-phase demineralization may be performed, for example, by immersing plant raw materials or plant-derived char in an acidic solution. The acidic solution is a mixture of an acid and an aqueous solution. The acid is not particularly limited, but examples thereof include aqueous solutions of mineral acids such as hydrochloric acid and sulfuric acid, and organic acids such as acetic acid, butyric acid, and citric acid. From the viewpoint of avoiding unnecessary ions remaining in the demineralized material, it is preferable to use an organic acid as the acid, and from the viewpoints of efficiency of demineralization, economic efficiency such as the price of the acid, and comparative ease of waste liquid treatment after use, it is more preferable to use acetic acid and/or citric acid. Examples of the aqueous solution include water, and mixtures of water and a water-soluble organic solvent. Examples of the water-soluble organic solvent include alcohols such as methanol, ethanol, propylene glycol, and ethylene glycol.

The acid concentration in the acidic solution is not particularly limited, but since the deashing rate is affected by the acid concentration, it is preferably in the range of 0.001 to 1 M, more preferably in the range of 0.002 to 0.9 M, and even more preferably in the range of 0.005 to 0.5 M. The amount of acidic solution used is also not particularly limited, but it is preferably such that the plant material or plant-derived char to be immersed is immersed in the acidic solution. For example, the mass of the acidic solution relative to the mass of the plant material or plant-derived char to be immersed is preferably 100 to 1000 mass%, more preferably 200 to 900 mass%, and even more preferably 250 to 800 mass%.

The temperature for liquid-phase de-ashing can be determined according to the plant raw material or plant-derived char to be de-ashed, and may be, for example, 10 to 120°C, preferably 20 to 100°C, and more preferably 25 to 95°C. When the de-ashing temperature is within the above range, de-ashing can be performed efficiently while suppressing the decrease in carbon content due to hydrolysis of the organic matter that constitutes the plant.

The time for liquid phase demineralization is not particularly limited, but may be, for example, 0.1 to 100 hours, preferably 0.2 to 50 hours, and more preferably 0.5 to 20 hours. Liquid phase demineralization may be performed by continuously immersing the plant raw material or plant-derived char in an acidic solution, or may be performed in multiple steps while refreshing the acidic solution used for demineralization. When liquid phase demineralization is performed in multiple steps, the total demineralization time is regarded as the liquid phase demineralization time.

The equipment used for liquid-phase demineralization is not particularly limited as long as it is capable of immersing the plant raw material or plant-derived char in an acidic solution. For example, a glass-lined stirring tank can be used.

Gas-phase demineralization may be performed on either the plant raw material or the plant-derived char. Gas-phase demineralization may be performed, for example, by heat treating the plant raw material or the plant-derived char in a gas phase containing a halogen compound. The halogen compound is not particularly limited, and examples thereof include fluorine, chlorine, bromine, iodine, hydrogen fluoride, hydrogen chloride, hydrogen bromide, iodine bromide, chlorine fluoride (ClF), iodine chloride (ICl), iodine bromide (IBr), bromine chloride (BrCl), and the like. Compounds that generate these halogen compounds by thermal decomposition or mixtures thereof may also be used. The halogen compound is preferably hydrogen chloride from the viewpoints of supply stability and stability of the halogen compound used.

Gas-phase deashing may be carried out in a gas phase containing a mixture of a halogen compound and an inert gas. There are no particular limitations on the inert gas, so long as it does not react with the material to be deashed (the plant raw material or the plant-derived char) and the plant raw material or the plant-derived char after deashing at the deashing temperature. Examples include nitrogen, helium, argon, krypton, or a mixture of these gases. From the viewpoints of supply stability and economic efficiency, it is preferable that the inert gas is nitrogen.

When gas-phase deashing is performed in a gas phase in which a halogen compound and an inert gas are mixed, the mixing ratio of the halogen compound and the inert gas is not particularly limited as long as sufficient deashing can be achieved. For example, the amount of the halogen compound relative to the inert gas is preferably 0.01 to 10.0% by volume, more preferably 0.05 to 8.0% by volume, and even more preferably 0.1 to 5.0% by volume.

The temperature for gas-phase de-ashing may be determined according to the plant raw material or plant-derived char to be de-ashed, and may be, for example, 500 to 1100°C, preferably 600 to 1050°C, more preferably 650 to 1000°C, and even more preferably 850 to 1000°C. If the de-ashing temperature is too low, the de-ashing efficiency decreases and sufficient de-ashing may not be achieved. If the de-ashing temperature is too high, activation by halogen compounds may occur.

The time for gas phase demineralization is not particularly limited, but is, for example, 5 to 300 minutes, preferably 10 to 200 minutes, and more preferably 15 to 150 minutes.

The amount of gas supplied (flow rate) in gas-phase demineralization is not particularly limited, and is, for example, preferably 1 ml/min or more, more preferably 5 ml/min or more, and even more preferably 10 ml/min or more per gram of plant raw material or plant-derived char.

The apparatus used for gas-phase demineralization is not particularly limited as long as it is an apparatus capable of heating while mixing the plant raw material or plant-derived char with the gas phase containing halogen compounds. For example, an apparatus using a fluidized furnace and a continuous or batch-type in-bed flow system using a fluidized bed or the like can be used.

When gas-phase demineralization is performed, a heat treatment in the absence of a halogen compound may be performed after the heat treatment in the gas phase containing a halogen compound. Usually, the plant raw material or the plant-derived char contains halogen due to the heat treatment in the gas phase containing a halogen compound. The halogen contained in the plant raw material or the plant-derived char can be removed by heat treatment in the absence of a halogen compound. For example, after the heat treatment in the gas phase containing the halogen compound, the supply of the halogen compound is cut off and the heat treatment is performed to remove the halogen. Specifically, the heat treatment in the absence of a halogen compound may be performed by heat treatment at 500°C to 1100°C, preferably 600°C to 1050°C, more preferably 650°C to 1000°C, and even more preferably 850°C to 1000°C in an inert gas atmosphere not containing a halogen compound. The temperature of the heat treatment in the absence of a halogen compound is preferably the same as or higher than the temperature of the heat treatment in the gas phase containing a halogen compound. The time for heat treatment in the absence of a halogen compound is not particularly limited, but is preferably 5 to 300 minutes, more preferably 10 to 200 minutes, and even more preferably 10 to 100 minutes.

In this embodiment, the liquid-phase demineralization and gas-phase demineralization are processes for removing ash such as potassium and iron contained in the plant raw material or plant-derived char. The potassium element content of the carbon precursor obtained after the liquid-phase demineralization process or the gas-phase demineralization process is preferably 1000 ppm (0.1 mass%) or less, more preferably 500 ppm or less, and even more preferably 300 ppm or less. The iron element content of the carbon precursor obtained after the liquid-phase demineralization process or the gas-phase demineralization process is preferably 200 ppm or less, more preferably 150 ppm or less, and even more preferably 100 ppm or less. If the potassium element and iron element contents of the carbon precursor are below the above upper limit, when the obtained carbonaceous material is used for an electrode for an electrochemical device such as a nonaqueous electrolyte secondary battery, the elution of impurities into the electrolyte during dedoping can be reduced, which is preferable in terms of improving the performance and reliability of the electrochemical device.

The specific surface area of the carbon precursor (specific surface area after the pulverization step when the pulverization step described later is applied to the carbon precursor) is preferably 500 m ² /g or less, more preferably 450 m ² /g or less. When the specific surface area of the carbon precursor is the upper limit or less, the carbon surface is sufficiently modified, and a preferable pore structure is likely to be obtained after heat treatment. The lower limit of the specific surface area of the carbon precursor is not particularly limited, but is usually 25 m ² /g or more. The specific surface area of the carbon precursor can be adjusted to the upper limit or less by appropriately adjusting the type of carbon precursor, the temperature and time of the calcination, the atmosphere in which the calcination is performed, and the like. The specific surface area of the carbon precursor can be measured, for example, using the BET method.

[Temperature increasing process]
In a preferred embodiment of the production method of the present invention, the temperature raising step can be carried out in the presence of a volatile organic substance. In the present invention, the volatile organic substance is preferably an organic substance having a carbon residue rate of less than 5% by mass, and is preferably an organic substance having a carbon residue rate of less than 5% by mass when incinerated at 800° C. The volatile organic substance is preferably one that generates a volatile substance (e.g., a hydrocarbon gas, a tar). In the volatile organic substance, the content of the volatile substance (e.g., a hydrocarbon gas or a tar component) is not particularly limited, but is preferably 10% by mass or more from the viewpoint of stable operation of the equipment used. In addition, the upper limit of the content of the volatile component is not particularly limited, but is preferably 95% by mass or less, more preferably 80% by mass or less, and even more preferably 50% by mass or less from the viewpoint of suppressing the generation of tar components in the equipment. The volatile component is calculated from the ignition residue after igniting the sample in an inert gas and the amount of the sample charged. For ignition, about 1 g of the volatile organic material (this exact mass is designated as _W0 (g)) is placed in a crucible, and the crucible is heated to 800° C. at 10° C./min in an electric furnace while flowing 20 liters of nitrogen per minute, and then ignited at 800° C. for 1 hour. The residue at this stage is designated as the ignition residue, and its mass is designated as W (g), and the volatile component P (%) is calculated using the following formula:

Examples of volatile organic substances include thermoplastic resins and low molecular weight organic compounds. Specifically, examples of thermoplastic resins include polystyrene, polyethylene, polypropylene, poly(meth)acrylic acid, and poly(meth)acrylic acid esters. In this specification, (meth)acrylic is a general term for methacryl and acrylic. Examples of low molecular weight organic compounds include toluene, xylene, mesitylene, styrene, naphthalene, phenanthrene, anthracene, and pyrene. Since it is preferable for the thermoplastic resin to volatilize within a temperature range and not oxidize and activate the surface of the carbon precursor when thermally decomposed, polystyrene, polyethylene, and polypropylene are preferred. Furthermore, it is preferable for the low molecular weight organic compound to have low volatility at room temperature from the viewpoint of safety, and naphthalene, phenanthrene, anthracene, pyrene, and the like are preferred.

In one embodiment of the present invention, examples of the thermoplastic resin include olefin resins, styrene resins, and (meth)acrylic acid resins. Examples of the olefin resins include polyethylene, polypropylene, random copolymers of ethylene and propylene, and block copolymers of ethylene and propylene. Examples of the styrene resins include polystyrene, poly(α-methylstyrene), and copolymers of styrene and (meth)acrylic acid alkyl esters (the number of carbon atoms in the alkyl group is 1 to 12, preferably 1 to 6). Examples of the (meth)acrylic acid resins include polyacrylic acid, polymethacrylic acid, and (meth)acrylic acid alkyl ester polymers (the number of carbon atoms in the alkyl group is 1 to 12, preferably 1 to 6).

In one embodiment of the present invention, for example, a hydrocarbon compound having 1 to 20 carbon atoms can be used as the low molecular weight organic compound. The number of carbon atoms in the hydrocarbon compound is preferably 2 to 18, more preferably 3 to 16. The hydrocarbon compound may be a saturated or unsaturated hydrocarbon compound, a chain-like hydrocarbon compound, or a cyclic hydrocarbon compound. In the case of an unsaturated hydrocarbon compound, the unsaturated bond may be a double bond or a triple bond, and the number of unsaturated bonds contained in one molecule is not particularly limited. For example, the chain-like hydrocarbon compound is an aliphatic hydrocarbon compound, and examples of the chain-like hydrocarbon compound include linear or branched alkanes, alkenes, or alkynes. Examples of the cyclic hydrocarbon compound include alicyclic hydrocarbon compounds (e.g., cycloalkanes, cycloalkenes, cycloalkynes) or aromatic hydrocarbon compounds. Specifically, examples of the aliphatic hydrocarbon compound include methane, ethane, propane, butane, pentane, hexane, octane, nonane, decane, ethylene, propylene, butene, pentene, hexene, or acetylene. Examples of the alicyclic hydrocarbon compound include cyclopentane, cyclohexane, cycloheptane, cyclooctane, cyclononane, cyclopropane, cyclopentene, cyclohexene, cycloheptene, cyclooctene, decalin, norbornene, methylcyclohexane, and norbornadiene. Examples of the aromatic hydrocarbon compound include monocyclic aromatic compounds such as benzene, toluene, xylene, mesitylene, cumene, butylbenzene, styrene, α-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, vinylxylene, p-tert-butylstyrene, and ethylstyrene, and condensed polycyclic aromatic compounds having 3 to 6 rings such as naphthalene, phenanthrene, anthracene, and pyrene, and are preferably condensed polycyclic aromatic compounds, and more preferably naphthalene, phenanthrene, anthracene, or pyrene. Here, the hydrocarbon compound may have any substituent. The substituent is not particularly limited, but examples include an alkyl group having 1 to 4 carbon atoms (preferably an alkyl group having 1 to 2 carbon atoms), an alkenyl group having 2 to 4 carbon atoms (preferably an alkenyl group having 2 carbon atoms), and a cycloalkyl group having 3 to 8 carbon atoms (preferably a cycloalkyl group having 3 to 6 carbon atoms).

The volatile organic substance is preferably solid at room temperature, and more preferably a thermoplastic resin that is solid at room temperature, such as polystyrene, polyethylene, or polypropylene, or a low molecular weight organic compound that is solid at room temperature, such as naphthalene, phenanthrene, anthracene, or pyrene. Since it is preferable that the surface of the carbon precursor is not oxidized and activated when it volatilizes and is thermally decomposed within the elevated temperature range, the thermoplastic resin is preferably an olefin resin or a styrene resin, and more preferably polystyrene, polyethylene, or polypropylene. From the viewpoint of safety, the low molecular weight organic compound is preferably a hydrocarbon compound having 1 to 20 carbon atoms, more preferably a condensed polycyclic aromatic compound, and even more preferably naphthalene, phenanthrene, anthracene, or pyrene. Furthermore, from the viewpoint of the residual carbon rate, a thermoplastic resin is preferable, more preferably an olefin resin or a styrene resin, more preferably polystyrene, polyethylene, or polypropylene, and particularly preferably polystyrene or polyethylene.

The carbon content is measured by quantifying the amount of carbon in the ignition residue after igniting the sample in an inert gas. Ignition involves placing approximately 1 g of volatile organic matter (the exact mass is designated _W1 (g)) in a crucible, heating the crucible in an electric furnace from room temperature to 800°C at a heating rate of 10°C/min while flowing 20 liters of nitrogen per minute, and then igniting at 800°C for one hour. The material remaining at this time is designated the ignition residue, and its mass is designated _W2 (g).

Next, the ignition residue is subjected to elemental analysis in accordance with the method defined in JIS M8819 to measure the mass percentage P ₁ (mass%) of carbon. The residual carbon percentage P ₂ (mass%) is calculated by the following formula.

In the present invention, the method of heating the carbon precursor and the volatile organic substance is not particularly limited. The carbon precursor and the organic substance may be mixed in advance before heating, or the carbon precursor and the volatile organic substance may be placed separately in the heating system. The embodiment in which the carbon precursor and the volatile organic substance are mixed in advance is preferable because the surface of the carbon precursor is easily modified uniformly.

In the present invention, the heating rate from 600°C to 900°C in the heating step is preferably 60°C/min or less, more preferably 50°C/min or less, even more preferably 40°C/min or less, even more preferably 30°C/min or less, and particularly preferably 20°C/min or less. The lower limit of the heating rate is usually 5°C/min or more. If the heating rate is within the above range, it is preferable because the carbon surface is easily modified sufficiently.

The rate of temperature rise from any starting temperature below 600°C (e.g., room temperature) to 600°C is not particularly limited, but from a commercial perspective, it is preferably 5 to 300°C/min, more preferably 10 to 60°C/min.

As the heating device, any device normally used in the production of carbonaceous materials can be used. Examples of such devices include a circulation dryer, an oven, or a rotary kiln. To raise the temperature uniformly, the mixture may be heated while being appropriately stirred.

When the volatile organic substance is a solid at room temperature, it is preferable to mix it in the form of particles, but the shape and particle size are not particularly limited. From the viewpoint of uniformly dispersing the volatile organic substance in the carbon precursor, the average particle size of the volatile organic substance is preferably 0.1 to 2000 μm, more preferably 1 to 1000 μm, and even more preferably 2 to 600 μm.

The mixture may contain other components in addition to the carbon precursor and the volatile organic substance. For example, it may contain natural graphite, artificial graphite, carbon black, carbon nanofiber, metal-based materials, alloy-based materials, or oxide-based materials. The content of the other components is not particularly limited, but is preferably 50 parts by mass or less, more preferably 30 parts by mass or less, even more preferably 20 parts by mass or less, and particularly preferably 10 parts by mass or less, per 100 parts by mass of the mixture of the carbon precursor and the volatile organic substance.

The mass ratio of the carbon precursor to the volatile organic substance in the temperature-raising system is not particularly limited, but is preferably 97:3 to 40:60, more preferably 95:5 to 60:40, and even more preferably 93:7 to 80:20. When the amount of the volatile organic substance is 3 parts by mass or more, the modification is likely to be carried out sufficiently. On the other hand, if there is too much volatile organic substance, it is not preferable because it may react excessively on the surface layer of the powder and tend to generate lumps.

The heating step is preferably carried out in an inert gas atmosphere. Examples of inert gases include nitrogen and argon. The heating step may be carried out under atmospheric pressure or reduced pressure. When carried out under reduced pressure, the heating step may be carried out at, for example, 10 kPa or less.

In another embodiment of the present invention, the temperature raising step may be carried out in the presence of a carbon precursor and a volatile substance derived from a volatile organic substance (hereinafter, sometimes simply referred to as "volatile substance"). The volatile substance is a substance that is a gas that is formed by the volatilization of the volatile organic substance, and a substance that is generated by the thermal decomposition of the volatile organic substance. A specific example of a gas that is a gas that is formed by the volatilization of a volatile organic substance may be, for example, a hydrocarbon compound having 1 to 20 carbon atoms. The number of carbon atoms in the hydrocarbon compound is preferably 2 to 18, more preferably 3 to 16. The hydrocarbon compound may be a saturated or unsaturated hydrocarbon compound, and may be a chain-like hydrocarbon compound or a cyclic hydrocarbon compound. In the case of an unsaturated hydrocarbon compound, the unsaturated bond may be a double bond or a triple bond, and the number of unsaturated bonds contained in one molecule is not particularly limited. For example, the chain-like hydrocarbon compound is an aliphatic hydrocarbon compound, and examples of the chain-like hydrocarbon compound include linear or branched alkanes, alkenes, or alkynes. Examples of cyclic hydrocarbon compounds include alicyclic hydrocarbon compounds (e.g., cycloalkanes, cycloalkenes, cycloalkynes) or aromatic hydrocarbon compounds.Specific examples of aliphatic hydrocarbon compounds include methane, ethane, propane, butane, pentane, hexane, octane, nonane, decane, ethylene, propylene, butene, pentene, hexene, and acetylene.Examples of alicyclic hydrocarbon compounds include cyclopentane, cyclohexane, cycloheptane, cyclooctane, cyclononane, cyclopropane, cyclopentene, cyclohexene, cycloheptene, cyclooctene, decalin, norbornene, methylcyclohexane, and norbornadiene. Further, examples of aromatic hydrocarbon compounds include monocyclic aromatic compounds such as benzene, toluene, xylene, mesitylene, cumene, butylbenzene, styrene, α-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, vinylxylene, p-tert-butylstyrene, and ethylstyrene, and condensed polycyclic aromatic compounds having 3 to 6 rings such as naphthalene, phenanthrene, anthracene, and pyrene. From the viewpoint of reactivity with carbonaceous materials and ease of handling, monocyclic aromatic compounds such as benzene, toluene, xylene, mesitylene, cumene, butylbenzene, styrene, α-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, vinylxylene, p-tert-butylstyrene, and ethylstyrene are more preferred.

The concentration of the volatile substance in the heating system is preferably 1.0 vol.% or more, more preferably 1.5 vol.% or more, and even more preferably 5 vol.% or more, and is preferably 95 vol.% or less, more preferably 85 vol.% or less, and even more preferably 75 vol.% or less. When the concentration of the volatile substance is within the above range, the carbon precursor is sufficiently modified and the effect on the heat treatment equipment is likely to be reduced.

The gas other than the volatile substances contained in the heating system may be an inert gas, specifically nitrogen, argon, etc. The heating process may be carried out under atmospheric pressure or reduced pressure, and when carried out under reduced pressure, it may be carried out at, for example, 10 kPa or less.

When the heating step is carried out in the presence of a volatile substance, for example, the volatile organic substance alone may be placed in a furnace or the like and then heated, and the carbon precursor may be introduced into the system after the system is filled with the volatile substance, or the volatile substance may be introduced into the system in which the carbon precursor is present.

In another preferred embodiment of the present invention, the temperature-raising step may be carried out in the absence of volatile organics and volatile substances. In the present invention, "the absence (absence) of volatile organics and volatile substances" refers to the proportion of volatile organics in the temperature-raising system being preferably 2 mass% or less, more preferably 1 mass% or less, relative to the mass of the carbon precursor, and the concentration of volatile substances being preferably less than 1 volume%, more preferably 0.5 volume% or less.

Even when the temperature is increased in the absence of volatile organic substances and volatile substances, the temperature increase rate from 600° C. to 900° C. in the temperature increase step is preferably 60° C./min or less, more preferably 50° C./min or less, even more preferably 40° C./min or less, still more preferably 30° C./min or less, and particularly preferably 20° C./min or less. The lower limit of the temperature increase rate is usually 5° C./min or more.
Similarly to the case where the heating step is carried out in the presence of a volatile organic substance and a volatile substance, the heating rate from any starting temperature equal to or lower than 600° C. (for example, room temperature) to 600° C. is not particularly limited, but is preferably 5 to 300° C./min, more preferably 10 to 60° C./min, from a commercial viewpoint.

When the heating is carried out in the absence of volatile organic substances and volatile substances, the heating step is preferably carried out in an inert gas atmosphere. Examples of inert gases include nitrogen and argon. The heating step may be carried out under atmospheric pressure or reduced pressure, and when carried out under reduced pressure, it may be carried out at, for example, 10 kPa or less.

When the temperature rise is carried out in the absence of volatile organics and volatile substances, other components besides the carbon precursor may be included in the system. For example, natural graphite, artificial graphite, carbon black, carbon nanofiber, metal-based materials, alloy-based materials, or oxide-based materials may be included. The amount of other components in the temperature rise system is not particularly limited, but is preferably 50 parts by mass or less, more preferably 30 parts by mass or less, and even more preferably 20 parts by mass or less, per 100 parts by mass of the carbon precursor.

[Heat treatment process]
In the present invention, the temperature of the heat treatment step is preferably 900° C. or more and 1260° C. or less. When the temperature of the heat treatment step is within the above range, it is possible to quickly pre-dope, and it is easy to obtain a carbonaceous material that simultaneously satisfies high capacity, high initial efficiency, and high cycle durability. The temperature of the heat treatment step is more preferably 930° C. or more, even more preferably 1020° C. or more, more preferably 1200° C. or less, and even more preferably 1170° C. or less.

In a preferred embodiment of the present invention, when heating is performed in the absence of volatile organics and volatile substances, the temperature of the heat treatment step is preferably greater than 1100°C, more preferably 1140°C or higher, and preferably 1260°C or lower, more preferably 1230°C or lower. When the temperature of the heat treatment step is within the above range, high-speed pre-doping is possible without using volatile organics during the heating step, and it is easy to obtain a carbonaceous material that simultaneously satisfies high capacity, high initial efficiency, and high cycle durability.

The time for the heat treatment step is preferably 10 minutes or more, more preferably 20 minutes or more, regardless of the presence or absence of volatile organic substances, and is preferably less than 360 minutes, more preferably 180 minutes or less, even more preferably 90 minutes or less, and particularly preferably 50 minutes or less. If the time for the heat treatment step is within the above range, it is easy to obtain a carbonaceous material with a high discharge capacity.

The heat treatment step is preferably carried out in an inert gas atmosphere. Examples of the inert gas include nitrogen, argon, etc. The heat treatment step may be carried out under atmospheric pressure or reduced pressure. When the heat treatment step is carried out under reduced pressure, it may be carried out at, for example, 10 kPa or less.

As described above, it is presumed that the following reaction occurs by increasing the temperature of the volatile organic substance and the carbon precursor, and/or by heat-treating the carbon precursor in the presence of a volatile substance derived from the volatile organic substance. It is presumed that in the temperature increase and/or heat treatment process, a skin portion can be formed on the surface of the heat-treated carbon precursor, the volatile component being the core. At this time, it is presumed that the skin portion can be effectively formed by appropriately adjusting the temperature increase rate in the temperature increase and/or heat treatment process, thereby narrowing the pores of the carbon precursor and forming ink bottle-shaped pores with openings (the formation of the skin portion is sometimes referred to as modification). It is presumed that the carbonaceous material having such a structure has high cycle durability while maintaining the discharge capacity, because the active sites that are the starting points of side reactions are reduced by the modification by the volatile substance derived from the volatile organic substance, even at a low heat treatment temperature. However, even if the actual embodiment differs from the above presumption, it is included in the scope of the present invention.
Furthermore, the inventors have found that by setting the temperature of the heat treatment step in an appropriate range, a carbonaceous material that simultaneously satisfies high capacity, high initial efficiency, and high cycle durability can be obtained even without the presence of volatile organic substances and volatile substances. In addition, the inventors have found that by having a specific mesopore volume, the diffusibility of the electrolyte is improved and the pre-doping characteristics are also satisfied.

[Crushing process]
In the production method of the present invention, in order to obtain a carbonaceous material having a desired particle size, a pulverization step of pulverizing the carbon precursor and/or the carbon precursor after the heat treatment may be carried out as necessary. In addition, when the pulverization step is carried out, it is preferable to also carry out a classification step.

Since the carbon precursor does not dissolve in the heating and heat treatment steps, the order of the pulverization steps is not particularly limited, and the carbon precursor may be pulverized before the heating and heat treatment steps, or after the heating and heat treatment steps. From the viewpoint of suppressing surface oxidation due to pulverization, it is preferable to pulverize the carbon precursor before the heating and heat treatment steps.

The carbon precursor shrinks by about 0 to 20% depending on the conditions of the heating and/or heat treatment process. Therefore, when pulverizing the carbon precursor before the heating and heat treatment process, it is preferable to prepare the average particle size of the carbon precursor to be about 0 to 20% larger than the average particle size desired for the carbonaceous material.

The grinding machine used in the grinding step is not particularly limited, and for example, a jet mill, a ball mill, a hammer mill, or a rod mill can be used. From the viewpoint of generating less fine powder, a jet mill equipped with a classification function is preferable. When using a ball mill, a hammer mill, or a rod mill, the fine powder can be removed by classification after the grinding step.

The grinding may be either wet grinding or dry grinding. Dry grinding is preferred because it does not require post-processing such as drying after grinding.

The classification process makes it possible to more precisely adjust the average particle size of the carbonaceous material.

The classification method is not particularly limited, but examples include classification using a sieve, wet classification, and dry classification. Examples of wet classifiers include classifiers that utilize the principles of gravity classification, inertial classification, hydraulic classification, centrifugal classification, etc. Examples of dry classifiers include classifiers that utilize the principles of sedimentation classification, mechanical classification, centrifugal classification, etc.

The pulverization and classification processes can also be carried out using one device. For example, the pulverization and classification processes can be carried out using a jet mill equipped with a dry classification function. Furthermore, a device having a pulverizer and a classifier independent of each other can also be used. In this case, pulverization and classification can be carried out continuously, or pulverization and classification can be carried out discontinuously.

In order to obtain a carbonaceous material having a desired average particle size, two or more carbon precursors or heat-treated carbon precursors (carbonaceous materials) having specific different average particle sizes that have been subjected to a grinding process and, optionally, a classification process can be mixed.

<Electrochemical Devices>
The carbonaceous material of the present invention can be suitably used in electrochemical devices.
Examples of electrochemical devices include aqueous electrolyte batteries such as lead-carbon batteries, lithium ion secondary batteries, nickel hydrogen secondary batteries, nickel cadmium secondary batteries, sodium ion batteries, lithium sulfur batteries, lithium air batteries, nonaqueous electrolyte batteries such as all-solid-state batteries and organic radical batteries, various batteries such as fuel cells, and capacitors such as electric double layer capacitors, hybrid capacitors and lithium ion capacitors. Of these, the electrochemical device may preferably be a nonaqueous electrolyte secondary battery (e.g., lithium ion secondary battery, sodium ion battery, lithium sulfur battery, lithium air battery, all-solid-state battery, organic radical battery, etc.), and is particularly preferably a lithium ion secondary battery.

When metal ions are pre-doped in an electrochemical device, the pre-doped metal ions are preferably alkali metal ions, more preferably lithium ions, sodium ions, and potassium ions, and particularly preferably lithium ions.

Thus, the present invention is also directed to an electrochemical device comprising the carbonaceous material of the present invention.
In such electrochemical devices, as the components other than the carbonaceous material of the present invention, generally used components can be used. For example, in a lithium ion secondary battery, a negative electrode containing the carbonaceous material of the present invention can be produced by adding a binder to the carbonaceous material of the present invention, adding an appropriate amount of a suitable solvent, kneading, preparing an electrode mixture, applying it to a current collector made of a metal plate or the like, drying it, and then pressure molding it.

By using the carbonaceous material of the present invention, an electrode having high conductivity can be manufactured without adding a conductive assistant. In order to impart even higher conductivity, a conductive assistant can be added as necessary when preparing the electrode mixture. As the conductive assistant, conductive carbon black, vapor-grown carbon fiber (VGCF), nanotubes, etc. can be used. The amount of conductive assistant added varies depending on the type of conductive assistant used, but if the amount added is too small, the expected conductivity may not be obtained, and if the amount added is too large, the dispersion in the electrode mixture may be poor. From this perspective, the preferred proportion of conductive assistant to be added is 0.5 to 10 mass% (where the amount of active material (carbonaceous material) + the amount of binder + the amount of conductive assistant = 100 mass%), more preferably 0.5 to 7 mass%, and particularly preferably 0.5 to 5 mass%. The binder is not particularly limited as long as it does not react with the electrolyte, such as PVDF (polyvinylidene fluoride), polytetrafluoroethylene, and a mixture of SBR (styrene butadiene rubber) and CMC (carboxymethyl cellulose). Among them, PVDF is preferable because the PVDF attached to the surface of the active material does not inhibit lithium ion movement and therefore good input/output characteristics can be obtained. A polar solvent such as N-methylpyrrolidone (NMP) is preferably used to dissolve PVDF and form a slurry, but an aqueous emulsion such as SBR or CMC can also be dissolved in water and used. If the amount of binder added is too large, the resistance of the resulting electrode increases, and the internal resistance of the battery increases, which may reduce the battery characteristics. In addition, if the amount of binder added is too small, the binding between the particles of the negative electrode material and with the current collector may be insufficient. The preferred amount of binder added varies depending on the type of binder used, but for example, for PVDF-based binders, it is preferably 3 to 13 mass%, and more preferably 3 to 10 mass%. On the other hand, binders that use water as a solvent often use a mixture of multiple binders, such as a mixture of SBR and CMC, and the total amount of all binders used is preferably 0.5 to 5 mass%, and more preferably 1 to 4 mass%.

The electrode active material layer is basically formed on both sides of the current collector plate, but may be formed on one side if necessary. The thicker the electrode active material layer, the fewer current collector plates, separators, etc. are required, which is preferable for increasing capacity. 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 preferred thickness of the active material layer (per side) is 10 to 80 μm, more preferably 20 to 75 μm, and particularly preferably 20 to 60 μm.

When the carbonaceous material of the present invention is used to form a negative electrode for a lithium ion secondary battery, the other materials constituting the battery, such as the positive electrode material, separator, and electrolyte, are not particularly limited, and various materials that have been conventionally used or proposed for lithium ion secondary batteries can be used.

For example, the positive electrode material is preferably a composite metal chalcogen compound of a layered oxide system (represented as _LiMO2 , where M is a metal, e.g., _LiCoO2 , _LiNiO2 , _LiMnO2 , or LiNi _x Co _y Mo _{z O2} (where x, y, and z represent the composition ratio)), an olivine system (represented as _LiMPO4 , where M is a metal, e.g., _LiFePO4 , etc.), or a spinel system (represented as _LiM2O4 , where M is _a metal, e.g., _LiMn2O4 , _etc. ), and these chalcogen compounds may be mixed as necessary. These positive electrode materials are molded together with a suitable binder and a carbon material for imparting conductivity to the electrode, and a layer is formed on a conductive current collector to form a positive electrode.

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-butyl lactone, tetrahydrofuran, 2-methyltetrahydrofuran, sulfolane, or 1,3-dioxolane can be used alone or in combination of two or more. 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 can be used.

Lithium ion secondary batteries are generally formed by placing the positive and negative electrodes formed as described above opposite each other, optionally with a permeable separator made of nonwoven fabric or other porous material between them, and immersing them in an electrolyte. As the separator, a permeable separator made of nonwoven fabric or other porous material that is commonly used in secondary batteries can be used. Alternatively, a solid electrolyte made of a polymer gel impregnated with an electrolyte can be used instead of or together with the separator.

When the above-mentioned lithium ion secondary battery is used after pre-doping, a pre-doping process can be carried out in which metal ions are pre-absorbed into the negative electrode active material in the negative electrode before the initial charging of the battery formed by combining a positive electrode, a negative electrode, a separator, and an electrolyte.
The method for doping the negative electrode active material with lithium ions is not particularly limited, and examples thereof include a method in which a negative electrode active material and metallic lithium are dispersed in an electrolyte to prepare a slurry, and the prepared slurry is kneaded and mixed (in this case, lithium ions in an amount equivalent to the amount of metallic lithium added can be doped into the negative electrode active material), a method in which a negative electrode active material layer, a separator, and a lithium metal layer (e.g., lithium metal foil) prepared using the negative electrode active material are laminated in this order, the laminate is sandwiched between a pair of current collectors (e.g., copper foil), the negative electrode active material layer and the lithium metal layer of the laminate are externally short-circuited using a known charge/discharge device, and the negative electrode active material layer is charged to perform electrochemical pre-doping, and the like.

<Measurement of carbon dioxide adsorption/desorption isotherm>
For the carbonaceous materials obtained in the examples and comparative examples, the adsorption and desorption of carbon dioxide at 273 K was measured using a gas adsorption measuring device (AUTOSORB-iQ MP-XR, manufactured by Quantachrome) at relative pressures (p/p ₀ ) ranging from 0.00075 to 0.030 to obtain adsorption and desorption isotherms.

[Pore volume]
The adsorption/desorption isotherm obtained above was analyzed by the Grand Canonical Monte Carlo method using "CO ₂ at 273K on carbon" as a calculation model to determine the pore volume of pores with diameters of 0.35 to 1.47 nm.

[Amount of carbon dioxide adsorption/desorption]
From the adsorption/desorption isotherm thus obtained, the ratio of the desorption amount to the adsorption amount (desorption amount/adsorption amount) at a relative pressure of 0.01 was determined.

<Mesopore volume>
Using a BELSORP-mini manufactured by BEL JAPAN, the carbonaceous materials obtained in the Examples and Comparative Examples were filled into a sample tube and heat-treated at 300° C. for 5 hours under reduced pressure, and then the nitrogen adsorption isotherm of the carbonaceous material was measured at 77 K. The Barrett-Joyner-Halenda (BJH) method was applied to the obtained adsorption isotherm, and the range of pore diameters from 2.5 nm to 33 nm was determined as the mesopore volume.

<Average particle diameter (D ₅₀ )>
The average particle diameter D ₅₀ (particle size distribution) of the carbon precursor used in the examples and comparative examples and the carbonaceous material obtained in the examples and comparative examples was measured by a laser scattering method as follows. The carbon precursor and carbonaceous material samples of the examples and comparative examples described below were put into an aqueous solution containing 0.3 mass% of a surfactant ("ToritonX 100" 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 was measured using a particle size/particle size distribution measuring instrument ("Microtrac M T3000" manufactured by Nikkiso Co., Ltd.) with a solvent refractive index of 1.33 and particle permeability as absorption. The particle diameter at which the cumulative volume was 50% was taken as the average particle diameter D ₅₀ .

前記の近似式を用いて、液体窒素温度における、窒素吸着による３点法によりｖ_ｍを求め、次式により試料の比表面積を計算した。

このとき、ｖ_ｍは試料表面に単分子層を形成するのに必要な吸着量（ｃｍ^３／ｇ）、ｖは実測される吸着量（ｃｍ^３／ｇ）、ｐ_０は飽和蒸気圧、ｐは絶対圧、ｃは定数（吸着熱を反映）、Ｎはアボガドロ数６．０２２×１０^２３、ａ（ｎｍ^２）は吸着質分子が試料表面で占める面積（分子占有断面積）である。 <BET specific surface area by nitrogen adsorption method>
The specific surface areas of the carbon precursors used in the examples and comparative examples and the carbonaceous materials obtained in the examples and comparative examples are determined by the BET method (nitrogen adsorption BET three-point method) (BET specific surface area). The approximate formula derived from the BET formula is shown below.

Using the above approximation formula, _vm was determined by the three-point method using nitrogen adsorption at liquid nitrogen temperature, and the specific surface area of the sample was calculated using the following formula.

Here, _vm is the amount of adsorption required to form a monolayer on the sample surface ( ^cm3 /g), v is the measured amount of adsorption ( ^cm3 /g), _p0 is the saturated vapor pressure, p is the absolute pressure, c is a constant (reflecting the heat of adsorption), N is Avogadro's number 6.022 x ¹⁰²³ , and a ( ^nm2 ) is the area occupied by the adsorbate molecules on the sample surface (molecular occupied cross-sectional area).

Specifically, the amount of nitrogen adsorbed to the sample at liquid nitrogen temperature was measured using a "BELL Sorb Mini" manufactured by BELL Japan Co., Ltd., as follows. The sample was filled into a sample tube and heated at 300°C for 5 hours under reduced pressure. The sample tube was then cooled to -196°C and the pressure was reduced once, after which nitrogen (purity 99.999%) was adsorbed onto the sample at the desired relative pressure. The amount of nitrogen adsorbed into the sample when equilibrium pressure was reached at each desired relative pressure was taken as the amount of adsorbed gas v.

<Plane spacing d ₀₀₂ of (002) plane>
Using "MiniFlexII" manufactured by Rigaku Corporation, the carbonaceous materials obtained in the examples and comparative examples were filled into a sample holder, and CuKα rays monochromatized by a Ni filter were used as the radiation source to obtain an X-ray diffraction pattern. The peak positions of the diffraction patterns were determined by the centroid method (a method of determining the centroid position of the diffraction lines and determining the peak position at the corresponding 2θ value), and were corrected 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 0.15418 nm, and d ₀₀₂ was calculated using the Bragg formula described below.

<Measurement of residual carbon rate>
The carbon content was measured by quantifying the amount of carbon in the ignition residue after igniting the sample in an inert gas. Ignition was performed by placing approximately 1 g of volatile organic matter (the exact mass was designated _W1 (g)) in a crucible, and heating the crucible in an electric furnace from room temperature to 800°C at a heating rate of 10°C/min while flowing nitrogen at 20 liters per minute, and then igniting at 800°C for 1 hour. The remaining material was designated the ignition residue, and its mass was designated _W2 (g).
Next, the ignition residue was subjected to elemental analysis in accordance with the method defined in JIS M8819 to measure the mass percentage _P1 (mass%) of carbon. The residual carbon percentage _P2 (mass%) was calculated by the following formula.

<Preparation of carbon precursor>
Coconut shells were crushed and dry distilled at 500°C to obtain 100 g of coconut shell char A (containing 98% by mass of particles having a particle size of 0.850 to 2.360 mm). Nitrogen gas containing 1% by volume of hydrogen chloride gas was supplied at a flow rate of 10 L/min to the coconut shell char A, which was then treated at 950°C for 80 minutes. After that, the supply of hydrogen chloride gas was stopped, and the coconut shell char A was further heat-treated at 950°C for 30 minutes.
The mixture was then pulverized in a Fine Mill SF5 (manufactured by Nippon Coke) to an average particle size of 10 μm, and then pulverized in a compact jet mill (Cojet System α-mkIII, manufactured by Seishin Enterprise Co., Ltd.). It was then classified using Labo Classil N-01 (manufactured by Seishin Enterprise Co., Ltd.) to obtain carbon precursor A with an average particle size of 5.1 μm (specific surface area of 410 ^m2 /g) and carbon precursor B with an average particle size of 9.7 μm (specific surface area of 400 ^m2 /g).
The obtained carbon precursor A having an average particle size of 5.1 μm was further pulverized with a fine mill SF5 (manufactured by Nippon Coke Co., Ltd.) to obtain carbon precursors having average particle sizes of 1.3 μm, 2.2 μm, 2.6 μm and 3.1 μm (referred to as carbon precursors C, D, E and F, respectively).

Example 1
0.9g of polystyrene (manufactured by Sekisui Chemical Co., Ltd., average particle size 400μm, residual carbon rate 1.2% by mass) was mixed with 9.1g of carbon precursor B having an average particle size of 9.7μm. 10g of this mixture was placed in a graphite sheath so that the sample layer thickness was about 3mm, and placed in a high-speed heating furnace manufactured by Motoyama Co., Ltd., and the heating rate from 600°C to 900°C was 5°C per minute (heating time 60 minutes) under a nitrogen flow rate of 5L per minute, and 60°C per minute in other temperature ranges. After heating to 900°C, the temperature was held for 20 minutes and then naturally cooled. After confirming that the temperature in the furnace had dropped to 200°C or less, the carbonaceous material was removed from the furnace to obtain a carbonaceous material having an average particle size of 9.6μm.
Carbon precursor D having an average particle size of 2.2 μm was treated in the same manner as carbon precursor B having an average particle size of 9.7 μm to obtain a carbonaceous material having an average particle size of 2.1 μm.
Next, a carbonaceous material having an average particle size of 2.1 μm and a carbonaceous material having an average particle size of 9.7 μm were mixed in a mass ratio of 1:1 to obtain a carbonaceous material having an average particle size of 4.5 μm.

Example 2
The same treatment as in Example 1 was conducted except that the heating rate from 600°C to 900°C was 20°C per minute (heating time: 15 minutes) and the temperature was held at 1000°C for 20 minutes after heating to 1000°C, to obtain a carbonaceous material.

Example 3
0.9g of polystyrene (manufactured by Sekisui Chemical Co., Ltd., average particle size 400μm, residual carbon rate 1.2% by mass) was mixed with 9.1g of carbon precursor D having an average particle size of 2.2μm. 10g of this mixture was placed in a graphite sheath so that the sample layer thickness was about 3mm, and placed in a high-speed heating furnace manufactured by Motoyama Co., Ltd., and the heating rate from 600°C to 900°C was 20°C per minute (heating time 15 minutes) under a nitrogen flow rate of 5L per minute, and 60°C per minute in other temperature ranges. After heating to 1100°C, the temperature was held for 20 minutes and then naturally cooled. After confirming that the temperature in the furnace had dropped to 200°C or less, the carbonaceous material was removed from the furnace to obtain a carbonaceous material having an average particle size of 2.1μm.

Example 4
The same treatment as in Example 3 was carried out except that carbon precursor E having an average particle size of 2.6 μm was used, to obtain a carbonaceous material having an average particle size of 2.5 μm.

Example 5
The same treatment as in Example 3 was carried out except that a carbon precursor having an average particle size of 3.1 μm was used, to obtain a carbonaceous material having an average particle size of 3.0 μm.

Example 6
The carbonaceous material having an average particle size of 3.0 μm obtained in Example 5 and the carbonaceous material having an average particle size of 9.6 μm obtained in Comparative Example 3 described below were mixed in a mass ratio of 1:1. The average particle size of the resulting carbonaceous material was 4.8 μm.

Example 7
The carbonaceous material having an average particle size of 2.1 μm obtained in Example 3 and the carbonaceous material having an average particle size of 9.6 μm obtained in Comparative Example 3 described below were mixed in a mass ratio of 1:1. The average particle size of the resulting carbonaceous material was 4.5 μm.

Example 8
The same treatment as in Example 1 was conducted except that the heating rate from 600°C to 900°C was 20°C per minute (heating time: 15 minutes) and the temperature was held at 1,175°C for 20 minutes after heating to 1,175°C, to obtain a carbonaceous material.

<Example 9>
9.1 g of carbon precursor A having an average particle size of 5.1 μm was placed in a graphite sheath so that the sample layer thickness was about 3 mm, and placed in a high-speed heating furnace manufactured by Motoyama Co., Ltd., and under a nitrogen flow rate of 5 L per minute, the heating rate from 600 ° C. to 900 ° C. was 60 ° C. per minute (heating time 5 minutes), and also in other temperature ranges, 60 ° C. per minute. After heating to 1150 ° C., the temperature was maintained for 20 minutes, and then naturally cooled. After confirming that the temperature in the furnace had dropped to 200 ° C. or less, the carbonaceous material was removed from the furnace, and a carbonaceous material having an average particle size of 5.0 μm was obtained.

<Comparative Example 1>
The same treatment as in Example 1 was carried out except that the heating rate from 600° C. to 900° C. was 300° C. per minute (heating time: 1 minute), to obtain a carbonaceous material.

<Comparative Example 2>
The same treatment as in Example 3 was carried out except that carbon precursor C having an average particle size of 1.3 μm was used, to obtain a carbonaceous material having an average particle size of 1.2 μm.

<Comparative Example 3>
The same treatment as in Example 3 was carried out except that carbon precursor B having an average particle size of 9.7 μm was used, to obtain a carbonaceous material having an average particle size of 9.6 μm.

<Comparative Example 4>
The same treatment as in Example 1 was conducted except that the heating rate from 600°C to 900°C was 60°C per minute (heating time was 5 minutes) and the temperature was held at 1270°C for 20 minutes after heating to 1270°C, to obtain a carbonaceous material.

<Comparative Example 5>
A carbonaceous material was obtained in the same manner as in Example 9, except that the heating rate from 600°C to 900°C was 60°C per minute (heating time: 5 minutes), and after heating to 1100°C, the temperature was held for 20 minutes.

<Comparative Example 6>
A carbonaceous material was obtained in the same manner as in Example 9, except that the heating rate from 600°C to 900°C was 60°C per minute (heating time: 5 minutes), and after heating to 1100°C, the temperature was maintained for 60 minutes.

<Comparative Example 7>
A carbonaceous material was obtained in the same manner as in Example 9, except that the heating rate from 600°C to 900°C was 60°C per minute (heating time: 5 minutes), and after heating to 1,050°C, the temperature was maintained for 360 minutes.

For the carbonaceous materials obtained in the Examples and Comparative Examples, the pore volume, mesopore volume, carbon dioxide adsorption amount, desorption amount, and ratio of the adsorption amount to the desorption amount (adsorption amount/desorption amount), average particle size ( _D50 ), specific surface area, and interplanar spacing _d002 are shown in Table 1.

<Battery evaluation>
[Preparation of carbon electrodes]
96.2 parts by mass of the carbonaceous material obtained in the Examples and Comparative Examples, 2 parts by mass of conductive carbon black ("Super-P (registered trademark)" manufactured by TIMCAL), 1 part by mass of CMC, a predetermined amount of SBR and water were mixed to obtain a slurry. The obtained slurry was applied to a copper foil, dried and pressed to obtain an electrode having a thickness of 60 to 80 μm. The density of the obtained electrode was 0.95 g/ ^cm3 . This electrode was punched into a disk having a diameter of 14 mm to obtain a carbon electrode plate.

[Preparation of negative electrode half cell]
The obtained carbon electrode was punched into a disk shape with a diameter of 14 mm to be used as the working electrode, and metallic lithium was used as the counter electrode. Ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate were mixed in a volume ratio of 1:1:1 and used as the solvent. _LiPF6 was dissolved in this solvent at 1 mol/L and used as the electrolyte. A polypropylene membrane was used as the separator. A coin cell was prepared in a glove box under an argon atmosphere.

[Measurement of discharge capacity and initial efficiency]
A charge/discharge test was performed on the negative electrode half cell of the above configuration in a thermostatic chamber at 25° C. using a charge/discharge tester (manufactured by Toyo Systems Co., Ltd., “TOSCAT”). Lithium doping was performed at a rate of 70 mA/g relative to the active material mass, and doping was performed until the lithium potential was 1 mV. A constant voltage of 1 mV was applied to the lithium potential for 8 hours to terminate the doping. The capacity at this time was taken as the charge capacity (mAh/g). Next, dedoping was performed at a rate of 70 mA/g relative to the active material mass until the lithium potential was 1.5 V, and the capacity discharged at this time was taken as the discharge capacity (mAh/g), and the percentage of the value obtained by dividing the discharge capacity (mAh/g) by the charge capacity (mAh/g) was taken as the charge/discharge efficiency (initial efficiency) (%), which was used as an index of the utilization efficiency of lithium ions in the battery. The discharge capacity measured according to this embodiment is preferably 430 mAh/g, more preferably 470 mAh/g or more, and even more preferably 480 mAh/g or more. The initial efficiency is preferably 75% or more, more preferably 77% or more, and even more preferably 80% or more.

[Input characteristic measurement]
Following the discharge capacity and initial efficiency measurements, a charge/discharge test was performed on the negative electrode half cell using a charge/discharge tester (manufactured by Toyo Systems Co., Ltd., "TOSCAT") to evaluate the input characteristics. In a thermostatic chamber at 25°C, doping was performed at a rate of 500 mA/g relative to the negative electrode active material mass to 0 mV relative to the lithium potential. Next, dedoping was performed at a rate of 100 mA/g relative to the active material mass to 1.5 V relative to the lithium potential, and the capacity discharged at this time was taken as the discharge capacity (mAh/g) at 25°C 1C.
Next, doping was performed at a rate of 100 mA/g relative to the mass of the negative electrode active material in a thermostatic chamber at −20° C. until the lithium potential reached 0 mV. Next, undoping was performed at a rate of 100 mA/g relative to the mass of the active material until the lithium potential reached 1.5 V, and the discharge capacity at this time was taken as the discharge capacity (mAh/g) at −20° C. and 0.2 C.
Subsequently, doping was performed at a rate of 500 mA/g relative to the mass of the negative electrode active material in a thermostatic chamber at −20° C. until the lithium potential reached 0 mV. Next, undoping was performed at a rate of 100 mA/g relative to the mass of the active material until the lithium potential reached 1.5 V, and the discharge capacity at this time was taken as the discharge capacity (mAh/g) at −20° C. and 1C.
And, -20°C 1C/25°C 1C and -20°C 1C/-20°C 0.2C were used as the indexes of input characteristics and pre-doping. When measured according to this embodiment, the value of -20°C 1C/25°C 1C is preferably 30% or more, more preferably 40% or more, and even more preferably 45% or more, and the value of -20°C 1C/-20°C 0.2C is preferably 50% or more, more preferably 70% or more, and even more preferably 75% or more.

[Preparation of Positive Electrode]
As a positive electrode active material, 90 parts by mass of lithium iron phosphate (LiFePO ₄ ), 5 parts by mass of PVDF (polyvinylidene fluoride), 5 parts by mass of acetylene black, and NMP (N-methylpyrrolidone) were mixed to obtain a slurry. The obtained slurry was applied to an aluminum foil, dried, and pressed to obtain an electrode having a thickness of 80 to 140 μm. The density of the obtained electrode was 1.8 g/cm ^3. This electrode was punched into a disk shape with a diameter of 14 mm to obtain a positive electrode plate.

[Preparation of positive electrode half cell]
Metallic lithium was used as a counter electrode and a reference electrode for the obtained positive electrode. Ethylene carbonate and methyl ethyl carbonate were mixed in a volume ratio of 3:7 and used as a solvent. _LiPF6 was dissolved in this solvent at 1 mol/L and used as an electrolyte. A glass fiber nonwoven fabric was used as a separator. A coin cell was prepared in a glove box under an argon atmosphere.
A charge/discharge test was performed on the positive electrode half cell of the above configuration using a charge/discharge tester (manufactured by Toyo Systems Co., Ltd., "TOSCAT"). Lithium de-doping from the positive electrode was performed at a rate of 15 mA/g relative to the active material mass until the lithium potential reached 4.0 V, and the capacity at this time was taken as the charge capacity. Next, lithium doping into the positive electrode was performed at a rate of 15 mA/g relative to the active material mass until the lithium potential reached 2.0 V, and the capacity at this time was taken as the discharge capacity. The obtained charge capacity was 153 mAh/g, the discharge capacity was 141 mAh/g, and the charge/discharge efficiency (initial charge/discharge efficiency) calculated as a percentage of the discharge capacity/charge capacity was 92%.

[Preparation of coin cells (full cells)]
The obtained carbon electrode was punched out into a disk shape with a diameter of 15 mm and used as the negative electrode. The composite coated surfaces of the negative electrode and the positive electrode were opposed to each other through a separator made of glass fiber nonwoven fabric so that the positive electrode (diameter 14 mm) would not protrude from the negative electrode surface. At this time, the ratio of the negative electrode charge capacity (mAh) to the positive electrode charge capacity (mAh) per opposing area (negative electrode capacity/positive electrode capacity) was adjusted to 1.05. As the solvent, ethylene carbonate and methyl ethyl carbonate were mixed to a volume ratio of 3:7 and used. 1 mol/L of LiPF ₆ was dissolved in this solvent and used as the electrolyte. A coin cell was prepared in a glove box under an argon atmosphere.

[Charge/discharge test (cycle durability test)]
A charge/discharge test was performed on the coin cell (full cell) having the above configuration using a charge/discharge tester (manufactured by Toyo Systems Co., Ltd., "TOSCAT"). Charging was performed at a rate of 70 mA/g of the negative electrode active material mass until the lithium potential reached 4.0 V. Discharging was then performed at a rate of 70 mA/g of the negative electrode active material mass until the lithium potential reached 2.0 V. This cycle was repeated three times.
Thereafter, charging was performed at a rate of 500 mA/g relative to the mass of the negative electrode active material until the lithium potential reached 4.0 V, and the capacity at this time was taken as the charging capacity. Discharging was then performed at a rate of 500 mA/g relative to the mass of the negative electrode active material until the lithium potential reached 2.0 V, and the capacity at this time was taken as the discharging capacity. This cycle was repeated 500 cycles. The percentage of the value obtained by dividing the discharge capacity at the 500th cycle by the discharge capacity at the 1st cycle was taken as the 500 cycle retention rate. The cycle retention rate measured according to this embodiment is preferably 70% or more, more preferably 75% or more, and even more preferably 80% or more.

Table 2 shows the results of the characteristics of the batteries containing the carbonaceous materials obtained in the examples and comparative examples.

It can be seen that the nonaqueous electrolyte secondary batteries equipped with negative electrodes containing the carbonaceous materials obtained in Examples 1 to 9 can be pre-doped quickly, and simultaneously satisfy high capacity, high initial efficiency, and high cycle durability. On the other hand, the carbonaceous materials obtained in Comparative Examples 1, 2, 5, and 7 have low initial efficiency and cycle retention rate, and the carbonaceous materials obtained in Comparative Examples 2 and 4 have low discharge capacity. Furthermore, it can be seen that the carbonaceous materials obtained in Comparative Examples 3 and 6 have poor pre-doping characteristics.

Claims (12)

A carbonaceous material having a pore volume of 0.05 cm ³ /g or more and 0.20 cm ³ /g or less, as determined by a Grand Canonical Monte Carlo simulation of a carbon dioxide adsorption/desorption isotherm, a ratio of the desorption amount to the adsorption amount at a relative pressure of 0.01 in the adsorption/desorption isotherm of 1.05 or more, and a mesopore volume of 3.7 mm ³ /g or more and 41 mm ³ /g or less, as determined by the BJH method. The carbonaceous material according to claim 1, having an average particle size (D ₅₀ ) of 1.3 μm or more and 9.5 μm or less. 3. The carbonaceous material according to claim 1, which has a specific surface area of 3 m ² /g or more and 60 ^{m 2} /g or less, as determined by a BET method using a nitrogen adsorption method. The carbonaceous material according to any one of claims 1 to 3, wherein the average interplanar spacing d ₀₀₂ of the (002) plane calculated using the Bragg equation by wide-angle X-ray diffraction is 0.36 nm or more and 0.42 nm or less. The carbonaceous material according to any one of claims 1 to 4, which is for use in an electrochemical device. The carbonaceous material according to claim 5, which is pre-doped with metal ions. An electrochemical device comprising the carbonaceous material according to any one of claims 1 to 6. The method for producing a carbonaceous material according to any one of claims 1 to 6, comprising: a temperature increasing step of increasing the temperature of a carbon precursor from a temperature of 600°C or lower to 900°C; and a heat treatment step of heat treating the carbon precursor at a temperature of 900°C or higher and 1260°C or lower. The method according to claim 8, wherein the temperature increasing step is carried out in the presence of a volatile organic substance and/or a volatile substance derived from a volatile organic substance. The method of claim 8, wherein the temperature increasing step is carried out in the absence of volatile organic substances and volatile substances derived from volatile organic substances, and the heat treatment step is carried out at a temperature of more than 1100°C. The manufacturing method according to any one of claims 8 to 10, further comprising a grinding step of grinding the carbon precursor and/or the carbon precursor after the heat treatment. The manufacturing method according to any one of claims 8 to 11, wherein in the heating step, the heating rate from 600°C to 900°C is 60°C/min or less.