JP7340188B2 - Spherical carbon particles containing nitrogen element, manufacturing method thereof, electrodes and batteries - Google Patents

Description

The present invention relates to spherical carbon particles containing nitrogen element, a method for producing the same, an electrode, and a battery.

Carbon materials are used as battery materials because they are thermally and chemically stable and have electrical conductivity. In addition, in recent years, attempts have been made to improve the particle performance of various particle materials by reducing the particle size and making them spheroidal.In battery materials, improvements in conductivity and output performance are expected. be done.

For example, in Patent Document 1, in an aqueous suspension of colloidal silica, at least one amino monomer compound consisting of a polyfunctional amino compound and an aldehyde compound are reacted under basic conditions, and a water-soluble A method for producing cured amino resin particles, comprising the steps of generating an aqueous solution of an initial condensate of an amino resin, and adding at least two types of acid catalysts to the aqueous solution to precipitate spherical cured amino resin particles. It is also disclosed that the polyfunctional amino compound can be melamine.

Patent Document 2 describes (1) a step of wet crushing an inorganic pigment in an aqueous medium to prepare an aqueous dispersion of the inorganic pigment, (2) mixing the aqueous dispersion and an amino resin initial reactant, A step of preparing a colored resin liquid; (3) a step of emulsifying or suspending and dispersing the colored resin liquid in an aqueous medium to prepare a colored resin dispersion; (4) condensing the colored resin dispersion under heating. A method for producing colored resin spherical fine particles is disclosed, which comprises a step of separating after curing to obtain colored resin fine particles, in which the amino resin initial reactant is a resin obtained by polycondensation reaction of melamine and formaldehyde. Good things are also disclosed.

Patent Document 3 discloses spherical ultrafine particles that are non-pulverized, have a roundness of 0.9 to 1.0, and a particle size of 0.01 to 10 μm, and as a method for producing the same, By vibrating a base with many through holes at a constant speed, the slurry-like liquid material of inorganic or organic substances being pumped is divided into uniform liquid particles, and the uniform liquid particles are subjected to processes such as carbonization, activation, oxidation, reduction, and dealkalization. A method for producing spherical ultrafine particles is also disclosed. The document also discloses that the organic material may be a thermosetting resin such as a phenolic resin and a melamine resin.

Further, Patent Document 4 discloses a method for producing carbon fine particles, in which lignin as a raw material is carbonized and pulverized, and then subjected to plasma treatment.

International Publication No. 2013/176057 Japanese Patent Application Publication No. 2002-201336 Japanese Patent Application Publication No. 2006-168593 International Publication No. 2019/111770

However, Patent Documents 1 and 2 do not describe carbonizing the obtained particles. Furthermore, according to the studies of the present inventors, even if the particles described in Patent Documents 1 and 2 are subjected to carbonization treatment, the template (nucleating agent) such as colloidal silica or inorganic pigment contained in these particles will not be carbonized. Since it remains in the particles even after treatment, it is difficult to obtain pure carbon particles, and therefore, even if carbon particles obtained by such a method are used in batteries, it is difficult to obtain excellent characteristics. Furthermore, when these particles are subjected to carbonization treatment, activation by the template (carbon erosion due to thermal reduction of the metal compound added as an emulsifier) occurs, which can significantly reduce the productivity of carbon particles. . The method described in Patent Document 3 has problems in that a special device is required and the number of steps is large. Furthermore, Patent Document 4 examines a method for producing fine particles using lignin, but according to the studies of the present inventors, there are problems such as the need for thermal plasma treatment and the need for special equipment. There is.

Under these circumstances, the problem to be solved by the present invention is to provide spherical carbon particles and an efficient and safe manufacturing method for the spherical carbon particles, and to provide a non-aqueous electrolyte secondary battery with excellent electrical properties. That's true.

The present inventors have completed the present invention as a result of detailed studies to solve the above problems.

That is, the present invention includes the following preferred embodiments.
[1] The sulfur element content is 0.5 mass% or more, the nitrogen element content is 1 mass% or more and less than 20 mass%, the oxygen element content is 1 mass% or more and 5 mass% or less, and CuKα A spherical carbon particle in which the interplanar spacing d ₀₀₂ of the (002) plane measured using a line is 3.5 Å or more and 3.8 Å or less.
[2] The spherical carbon particles according to [1], wherein the half-width of the D band near 1360 cm ^-1 in the Raman spectrum of the spherical carbon particles is 200 cm ^-1 or more and 270 cm ^-1 or less.
[3] The spherical carbon particles according to [1] or [2], wherein the spherical carbon particles have a volume average particle diameter of 100 nm or more and 5.0 μm or less.
[4] Mixing lignin, amine, water, and alhyde to obtain an aqueous solution;
spray drying the aqueous solution, and
The method for producing spherical carbon particles according to any one of [1] to [3], which includes a step of carbonizing the obtained spray-dried product to obtain spherical carbon particles.
[5] The method according to [4], wherein the carbonization step is performed at a temperature of 700° C. or higher and 1800° C. or lower in an inert gas atmosphere.
[6] An electrode for a non-aqueous electrolyte battery, comprising the spherical carbon particles according to any one of [1] to [3].
[7] A non-aqueous electrolyte secondary battery comprising the electrode according to [6].

According to the present invention, it is possible to provide spherical carbon particles and an efficient and safe manufacturing method for the spherical carbon particles, and to provide a nonaqueous electrolyte secondary battery with excellent electrical properties.

1 is an electron microscope photograph of spherical carbon particles produced according to Example 2. 3 is an electron microscope photograph of a carbide produced according to Comparative Example 2.

Embodiments of the present invention will be described in detail below. Note that the following is a description illustrating the embodiments of the present invention, and is not intended to limit the present invention to the following embodiments.

<Spherical carbon particles>
In the spherical carbon particles of the present invention, the sulfur element content is 0.5% by mass or more, the nitrogen element content is 1 mass% or more and less than 20 mass%, and the oxygen element content is 1 mass% or more and less than 5 mass%. The interplanar spacing d ₀₀₂ of the (002) plane measured using CuKα radiation is 3.5 Å or more and 3.8 Å or less.

[Sulfur element content]
The sulfur element content of the spherical carbon particles of the present invention is 0.5% by mass or more. If the sulfur element content is less than 0.5% by mass, the battery may have poor battery capacity. The sulfur element content is preferably 0.6% by mass or more, more preferably 0.8% by mass or more. Further, the upper limit of the sulfur element content of the spherical carbon particles of the present invention is not particularly limited, but is usually 3.0% by mass or less, preferably 2.0% by mass or less, and more preferably 1.8% by mass. % or less. When the sulfur element content of the spherical carbon particles is equal to or higher than the lower limit, it is easy to obtain a battery with excellent battery capacity. The sulfur element content of the spherical carbon particles of the present invention can be determined, for example, by hydrolyzing a material that is a raw material for spherical carbon particles containing sulfur element by heating it with an aqueous solution of caustic soda, or by heating a material that is a raw material for spherical carbon particles containing sulfur element. By modifying with a substance containing a sulfur element such as sulfuric acid and adjusting the amount of modification, the value can be adjusted to be equal to or higher than the lower limit. Further, the sulfur element content can be determined, for example, by elemental analysis, fluorescent X-ray analysis, or the like.

[Nitrogen element content]
The nitrogen element content of the spherical carbon particles of the present invention is 1% by mass or more and less than 20% by mass. If the nitrogen element content is less than 1% by mass, the carbon structure is less likely to be disturbed by the introduction of the nitrogen element, and it is difficult to increase the number of occlusion sites when introducing lithium ions, making it impossible to obtain the desired battery capacity. there is a possibility. If the nitrogen element content is 20% by mass or more, thermal stability may be low and the shape may not be maintained. The nitrogen element content is preferably 2% by mass or more, more preferably 3% by mass or more, even more preferably 4% by mass or more, and preferably 15% by mass or less, more preferably 13% by mass or less, even more preferably 10% by mass or less. % by mass or less. When the nitrogen element content is above the lower limit and below the upper limit, defects or disorder can be appropriately introduced into the carbon structure in the spherical carbon particles, and lithium ions are also captured by the nitrogen element. , it is possible to increase the number of occlusion sites when doping lithium ions. The nitrogen element content of the spherical carbon particles of the present invention can be controlled to be equal to or higher than the lower limit value and lower than the upper limit value by, for example, compounding the raw material of the spherical carbon particles with a substance containing nitrogen element, such as amine. Can be adjusted. Further, the nitrogen element content can be determined, for example, by the method described in Examples below.

[Oxygen element content]
The oxygen element content of the spherical carbon particles of the present invention is 1% by mass or more and 5% by mass or less. If the oxygen element content is less than 1% by mass, it may be difficult to obtain the effects (for example, solvent affinity) caused by containing oxygen element. If the oxygen element content exceeds 5% by mass, moisture in the air will be easily adsorbed, and self-discharge may occur due to the reaction between the adsorbed moisture and lithium ions. The oxygen element content is preferably 1.1% by mass or more, more preferably 1.2% by mass or more, even more preferably 1.3% by mass or more, and preferably 4.9% by mass or less, more preferably 4% by mass or more. .8% by mass or less, more preferably 4.7% by mass or less. When the oxygen element content is equal to or higher than the lower limit value and lower than the upper limit value, the solvent affinity is excellent while suppressing the amount of moisture absorption, so that it is easy to obtain a battery with high stability during repeated charging and discharging and excellent output characteristics. The oxygen element content of the spherical carbon particles of the present invention can be determined, for example, by using lignin as a starting material, making the lignin water-solubilized, and suppressing thermal decomposition, as described in the method for producing spherical carbon particles of the present invention described below. By carbonizing at a temperature, the temperature can be adjusted to be above the lower limit value and below the upper limit value. Further, the oxygen element content can be determined, for example, by the method described in Examples below.

[Spacing d ₀₀₂ of (002) plane measured using CuKα ray]
The interplanar spacing d ₀₀₂ (hereinafter also simply referred to as "planar spacing d ₀₀₂ ") of the (002) planes of the spherical carbon particles of the present invention measured using CuKα radiation is 3.5 Å or more and 3.8 Å or less. If the interplanar spacing _d002 is less than 3.5 Å, the resistance when lithium ions are inserted into the carbon particles increases, and as a result, the resistance at the time of output increases, making it difficult to use as a lithium ion secondary battery. Output characteristics may deteriorate. When the interplanar spacing d ₀₀₂ exceeds 3.8 Å, the volume of the carbon particles becomes large, and the battery capacity per volume may become small. The interplanar spacing d ₀₀₂ is preferably 3.55 Å or more, more preferably 3.6 Å or more, preferably 3.8 Å or less, more preferably 3.76 Å or less, and still more preferably 3.7 Å or less. When the interplanar spacing d ₀₀₂ is not less than the lower limit value and not more than the upper limit value, the crystallinity of carbon is high and there are few starting points for side reactions, so that the irreversible capacity of the battery is likely to be reduced. The interplanar distance d ₀₀₂ can be adjusted, for example, by the solid content concentration or discharge rate during spray drying, or the temperature or time during carbonization. Further, the interplanar spacing d ₀₀₂ can be determined by X-ray diffraction.

[Half width of D band near 1360 cm ⁻¹ in Raman spectrum]
The spherical carbon particles of the present invention have a peak around 1360 cm ⁻¹ in laser Raman spectroscopy. The peak is a Raman peak generally referred to as the D band, and is caused by disorder and defects in the graphite structure. The half-width of the D band around 1360 cm ⁻¹ represents the amount of disordered structure, and in one preferred embodiment of the present invention, it is preferably 200 cm ⁻¹ or more, more preferably 210 cm ⁻¹ or more, and preferably It is 270 cm ^-1 or less, more preferably 250 cm ^-1 or less. When the half-width of the D band is equal to or greater than the lower limit value and equal to or less than the upper limit value, the number of terminal structures is not too large and an increase in electrical resistance is suppressed, so that irreversible capacity tends to be reduced and cycle durability is improved. be. For example, as described in the method for producing spherical carbon particles of the present invention described later, the half width of the D band can be adjusted to be equal to or higher than the lower limit value and lower than the upper limit value. By compounding with a substance such as an amine and carbonizing at a temperature that suppresses thermal decomposition, the temperature can be adjusted to be above the lower limit and below the upper limit. Further, the method for measuring the half width of the D band using a Raman spectrum is as described in Examples below.

[Volume average particle diameter]
The volume average particle diameter (hereinafter also referred to as " _D50 " or "average particle diameter") of the spherical carbon particles of the present invention is preferably 100 nm or more, more preferably 110 nm or more, still more preferably 120 nm or more, even more preferably 150 nm. or more, preferably 5.0 μm or less, more preferably 4.9 μm or less, still more preferably 4.5 μm or less, even more preferably 3.0 μm or less. It is preferable that the volume average particle diameter of the spherical carbon particles of the present invention is not less than the lower limit value and not more than the upper limit value because it is easy to obtain good mechanical strength of the spherical carbon particles and it is easy to maintain the spherical shape. The volume average particle diameter of the spherical carbon particles of the present invention can be adjusted, for example, by appropriately changing the spray drying conditions in the method for producing spherical carbon particles, as described in Examples below. The volume average particle diameter of the spherical carbon particles of the present invention can be determined, for example, by the method described in Examples below.

By making the spherical carbon particles of the present invention spherical in particle shape, it is possible to reduce the edge portion that becomes the starting point of side reactions, and it is possible to reduce the irreversible capacity of the battery. In addition, it is possible to improve the packing density, and it is expected that the volumetric efficiency of the battery will be improved by increasing the electrode density. In the spherical carbon particles of the present invention, particles having no pointed portion or flat portion preferably account for 90% or more, more preferably 95% or more, and even more preferably 95% or more of the total number of spherical carbon particles. It is 97% or more, even more preferably 98% or more, particularly preferably 99% or more. The number of particles that do not have a pointed portion or a flat portion can be measured using, for example, a scanning microscope.
In the present invention, spherical shape refers to one or more shapes selected from the group consisting of true spherical shape, elliptical spherical shape, donut shape, and spherical shape with a plurality of holes. The spherical carbon particles of the present invention may have, for example, irregularities on the surface, or may have a distorted or partially chipped portion. Further, the spherical carbon particles may include particles having a shape (eg, snowman shape, bow tie shape, grape cluster shape, etc.) in which 2 to 10 spherical carbon particles are bonded together. The shape of the spherical carbon particles of the present invention can be observed using, for example, a particle size measuring device equipped with a shape observing device, a scanning electron microscope, or the like. Note that the spherical shape does not mean a rod shape, a fiber shape, a plate shape, or the like.

<Method for manufacturing spherical carbon particles>
The spherical carbon particles of the present invention are, for example,
mixing lignin, amine, water, and alhyde to obtain an aqueous solution;
spray drying the aqueous solution, and
It can be produced by a method including a step of carbonizing the obtained spray-dried product to obtain spherical carbon particles. By this production method, the spherical carbon particles of the present invention can be produced efficiently and safely.

The spherical carbon particles of the present invention are preferably derived from lignin, and more preferably lignin containing 0.1% by mass or more of sulfur is used. Generally, such lignin is called kraft lignin and is obtained as a waste product after cellulose extraction in the paper manufacturing industry. Specifically, it can be obtained, for example, by acidifying black liquor produced in the pulp manufacturing process with a mineral acid and washing the precipitate. During distillation by the Kraft method, lignin in the wood cell wall is significantly reduced in molecular weight by cleavage of its main bonds, ether bonds, and its molecular weight is usually about 3,500 to 4,500. The content of elemental sulfur contained in lignin is more preferably 0.2% by mass or more, particularly preferably 0.5% by mass or more, and preferably 5% by mass or less, more preferably 4.5% by mass or less. be. When the sulfur element content is at least the lower limit, it is easy to suppress a decrease in the molecular weight of lignin, and it is easy to achieve sufficient progress of carbon condensation. Moreover, when the sulfur element content is below the upper limit value, emissions of sulfur dioxide and the like that may corrode the equipment used are likely to be suppressed. The sulfur element content can be adjusted by, for example, hydrolyzing lignin containing sulfur by heating it together with an aqueous solution of caustic soda, or by modifying lignin with a substance containing sulfur such as sulfuric acid, and adjusting the amount of denaturation. By doing so, it is possible to adjust the temperature to be greater than or equal to the lower limit value and less than or equal to the upper limit value. The elemental sulfur content can be measured by elemental analysis or X-ray fluorescence analysis. In addition, kraft lignin has a large amount of phenolic hydroxyl groups and is rich in chemical activity compared to lignin isolated by other methods, which is favorable for the formation of high density carbon. Only one type of lignin may be used, or two or more types of lignin that differ in one or more of sulfur element content, melting point, molecular weight, and volatile component content may be used in combination. When two or more types of lignin are used in combination, at least one of the lignins preferably has the above-mentioned preferred sulfur element content and/or molecular weight.

[Water solubilization process]
In the method for producing spherical carbon particles of the present invention, in order to obtain nitrogen-containing spherical carbon particles, lignin, amine, water, and aldehyde are mixed to obtain an aqueous solution. In this step, lignin can be made water-soluble by reacting lignin with an amine to form an ammonium salt of lignin. Furthermore, by reacting dissolved lignin with aldehyde, a crosslink can be formed between the phenol group of lignin and the aldehyde. Here, the amine can act as a catalyst in crosslinking lignin. In addition, some of the amines may react with aldehydes, and by forming imine structures, the rate of crosslinking with aldehydes can be increased. Crosslinking the lignin can prevent loss of shape due to melting during carbonization or contamination or corrosion of equipment. Although crosslinking can proceed even at room temperature, it can be accelerated by heating treatment. Furthermore, in order to allow the crosslinking reaction to proceed more uniformly, it is preferable to water-solubilize the lignin with an amine before adding the aldehyde.

The amines that can be used in the production process of the spherical carbon particles of the present invention are not particularly limited, and include primary amines such as methylamine, ethylamine, butylamine and aniline, and secondary amines such as dimethylamine, diethylamine and dibutylamine. , polyamines such as ethylenediamine and polyethyleneimine, or ammonia, etc. can be used. These may be used alone or in combination. Considering availability, economy and carbonization efficiency, it is preferred to use ammonia.

The amount of amine used in the production process of the spherical carbon particles of the present invention is not limited as it depends on the lignin and aldehyde used, but in consideration of crosslinking efficiency and water solubility, the amount of amine used is usually determined by the amount of aldehyde used. The amount is preferably 0.01 to 10 parts by weight, more preferably 0.02 to 9 parts by weight, and even more preferably 0.05 to 8 parts by weight.

The aldehyde that can be used in the process of producing spherical carbon particles of the present invention is not particularly limited, and includes monoaldehydes such as formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, valeraldehyde, isovaleraldehyde, hexanal, and benzaldehyde; Dialdehydes such as glyoxal, 1,4-butanedial, 1,6-hexanedial, 1,9-nonanedial, orthophthalaldehyde, metaphthalaldehyde, and terephthalaldehyde can be used. These may be used alone or in combination. In consideration of availability, economy, and carbonization efficiency, formaldehyde, benzaldehyde, glyoxal, and terephthaldehyde are preferred, and formaldehyde is more preferred. When using an aldehyde that is sparingly soluble in water, an organic solvent may be used. The organic solvent used is not particularly limited, and for example, alcohols such as methanol, ethanol, and propanol, and ketones such as acetone can be used. In this specification, even when an organic solvent is used in the aqueous solution preparation step, the term "aqueous solution" is used for convenience. The amount of organic solvent used may be adjusted as appropriate depending on the type of aldehyde, but it is usually preferable to use an amount 2 to 100 times the weight of the aldehyde.

The amount of aldehyde used in the production process of the spherical carbon particles of the present invention is not particularly limited as it varies depending on the properties of the lignin used, but in consideration of the reactivity and crosslinking efficiency of the aldehyde, it is usually The amount is preferably 0.01 to 20% by mass, more preferably 0.05 to 18% by mass, and even more preferably 0.1 to 15% by mass, based on the mass of lignin.

In the production process of spherical carbon particles of the present invention, the concentration of lignin in the lignin aqueous solution is not particularly limited, but from the viewpoint of facilitating the next step of spray drying, and the particle size of the obtained spherical carbon particles. From the viewpoint of adjusting the amount to a desired range, preferably 0.1 to 40% by mass, more preferably 0.2 to 30% by mass, and even more preferably 0.4 to 20% by mass, based on the mass of the entire ligrin aqueous solution. %.

In the step of reacting lignin with an amine to form an ammonium salt of lignin, if lignin is difficult to dissolve, the aqueous solution may be heated to about 90° C. as necessary. If lignin is insufficiently dissolved and solids derived from undissolved lignin remain in the lignin aqueous solution, crosslinking may progress locally, resulting in a non-uniform structure of the resulting spherical carbon particles. There is sex. Therefore, it is preferable to completely dissolve the lignin, but this does not preclude crosslinking with solids remaining. The heating method is not particularly limited, and heating may be performed using an oil bath, water bath, or the like.

In the water solubilization step, the temperature at which lignin is mixed with amine, water, and aldehyde is not particularly limited, but is usually in the range of 5 to 90°C to prevent water, which is a solvent, from being lost due to boiling. In consideration of reactivity and volatility, the temperature is preferably in the range of 10 to 70°C, more preferably in the range of 20 to 60°C. The mixing time is also not limited, but is usually 0.1 to 10 hours, preferably 0.2 to 9 hours, and more preferably 0.3 to 8 hours.

In the water solubilization step, an acid may be added as a catalyst in order to smoothly advance the crosslinking reaction by aldehyde. When using an acid, the amount used is not particularly limited, and may be changed as appropriate depending on the type of lignin and the type of amine used. Generally, it is added in an amount of 0.1 to 50% by weight, preferably 0.5 to 30% by weight, based on the weight of the amine. The acids that can be used are not particularly limited, and mineral acids such as hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid, and organic acids such as formic acid, acetic acid, propionic acid, oxalic acid, citric acid, and tartaric acid can be used. can. These may be used alone or in combination. Considering economy and reactivity, it is preferable to use hydrochloric acid or acetic acid.

[Spray drying process]
In the method for producing spherical carbon particles of the present invention, a spherical spray-dried product can be obtained by spray drying the aqueous solution obtained in the water solubilization step. The method of spray drying is not particularly limited as long as it is a method of turning an aqueous solution into droplets, heating it, and volatilizing the water, and it is also possible to atomize it while introducing ultrasonic waves or gas and dry it by heating. Fine droplets may be created by a method such as spraying, and the resulting droplets may be dried by heating.

The removal of the solvent by heating and drying may be carried out either under normal pressure or under reduced pressure. When carrying out under normal pressure, it is preferable to carry out under an inert gas atmosphere, for example, a nitrogen atmosphere from the viewpoint of safety.

The temperature for heating and drying is not particularly limited, but is preferably higher than the temperature at which the aqueous solution is prepared, more preferably from 80 to 600°C, still more preferably from 100 to 400°C, particularly preferably from 120 to 300°C. It is.

[Carbonization process]
In the method for producing spherical carbon particles of the present invention, spherical carbon particles can be obtained by carbonizing the spherical spray-dried product obtained above. The carbonization process may be a single-stage carbonization process or a multi-stage carbonization process. When carrying out a multi-stage carbonization process, it may be carried out continuously or after cooling once.

Specifically, the carbonization step in the manufacturing process of the present invention is preferably carried out at a temperature of 500° C. or more and 1800° C. or less under an inert gas atmosphere.

The inert gas is not particularly limited, and for example, helium, nitrogen, argon, or the like can be used alone or in combination of two or more. Furthermore, it is also possible to carry out carbonization in a gas atmosphere in which a halogen gas such as chlorine is mixed with the inert gas. The lower the concentration of the oxidizing gas in the gas used, the better. In such a case, the amount of oxidizing gas (particularly oxygen) mixed in the inert gas is usually 1% by volume or less, preferably 1000 ppm by volume or less. When the amount of oxidizing gas mixed is below the upper limit value, oxidation is difficult to proceed during the carbide generation process, and construction of the desired structure is likely to proceed. In addition, oxidative decomposition of the generated structure is less likely to occur.

The amount of inert gas supplied (flow amount) is also not limited, but per 1 g of spherical spray-dried material, preferably 1 mL/min or more, more preferably 5 mL/min or more, and even more preferably 10 mL/min or more. be. Further, the main carbonization step can also be performed under reduced pressure, for example, under a pressure of 10 KPa or less.

In the one-stage or multi-stage carbonization process, the rate of temperature increase in each carbonization process is not particularly limited. Although it varies depending on the heating method, the heating rate is preferably 1°C/min or more, more preferably 2°C/min or more, and preferably 20°C/min or less, more preferably 18°C/min or less. If the temperature increase rate is not less than the lower limit value and not more than the upper limit value, it is preferable from the viewpoint of economical efficiency since it is easy to obtain good productivity. Further, the progress of activation due to the generated carbonized gas is easily suppressed, and a good carbon density is easily obtained.

In the one-stage or multi-stage carbonization step, the carbonization temperature is preferably 500°C or higher, more preferably 700°C or higher, and preferably 1800°C or lower, more preferably 1500°C, and still more preferably 1300°C or lower. When the carbonization temperature is equal to or higher than the lower limit value and lower than the upper limit value, it is easy to build the desired structure and easily obtain spherical carbon particles having desired characteristics.

In the one-stage or multi-stage carbonization process, the holding time of the carbonization temperature in each carbonization process is not particularly limited, and is preferably 0.1 hour or more, more preferably 0.5 hour or more, and preferably 20 hours or less. , more preferably 15 hours or less. It is preferable that the holding time is not less than the lower limit value and not more than the upper limit value because carbonization will proceed sufficiently and ignition of carbide will be less likely to occur in the process of producing spherical carbonized particles. Further, it is preferable because it is easy to obtain spherical carbon particles having desired characteristics and the time required is reasonable from the economic point of view.

[Crushing process]
In the production method of the present invention, crushing may be performed after spray drying or after the carbonization step. In this step, it is possible to eliminate the fusion and agglomeration of fine powder during the spray drying and/or carbonization step, and adjust the particle size to the desired size.

The device used for crushing is not particularly limited. For example, a jet mill, a ball mill, a hammer mill, a rod mill, or the like can be used alone or in combination. From the viewpoint of generating less fine powder, a jet mill equipped with a classification function is preferable. On the other hand, when using a ball mill, hammer mill, rod mill, etc., fine powder can be removed by classifying after crushing. During crushing, it is necessary to appropriately set the crushing strength and crushing time so that the spherical carbon particles are crushed and no pointed portions or flat portions are generated.

[Classification process]
In the production method of the present invention, classification may be performed after the carbonization step or after the crushing step, which may be performed as necessary. By classification, the volume average particle size of spherical carbon particles can be adjusted more accurately, and particles smaller than a certain size (for example, particles with a volume average particle size of less than 0.1 μm) and particles larger than a certain size can be classified by classification. Particles (for example, particles having a volume average particle diameter of 50 μm or more) can also be removed.
When performing classification, examples thereof include classification using a sieve, wet classification, and dry classification. Examples of the wet classifier include classifiers that utilize the principles of gravity classification, inertial classification, hydraulic classification, centrifugal classification, and the like. Examples of the dry classifier include classifiers that utilize the principles of sedimentation classification, mechanical classification, or centrifugal classification.

When classifying is performed after the crushing step, crushing and classification can be performed using one device (for example, a jet mill equipped with a dry classification function), as described above. Alternatively, an apparatus in which the crusher and classifier are independent may be used, and in this case, crushing and classification may be performed continuously or discontinuously.

<Electrode for non-aqueous electrolyte batteries>
The spherical carbon particles of the present invention can be used as electrodes of non-aqueous electrolyte batteries such as lithium ion secondary batteries.

The spherical carbon particles of the present invention can be used for electrodes (negative electrodes). Specifically, for example, an electrode mixture is prepared by kneading spherical carbon particles, a binder, and a solvent, applied to a current collector plate made of a metal plate, etc., dried, and then pressure-molded. Electrodes can be manufactured by doing this.
The binder is not particularly limited as long as it does not react with the electrolyte. Examples of binders include PVDF (polyvinylidene fluoride), polytetrafluoroethylene, and mixtures of SBR (styrene butadiene rubber) and CMC (carboxymethylcellulose). Among these, PVDF is preferable because PVDF attached to the surface of the active material hardly inhibits the movement of lithium ions and thus obtains good input/output characteristics. A polar solvent such as N-methylpyrrolidone (NMP) is preferably used to dissolve the PVDF and form a slurry, although an aqueous emulsion such as SBR or an aqueous solution of CMC may also be used. If the amount of the binder added is too large, the resistance of the resulting electrode will increase, which increases the internal resistance of the battery and deteriorates the battery characteristics, which is not preferable. Furthermore, if the amount of the binder added is too small, the bonding between the negative electrode material particles and the current collector becomes insufficient, which is not preferable. The preferred amount of the binder added varies depending on the type of binder used, but in the case of a PVDF binder, it is preferably 3 to 13% by mass, more preferably 3 to 10% by mass based on the total weight of the electrode mixture. Mass%. On the other hand, for binders that use water as a solvent, multiple binders are often used in combination, such as a mixture of SBR and CMC, and the total amount of all binders used is based on the total weight of the electrode mixture. It is preferably 0.5 to 5% by weight, more preferably 1 to 4% by weight.
By using the spherical carbon particles of the present invention, it is possible to produce an electrode with high conductivity without adding a conductive aid, but if necessary, the electrode can be manufactured with the aim of imparting even higher conductivity. A conductive additive may be added when preparing the mixture. As the conductive aid, conductive carbon black, vapor grown carbon fiber (VGCF), nanotube, etc. can be used. The amount added varies depending on the type of conductive additive used, but if the amount added is too small, it will be difficult to obtain the expected conductivity, so it is not preferable, and if it is too large, dispersion in the electrode mixture will be poor, so it is not preferable. . From this point of view, when adding a conductive aid, the proportion of the conductive aid is preferably 0.5 to 10% by mass (here, amount of active material + amount of binder + amount of conductive aid = 100% by mass) ), more preferably 0.5 to 7% by mass, and even more preferably 0.5 to 5% by mass.
The electrode active material layer is usually formed on both sides of the current collector plate, but may be formed on one side if necessary. A thicker electrode active material layer is preferable for increasing capacity because it requires fewer current collector plates and separators, but if the active material layer is too thick, ion diffusion resistance within the electrode increases and input/output characteristics deteriorate. It is not desirable because The thickness of the active material layer (per side) is preferably 10 to 80 μm, more preferably 20 to 75 μm, and still more preferably 20 to 60 μm.

<Nonaqueous electrolyte secondary battery>
The non-aqueous electrolyte secondary battery of the present invention includes the electrode of the present invention. A non-aqueous electrolyte secondary battery using a negative electrode for a non-aqueous electrolyte secondary battery using spherical carbon particles of the present invention has a high electrode density and improves the volume capacity efficiency of the battery.

When the spherical carbon particles of the present invention are used to form the negative electrode of a non-aqueous electrolyte secondary battery, other materials constituting the battery, such as the positive electrode material, separator, and electrolyte, are not particularly limited. Various materials conventionally used or proposed for water-solvent secondary batteries can be used.
For example, the positive electrode material may be a layered oxide type (LiMO ₂ (where M represents a metal)) such as LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , or _LiNix Co _y Mo _z O ₂ ( Here, x, y, z represent the composition ratio)), olivine type (represented as LiMPO ₄ (here, M represents a metal): e.g. LiFePO _4, etc.), spinel type (LiM ₂ O ₄ (Here, M represents a metal. For example, LiMn ₂ O ₄ etc.) Composite metal chalcogen compounds are preferred, and these chalcogen compounds may be mixed as necessary. For example, a positive electrode can be manufactured by molding these positive electrode materials together with a suitable binder and spherical carbon particles for imparting conductivity to the electrode, and forming a layer on a conductive current collector.

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. Examples of non-aqueous solvents include 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. One type or a combination of two or more types can be used. Further, as the electrolyte, for example, 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 may be used. I can do it. A secondary battery is generally manufactured by placing the positive electrode active material layer and the negative electrode active material layer formed as described above facing each other with a permeable separator made of nonwoven fabric or other porous material interposed therebetween, as required, and placing them in an electrolytic solution. Formed by immersion. As the separator, a permeable separator made of nonwoven fabric or other porous material commonly used in secondary batteries can be used. Alternatively, a solid electrolyte made of a polymer gel impregnated with an electrolytic solution can also be used instead of or together with the separator.

EXAMPLES Hereinafter, the present invention will be specifically explained with reference to Examples, but these are not intended to limit the scope of the present invention.
The physical property values of the spherical carbon particles of the present invention ("element content", "(002) plane spacing _d002 ", "half width of D band near 1360 cm ^-1 in Raman spectrum", "volume") of the spherical carbon particles of the present invention are described below. The physical property values described in this specification, including the Examples, are based on the values determined by the following methods.

<Sulfur element content>
The sulfur element content was measured using "Carbon/Sulfur Analyzer EMIA-920V2" manufactured by Horiba, Ltd. The detection method of this device is combustion in an oxygen stream (high-frequency induction heating furnace method) - non-dispersive infrared absorption method (NDIR), and the calibration is performed using combustion improvers W (tungsten) and Sn (tin) in an alumina crucible. The test was conducted using standard substances JSS152-18 (S: 0.0056%) and JSS150-16 (S: 0.0296%). 50 mg of a sample that had been dehydrated for about 10 minutes at 250°C as a pretreatment was weighed into an alumina crucible along with 1.5 g of particulate tungsten and 0.3 g of particulate tin, and degassed for 30 seconds in an elemental analyzer. Measurements were carried out by heating and burning with high frequency in a pure oxygen stream. Three samples were analyzed, and the average value was taken as the analytical value.

<Nitrogen element and oxygen element content>
The nitrogen element and oxygen element contents were measured using "Oxygen/Nitrogen/Hydrogen Analyzer EMGA-930" manufactured by Horiba, Ltd. The detection method of this device is oxygen: inert gas melting-non-dispersive infrared absorption method (NDIR), nitrogen: inert gas melting-thermal conductivity method (TCD), and the calibration is Sn capsule and SS- 3 (standard sample). 20 mg of a sample that had been dehydrated at 250° C. for about 10 minutes as a pretreatment was weighed into an Sn capsule, degassed for 30 seconds in an elemental analyzer, and then measured. Three samples were analyzed, and the average value was taken as the analytical value.

<(002) plane spacing d ₀₀₂ >
Using "MiniFlex II" manufactured by Rigaku Co., Ltd., spherical carbon particles were filled in a sample holder, and an X-ray diffraction pattern was obtained using CuKα rays made monochromatic with a Ni filter as a radiation source. The peak position of the diffraction pattern was determined by the centroid method (a method of determining the centroid position of the diffraction line and calculating the peak position using the corresponding 2θ value), using the diffraction peak of the (111) plane of high-purity silicon powder for standard material. I corrected it. The wavelength of the CuKα ray was set to 0.15418 nm, and d ₀₀₂ was calculated using Bragg's formula described below.

<Half width of D band near 1360 cm ⁻¹ in Raman spectrum>
Raman spectra were measured using "LabRAM ARAMIS" manufactured by Horiba, Ltd. and a light source with a laser wavelength of 532 nm. In the test, particles were randomly sampled at three locations in each sample, and measurements were further made at two locations within each sampled particle. The measurement conditions were a wavelength range of 50 to 2000 cm ⁻¹ and 100 integrations, and the average value of six points in total was calculated as the measured value. The half-width of the D band is determined by fitting the peaks of the D band (around 1360 cm ^-1 ) and the G band (around 1590 cm ^-1 ) with a Gaussian function to the spectrum obtained under the above measurement conditions. ,It was measured.

<Volume average particle diameter>
The volume average particle diameter (particle size distribution) was measured by the following method. The sample was placed in an aqueous solution containing 0.3% by mass of a surfactant (“Triton . Particle size distribution was measured using this dispersion. Particle size distribution measurement was performed using a particle size/particle size distribution measuring device ("Microtrack MT3000" manufactured by Nikkiso Co., Ltd.). _D50 is the particle diameter at which the cumulative volume is 50%, and this value was used as the volume average particle diameter.

<Particle shape>
The shape of the particles was observed using a scanning electron microscope (SEM) (“VE-8800” manufactured by Keyence Corporation). Images are taken in a field of view that includes 100 or more particles, and 100 particles are randomly selected from among them, and those with a ratio of 90% or more of particles that do not have a pointed part or a flat part are visually inspected. Those with less than 90% spherical shape were classified as ``non-spherical''.

<Example 1>
60 g of lignin with a sulfur element content of 2% by mass was weighed into a 1L separable flask, 570 mL of ion-exchanged water was added, and 200 mL of ammonia water (28% by mass) was added while stirring with a mechanical stirrer. A mixed solution of 20.4 mL of formaldehyde aqueous solution (36% by mass), 5 mL of aqueous ammonia (28% by mass), and 0.5 g of acetic acid was added thereto, and the mixture was stirred at room temperature for 20 minutes. Furthermore, heating was started in an oil bath, and the mixture was stirred for 1.5 hours at an internal temperature of 80°C. Thereafter, the mixture was cooled to room temperature while stirring to obtain a lignin aqueous solution.
16 g of the obtained aqueous solution (solid content: 1.2 g) was dissolved in 284 mL of ion-exchanged water, and the mixture was heated using a spray dryer B-290 (manufactured by Buchi) equipped with a standard cyclone while flowing air at a nitrogen flow rate of 819 L/hour. Spray drying was performed with the insertion portion heated to 200°C. The solid content yield at this time was 68%.
2 g of the obtained spherical carbon particle precursor was placed in a boat-shaped crucible and introduced into a tubular furnace (tube diameter: 42 mmφ x 500 mm) manufactured by As One Corporation. In an inert gas flow of 1 L/min of nitrogen, the temperature was raised from room temperature to 1200°C (heating rate 10°C/min), held at 1200°C for 3 hours, and then allowed to cool naturally from 1200°C to room temperature over 8 hours. Then, spherical carbon particles were taken out.
The yield was 1.71 g (yield 85.5%). Table 1 shows the analysis results of the obtained spherical carbon particles.

<Example 2>
Spherical carbon particles were obtained by performing the same operation as in Example 1 except that the carbonization temperature was 1000°C. The yield was 1.80 g (90% yield). Table 1 shows the analysis results of the obtained spherical carbon particles. Furthermore, an electron microscope photograph of the obtained spherical carbon particles is shown in FIG.

<Example 3>
Spherical carbon particles were obtained by performing the same operation as in Example 1 except that the amount of ammonia water added was 100 mL. The yield was 1.60 g (yield 80%). Table 1 shows the analysis results of the obtained spherical carbon particles.

<Comparative example 1>
60 g of lignin was weighed into a 1 L separable flask, 570 mL of ion-exchanged water was added, and 200 mL of ammonia water (28% by mass) was added while stirring with a mechanical stirrer. A mixed solution of 20.4 mL of formaldehyde aqueous solution (36% by mass), 5 mL of aqueous ammonia (28% by mass), and 0.5 g of acetic acid was added thereto, and the mixture was stirred at room temperature for 20 minutes. Furthermore, heating was started in an oil bath, and the mixture was stirred for 1.5 hours at an internal temperature of 80°C. Thereafter, the mixture was cooled to room temperature while stirring to obtain a lignin aqueous solution.
400 g of water was distilled off from the obtained aqueous solution using an evaporator at a bath temperature of 80° C. and under reduced pressure of 3 kPa. The obtained concentrate was transferred to a 1 L beaker and dried in an explosion-proof hot air dryer at 80° C. for 12 hours to solidify. The amount of solid obtained was 45 g (yield 75%).
10.0 g of the obtained solid was placed in a boat-shaped crucible, and as a first carbonization step, this boat-shaped crucible was introduced into a tube furnace manufactured by Motoyama Co., Ltd. (tube diameter 200 mmφ x 1800 mm). As the first carbonization step, nitrogen was introduced at a flow rate of 10 L/min for 1 hour to replace the inside of the furnace with nitrogen, and the temperature was raised from room temperature to 600°C (heating rate 2.5°C/min). After holding for 1 hour, it was naturally cooled from 600° C. to room temperature over 12 hours and then taken out. 5.8 g (yield 58%) of carbide was obtained.
After pulverizing the obtained carbide to a volume average particle diameter of 8.1 μm using a mixer mill, 5.0 g of the pulverized material was placed in a boat-shaped crucible, and as a second carbonization step, it was introduced again into a 5L tube furnace manufactured by Motoyama Co., Ltd. The inside of the furnace was replaced with nitrogen by introducing nitrogen at a flow rate of /min for 1 hour, and the temperature was raised from room temperature to 1200℃ (heating rate 10℃/min), held at 1200℃ for 30 minutes, and then heated for 12 hours. It was naturally cooled from 1200°C to room temperature and then taken out. 4.52 g (yield 90.4%) of carbide was obtained. Table 1 shows the physical properties of the obtained carbide.

<Comparative example 2>
A carbide was obtained by performing the same operation as in Comparative Example 1, except that the second carbonization temperature was 1000° C. and the particles were ground so that the volume average particle diameter was 8.0 μm. The yield was 4.65 g (yield 93.0%). Table 1 shows the analysis results of the obtained carbide. Furthermore, an electron microscope photograph of the obtained carbide is shown in FIG.

<Preparation of electrodes and batteries>
A negative electrode was produced using the spherical carbon particles or carbide obtained in Examples and Comparative Examples according to the following procedure.

[Preparation of negative electrode]
95 parts by mass of spherical carbon particles or carbide, 2 parts by mass of conductive carbon black ("Super-P (registered trademark)" manufactured by TIMCAL), 3 parts by mass of PVDF (manufactured by Kureha) and 90 parts by mass of NMP were mixed to obtain a slurry. The obtained slurry was applied to a copper foil with a thickness of 18 μm, dried and then pressed to obtain an electrode with a thickness of 45 μm.

[Preparation of non-aqueous electrolyte secondary battery]
The electrode produced above was used as a working electrode, and metallic lithium was used as a counter electrode and a reference electrode. As a solvent, ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate were mixed and used in a volume ratio of 1:1:1. 1 mol/L of LiPF ₆ was dissolved in this solvent, and the resulting solution was used as an electrolyte. A polypropylene membrane was used as the separator. A coin cell was fabricated in a glove box under an argon atmosphere.

<Irreversible capacity and charge/discharge efficiency during initial charge/discharge>
A charge/discharge test was conducted on the lithium secondary battery having the above configuration at 25° C. using a charge/discharge test device (“TOSCAT” manufactured by Toyo System Co., Ltd.). The doping reaction of lithium onto the carbon electrode was carried out by a constant current constant voltage method, and the dedoping reaction was carried out by a constant current method. Here, in a battery that uses a lithium chalcogen compound as the positive electrode, the doping reaction of lithium to the carbon electrode is "charging," and in a battery that uses lithium metal as the counter electrode, such as the test battery of the present invention, the carbon electrode The doping reaction of lithium is called "discharge," and the name for the doping reaction of lithium to the same carbon electrode differs depending on the counter electrode used. Therefore, for convenience, the reaction of doping lithium into the carbon electrode will be referred to as "charging" here. Conversely, "discharge" is a charging reaction in the test battery, but since it is a dedoping reaction of lithium from spherical carbon particles, it will be described as "discharge" for convenience. The charging method adopted here is the constant current constant voltage method. Specifically, constant current charging is performed at 0.5 mA/ ^cm2 until the terminal voltage reaches 0 mV, and after the terminal voltage reaches 0 mV, the terminal voltage Constant voltage charging was performed at 0 mV and charging was continued until the current value reached 20 μA. The value obtained by dividing the total charging capacity at this time by the mass of the spherical carbon particles of the electrode is defined as the initial charging capacity per unit mass of the spherical carbon particles (mAh/g). After charging was completed, the battery circuit was opened for 30 minutes and then discharged. Discharge was carried out at a constant current of 0.5 mA/cm ² with a final voltage of 1.5V. The value obtained by dividing the amount of electricity discharged at this time by the weight of the spherical carbon material of the electrode is defined as the initial discharge capacity (mAh/g) per unit weight of the spherical carbon material. The difference between the initial charge capacity and the initial discharge capacity is defined as irreversible capacity (mAh/g). Furthermore, the ratio of the initial discharge capacity to the initial charge capacity was defined as the charge/discharge efficiency (%), and was used as an index of the utilization efficiency of lithium ions in the battery. The results are shown in Table 2.

<3C/1C discharge capacity ratio>
For each spherical carbon particle, the current density at which the initial discharge capacity can be charged and discharged in 5 hours is calculated, and this is defined as 0.2C current density (mA/cm ² ). After charging each battery at a current density of 0.2C, the discharge capacity ratio when discharging at a current density 5 times (1C) and 15 times (3C) that of the previous period was calculated as 3C/1C. It was defined as the discharge capacity ratio (%) and was used as an index of the battery's output characteristics. The results are shown in Table 2.

It can be seen that the nonaqueous electrolyte secondary batteries equipped with negative electrodes containing spherical carbon particles of Examples 1 to 3 have low irreversible capacities and high electrode densities. Furthermore, the high 3C/1C discharge capacity ratio indicates that the battery has excellent output characteristics. Furthermore, the spherical carbon particles of the present invention could be produced efficiently and safely. On the other hand, the non-aqueous electrolyte secondary batteries equipped with negative electrodes containing carbides of Comparative Examples 1 and 2 have high irreversible capacities and low electrode densities. Furthermore, the value of the 3C/1C discharge capacity ratio is also low.

Claims (7)

The sulfur element content is 0.5 mass% or more, the nitrogen element content is 1 mass% or more and less than 20 mass%, the oxygen element content is 1 mass% or more and 5 mass% or less, and CuKα radiation is used. A spherical carbon particle in which the interplanar spacing d ₀₀₂ of the (002) plane measured by the method is 3.5 Å or more and 3.8 Å or less. The spherical carbon particles according to claim 1, wherein the half-width of the D band near 1360 cm ^-1 in the Raman spectrum of the spherical carbon particles is 200 cm ^-1 or more and 270 cm ^-1 or less. The spherical carbon particles according to claim 1 or 2, wherein the spherical carbon particles have a volume average particle diameter of 100 nm or more and 5.0 μm or less. A step of obtaining an aqueous solution by mixing lignin containing 0.1% by mass or more of sulfur, an amine, water, and an alhyde of 0.01% by mass or more based on the mass of the lignin ;
spray drying the aqueous solution, and
The method for producing spherical carbon particles according to any one of claims 1 to 3, comprising the step of carbonizing the obtained spray-dried product at a temperature of 500 ° C. to 1800 ° C. in an inert gas atmosphere to obtain spherical carbon particles. . The method according to claim 4 , wherein the carbonization step is performed at a temperature of 700 °C or more and 1800°C or less. An electrode for a non-aqueous electrolyte battery, comprising the spherical carbon particles according to any one of claims 1 to 3. A non-aqueous electrolyte secondary battery comprising the electrode according to claim 6.