JP7520546B2 - Carbonaceous material for negative electrode active material of non-aqueous electrolyte secondary battery, negative electrode for non-aqueous electrolyte secondary battery - Google Patents

Description

The present invention relates to a carbonaceous material suitable for use as a negative electrode active material in a nonaqueous electrolyte secondary battery, a negative electrode for a nonaqueous electrolyte secondary battery that contains the carbonaceous material, a nonaqueous electrolyte secondary battery that has the negative electrode, and a method for producing the carbonaceous material.

Non-aqueous electrolyte secondary batteries such as lithium-ion secondary batteries have a high energy density and excellent output characteristics, and are therefore widely used in small portable devices such as mobile phones and laptops. In recent years, their use in vehicles such as hybrid cars and electric cars has been promoted, and there is a demand for even higher capacity non-aqueous electrolyte secondary batteries. In response to this, non-graphitizable carbon has been developed and used as the negative electrode material for lithium-ion secondary batteries, which can be doped (charged) and de-doped (discharged) with lithium in amounts that exceed the theoretical capacity of graphite, 372 mAh/g (for example, Patent Document 1).

When producing these non-graphitizable carbons, it has been disclosed that the charge/discharge capacity can be increased by lowering the sintering temperature to 1000°C or lower, but the irreversible capacity increases and the charge/discharge efficiency decreases because many surface functional groups remain (Non-Patent Document 1). In addition, non-graphitizable carbons produced in this way have problems such as moisture adsorption to the surface functional groups and deterioration due to oxidation.

Therefore, as a means of increasing the charge/discharge capacity of non-graphitizable carbon without reducing charge/discharge efficiency, a method has been disclosed in which nitrogen is introduced into the carbonaceous material to increase the number of sites for absorbing and desorbing lithium ions during charging and discharging (for example, Patent Document 2).

In addition, in order to make the non-graphitizable carbon resistant to oxidation deterioration, a method has been disclosed in which a mixture of a carbon precursor and a volatile organic substance is calcined to reduce the specific surface area of the non-graphitizable carbon (Patent Document 3). This makes it possible to obtain a surface structure that balances the amount of lithium ions adsorbed and the amount of lithium ions consumed by reaction on the surface of the carbonaceous material, and as a result, it is disclosed that charge/discharge efficiency is improved.

JP 2006-083012 A International Publication No. 2019/009333 JP 2016-152225 A

Electrochimica Acta 45 (1999) 121-130

However, in the negative electrode material of the lithium-ion secondary battery described in Patent Document 2, unincorporated nitrogen elements may be discharged as nitrogen-containing gases such as HCN and NOx, and the manufacturing process may impose a heavy process load when processing them. In addition, Patent Document 3 has a low nitrogen content, so the amount of nitrogen-containing gas discharged is small, but this does not result in a significant improvement in discharge capacity.

The present invention therefore aims to provide a carbonaceous material suitable as a negative electrode active material for non-aqueous electrolyte secondary batteries (e.g., lithium ion secondary batteries, sodium ion batteries, lithium sulfur batteries, lithium air batteries, etc.) that have high charge/discharge capacity and good charge/discharge efficiency, using a manufacturing method with a small process load and low nitrogen-containing gas emissions, a negative electrode containing the carbonaceous material, and a non-aqueous electrolyte secondary battery having the negative electrode.

The present inventors have found that the above object can be achieved by using a carbonaceous material having a specific structure described below as an active material for a negative electrode of a non-aqueous electrolyte secondary battery.
That is, the present invention includes the following preferred embodiments.
[1] A carbonaceous material having a nitrogen element content of 0.3 mass% or more and less than 1.0 mass% as determined by elemental analysis, and an absorption intensity ratio at 1350°C to the absorption intensity at 1000°C of 0.45 or more and 3.0 or less, in an amount of oxygen detected as carbon monoxide or carbon dioxide by elemental analysis.
[2] The carbonaceous material according to [1], wherein the half width of a peak in the vicinity of 1360 cm ⁻¹ in a Raman spectrum observed by laser Raman spectroscopy is 180 cm ⁻¹ or more and 230 cm ⁻¹ or less.
[3] The carbonaceous material according to [1] or [2], which has a specific surface area measured by a BET method of 100 m ² /g or less.
[4] The carbonaceous material according to any one of [1] to [3] above, having an average particle size _D50 of 30 μm or less.
[5] The carbonaceous material according to any one of [1] to [4] above, wherein the carbon interplanar spacing d ₀₀₂ calculated using the Bragg equation by wide-angle X-ray diffraction is 3.75 Å or more.
[6] The carbonaceous material according to any one of [1] to [5] above, which is derived from a substance having a saccharide skeleton.
[7] A negative electrode for a non-aqueous electrolyte secondary battery, comprising the carbonaceous material according to any one of [1] to [6].
[8] A non-aqueous electrolyte secondary battery having the negative electrode for a non-aqueous electrolyte secondary battery according to [7].

The present invention provides a negative electrode material that is useful for non-aqueous electrolyte secondary batteries, and has high charge/discharge capacity and good charge/discharge efficiency. A non-aqueous electrolyte secondary battery using a negative electrode containing the carbonaceous material of the present invention has high charge/discharge capacity and good charge/discharge efficiency. In addition, since less nitrogen-containing gas is discharged during production than nitrogen-containing non-graphitizable carbon, effects such as reduced process load can be expected.

The following describes in detail the embodiments of the present invention. Note that the scope of the present invention is not limited to the embodiments described here, and various modifications can be made without departing from the spirit of the present invention.

In the carbonaceous material of the present invention, in order to reduce the amount of nitrogen-containing gas discharged, the nitrogen element content determined by elemental analysis must be less than 1.0 mass%, preferably 0.95 mass% or less, more preferably 0.90 mass% or less, and even more preferably 0.85 mass% or less.
On the other hand, in the carbonaceous material of the present invention, in order to increase the charge/discharge capacity, voids capable of storing lithium clusters are necessary, and in order to create many voids, carbon distortion is required. On the other hand, by introducing nitrogen into the carbonaceous material, appropriate carbon distortion can be created, and from this viewpoint, the nitrogen element content needs to be 0.3 mass% or more, preferably 0.45 mass% or more, more preferably 0.5 mass% or more, and even more preferably 0.6 mass% or more.
The details of the measurement of the nitrogen element content are as described later, and are measured by elemental analysis (inert gas dissolution method). The method of adjusting the nitrogen element content in the carbonaceous material to the above range is not limited in any way, but for example, a method of manufacturing a carbonaceous material described later, which includes a step of heat-treating a carbide, which is a raw material of the carbonaceous material, under an inert gas atmosphere, can be used. In particular, when the amount of inert gas supplied is increased, the heating rate is decreased, or the heat treatment temperature is increased, the nitrogen element tends to be easily desorbed, so the amount of inert gas supplied, the heating rate, and the heat treatment temperature can be adjusted to adjust the nitrogen element content to a desired range.

In addition, when creating many voids in which the lithium clusters can be stored, carbon distortion is likely to occur if there are carbonyl groups in the carbon skeleton. On the other hand, in the amount of oxygen detected as carbon monoxide or carbon dioxide by elemental analysis, the absorption intensity at 1350°C corresponds to the decomposition of carbonyl groups, so the intensity can be used as an index of the amount of carbonyl groups in the carbon skeleton. In contrast, the absorption intensity at 1000°C in the above amount of oxygen corresponds to the decomposition of hydroxyl groups and ether groups, but the hydroxyl groups at the edge portions of the carbon skeleton capture lithium during charging, causing a decrease in discharge capacity. For these reasons, when the carbonaceous material has sufficient voids to store lithium ions and there are few functional groups that capture lithium at the edge portions of the carbon skeleton, a high charge/discharge capacity can be obtained.
It is presumed that the carbonyl group in the carbon skeleton is generated by the change of the oxygen-containing functional group contained in the raw material during the calcination process, and the amount of carbonyl groups with a high thermal decomposition temperature can be increased by increasing the calcination temperature. However, it is known that when the calcination temperature is increased, the amount of voids in which lithium clusters can be stored decreases due to the progression of graphitization, and the charge/discharge capacity of the resulting carbonaceous material decreases (for example, Non-Patent Document 1). Therefore, in order to obtain a high charge/discharge capacity, it is necessary to set calcination conditions that balance the reduction in voids during calcination and the amount of carbonyl groups that facilitate the generation of carbon distortion.
For these reasons, in the carbonaceous material of the present invention, in the amount of oxygen detected as carbon monoxide or carbon dioxide by elemental analysis, the ratio of the absorption intensity at 1350°C to the absorption intensity at 1000°C must be 0.45 or more, preferably 0.60 or more, more preferably 0.80 or more, and even more preferably 1.0 or more.
In addition, if the amount of carbonyl groups in the carbon skeleton increases and the distortion caused by the carbonyl groups becomes too large, the carbon skeleton collapses and lithium becomes difficult to absorb. Therefore, the ratio of the absorption intensity at 1350° C. to the absorption intensity at 1000° C. must be 3.0 or less, preferably 2.5 or less, and more preferably 2.0 or less.

In the carbonaceous material of the present invention, the hydrogen element content is preferably 0.15% by mass or less, since the edge portion of the carbon skeleton is reduced, and as a result, the carbon plane is expanded, facilitating the movement of electrons, and is more preferably 0.13% by mass or less, and even more preferably 0.10% by mass or less. In addition, the hydrogen element content is preferably 0.01% by mass or more, since it facilitates the adsorption and desorption of lithium ions, and is more preferably 0.02% by mass or more. The details of the measurement of the hydrogen element content are as described below, and it is measured by elemental analysis (inert gas dissolution method).

In the carbonaceous material of the present invention, the oxygen element content is preferably 1.0 mass% or more, since it generates carbon distortion and increases the charge/discharge capacity, more preferably 1.1 mass% or more, and even more preferably 1.2 mass% or more. In addition, the oxygen element content is preferably 2.0 mass% or less, since it can suppress the reaction with lithium ions, more preferably 1.8 mass% or less, and even more preferably 1.7 mass% or less. The details of the measurement of the oxygen element content are as described below, and it is measured by elemental analysis (inert gas dissolution method).

In the carbonaceous material of the present invention, the half width of the peak near 1360 cm ^-1 in the Raman spectrum observed by laser Raman spectroscopy is preferably 180 cm ^-1 or more and 230 cm ^-1 or less. Here, the peak near 1360 cm ^-1 is a Raman peak generally called a D band, which is a peak caused by disorder/defects in the graphite structure. The peak near 1360 cm ^-1 is usually observed in the range of 1345 cm ^-1 to 1375 cm ^-1 , preferably 1350 cm ^-1 to 1370 cm ^-1 . The half width in this specification is the full width at half maximum.

The value of the half width of the peak near 1360 cm ^-1 is related to the amount of disorder and defects in the graphite structure contained in the carbonaceous material. Such disorder of the structure can be caused, for example, by the introduction of nitrogen atoms into the carbon skeleton. When the value of the half width of the peak near 1360 cm ^-1 is greater than 180 cm ^-1 , the disorder and defects in the graphite structure contained in the carbonaceous material increase, and the micropores between the crystals increase due to the underdevelopment of the graphite structure. As a result, the number of sites where lithium ions are absorbed increases, and the charge and discharge capacity is improved. From the viewpoint of easily increasing the charge and discharge capacity, the value of the half width of the peak near 1360 cm ^-1 is preferably 185 cm ^-1 or more, more preferably 190 cm ^-1 or more. In addition, when the half width is smaller than 230 cm ^-1 , the disorder and defects in the graphite structure contained in the carbonaceous material are reduced, so that the amorphous portion decreases and the sites that can absorb lithium derived from the graphite structure increase. As a result, the amount of lithium ions absorbed is increased, and the charge/discharge capacity is improved. From the viewpoint of easily increasing the charge/discharge capacity, the half width value of the peak near 1360 cm ⁻¹ is preferably 225 cm ⁻¹ or less, more preferably 220 cm ⁻¹ or less, even more preferably 215 cm ⁻¹ or less, even more preferably 212 cm ⁻¹ or less, even more preferably 210 cm ⁻¹ or less, even more preferably 208 cm ⁻¹ or less, and particularly preferably 206 cm ⁻¹ or less.

The Raman spectrum is measured using a Raman spectrometer (for example, a Raman spectrometer "LabRAM ARAMIS (VIS)" manufactured by Horiba, Ltd.). Specifically, for example, the particles to be measured are set on an observation stage, the magnification of the objective lens is set to 100 times, the focus is adjusted, and 532 nm argon ion laser light is irradiated into the measurement cell, with an exposure time of 1 second, an accumulation count of 100, and a measurement range of 50-2000 cm ^-1 .

The method for adjusting the half-width value of the peak near 1360 cm ⁻¹ to the above range is not limited in any way, but for example, a method for producing a carbonaceous material, which includes a step of heat-treating a carbide, which is a raw material for the carbonaceous material, under an inert gas atmosphere, can be used. In particular, when the amount of inert gas supplied is increased, the heating rate is decreased, or the heat treatment temperature is increased, nitrogen atoms, which are factors that cause disorder and defects in the graphite structure contained in the carbonaceous material, tend to be desorbed, and as a result, the half-width value of the peak near 1360 cm ⁻¹ tends to be smaller. Therefore, the amount of inert gas supplied, the heating rate, and the heat treatment temperature can be adjusted to adjust the half-width value to a desired range.

In the carbonaceous material of the present invention, the intensity ratio (R value = I ₁₃₆₀ /I ₁₅₈₀ ) of the peak intensity (I ₁₃₆₀ ) near 1360 cm ^-1 in the Raman spectrum to the peak intensity (I ₁₅₈₀ ) near 1580 cm ^-1 in the Raman spectrum is related to the crystallinity of the carbonaceous material. When the crystallinity of the carbonaceous material is low, the edges of the carbon skeleton are increased, and the insertion sites of Li are increased. Therefore, there are advantages such as improved characteristics at low temperatures and reduced resistance. For these reasons, from the viewpoint of easily lowering the internal resistance of the nonaqueous electrolyte secondary battery, the R value is preferably 1.10 or more, more preferably 1.13 or more, even more preferably 1.15 or more, and particularly preferably 1.17 or more. In addition, when the crystallinity of the carbonaceous material is high, the amorphous portion is reduced, the edges of the carbon skeleton are reduced, and the reactive groups at the carbon terminals that react with lithium are reduced. Therefore, the utilization efficiency of lithium ions is increased. For this reason, the R value is preferably 1.28 or less, more preferably 1.25 or less, and even more preferably 1.22 or less. Here, the peak near 1360 cm ^-1 is a Raman peak generally called a D band, as described above with respect to the half-width, which is a peak caused by disorder/defects in the graphite structure. The peak near 1580 cm ^-1 is a Raman peak generally called a G band, which is a peak caused by the graphite structure. Here, the peak near 1580 cm ^-1 is usually observed in the range of 1565 cm ^-1 to 1615 cm ^-1 , preferably 1560 cm ^-1 to 1610 cm ^-1 .

The smaller the specific surface area of the carbonaceous material of the present invention measured by the nitrogen adsorption BET method, the easier it is to reduce the hygroscopicity of the carbonaceous material, and the easier it is to reduce the amount of moisture present in the carbonaceous material, and as a result, the hydrolysis of the electrolyte solution and the electrolysis of water due to moisture are suppressed, and the easier it is to suppress the generation of acid and gas associated with these. In addition, the smaller the specific surface area, the easier it is to reduce the contact area between the air and the carbonaceous material, and the easier it is to suppress the oxidation of the carbonaceous material itself. Furthermore, since there is an amount of lithium ions that react and are consumed on the surface of the carbonaceous material, the smaller the specific surface area, the easier it is to reduce the amount of lithium ions consumed. For these reasons, the smaller the specific surface area, the more preferable it is, and it is preferably 100 m ² /g or less, more preferably 60 m ² /g or less, even more preferably 30 m ² /g or less, even more preferably 28 m ² /g or less, and particularly preferably 25 m ² /g or less. The lower limit of the specific surface area of the carbonaceous material measured by the nitrogen adsorption BET method is not particularly limited, but from the viewpoint of increasing the contact area with the electrolyte and easily reducing the resistance of the battery, it is preferably 3 m ² /g or more, more preferably 5 m ² /g or more. In this specification, the specific surface area measured by the BET method means the specific surface area determined by the nitrogen adsorption BET multipoint method. Specifically, it can be measured using the method described later.

There is no limitation on the method for adjusting the specific surface area by the BET method to the above range, but for example, in the manufacturing method of a carbonaceous material described below, if the temperature in the process for obtaining a carbon precursor and/or the process for obtaining a carbide is lowered or the heating time is shortened, the BET specific surface area of the carbonaceous material finally obtained tends to be larger due to suppression of shrinkage of the structure due to heat, etc. Therefore, in order to obtain a carbonaceous material having a BET specific surface area in the desired range, the firing temperature and firing time can be adjusted.

The average particle diameter D ₅₀ of the carbonaceous material of the present invention is 30 μm or less, which not only improves the coating property during electrode preparation, but also reduces the free diffusion path of lithium ions within the particles of the carbonaceous material, making it easier to obtain rapid charge and discharge, which is preferable. Furthermore, in lithium ion secondary batteries, it is important to increase the electrode area in order to improve input/output characteristics, and for this purpose, it is necessary to reduce the coating thickness of the active material on the current collector plate during electrode preparation. From these viewpoints, the smaller the average particle diameter D ₅₀ , the more preferable it is, and it is preferably 30 μm or less, more preferably 25 μm or less, even more preferably 20 μm or less, particularly preferably 18 μm or less, and most preferably 15 μm or less. When the average particle diameter of the carbonaceous material to be the active material is equal to or less than the above upper limit, it is easy to reduce the coating thickness during electrode preparation. In addition, the average particle diameter D ₅₀ of the carbonaceous material of the present invention is 2 μm or more, which is preferable because it suppresses the increase in specific surface area and the increase in reactivity with the electrolyte due to fine powder in the carbonaceous material, and makes it easier to suppress the increase in irreversible capacity. In addition, when a negative electrode is manufactured using a carbonaceous material, it is easy to secure the voids formed between the carbonaceous material, the movement of lithium ions in the electrolyte is not easily suppressed, and the resistance of the nonaqueous electrolyte secondary battery is easily reduced. From these viewpoints, the average particle diameter D ₅₀ is preferably 2 μm or more, more preferably 3 μm or more, even more preferably 4 μm or more, and particularly preferably 5 μm or more. The average particle diameter D ₅₀ is the particle diameter at which the cumulative volume is 50%, and can be obtained by measuring the particle size distribution by a laser scattering method using, for example, a particle diameter/particle size distribution measuring device (Microtrac MT3300EXII manufactured by Microtrac Bell Co., Ltd.).

In the carbonaceous material of the present invention, the carbon interplanar spacing d ₀₀₂ calculated using the Bragg formula by wide-angle X-ray diffraction is about 3.35 to 3.40 Å when the carbon planes are closest to each other, as in graphite, and when it exceeds 4.00 Å, the carbon planes cannot interact with each other and the layer structure cannot be maintained. The larger the carbon interplanar spacing d ₀₀₂ , the more efficiently lithium ions can move, and from the viewpoint of easily reducing the resistance of the nonaqueous electrolyte secondary battery, it is preferably 3.75 Å or more, more preferably 3.80 Å or more, even more preferably 3.81 Å or more, and particularly preferably 3.82 Å or more. From the viewpoint of easily maintaining the layer structure, the carbon interplanar spacing d ₀₀₂ is preferably 4.00 Å or less, more preferably 3.97 Å or less, and even more preferably 3.95 Å or less. Details of the method for measuring the carbon interplanar spacing d ₀₀₂ are as described in the Examples, and are calculated from the peak position (diffraction angle 2θ) observed by powder X-ray diffraction using the Bragg formula.

The raw material for the carbonaceous material of the present invention is not limited, and known non-graphitizable carbon raw materials such as petroleum pitch, coal pitch, and coconut shells can be used. However, it is preferable to use a substance having a saccharide skeleton as a raw material that is easy to obtain the carbonaceous material of the present invention having the above characteristics and is easy to modify the structure, such as a crosslinked structure. By using a substance having a saccharide skeleton as a raw material, a carbonaceous material derived from a substance having a saccharide skeleton can be obtained. Examples of substances having a saccharide skeleton (saccharides) include monosaccharides such as glucose, galactose, mannose, fructose, ribose, and glucosamine, disaccharides such as sucrose, trehalose, maltose, cellobiose, maltitol, lactobionic acid, and lactosamine, and polysaccharides such as starch, glycogen, agarose, pectin, cellulose, chitin, and chitosan. These saccharides can be used alone or in combination of two or more. Among these saccharides, starch is preferable because it is easier to obtain the carbonaceous material of the present invention and the structure of the carbonaceous material can be easily controlled. From the viewpoint of obtaining a higher charge/discharge capacity, it is preferable to reduce the molecular weight of starch. For example, dextrin, which is obtained by hydrolyzing starch with acid or enzymes, can be mentioned. With reduced molecular weight starch, the number of terminals increases and the amount of aldehyde increases, which changes the form of the oxygen functional group in the carbonaceous material, increasing the number of sites for occluding lithium ions and tends to obtain a high charge/discharge capacity.

The carbonaceous material of the present invention is
(1) A step of heating a raw material in an inert gas atmosphere to a temperature between 100 and 250° C. at a heating rate of 100° C./hour or more to obtain a carbon precursor;
(2A) heating the carbon precursor to a first temperature in the range of 500 to 900° C. at a heating rate of 100° C./hour or more under an inert gas atmosphere;
(2B) A step of heat treating the carbon precursor at a temperature of 500 to 900° C. under an inert gas supply to obtain a carbide.
(3A) The carbonized material is heated at a heating rate of 100° C./hour or more in an inert gas atmosphere.
(3B) heating the carbide to a second temperature in the range of 0 to 1400° C., and (3B) heat treating the carbide at a temperature of 1000 to 1400° C. under an inert gas supply to obtain a carbonaceous material.

In addition to the above-mentioned sugars, a crosslinking agent may be added to the raw material. The crosslinking agent to be added is not particularly limited, and examples thereof include organic acids. The organic acids are not particularly limited, and examples thereof include aliphatic carboxylic acids such as formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, undecanoic acid, palmitic acid, stearic acid, succinic acid, linoleic acid, oleic acid, and adipic acid; aromatic carboxylic acids such as benzoic acid, salicylic acid, phthalic acid, and terephthalic acid; hydroxycarboxylic acids such as lactic acid, tartaric acid, citric acid, and malic acid; carboxylic acids such as ethylenediaminetetraacetic acid, and sulfonic acids such as p-toluenesulfonic acid and methanesulfonic acid. By mixing an organic acid with starch or the like and subjecting it to heat treatment, the form of the oxygen functional group in the carbonaceous material changes, the number of sites for occluding lithium ions increases, and a high charge/discharge capacity tends to be obtained. From the viewpoint of the ease of obtaining the effect of forming lithium ion occlusion sites, polyvalent carboxylic acids are preferred.

The amount of organic acid in the carbon precursor is preferably 1 to 50 parts by mass, more preferably 3 to 30 parts by mass, and even more preferably 5 to 20 parts by mass, per 100 parts by mass of the raw material. The method of mixing the raw material of the carbon precursor with the organic acid is not particularly limited, and the raw material of the carbon precursor and the organic acid may be mixed directly, or the raw material and/or the organic acid may be mixed in a state in which they are dispersed and/or dissolved in at least one liquid. In addition, when mixing is performed using at least one liquid, the liquid may be removed by evaporation or the like as necessary to obtain a mixture. When the raw material is a polysaccharide such as starch and mixing is performed using at least one liquid, the raw material may be reduced in molecular weight due to the action of the acid catalyst of the organic acid. The reduced molecular weight starch changes the form of the oxygen functional group in the carbonaceous material by increasing the terminal aldehyde, and the site for occluding lithium ions increases, tending to obtain a high charge/discharge capacity. From this viewpoint and from the viewpoint of easily obtaining a uniform mixture, it is preferable to add and mix the raw material of the carbon precursor into a solution in which at least one organic acid is dissolved in at least one liquid, and then to distill off the liquid to obtain a mixture.

Here, in step (1), the raw material reacts with the crosslinking agent by heat treatment, and raw materials such as starch are ester-crosslinked. As a result, it is believed that the raw material of the carbon precursor is not melted by heat treatment, and a carbon precursor that maintains a fine structure is obtained. Note that step (1) may be omitted.

In step (1), the raw material is heated and heat-treated for 1 to 12 hours at a temperature range of 100 to 250°C as described above. The heat treatment temperature in step (1) is preferably 120 to 230°C, more preferably 130 to 200°C, from the viewpoint of facilitating the reaction between the raw material and the crosslinking agent and of facilitating the final production of a carbonaceous material having the above characteristics, and the heat treatment time is preferably 2 to 8 hours, more preferably 2.5 to 6 hours, and even more preferably 3 to 5 hours. Here, the heat treatment temperature may be a constant temperature, but is not particularly limited as long as it is within the above range.

Step (2A) is a step of heating the carbon precursor or raw material obtained in step (1) to a first temperature in the range of 500 to 900°C in an inert gas atmosphere at a heating rate of 100°C/hour or more, and step (2B) is a step of heat treating the carbon precursor obtained in (2A) at a temperature of 500 to 900°C under the supply of inert gas to obtain a carbide. Step (2A) is performed in an inert gas atmosphere, and step (2B) is performed under the supply of inert gas. Here, a step performed under an inert gas atmosphere means that the step is performed in an inert gas atmosphere, and active supply of inert gas may or may not be performed. In contrast, a step performed under an inert gas supply means that the step is performed under an atmosphere to which an inert gas is supplied. For example, a heat treatment simply in an inert gas atmosphere cannot be said to be actively supplied with an inert gas, and cannot be said to be heat treatment under the supply of an inert gas. In this specification, steps (2A) and/or (2B) are also referred to as low-temperature firing (steps). Examples of inert gases include argon gas, helium gas, and nitrogen gas, and nitrogen gas is preferred.

The heating rate in step (2A) is preferably 100°C/hour or more, more preferably 300°C/hour or more, even more preferably 400° ^C /hour or more, and particularly preferably 500°C/hour or more, from the viewpoint of easily obtaining a carbonaceous material having the above characteristics, particularly from the viewpoint of easily adjusting the nitrogen element content and the half-width of the Raman peak near 1360 cm-1 to the above range. The upper limit of the heating rate is not particularly limited, but from the viewpoint of easily suppressing an increase in the specific surface area due to rapid thermal decomposition, it is preferably 1000°C/hour or less, more preferably 800°C/hour or less. The first temperature in step (2A) is 500 to 900°C, preferably 530 to 880°C, more preferably 550 to 850°C, and even more preferably 600 to 800°C.

Next, in step (2B), the carbon precursor is heat-treated at a temperature of 500 to 900°C under the supply of an inert gas to obtain a carbide. The heat treatment temperature in step (2B) is also referred to as the low-temperature firing temperature below. The low-temperature firing temperature in step (2B) is 500 to 900°C, preferably 530 to 880°C, more preferably 550 to 850°C, and even more preferably 600 to 800°C, from the viewpoint of easily obtaining a carbonaceous material having the above characteristics. The low-temperature firing temperature may be a constant temperature, but is not particularly limited as long as it is within the above range. It is preferable that step (2A) is also performed while supplying the above-mentioned inert gas. In addition, in order to simplify and facilitate the operation, it is preferable that the first temperature in step (2A) and the heat treatment temperature in step (2B) are equal. The heat treatment time in step (2B) is preferably 0.1 to 5 hours, more preferably 0.3 to 3 hours, and even more preferably 0.5 to 2 hours.

Step (3A) is a step of heating the carbide obtained in step (2B) to a second temperature in the range of 1000 to 1400°C at a heating rate of 100°C/hour or more in an inert gas atmosphere, and step (3B) is a step of heat treating the carbide at a temperature of 1000 to 1400°C under the supply of inert gas to obtain a carbonaceous material. Here, step (3A) is performed in an inert gas atmosphere, and step (3B) is performed under the supply of inert gas. Here, the conditions of under an inert gas atmosphere and under the supply of inert gas are as described above for (2A) and (2B). In addition, in this specification, step (3A) and/or (3B) are also referred to as high-temperature firing (step). Examples of inert gas include those described above for (2A) and (2B), and preferably nitrogen gas.

The heating rate in step (3A) is preferably 100°C/hour or more, more preferably 300°C/hour or more, even more preferably 400° ^C /hour or more, and particularly preferably 500°C/hour or more, from the viewpoint of easily obtaining a carbonaceous material having the above characteristics, particularly from the viewpoint of easily adjusting the nitrogen element content and the half-width of the Raman peak near 1360 cm-1 to the above range. The upper limit of the heating rate is not particularly limited, but from the viewpoint of easily suppressing an increase in the specific surface area due to rapid thermal decomposition, it is preferably 800°C/hour or less, more preferably 700°C/hour or less, and even more preferably 600°C/hour or less. The second temperature in step (3A) is 1000 to 1400°C, preferably 1050 to 1380°C, more preferably 1100 to 1370°C, even more preferably 1150 to 1360°C, and particularly preferably 1200 to 1350°C.

From the viewpoint of creating a structure that easily absorbs lithium ions and increasing the discharge capacity, step (3A) is usually performed following step (2B). Therefore, the temperature-raising step in step (3A) is a step of raising the temperature from a low-temperature firing temperature in the range of 500 to 900°C to the second temperature in the range of 1000 to 1400°C. For example, at the above heating rate, the temperature is raised from the low-temperature firing temperature (500-900°C) to the second temperature (1000-1400°C), preferably from the low-temperature firing temperature (530-880°C) to the second temperature (1050-1380°C), more preferably from the low-temperature firing temperature (550-850°C) to the second temperature (1100-1370°C), even more preferably from the low-temperature firing temperature (600-850°C) to the second temperature (1150-1360°C), and particularly preferably from the low-temperature firing temperature (600-800°C) to the second temperature (1200-1350°C).

Next, in step (3B), the carbide is heat-treated at a temperature of 1000 to 1400°C under the supply of an inert gas to obtain a carbonaceous material. The heat treatment temperature in step (3B) is also referred to as the high-temperature firing temperature below. The high-temperature firing temperature in step (3B) is 1000 to 1400°C, preferably 1050 to 1380°C, more preferably 1100 to 1370°C, even more preferably 1150 to 1360°C, and particularly preferably 1200 to 1350°C, from the viewpoint of making the operation easy and easily obtaining a carbonaceous material having the above characteristics. The high-temperature firing temperature may be a constant temperature, but is not particularly limited as long as it is within the above range. The heat treatment time in step (3B) is preferably 0.1 to 5 hours, more preferably 0.3 to 3 hours, and even more preferably 0.5 to 2 hours. It is preferable that step (3A) is also performed while supplying the above inert gas. In addition, from the viewpoint of simplifying the operation, it is preferable that the second temperature in step (3A) is equal to the heat treatment temperature in step (3B).

The high-temperature firing temperature (i.e., the firing temperature in step (3B)) is preferably equal to the second temperature in step (3A) above, and is preferably equal to or higher than the firing temperature in step (2B) (the first temperature in step (2A) in a preferred embodiment) from the viewpoint of easily obtaining a carbonaceous material that provides high charge/discharge capacity, charge/discharge efficiency, and low resistance when used in an electrode. The high-temperature firing temperature is preferably 50 to 700°C, more preferably 100 to 600°C, and even more preferably 200 to 500°C higher than the low-temperature firing temperature.

The carbonaceous material of the present invention can be suitably used as a negative electrode active material for a nonaqueous electrolyte secondary battery. The present invention also provides a negative electrode for a nonaqueous electrolyte secondary battery that contains the carbonaceous material of the present invention, and a nonaqueous electrolyte secondary battery that has the negative electrode.

The method for producing the negative electrode for the non-aqueous electrolyte secondary battery of the present invention will be specifically described below. The negative electrode of the present invention is prepared, for example, by adding a binder to the carbonaceous material of the present invention, adding an appropriate amount of a suitable solvent, and then kneading these to prepare an electrode mixture. The obtained electrode mixture can be applied to a current collector made of a metal plate or the like, dried, and then pressure-molded to produce the negative electrode for the non-aqueous electrolyte secondary battery of the present invention.

By using the carbonaceous material of the present invention, an electrode (negative 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, a mixture of SBR and CMC is preferable because the SBR and CMC attached to the surface of the active material do not inhibit the movement of lithium ions, and good input/output characteristics can be obtained. A polar solvent such as water is preferably used to dissolve the aqueous emulsion of SBR or CMC to form a slurry, but a solvent-based emulsion of PVDF or the like can also be dissolved in N-methylpyrrolidone 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. Also, 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 to be added varies depending on the type of binder used. For example, in binders that use water as a solvent, a mixture of SBR and CMC is often used in combination, and the total amount of all binders used is preferably 0.5 to 5 mass%, more preferably 1 to 4 mass%. On the other hand, in PVDF-based binders, the amount is preferably 3 to 13 mass%, more preferably 3 to 10 mass%. The amount of the carbonaceous material of the present invention in the electrode mixture is preferably 80 mass% or more, more preferably 90 mass% or more. The amount of the carbonaceous material of the present invention in the electrode mixture is preferably 100 mass% or less, more preferably 97 mass% or less.

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 and separators are required, which is preferable for high 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 thickness of the active material layer (per side) is preferably 10 to 80 μm, more preferably 20 to 75 μm, and even more preferably 30 to 75 μm.

The nonaqueous electrolyte secondary battery of the present invention includes the negative electrode for a nonaqueous electrolyte secondary battery of the present invention. A nonaqueous electrolyte secondary battery having a negative electrode for a nonaqueous electrolyte secondary battery that includes the carbonaceous material of the present invention has a high charge/discharge capacity.

When the carbonaceous material of the present invention is used to form a negative electrode for a non-aqueous electrolyte 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 non-aqueous solvent secondary batteries can be used.

For example, the positive electrode material may be a layered oxide (represented as _LiMO2 or _NaMO2 , where M is a metal: for example, _LiCoO2 , _LiNiO2 , _LiMnO2 , _NaFeO2 , _NaNiO2 , _NaCoO2 , _NaMnO2 , _NaVO2 or LiNi _x Co _y Mn _{z O2} , NaNi _x Mn _{z O2} (where x, y, and z represent the composition ratio)), an olivine (represented as _LiMPO4 or _NaMPO4 , where M is a metal: for example, _LiFePO4 , _NaFePO4 , etc.), a spinel (represented as LiM2O4 or NaM2O4, where M is a metal: for example, _LiMn2O4 , NaMn2O4, etc.), or a zeolite (represented as _LiM2O4 or _NaM2O4 , where M is a metal: for example _{, LiMn2O4} , _{NaMn2O4 ,} etc.). The composite metal chalcogen compounds of the above-mentioned formulas (1) to ₍₄ ) are preferred, and these chalcogen compounds may be mixed and used as necessary. The positive electrode material is molded together with a suitable binder and a carbon material for imparting electrical conductivity to the electrode, and the molded 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, which may be, for example, one or more of organic solvents such as propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, dimethoxyethane, diethoxyethane, γ-butyllactone, tetrahydrofuran, 2-methyltetrahydrofuran, sulfolane, or 1,3-dioxolane, which may be used alone or in combination. As the electrolyte, for lithium ion secondary batteries, _LiClO4 , _LiPF6 , _LiBF4 , _{LiCF3SO3 , LiAsF6} , LiCl, LiBr, LiB( _C6H5 ) ₄ , LiN( _SO3CF3 ) ₂ , etc. are used, and for sodium ion secondary batteries _{, NaClO4} , _NaPF6 , _NaBF4 , _{NaCF3SO3 , NaAsF6} , NaCl, NaBr, NaB( _C6H5 ) ₄ , NaN _{( SO3CF3 ) 2 ,} etc. are used.

Non-aqueous electrolyte secondary batteries are generally formed by placing the positive and negative electrodes formed as described above opposite each other, with a liquid-permeable separator interposed between them as necessary, and immersing them in an electrolyte. As such a separator, a nonwoven fabric or other permeable or liquid-permeable separator made of a 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.

The carbonaceous material of the present invention is suitable as a carbonaceous material for batteries (typically nonaqueous electrolyte secondary batteries for driving vehicles) mounted on vehicles such as automobiles. In the present invention, the vehicle can be, without particular limitation, what is usually known as an electric vehicle, a hybrid vehicle with a fuel cell or an internal combustion engine, etc., and is equipped with at least a power supply device equipped with the above-mentioned battery, an electric drive mechanism driven by power supply from the power supply device, and a control device for controlling this. The vehicle may further be equipped with a generator brake or a regenerative brake, and a mechanism for converting energy generated by braking into electricity and charging the nonaqueous electrolyte secondary battery.

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

(Elemental Analysis)
Elemental analysis was carried out based on the inert gas dissolution method using an oxygen/nitrogen/hydrogen analyzer EMGA-930 manufactured by Horiba, Ltd.
The detection methods of this device are oxygen: inert gas fusion-non-dispersive infrared absorption (NDIR), nitrogen: inert gas fusion-thermal conduction (TCD), and hydrogen: inert gas fusion-non-dispersive infrared absorption (NDIR). Calibration was performed with (oxygen/nitrogen) Ni capsule, TiH ₂ (H standard sample), and SS-3 (N, O standard sample). As a pretreatment, 20 mg of a sample whose moisture content was measured at 250°C for about 10 minutes was placed in a Ni capsule and degassed for 30 seconds in an elemental analyzer before measurement. Three samples were analyzed in the test, and the average value was used as the analytical value. As described above, the nitrogen element content, oxygen element content, and hydrogen element content in the sample were obtained.

<Measurement of carbon monoxide or carbon dioxide amount when thermally decomposed in the absence of oxygen>
In the above elemental analysis, after the Sn capsule was inserted, the temperature was raised at a rate of 10°C/sec, and the detection intensity of carbon monoxide or carbon dioxide, which is an oxygen compound decomposition gas, was plotted against the detection temperature, and the cumulative detection amount ratio in each temperature range was calculated.

(Raman spectrum)
Using a Raman spectrometer (Horiba, Ltd.'s "LabRAM ARAMIS (VIS)"), the particles to be measured (carbonaceous material or carbide) were set on the observation stage, the objective lens was set at 100x magnification, the focus was adjusted, and measurements were performed while irradiating argon ion laser light. The details of the measurement conditions are as follows, and the half-width value of the peak near 1360 cm ^-1 in the obtained Raman spectrum and the intensity ratio (R value, I ₁₃₆₀ /I ₁₅₈₀ ) between the peak intensity near 1360 cm ^-1 in the Raman spectrum (I 1360 ) and the peak intensity near _{1580 cm -1 (I 1580} ⁾ _were calculated.
Wavelength of argon ion laser light: 532 nm
Laser power on sample: 15 mW
Resolution: 5-7cm ^-1
Measurement range: 50-2000 ^cm
Exposure time: 1 second Number of integrations: 100 Peak intensity measurement: Baseline correction Automatic correction with Polynom-3rd order
Peak search and fitting processing GaussLoren

(Specific surface area by nitrogen adsorption BET method)
The approximate formula derived from the BET formula is shown below.

Using the above approximation formula, the amount of adsorption (v) actually measured at a given relative pressure (p/p ₀ ) by the multipoint method using nitrogen adsorption at liquid nitrogen temperature was substituted to determine v _m , and the specific surface area (SSA: unit is m ² g ⁻¹ ) of the sample was calculated using the following formula.

In the above formula, _vm is the adsorption amount ( ^cm3 /g) required to form a monolayer on the sample surface, v is the measured adsorption amount ( ^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 carbonaceous material at liquid nitrogen temperature was measured using "Autosorb-iQ-MP" manufactured by Quantachrome, as follows. The measurement sample was filled into a sample tube, and the sample tube was cooled to -196°C, and then the pressure was reduced once, and nitrogen (purity 99.999%) was adsorbed into the measurement sample at a desired relative pressure. The amount of nitrogen adsorbed into the sample when equilibrium pressure was reached at each desired relative pressure was defined as the amount of adsorbed gas v.

(Average particle diameter _D50 measured by laser scattering method)
The average particle size (particle size distribution) of the carbonaceous material or carbide was measured by the following method. The sample was put into an aqueous solution containing 5% by mass of a surfactant ("ToritonX100" 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 device ("Microtrac MT3300EXII" manufactured by Microtrac Bell Co., Ltd.). _D50 is the particle size at which the cumulative volume is 50%, and this value was used as the average particle size.

(X-ray diffraction)
The powder of the carbonaceous material or carbide was filled into a sample holder, and X-ray diffraction measurements were performed using a MiniFlex II manufactured by Rigaku Corp. The radiation source was CuKα (λ=1.5418 Å), and the scanning range was 10°<2θ<35°.

(Nitrogen-containing gas emissions)
The amount of nitrogen-containing gas discharged during firing of the raw material was calculated as follows: The weight of nitrogen per 100 g of the raw material and the weight of nitrogen in the carbonaceous material obtained from the raw material were calculated based on the nitrogen element content by elemental analysis. The difference in the weight of nitrogen was calculated as the amount of nitrogen-containing gas emitted. In reality, gas is emitted in the form of nitrogen combined with oxygen and carbon, so the amount of emissions is less than the calculated value. Elemental analysis involves the use of powder samples, but the coconut shells used in Comparative Example 3 could not be powdered, and analysis was not possible due to problems with the measurement method. It was stated that nitrogen gas emissions could not be measured.

Example 1
After dissolving 5.0 g of citric acid in 60 mL of pure water, 50 g of starch was added, mixed with a spatula, and dried at 50° C. to obtain a mixture containing low molecular weight starch. The obtained mixture was heated to 130° C. in a nitrogen gas atmosphere. At this time, the heating rate to 130° C. was 600° C./hour (10° C./minute). A carbon precursor was obtained by heat treatment at 130° C. for 5 hours under a nitrogen gas flow. At this time, the nitrogen gas supply rate was 1 L/minute per 20 g of starch.
The carbon precursor was heated to 600°C in a nitrogen gas atmosphere. At this time, the heating rate up to 600°C was 600°C/hour (10°C/minute). Next, the carbonized material was obtained by heat-treating the material at 600°C for 60 minutes under a nitrogen gas flow (first firing). At this time, the nitrogen gas supply rate was 3 L/minute per 40 g of the carbon precursor. The obtained carbide was then pulverized in a ball mill to obtain a pulverized carbide. Next, the pulverized carbide was heated to 1200°C and heat-treated at 1200°C for 60 minutes to obtain a carbonaceous material (second firing). At this time, the heating rate up to 1200°C was 600°C/hour (10°C/minute). The heating and heat treatment were performed under a nitrogen gas flow. The nitrogen gas supply rate was 3 L/minute per 5 g of pulverized carbide.

Example 2
A mixture was obtained by mixing 5.0 g of citric acid and 50 g of starch in powder form. The mixture was heated to 130° C. in a nitrogen gas atmosphere. The heating rate to 130° C. was 600° C./hour (10° C./minute). A carbon precursor was obtained by heat-treating the mixture at 130° C. for 5 hours under a nitrogen gas flow. The nitrogen gas supply rate was 1 L/minute per 20 g of starch.
This carbon precursor was used in place of the carbon precursor of Example 1, and the first firing, pulverization, and second firing were carried out in the same manner as in Example 1 to obtain a carbonaceous material.

Example 3
A carbonaceous material was obtained in the same manner as in Example 2, except that 5.0 g of citric acid was replaced with 3.8 g of adipic acid.

Example 4
A mixture was obtained by mixing 4.3 g of terephthalic acid and 50 g of starch in powder form. This mixture was used instead of the carbon precursor of Example 1, and a carbonaceous material was obtained by carrying out the first firing, pulverization, and second firing in the same manner as in Example 1.

Example 5
Instead of the carbon precursor of Example 1, 40 g of dextrin was used, and the first baking, pulverization, and second baking were carried out in the same manner as in Example 1 to obtain a carbonaceous material.

(Comparative Example 1)
A carbonaceous material was obtained in the same manner as in Example 5, except that 40 g of starch was used instead of 40 g of dextrin.

(Comparative Example 2)
Glucose and ammonium chloride were mixed in a mortar. The mixture was heated to 1000°C in a nitrogen gas atmosphere. At this time, the heating rate to 1000°C was 240°C/hour (4°C/minute). Next, the mixture was heat-treated at 1000°C for 60 minutes under a nitrogen gas flow to obtain a carbonized material (first firing). At this time, the amount of nitrogen gas supplied was 1 L/minute per 5 g of glucose. Then, the obtained carbonized material was pulverized in a ball mill to obtain a pulverized carbide. Next, the pulverized carbide was heated to 1200°C and heat-treated at 1200°C for 60 minutes to obtain a carbonaceous material (second firing step). At this time, the heating rate to 1200°C was 600°C/hour (10°C/minute). The above heating and heat treatment were performed under a nitrogen gas flow. The amount of nitrogen gas supplied was 3 L/minute per 5 g of pulverized carbide.

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

(Comparative Example 4)
A mixture was obtained by mixing 43 g of citric acid and 100 g of starch in powder form. The mixture was heated to 160° C. in a nitrogen gas atmosphere. A carbon precursor was obtained by heat-treating the mixture at 160° C. for 3 minutes under a nitrogen gas flow.
The carbon precursor was heated to 600°C in a nitrogen gas atmosphere. Then, the carbonization treatment was performed by heat treatment at 600°C for 30 minutes under a nitrogen gas flow, and a carbide was obtained (first firing). At this time, the supply amount of nitrogen gas was 1 L/min per 10 g of the carbon precursor. Next, the obtained carbide was pulverized in a ball mill to obtain a pulverized carbide. Thereafter, the pulverized carbide was heated to 800°C and heat-treated at 800°C for 60 minutes to obtain a carbonaceous material (second firing). At this time, the heating rate up to 800°C was 600°C/hour (10°C/min). The above heating and heat treatment were performed under a nitrogen gas flow. The supply amount of nitrogen gas was 3 L/min per 5 g of pulverized carbide.

(Preparation of electrodes)
Using each of the carbonaceous materials obtained in each of the Examples and Comparative Examples, negative electrodes were produced according to the following procedure.
A slurry was obtained by mixing 95 parts by mass of a carbonaceous material, 2 parts by mass of conductive carbon black ("Super-P (registered trademark)" manufactured by TIMICAL), 1 part by mass of CMC, 2 parts by mass of SBR, and 90 parts by mass of water. The obtained slurry was applied to a copper foil having a thickness of 18 μm, dried, and pressed to obtain an electrode having a thickness of 45 μm.

(Initial battery capacity and charge/discharge efficiency)
The electrode prepared above was used as the working electrode, and metallic lithium was used as the counter electrode and reference electrode. As the solvent, ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate were mixed in a volume ratio of 1:1:1 and used. _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.
A charge/discharge test was performed on the lithium secondary battery having the above configuration 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, until the lithium potential reached 1 mV. A constant voltage of 1 mV was applied to the lithium potential for 8 hours to terminate the doping. The capacity (mAh/g) at this time was taken as the charge capacity. Next, dedoping was performed at a rate of 70 mA/g relative to the active material mass until the lithium potential reached 2.5 V, and the capacity discharged at this time was taken as the discharge capacity. The percentage of the discharge capacity/charge capacity was taken as the charge/discharge efficiency (initial charge/discharge efficiency), which was used as an index of the utilization efficiency of lithium ions in the battery. The results obtained are shown in Table 4 as the charge capacity, discharge capacity, and charge/discharge efficiency.

The manufacturing conditions for the carbonaceous materials in each example and comparative example, the evaluation results of the physical properties of the obtained carbonaceous materials, and the evaluation results of the battery characteristics are shown in the following tables.

Examples 1 to 5 are carbonaceous materials whose nitrogen element content determined by elemental analysis is 0.3% by mass or more and less than 1.0% by mass, and whose absorption intensity ratio at 1350°C to the absorption intensity at 1000°C is 0.45 or more and 3.0 or less, in the amount of oxygen detected as carbon monoxide or carbon dioxide by elemental analysis. These carbonaceous materials emit small amounts of nitrogen-containing gas during production, and batteries made using the carbonaceous materials exhibit high discharge capacity and good charge/discharge efficiency.

In contrast, Comparative Examples 1, 3, and 4 are carbonaceous materials in which the ratio of absorption intensity at 1350°C to absorption intensity at 1000°C is less than 0.45 in the amount of oxygen detected as carbon monoxide or carbon dioxide by elemental analysis. The batteries fabricated using these carbonaceous materials had low discharge capacities in Comparative Examples 1 and 3, and low discharge capacity and charge/discharge efficiency in Comparative Example 4.

Comparative Example 2 is a carbonaceous material with a nitrogen element content of 1.0 mass% or more as determined by elemental analysis. In this case, the amount of nitrogen-containing gas discharged was large.

* Emissions per 100g of raw material.

*Ratio of absorption intensity at 1350°C to absorption intensity at 1000°C

Claims (7)

A carbonaceous material having a nitrogen element content determined by elemental analysis of 0.3 mass% or more and less than 1.0 mass%, an oxygen content determined by elemental analysis of 1.0 mass% or more, an absorption intensity ratio at 1350°C to an absorption intensity at 1000°C of 0.60 or more and 3.0 or less, in an amount of oxygen detected as carbon monoxide or carbon dioxide by elemental analysis, and a half-width value of a peak near 1360 cm ^-1 in a Raman spectrum observed by laser Raman spectroscopy of 180 cm ^-1 or more and 230 cm ^-1 or less . 2. The carbonaceous material according to claim 1, which has a specific surface area, as determined by the BET method, of 100 m ² /g or less. The carbonaceous material according to claim 1 or 2 , having an average particle size _D50 of 30 μm or less. The carbonaceous material according to any one of claims 1 to 3 , wherein the carbon interplanar spacing _d002 calculated using the Bragg equation by wide-angle X-ray diffraction is 3.75 Å or more. The carbonaceous material according to any one of claims 1 to 4 , which is derived from a substance having a saccharide skeleton. A negative electrode for a non-aqueous electrolyte secondary battery, comprising the carbonaceous material according to any one of claims 1 to 5 . A non-aqueous electrolyte secondary battery comprising the negative electrode for non-aqueous electrolyte secondary batteries according to claim 6 .