JPWO2020071428A1 - Carbon precursor and method for producing carbon precursor - Google Patents

Abstract

The present invention is the ratio of oxygen atom content to carbon atom content by elemental analysis (O / C) is 0.10 to 0.85, and the intensity of the peak near 1720 cm ^-1 in the IR spectrum _{(I A} ) and 3330cm ratio of ^-1 near the peak intensity _{(I B) (I a /} I B) is 0.50 or more, to provide a carbon precursor.

Description

The present invention relates to a carbon precursor useful for producing a carbonaceous material suitable for a negative electrode active material of a non-aqueous electrolyte secondary battery, and a method for producing the carbon precursor.

Non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries are widely used in small portable devices such as mobile phones and notebook computers because of their high energy density and excellent output characteristics. In recent years, its application to in-vehicle applications such as hybrid vehicles and electric vehicles has been promoted. As a negative electrode material for a lithium ion secondary battery, non-graphitizable carbon capable of doping (charging) and dedoping (discharging) lithium in an amount exceeding the theoretical capacity of graphite of 372 mAh / g has been developed and used. ..

As the raw material for the refractory carbon, a resin composition such as petroleum pitch, coal pitch, phenol resin, and a plant-derived raw material such as coconut shell are used. From the viewpoint of raw material cost, plant-derived raw materials are preferable, but since many plant-derived raw materials contain impurity metals, a purification step is required to stabilize the quality as an industrial raw material.

Among the plant-derived raw materials, those that have undergone a purification step in advance include, for example, sugars such as starch, and attempts have been made to obtain carbon materials using these (for example, Non-Patent Document 1). Further, as a method of denaturing sugars, a method of lowering the viscosity by roasting starch at a high temperature is also known (Patent Document 1).

Japanese Unexamined Patent Publication No. 2012-100650

Materials Letters 2008, Vol. 62, pp. 3322-3324

In recent years, application of lithium ion secondary batteries to in-vehicle applications and the like has been studied, and further increase in capacity of lithium ion secondary batteries is required. Further, in order to further enhance the input / output characteristics of the non-aqueous electrolyte secondary battery, a carbonaceous material that provides a battery having a low internal resistance is also required.

For example, the carbon material described in Non-Patent Document 1 has a graphite-like structure and does not have a sufficient charge / discharge capacity. Further, in order to obtain graphitizable carbon having a high discharge capacity using saccharides, it is conceivable to modify the saccharides to adjust the structure. For example, the method described in Patent Document 1 is mainly used. This method is oriented toward food applications, and is not suitable as a method for obtaining a precursor of graphitizable carbon having a high discharge capacity.

Therefore, the present invention is suitable for the negative electrode active material of a non-aqueous electrolyte secondary battery (for example, lithium ion secondary battery, sodium ion secondary battery, lithium sulfur battery, lithium air battery) having high charge / discharge capacity and low resistance. It is an object of the present invention to provide a carbon precursor useful for producing a carbonaceous material.

As a result of diligent studies to solve the above problems, the present inventor has found that the ratio (O / C) of the oxygen atom content to the carbon atom content by elemental analysis is 0.10 to 0.85. the carbon precursor ratio of the peak intensity at 1720 cm ^-1 vicinity of the intensity of peak _{(I a)} and 3330cm around ^-1 of the IR spectrum _{(I B) (I a /} I B) is 0.50 or more, the We have found that the problems can be solved and have completed the present invention.

That is, the present invention includes the following preferred embodiments.
[1] is the ratio of oxygen atom content by elemental analysis and the carbon atom content (O / C) is 0.10 to 0.85, and the intensity of the peak near 1720 cm ^-1 in the IR spectrum _(I A) and 3330cm ratio of ^-1 near the peak intensity _{(I B) (I a /} I B) is 0.50 or more, carbon precursor.
[2] The carbon precursor according to the above [1], which does not have an endothermic peak in the range of 100 to 500 ° C. in the DTA curve measured by TG-DTA.
[3] The carbon precursor according to the above [1] or [2], which has a peak in the range of 0 to 50 ppm in the ^{13 C-NMR spectrum.}
[4] The carbon precursor according to any one of [1] to [3] above, which is derived from a substance having a saccharide skeleton.
[5] The raw material of the carbon precursor is heat-treated in a temperature range of 215 to 240 ° C. for 1 to 12 hours under the supply of an oxygen-containing gas to obtain a carbon precursor, according to any one of the above [1] to [4]. The method for producing a carbon precursor according to the above.
[6] The production method according to the above [5], wherein the supply amount of the oxygen-containing gas is 0.005 to 5.0 L / (minute · m ^{2) per unit surface area of the raw material of the carbon precursor.}

According to the present invention, it is possible to provide a carbon precursor useful for producing a carbonaceous material suitable for a negative electrode active material of a non-aqueous electrolyte secondary battery having a high charge / discharge capacity and a low resistance.

It is a figure which shows the SEM image of the carbon precursor obtained in Example 1. FIG. It is a figure which shows the SEM image of the carbon precursor obtained in the comparative example 1. FIG.

Hereinafter, embodiments of the present invention will be described in detail. 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 present invention, the carbon precursor is a raw material used for producing a carbonaceous material, which is obtained by subjecting a raw material of a carbon precursor such as a carbohydrate, a plant raw material, or a substance having a saccharide skeleton to, for example, heat treatment. .. The carbon precursor of the present invention is a substance that can be led to a carbonaceous material by, for example, further heat-treating at a high temperature.

The carbon precursor of the present invention is produced by subjecting a raw material of the carbon precursor to, for example, heat treatment. In such a heat treatment step, it is considered that the physically adsorbed water contained in the substance as a raw material of the carbon precursor is dried and a dehydration reaction occurs at the molecular level. When the drying and dehydration of water in the above steps are insufficient, a large amount of water vapor is generated from the carbon precursor when the carbon precursor is further heat-treated at a high temperature in order to obtain a carbonaceous material, and the water vapor causes carbon. It was revealed that the precursor melted and a carbonaceous material having a structure suitable for increasing the charge / discharge capacity could not be obtained. Further, when the dehydration reaction in the above step proceeds too much, the structure is over-immobilized and it is difficult for the structure to be formed in the subsequent heat treatment. Therefore, the carbon precursor is heated at a high temperature in order to obtain a carbonaceous material. It was found that during further heat treatment, sites that absorb and desorb lithium ions are unlikely to be formed.

Further, when the raw material of the carbon precursor is subjected to, for example, heat treatment to produce the carbon precursor of the present invention, in addition to the dehydration reaction described above, a cross-linking reaction in which a cross-linked structure having a carbonyl group is formed proceeds. it seems to do. The mechanism by which the above crosslinked structure is formed is not clear, but due to the formation of such a structure, there are sites that absorb and desorb lithium ions when the carbon precursor is further heat-treated at a high temperature to obtain a carbonaceous material. It was found that it was easily formed, and as a result, it was easy to increase the charge / discharge capacity of the non-aqueous electrolyte secondary battery and to reduce the resistance.

From the above viewpoint, in the carbon precursor of the present invention, the ratio (O / C) of the oxygen atom content to the carbon atom content by elemental analysis is 0.10 to 0.85. When the ratio of the oxygen atom content to the carbon atom content is larger than 0.85, the drying and dehydration of water in the above step is insufficient, and when the ratio is smaller than 0.10, the dehydration reaction occurs. It can be said that it is progressing too much. The ratio of the oxygen atom content to the carbon atom content is preferable from the viewpoint that it is easy to prevent the carbon precursor from melting, it is easy to form a structure that absorbs and desorbs lithium ions, and as a result, it is easy to increase the charge / discharge capacity. Is 0.2 or more and 0.80 or less, more preferably 0.3 or more and 0.79 or less, and further preferably 0.4 or more and 0.78 or less.

In the carbon precursor of the present invention, the oxygen atom content by elemental analysis is preferably 35% by mass or more, more preferably 38% by mass or more, and even more preferably 40% by mass or more. The oxygen atom content is preferably 45% by mass or less, more preferably 43% by mass or less, and even more preferably 42% by mass or less. When the oxygen atom content is within the above range, it is easy to prevent the carbon precursor from melting, and it is easy to form a structure that absorbs and desorbs lithium ions.

In the carbon precursor of the present invention, the carbon atom content by elemental analysis is preferably 45% by mass or more, more preferably 48% by mass or more, still more preferably 50% by mass or more, and particularly preferably 51% by mass or more. .. The carbon atom content is preferably 60% by mass or less, more preferably 57% by mass or less, still more preferably 55% by mass or less, and particularly preferably 54% by mass or less. When the carbon atom content is within the above range, it is easy to prevent the carbon precursor from melting, and it is easy to form a structure that absorbs and desorbs lithium ions.

The details of the measurement of the oxygen atom content and the carbon atom content are as described later, and are measured by an elemental analysis method (inert gas dissolution method). Further, the ratio (O / C) of the oxygen atom content to the carbon atom content can be calculated by dividing the oxygen atom content by the carbon atom content. The method for adjusting the ratio to the above range is not limited, and for example, a method of heat-treating the raw material of the carbon precursor in a temperature range of 215 to 240 ° C. for 1 to 12 hr under the supply of an oxygen-containing gas can be used. can. In particular, if the amount of the raw material of the carbon precursor is increased or the amount of the oxygen-containing gas supplied is reduced, it becomes difficult to remove water vapor when the dehydration reaction occurs, and the raw material reacts hydrothermally with the water vapor, and as a result, contains oxygen atoms. The amount tends to increase. Therefore, the ratio of the oxygen atom content and the carbon atom content can be adjusted within the above range by adjusting the amount of the raw material and the supply amount of the oxygen-containing gas.

In the carbon precursor of the present invention, the ratio of the peak intensity at 1720cm around ^-1 of the IR spectrum _{(I A)} and 3330Cm ^-1 near the peak intensity _{(I B) (I A /} I B) is 0.50 That is all. Peak around 1720 cm ^-1 of the IR spectrum _{(I A)} is a peak derived from a carbonyl group, are observed in the normal 1695~1750cm ^-1. Further, 3330Cm ^-1 vicinity of the peak _{(I B)} is a peak derived from a hydroxyl group, are observed in the normal 3200~3600cm ^-1. In the heat treatment in the preparation of the carbon precursor, I _A increases the crosslinking reaction crosslinked structure having a carbonyl group is formed proceeds, at the same time, the I _B decreases as dehydration reaction proceeds. By these reactions proceed, it is considered to be I A _/ I _B increases. I and A _/ I _B is 0.50 less than, or crosslinking reaction is insufficient, because dehydration reaction is insufficient, when performing heat treatment at a high temperature to obtain a carbonaceous material from a carbon precursor , The carbon precursor melts. Prevent melting of the carbon precursor, the lithium ions to form a structure for adsorption and desorption, the discharge capacity from the enhanced easily standpoint, I A _/ I _B is preferably 0.55 or more, more preferably, 0.60 or more , More preferably 0.65 or more. While I limit A _/ I _B is not particularly limited, from the viewpoint of not too allowed to proceed dehydration reaction, preferably 2.0 or less, more preferably 1.6 or less.

In the carbon precursor of the present invention, the peak intensity _{(I A)} in the vicinity of 1720 cm ^-1 of the IR spectrum, preferably 0.005 to 0.05, more preferably 0.008 to 0.045, more preferably 0. It is 010 to 0.040. Within the range 1720 cm ^-1 vicinity of the peak intensity (I _A) is in the above, easy to prevent melting of the carbon precursor, it tends to form a structure that desorb lithium ions.

In the carbon precursor of the present invention, the peak intensity in the vicinity of 3330cm ^-1 of the IR spectrum _{(I B)} is preferably from 0.015 to 0.060, more preferably from 0.020 to 0.055, more preferably 0. It is 025 to 0.050. Within the range 3330cm ^-1 vicinity of the peak intensity (I _B) is in the above, easy to prevent melting of the carbon precursor, it tends to form a structure that desorb lithium ions.

The details of the IR measuring method are as described in Examples, and the IR is measured by the ATR method (total reflection measuring method) described later. A method of adjusting the I _A / _{I B} in the above range is not limited in any way, for example, the raw material of the carbon precursor under supply of oxygen-containing gas, a method of 1~12hr heat treated at a temperature in the range of 215-240 ° C. Can be used. In particular, if the amount of the raw material of the carbon precursor is increased or the amount of oxygen-containing gas supplied is reduced, it becomes difficult for the cross-linking reaction to proceed and it becomes difficult to remove water vapor when the dehydration reaction occurs, and the raw materials are water vapor and water heat. react. As a result, _{I A} is small, and / or, the greater the _{I B,} there is a tendency that the I A / _{I B} is reduced. Therefore, by adjusting the supply amount of the raw material amounts and oxygen-containing gas, it is possible to adjust the I A _/ I _B in the above range.

The carbon precursor of the present invention preferably does not have an endothermic peak in the range of 100 to 500 ° C. in the DTA curve measured by TG-DTA. Having an endothermic peak in the above temperature range means having a melting point in the above temperature range. When the carbon precursor does not have a heat absorption peak between 100 and 500 ° C., the carbon structure in the carbon precursor is immobilized and when heat treatment is performed at a high temperature to obtain a carbonaceous material from the carbon precursor. It is considered that the carbon precursor is hard to melt, the charge / discharge capacity of the obtained non-aqueous electrolyte secondary battery is easily increased, and the resistance is easily reduced. Details of the TG-DTA measurement are as described in the Examples. In the DTA curve, the method of eliminating the endothermic peak between 100 and 500 ° C. is not limited, but for example, the raw material of the carbon precursor is provided in a temperature range of 215 to 240 ° C. under the supply of an oxygen-containing gas. A method of heat-treating for 1 to 12 hours can be used. In particular, when the amount of the raw material of the carbon precursor is increased and the amount of the oxygen-containing gas supplied is reduced, the structure tends to have an endothermic peak between 100 and 500 ° C. Therefore, by adjusting the amount of the raw material and the supply amount of the oxygen-containing gas, it is possible to adjust so as not to have an endothermic peak in the range of 100 to 500 ° C.

The carbon precursor of the present invention preferably has a peak between 0 and 50 ppm ^{in the 13 C-NMR spectrum. 13 The} peak observed between 0 and 50 ppm in the C-NMR spectrum is a peak derived from carbon of a methyl group, a methylene group, or a methine group. Having a peak in the above range means that the structure of the saturated hydrocarbon is included in the structure of the carbon precursor. Since saturated hydrocarbons have the effect of bridging the structural skeletons of carbon precursors, the inclusion of the saturated hydrocarbon structure in the carbon precursor fixes the structure of the carbon precursor and makes it difficult to melt. Become. As a mechanism for forming the structure of the saturated hydrocarbon, it is conceivable that a part of the alicyclic structure contained in the raw material is opened and re-reacted by a dehydration reaction or the like. ¹³ Details of C-NMR measurement are as described in Examples, and are measured by the solid-state NMR method described later. ^{13 The} method of having a peak at 0 to 50 ppm by C-NMR is not limited, but for example, the raw material of the carbon precursor is heat-treated for 1 to 12 hr in a temperature range of 215 to 240 ° C. under the supply of an oxygen-containing gas. Can be used. In particular, when the heat treatment temperature is high, the alicyclic structure is difficult to open and the crosslinked structure is difficult to form, so that the peak tends not to be observed between 0 and 50 ppm. Therefore, by adjusting the heat treatment temperature, it is possible to have a peak in the above range.

In the carbon precursor of the present invention, the circularity measured by the shape particle size distribution measurement is preferably 0.95 or more, more preferably 0.97 or more, still more preferably 0.980 or more, still more preferably 0. It is 981 or more, particularly preferably 0.983 or more. When the circularity is equal to or higher than the above lower limit, it is considered that the immobilization of the structure has sufficiently progressed and the carbon precursor particles have not been melted or the carbon precursor particles have not been fused to each other. As a result, it is easy to promote the structural immobilization of the carbon precursor, form a structure for absorbing and desorbing lithium ions, and easily increase the charge / discharge capacity. Further, in the carbonaceous material obtained from the carbon precursor, the electrode density can be easily increased. The details of the method for measuring the circularity are as described in Examples, and the measurement is performed by the shape particle size distribution measuring method described later. The method for adjusting the circularity to the above range is not limited, and for example, a method of heat-treating the raw material of the carbon precursor in a temperature range of 215 to 240 ° C. for 1 to 12 hr under the supply of an oxygen-containing gas can be used. can. In particular, if the amount of the raw material of the carbon precursor is increased and the supply amount of the oxygen-containing gas is reduced, the carbon precursor is likely to be melted when the carbonaceous material is produced from the carbon precursor. Therefore, the circularity can be adjusted within the above range by adjusting the amount of the raw material and the supply amount of the oxygen-containing gas to prevent the carbon precursor from melting.

_{The average particle size (D 50} ) of the carbon precursor of the present invention is preferably 30 μm or less, more preferably 25 μm or less, even more preferably 20 μm or less, even more preferably 18 μm or less, particularly preferably 16 μm or less, most preferably. It is 15 μm or less. When the mean particle size is not more than the above upper limit, the coatability at the time of electrode fabrication is good, and the diffusion free path of lithium ions in the particles of the carbonaceous material obtained from the carbon precursor is small. Therefore, rapid charge / discharge can be easily obtained. Furthermore, in lithium-ion secondary batteries, it is important to increase the electrode area in order to improve the input / output characteristics, and for that purpose, it is necessary to reduce the coating thickness of the active material on the current collector plate when preparing the electrodes. There is. When the average particle size of the carbon precursor is equal to or less than the above upper limit, the average particle size of the carbonaceous material as the active material is likely to be reduced, and as a result, the coating thickness is likely to be reduced at the time of electrode preparation. The average particle diameter D ₅₀ of the carbon precursor of the present invention is preferably 2μm or more, more preferably 3μm or more, even more preferably 4μm or more, still more preferably 5μm or more, even more preferably 6μm or more, even more It is preferably 7 μm or more, even more preferably 8 μm or more, and particularly preferably 9 μm or more. When the average particle size D ₅₀ is equal to or higher than the above lower limit, the increase in specific surface area and the increase in reactivity with the electrolytic solution due to the fine powder of the carbonaceous material derived from the fine powder in the carbon precursor are suppressed, and the irreversible capacity is increased. Is easy to suppress. Further, when a negative electrode is manufactured using a carbonaceous material obtained from a carbon precursor, it is easy to secure voids formed between the carbonaceous materials, and it is difficult to suppress the movement of lithium ions in the electrolytic solution. It tends to reduce the resistance of non-aqueous electrolyte secondary batteries. The average particle size D ₅₀ is a particle size at which the cumulative volume is 50%. For example, the particle size distribution is performed by a laser scattering method using a particle size / particle size distribution measuring device (“Microtrack MT3300EXII” manufactured by Microtrack Bell Co., Ltd.). Can be obtained by measuring.

The method for producing the carbon precursor of the present invention is not particularly limited as long as a carbon precursor having the above characteristics can be obtained, but for example, it can be produced by using the production method described later.

The present invention is suitable for negative electrode active materials or conductive materials of non-aqueous electrolyte secondary batteries (eg, lithium ion secondary batteries, sodium ion batteries, lithium sulfur batteries, lithium air batteries) having high charge / discharge capacity and low resistance. Also provided are methods of producing carbon precursors that are useful in producing carbonaceous materials.

In one aspect of the present invention, the method for producing a carbon precursor of the present invention is:
(1) A production method in which a raw material of a carbon precursor is heat-treated in a temperature range of 215 to 240 ° C. for 1 to 12 hours under the supply of an oxygen-containing gas to obtain a carbon precursor.

In another aspect of the present invention, the method for producing a carbonaceous material of the present invention is:
(2) A mixture obtained by mixing a raw material of a carbon precursor with at least one heat-resistant oil of 80 to 500 parts by mass with respect to 50 parts by mass of the raw material is obtained in a temperature range of 150 to 300 ° C. This is a production method in which a carbon precursor is obtained by heat treatment for 5 to 12 hours.

The raw materials for the carbon precursors described in the above-mentioned production methods (1) and (2) are given the carbon precursor of the present invention through subsequent steps such as heat treatment, and are finally carbonaceous materials through subsequent steps such as heat treatment. The substance is not particularly limited as long as it is a substance that gives By using a substance having a saccharide skeleton as a raw material, a carbon precursor derived from the substance having a saccharide skeleton can be obtained. Examples of substances (sugars) having a saccharide skeleton include monosaccharides such as glucose, galactose, mannose, fructose, ribose, and glucosamine, disaccharides such as sucrose, trehalose, maltose, cellobiose, maltitol, lactobionic acid, and lactosamine, and starch. , Glycogen, agarose, pectin, cellulose, chitin, and polysaccharides such as chitosan. These sugars can be used alone or in combination of two or more. Among these sugars, starch is preferable because it is easily available in large quantities.

The above-mentioned production method (1) of the present invention is a production method for obtaining a carbon precursor by heat-treating a raw material of a carbon precursor in a temperature range of 215 to 240 ° C. for 1 to 12 hours under the supply of an oxygen-containing gas. .. The oxygen-containing gas is not particularly limited as long as it is a gas containing oxygen, but may be air, oxygen, air or a mixed gas of oxygen and another gas such as an inert gas. The oxygen concentration in the oxygen-containing gas is also not particularly limited. From the viewpoint of facilitating the implementation of the process and reducing the manufacturing cost, it is preferable that the oxygen-containing gas is air.

Performing the heat treatment while supplying the oxygen-containing gas means performing the heat treatment while supplying the oxygen-containing gas. Here, for example, the heat treatment of an oxygen-containing gas such as air in a mere atmosphere, for example, the heat treatment in a mere atmosphere, does not mean that the oxygen-containing gas is actively supplied, and the oxygen-containing gas is used. It cannot be said that the heat treatment is performed under the supply. Therefore, such a manufacturing method does not correspond to the manufacturing method (1) of the present invention. The amount of the oxygen-containing gas supplied is not particularly limited as long as it is supplied, but is preferably 0.007 to 3.0 L / (min · m ² ), more preferably 0, per unit surface area of the raw material of the carbon precursor, for example. .009~2.0L / (min · ^m 2), more preferably from 0.01~0.50L / (min · ^{m 2).} The supply amount per unit surface area is calculated by dividing, for example, the supply amount of oxygen-containing gas per minute by the product of the weight of the object to be treated (raw material of the carbon precursor) and the specific surface area.

Here, in the above heat treatment step, the heat treatment dries the physically adsorbed water contained in the raw material of the carbon precursor, and at the same time, a dehydration reaction occurs at the molecular level in the raw material of the carbon precursor, so that the carbon precursor is produced. It is thought that it will be obtained. Further, in the above step, it is considered that a cross-linking reaction in which a cross-linked structure having a carbonyl group is formed is also in progress. By performing this step under the supply of an oxygen-containing gas, the mechanism described later does not limit the present invention at all, but is supplied when water is removed from the raw material of the carbon precursor by drying or dehydration. Oxygen interacts with the raw material of the carbon precursor to form a crosslinked structure with a carbonyl group, and at the same time the water to be removed is removed from the system along with the gas. As a result, it is considered that a carbon precursor that maintains a fine structure can be obtained without melting the raw material of the carbon precursor by heat treatment.

In the production method (1) of the present invention, the temperature of the raw material is raised, and heat treatment is performed in the temperature range of 215 to 240 ° C. for 1 to 12 hours as described above. The heat treatment temperature in the production method (1) of the present invention is preferably 217 to 235 ° C, more preferably 219 to 230 ° C. 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. When the heat treatment temperature and time are within the above ranges, it is easy to efficiently and sufficiently remove water from the raw material of the carbon precursor by drying and dehydration, and it is easy to finally obtain a carbonaceous material having the above characteristics. Conceivable. Here, the heat treatment temperature may be a constant temperature, but is not particularly limited as long as it is within the above range.

The above-mentioned production method (2) of the present invention is a mixture obtained by mixing a raw material of a carbon precursor with at least one heat-resistant oil of 80 to 500 parts by mass with respect to 50 parts by mass of the raw material. This is a production method for obtaining a carbon precursor by heat treatment in a temperature range of about 300 ° C. for 0.5 to 12 hours. The heat-resistant oil is not particularly limited as long as it is a substance that does not volatilize or deteriorate in at least the heat treatment temperature range. For example, silicon oil, fluorine oil, creosote oil, diethylene glycol, triethylene glycol, polyethylene glycol and the like can be used. Can be mentioned.

The amount of the heat-resistant oil to be mixed with the raw material of the carbon precursor is 80 to 500 parts by mass, preferably 100 to 100 parts by mass with respect to 50 parts by mass of the raw material of the carbon precursor from the viewpoint of dispersing the raw materials and making it difficult to cause fusion. It is 400 parts by mass, more preferably 150 to 300 parts by mass, and even more preferably 180 to 280 parts by mass. The method of mixing the raw material of the carbon precursor with the heat-resistant oil is not particularly limited, and the raw material of the carbon precursor may be directly mixed with the heat-resistant oil, or at least one carbon precursor and / or an organic acid may be mixed. It may be mixed in a state of being dispersed and / or dissolved in a liquid. Further, when mixing is performed using at least one kind of liquid, the liquid may be removed by evaporation or the like, if necessary, to obtain a mixture.

Here, in the above heat treatment step, the heat treatment dries the physically adsorbed water contained in the raw material of the carbon precursor, and at the same time, a dehydration reaction occurs at the molecular level in the raw material of the carbon precursor, so that the carbon precursor is produced. It is thought that it will be obtained. Further, in the above step, it is considered that a cross-linking reaction in which a cross-linked structure having a carbonyl group is formed is also in progress. By performing this step in a state of being mixed with the heat-resistant oil, the mechanism described later does not limit the present invention at all, but the water generated by drying and dehydrating the raw material of the carbon precursor is the presence of the heat-resistant oil. It is considered that the carbon precursor is efficiently removed from the surface of the carbon precursor. As a result, it is considered that a carbon precursor that maintains a fine structure can be obtained without melting the raw material of the carbon precursor by heat treatment.

In the production method (2) of the present invention, a mixture obtained by mixing a raw material of a carbon precursor with a heat-resistant oil is heat-treated in a temperature range of 50 to 300 ° C. for 0.5 to 12 hours to obtain a carbon precursor. The heat treatment temperature in the step (7) is 50 to 300 ° C., preferably 150 to 300 ° C., more preferably 180 to 280 ° C., even more preferably 200 to 260 ° C., and particularly preferably 210 to 250 ° C. The heat treatment time is 0.5 to 12 hours, preferably 1 to 8 hours, more preferably 2 to 6 hours, and even more preferably 3 to 5 hours. When the heat treatment temperature and time are within the above ranges, it is easy to efficiently and sufficiently remove water from the raw material of the carbon precursor by drying and dehydration, and the charge / discharge capacity is high and the resistance is low. It is considered that it is easy to finally obtain a carbonaceous material suitable for manufacturing a battery. Here, the heat treatment temperature may be a constant temperature, but is not particularly limited as long as it is within the above range.

A carbonaceous material can be produced from the carbon precursor of the present invention by a method including at least the following steps:
(3A) A step of heating the carbon precursor of the present invention to a first temperature in the range of 500 to 900 ° C. at a heating rate of 100 ° C./hour or more in an inert gas atmosphere.
(3B) A step of heat-treating the carbon precursor at a temperature of 500 to 900 ° C. under the supply of an inert gas to obtain carbides, wherein the supply amount of the inert gas is 0. 01 to 5.0 L / (minutes / m ² ),
(4A) The step of heating the carbide 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 (4B) the carbide is an inert gas. In the process of obtaining a carbonaceous material by heat treatment at a temperature of 1000 to 1400 ° C., the supply amount of the inert gas is 0.01 to 5.0 L / (minute · m ² ) per unit surface area of the carbide. Is.

Step (3A) is a step of heating the carbon precursor obtained by the production method of the present invention 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. The step (3B) is then a step of heat-treating the carbon precursor at a temperature of 500 to 900 ° C. under the supply of an inert gas to obtain a carbide. The step (3A) is carried out in an atmosphere of an inert gas, the step (3B) is carried out under the supply of an inert gas, and the amount of the inert gas supplied in the step (3B) is per unit surface area of the carbon precursor. It is 0.01 to 5.0 L / (minutes / m ² ). Here, the fact that the step is carried out in the atmosphere of the inert gas means that the step is carried out in the atmosphere of the inert gas, and even if the active gas is actively supplied, it is not carried out. You may. On the other hand, the fact that the step is performed under the supply of the inert gas means that the process is performed in an atmosphere in which the inert gas is supplied. For example, heat treatment of the inert gas in a mere atmosphere is not positive. It cannot be said that the active gas is supplied, and it cannot be said that the heat treatment is performed under the supply of the inert gas. In addition, in this specification, the said step (3A) and / or (3B) is also referred to as low temperature firing (step). Examples of the inert gas include argon gas, helium gas, and nitrogen gas, and nitrogen gas is preferable.

The rate of temperature rise in the step (3A) is preferably 100 ° C./hour or more from the viewpoint of easily obtaining a carbonaceous material suitable for producing a non-aqueous electrolyte secondary battery having a high charge / discharge capacity and low resistance. , More preferably 300 ° C./hour or higher, still more preferably 400 ° C./hour or higher, and particularly preferably 500 ° C./hour or higher. The upper limit of the temperature rising rate is not particularly limited, but is preferably 1000 ° C./hour or less, more preferably 800 ° C./hour or less, from the viewpoint of easily suppressing an increase in the specific surface area due to rapid thermal decomposition. The first temperature in the step (3A) is 500 to 900 ° C., preferably 550 to 880 ° C., more preferably 600 to 860 ° C., still more preferably 700 to 840 ° C.

Then, in step (3B), the carbon precursor is heat-treated at a temperature of 500 to 900 ° C. under the supply of an inert gas to obtain carbides. The heat treatment temperature in the step (3B) is also referred to as a low temperature firing temperature below. The low temperature firing temperature in the step (3B) is 500 to 900 ° C., preferably 550 to 880 ° C., more preferably 600 to 860 ° C., still more preferably 700 to 840 ° C. When the low-temperature firing temperature is within the above range, it is easy to finally obtain a carbonaceous material suitable for producing a non-aqueous electrolyte secondary battery having a high charge / discharge capacity and low resistance. The low-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 the 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. ^{The amount of the inert gas supplied is 0.01 to 5.0 L / (minutes / m 2} ), preferably 0.015 to 4.0 L / (minutes / m ² ), more preferably 0.01 to 5.0 L / (minutes / m 2) per unit surface area of the carbon precursor. It is 0.020 to 3.0 L / (minutes / m ² ). It is preferable that the step (3A) is also carried out while supplying the inert gas with the above-mentioned amount of the inert gas supplied. Further, from the viewpoint of facilitating the operation, it is preferable that the first temperature in the step (3A) and the heat treatment temperature in the step (3B) are equal to each other.

The step (4A) is a step of heating the carbide obtained in the step (3B) 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. Step (4B) is then a step of heat-treating the carbide at a temperature of 1000 to 1400 ° C. under the supply of an inert gas to obtain a carbonaceous material. Here, the step (4A) is carried out in an atmosphere of an inert gas, the step (4B) is carried out under the supply of an inert gas, and the amount of the inert gas supplied in the step (4B) is that of the carbon precursor. It is 0.01 to 5.0 L / (minute · m ² ) per unit surface area. Here, the conditions under the atmosphere of the inert gas and the supply of the inert gas are as described for (3A) and (3B) above. Further, in the present specification, the steps (4A) and / or (4B) are also referred to as high-temperature firing (steps). Examples of the inert gas include those described above for (3A) and (3B), and nitrogen gas is preferable.

The rate of temperature rise in the step (4A) is preferably 100 ° C./hour or more from the viewpoint of easily obtaining a carbonaceous material suitable for producing a non-aqueous electrolyte secondary battery having a high charge / discharge capacity and low resistance. , More preferably 300 ° C./hour or higher, still more preferably 400 ° C./hour or higher, and particularly preferably 500 ° C./hour or higher. The upper limit of the heating rate is not particularly limited, but from the viewpoint of easily suppressing the increase in 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. It's less than an hour. The second temperature in the step (4A) is 1000 to 1400 ° C, preferably 105 to 1380 ° C, more preferably 1100 to 1370 ° C, still more preferably 1150 to 1360 ° C, and particularly preferably 1200 to 1350 ° C.

The step (4A) is usually followed by the step (3B) from the viewpoint of creating a structure that easily occludes lithium ions and easily increasing the discharge capacity. Therefore, the temperature raising step in the step (4A) is a step of raising the temperature from the 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 low temperature firing temperature (500 to 900 ° C.) to the second temperature (1000 to 1400 ° C.), preferably the low temperature firing temperature (550 to 880 ° C.) to the second temperature (1050 to 1380 ° C.). ), More preferably from the low temperature firing temperature (600 to 860 ° C.) to the second temperature (1100 to 1370 ° C.), and even more preferably from the low temperature firing temperature (600 to 860 ° C.) to the second temperature (1150 to 1360 ° C.). The temperature is raised from a low temperature firing temperature (700 to 840 ° C.) to a second temperature (1200 to 1350 ° C.), particularly preferably.

Then, in step (4B), 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 the step (4B) is also referred to as a high temperature firing temperature below. The high-temperature firing temperature in the step (4B) is 1000 to 1400 ° C. from the viewpoint of easy operation, high charge / discharge capacity, and easy acquisition of a carbonaceous material suitable for producing a non-aqueous electrolyte secondary battery having low resistance. It is preferably 105 to 1380 ° C., more preferably 1100 to 1370 ° C., further preferably 1150 to 1360 ° C., and particularly preferably 1200 to 1350 ° C. 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 the step (4B) is preferably 0.1 to 5 hours, more preferably 0.3 to 3 hours, and even more preferably 0.5 to 2 hours. The supply amount of the inert gas per unit surface area of the carbide 0.01~5.0L / (min · ^m 2), preferably 0.015~4.0L / (min · ^m 2), more preferably 0. It is 020 to 3.0 L / (minutes / m ² ). It is preferable that the step (4A) is also carried out while supplying the inert gas with the above-mentioned amount of the inert gas supplied. Further, from the viewpoint of facilitating the operation, it is preferable that the second temperature in the step (4A) and the heat treatment temperature in the step (4B) are equal to each other.

The high temperature firing temperature (ie, the firing temperature in step (4B)) is preferably equal to the second temperature in step (4A) and is a carbonaceous material that gives high charge / discharge capacity and charge / discharge efficiency and low resistance when used in electrodes. From the viewpoint of easily obtaining the material, it is preferable that the temperature is equal to or higher than the firing temperature in the step (3B) (the first temperature in the step (3A) in a preferred embodiment). The high-temperature firing temperature is preferably 50 to 700 ° C., more preferably 100 to 600 ° C., even more preferably 150 to 500 ° C., and particularly preferably 200 to 400 ° C. higher than the low-temperature firing temperature.

A step (10) of adding at least one volatile organic compound to the carbide obtained in the step (3B) may be further included before the carbides are subjected to the steps (4A) and (4B) of firing at a high temperature. By performing the step (10), the organic matter volatilized when the carbide is calcined at a high temperature adheres to the surface of the carbide, and as a result, it becomes easy to produce a carbonaceous material having a lower specific surface area. Such a carbonaceous material reduces the amount of water present in the carbonaceous material while maintaining a high charge / discharge capacity and low resistance, and suppresses hydrolysis of the electrolytic solution and electrolysis of water by water. Can be done.

Volatile organic substances are hardly carbonized (for example, preferably 80% or more, more preferably 90% or more of the substance) when heat-treated in an inert gas atmosphere such as nitrogen at a temperature of, for example, 500 ° C. or higher. It is an organic compound that volatilizes (vaporizes or thermally decomposes into gas). Examples of volatile organic compounds include, but are not limited to, thermoplastic resins and small molecule organic compounds. Examples of the thermoplastic resin include polystyrene, polyethylene, polypropylene, poly (meth) acrylic acid, and poly (meth) acrylic acid ester. In this specification, (meth) acrylic is a general term for methacryl and acrylic. Examples of the low molecular weight organic compound include toluene, xylene, mesitylene, styrene, naphthalene, phenanthrene, anthracene, pyrene and the like. Polystyrene, polyethylene, and polypropylene are preferable as the thermoplastic resin because those that volatilize at the firing temperature and do not oxidize and activate the surface of the carbon precursor when thermally decomposed are preferable. As the small molecule organic compound, a compound having low volatility at room temperature (for example, 20 ° C.) is more preferable from the viewpoint of safety, and naphthalene, phenanthrene, anthracene, pyrene and the like are particularly preferable.

In step (10), at least one volatile organic compound is added to the carbide obtained in step (3B). The method of addition is not particularly limited, but for example, the carbide obtained in step (3B) and at least one volatile organic compound may be mixed and added. The amount of the volatile organic compound added is not particularly limited, but is preferably 2 to 30 parts by mass, more preferably 4 to 20 parts by mass, and further preferably 5 to 15 parts by mass with respect to 100 parts by mass of the carbide.

The method for producing a carbonaceous material may further include a step (11) of pulverizing a carbon precursor, a carbide and / or a carbonaceous material. The pulverization step (11) may be performed on the carbon precursor, carbide and / or carbonaceous material by a usual method, for example, a method using a ball mill or a jet mill. The pulverization step (11) may be performed after, for example, steps (1), (3B) and / or (4B), and shrinkage or shape change due to heat treatment is unlikely to occur, the charge / discharge capacity is high, and the resistance is low. From the viewpoint that a carbonaceous material suitable for producing a water electrolyte secondary battery can be finally obtained easily, it is preferable to carry out after the step (3B) or (4B).

The carbon precursor of the present invention or the carbon precursor obtained by the production method of the present invention can be used as a raw material for producing a carbonaceous material that can be suitably used as a negative electrode active material for a non-aqueous electrolyte secondary battery. Are suitable.

Hereinafter, a method for producing a negative electrode for a non-aqueous electrolyte secondary battery will be specifically described using the carbonaceous material produced by the above-mentioned production method using the carbon precursor of the present invention as a raw material. For the negative electrode, for example, a binder is added to a carbonaceous material, an appropriate amount of a suitable solvent is added, and then these are kneaded to prepare an electrode mixture. A negative electrode for a non-aqueous electrolyte secondary battery can be manufactured by applying the obtained electrode mixture to a current collector plate made of a metal plate or the like, drying it, and then pressure-molding it.

By using the carbonaceous material produced from the carbon precursor of the present invention, it is possible to produce an electrode (negative electrode) having high conductivity without adding a conductive auxiliary agent. If necessary, a conductive auxiliary agent can be added at the time of preparing the electrode mixture for the purpose of imparting higher conductivity. As the conductive auxiliary agent, conductive carbon black, vapor-grown carbon fiber (VGCF), nanotubes and the like can be used. The amount of the conductive auxiliary agent added varies depending on the type of the conductive auxiliary agent used, but if the amount added is too small, the expected conductivity may not be obtained, and if it is too large, the dispersion in the electrode mixture is poor. May become. From this point of view, the preferable ratio of the conductive auxiliary agent to be added is 0.5 to 10% by mass (here, the amount of the active material (carbonaceous material) + the amount of the binder + the amount of the conductive auxiliary agent = 100% by mass). Yes, even more preferably 0.5 to 7% by mass, particularly preferably 0.5 to 5% by mass. The binder is particularly limited as long as it does not react with the electrolytic solution, such as PVDF (polyvinylidene fluoride), polytetrafluoroethylene, and a mixture of SBR (styrene-butadiene rubber) and CMC (carboxymethyl cellulose). Not done. Above all, a mixture of SBR and CMC is preferable because SBR and CMC adhering to the surface of the active material do not hinder the movement of lithium ions and good input / output characteristics can be obtained. A polar solvent such as water is preferably used to dissolve an aqueous emulsion such as SBR or CMC to form a slurry, but a solvent emulsion such as PVDF can also be used by dissolving it in N-methylpyrrolidone or the like. If the amount of the binder added is too large, the resistance of the obtained electrode becomes large, so that the internal resistance of the battery becomes large and the battery characteristics may be deteriorated. Further, if the amount of the binder added is too small, the bonding between the particles of the negative electrode material and the current collector may be insufficient. The preferable amount of the binder added depends on the type of binder used, but for example, in a binder using water as a solvent, a plurality of binders such as a mixture of SBR and CMC are often mixed and used. The total amount of the total binder to be added is preferably 0.5 to 5% by mass, more preferably 1 to 4% by mass. On the other hand, the PVDF-based binder is preferably 3 to 13% by mass, more preferably 3 to 10% by mass. The amount of the carbonaceous material in the electrode mixture is preferably 80% by mass or more, more preferably 90% by mass or more. The amount of the carbonaceous material in the electrode mixture is preferably 100% by mass or less, more preferably 97% by 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 smaller the number of current collector plates and separators, which is preferable for increasing the capacity. However, the wider the electrode area facing the counter electrode is, the more advantageous it is to improve the input / output characteristics. Therefore, if the electrode active material layer is too thick, the input / output characteristics may deteriorate. The thickness of the active material layer (per one side) is preferably 10 to 80 μm, more preferably 20 to 75 μm, and even more preferably 30 to 75 μm from the viewpoint of output when the battery is discharged.

A non-aqueous electrolyte secondary battery using a carbonaceous material produced from the carbon precursor of the present invention has a high charge / discharge capacity and low resistance. When a negative electrode for a non-aqueous electrolyte secondary battery is formed using a carbonaceous material produced from the carbon precursor of the present invention, other materials constituting the battery such as a positive electrode material, a separator, and an electrolytic solution are particularly limited. It is possible to use various materials conventionally used or proposed as a non-aqueous solvent secondary battery without using.

For example, as the cathode material, one represented layered oxide (LiMO _2, M is a metal: for example LiCoO _2, LiNiO _2, LiMnO ₂ or _{LiNi x Co y Mo z O 2} ( where x,, y , Z represents the composition ratio)), olivine type ( _{represented by LiMPO 4} , M is a metal: for example LiFePO ₄ ), spinel type ( _{represented by LiM 2} O ₄ , M is a metal: for example LiMn ₂ O ₄ etc.) ) Is preferable, and these chalcogen compounds may be mixed and used as necessary. A positive electrode is formed by molding these positive electrode materials together with an appropriate binder and a carbon material for imparting conductivity to the electrodes and forming a layer on the conductive current collector.

The non-aqueous solvent type electrolytic solution used in combination with these positive electrodes and negative electrodes is generally formed by dissolving the electrolyte in a non-aqueous solvent. Examples of the non-aqueous solvent include organic solvents such as propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, dimethoxyethane, diethoxyethane, γ-butyl lactone, tetrahydrofuran, 2-methyltetrahydrofuran, sulfolane, and 1,3-dioxolane. Can be used alone or in combination of two or more. As the electrolyte, LiClO ₄ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO _{3 , LiAsF 6} , LiCl, LiBr, LiB (C ₆ H ₅ ) ₄ , LiN (SO ₃ CF ₃ ) _2, or the like is used.

The non-aqueous electrolyte secondary battery is generally formed by facing the positive electrode and the negative electrode formed as described above with each other via a liquid permeable separator and immersing the battery in the electrolytic solution. As such a separator, a permeable or liquid-permeable separator made of a non-woven fabric or other porous material usually used for a secondary battery can be used. Alternatively, a solid electrolyte composed of a polymer gel impregnated with an electrolytic solution can be used instead of or in combination with the separator.

The carbon precursor of the present invention is suitable as a raw material for producing a carbonaceous material for a battery (typically, a non-aqueous electrolyte secondary battery for driving a vehicle) mounted on a vehicle such as an automobile. In the present invention, the vehicle can be a target without particular limitation, such as a vehicle generally known as an electric vehicle, a hybrid vehicle with a fuel cell or an internal combustion engine, and the like, but at least a power supply device including the above battery. And an electric drive mechanism driven by power supply from the power supply device, and a control device for controlling the electric drive mechanism. The vehicle may further be provided with a dynamic brake or a regenerative brake, and may be provided with a mechanism for converting energy from braking into electricity to charge the non-aqueous electrolyte secondary battery.

Since the carbonaceous material produced using the carbon precursor of the present invention has low resistance, it can be used, for example, as an additive for imparting conductivity to the electrode material of the battery. The type of battery is not particularly limited, but a non-aqueous electrolyte secondary battery and a lead storage battery are preferable. By adding it to the electrode material of such a battery, a conductive network can be formed, and by increasing the conductivity, an irreversible reaction can be suppressed, so that the life of the battery can be extended.

The present invention is also suitable for negative electrode active materials or conductive materials of non-aqueous electrolyte secondary batteries (eg, lithium ion secondary batteries, sodium ion batteries, lithium sulfur batteries, lithium air batteries) having high charge / discharge capacity and low resistance. Also provided is a method for producing a carbon precursor, which is a raw material for a carbonaceous material. The production method is a method in which a substance having a saccharide skeleton is used as a raw material and heat-treated for 1 to 12 hours in a temperature range of 215 to 240 ° C., and the carbon precursor of the present invention can be obtained by such a method.

Hereinafter, the present invention will be specifically described with reference to Examples, but these do not limit the scope of the present invention. The method for measuring the physical characteristic value of the carbonaceous material is described below, but the physical characteristic value described in the present specification including the examples is based on the value obtained by the following method.

(Elemental analysis)
Elemental analysis was performed based on the inert gas dissolution method using the oxygen / nitrogen / hydrogen analyzer EMGA-930 manufactured by HORIBA, Ltd.
The detection method of the device is oxygen: inert gas melting-non-dispersion infrared absorption method (NDIR), nitrogen: inert gas melting-heat conduction method (TCD), hydrogen: inert gas melting-non-dispersion infrared absorption method. It is a method (NDIR), and calibration is performed with (oxygen / nitrogen) Ni capsule, TiH ₂ (H standard sample), SS-3 (N, O standard sample), and the pretreatment is 250 ° C., moisture in about 10 minutes. 20 mg of the measured sample was taken in a Ni capsule, degassed in an element analyzer for 30 seconds, and then measured. The test was analyzed with 3 samples, and the average value was used as the analysis value. As described above, the oxygen atom content, the nitrogen atom content and the hydrogen atom content in the carbon precursor were obtained. The carbon atom content was then calculated by subtracting the oxygen, nitrogen and hydrogen atom contents from 100% by weight.

(IR measurement)
IR measurement was performed based on the total reflection measurement method using a Fourier transform infrared spectrophotometer Nicolet is10 + Nicolet Continum manufactured by Thermo Fisher Scientific Co., Ltd. The measurement sample was placed on a diamond cell, irradiated with infrared light, and the obtained spectral data was collected.

(TG-DTA measurement)
TG analysis was performed using a TG-DTA analyzer TG / DTA6300 (trade name) manufactured by Hitachi High-Tech Science Corporation. 10 mg of the sample was placed in a sample pan made of alumina, and the temperature was raised to 500 ° C. at a heating rate of 10 ° C./min under a nitrogen stream of 100 mL / min. In the differential thermal (DTA) curve obtained at this time, the presence or absence of an endothermic peak was confirmed in the range of 100 to 500 ° C. When the endothermic peak was present in the above range, it was evaluated as “◯”, and when it was not present, it was evaluated as “x”.

( ¹³ C-NMR measurement)
^{CP / MAS-13} C-NMR was measured by a nuclear magnetic resonance apparatus AVANCE 300 manufactured by BRUKER. At the time of measurement, the peak derived from methine was set to 29.47 ppm using adamantane as a reference substance. In the obtained results, the presence or absence of a peak was confirmed in the range of 0 to 50 ppm. When the peak was present in the above range, it was evaluated as "○", and when it was not present, it was evaluated as "×".

(Circularity)
The roundness of the carbon precursor was measured by the following method. The sample was put into an aqueous solution containing 5% by mass of a surfactant (“Toriton X100” manufactured by Wako Pure Chemical Industries, Ltd.) and dispersed in the aqueous solution. Using this dispersion, the shape particle size distribution was measured using the shape particle size distribution measuring device FPIA-3000 manufactured by Sysmex Corporation, and the circularity was calculated.

(Average particle size by laser scattering method)
The average particle size (particle size distribution) of the carbon precursor was measured by the following method. The sample was put into an aqueous solution containing 5% by mass of a surfactant (“Toriton X100” manufactured by Wako Pure Chemical Industries, Ltd.) and dispersed in the aqueous solution. The particle size distribution was measured using this dispersion. The particle size distribution measurement was performed using a particle size / particle size distribution measuring device (“Microtrack MT3300EII” manufactured by Microtrack Bell Co., Ltd.). D ₅₀ is a particle size having a cumulative volume of 50%, and this value was used as the average particle size.

(Electrode density)
The electrode density was calculated by measuring the weight of the electrode produced by the method of Reference Example 1 described later and dividing the weight by the electrode volume calculated from the product of the electrode area and the thickness of the electrode.

(Example 1)
10 g of starch was heated to 215 ° C. in an air atmosphere. At this time, the heating rate up to 215 ° C. was set to 600 ° C./hour (10 ° C./min). Then, a carbon precursor was obtained by heat-treating at 215 ° C. for 8 hours under an air stream. At this time, the amount of air supplied was 35 L / min per 100 g of starch and 0.49 L / (min / m ² ) per unit surface area of starch.

(Example 2)
The treatment was carried out in the same manner as in Example 1 except that the heat treatment temperature was 220 ° C. and the amount of air supplied was 10 L / min per 100 g of starch (0.14 L / min / m ^{2 per unit surface area of starch), and carbon was used.} A precursor was obtained.

(Example 3)
The treatment was carried out in the same manner as in Example 2 except that the amount of starch was 20 g and the amount of air supplied was 50 L / min per 100 g of starch (0.35 L / (min · m ^{2) per unit surface area of starch), and carbon was used.} A precursor was obtained.

(Comparative Example 1)
A carbon precursor was obtained in the same manner as in Example 1 except that the inflowing gas was nitrogen.

(Comparative Example 2)
The amount of starch was 20 g, and the treatment was carried out in the same manner as in Example 1 except that the gas did not flow in to obtain a carbon precursor.

(Comparative Example 3)
The treatment was carried out in the same manner as in Example 1 except that the treatment temperature was 250 ° C. and the treatment time was 6 hours to obtain a carbon precursor.

Table 1 shows the firing conditions in each Example and each Comparative Example, and Table 2 shows the evaluation results of the physical properties of the obtained carbon precursor. Regarding TG-DTA in Table 2, when the endothermic peak is observed in the range of 100 to 500 ° C. according to the above TG-DTA measurement, it is described as ◯, and when it is not observed, it is described as ×. ^{Further, regarding 13} C-NMR in Table 2, ^{when a peak is observed in the range of 0 to 50 ppm according to the above 13} C-NMR measurement, it is marked as ◯, and when it is not observed, it is marked as ×. Further, the SEM image of the carbon precursor obtained in Example 1 is shown in FIG. 1, and the SEM image of the carbon precursor obtained in Comparative Example 1 is shown in FIG.

(Reference example 1)
Using the carbon precursor obtained in Example 1, the temperature was raised to 600 ° C. in a nitrogen gas atmosphere. At this time, the heating rate up to 600 ° C. was set to 600 ° C./hour (10 ° C./min). Next, a carbide was obtained by performing a carbonization treatment by heat-treating at 600 ° C. for 60 minutes under a nitrogen gas stream. At this time, the amount of nitrogen gas supplied was 1 L / min per 10 g of the carbon precursor. Then, the obtained carbide was pulverized with 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 perform a high-temperature calcination treatment to obtain a carbonaceous material. At this time, the heating rate up to 1200 ° C. was set to 600 ° C./hour (10 ° C./min). The above temperature rise and heat treatment were performed under a nitrogen gas stream. The amount of nitrogen gas supplied was 3 L / min per 5 g of pulverized carbide.

(Preparation of electrodes)
Using the carbonaceous material obtained in Reference Example 1, a negative electrode was prepared 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 TIMCAL), 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. The densities of the obtained electrodes were as shown in Table 3.

(Impedance)
Using the electrode produced above, using an electrochemical measuring device (“1255WB type high-performance electrochemical measuring system” manufactured by Solartron), an amplitude of 10 mV centered on 0 V is applied at 25 ° C., and a frequency of 10 MHz to 1 MHz is applied. The constant voltage AC impedance was measured at the frequency, and the real resistance at a frequency of 1 kHz was measured as the impedance resistance. The obtained results are shown in Table 3 as the impedance at the time of initial charge / discharge.

(DC resistance value, 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 the reference electrode. As a solvent, ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate were mixed and used so as to have a volume ratio of 1: 1: 1. _{LiPF 6} was dissolved in this solvent at 1 mol / L and used as an electrolyte. A polypropylene film was used for the separator. A coin cell was prepared in a glove box under an argon atmosphere.
The lithium secondary battery having the above configuration was subjected to a charge / discharge test after measuring the DC resistance value before the initial charge using a charge / discharge test device (manufactured by Toyo System Co., Ltd., “TOSCAT”). Lithium was doped at a rate of 70 mA / g relative to the mass of the active material and doped until it reached 1 mV with respect to the lithium potential. Further, a constant voltage of 1 mV was applied to the lithium potential for 8 hours to complete the doping. The capacity (mAh / g) at this time was taken as the charging capacity. Next, dedoping was performed at a rate of 70 mA / g with respect to the mass of the active material until it became 2.5 V with respect to the lithium potential, and the discharged capacity at this time was defined as the discharge capacity. The charge / discharge efficiency (initial charge / discharge efficiency) was defined as the percentage of the discharge capacity / charge capacity, and was used as an index of the lithium ion utilization efficiency in the battery.

Table 3 shows the results of evaluating the batteries as described above.

When the carbon precursor of Example 1 was used and fired at a high temperature, no melting or fusion occurred, and a carbonaceous material was obtained while maintaining the particle shape of the raw material, showing a carbon structure suitable as a battery material. In particular, the battery produced using the carbonaceous material shown in Reference Example 1 had a low resistance value and a high discharge capacity. On the other hand, do not show a predetermined range O / C ratio, show no I A _/ I _B, using carbon precursors, Comparative Examples, in the same manner as in Reference Example 1, carbide, when the high temperature firing The obtained carbonaceous material did not show a carbon structure suitable for the battery material.

Claims (6)

The ratio of oxygen atom content to carbon atom content by elemental analysis (O / C) is 0.10 to 0.85, and the intensity of the peak near 1720 cm ^-1 in the IR spectrum _{(I A)} 3330cm ^- the ratio of ¹ near the peak intensity _{(I B) (I a /} I B) is 0.50 or more, carbon precursor. The carbon precursor according to claim 1, which has no endothermic peak in the range of 100 to 500 ° C. in the DTA curve measured by TG-DTA. ¹³ The carbon precursor according to claim 1 or 2, which has a peak in the range of 0 to 50 ppm in the C-NMR spectrum. The carbon precursor according to any one of claims 1 to 3, which is derived from a substance having a saccharide skeleton. The carbon precursor according to any one of claims 1 to 4, wherein the raw material of the carbon precursor is heat-treated in a temperature range of 215 to 240 ° C. for 1 to 12 hours under the supply of an oxygen-containing gas to obtain the carbon precursor. Production method. The production method according to claim 5, wherein the supply amount of the oxygen-containing gas is 0.005 to 5.0 L / (min · m ^{2) per unit surface area of the raw material of the carbon precursor.}

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