Porous carbon, positive electrode additive for non-aqueous electrolyte secondary battery, non-aqueous electrolyte secondary battery, and method for producing porous carbon

Abstract

To provide porous carbon suitable for a positive electrode additive, capable of improving input / output characteristics of a nonaqueous electrolyte secondary battery at room temperature and securing peel strength of an electrode.SOLUTION: Wherein the porous carbon has a pore volume of 2 nm or more and 200 nm or less measured by the BJH method of 0.8cm3 / g or more, a bulk density of 0.10g / cm3 or less, a mode diameter of pores measured by the BJH method of 150 nm or less, and an average primary particle size of 1 μm or more and 100 μm or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This patent application claims priority under the Paris Convention to Japanese Patent Application No. 2021-092329 (filing date: June 1, 2021), the entire contents of which are incorporated herein by reference. The present invention relates to porous carbon suitable as a positive electrode additive for non-aqueous electrolyte secondary batteries, a positive electrode additive comprising the porous carbon material, a positive electrode for non-aqueous electrolyte secondary batteries comprising the positive electrode additive, a non-aqueous electrolyte secondary battery having the positive electrode, and a method for producing the porous carbon. [Background technology]

[0002] Demand for non-aqueous electrolyte secondary batteries, such as lithium-ion secondary batteries, is rapidly expanding due to their small size, light weight, high energy density, and ability to be repeatedly charged and discharged. Because of their relatively high energy density, lithium-ion secondary batteries are used in fields such as mobile phones, laptop computers, and electric vehicles. As their applications expand and develop, improvements in the output characteristics of these lithium-ion secondary batteries are required.

[0003] As a method for improving the output characteristics of lithium ion secondary batteries, a method of adding activated carbon or the like to the positive electrode has been proposed.

[0004] For example, in Patent Document 1, the pore volume of pores with a diameter of 20 Å or more is 0.418 cc / g or more, and the specific surface area is 1200 m 2 It has been reported that adding activated carbon of 0.1g or more to the positive electrode improves the output characteristics at -30°C.

[0005] Ketjen black is known as a porous carbon having a large pore volume with pore diameters of 2 nm or more and large voids with pore diameters of 200 nm or more, i.e., a low bulk density, and is used as an additive to positive electrodes (Patent Document 2). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 4964404 [Patent Document 2] Patent No. 4727386 Summary of the Invention [Problem to be solved by the invention]

[0007] However, according to the investigations of the present inventors, even if the activated carbon disclosed in the above Patent Document 1 is added to the positive electrode, sufficient improvement in input / output characteristics at room temperature is not always observed.

[0008] Furthermore, when the Ketjen black described in Patent Document 2 is added to the positive electrode, not only is there little improvement in input / output characteristics, but the dispersibility of the positive electrode slurry is likely to be impaired due to the adsorption of the binder to the Ketjen black and the aggregation of the conductive agent, making it difficult in some cases to ensure the peel strength of the resulting electrode.

[0009] The present invention has been made in view of the above circumstances, and aims to provide a porous carbon that is suitable as a positive electrode additive, which can improve the input / output characteristics of a non-aqueous electrolyte secondary battery at room temperature and ensure the peel strength of the electrode. [Means for solving the problem]

[0010] As a result of extensive research into solving the above problems, the inventors discovered that the above problems can be solved by adding porous carbon having specific physical properties to the positive electrode, and thus arrived at the present invention.

[0011] That is, the present invention includes the following preferred embodiments. [1] The pore volume measured by the BJH method is 0.8 cm2, with a diameter of 2 nm or larger and 200 nm or smaller. 3 / g or more, and the bulk density is 0.10 g / cm 3The porous carbon has a pore mode diameter of 150 nm or less as measured by the BJH method, and an average primary particle diameter of 1 μm or more and 100 μm or less. [2] The pore volume of less than 2 nm measured by DFT is 0.35 cm 3 / g or less. [3] The specific surface area measured by the BET method is 500 m 2 / g or more 1200m 2 / g or less. [4] The porous carbon according to any one of [1] to [3], wherein the calcium content is 20 ppm or more and 2000 ppm or less. [5] The porous carbon according to any one of [1] to [4], wherein the sulfur content is 1000 ppm or less and the silicon content is 1000 ppm or less. [6] Bulk density is 0.05 g / cm 3 The porous carbon according to any one of [1] to [5] below: [7] (1) obtaining a mixture containing a carbon source and a calcium compound; (2) heat-treating the mixture in an inert gas atmosphere to obtain a carbide; and (3) removing calcium compounds from the carbonized material The method for producing porous carbon according to any one of [1] to [6], comprising: [8] The method according to [7], wherein the mixture in step (1) further contains at least one selected from the group consisting of polyhydric alcohols and carboxylic acids. [9] The method according to [7] or [8], wherein the melting point of the calcium compound is 300°C or less.

[10] The method according to any one of [7] to [9], wherein the calcium compound is at least one selected from the group consisting of calcium chloride hydrate, calcium hydroxide, calcium oxide, calcium carbonate, and calcium acetate.

[11] The method according to any one of [7] to

[10] , wherein the carbon source is a sugar.

[12] The method according to

[11] , wherein the saccharide is at least one selected from the group consisting of monosaccharides, disaccharides, and polysaccharides.

[13] The method according to any one of [7] to

[12] , wherein the removal of the calcium compound in the step (3) is carried out by acid washing.

[14] The method according to any one of [7] to

[13] , wherein the temperature in the heat treatment step in the step (2) is 400°C or higher and 1300°C or lower.

[15] The method according to any one of [7] to

[14] , wherein the temperature increase rate in the heat treatment step in step (2) is 2°C / min or more.

[16] The porous carbon according to any one of [1] to [6], which is an additive for a positive electrode of a non-aqueous electrolyte secondary battery.

[17] The porous carbon according to any one of [1] to [6], which is an additive for a positive electrode of a lithium ion secondary battery.

[18] A composition for a positive electrode of a non-aqueous electrolyte secondary battery, comprising the porous carbon according to any one of [1] to [6].

[19] A composition for a positive electrode of a lithium ion secondary battery, comprising the porous carbon according to any one of [1] to [6].

[20] A non-aqueous electrolyte secondary battery comprising a positive electrode containing the composition for a positive electrode of a non-aqueous electrolyte secondary battery according to

[18] .

[21] A lithium ion secondary battery comprising a positive electrode containing the composition for a positive electrode of a non-aqueous electrolyte secondary battery according to

[19] . [Effects of the Invention]

[0012] According to the present invention, it is possible to provide a porous carbon suitable for use as a positive electrode additive, which can improve the input / output characteristics of a non-aqueous electrolyte secondary battery at room temperature and ensure the peel strength of the electrode. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a transmission electron microscope (TEM) photograph of the porous carbon of Example 6. [Figure 2] 1 is a transmission electron microscope (TEM) photograph of the porous carbon of Example 6. [Figure 3]1 is a scanning electron microscope (SEM) photograph of the porous carbon of Example 8. [Figure 4] 1 is a scanning electron microscope (SEM) photograph of the porous carbon of Example 8. [Figure 5] 1 is a transmission electron microscope (TEM) photograph of the porous carbon of Comparative Example 9. [Figure 6] 1 is a transmission electron microscope (TEM) photograph of the porous carbon of Comparative Example 9. [Figure 7] 1 is a scanning electron microscope (SEM) photograph of the porous carbon of Comparative Example 9. [Figure 8] 1 is a scanning electron microscope (SEM) photograph of the porous carbon of Comparative Example 9. [Figure 9] 1 is a scanning electron microscope (SEM) photograph of the porous carbon of Comparative Example 13. [Figure 10] 1 is a scanning electron microscope (SEM) photograph of the porous carbon of Comparative Example 13. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, embodiments of the present invention will be described in detail. Note that the following description is for illustrating embodiments of the present invention, and is not intended to limit the present invention to the following embodiments.

[0015] <Porous carbon> The porous carbon of the present invention has a pore volume of 0.8 cm3 having a pore size of 2 nm or more and 200 nm or less as measured by the BJH method. 3 / g or more, and the bulk density is 0.10 g / cm 3 The pore mode diameter measured by the BJH method is 150 nm or less, and the average primary particle diameter is 1 μm or more and 100 μm or less.

[0016] In the porous carbon of the present invention, the pore volume of pores having a diameter of 2 nm or more and 200 nm or less measured by the BJH method is 0.8 cm 3 / g or more. The pore volume of pores with a diameter of 2 nm or more and 200 nm or less is 0.8 cm 3 / g or more, the storage of lithium ions in the pores and the mobility of lithium ions near the positive electrode active material are excellent, and lithium ions can be supplied abundantly to the periphery of the positive electrode active material. This promotes smooth insertion and desorption of lithium ions into the positive electrode active material, improving input / output characteristics. The pore volume of 2 nm to 200 nm is 0.8 cm 3 If the pore volume is less than 0.9 cm3 / g, the mobility of lithium ions tends to decrease, and the pores tend to be blocked by gas generated when the electrolyte solution decomposes in the electrochemical element, further reducing the mobility of the electrolyte. 3 / g or more, more preferably 1.00 cm 3 / g or more, more preferably 1.30 cm 3 / g or more, and even more preferably 1.60 cm 3 / g or more, particularly preferably 1.65 cm 3 / g or more, particularly preferably 1.90 cm 3 / g or more, and most preferably 2.30 cm 3 / g or more, particularly preferably 3.20 cm 3 / g or more. When the pore volume of 2 nm or more and 200 nm or less is equal to or greater than the lower limit, the input / output characteristics tend to be further improved. Furthermore, when the pore volume of 2 nm or more and 200 nm or less is large, the electrolyte retention ability and electrolyte mobility tend to be excellent. Therefore, although the upper limit is not particularly limited, it is preferably 4.00 cm 3 / g or less, more preferably 3.90 cm 3 / g or less. The pore volume of 2 nm or more and 200 nm or less can be adjusted to within the above range, for example, by appropriately adjusting the type and / or amount of the carbon source and calcium compound, the temperature and / or time of the heat treatment step, etc. in the method for producing porous carbon described below. The pore volume of 2 nm or more and 200 nm or less can be measured by pore distribution analysis using the BJH method in nitrogen adsorption measurement, for example, by the method described in the Examples described below.

[0017] In the porous carbon of the present invention, the bulk density is 0.10 g / cm3 The bulk density of porous carbon indicates the degree of development of the pore structure, and when the volume of pores of 200 nm or less is the same, the lower the bulk density, the larger the volume of voids of 200 nm or more. It is considered that pores of 2 nm or more and 200 nm or less function to store and move lithium ions, while voids of 200 nm or more function to retain the electrolyte and supply lithium ions to pores of 2 nm or more and 200 nm or less. Therefore, in the present invention, it is preferable that in addition to pores of 2 nm or more and 200 nm or less, the volume of voids of 200 nm or more is large, that is, the bulk density is small. A bulk density of 0.10 g / cm 3 If the bulk density exceeds 0.07 g / cm, the electrolyte may not be retained sufficiently, resulting in a decrease in input / output characteristics. 3 or less, more preferably 0.06 g / cm 3 In one embodiment of the present invention, the bulk density is 0.05 g / cm 3 It is more preferable that the concentration is 0.015 g / cm or less, and even more preferable that the concentration is 0.015 g / cm or less. 3 Below 0.014 g / cm, particularly preferably 3 More particularly preferably 0.013 g / cm or less 3 Below, more particularly preferably 0.012 g / cm 3 Below 0.011 g / cm, very preferably 0.011 g / cm 3 Below, more preferably 0.010 g / cm 3 Below, more preferably 0.009 g / cm 3 Below, even more preferably 0.008 g / cm 3 When the bulk density is equal to or less than the upper limit, the electrolyte can be abundantly retained in voids of 200 nm or more, and the input / output characteristics are likely to be further improved. In addition, if the bulk density is too low, it may be difficult to maintain the strength of the carbon skeleton. Therefore, from the viewpoint of easily maintaining the peel strength of the electrode, the bulk density is usually set to 0.003 g / cm. 3The above is preferable. The bulk density can be adjusted to within the above range by, for example, appropriately adjusting the type and / or amount of the carbon source and calcium compound in the method for producing porous carbon described below, the temperature and / or time of the heat treatment step, etc. The bulk density can be measured, for example, by the method described in the Examples described below.

[0018] In the porous carbon of the present invention, the mode diameter of the pores measured by the BJH method is 150 nm or less. Here, "mode diameter" refers to the pore diameter with the largest occurrence ratio in the logarithmic differential pore volume distribution (dV / d(log D)), obtained by differentiating the cumulative pore volume (V) with the common logarithm of the pore diameter (D). When the mode diameter of the porous carbon is 150 nm or less, lithium ions are smoothly stored in the pores and migrate toward the positive electrode active material, allowing for an abundant supply of lithium ions to the positive electrode active material. This facilitates improved input / output characteristics. Furthermore, adsorption of the binder into the pores of the porous carbon during slurry preparation can be suppressed, which tends to improve the electrode peel strength and prevent electrode chipping. When the mode diameter exceeds 150 nm, the amount of lithium ions stored in the pores decreases, resulting in a reduced supply of lithium ions to the active material surface. Furthermore, the binder is more likely to be adsorbed into the pores of the porous carbon during slurry preparation. The mode diameter is preferably 145 nm or less, more preferably 100 nm or less, even more preferably 55 nm or less, even more preferably 50 nm or less, particularly preferably 30 nm or less, even more particularly preferably 25 nm or less, even more particularly preferably 20 nm or less, extremely preferably 15 nm or less, and even extremely preferably 13 nm or less. A mode diameter below the upper limit of the range indicated above facilitates improved input / output characteristics. While there is no lower limit for the mode diameter, if the mode diameter is too small, lithium ion mobility is likely to decrease. Furthermore, gas generated when the electrolyte decomposes in the electrochemical device may clog the pores, further reducing electrolyte mobility. Therefore, the mode diameter is typically 2 nm or more, more preferably 9 nm or more. The mode diameter can be adjusted within the above range by, for example, appropriately adjusting the type and / or amount of the carbon source and calcium compound in the porous carbon manufacturing method described below; the temperature and / or time of the heat treatment step; etc. The mode diameter can be measured by pore distribution analysis using the BJH method in nitrogen adsorption measurements, for example, by the method described in the Examples described below.

[0019] The porous carbon of the present invention has an average primary particle diameter of 1 μm or more and 100 μm or less. An average primary particle diameter of 1 μm or more and 100 μm or less facilitates the storage and diffusion of lithium ions, resulting in favorable input / output characteristics. Furthermore, since the porous carbon particles are less likely to aggregate, uneven coating after electrode coating is less likely to occur, and the peel strength of the electrode can be improved. If the average primary particle diameter is less than 1 μm, the fine powder contained therein is likely to be separated from the electrode due to insufficient binder or other agent. Furthermore, the fine powder particles are more likely to aggregate within the electrode. This results in uneven coating after electrode coating, reducing the electrode's peel strength. Furthermore, if the average primary particle diameter exceeds 100 μm, it is difficult to form good ion diffusion paths between the active materials, making it difficult to improve input / output characteristics. Furthermore, coarse particles are more likely to cause unevenness in the electrode, reducing the electrode's peel strength. From these viewpoints, the average primary particle diameter is preferably 2 μm or more, more preferably 5 μm or more, and preferably 80 μm or less, more preferably 60 μm or less. When the average primary particle diameter is within the above range, the input / output characteristics of a nonaqueous electrolyte secondary battery at room temperature can be further improved, and the peel strength of the electrode can be more easily increased. The average primary particle diameter can be adjusted to within the above range, for example, by appropriately adjusting the type of carbon source and the conditions of the pulverization step in the method for producing porous carbon described below. In the present invention, the average primary particle diameter is the particle diameter at which the cumulative volume measured by laser diffraction / scattering is 50%, and this value is used as the average primary particle diameter. However, when measurement by laser diffraction / scattering is not possible, the average particle diameter may refer to the average particle diameter obtained by measuring the particle diameters of primary particles shown in an electron microscope image and calculating the average value.

[0020] In the porous carbon of the present invention, the pore volume of less than 2 nm measured by the DFT method is preferably 0.35 cm 3 / g or less, more preferably 0.30 cm 3 / g or less, more preferably 0.20 cm 3 / g or less, even more preferably 0.15 cm 3 / g or less, particularly preferably 0.13 cm 3 / g or less, more particularly preferably 0.12 cm3 / g or less, and more particularly preferably 0.10 cm 3 / g or less, even more particularly preferably 0.09 cm 3 / g or less, and most preferably 0.08 cm 3 When the volume of pores less than 2 nm is equal to or less than the upper limit, lithium ions are less likely to be adsorbed into the pores less than 2 nm, and therefore lithium ions can be supplied to the active material, and input / output characteristics are likely to be improved. The lower limit of the volume of pores less than 2 nm is not particularly limited, but is preferably 0.01 cm 3 / g or more. The pore volume of less than 2 nm can be adjusted to within the above range, for example, by appropriately adjusting the type and / or amount of the carbon source and calcium compound, the temperature and / or time of the heat treatment step, etc. in the method for producing porous carbon described below. The pore volume of less than 2 nm can be measured by pore distribution analysis using the DFT method in nitrogen adsorption measurement, for example, by the method described in the Examples described below.

[0021] In the porous carbon of the present invention, the pore volume of pores having a diameter of 2 nm or more and 10 nm or less measured by the DH method is preferably 0.55 cm 3 / g or less, more preferably 0.53 cm 3 / g or less, more preferably 0.45 cm 3 / g or less, and even more preferably 0.40 cm 3 / g or less, particularly preferably 0.35 cm 3 / g or less, more particularly preferably 0.30 cm 3 / g or less, and more particularly preferably 0.25 cm 3 / g or less, most preferably 0.20 cm 3 / g or less. The pore volume of pores with a diameter of 2 nm or more and 10 nm or less is 0.55 cm 3 / g or less, it is easy to increase the mobility of lithium ions near the positive electrode active material, and since the pores are less likely to be clogged by gas generated when the electrolyte decomposes in the electrochemical device, it is easy to supply lithium ions abundantly to the periphery of the positive electrode active material. This facilitates smooth insertion and desorption of lithium ions into the positive electrode active material, which tends to improve input / output characteristics. Furthermore, when the pore volume is reduced from 2 nm to 10 nm, the electrolyte mobility also tends to be excellent. Therefore, although the lower limit is not particularly limited, it is preferably 0.01 cm. 3 / g or more, more preferably 0.05 cm 3 / g or more, more preferably 0.10 cm 3 / g or more. The pore volume of 2 nm or more and 10 nm or less can be adjusted to within the above range, for example, by appropriately adjusting the type and / or amount of the carbon source and calcium compound, the temperature and / or time of the heat treatment step, etc. in the method for producing porous carbon described below. The pore volume of 2 nm or more and 10 nm or less can be measured by pore distribution analysis using the DH method in nitrogen adsorption measurement, for example, by the method described in the Examples described below.

[0022] The porous carbon of the present invention preferably has a specific surface area of ​​500 m2 or less as measured by the BET method. 2 / g or more, more preferably 600m 2 / g or more, more preferably 650m 2 / g or more, and even more preferably 700m 2 / g or more, preferably 1200m 2 / g or less, more preferably 1000m 2 / g or less, more preferably 900m 2 / g or less. When the specific surface area is within this range, lithium ions in the electrolyte are easily retained, and input / output characteristics are likely to be improved. Furthermore, lithium ions are easily diffused, and coating stability is likely to be good. The specific surface area can be adjusted to within the above range, for example, by appropriately adjusting the type and / or amount of the carbon source and calcium compound in the method for producing porous carbon described below; the temperature and / or time of the heat treatment step; etc. The specific surface area can be measured, for example, by the method described in the Examples described below.

[0023] In the porous carbon of the present invention, the calcium content is preferably 20 ppm or more, more preferably 50 ppm or more, even more preferably 100 ppm or more, and preferably 2000 ppm or less, more preferably 1500 ppm or less, and even more preferably 1000 ppm or less. When the calcium content is within the above range, excessive increases in the mass of the porous carbon tend to be suppressed, and productivity also tends to be excellent. The calcium content can be adjusted to within the above range, for example, by appropriately adjusting the conditions for the step of removing calcium compounds in the method for producing porous carbon described below (e.g., the type and / or concentration of acid used for acid washing, the time and temperature of acid and / or water washing, etc.).

[0024] In the porous carbon of the present invention, the sulfur content is preferably 1000 ppm or less, more preferably 900 ppm or less, and even more preferably 800 ppm or less. The silicon content is preferably 1000 ppm or less, more preferably 900 ppm or less, and even more preferably 800 ppm or less. When the sulfur and silicon contents are within the above ranges, side reactions in the positive electrode are suppressed, making it easier to improve input / output characteristics. The lower limits of the sulfur and silicon contents are not particularly limited and may be 0 ppm. The sulfur and silicon contents can be adjusted within the above ranges, for example, by the type of carbon source in the porous carbon production method described below; and the conditions of the calcium compound removal step (e.g., the type and / or concentration of acid used in acid washing, the time and temperature of acid and / or water washing, etc.). The calcium, sulfur, and silicon contents can be measured by fluorescent X-ray analysis, for example, by the method described in the Examples described below.

[0025] In general porous carbon, mesopores may form a three-dimensional network structure, with the mesopores interconnected. Such a three-dimensional network structure typically involves dead ends (blocked sections) of the pores. However, the present inventors have discovered that one embodiment of the porous carbon of the present invention can have an interconnected pore structure in which all pores are three-dimensionally connected and have no dead ends (see Figures 5 and 6). In one embodiment of the porous carbon of the present invention, the interconnected pore structure increases the diffusion rate of lithium ions within the pores, thereby improving the input / output characteristics of nonaqueous electrolyte secondary batteries at room temperature and ensuring the peel strength of the electrode. It has also been discovered that this porous carbon is suitable for use as a positive electrode additive. It has also been discovered that such an interconnected pore structure can be achieved by applying a manufacturing method described below.

[0026] In addition, common porous carbons used as positive electrode additives, such as carbon black and Ketjen black, can form three-dimensional dendritic particle structures due to the aggregation and connection of primary particles (Figures 9 and 10). Such three-dimensional dendritic structures have low bulk density due to the voids between the branches, and can form short-distance lithium ion diffusion paths by being arranged between adjacent active materials in the electrode. On the other hand, the inventors have discovered that one embodiment of the porous carbon of the present invention can have a flaky shape (Figures 3 and 4). When the porous carbon has the flaky shape described above, the voids formed by the wrinkles on the flake surface significantly reduce the bulk density. Furthermore, the porous carbon is arranged in contact with not only adjacent active materials but also more distant active materials in the electrode, which is thought to form long-distance lithium ion diffusion paths. Therefore, when flaky porous carbon is used in combination with three-dimensional dendritic porous carbon or granular porous carbon (Figures 7 and 8), both short-distance and long-distance ion diffusion paths can be formed, thereby ensuring better ion diffusion paths throughout the electrode. Therefore, it has been found that one embodiment of the porous carbon of the present invention is a porous carbon suitable for use as a positive electrode additive, which can further improve the input / output characteristics of a non-aqueous electrolyte secondary battery at room temperature and ensure the peel strength of the electrode. It has also been found that such a flaky shape having wrinkles on the flake surface can be achieved by applying a manufacturing method described below.

[0027] <Method of manufacturing porous carbon> The porous carbon of the present invention is, for example, (1) obtaining a mixture containing a carbon source and a calcium compound; (2) heat-treating the mixture in an inert gas atmosphere to obtain a carbide; and (3) removing calcium compounds from the carbonized material It can be produced by a method comprising:

[0028] The carbon source is not particularly limited, but sugars are preferred to enhance uniform dispersion with the calcium compound. Examples of sugars 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, and pectin. These sugars can be used alone or in combination of two or more. Among these sugars, glucose and starch are preferred because they are easy to produce porous carbon that improves the input / output characteristics of non-aqueous electrolyte secondary batteries at room temperature and are readily available in large quantities.

[0029] The starch is not particularly limited, and starches derived from, for example, corn, cassava, potato, sweet potato, tapioca, beans, wheat, rice, etc. can be used. The amylose content of the starch preferred in the present invention is preferably 50% by mass or less, more preferably 30% by mass or less. Since the lower the amylose content of starch, the lower the gelatinization temperature tends to be. Therefore, starch having an amylose content below the upper limit mentioned above is preferred because it is more likely to gelatinize at low temperatures and has increased compatibility with calcium compounds. The amylose content can be determined, for example, by iodine colorimetry. The starch may also be modified. Examples of modified starches include etherified starch, esterified starch, cationized starch, and cross-linked starch. One type of starch may be used alone, or two or more types may be used in combination.

[0030] The calcium compound is not particularly limited, and examples include calcium chloride, calcium hydroxide, calcium oxide, calcium carbonate, calcium acetate, calcium fluoride, calcium bromide, calcium iodide, calcium carbide, calcium bicarbonate, calcium nitrate, calcium sulfate, calcium silicate, calcium phosphate, calcium pyrophosphate, calcium gluconate, and calcium lactate. Among these calcium compounds, calcium compounds with a melting point of 300°C or less are preferred because they facilitate the production of porous carbon that improves the input / output characteristics of nonaqueous electrolyte secondary batteries at room temperature. (When the mixture contains a polyhydric alcohol or a carboxylic acid, the melting point of the eutectic compound between the calcium compound and the polyhydric alcohol or the carboxylic acid is 300°C or less.) More preferred are at least one selected from the group consisting of calcium chloride hydrate, calcium hydroxide, calcium oxide, calcium carbonate, and calcium acetate. Calcium chloride hydrate exists as a dihydrate, tetrahydrate, and hexahydrate, but the dihydrate is preferred due to its favorable reactivity with sugars.

[0031] The mixture containing a carbon source and a calcium compound may further contain at least one selected from the group consisting of a polyhydric alcohol and a carboxylic acid. When a polyhydric alcohol and / or a carboxylic acid is present in the mixture, the calcium compound dissolves in the polyhydric alcohol and / or the carboxylic acid, forming a eutectic compound. The eutectic compound is believed to be formed by coordination of calcium with the hydroxyl, carboxylate, or carboxyl groups in the polyhydric alcohol and / or the carboxylic acid. Therefore, a calcium compound that has a melting point of 300°C or higher alone can have a melting point of 300°C or lower as a eutectic compound. Therefore, in the present invention, the phrase "a calcium compound having a melting point of 300°C or lower" also encompasses the phrase "a eutectic compound of a polyhydric alcohol and / or a carboxylic acid with a calcium compound having a melting point of 300°C or lower." Examples of polyhydric alcohols that can be used in the present invention include glycerin, ethylene glycol, propylene glycol, polyethylene glycol, and polypropylene glycol. Among these, glycerin and ethylene glycol are preferred because they readily form a eutectic with calcium compounds and are readily available in large quantities. Examples of carboxylic acids include formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, lactic acid, malic acid, citric acid, benzoic acid, phthalic acid, salicylic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, fumaric acid, and maleic acid, and among these, formic acid and acetic acid are preferred from the viewpoints of their ease of dissolving calcium compounds and their ease of mass procurement. When one or more polyhydric alcohols and one or more carboxylic acids are used in combination, the mixing ratio of the polyhydric alcohol and the carboxylic acid can be appropriately changed depending on the desired properties of the porous carbon.

[0032] The method for mixing the carbon source and calcium compound, and optionally the polyhydric alcohol and / or carboxylic acid, is not particularly limited, and they can be mixed by any mixing method.

[0033] The amount of calcium compound mixed with the carbon source is preferably 70 parts by mass or more, more preferably 80 parts by mass or more, even more preferably 130 parts by mass or more, and even more preferably 180 parts by mass or more, per 100 parts by mass of saccharides, and is preferably 500 parts by mass or less, more preferably 400 parts by mass or less, and even more preferably 300 parts by mass or less. When the amount of calcium compound is within the above range, the pore volume and pore diameter of the obtained porous carbon tend to be appropriate.

[0034] When the mixture containing a carbon source and a calcium compound further contains a polyhydric alcohol and / or a carboxylic acid, the amount of the polyhydric alcohol and / or the carboxylic acid is preferably 50 parts by mass or more, more preferably 100 parts by mass or more, even more preferably 150 parts by mass or more, and preferably 500 parts by mass or less, more preferably 400 parts by mass or less, and even more preferably 300 parts by mass or less, relative to 100 parts by mass of the sugars (when one or more polyhydric alcohols and one or more carboxylic acids are used in combination, this refers to the total amount). When the amount of the polyhydric alcohol and / or the carboxylic acid is within the above range, it is easy to form a eutectic compound with the calcium compound, and the eutectic compound is easily compatible with the sugars, so the pore volume and pore diameter of the resulting porous carbon tend to be appropriate.

[0035] In the production method of the present invention, a carbide is obtained by heat-treating a mixture containing a carbon source and a calcium compound in an inert gas atmosphere. Examples of inert gases include nitrogen and argon. The lower the concentration of oxidizing gas in the gas used, the better. The amount of oxidizing gas, particularly oxygen, mixed in is usually 1% by volume or less, more preferably 0.1% by volume or less. When the oxygen concentration is below the above-mentioned upper limit, oxidation of the carbide is easily suppressed, making it easier to obtain a structure with the desired characteristics. Oxidative decomposition of the resulting structure can also be suppressed. The heat treatment temperature is preferably 400°C or higher, more preferably 500°C or higher, even more preferably 700°C or higher, and even more preferably 800°C or higher, and preferably 1300°C or lower, more preferably 1200°C or lower, and even more preferably 1000°C or lower. When the heat treatment temperature is within the above-mentioned range, the resulting porous carbon tends to have an appropriate pore volume of 2 nm to 200 nm, and also tends to facilitate the removal of calcium compounds from the carbide in the subsequent step of removing calcium compounds. The heat treatment may be carried out in multiple stages, for example, by evaporating the water in the mixture at 50 to 300° C., followed by heat treatment (carbonization) at 400 to 900° C., and then heat treatment (firing) at 900 to 1300° C. By carrying out the heat treatment in multiple stages, a carbide having more uniform physical properties can be obtained.

[0036] The heat treatment time is not particularly limited, but is, for example, 0.5 hours or more, more preferably 1 hour or more, even more preferably 3 hours or more, and preferably 24 hours or less, more preferably 12 hours or less, and even more preferably 8 hours or less. A heat treatment time within the above range is preferable because carbonization proceeds sufficiently and ignition is less likely to occur. Also, from an economical viewpoint, it is preferable because the time is appropriate.

[0037] In the manufacturing method of the present invention, the temperature rise rate during the heat treatment step is preferably 2°C / min or more, more preferably 10°C / min or more, and even more preferably 20°C / min or more. When the temperature rise rate is equal to or higher than the lower limit, the pore size tends to be appropriate. There is no particular upper limit to the temperature rise rate, but from the viewpoint of realizing uniform heat treatment, it is preferably 200°C / min or less.

[0038] The furnace used for heat treatment can be of various types, such as a rotary kiln, fluidized bed furnace, fixed bed furnace, moving bed furnace, or moving bed furnace. Both continuous furnaces, which continuously charge raw materials and remove products, and batch furnaces, which do so intermittently, can be used. Any heating means can be used as long as it is capable of heating to a predetermined temperature, and examples of applicable heating means include electric heating, gas combustion heating, high-frequency induction heating, and electric current heating. These heating means can be used alone or in combination.

[0039] The porous carbon of the present invention can be obtained by removing calcium compounds from the resulting carbide. The removal of calcium compounds is preferably carried out, for example, by acid washing. Examples of acids used in acid washing include hydrochloric acid, sulfuric acid, and nitric acid. Hydrochloric acid is preferred because it easily dissolves metal compounds in the carbide, is less likely to leave impurities such as sulfur, and is more likely to inhibit oxidation of the carbide. The concentration of the acid used in acid washing may be varied depending on the type of acid used. For example, when hydrochloric acid is used, the concentration is preferably in the range of 0.01 to 1.0 mol / L, more preferably 0.05 to 0.5 mol / L. A hydrochloric acid concentration within the above range is preferred because it facilitates removal of metal compounds and is less likely to leave hydrochloric acid in the carbide.

[0040] The pH of the acid used during acid washing may be appropriately changed depending on the type, concentration, temperature, etc. of the acid used, but is preferably not more than 3, more preferably not more than 2.5. When the pH of the acid is not more than the upper limit, metal compounds can be easily and efficiently removed.

[0041] Acid washing may be carried out, for example, by immersing the obtained carbide in the acid. When acid washing is carried out by immersion in acid, the mass ratio of the acid to the carbide may be appropriately adjusted depending on the type, concentration, temperature, etc. of the acid used. The mass of the carbide to be immersed relative to the mass of the acid is preferably 2 mass% or more, more preferably 5 mass% or more. The upper limit of the mass ratio is preferably 50 mass% or less, more preferably 30 mass% or less. When the mass ratio of the carbide to be immersed relative to the mass of the acid is within the above range, a sufficient washing effect is likely to be obtained.

[0042] The method for acid-washing the carbide is not particularly limited as long as it allows the carbide to be immersed in acid, and may include a method in which acid is continuously added, retained for a predetermined time, and immersed while removing the acid, or a method in which the carbide is immersed in acid, retained for a predetermined time, drained, and then new acid is added, and the immersion-draining process is repeated. Furthermore, the acid may be entirely renewed, or part of the acid may be renewed. Furthermore, the acid may be stirred during immersion.

[0043] The atmosphere in which the acid washing is carried out is not particularly limited and may be appropriately selected depending on the method used for washing. In the present invention, the acid washing is usually carried out in an air atmosphere.

[0044] The time for immersing the carbide in acid can be adjusted as appropriate depending on the acid used, the treatment temperature, etc., but from the viewpoint of sufficient removal of metal compounds, it is preferably 5 minutes or more, and from the viewpoint of productivity, it is preferably 60 minutes or less, more preferably 40 minutes or less, and even more preferably 35 minutes or less.

[0045] After the carbonized material is acid-washed, it is preferable to remove the acid in the porous carbon by washing with water. This acid washing and water washing may be repeated until the calcium compounds in the porous carbon are completely removed. Furthermore, the temperature of the solution used in acid washing and water washing is preferably high from the viewpoint of the efficiency of removing calcium compounds and residual acid, and is usually 60°C or higher.

[0046] In one embodiment of the present invention, a mixture containing a carbon source and a calcium compound may be heat-treated (carbonized) at 500 to 900°C, followed by acid washing, and the acid-washed porous carbon may be heat-treated (calcined) at 900 to 1300°C. By carrying out carbonization at 900°C or less, it becomes easy to remove metal compounds derived from the calcium compound in the acid washing step, and by calcining at a higher temperature of 900 to 1300°C, it becomes easy to obtain the desired pore volume and specific surface area.

[0047] After acid washing and water rinsing, the porous carbon may be dried using a known dryer such as a hot air dryer or a reduced pressure dryer. Drying is preferably carried out at a temperature of 50 to 150°C. A drying temperature within the above range is preferred because oxidation of the porous carbon is unlikely to occur and drying proceeds appropriately.

[0048] The dried porous carbon may be pulverized. The pulverization step is a step for controlling the shape, particle size, etc. of the finally obtained porous carbon to a desired shape, particle size, etc. The pulverization method is not particularly limited, and known pulverizers such as a ball mill, centrifugal roll mill, ring roll mill, centrifugal ball mill, jet mill, cone crusher, double roll crusher, disc crusher, and rotary crusher can be used alone or in combination.

[0049] In the present invention, the method for producing porous carbon may further include a classification step after the pulverization step. For example, by removing particles that are significantly smaller or larger than the desired particle size, porous carbon with a narrow particle size distribution can be obtained. The classification method is not particularly limited, but examples include classification using a sieve, wet classification, and dry classification. Examples of wet classifiers include classifiers that utilize the principles of gravity classification, inertial classification, hydraulic classification, and centrifugal classification. Examples of dry classifiers include classifiers that utilize the principles of sedimentation classification, mechanical classification, and centrifugal classification. From an economical standpoint, it is preferable to use a dry classification device. Furthermore, to prevent surface oxidation during pulverization, it is preferable to perform the pulverization and classification steps in an inert gas atmosphere.

[0050] Pulverization and classification can also be performed using a single device. For example, pulverization and classification can be performed using a jet mill equipped with a dry classification function. Furthermore, devices having a pulverizer and a classifier independent from each other can also be used. In this case, pulverization and classification can be performed continuously, or pulverization and classification can be performed discontinuously.

[0051] <Additives for positive electrodes of non-aqueous electrolyte secondary batteries> The porous carbon of the present invention can be preferably used as a positive electrode additive for non-aqueous electrolyte secondary batteries. Because the porous carbon of the present invention has the above-mentioned specific pores and a low bulk density, when used as a positive electrode additive for non-aqueous electrolyte secondary batteries, it not only improves the diffusibility of lithium ions into the positive electrode and the adsorption of lithium ions into the pores, making it easier to insert and extract lithium ions into the positive electrode active material, thereby improving the input / output characteristics of non-aqueous electrolyte secondary batteries, but also suppresses binder adsorption to the additive and aggregation of the additives during electrode production, thereby contributing to improving the manufacturing stability of the electrode and improving the peel strength of the electrode.

[0052] Examples of the non-aqueous electrolyte secondary battery include a lithium ion secondary battery, a sodium ion secondary battery, and a lithium-sulfur battery. In a preferred embodiment of the present invention, the porous carbon of the present invention can be used as an additive for a positive electrode of a lithium ion secondary battery.

[0053] <Nonaqueous electrolyte secondary battery positive electrode composition> The present invention also encompasses a composition for a positive electrode of a non-aqueous electrolyte secondary battery containing the above-described additive for a positive electrode of a non-aqueous electrolyte secondary battery and a positive electrode active material. Furthermore, the present invention also encompasses a composition for a positive electrode of a lithium ion secondary battery containing the above-described additive for a positive electrode of a lithium ion secondary battery. The composition for a positive electrode of a non-aqueous electrolyte secondary battery of the present invention may optionally contain other components in addition to the additive for a positive electrode of a non-aqueous electrolyte secondary battery and the positive electrode active material.

[0054] [Cathode active material] As the cathode active material contained in the composition for the cathode of a non-aqueous electrolyte secondary battery, known cathode active materials can be used without particular limitation. For example, lithium-containing cobalt oxide (LiCoO2), lithium manganate (LiMn2O4), lithium-containing nickel oxide (LiNiO2), lithium-containing composite oxides of Co-Ni-Mn, lithium-containing composite oxides of Ni-Mn-Al, lithium-containing composite oxides of Ni-Co-Al, olivine-type lithium iron phosphate (LiFePO4), olivine-type lithium manganese phosphate (LiMnPO4), Li 1+x Mn 2-x excess lithium spinel compounds represented by O4 (0 < X < 2), Li[Ni 0.17 Li 0.2 Co 0.07 Mn 0.56 O2, LiNi 0.5 Mn 1.5 O4 and other metal oxides, sulfur, compounds and polymers having nitroxyl radicals, compounds and polymers having oxyl radicals, compounds and polymers having nitrogen radicals, organic radicals such as compounds and polymers having a fulvalene skeleton, etc. can be mentioned.

[0055] These can be used alone or in combination of two or more. And among those mentioned above, from the viewpoint of improving the battery capacity etc. of the secondary battery, as the cathode active material, lithium-containing cobalt oxide (LiCoO2); lithium-containing nickel oxide (LiNiO2); lithium-containing composite oxides of Co-Ni-Mn, for example, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, etc.; lithium-containing composite oxides of Ni-Co-Al, for example LiNi 0.8 Co 0.1 Al 0.1 O2, LiNi 0.8 Co 0.15 Al 0.05 O2, etc. are preferably used.

[0056] The particle size of the positive electrode active material is not particularly limited and can be the same as that of conventionally used positive electrode active materials. Typically, a positive electrode active material having a particle size in the range of 0.1 to 40 μm, more preferably 0.5 to 20 μm, can be used.

[0057] In the composition for a positive electrode of a non-aqueous electrolyte secondary battery of the present invention, the content of the positive electrode active material is preferably 40 to 97 mass %, more preferably 45 to 95 mass %, based on the total mass of the solid content of the composition.

[0058] The content of the additive for a positive electrode of a non-aqueous electrolyte secondary battery is preferably 0.5% by mass or more, more preferably 1% by mass or more, and preferably 10% by mass or less, more preferably 8% by mass or less, and even more preferably 6% by mass or less, relative to the total mass of the positive electrode active material. When the content of the additive for a positive electrode of a non-aqueous electrolyte secondary battery is within the above range, the effect of reducing electrode resistance is easily exerted sufficiently, and the overall mass of the positive electrode active material is not reduced, making it difficult for the capacity to decrease.

[0059] The mixing ratio of the additive for a positive electrode of a non-aqueous electrolyte secondary battery to the positive electrode active material may be 1:99 to 10:90 by mass. When the mixing ratio of the additive for a positive electrode of a non-aqueous electrolyte secondary battery to the positive electrode active material is within this range, a non-aqueous electrolyte secondary battery with excellent input / output characteristics is likely to be obtained.

[0060] [solvent] The composition for a positive electrode of a non-aqueous electrolyte secondary battery of the present invention may contain a solvent. As the solvent, for example, an organic solvent can be used, and among them, a polar organic solvent capable of dissolving the binder described below is preferred. Specifically, examples of organic solvents that can be used include acetonitrile, N-methylpyrrolidone (NMP), acetylpyridine, cyclopentanone, N,N-dimethylacetamide, dimethylformamide, dimethyl sulfoxide, methylformamide, methyl ethyl ketone, furfural, and ethylenediamine. Among these, N-methylpyrrolidone is preferred from the viewpoints of ease of handling, safety, and ease of synthesis. These organic solvents may be used alone or in combination of two or more.

[0061] The solvent can be used in an amount such that the solids concentration in the composition for a positive electrode of a non-aqueous electrolyte secondary battery is preferably 1 to 80 mass %, more preferably 5 to 70 mass %, and even more preferably 10 to 60 mass %. By setting the solids concentration within the above range, the positive electrode active material, the additive for a positive electrode of a non-aqueous electrolyte secondary battery, and other components contained therein can be uniformly dispersed, which is preferable.

[0062] [binder] The positive electrode composition for a nonaqueous electrolyte secondary battery of the present invention preferably contains a binder to effectively adhere positive electrode active material particles to each other and to effectively adhere the positive electrode active material to a current collector. Examples of binders that may be used include, but are not limited to, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, and nylon. These binders may be used alone or in combination of two or more. In the composition for a positive electrode of a non-aqueous electrolyte secondary battery of the present invention, the content of the binder is preferably 0.5 to 10 mass %, more preferably 1 to 7 mass %, based on the total mass of the positive electrode in the composition.

[0063] [Conductive material] The composition for a positive electrode of a nonaqueous electrolyte secondary battery of the present invention may further contain a conductive material to further enhance the conductivity of the positive electrode formed on the current collector. Any electrically conductive material that does not undergo chemical changes in the resulting nonaqueous electrolyte secondary battery may be used as the conductive material. Specific examples of the conductive material include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, and carbon fiber; metal-based materials such as metal powders and metal fibers of copper, nickel, aluminum, and silver; and conductive polymers such as polyphenylene derivatives. These conductive materials may be used alone or in combination of two or more. In the composition for a positive electrode of a non-aqueous electrolyte secondary battery of the present invention, the content of the conductive material is preferably 1 to 10 mass %, more preferably 1 to 7 mass %, based on the total mass of the positive electrode solid content in the composition.

[0064] <Method for producing a composition for a positive electrode of a non-aqueous electrolyte secondary battery> The method for producing the non-aqueous electrolyte secondary battery positive electrode composition of the present invention can be carried out by mixing the above-mentioned additive for the non-aqueous electrolyte secondary battery positive electrode, the positive electrode active material, and, if necessary, a solvent and other components. The mixing method is not particularly limited, and a general mixing device such as a disperser, mill, or kneader can be used. It is preferable to use such a mixing device and stir the mixture for, for example, 20 minutes to 120 minutes.

[0065] The mixing temperature is not particularly limited, and mixing can be performed, for example, in the range of 0 to 160° C., preferably in the range of 20 to 80° C. If the mixing temperature is within the above range, the composition tends to have a viscosity suitable for coating, and evaporation of the organic solvent is less likely to occur, which is preferable.

[0066] The atmosphere in which the mixture is mixed is not particularly limited, but mixing is usually carried out in the air.

[0067] <Nonaqueous electrolyte secondary battery> The nonaqueous electrolyte secondary battery positive electrode composition of the present invention can be usefully used in nonaqueous electrolyte secondary batteries. Accordingly, the present invention also encompasses nonaqueous electrolyte secondary batteries having a positive electrode prepared using the above-described nonaqueous electrolyte secondary battery positive electrode composition. By incorporating the above-described additive for a nonaqueous electrolyte secondary battery positive electrode, the nonaqueous electrolyte secondary battery of the present invention can improve the diffusibility of electrolyte ions in the positive electrode, thereby improving the input / output characteristics of the battery. The nonaqueous electrolyte secondary battery of the present invention preferably operates at 2 V to 5 V, and examples thereof include lithium ion secondary batteries and capacitors. Accordingly, the present invention also encompasses lithium ion secondary batteries comprising a positive electrode containing the lithium ion secondary battery positive electrode composition of the present invention.

[0068] When the non-aqueous electrolyte secondary battery of the present invention is, for example, a lithium ion secondary battery, the lithium ion secondary battery comprises a positive electrode, a negative electrode, and an electrolyte.

[0069] [Positive electrode] The positive electrode is produced using the composition for a positive electrode of a non-aqueous electrolyte secondary battery of the present invention, and includes a current collector and a positive electrode active material layer. The positive electrode active material layer is formed by applying the composition for a positive electrode of a non-aqueous electrolyte secondary battery of the present invention to the current collector.

[0070] The method for applying the nonaqueous electrolyte secondary battery positive electrode composition to the current collector is not particularly limited, and known methods can be used. Specifically, for example, a doctor blade method, a dipping method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, a brush coating method, etc. can be used. In this case, the nonaqueous electrolyte secondary battery positive electrode composition may be applied to only one side of the current collector, or may be applied to both sides. The thickness of the composition film on the current collector after application and before drying may be appropriately set depending on the thickness of the positive electrode active material layer obtained by drying.

[0071] As the current collector to which the composition for a positive electrode of a nonaqueous electrolyte secondary battery is applied, it is preferable to use a material that is electrically conductive and electrochemically durable. Specifically, a current collector made of aluminum or an aluminum alloy can be used. In this case, aluminum and an aluminum alloy may be used in combination, or different types of aluminum alloys may be used in combination. Aluminum and aluminum alloys are excellent current collector materials because they are heat resistant and electrochemically stable.

[0072] The method for drying the composition for a positive electrode of a non-aqueous electrolyte secondary battery on the current collector is not particularly limited and any known method can be used, for example, drying with warm air, hot air, or low-humidity air, vacuum drying, or drying by irradiation with infrared rays or electron beams, etc. By drying the composition for a positive electrode of a non-aqueous electrolyte secondary battery on the current collector in this manner, a positive electrode active material layer can be formed on the current collector, and a positive electrode including the current collector and the positive electrode active material layer can be obtained.

[0073] After the drying step, the positive electrode active material layer may be subjected to pressure treatment using a mold press, a roll press, etc. Pressure treatment can improve the adhesion between the positive electrode active material layer and the current collector.

[0074] [Negative electrode] The negative electrode includes a current collector and a negative electrode active material layer formed on the current collector, the negative electrode active material layer including a negative electrode active material. The process for manufacturing the negative electrode is a process well known in the art.

[0075] The negative electrode active material includes a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, a lithium metal alloy, a material capable of doping and dedoping lithium, or a transition metal oxide.

[0076] Examples of substances that can reversibly intercalate / deintercalate lithium ions include crystalline carbon and amorphous carbon, and these can be used alone or in combination of two or more. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flaky, spherical or fibrous natural graphite or artificial graphite. Examples of the amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, etc.

[0077] Examples of the alloy of the lithium metal include alloys of lithium and metals selected from the group consisting of Na, K, Mg, Ca, Sr, Si, Sb, In, Zn, Ge, Al and Sn.

[0078] Examples of substances that can be doped and undoped with lithium include alloys such as Si, SiMg, SiO x (0 < x < 2), Sn, SnO2, etc.

[0079] The content of the negative electrode active material in the negative electrode active material layer is preferably 70 to 100% by mass based on the total mass of the negative electrode active material layer, and the negative electrode active material layer may consist only of the negative electrode active material.

[0080] The negative electrode active material layer may contain a binder and optionally may further contain a conductive material. The content of the binder in the negative electrode active material layer is preferably 1 to 5% by mass based on the total mass of the negative electrode active material layer. When further containing a conductive material, the negative electrode active material may be used at 80 to 98% by mass, the binder at 1 to 10% by mass, and the conductive material at 1 to 10% by mass.

[0081] The binder serves to make the negative electrode active material particles adhere well to each other and also make the negative electrode active material adhere well to the current collector. As the binder, a water-insoluble binder, a water-soluble binder or a combination thereof may be used.

[0082] Examples of the non-water-soluble binder include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, and combinations thereof.

[0083] Examples of the water-soluble binder include styrene-butadiene rubber, acrylated styrene-butadiene rubber, polyvinyl alcohol, sodium polyacrylate, a copolymer of propylene and an olefin having 2 to 8 carbon atoms, a copolymer of (meth)acrylic acid and a (meth)acrylic acid alkyl ester, and combinations thereof.

[0084] When a water-soluble binder is used as the negative electrode binder, a cellulose-based compound capable of imparting viscosity to the negative electrode active material layer may be further used as a thickener. Examples of the cellulose-based compound include carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, and alkali metal salts thereof. Such a thickener may be added in an amount of 0.1 to 100 parts by mass per 100 parts by mass of the binder.

[0085] The conductive material is used to impart conductivity to the electrodes, and any electron-conductive material that does not undergo chemical changes in the resulting battery can be used. Specific examples of the conductive material include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, and carbon fiber; metal-based materials such as metal powders or metal fibers of copper, nickel, aluminum, and silver; and conductive polymers such as polyphenylene derivatives. These conductive materials may be used alone or in combination of two or more.

[0086] The current collector may be selected from the group consisting of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof.

[0087] The electrolyte preferably contains a non-aqueous organic solvent and a lithium salt.

[0088] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can migrate.

[0089] The non-aqueous organic solvent may be a carbonate, ester, ether, ketone, alcohol, or aprotic solvent. The carbonate solvent may be dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), or the like. The ester solvent may be n-methyl acetate, n-ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, decanolide, valerolactone, mevalonolactone, caprolactone, or the like. The ether may be dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, etc., and the ketone solvent may be cyclohexanone, etc. Furthermore, the alcohol solvent may be ethyl alcohol, isopropyl alcohol, etc., and the aprotic solvent may be nitriles such as R-CN (R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, which may contain a double bond, an aromatic ring, or an ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, sulfolanes, etc.

[0090] The non-aqueous organic solvents may be used alone or in combination of two or more kinds. When two or more kinds are used in combination, the mixing ratio may be appropriately adjusted depending on the desired battery performance.

[0091] In addition, in the case of the carbonate-based solvent, it is preferable to use a mixture of a cyclic carbonate and a chain carbonate in a volume ratio of 1:1 to 1:9, which tends to further improve the performance of the electrolyte solution.

[0092] The lithium salt is a substance that is dissolved in an organic solvent and acts as a lithium ion supply source in the battery, enabling basic operation of a lithium ion secondary battery and promoting the movement of lithium ions between the positive electrode and the negative electrode. Representative examples of such lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiCF3SO3, LiN(SO2C2F5)2, Li(CF3SO2)2N, LiC4F9SO3, LiClO4, LiAlO4, LiAlCl4, LiN(C x F 2x+1 SO2)(C y F 2y+1 Examples of lithium salts include lithium bis(oxalatoborate) (LiB(C2O4)2) (where x and y are natural numbers), LiCl, LiI, and LiB(C2O4)2 (lithium bis(oxalatoborate) (LiBOB)). These may be used alone or in combination of two or more. The lithium salt concentration is preferably within the range of 0.1 to 2.0 M. When the lithium salt concentration is within this range, the electrolyte has good conductivity, making it easy to maintain electrolyte performance, and the viscosity is appropriate, making it easy to improve the mobility of lithium ions.

[0093] The electrolyte may further contain a vinylene carbonate or ethylene carbonate compound as a life-promoting agent to improve the battery life.

[0094] Representative examples of the ethylene carbonate-based compound include difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, fluoroethylene carbonate, etc. When such a life extender is further used, the amount used can be appropriately adjusted depending on the type of compound used.

[0095] In the lithium ion secondary battery of the present invention, a separator may be present between the positive electrode and the negative electrode. Such a separator may be made of polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more of these, or a mixed multilayer film such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator.

[0096] A lithium ion secondary battery is generally formed by arranging the above-mentioned positive electrode and negative electrode (with a separator interposed between them as necessary) facing each other and immersing them in an electrolyte solution. [Example]

[0097] The present invention will be described in more detail below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0098] <BET specific surface area, pore volume and mode diameter by nitrogen adsorption method> [BET specific surface area] Below is an approximate formula derived from the BET formula.

number

[0099] Using the above approximation formula, we substitute the amount of adsorption (v) measured at liquid nitrogen temperature using the multipoint method for nitrogen adsorption at relative pressures (p / p0) of 0.05 to 0.1 to obtain vm The specific surface area (SSA: unit is m 2 / g) was calculated.

number

[0100] In the above formula, v m is the amount of adsorption (cm) required to form a monolayer on the sample surface. 3 / g), and v is the measured adsorption amount (cm 3 / g), p0 is the saturated vapor pressure, p is the absolute pressure, c is a constant (reflecting the heat of adsorption), and N is Avogadro's number 6.022 × 10 23 , a(nm 2 ) is the area occupied by the adsorbate molecule on the sample surface (molecular occupied cross-sectional area).

[0101] Specifically, the amount of nitrogen adsorbed to the carbon material at liquid nitrogen temperature was measured using an "Autosorb-iQ-MP" manufactured by Quantachrome, as follows: The carbon material serving as 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 onto the measurement sample at the desired relative pressure. The amount of nitrogen adsorbed by the sample when equilibrium pressure was reached at each desired relative pressure was defined as the adsorbed gas amount v.

[0102] [Pore volume] The adsorption isotherm obtained by measuring the amount of adsorbed nitrogen was analyzed by the QS-DFT method, and the volume of pores having a pore diameter of less than 2 nm was calculated as the micropore volume.

[0103] The adsorption isotherm obtained by measuring the amount of adsorbed nitrogen was analyzed by the BJH method, and the volume of pores having a pore size (pore diameter) of 2 nm or more and 200 nm or less was calculated.

[0104] The adsorption isotherm obtained by measuring the amount of adsorbed nitrogen was analyzed by the DH method, and the volume of pores having a pore size (pore diameter) of 2 nm or more and 10 nm or less was calculated.

[0105] [Mode diameter] Using the BJH method described above, the logarithmic differential pore volume distribution (dV / d(log D)) was calculated by differentiating the cumulative pore volume (V) with the common logarithm of the pore diameter (D), and the pore diameter with the highest appearance ratio was taken as the mode diameter.

[0106] <Bulk density> The bulk density was measured using a Powder Tester PT-X manufactured by Hosokawa Micron Corp. The sample was placed in an automatic tap density measuring unit, and the bulk density was calculated from the volume after tapping 3,000 times.

[0107] <Average primary particle diameter> The average primary particle size was measured by the following method. Samples of Examples 1 to 13 and Comparative Examples 1 to 11 described below were placed in an aqueous solution containing 5% by mass of a surfactant ("Toriton X100" sold by Wako Pure Chemical Industries, Ltd.), treated in an ultrasonic cleaner for 10 minutes or more, and dispersed in the aqueous solution. The particle size distribution was measured using this dispersion. The particle size distribution measurement was performed using a particle size / particle size distribution measuring device ("Microtrac MT3300EXII" manufactured by Microtrac-Bell Corporation), and the particle size at which the cumulative volume reached 50% was defined as the average primary particle. For samples of Comparative Examples 12 and 13 described below, the particle size distribution could not be measured using the above particle size distribution measurement method, so the particle sizes of 1,000 primary particles shown in the electron microscope image were measured using a transmission electron microscope, and the average value was calculated.

[0108] <Impurity element content> The content of impurity elements was measured using the following method. Carbon samples containing predetermined amounts of impurity elements were prepared in advance, and a calibration curve was created using an X-ray fluorescence analyzer to plot the relationship between Kα ray intensity and impurity element content. The sample was then measured for impurity element Kα ray intensity in X-ray fluorescence analysis, and the impurity element content was determined from the previously prepared calibration curve. X-ray fluorescence analysis was performed using a LAB CENTER XRF-1700 (Shimadzu Corporation) under the following conditions: A top-illumination holder was used, and the sample measurement area was set to a circumference with a diameter of 20 mm. The sample to be measured was placed in a polyethylene container with an inner diameter of 25 mm, with 0.5 g of the sample placed inside. The back was held down with a plankton net, and the measurement surface was covered with polypropylene film. The X-ray source was set to 40 kV and 60 mA.

[0109] <Particle shape> The particle shape was observed using a scanning electron microscope (Keyence Corporation VE-8800) with an accelerating voltage of 5 to 20 kV and a measurement magnification of 1000 to 10000 times.

[0110] <Preparation of a composition for a positive electrode of a lithium ion secondary battery> 30 parts by mass of N-methylpyrrolidone solution containing 3 parts by mass of polyvinylidene fluoride (KF Polymer 7200 manufactured by Kureha Corporation), LiNi as the positive electrode active material 1 / 3 Co 1 / 3 Mn 1 / 3 93 parts by mass of O2 (manufactured by Nippon Chemical Industry Co., Ltd., "Cellseed C-5H"), 2 parts by mass of acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd., "Denka Black") as a conductive material, and 2 parts by mass of the porous carbon prepared in the examples and comparative examples described below were mixed together, and the mixture was stirred and dispersed in a homomixer (manufactured by Primix Corporation) (4500 rpm) while adding N-methylpyrrolidone appropriately so that the solids concentration of the composition became 50% by mass, thereby obtaining a composition for a lithium-ion secondary battery positive electrode.

[0111] <Preparation of positive electrodes for lithium-ion secondary batteries> The lithium-ion secondary battery positive electrode composition was applied to an aluminum foil current collector ("1N30-H" manufactured by Fuji Kakoshi) using a bar coater ("T101" manufactured by Matsuo Sangyo Co., Ltd.). The coated foil was then dried at 80°C for 30 minutes in a hot air dryer (manufactured by Yamato Scientific Co., Ltd.), followed by rolling using a roll press (manufactured by Hosen Co., Ltd.). The resulting cathodes (φ14 mm) were punched out and then secondary dried at 120°C for 3 hours under reduced pressure to produce lithium-ion secondary battery positive electrodes. The moisture content of the dried electrodes (φ14 mm) was measured by heating them to 250°C using a Karl Fischer meter (manufactured by Mitsubishi Chemical Analytech Co., Ltd.) under a nitrogen stream. The moisture content was controlled to be 20 ppm or less, allowing the added porous carbon to perform functions other than water absorption.

[0112] <Production of lithium-ion secondary batteries> The positive electrode for the lithium-ion secondary battery was transferred to a glove box (Miwa Manufacturing Co., Ltd.) under an argon gas atmosphere. A laminate consisting of a metallic lithium foil (0.2 mm thick, φ16 mm) as the negative electrode active material layer and a stainless steel foil (0.2 mm thick, φ17 mm) as the current collector was used for the negative electrode. A polypropylene separator (Celgard #2400, Polypore) was used as the separator. The electrolyte was a mixed solvent of lithium hexafluorophosphate (LiPF6) in ethylene carbonate (EC), ethyl methyl carbonate (EMC), and vinylene carbonate (VC) (1M-LiPF6, EC / EMC = 3 / 7 vol%, VC = 2 wt%). A coin-type lithium-ion secondary battery (2032 type) was fabricated.

[0113] Example 1 One gram of starch (corn-derived, amylose content approximately 26%, sold by Fujifilm Wako Pure Chemical Industries, Ltd.) was mixed with 2 g of calcium chloride dihydrate (sold by Fujifilm Wako Pure Chemical Industries, Ltd.) (200 parts by mass per 100 parts by mass of starch). The resulting mixture was heated to 700°C in a nitrogen gas atmosphere. The heating rate to 700°C was 10°C / min. A carbonized product was then obtained by heat-treating the mixture at 700°C for 60 minutes under a nitrogen gas flow. After washing with 0.1 mol / L hydrochloric acid at 80°C for 30 minutes, the carbonized product was removed onto a Buchner funnel and washed with water until the pH of the filtrate reached a range of 6 to 8. The acid washing and water washing were repeated three times, followed by hot air drying at 80°C, yielding a porous carbon. The resulting porous carbon was then heat-treated (calcined) at 900°C for 60 minutes.

[0114] Example 2 A porous carbon was obtained in the same manner as in Example 1, except that the temperature was raised at a rate of 5° C. / min under a nitrogen gas flow.

[0115] Example 3 A porous carbon was obtained in the same manner as in Example 1, except that the temperature was raised at a rate of 20° C. / min under a nitrogen gas flow.

[0116] Example 4 A porous carbon was obtained in the same manner as in Example 1, except that the amount of calcium chloride dihydrate added was 150 parts by mass per 100 parts by mass of starch.

[0117] Example 5 A porous carbon was obtained in the same manner as in Example 1, except that the amount of calcium chloride dihydrate added was 300 parts by mass per 100 parts by mass of starch.

[0118] Example 6 The porous carbon was obtained in the same manner as in Example 1, except that the obtained porous carbon was not further heat-treated (calcined) at 900° C. for 60 minutes.

[0119] Example 7 The porous carbon was obtained by carrying out the same treatment as in Example 1, except that the obtained porous carbon was further heat-treated (calcined) at 1200°C for 60 minutes instead of at 900°C for 60 minutes.

[0120] Example 8 1 g of glucose (available from Fujifilm Wako Pure Chemical Industries, Ltd.) was mixed with 1.1 g of calcium chloride dihydrate (110 parts by mass per 100 parts by mass of glucose), and the resulting mixture was heated to 700°C in a nitrogen gas atmosphere. The heating rate to 700°C was 10°C / min. A carbonized product was then obtained by heat-treating the mixture at 700°C for 60 minutes under a nitrogen gas stream. After washing with 0.1 mol / L hydrochloric acid at 80°C for 30 minutes, the carbonized product was removed onto a Buchner funnel and washed with water until the pH of the filtrate reached a range of 6 to 8. The acid washing and water washing were repeated three times, followed by hot air drying at 80°C to obtain porous carbon. The resulting porous carbon was then heat-treated (calcined) at 900°C for 60 minutes.

[0121] Example 9 A porous carbon was obtained in the same manner as in Example 8, except that the amount of calcium chloride dihydrate added was 150 parts by mass per 100 parts by mass of glucose.

[0122] Example 10 A porous carbon was obtained in the same manner as in Example 8, except that the amount of calcium chloride dihydrate added was 200 parts by mass per 100 parts by mass of glucose.

[0123] Example 11 A porous carbon was obtained in the same manner as in Example 8, except that the amount of calcium chloride dihydrate added was 300 parts by mass per 100 parts by mass of glucose.

[0124] Example 12 1 g of starch was mixed with 0.75 g of calcium hydroxide (available from Fujifilm Wako Pure Chemical Industries, Ltd.) (75 parts by weight per 100 parts by weight of starch) and 1.85 g of glycerin (available from Fujifilm Wako Pure Chemical Industries, Ltd.) (185 parts by weight per 100 parts by weight of starch). The resulting mixture was heated to 700°C in a nitrogen gas atmosphere at a heating rate of 10°C / min. A carbonized product was then obtained by heat-treating the mixture at 700°C for 60 minutes under a nitrogen gas flow. After washing with 0.1 mol / L hydrochloric acid at 80°C for 30 minutes, the carbonized product was removed from the funnel and washed with water until the pH of the filtrate reached a range of 6 to 8. The acid washing and water washing were repeated three times, followed by hot air drying at 80°C to obtain porous carbon. The resulting porous carbon was then heat-treated (calcined) at 900°C for 60 minutes.

[0125] Example 13 A porous carbon was obtained in the same manner as in Example 12, except that the amount of calcium hydroxide added was 150 parts by mass per 100 parts by mass of starch.

[0126] (Comparative Example 1) A porous carbon was obtained in the same manner as in Example 1, except that magnesium chloride dihydrate (available from Fujifilm Wako Pure Chemical Industries, Ltd.) was used instead of calcium chloride dihydrate.

[0127] (Comparative Example 2) A porous carbon was obtained in the same manner as in Example 1, except that calcium chloride anhydrous (available from Fujifilm Wako Pure Chemical Industries, Ltd.) was used instead of calcium chloride dihydrate.

[0128] (Comparative Example 3) A porous carbon was obtained in the same manner as in Example 1, except that polyvinyl alcohol (PVA) (available from Fujifilm Wako Pure Chemical Industries, Ltd.) was used instead of starch.

[0129] Comparative Example 4 A porous carbon was obtained by carrying out the same treatment as in Example 1, except that calcium hydroxide (sold by Fujifilm Wako Pure Chemical Industries, Ltd.) was used in place of calcium chloride dihydrate in an amount of 75 parts by mass per 100 parts by mass of starch.

[0130] (Comparative Example 5) A porous carbon was obtained by carrying out the same treatment as in Comparative Example 4, except that the amount of calcium hydroxide added was 150 parts by mass per 100 parts by mass of starch.

[0131] (Comparative Example 6) A porous carbon was obtained by carrying out the same treatment as in Comparative Example 4, except that the amount of calcium hydroxide added was 200 parts by mass per 100 parts by mass of starch.

[0132] (Comparative Example 7) A porous carbon was obtained in the same manner as in Comparative Example 6, except that zinc chloride (sold by Fujifilm Wako Pure Chemical Industries, Ltd.) was used instead of calcium hydroxide.

[0133] (Comparative Example 8) One gram of polyvinyl alcohol (PVA) was mixed with 4 g of magnesium citrate (Fujifilm Wako Pure Chemical Industries, Ltd.) (400 parts by mass per 100 parts by mass of PVA), and the resulting mixture was heated to 700°C in a nitrogen gas atmosphere. The heating rate to 700°C was 10°C / min. A carbonized product was then obtained by heat-treating the mixture at 700°C for 60 minutes under a nitrogen gas stream. After washing with 1 mol / L sulfuric acid at 80°C for 30 minutes, the carbonized product was removed onto a Buchner funnel and washed with water until the pH of the filtrate reached a range of 6 to 8. The acid wash and water wash were repeated three times, followed by hot air drying at 80°C, yielding a porous carbon. The resulting porous carbon was then heat-treated (calcined) at 900°C for 60 minutes.

[0134] (Comparative Example 9) 1 g of polyvinyl alcohol (PVA) was mixed with 1 g of magnesium oxide particles with an average particle size of 10 nm (100 parts by mass relative to 100 parts by mass of PVA), and the resulting mixture was heated to 700°C in a nitrogen gas atmosphere. The heating rate to 700°C was 10°C / min. A carbonized product was then obtained by heat-treating the mixture at 700°C for 60 minutes under a nitrogen gas stream. After washing with 1 mol / L sulfuric acid at 80°C for 30 minutes, the carbonized product was removed onto a Buchner funnel and washed with water until the pH of the filtrate reached a range of 6 to 8. The acid washing and water washing were repeated three times, followed by hot air drying at 80°C to obtain porous carbon. The resulting porous carbon was then heat-treated (calcined) at 900°C for 60 minutes.

[0135] (Comparative Example 10) Porous carbon was obtained in the same manner as in Comparative Example 9, except that magnesium oxide particles having an average particle diameter of 30 nm were used instead of magnesium oxide particles having an average particle diameter of 10 nm.

[0136] (Comparative Example 11) Porous carbon was obtained in the same manner as in Comparative Example 9, except that magnesium oxide particles having an average particle diameter of 150 nm were used instead of magnesium oxide particles having an average particle diameter of 10 nm.

[0137] (Comparative Example 12) Ketjenblack (EC600JD manufactured by Lion Corporation) was used as the porous carbon.

[0138] (Comparative Example 13) Carbon black (SuperP-Li manufactured by Imerys Graphite & Carbon Co.) was used as the porous carbon.

[0139] Table 1 shows the production conditions for the porous carbons obtained in the examples and comparative examples, and Table 2 shows their physical properties. [Table 1]

[0140] [Table 2]

[0141] <Measurement of charge / discharge capacity, initial charge / discharge efficiency, and DC resistance of lithium-ion secondary batteries> Lithium ion secondary batteries were fabricated according to the above-described method using the porous carbons obtained in Examples 1 to 13 and Comparative Examples 1 to 13. The resulting lithium ion secondary batteries were placed in a thermostatic chamber at 25°C, and a charge / discharge tester ("TOSCAT" manufactured by Toyo Systems Co., Ltd.) was used to measure the DC resistance before initial charging, followed by a charge / discharge test. The DC resistance was measured when a current of 0.7 mA was applied for 3 seconds. The charge capacity was measured by charging at a constant current of 0.2 C up to 4.2 V relative to the lithium potential. The discharge capacity was measured by discharging at a constant current of 0.2 C up to 3 V relative to the lithium potential. The initial charge / discharge efficiency (%) was calculated using the formula: (discharge capacity) / (charge capacity)×100.

[0142] <Measurement of charge capacity retention rate of lithium secondary batteries> Lithium ion secondary batteries were fabricated according to the above-described method using the porous carbons obtained in Examples 1 to 13 and Comparative Examples 1 to 13. The resulting lithium ion secondary batteries were placed in a thermostatic chamber at 25°C, and the charge capacity retention rate was measured using a charge-discharge tester (TOSCAT, manufactured by Toyo Systems Co., Ltd.). Charging involved constant current charging at 0.2 C up to 4.2 V relative to the lithium potential, and discharging involved constant current discharging at 0.2 C up to 3 V relative to the lithium potential. After three initial charge-discharge cycles under the above-described conditions, the charge rate was changed to 2 C, and one charge-discharge cycle was performed. The ratio of the charge capacity at 2 C to the charge capacity at 0.2 C was defined as the charge capacity retention rate.

[0143] <Measurement of discharge capacity retention rate of lithium secondary batteries> Lithium-ion secondary batteries were fabricated according to the above-described method using the porous carbons obtained in Examples 1 to 13 and Comparative Examples 1 to 13. The resulting lithium-ion secondary batteries were placed in a thermostatic chamber at 25°C, and the discharge capacity retention rate was measured using a charge-discharge tester (TOSCAT, manufactured by Toyo Systems Co., Ltd.). Charging was performed at a constant current of 0.2 C up to 4.2 V relative to the lithium potential, and discharging was performed at a constant current of 0.2 C up to 3 V relative to the lithium potential. After three initial charge-discharge cycles under the above conditions, the discharge rate was changed to 2 C, and one charge-discharge cycle was performed. The ratio of the 2 C discharge capacity to the 0.2 C discharge capacity was defined as the discharge capacity retention rate. It is generally known that when a battery has poor input-output characteristics, the insertion and extraction of lithium ions into and from the electrode tends to become less smooth as the charge-discharge rate increases. Therefore, a large ratio of the high-rate charge-discharge capacity to the low-rate charge-discharge capacity (charge-discharge capacity retention rate) indicates excellent input-output characteristics of the battery.

[0144] <Evaluation of peel strength and number of chips on positive electrodes of lithium-ion secondary batteries> For the positive electrodes for lithium secondary batteries prepared by the above-described method from the porous carbons obtained in Examples 1 to 13 and Comparative Examples 1 to 13, the strength was measured when the slurry-coated surface was peeled off from the aluminum foil current collector. Specifically, the slurry-coated surface of the resulting lithium secondary battery electrode was attached to a stainless steel plate using double-sided tape (double-sided tape manufactured by Nichiban), and the 180° peel strength (peel width 10 mm, peel speed 100 mm / min) was measured using a 50 N load cell (manufactured by Imada Co., Ltd.). To determine the number of electrode chips, 10 electrodes were punched out of the positive electrodes for lithium ion secondary batteries using a φ14 mm punching machine, and the number of electrodes in which the active material peeled off from the current collector was counted.

[0145] Table 3 shows the test results for charge / discharge capacity, initial charge / discharge efficiency, DC resistance, charge capacity retention rate, discharge capacity retention rate, peel strength, and the number of electrode chips. [Table 3]

[0146] The porous carbons of Examples 1 to 13 had high charge / discharge capacity retention rates and peel strengths, and no electrode chipping occurred, demonstrating that they are suitable as positive electrode additives, capable of improving the input / output characteristics of non-aqueous electrolyte secondary batteries at room temperature and ensuring electrode peel strength. On the other hand, the porous carbons of Comparative Examples 1 to 13 were insufficient in at least one of the charge / discharge capacity retention rates, peel strength, and number of electrode chipping occurrences.

Claims

1. The pore volume of pores measuring 2 nm or more and 200 nm or less, measured by the BJH method, is 0.8 cm ３ / g or more, and the bulk density is 0.10 g / cm ３ The porous carbon has a pore mode diameter of 150 nm or less as measured by the BJH method, and an average primary particle diameter of 1 μm or more and 100 μm or less.

2. The pore volume of less than 2 nm measured by the DFT method is 0.35 cm ３ The porous carbon according to claim 1, wherein the molecular weight of the porous carbon is 1 / g or less.

3. The specific surface area measured by the BET method is 500 m ２ / g or more 1200m ２ The porous carbon according to claim 1, wherein the molecular weight of the porous carbon is 1 / g or less.

4. 2. The porous carbon according to claim 1, wherein the calcium content is 20 ppm or more and 2000 ppm or less.

5. 2. The porous carbon of claim 1, wherein the sulfur content is 1000 ppm or less and the silicon content is 1000 ppm or less.

6. The bulk density is 0.05 g / cm ３ 2. The porous carbon of claim 1, wherein:

7. (1) obtaining a mixture containing a carbon source and a calcium compound; (2) heat-treating the mixture in an inert gas atmosphere to obtain a carbide; and (3) A step of removing calcium compounds from the carbide The method for producing porous carbon according to any one of claims 1 to 6, comprising:

8. The method according to claim 7, wherein the mixture in step (1) further comprises at least one selected from the group consisting of polyhydric alcohols and carboxylic acids.

9. 8. The method of claim 7, wherein the melting point of the calcium compound is 300°C or less.

10. 8. The method according to claim 7, wherein the calcium compound is at least one selected from the group consisting of calcium chloride hydrate, calcium hydroxide, calcium oxide, calcium carbonate, and calcium acetate.

11. The method of claim 7 , wherein the carbon source is a sugar.

12. The method according to claim 11, wherein the saccharide is at least one selected from the group consisting of monosaccharides, disaccharides and polysaccharides.

13. The method according to claim 7, wherein the removal of calcium compounds in step (3) is carried out by acid washing.

14. The method according to claim 7, wherein the temperature of the heat treatment step in step (2) is 400°C or higher and 1300°C or lower.

15. The method according to claim 7, wherein the temperature increase rate in the heat treatment step in step (2) is 2°C / min or more.

16. The porous carbon according to any one of claims 1 to 6, which is an additive for a positive electrode of a non-aqueous electrolyte secondary battery.

17. The porous carbon according to any one of claims 1 to 6, which is an additive for a positive electrode of a lithium ion secondary battery.

18. A positive electrode composition for a non-aqueous electrolyte secondary battery, comprising the porous carbon according to any one of claims 1 to 6.

19. A composition for a positive electrode of a lithium ion secondary battery, comprising the porous carbon according to any one of claims 1 to 6.

20. A non-aqueous electrolyte secondary battery comprising a positive electrode containing the composition for a positive electrode of a non-aqueous electrolyte secondary battery according to claim 18.

21. A lithium ion secondary battery comprising a positive electrode containing the positive electrode composition of claim 19.

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