Porous carbon, cathode 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 with respect to Japanese Patent Application No. 2021-092329 (filing date: June 1, 2021), which is incorporated herein by reference in its entirety. The present invention relates to porous carbon suitable as a positive electrode additive for a non-aqueous electrolyte secondary battery, a positive electrode additive made of the porous carbon material, a positive electrode for a non-aqueous electrolyte secondary battery 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] Non-aqueous electrolyte secondary batteries, such as lithium-ion batteries, are rapidly expanding in demand due to their characteristics: small size, light weight, high energy density, and the ability to be repeatedly charged and discharged. Because of their relatively high energy density, lithium-ion batteries are used in fields such as mobile phones, notebook computers, and electric vehicles. As the applications of these lithium-ion batteries expand and develop, there is a need for improvements in their output characteristics.

[0003] One proposed method for improving the output characteristics of lithium-ion secondary batteries is to add activated carbon or similar materials to the positive electrode.

[0004] For example, Patent Document 1 states that the pore volume of a pore with a pore diameter of 20 Å or more is 0.418 cc / g or more, and the specific surface area is 1200 m². 2 It has been reported that adding activated carbon of 1g or more to the positive electrode improves the output characteristics at -30°C.

[0005] Furthermore, Ketjenblack is known as a porous carbon with a large pore volume of pores with a diameter of 2 nm or more, and large voids with a pore diameter of 200 nm or more, i.e., low bulk density, and is used as an additive to cathodes (Patent Document 2). [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Patent No. 4964404 [Patent Document 2] Patent No. 4727386 [Overview of the project] [Problems that the invention aims to solve]

[0007] However, according to the inventors' research, even when the activated carbon described in Patent Document 1 was added to the positive electrode, sufficient improvement in the input / output characteristics at room temperature was not observed.

[0008] Furthermore, when Ketjenblack, as 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 easily impaired due to the adsorption of the binder to the Ketjenblack and the aggregation of the conductive agent, making it difficult to ensure the peel strength of the resulting electrode.

[0009] This invention has been made in view of the above circumstances, and aims to provide a porous carbon suitable as a positive electrode additive that 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 detailed investigations to solve the aforementioned problems, the inventors discovered that the problems could be solved by adding porous carbon having specific physical properties to the cathode, leading to the present invention.

[0011] In other words, the present invention encompasses the following preferred embodiments. [1] The pore volume of 2 nm to 200 nm measured by the BJH method was 0.8 cm³. 3 The amount is greater than or equal to / g, and the bulk density is 0.10 g / cm³. 3Porous carbon having the following characteristics: the mode diameter of the pores measured by the BJH method is 150 nm or less, and the average primary particle diameter is between 1 μm and 100 μm. [2] The pore volume of less than 2 nm measured by DFT was 0.35 cm³. 3 Porous carbon as described in [1], which is less than or equal to / g. [3] The specific surface area measured by the BET method was 500 m². 2 / g or more 1200m 2 Porous carbon as described in [1] or [2], wherein the amount is less than or equal to / g. [4] A porous carbon described in any of [1] to [3], having a calcium content of 20 ppm or more and 2000 ppm or less. [5] A porous carbon material as described in any of [1] to [4], 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 / cm³. 3 Porous carbon described in any of the following [1] to [5]. [7] (1) A step of obtaining a mixture containing a carbon source and a calcium compound, (2) A step of heat-treating the mixture in an inert gas atmosphere to obtain a carbide, (3) Step of removing calcium compounds from the carbide A method for producing porous carbon according to any one of [1] to [6], including the above. [8] The method according to [7], wherein the mixture in step (1) further comprises 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 sugar is at least one selected from the group consisting of monosaccharides, disaccharides and polysaccharides.

[13] The removal of the calcium compound in step (3) is carried out by acid washing, according to any one of [7] to

[12] .

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

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

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

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

[16] A porous carbon described in any of [1] to [6], which is an additive for the positive electrode of a non-aqueous electrolyte secondary battery.

[17] A porous carbon described in any of [1] to [6], which is an additive for the positive electrode of a lithium-ion secondary battery. A composition for the positive electrode of a non-aqueous electrolyte secondary battery, comprising porous carbon as described in any of

[18] [1] to [6]. A composition for the positive electrode of a lithium-ion secondary battery, comprising porous carbon as described in any of

[19] [1] to [6]. A non-aqueous electrolyte secondary battery comprising a positive electrode containing the positive electrode composition for a non-aqueous electrolyte secondary battery described in

[20]

[18] . A lithium-ion secondary battery comprising a positive electrode containing the positive electrode composition for a non-aqueous electrolyte secondary battery described in

[21]

[19] . [Effects of the Invention]

[0012] According to the present invention, it is possible to provide porous carbon suitable for a positive electrode additive that 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 drawing]

[0013] [Figure 1] This is a transmission electron microscope (TEM) image of the porous carbon from Example 6. [Figure 2] This is a transmission electron microscope (TEM) image of the porous carbon from Example 6. [Figure 3]These are scanning electron microscope (SEM) observation images of the porous carbon of Example 8. [Figure 4] These are scanning electron microscope (SEM) observation images of the porous carbon of Example 8. [Figure 5] These are transmission electron microscope (TEM) observation images of the porous carbon of Comparative Example 9. [Figure 6] These are transmission electron microscope (TEM) observation images of the porous carbon of Comparative Example 9. [Figure 7] These are scanning electron microscope (SEM) observation images of the porous carbon of Comparative Example 9. [Figure 8] These are scanning electron microscope (SEM) observation images of the porous carbon of Comparative Example 9. [Figure 9] These are scanning electron microscope (SEM) observation images of the porous carbon of Comparative Example 13. [Figure 10] These are scanning electron microscope (SEM) observation images of the porous carbon of Comparative Example 13. Description of Embodiments

[0014] Hereinafter, embodiments of the present invention will be described in detail. The following description is an exemplification of embodiments of the present invention, and is not intended to limit the present invention to the following embodiments.

[0015] <Porous Carbon> 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 bulk density is 0.10 g / cm 3 or less, the mode diameter of pores 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 having a diameter of 2 nm or more and 200 nm or less is 0.8 cm 3When the lithium ion density is greater than or equal to 1g / g, it exhibits excellent storage of lithium ions within the pores and high lithium ion mobility near the positive electrode active material, allowing for a plentiful supply of lithium ions around the positive electrode active material. This promotes smooth insertion and removal of lithium ions into and out of the positive electrode active material, improving input / output characteristics. The pore volume is 0.8 cm³ between 2 nm and 200 nm. 3 If the value is less than / g, lithium ion mobility tends to decrease, and pore blockage occurs due to gases generated when the electrolyte decomposes in the electrochemical element, further reducing electrolyte mobility. The pore volume between 2nm and 200nm is preferably 0.9cm³. 3 / g or more, more preferably 1.00 cm 3 / g or more, more preferably 1.30cm 3 / g or more, more preferably 1.60cm 3 / g or more, particularly preferably 1.65cm 3 / g or more, particularly preferably 1.90cm 3 / g or more, most preferably 2.30cm 3 / g or more, especially preferably 3.20cm 3 The value is 1 / g or more. When the pore volume between 2 nm and 200 nm is above the lower limit, the input / output characteristics tend to improve further. Also, when the pore volume between 2 nm and 200 nm is large, the electrolyte retention capacity and electrolyte mobility tend to be excellent, so there is no particular upper limit, but it is preferably 4.00 cm 3 Less than or equal to / g, more preferably 3.90cm 3 The amount is less than or equal to / g. The pore volume between 2 nm and 200 nm can be adjusted to within the above range by appropriately adjusting, for example, the type and / or amount of carbon source and calcium compound in the porous carbon manufacturing method described later; the temperature and / or time of the heat treatment process, etc. The pore volume between 2 nm and 200 nm can be measured by pore distribution analysis using the BJH method in nitrogen adsorption measurement, for example, by the method described in the examples below.

[0017] In the porous carbon of the present invention, the bulk density is 0.10 g / cm³.3 The following applies. Bulk density in porous carbon indicates the degree of development of the pore structure. When the pore volume below 200 nm is the same, a lower bulk density means a larger volume of voids above 200 nm. Pores between 2 nm and 200 nm are thought to be responsible for the storage and transport of lithium ions, while voids above 200 nm are thought to be responsible for holding the electrolyte and supplying lithium ions to the pores between 2 nm and 200 nm. Therefore, in addition to pores between 2 nm and 200 nm, it is preferable in this invention for the volume of voids above 200 nm to be large, i.e., for a low bulk density. Bulk density of 0.10 g / cm³ 3 If the value exceeds this, the electrolyte may not be retained sufficiently, and the input / output characteristics will deteriorate. The bulk density is preferably 0.07 g / cm³. 3 More preferably, 0.06 g / cm³ 3 The following applies, and in one embodiment of the present invention, the bulk density is 0.05 g / cm³. 3 It is even more preferable, and even more preferably, to be less than 0.015 g / cm³. 3 The following is particularly preferred: 0.014 g / cm³ 3 More preferably, 0.013 g / cm³ 3 More preferably, 0.012 g / cm³ 3 The following is very preferably 0.011 g / cm³ 3 More preferably, 0.010 g / cm³ 3 Further, and most preferably, 0.009 g / cm³ 3 More preferably, 0.008 g / cm³ 3 The following applies: When the bulk density is below the aforementioned upper limit, the electrolyte can be abundantly held in voids of 200 nm or more, making it easier to improve input / output characteristics. Also, if the bulk density is too low, it may be difficult to maintain the strength of the carbon skeleton, so from the viewpoint of easily maintaining the peel strength of the electrode, it is usually 0.003 g / cm³. 3The above is preferable. The bulk density can be adjusted within the above range by appropriately adjusting, for example, the type and / or amount of carbon source and calcium compound in the porous carbon manufacturing method described later; the temperature and / or time of the heat treatment process, etc. The bulk density can be measured, for example, by the method described in the examples 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 respect to the common logarithm of the pore diameter (D). When the mode diameter of the porous carbon is 150 nm or less, the storage of lithium ions in the pores and the movement of lithium ions to the vicinity of the positive electrode active material proceed smoothly, and lithium ions can be abundantly supplied around the positive electrode active material. This makes it easier to improve input / output characteristics. In addition, it is possible to suppress the adsorption of binder into the pores of the porous carbon during slurry preparation, which tends to improve the peel strength of the electrode and suppress electrode chipping. When the mode diameter exceeds 150 nm, the amount of lithium ions stored in the pores decreases, and the supply of lithium ions to the surface of the active material decreases. Also, the binder is more likely to adsorb 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 preferably 25 nm or less, even more preferably 20 nm or less, extremely preferably 15 nm or less, and most extremely preferably 13 nm or less. When the mode diameter is below the above upper limit, the input / output characteristics are more easily improved. The lower limit of the mode diameter is not limited, but if the mode diameter is too small, the mobility of lithium ions tends to decrease, and pore blockage may occur due to gas generated when the electrolyte decomposes in the electrochemical element, further reducing the mobility of the electrolyte. Therefore, it is usually 2 nm or more, more preferably 9 nm or more. The mode diameter can be adjusted within the above range by appropriately adjusting, for example, the type and / or amount of carbon source and calcium compound in the porous carbon manufacturing method described later; the temperature and / or time of the heat treatment process, etc. The mode diameter can be measured by pore distribution analysis by the BJH method in nitrogen adsorption measurement, for example, by the method described in the examples below.

[0019] In the porous carbon of the present invention, the average primary particle diameter is 1 μm or more and 100 μm or less. An average primary particle diameter of 1 μm or more and 100 μm or less allows for appropriate storage and diffusion of lithium ions, resulting in good input / output characteristics. Furthermore, because aggregation of porous carbon particles is less likely to occur, coating unevenness after electrode coating is less likely to occur, and the peel strength of the electrode can be increased. If the average primary particle diameter is less than 1 μm, the presence of fine particles makes it difficult to control them with binders, etc., and they easily detach from the electrode. Also, aggregation of fine particles within the electrode is more likely to occur. This results in coating unevenness after electrode coating and a decrease in the peel strength of the electrode. Furthermore, if the average primary particle diameter exceeds 100 μm, it is difficult to form good ion diffusion pathways between active materials, making it difficult to improve input / output characteristics. In addition, coarse particles are more likely to cause irregularities on the electrode, and the peel strength of the electrode decreases. From these viewpoints, the average primary particle diameter is preferably 2 μm or more, more preferably 5 μm or more, preferably 80 μm or less, and more preferably 60 μm or less. When the average primary particle diameter is within the aforementioned range, the input / output characteristics of the non-aqueous electrolyte secondary battery at room temperature can be further improved, and the electrode peel strength can be more easily increased. The average primary particle diameter can be adjusted to within the aforementioned range by appropriately adjusting, for example, the type of carbon source in the porous carbon manufacturing method described later; the conditions of the grinding process; etc. In the present invention, the average primary particle diameter is the particle diameter at which the cumulative volume measured by laser diffraction / scattering method becomes 50%, and this value is used as the average primary particle diameter. However, if measurement by laser diffraction / scattering method is not possible, the average particle diameter may be obtained by measuring the particle diameter of primary particles displayed 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, as measured by the DFT method, is preferably 0.35 cm³. 3 Less than or equal to / g, more preferably 0.30cm 3 Less than or equal to / g, more preferably 0.20cm 3 Less than or equal to / g, more preferably 0.15cm 3 Less than or equal to / g, particularly preferably 0.13cm 3 Less than or equal to / g, more preferably 0.12cm3 Less than or equal to / g, and more preferably 0.10cm 3 Less than or equal to / g, and more preferably 0.09cm 3 Less than or equal to / g, most preferably 0.08cm 3 It is less than or equal to / g. When the pore volume of less than 2 nm is below the above upper limit, adsorption of lithium ions into pores less than 2 nm is less likely to occur, thus allowing lithium ions to be supplied to the active material and improving input / output characteristics. The lower limit of the pore volume of less than 2 nm is not particularly limited, but is preferably 0.01 cm. 3 The value is 1 / g or more. Pore volumes of less than 2 nm can be adjusted to within the above range by appropriately adjusting, for example, the type and / or amount of carbon source and calcium compound in the porous carbon manufacturing method described later; the temperature and / or time of the heat treatment process, etc. Pore volumes 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 below.

[0021] In the porous carbon of the present invention, the pore volume of 2 nm to 10 nm, as measured by the DH method, is preferably 0.55 cm³. 3 Less than or equal to / g, more preferably 0.53cm 3 Less than or equal to / g, more preferably 0.45cm 3 Less than or equal to / g, more preferably 0.40cm 3 Less than or equal to / g, particularly preferably 0.35cm 3 Less than or equal to / g, more preferably 0.30cm 3 Less than or equal to / g, and more preferably 0.25cm 3 Less than or equal to / g, most preferably 0.20cm 3 It is less than / g. The pore volume of 2nm to 10nm is 0.55cm³. 3When the pore volume is less than or equal to 0.01 cm³, the mobility of lithium ions to the vicinity of the positive electrode active material is increased, and pore blockage by gases generated when the electrolyte decomposes in the electrochemical element is less likely to occur, thus facilitating a rich supply of lithium ions around the positive electrode active material. This promotes smooth insertion and removal of lithium ions into and out of the positive electrode active material, and tends to improve input / output characteristics. Furthermore, when the pore volume is smaller than 2 nm to 10 nm, the mobility of the electrolyte also tends to be excellent, so there is no particular lower limit, but preferably 0.01 cm³. 3 / g or more, more preferably 0.05cm 3 / g or more, more preferably 0.10cm 3 The amount is 1 / g or more. The pore volume between 2 nm and 10 nm can be adjusted to within the above range by appropriately adjusting, for example, the type and / or amount of carbon source and calcium compound in the porous carbon manufacturing method described later; the temperature and / or time of the heat treatment process, etc. The pore volume between 2 nm and 10 nm can be measured by pore distribution analysis using the DH method in nitrogen adsorption measurement, for example, by the method described in the examples below.

[0022] In the porous carbon of the present invention, the specific surface area measured by the BET method is preferably 500 m². 2 / g or more, more comfortably 600m 2 / g or more, more preferably 650m 2 / g or more, more preferably 700m 2 It is 1200m or more / g, preferably 1200m 2 Less than / g, more preferably 1000m 2 / g or less, more preferably 900m 2It is less than or equal to / g. When the specific surface area is within the above range, lithium ions in the electrolyte are easily retained, and input / output characteristics tend to improve. In addition, lithium ions diffuse easily, and coating stability tends to be good. The specific surface area can be adjusted to within the above range by appropriately adjusting, for example, the type and / or amount of carbon source and calcium compound in the porous carbon manufacturing method described later; the temperature and / or time of the heat treatment process, etc. The specific surface area can be measured, for example, by the method described in the examples 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, 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, it is easier to suppress an excessive increase in the mass of the porous carbon and productivity tends to be excellent. The calcium content can be adjusted within the above range by appropriately adjusting the conditions of the step to remove calcium compounds in the method for producing porous carbon described later (for example, the type and / or concentration of the acid used for acid washing, the time of acid and / or water washing, the temperature, 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 also preferably 1000 ppm or less, more preferably 900 ppm or less, and even more preferably 800 ppm or less. When the sulfur and silicon content is within the above range, side reactions in the positive electrode are suppressed, and input / output characteristics are easily improved. The lower limit of the sulfur and silicon content is not particularly limited and may be 0 ppm. The sulfur and silicon content can be adjusted within the above range by, for example, the type of carbon source in the method for producing porous carbon described later; and the conditions of the step for removing calcium compounds (for example, the type and / or concentration of the acid used for acid washing, the time of acid and / or water washing, temperature, etc.). The calcium, sulfur, and silicon content can be measured by fluorescent X-ray analysis, for example, by the method described in the examples below.

[0025] In typical porous carbon, mesopores can form a three-dimensional network structure in which the mesopores are interconnected. In such a three-dimensional network structure, there are usually dead ends (blockages) in the pores. However, in one embodiment of the porous carbon of the present invention, the inventors have found that all pores are continuously connected in three dimensions, and there are no dead ends in the pores, resulting in a connected pore structure (see Figures 5 and 6). In one embodiment of the porous carbon of the present invention, having the above-mentioned connected pore structure increases the diffusion rate of lithium ions within the pores, thereby improving the input / output characteristics of non-aqueous electrolyte secondary batteries at room temperature and ensuring electrode peel strength, making it a porous carbon suitable as a positive electrode additive. Furthermore, it has been found that such a connected pore structure can be achieved by applying a manufacturing method described later.

[0026] Furthermore, in common porous carbons used as cathode additives, such as carbon black and Ketjenblack, primary particles can aggregate and link together to form a three-dimensional dendritic particle structure (Figures 9 and 10). Such a three-dimensional dendritic structure has a low bulk density due to the voids between the branches, and by being positioned between adjacent active materials within the electrode, it can form short-distance lithium ion diffusion pathways. On the other hand, the inventors have discovered that one embodiment of the porous carbon of the present invention can take the form of a flake shape (Figures 3 and 4). When porous carbon takes the above flake shape, the bulk density is significantly reduced due to the voids formed by wrinkles on the surface of the flake, and it is positioned in contact not only with adjacent active materials but also with more distant active materials within the electrode, so it is thought that it can form long-distance lithium ion diffusion pathways. Therefore, it is thought that by using flake-shaped porous carbon in combination with three-dimensional dendritic porous carbon and granular porous carbon (Figures 7 and 8), both short-distance and long-distance ion diffusion pathways can be formed, ensuring better ion diffusion pathways throughout the electrode. Therefore, it was found that one embodiment of the porous carbon of the present invention is suitable as a positive electrode additive, as it 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 was also found that such a flaky shape with wrinkles on the surface of the flaks can be achieved by applying a manufacturing method described later.

[0027] <Method for producing porous carbon> The porous carbon of the present invention is, for example, (1) A step of obtaining a mixture containing a carbon source and a calcium compound, (2) A step of heat-treating the mixture in an inert gas atmosphere to obtain a carbide, (3) Step of removing calcium compounds from the carbide It can be manufactured by a method that includes [a specific component].

[0028] While there are no particular limitations on the carbon source, sugars are preferred to improve uniform dispersibility with calcium compounds. 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 individually 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 corn, cassava, potatoes, sweet potatoes, tapioca, beans, wheat, rice, etc., can be used. The preferred amylose content of the starch for the present invention is preferably 50% by mass or less, more preferably 30% by mass or less. Since the gelatinization temperature tends to decrease as the amylose content of the starch decreases, it is preferable that the amylose content of the starch be below the above upper limit, as it is easier to gelatinize at low temperatures and the compatibility with calcium compounds tends to increase. The above amylose content can be determined by, for example, the iodine colorimetric method. Furthermore, the starch may be modified starch. Examples of modified starches include etherified starch, esterified starch, cationized starch, and crosslinked starch. One type of starch may be used alone, or two or more types may be used in mixture.

[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, calcium lactate, etc. Among these calcium compounds, a calcium compound with a melting point of 300°C or less (or, if the mixture contains a polyhydric alcohol or carboxylic acid as described later, the melting point of the eutectic compound between the calcium compound and the polyhydric alcohol or carboxylic acid is 300°C or less) is preferred because it is easy to produce porous carbon that improves the input / output characteristics of non-aqueous electrolyte secondary batteries at room temperature. More preferably, it is 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 in dihydrate, tetrahydrate, and hexahydrate forms, but the dihydrate is preferred because it has good 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 polyhydric alcohols and carboxylic acids. When a polyhydric alcohol and / or carboxylic acid is included in the mixture, it is thought that the calcium compound dissolves in the polyhydric alcohol and / or carboxylic acid, forming a eutectic compound. The eutectic compound is thought to be formed when the hydroxyl group, carboxylate, or carboxyl group in the polyhydric alcohol and / or carboxylic acid coordinates with calcium. Therefore, it is possible to make the melting point of the calcium compound, which has a melting point of 300°C or higher on its own, 300°C or lower as the melting point of the eutectic compound. Accordingly, in the present invention, "the melting point of the calcium compound is 300°C or lower" also includes "the melting point of the eutectic compound of the polyhydric alcohol and / or carboxylic acid and the calcium compound is 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 which glycerin and ethylene glycol are preferred from the viewpoint of readily eutectic with calcium compounds and 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. Among these, formic acid and acetic acid are preferred because they readily dissolve calcium compounds and are readily available in large quantities. When using a mixture of one or more polyhydric alcohols and one or more carboxylic acids, the mixing ratio of the polyhydric alcohols and carboxylic acids can be appropriately changed according to the desired properties of the porous carbon.

[0032] The method of mixing the carbon source and calcium compound, and optionally polyhydric alcohols and / or carboxylic acids, is not particularly limited and can be mixed in any manner.

[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, with a preference of 500 parts by mass or less, more preferably 400 parts by mass or less, and even more preferably 300 parts by mass or less, per 100 parts by mass of sugars. When the amount of calcium compound is within the above range, the pore volume and pore diameter of the resulting porous carbon tend to be appropriate.

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

[0035] In the manufacturing 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, especially oxygen, is usually 1% by volume or less, more preferably 0.1% by volume or less. When the oxygen concentration is below the above upper limit, oxidation of the carbide is easily suppressed, and a structure with desired characteristics is easily obtained. Furthermore, oxidative decomposition of the generated structure can 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, even more preferably 800°C or higher, 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 range, the pore volume of the resulting porous carbon tends to be appropriate, ranging from 2 nm to 200 nm, and the subsequent step of removing the calcium compound from the carbide tends to be easier. Furthermore, the heat treatment may be carried out in multiple stages. For example, the mixture may be heat-treated (carbonized) at 50-300°C, then heat-treated (fired) at 400-900°C, and then heat-treated (calcined) at 900-1300°C. By carrying out the heat treatment in multiple stages, a carbide with more homogeneous 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, 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 it allows carbonization to proceed sufficiently and makes ignition less likely. It is also preferable from an economic standpoint because it is a reasonable time.

[0037] In the manufacturing method of the present invention, the heating 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 heating rate is above the lower limit, the pore size tends to be appropriate. The upper limit of the heating rate is not particularly limited, but from the viewpoint of achieving uniform heat treatment, 200°C / min or less is preferred.

[0038] Various types of furnaces can be used for heat treatment, including rotary kilns, fluidized bed furnaces, fixed bed furnaces, moving bed furnaces, and moving bed furnaces. Both continuous furnaces, where raw materials are continuously fed in and products are removed, and batch furnaces, where this is done intermittently, are applicable. Any heating method capable of reaching the desired temperature is acceptable, including electric heating, gas combustion heating, high-frequency induction heating, and electrostatic heating. These heating methods may be used individually or in combination.

[0039] The porous carbon of the present invention can be obtained by removing calcium compounds from the obtained carbide. The removal of the calcium compounds is preferably carried out by acid washing, for example. Examples of acids that can be used for acid washing include hydrochloric acid, sulfuric acid, and nitric acid, but hydrochloric acid is preferred because it readily dissolves metal compounds in the carbide, leaves fewer impurities such as sulfur behind, and suppresses oxidation of the carbide. The concentration of the acid used during acid washing may be appropriately changed depending on the type of acid used, but for example, when using hydrochloric acid, it is preferably in the range of 0.01 to 1.0 mol / L, more preferably in the range of 0.05 to 0.5 mol / L. A hydrochloric acid concentration within the above range is preferable because it readily removes metal compounds and prevents hydrochloric acid from remaining in the carbide.

[0040] The pH of the acid used during acid washing may be adjusted as appropriate depending on the type, concentration, and temperature of the acid used, but is preferably 3 or less, and more preferably 2.5 or less. When the pH of the acid is below the above upper limit, metal compounds can be removed more efficiently.

[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 acid to carbide may be appropriately adjusted according to the type, concentration, and temperature of the acid used. The mass of the carbide to be immersed relative to the mass of acid is preferably 2% by mass or more, more preferably 5% by mass or more. The upper limit of the mass ratio is preferably 50% by mass or less, more preferably 30% by mass or less. If the mass ratio of the carbide to be immersed relative to the mass of 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 the carbide can be immersed in the acid. It may be a method in which the acid is continuously added, left for a predetermined time, and then removed while immersing, or a method in which the carbide is immersed in the acid, left for a predetermined time, dehydrated, and then new acid is added and the immersion-dehydration process is repeated. It may also be a method in which all of the acid is replaced, or a method in which only part of the acid is replaced. Furthermore, the acid may be stirred during immersion.

[0043] The atmosphere in which acid cleaning is performed is not particularly limited and may be appropriately selected depending on the cleaning method used. In this invention, acid cleaning is usually performed in an atmospheric environment.

[0044] The immersion time of the carbide in the acid can be adjusted as appropriate depending on the acid used, the treatment temperature, etc., but from the viewpoint of sufficiently removing 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] It is preferable to remove the acid from the porous carbon by acid washing the carbide and then rinsing with water. This acid washing and rinsing may be repeated until the calcium compounds in the porous carbon are removed. Furthermore, from the viewpoint of the efficiency of removing calcium compounds and residual acid, it is preferable that the solution temperature during acid washing and rinsing be high, and is usually 60°C or higher.

[0046] As 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 porous carbon after acid washing may be heat-treated (calcined) at 900 to 1300°C. Performing carbonization at 900°C or lower facilitates the removal of metal compounds derived from the calcium compound in the acid washing process, and calcining at a higher temperature of 900 to 1300°C makes it easier to obtain the desired pore volume and specific surface area.

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

[0048] The porous carbon after drying may be pulverized. The pulverization step is a process for controlling the shape, particle size, etc., of the porous carbon that is ultimately obtained to a desired shape, particle size, etc. The pulverization method is not particularly limited, and known pulverizers such as ball mills, centrifugal roll mills, ring roll mills, centrifugal ball mills, jet mills, cone crushers, double roll crushers, disc crushers, and rotary crushers can be used individually or in combination.

[0049] In the present invention, the method for producing porous carbon may further include a classification step after the grinding step. For example, by removing particles that are extremely small or large compared to the desired particle size, it is possible to obtain porous carbon with a narrow particle size distribution width. The classification method is not particularly limited, but examples include classification using a sieve, wet classification, and dry classification. Examples of wet classifiers include those that utilize the principles of gravity classification, inertial classification, hydraulic classification, and centrifugal classification. Examples of dry classifiers include those that utilize the principles of sedimentation classification, mechanical classification, and centrifugal classification. From an economic standpoint, it is preferable to use a dry classifier. Furthermore, in order to prevent oxidation of the surface during grinding, it is preferable to carry out the grinding step and the classification step in an inert gas atmosphere.

[0050] Grinding and classification can also be performed using a single device. For example, grinding and classification can be carried out using a jet mill equipped with a dry classification function. Furthermore, it is also possible to use a device in which the grinder and classifier are independent. In this case, grinding and classification can be performed continuously or discontinuously.

[0051] <Additive for cathodes of non-aqueous electrolyte secondary batteries> The porous carbon of the present invention can preferably be used as a positive electrode additive for non-aqueous electrolyte secondary batteries. Because the porous carbon of the present invention has the specific pores described above and has a low bulk density, when used as a positive electrode additive for non-aqueous electrolyte secondary batteries, it improves the diffusivity of lithium ions into the positive electrode and the adsorption of lithium ions into the pores, facilitating the insertion and removal of lithium ions from the positive electrode active material, thereby improving the input / output characteristics of non-aqueous electrolyte secondary batteries. Furthermore, it suppresses binder adsorption to the additive and aggregation of additives during electrode fabrication, contributing to improved manufacturing stability of the electrode and improved electrode peel strength.

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

[0053] <Nonaqueous electrolyte secondary battery positive electrode composition> The present invention also encompasses compositions for the positive electrode of non-aqueous electrolyte secondary batteries, comprising the above-described additives and positive electrode active materials described above. Furthermore, the present invention also encompasses compositions for the positive electrode of lithium-ion secondary batteries, comprising the above-described additives for the positive electrode of lithium-ion secondary batteries. The compositions for the positive electrode of non-aqueous electrolyte secondary batteries of the present invention may optionally contain other components besides the additives and positive electrode active materials described above.

[0054] [Cathode active material] The positive electrode active material contained in the composition for a positive electrode of a non-aqueous electrolyte secondary battery is not particularly limited, and known positive electrode active materials can be used. Examples include lithium-containing cobalt oxide (LiCoO₂), lithium manganese oxide (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 lithium-excess 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 metal oxides such as O₄, sulfur, compounds and polymers having nitroxyl radicals, compounds and polymers having oxyl radicals, compounds and polymers having nitrogen radicals, and organic radicals such as compounds and polymers having a fulvalene skeleton.

[0055] These may be used alone, or two or more of these may be used in combination. Among the above, from the viewpoint of improving the battery capacity and other properties of the secondary battery, as the positive electrode active material, lithium-containing cobalt oxide (LiCoO₂); lithium-containing nickel oxide (LiNiO₂); and 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, and the like; and 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, and the like 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, positive electrode active materials in the range of 0.1 to 40 μm, more preferably in the range of 0.5 to 20 μm, can be used.

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

[0058] The content of the additive for the positive electrode of a non-aqueous electrolyte secondary battery is preferably 0.5% by mass or more, more preferably 1% by mass or more, 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 the positive electrode of a non-aqueous electrolyte secondary battery is within the above range, the effect of reducing electrode resistance is easily exerted, and the overall mass of the positive electrode active material does not decrease, so the capacity does not decrease easily.

[0059] The mixing ratio of the additive for the 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 the positive electrode of a non-aqueous electrolyte secondary battery to the positive electrode active material falls within this range, it is easier to obtain a non-aqueous electrolyte secondary battery with excellent input / output characteristics.

[0060] [solvent] The non-aqueous electrolyte secondary battery positive electrode composition of the present invention may contain a solvent. As the solvent, for example, an organic solvent can be used, and among these, a polar organic solvent capable of dissolving the binder described later is preferred. Specifically, suitable organic solvents 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 viewpoint of ease of handling, safety, and ease of synthesis. These organic solvents may be used individually or in combination of two or more.

[0061] The solvent can be used in an amount such that the solid content concentration in the non-aqueous electrolyte secondary battery positive electrode composition is preferably in the range of 1 to 80% by mass, more preferably 5 to 70% by mass, and even more preferably 10 to 60% by mass. Setting the solid content concentration within this range is preferable because it allows for uniform dispersion of the positive electrode active material, additives for the non-aqueous electrolyte secondary battery positive electrode, and other components contained therein.

[0062] [binder] The present invention preferably contains a binder for the positive electrode of a non-aqueous electrolyte secondary battery that allows positive electrode active material particles to adhere well to each other and for the positive electrode active material to adhere well to the current collector. Examples of binders include, but are not limited to, polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, diacetylcellulose, 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 may be used individually or in combination of two or more. In the non-aqueous electrolyte secondary battery positive electrode composition of the present invention, the binder content is preferably 0.5 to 10% by mass, and more preferably 1 to 7% by mass, relative to the total mass of the positive electrode in the composition.

[0063] [Conductive material] The present invention's composition for the positive electrode of a non-aqueous electrolyte secondary battery may further contain a conductive material to further enhance the conductivity of the positive electrode formed on the current collector. Any electronically conductive material that does not cause a chemical change in the non-aqueous electrolyte secondary battery in which it is constructed can be used as the conductive material. Specific examples of conductive materials include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjenblack, and carbon fibers; metallic 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 individually or in combination of two or more. In the non-aqueous electrolyte secondary battery positive electrode composition of the present invention, the content of the conductive material is preferably 1 to 10% by mass, and more preferably 1 to 7% by mass, relative to the total mass of positive electrode solids in the composition.

[0064] <Method for producing a composition for the positive electrode of a non-aqueous electrolyte secondary battery> The present invention provides a method for producing the non-aqueous electrolyte secondary battery positive electrode composition by mixing the above-mentioned non-aqueous electrolyte secondary battery positive electrode additive, positive electrode active material, and, if necessary, a solvent and other components. There are no particular restrictions on the mixing method; for example, general mixing equipment such as a disper, mill, or kneader can be used. It is preferable to use these mixing equipment and stir for, for example, 20 minutes to 120 minutes.

[0065] The mixing temperature is not particularly limited; for example, it can be mixed in the range of 0 to 160°C, preferably in the range of 20 to 80°C. Mixing within this range is preferable because it makes it easier for the composition to have a viscosity suitable for coating and reduces the volatilization of organic solvents.

[0066] While there are no particular limitations on the atmosphere in which the mixtures occur, they usually mix in an atmospheric environment.

[0067] <Nonaqueous electrolyte secondary battery> The non-aqueous electrolyte secondary battery positive electrode composition of the present invention can be usefully used in non-aqueous electrolyte secondary batteries. Therefore, the present invention also includes non-aqueous electrolyte secondary batteries having a positive electrode made using the above-described non-aqueous electrolyte secondary battery positive electrode composition. By containing the above-described non-aqueous electrolyte secondary battery positive electrode additive, the non-aqueous electrolyte secondary battery of the present invention can improve the diffusion of electrolyte ions at the positive electrode and improve the input / output characteristics of the battery. The non-aqueous electrolyte secondary battery of the present invention preferably operates at 2V to 5V, and examples include lithium-ion secondary batteries or capacitors. Therefore, the present invention also includes 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 prepared using the non-aqueous electrolyte secondary battery positive electrode composition 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 coating the current collector with the non-aqueous electrolyte secondary battery positive electrode composition of the present invention.

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

[0071] For current collectors coated with non-aqueous electrolyte secondary battery positive electrode compositions, it is preferable to use materials that are electrically conductive and electrochemically durable. Specifically, current collectors made of aluminum or aluminum alloys can be used. In this case, aluminum and aluminum alloys 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 non-aqueous electrolyte composition for the positive electrode of a secondary battery on a current collector is not particularly limited and known methods can be used, such as drying with warm air, hot air, low humidity air, vacuum drying, or irradiation with infrared rays or electron beams. By drying the non-aqueous electrolyte composition for the positive electrode of a secondary battery on a current collector in this way, a positive electrode active material layer is formed on the current collector, and a positive electrode comprising a current collector and a positive electrode active material layer can be obtained.

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

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

[0075] The above-mentioned negative electrode active material includes a substance capable of reversibly intercalating / deintercalating lithium ions, lithium metal, an alloy of lithium metal, a lithium-doped and dedoped substance, or a transition metal oxide.

[0076] Examples of the substances capable of reversibly intercalating / deintercalating lithium ions include crystalline carbon and amorphous carbon, and these may be used alone or in a mixture of two or more. Examples of the crystalline carbon include graphite such as amorphous, tabular, scaly, spherical or fibrous natural graphite, or artificial graphite. Examples of the amorphous carbon include soft carbon or hard carbon, mesophase pitch carbides, and calcined coke.

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

[0078] Examples of the substances capable of doping and undoping lithium include alloys such as Si and SiMg, SiO x (0<x<2), Sn, SnO2, and the like.

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

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

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

[0082] Examples of the above-mentioned water-insoluble binders include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyimide, or combinations thereof.

[0083] Examples of the above-mentioned water-soluble binders include styrene-butadiene rubber, acrylated styrene-butadiene rubber, polyvinyl alcohol, sodium polyacrylate, copolymers of propylene and olefins having 2 to 8 carbon atoms, copolymers of (meth)acrylic acid and alkyl (meth)acrylate esters, or combinations thereof.

[0084] When a water-soluble binder is used as the negative electrode binder, a cellulosic compound that can impart viscosity to the negative electrode active material layer may be further used as a thickening agent. Examples of such cellulosic compounds include carboxymethylcellulose, hydroxypropylmethylcellulose, methylcellulose and its alkali metal salts, and such a thickening agent can 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 described above is used to impart conductivity to the electrodes, and any electronically conductive material that does not cause chemical changes in the battery it is constructed from can be used. Specific examples of conductive materials include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjenblack, and carbon fibers; metallic 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 individually or in combination of two or more.

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

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

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

[0089] As the non-aqueous organic solvent, carbonate-based, ester-based, ether-based, ketone-based, alcohol-based, or non-protonate solvents may be used. As the carbonate-based solvents, 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), etc. may be used, and as the ester-based solvents, n-methyl acetate, n-ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, decanolide, valerolactone, mevalonolactone, caprolactone, etc. may be used. As the ether mentioned above, dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, etc. may be used, and as the ketone solvent mentioned above, cyclohexanone, etc. may be used. As the alcohol solvent mentioned above, ethyl alcohol, isopropyl alcohol, etc. may be used, and as the non-protonate solvent mentioned above, nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, and may include double bonds, aromatic rings, or ether bonds), amides such as dimethylformamide, dioxolanes and sulforanes such as 1,3-dioxolane, etc. may be used.

[0090] The non-aqueous organic solvent described above may be used alone or as a mixture of two or more types. When two or more types are used in combination, the mixing ratio may be appropriately adjusted according to the desired battery performance.

[0091] Further, in the case of the carbonate-based solvent described above, it is preferable to use a mixture of a cyclic carbonate and a chain carbonate. In this case, when the cyclic carbonate and the chain carbonate are mixed at a volume ratio of 1:1 to 1:9, the performance of the electrolytic solution is more likely to be further improved.

[0092] The lithium salt described above is a substance that is dissolved in an organic solvent, acts as a supply source of lithium ions in a battery to enable the operation of a basic lithium ion secondary battery, and plays a role in 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 SO₂) (wherein x and y are natural numbers), LiCl, LiI, and LiB(C₂O₄)₂ (lithium bis(oxalato)borate (LiBOB)). These may be used alone or as a mixture of two or more types. The concentration of the lithium salt is preferably used within the range of 0.1 to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte has good conductivity, so it is easy to maintain electrolyte performance, and the viscosity is appropriate, so the mobility of lithium ions tends to be good.

[0093] The electrolyte described above may further contain a vinylene carbonate or ethylene carbonate-based compound as a life improving agent in order to improve battery life.

[0094] Typical examples of the ethylene carbonate compounds mentioned above include difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, or fluoroethylene carbonate. When further life-extending agents are 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. As such a separator, polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof may be used, 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 may be used.

[0096] Lithium-ion secondary batteries are generally formed by placing the positive and negative electrodes (with a separator if necessary) opposite each other and immersing them in an electrolyte solution. [Examples]

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

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

number

[0099] Using the above approximation formula, substitute the measured adsorption amount (v) at relative pressures (p / p0) of 0.05 to 0.1 by the multipoint method due to nitrogen adsorption at liquid nitrogen temperature.m was obtained, and the specific surface area (SSA, unit: m 2 / g) of the sample was calculated by the following formula. [Mathematical formula]

[0100] In the above formula, v m m is the adsorption amount required to form a monomolecular layer on the sample surface (cm 3 / g), v is the actually 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), N is Avogadro's constant 6.022×10 23 , a(nm 2 ) is the area occupied by adsorbate molecules on the sample surface (molecular occupied cross-sectional area).

[0101] Specifically, using "Autosorb-iQ-MP" manufactured by Quantachrome, the adsorption amount of nitrogen on the carbon material at liquid nitrogen temperature was measured as follows. The carbon material as the measurement sample was filled into a sample tube, the sample tube was cooled to -196°C, the pressure was once reduced, and then nitrogen (purity 99.999%) was adsorbed onto the measurement sample at a desired relative pressure. The amount of nitrogen adsorbed to the sample when the equilibrium pressure was reached at each desired relative pressure was defined as the adsorbed gas amount v.

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

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

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

[0105] [Mode Pore Diameter] Using the BJH method described above, the logarithmic derivative pore volume distribution (dV / d(log D)) was calculated by differentiating the cumulative pore volume (V) with respect to the common logarithm of the pore diameter (D), and the pore diameter with the highest occurrence ratio was defined as the mode diameter.

[0106] <Bulk density> Bulk density was measured using a Hosokawa Micron PT-X powder tester. The sample was placed in an automated tap density measurement unit, and the bulk density was calculated from the volume after 3000 taps.

[0107] <Average primary particle diameter> The average primary particle size was measured by the following method. The samples from Examples 1 to 13 and Comparative Examples 1 to 11, described later, were placed in an aqueous solution containing 5% by mass of a surfactant ("Toriton X100" sold by Wako Pure Chemical Industries, Ltd.), treated with an ultrasonic cleaner for 10 minutes or more, and dispersed in the aqueous solution. The particle size distribution was measured using this dispersion. The particle size distribution measurement was performed using a particle size and particle size distribution analyzer ("Microtrac MT3300EXII" manufactured by Microtrac Bell Co., Ltd.), and the particle size at which the cumulative volume reached 50% was defined as the average primary particle. For the samples from Comparative Examples 12 and 13, described later, measurement was not possible using the above particle size distribution measurement method, so the particle size of 1000 primary particles displayed in the electron microscope image was measured using a transmission electron microscope, and the average value was calculated.

[0108] <Content of impurity elements> The content of impurity elements was measured by the following method. A carbon sample containing a predetermined amount of impurity elements was prepared in advance, and a calibration curve relating the intensity of Kα rays and the content of impurity elements was created using an X-ray fluorescence analyzer. Then, the Kα rays of the impurity elements were measured in the sample using X-ray fluorescence analysis, and the content of the impurity elements was determined from the calibration curve created earlier. X-ray fluorescence analysis was performed using a Shimadzu Corporation LAB CENTER XRF-1700 under the following conditions. An upper irradiation 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 to be measured placed, the back was secured with a plankton net, and the measurement surface was covered with a polypropylene film before measurement. The X-ray source was set to 40 kV, 60 mA for measurement.

[0109] <Particle shape> Particle shape was observed using a scanning electron microscope. A 3D Real Surface View Microscope VE-8800 manufactured by Keyence Corporation was used, with an acceleration voltage of 5 to 20 kV and a measurement magnification of 1,000 to 10,000 times.

[0110] <Preparation of compositions for lithium-ion secondary battery cathodes> 30 parts by mass of N-methylpyrrolidone solution obtained by dissolving 3 parts by mass of polyvinylidene fluoride (KF Polymer 7200, manufactured by Kureha Corporation), and 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 Industrial 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 porous carbon prepared in the examples and comparative examples described later were added and mixed. The mixture was then stirred and dispersed using a Primix homomixer (4500 rpm) while adding N-methylpyrrolidone as appropriate to achieve a solid content concentration of 50% by mass of the composition, to obtain a lithium-ion secondary battery cathode composition.

[0111] <Fabrication of positive electrodes for lithium-ion secondary batteries> The above lithium-ion secondary battery positive electrode composition was coated onto aluminum foil current collector ("1N30-H," manufactured by Fuji Kako Paper Co., Ltd.) using a bar coater ("T101," manufactured by Matsuo Sangyo Co., Ltd.), and after primary drying at 80°C for 30 minutes in a hot air dryer (manufactured by Yamato Kagaku Co., Ltd.), it was rolled using a roll press (manufactured by Hosen Co., Ltd.). After that, the lithium-ion secondary battery positive electrode (φ14 mm) was punched out and secondary drying was performed at 120°C for 3 hours under reduced pressure to produce the lithium-ion secondary battery positive electrode. The moisture content at this time was measured by taking the produced and dried electrode (φ14 mm), heating it to 250°C in a Karl Fischer (manufactured by Mitsubishi Chemical Analytec Co., Ltd.), and measuring the moisture content under a nitrogen stream. The moisture content was controlled to be 20 ppm or less so that the added porous carbon could exert effects other than water absorption.

[0112] (Manufacturing of lithium-ion secondary batteries) The positive electrode for the lithium-ion secondary battery described above was transferred to a glove box (manufactured by Miwa Seisakusho) under an argon gas atmosphere. For the negative electrode, a laminate consisting of metallic lithium foil (thickness 0.2 mm, φ16 mm) as the negative electrode active material layer and stainless steel foil (thickness 0.2 mm, φ17 mm) as the current collector was used. A polypropylene-based separator (Cellguard #2400, manufactured by Polypore) was used, and the electrolyte was injected using a mixed solvent system (1M-LiPF6, EC / EMC = 3 / 7 vol%, VC 2 mass%) of lithium hexafluoride phosphate (LiPF6) with added vinylene carbonate (EMC). A coin-type lithium-ion secondary battery (2032 type) was fabricated.

[0113] (Example 1) 1 g of starch (derived from corn, 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 at a heating rate of 10°C / min. Next, the mixture was heat-treated at 700°C for 60 minutes under a nitrogen gas stream to obtain a carbide. After that, it was washed with 0.1 mol / L hydrochloric acid at 80°C for 30 minutes, and then the carbide was removed onto a Buchner funnel and washed with water until the pH of the filtrate was in the range of 6 to 8. The acid washing and water washing were repeated three times, and the mixture was dried with hot air at 80°C to obtain porous carbon. The obtained porous carbon was further heat-treated (calcined) at 900°C for 60 minutes.

[0114] (Example 2) Porous carbon was obtained by the same procedure as in Example 1, except that the heating rate under a nitrogen gas stream was set to 5°C / min.

[0115] (Example 3) Porous carbon was obtained by the same procedure as in Example 1, except that the heating rate under a nitrogen gas stream was set to 20°C / min.

[0116] (Example 4) Porous carbon was obtained by the same procedure 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) Porous carbon was obtained by the same procedure 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 obtained was processed in the same manner as in Example 1, except that it was not further heat-treated (calcined) at 900°C for 60 minutes.

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

[0120] (Example 8) 1 g of glucose (sold by Fujifilm Wako Pure Chemical Industries) 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. Next, the mixture was heat-treated at 700°C for 60 minutes under a nitrogen gas stream to obtain a carbide. After that, the mixture was washed with 0.1 mol / L hydrochloric acid at 80°C for 30 minutes, and the carbide was removed onto a Buchner funnel and washed with water until the pH of the filtrate was in the range of 6 to 8. The acid washing and water washing were repeated three times, and the mixture was dried with hot air at 80°C to obtain porous carbon. The obtained porous carbon was further heat-treated (calcined) at 900°C for 60 minutes.

[0121] (Example 9) Porous carbon was obtained by the same procedure 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) Porous carbon was obtained by the same procedure 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) Porous carbon was obtained by the same procedure 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 (sold by Fujifilm Wako Pure Chemical Industries, Ltd.) (75 parts by mass per 100 parts by mass of starch) and 1.85 g of glycerin (sold by Fujifilm Wako Pure Chemical Industries, Ltd.) (185 parts by mass per 100 parts by mass of starch). The resulting mixture was heated to 700°C in a nitrogen gas atmosphere at a heating rate of 10°C / min. Next, the mixture was heat-treated at 700°C for 60 minutes under a nitrogen gas stream to obtain a carbide. After washing with 0.1 mol / L hydrochloric acid at 80°C for 30 minutes, the carbide was removed onto a Buchner funnel and washed with water until the pH of the filtrate was in the range of 6 to 8. The acid washing and water washing were repeated three times, and the mixture was dried with hot air at 80°C to obtain porous carbon. The obtained porous carbon was further heat-treated (calcined) at 900°C for 60 minutes.

[0125] (Example 13) Porous carbon was obtained by the same procedure 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) Porous carbon was obtained by the same procedure as in Example 1, except that magnesium chloride dihydrate (sold by Fujifilm Wako Pure Chemical Industries, Ltd.) was used instead of calcium chloride dihydrate.

[0127] (Comparative Example 2) Porous carbon was obtained by the same procedure as in Example 1, except that anhydrous calcium chloride (sold by Fujifilm Wako Pure Chemical Industries, Ltd.) was used instead of calcium chloride dihydrate.

[0128] (Comparative Example 3) Porous carbon was obtained by the same procedure as in Example 1, except that polyvinyl alcohol (PVA) (distributed by Fujifilm Wako Pure Chemical Industries, Ltd.) was used instead of starch.

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

[0130] (Comparative Example 5) Porous carbon was obtained by the same procedure 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) Porous carbon was obtained by the same procedure 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) Porous carbon was obtained by the same procedure 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) 1 g of polyvinyl alcohol (PVA) was mixed with 4 g of magnesium citrate (sold by 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. Next, the mixture was heat-treated at 700°C for 60 minutes under a nitrogen gas stream to obtain carbides. After that, the mixture was washed with 1 mol / L sulfuric acid at 80°C for 30 minutes, and the carbides were removed onto a Buchner funnel and washed with water until the pH of the filtrate was in the range of 6 to 8. The acid washing and water washing were repeated three times, and the mixture was dried with hot air at 80°C to obtain porous carbon. The obtained porous carbon was further heat-treated (calcined) at 900°C for 60 minutes.

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

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

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

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

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

[0139] Table 1 shows the production conditions for the porous carbon obtained in the examples and comparative examples, and Table 2 shows its 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 using the porous carbon obtained in Examples 1-13 and Comparative Examples 1-13, in accordance with the above description. The obtained lithium-ion secondary batteries were placed in a constant temperature bath at 25°C, and charge-discharge tests were performed using a charge-discharge test apparatus (Toyo System Co., Ltd., "TOSCAT") after measuring the DC resistance value before initial charging. For DC resistance, the resistance value was measured when 0.7mA was applied for 3 seconds. The charging capacity was measured by constant current charging at 0.2C up to 4.2V relative to the lithium potential. The discharge capacity was measured by constant current discharge at 0.2C up to 3V relative to the lithium potential. The initial charge-discharge efficiency (%) was calculated using the formula: (discharge capacity) / (charging capacity) × 100.

[0142] <Measurement of charge capacity retention rate of lithium secondary batteries> Lithium-ion secondary batteries were fabricated using the porous carbon obtained in Examples 1-13 and Comparative Examples 1-13, in accordance with the above description. The obtained lithium-ion secondary batteries were placed in a constant temperature bath at 25°C, and the charge capacity retention rate was measured using a charge / discharge test apparatus (Toyo System Co., Ltd., "TOSCAT"). For charging, a constant current charge of 0.2C was performed up to 4.2V relative to the lithium potential, and for discharging, a constant current discharge of 0.2C was performed up to 3V relative to the lithium potential. After performing three initial charge / discharge cycles under the above conditions, the charge rate was changed to 2C and one charge / discharge cycle was performed. The ratio of the charge capacity at 2C to the charge capacity at 0.2C at this time 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 using the porous carbon obtained in Examples 1-13 and Comparative Examples 1-13, in accordance with the above description. The obtained lithium-ion secondary batteries were placed in a constant temperature bath at 25°C, and the discharge capacity retention rate was measured using a charge / discharge test apparatus (Toyo System Co., Ltd., "TOSCAT"). For charging, constant current charging at 0.2C was performed up to 4.2V relative to the lithium potential, and for discharging, constant current discharge at 0.2C was performed up to 3V relative to the lithium potential. After performing three initial charge / discharge cycles under the above conditions, the discharge rate was changed to 2C and one charge / discharge cycle was performed. The ratio of the discharge capacity at 2C to the discharge capacity at 0.2C was defined as the discharge capacity retention rate. Generally, it is known that when the input / output characteristics of a battery are poor, the insertion and removal of lithium ions into and out of the electrodes tends to become less smooth as the charge / discharge rate increases. Therefore, a large ratio of the charge / discharge capacity at high rates to the charge / discharge capacity at low rates (charge / discharge capacity retention rate) indicates that the input / output characteristics of the battery are excellent.

[0144] <Evaluation of peel strength and chipping rate of lithium-ion secondary battery cathodes> For the lithium secondary battery positive electrodes prepared using the method described above from porous carbon obtained in Examples 1-13 and Comparative Examples 1-13, the strength of the slurry-coated surface when peeled from the aluminum foil current collector was measured. Specifically, the slurry-coated surface of the obtained lithium secondary battery electrodes and a stainless steel plate were bonded together using double-sided tape (Nichiban double-sided tape), and the 180° peel strength (peeling width 10 mm, peeling speed 100 mm / min) was measured using a 50N load cell (Imada Co., Ltd.). The number of electrode chips was determined by punching out 10 electrodes with a φ14 mm punching machine for the lithium-ion secondary battery positive electrodes, and counting the number of electrodes from which the active material peeled off from the current collector.

[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 number of electrode chips. [Table 3]

[0146] The porous carbons of Examples 1 to 13 exhibited high charge / discharge capacity retention and peel strength, and no electrode chipping occurred. This indicates that they are suitable porous carbons for cathode additives, capable of improving the input / output characteristics of non-aqueous electrolyte secondary batteries at room temperature while ensuring electrode peel strength. On the other hand, the porous carbons of Comparative Examples 1 to 13 were not sufficient in at least one of the following aspects: charge capacity retention, discharge capacity retention, peel strength, and the number of electrode chips.

Claims

1. The pore volume of 2 nm to 200 nm, as measured by the BJH method, was 0.8 cm³. ３ Porous carbon having a concentration of 1.5% / g or more, a pore mode diameter of 150 nm or less measured by the BJH method, an average primary particle diameter of 1 μm to 100 μm, a pore volume of less than 2 nm measured by the DFT method of 0.35 cm³ / g or less, and a sulfur content of 1000 ppm or less.

2. The specific surface area measured by the BET method was 500 m². ２ / g or more 1200m ２ The porous carbon according to claim 1, wherein the amount is less than or equal to / g.

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

4. The porous carbon according to claim 1, wherein the silicon content is 1000 ppm or less.

5. The bulk density is 0.10 g / cm³. ３ The porous carbon described in claim 1, which is as follows:

6. (1) A step of obtaining a mixture containing a carbon source and a calcium compound, (2) A step of heat-treating the mixture in an inert gas atmosphere to obtain a carbide, (3) Step of removing calcium compounds from the carbide A method for producing porous carbon according to any one of claims 1 to 5, including

7. The method according to claim 6, wherein the mixture in step (1) further comprises at least one selected from the group consisting of polyhydric alcohols and carboxylic acids.

8. The method according to claim 6, wherein the melting point of the calcium compound is 300°C or less.

9. The method according to claim 6, 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.

10. The method according to claim 6, wherein the carbon source is a sugar.

11. The method according to claim 10, wherein the sugar is at least one selected from the group consisting of monosaccharides, disaccharides, and polysaccharides.

12. The method according to claim 6, wherein the removal of the calcium compound in step (3) is carried out by acid washing.

13. The method according to claim 6, wherein the temperature of the heat treatment step in step (2) is 400°C or more and 1300°C or less.

14. The method according to claim 6, wherein the heating rate of the heat treatment step in step (2) is 2°C / min or more.

15. A porous carbon according to any one of claims 1 to 5, which is an additive for the positive electrode of a non-aqueous electrolyte secondary battery.

16. A porous carbon according to any one of claims 1 to 5, which is an additive for the positive electrode of a lithium-ion secondary battery.

17. A composition for the positive electrode of a non-aqueous electrolyte secondary battery, comprising porous carbon according to any one of claims 1 to 5.

18. A composition for the positive electrode of a lithium-ion secondary battery, comprising porous carbon according to any one of claims 1 to 5.

19. A non-aqueous electrolyte secondary battery comprising a positive electrode containing the positive electrode composition for a non-aqueous electrolyte secondary battery described in claim 17.

20. A lithium-ion secondary battery comprising a positive electrode containing the positive electrode composition for a lithium-ion secondary battery described in claim 18.

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