Porous carbon, positive electrode additive for non-aqueous electrolyte secondary batteries, non-aqueous electrolyte secondary batteries, and methods for manufacturing porous carbon.

Abstract

The purpose of this invention is to provide a porous carbon suitable as a positive electrode additive, which can improve the input and output characteristics of non-aqueous electrolyte secondary batteries at room temperature and ensure the peel strength of the electrodes. This invention relates to a porous carbon having a pore volume of 2 nm to 200 nm (measured by the BJH method) of 0.8 cm³ / g or more, a bulk density of 0.10 g / cm³ or less, a modal diameter of the pores (measured by the BJH method) of 150 nm or less, and an average primary particle size of 1 μm to 100 μm or less.

Description

Technical Field

[0001] This patent application claims priority under the Paris Convention against Japanese Patent Application No. 2021-092329 (filed on June 1, 2021), the entire contents of which are incorporated herein by reference. This invention relates to porous carbon as a positive electrode additive for non-aqueous electrolyte secondary batteries, a positive electrode additive containing the porous carbon material, a positive electrode for non-aqueous electrolyte secondary batteries containing the positive electrode additive, a non-aqueous electrolyte secondary battery having the positive electrode, and a method for manufacturing the porous carbon. Prior Technology

[0002] The demand for non-aqueous electrolyte secondary batteries, such as small, lightweight, high-energy-density, and rechargeable lithium-ion batteries, is rapidly increasing due to their unique characteristics. Lithium-ion batteries are used in mobile phones, laptops, and electric vehicles due to their high energy density. For these lithium-ion secondary batteries, there is a need to expand their applications and improve their output characteristics through further development.

[0003] One method proposed to improve the output characteristics of lithium-ion secondary batteries is to add activated carbon to the positive electrode.

[0004] For example, Patent Document 1 reports that by adding activated carbon with a pore size of 20 Å or more, a pore volume of 0.418 cc / g or more, and a specific surface area of ​​1200 m2 / g or more to the positive electrode, the output characteristics at -30°C can be improved.

[0005] Furthermore, Ketjenblack is known as a porous carbon with a pore size of 2 nm or more, a large pore volume, and a large porosity of pore size 200 nm or more, i.e., a low bulk density, and it has been used as an additive for cathodes (Patent Document 2). [Previous Technical Documents] [Patent Literature]

[0006] [Patent Document 1] Japanese Patent No. 4964404 [Patent Document 2] Japanese Patent No. 4727386 Summary of the Invention

[0007] [The problem the invention aims to solve] However, according to the inventors' research, even with the addition of activated carbon as shown in Patent Document 1 to the positive electrode, there was no sufficient improvement in the input and output characteristics at room temperature.

[0008] Furthermore, when adding Ketjenblack as described in Patent Document 2 to the positive electrode, not only is the improvement in input and output characteristics small, but the dispersibility of the positive electrode slurry is easily damaged due to the adsorption of Ketjenblack by the binder and the aggregation of the conductive agent, making it difficult to ensure the peel strength of the resulting electrode.

[0009] The present invention was made in view of the above-mentioned actual situation, and its purpose is to provide a porous carbon that can improve the input and output characteristics of non-aqueous electrolyte secondary batteries at room temperature and ensure the peel strength of the electrode, and is suitable for positive electrode additives. [Methods used to solve problems]

[0010] In order to solve this problem, the inventor conducted a detailed study and found that the above problem could be solved by adding porous carbon with specific physical properties to the positive electrode, thus completing the present invention.

[0011] That is, the present invention includes the following preferred embodiments. [1] A porous carbon having a pore volume of 2 nm to 200 nm as measured by the BJH method of 0.8 cm3 / g or more, a bulk density of 0.10 g / cm3 or less, a modal diameter of pores as measured by the BJH method of 150 nm or less, and an average primary particle size of 1 μm to 100 μm or more. [2] Porous carbon as in [1], wherein the pore volume of less than 2 nm as measured by DFT is less than 0.35 cm3 / g. [3] Porous carbon such as [1] or [2], wherein the specific surface area measured by the BET method is more than 500 m2 / g and less than 1200 m2 / g. [4] Porous carbon such as any one of [1] to [3], wherein the calcium content is more than 20 ppm and less than 2000 ppm. [5] Porous carbon of any one of [1] to [4], wherein the sulfur content is less than 1000 ppm and the silicon content is less than 1000 ppm. [6] Porous carbon such as any one of [1] to [5] has a bulk density of less than 0.05 g / cm3. [7] A method for manufacturing porous carbon, which is a method for manufacturing porous carbon as described in any one of [1] to [6], comprising: (1) The step of obtaining a mixture containing a carbon source and a calcium compound; (2) The step of heat-treating the mixture in an inert gas environment to obtain a carbide; and (3) The step of removing calcium compounds from the carbide. [8] The method of [7] wherein the mixture in step (1) further contains at least one selected from the group consisting of polyols and carboxylic acids. [9] The method of [7] or [8] wherein the melting point of the calcium compound is below 300°C.

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

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

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

[12] The method of

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

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

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

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

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

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

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

[16] Porous carbon such as any one of [1] to [6] is an additive for the positive electrode of a non-aqueous electrolyte secondary battery.

[17] Porous carbon such as any one of [1] to [6] is an additive for the positive electrode of lithium-ion secondary batteries.

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

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

[20] A non-aqueous electrolyte secondary battery, which is formed by a positive electrode containing a composition of a non-aqueous electrolyte secondary battery as described in

[18] .

[21] A lithium-ion secondary battery, which is a positive electrode containing a composition of a secondary battery containing a non-aqueous electrolyte as described in

[19] . [Effects of the Invention]

[0012] According to the present invention, a porous carbon suitable for positive electrode additives can be provided, which can improve the input and output characteristics of non-aqueous electrolyte secondary batteries at room temperature and ensure the peel strength of the electrodes. Simple Explanation of the Diagram

[0013] Figure 1 shows a transmission electron microscope (TEM) image of porous carbon in Example 6. Figure 2 is a transmission electron microscope (TEM) image of porous carbon in Example 6. Figure 3 shows a scanning electron microscope (SEM) image of porous carbon in Example 8. Figure 4 shows a scanning electron microscope (SEM) image of porous carbon in Example 8. Figure 5 shows a transmission electron microscope (TEM) image of porous carbon in Comparative Example 9. Figure 6 shows a transmission electron microscope (TEM) image of porous carbon in Comparative Example 9. Figure 7 shows a scanning electron microscope (SEM) image of the porous carbon of Comparative Example 9. Figure 8 shows a scanning electron microscope (SEM) image of the porous carbon of Comparative Example 9. Figure 9 is a scanning electron microscope (SEM) image of porous carbon in Comparative Example 13. Figure 10 shows a scanning electron microscope (SEM) image of porous carbon from Comparative Example 13. Implementation

[0014] [The form in which the invention is carried out] The embodiments of the present invention are described in detail below. However, the following description is illustrative of embodiments of the present invention and is not intended to limit the present invention to these embodiments.

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

[0016] In the porous carbon of this invention, the pore volume of 2 nm to 200 nm, measured by the BJH method, is 0.8 cm³ / g or more. If the pore volume of 2 nm to 200 nm is 0.8 cm³ / g or more, the storage of lithium ions within the pores and the mobility of lithium ions to the vicinity of the positive electrode active material are excellent, allowing for abundant supply of lithium ions to the periphery of the positive electrode active material. This promotes the smooth insertion and detachment of lithium ions from the positive electrode active material, thereby improving input and output characteristics. If the pore volume of 2 nm to 200 nm is less than 0.8 cm³ / g, the mobility of lithium ions tends to decrease, and there is a tendency for pore blockage due to gases generated during electrolyte decomposition in the electrochemical element, leading to reduced electrolyte mobility. The pore volume of particles between 2 nm and 200 nm is preferably 0.9 cm³ / g or higher, more preferably 1.00 cm³ / g or higher, even more preferably 1.30 cm³ / g or higher, even more preferably 1.60 cm³ / g or higher, particularly preferably 1.65 cm³ / g or higher, particularly preferably 1.90 cm³ / g or higher, extremely preferably 2.30 cm³ / g or higher, and especially extremely preferably 3.20 cm³ / g or higher. If the pore volume between 2 nm and 200 nm is above this lower limit, there is a tendency for further improvement in input and output characteristics. Furthermore, if the pore volume between 2 nm and 200 nm increases, there is a tendency for excellent electrolyte retention performance and excellent electrolyte mobility; therefore, the upper limit is not particularly limited, but it is preferably 4.00 cm³ / g or lower, more preferably 3.90 cm³ / g or lower. The pore volume of 2 nm to 200 nm can be adjusted to this range, for example, by appropriately adjusting the type and / or amount of carbon source and calcium compound, and the temperature and / or time of heat treatment steps in the method for manufacturing porous carbon described later. The pore volume of 2 nm to 200 nm can be measured by pore distribution analysis performed by the BJH method using nitrogen adsorption measurement, for example, by the method described in the examples below.

[0017] In the porous carbon of this invention, the bulk density is 0.10 g / cm³ or less. The bulk density of the porous carbon indicates the degree of development of the micropore structure. Given the same volume of micropores below 200 nm, those with lower bulk density have larger volumes of pores above 200 nm. It is believed that micropores between 2 nm and 200 nm function to store and move lithium ions, while pores above 200 nm function to retain the electrolyte and supply lithium ions to the micropores between 2 nm and 200 nm. Therefore, apart from micropores between 2 nm and 200 nm, in this invention, it is preferable that the volume of pores above 200 nm is large, i.e., the bulk density is low. If the bulk density exceeds 0.10 g / cm³, the retention of the electrolyte may be insufficient, and the input / output characteristics will decrease. The bulk density is preferably 0.07 g / cm³ or less, more preferably 0.06 g / cm³ or less. In one embodiment of the present invention, the bulk density is even more preferably 0.05 g / cm³ or less, even more preferably 0.015 g / cm³ or less, particularly preferably 0.014 g / cm³ or less, especially preferably 0.013 g / cm³ or less, even more preferably 0.012 g / cm³ or less, extremely preferably 0.011 g / cm³ or less, even more preferably 0.010 g / cm³ or less, even more extremely preferably 0.009 g / cm³ or less, and even more extremely preferably 0.008 g / cm³ or less. If the bulk density is below this upper limit, the electrolyte can be abundantly maintained in a gap of 200 nm or more, which can easily further improve the input and output characteristics. Furthermore, if the bulk density is too low, it may be difficult to maintain the strength of the carbon skeleton. Therefore, from the viewpoint of easily maintaining the peel strength of the electrode, a density of 0.003 g / cm³ or higher is generally preferred. For example, the bulk density can be adjusted to this range by appropriately adjusting the type and / or amount of carbon source and calcium compound, the temperature and / or time of the heat treatment step, etc., in the porous carbon manufacturing method described later. The bulk density can be measured, for example, by the method described in the examples below.

[0018] In the porous carbon of this invention, the mode diameter of the pores, measured by the BJH method, is 150 nm or less. Here, the "mode diameter" refers to the pore size with the largest proportion in the logarithmic differential pore volume distribution (dV / d(log D)) obtained by differentiating the common logarithm of the pore diameter (D) with respect to the cumulative pore volume (V). If the mode diameter of the porous carbon is 150 nm or less, lithium ions can be smoothly stored within the pores and moved to the vicinity of the positive electrode active material, thus abundantly supplying lithium ions to the periphery of the positive electrode active material. This facilitates further improvement in input / output characteristics. Furthermore, during slurry preparation, the adsorption of binder on the pores of the porous carbon can be suppressed, tending to increase the peel strength of the electrode and suppress electrode defects. If the mode diameter exceeds 150 nm, the amount of lithium ions stored within the pores decreases, and the supply of lithium ions to the surface of the active material becomes less. Furthermore, during slurry preparation, the binder is easily adsorbed into the fine pores of the porous carbon. 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, especially preferably 25 nm or less, even more preferably 20 nm or less, most preferably 15 nm or less, and most preferably 13 nm or less. If the mode diameter is below this upper limit, the input and output characteristics can be further improved. There is no lower limit for the mode diameter. If the mode diameter is too small, the mobility of lithium ions is easily reduced, and in electrochemical devices, the gas generated during electrolyte decomposition may cause pore blockage, further reducing electrolyte mobility. Therefore, it is usually 2 nm or more, more preferably 9 nm or more. For example, by appropriately adjusting the type and / or amount of carbon source and calcium compound in the porous carbon manufacturing method described below, as well as the temperature and / or time of the heat treatment step, the mode diameter can be adjusted to within this range. The mode diameter can be measured by means of pore distribution analysis, such as by the BJH method using nitrogen adsorption, or by the method described in the examples below.

[0019] In the porous carbon of this invention, the average primary particle size is 1 μm to 100 μm. By maintaining an average primary particle size of 1 μm to 100 μm, lithium ion storage and diffusion are easily and appropriately achieved, resulting in good input / output characteristics. Furthermore, the porous carbon is less prone to agglomeration, thus reducing uneven coating after electrode coating and improving electrode peel strength. If the average primary particle size is less than 1 μm, the presence of microparticles cannot be completely suppressed by binders, leading to easy leaching from the electrode. Additionally, microparticles within the electrode are prone to agglomeration. This results in uneven coating after electrode coating, leading to reduced electrode peel strength. Furthermore, if the average primary particle size exceeds 100 μm, it is difficult to form good ion diffusion paths between active materials, hindering the improvement of input / output characteristics. Moreover, the large particles easily cause unevenness in the electrode, further reducing its peel strength. From the above perspective, the average primary particle size is preferably 2 μm or more, more preferably 5 μm or more, more preferably 80 μm or less, and more preferably 60 μm or less. If the average primary particle size is within this range, the input and 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. For example, by appropriately adjusting the type of carbon source and the conditions of the pulverization step in the porous carbon manufacturing method described later, the average primary particle size can be adjusted to this range. In this invention, the so-called average primary particle size refers to the particle size that constitutes 50% of the cumulative volume as measured by laser diffraction / scattering method. This value is used as the average primary particle size. However, in cases where laser diffraction / scattering method cannot be used, it refers to the average particle size obtained by measuring the particle size of the primary particles appearing in the 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 / g or less, more preferably 0.30 cm³ / g or less, even more preferably 0.20 cm³ / g or less, even more preferably 0.15 cm³ / g or less, particularly preferably 0.13 cm³ / g or less, especially preferably 0.12 cm³ / g or less, even more preferably 0.10 cm³ / g or less, even more preferably 0.09 cm³ / g or less, and most preferably 0.08 cm³ / g or less. If the pore volume of less than 2 nm is below this upper limit, lithium ions are less likely to be adsorbed in the pores of less than 2 nm, thus lithium ions can be supplied to the active material, and the input and output characteristics can be easily improved. The lower limit of the pore volume of less than 2 nm is not particularly limited, but is preferably 0.01 cm³ / g or more. For example, by appropriately adjusting the type and / or amount of carbon source and calcium compound, and the temperature and / or time of the heat treatment step in the method for manufacturing porous carbon described later, the pore volume of less than 2 nm can be adjusted to this range. The pore volume of less than 2 nm can be measured by pore distribution analysis performed by DFT method in nitrogen adsorption measurement, for example, by the method described in the examples described later.

[0021] In the porous carbon of the present invention, the pore volume of 2 nm to 10 nm, measured by the DH method, is preferably 0.55 cm³ / g or less, more preferably 0.53 cm³ / g or less, even more preferably 0.45 cm³ / g or less, even more preferably 0.40 cm³ / g or less, particularly preferably 0.35 cm³ / g or less, especially preferably 0.30 cm³ / g or less, even more preferably 0.25 cm³ / g or less, and most preferably 0.20 cm³ / g or less. If the pore volume of 2 nm to 10 nm is less than 0.55 cm³ / g, the mobility of lithium ions to the vicinity of the positive electrode active material is easily increased, and pore blockage caused by gases generated during electrolyte decomposition in the electrochemical element is less likely to occur, thus easily and abundantly supplying lithium ions to the periphery of the positive electrode active material. This promotes the smooth insertion and detachment of lithium ions from the positive electrode active material, resulting in improved input and output characteristics. Furthermore, if the pore volume of 2 nm to 10 nm decreases, there is a tendency for excellent electrolyte mobility. Therefore, the lower limit is not particularly limited, but it is preferably 0.01 cm³ / g or higher, more preferably 0.05 cm³ / g or higher, and even more preferably 0.10 cm³ / g or higher. For example, by appropriately adjusting the type and / or amount of carbon source and calcium compound, the temperature and / or time of the heat treatment step in the method for manufacturing porous carbon described later, the pore volume of 2 nm to 10 nm can be adjusted to this range. The pore volume of 2 nm to 10 nm can be measured by pore distribution analysis performed by 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 / g or more, more preferably 600 m² / g or more, even more preferably 650 m² / g or more, even more preferably 700 m² / g or more, preferably 1200 m² / g or less, even more preferably 1000 m² / g or less, and even more preferably 900 m² / g or less. If the specific surface area is within this range, it is easy to retain lithium ions in the electrolyte, thereby easily improving the input and output characteristics. Furthermore, lithium ions diffuse easily, which also facilitates good coating stability. For example, by appropriately adjusting the type and / or amount of carbon source and calcium compound, the temperature and / or time of the heat treatment step in the method for manufacturing the porous carbon described later, the specific surface area can be adjusted to this range. 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, even more preferably 1500 ppm or less, and even more preferably 1000 ppm or less. If the calcium content is within this range, there is a tendency to easily suppress excessive mass increase of the porous carbon and to achieve excellent productivity. For example, by appropriately adjusting the conditions of the calcium compound removal step in the method for manufacturing the porous carbon described below (e.g., the type and / or concentration of the acid used in acid cleaning, the time and temperature of acid and / or water cleaning, etc.), the calcium content can be adjusted to within this range.

[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. Similarly, the silicon content is preferably 1000 ppm or less, more preferably 900 ppm or less, and even more preferably 800 ppm or less. If the sulfur and silicon contents are within this range, side reactions within the positive electrode are easily suppressed, thereby improving input and output characteristics. The lower limit for the sulfur and silicon contents is not particularly limited and can be 0 ppm. For example, by appropriately adjusting the type of carbon source in the method for manufacturing the porous carbon described later, and the conditions of the calcium compound removal step (e.g., the type and / or concentration of acid used in acid cleaning, the time and temperature of acid and / or water cleaning, etc.), the sulfur and silicon contents can be adjusted to this range. The contents of calcium, sulfur, and silicon can be measured by fluorescence X-ray analysis, for example, by the method described in the examples below.

[0025] In typical porous carbon, mesopores sometimes form a three-dimensional network structure, becoming interconnected. Such a three-dimensional network structure usually contains pore terminations (blockages). However, the inventors of this invention have discovered that in one embodiment of the porous carbon of this invention, all pores are three-dimensionally continuous and interconnected, without pore terminations, thus possessing a connected pore structure (see Figures 5 and 6). Furthermore, it has been found that in one embodiment of the porous carbon of this invention, due to the aforementioned connected pore structure, the diffusion rate of lithium ions within the pores is increased, improving the input and output characteristics of non-aqueous electrolyte secondary batteries at room temperature, and ensuring electrode peel strength, making it suitable as a positive electrode additive. It has also been found that such a connected pore structure can be achieved using a manufacturing method described later.

[0026] Furthermore, in general porous carbon used as a cathode additive, a three-dimensional dendritic particle structure is sometimes formed due to the aggregation and connection of primary particles such as carbon black and Ketjen black (Figures 9 and 10). Such a three-dimensional dendritic structure has a low bulk density due to the gaps between the branches, and by being disposed between adjacent active materials within the electrode, a short-distance lithium-ion diffusion path can be formed. On the other hand, the inventors of this invention have discovered that in one embodiment of the porous carbon of the present invention, a sheet-like shape can be formed (Figures 3 and 4). It is believed that when the porous carbon forms the aforementioned sheet-like shape, the bulk density is significantly reduced due to the gaps formed by the wrinkles on the sheet surface. Moreover, it is disposed not only in contact with adjacent active materials within the electrode but also with active materials further apart, thus forming a long-distance lithium-ion diffusion path. Therefore, it is believed that, in particular, combining sheet-like porous carbon with three-dimensional dendritic porous carbon and granular porous carbon (Figures 7 and 8) can form both short-distance and long-distance ion diffusion paths, thus ensuring a better ion diffusion path within the entire electrode. It has been found that an embodiment of the porous carbon of the present invention can further improve the input and output characteristics of non-aqueous electrolyte secondary batteries at room temperature and ensure the peel strength of the electrode, making it a suitable porous carbon for positive electrode additives. Furthermore, this sheet-like shape with a wrinkled surface can be achieved using a manufacturing method described later.

[0027] <Methods for Manufacturing Porous Carbon> The porous carbon of the present invention can be manufactured, for example, by a method comprising the following steps: (1) The step of obtaining a mixture containing a carbon source and a calcium compound; (2) The step of heat-treating the mixture in an inert gas environment to obtain a carbide; and (3) The step of removing calcium compounds from the carbide.

[0028] There are no particular limitations on the carbon source, but sugars are preferred to improve the uniform dispersion 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. Two or more of these sugars can be used alone or in combination. Among these sugars, glucose and starch are preferred because they readily produce porous carbon that improves the input and output characteristics of non-aqueous electrolyte secondary batteries at room temperature and are readily available in large quantities.

[0029] There are no particular limitations on the starch used; for example, starches derived from corn, cassava, potato, sweet potato, tapioca, beans, wheat, rice, etc., can be used. In this invention, the amylose content of the preferred starch is preferably 50% by mass or less, and more preferably 30% by mass or less. The lower the amylose content of the starch, the lower the gelatinization temperature tends to be. Therefore, if the amylose content of the starch is below this upper limit, it is easier to gelatinize at low temperatures, and its compatibility with calcium compounds is more easily improved, which is preferable. The amylose content mentioned above can be determined, for example, by iodine colorimetric methods. Furthermore, the starch can be a modified starch. Examples of modified starches include etherified starch, esterified starch, cationic starch, and cross-linked starch. One type of starch can be used alone, or two or more types can be used in combination.

[0030] The calcium compound is not particularly limited, and examples include calcium chloride, calcium hydroxide, calcium oxide, calcium carbonate, calcium acetate, calcium fluoride, calcium bromide, calcium iodide, calcium carbide, calcium bicarbonate, calcium nitrate, calcium sulfate, calcium silicate, calcium phosphate, calcium pyrophosphate, calcium gluconate, and calcium lactate. Among these calcium compounds, from the perspective of easily manufacturing porous carbon that improves the input and output characteristics of non-aqueous electrolyte secondary batteries at room temperature, it is preferable to include a calcium compound with a melting point below 300°C (when the mixture contains polyols or carboxylic acids, the melting point of the eutectic compound of the calcium compound and the polyol or carboxylic acid is below 300°C), and more preferably, it is a calcium compound containing at least one of the group consisting of calcium chloride hydrate, calcium hydroxide, calcium oxide, calcium carbonate, and calcium acetate. Calcium chloride hydrate can be dihydrate, tetrahydrate, or hexahydrate, and from the perspective of good reactivity with sugars, dihydrate is preferred.

[0031] The mixture containing a carbon source and a calcium compound may further contain at least one from the group consisting of polyols and carboxylic acids. It is believed that if the mixture contains a polyol and / or a carboxylic acid, the calcium compound dissolves in the polyol and / or carboxylic acid to form a eutectic compound. It is believed that the eutectic compound is formed by coordination of calcium with hydroxyl groups, carboxyl esters, and carboxyl groups in the polyol and / or carboxylic acid. Therefore, the melting point of the calcium compound having a melting point of 300°C or higher can be used alone as the melting point of the eutectic compound, thus keeping it below 300°C. Therefore, the phrase "the melting point of the calcium compound is below 300°C" in this invention also includes "the melting point of the eutectic compound of the polyol and / or carboxylic acid and the calcium compound is below 300°C." Examples of polyols that can be used in this invention include glycerol, ethylene glycol, propylene glycol, polyethylene glycol, and polypropylene glycol, among which glycerol and ethylene glycol are preferred from the viewpoint of being 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, hexanoic 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. From the perspective of readily dissolving calcium compounds and being readily available in large quantities, formic acid and acetic acid are preferred. When using a mixture of one or more polyols and one or more carboxylic acids, the mixing ratio of the polyol to the carboxylic acid can be appropriately varied according to the desired properties of the porous carbon.

[0032] There are no particular limitations on the method of mixing carbon sources and calcium compounds, as well as polyols and / or carboxylic acids as appropriate; they can be mixed in any way.

[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, even more preferably 180 parts by mass or more, preferably 500 parts by mass or less, even more preferably 400 parts by mass or less, and even more preferably 300 parts by mass or less, relative to 100 parts by mass of sugar. If the amount of calcium compound is within this range, it is easy to obtain porous carbon with appropriate pore volume and pore size.

[0034] In cases where the mixture containing a carbon source and a calcium compound further contains a polyol and / or a carboxylic acid, the amount of the polyol and / or carboxylic acid relative to 100 parts by mass of the sugar 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 less than 500 parts by mass, even more preferably less than 400 parts by mass, and even more preferably less than 300 parts by mass (in cases where one or more polyols and one or more carboxylic acids are used in combination, the total amount refers to this mixture). If the amount of polyol and / or carboxylic acid is within this range, it is easy to prepare a eutectic compound with the calcium compound, which is readily compatible with the sugar, and the resulting porous carbon readily possesses appropriate pore volume and pore size.

[0035] In the manufacturing method of this invention, a carbide is obtained by heat-treating a mixture containing a carbon source and a calcium compound in an inert gas environment. Examples of inert gases include nitrogen and argon. The lower the concentration of the oxidizing gas in the gas used, the better. The amount of oxidizing gas, especially oxygen, is generally preferably 1% by volume or less, more preferably 0.1% by volume or less. If the oxygen concentration is below this upper limit, the oxidation of the carbide is easily suppressed, and a structure with the desired characteristics is easily obtained. The oxidative decomposition of the generated structure is also 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. If the heat treatment temperature is within this range, it is easy to obtain porous carbon with a pore volume of 2 nm to 200 nm that is suitable, and in the subsequent step of removing calcium compounds from the carbide, calcium compounds tend to be easily removed. Furthermore, this heat treatment can be carried out in multiple stages. For example, after evaporating the moisture in the mixture at 50–300 °C, heat treatment (carbonization) can be performed at 400–900 °C, followed by heat treatment (firing) at 900–1300 °C. By performing the heat treatment in multiple stages, carbides with more homogeneous properties can be obtained.

[0036] The heat treatment time is not particularly limited, but it is preferably 0.5 hours or more, more preferably 1 hour or more, even more preferably 3 hours or more, preferably less than 24 hours, even more preferably less than 12 hours, and even more preferably less than 8 hours. If the heat treatment time is within this range, carbonization will be sufficient and ignition will be less likely, which is preferable. Furthermore, from an economic point of view, this is an appropriate time, and therefore preferable.

[0037] In the manufacturing method of this 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. If the heating rate is above this lower limit, it is easier to achieve a suitable fine pore size. There is no particular limitation on the upper limit of the heating rate, but from the viewpoint of achieving uniform heat treatment, it is preferably 200°C / min or less.

[0038] As a furnace used for heat treatment, various types of furnaces can be used, such as rotary kilns, fluidized bed furnaces, fixed bed furnaces, moving bed furnaces, and moving plate furnaces. Both continuous furnaces (for continuous feeding of raw materials and removal of products) and batch furnaces (for intermittent feeding of raw materials and removal of products) can be used. As for the heating method, any method capable of heating to a predetermined temperature is acceptable; electric heating, gas combustion heating, high-frequency induction heating, and electrostatic heating can be used. Furthermore, these heating methods can be used individually or in combination without issue.

[0039] The porous carbon of the present invention can be obtained by removing calcium compounds from the resulting carbide. The removal of these calcium compounds is preferably carried out, for example, by acid washing. Examples of acids used for acid washing include hydrochloric acid, sulfuric acid, and nitric acid. Hydrochloric acid is preferred because it readily dissolves metal compounds in the carbide, does not leave residual sulfur or other impurities, and easily inhibits the oxidation of the carbide. The acid concentration during acid washing can be appropriately varied depending on the type of acid used. For example, when using hydrochloric acid, a concentration in the range of 0.01 to 1.0 mol / L is preferred, and more preferably, a concentration in the range of 0.05 to 0.5 mol / L. If the concentration of hydrochloric acid is within this range, it is easier to remove metal compounds and less likely to leave hydrochloric acid residue in the carbide, which is therefore preferable.

[0040] During acid cleaning, the pH of the acid can be appropriately adjusted according to the type, concentration, and temperature of the acid used, preferably below 3, and more preferably below 2.5. If the pH of the acid is below this upper limit, metal compounds can be removed efficiently.

[0041] Acid cleaning can be performed, for example, by immersing the obtained carbide in an acid. When performing acid cleaning by immersion in acid, the mass ratio of acid to carbide can be appropriately adjusted according to the type, concentration, and temperature of the acid used. The mass of carbide immersed in the 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 carbide immersed in the acid is within this range, a sufficient cleaning effect is easily obtained.

[0042] There are no particular limitations on the method of acid cleaning of carbides, as long as the carbides can be immersed in acid. This can be done by continuously adding acid, allowing the carbides to remain in the acid for a predetermined time, and then draining the acid while simultaneously immersing them; or by immersing the carbides in acid for a predetermined time, draining the acid, and then adding more acid to repeat the immersion-draining process. Alternatively, all the acid can be replaced, or only some of the acid can be replaced. Furthermore, the acid can be stirred during immersion.

[0043] There are no particular limitations on the environment in which acid cleaning is performed; it can be appropriately selected depending on the cleaning method used. In this invention, acid cleaning is typically carried out in an atmospheric environment.

[0044] The time for immersing the carbide in acid can be appropriately adjusted according to the acid used and the processing temperature. From the viewpoint of fully removing the metal compound, it is preferable to be more than 5 minutes, and from the viewpoint of productivity, it is preferable to be less than 60 minutes, more preferably less than 40 minutes, and even more preferably less than 35 minutes.

[0045] After acid cleaning of the carbides, it is preferable to remove the acid from the porous carbon by washing with water. This acid cleaning and washing can be repeated until the calcium compounds in the porous carbon are removed. Furthermore, from the viewpoint of removing calcium compounds and residual acid, the higher the temperature of the solution during acid cleaning and washing, the better; it is usually carried out at 60°C or higher.

[0046] As an embodiment of the present invention, the mixture containing a carbon source and a calcium compound can be heat-treated (carbonized) at 500-900°C, followed by acid cleaning, and then the porous carbon after acid cleaning can be heat-treated (fired) at 900-1300°C. By performing carbonization at a temperature below 900°C, the metal compounds derived from the calcium compound in the acid cleaning step can be easily removed, and by performing firing at a higher temperature of 900-1300°C, the desired pore volume and specific surface area can be easily obtained.

[0047] Porous carbon after acid cleaning and water washing can also be dried using conventional dryers such as hot air dryers and vacuum dryers. Drying is preferably carried out at a temperature of 50–150°C. Within this temperature range, oxidation of the porous carbon is less likely to occur, while still allowing for proper drying, which is therefore preferable.

[0048] The dried porous carbon can also be pulverized. The pulverization step is used to control the shape and particle size of the final porous carbon to the desired shape and particle size. As for the pulverization method, there is no particular limitation. For example, conventional pulverizers such as ball mills, centrifugal roller mills, ring roller mills, centrifugal ball mills, jet mills, cone crushers, twin-roll crushers, disc crushers, and rotary crushers can be used alone or in combination.

[0049] In this invention, the method for manufacturing porous carbon may further include a classification step after the pulverization step. For example, by removing particles that are extremely smaller or larger than the expected particle size, porous carbon with a narrow particle size distribution can be obtained. The classification method is not particularly limited, and examples include: classification using sieves, wet classification, and dry classification. Examples of wet classifiers include: classifiers utilizing gravity classification, inertial classification, hydraulic classification, and centrifugal classification principles. Examples of dry classifiers include: classifiers utilizing sedimentation classification, mechanical classification, and centrifugal classification principles. From an economic point of view, a dry classification device is preferred. Furthermore, to prevent surface oxidation during pulverization, the pulverization and classification steps are preferably carried out in an inert gas environment.

[0050] A single device can be used for both crushing and grading. For example, a jet mill with dry grading capabilities can be used for both. Alternatively, the crusher and grader can be separate devices. In this case, crushing and grading can be performed continuously or discontinuously.

[0051] Additives for the positive electrode of non-aqueous electrolyte secondary batteries The porous carbon of the present invention can be preferably used as an additive for the positive electrode of non-aqueous electrolyte secondary batteries. Because the porous carbon of the present invention has the aforementioned specific fine pores and low bulk density, when used as an additive for the positive electrode of non-aqueous electrolyte secondary batteries, it easily improves the diffusion and adsorption of lithium ions within the positive electrode and within the fine pores. This facilitates the insertion and detachment of lithium ions from the positive electrode active material, not only improving the input and output characteristics of the non-aqueous electrolyte secondary battery, but also inhibiting the adsorption of binder on the additive and the aggregation of additives during electrode fabrication. Furthermore, it helps improve the manufacturing stability and peel strength of the electrode.

[0052] Examples of non-aqueous electrolyte secondary batteries include lithium-ion secondary batteries, sodium-ion secondary batteries, and lithium-sulfur batteries. As 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] <Composition for positive electrode of non-aqueous electrolyte secondary battery> The present invention also includes a composition for a positive electrode of a non-aqueous electrolyte secondary battery containing the above-mentioned additive for a positive electrode of a non-aqueous electrolyte secondary battery and a positive electrode active material. Furthermore, the present invention also includes a composition for a positive electrode of a lithium ion secondary battery containing the above-mentioned additive for a positive electrode of a lithium ion secondary battery. The composition for a positive electrode of a non-aqueous electrolyte secondary battery of the present invention may optionally contain other components other than the additive for a positive electrode of a non-aqueous electrolyte secondary battery and a positive electrode active material.

[0054] [Positive electrode 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 cobalt composite oxide (LiCoO2), lithium manganate (LiMn2O4), lithium nickel composite 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), spinel compounds with excess lithium represented by Li1+xMn2-xO4 (0 < X < 2), Li[Ni0.17Li0.2Co0.07Mn0.56]O2, LiNi0.5Mn1.5O4 and other metal oxides, compounds and polymers having sulfur, nitroxyl radicals, compounds and polymers having oxy radicals, compounds and polymers having nitrogen radicals, organic radicals such as compounds and polymers having a fulvalene skeleton.

[0055] These can be used alone or in combination of two or more. Then, among the above, from the viewpoint of improving the battery capacity of the secondary battery, etc., as the positive electrode active material, it is preferable to use lithium cobalt composite oxide (LiCoO2); lithium nickel composite oxide (LiNiO2); lithium-containing composite oxides of Co-Ni-Mn, such as LiNi1 / 3Co1 / 3Mn1 / 3O2, LiNi0.5Co0.2Mn0.3O2, LiNi0.8Co0.1Mn0.1O2, etc.; lithium-containing composite oxides of Ni-Co-Al, such as LiNi0.8Co0.1Al0.1O2, LiNi0.8Co0.15Al0.05O2, etc.

[0056] In addition, the particle size of the positive electrode active material is not particularly limited and can be the same as the positive electrode active material used in the past. Usually, a positive electrode active material 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 positive electrode active material is preferably 40-97% by mass, more preferably 45-95% by mass, relative to the total mass of the solid components of the composition.

[0058] The content of additives for the positive electrode of non-aqueous electrolyte secondary batteries, relative to the overall mass of the positive electrode active material, 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. If the content of additives for the positive electrode of non-aqueous electrolyte secondary batteries is within this range, it is easy to fully exert the effect of reducing electrode resistance without causing a decrease in the overall mass of the positive electrode active material, and the capacity is not easily reduced.

[0059] The mixing ratio of additives to positive electrode active materials in non-aqueous electrolyte secondary batteries, by mass ratio, can also be 1:99 to 10:90. When the mixing ratio of additives to positive electrode active materials in non-aqueous electrolyte secondary batteries falls within this range, it is easy to obtain non-aqueous electrolyte secondary batteries with excellent input and output characteristics.

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

[0061] The solvent can be used in an amount where the concentration of solid components in the composition of the positive electrode for non-aqueous electrolyte secondary batteries is preferably in the range of 1-80% by mass, more preferably 5-70% by mass, and even more preferably 10-60% by mass. By maintaining the concentration of solid components within this range, the positive electrode active material, the additives for the positive electrode of non-aqueous electrolyte secondary batteries, and other contained components can be uniformly dispersed, which is preferable.

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

[0063] [Conductive materials] In the composition of the positive electrode for the non-aqueous electrolyte secondary battery of the present invention, a conductive material may be further included to further improve the conductivity of the positive electrode formed on the current collector. As the conductive material, any conductive material that does not cause chemical changes in the constructed non-aqueous electrolyte secondary battery can be used. Specific examples of conductive materials include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, and carbon fiber; metal-based materials such as copper, nickel, aluminum, and silver powders and metal fibers; and conductive polymers such as polyphenylene derivatives. One such conductive material may be used alone or in combination of two or more. In the composition for the positive electrode of the non-aqueous electrolyte secondary battery of the present invention, the content of the above-mentioned conductive material is preferably 1 to 10% by mass, and more preferably 1 to 7% by mass, relative to the total mass of the positive electrode solid component in the composition.

[0064] <Manufacturing Method of Components for the Positive Electrode of Non-Aqueous Electrolyte Secondary Batteries> As a method for manufacturing the composition for the positive electrode of a non-aqueous electrolyte secondary battery according to the present invention, it can be manufactured by mixing the above-mentioned additives for the positive electrode of a non-aqueous electrolyte secondary battery, the positive electrode active material, and solvents and other components as required. The mixing method is not particularly limited; for example, a general mixing apparatus such as a disperser, mill, or kneader can be used. Preferably, such a mixing apparatus is used to stir for, for example, 20 minutes to 120 minutes.

[0065] There are no particular limitations on the mixing temperature; for example, it can be mixed in the range of 0 to 160°C, preferably in the range of 20 to 80°C. If the mixing temperature is within this range, it is easier to make the composition have a viscosity suitable for coating, and it is less likely to cause the evaporation of organic solvents, which is therefore preferable.

[0066] The mixing environment is not particularly limited, and it usually takes place in the atmospheric environment.

[0067] Non-aqueous electrolyte secondary batteries The non-aqueous electrolyte secondary battery positive electrode composition of the present invention can be effectively used in non-aqueous electrolyte secondary batteries. Therefore, the present invention also includes a non-aqueous electrolyte secondary battery having a positive electrode made using the above-described non-aqueous electrolyte secondary battery positive electrode composition. The non-aqueous electrolyte secondary battery of the present invention improves the diffusion of electrolyte ions in the positive electrode by containing the above-described non-aqueous electrolyte secondary battery positive electrode additive, thereby improving the battery's input and output characteristics. The non-aqueous electrolyte secondary battery of the present invention is preferably designed to operate at 2V to 5V; examples include lithium-ion secondary batteries or capacitors. Therefore, the present invention also includes a lithium-ion secondary battery comprising a positive electrode containing the lithium-ion secondary battery positive electrode composition of the present invention.

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

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

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

[0071] As a current collector for the positive electrode composition of a non-aqueous electrolyte secondary battery, it is preferable to use a material that is both conductive and electrochemically durable. Specifically, a current collector containing aluminum or an aluminum alloy can be used. Alternatively, aluminum and aluminum alloys can be used in combination, or different types of aluminum alloys can be combined. Aluminum and aluminum alloys are heat-resistant and electrochemically stable, making them excellent current collector materials.

[0072] The method for drying the components of the non-aqueous electrolyte secondary battery positive electrode on the current collector is not particularly limited. Conventional methods can be used, such as drying with warm air, hot air, or low-humidity air, vacuum drying, and drying by irradiation with infrared rays or electron beams. In this way, by drying the components of the non-aqueous electrolyte secondary battery positive electrode on the current collector, a positive electrode active material layer can be formed on the current collector, and a positive electrode with a current collector and a positive electrode active material layer can be obtained.

[0073] Alternatively, after the drying step, pressure treatment can be applied to the positive electrode active material layer using molding or rolling. This 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, wherein the negative electrode active material layer comprises a negative electrode active material. The steps for manufacturing the negative electrode are well known in the art.

[0075] The aforementioned negative electrode active material is a material that enables reversible insertion / deintercalation of lithium ions, including lithium metal, lithium metal alloys, materials that can be doped with lithium and dedoped with lithium, or transition metal oxides.

[0076] Examples of substances that enable the reversible insertion / release of lithium ions include crystalline carbon and amorphous carbon, which can be used alone or in combination. Examples of crystalline carbon include irregularly shaped, plate-like, flake-like, spherical, or fibrous natural or artificial graphite. Examples of amorphous carbon include soft or hard carbon, mesophase pitch carbides, and coking coal.

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

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

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

[0080] The negative electrode active material layer may also contain a binder and may further optionally contain a conductive material. The content of the binder in the above 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 further containing a conductive material, the negative electrode active material may be 80 to 98% by mass, the binder may be 1 to 10% by mass, and the conductive material may be 1 to 10% by mass for use.

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

[0082] Examples of the above water-insoluble binder include, for example, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

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

[0084] When using a water-soluble binder as the above negative electrode binder, a cellulose-based compound that can impart viscosity to the negative electrode active material layer may also be further used as a thickener. Examples of such cellulose-based compound include carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, and their alkali metal salts, etc. Such a thickener may be added in an amount of 0.1 to 100 parts by mass relative to 100 parts by mass of the binder.

[0085] The aforementioned conductive materials are used to impart conductivity to the electrodes. Any material can be used as long as it is a conductive material that will not cause a chemical change in the constructed battery. Specific examples of conductive materials include carbon-based substances such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, and carbon fiber; metallic substances such as metal powders or fibers of copper, nickel, aluminum, and silver; and conductive polymers such as polystyrene derivatives. These conductive materials can be used alone or in combination of two or more.

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

[0087] The electrolytes mentioned above preferably contain non-aqueous organic solvents and lithium salts.

[0088] The aforementioned non-aqueous organic solvents act as a medium, enabling the movement of ions associated with the electrochemical reactions of the battery.

[0089] As a non-aqueous organic solvent, carbonate-based, ester-based, ether-based, ketone-based, alcohol-based, or non-cationic solvents can also be used. Among the aforementioned 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), ethyl carbonate (EC), propyl carbonate (PC), and butyl carbonate (BC) can be used. Among the aforementioned ester-based solvents, n-methyl acetate, n-ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, decanolactone, valproic acid lactone, mevalonolactone, and caprolactone can also be used. As the aforementioned ethers, dibutyl ether, tetra(ethylene glycol dimethyl ether), di(ethylene glycol dimethyl ether), dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, etc., can also be used. As the aforementioned ketone solvents, cyclohexanone, etc., can also be used. Furthermore, as the aforementioned alcohol solvents, ethanol, isopropanol, etc., can also be used. As the aforementioned non-cationic solvents, nitriles such as R-CN (R is a straight-chain, branched, or cyclic hydrocarbon group with 2 to 20 carbon atoms, which may also contain double bonds, aromatic rings, or ether bonds), amides such as dimethylformamide, dimethylamine such as 1,3-dimethylamine, cyclobutane, etc., can also be used.

[0090] The above-mentioned non-aqueous organic solvents can be used alone or in combination of two or more. When two or more are used together, the mixing ratio can also be adjusted appropriately according to the target battery performance.

[0091] Furthermore, in the case of carbonate-based solvents, it is preferable to use a mixture of cyclic carbonates and chain carbonates. In this case, if cyclic carbonates and chain carbonates are mixed in a volume ratio of 1:1 to 1:9, the performance of the electrolyte can be further improved.

[0092] The aforementioned lithium salts are substances that dissolve in organic solvents and function as a lithium-ion supply source within the battery, enabling the basic operation of the lithium-ion secondary battery and promoting the movement of lithium ions between the positive and negative electrodes. Representative examples of such lithium salts include: LiPF6, LiBF4, LiSbF6, LiAsF6, LiCF3SO3, LiN(SO2C2F5)2, Li(CF3SO2)2N, LiC4F9SO3, LiClO4, LiAlO4, LiAlCl4, LiN(CxF2x+1SO2)(CyF2y+1SO2) (where x and y are natural numbers), LiCl, LiI, and LiB(C2O4)2 (lithium dioxolane borate (LiBOB)). These can be used alone or in combination of two or more. The preferred concentration of the lithium salt is in the range of 0.1 to 2.0 M. If the concentration of lithium salt is within this range, the electrolyte has good conductivity, thus making it easy to maintain electrolyte performance. Also, because the viscosity is appropriate, it is easy to make it a good carrier of lithium ions.

[0093] In order to improve battery life, the electrolyte may also contain vinylene carbonate or ethylene carbonate compounds as life extenders.

[0094] Representative examples of the aforementioned ethyl carbonate compounds include: difluoroethyl carbonate, chloroethyl carbonate, dichloroethyl carbonate, bromoethyl carbonate, dibromoethyl carbonate, nitroethyl carbonate, cyanoethyl carbonate, or fluoroethyl carbonate. When using this lifespan extender, the amount used can be appropriately adjusted according to the type of compound used.

[0095] In the lithium-ion secondary battery of the present invention, a separator may also exist between the positive electrode and the negative electrode. As such a separator, polyethylene, polypropylene, polyvinylidene fluoride, or multilayer films of two or more layers may also be used, as well as mixed multilayer films such as two-layer separators of polyethylene / polypropylene, three-layer separators of polyethylene / polypropylene / polyethylene, and three-layer separators of polypropylene / polyethylene / polypropylene.

[0096] Lithium-ion secondary batteries are generally formed by immersing the positive and negative electrodes (separated by a separator as needed) in an electrolyte solution. [Example]

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

[0098] <Determining the specific surface area, pore volume, and mode diameter of BET using nitrogen adsorption> [BET specific surface area] The following describes approximate formulas derived from the BET formula.

[0099] Using the above approximation, substitute the adsorption amount (v) measured by the multi-point method of nitrogen adsorption at liquid nitrogen temperature from 0.05 to 0.1 to obtain vm, and then calculate the specific surface area of ​​the sample (SSA: unit is m2 / g) using the following formula.

[0100] In the above formula, vm is the amount of adsorption required to form a monolayer on the sample surface (cm3 / g), v is the measured amount of adsorption (cm3 / g), p0 is the saturated vapor pressure, p is the absolute pressure, c is a constant (heat of adsorption), N is the Avogadro constant 6.022×1023, and a (nm2) is the area occupied by the adsorbate molecule on the sample surface (molecular occupancy cross-sectional area).

[0101] Specifically, using the Quantachrome Autosorb-iQ-MP instrument, the adsorption amount of nitrogen on carbon materials at liquid nitrogen temperature was measured as follows: Carbon materials, used as the test sample, were filled into a test tube. The pressure was temporarily reduced while the test tube was cooled to -196°C. Then, nitrogen (99.999% purity) was adsorbed onto the test sample at the desired relative pressure. The amount of nitrogen adsorbed onto the sample at the equilibrium pressure reached under each desired relative pressure was defined as the adsorbed gas volume v.

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

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

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

[0105] [Mode diameter] Using the BJH method described above, the logarithm of the pore diameter (D) is differentiated with respect to the cumulative pore volume (V) to calculate the logarithmic differential pore volume distribution (dV / d(log D)). The pore diameter with the largest proportion is set as the mode diameter.

[0106] <Volume Density> Bulk density was measured using a Hosokawa Micron Powder Tester PT-X. The sample was placed into an automated tapped density measuring unit, and the bulk density was calculated from the volume after 3000 taps.

[0107] <Average primary particle size> The average primary particle size was measured as follows. The samples from Examples 1-13 and Comparative Examples 1-11 (described later) were placed in an aqueous solution containing 5% by mass of a surfactant (Toriton X100, sold by Wako Pure Chemical Industries, Ltd.), and treated with an ultrasonic cleaner for at least 10 minutes to disperse them in the aqueous solution. The particle size distribution was measured using this dispersion. The particle size distribution was measured using a particle size / particle size distribution measuring device (Microtrac MT3300 EXII, manufactured by MicrotracBEL Co., Ltd.), and the particle size representing 50% of the cumulative volume was defined as the average primary particle size. For the samples from Comparative Examples 12 and 13 (described later), since the particle size distribution could not be measured in the above method, a transmission electron microscope was used to measure the particle size of 1000 primary particles displayed in the electron microscope image, and the average value was calculated.

[0108] <Content of impurity elements> The content of impurity elements was measured using the following method. A carbon sample containing a predetermined amount of impurity elements was prepared in advance. A calibration curve relating the intensity of the Kα line to the content of the impurity element was constructed using a fluorescence X-ray analysis device. Then, the Kα line of the impurity element in the fluorescence X-ray analysis of the sample was measured, and the content of the impurity element was determined from the previously constructed calibration curve. The fluorescence X-ray analysis was performed using a Shimadzu Corporation LAB CENTER XRF-1700 under the following conditions: A top-irradiation holder was used to hold the sample within a circumference with a diameter of 20 mm. The test sample was set by placing 0.5 g of the test sample into a polyethylene container with an inner diameter of 25 mm, pressing the back with a plankton net, and covering the measurement surface with a polypropylene film. The X-ray source was set to 40 kV and 60 mA for measurement.

[0109] <Particle Shape> Particle shapes were observed using a scanning electron microscope. A KEYENCE VE-8800 3D Real Surface View microscope was used, with an accelerating voltage of 5-20 kV and a magnification of 1000-10000x.

[0110] <Preparation of Components for the Positive Electrode of Lithium-ion Secondary Batteries> 30 parts by mass of an N-methylpyrrolidone solution containing 3 parts by mass of polyvinylidene fluoride (KUREHA Co., Ltd., KF polymer 7200), 93 parts by mass of LiNi1 / 3Co1 / 3Mn1 / 3O2 (Nippon Kagaku Kogyo Co., Ltd., "CELL SEED C-5H") as the positive electrode active material, 2 parts by mass of acetylene black (Denka Black) as the conductive material, and 2 parts by mass of porous carbon prepared in the examples and comparative examples described later were added and mixed to achieve a solid component concentration of 50% by mass. While appropriately adding N-methylpyrrolidone, the mixture was stirred and dispersed using a PRIMIX Homomixer (4500 rpm) to obtain a composition for a lithium-ion secondary battery positive electrode.

[0111] <Fabrication of the Positive Electrode for Lithium-ion Secondary Batteries> The aforementioned lithium-ion secondary battery positive electrode composition was coated onto aluminum foil (1N30-H, Fuji Processing Paper) of the current collector using a rod coating machine ("T101", Matsuo Sangyo). After a first drying at 80°C for 30 minutes using a hot air dryer (Yamato Scientific), it was calendered using a roll press (House Sen). Following this, it was punched to form a lithium-ion secondary battery positive electrode (φ14mm) and then subjected to a second drying at 120°C under reduced pressure for 3 hours, thus producing the positive electrode for lithium-ion secondary batteries. The moisture content at this stage was measured using a Kelvin Fisher (Mitsubishi Chemical Analytech) electrode (φ14mm) heated to 250°C under a nitrogen flow. The moisture content was managed to be below 20 ppm, allowing the added porous carbon to perform functions beyond water absorption.

[0112] <The Making of Lithium-ion Secondary Batteries> The above-mentioned lithium-ion secondary battery was transferred to a glove box (manufactured by Miwa Manufacturing Co., Ltd.) under an argon atmosphere using the positive electrode. The negative electrode system used a laminate containing a lithium metal foil (0.2 mm thick, φ16 mm) as the negative electrode active material layer and a stainless steel foil (0.2 mm thick, φ17 mm) as the current collector. Furthermore, a polypropylene-based separator (Celcard #2400, manufactured by Polypore) was used, and the electrolyte was a mixed solvent system (1M-LiPF6, EC / EMC = 3 / 7 vol%, VC2 wt%) consisting of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) of lithium hexafluoride phosphate (LiPF6) with added ethylene carbonate (VC). This mixture was then injected to fabricate a coin-shaped lithium-ion secondary battery (Type 2032).

[0113] (Example 1) 1 g of starch (from corn, amylose content approximately 26%, sold by FUJIFILM Wako Chemicals) was mixed with 2 g of calcium chloride dihydrate (sold by FUJIFILM Wako Chemicals) (200 parts by mass relative to 100 parts by mass of starch). The resulting mixture was heated to 700°C under a nitrogen atmosphere. The heating rate before reaching 700°C was 10°C / min. Then, under a nitrogen flow, the mixture was heat-treated at 700°C for 60 minutes to obtain a carbide. After washing with 0.1 mol / L hydrochloric acid at 80°C for 30 minutes, the carbide was transferred to a Buchner funnel and washed with water until the pH of the filtrate was in the range of 6-8. The acid washing and water washing were repeated three times, followed by hot air drying at 80°C to obtain porous carbon. The obtained porous carbon was then heat-treated (calcined) at 900°C for 60 minutes.

[0114] (Example 2) The heating rate under nitrogen flow was 5°C / min, and the process was otherwise the same as in Example 1 to obtain porous carbon.

[0115] (Example 3) The heating rate under nitrogen flow was 20°C / min, and the process was otherwise the same as in Example 1 to obtain porous carbon.

[0116] (Example 4) The amount of calcium chloride dihydrate added was 150 parts by weight relative to 100 parts by weight of starch. Otherwise, the process was carried out in the same manner as in Example 1 to obtain porous carbon.

[0117] (Example 5) The amount of calcium chloride dihydrate added was 300 parts by weight relative to 100 parts by weight of starch. Otherwise, the treatment was carried out in the same manner as in Example 1 to obtain porous carbon.

[0118] (Example 6) The obtained porous carbon was not further heat-treated (fired) at 900°C for 60 minutes. Otherwise, it was treated in the same way as in Example 1 to obtain porous carbon.

[0119] (Example 7) The obtained porous carbon was further heat-treated (fired) at 1200°C for 60 minutes instead of heat-treated (fired) at 900°C for 60 minutes. Otherwise, the process was the same as in Example 1 to obtain porous carbon.

[0120] (Example 8) 1 g of glucose (sold by FUJIFILM Wako Chemicals) was mixed with 1.1 g of calcium chloride dihydrate (110 parts by mass relative to 100 parts by mass of glucose), and the resulting mixture was heated to 700°C under a nitrogen atmosphere. The heating rate before reaching 700°C was 10°C / min. The mixture was then heat-treated at 700°C for 60 minutes under a nitrogen atmosphere to obtain a carbide. Afterward, the carbide was washed with 0.1 mol / L hydrochloric acid at 80°C for 30 minutes, and then transferred to a Buchner funnel and washed with water until the pH of the filtrate was in the range of 6-8. 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 then heat-treated (calcined) at 900°C for 60 minutes.

[0121] (Example 9) The amount of calcium chloride dihydrate added was 150 parts by mass relative to 100 parts by mass of glucose. Otherwise, the treatment was carried out in the same manner as in Example 8 to obtain porous carbon.

[0122] (Example 10) The amount of calcium chloride dihydrate added was 200 parts by mass relative to 100 parts by mass of glucose. Otherwise, the treatment was carried out in the same manner as in Example 8 to obtain porous carbon.

[0123] (Example 11) The amount of calcium chloride dihydrate added was 300 parts by mass relative to 100 parts by mass of glucose. Otherwise, the treatment was carried out in the same manner as in Example 8 to obtain porous carbon.

[0124] (Example 12) 1 g of starch was mixed with 0.75 g of calcium hydroxide (sold by FUJIFILM Wako Chemicals) (75 parts by weight relative to 100 parts by weight of starch) and 1.85 g of glycerol (sold by FUJIFILM Wako Chemicals) (185 parts by weight relative to 100 parts by weight of starch). The resulting mixture was heated to 700°C under a nitrogen atmosphere. The heating rate before reaching 700°C was 10°C / min. The mixture was then heat-treated at 700°C for 60 minutes under a nitrogen atmosphere to obtain a carbide. Afterward, the carbide was washed with 0.1 mol / L hydrochloric acid at 80°C for 30 minutes. The carbide was then transferred to a Buchner funnel and washed with water until the pH of the filtrate was in the range of 6-8. 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 porous carbon was then heat-treated (calcined) at 900°C for 60 minutes.

[0125] (Example 13) The amount of calcium hydroxide added was 150 parts by weight relative to 100 parts by weight of starch. Otherwise, the treatment was carried out in the same manner as in Example 12 to obtain porous carbon.

[0126] (Comparative Example 1) Magnesium chloride dihydrate (sold by FUJIFILM Wako Chemicals) was used instead of calcium chloride dihydrate, and the process was otherwise performed in the same manner as in Example 1 to obtain porous carbon.

[0127] (Comparative Example 2) Using calcium chloride anhydride (sold by FUJIFILM Wako Chemicals) instead of calcium chloride dihydrate, the same treatment as in Example 1 was performed to obtain porous carbon.

[0128] (Comparative Example 3) Polyvinyl alcohol (PVA) (sold by FUJIFILM Wako Chemicals) was used instead of starch, and the process was otherwise the same as in Example 1 to obtain porous carbon.

[0129] (Comparative Example 4) As a substitute for calcium chloride dihydrate, calcium hydroxide (sold by FUJIFILM Wako Chemicals) was used in a ratio of 75 parts by weight to 100 parts by weight of starch. Otherwise, the process was the same as in Example 1 to obtain porous carbon.

[0130] (Comparative Example 5) The amount of calcium hydroxide added was 150 parts by mass relative to 100 parts by mass of starch. Otherwise, the process was the same as in Comparative Example 4 to obtain porous carbon.

[0131] (Comparative Example 6) The amount of calcium hydroxide added was 200 parts by mass relative to 100 parts by mass of starch, and the process was otherwise the same as in Comparative Example 4 to obtain porous carbon.

[0132] (Comparative Example 7) Zinc chloride (sold by FUJIFILM Wako Chemicals) was used instead of calcium hydroxide, and the process was otherwise the same as in Comparative Example 6 to obtain porous carbon.

[0133] (Comparative Example 8) 1 g of polyvinyl alcohol (PVA) was mixed with 4 g of magnesium citrate (sold by FUJIFILM Wako Chemicals) (400 parts by mass relative to 100 parts by mass of PVA). The resulting mixture was heated to 700°C under a nitrogen atmosphere. The heating rate before reaching 700°C was 10°C / min. The mixture was then heat-treated at 700°C for 60 minutes under a nitrogen atmosphere to obtain a carbide. Afterward, the carbide was washed with 0.1 mol / L sulfuric acid at 80°C for 30 minutes. The carbide was then transferred to a Buchner funnel and washed with water until the pH of the filtrate was in the range of 6-8. The acid washing and water washing were repeated three times, followed by hot air drying at 80°C to obtain porous carbon. The resulting porous carbon was then heat-treated (calcined) at 900°C for 60 minutes.

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

[0135] (Comparative Example 10) 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. Otherwise, the same treatment as in Comparative Example 9 was performed to obtain porous carbon.

[0136] (Comparative Example 11) 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. Otherwise, the same treatment as in Comparative Example 9 was performed to obtain porous carbon.

[0137] (Comparative Example 12) Ketjen Black (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] The manufacturing conditions of the porous carbon obtained in the examples and comparative examples are shown in Table 1, and the physical properties are shown in Table 2. [Table 1] carbon source Metal salts polyols or carboxylic acids carbonization temperature [℃] heating speed [℃ / min] Firing temperature [℃] type Added amount [Parts by mass relative to 100 parts by mass of carbon source] type Added amount [Parts by mass relative to 100 parts by mass of carbon source] Example 1 starch CaCl2·2H2O 200 - - 700 10 900 2 starch CaCl2·2H2O 200 - - 700 5 900 3 starch CaCl2·2H2O 200 - - 700 20 900 4 starch CaCl2·2H2O 150 - - 700 10 900 5 starch CaCl2·2H2O 300 - - 700 10 900 6 starch CaCl2·2H2O 200 - - 700 10 - 7 starch CaCl2·2H2O 200 - - 700 10 1200 8 glucose CaCl2·2H2O 110 - - 700 10 900 9 glucose CaCl2·2H2O 150 - - 700 10 900 10 glucose CaCl2·2H2O 200 - - 700 10 900 11 glucose CaCl2·2H2O 300 - - 700 10 900 12 starch Ca(OH)2 75 glycerin 185 700 10 900 13 starch Ca(OH)2 150 glycerin 185 700 10 900 Comparative example 1 starch MgCl2·2H2O 200 - - 700 10 900 2 starch CaCl2 200 - - 700 10 900 3 PVA CaCl2·2H2O 200 - - 700 10 900 4 starch Ca(OH)2 75 - - 700 10 900 5 starch Ca(OH)2 150 - - 700 10 900 6 starch Ca(OH)2 200 - - 700 10 900 7 starch Zinc chloride 200 - - 700 10 900 8 PVA Magnesium citrate 400 - - 700 10 900 9 PVA MgO particles (Average particle size 10nm) 100 - - 700 10 900 10 PVA MgO particles (Average particle size 30nm) 100 - - 700 10 900 11 PVA MgO particles (Average particle size 150nm) 100 - - 700 10 900 12 Kochen Black - - - - - - - 13 carbon black - - - - - - -

[0140] [Table 2] 2~200nm Fine pore volume [cm3 / g] volume density [g / cm3] mode diameter [nm] average once Particle size [μm] Fine pores smaller than 2nm volume [cm3 / g] Comparison Table area [m2 / g] 2-10nm Fine pore volume (DH method) [cm3 / g] Impurities [ppm] particle shape calcium sulfur Silicon Example 1 1.59 0.012 twenty one twenty four 0.12 727 0.28 653 twenty three 116 thin sheet 2 1.83 0.011 51 26 0.13 612 0.11 650 25 117 thin sheet 3 1.28 0.014 14 twenty three 0.10 635 0.29 668 26 120 thin sheet 4 0.99 0.015 14 27 0.10 584 0.22 625 28 111 thin sheet 5 2.20 0.008 147 28 0.14 675 0.19 715 27 121 thin sheet 6 1.58 0.010 twenty one 26 0.11 679 0.27 645 26 116 thin sheet 7 1.62 0.017 twenty one 28 0.13 756 0.28 678 29 125 thin sheet 8 0.81 0.013 9 25 0.10 666 0.50 594 25 115 thin sheet 9 1.67 0.009 14 28 0.09 844 0.48 615 27 117 thin sheet 10 3.18 0.005 18 twenty three 0.06 1006 0.32 658 26 118 thin sheet 11 3.65 0.004 59 26 0.05 1103 0.25 702 28 121 thin sheet 12 1.65 0.068 28 26 0.20 753 0.29 751 28 120 granular 13 1.26 0.074 33 twenty four 0.22 798 0.36 758 27 118 granular Comparative example 1 0.19 0.355 195 26 0.12 348 0.01 328 28 116 granular 2 0.09 0.421 2 25 0.11 273 0.03 689 27 120 granular 3 0.22 0.401 195 26 0.00 75 0.02 712 15 118 granular 4 0.54 0.080 147 28 0.14 364 0.06 685 30 131 granular 5 0.91 0.045 195 27 0.23 756 0.34 629 28 128 granular 6 1.19 0.050 195 28 0.15 587 0.28 682 27 117 granular 7 1.61 0.212 3 28 0.56 1773 0.92 316 33 111 granular 8 1.91 0.170 4 57 0.13 1503 1.41 53 11700 162 granular 9 2.22 0.102 11 5 0.18 1096 0.91 119 15700 307 granular 10 2.56 0.106 28 5 0.05 798 0.48 92 22100 357 granular 11 1.21 0.103 195 4 0.07 334 0.13 225 22000 318 granular 12 3.88 0.055 147 0.034 0.15 1376 0.94 63 159 192 3D tree 13 0.29 0.056 171 0.04 0.01 59 0.00 51 169 169 3D tree

[0141] Measurement of charge / discharge capacity, initial charge / discharge efficiency, and DC resistance of lithium-ion secondary batteries. Using the porous carbon obtained in Examples 1-13 and Comparative Examples 1-13, lithium-ion secondary batteries were fabricated according to the above description. The resulting lithium-ion secondary batteries were placed in a constant temperature bath at 25°C, and charge-discharge tests were conducted using a charge-discharge test apparatus (manufactured by Toyo Systems Co., Ltd., "TOSCAT"), measuring the DC resistance value before initial charging. The DC resistance was measured when 0.7 mA was applied for 3 seconds. The charging capacity was measured relative to the lithium potential up to 4.2V when charging at a constant current of 0.2C. The discharging capacity was measured relative to the lithium potential up to 3V when discharging at a constant current of 0.2C. The initial charge-discharge efficiency (%) was calculated using the formula: (discharge capacity) / (charge capacity) × 100.

[0142] Measurement of the charge capacity retention rate of lithium secondary batteries Using the porous carbon obtained in Examples 1-13 and Comparative Examples 1-13, lithium-ion secondary batteries were fabricated according to the above description. The resulting 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 (manufactured by Toyo Systems Co., Ltd., "TOSCAT"). During charging, the batteries were charged to 4.2V at a constant current of 0.2C relative to the lithium potential; during discharging, the batteries were discharged to 3V at a constant current of 0.2C 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 2C charge capacity to the 0.2C charge capacity at this time was defined as the charge capacity retention rate.

[0143] Measurement of discharge capacity retention of lithium secondary batteries Using the porous carbon obtained in Examples 1-13 and Comparative Examples 1-13, lithium-ion secondary batteries were fabricated according to the above description. The resulting 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 (manufactured by Toyo Systems Co., Ltd., "TOSCAT"). During charging, the batteries were charged to 4.2V at a constant current of 0.2C relative to the lithium potential, and during discharging, they were discharged to 3V at a constant current of 0.2C 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. It is generally known that in cases of poor battery input-output characteristics, there is a tendency for lithium ions to insert and detach from the electrodes 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 excellent battery input-output characteristics.

[0144] Evaluation of the peel strength and defect quantity of the positive electrode in lithium-ion secondary batteries For the positive electrode for lithium-ion secondary batteries made from the porous carbon obtained in Examples 1-13 and Comparative Examples 1-13 using the above method, the strength of peeling the slurry-coated surface from the aluminum foil serving as the current collector was measured. Specifically, the slurry-coated surface of the obtained lithium-ion secondary battery electrode was bonded to a stainless steel plate using double-sided adhesive (NICHIBAN double-sided adhesive), and the 180° peel strength (peel width 10 mm, peel speed 100 mm / min) was measured using a 50 N force sensor (IMADA Co., Ltd.). The number of electrode defects was determined by punching 10 electrodes with a φ14 mm punch for the positive electrode for lithium-ion secondary batteries, and counting the number of electrode pieces from which active material peeled off from the current collector.

[0145] The test results for charge / discharge capacity, initial charge / discharge efficiency, DC resistance, charge capacity retention rate, discharge capacity retention rate, peel strength, and the number of electrode defects are shown in Table 3. [Table 3] Charging capacity [mAh / g] Discharge capacity [mAh / g] First time Charge and discharge efficiency [%] DC resistance [Ω] Charging capacity Maintenance rate (2C / 0.2C) [%] Discharge capacity Maintenance rate (2C / 0.2C) [%] Peel strength [N / m] Electrode defects Number of products generated [indivual] Example 1 165 144 87 205 70 60 81 0 2 165 144 87 269 72 57 81 0 3 165 143 87 188 72 62 82 0 4 166 145 87 227 67 54 86 0 5 165 143 87 258 67 56 82 0 6 165 143 87 216 63 55 85 0 7 165 144 87 254 69 60 85 0 8 165 144 87 212 66 56 84 0 9 166 145 87 215 68 57 82 0 10 165 144 87 203 75 66 80 0 11 165 144 87 208 74 64 80 0 12 166 144 87 173 56 48 84 0 13 165 144 87 160 56 50 88 0 Comparative Example 1 165 144 87 657 twenty five 37 74 1 2 165 143 87 612 10 34 70 1 3 164 143 87 630 6 31 64 2 4 165 144 87 175 45 35 85 0 5 165 144 87 177 50 46 72 1 6 164 143 87 179 55 50 68 2 7 166 144 87 202 25 54 100 0 8 166 142 85 266 36 48 82 0 9 166 143 86 208 50 59 34 6 10 166 144 87 235 48 51 39 5 11 165 144 87 297 47 48 57 3 12 162 140 86 266 63 55 50 4 13 163 143 87 421 16 41 75 1

[0146] The porous carbon in Examples 1-13 exhibits high charge / discharge capacity retention and peel strength, and does not produce electrode defects. Therefore, it can improve the input / output characteristics of non-aqueous electrolyte secondary batteries at room temperature and ensure electrode peel strength, making it a suitable porous carbon for cathode additives. On the other hand, in the porous carbon of Examples 1-13, at least one of the following is insufficient: charge capacity retention, discharge capacity retention, peel strength, and number of electrode defects.

Claims

1. A porous carbon having a pore volume of 2 nm to 200 nm as measured by the BJH method of 0.8 cm3 / g or more, a bulk density of 0.10 g / cm3 or less, a modal diameter of the pores as measured by the BJH method of 150 nm or less, and an average primary particle size of 1 μm to 100 μm or more.

2. The porous carbon as claimed in claim 1, wherein the pore volume of less than 2 nm as measured by DFT is less than 0.35 cm3 / g.

3. Porous carbon as claimed in Item 1, wherein the specific surface area measured by the BET method is more than 500 m2 / g and less than 1200 m2 / g.

4. The porous carbon as requested in item 1, wherein the calcium content is between 20 ppm and 2000 ppm.

5. The porous carbon as claimed in claim 1, wherein the sulfur content is less than 1000 ppm and the silicon content is less than 1000 ppm.

6. The porous carbon as requested in item 1 has a bulk density of less than 0.05 g / cm3.

7. A method for manufacturing porous carbon as claimed in any one of claims 1 to 6, comprising: (1) obtaining a mixture comprising a carbon source and a calcium compound; (2) heat-treating the mixture in an inert gas environment to obtain a carbide; and (3) removing the calcium compound from the carbide; wherein the carbon source is a sugar, and the amount of the calcium compound is 70 to 500 parts by mass relative to 100 parts by mass of the sugar.

8. The method of claim 7, wherein the mixture in step (1) further contains at least one selected from the group consisting of polyols and carboxylic acids.

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

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

11. The method of claim 7, wherein the sugar is selected from at least one of the group consisting of monosaccharides, disaccharides and polysaccharides.

12. The method of claim 7, wherein the removal of calcium compounds in step (3) is performed by acid washing.

13. The method of claim 7, wherein the temperature of the heat treatment step in step (2) is above 400°C and below 1300°C.

14. The method of claim 7, wherein the heating rate of the heat treatment step in step (2) is 2°C or more.

15. A positive electrode composition for a non-aqueous electrolyte secondary battery, comprising porous carbon as claimed in any one of claims 1 to 6.

16. A composition for the positive electrode of a lithium-ion secondary battery, comprising porous carbon as claimed in any one of claims 1 to 6.

17. A non-aqueous electrolyte secondary battery comprising a positive electrode of a composition including the positive electrode of a non-aqueous electrolyte secondary battery as claimed in claim 15.

18. A lithium-ion secondary battery comprising a positive electrode containing a composition of a lithium-ion secondary battery as claimed in claim 16.

Images