Composition for positive electrode, positive electrode for nonaqueous electrolyte secondary battery, and nonaqueous electrolyte secondary battery

Abstract

The present invention is a composition for a positive electrode, containing a positive electrode active material, porous carbon, fibrous carbon, and a binder, wherein the positive electrode active material is an inorganic compound, and the porous carbon has a 2-200 nm pore volume as measured by a BJH method of 0.8 cm3 / g or more, the average fiber diameter of the fibrous carbon is 0.5-200 nm, and the average fiber length thereof is 1-1000 μm.

Description

Positive electrode composition, positive electrode for non-aqueous electrolyte secondary battery, and non-aqueous electrolyte secondary battery

[0001] The present invention relates to a positive electrode composition, a positive electrode for a non-aqueous electrolyte secondary battery, and a non-aqueous electrolyte secondary battery.

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

[0003] Adding activated carbon or the like to the positive electrode has been proposed as a method for improving the output characteristics of lithium-ion secondary batteries. For example, Patent Document 1 discloses adding porous carbon having a specific range of pore volume, bulk density, pore mode diameter, and average primary particle size to the positive electrode. Patent Document 2 discloses a positive electrode mixture containing a positive electrode active material, carbon black, fibrous carbon, and a binder, and shows the results of evaluating the cycle characteristics and rate characteristics at a temperature of 45°C. Furthermore, secondary battery electrodes using ferrocene derivatives or trioxotriangulene derivatives as positive electrode active materials have also been disclosed (Patent Documents 3 and 4).

[0004] International Publication No. 2022 / 255359 Japanese Patent Application Laid-Open No. 2023-8483 Japanese Patent Application Laid-Open No. 2009-238945 Japanese Patent Application Laid-Open No. 2021-192353

[0005] One of the characteristics required for non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries is high cycle performance, but when an organic compound such as a ferrocene derivative or a trioxotriangulene derivative is used as the positive electrode active material, it has been difficult to sufficiently improve the cycle performance because the organic compound is prone to deterioration, etc. The present inventors have focused on the fact that the cycle performance can be improved by using an inorganic compound as the positive electrode active material and conducted various studies, but when an inorganic compound is used as the positive electrode active material, the rate performance, particularly the rate performance at low temperatures, was sometimes insufficient.

[0006] Therefore, an object of the present invention is to provide a positive electrode composition, a positive electrode including the positive electrode composition, and a nonaqueous electrolyte secondary battery including the positive electrode, which use an inorganic compound as a positive electrode active material and provide a nonaqueous electrolyte secondary battery having high cycle characteristics and good rate characteristics, particularly good rate characteristics at low temperatures.

[0007] The present inventors have found that the above object can be achieved by the positive electrode composition of the present invention described below. That is, the present invention encompasses the following preferred embodiments: [1] A positive electrode composition comprising a positive electrode active material, porous carbon, fibrous carbon, and a binder, wherein the positive electrode active material is an inorganic compound, and the porous carbon has a pore volume of 2 nm or more and 200 nm or less measured by the BJH method of 0.8 cm3. ３ / g or more, wherein the fibrous carbon has an average fiber diameter of 0.5 to 200 nm and an average fiber length of 1 to 1000 μm. [2] The positive electrode composition according to [1], wherein the fibrous carbon has a tubular structure. [3] The positive electrode composition according to [1] or [2], wherein the fibrous carbon is at least one type selected from the group consisting of carbon nanotubes and vapor-grown carbon fibers. [4] The positive electrode composition according to any one of [1] to [3], wherein the total content of the porous carbon and the fibrous carbon is 0.2 to 15 mass% relative to the solid content of the positive electrode composition, and the ratio of the content of the porous carbon to the content of the fibrous carbon (porous carbon:fibrous carbon) is 1:9 to 9:1. [5] The positive electrode composition according to any one of [1] to [4], wherein the positive electrode active material contains at least one compound selected from the group consisting of lithium nickel cobalt manganese oxide (NCM), lithium nickel oxide (NCA), lithium cobalt oxide (LCO), lithium manganese oxide (LMO), lithium nickel manganese oxide (LNMO), lithium manganese iron phosphate (LMFP), and lithium iron phosphate (LFP). [6] The positive electrode composition according to any one of [1] to [5], wherein the porous carbon has a pore mode diameter of 150 nm or less as measured by the BJH method. [7] The porous carbon has a median particle diameter D ５０ [8] A positive electrode composition for a non-aqueous electrolyte secondary battery, comprising the positive electrode composition according to any one of [1] to [7]. [9] A non-aqueous electrolyte secondary battery, comprising the positive electrode according to [8].

[0008] According to the present invention, it is possible to provide a positive electrode composition that provides a nonaqueous electrolyte secondary battery having high rate characteristics at room temperature and low temperatures, a positive electrode including the positive electrode composition, and a nonaqueous electrolyte secondary battery including the positive electrode.

[0009] Hereinafter, embodiments of the present invention will be described in detail. Note that the scope of the present invention is not limited to the embodiments described here, and various modifications can be made without departing from the spirit of the present invention.

[0010] <Positive electrode composition> The positive electrode composition of the present invention is a positive electrode composition comprising a positive electrode active material, porous carbon, fibrous carbon, and a binder, wherein the positive electrode active material is an inorganic compound, and the porous carbon has a pore volume of 2 nm or more and 200 nm or less measured by the BJH method of 0.8 cm ３ / g or more, and the average fiber diameter of the fibrous carbon is 0.5 to 200 nm and the average fiber length is 1 to 1000 μm.

[0011] (Porous Carbon) The porous carbon contained in the positive electrode composition of the present invention has a pore volume of 2 nm or more and 200 nm or less measured by the BJH method of 0.8 cm ３ / g or more. The pore volume of pores having a diameter of 2 nm or more and 200 nm or less is 0.8 cm ３ / g or more, the storage of lithium ions in the pores and the mobility of lithium ions near the positive electrode active material are excellent, and lithium ions can be supplied abundantly to the periphery of the positive electrode active material. This can promote smooth insertion and desorption of lithium ions into and from the positive electrode active material, thereby improving input / output characteristics. ３ If the pore volume is less than 1 / g, the mobility of lithium ions tends to decrease, and the pores tend to be blocked by gas generated when the electrolyte solution decomposes in the electrochemical element, further reducing the mobility of the electrolyte. ３ / g, more preferably 0.9 to 4.0 cm ３ / g, more preferably 1.0 to 3.9 cm ３ / g, more preferably 1.3 to 3.9 cm ３ / g, and even more preferably 1.6 to 3.8 cm ３ / g, particularly preferably 1.7 to 3.8, and particularly preferably 1.9 to 3.7 cm ３ / g, very preferably 2.3 to 3.7 cm ３ / g, very particularly preferably 2.6 to 3.5 cm ３ / g. When the pore volume of 2 nm or more and 200 nm or less is equal to or greater than the lower limit, input / output characteristics tend to be further improved. Furthermore, when the pore volume of 2 nm or more and 200 nm or less is large, the electrolyte retention ability and electrolyte mobility also tend to be excellent. The pore volume of 2 nm or more and 200 nm or less can be adjusted within the above range by, for example, appropriately adjusting the type and / or amount of the carbon source and calcium compound; the temperature and / or time of the heat treatment step, etc. in the method for producing porous carbon described below. The pore volume of 2 nm or more and 200 nm or less can be measured by pore distribution analysis using the BJH method in nitrogen adsorption measurement, and can be measured, for example, by the method described in the Examples described below.

[0012] The mode diameter of the pores of the porous carbon contained in the positive electrode composition of the present invention, measured by the BJH method, is preferably 150 nm or less from the viewpoint of improving input-output characteristics. Here, "mode diameter" refers to the pore diameter with the largest occurrence ratio in the logarithmic differential pore volume distribution (dV / d(log D)), obtained by differentiating the cumulative pore volume (V) with the common logarithm of the pore diameter (D). A mode diameter of the porous carbon of 150 nm or less facilitates the storage of lithium ions in the pores and the migration of lithium ions to the vicinity of the positive electrode active material, facilitating a more abundant supply of lithium ions to the periphery of the positive electrode active material. This also prevents the binder from being adsorbed into the pores of the porous carbon during slurry preparation, which is preferable from the viewpoints of improving the peel strength of the electrode and preventing electrode chipping. 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, and particularly preferably 35 nm or less. A mode diameter of less than the upper limit facilitates the improvement of input-output characteristics. The lower limit of the mode diameter is not particularly limited, but from the viewpoint of improving the mobility of lithium ions and suppressing pore blockage due to gas generated when the electrolyte solution decomposes in the electrochemical device, thereby suppressing a decrease in electrolyte mobility, it is preferably 2 nm or more, more preferably 9 nm or more, and even more preferably 15 nm or more. Therefore, the mode diameter is preferably 2 to 150 nm, more preferably 2 to 145 nm, even more preferably 9 to 100 nm, even more preferably 9 to 55 nm, particularly preferably 15 to 50 nm, and especially preferably 15 to 35 nm. The mode diameter can be adjusted within the above range, for example, by appropriately adjusting the type and / or amount of the carbon source and calcium compound in the method for producing porous carbon described below; the temperature and / or time of the heat treatment step; etc. The mode diameter can be measured by pore distribution analysis using the BJH method in nitrogen adsorption measurements, for example, by the method described in the Examples described below.

[0013] The median particle diameter D of the porous carbon contained in the positive electrode composition of the present invention ５０ From the viewpoint of improving input / output characteristics, the median particle diameter D is preferably 0.1 to 100 μm. ５０When the median particle diameter D is 0.1 to 100 μm, the storage and diffusion of lithium ions occur appropriately, and the input / output characteristics are likely to be improved. In addition, it is preferable from the viewpoint of suppressing aggregation of the porous carbon particles, suppressing coating unevenness after electrode coating, and improving the peel strength of the electrode. ５０ is the particle size at which the cumulative volume measured by the laser diffraction / scattering method becomes 50%.

[0014] Median particle diameter D of porous carbon ５０ is preferably 0.1 to 80 μm, more preferably 0.1 to 50 μm, even more preferably 0.1 to 30 μm, still more preferably 0.1 to 20 μm, particularly preferably 0.1 to 10 μm, and particularly preferably 0.1 to 5 μm, from the viewpoint of enhancing the interaction with fibrous carbon having an average fiber diameter and an average fiber length in a specific range described later and improving the rate characteristics at low temperatures.

[0015] The bulk density of the porous carbon is preferably 0.01 to 0.1 g / cm from the viewpoint of enhancing the interaction with fibrous carbon having an average fiber diameter and an average fiber length in a specific range described later and improving the rate characteristics at low temperatures. ３ , more preferably 0.015 to 0.08 g / cm ３ , more preferably 0.015 to 0.06 g / cm ３ , and even more preferably 0.015 to 0.05 g / cm ３ is.

[0016] The content of porous carbon in the positive electrode composition of the present invention is preferably 0.2 to 15 mass%, more preferably 0.3 to 10 mass%, and even more preferably 0.4 to 5 mass%, based on the solid content of the positive electrode composition. When the content of porous carbon is below the above-mentioned upper limit, the electrode density of the resulting positive electrode can be maintained high, which is preferable from the viewpoint of improving the charge / discharge capacity per volume of the nonaqueous electrolyte secondary battery. It is assumed that the electrolyte solution is retained in the porous carbon. When the content of porous carbon is above the above-mentioned lower limit, the amount of porous carbon present near the active material increases, thereby increasing the amount of electrolyte solution present near the active material. This enables the transfer of a large amount of Li ions even when the viscosity of the electrolyte solution increases at low temperatures, which is considered preferable from the viewpoint of rate characteristics, particularly at low temperatures. Furthermore, a relative mass reduction of the positive electrode active material can be prevented, thereby preventing a decrease in capacity.

[0017] The content of the porous carbon in the positive electrode composition of the present invention is preferably 0.2 to 16 mass %, more preferably 0.3 to 11 mass %, and even more preferably 0.4 to 6 mass %, relative to the content of the positive electrode active material, from the viewpoint of improving the input / output characteristics and rate characteristics of the battery.

[0018] (Fiberous Carbon) The positive electrode composition of the present invention contains fibrous carbon having an average fiber diameter of 0.5 to 200 nm and an average fiber length of 1 to 1,000 μm. It has been found that when fibrous carbon having the above characteristics and porous carbon having the above characteristics are present as a conductive additive in a positive electrode using an inorganic compound as a positive electrode active material, excellent rate characteristics, particularly excellent rate characteristics at low temperatures, are achieved in a nonaqueous electrolyte secondary battery using a positive electrode containing the positive electrode composition. The reason for this is unclear, but it is thought that the presence of porous carbon retaining an electrolyte solution in its pores between the positive electrode active materials improves lithium ion diffusibility, and that the conductive fibrous carbon connects the pores of the porous carbon and / or the positive electrode active material, forming a long-distance conductive path, leading to high rate characteristics, particularly at low temperatures.

[0019] The average fiber diameter of the fibrous carbon is 0.5 to 200 nm. If the average fiber diameter is less than 0.5 nm, production is difficult, and if the average fiber diameter is more than 200 nm, dispersibility in the electrode decreases, hindering high-density electrode formation. From the viewpoint of improving rate characteristics, the average fiber diameter is preferably 1 to 100 nm, more preferably 3 to 50 nm, and even more preferably 5 to 20 nm. The average fiber diameter of the fibrous carbon can be measured by obtaining an image of the fiber cross section using an electron microscope and then analyzing the image.

[0020] The average fiber length of the fibrous carbon is 1 to 1000 μm. If the average fiber length is less than 1 μm, a conductive path is not formed, making it difficult to impart conductivity to the electrode. If the average fiber diameter exceeds 1000 μm, aggregates are likely to be formed, reducing the dispersibility of the fibrous carbon in the electrode. From the viewpoint of improving rate characteristics and dispersibility of the fibrous carbon, the average fiber length is preferably 1 to 200 μm, more preferably 1 to 100 μm, and even more preferably 1 to 50 μm. The average fiber length of the fibrous carbon can be measured by obtaining an image of the fiber using an electron microscope and then analyzing the image.

[0021] The fibrous carbon is not particularly limited as long as it is fibrous carbon having the above-mentioned average fiber length and average fiber diameter, and examples thereof include carbon nanotubes, vapor-grown carbon fibers, etc. The fibrous carbon may contain one type of fibrous carbon or two or more types of fibrous carbon.

[0022] In a preferred embodiment of the present invention, from the viewpoint of improving conductivity through long-distance paths within the electrode, the fibrous carbon is preferably at least one selected from the group consisting of carbon nanotubes and vapor-grown carbon fibers. Carbon nanotubes are fibrous carbons having a tubular structure composed of carbon, and may be single-walled carbon nanotubes (SWCNTs) consisting of a single tubular layer, or multi-walled carbon nanotubes (MWCNTs) consisting of multiple overlapping tubular layers. Vapor-grown carbon fibers are fibrous carbons produced from the gas phase, and examples include carbon nanofibers (CNFs) and carbon nanotubes (CNTs) produced from the gas phase. From the viewpoint of improving low-temperature rate characteristics, single-walled carbon nanotubes are more preferred as the fibrous carbon. However, from the viewpoint of achieving both improved low-temperature rate characteristics and improved dispersibility, multi-walled carbon nanotubes are preferred. The fibrous carbon preferably has a tubular structure from the viewpoint of improving electrical conductivity and ion diffusibility, and improving rate characteristics at low temperatures.

[0023] From the viewpoint of improving rate characteristics, particularly at low temperatures, the total content of the porous carbon and the fibrous carbon contained in the positive electrode composition of the present invention is preferably 0.2 to 15 mass %, more preferably 0.3 to 10 mass %, and even more preferably 0.4 to 5 mass %, relative to the solid content of the positive electrode composition. Furthermore, the mass ratio of the content of the porous carbon to the content of the fibrous carbon (porous carbon:fibrous carbon) is preferably 1:9 to 9:1, more preferably 2:8 to 8:2, and even more preferably 3:7 to 7:3.

[0024] The total content of the porous carbon and the fibrous carbon relative to the total amount of the electrode active material contained in the positive electrode composition of the present invention is preferably 0.2 to 16 mass%, more preferably 0.3 to 11 mass%, and even more preferably 0.4 to 6 mass%.

[0025] The total content of the porous carbon and the fibrous carbon relative to the total amount of conductive additives contained in the positive electrode composition of the present invention is preferably 10 to 100% by mass, more preferably 20 to 100% by mass, and even more preferably 30 to 100% by mass. The positive electrode composition may contain a conductive additive other than the porous carbon and the fibrous carbon. However, from the viewpoint of not interfering with the effects of the high ion diffusivity and conductive path formation provided by the porous carbon and the fibrous carbon and the improvement in rate characteristics at low temperatures, the content of the conductive additive other than the porous carbon and the fibrous carbon may be low. Preferred conductive additives other than the porous carbon and the fibrous carbon include amorphous carbon (e.g., acetylene black, carbon black, and other porous carbons not falling under the category of porous carbon), graphene, and graphite. The total content of the porous carbon and the fibrous carbon relative to the total amount of conductive additives contained in the positive electrode composition of the present invention may be, for example, 50 to 100% by mass, 70 to 100% by mass, 90 to 100% by mass, or 95 to 100% by mass.

[0026] (Positive Electrode Active Material) The positive electrode composition of the present invention contains an inorganic compound as a positive electrode active material. It has been found that when an inorganic compound is used as a positive electrode active material, cycle characteristics can be improved compared to when an organic compound is used. Examples of the inorganic positive electrode active material include lithium-containing cobalt oxide (LiCoO ２ ), lithium manganese oxide (LiMn ２ O ４ ), lithium-containing nickel oxide (LiNiO ２ ), Co—Ni—Mn lithium-containing composite oxide, Ni—Mn—Al lithium-containing composite oxide, Ni—Co—Al lithium-containing composite oxide, olivine-type lithium iron phosphate (LiFePO ４ ), olivine-type lithium manganese phosphate (LiMnPO ４ ), Li １＋ｘ Mn ２－ｘ O ４ (0<X<2) Lithium-excess spinel compound represented by Li[Ni ０．１７ Li ０．２ Co ０．０７ Mn ０．５６ ]O ２ , LiNi０．５ Mn １．５ O ４ and sulfur.

[0027] As the positive electrode active material, a composite oxide containing lithium and at least one selected from the group consisting of nickel, cobalt, and manganese, which are transition metals, is preferred. The positive electrode active material more preferably contains at least one compound selected from the group consisting of lithium nickel cobalt manganese oxide (NCM), lithium nickel oxide (NCA), lithium cobalt oxide (LCO), lithium manganese oxide (LMO), lithium nickel manganese oxide (LNMO), lithium manganese iron phosphate (LMFP), and lithium iron phosphate (LFP).

[0028] The content of the positive electrode active material contained in the positive electrode composition of the present invention is preferably 80 to 99 mass %, more preferably 85 to 98 mass %, and even more preferably 90 to 97 mass %, relative to the solid content of the positive electrode composition, from the viewpoint of improving rate characteristics particularly at low temperatures.

[0029] The particle size of the positive electrode active material is not particularly limited and can be the same as that of conventionally used positive electrode active materials. Typically, a positive electrode active material having a particle size in the range of 0.1 to 40 μm, more preferably 0.5 to 20 μm, can be used.

[0030] (Binder) The positive electrode composition of the present invention contains a binder. The binder is a component that effectively adheres the positive electrode active material particles, porous carbon, and fibrous carbon to one another and to the current collector. Examples of binders that may be used include, but are not limited to, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, and nylon. These may be used alone or in combination of two or more.

[0031] In the positive electrode composition of the present invention, the content of the binder is preferably 0.5 to 10 mass %, more preferably 1 to 7 mass %, based on the solid content of the positive electrode composition.

[0032] (Other Components) The positive electrode composition of the present invention may contain other components in addition to the above-described components, such as a solvent, another conductive additive, a positive electrode active material that is an inorganic compound other than the composite oxide, and another binder.

[0033] [Solvent] The positive electrode composition of the present invention may contain a solvent. For example, an organic solvent can be used as the solvent, and among these, a polar organic solvent capable of dissolving the binder described below is preferred. Specifically, the organic solvent may be acetonitrile, N-methylpyrrolidone (NMP), acetylpyridine, cyclopentanone, N,N-dimethylacetamide, dimethylformamide, dimethyl sulfoxide, methylformamide, methyl ethyl ketone, furfural, ethylenediamine, or the like. Among these, N-methylpyrrolidone is preferred from the viewpoints of ease of handling, safety, ease of synthesis, and the like. These organic solvents may be used alone or in combination of two or more.

[0034] The solvent can be used in an amount such that the solids concentration in the positive electrode composition is preferably 1 to 80 mass %, more preferably 5 to 70 mass %, and even more preferably 10 to 60 mass %. By setting the solids concentration within the above range, the positive electrode active material, porous carbon, fibrous carbon, binder, and other components contained therein can be uniformly dispersed, which is preferable.

[0035] [Other conductive aids] Examples of other conductive aids that may be used include carbon-based substances such as natural graphite, artificial graphite, amorphous carbon (e.g., carbon black, acetylene black, ketjen black, and other porous carbons not falling under the category of the porous carbons described above), and carbon fibers different from the above-mentioned fibrous carbon; metal-based substances such as metal powders and metal fibers of copper, nickel, aluminum, silver, and the like; and conductive polymers such as polyphenylene derivatives.

[0036] <Method for Producing Porous Carbon> The porous carbon contained in the positive electrode composition of the present invention can be produced by a method including, for example, (1) a step of obtaining a mixture containing a carbon source and a calcium compound, (2) a step of heat-treating the mixture in an inert gas atmosphere to obtain a carbide, and (3) a step of removing the calcium compound from the carbide.

[0037] The carbon source is not particularly limited, but sugars are preferred to enhance uniform dispersion with the calcium compound. Examples of sugars include monosaccharides such as glucose, galactose, mannose, fructose, ribose, and glucosamine; disaccharides such as sucrose, trehalose, maltose, cellobiose, maltitol, lactobionic acid, and lactosamine; and polysaccharides such as starch, glycogen, and pectin. These sugars can be used alone or in combination of two or more. Among these sugars, glucose and starch are preferred because they are easy to produce porous carbon that improves the input / output characteristics of non-aqueous electrolyte secondary batteries at room temperature and are readily available in large quantities.

[0038] The starch is not particularly limited, and starches derived from, for example, corn, cassava, potato, sweet potato, tapioca, beans, wheat, rice, etc. can be used. The amylose content of the starch preferred in the present invention is preferably 50% by mass or less, more preferably 30% by mass or less. Since the lower the amylose content of starch, the lower the gelatinization temperature tends to be. Therefore, starch having an amylose content below the upper limit is preferred because it is more likely to gelatinize at low temperatures and has increased compatibility with calcium compounds. The amylose content can be determined, for example, by iodine colorimetry. The starch may also be modified. Examples of modified starches include etherified starch, esterified starch, cationized starch, and cross-linked starch. One type of starch may be used alone, or two or more types may be used in combination.

[0039] The calcium compound is not particularly limited, and examples thereof include calcium chloride, calcium hydroxide, calcium oxide, calcium carbonate, calcium acetate, calcium fluoride, calcium bromide, calcium iodide, calcium carbide, calcium bicarbonate, calcium nitrate, calcium sulfate, calcium silicate, calcium phosphate, calcium pyrophosphate, calcium gluconate, and calcium lactate. Among these calcium compounds, calcium compounds with a melting point of 300°C or less (when the mixture contains a polyhydric alcohol or carboxylic acid, as described below, the melting point of the eutectic compound between the calcium compound and the polyhydric alcohol or carboxylic acid is 300°C or less) are preferred because they facilitate the production of porous carbon that improves the input / output characteristics of nonaqueous electrolyte secondary batteries at room temperature. More preferred are calcium compounds selected from the group consisting of calcium chloride hydrate, calcium hydroxide, calcium oxide, calcium carbonate, and calcium acetate. Calcium chloride hydrate exists as a dihydrate, tetrahydrate, and hexahydrate, but the dihydrate is preferred due to its favorable reactivity with sugars.

[0040] The mixture containing a carbon source and a calcium compound may further contain at least one selected from the group consisting of a polyhydric alcohol and a carboxylic acid. When the mixture contains a polyhydric alcohol and / or a carboxylic acid, the calcium compound dissolves in the polyhydric alcohol and / or the carboxylic acid, forming a eutectic compound. The eutectic compound is believed to be formed by coordination of calcium with hydroxyl groups, carboxylate groups, and carboxyl groups in the polyhydric alcohol and / or the carboxylic acid. Therefore, a calcium compound having a melting point of 300°C or higher alone can have a melting point of 300°C or lower as a eutectic compound. Therefore, in the present invention, "a calcium compound having a melting point of 300°C or lower" also encompasses "a eutectic compound of a polyhydric alcohol and / or a carboxylic acid with a calcium compound having a melting point of 300°C or lower." Examples of polyhydric alcohols that can be used in the present invention include glycerin, ethylene glycol, propylene glycol, polyethylene glycol, and polypropylene glycol. Among these, glycerin and ethylene glycol are preferred because they readily form a eutectic with the calcium compound and are readily available in large quantities. Examples of carboxylic acids include formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, lactic acid, malic acid, citric acid, benzoic acid, phthalic acid, salicylic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, fumaric acid, and maleic acid, and among these, formic acid and acetic acid are preferred from the viewpoints of their ease of dissolving calcium compounds and their ease of mass procurement. When one or more polyhydric alcohols and one or more carboxylic acids are used in combination, the mixing ratio of the polyhydric alcohol and the carboxylic acid can be appropriately changed depending on the desired properties of the porous carbon.

[0041] The method for mixing the carbon source, the calcium compound, and optionally the polyhydric alcohol and / or the carboxylic acid is not particularly limited, and they can be mixed by any mixing method.

[0042] The amount of calcium compound mixed with the carbon source is preferably 70 parts by mass or more, more preferably 80 parts by mass or more, even more preferably 130 parts by mass or more, and still more preferably 180 parts by mass or more, per 100 parts by mass of saccharides, and is preferably 500 parts by mass or less, more preferably 400 parts by mass or less, and even more preferably 300 parts by mass or less. When the amount of calcium compound is within the above range, the pore volume and pore diameter of the obtained porous carbon tend to be appropriate.

[0043] When the mixture containing a carbon source and a calcium compound further contains a polyhydric alcohol and / or a carboxylic acid, the amount of the polyhydric alcohol and / or the carboxylic acid is preferably 50 parts by mass or more, more preferably 100 parts by mass or more, even more preferably 150 parts by mass or more, and preferably 500 parts by mass or less, more preferably 400 parts by mass or less, even more preferably 300 parts by mass or less, per 100 parts by mass of the saccharides (when one or more polyhydric alcohols and one or more carboxylic acids are used in combination, this refers to the total amount). When the amount of the polyhydric alcohol and / or the carboxylic acid is within the above range, it is easy to form a eutectic compound with the calcium compound, and the covalent compound is easily compatible with the saccharides, so that the pore volume and pore diameter of the resulting porous carbon tend to be appropriate.

[0044] In the above-described manufacturing method, a carbide is obtained by heat-treating a mixture containing a carbon source and a calcium compound in an inert gas atmosphere. Examples of inert gases include nitrogen and argon. The lower the concentration of oxidizing gas in the gas used, the better. The amount of oxidizing gas, particularly oxygen, mixed in is typically 1% by volume or less, more preferably 0.1% by volume or less. When the oxygen concentration is below the above-described upper limit, oxidation of the carbide is easily suppressed, making it easier to obtain a structure with the desired characteristics. Oxidative decomposition of the resulting structure can also be suppressed. The heat treatment temperature is preferably 400°C or higher, more preferably 500°C or higher, even more preferably 700°C or higher, and even more preferably 800°C or higher, and preferably 1300°C or lower, more preferably 1200°C or lower, and even more preferably 1000°C or lower. When the heat treatment temperature is within the above-described range, the resulting porous carbon tends to have an appropriate pore volume of 2 nm to 200 nm, and also tends to facilitate the subsequent removal of calcium compounds from the carbide in the subsequent step of removing calcium compounds. The heat treatment may be carried out in multiple stages, for example, by evaporating the water in the mixture at 50 to 300° C., followed by heat treatment (carbonization) at 400 to 900° C., and then heat treatment (firing) at 900 to 1300° C. By carrying out the heat treatment in multiple stages, a carbide having more uniform physical properties can be obtained.

[0045] The heat treatment time is not particularly limited, but is, for example, 0.5 hours or more, more preferably 1 hour or more, even more preferably 3 hours or more, and preferably 24 hours or less, more preferably 12 hours or less, and even more preferably 8 hours or less. A heat treatment time within the above range is preferable because carbonization proceeds sufficiently and ignition is less likely to occur. Also, from the viewpoint of economy, it is preferable because the time is appropriate.

[0046] In the above manufacturing method, the temperature rise rate during the heat treatment step is preferably 2°C / min or more, more preferably 10°C / min or more, and even more preferably 20°C / min or more. When the temperature rise rate is equal to or higher than the lower limit, the pore size tends to be appropriate. The upper limit of the temperature rise rate is not particularly limited, but is preferably 200°C / min or less from the viewpoint of realizing uniform heat treatment.

[0047] The furnace used for heat treatment can be of various types, such as a rotary kiln, fluidized bed furnace, fixed bed furnace, moving bed furnace, or moving bed furnace. Both continuous furnaces, which continuously charge raw materials and remove products, and batch furnaces, which do so intermittently, can be used. Any heating means can be used as long as it is capable of heating to a predetermined temperature, and examples of applicable heating means include electric heating, gas combustion heating, high-frequency induction heating, and electric current heating. These heating means can be used alone or in combination.

[0048] By removing the calcium compound from the resulting carbide, porous carbon suitable for producing the positive electrode composition of the present invention can be obtained. The removal of the calcium compound is preferably carried out, for example, by acid washing. Examples of acids used for acid washing include hydrochloric acid, sulfuric acid, and nitric acid. However, hydrochloric acid is preferred because it easily dissolves metal compounds in the carbide, is less likely to leave impurities such as sulfur, and is more likely to inhibit oxidation of the carbide. The acid concentration used during acid washing may be varied depending on the type of acid used. For example, when using hydrochloric acid, the concentration is preferably in the range of 0.01 to 1.0 mol / L, more preferably 0.05 to 0.5 mol / L. A hydrochloric acid concentration within the above range is preferred because it facilitates removal of metal compounds and is less likely to leave hydrochloric acid remaining in the carbide.

[0049] The pH of the acid used during acid washing may be appropriately changed depending on the type, concentration, temperature, etc. of the acid used, but is preferably not more than 3, more preferably not more than 2.5. When the pH of the acid is not more than the above upper limit, metal compounds can be easily removed efficiently.

[0050] The acid washing may be carried out, for example, by immersing the obtained carbide in the acid. When the acid washing is carried out by immersion in acid, the mass ratio of the acid to the carbide may be appropriately adjusted depending on the type, concentration, temperature, etc. of the acid used. The mass of the carbide to be immersed relative to the mass of the acid is preferably 2 mass% or more, more preferably 5 mass% or more. The upper limit of the mass ratio is preferably 50 mass% or less, more preferably 30 mass% or less. When the mass ratio of the carbide to be immersed relative to the mass of the acid is within the above range, a sufficient washing effect is likely to be obtained.

[0051] The method for acid-washing the carbide is not particularly limited as long as it allows the carbide to be immersed in acid, and may include a method in which acid is continuously added, retained for a predetermined time, and immersion is continued while the acid is removed, or a method in which the carbide is immersed in acid, retained for a predetermined time, drained, and then new acid is added, and the immersion-drainage process is repeated. Furthermore, the acid may be entirely renewed, or part of the acid may be renewed. Furthermore, the acid may be stirred during immersion.

[0052] The atmosphere in which the acid washing is carried out is not particularly limited and may be appropriately selected depending on the method used for washing. In the present invention, the acid washing is usually carried out in an air atmosphere.

[0053] The time for immersing the carbide in acid can be adjusted as appropriate depending on the acid used, the treatment temperature, etc., but from the viewpoint of sufficient removal of metal compounds, it is preferably 5 minutes or more, and from the viewpoint of productivity, it is preferably 60 minutes or less, more preferably 40 minutes or less, and even more preferably 35 minutes or less.

[0054] After the carbonized material is acid-washed, it is preferable to remove the acid in the porous carbon by washing with water. This acid washing and water washing may be repeated until the calcium compounds in the porous carbon are completely removed. Furthermore, the temperature of the solution used in acid washing and water washing is preferably high from the viewpoint of the efficiency of removing calcium compounds and residual acid, and is usually 60°C or higher.

[0055] In one embodiment of the present invention, a mixture containing a carbon source and a calcium compound may be heat-treated (carbonized) at 500 to 900° C., followed by acid washing, and the acid-washed porous carbon may be heat-treated (calcined) at 900 to 1300° C. By carrying out carbonization at 900° C. or less, it becomes easy to remove metal compounds derived from the calcium compound in the acid washing step, and by calcining at a higher temperature of 900 to 1300° C., it becomes easy to obtain the desired pore volume and specific surface area.

[0056] After acid washing and water rinsing, the porous carbon may be dried using a known dryer such as a hot air dryer or a reduced pressure dryer. Drying is preferably carried out at a temperature of 50 to 150° C. A drying temperature within the above range is preferred because oxidation of the porous carbon is unlikely to occur and drying proceeds appropriately.

[0057] From the viewpoint of adjusting the average primary particle size of the porous carbon to within a desired range, the above-mentioned production method preferably further includes a step of pulverizing the dried porous carbon. The pulverization step is a step for controlling the shape, particle size, etc. of the finally obtained porous carbon to a desired shape, particle size, etc. The pulverization method is not particularly limited, and for example, known pulverizers such as a ball mill, centrifugal roll mill, ring roll mill, centrifugal ball mill, jet mill, cone crusher, double roll crusher, disc crusher, rotary crusher, etc. can be used alone or in combination.

[0058] In order to adjust the average primary particle size of the porous carbon to within the desired range, the above-described manufacturing method may further include a classification step after the pulverization step. For example, by removing particles that are significantly smaller or larger than the desired particle size, porous carbon having a narrow particle size distribution can be obtained. The classification method is not particularly limited, but examples include sieve classification, wet classification, and dry classification. Examples of wet classifiers include classifiers that utilize the principles of gravity classification, inertial classification, hydraulic classification, and centrifugal classification. Examples of dry classifiers include classifiers that utilize the principles of sedimentation classification, mechanical classification, and centrifugal classification. From an economical standpoint, it is preferable to use a dry classification device. Furthermore, to prevent surface oxidation during pulverization, it is preferable to perform the pulverization and classification steps in an inert gas atmosphere.

[0059] Pulverization and classification can also be performed using a single device. For example, pulverization and classification can be performed using a jet mill equipped with a dry classification function. Furthermore, devices having a pulverizer and a classifier independent from each other can also be used. In this case, pulverization and classification can be performed continuously, or pulverization and classification can be performed discontinuously.

[0060] <Method for Producing Positive Electrode Composition> The positive electrode composition of the present invention can be produced by mixing the above-described positive electrode active material, porous carbon, fibrous carbon, and binder with a solvent and other components as needed. There are no particular limitations on the mixing method, and a general mixing device such as a disperser, mill, or kneader can be used. It is preferable to use such a mixing device and stir for, for example, 20 minutes to 120 minutes.

[0061] The mixing temperature is not particularly limited, and mixing can be performed, for example, in the range of 0 to 160°C, preferably in the range of 20 to 80°C. If the mixing temperature is within the above range, the composition is likely to have a viscosity suitable for coating, and evaporation of the organic solvent is unlikely to occur, which is preferable. The mixing atmosphere is also not particularly limited, and mixing is usually performed in the air.

[0062] <Positive electrode for non-aqueous electrolyte secondary battery and non-aqueous electrolyte secondary battery> The present invention also provides a positive electrode for non-aqueous electrolyte secondary battery containing the above-mentioned positive electrode composition, and a non-aqueous electrolyte secondary battery containing the positive electrode. Note that when the positive electrode composition of the present invention contains, for example, a solvent such as those described above, the solvent is removed during the production of the positive electrode, so the positive electrode for non-aqueous electrolyte secondary battery containing the positive electrode composition of the present invention is a positive electrode for non-aqueous electrolyte secondary battery containing the solid content of the positive electrode composition of the present invention.

[0063] Examples of the non-aqueous electrolyte secondary battery include a lithium ion secondary battery, a sodium ion secondary battery, and a lithium sulfur battery.

[0064] The positive electrode composition of the present invention can be usefully used in the positive electrode of a nonaqueous electrolyte secondary battery. By including the above-described positive electrode, the nonaqueous electrolyte secondary battery of the present invention improves the diffusibility of electrolyte ions in the positive electrode, and a conductive path is formed by the fibrous carbon, thereby improving the input / output characteristics of the battery, particularly the rate characteristics at low temperatures. The nonaqueous electrolyte secondary battery of the present invention preferably operates at 2 V to 5 V, and examples thereof include lithium ion secondary batteries and capacitors.

[0065] When the non-aqueous electrolyte secondary battery of the present invention is, for example, a lithium ion secondary battery, the lithium ion secondary battery comprises a positive electrode, a negative electrode, and an electrolyte.

[0066] [Positive Electrode] The positive electrode is produced using the positive electrode composition of the present invention and includes a current collector and a positive electrode active material layer. The positive electrode active material layer is formed by applying the positive electrode composition of the present invention to the current collector.

[0067] The method for applying the nonaqueous electrolyte secondary battery positive electrode composition to the current collector is not particularly limited, and known methods can be used. Specifically, for example, a doctor blade method, a dipping method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, a brush coating method, etc. can be used. In this case, the positive electrode composition may be applied to only one side of the current collector, or may be applied to both sides. The thickness of the composition film on the current collector after application and before drying may be appropriately set depending on the thickness of the positive electrode active material layer obtained by drying.

[0068] As the current collector to which the composition for a positive electrode of a nonaqueous electrolyte secondary battery is applied, it is preferable to use a material that is electrically conductive and electrochemically durable. Specifically, a current collector made of aluminum or an aluminum alloy can be used. In this case, aluminum and an aluminum alloy may be used in combination, or different types of aluminum alloys may be used in combination. Aluminum and aluminum alloys are excellent current collector materials because they are heat resistant and electrochemically stable.

[0069] The method for drying the positive electrode composition on the current collector is not particularly limited and can be a known method, for example, drying with warm air, hot air, or low-humidity air, vacuum drying, or drying by irradiation with infrared rays or electron beams, etc. By drying the positive electrode composition for nonaqueous electrolyte secondary batteries on the current collector in this manner, a positive electrode active material layer can be formed on the current collector, and a positive electrode including the current collector and the positive electrode active material layer can be obtained.

[0070] After the drying step, the positive electrode active material layer may be subjected to pressure treatment using a mold press, a roll press, etc. Pressure treatment can improve the adhesion between the positive electrode active material layer and the current collector.

[0071] [Negative Electrode] The negative electrode includes a current collector and a negative electrode active material layer formed on the current collector, the negative electrode active material layer including a negative electrode active material. The process for producing the negative electrode is a process widely known in the art.

[0072] The negative electrode active material includes a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, a lithium metal alloy, a material capable of being doped with and dedoped from lithium, or a transition metal oxide.

[0073] The material capable of reversibly intercalating / deintercalating lithium ions includes crystalline carbon and amorphous carbon, which can be used alone or in combination of two or more. Examples of the crystalline carbon include amorphous, plate-like, flake-like, spherical, or fibrous natural graphite, or graphite such as artificial graphite. Examples of the amorphous carbon include soft carbon, hard carbon, mesophase pitch carbide, and calcined coke.

[0074] The lithium metal alloy includes an alloy of lithium and a metal selected from the group consisting of Na, K, Mg, Ca, Sr, Si, Sb, In, Zn, Ge, Al, and Sn.

[0075] The materials capable of doping and dedoping lithium include Si, alloys such as SiMg, SiO ｘ (0<x<2), Sn, SnO ２ Examples include:

[0076] The content of the negative electrode active material in the negative electrode active material layer is preferably 70 to 100% by mass relative to the total mass of the negative electrode active material layer, and the negative electrode active material layer may consist of only the negative electrode active material.

[0077] The negative electrode active material layer may contain a binder and may optionally further contain a conductive material. The content of the binder in the negative electrode active material layer is preferably 1 to 5 mass% based on the total mass of the negative electrode active material layer. When a conductive material is further contained, the negative electrode active material may be used in an amount of 80 to 98 mass%, the binder in an amount of 1 to 10 mass%, and the conductive material in an amount of 1 to 10 mass%.

[0078] The binder serves to effectively adhere the negative electrode active material particles to each other and to the current collector. The binder may be a water-insoluble binder, a water-soluble binder, or a combination thereof.

[0079] Examples of the non-water-soluble binder include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, and combinations thereof.

[0080] Examples of the water-soluble binder include styrene-butadiene rubber, acrylated styrene-butadiene rubber, polyvinyl alcohol, sodium polyacrylate, a copolymer of propylene and an olefin having 2 to 8 carbon atoms, a copolymer of (meth)acrylic acid and a (meth)acrylic acid alkyl ester, and combinations thereof.

[0081] When a water-soluble binder is used as the negative electrode binder, a cellulose-based compound capable of imparting viscosity to the negative electrode active material layer may be further used as a thickener. Examples of the cellulose-based compound include carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, and alkali metal salts thereof. Such a thickener may be added in an amount of 0.1 to 100 parts by weight per 100 parts by weight of the binder.

[0082] The conductive material is used to impart conductivity to the electrode, and any electron-conductive material that does not undergo chemical changes in the battery that is constructed can be used. Specific examples of the conductive material include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, and carbon fiber; metal-based materials such as metal powders or metal fibers of copper, nickel, aluminum, and silver; and conductive polymers such as polyphenylene derivatives. These conductive materials may be used alone or in combination of two or more.

[0083] The current collector may be selected from the group consisting of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof.

[0084] The electrolyte preferably contains a non-aqueous organic solvent and a lithium salt.

[0085] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can migrate.

[0086] The non-aqueous organic solvent may be a carbonate, ester, ether, ketone, alcohol, or aprotic solvent. Examples of the carbonate solvent include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC). Examples of the ester solvent include n-methyl acetate, n-ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, decanolide, valerolactone, mevalonolactone, and caprolactone. Examples of the ether that can be used include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, and tetrahydrofuran. Examples of the ketone solvent that can be used include cyclohexanone. Examples of the alcohol solvent that can be used include ethyl alcohol and isopropyl alcohol. Examples of the aprotic solvent that can be used include nitriles such as R—CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, which may contain a double bond, an aromatic ring, or an ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, and sulfolanes.

[0087] The non-aqueous organic solvents may be used alone or in combination of two or more kinds. When two or more kinds are used in combination, the mixing ratio may be appropriately adjusted depending on the desired battery performance.

[0088] In addition, in the case of the carbonate-based solvent, it is preferable to use a mixture of a cyclic carbonate and a chain carbonate in a volume ratio of 1:1 to 1:9, which tends to further improve the performance of the electrolyte solution.

[0089] The lithium salt is dissolved in an organic solvent and acts as a lithium ion supply source in the battery, enabling basic operation of the lithium ion secondary battery and promoting the movement of lithium ions between the positive electrode and the negative electrode. A representative example of such a lithium salt is LiPF. ６ , LiBF ４ , LiSbF ６ , LiAsF ６ , LiCF ３ SO ３ , LiN(SO ２ C ２ F ５ ) ２ , Li(CF ３ SO ２ ) ２ N, LiC ４ F ９ SO ３ , LiClO ４ , LiAlO ４ , LiAlCl ４ , LiN(C ｘ F ２ｘ＋１ SO ２ ) (C ｙ F ２ｙ＋１ SO ２ ) (where x and y are natural numbers), LiCl, LiI and LiB(C ２ O ４ ) ２ (lithium bis(oxalato)borate (LiBOB)). These may be used alone or in combination of two or more. The concentration of the lithium salt is preferably within the range of 0.1 to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte has good conductivity, making it easy to maintain the electrolyte performance, and the viscosity is appropriate, making it easy to improve the mobility of lithium ions.

[0090] The electrolyte may further contain a vinylene carbonate or ethylene carbonate compound as a life-promoting agent to improve the battery life.

[0091] Representative examples of the ethylene carbonate-based compound include difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, fluoroethylene carbonate, etc. When such a life extender is further used, the amount used can be appropriately adjusted depending on the type of compound used.

[0092] In the lithium ion secondary battery of the present invention, a separator may be present between the positive electrode and the negative electrode. Such a separator may be made of polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof, or may be a mixed multilayer film such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator.

[0093] A lithium ion secondary battery is generally formed by arranging the above-mentioned positive electrode and negative electrode (with a separator interposed therebetween as necessary) so that they face each other and immersing them in an electrolyte solution.

[0094] The present invention will be described in more detail below with reference to examples, but these examples are not intended to limit the scope of the present invention. Measurement methods for physical properties are described below, but the physical properties described in this specification, including the examples, are based on values ​​determined by the following methods.

[0095] <Pore volume and mode diameter of 2 nm to 200 nm by nitrogen adsorption method> Using a gas adsorption measurement device (Microtrac-Bell, "BELSORP-max II"), porous carbon was used as a measurement sample, and a nitrogen adsorption isotherm showing the relationship between the relative pressure of nitrogen gas and the amount of adsorbed nitrogen gas at 77 K was obtained. The nitrogen adsorption isotherm obtained as described above was analyzed by the BJH method, and the volume of pores having a pore diameter of 2 nm to 200 nm was calculated. In addition, the nitrogen adsorption isotherm obtained as described above was analyzed by the BJH method, and the logarithmic differential pore volume distribution (dV / d(log D)) was obtained by differentiating the cumulative pore volume (V) with the common logarithm of the pore diameter (D), and the pore diameter with the largest occurrence ratio was adopted as the mode diameter of the measurement sample.

[0096] <Median particle diameter D ５０ The sample was placed in an aqueous solution containing 5% by mass of a surfactant ("Toriton X100" sold by Wako Pure Chemical Industries, Ltd.), and treated in an ultrasonic cleaner for 10 minutes or more to disperse the sample in the aqueous solution. Using this dispersion, the particle size distribution was measured using a particle size / particle size distribution measuring device ("Microtrac MT3300EXII" manufactured by Microtrac Bell Co., Ltd.). The particle size at which the cumulative volume reached 50% was determined as the median particle size D of the porous carbon sample. ５０ (average primary particle size).

[0097] <Preparation of Porous Carbon A> 1 g of glucose (available from Fujifilm Wako Pure Chemical Industries, Ltd.), 2 g of calcium chloride dihydrate (200 parts by weight per 100 parts by weight of glucose), and 1 g of ion-exchanged water (100 parts by weight per 100 parts by weight of glucose) were mixed. The resulting mixture was heated to 350°C at a heating rate of 20°C / min under a nitrogen gas flow of 1250 mL / min per 1 g of mixture and heat-treated (phase-separated) at this temperature for 30 minutes. Next, while flowing nitrogen gas at the same gas supply rate, the mixture was heated to 700°C at a heating rate of 10°C / min and heat-treated at this temperature for 60 minutes to obtain a carbonized product. The carbonized product was immersed in 0.2 L of 0.1 mol / L hydrochloric acid and washed by stirring at 80°C for 30 minutes, then transferred to a Buchner funnel. The filtrate was washed with water until the pH reached the range of 6-8. After acid washing and water washing were repeated three times, the carbonized material was dried with hot air at 80°C. The carbonized material after hot air drying was mixed with 12 mL of ion-exchanged water, and the carbonized material was heated to 1200°C at a temperature increase rate of 10°C / min while flowing nitrogen gas through the resulting mixture at the same gas supply rate as above, and heat-treated for 60 minutes. The carbonized material after the heat treatment was ball milled for 10 minutes to obtain porous carbon A. The pore volume of porous carbon A with a size of 2 nm or more and 200 nm or less, measured by the BJH method, was 3.15 cm ３ / g, and the mode diameter of the pores was 28 nm. ５０ The particle size was 3 μm and the bulk density was 0.05 g / cc.

[0098] <Production of Porous Carbon B> Porous carbon B was obtained in the same manner as in the production of porous carbon A, except that the raw materials used in the production of porous carbon A were 0.72 g of glucose (sold by Fujifilm Wako Pure Chemical Industries, Ltd.), 2.18 g of calcium chloride dihydrate, and 1.09 g of ion-exchanged water. The pore volume of porous carbon B with a diameter of 2 nm or more and 200 nm or less, measured by the BJH method, was 1.18 cm ３ / g, and the mode diameter of the pores was 37 nm. ５０ The particle size was 3 μm and the bulk density was 0.05 g / cc.

[0099] <Production of Porous Carbon C> Porous carbon C was obtained in the same manner as in the production of porous carbon A, except that the raw material used in the production of porous carbon A was 1.5 g of starch (derived from corn, amylose content: approximately 26%, sold by Fujifilm Wako Pure Chemical Industries, Ltd.). The pore volume of porous carbon C having a size of 2 nm or more and 200 nm or less, measured by the BJH method, was 0.51 cm ３ / g, and the mode diameter of the pores was 32 nm. ５０ The particle size was 3 μm and the bulk density was 0.15 g / cc.

[0100] Example 1 Preparation of Lithium-Ion Secondary Battery Positive Electrode Composition 3 parts by mass of polyvinylidene fluoride, 96 parts by mass of lithium nickel cobalt manganese oxide (NCM811) as a positive electrode active material, 0.5 parts by mass of multi-walled carbon nanotubes (MWCNT) (average fiber length: 20 μm, average fiber diameter: 11 nm) as a conductive additive, and 0.5 parts by mass of porous carbon A prepared by the method described above were mixed together, and the mixture was stirred with a Homodisper 2.5 manufactured by Primix Corporation while appropriately adding N-methylpyrrolidone so that the solids concentration of the composition became 67.3% by mass. The mixture was then degassed with an ARE-310 manufactured by Thinky Corporation, to obtain a positive electrode composition.

[0101] <Preparation of Lithium-Ion Secondary Battery> The positive electrode composition obtained by the above-described method was applied to aluminum foil to prepare a positive electrode sheet. A negative electrode sheet was prepared by mixing graphite powder and active material powder. The positive electrode sheet and the negative electrode sheet were punched using a Thomson punch to obtain a 60 x 60 mm positive electrode and a 65 x 65 mm negative electrode. An aluminum tab was attached to the aluminum foil of the positive electrode, and a nickel-plated copper tab was attached to the copper foil of the negative electrode using an ultrasonic welder. The positive electrode and the negative electrode were alternately stacked with separators interposed between them to prepare an electrode laminate in which the outermost layer was the negative electrode. A polyolefin film (25 μm thick) was used as the separator. The electrode laminate was sandwiched between aluminum laminate films, and the three sides were laminated and sealed. Next, the electrolyte was poured into the one side that remained unsealed, the cell was placed in a vacuum sealer, and after evacuating to -80 kPa, the exterior film was sealed to produce a laminated full cell. The electrolyte was prepared by mixing ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) in a volume ratio of 3:4:3, with 1 mass% vinylene carbonate (VC) and lithium hexafluorophosphate (LiPF ６ ) to a concentration of 1 mol / L.

[0102] [Example 2] A laminated full cell of Example 2 was produced in the same manner as Example 1, except that the conductive additive of Example 1 (0.5 parts by mass of MWCNT and 0.5 parts by mass of porous carbon A) was changed to 0.5 parts by mass of MWCNT and 0.5 parts by mass of porous carbon B.

[0103] Comparative Example 1 A laminated full cell of Comparative Example 1 was produced in the same manner as in Example 1, except that the conductive additives (0.5 parts by mass of MWCNT and 0.5 parts by mass of porous carbon A) in Example 1 were changed to 0.5 parts by mass of MWCNT and 0.5 parts by mass of carbon black.

[0104] <Measurement of Charge Capacity Retention Rate of Lithium Secondary Battery> Using the fabricated laminated full cell, the charge capacity retention rate was measured at 25°C, 0°C, and -20°C. The temperature inside a thermostatic chamber was set to the evaluation temperature, and the resulting laminated full cell was placed in the thermostatic chamber for 1 hour. The charge capacity retention rate was measured using a charge-discharge device ("TOSCAT" manufactured by Toyo Systems Co., Ltd.). The cells were charged at a constant current of 0.2 C up to 4.2 V. After reaching 4.2 V, the cells were charged at a constant current of 0.2 C to a constant voltage of 0.05 C to maintain the cell voltage at 4.2 V. The cells were discharged at a constant current of 0.2 C down to 2.5 V. After one cycle under the above conditions, the charge rate was changed to 0.2 C to 3 C (0.2 C to 1 C at -20°C), and one charge-discharge cycle was performed. The ratio of the discharge capacity at 0.5C to 3C (0.5C to 1C at -20°C) to the charge capacity at 0.2C was defined as the discharge capacity retention rate.

[0105] <Measurement of Discharge Capacity Retention Rate of Lithium Secondary Battery> Using the fabricated laminated full cell, the discharge capacity retention rate was measured at 25°C, 0°C, and -20°C. The discharge capacity retention rate was measured by setting the temperature inside a thermostatic chamber to the evaluation temperature, placing the resulting laminated full cell in the thermostatic chamber for 1 hour, and using a charge / discharge device ("TOSCAT" manufactured by Toyo Systems Co., Ltd.). Charge was performed at a constant current of 0.2 C up to 4.2 V, and after reaching 4.2 V, constant current / constant voltage charging was performed, in which the current was reduced to a current value of 0.05 C to maintain the cell voltage at 4.2 V. Discharge was performed at a constant current of 0.2 C down to 2.5 V. After performing one cycle under the above conditions, the discharge rate was changed to 0.2 C to 4 C (0.2 C to 1 C at -20°C), and one charge / discharge cycle was performed. The ratio of the discharge capacity at 0.5C to 4C (0.5C to 1C at -20°C) to the discharge capacity at 0.2C was defined as the discharge capacity retention rate.

[0106] <Measurement of Charge Transfer Resistance and Ion Diffusion Resistance (Impedance Measurement)> Impedance measurements were performed using the prepared laminated full cell at 25°C, 0°C, and -20°C. A 1255WB high-performance electrochemical measurement system manufactured by Solartron, UK, was used for the impedance measurements. The laminated full cell placed in a thermostatic chamber at 25°C was charged to 50% SOC using a constant current constant voltage method at 0.2C to 0.05C. The temperature inside the thermostatic chamber was then set to the evaluation temperature, and the resulting laminated full cell was placed in the thermostatic chamber for 1 hour. Measurements were then performed using an AC impedance meter over a measurement frequency range of 1MHz to 1mHz. The arc portion of the Cole-Cole plot obtained by impedance measurement under the above conditions was taken as the charge transfer resistance, and the straight line at 45°C as the diffusion resistance, and the respective resistance values ​​were obtained.

[0107] The compositions of the positive electrode compositions obtained in the examples and comparative examples are shown in Table 1. The blending ratios (mass %) shown in Table 1 are blending ratios relative to the solid content of the positive electrode composition. Furthermore, Table 2 shows the results of measuring the battery characteristics of lithium secondary batteries obtained using the positive electrode compositions of the examples and comparative examples.

[0108] Comparative Example 2 A laminated full cell of Comparative Example 2 was produced in the same manner as in Example 1, except that the amount of carbon black was changed from 0.5 parts by mass of MWCNT to 0.5 parts by mass.

[0109] Comparative Example 3 A laminated full cell of Comparative Example 3 was produced in the same manner as in Example 1, except that the conductive additive (0.5 parts by mass of MWCNT and 0.5 parts by mass of porous carbon A) in Example 1 was changed to 1 part by mass of MWCNT.

[0110] Comparative Example 4 A laminated full cell of Comparative Example 4 was produced in the same manner as in Example 1, except that the conductive additives (0.5 parts by mass of MWCNT and 0.5 parts by mass of porous carbon A) in Example 1 were replaced with 0.5 parts by mass of extra-thick carbon fiber (average fiber diameter of approximately 40 μm) having an average fiber diameter significantly exceeding 200 nm and 0.5 parts by mass of porous carbon A. Because the average fiber diameter of the carbon fiber was large, sufficient conductive paths were not formed in this cell, and the rate characteristics at room temperature and low temperatures were poor.

[0111] [Comparative Example 5] A laminated full cell of Comparative Example 5 was produced in the same manner as in Example 1, except that the conductive additives (0.5 parts by mass of MWCNT and 0.5 parts by mass of porous carbon A) in Example 1 were changed to 0.5 parts by mass of MWCNT and 0.5 parts by mass of porous carbon C.

[0112] The discharge capacity retention rate and charge capacity retention rate were also measured in the same manner for the laminate-type full cells obtained in Comparative Examples 2 to 5. The results are shown in Table 2. As shown in Table 2, the charge capacity retention rate and discharge capacity retention rate at room temperature and low temperature for the laminate-type full cells obtained in the Comparative Examples were lower than those for the laminate-type full cells obtained in the Examples.

[0113]

[0114]

Claims

A positive electrode composition comprising a positive electrode active material, porous carbon, fibrous carbon, and a binder, the positive electrode active material is an inorganic compound, The pore volume of the porous carbon having a diameter of 2 nm or more and 200 nm or less measured by the BJH method is 0.8 cm ３ / g or more, The average fiber diameter of the fibrous carbon is 0.5 to 200 nm, and the average fiber length is 1 to 1000 μm. Positive electrode composition. 　 The positive electrode composition according to claim 1 , wherein the fibrous carbon has a tubular structure.

3. The positive electrode composition according to claim 1, wherein the fibrous carbon is at least one selected from the group consisting of carbon nanotubes and vapor-grown carbon fibers.

4. The positive electrode composition according to claim 1, wherein a total content of the porous carbon and the fibrous carbon is 0.2 to 15 mass% with respect to a solid content of the positive electrode composition, and a ratio of the content of the porous carbon to the content of the fibrous carbon (porous carbon:fibrous carbon) is 1:9 to 9:

1. The positive electrode composition according to any one of claims 1 to 4, wherein the positive electrode active material comprises at least one compound selected from the group consisting of lithium nickel cobalt manganese oxide (NCM), lithium nickel oxide (NCA), lithium cobalt oxide (LCO), lithium manganese oxide (LMO), lithium nickel manganese oxide (LNMO), lithium manganese iron phosphate (LMFP), and lithium iron phosphate (LFP).

6. The positive electrode composition according to claim 1, wherein the porous carbon has a pore mode diameter of 150 nm or less as measured by the BJH method. 　 The median particle diameter D of the porous carbon ５０ The positive electrode composition according to any one of claims 1 to 6, wherein the thickness is 0.1 to 100 µm. 　 A positive electrode for a non-aqueous electrolyte secondary battery, comprising the positive electrode composition according to any one of claims 1 to 7. 　 A non-aqueous electrolyte secondary battery comprising the positive electrode according to claim 8 .

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