Composite carbon particles, electricity storage device, and method for producing composite carbon particles

Abstract

To enhance a high-rate characteristic of a power storage device.SOLUTION: A composite carbon particle is a composite carbon particle obtained by composing a graphite particle and an amorphous carbon, and has a pore diameter calculated by a nitrogen adsorption measurement of 40 μL / g or more and an average pore diameter calculated by the nitrogen adsorption measurement of 7 nm. A manufacturing method of the composite carbon particle, comprises: a granulation step of obtaining a granulation powder by using a raw material liquid containing a graphite particle and a metal carboxylate; a thermal processing step of generating a metal and / or a metal chemical compound, derived from the metal carboxylate while performing a thermal processing to the granulation powder to carbonize it; and a removing step of removing the metal and / or the metal chemical compound from the granulation power after the thermal processing step.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to composite carbon particles, an electricity storage device, and a method for producing composite carbon particles. [Background technology]

[0002] Previously, secondary batteries have been developed that use graphite negative electrodes, such as massive artificial graphite (MAG) or porous lithiated graphite lamina (PLGL), to utilize the lithium deposition and dissolution capacity on graphite in addition to the charge / discharge capacity of graphite (lithium intercalation and deintercalation capacity of graphite) (see, for example, Non-Patent Documents 1 and 2). The present inventors have also proposed secondary batteries that use nonwoven carbon fiber aggregates as negative electrodes to utilize the lithium deposition and dissolution capacity on carbon fibers in addition to the charge / discharge capacity of carbon fibers (lithium intercalation and deintercalation capacity of carbon fibers) (see, for example, Patent Documents 1 to 4). Furthermore, secondary batteries have been proposed that use carbon-lithium composite powders, in which lithium metal is supported by a carbon material as a framework, as negative electrodes to utilize the lithium deposition and dissolution capacity on carbon materials in addition to the lithium intercalation and deintercalation capacity of carbon materials (see, for example, Patent Document 5). Thus, by utilizing the lithium deposition and dissolution capacity on the negative electrode in addition to the lithium intercalation and deintercalation capacity on the negative electrode, the energy density of secondary batteries can be increased. Secondary batteries that utilize the storage of lithium metal in the subnanopores of hard carbon are also being investigated (see, for example, Non-Patent Document 3). In this way, by utilizing the subnanopores of hard carbon, it is possible to suppress the dendrite growth of lithium metal and improve the coulombic efficiency and cycle stability of secondary batteries. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-96475 [Patent Document 2] Japanese Patent Application Publication No. 2019-135689 [Patent Document 3] Japanese Patent Application Publication No. 2019-160730 [Patent Document 4] Japanese Patent Publication No. 2020-17479 [Patent Document 5] Japanese Patent Application Publication No. 2020-13779 [Non-patent literature]

[0004] [Non-Patent Document 1] Chem, 1, 287-297 (2016) [Non-patent document 2] ACS Nano, 14, 1837-1845 (2020) [Non-patent document 3] Chem. Eng. J., 450, 138049 (2022) Summary of the Invention [Problem to be solved by the invention]

[0005] However, the secondary batteries disclosed in Patent Documents 1 to 5 and Non-Patent Documents 1 to 3 utilize the deposition and dissolution capacity of lithium, which is a charge carrier, but they sometimes have poor high-rate characteristics. Therefore, there has been a demand for further improving the high-rate characteristics of electricity storage devices.

[0006] The present disclosure has been made in consideration of such problems, and has as its main object to further improve the high-rate characteristics of electricity storage devices. [Means for solving the problem]

[0007] In order to achieve the above-mentioned object, the present inventors have conducted extensive research. They have come up with the idea of ​​producing composite carbon particles by preparing a granulated powder using a raw material liquid containing graphite particles and a metal sugar carboxylate, carbonizing the powder by heat treatment and generating a metal and / or metal compound derived from the metal sugar carboxylate, and removing the generated metal and / or metal compound. The composite carbon particles thus obtained are a composite of graphite particles and amorphous carbon and have a predetermined pore structure. They have found that, when used in an electrode of an electricity storage device, they can exhibit a charge carrier precipitation / dissolution capacity in addition to the charge carrier insertion / desorption capacity to graphite, and can further improve high-rate performance, leading to the completion of the present disclosure.

[0008] That is, the composite carbon particles disclosed in the present specification are The composite carbon particles are made by combining graphite particles and amorphous carbon, and have a pore volume calculated by nitrogen adsorption measurement of 40 μL / g or more and an average pore diameter calculated by nitrogen adsorption measurement of 7 nm or less.

[0009] The electricity storage device disclosed in this specification comprises: The battery is provided with an electrode containing the above composite carbon particles as an electrode active material.

[0010] The method for producing composite carbon particles disclosed herein includes the steps of: a granulation step of obtaining a granulated powder using a raw material liquid containing graphite particles and a sugar carboxylate metal salt; a heat treatment step in which the granulated powder is heat-treated to carbonize it and generate a metal and / or a metal compound derived from the sugar carboxylate metal salt; a removing step of removing the metal and / or metal compound from the granulated powder after the heat treatment step; It includes: [Effects of the Invention]

[0011] The present disclosure can improve the high-rate characteristics of an electricity storage device. The reason for this effect is presumed to be as follows. For example, when the composite carbon particles of the present disclosure are used in an electrode of an electricity storage device, charge carriers are inserted into and removed from the graphite particles, while the amorphous carbon reduces the deposition overpotential of the charge carriers, contributing to the precipitation and dissolution of the charge carriers. It is believed that pores are formed in this amorphous carbon by, for example, carbonizing the sugar and / or sugar carboxylic acid of the sugar carboxylate metal salt and removing the metal and / or metal compound derived from the sugar carboxylate metal salt. These pores also function as a deposition field for the charge carriers. It is presumed that the favorable pore structure of such composite carbon particles allows smooth insertion and desorption of charge carriers into and from the graphite, and smooth precipitation and dissolution of the charge carriers, thereby further improving the high-rate characteristics. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a cross-sectional schematic diagram of a composite carbon particle 10. FIG. [Figure 2] 1 is a schematic diagram showing an example of a method for producing a composite carbon particle 10. FIG. [Figure 3] FIG. 2 is a schematic diagram of an electricity storage device 50. [Figure 4] 1 is an SEM image of composite carbon particles of Experimental Example 3. [Figure 5] N2 adsorption isotherm of composite carbon particles of Experimental Example 3. [Figure 6] TG curve of composite carbon particles of Experimental Example 3. [Figure 7] 1 is an X-ray diffraction pattern of composite carbon particles of Experimental Example 3. [Figure 8] 10 shows charge-discharge curves for the cell of Experimental Example 3 after 10 cycles. DETAILED DESCRIPTION OF THE INVENTION

[0013] [Composite carbon particles] The composite carbon particles of the present disclosure are used, for example, as an electrode active material for an electrode of an electricity storage device. The electricity storage device may be, for example, a secondary battery such as an alkali metal ion secondary battery, a hybrid capacitor, or an air battery. The electricity storage device may use an alkali metal or a Group 2 metal as a charge carrier. Examples of alkali metals include lithium, sodium, and potassium, with lithium being preferred. Examples of Group 2 metals include magnesium, calcium, strontium, and barium. An electrode for an electricity storage device becomes either a positive electrode or a negative electrode depending on the potential of the counter electrode relative to the potential of the electrode active material. When lithium is used as a carrier, the electrode is preferably a negative electrode. In this embodiment, the case where the composite carbon particles are used as a negative electrode active material for a lithium ion secondary battery will be mainly described.

[0014] The composite carbon particles are composite carbon particles in which graphite particles and amorphous carbon are composited, and have a pore volume of 40 μL / g or more as calculated by nitrogen adsorption measurement and an average pore diameter of 7 nm or less as calculated by nitrogen adsorption measurement. When the pore volume is 40 μL / g or more and the average pore diameter is 7 nm or less, the high-rate characteristics can be further improved. In this disclosure, the terms "pore volume," "average pore diameter," and "specific surface area" refer to values ​​determined by nitrogen adsorption measurement and BET analysis, respectively, unless otherwise specified. In this disclosure, "pore volume" refers to the pore volume per unit mass. The pore volume may be, for example, 200 μL / g or less, 150 μL / g or less, or 100 μL or less, from the viewpoint of further improving the high-rate characteristics and further suppressing a decrease in the initial charge / discharge efficiency. The pore volume may be, for example, 45 μL / g or more, or 50 μL / g or more, from the viewpoint of further improving cycle characteristics. The average pore diameter may be, for example, 1 nm or more, 2 nm or more, or 2.2 nm or more, from the viewpoint of further improving high-rate characteristics and further suppressing a decrease in initial charge / discharge efficiency. The average pore diameter may be, for example, 6 nm or less, 5 nm or less, or 4 nm or less, from the viewpoint of further improving cycle characteristics. The composite carbon particles have a specific surface area calculated by nitrogen adsorption measurement of 30 m 2 / g or more 250m 2 The specific surface area may be, for example, 200 m / g or less from the viewpoint of further improving the high-rate characteristics and further suppressing the decrease in the initial charge / discharge efficiency. 2 / g or less, 170m 2 In addition, the specific surface area may be set to 50 m / g or less from the viewpoint of further improving cycle characteristics. 2 / g or more, and 2 / g or more, and 100m 2 / g or more. These composite carbon particles may be such that no steps specific to graphite are observed in their Kr adsorption isotherms. Regarding the steps specific to graphite, according to Horikawa et al., "Gas Adsorption on Graphite Surfaces" (Acc. Mater. Surf. Res., 3, 51-62 (2018)), the Kr adsorption behavior on the graphite surface is such that the amount of Kr adsorbed increases stepwise as the number of layers increases, with Kr forming layers on the graphite surface, and the adsorption isotherm is classified as a type VI adsorption isotherm in the IUPAC classification. In the composite carbon particles of the present disclosure, amorphous carbon is formed on the surface of the crystalline structure of graphite, so that there are almost no widely exposed portions of the graphite surface, and therefore it is presumed that no steps specific to graphite are observed.

[0015] The composite carbon particles may be aggregated particles containing a plurality of graphite particles and formed by aggregating the plurality of graphite particles with amorphous carbon. In the aggregated particles, amorphous carbon may be present between the graphite particles, and the graphite particles may be bound together by the amorphous carbon. In the aggregated particles, the graphite particles preferably have a flat shape, such as a scale shape.

[0016] The composite carbon particles may be spherical. When spherical composite carbon particles are used in an electrode of an electricity storage device, it is believed that the degree of curvature in the electrode film thickness direction in the lithium migration path is less likely to increase, current concentration on the electrode surface can be suppressed, and lithium precipitation on the electrode surface can be further suppressed. The average particle size of the composite carbon particles may be, for example, 8 μm or more, 10 μm or more, or 12 μm or more. The average particle size of the composite carbon particles may be, for example, 50 μm or less, 30 μm or less, or 20 μm or less. In the present disclosure, "average particle size" may refer to the median diameter D50 measured by laser diffraction.

[0017] The composite carbon particles may contain amorphous carbon in a proportion of 1% by mass or more and 50% by mass or less, or in a proportion of 1.5% by mass or more and 30% by mass or less, or in a proportion of 2% by mass or more and 20% by mass or less. The proportion of amorphous carbon (coating amount) may be a value calculated from the yields in the heat treatment step, removal treatment step, and firing step in the method for producing composite carbon particles described below. Specifically, first, the masses Xh1 [g] and Xh2 [g] of the granulated powder before and after the heat treatment step, the masses Xr1 [g] and Xr2 [g] of the granulated powder before and after the removal treatment step, and the masses Xf1 [g] and Xf2 [g] of the granulated powder before and after the firing step are measured. Then, using the ratio g [%] of graphite particles in the raw material liquid and the ratio c [%] of the coating source (sugar carboxylic acid metal salt and sugar compound) (where g + c = 100), the mass of graphite particles in the granulated powder before the heat treatment process Gh1 [g] = Xh1 × g / 100 and the mass of the coating source Ch1 [g] = Xh1 × c / 100 are calculated. Next, using the yield s [%] of the heat treatment process when the heat treatment process is performed on graphite particles alone, the mass of graphite particles in the granulated powder after the heat treatment process Gh2 [g] = Gh1 × s / 100 is calculated, and the mass of the coating source Ch2 [g] = Xh2 - Gh2 is calculated. Next, the mass of graphite particles in the granulated powder before the removal process Gr1 [g] = Xr1 × Gh2 / Xh2 and the mass of the coating source Cr1 [g] = Xr1 × Ch2 / Xh2 are calculated. Then, the mass of the remaining coating source, Cr2' [g] = Cr1 × t / 100, is calculated from the theoretical yield t [%] when all of the MgO is removed from the coating source. Assuming that losses due to filtration and washing are equal between the graphite particles and the remaining coating source, the mass of the graphite particles in the granulated powder after the removal treatment step, Gr2 [g] = Xr2 × Gr1 / (Gr1 + Cr2'), and the mass of the coating source, Cr2 [g] = Xr2 × Cr2' / (Gr1 + Cr2'), are calculated. Next, the mass of the graphite particles in the granulated powder before the firing step, Gf1 [g] = Xf1 × Gr2 / Xr2, and the mass of the coating source, Cf1 [g] = Xf1 × Cr2 / Xr2, are calculated. Next, the mass of the graphite particles in the granulated powder (composite carbon particles) after the firing process, Gf2 [g] = Gf1 × u / 100, is calculated using the yield u [%] in the firing process when the graphite particles after the heat treatment process are subjected to the firing process alone, and the mass of the coating, Cf2 [g] = Xf2 - Gf2, is calculated.The value of Cf2 / Xf2×100 is the proportion of amorphous carbon in the composite carbon particles (coating amount). The composite carbon particles may have a mass loss of 1% to 50%, 1.5% to 30%, or 2% to 20% at 600°C in thermogravimetry. This mass loss correlates to some extent with the proportion of amorphous carbon calculated from the yields in the heat treatment step, removal treatment step, and firing step.

[0018] The composite carbon particles may be, for example, graphite particles in which at least a portion of the surface is coated with amorphous carbon, graphite particles in which amorphous carbon is interposed between the graphite particles to connect the graphite particles, graphite particles in which amorphous carbon is inserted between the graphite layers, or composite carbon particles in which a combination of these is satisfied. Note that, since the composite carbon particles are considered to have at least a portion of the surface of the graphite particles coated with amorphous carbon, in the present disclosure, the amorphous carbon is also referred to as the "coat," and the proportion of amorphous carbon is also referred to as the "coat amount."

[0019] The composite carbon particles may contain lithium in an amount exceeding 8.8% by mass of the composite carbon particles when the SOC of the power storage device is 100%, or may contain lithium in an amount equal to or greater than 10% by mass. When graphite is used as the negative electrode active material, C6Li in a state of 100% SOC contains lithium in an amount equal to 8.8% by mass of the graphite. In contrast, when the composite carbon particles of the present disclosure are used as the negative electrode active material, lithium metal can be precipitated / dissolved to utilize the charge / discharge capacity. In this case, the composite carbon particles may contain lithium in an amount equal to or greater than 8.8% by mass of the composite carbon particles, or may contain Li in an amount equal to or greater than 10% by mass.

[0020] The graphite particles may be natural graphite (scale graphite, flake graphite) or artificial graphite, but natural graphite is more preferred. This is because natural graphite is generally cheaper than artificial graphite, which requires graphitization. The graphite may be mechanically shape-controlled, for example, by rounding the corners of the graphite, rounding it into a spherical shape, or crushing it. It is believed that such shape control can suppress selective orientation and inhibit the insertion and desorption of lithium ions. The graphite particles may be modified from graphite particles before composite formation by heat treatment or the like. The average particle size of the graphite particles may be, for example, 1 μm to 20 μm, or 5 μm to 10 μm. The average particle size may be a value measured on the graphite particles before composite formation.

[0021] The graphite particles may have the following pore structure. For example, the pore volume calculated by nitrogen adsorption measurement may be smaller than the pore volume of the composite carbon particles, e.g., less than 40 μL / g. The average pore diameter calculated by nitrogen adsorption measurement may be larger than the average pore diameter of the composite carbon particles, e.g., more than 7 nm. The specific surface area calculated by nitrogen adsorption measurement may be smaller than the specific surface area of ​​the composite carbon particles, e.g., more than 30 m 2 / g. Alternatively, a step specific to graphite may be observed in a Kr adsorption isotherm. Such a pore structure may be determined by performing nitrogen adsorption measurement or Kr adsorption measurement on graphite particles before composite formation.

[0022] Amorphous carbon may be, for example, a carbonized sugar and / or sugar carboxylic acid of a sugar carboxylate metal salt, or a carbonized sugar compound. In the present disclosure, the sugar carboxylate metal salt and the sugar compound are also referred to as amorphous carbon sources. The sugar of the sugar carboxylate metal salt or the sugar compound may be a monosaccharide, an oligosaccharide in which 2 to 20 monosaccharide molecules are bonded, or a polysaccharide in which even more monosaccharides are bonded. Among these, monosaccharides and oligosaccharides are preferred, and monosaccharides and disaccharides are more preferred. More specifically, the monosaccharides and disaccharides are preferably one or more selected from the group consisting of monosaccharides such as glucose and fructose, and disaccharides such as sucrose, lactose, maltose, trehalose, turanose, cellobiose, and derivatives thereof. These sugars have small molecular weights (180 to 350) and small molecular sizes, and are therefore considered to be easily distributed over the entire surface of the graphite particles. Among these, glucose is more preferred. The amorphous carbon may be, for example, non-graphitizable carbon.

[0023] The amorphous carbon may have pores. The pore volume of the amorphous carbon may be larger than the pore volume of the graphite particles, for example, 50 μL / g or more, 60 μL / g or more, or 70 μL / g or more. This pore volume may be 500 μL / g or less, 300 μL / g or less, or 100 μL / g or less. The average pore diameter of the amorphous carbon may be smaller than the average pore diameter of the graphite particles, for example, 10 nm or less, 5 nm or less, or 2 nm or less. This average pore diameter may be 0.5 nm or more, 1 nm or more, or 1.5 nm or more. The specific surface area of ​​the amorphous carbon may be larger than the specific surface area of ​​the graphite particles, for example, 50 m 2 / g or more, and 100m 2 / g or more, and 200m 2 / g or more. This specific surface area is 1000m 2 / g or less, and 700m 2 / g or less, and 500m 2The pore volume, average pore diameter, and specific surface area of ​​the amorphous carbon may be values ​​measured for particles produced in a method for producing composite carbon particles described below, in which graphite particles are omitted from the raw material liquid.

[0024] The amorphous carbon may be such that the pore volume Vc [μL / g] of a composite carbon particle is expressed as Vc = Va × Ca / 100 + Vg × (100 − Ca) / 100, where Vc is the amorphous carbon percentage [%], Va is the amorphous carbon pore volume [μL / g], Vg is the graphite particle percentage [%], and Vg is the graphite particle pore volume [μL / g]. The theoretical pore volume Va calculated by substituting the measured or calculated values ​​of Vc, Vg, and Ca into this formula satisfies the following: For example, the theoretical pore volume Va may be 100 μL / g or more, 200 μL / g or more, or 400 μL / g or more. Furthermore, the theoretical pore volume Va may be, for example, 3000 μL / g or less, 1000 μL / g or less, or 900 μL / g or less. In addition, the amorphous carbon has a ratio of amorphous carbon Ca [%] and a specific surface area of ​​amorphous carbon Sa [m 2 / g], the ratio of graphite particles is (100-Ca) [%], and the specific surface area of ​​graphite particles is Sg [m 2 / g], the specific surface area of ​​the composite carbon particles Sc [m 2 / g] is assumed to be expressed as Sc = Sa × Ca / 100 + Sg × (100 - Ca) / 100, and the theoretical specific surface area obtained by substituting the measured or calculated values ​​of Sc, Sg, and Ca into this formula may be considered to satisfy the following. For example, the theoretical specific surface area Sa may be calculated as follows: 2 / g or more, and 500m 2 / g or more, and 1500m 2 The theoretical specific surface area Sa may be 5000 m / g or more. 2 / g or less, and 4000m 2 / g or less, and 3000m 2 The pore volume Vg and specific surface area Sg of the graphite particles may be values ​​measured for particles produced in the same manner as in the method for producing composite particles of the present disclosure, except that no coating source is used.

[0025] FIG. 1 is a cross-sectional schematic diagram of a composite carbon particle 10, which is an example of the composite carbon particle of the present disclosure. The composite carbon particle 10 is a particle obtained by compositing graphite particles 20 and amorphous carbon 30. The composite carbon particle 10 has a pore volume of 40 μL / g or more, as calculated by nitrogen adsorption measurement, and an average pore diameter of 7 nm or less, as calculated by nitrogen adsorption measurement. The composite carbon particle 10 includes a plurality of flake-like graphite particles 20, with amorphous carbon 30 present between the graphite particles 20, and is an aggregate particle formed by agglomerating the plurality of graphite particles 20 with the amorphous carbon 30. The composite carbon particle 10 is substantially spherical. The graphite particles 20 may be, for example, flake graphite. The amorphous carbon 30 may be, for example, carbonized sugar and / or sugar carboxylic acid, or may be non-graphitizable carbon. The amorphous carbon 30 may have pores 31.

[0026] [Method of manufacturing composite carbon particles] The method for producing composite carbon particles according to the present disclosure includes a granulation step of obtaining a granulated powder using a raw material liquid containing graphite particles and a sugar metal carboxylate, a heat treatment step of heat-treating the granulated powder to carbonize it and generate metals and / or metal compounds derived from the sugar metal carboxylate, and a removal step of removing the metals and / or metal compounds derived from the sugar metal carboxylate from the granulated powder after the heat treatment step. This method for producing composite carbon particles may also include a firing step of firing the granulated powder after the removal step. This method for producing composite carbon particles may be, for example, the method for producing the composite carbon particles described above.

[0027] (granulation process) In the granulation step, a raw material liquid containing graphite particles and a sugar carboxylate metal salt is used to produce granulated powder. The raw material liquid may contain a sugar compound in addition to the graphite particles and the sugar carboxylate metal salt. The raw material liquid may be a slurry in which the graphite particles are dispersed in a solvent. The solvent may be a solvent capable of dissolving the sugar carboxylate metal salt or a solvent capable of dissolving the sugar compound. The raw material liquid may also contain a thickener.

[0028] The graphite particles may be natural graphite (scale graphite, flake graphite) or artificial graphite, with natural graphite being more preferred. The graphite may be mechanically shape-controlled, for example, by rounding the corners of the graphite, rounding it into a spherical shape, or crushing it. The average particle size of the graphite particles may be, for example, from 1 μm to 20 μm, or from 5 μm to 10 μm.

[0029] The graphite particles may have the following pore structure. For example, the pore volume calculated by nitrogen adsorption measurement may be smaller than the pore volume of the composite carbon particles, e.g., less than 40 μL / g. The average pore diameter calculated by nitrogen adsorption measurement may be larger than the average pore diameter of the composite carbon particles, e.g., more than 7 nm. The specific surface area calculated by nitrogen adsorption measurement may be smaller than the specific surface area of ​​the composite carbon particles, e.g., more than 30 m 2 / g or less. Also, a step specific to graphite may be observed in the Kr adsorption isotherm.

[0030] The sugar of the sugar carboxylate metal salt may be a monosaccharide, an oligosaccharide in which 2 to 20 monosaccharide molecules are bonded, or a polysaccharide in which even more monosaccharide molecules are bonded. Among these, monosaccharides and oligosaccharides are preferred, and monosaccharides and disaccharides are more preferred. More specifically, the monosaccharide and disaccharide are preferably one or more selected from the group consisting of monosaccharides such as glucose and fructose, disaccharides such as sucrose, lactose, maltose, trehalose, turanose, cellobiose, and derivatives thereof, with glucose being more preferred. The sugar carboxylic acid has a structure in which one or more oxygen functional groups of these sugars are oxidized to form a carboxy group, with gluconic acid being more preferred. The metal of the sugar carboxylate metal salt may be, for example, an alkali metal or a Group 2 metal. Examples of alkali metals include lithium, sodium, and potassium. Examples of Group 2 metals include magnesium, calcium, strontium, and barium. Among these, Group 2 metals are preferred, and magnesium is more preferred. As the metal sugar carboxylate, for example, magnesium gluconate is preferable. The metal sugar carboxylate may be a hydrate.

[0031] The sugar compound is different from the sugar carboxylate metal salt and may be a monosaccharide, an oligosaccharide in which 2 to 20 monosaccharide molecules are bonded, or a polysaccharide in which even more monosaccharide molecules are bonded. Of these, monosaccharides and oligosaccharides are preferred, and monosaccharides and disaccharides are more preferred. More specifically, the monosaccharide and disaccharide are preferably one or more selected from the group consisting of monosaccharides such as glucose and fructose, disaccharides such as sucrose, lactose, maltose, trehalose, turanose, cellobiose, and derivatives thereof, and glucose is more preferred. The sugar compound may be the same or different from the sugar in the sugar carboxylate metal salt, but is preferably the same.

[0032] The solvent is not particularly limited, and examples thereof include aqueous solvents and organic solvents such as N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethylenetriamine, N,N-dimethylaminopropylamine, ethylene oxide, and tetrahydrofuran, which can be used alone or as a mixture of two or more. Among these, the solvent is preferably an aqueous solvent, and more preferably water.

[0033] The thickener may be, for example, a cellulose derivative (polysaccharide) such as carboxymethyl cellulose (CMC) or carboxyethyl cellulose, or polyacrylic acid, which may be used alone or as a mixture of two or more. Of these, carboxymethyl cellulose is preferred. Carboxymethyl cellulose may be, for example, an inorganic salt in which the carboxymethyl group is terminated with sodium or calcium, or an ammonium salt in which the carboxymethyl group is terminated with ammonium. The same applies to carboxyethyl cellulose. The content of the thickener may be 0.1% to 2% or 0.5% to 1.5% relative to the graphite particles.

[0034] The raw material liquid may contain the sugar carboxylate metal salt in a range of 0.1 parts by mass to 100 parts by mass, 0.5 parts by mass to 70 parts by mass, or 1 part by mass to 50 parts by mass, per 10 parts by mass of graphite particles. The raw material liquid may also contain the sugar compound in a range of 0.1 parts by mass to 100 parts by mass, 0.2 parts by mass to 30 parts by mass, or 0.3 parts by mass to 20 parts by mass, per 10 parts by mass of graphite particles. The raw material liquid may contain the sugar compound in a mass ratio of 0.01 to 10 times, 0.1 to 1 time, or 0.2 to 0.7 times, relative to the sugar carboxylate metal salt.

[0035] The raw material liquid may be prepared, for example, by mixing a graphite slurry in which graphite particles are dispersed in a solvent with a sugar carboxylate metal salt solution in which a sugar carboxylate metal salt is dissolved in a solvent. The graphite slurry may be prepared by mixing graphite particles with a thickener, and then adding a solvent and mixing. The sugar carboxylate metal salt solution may be prepared by dissolving a sugar carboxylate metal salt and a sugar compound in a solvent. In the present disclosure, the raw material liquid containing a sugar carboxylate metal salt or a sugar compound is also referred to as a coating liquid. The coating liquid is the portion of the raw material liquid excluding the graphite particles.

[0036] A preferred granulation method is, for example, spray drying. Spray drying produces spherical granulated powder and is therefore suitable for producing spherical composite carbon particles. Spray drying may be performed using a spray dryer. Spray drying conditions may be adjusted appropriately depending on, for example, the scale of the apparatus and the amount of composite carbon particles to be produced. The drying temperature is preferably, for example, in the range of 100°C or higher and 250°C or lower. At 100°C or higher, the solvent can be sufficiently removed, while at 250°C or lower, energy consumption can be further reduced, which is preferable. The drying temperature is more preferably 120°C or higher, and more preferably 180°C or lower. The amount of liquid supplied may vary depending on the scale of production, but may be, for example, in the range of 0.1 L / h to 2 L / h. The nozzle size for spraying the raw material liquid may vary depending on the scale of production, but may be, for example, in the range of 0.5 mm to 5 mm in diameter.

[0037] (Heat treatment process) In the heat treatment step, the granulated powder is heat-treated to carbonize it and generate a metal and / or metal compound derived from the sugar carboxylate metal salt. In the heat treatment step, a carbon material may be generated in which the sugar and / or sugar carboxylic acid of the sugar carboxylate metal salt is carbonized. The carbon material may contain a carbonized sugar compound. The carbon material may be amorphous carbon or a precursor of amorphous carbon. In the heat treatment step, fine particles of the metal and / or metal compound derived from the sugar carboxylate metal salt may be generated. The average particle size of the fine particles may be, for example, 7 nm or less, 6 nm or less, 5 nm or less, or 4 nm or less. The average particle size of the fine particles may be, for example, 1 nm or more, 2 nm or more, or 2.2 nm or more. The fine particles may be dispersed, or may be partially or completely linked. The metal compound generated in the heat treatment step may be, for example, an oxide or hydroxide, with oxide being preferred. The heat treatment temperature may be, for example, 400°C or higher, 600°C or higher, 800°C or higher, or 850°C or higher. The heat treatment temperature may be, for example, 1300°C or lower, 1100°C or lower, 1000°C or lower, or 950°C or lower. The heat treatment atmosphere may be an inert atmosphere such as an Ar atmosphere or an N2 atmosphere, or a superheated steam atmosphere. The heat treatment time may be, for example, 30 minutes or more and 120 minutes or less.

[0038] (Removal process) In the removal step, metals and / or metal compounds derived from the sugar carboxylate metal salt are removed from the granulated powder after the heat treatment step. In the removal step, the metals and / or metal compounds derived from the sugar carboxylate metal salt may be selectively removed by acid treatment or alkali treatment. Examples of acids or alkalis include hydrochloric acid, sulfuric acid, sodium hydroxide, and ammonia. The acid or alkali may be in the form of an aqueous solution. The concentration of the acid or alkali may be, for example, from 0.1 mol / L to 5 mol / L. The acid treatment or alkali treatment may be performed by immersing the granulated powder after the heat treatment step in an acid or alkali solution, and stirring may be performed during this process. The time for the acid treatment or alkali treatment may be, for example, from 60 minutes to 600 minutes. It is desirable to remove the acid or alkali from the granulated powder after the acid treatment or alkali treatment by filtration or washing.

[0039] (Firing process) In the firing step, the granulated powder after the removal step is fired. In the firing step, the granulated powder may be fired at a high temperature capable of removing the metal and / or metal compound derived from the sugar carboxylate metal salt. In this case, the firing step may also serve as the removal step. The firing step may further promote carbonization of the granulated powder. In the firing step, for example, when the carbon material generated in the heat treatment step is an amorphous carbon precursor, the firing step may convert the amorphous carbon precursor into amorphous carbon. The firing temperature may be higher than the heat treatment temperature in the heat treatment step, for example, 1000°C or higher, 1200°C or higher, or 1400°C or higher. The firing temperature may be, for example, 2000°C or lower, 1800°C or lower, or 1600°C or lower. The firing atmosphere may be an inert atmosphere such as an Ar atmosphere or an N2 atmosphere, or a superheated steam atmosphere. The baking time may be, for example, 30 minutes or more and 120 minutes or less.

[0040] FIG. 2 shows an example of a method for producing composite carbon particles according to the present disclosure. FIG. 2 is a schematic diagram illustrating an example of a method for producing composite carbon particles 10. This production method includes a granulation step, a heat treatment step, a removal step, and a firing step. In the granulation step, first, a raw material liquid 12 containing graphite particles 20 and a coating liquid 32 containing a sugar carboxylate metal salt 33 is prepared (FIG. 2A). For example, flake graphite, which is natural graphite, is suitable as the graphite particles 20. For example, magnesium gluconate is suitable as the sugar carboxylate metal salt 33. The coating liquid 32 may contain a sugar compound (not shown). For example, glucose is suitable as the sugar compound. Then, the raw material liquid 12 is spray-dried to obtain a granulated powder 14 (FIG. 2B). This granulation step produces a granulated powder 14 containing a plurality of graphite particles 20 and a solid content 34 remaining after the coating liquid 32 has dried. The solid content 34 includes the sugar carboxylate metal salt 33 and sugar carboxylic acid contained in the coating liquid 32. The solid content 34 may be formed, for example, so as to cover at least a portion of the surface of the graphite particles 20. In the subsequent heat treatment step, the granulated powder 14 is heat-treated to obtain the granulated powder 16 after the heat treatment step (FIG. 2C). This heat treatment step produces the granulated powder 16 including the graphite particles 20 and a carbon material 36 formed by carbonizing the solid content 34. The carbon material 36 may be amorphous carbon or a precursor of amorphous carbon. The carbon material 36 contains a metal and / or metal compound 37 derived from the sugar carboxylate metal salt 33. When the sugar carboxylate metal salt is magnesium gluconate, the metal and / or metal compound 37 is, for example, magnesium oxide. In the subsequent removal step, the metal and / or metal compound 37 is removed from the heat-treated granulated powder 16 to obtain the granulated powder 18 after the removal step (FIG. 2D). An example of a removal method is acid treatment using hydrochloric acid or the like. This removal step removes part or all of the metal and / or metal compound 37 from the granulated powder 16 after the heat treatment step, and pores 31 are formed in those portions, resulting in granulated powder 18 after the removal step. In the final firing step, the granulated powder 18 after the removal step is fired to obtain composite carbon particles 10. This firing step may also advance carbonization of the carbon material 36, resulting in amorphous carbon 30.Furthermore, this firing step may remove metals and / or metal compounds 37 that were not completely removed in the removal treatment, thereby expanding pores 31. If the carbon material 36 produced in the heat treatment step is amorphous carbon, this firing step may be omitted. In this manner, composite carbon particles 10 are obtained.

[0041] [electrode] The electrode of the present disclosure is an electrode for an electricity storage device, and contains the above-described composite carbon particles as an electrode active material. The composite carbon particles function as an electrode active material by absorbing and releasing lithium. In this electrode, the composite carbon particles exhibit not only the insertion / extraction capacity of the charge carrier lithium into / from graphite, but also the deposition / dissolution capacity of the charge carrier lithium. This electrode may be formed, for example, by mixing the above-described composite carbon particles, a binder, and, if necessary, a conductive material, adding an appropriate solvent to form a paste-like electrode mixture, which is then applied to the surface of a current collector, dried, and, if necessary, compressed to increase electrode density. The binder serves to bind the composite carbon particles and the conductive material particles, and can be, for example, fluorine-containing resins such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), and fluororubber; thermoplastic resins such as polypropylene and polyethylene; ethylene propylene diene monomer (EPDM) rubber; sulfonated EPDM rubber; natural butyl rubber (NBR); or the like, either alone or in a mixture of two or more thereof. Aqueous binders such as cellulose-based binders or aqueous dispersions of styrene-butadiene rubber (SBR) can also be used. The conductive material is not particularly limited as long as it is an electronically conductive material that does not adversely affect battery performance. For example, acetylene black, carbon black, ketjen black, carbon whiskers, needle coke, carbon fiber, and metals (copper, nickel, aluminum, silver, gold, etc.) can be used alone or in combination. Among these, carbon black and acetylene black are preferred as the conductive material from the viewpoints of electronic conductivity and coatability. Examples of solvents that can be used to disperse the composite carbon particles, binder, and conductive material include organic solvents such as N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethylenetriamine, N,N-dimethylaminopropylamine, ethylene oxide, and tetrahydrofuran. Alternatively, a dispersant, a thickener, etc. can be added to water, and the active material can be slurried with a latex such as SBR. As the thickener, for example, polysaccharides such as carboxymethyl cellulose and methyl cellulose can be used alone or as a mixture of two or more kinds.As coating methods, for example, roller coating such as an applicator roll, screen coating, doctor blade method, spin coating, bar coater, etc. can be mentioned, and any thickness and shape can be obtained using any of these. As the current collector, in addition to copper, nickel, stainless steel, titanium, aluminum, fired carbon, conductive polymer, conductive glass, Al-Cd alloy, etc., for the purpose of improving adhesion, conductivity and reduction resistance, for example, those obtained by treating the surface of copper or the like with carbon, nickel, titanium, silver, etc. can also be used. For these, it is also possible to perform surface oxidation treatment. Regarding the shape of the current collector, examples include foil shape, film shape, sheet shape, net shape, punched or expanded shape, lath body, porous body, foam body, formed body of fiber group, etc. The thickness of the current collector is, for example, 1 to 500 μm.

[0042] [Power storage device] The power storage device of the present disclosure includes the electrode described above. This power storage device may, for example, include a negative electrode which is the above-described electrode, a positive electrode, and an ion conduction medium interposed between the negative electrode and the positive electrode and conducting lithium ions.

[0043] The positive electrode may contain a positive electrode active material capable of occluding and releasing lithium. The positive electrode may be formed, for example, by mixing a positive electrode active material, a conductive material, and a binder, adding an appropriate solvent to form a paste-like positive electrode composite material, applying and drying it on the surface of the current collector, and compressing it as necessary to increase the electrode density. As the positive electrode active material, sulfides containing transition metal elements, oxides containing lithium and transition metal elements, etc. can be used. Specifically, transition metal sulfides such as TiS2, TiS3, MoS3, FeS2, the basic composition formula of Li (1-x) MnO2 (0 < x < 1, etc., the same below), Li (1-x) such as Mn2O4 and other lithium manganese composite oxides, the basic composition formula of Li (1-x) such as CoO2 and other lithium cobalt composite oxides, the basic composition formula of Li (1-x) such as NiO2 and other lithium nickel composite oxides, the basic composition formula of Li (1-x) Ni a Cob Mn c Examples of materials that can be used include lithium nickel cobalt manganese composite oxides with a basic formula such as LiV2O2 (a+b+c=1), lithium vanadium composite oxides with a basic formula such as LiV2O3, and transition metal oxides with a basic formula such as V2O5. Among these, lithium transition metal composite oxides, such as LiCoO2, LiNiO2, LiMnO2, and LiV2O3, are preferred. The term "basic formula" refers to the possibility of including other elements (e.g., Al, Mg, etc.). The binder, conductive material, solvent, and coating method used in the positive electrode can be the same as those exemplified for the electrodes described above. Examples of current collectors include aluminum, titanium, stainless steel, nickel, iron, calcined carbon, conductive polymers, and conductive glass. For the purpose of improving adhesion, conductivity, and oxidation resistance, aluminum or copper surfaces treated with carbon, nickel, titanium, or silver can also be used. These surfaces can also be oxidized. The shape of the current collector can be the same as that exemplified for the electrodes described above.

[0044] The ion-conducting medium may be a non-aqueous electrolyte solution containing a supporting salt, a non-aqueous gel electrolyte solution, etc. Examples of solvents for the non-aqueous electrolyte solution include carbonates, esters, ethers, nitriles, furans, sulfolanes, and dioxolanes, which may be used alone or in combination. Specific examples of carbonates include cyclic carbonates such as ethylene carbonate, propylene carbonate, vinylene carbonate, butylene carbonate, and chloroethylene carbonate; chain carbonates such as dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethyl-n-butyl carbonate, methyl-t-butyl carbonate, di-i-propyl carbonate, and t-butyl-i-propyl carbonate; cyclic esters such as γ-butyl lactone and γ-valerolactone; chain esters such as methyl formate, methyl acetate, ethyl acetate, and methyl butyrate; ethers such as dimethoxyethane, ethoxymethoxyethane, and diethoxyethane; nitriles such as acetonitrile and benzonitrile; furans such as tetrahydrofuran and methyltetrahydrofuran; sulfolanes such as sulfolane and tetramethylsulfolane; and dioxolanes such as 1,3-dioxolane and methyldioxolane. Among these, a combination of cyclic carbonates and chain carbonates is preferred. This combination not only provides excellent cycle characteristics, which represent battery characteristics during repeated charge and discharge, but also balances the viscosity of the electrolyte, the electrical capacity of the resulting battery, and battery output. It is believed that the cyclic carbonates have a relatively high dielectric constant, which increases the dielectric constant of the electrolyte, while the chain carbonates suppress the viscosity of the electrolyte. The supporting salt may be, for example, an inorganic salt such as LiPF, LiBF, LiAsF, or LiClO, or an organic salt such as LiCF, SO, LiN(CF, SO), or LiC(CF, SO). The concentration of this supporting salt in the nonaqueous electrolyte is preferably 0.1 mol / L or more and 5 mol / L or less, and more preferably 0.5 mol / L or more and 2 mol / L or less. When the concentration of the dissolving supporting electrolyte is 0.1 mol / L or more, a sufficient current density can be obtained, and when it is 5 mol / L or less, the electrolyte can be made more stable.This ion-conducting medium may contain a phosphorus-based or halogen-based flame retardant. Instead of a liquid ion-conducting medium, a solid ion-conducting polymer may be used as the ion-conducting medium. Examples of the ion-conducting polymer include polymer gels composed of a polymer such as acrylonitrile, ethylene oxide, propylene oxide, methyl methacrylate, vinyl acetate, vinylpyrrolidone, or vinylidene fluoride and a supporting salt. Furthermore, a combination of an ion-conducting polymer and a nonaqueous electrolyte may also be used. In addition to ion-conducting polymers, inorganic solid electrolytes, mixtures of organic polymer electrolytes and inorganic solid electrolytes, or inorganic solid powders bound by an organic binder may also be used as the ion-conducting medium.

[0045] This electricity storage device may include a separator between the negative electrode and the positive electrode. The separator is not particularly limited as long as it has a composition that can withstand the range of use of the electricity storage device, but examples thereof include polymer nonwoven fabrics such as polypropylene nonwoven fabrics and polyphenylene sulfide nonwoven fabrics, and thin microporous films of olefin resins such as polyethylene and polypropylene. These may be used alone or in combination.

[0046] In this electricity storage device, lithium may be deposited in the negative electrode (more preferably, inside the composite carbon particles) when fully charged. In this case, lithium may be deposited as lithium metal, a lithium alloy, or both. Whether the electricity storage device is fully charged may be determined by whether the voltage of the electricity storage device has reached a preset full charge voltage.

[0047] This energy storage device preferably has a higher high-rate charge / discharge efficiency, preferably 85% or higher, more preferably 90% or higher, and even more preferably 95% or higher. The high-rate charge / discharge efficiency is defined as the charge / discharge efficiency when the device is charged at a high rate of 0.25 C and then discharged at 0.05 C. In this disclosure, "charging" refers to the insertion and precipitation of charge carriers into the composite carbon particles, and "discharging" refers to the desorption and elution of charge carriers from the composite carbon particles. This energy storage device also preferably has a higher initial charge / discharge efficiency, preferably 60% or higher, more preferably 70% or higher, and even more preferably 75% or higher. This energy storage device also preferably has a higher post-cycle charge / discharge efficiency, preferably 90% or higher, more preferably 95% or higher, and even more preferably 96% or higher.

[0048] The shape of this electricity storage device is not particularly limited, and examples thereof include coin-shaped, button-shaped, sheet-shaped, laminated, cylindrical, flat, and rectangular shapes. The device may also be applied to large devices used in electric vehicles and the like. FIG. 3 is a schematic diagram of an electricity storage device 50, an example of an electricity storage device according to the present disclosure. The electricity storage device 50 includes a cup-shaped case 51, a positive electrode 52 having a positive electrode active material and disposed at the bottom of the case 51, a negative electrode 53 having a negative electrode active material and disposed opposite the positive electrode 52 with a separator 54 interposed therebetween, a gasket 55 formed of an insulating material, and a sealing plate 56 disposed at the opening of the case 51 and sealing the case 51 via the gasket 55. In the electricity storage device 50, an ion-conducting medium 57 is filled in the space between the positive electrode 52 and the negative electrode 53. The negative electrode 53 contains the composite carbon particles 10 described above.

[0049] The power storage device of the present disclosure is preferably used by charging it until the negative electrode potential becomes lower than the redox potential of lithium, which is the charge carrier. When the negative electrode potential becomes lower than the redox potential of lithium (for example, until fully charged), lithium precipitates at the negative electrode and is stored in the negative electrode. When the negative electrode potential is then raised above the redox potential of lithium, lithium dissolves at the negative electrode, and the resulting energy can be extracted as discharge capacity. In this way, when the device is used by charging it until the negative electrode potential becomes lower than the redox potential of lithium, the lithium precipitation and dissolution capacity can be utilized, thereby further increasing the energy density of the power storage device.

[0050] The present disclosure, as described above in detail, can further improve the high-rate characteristics of an electricity storage device. The reason for this effect is presumed to be as follows. For example, when the composite carbon particles of the present disclosure are used in an electrode of an electricity storage device, charge carriers are inserted into and removed from the graphite particles, while the amorphous carbon reduces the deposition overpotential of the charge carriers, contributing to the precipitation and dissolution of the charge carriers. It is believed that pores are formed in this amorphous carbon by, for example, carbonizing the sugar and / or sugar carboxylic acid of the sugar carboxylate metal salt and removing the metal and / or metal compound derived from the sugar carboxylate metal salt. These pores also function as a deposition field for the charge carriers. It is presumed that the favorable pore structure of such composite carbon particles allows smooth insertion and desorption of charge carriers into and from the graphite, and smooth precipitation and dissolution of the charge carriers, thereby further improving the high-rate characteristics.

[0051] It goes without saying that the present disclosure is not limited to the above-described embodiments, and can be embodied in various forms as long as they fall within the technical scope of the present disclosure.

[0052] For example, in the above-described embodiment, the charge carrier of the power storage device is lithium, but this is not particularly limited, and may be an alkali metal ion such as sodium or potassium, or a Group 2 element ion such as calcium ion or magnesium ion. The positive electrode active material may contain a carrier ion. The electrolyte solution is a non-aqueous electrolyte solution, but may also be an aqueous electrolyte solution.

[0053] In the above-described embodiment, the positive electrode active material is a transition metal composite oxide or the like, but is not particularly limited thereto, and may be, for example, a carbon material used in a capacitor. The carbon material is not particularly limited, but examples thereof include activated carbons, cokes, glassy carbons, graphites, non-graphitizable carbons, pyrolytic carbons, carbon fibers, carbon nanotubes, and polyacenes. Among these, activated carbons exhibiting a high specific surface area are preferred. Activated carbons as carbon materials have a specific surface area of ​​1000 m 2 / g or more, and 1500m 2 / g or more is more preferable. 2 / g or more, the discharge capacity can be further increased. The specific surface area of ​​this activated carbon is 3000 m 2 / g or less, and 2 It is considered that the positive electrode stores electricity by adsorbing and desorbing at least one of anions and cations contained in the ionically conductive medium, but it may also store electricity by inserting and desorbing at least one of anions and cations contained in the ionically conductive medium.

[0054] The present disclosure may be any of the following [1] to

[11] . [1] Composite carbon particles comprising graphite particles and amorphous carbon, which have a pore volume of 40 μL / g or more as calculated by nitrogen adsorption measurement and an average pore diameter of 7 nm or less as calculated by nitrogen adsorption measurement. [2] The composite carbon particles according to [1], which contain a plurality of the graphite particles, the amorphous carbon being present between the graphite particles, and which are aggregated particles formed by the amorphous carbon. [3] The composite carbon particles according to [1] or [2], wherein the pore volume is 50 μL / g or more and 100 μL / g or less. [4] The composite carbon particles according to any one of [1] to [3], wherein the average pore diameter is 2.2 nm or more and 5 nm or less. [5] Composite carbon particles according to any one of [1] to [4], which satisfy one or more of the following (1) to (2): (1) The amorphous carbon is contained in an amount of 2% by mass or more and 20% by mass or less. (2) The graphite particles are natural graphite. [6] An electricity storage device comprising an electrode containing the composite carbon particles according to any one of [1] to [5] as an electrode active material. [7] A granulation step of obtaining a granulated powder using a raw material liquid containing graphite particles and a sugar carboxylate metal salt; a heat treatment step in which the granulated powder is heat-treated to carbonize it and generate a metal and / or a metal compound derived from the sugar carboxylate metal salt; a removing step of removing the metal and / or metal compound from the granulated powder after the heat treatment step; A method for producing composite carbon particles, comprising: [8] The method for producing composite carbon particles according to [7], wherein the raw material liquid contains a sugar compound. [9] The method for producing composite carbon particles according to [7] or [8], which satisfies one or more of the following (3) to (5): (3) The metal sugar carboxylate is a gluconate. (4) The metal salt of a sugar carboxylate is a magnesium salt. (5) The raw material solution contains a sugar compound, and the sugar compound is glucose.

[10] In the removal step, the metal and / or metal compound is removed by acid treatment. The method for producing composite carbon particles according to any one of [7] to [9].

[11] An electrode comprising the composite carbon particles according to any one of [1] to [5] as an electrode active material. [Example]

[0055] Specific examples of the composite carbon particles, electrodes, and electricity storage devices described above will be described below as examples. Experimental Examples 1 to 6 correspond to Examples, and Experimental Examples 7 to 11 correspond to Comparative Examples.

[0056] [Experimental Example 1] (Preparation of composite carbon particles) 10 g of flake natural graphite (Fuji Graphite Industries, BF-8A) and 0.1 g of carboxymethylcellulose (Dai-ichi Kogyo Seiyaku, BSH-6) were mixed, followed by the addition of 20 g of water. A slurry was obtained using a mixer (Thinky, ARE-310). 0.26 g of glucose (Tokyo Chemical Industry, Ltd.) and 0.6 g of magnesium gluconate (Tokyo Chemical Industry, Ltd.) were dissolved in 130 g of water and mixed with the slurry to prepare a raw material solution containing a uniform mixture of graphite, glucose, and magnesium gluconate. The raw material solution was sprayed at a flow rate of 0.5 L / h from a 0.7 mm nozzle using a spray dryer (Nihon Buchi, B-290) under a dry air stream at 140 °C to obtain granulated powder (granulation process). The granulated powder was then heat-treated at 900 °C in an Ar atmosphere for 1 hour (heat treatment process). The mixture was then mixed in 100 ml of 1 mol / L hydrochloric acid for 3 hours to dissolve the Mg component (removal step). After filtration and washing, the mixture was vacuum dried at 120°C. Finally, heat treatment was carried out at 1500°C in an Ar atmosphere for 1 hour (sintering step). In this way, composite carbon particles of Experimental Example 1 were obtained. The amorphous carbon proportion (coating amount) in the composite carbon particles was calculated from the yields in the heat treatment step, removal treatment step, and firing step, and was found to be 1% in Experimental Example 1.

[0057] (Morphological observation of composite carbon particles) The particle morphology of the composite carbon particles was confirmed by SEM observation at 5000x magnification using a scanning electron microscope (Hitachi High-Tech Regulus 8230), and it was determined whether the particles were primarily spherical or scale-like.

[0058] (Pore analysis of composite carbon particles) Using a pore analyzer (MicrotrackBell BELSORP-maxII), The specific surface area, average pore diameter, and pore volume of the composite carbon particles were calculated by BET analysis of the N2 adsorption isotherm measured at °C.

[0059] (Study on measuring method for amorphous carbon coating amount) A thermogravimetric (TG) measurement device (Rigaku ThermoPlusTG8120) was used to obtain a TG curve by increasing the temperature from room temperature to 500°C at a rate of 20°C / min, and then increasing the temperature from 500°C to 800°C at a rate of 2°C / min. The measurement atmosphere was air at 250cc / min.

[0060] (X-ray diffraction measurement of composite carbon particles) X-ray diffraction measurements were carried out using an X-ray diffraction measurement device (Rigaku Ultima IV).

[0061] (Electrode preparation) After mixing 90 parts by mass of the composite carbon particles and 10 parts by mass of polyvinylidene fluoride (PVdF, manufactured by Kureha, #9300), the weight of the composite material was 4 mg / cm 2 After vacuum drying, the mixture was compressed with a roll press to a density of 1.1 g / cm. 3 By adjusting the temperature so that the temperature satisfies the above, a sheet-like electrode for the negative electrode was produced.

[0062] (Charge / discharge evaluation) The above electrode is 16 mm in diameter (2 cm 2 The cells were punched out into a rectangular shape, and then placed opposite a lithium metal counter electrode via a separator. An electrolyte solution was then injected into the cells to prepare cells for charge / discharge evaluation. The electrolyte solution used was a 1M solution of LiPF6 in a mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC). The current was 0.15 mA / cm. 2Constant current / constant voltage charge / discharge evaluation was performed in the voltage range of 0.005-1.5V at a current density of 0.05C, and the initial charge / discharge efficiency for lithium insertion / desorption into and from the electrode containing the composite carbon particles was calculated. Note that "charge" refers to the insertion / precipitation of Li into the composite carbon particles, and "discharge" refers to the desorption / elution of Li from the composite carbon particles. The charge / discharge efficiency was calculated using a current density of 0.75mA / cm. 2 (0.25C) current value is 3mAh / cm 2 After charging to a capacity of 0.15mA / cm 2 The battery was discharged at a constant current and constant voltage up to 1.5 V at a current value of 0.15 mA / cm, and the charge / discharge efficiency at this time was calculated as the high-rate charge / discharge efficiency to evaluate the high-rate characteristics. 2 At a current value of 3mAh / cm 2 After constant current charging (20h) to a capacity of 0.15mA / cm 2 The cycle of constant current-constant voltage discharge to 1.5 V was repeated 10 times, and the charge-discharge efficiency after 10 cycles was calculated to evaluate the charge-discharge cycle characteristics.

[0063] [Experimental Examples 2-5] Experimental Example 2 was carried out in the same manner as Experimental Example 1, except that the amounts of glucose and magnesium gluconate mixed with 10 g of scaly natural graphite were 0.5 g and 1.2 g, respectively (coating amount 2%). Experimental Example 3 was carried out in the same manner as Experimental Example 1, except that the amounts of glucose and magnesium gluconate mixed with 10 g of scaly natural graphite were 1.0 g and 2.5 g, respectively (coating amount 4%). Experimental Example 4 was carried out in the same manner as Experimental Example 1, except that the amounts of glucose and magnesium gluconate mixed with 10 g of scaly natural graphite were 6.5 g and 15 g, respectively (coating amount 20%). Experimental Example 5 was carried out in the same manner as Experimental Example 1, except that the amounts of glucose and magnesium gluconate mixed with 10 g of scaly natural graphite were 26 g and 60 g, respectively (coating amount 50%).

[0064] [Experimental Example 6] Experimental Example 6 was carried out in the same manner as Experimental Example 1, except that glucose was omitted and the amount of magnesium gluconate mixed per 10 g of flake natural graphite was 5 g (coating amount 4%).

[0065] [Experimental Example 7] Experimental Example 7 was carried out in the same manner as Experimental Example 1, except that magnesium gluconate was omitted, the amount of glucose mixed per 10 g of flake natural graphite was 2 g (coating amount 4%), and the heat treatment step was omitted.

[0066] [Experimental Example 8] Instead of the granulation step, a mixing step was carried out in which 10 g of flake natural graphite was mixed with 1.0 g of glucose and 2.5 g of magnesium gluconate (coating amount 4%) in a mortar. Otherwise, Experimental Example 8 was carried out in the same manner as Experimental Example 1.

[0067] [Experimental Example 9] Experimental Example 9 was carried out in the same manner as Experimental Example 1, except that flake natural graphite was used as it was instead of the composite carbon particles.

[0068] [Experimental Example 10] Experimental Example 10 was carried out in the same manner as Experimental Example 1, except that flake natural graphite that had been heat-treated at 1500° C. in an Ar atmosphere was used instead of the composite carbon particles.

[0069] [Experimental Example 11] 10 g of the flake natural graphite and 0.1 g of the carboxymethyl cellulose were mixed, and then 20 g of water was added to obtain a slurry using the mixer. 130 g of water was added to dilute the mixture, and the mixture was spray-dried to obtain a powder. This was heat-treated in an Ar atmosphere at 1500°C. Experimental Example 11 was carried out in the same manner as Experimental Example 1, except that the particles thus prepared were used instead of the composite carbon particles.

[0070] [Results and Discussion] Figure 4 shows SEM images of the composite carbon particles of Experimental Example 3 (Figures 4A and 4B) as an example of the morphology of composite carbon particles. Figure 4 also shows SEM images of graphite particles of Experimental Example 9 (Figures 4C and 4D). As shown in Figures 4A and 4B, in the experiment in which graphite particles were mixed with an amorphous carbon source and spray-dried, it was found that multiple scaly graphite particles aggregated to form agglomerated particles, and the particle morphology became spherical. This is presumably because the amorphous carbon source acted as a "binder" during the spray-drying process, forming secondary particles as the droplets of the sprayed solution containing the graphite particles and the amorphous carbon source dried. On the other hand, even in the case of the spray-dried samples that did not contain the amorphous carbon source, the particles remained scaly. This suggests that an amorphous carbon source is necessary to obtain agglomerated particles such as spherical particles.

[0071] Figure 5 shows the N adsorption isotherm of the composite carbon particles from Experimental Example 3 (Figure 5A) as an example of N adsorption isotherm measurement. Figure 5 also shows the N adsorption isotherm of the graphite particles from Experimental Example 9. It was found that the N adsorption capacity of the composite carbon particles composited with amorphous carbon increased significantly. Figure 5 also shows the pore volume of the particle surface calculated using the BET method. Figure 5 shows that the composite treatment significantly increased the pore volume. Glucose, the raw material for amorphous carbon components, is known to become non-graphitizable carbon upon heat treatment. It is also known that its magnesium salt, magnesium gluconate, similarly generates magnesium oxide crystallites within its structure when heat-treated. It is also known that removing these magnesium oxide crystallites with acid treatment can yield porous carbon materials (Kamiyama et al., Angew. Chem. Int. Ed. 2021, 60, 5114-5120). It was found that the composite carbon particles of Experimental Examples 1 to 6 had surfaces with moderately increased pore volumes. Of these, it was found that Experimental Examples 5 and 6 showed particularly large increases in pore volume. For reference, FIG. 5 also shows Kr adsorption isotherms for the composite carbon particles of Experimental Example 3 and the graphite particles of Experimental Example 9 (FIG. 5B). As shown in FIG. 5B, steps specific to graphite were observed in Experimental Example 9, whereas no such steps were observed in Experimental Example 3.

[0072] As an example of TG measurement, Figure 6 shows the TG curve of the composite carbon particles of Experimental Example 3. The TG curve confirmed a two-stage weight loss behavior, and it was inferred that the weight loss up to around 600°C was due to the amorphous carbon component, and the weight loss from 650°C onwards was due to the graphite itself. In Experimental Example 3 (where the coating amount calculated from the yields in the heat treatment step, removal treatment step, and firing step was 4%), the weight loss up to 600°C was approximately 4%, which was similar to the coating amount calculated from the yield. From this, it was inferred that the amorphous carbon coating amount could be predicted to some extent based on the weight loss up to 600°C in the TG curve. For reference, the calculation process for the coating amount in Experimental Example 3 is shown below. Mass before heat treatment Granulated powder Xh1: 2.9691g (graphite Gh1: 2.0763g, coating source Ch1: 0.8928g) Mass after heat treatment Granulated powder Xh2: 2.2018g (graphite Gh2: 2.0690g, coating source Ch2: 0.1328g) *Graphite mass calculated from yield s=99.65% when graphite alone is subjected to the heat treatment process. The remainder was calculated as the coat source mass. Mass before removal treatment (acid treatment) Granulated powder Xr1: 2.1163g (graphite Gr1: 1.9887g, coating source Cr1: 0.1276g) Mass after removal treatment (acid treatment) Granulated powder Xr2: 1.9420 g (graphite Gr2: 1.8438 g, coating source Cr2: 0.0982 g) *Theoretical yield t = 83% when MgO is removed from the coating source. Calculations were made assuming that losses due to filtration, etc. were equal between graphite and the coating source from which MgO has been removed. Mass before firing Granulated powder Xf1: 1.8773 g (graphite Gf1: 1.7824 g, coating material Cf1: 0.0949 g) Mass after firing process Granulated powder Xf2: 1.8537g (graphite Gf2: 1.7783g, coated Cf2: 0.0754g) *The graphite mass was calculated from the yield u=99.77% when the calcination process was carried out using graphite alone. The remainder was calculated as the coat source mass. Calculation of the proportion of amorphous carbon (coating amount) in composite carbon particles Coating amount = Cf2 / Xf2 x 100 ≒ 4

[0073] As an example of X-ray diffraction measurement, Figure 7 shows the X-ray diffraction pattern of the composite carbon particles of Experimental Example 3. Figure 7 also shows the X-ray diffraction pattern of the raw graphite particles of Experimental Example 9. Compared to the raw graphite particles of Experimental Example 9, the background intensity on the low-angle side of Experimental Example 3 was increased. This was presumably due to the presence of an amorphous carbon component, which increases the intensity in the low-angle region where the interplanar spacing is large, as well as the influence of X-ray scattering due to the pore structure contained in the amorphous carbon component. This confirmed that graphite particles and amorphous carbon were composited in Experimental Example 3.

[0074] As an example of charge / discharge evaluation, Figure 8 shows the charge / discharge curves of the cell of Experimental Example 3 after 10 cycles. The charge / discharge curves confirmed that in addition to the Li insertion / extraction capacity, Li precipitation / dissolution capacity was also exhibited. It was found that the Li precipitation / dissolution capacity could be utilized to further increase the charge / discharge capacity and energy density.

[0075] Tables 1 and 2 summarize the composite conditions, physical properties of the composite carbon particles, and battery performance for Experimental Examples 1 to 11. As shown in Table 1, Experimental Examples 1 to 6 were found to have high high-rate charge-discharge efficiency. This is presumably because, for example, the pore structure of the composite carbon particles was favorable in Experimental Examples 1 to 6, which allowed for smooth insertion and desorption of charge carriers into and precipitation and dissolution of charge carriers. It is also presumed that, for example, the spherical particle shape improved ionic conduction within the electrode, thereby promoting uniform charging (Li deposition). Note that, although the composite carbon particles of Experimental Example 7 also had a spherical particle shape, the pore volume was small, providing few reaction sites for lithium ion insertion or deposition, and therefore it is presumed that the effects of Experimental Examples 1 to 6 were not obtained. As shown in Table 2, the theoretical specific surface areas and theoretical pore volumes of the amorphous carbons of Experimental Examples 1 to 5 and 8, which used glucose and magnesium gluconate as the coating source, were larger than the specific surface area and pore volume of the particles of the Reference Example, which was produced using glucose and magnesium gluconate to form amorphous carbon alone. This is presumably due to the influence of pores formed at the junctions between the graphite particles and the amorphous carbon.

[0076] Among Experimental Examples 1 to 6, Experimental Examples 2 to 4 in particular were found to exhibit favorable performance in terms of charge / discharge efficiency, high-rate charge / discharge efficiency, and charge / discharge efficiency after cycling. Below, suitable conditions were investigated from each viewpoint.

[0077] Regarding the initial charge-discharge efficiency, in Experimental Examples 9 to 11, which were not coated with amorphous carbon, Experimental Examples 10 and 11, which were heat-treated at 1500°C, tended to have higher initial charge-discharge efficiencies than Experimental Example 9, which was not heat-treated. On the other hand, in Examples 1 to 8, which were coated with amorphous carbon and were heat-treated at 1500°C, the initial charge-discharge efficiencies were slightly lower than those of Experimental Examples 10 and 11, which were not coated with amorphous carbon. This is presumed to be due to irreversible lithium trapping in the amorphous carbon coating. However, in all of Experimental Examples 1 to 8, the initial charge-discharge efficiencies were 60% or higher, which was acceptable. Among Experimental Examples 1 to 8, Experimental Examples 1 to 4 and 7 to 8, which had a pore volume of 100 μL / g or less and an average pore diameter of 2.2 nm or more, showed a small decrease in the initial charge-discharge efficiency. From this, it was inferred that, from the viewpoint of suppressing a decrease in the initial charge / discharge efficiency, it is preferable that the pore volume is 100 μL / g or less and the average pore diameter is 2.2 nm or more.

[0078] Regarding the charge / discharge efficiency during high-rate charging, high values ​​of 90% or more were obtained in Experimental Examples 1 to 6. In Experimental Examples 1 to 6, the pore volume was relatively large, at 40 μL / g or more, and the average pore diameter was small, at 7 nm or less, and it was presumed that such a pore structure was particularly suitable for improving high-rate characteristics.

[0079] The charge-discharge efficiency after 10 cycles was high in Experimental Examples 2 to 4 and 6. This is presumably because, as with the charge-discharge efficiency during high-rate charging mentioned above, the ion conduction pathways within the electrode were secured, and the graphite particle surface had pores suitable for lithium deposition, allowing the lithium deposition / dissolution reaction to proceed smoothly. In Experimental Examples 2 to 4 and 6, the pore volume was 50 μL / g or more, the average pore diameter was 5 nm or less, and the specific surface area was 50 m 2 / g or more 200m 2 From this, from the viewpoint of improving cycle characteristics, it is necessary to have a pore volume of 50 μL / g or more, an average pore diameter of 5 nm or less, and a specific surface area of ​​50 m 2 / g or more 200m 2 / g or less.

[0080] These results indicate that when the composite carbon particles of Experimental Examples 2 to 4, in which the graphite particle surfaces are composited with an amorphous carbon component, have a pore volume of 50 μL / g to 100 μL / g calculated by N adsorption measurement and BET analysis, an average pore diameter of 2.2 nm to 5 nm, and are spherical, are used as negative electrodes, the resulting graphite negative electrodes are particularly suitable for charge / discharge, utilizing the lithium deposition / dissolution capacity in addition to lithium insertion / extraction into / from the graphite particles. The following reasons are inferred for the good results obtained in Experimental Examples 2 to 4. For example, it is inferred that the graphite particles are coated with an amorphous carbon layer, which reduces the lithium deposition overpotential and allows for uniform lithium deposition. Furthermore, it is inferred that the spherical shape of the graphite particles results in high reaction uniformity in the film thickness direction when the charge rate is increased, resulting in a high subsequent discharge capacity. In addition, the pore volume measured by N2 adsorption measurement was between 50 μL / g and 100 μL / g, which is presumed to be due to the optimal storage of lithium metal within these pores. Furthermore, the average pore diameter was between 2.2 nm and 5 nm, which is presumed to be due to the suppression of the amount of film formed within the pores, thereby improving the initial charge / discharge efficiency and allowing for efficient storage of lithium metal. Furthermore, the proportion of amorphous carbon was between 2% and 20%, which is presumed to be due to the suppression of the increase in irreversible capacity during the initial charge / discharge due to the amorphous carbon, while demonstrating the effect of the composite with amorphous carbon.

[0081] [Table 1]

[0082] [Table 2] [Industrial Applicability]

[0083] The present disclosure is applicable to the technical field of electricity storage devices. [Explanation of symbols]

[0084] 10 composite carbon particles, 12 raw material liquid, 14 granulated powder, 16 granulated powder after heat treatment process, 18 granulated powder after acid treatment, 20 graphite particles, 30 amorphous carbon, 31 pores, 32 coating liquid, 33 sugar carboxylic acid metal salt, 34 solid content, 36 carbon material, 37 metal and / or metal compound, 50 electricity storage device, 51 case, 52 positive electrode, 53 negative electrode, 54 separator, 55 gasket, 56 sealing plate, 57 ion conductive medium.

Claims

1. Composite carbon particles obtained by compositing graphite particles and amorphous carbon, which have a pore volume calculated by nitrogen adsorption measurement of 40 μL / g or more and 200 μL / g or less and an average pore diameter calculated by nitrogen adsorption measurement of 1 nm or more and 7 nm or less. Composite carbon particles.

2. The amorphous carbon is present between the graphite particles, and the graphite particles are aggregated by the amorphous carbon. The composite carbon particle according to claim 1 .

3. 3. The composite carbon particles according to claim 1, wherein the pore volume is 50 μL / g or more and 100 μL / g or less.

4. 3. The composite carbon particles according to claim 1, wherein the average pore diameter is 2.2 nm or more and 5 nm or less.

5. The composite carbon particles according to claim 1 or 2, which satisfy one or more of the following (1) to (2): (1) The amorphous carbon is contained in a proportion of 2% by mass or more and 20% by mass or less. (2) The graphite particles are natural graphite.

6. Composite carbon particles as described in claim 1 or 2, wherein the pore volume is 44.28 μL / g or more and 157.46 μL / g or less, and the average pore diameter is 2.01 nm or more and 5.38 nm or less.

7. An electrode comprising the composite carbon particle according to claim 1 or 2 as an electrode active material. Energy storage device.

8. a granulation step of obtaining a granulated powder using a raw material liquid containing graphite particles and a sugar carboxylate metal salt; a heat treatment step in which the granulated powder is heat-treated to carbonize it and generate a metal and / or a metal compound derived from the sugar carboxylate metal salt; a removing step of removing the metal and / or metal compound from the granulated powder after the heat treatment step; A method for producing composite carbon particles, comprising:

9. The raw material solution contains a sugar compound. The method for producing composite carbon particles according to claim 8 .

10. The method for producing composite carbon particles according to claim 8, which satisfies one or more of the following (3) to (5): (3) The metal sugar carboxylate is a gluconate. (4) The metal salt of a sugar carboxylate is a magnesium salt. (5) The raw material solution contains a sugar compound, and the sugar compound is glucose.

11. In the removing step, the metal and / or metal compound is removed by acid treatment. The method for producing composite carbon particles according to any one of claims 8 to 10.

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